MXPA00009594A - Lactic acid residue containing polymer composition, product method for preparation and use - Google Patents

Abstract

The invention relates to a lactic acid residue containing polymer composition and product having improved stability and to methods for the preparation and use thereof. The lactic acid residue containing polymer preferably includes a polylactide polymer having a number average molecular weight of between about 25,000 and about 200,000, lactide, if present at all, present in a concentration of less than 0.5 wt.%based on the weight of the composition, and deactivating agents. Articles which can be manufactured from the lactic acid residue containing polymer composition include fibers, coated paper, films, moldings, and foam.

Description

POLYMERIC COMPOSITION CONTAINING LACTIC ACID RESIDUE: PRODUCT: METHOD OF PREPARATION AND USE FIELD OF THE INVENTION The invention relates to a polymeric composition containing lactic acid residue and to the product having improved stability; and to a method for its preparation and its use. In particular, the invention relates to the use of multifunctional carboxylic acid to stabilize polymers containing lactic acid residue.

BACKGROUND OF THE INVENTION In recent years attention has been focused on preferred degradable polymers, which can be converted to the desired substrates or articles. Much of that attention has been focused on polymers that include, as monomer units of them, the result of the polymerization of lactic acid or lactide. Attention is drawn, for example, to US Pat. Nos. 5, 142, 023, to Gruber and co-inventors; 5,338,822, by Gruber and co-inventors; 5,475,080, from Gruber and co-inventors; . 359,026, by Gruber and 5,594,095, by Gruber and co-inventors; whose full descriptions are incorporated herein by means of this reference. It is to be noted that U.S. Patent Nos. 5,142,023, 5,338,822, 5,475,080, 5,359,026 and 5,594,095 are owned by Cargill Incorporated, of Minneapolis, Minnesota, E. U. A. Cargill Incorporated is also the assignee of the present application. Other published documents that refer to lactic acid or lactide polymers include: International Publication No. WO 94/06856, Sinclair and co-inventors, published March 31, 1994; International Publication No. WO 92/04413 to Sinclair and co-inventors, published March 19, 1992; and international publication No. WO 90/01521, Sinclair and co-inventors, published February 2, 1990. It has been reported that polymers containing lactic acid residue, if left untreated, are unstable in processing at high temperatures. See U.S. Patent No. 5,338,822 to Gruber and co-inventors. There are three conventional techniques for forming linear polyesters. Those techniques include the reaction of condensation of a diacid with a diol; the condensation reaction of a hydroxy acid and / or an ester, and the ring-opening polymerization of a cyclic ester. While the polymer resulting from each of these techniques contains the characteristic ester ligation, the structure of the polymer may be different. In the technique comprising the condensation reaction of a diacid with a diol, the repeating unit will have a head-tail-tail-head configuration, as shown by the general formula - [(CR2) xO-CO- (CR ' 2) y-CO-O-]. In contrast, techniques comprising the condensation of a hydroxy acid and / or an ester and the ring-opening polymerization of a cyclic ester, provide a polymer having a simpler repeating formula, and a head-tail-head structure. tail, as shown by the general formula: - [(CR "2) y-CO-O] - This difference is similar to the difference between nylon 6,6 and nylon 6. Polyesters produced by condensation reaction of a hydroxyacid and / or an ester and / or by the ring-opening polymerization of a cyclic ester, can be depolymerized by a "descurrer" or depolymerization reaction.An exemplary depolymerization reaction is demonstrated by the opposite arrow in the reaction equilibrium for the active pol i I shown below: There is a possibility for copolymers when each of the monomer units can be drawn in a cyclic manner. In the case of a polymer formed by polymerizing lactic acid, the depolymerization reaction can lead to the formation of lactide, a cyclic ester (diester). The formation of lactide by depolymerization during melt processing is undesirable. At certain levels, the formation of lactide can cause a change in the physical properties of the molten polylactide polymer, such as reduction in melt polymer viscosity and melt elasticity. In addition, the lactide is volatile and can result in fume formation and / or faults in the processing equipment. Additionally it is probable that the depolymerized lactide in the final product causes a decrease in the shelf life. Lactide is generally more susceptible to hydrolysis, which leads to acidity in the final product, which can catalyze the hydrolysis of the polymer. In certain applications, high levels of lactide may make migration to food more worrisome. The tendency to form lactide is also a potential source of difficulty in the preparation of a polylactide composition, with a low residual level of lactide. The residual lactide can be removed at elevated temperatures under vacuum. However, the tendency to form additional lactide will be a competitive reaction, which gives a composition with a higher residual level of lactide. Additional lactide can also be formed in the equipment and in the piping, after the devolatilization zone. Consequently, it is important to minimize the time that the polymer is exposed to high temperature, after the devolatilization zone. The formation of the cyclic ester (lactide) can be considered as the "opposite reaction". In fact, it is the opposite reaction for the ring-opening polymerization reaction of the polymerization of lactide; but it can also be considered as an opposite reaction in the case of the polymerization of lactic acid by direct condensation. It has been found that the propensity to form the cyclic ester by depolymerization is related to the concentration and activity of the catalyst, and to the equilibrium of the reaction, as described in U.S. Patent No. 5,338,822, to Gruber and co-inventors, which was issued on August 16, 1994, and by Witzke and co-authors, Macromolecules, 30, 7075-7085, 1997. There is comparatively little literature that discusses the equilibrium relations for most annular systems, as compared to non-annular systems. Lactide is one of the best-known ring systems, and the equilibrium ratio in: lactide and polylactide has been described in several references, including US Patent 5,338,822, by Gruber and co-inventors. Other annular systems have been tested to determine the general feasibility of the polymerization and the results have been reported in references such as MH Hartmann, High Molecular Weight Polylactic Acid Polymers, chapter 15, pages 367-411, Biopolymers from Renewable Resources, Kaplan, D ( ed.), Springer-Verlag, Berlin, published in July 1998; R. D. Lundberg and E. F. Cox, Lactones, chapter 6, pages 247-302, Kinetics and Mechanisms of Polymerization, volume 2, 1969; D ,. B. Johns, R. W. Lenz and A. Luecke, Lactones, chapter 7, page 461-521, Ring-Opening Polymerization, 1984; Y. Chujo and T. Saegusa, Ring-Opening Polymerization, pages 662-647, Encyclopedia of Polymer Science and Eng., Volume 1, 1988, John, Wiley & Sons, New York. An annular system that does not tend to polymerize in the presence of catalyst, under high temperature, can be described as a stable ring system. In such a system, the equilibrium condition is quite to the left in the equilibrium reaction shown further back. Systems that do not polymerize are of little concern, because they do not form polymers. A system that polymerizes easily corresponds to a system that moves quite to the right. These types of systems are usually inherently stable against depolymerization by the formation of cyclic ester. Systems that polymerize to some degree, but not completely, are of the utmost concern. This is because once they have been successfully polymerized there may be a strong tendency to depolymerize during the melt processing, forming the cyclic esters and incurring the problems described above. Previous attempts to stabilize the polylactide polymers include the extreme coronation of the polymer, the removal or precipitation of the polymer catalyst, the control of the catalyst level or the deactivation of the catalyst. The use of certain phosphite compounds as chain extension agents has been noted in the literature for use in polyethylene terephthalate and some other polyesters. See, for example, U.S. Patent No. 4,417,031, and U.S. Patent No. 4,568,720, and Aharoni and co-authors, J. Poly. Sci. A, volume 24, pages 1281-1296 (1986).

BRIEF DESCRIPTION OF THE INVENTION By means of the present invention there is provided a polymer composition containing lactic acid residue, which has improved stability. By providing improved stability it is meant that the composition provides at least one or all of the following: stability to lactide formation, stability to molecular weight degradation and color stability. Preferably the polymer composition containing lactic acid residue includes a polylactide polymer having an average number-average molecular weight of between about 25,000 and about 200,000, and between about 0.01% by weight and about 2% by weight of deactivating agent. Two general classes of deactivating agent are described in this application. The first class of deactivating agent includes phosphite antioxidants. The second class of deactivating agent includes multifunctional carboxylic acids, in particular those in which the acids are on carbon atoms that are no more than six separate carbon atoms, including the carbon atoms counted carbonyl carbon atom. Examples of polycarboxylic acids include dicarboxylic acids, such as tartaric acid, succinic acid, malic acid, fumaric acid and adipic acid. Another type of multifunctional carboxylic acid includes polycarboxylic acid which includes oligomers and polymers containing three or more carboxylic acid groups and a molecular weight greater than about 500. A particularly preferred polycarboxylic acid includes polyacrylic acid. A method for stabilizing a polymer composition containing lactic acid residue is provided in the present invention. The method includes providing a polymeric composition containing lactic acid residue, comprising a polylactide polymer having a number average molecular weight of from about 5,000 to about 200,000; and introducing a catalyst deactivating agent therein. It is preferred that the catalyst deactivating agent have a molecular weight greater than about 500, and is provided in an amount of about 0.01% by weight and about 2% by weight, based on the weight of the composition. polymer that contains lactic acid residue. An advantage of providing a deactivating agent having a molecular weight of more than about 500 is that it is less likely to be devolatilized under conditions normally encountered during the devolatilization of polylactide. If the deactivating agent is relatively volatile under conditions of destabilization of the polylactide, it is generally convenient to introduce the deactivating agent after the devolatilization step of the polylactide is completed, or almost at the end of the devolatilization step of the polylactide. A method for making a polymeric composition containing lactic acid residue is provided in the present invention. The method includes the steps of providing a polymerization mixture including lactide, catalyst, phosphite deactivating agent, and polymerizing the polymerization mixture. The invention further relates to articles that can be provided from polymeric compositions containing stabilized lactic acid residue, and to methods for preparing articles from the polymeric composition containing stabilized lactic acid residue. Exemplary types of articles that can be prepared include fibers and nonwovens, coated paper, films, mounds and foam. The methods for making articles include a step of processing in fusion.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation of a method for preparing the stabilized polymer product, according to the principles of the present invention, which comprises introducing the deactivating agent into the polymer, before devolatilizing the polymer. Figure 2 is a schematic representation of a method for preparing the stabilized polymer product, according to the principles of the present invention, which comprises introducing deactivating agent into the polymer after devolatilizing the polymer. Figure 3 is a schematic representation of a method for preparing stabilized polymer product, in accordance with the principles of the present invention, which includes introducing deactivating agent into a polymer, in a secondary device for effecting the composition. Figure 4 is a schematic representation of a cleaned film evaporator, for devolatilizing polymer, in accordance with the principles of the present invention; and Figure 5 is a graph of the equilibrium-moisture curve for polylactide, at 25 ° C.

DETAILED DESCRIPTION OF THE INVENTION The present invention has to do with providing stability to the polylactide polymer compositions. In general, the stability concept of the polylactide polymer can be broken down into three types or forms of stability. Those three types of stability include: stability to lactide formation, stability to molecular weight degradation, and color stability. Stability to lactide formation generally refers to the resistance of the polylactide polymer composition to depolymerization to form lactide. The formation of lactide is called the opposite reaction. Processing polylactide at alias temperatures and for long periods tends to favor the formation of lactide in the molten polymer. The formation of lactide is problematic, because the lactide can quickly evaporate from the polymer during processing, causing fumes and causing the equipment to fail. In addition, the presence of large amounts of lactide in the final product can adversely affect physical properties and shelf life. The stability to molecular weight degradation refers, in general, to the resistance of the polylactide polymer composition to greatly lowering its molecular weight. Molecular weight degradation is frequently characterized by chain trimming. A reduction in molecular weight, during processing, is a problem for polylactide polymers, due to their effect on viscosity and physical properties, such as tensile strength, plasticity, impact resistance, etc. It is important to control and / or maintain molecular weight in order to maintain quality. Color stability generally refers to the resistance of the polylactide polymer composition to yellowing. Polylactide polymer compositions are likely to develop a yellow / brown color when exposed to heat for a long time. This coloration may be due to the presence of impurities. This is undesirable in many applications, particularly when a transparent white color is desirable.

The polylactide polymer composition of the invention can be used in those applications where maintaining any or all of the stability types described above is a convenient aspect. Exemplary applications include: extrusion for the production of fibers, non-woven articles, woven articles, films and coated articles, or multilayer structures, such as coated paper and bags, injection molding, and foamed articles. 1. - POLYMERIC COMPOSITION In general, the preferred polymeric compositions that can be provided in accordance with the present invention include, as at least one component, polylactide or polylactic acid (collectively, polylactide and polylactic acid are referred to herein as pol i I). ao PLA). Accordingly, the invention is related to the improvement in the stability of the polylactide. In general, the nomenclature of polymers sometimes refers to polymers on the basis of the monomer from which the polymer is made; and in other cases characterizes the polymer based on the smallest repeating unit found in the polymer. For example, the smallest repeating unit in polylactide is lactic acid (actually residues of lactic acid). However, in typical cases, commercial polylactide will be manufactured by polymerizing the lactide monomer, instead of lactic acid. Of course, the lactide monomer is a lactic acid dimer. It is intended herein that the terms "polylactic acid", "polylactide" and "PLA" include within their scope both polymers based on polylactic acid and polymers based on polylactide, those terms being used interchangeably. That is, the terms "polylactic acid", "polylactide" and "PLA" are not limited to being limiting with respect to the manner in which the polymer is formed. It is intended that the terms "polymer" based on polylactide "or polymer" based on polylactic acid "refer to polymers of polylactic acid or polylactide, as well as to copolymers of lactic acid or lactide, where the resulting polymer comprises at least 50% by weight of repeating units of lactic acid residue or repeating units of lactide residue In this context, the term "repeating unit of lactic acid residue" is intended to refer to the following unit: HO I II - (- o - c - c -) - CH - In view of the above definition, it should be clear that the polylactide can be referred to as a polymer containing lactic acid residue, and as a polymer containing lactide residue. Here, the term "repeating unit of lactide residue" is intended to mean the following repeating unit: H O H O I II I II • (-O - c - c - o C c - I CH3 CH- It should be appreciated that the repeating lactide residue unit can be obtained from L-lactide, D-lactide and meso-lactide. L-lactide is structured from two S-lactic acid residues; D-lactide is structured from two R-lactide acid residues; and the meso-lactide is structured from an S-lactic acid residue and an R-lactic acid residue. It should be understood that the phrases "PLA polymer" and "polylactide polymer" are not intended to limit the polymer to one containing only lactide residues and / or lactic acid residues, unless specifically identified in that manner. As used herein, the phrases "PLA polymer" and "polylactide polymer" cover polymers containing the repeating lactic acid residue unit, described above, in an amount of at least 50% by weight, based on the total of the repeating units present in the polymer. Additionally, the phrases "PLA composition" and "polylactide composition" are not intended to limit the composition of the polymer to one containing only polylactide or polylactic acid as a component of the polymer, unless specifically identified in that manner. The composition may include other polymers or components blended with the polymer, containing at least 50% by weight of repeating lactic acid residue units. In most applications it is believed that the polylactide component of the composition will be the dominant polymer component, but that is not a requirement. It should be appreciated that the invention relates to stabilizing polylactide polymer, whether it constitutes a major component or a minor component of the composition. In general, it is expected that at least about 20% of the composition will consist of polylactide material. It is preferable that the composition include at least about 70% by weight of polylactide and, more preferably, at least about 90% by weight of polylactide. It should be appreciated that the amount of polylactide present in a particular composition depends on the property it is desired to impart to that composition. In certain compositions, 100 percent by weight of the polymer component of the composition can be polylactide.

A.- PLA (POLYLACTIC ACID OR POLYLACTIC) The polymeric compositions based on PLA, according to the present invention, are generally prepared from the polymerization of lactide or lactic acid. In some applications, the polymerization may be a copolymerization, copolymerizing the lactide monomer or lactic acid with another material. In some cases lactic acid or lactide can be polymerized first, and then the resulting polymer mixture is reacted, for example, it can be copolymerized, with another material, in order to provide some desired modification, for example, concerning ductility , impact resistance, molecular weight or polydispersity. It has become increasingly important to provide polymers derived from renewable resources. This will become particularly important as oil reserves decrease in the future, boosting the costs of petroleum-based polymers. Additionally, it is becoming increasingly important to provide polymers that are prepared by processes that are increasingly friendly to the environment. U.S. Patent No. 5,510,5626, to Baniel and co-inventors, describes the recovery of lactic acid from a fermentation broth. The lactic acid, once recovered, can be processed according to US Pat. No. 5, 142,023, by Gruber and coinventores, in order to provide a polylactide polymer. The specification of those patents that relate to the recovery of lactic acid, to the polymerization of lactic acid, to its depolymerization and its purification to give lactide, and to the polymerization of lactide, such as those described in U.S. Patent No. 5,510,526, and 5,142,023, and 5,4338,822, as well as in U.S. Patent Applications No. 08 / 862,612 and 08 / 850,319, are incorporated herein by this reference. The polylactide polymer is particularly advantageous because it can be supplied from renewable resources and can be composed relatively quickly, so that its biosack can be reintroduced into the environment. Therefore, the polylactide polymer can be considered as a relatively benign polymer, in terms of the total impact on the environment. The inventors have discovered that the concentration of acid in a polylactide polymer composition generally influences the rate of hydrolysis. It is believed that the impact of increasing acid concentrations promotes more rapid degradation by hydrolysis. Consequently, it may be important to minimize the concentration of acid residues (including acid and residual lactide concentrations) in order to resist hydrolysis and, thus, prolong shelf life. The inventors believe that by adding a certain type and a certain amount of carboxylic acid to the polylactide composition, it is allowed to provide a polylactide composition having lower levels of lactide, as compared to compositions not provided with the small amount of carboxylic acid. It is expected that this will provide increased resistance to hydrolysis. Conversely, it is expected that as the acid concentration increases, the rate of hydrolysis increases, thereby increasing the rate of degradation.

B.- THE COPOLYMERS The polymeric compositions containing lactic acid residue include the copolymers and are generally prepared from monomers including lactic acid or lactide. Polymers which are considered to be polymers containing lactic acid residue include poly (lactide) polymers, poly (lactic acid) polymers and copolymers, such as random and / or block copolymers of D-, L- or meso-lactide, and / or R- or S-lactic acid. A particularly preferred copolymer includes residues of both L-lactide residue and meso-lactide residue, as repeating units. Particularly preferred modified viscosity polylactide polymers include copolymers of lactide and multifunctional epoxides. Particular preference is given to epoxidized linseed oil and epoxidized soybean oil. In many situations it is preferred to prepare the polymer from 0.1 to 0.5 weight percent epoxidized multifunctional oil and molten lactide monomer. It should be understood that while many different types of components or reagents can be introduced into the polylactide polymer, their presence does not necessarily make them repeating units. It should be clear that the presence of a component! or its residue, at a concentration corresponding to the presence of a few components or residues in a polymer chain, is not repetitive. Other preferred copolymers include the copolymers of PLA with other biodegradable polymers, especially aliphatic polyesters. A preferred method for forming the copolymers would be by means of interesterification or coupling in a post-polymerization process, such as reactive extrusion. This method could include techniques such as extruding in the presence of a chain coupling agent, including, for example, TPP and / or TNPP, as described in more detail below, or by interlacing with an agent such as peroxide, as described in U.S. Patents 5,359,026 and 5,694,095, to Gruber and co-inventors; complete patents are incorporated herein by means of this reference. Alternatively, copolymers of lactide and other cyclic esters, cyclic ethers and cyclic ester-amides are possible. In this case, the comonomers would include a lactide with glycolide, paradioxanone, morpholinodinones, dioxepan-2-opa, dioxanones (such as p-dioxanone), lactones (such as epsilon-caprolactone or 4-valerolactone), dioxan (dione) s, (as glycolide or tetramethyl-1-dioxane-2,5-dione) or esteramides (such as morpholino-2,5-dion a). Also possible are copolymers of lactic acid and other hydroxy acids or low molecular weight polyesters, terminated with hydroxy and / or with acid. Aliphatic polyesters or aliphatic polyester-amides are preferred.

C- MIXTURES As discussed above, many different types of polymers can be mixed with polylactide, and they can be used in the present invention. Exemplary types of polymers that can be mixed with polylactide or used as separate components in a multi-component fiber include polyolefins, polyamides, aromatic / aliphatic polyesters, including polybutylene terephthalate and polyethylene terephthalate, as well as combinations thereof. Other types of polymers that may be used include the destructurized starch compositions, the polyhydric alcohols and their derivatives; derivatives of hydroxypropyl celluloses, cellulose esters, biodegradable aliphatic polyesters, ethers, urethanes and biodegradable aliphatic-aromatic polyesters. Examples of destructurized starch compositions include the starch in combination with ethylene vinyl alcohol (EVOH), obtainable as "Mater-B" from Novamont. Exemplary polyhydric alcohols and their derivatives include polyvinyl alcohol modified with appropriate plasticizers, such as glycerol, ethylene glycol, polyvinyl alcohol in combination with poly (alkenoxy) acrylate, which is available as "Vinex" from Air Products and Chemicals. An example of a hydroxypropyl cellulose derivative includes the hydroxypropyl cellulose-nonionic cellulose ether, which is available as "KLUCEL" from Hercules. Examples of cellulose esters include cellulose acetates ("Tenites", obtainable from Eastman and including propionates and butyrates); propionate of cellulose acetate and cellulose acetate butyrates. Examples of biodegradable aliphatic polyesters include polyhydroxybutyrate (PHP), polyhydroxybutyrate-co-valerate (PHBV), obtainable as "Biopol" and polycaprolactane, obtainable as "Tone", from Union Carbide; polybutylene succinate, obtainable as "Bionelle" 1000 series, from Showa; polybutylene succinate-co-adipate, obtainable as Showa Bionelle 3000, polygonic acid (PGA), various grades of polylactide (PLA), polybutylene oxalate, polyethylene adipate, poliparadioxanone, polymorpholinoviones and polydioxipan -2-one . Examples of ethers include: polypropylene oxide and copolymers of polypropylene oxide and polyethylene oxide, and polyethylene oxide copolymers. Examples of polycarbonates include: polyethylene carbonate, polybutylene carbonate and polytrimethylene carbonate and their derivatives. Examples of urethanes include urethanes made with polyester or ethers or mixtures thereof, or made from polyesters and urethanes, to give aliphatic polyester urethanes. The biodegradable aliphatic-aromatic polyesters include: polybutilepo succinate-co-terephthalate, obtainable from Eastman and "Biomax", obtainable from DuPont. Additional components that can be mixed with PLA or used as another component of a multi-component film include thermoplastic resins, such as hydrocarbons, polyesters, polyvinyl alcohols, poly (acrylonitrile) polymers, and esters of strongly substituted cellulose, selected. Examples of hydrocarbons include polyethylene and polypropylene. Examples of polyesters include aromatic polyesters, such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Preferred polymers that can be blended include natural rubber, synthetic rubbers and epoxidized natural rubbers, such as those described in U.S. Patent No. 5,714,573, which was issued on February 3, 1998; whose full description is incorporated herein by means of this reference.

II.- THE TECHNIQUES FOR STABILIZING THE POLYMERIC COMPOSITION With reference now to figures 1 to 4, various schematic representations are given to stabilize the polymeric product. In Figure 1 there is provided a polymerization reactor 10, which receives the lactide from the lactide feed line 12, and the catalyst from the catalyst feed line 14. In a preferred process, the polylactide is polymerized at a temperature of at least about 160 ° C, with sufficient amount of catalyst and for a sufficient time to reach a conversion of at least about 85%. Preferably the polymerization reactor is a clogged flow reactor, with recirculation capacity, or a series of clogged flow reactors, with recirculation capacity, although stirred, continuous, series tank reactors are also suitable. In a preferred embodiment, the catalyst is provided in an amount ranging from about 0.09 to about 1.39 meq / kg and, more preferably, between about 0.17 and about 0.69 meq / kg. It is preferred that the length of the polymerization be between about 0.5 and 14 hours and, more preferably, between about 1.5 and 7 hours. The polylactide polymer leaves the polymerization reactor 10 as a molten material, through line 16, and flows into the melting mixer 18, which is provided to bring the deactivating agent 20, from the deactivator inlet 22, to the molten polymer. The mixer can be any apparatus that adequately works the deactivating agent in the molten polymer. Exemplary types of fusion mixers include extruders, static mixers and pumps. It is preferred to add the deactivating agent in an amount of between about 0.001% and 0.5% by weight and, more preferably, between 0.01% and 0.2% by weight, based on the total weight of the polymer composition. In the context of the present invention, the reference to a deactivating agent means that it refers to an agent that deactivates the catalyst and that can be called a catalyst deactivating agent. It should be appreciated that this catalyst deactivation action is a theory that the inventors believe describes the manner in which the deactivating agent provides increased stability to the polylactide polymer composition. It is not the intention of the inventors to adhere to this theory; and it should be appreciated that it is the stabilizing effect of the deactivating agent that matters. Accordingly, the deactivating agent can also be referred to as a stabilizing agent, due to its stabilizing effect on the polylactide polymer composition.

The combination of molten polymer and deactivating agent leaves the melting mixer 18 via line 24 and enters the devolatilizer 26. It is the purpose of the devolatilizer 26 to remove the residual lactide and any other volatile impurities. Consequently, the devolatilizer is preferably maintained at a temperature between about 200 ° C and 260 ° C, and at a pressure less than 2 mm Hg absolute pressure. The lactide is removed from the devolatilizer 26 as a vapor by the volatile removal line 30. Exemplary types of devolatilizers include extruders, especially twin screw extruders, rubble film evaporators, down-stream evaporators, rotary de-volatilisers, rotary disc devolatilizers, centrifugal devolatilizers, and flat plate devolatilizers. . The polymer and deactivating agent combination leaves the devolatilizer 26 on the line 32, as a melt, and enters the pelletizer 34. In the pelletizer 34, it is where the polymer composition is cooled and pelletized, to give a solid capable of flowing. It is preferred that the pellet former includes a pelletizer with a front die cutter. Said pellet formachlor usually includes a cooling medium, a plurality of extrusion holes and a rotary front cutter. A strand cut pellet former is also suitable. The pelletized polymer 36 is then either directed to a dryer 38 to remove moisture, or cooled to a crystallizer 40. It should be understood that both the dryer and the crystallizer are optional and, if it is not desired to dry or crystallize subsequently. , these devices can be omitted. Conventional crystallizers can be used, such as those obtainable from Unidyne, Conair Group, Gala, Novatech Inc., Witte Company Inc. and Hosokowa-Bepex Corporation. The inventors discovered that, when the deactivating agent is added before devolatilization, the deactivating agent must be sufficiently non-volatile, under the operating conditions in the devolatilizer 26, so that the deactivating agent remains with the polymer during the devolatilization process. In the case that the deactivating agent is relatively volatile under the devolatilization conditions, it may be convenient to add the deactivating agent after the devolatilization. In the situation where the deactivating agent is relatively volatile, or at least partially volatile during the devolatilization process, preferably the deactivating agent is added at the end of the devolatilization process or after the devolatilization process. Figures 2 and 4 illustrate embodiments of the invention in which the deactivating agent is added after the steps of devolatilizing. It should be appreciated that the deactivating agent can be added before completing the devolatilization process; but one must wait until at least a part of the volatile deactivating agent has been volatilized during the devolatilization process. Referring now to Figure 2 there is shown, in a more detailed schematic, the devolatilizer 48, for the addition of a relatively volatile deactivating agent. In a preferred embodiment, the devolatilizer 48 includes an inlet 50 for receiving a composition, including molten polymer containing residual lactide, through the feed line 52. The inlet 50 is provided within the feed section 54 of the devolatilizer 48. The feed section 54 is separated from the vacuum port 56 by a melt seal element 58. Even when the molten polymer containing residual lactide is provided within the section 56 of the vacuum port, the lactide is vaporized under reduced pressure and elevated temperature, and is removed by the suction of lactide 60. Then the molten composition passes beyond the fusion seal element 62, towards section 64 of the vacuum gate. The composition is again subjected to elevated temperature and reduced pressure and the lactide is vaporized and removed by suction 66 of lactide. The molten composition then flows past the melt seal element 68 and into the final mixing stage 70. In this mixing stage 70 where the deactivating agent can be added through line 73, and can be mixed in the molten polymer, by virtue of the mixing element 71. The composition of the devolatilizer is then removed, by line 72, and continues for further processing, which may include the formation of pellets, as discussed above.

It should be appreciated that, although the invention is described in the context of a devolatilizer 48 having two vacuum port sections, the desired number of vacuum port sections and the residence time within each of them are a function of the Lactide level provided within the melted composition and the desired level of lactide in the polymer product. Thus, the devolatilizer can be provided with one or more vacuum port sections, as desired. Reference is now made to Figure 3, which shows a schematic representation of a method for preparing the stabilized polymer product, which includes introducing a deactivating agent into a secondary composition apparatus. The devolatilized polymer pellets 100 are introduced through the line 102 into an extruder 104. The polymer pellets are melted into the extruder 104 to give a molten polymer composition 108, and the deactivating agent 106 is added to the composition. 108 of molten polymer, through inlet 110 for deactivating agent. Reference may be made to the resulting composition as the stabilized composition, which includes polymer and deactivating agent, and which can be processed into articles or pellets. Exemplary types of items include: mounds, coatings, fibers, foams and films. Preferably the extruder 104 is a twin-screw extruder, open to the atmosphere, with at least one series of mixing elements. It is preferred that the deactivating agent be added to the polymer after it is completely melted. This facilitates the introduction of the deactivating agent into the polymer. Reference is now made to Figure 4, in which a schematic representation of a preferred desvolatilizachlor is provided, with the reference number 150. The devolatilizer 150 can be termed a wiped or wiped film evaporator and includes an inlet 152 for polymer and a suction 154 for lactide. The molten polymer 158 that enters the cleaned film evaporator is spread along the interior hot walls 156. In general, conditions are preferably provided within the evaporator 150 of cleaned film at a temperature of between about 200 ° C and 260 ° C, and at a pressure of about 0.5 mm Hg and about 5 mm Hg. Hg. Under these conditions, it vaporizes the residual lactide that is inside the molten polymer and is eliminated through the suction of lactide. The inventors have found that the cleaned film evaporator 154 advantageously increases the surface area of the polymer, compared to conventional devolatilizers, such as extruder-type devolatilizers. Additionally, the cleaned film evaporator 150 provides agitation of the polymer film, which increases mixing and increases the rate of removal of the residual lactide, from the molten polymer. In a preferred embodiment, the devolatilization 150 is used as the devolatilizer 26 in the process illustrated in Figure 1. In that situation, the deactivating agent is added to the molten polymer in a static mixer. Alternatively, the deactivating agent can be added after the devolatilization step, as shown in Figure 4. The melted, devolatilized polymer 160 is collected in the collection area 162 of the cleaned film evaporator 150. The deactivating agent can be added to the molten and devolatilized polymer 160 as it is taken out of the cleaned film evaporator 150, by means of a melt pump or gear pump 166. Once the deactivating agent 164 is introduced into the molten polymer and devolatilized 160, the composition is preferably subjected to mixing in a mixing element 168. The mixed composition can then be processed through a pelletizer. Of course the mixing element 168 can be omitted if the deactivating agent is mixed in the polymer, before devolatilizing. It should be noted that the devolatilized polymer, before forming the pellets, can be considered sufficiently dry, as a result of the devolatilization step. Thus, by using a pelletizing system, which avoids contacting the polymeric composition with water, it is possible to provide dry pellets and avoid the need to provide a dryer, after pelletization. In a preferred embodiment the deactivating agent is added to the polymer in an amount ranging from about 0.001% by weight to about 0.5% by weight and, more preferably, from 0.01 to about 0.2% by weight, based on the weight total of the polymer composition. The devolatilized polymer that has been pelletized can be stored for subsequent use, or it can be fed directly to a compounder / finisher to produce stabilized product, based on the lactide polymer. For certain deactivating agents, such as phosphite antioxidants, the inventors have found the beneficial effect of adding phosphite antioxidant to the polymerization mixture. Phosphite antioxidant can be added to the lactide monomer mixture, prior to polymerization, or to the polymerized mixture at some point during polymerization. Phosphite helps prevent molecular weight decline and brown-colored reaction during polymerization . Subsequently, the phosphite can also serve as a deactivating agent to reduce the rate of lactide formation. The inventors believe that exposure to moisture, as in an underwater pelletizer, can modify the phosphite to provide the deactivation function. The inventors speculate that exposure to moisture could also be effected, for example, by the addition of steam to a devolatilizing extruder, in order to deactivate the catalyst after polymerization but before devolatilization, or simultaneously with it. It should be understood that another technique for removing lactide from the polylactide polymer comprises "solid deposition". Frequently people confuse devolatilization with solid deposition. In general, solid deposition refers to the reduction of the lactide level by promoting the positive reaction of lactide to polylactide. The solid deposition process of polylactide also includes conditions of about 100 ° C to 130 ° C for times of about 1 day to about 1 week. Crystallization of the polymer during solid deposition can help reduce the level of lactide. Dissertation from Dr. Witzke, Michigan State University, 1997. The inventors have found that devolatilizing polylactide to remove lactide is commercially more advantageous than the solid deposition process.

A.- STABILITY BY RE-FORMATION OF LACTIDA 1.- DISABLING AGENT The inventors have found that the lactide reformation reaction (the opposite reaction) can be effectively delayed at high temperatures in the polylactide polymers by introducing appropriate agents that can be termed deactivating agents or simply deactivators. It is believed that these agents can act by deactivating the catalyst and, thereby, essentially eliminating the effectiveness of the catalyst for the opposite reaction. The inventors have discovered that these deactivating agents can be particularly effective in tin-catalyzed polylactide polymer compositions, especially those in which the tin is in the +2 oxidation state. That is, it is believed that these deactivating agents are particularly effective in deactivating tin catalysts, or in stabilizing lactide compositions, which have been polymerized using a tin catalyst. It is expected that deactivating agents are effective in stopping tin-catalyzed degradation reactions in other types of polymer systems. Applicants have identified various types of deactivators. A class of deactivators includes the phosphite antioxidant. A second class of deactivator includes multifunctional carboxylic acids, particularly those in which the acid groups are on carbon atoms not more than six carbon atoms apart (including carbonyl carbon) and, preferably, two carbon atoms. five carbon atoms of separation. This second class can be generalized to include compounds containing electronegative groups, which preferably are at a separation of four to seven atoms (including the electronegative atom). The salts and esters of multifunctional carboxylic acids and ketone structures could also be included. Carboxylic acids, such as tartaric acid, are preferred because of government regulations and because they are used as food ingredients. Carboxylic acids, such as polyacrylic acid, are preferred, due to their lack of volatility under the conditions of high temperature and low pressure associated with the devolatilization of lactide. The inventors have discovered that acid structures are particularly effective. (a) .- THE PHOSPHITE ANTIOXIDANTS As shown in example 1, it has been found that phosphite antioxidants provide excellent stabilization against the formation of lactide. Table 1 shows the results obtained using trinonylphenyl phosphite (TNPP), triphenyl phosphite (TPP) and distearylpentaerythritol diphosphite (Weston 618) as deactivation agents. It was found that each of these compounds significantly reduced the rate of new formation (re-formation) of lactide. It has been found that these and other phosphite antioxidants are described in US Patent 5,388,822, by Gruber and co-inventors, in column 13, lines 15-25; provide protection against the formation of new lactide (re-formation of lactide). These phosphite antioxidants include trialkyl phosphites, mixed alkylaryl phosphites, alkylated aryl phosphites, sterically hindered aryl phosphites, aliphatic spirocyclic phosphites, tightly hindered phenyl-spirocyclics and sterically hindered bisphosphonites. The result is surprising because the inventors believe that the phosphite antioxidants function as catalyst deactivating agents, but can be added at the beginning of the polymerization to prevent color formation and molecular weight degradation, apparently without affecting the activity of the catalyst. The inventors have the theory that exposure to moisture, during polymerization and thereafter, modifies the phosphites to give an agent that effectively stops the re-formation of lactide. An exemplary phosphite antioxidant that can be used, is available under the name ULTRANOX® 641 from GE Specialty Chemicals. This phosphite antioxidant can be characterized as a mixed alkyl / aryl phosphite and as a sterically hindered aryl phosphite. This phosphite antioxidant is considered advantageous because its melting point is 90 ° C. In general, phosphite antioxidants having melting points below about 100 ° C are advantageous because of the ease with which they can be hand Phosphite antioxidants are conveniently used at a concentration that provides the desired degree of stability and avoids using too much, which can be a waste. It is expected that the amount of phosphite antioxidant is a function of the catalyst level. The higher the catalyst level, the more phosphite antioxidant may be convenient. This corresponds, in general, to a concentration of more than about 0.1 weight percent, and a concentration of less than about 2 weight percent. It is preferable that the phosphite antioxidant concentration be provided within a range of about 0.2 weight percent to 1 weight percent and, more preferable, between about 0.25 weight percent and about 0 5 percent by weight. weight. (b) ARBITRICAL ACIDS Another category of materials that have been found to be surprisingly effective in reducing depolymerization include dicarboxylic acids. As shown in Examples 1, 2 and 9, tartaric acid, succinic acid, adipic acid, fumaric acid and malic acid, as well as Sylvatac 140 (a rosin with high levels of acid dimer) were effective at 260 ° C to slow down the re-formation of lactide. The most effective of the dicarboxylic acids was tartaric acid, which is also a dihydroxy acid. Tartaric acid, succinic acid, malic acid, and fumaric acid have acid groups that are separated by four carbon atoms (including carbonyl carbon). The adipic acid has acid groups that are at a separation of six carbon atoms (including the carbon atom of carbon). The superior performance of the dicarboxylic acids is surprising in view of the deficient functioning of the monocarboxylic acids. Lactic acid, ethyl lactylate (DP2), alginic acid and aspartic acid were tested and found to be poor in preventing the re-formation of the acid at 260 ° C. Note that both lactic acid and DP2 are hydroxy acids; that alginic and stearic acids are simply carboxylic acids, and that aspartic acid is an amino acid. It was found that dicarboxylic acids, exemplified by tartaric acid, were effective at levels of only 0.026 weight percent, and that they are likely to be effective at higher amounts. The inventors believe that amounts up to 1% by weight or more could be used, with little adverse effect on the melt, although the shelf life due to the higher acid content can decrease. For applications where rapid degradation is desirable, this could be advantageous. It is expected that the preferred dicarboxylic acid scales to provide the desired stabilization will depend on the catalyst level. At a higher level of catalyst, more dicarboxylic acid may be convenient. At the preferred catalyst levels, identified above, the amount of the carboxylic acid preferably an amount of at least about 0.01 weight percent and an amount of less than about 0.05 weight percent. 2 percent by weight. It is preferable that the amount of dicarboxylic acid is an amount within the range of about 0.02 weight percent and 1 weight percent and, more preferably, within the range of about 0.04 weight percent and 0.3 weight percent , based on the total weight of the polymer composition. An ester of tartaric acid, diethyl L-tartrate, was tested and found to be ineffective in reducing lactide formation. The tartaric acid salts were further tested and found to appear to reduce the formation of lactide but, apparently, cause molecular weight degradation. A test was carried out to compare the optical isomers of tartaric acid. Surprisingly, when tested on a polylactide sample (primarily residues of L-lactide), it was found that D-tartaric acid was more effective in preventing the formation of lactide than L-tartaric acid. It is expected that the meso-tartaric acid be effective to prevent the re-formation of lactide. The inventors have discovered that, under the conditions of devolatilization of lactide, tartaric acid tends to volatilize from the polymer composition. Consequently, if tartaric acid is added to the polylactide polymer as a deactivating agent, it is preferable to add it after the devolatilization step. While it is generally considered that tartaric acid is non-volatile, the inventors have found that it is sufficiently volatile under the conditions found during the devolatilization of polylactide, so that at least a portion of the tartaric acid tends to exit the polylactic polymer. . As discussed above, the process of devolatilization of the polylactide polymer generally occurs at a temperature between about 200 ° C and about 260 ° C, and at a pressure between about 0.5 mm Hg and about 10 mm Hg, during a time of residence of up to about 20 minutes. If devolatilization occurs at a lower temperature, the volatility of tartaric acid may not be a concern, and may be added before devolatilization. (c) POLYCARBODYLIC ACID In the context of the present invention, the expression "polycarboxylic acid" describes a carboxylic acid containing molecules having three or more carboxylic acid groups and, preferably, describes oligomers and polymers containing three or more carboxylic acid groups. In general, the polycarboxylic acid has a molecular weight that is greater than about 500 and provides the desired degree of non-volatility during the devolatilization processes encountered when the polylactide is devolatilized. It is preferable that the molecular weight of the polycarboxylic acid ssa greater than about 1,000. In order to provide the desired degree of deactivating agent or stabilizing agent activity, it is desirable that the polycarboxylic acid includes at least one carboxylic acid group per 250 u.m.a. (atomic mass units). The inventors have found that the polyacrylic acid works advantageously well to reduce the formation of lactide. This effect has been observed both for the high molecular weight polyacrylic acid and for the low molecular weight polyacrylic acid. The acid concentration for the polyacrylic acid corresponds to an acid group per 72 u.m.a. In general, the high molecular weight polyacrylic acid has a number average molecular weight of between about 40,000 and about 50,000. A preferred high molecular weight polyacrylic acid has a number average molecular weight of between about 50,000 and about 200,000. The low molecular weight polyacrylic acid preferably has a number average molecular weight of between about 500 and 40,000. The preferred polyacrylic acid, of low molecular weight, has a number average molecular weight between 1,000 and 20,000. As shown in Table 2, polyacrylic acid was found to be effective at 0.06 weight percent. It is expected that the polyacrylic acid will provide effectiveness at a level of about 0.01 weight percent or about 0.02 weight percent. Additionally, it was found that a level of 0.25 percent in pe: > or it was effective, without adverse consequences. The inventors hope that the polyacrylic acid can be included at approximate levels of 1 or 2 weight percent, without adverse reaction. It is expected that too much polyacrylic acid results in a high acid content, which can cause the depolymerization of the polilactids. The preferred amount of multifunctional carboxylic acid depends on the level of catalyst and the acid functionality per unit mass of atomic mass. (u.m.a.). It is expected that at the preferred catalyst levels, identified above, and for the multifunctional carboxylic acids, which have acid functionality greater than about 1 carboxylic acid group per 250 amu, the preferred level of multifunctional carboxylic acid is within the approximate scale of 0.01 weight percent to 2 weight percent; and preferably, which is within the range of about 0.02 weight percent to about 1 weight percent, and, more preferably, within the approximate range of 0.04 weight percent and 0.3 weight percent. The inventors noted that the polyacrylic acid has a structure shown by the following formula: Although this structure is a polymer, it is a carboxylic acid having acid groups in carbons that are separated by five carbon atoms (including the carbonyl atom). The inventors believe that the mode of stabilization for polyacrylic acid is probably similar to the mode for dicarboxylic acids. It should be understood that polyacrylic acid copolymers can be used. In order to maintain the separation between the acid groups, the polyacrylic acid copolymers which are preferred include block copolymers of polyacrylic acid. Other experiments were carried out to determine the key aspects of stabilization. A copolymer was prepared, named PAA-MMA in the table, by random copolymerization of acrylic acid and methyl methacrylate, with 41.7 mol% of acrylic acid residues. This compound was tested at 0.3% by weight in PLA, in order to provide the same acid content as 0.12% by weight of polyacrylic acid (PAA). Table 1 shows that, although the PAA-MMA copolymer was effective in decreasing the lactide re-formation, it was much less effective than an equivalent acid content in the regular PAA. This supports the theory of the inventors that the separation between carboxylic acid groups is important to provide catalyst deactivating effect. A second polymer, PMA-MMA, was prepared as a random copolymer of maleic anhydride and methyl methacrylate, with 23.4 mol% of maleic anhydride residues. It was found that this polymer was ineffective in preventing the re-formation of lactide. The maleic anhydride residues have the potential to form a couple of carboxylic acid groups in carbons at a spacing of 4 atoms, if they are reacted with water. The lack of effectiveness of the anhydrides, in dry conditions, shows that the mechanism of action is not through the formation of anhydride. It could be expected that the anhydrides, formed either in situ or directly added, will react with the hydroxyl groups and cause end coronation. However, these results show that the anhydrides do not significantly decrease the formation of lactide at 260 ° C. The results reported in the table for stearic anhydride, corroborate that the anhydrides are ineffective under the conditions of fusion mixing and processing in fusion, to prevent the re-formation of lactide.

It is expected that, under humid conditions, some anhydrides may be useful, once they have been hydrated to the diacid form. It should be appreciated that, by using an oligomer or polymers as deactivating agents for polymeric compositions based on polylactide, it can be said that the resulting composition is a mixture of polymers. Other polycarboxylic acids which can act as deactivating agents include copolymers of acrylic acid with other monomers, to form polymers such as poly (ethylene-co-acrylic acid), poly (styrene-co-acrylic acid), other polymers with acid-dependent groups , such as poly (malic acid) and copolymers, poly (maleic acid), polymers of amino acids, especially polymers of acidic amino acids, such as poly (acetic or aspartic), poly (glutamic acid) and their copolymers. In some cases, it may be desirable to improve the compatibility between the polycarboxylic acid and the polylactide polymer, in which case a variety of techniques may be desirable. A particularly advantageous technique can be to form polylactide / polycarboxylic acid block copolymers, for example, by reacting a low molecular weight polycarboxylic acid, terminated on hydroxyl or amine, with the lactide. The inventors believe that it would also be possible to prepare useful deactivating agents by partially hydrolyzing anhydride polymers and copolymers, for example by partially hydrolyzing poly (styrene-maleic anhydride), poly (ethylene-maleic anhydride), poly (propylene-maleic anhydride) or poly ( lactide) grafted into maleic anhydride. The anhydride groups are beneficial in that, after hydrolysis of the acid groups, they will provide a preferred spacing or spacing. Other potential candidates include naturally derived products, such as carboxymethylcellulose and other acidified or negatively charged gums. Supported materials such as cation exchange resins, which include materials such as sulfonated polystyrene resin, may also be useful. A variety of polyesters with dependent carboxylic acid groups could be useful. Said polyesters could be formed, for example, by the reaction of diols with dianhydrides or with multifunctional acids. The diols could also have an acid-dependent group, and be coupled with conventional coupling agents. An example would be the reaction of dimethylolpropionic acid, coupled with an isocyanate. (d) OTHER MATERIALS It was found that polyphosphoric acid, a strong mineral acid, effectively slowed the re-formation of lactide, but in general a polymer of poor color and lower molecular weight was obtained as a result. It is believed that other strong acids, defined herein as those having a pKa of less than about 2, would also provide stabilization. Such acids have been used in the art, often in combination with a solvent, to deactivate the catalyst. The inventors believe that under the conditions of melt mixing or melt processing, the strong acids will lead to a dark color and unfavorable characteristics of the polymer. The carboxylic acids tested generally have pKa values of 2.5 to 6.0 and provide the dark color observed when polyphosphoric acid is used. The citric acid was not found to be effective at high temperature, although it did provide stabilization at 240 ° C. It is believed that citric acid decomposes at the highest temperature and, therefore, is a less preferred multicarboxylic acid. EDTA (ethylenediaminetetraacetic acid) and MD1024 (MD1024 is available under the brand name Irganox ™ from Ciba-Geigy Corporation, and is 1,2-bis (3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl) hydrazine) were also tested and found that they were somewhat effective at 240 ° C, but significantly less effective at 260 ° C. It was found that EDTA was more effective than MD1024.

EXTREME CORONATION Another method to reduce cyclic monomer formation involves end coronation. In the context of polylactide polymers, it is believed that the reaction can occur "descorrimiento" by means of the mechanism of "retromordida", where the free hydroxyl group attacks the ester group. It is expected that the end caption of the hydroxyl group can stabilize the polymer, to prevent the formation of the cyclic ester. However, it should be appreciated that the extreme groups that had not been crowned will still be active and that it would be expected that a certain level of re-formation would occur. Also generally hydrolysis or other chain cleavage is observed, randomly, during processing that would create new hydroxyl end groups that would be active to attack the ester groups. Additionally it should be noted that the "back-bite" reaction may not occur in the extreme group at all but, in fact, may be the opposite reaction of a medium chain insertion reaction. Prior end coronation techniques use an anhydride, such as acetic anhydride, in the presence of a solvent. In this technique of the prior art it is not clear whether the observed results may be due to a treatment artifact, rather than to the coronation of the intended end. 3. USE OF POLYMER CHAIN SWITCHES The inventors hope that the rate of formation of the cyclic monomer can be reduced, including units in the polymer chain that are slow to form the cyclic monomer or that do not form a cyclic monomer at all. The inventors expect that the copolymeric agents, including caprolactone, morpholino-dione, epoxide-functional monomers, carbonates, anhydrides, ester-ethers and cyclic diesters, would be difficult to re-form. Consequently, polymerizing lactide with these monomeric materials would be expected to provide a relatively high molecular weight polylactide (in contrast to the molecular weight of the polylactide obtained by direct condensation of lactic acid) having increased stability. 4. THE CONCENTRATION OF THE CATALYST Another method to reduce the formation of the cyclic monomer comprises controlling the initial concentration of the catalyst and / or the removal of the catalyst residue. Previous teachings indicate that some increase in polymer stability can be achieved by removing the catalyst. One technique comprises dissolving the polymer in a solvent and then treating with a second solvent to remove the catalyst, and then precipitating the polymer. In the preferred embodiments of the present invention, the polymer is treated in the melt and without the addition of solvent. This means that the removal of the catalyst would be difficult, but it results in a simpler process, more cost effective and more environmentally safe. Example 7 presents a calculation showing how the polymerization time will vary to obtain 90% conversion, as a function of the catalyst level, at a polymerization temperature of 190 ° C. The calculated regimens of lactide re-formation are also shown. The reduction of the catalyst level reduces the rate of lactide re-formation, but at the expense of longer polymerization times. This leads to a more expensive process, as well as some additional degradation during the polymerization. The inventors believe that, in order to produce a highly stable polymer, it will be convenient to control the level of catalyst addition to deactivate the catalyst residue.

B. STABILITY AGAINST MOLECULAR WEIGHT DEGRADATION Molecular weight degradation has at least two main components: The first, especially active at low temperature and from there to the processing temperatures on fusion, is the random division of the chain, due to the hydrolysis. This process is well known in polyesters. Consequently, it is generally convenient to perfectly dry the aliphatic polyesters before melt processing, in order to reduce the chain scission. The inventors believe that at typical melt processing conditions the hydrolysis reaction is catalyzed at least partially. See example 3 of the US patent 5, 338,822. The dissertation of Dr. Witzke, Michigan State University, 1997, showed that the hydrolysis reaction was characterized by an activation energy of about 33 kJ / mol, in the presence of an Sn (+ 2) catalyst. At melt processing temperatures of about 200 ° C or less, this will be a dominant form of molecular weight loss, and catalyst deactivators can slow the reaction and provide some stabilization. However, perfect drying is still important. An extruder screw design open to the atmosphere (vacuum or inert gas sweeping) can also sweep system moisture. Figure 5 provides a humidity versus relative humidity curve for polylactide. It can be seen that moisture contents of more than 1,000 ppm will be reached if polylactide is stored at a relative humidity of more than 25%. As a result, perfect drying is important. Line drying is preferred, and a sealed environment is desirable. At higher temperatures, such as 230 ° C or more, such as are present in some applications, other forms of degradation become more important. These are generally referred to as thermal degradation reactions, and have been discussed in various references. The activation energy for this complex of reactions seems to be around 126 kJ / mol. Dissertation from Dr. Witzke, Michigan State University, 1997. A clear dependence on normal catalyst activity has not been demonstrated, and the deactivation described above is not expected to have a strong effect on that basis. Fiber production from melt-blown or meltblowing operations, and paper coating, are two very high temperature applications, where this type of degradation can be particularly important. It is expected that free radical scavengers or terminators are useful in this application to control molecular weight loss. These same reactions, or perhaps oxidative degradation, may also be important in the anhydrous conditions experienced during polymerization. Various examples of U.S. Patent No. 5,338,822 show the effectiveness of phosphite antioxidants in the po I i I actives of higher molecular weight; and when they are added during the polymerization. Table 2 reports the apparent decline of molecular pedeus during the lactide re-formation test at 260 ° C and 20 minutes. The results are reported, based on the number average molecular weight, as chain excision events, in meq / kg-hour. Some of the additives, such as tartaric acid, are effective in preventing re-formation, but not to prevent molecular weight degradation. This confirms the idea that molecular weight degradation, under these conditions, is not primarily catalytic. It was found that phosphite stabilizers, particularly TNPP, reduced the apparent molecular weight decline. This may be due to a chain coupling effect, as reported in the literature for PET / TNPP or nylon-6 / TNPP. That is, the chains are still breaking, but a chain coupling agent is present and recombines them. In the present case, the inventors have even found an increase in the molecular weight when composing the phosphites in the polymer composition, as shown in example 5. Surprisingly, for polylactide, it was found that even the distearylpentaerythritol diphosphite (Weston 618) was at least somewhat effective. Aharoni and co-authors, J. Polym. Sci., Polym. Chem., 22, 2567, 2577 (1984) have tested a variety of nylon-6 'phosphites and found that they were very ineffective as chain coupling agents. The inventors have found that polyacrylic acid functions to reduce the rate of molecular weight decline. There is no obvious chain coupling mechanism that is apparent to this system. The fact that the phosphite compounds are useful as chain extension agents could make them useful for forming copolymers, such as between polycaprolactane and PLA or other pairs of aliphatic polyesters. It could also work between an aliphatic polyester and an aromatic polyester. The copolymers would be formed when a single phosphite center was joined with two or more disparate types of polyester, to form a single new copolymer molecule. This reaction could be carried out in a reactive extrusion process.

C. STABILITY AGAINST COLOR FORMATION It had previously been reported that phosphite antioxidants stabilized against color formation in U.S. Patent No. 5,338,822. The inventors have confirmed this discovery and have found that polyacrylic acids, when compounded in the polymer, reduce color formation during subsequent processing. It was found that additives, such as alginic acid, aspartic acid and polyphosphoric acid caused greater yellowing or brown imparting. This is shown in example 1. The purity of the lactide used in the polymerization also affects the color formation, with less color formed when high purity lactide is used. The use of dyes, especially blue or violet dyes, is allowed to counteract the yellow color in polylactide.

III. ADDITIONAL COMPONENTS OF POLYMERIC COMPOSITION The polylactide polymer composition of the invention may include additional components or additives, in addition to the stabilizing agents described above. These additional components include: plasticizers, nucleating agents, fillers, surface treatments, surfactants, pigments, catalysts, terminating oils, lubricants, rheology modifiers, crystallinity modifiers and antioxidants.

PLASTICIZERS For most polylactide polymer compositions, it is believed that the glass transition temperature can be lowered to convenient levels by adding a plasticizer component to give an approximate concentration of 0.5 to 20 weight percent plasticizer, based on the weight of the polymer composition. In general, a sufficient amount of plasticizer should be incorporated to give a desired reduction in Tg. It is believed that the level of plasticizer should be above at least 1 percent by weight and, more preferably, at more than at least 2 percent by weight, to give sufficient flexibility and smoothness. Consequently, the plasticizer must be included to provide an approximate concentration level of 1 to 10 weight percent. The selection of the plasticizer may involve the consideration of various criteria. In particular because the large polymer surface area exposed during the fiber formation, it is convenient to provide a plasticizer which does not volatilize to any significant degree. In addition to the reduction in fumes, this would result in a reduction in deposition. It is generally convenient to provide as much biodegradability as possible; and it is preferred to use a plasticizer that is biodegradable, non-toxic, compatible with the resin and relatively non-volatile. Preferred are plasticizers of the general class of the aliphatic or aliphatic esters, ether and multifunctional-functional esters and / or ethers. These include: alkyl phosphate esters, dialkyl ether diesters, tricarboxylic esters, epoxidized oils and esters, polyesters, diesters, alkyl diesters, aliphatic diesters, alkyl ether monoesters, citrate esters, esters dicarboxylics, vegetable oils and their derivatives, and glycerin esters. Preferred plasticizers are tricarboxylic esters, citrate esters, glycerin esters and dicarboxylic esters. It is more preferred that the citrate esters are those selected, since it is believed that these esters are biodegradable. These plasticizers can be obtained under the names Citroflex A-4®, Citroflex A-2®, Citroflex C-2®, Citroflex C-4® (from Morflex). Volatility is determined by the vapor pressure of the plasticizer. An appropriate plasticizer must be sufficiently non-volatile so that the plasticizer remains substantially in the composition throughout the process necessary to produce the structure of various layers, and to provide desired properties when the structure is used. The Excessive volatility can lead to faults in the processing equipment and can result in undesirable migration of the plasticizer. The preferred plasticizer sd have a vapor pressure of less than about 10 mm Hg at 170 ° C and a more preferred plasticizer sd have a vapor pressure of less than about 10 mm Hg at 200 ° C. The most preferred plasticizer has a vapor pressure of less than 1 mm Hg at 200 ° C. An internal plasticizer may also be useful in the present invention, which is attached to the polymer containing the lactic acid residue. An exemplary plasticizer that can be attached to the polymer includes the epoxides. Plasticizers that are normally solid at room temperature can also be used.

NUCLEATING AGENTS It may be convenient to include nucleating agents when increased crystallinity is desired. Nucleating agents may include selected, finely divided minerals; organic compounds, salts of organic acids and microns, and finely divided crystalline polymers, with a melting point higher than the processing temperature of poly (lactide). Examples of useful nucleating agents include: talc, saccharin sodium salt, calcium silicate, sodium benzoate, calcium titanate, boron nitride, copper phthalocyanine, isotactic polypropylene, low molecular weight poly (lactide) and terephthalate. polybutylene. It has also been observed that plasticizers increase the rate of crystallization. In the present invention, it is considered that a polymer composition is semicrystalline if it exhibits a net fusion endotherm of more than 10 J / g of polymer, when analyzed by differential scanning calorimetry (DSC). To determine whether a polymer composition layer is semi-crystalline, it can be tested in a differential scanning calorimeter, such as by Mettler. The details for carrying out a crystallinity test are known to those skilled in the art and are identified in U.S. Patent Application Serial No. 08 / 110,394, filed on August 23, 1993, the entire description of which is incorporated herein by reference. this reference.

An exemplary application, when crystallinity may be desirable, includes pellets that are provided for further processing in an extruder. In general, it is advantageous for the pellets to be semicrystalline, in order to reduce the incidence of adhesion during storage or in the hopper, before melting, or to the screw or cylinder of the extruder, during melt processing in an extruder.

LOADS Charges may be desirable in order to modify the density, conductivity or mus. In certain applications they may be useful to prevent block formation or polymer adhesion during storage and transport.

Said applications include, for example, rolls of films and stacks of thermoformed articles. In the case of fiber formation, the charges are generally not convenient, because they sometimes plug the spinners. Inorganic fillers include clays and minerals, whether modified or not. Examples include: talc, diatomaceous earth, silica, mica, kaolin, titanium dioxide and wollastonite. The preferred inorganic fillers are environmentally stable and non-toxic. Organic loads include a variety of forest and agricultural prts, with or without modification. Examples include: cellulose, wheat, starch, modified starch, chitin, chitosan, keratin, cellulosic materials derived from agricultural prts, gluten, nut shell flour, wood flour, corn flour and guar gum. The preferred organic fillers are those derived from renewable sources and are biodegradable. Charges can be used either alone or as mixtures of two or more charges.

SUPERFICIAL TREATMENTS Surface treatments can also be used to modify the properties of the polymer. For example, to increase the possibility of printing, to modify glass or to reduce blocking. These treatments include crown and flame treatments, which reduce the surface tension between the poly (lactide) -based polymer and the adjacent surface. Embossing and calendering techniques and needle piercing are also included. These techniques can be used to modify roughness, friction, etc.

SURGICAL AGENTS Surfactants that are useful can be subdivided into cationic, anionic and non-ionic agents. With respect to cationic compounds, the active molecule part generally consists of a bulky cation which frequently contains a long alkyl residue (eg, a salt of quaternary ammonium, of phosphonium or of sulfonium), whereby the quaternary group can also occur in an annular system (for example, imidazoline). In most cases the anion is chle, methosulfate or nitrate, which inate from the quaternization process. In the anionic compounds the active molecule part in this class of compounds is the anion, most notably an alkyl sulfonate, sulfate or phosphate, a dithiocarbamate or carboxylate. Alkali metals often serve as cations. The non-ionic antistatic agents are uncharged surfactant molecules, of significantly lower polarity than the ionic compounds mentioned above, and include esters or polyethylene glycol ethers, fatty acid esters or ethanolamides, monoglycerides or diglycerides or ethoxylated fatty amines. The above surfactants can also act as antistatic agents, which may be convenient.

COLORANTS You can also add pigments, dyes or colored agents, as needed. Examples include titanium dioxide, clays, calcium carbonate, talc, mica, silica, silicates, iron oxides and hydroxides, carbon black, magnesium oxide, quinacridone, copper phthalocyanine, ultramarine blue, anthraquinoride, pyrazolone, violet B, azo dyes, 2,2 '- (1,2-ethenediyl-di-4,1-phenylene) bisbenzoxazole and 2,2' - (2,5-thiophenediyl) bis (5-tert-butylbenzoxazole).

CATALYSTS In the manufacture of polylactide compositions of the present invention, the reaction to polymerize is preferably catalyzed. Many catalysts have been cited in the literature for use in ring-opening polymerization of lactones. These include, but are not limited to: SnCl2, SnBr2, SnCl4, SnBr4, aluminum alkoxides, tin alkoxides, zinc alkoxides, are, PbO, (2-ethylhexanoates) of Sn, (2-ethylhexanoates) of Sb (some sometimes called octoates), stearates of Ca, stearates of Mg, stearates of Zn and tetraphenyltin. The catalysts based on rare earth metals are also effective for ring opening polymerization. Applicants have also tested various catalysts for the polymerization of lactide at 180 ° C, which include: tin (II) bis (2-ethylhexanoate) (commercially available from Atochem as Fascat 2003, and Air Products as DABCO T-9) , dibutyltin diacetate (Fascat 4200®, Atochem), butyltin tris- (2-ethylhexanoate) (Fascat 9102®, Atochem), hydrous monobutyltin oxide (Fascat 9100®, Atochem), antimony triacetate (S-21, Atochem) ), and antimony tris (ethylene glycoxide) (S-24, Atochem). Of these catalysts, tin bis (2-ethylhexanoate) (ll), butyltin tris (2-ethylhexanoate) and dibutyltin diacetate appear to be the most effective.

FINISH OILS For some applications it may also be useful to apply surface treatments to provide fiber lubricity, change hydrophilicity, alter static characteristics, modify the appearance of the fiber and, ultimately, affect fiber cohesion. An example of such surface treatments are the finishing oils. The finishing oils can affect the previous properties of the fiber, but they can also affect the fiber processes, downstream. These processes include the manufacture of threads and carding. Examples of some of the finishing oils that could be used for PLA include stearates or other oils, obtainable commercially from their manufacturers.

THE LUBRICANTS For certain applications, it is convenient to provide good sliding properties. Lubricating solids, such as fluoropolymer or graphite powders, are sometimes incorporated into materials to increase sliding properties. Fatty acid esters or hydrocarbon waxes, commonly used as lubricants for the molten state, are exuded gradually, if used in very high concentrations; thus producing permanent lubricating effects. Certain additives migrate so strongly to the surface, even during cooling, that a thin, uniform, invisible coating is formed. Thus, these sliding agents can be important in the production of coatings that are used in automatic packing machines. It has been found that preferred lubricants reduce the amperage to operate the screw of an extruder by about 10 to 15% when added to about 1000 ppm by weight (as compared to the amperage and lubricant). The internal lubricants that may be used in the present invention include the fatty acid esters, fatty acid amides, metal salts and soaps, and paraffin or hydrocarbon waxes. Examples of useful lubricants include zinc stearate, calcium stearate, aluminum stearate, stearic acetate, white beeswax, candelilla wax, high MFI LDPE, Epolene N21 from Eastman, Epolene E20 from Eastman and Loxiol HOB71109. Preferred internal lubricants include aluminum stearate and stearic acetate.

IV. PREFERRED ACTERISTICS OF POLYACACY FOR DIVERSE APPLICATIONS It is convenient to provide a polylactide polymer composition for a given application with desirable physical properties and desirable stability properties. Various applications for the composition of the polylactide polymer of the invention include fiber formation, coating paper, film formation, injection molding, thermal formation, blow molding, preparation of articles with film. and the preparation of torzales. It should be noted that the stability requirements for an application may be stricter or less stringent than the stability requirements for another application. The various processing conditions and the stability aspects preferred for various categories of the polymer composition, as described in detail below. Although the specific polymer compositions of polylactic a, for given applications, are described below, there are general acteristics suitable for the polylactide polymer composition. Preferably, the polylactide polymer has a number average molecular weight on the scale of about 25,000 to 200,000 and, more preferably, within the range of about 75,000 to about 125,000. In addition, the polylactide polymer preferably has a weight average molecular weight within the range of about 50,000 to 400,000 and, more preferably, within the range of about 150,000 to 250,000. The devolatilized and dry composition preferably has a lactide level that is less than 1% by weight. More preferably, the level of lactide is less than about 0.5% by weight and still more preferable, less than about 0.2%. Although it is believed convenient to completely remove the lactide from the composition, this may not be practical because small amounts of lactide can be formed again. Consequently it is expected that the level of lactide is at least higher than 0.001% by weight.

In the devolatilized and dried composition it is convenient for the water concentration to be less than about 500 ppm and more preferably less than about 200 ppm. In a particularly preferred embodiment, the water concentration is less than about 100 ppm. The composition of the polylactide polymer can be acterized in terms of its stability against the lactide reforming reaction, under conditions frequently encountered during melt processing. Accordingly, the stabilized polylactide polymer composition will preferably satisfy the next relatively severe test. In this test a portion of the composition is devolatilized and dried to give a lactide concentration of less than about 1% by weight and a water concentration of less than about 500 ppm. After maintaining the devolatilized polylactide polymer composition and dried at 260 ° C for 20 minutes in a closed vessel, the increase in lactide weight percentage should be less than 2% by weight. It is preferred that the increase in the weight percentage of lactide should be less than 1% by weight and, more preferably, less than 0.5% by weight. In particularly stable polylactide polymer compositions, the increase in the weight percentage of lactide will be less than 0.2% by weight. It should be appreciated that the test can be specified because devolatilization occurs and dried until the composition reaches a lactide concentration of 1% by weight and a water level of 500 ppm. Additionally, if the composition to be tested already has a lactide concentration of less than 1% by weight and a water concentration of less than 500 ppm; there is no need to devolatilize and dry before holding the sample at 260 ° C for twenty minutes.

A. THE FIBER QUALITY POLYLACTICATE The inventors have discovered that the conditions of fiber formation tend to be quite extreme, in comparison with other applications, and that the conditions tend to promote the re-formation of lactide and the degradation of molecular weight. The conditions in the extruder often exceed 200 ° C and the surface area generated during fiber formation frequently results in increased contact between the equipment and / or the air and the molten polylactide. The processing condition may be more extreme, for example, than the conditions frequently encountered when processing polylactide in films or molds. As a result, conditions during fiber formation favor polymer degradation. Consequently, in order to ensure convenient fiber properties, it is advantageous to provide the polylactide polymer composition, before melt processing, with the desired molecular weight scales, PDI, optical composition and melt stability desired. In the context of fiber formation, the description of the US patent application Serial No. 08 / 850,319, filed on May 2, 1997, is incorporated herein in its entirety, by this reference. In the case of meltblown fibers it is preferable that the polylactide polymer is provided with a number average molecular weight of between about 25,000 and 110,000. Or, preferably, the average number-average molecular weight is provided around 30,000 and about 75,000, and even more preferably, between about 32,000 and about 60,000. In highly preferred applications, it is anticipated that the polylactide polymer will have a molecular weight within an approximate range of 35,000 and 45,000. It should be understood that the lower limit in the number average molecular weight is determined by physical properties, such as tensile strength. The upper limit on the number average molecular weight is generally determined by consideration such as the viscosity in the meltblowing process. In the case of spun bonding or melt spinning it is convenient to provide an average number-average molecular weight of around 25,000 to about 150,000. It is preferred that the number average molecular weight be provided within a range of about 45,000 to about 105,000, more preferable, between an approximate scale of 50,000 and about 90,000.; and it is believed that the number average molecular weight will be very preferable on a scale of about 55,000 and about 75,000. In spunbond or melt spinning processes it should be appreciated that the lower limit on molecular weight is generally a function of melt strength and tensile strength. The upper limit in molecular weight is generally determined by the pressure drop across the die, and the desire not to process the polymer at excessively high temperatures. Additionally, the melt flow rate of the polylactide polymer should be between about 10 and about 50, using the normal ASTM melt flow test procedures (ASST.D1238), measured at 210 ° C with a weight of 2.16 kg. More preferably, the melt flow index is between about 15 and about 45. Preferred polylactide polymers for use in fiber formation are preferably melt stable. Mediating this expression is meant that the polylactide polymer will be relatively stable to the re-formation of lactide and to depolymerization, at the temperatures encountered during the melt processing. With respect to this, the descriptions relating to melt stability, provided in U.S. Patent Nos. 5,338,822 and 5,525,706, are incorporated herein by this reference. Additionally, it is to be understood that preferred melt stable polylactide compositions for fiber formation preferably include a lactide concentration of less than about 1% by weight, more preferably, a lactide concentration of less than about 0.5. % by weight and still more preferable, a lactide concentration of less than 0.3% by weight. Most preferably, to ensure the melt stability properties it is preferred that the lactide concentration is less than about 0.15% by weight. In addition, it is preferred that the degree of lactide generation during melt processing, such as through an extruder, provides for the generation of less than about 0.5% by weight of lactide. Thus, it is expected that for the preferred melt-stable polylactide polymers, the melt processing will only generate less than about 0.5% lactide, and still more preferably, less than about 0.3% by weight lactide.

B. THE COATING QUALITY POLYLACTATION In order to process the polylactide polymer in commercial extrusion coating equipment, the polylactide polymer must have good melt elasticity. This is because it is convenient to extrude and stretch thin coatings of the polylactide polymer with a minimum neck at high speeds, at the high temperatures necessary for good adhesion to the paper. The details of coating paper with a polylactide polymer composition are described in detail in U.S. Patent Application Serial No. 08 / 862,612, filed May 23, 1997; whose full description is incorporated herein by this reference. The coating quality polylactide has characteristics that allow it to be processed in conventional paper coating equipment, typically designed to process polyethylene. Applicants have discovered that linear polylactide is generally not suitable for processing in conventional paper coating equipment. It is believed that the reason for this is that the linear polylactide does not possess the fusion elasticity necessary to give a commercially acceptable production at acceptable levels of neck formation and stability. Linear polylactide will generally have a molecular weight characterized by a Flory-Schultz distribution (also known as a "very probable distribution"). This distribution is generally characterized by a polydispersity index (PDI) of less than about 2.2 (ideally around 2.0) and a Mz / Mn ratio of around 3.0. The polylactide polymers linear, very conventional, will have values somewhat close to these values PDI and Mz / Mn. Some deviation due to variations in polymer processing is expected; but it is also expected that the polymer exhibits general linear polymer characteristics. This is equal to a low degree of chain entanglement and low melt elasticity. Methods for increasing molecular interaction or chain entanglement are described in detail in U.S. Patent No. 5,594,095, in columns 4-24; This portion of U.S. Patent No. 5,594,095 is incorporated herein by this reference. In general these methods involve the increase of molecular weight, the increase of branching or the increase in the formation of bridges. It has been observed that the molecular weight that increases tends to increase the molecular entanglement and also increases the viscosity. If the viscosity becomes too high, the polymer will no longer be processable or penetrate the surface of the paper for adhesion. Raising the temperature to the level necessary to process linear polylactide is not practical, because the melt elasticity is sacrificed and the degree of polymer degradation is increased. To compensate for the seemingly contradictory properties, to increase the melt elasticity, while maintaining the low viscosity, it is preferred to widen the molecular weight distribution. The amplitude of the molecular weight distribution (MWD), I can be characterized by the polydispersity index (PDI, defined as Mw / Mn) or by the Mz / Mn ratio. In addition to increasing the MWD, the high viscosities resulting from the increased weight average molecular weight (Mw) can be compensated by mixing the low molecular weight polymer back into the resin. It is believed that this can be done by adding resin thickeners or low molecular weight fractions of the polylactide. Bridging and branching are preferred methods for increasing chain entanglement and, thereby, broadening the molecular weight distribution. The degree of chain entanglement is proportional to the type of chain branching or bridge formation. The long chain branching favors chain entanglement, with respect to the short chain branching. The inventors have found that a widened molecular weight distribution generally provides the desirable melt elasticity. The melting elasticity can be determined directly, measuring the die swell ratio in the extrudate of an instrument to determine the melt flow index, according to ASTM-D1238, with a die of 2.09 mm in diameter and made at 210 ° C and 2.16 kg, and reported in grams of polymer for 10 minutes. The swelling of the die is a measure of the ratio of the diameter of the extrudate to that of the die. In the context of this invention, the "die swell" property is determined by cutting-off the polymer strand that comes out of the melt flow index test, when it has a length of 2.54 cm. The diameter of the strand is measured in at least 3 sites, and averaged. In general, this test is repeated about five times to improve reproducibility. A Newtonian fluid demonstrates the swelling ratios of about 1.1 or less. As the elasticity increases, the die swelling increases. Accordingly, it is convenient to provide polylactide polymer with a die swell of more than about 1.25, and preferably more than about 1.3. Most preferably, the die swell for the polylactide according to the invention is greater than about 1.4. In comparison, die swelling of the linear polylactide is about 1.2 or less for a melt flow index of 8 or more, and is about 1.4 or less for the melt flow index of 4 or more, and is estimated which is about 1.5 or less for a melt flow index of 2 or more. This is shown by FIG. 7. The die swell ratio can be used to access the difference in melt elasticity between the polylactide and a commercial quality low density polyethylene used in the extrusion coating. Using a melt flow index instrument at 210 ° C and 2.16 kg force, a swelling ratio for PLA line is generally less than, or equal to 1.1, while the swelling ratio for LDPE can be 1.5 or more. At the same time, the linear PLA tends to provide a large neck with poor stretching characteristics. The molten polymer must be provided at a melt viscosity that is sufficient to provide an operating die pressure and allow the desired adhesion of the melt polymer to the paper substrate. As discussed above, increasing the chain entanglement tends to improve the melt elasticity of the polylactide, further tends to raise the melt viscosity, particularly if the molecular weight is increased. In a preferred process, long chain branching induced by bridging (i.e., by modification with peroxide) is used to increase chain entanglement, without dramatically increasing the melt viscosity. The melt flow index (MFI), as described above, is a useful measure of viscosity. In general, a high MFI corresponds to a low viscosity material and a low MFI corresponds to a high viscosity material. The linear polylactide exhibits a strong correlation between the weight average molecular weight (Mx) and the MFI, with an additional correlation between the level of residual lactide and MFI. The long chain branching, as preferred in the present composition, causes a deviation from this ratio. For extrusion coating, applicants have found that the MFI should preferably be within the approximate range of 2 to 30. More preferably, the MFI should be on the approximate scale of 8 to 20 and, most preferably, on the approximate scale of 12 to 16, It is expected that the linear polylactide polymer exhibits lower die swelling values than those exhibited by the modified polylactide polymer with epoxidized soybean oil. It should be appreciated that a high die swelling for the linear polylactide polymer can be obtained, but only at very low MFI values (of about 2 or less). For preferred paper coating operations, it is convenient to provide a melt flow rate of more than about 1.2. In the preferred compositions, the melt flow index will be greater than about 2, and die swelling values of more than about 1.3. Even more preferable, the swelling of deid must be above about 1.4. In general, preferred compositions exhibit MFI and die swell values above the solid line shown in Figure 7. It is preferred that the compositions exhibit an MFI greater than 10 and a die swell of more than 1.3 (preferably 1 ,4). It should be understood that compositions that exhibit a melt flow index of less than 2 are generally not suitable for paper coating applications. The reason for the difference in the width of the dice and the width of the paper, counts for a phenomenon known as "neck formation". Neck formation refers to the narrowing of the width of a film, when it leaves the die. During certain melt processing operations, linear polymers, such as a linear polylactide, exhibit certain undesirable flow properties, such as neck formation. For example, if the polylactide is extruded as a film on a mobile substrate, the polylactide film that is directed onto the substrate will tend to form a neck under the tensile forces caused by the moving substrate. This phenomenon of neck formation tends to problems with the control of the process and problems with the maintenance of the consistency in the film thickness. Linear polymers, such as linear polylactide, also tend to exhibit hydrodynamic instability or tensile resonance at high rates of stretching. This stretch resonance can cause a periodic variation in a coating and / or in thickness, for example, which can lead to the breakage of the continuous polymer film.

C. FILM QUALITY POLYLACTICS The properties of film grade polylactide and its applications in layered structures, such as bags, are discussed in detail in the US patent application.

No. 08 / 642,329, filed May 8, 1996, the complete description of which is incorporated herein by this reference. In general, many biodegradable polymers, such as polymers of unplasticized polylactic acid, are too fragile for use as flexible single layer films and / or sheets. Its Tg is generally greater than about 50 ° C, and it has been observed that they provide a film or sheet having low impact strength and tear resistance. The tear strength of a typical polylactide film, having a Tg above 50 ° C is less than about 6 gf / 25.4 μ. Other biodegradable polymers, including certain aliphatic polyesters, exhibit poor tear strength. These physical properties form films or sheets prepared from them, which are poor candidates for use as bags or envelopes. Items such as garbage bags, grocery bags, food wraps and the like should be flexible and resistant to tearing and punctures. By lowering the glass transition temperature (Tg) of the biodegradable polymers to about 20 ° C or less, it is possible to provide a film or sheet having improved flexibility and tear resistance to puncture. More preferably, it is convenient to lower the Tg to less than about 5 ° C and, more preferably, to below about -10 ° C. These glass transition temperatures must be lower than the temperature at which the polymer is used. When the biodegradable polymer is a polymer containing lactic acid residue, a preferred method for lowering the glass transition temperature (Tg) is by adding plasticizer. The plasticizer can be added to a polylactide polymer to lower the glass transition temperature (Tg) d 60 ° C, without plasticizer, at 19 ° C, at a level of 20% by weight of plasticizer. For most polymers containing lactic acid residue, it is believed that the glass transition temperature can be lowered to convenient levels by adding a plasticizer component to give a concentration of about 1 to 40 p.sup.-1 percent by weight of plasticizer, with based on the weight of the composition. In general, a sufficient amount of plasticizer should be incorporated to give a desired reduction in Tg and increase flexibility and tear resistance. It is believed that the level of plasticizer should be above at least 8 percent by weight and, more preferably, above at least 10 percent by weight, to provide sufficient flexibility and tear resistance. The upper limit on the plasticizer should be controlled by other considerations, such as the loss of integrity of the film or sheet, if too much plasticizer is used. Additionally, too high a concentration of plasticizer will promote the migration of plasticizer in the outer layer. Consequently, the plasticizer should be included to provide an approximate concentration level of 10 to 35 percent by weight, preferably an approximate concentration level of 12 to 30 percent by weight and, more preferably, a concentration level of about 20 percent by weight. to 35 weight percent. Although polymers containing lactic acid residue, plasticized, can provide resistance to tearing, they have shown severe blockade that makes them unsuitable as single layer pouches or wrappings. It should be understood that the term "block formation" is intended to describe the tendency of one layer of a structure to intertwine, entangle or adhere to another layer. In this way, two layers that exhibit high block formation can not be easily separated to form, for example, a bag. Applicants have found that, while reducing the Tg of polymers containing lactic acid residue improves flexibility and tear resistance, it also increases or promotes block formation. It is possible to create multilayer structures, which are relatively resistant to block formation over time, and which retain the desirable properties of a polymeric composition containing plasticized lactic acid residue, such as elongation and tear resistance. The formation of blocks was reduced by incorporating reducing layers of block formation, covering the central layer of polymer containing plasticized lactic acid residue. The blocking reducing layers could have a variety of compositions, so long as they reduce block formation. Preferred exemplary block-forming reducing layers are described in detail in U.S. Patent Application No. 08 / 642,329, the description of which covers the reducing layers of block formation, on pages 36-4, is incorporated herein by reference. this reference.

D. THE MOLDING QUALITY POLYLACTATION In order to process the polylactide polymer composition into slurries, it is convenient to control the molecular weight, the optical composition and the impact properties, depending on the particular article to be formed. For molding grade polylactide, for general purposes, suitable for thermoforming, it is generally convenient to control the concentration of residual lactide to less than 0.5% by weight, and more preferably to less than 0.3% by weight. In the context of controlling the optical properties, it is generally convenient to provide a residual concentration of R-lactic acid in the polymer of between about 2% and about 6%, based on the total concentration of lactic acid residue in the polymer. The term "lactic acid residue" refers to the repeating unit of lactic acid within the polymer. It is advantageous to control the concentration of R-lactic acid residue because it makes it possible to supply semicrystalline polymer pellets and non-crystalline (amorphous) thermoformed articles. The inventors have discovered that semicrystalline pellets are advantageous during extrusion, because they provide less adhesion to the screw, compared to amorphous pellets. The molding quality polylactide composition, for general purposes, preferably exhibits a melt flow index of between 6 and 10. Additionally, the weight average molecular weight of preference is greater than 160,000, more preferably, greater than 180,000 and , very preferable, greater than 200,000. It is expected that the average molecular weight for this type of polymer is less than about 350,000. Additionally preferably the number average molecular weight is greater than about 80,000, more preferable, greater than about 90,000 and, most preferably, greater than about 100,000. At lower molecular weights, it is difficult to cut the molding, without fracturing it. Additionally it should be appreciated that the molecular weights found for thermoforming are generally higher, in order to accommodate the use of a regrind fraction. The polylactide polymer composition, of molding quality, for general purposes, preferably includes a stabilizing agent and a lubricant. The lubricant is preferably provided in a concentration of between about 500 ppm and 1,000 ppm in order to provide better flow characteristics for the solid pellets, and to reduce the energy requirements during extrusion to articles. A preferred lubricant is aluminum stearate. A preferred polylactide copolymer, which may be used, includes the polymerization product of lactide and multifunctional epoxidized acetide. In the case of epoxidase soybean oil, the component is preferably provided at a concentration of 0.35% by weight.

E.- FOAM FORMATION QUALITY POLYLACTICATION It should be appreciated that the desired properties for the foam-forming polylactide are generally similar to the properties desired for the coating quality polylactide. Accordingly, reference can be made to the properties and characteristics of the coating quality polylactide section of this specification in the context of the foaming quality polylactide. For foam-forming polylactide, in general, it is desirable to provide a die swell of more than 1.45, which indicates a high degree of branching. In most foam forming applications it is usually advisable to prevent crystallization.

Consequently, in order to provide amorphous foams, applicants have found that it is advantageous to provide the polylactide polymer with a high level of R-lactic acid residue. That level of preference corresponds to more than 12% by weight and, more preferably, more than 17% by weight, of the lactic acid residues that form the polymer. The concentration of lactide in the composition should be less than about 0.5%. The density of the foam product may vary depending on the application. In the context of a food packaging application, for clam shell, the density should be between about 64.07 g / l and 96.10 g / l. It is expected that the foam thickness in said application is between about 2.03 mm and 2.54 mm. In the context of a tray for meat and poultry, it is convenient to provide a density of 48.05 g / l. In this type of application it is expected that the thickness of the foam is approximately 2.54 mm or more.

V. STABILIZATION OF POLYMERIC SYSTEMS WITHOUT POLYLACTIDE The inventors hope that their discovery regarding the stabilization of polylactide may be applicable to systems without polylactide, including, for example, polyesters and polyamides. The equilibrium ratio for ring-opening polymerization of cyclic esters is quite complicated. A system that does not polymerize will generally correspond to a stable annular system, favoring the equilibrium of large concentrations of reagents. - A system that polymerizes easily corresponds to a system that has high concentrations of reaction products. Another type of system polymerizes to some extent, but not completely. These systems are of the utmost concern, since once they have polymerized satisfactorily, there is still a strong tendency to depolymerize during the melt processing. Polylactide generally falls within this last category. It is estimated that the depolymerization problem described above can be important for any polymer, when the concentration of the cyclic ester is at least 0.1% by weight, at the processing temperature. If the concentration of the cyclic ester at the processing temperature is at least 0.5% by weight and in particular, if it is at least 1.0% by weight at the processing temperatures, then the methods for controlling the reaction of cyclic ester formation described here can be particularly useful. The polylactide is typically processed at least at 180 ° C and the equilibrium concentration of the lactide at that temperature is at least about 3% by weight. The categories of cyclic monomers that can be polymerized and, therefore, where the depolymerization to cyclic esters can be problematic, include cyclic esters, such as lactones, cyclic diesters such as glycolides, ester-ethers and ester-aides. Of particular concern are systems that can form 5, 6 or 7-membered rings. An example includes poliparadioxanone.

Although the problem is very noticeable in polymers that can form cyclic ester monomers, other polymers can form larger ring systems by interesterification. The formation of these macrocyclic oligomers can also be reduced by the method presented in the present specification. The following examples include several tests. The test methods on which several of the examples were based are given below. In the lactide formation test, a polymer sample is crushed or pelletized. It is then dried and devolatilized in a vacuum oven at 110-120 ° C for 18 to 48 hours. The level of lactide at this point should be less than 1% by weight. The sample is then placed in a closed container, with a medium for rapid heating to a pre-set temperature, with means provided to sample at various times and rapidly cool the samples. A convenient method is to use a cylinder with a capillary rheometer, such as Rosand model RH7X-2. This allows rapid heating and convenient sampling, by extruding a small sample into a container. The lactide level of the sample is then determined by precise means, such as the aforementioned FTIR method, a GPC method or by dissolving the polymer, precipitating and analyzing the lactide solution by gas chromatography. Lactide determinations were made by pressing films with a thickness of approximately 76.2 μ to 406.4 μ in a Carver press. The films were then analyzed using FTIR, in an instrument that had been calibrated for residual lactide in polylactide. The calibration standards had been analyzed using the primary method of gas chromatography, which had been developed using common additions and currents. Generally the molecular weights were determined using gel permeation chromatography (GPC). The polymer samples were dissolved in methylene chloride, as a 10% by weight solution; then it was further reduced to 20: 1 with THF to give a 0.5% by weight solution. This solution was passed through a series of Styragel * HR columns from Waters Chromatography. The mobile phase is THF at a temperature of 35 ° C. A refractive index detector with calibrations for molecular weight is used, using polystyrene standards. The Millennium Version 2.15 application program was used for acquisition and evaluation.

EXAMPLE I EFFECT OF ADDITIVES ON THE RE-FORMATION OF LACTIDA AND MOLECULAR WEIGHT Several tests were carried out using a polylactide polymer composition, which was prepared in a continuous reactor, at a temperature of 180 ° C. The polymer was prepared from a monomer mixture containing lactide; 0.35% by weight of epoxidized soybean oil (G-62, obtainable from C. P. Hall Co.) and 0.015% by weight process stabilizer, distearylpentaerythrine diphosphite (Weston 618, obtainable from General Electric). Catalyst was added at a molar ratio of catalyst to lactide of 1: 10,000. The catalyst was bis (2-ethylhexanoate tin (ll), which can be obtained as Dabco T-9 from Air Products and Chemicals, Inc. The reaction mixture was polymerized to give a polymer composition having an average number-average molecular weight. of 64,000, a weight average molecular weight of 194,000, a PDI of 3.0 and a residual lactide content of about 1.4% lactide.The polymer was found to have an optical composition of 4.2% R-lactic acid residue and 95.8%. % S-lactic acid residue, as determined by chiral liquid chromatography, in the saponified polymer The various additives cited in Table 1 were mixed in the lactide composition, using a Brabender mixing head, at an approximate temperature of around 190-200 ° C. The mixing time did not appear to be critical for the results and mixing times of 2-10 minutes were used.After mixing the polymer composition was ground and dried and devolatilized in a vacuum oven. Typical conditions were 110-120 ° C for 18-48 hours. The dried and devolatilized samples were then placed in a capillary rheometer, which was used to heat the samples and keep them at the desired temperature for the test, for twenty minutes. Normally samples were taken at t = minutes and t = 10 minutes, although only 20-minute times are reported here. The point t = 0 minutes corresponds to 5 minutes after placing the pellets in the capillary cylinder, and the initial heating time can be considered. Samples of t = 20 minutes were pressed to films in a Carver press, at approximately 150 ° C and 68.94 MPa. Residual levels of lactide were determined by infrared Fourier transformation spectroscopy (FTIR). The films were analyzed using FTIR on an instrument that had been calibrated for residual lactide and polylactide. The calibration standards had been analyzed using the primary method of gas chromatography, which had been developed using the normal addition method e¡s. Molecular weights were determined by gel permeation chromatography (GPC) In this case, the polymer samples were dissolved in chloroform and passed through a series of Ultrastyragel® columns from Waters Chromatograph. The mobile phase was PHF at a temperature of 35 ° C. A refractive index detector with molecular weight was used for calibration, using standards for polystyrene. The Millennium application program, version 2.10 was used for acquisition and evaluation. The color was evaluated subjectively. Samples that receive a "good" rating reflect a clear white to yellow color; "medium" reflects a light brown color; and "bad" reflects a dark brown to black color. Table 1 identifies the final weight average molecular weight values at test temperatures, and the change in lactide concentration, after operating the test for 20 minutes.

TABLE 1 CHANGE IN THE PERCENTAGE OF LACTIDA WEIGHT AFTER 20 MINUTES AT THE TEMPERATURES INDICATED PAA (1) is polyacrylic acid having a weight average molecular weight of about 2,000, which can be purchased from Aldrich Chemical Company. PAA (2) is polyacrylic acid having a weight average molecular weight of about 450,000, which can be obtained as Carbopol ™ 679 from BF Goodrich Co. PAA-MMA is a random copolymer of acrylic acid and methyl methacrylate, with 41 , .7 mol% of acrylic acid waste PMA-MMA is a random copolymer of maleic anhydride and methyl methacrylate, with 23.4 mol% of maleic anhydride residues. MD1024 is 1, 2- (bis (3,5-di-tert-butyl-4-hydroxyhydr-or-cinnamoyl) hydrazine, obtainable as Irganox ™ MD 1024, from CIBA-GEIGY Corp .. Luperco ™ 130XL is 2,5-dimethyl- 2,5-di- (tertbutyl-peroxy) hexine.3; 45% in CaCO3, from ELF Atochem North America Inc. This example shows the effectiveness of various compound additives to a polylactide polymer melt. The efficacy of the various additives can be judged by the amount of reformed lactide in 20 minutes at 260 ° C. Samples without stabilization appear on the lists as control samples and are formed, in general, with more than 6% by weight of lactide, which shows the high degree of lactide formation in the absence of additional catalyst deactivators.

EXAMPLE 2 A lactide polymer composition was prepared in a continuous reactor at a temperature of about 180 ° C. The polymer of a monomer mixture containing lactide was formed with 0. 35% by weight of epoxidized soybean oil (G-62, available from CP Hall Co.), with 0.015% by weight of distearylpentaerythritol diphosphite process stabilizer (Weston 618, obtainable from General Electric). Catalyst was added at a molar ratio of catalyst to lactide of 1: 80,000. The catalyst was tin bis (2-ethylhexanoate) (ll), which can be obtained as Dabco T-9 from Air Products and Chemicals, Inc. The mixture was polymerized to give a polymer composition having an average number-average molecular weight. of 80,000, a weight average molecular weight of 177,000 and a PDI of 2.2. The polymer was found to have an optical composition of 3.8% R-lactic acid residues and 96.2% S-lactic acid residues. Various additives mentioned in Table 2 were mixed in the polylactide polymer composition, using a Brabender mixing head, at a temperature of about 190 ° C for two minutes. A control sample of the base polymer, without additives, was subjected to the same procedure. The samples were then placed in a capillary rheometer, which was used to heat the samples and keep them at the desired test temperature for 20 minutes. Normally samples are taken at t = 5 minutes and t = 10 minutes, although only the tests are reported here at 20 minute times. The point t = 0 minutes corresponds to 5 minutes after placing the pellets in the capillary cylinder (initial heating time). Samples of t = 20 minutes were pressed to films in a Carver press at approximately 150 ° C and 68.94 MPa. FTIR was then used to determine residual lactide. GPC was used to determine the molecular weights. The control sample, after 20 minutes at 260 ° C had a final lactide level of 6.2% by weight and a weight average molecular weight of 76,000. The sample with 0.52% by weight of added TNPP had a final lactide level of 0.42% by weight, and a weight average molecular weight of 121,000. The initial lactide level, in each case, was between 0.2 and 0.3% by weight.

TABLE 2 CHANGE IN THE PERCENTAGE IN WEIGHT OF LACTIDA AFTER 10 MINUTES OR 20 MINUTES AT 260 ° C The dimerized rosin can be obtained as Sylvatec 140 from Arizona Chemicals. The lactyl lactylate is prepared by opening the lactide ring with water.

EXAMPLE 3 EFFECT OF THE CATALYST LEVEL ON THE SPEED OF RE-FORMATION OF LACTIDA Examples 1 and 2 detail the preparation of polylactide with two different levels of catalyst. Table 3 shows the rate of re-formation of lactide for the two polylactides, when they are maintained at 260 ° C in a cylinder of capillary rheometer.

TABLE 3 CONCENTRATION AND PERCENTAGE IN WEIGHT OF LACTIDA IN THE INDICATED TIMES The rate of lactide formation for the polymer with the highest catalyst level (1 / 10,000 / is much higher than for the polymer with the lowest concentration of catalyst.) It can be seen that the speed of lactide re-formation is slower for the sample with the highest catalyst concentration, since it starts to reach the equilibrium lactide value, which is believed to be 8 to 1% by weight at 260 ° C. The polymerization reaction of lactide is reversible and the speed depends on the catalyst at the first power, in the whole range of temperatures and catalyst levels Based on this information, it is expected that the opposite reaction, the re-formation of lactide, also depends on the level of catalyst, as shown in Example 7. Example 14 of U.S. Patent No. 5,338,822, which is incorporated herein by way of this reference, shows how the lactide reformation depends on the catalyst level.

EXAMPLE 4 BENEFITS OF ADDING TNPP BEFORE THE REACTION OF POLYMERIZATION Ampule polymerizations were used according to the procedure of Example 7 of US Pat. No. 5, 338,822, which is incorporated herein by reference, to prepare polylactide with various amounts of TNPP. The TNPP was added to the molten monomer, before polymerization. Tin (II) bis (2-ethylhexanoate) catalyst was then added, in a molar ratio of 1: 10,000, and the mixture was pipetted into the ampoules, sealed and polymerized in a 180 ° oil bath. ° C. Samples were taken at various times and analyzed by gel permeation chromatography to determine the degree of the reaction. The molecular weights were also determined. The number average molecular weights are also reported for theoretical conversion of 100%.

TABLE 4 Time = 45 minutes It is seen that the samples with TNPP have the highest conversion (fastest polymerization rate), the maximum molecular weights and, as the reaction progresses, the higher final molecular weights. The inventors expect that, by adding the stabilizer directly to the monomer mixture, it is possible to facilitate mixing (as compared to the addition to the polymer) to give better color.

EXAMPLE 5 EVIDENCE OF CHAIN EXTENSION BEHAVIOR The mixtures of Example 1 were tested for their molecular weight after the mixing / devolatilization step and before the stability test One of the phosphite treatments (TPP) and the peroxide treatment ( Luperco 130XL9 showed an increase in molecular weight with respect to the original polymer The polymer treated with TPP had a weight average molecular weight of 263,000, the peroxide-treated polymer had a weight average molecular weight of 213,000 These are larger than in the original polymer, which had a weight average molecular weight of 194,000.The other treatments generally resulted in lower molecular weights, although the TNPP almost did not change.It is believed that the increase in molecular weight indicates chain binding (also known as as an extension or coupling) for the TPP and is consistent with the entanglement for the peroxide.

EXAMPLE 6 DEMONSTRATION OF LACTIDA RE-FORMATION IN AN EXTRUDER, AND EFFECT OF TARTARIC ACID The pellet-dried, desvolatilized polymer of Example 2 was fed continuously, without additional additives to a Warner-Pfleiter twin-screw extruder, 30 mm, with zonal temperatures of 250-260 ° C, which gives a melting temperature of about 220-240 ° C. The polymer feed had a lactide concentration of 0.32% by weight. The extruder was operated without vacuum, in order to determine if lactide would re-form or not to those conditions, which are typical of the devolatilization temperatures. After passing through the extruder, the polymer was found to have a lactide concentration of 1.40% by weight, which shows that the lactide was in fact being formed during extrusion. Then tartaric acid was added directly to the polymer in the feed throat of the extruder, at a rate of 500 ppm of tartaric acid by weight, in the polymer. It was now found that the concentration of lactide after extrusion was only 0.39% by weight, which shows that the lactide re-formation had been effectively reduced.

EXAMPLE 7 SPEEDS OF POLYMERIZATION AND RE FORMATION OF LACTIDA, WITH CATALYST OF BIS -2-TIN-ETHYLXANATE (II) Witzke and co-authors, Reversible Kinetics and Thermodynamics of the Homopolymer of L-Lactide with 2-Ethylhexanoic Acid Tin (II) Salt, Macromolecules, Volume 30, No. 23, pages 7075-7085, 1997, whose description is incorporated herein by this reference, report on the kinetics and reversible thermodynamics for the polymerization of L-lactide, as function cel level and catalyst temperature Their results indicate that both the positive or forward reaction and the opposite reaction (reformation of lactide) are of first order in the catalyst cel concentration. They also report the activation energy for the polymerization of 71 kJ / mol, an enthalpy of -23 kJ / mol and an entropy of -22 J / mol-K. The activation energy for depolymerization can then be taken as 71 + 23 = 94 kJ / mol-K. Using this activation energy, one can calculate the relative velocity constants, as a function of temperature, as shown in table 5 below, and reported as 180 ° C.

As shown in Table 5, the rate constant for the re-formation of lactide is approximately 42 times higher at 260 ° C than at 180 ° C. This means that the lactide reformation, after 1 minute at 250 ° C, should be expected to be equal to 42 minutes and 180 ° C. You can use the data from the document that was referenced further back, to estimate the time needed for the polymerization as a function of the catalyst level and also the time for the lactide reformation. Table 6 shows the estimated time to reach 90% conversion in the polymerization at 190 ° C and the estimated levels of lactide, for unstabilized polymer, after one hour at 180 ° C and after 20 minutes at 260 ° C, assuming no lactide in the starting polymer.

TABLE 6 Table 6 shows that, although the decrease in catalyst level can help provide a more stable polymer, especially when measured at 180 ° C, still the resulting polymer may need stabilization, if it is processed at elevated temperatures and for times prolonged, indicated, for example, at 260 ° C for 20 minutes .. The drawback of the lower catalyst levels is shown by the sustained increase in polymerization time to reach 90% conversion. These longer times result in undesirable reactions in the polymer, including color formation, molecular weight decline and racemization. The increase in polymerization temperature will reduce the time requirement, but also increases the rate of degradation reactions.

EXAMPLE 8 ADDITION BEFORE POLYMERIZATION L-lactide weight, obtainable from Boehringer Ingelheim, epoxidized soybean oil, obtainable as G-62 from C, P. Hall Co. and tris- (nonylphenyl) phosphite, obtainable as Weston TNPP from General Electric, in flasks to give the compositions shown in the following table, and heated to 180 ° C, with stirring, to melt the lactide. Catalyst of tin bis (2-ethylhexanoate (II), at a ratio of 1 part of catalyst per 20,000 parts of lactide, was added on a molar basis, then the material was pipetted into ampoules, capped and polymerized in a bath of oil at 180 ° C. The ampoules were removed at 1 hour and 2 hours for kinetic analysis It was ruled out that samples for analysis of lactide re-formation would polymerize for about 6 hours, broke them into pieces and devolatilized under vacuum (0.4 mm absolute Hg) at 120 ° C for 26 hours, then samples were loaded on a capillary rheometer, five minutes were allowed to melt and reach the desired temperature (260 ° C for this test) and samples were taken at the indicated times (t0 is after five minutes of warm-up) The results of the test are reported in table 7.

TABLE 7 CONVERSION AGAINST POLYMERIZATION TIME The addition of TNPP to the monomer mixture, prior to polymerization, resulted in an increase in conversion over the control samples, either for the lactide homopolymer or for the poly (lactide-co-epoxidized soybean oil). The increases were observed in both the one-hour and the 2-hour samples. Table 8 shows the number average molecular weight (Mn), measured in relation to the standards for polystyrene or, using GPC: (1) for the samples after polymerizing (before devolatilizing); (2) after devolatilization; (3) after the 5 minute warm-up time (t = 0 minutes); (4) after 10 minutes at 260 ° C; and (5) after 20 minutes at 260 ° C. The specific rate of degradation at 260 ° C is calculated as the rate of molecular change between time (3) and time (5), calculated as meq / (kg * min).

TABLE 8 The addition of TNPP to the monomer mixture, prior to polymerization, resulted in a more stable polymer, as reflected in the higher molecular weight retention of the samples treated with TNPP, relative to the controls. Protection was obtained for both the poly (L-lactide) and the poly (lactide-co-epoxidized soybean oil) copolymer. The specific rate of chain cleavage was less than 1 of the control value for the material treated with TNPP. The results for the weight average molecular weight are generally similar. The results of the lactide re-formation experiments at 260 ° C are shown in Table 9. The lactide content was determined in films pressed from the samples and analyzed by FTIR. Lactide is expressed in% by weight.

TABLE 9 The TNPP greatly reduces the rate of reformation of lactide in the polymer, relative to the untreated controls.

EXAMPLE 9 A polylactide polymer composition was prepared in an intermittent reactor, at a temperature of approximately 180 ° C. The monomer mixture includes lactide, 0.35% by weight of epoxidized soybean oil (obtainable as G-62 from C. P. Hall Co.), with 0.015% by weight of trinonylphenyl phosphite (obtainable as Weston TNPP from General Electric). Catalyst was added at a molar ratio of catalyst to lactide of 1: 80,000. The catalyst was tin (2-ethylhexanoate II, which can be obtained as Dabco T-9 from Air Products and Chemicals, Inc. The mixture was polymerized for about 10 hours and then devolatilized to give a polymer composition with a weight average molecular number of 88,000, a weight average molecular weight of 200,000 and a F'DI of 2.3.The polymer had an optical composition of 1.5% R-lactic acid residues and 96.2% S-lactic acid residues. Various additives listed in Table 10, in polylactide, using a Plasticorder head at a temperature of 180 ° C for two minutes. Then the polymer was dried in a vacuum oven. Samples were then placed in a capillary rheometer, which was used to heat samples and keep them at the desired test temperature for 20 minutes (not including a warm-up time of 5 minutes). Samples were taken after heating for five minutes (t = zero) and at 10 and 20 minutes. FTIR was used to determine the lactide content and GPC was used to measure the molecular weight. The results are shown in the following table.

TABLE 10

Claims (23)

1. CLAIMS 1. A polymeric composition containing lactic acid residue, characterized in that it comprises: (a) polylactide polymer having a number molecular weight between 25,000 and 200,000; (b) lactide, if present, which is present in a concentration of less than 0.5% by weight, based on the weight of the polymer composition containing the lactic acid residue; (c) between 0.01 and 2% by weight of catalyst deactivating agent, having a molecular weight greater than 500; wherein the catalyst deactivating agent includes, on average, more than two carboxylic acid groups per molecule.
2. 2. A composition containing lactic acid residue, characterized in that it comprises polylactide polymer having an average number-average molecular weight of between 25,000 and 200,000, and between 0.01 and 2% by weight of catalyst deactivating agent; wherein the composition containing the lactic acid residue is sufficiently stable to the re-formation of lactide, that a sample thereof, devolatilized to give a lactide concentration of less than 1% by weight and a water concentration of less than 500 ppm will generate less than 2% by weight of lactide, after heating at 260 ° C for twenty minutes.
3. 3. A method for stabilizing a polymeric composition containing lactic acid residue, characterized in that the process comprises the steps of: (a) providing a polymeric composition containing lactic acid residue, comprising polylactide polymer having an average molecular weight of number between 25,000 and 200,000; (b) introducing into the polymeric composition containing lactic acid residue, a catalyst deactivating agent, having a molecular weight of more than 1,000 and in an amount of 0.01% by weight and 2% by weight, based on the weight of the polymer composition containing the lactic acid residue.
4. 4. A polymeric composition containing lactic acid residue, characterized in that it is prepared according to the method of claim 3.
5. 5. A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4 , further characterized in that the deactivating agent comprises polyacrylic acid.
6. 6 - A polymeric composition containing lactic acid residue, according to claim 5, further characterized in that the catalyst deactivating agent comprises a polycarboxylic acid having a molecular weight greater than 1.00C.
7. 7. A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4, further characterized in that the catalyst deactivating agent comprises polyacrylic acid provided at a concentration of between 0.04% by weight and 0.3% by weight. weight.
8. 8 - A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4, further characterized in that the catalyst deactivating agent comprises a polycarboxylic acid having a carboxylic acid group per 250 u.m.a.
9. 9. A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4, further characterized in that the polylactide polymer comprises a polymer of tin catalyzed polylactide.
10. 10. A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4, further characterized in that the catalyst deactivating agent comprises a hydrolyzed anhydride polymer.
11. 11. A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4, further characterized in that the polylactide polymer has a number average molecular weight within the scale of 75,000 to 125,000.
12. 12. A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4, further characterized in that the catalyst deactivating agent comprises a polycarboxylic acid having a molecular weight of more than 20, 000
13. 13. A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4, further characterized in that the catalyst deactivating agent is provided at a concentration of 0.01 to 2% by weight and comprises a carboxylic acid multifunctional having a separation between acid groups of no more than six carbon atoms apart, including carbonyl carbon.
14. 14. A polymeric composition containing lactic acid residue, according to any of the claims 1, 2 and 4, further characterized in that their sample will generate less than 1% by weight of lactide after heating at 260 ° C for 20 minutes.
15. 15. A polymeric composition containing lactic acid residue, according to any of the claims 1, 2 and 4-14, further characterized in that: (i) the polylactide polymer has a number average molecular weight of between 45,000 and 105,000; and (ii) the composition exhibits a melt flow index of between 10 and 50, according to ASTM D1238 at 210 ° C and 2.16 kg of weight.
16. 16. A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4-14, further characterized in that: (i) the polylactide polymer has an average number-average molecular weight between 50,000 and 90,000; and (i) the composition exhibits a melt flow index of between 16 and 30, according to ASTM D 1238 at 210 ° C and a weight of 2.16 kg.
17. 17. - A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4-14, further characterized in that: (i) the composition exhibits a melt flow index of 2 to 30, according to ASTM D1238 at 210 ° C, with a weight of 2.16 kg; and (ii) the polymer composition exhibits a die swell ratio of more than 1.25, when tested in accordance with ASTM D1238, with a die of 2.09 mm in diameter at 210 ° C and 2.16 kg in weight; (Ii) the polylactide polymer has a weight average molecular weight of between 50,000 and 400,000.
18. 18. A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4-14, further characterized in that: (i) the composition further comprises from 1 to 40 weight percent plasticizer; and (i) the polylactide polymer exhibits a weight average molecular weight of between 50,000 and 400,000.
19. 19. A polymeric composition containing lactic acid residue, according to any of claims 1, 2 and 4-14, further characterized in that: (i) the composition exhibits a melt flow index of between 6 and 10, compliance with ASTM D1238 at 210 ° C, with a weight of 2.16 kg; and (ii) the polylactide polymer has a weight average molecular weight of between 160,000 and 350,000.
20. 20. An article formed from the polymer composition containing the lactic acid residue, according to any of claims 1, 2 and 4-19.
21. 21. A fiber formed from the polymer composition containing the lactic acid residue, according to any of claims 1, 2 and 4-19.
22. 22. A coating formed from the polymeric composition containing the lactic acid residue, according to any of claims 1, 2 and 4-19.
23. 23. A film formed from the polymer composition containing the lactic acid residue, according to any of claims 1, 2 and 4-19. 24- A molding formed from the polymeric composition containing the lactic acid residue, according to any of claims 1, 2 and 4-19. 25, - A method according to claim 3, further characterized in that it further comprises the step of: (a) devolatilizing the polymer composition containing the lactic acid residue, which contains deactivating agent, at a temperature of between about 200 ° C and about 260 ° C, and at a pressure less than 10 mm Hg, to give a lactide concentration of less than 1% by weight.