BE1019340A3 - PROCESS FOR NUCLEATING AND ACCELERATING THE CRYSTALLIZATION OF THE POLYLACTIDE - Google Patents

Abstract

The present invention relates to a process for accelerating the crystallization of the polylactide, characterized in that it comprises the incorporation into the polylactide, of a polyester-urethane. The invention also relates to a polylactide composition characterized in that it comprises a polylactide and a polyester-urethane. The invention also relates to a method of manufacturing an article from said compostition as well as to an article obtainable by the method.

Description

The invention relates to a process for accelerating the crystallization of polylactide (PLA), either poly-L-lactide (PLLA) or poly -D-lactide (PDLA). The process of the invention relates in particular to the use of polyester-urethane obtained by extension of poly-L-lactide or poly-D-lactide chains, hydroxytelechelic oligomer, by reaction with diisocyanates and extenders of diamine or dialcohol chains, as a crystallization accelerating agent, or more commonly a nucleating agent.

2. State of the art:

In many potential applications, the low crystallization rate of the polylactide constitutes a major disadvantage.

The state of the art shows, in particular in the following documents: M.Spinu et al; J.M.S. Pure Appl. Chem. A33 (10), 1996; H.Li, M. Huneault; Polymer 48 (2007) 6855-6866; M. Salmeron Sanchez et al. ; Macromolecules (2007) 7989-7997; H. Tsuji, Y. Itikata; Polymer 36 (14) (1995) 2709-2716; M.L. Di Lorenzo; Eur. Pol. J. 41 (2005) 569-575; J. Y. Nam et al; Polymer 47 (2006) 1340-1347; US200601422505; that numerous research works have been carried out in order to accelerate this crystallization, either by promoting the mobility of the chains by the addition of plasticizer, or by promoting the nucleation of the crystallization by adding fillers, in particular mineral fillers such as talc. or montmorillonite, the talc having proved the most effective nucleating mineral filler but without being totally satisfactory, particularly because the additivation by mineral fillers necessitates the incorporation of large quantities of this filler, which adversely affect the properties optical PLA.

It has also been proposed the method of plasticization, but, if it makes it possible to accelerate the crystallization, it leads to a decrease in the glass transition temperature, and may be faced with problems of exudation of the plasticizer out of the matrix. The most frequently mentioned plasticizers for PLA are based on polyethylene glycol (PEG). In addition, at present, regardless of the route chosen, additives of non-renewable origin are used, which is detrimental to the environmental added value of the PLA.

Moreover, it has been known for several years that the combination of PLLA (poly-L-lactide) and PDLA (poly-D-lactide) chains generates stereocomplex crystals whose complexation and melting temperature (> 210 °) C) is several tens of degrees higher than the melting temperature of the crystals of a homopolymer PLLA or PDLA (<170 ° C). Stereocomplexes have mostly been studied for their intrinsic properties, in equal-weighted mixtures or close to equal weighting. However, we have already described in some recent articles, notably in H. Yamane, K. Sasai; Polymer 44 (2003) 2569-2575; S.C. Schmidt, M.A. Hillmyer; J. Pol Sei. Part B: Polym. Phys 39 (2001) 300-313 and K.S. Anderson, M.A. Hillmyer; Polymer 47 (2006) 2030-2035 that the incorporation of a small fraction of PDLA (<10 wt.%) In PLLA allowed the formation of stereocomplex crystals dispersed in the PLLA matrix which favor the nucleation of homocrystallization of PLLA. this matrix; however, this use leads to poor mechanical properties of the PLLA matrix.

In addition, the existing compositions have only high half-crystallization times, which leads to obtain a polylactide in its amorphous form.

There is therefore a need for a process which makes it possible to accelerate the crystallization of PLA, either PLLA or PDLA, without encountering the disadvantages of the solutions known to date. The method of the present invention is therefore intended to overcome the disadvantages mentioned above.

3. Aims of the invention

One of the objects of the process of the invention is to use a PLA crystallization accelerator, PLLA, or PDLA, or nucleating agent, which is derived from renewable resources and has an efficiency such that the half-crystallization time is reduced. at least 40% compared to the best existing polylactide compositions.

Another object of the process of the invention is to use a crystallization accelerator or PLA nucleating agent, either PLLA or PDLA, in small amounts, not exceeding 20%, and preferably not more than 10%, by weight relative to the total weight of the nucleating agent and PLA mixture (either PLLA or PDLA).

4. Detailed description of the invention

The present invention provides a method for accelerating the crystallization of polylactide of average molecular weight in the range of 30,000 to 200,000 g / mol, characterized in that it is incorporated in said polylactide, called polylactide matrix, of either L or D configuration. at a temperature of between 160 ° C. and 250 ° C., from 1 to 20% by weight relative to the total weight of the mixture, a polylactide-urethane copolymer whose configuration of the polylactide is the reverse of that of the polylactide matrix .

In the present invention, polylactide matrix of configuration L is understood to mean a polymer in which the majority of repeating units are L-lactide (PLLA) monomers and by polylactide matrix of configuration D, a polymer in which the majority of repetitive units are D-lactide monomers (PDLA).

In the present invention, the term polylactide-urethane copolymer whose configuration of the polylactide is the reverse of that of the polylactide matrix, a polylactide-urethane copolymer obtained for example from a PLLA by reaction with a diisocyanate in the presence a diamine or a dihydric alcohol while the polylactide matrix is a PDLA or a polylactide-urethane copolymer obtained for example from a PDLA by reaction with a diisocyanate in the presence of a diamine or a dihydric alcohol while the polylactide matrix is a PLLA.

According to one embodiment, the polylactide matrix is of L configuration and the polylactide-urethane copolymer is obtained by reaction of a polylactide of configuration D with a disocyanate in the presence of a diamine or a diaclool.

In another embodiment, the polylactide matrix is of configuration D and the polylactide-urethane copolymer is obtained by reaction of a polylactide of configuration L with a disocyanate in the presence of a diamine or a dihydric alcohol.

The Applicant has found, unexpectedly, that the incorporation of polylactide-urethane obtained by reaction of PDLA or PLLA preferably of molar mass average number between 1,000 and 40,000 g / mol), with a disocyanate, in each case. PLLA or PDLA, allowed to accelerate the crystallization of this PLLA or PDLA and thus meet the needs stated above.

In addition, and contrary to the teaching of the state of the art, the Applicant has now unexpectedly found that on the one hand the addition of a poly-D-lactide-urethane (PDEU) as an agent allowing accelerate the crystallization in a PLLA matrix and that, on the other hand, the addition of a poly-L-lactide-urethane (PLEU) as an agent for accelerating crystallization in a PDLA matrix made it possible to significantly improve the respective mechanical properties of the PLLA and PDLA matrices.

The present invention also provides a polylactide composition characterized in that it comprises from 80 to 99% by weight of polylactide with a number-average molar mass of between 30,000 and 200,000 g / mol, of either L or D configuration, called a matrix. polylactide, and from 1 to 20% by weight relative to the total weight of the composition, of a polylactide-urethane copolymer whose configuration of the polylactide is the reverse of that of the polylactide matrix. These compositions are characterized by a reduction in the half-crystallization time of at least 40% compared to that of the best existing PLLA or PDLA compositions.

The present invention also refers to a method of manufacturing an article characterized in that it comprises the transformation by thermoforming, injection or extrusion of the composition according to the invention.

The present invention also refers to an article capable of being obtained according to the method of the invention. The article can be a film or a fiber.

4.1 Obtaining the additive:

As polylactide-urethane that can be used in the method of the invention, there may be mentioned those described in WO2008 / 037773.

The additive intended to nucleate and accelerate the crystallization of the PLLA or PDLA matrix is respectively a poly-D-lactide-urethane (PDEU) or a poly-L-lactide-urethane (PLEU) produced in the manner previously announced, c that is to say from a PDLA or PLLA, a hydroxytelechelic oligomer, preferably having a tacticity of between 90 and 100%, more preferably between 95 and 100%, and preferably a number-average molecular weight of between 1,000 and 40,000. g / mol, more preferably between 5,000 and 20,000 g / mol.

PDEU and PLEU are obtained respectively from PDLA and PLLA by a chain extension reaction involving aromatic or aliphatic diisocyanates and aromatic or aliphatic diamines or dialcohols as described in particular in documents WO2008 / 037773 and WO2008 / 037,772.

4.2 Composition of the formulations:

Although the nucleating agent of the method of the invention can be added to any type of PLA, it has however been observed that better results are obtained when the matrix used is a PLLA or a PDLA preferably having a tacticity. between 90 and 100%, more preferably between 95 and 100% and a number average molar mass preferably between 30,000 and 200,000 g / mol, more preferably between 50,000 and 175,000 g / mol, even more preferentially between 70,000 and 150,000 g / mol. mol.

Then, according to the process of the invention, the polylactide-urethane additive intended to nucleate and accelerate the crystallization of the polylactide to the PLA matrix is incorporated at a level of from 1 to 20% by weight, preferably from 2 to 10% by weight. by weight, more preferably from 3 to 10% by weight relative to the total weight of the polylactide and polylactide-urethane mixture. For incorporation rates of less than 1%, the effectiveness of the polylactide-urethane additive as a promoter of nucleation and crystallization of polylactide is not significantly expressed. For incorporation rates greater than 20%, the effectiveness of the polylactide-urethane additive as a promoter of the nucleation and crystallization of polylactide remains established, but the stereocomplexed fraction assumes a non-negligible, even predominant, importance. with regard to the homocrystalline fraction, which leads to a material with properties significantly different from those of the matrix. Accelerated crystallization rate polylactide formulations may also contain other additives, such as those customarily used to modify the mechanical, thermal or optical properties of polyesters, for example plasticizers, mineral fillers, colorants, stabilizers, or implementing agents, this list should not be considered exhaustive.

4.3 Incorporation of the additive: The incorporation of the polylactide-urethane additive into the polylactide matrix can be done in the molten state, in an internal mixer or in an extruder. The temperature of use of the mixture must be greater than the melting temperature of the polylactide matrix, and preferably greater than the melting temperature of the stereocomplex formed by a fraction of the polylactide matrix and all or part of the polyester-polyester additive. urethane. The mixing is carried out at a temperature between 160 and 250 ° C, preferably between 180 and 230 ° C, more preferably between 200 and 230 ° C.

Other ingredients such as antioxidants, dyes, anti-UV, fire and the like may be incorporated into the polylactide matrix during the step of incorporating the polylactide-urethane additive or into one or more additional steps of formulation, this or these steps can be performed before or after the incorporation of the polyester-urethane additive.

The polylactide and the polylactide-urethane additive intended to nucleate and accelerate its crystallization can also be mixed according to different procedures, for example by dissolving the constituents in a solvent, for example chloroform, toluene or dichloromethane, p-xylene, dioxane or acetonitrile, followed by evaporation of the solvent.

4.4 Synthesis of the additive:

The copolymer of poly-D-lactide-urethane or poly-L-lactide-urethane can be obtained by the process described in WO2008 / 037773.

4.5 Advantages Provided by the Invention:

The process of the invention, by incorporation of the polylactide-urethane additive, makes it possible, unlike the incorporation of most of the other additives known today for this purpose, to improve nucleation (eg mineral fillers). or to accelerate the crystallization (eg plasticizers) of PLA significantly and more particularly so as to reduce the half-crystallization time by at least 40% over that of existing polylactide compositions; moreover, the polylactide-urethane of the process of the invention has the advantage of being of renewable origin.

The polylactide-urethane additive is a high molecular weight additive, which therefore does not have the risk of reducing the mechanical properties of the PLA matrix or of promoting their deterioration, unlike a low molecular weight PDLA incorporated in a PLLA matrix or a low molecular weight PLLA incorporated in a PDLA matrix. Finally, the polylactide-urethane additive exhibits a high nucleation and crystallization acceleration efficiency for a broad range, in terms of tacticity and average molecular weight, of polylactide, where the use of PDLA in a PLLA matrix or the use of PLLA in a PDLA matrix seems to require, according to the literature, an optimization at least in terms of number average molar mass since the nature of the matrix in terms of molar mass or tacticity is modified.

5. Examples:

Example 1

For the preparation of the film of this example, a commercial high purity PLLA, NatureWorks 6201D PLA, which has a 95% tacticity and a number average molecular weight of 93,000 g / mol, was used. This PLLA first underwent a precipitation step by dissolving in chloroform and then precipitating by dropwise addition of methanol. After filtration and drying, the PLLA thus obtained is named PLLA-X.

The PDEU used in this example is called VALI B140. It is obtained by mini-extruder chain extension from an α, ω-dihydroxylated PDLA, initiated by 1,4-butanediol and stabilized with 0.3% Ultranox 626, of molecular weight. apparent polystyrene standard of 7.600 g / mol. This is mixed in a beaker with a spatula with the chain extender, ie 4,4'-methylene diphenylisocyanate (MDI), and the difunctional compound, that is to say 4,4'-diaminodiphenylmethane (MDA), as well as an additional amount of Ultranox 626 at a rate of 0.3% by weight, just before introduction into the mini-extruder. It should be noted that the PDLA (OH) 2 used has not been purified beforehand and therefore still contains Sn (Oct) 2 / PPh 3, which is also the catalyst of the chain extension reaction. The mixture is introduced at a speed of 30 rpm, before increasing it to 75 rpm. The reaction time is taken into account as soon as the introduction of the material is complete and is 5 minutes. The temperature of implementation is 160 ° C. The ratio PLA / difunctional compound was set at 60/40 mol / mol and the ratio [NCO] / [OHPLa + NH2] at 1.1.

The PDLA (OH) 2 used (VALI B133b) for the synthesis of this PDEU is obtained by polymerization of D, D-LA at 160 ° C. in a glass reactor in the presence of Ultranox 626 as a stabilizer, of 1,4- butanediol as initiator and a mixture of tin octoate and triphenylphosphine (1: 1 equimolar) as a catalytic solution in toluene. Lactide, as well as Ultranox 626 at a rate of 0.3% by weight, are introduced into the reactor under an inert atmosphere. The medium is thermostatted at 160 ° C. with stirring at 50 rpm using a stirring pad. When all the lactide is melted, the initiator is added to the reactor, as is the catalytic solution SntOctVPPhs. The polymerization is stopped after 30 minutes. The polymer obtained is dissolved in chloroform, precipitated in 10 volumes of cold methanol, filtered and dried in a vacuum oven at 40 ° C. It should be noted that the 1,4-butanediol was dried over a molecular sieve (4A) for 48 hours and the triphenylphosphine recrystallized from ether before being dried by three successive azeotropic toluene distillations to be finally dissolved in dry toluene with tin octoate. In order to carry out the characterization by steric exclusion chromatography, the polymer obtained is freed of its catalytic residues by liquid-liquid extraction. This is dissolved in chloroform at a rate of 1 g of polymer in 4 ml of chloroform. The catalyst is extracted using a solution of 0.1M HCl of an equivalent volume. The organic phase is then washed twice with deionized water. Finally, the polymer is precipitated in 10 volumes of methanol, filtered and dried in a vacuum oven at 40 ° C. The targeted degree of polymerization of the VALI B133b sample is 70, for a theoretical mass of 9,600 g / mol. The apparent molecular mass in standard polystyrene determined by steric exclusion chromatography is 18,700 g / mol.

According to the process of the invention, 5% by weight of PDEU VALI B140 was incorporated in 95% by weight of PLLA-X. 2 g of this mixture was dissolved in 40 ml of chloroform. After complete dissolution, the solvent is evaporated in the open air and then overnight in an oven at 50 ° C under a vacuum vane pump and the film thus formed is recovered. This film will be subjected to heat treatment as described below.

Example 2

The procedure was as in Example 1 to prepare a film containing 95% by weight of a PLLA of very high optical purity and 5% by weight of a polyester-urethane additive PDEU.

However, this time a PLLA of very high optical purity obtained by a reactive extrusion synthesis method from L-lactide (L-L-LA) was used. It has a tacticity of 99.8% and a number average molar mass of 71,000 g / mol. After precipitation according to the procedure described in Example 1 for the case of PLLA-X, the precipitated PLLA is named A36.

The PDEU used in this example is the VALI B140 PDEU, the obtaining of which is described in Example 1.

The film thus obtained will be subjected to a heat treatment as described below Comparative example 1:

A film was prepared as described in Example 1, with the only PLLA-X and without incorporating anything therein. The resulting film will be subjected to heat treatment as described below.

Comparative Example 2

A film was prepared as described in Example 1 and with PLLA A36 alone and without incorporating anything therein. The resulting film will be subjected to heat treatment as described below.

Comparative Example 3

A film was prepared as described in Example 1 starting from 95% by weight of PLLA-X to which was incorporated 5% by weight of an LMLA PDLA additive of very high optical purity and low molecular mass produced by the method described in Example 1. The LMW PDLA used is the VALI B133b PDLA, which was used as a basis for the synthesis of the VALI B140 PDEU and whose production is described in Example 1.

Comparative Example 4

A film was prepared as described in Example 1 starting from 95% by weight of PLLA-X to which was incorporated 5% by weight of a high purity and high molecular weight PDLA HMW additive prepared by the method described in Example 1. The HMW PDLA used is obtained by ring opening polymerization of D-lactide (DD-LA) carried out in a sealed ampoule at 180 ° C. for 45 min initiated by 1-heptanol and catalyzed by the catalyst system octoate tin / triphenylphoshine 1/1 mol / mol. The PDLA thus obtained is solubilized in chloroform and reprecipitated in methanol in order to remove the residual monomer. It has a number-average molecular weight of 96,000 g / mol measured by steric exclusion chromatography (SEC) relative to polystyrene standards and is called EMDU D42b.

The resulting film will be subjected to heat treatment as described below. Comparative Example 5

A film was prepared as described in Example 1 starting from 95% by weight of PLLA A36 which was incorporated 5% by weight of an LMLA additive PDL of high optical purity and low molecular weight called PDLA VALI B133b as described in Example 1. The resulting film will be subjected to heat treatment as described below.

Comparative Example 6

A film was prepared as in Example 1 starting from 95% by weight of PLLA A36 which was incorporated 5% by weight of a high purity and high molecular weight PDLA HMW additive called PDLA EMDU D42b and prepared by the method described in Example 1. The resulting film will be subjected to heat treatment as described below.

All the films obtained in Examples 1 and 2 and in Comparative Examples 1 to 6 are subjected to a DSC (different scanning calorimetry) under nitrogen to a heat treatment as described below. Heating from -40 ° C to +220 ° C at 10 ° C / min, quenching (cooling) from +220 ° C to +130 ° C to 40 ° C / min, isothermal from 30 min to +130 ° C, quenching (cooling) from +130 ° C to -40 ° C at 20 ° C / min and then heated from -40 ° C to +220 ° C to 10 ° C / min. The half-crystallization time at 130 ° C is estimated according to ISO 11357-7 from the thermogram of the isothermal phase of the temperature program as the time elapsed between the start of this isothermal phase and the moment corresponding to half in terms of area, the peak of crystallization observed, disregarding the possible start of crystallization that may have occurred during the part of the quenching (cooling) preceding the isotherm. The results thus obtained are reported in Table 2, where it appears that the gain in terms of crystallization speed provided by the PDEU additive is far superior to that provided by the LMW or HMW PDLAs.

Table 1: Composition of the films of Examples 1 and 2 and Comparative Examples 1 to 6.

Table 2: Half-crystallization time in isothermal crystallization at 130 ° C of PLLA, PLLA / PDLA mixtures and PLLA / PDEU mixtures obtained by DSC analysis.

The examples E1 and E2 produced according to the process of the invention have a reduced half-crystallization time compared to the half-crystallization times of the best existing compositions (comparative examples EC3 and EC6).

Claims (10)

A method for accelerating the crystallization of the polylactide of a number-average molar mass of between 30,000 and 200,000 g / mol, characterized in that it is incorporated in said polylactide, called a polylactide matrix, of either L or D configuration at a temperature between 160 ° C and 250 ° C, from 1 to 20% by weight relative to the total weight of the mixture, a polylactide-urethane copolymer whose configuration of polylactide is the reverse of that of the polylactide matrix. 2. Method according to claim 1 characterized in that the polylactide matrix is of configuration D and in that the polylactide-urethane copolymer is obtained by reaction of a polylactide L configuration with a disocyanate in the presence of a diamine or a dialcohol. 3. Method according to claim 1 characterized in that the polylactide matrix is of L configuration and in that the polylactide-urethane is obtained by reaction of a polylactide of configuration D with a disocyanate in the presence of a diamine or a dialcohol. 4. Process according to any one of Claims 1 to 3, characterized in that the polylactide-urethane is incorporated in a proportion of 2 to 10% by weight and preferably in a proportion of 3 to 6% by weight relative to the weight. total of the polylactide and polylactide-urethane mixture. 5. A polylactide composition characterized in that it comprises from 80 to 99% by weight of polylactide of molar mass of between 30,000 and 200,000 g / mol, of either L or D configuration, called polylactide matrix, and from 1 to 20 % by weight relative to the total weight of the composition, a polylactide-urethane copolymer whose configuration of polylactide is the reverse of that of the polylactide matrix. 6. Composition according to claim 5, characterized in that it comprises from 80 to 99% by weight of poly-L-lactide and from 1 to 20% by weight relative to the total weight of the composition, of a polylactide copolymer. urethane whose polylactide is of configuration D. 7. Composition according to claim 5, characterized in that it comprises from 80 to 99% by weight of poly-D-lactide and from 1 to 20% by weight relative to the total weight of the composition, of a polylactide copolymer. urethane whose polylactide is of configuration L. 8. A method of manufacturing an article characterized in that it comprises the transformation by thermoforming, injection or extrusion of the composition according to any one of claims 5 to 7. 9. Article obtainable according to the method of claim 8. 10. Article according to claim 9 characterized in that the article is a film or a fiber.