JPH10501560A - Processable poly (hydroxy acid) - Google Patents

Abstract

  (57) [Summary] Processable poly (hydroxy acid) composition stabilized by adding 0.05 to 3% by weight of a peroxy compound to the polymer that causes one or more acid free radicals to decompose during the melt processing step. Thus, it has good melt strength and elasticity. The melt strength is high enough to process the film by conventional methods such as blown film methods.

Description

DETAILED DESCRIPTION OF THE INVENTION Processable Poly (hydroxy acid) The present invention relates to poly (hydroxy acid) compositions having high melt strength and processability. In particular, the invention relates to the use of these compositions in the production of films. Biodegradable polymers and biopolymers constitute a group of substances that are being continuously developed. Among these are poly (hydroxy acids), which are polymers whose monomers can have both carboxyl and hydroxyl groups. Examples of such polymers include polylactic acid (polylactide, PLA), poly (hydroxybutyrate), polyglycolide, and poly (ε-caprolactone). Polylactide or polylactic acid, most commonly produced from lactic acid dimer, lactide, has already been used for several years for medical or sustained release of drugs such as sutures, degradable bone and nails. The molecular weight of the polymers in these applications is typically very high, and the polymers are purified by dissolution and precipitation before processing, with low thermal degradation. The high price of the polymer and its in-process pyrolysis have limited its use in bulky applications such as packaging. The manufacture or handling of such polymers by methods such as those used for medical applications is not economically beneficial. Polylactic acid can be directly produced by a polycondensation reaction that is typical in producing polyester. However, the highest molecular weights are achieved by ring-opening polymerization of lactide. Polylactide is a thermoplastic polyester with properties similar to many conventional polymers. The problem, however, was that these polymers were difficult to process and, for example, the production of blown films was not possible. Non-medical uses of polylactide have also been of particular interest in recent years. Biodegradable compostable materials are being sought for packaging applications, either sanitary products, agricultural films and paper coatings or free films. The reason for this was the objective regarding the use of natural products instead of fossil raw materials and the good mechanical and barrier properties of polylactides, for example, comparable to starch-based thermoplastics. Polylactide is a thermoplastic polyester similar to many conventional polymers. However, there is the problem that the polymer decomposes during processing and the molecular weight is significantly reduced. As a result, the useful life of the end product and, in part, these mechanical properties are degraded. For conventional polymers, the use of stabilizers can eliminate these problems. The purpose of the use of stabilizers is to keep the molecular weight as constant as possible after the polymerization and especially during processing. Changes in molecular weight can be monitored, for example, by melt viscosity. Conventional stabilizers that can be used with aromatic polyesters have no effect on lactic acid polymers. According to DE-A-4102170, boric acid used for stabilizing poly (hydroxybutyrate) does not work with lactic acid polymers. Reliable experiments with various stabilizers have been published. In JP-A-68-008614, polylactic acid is stabilized with a lactone compound such as γ-butyrolactone or α-acetal-γ-butyrolactone. JP-A-68-002949 describes that isocyanate is added to improve the heat resistance of a lactic acid polymer. These methods have been tried, but have yielded poor results. Attempts to make processed films from pure polylactide have also been unsuccessful. Some films were made by blending with other polymers or from copolymers. In German Patent Application No. 4300420, a blend of polylactide and another aliphatic polyester, preferably polycaprolactone, is obtained. The polymer is mixed in solution, granulated, and the granules are treated for a long time at a temperature just prior to melting to achieve transesterification. PCT Publication No. 92/04493 discloses a polylactide composition having a large amount of lactide or lactide oligomer as a plasticizer for flexibility. In PCT Publication No. 94/07941, melt stable polylactide compositions are obtained which are said to be suitable for films. The lactide and moisture content of the residue should be very low and the exact amount of meso-lactide should be used for the polymerization. Several "films" were made in Example 2 by extrusion of a thick sheet. The thickness of the test product was between 1 and 13 mm. Test bars were used in all other examples. Even according to this patent application it is most preferred to use a polylactide blend, for example with polycaprolactone. Polylactides or copolymers have been produced into free-standing films by casting from solution or by compression, as already indicated in very old patent publications. For example, there are U.S. Pat. Nos. 2,703,316 and 4,045,418. Although many attempts have been made for film production, large-scale production based on the economical conventional large-scale blown film process for making thin stretched films has been conducted with low polymer melt strength. Obviously, it was not possible due to lack or loss. When films are obtained in several ways, these films are brittle and have a very low breaking value unless many plasticizers are added or blended with other polymer components. Has low elongation. Another important issue is melt stability. It is well known that polylactide decomposes at high temperatures during melt processing. Most of the mechanical properties are kept above a certain limiting molecular weight, but the viscosity drops drastically, and this also makes inflation of these polymers impossible. Melt-stable compounds are discussed only in PCT Patent Application Publication No. 94/07941, mentioned above, but even here the melt strength is not sufficient for the inflation method. The melt stability in this specification is the sum of many different factors, and there is a need for precisely defined polymer compounds. According to the invention, it has surprisingly been found that polylactic acid can be stabilized by adding various peroxides to the mixture during processing or in a separate step. Addition of peroxide can reduce chain breakage, ie, slow down molecular weight reduction. The stabilizing effect of the peroxide can also be seen from the melt viscosity values, which decrease considerably later during processing than without peroxide due to the peroxide addition. The effect of peroxide can be several-fold. Catalyst deactivation and end group capping appear to be possible mechanisms. Crosslinking can be ignored. This is because no gel formation is observed. The theoretical background of peroxide action is outside the scope of the present invention. Furthermore, it is an object of the present invention to achieve a polylactide composition having good melt strength and elongation. A further object is to achieve a composition having sufficient melt strength to form a film by conventional methods, such as the blown method. In the stabilization according to the present invention, a large number of commercially available organic peroxy compounds can be used. Particularly suitable are peroxy compounds, from which the acids are formed as decomposition products. It is clear that this acid radical stabilizes the hydroxyl end groups of the polymer. In addition, peroxides acting as stabilizers are characterized by short half-lives, preferably less than 10 seconds, but more preferably less than 5 seconds. Examples of suitable peroxides obtained include dilauroyl peroxide (half-life at 200 ° C., 0.057 seconds), tert-butylperoxy-diethyl acetate (0.452 seconds), t-butylperoxy-2-ethylhexanonate (0.278 seconds) ), Tert-butylperoxy-isobutyrate (0.463 seconds) and tert-butylperoxyacetate (3.9 seconds), tert-butylperoxybenzoate (4.47 seconds) and dibenzoyl peroxide (0.742 seconds). The last two mentioned proved to be particularly good. The above are only a few examples of working peroxides, and it is understood that other peroxides that work in a corresponding manner are also within the scope of the present invention. The amount of peroxide used is preferably from 0.01 to 3% by weight. The most preferred amount depends on the peroxy compound. Surprisingly, it has been found that stabilizing polylactide with certain peroxides results in very high melt strength and elongation after stabilization. The elongation is 150-300%. This allows for a polylactide inflation process using conventional commercial inflation equipment. This film can also be stretched effectively. The polylactide used can be produced from L-, D- or D, L-lactide or a blend thereof by any polymerization method. Copolymers or polymer blends can also be used, but are not required for use performance in the present invention. In particular, it is preferable to use poly-L-lactide. The polymers according to the invention have a weight average molecular weight (Mw) of about 20,000 to 400,000, preferably 40,000 to 200,000. This refers to a number average molecular weight (Mn) between 10,000 and 200,000, preferably between 10,000 and 100,000. Polylactide films can be easily finished for different purposes by adding small amounts of conventional plasticizers, pigments, fillers and the like. Generally suitable plasticizers are commercially available plasticizers such as di- or tricarboxylic esters, epoxide oils or esters, polymeric polyesters, aliphatic diesters, alkyl ether mono- or diesters and glycerin esters. is there. Blends of these plasticizers can also be used. If a plasticizer is used, the appropriate amount is 0.5-30% by weight. As fillers, all conventional inorganic or organic fillers can be used, such as calcium carbonate, kaolin, mica, talc, silicon oxide, zeolites, glass fibers or spheres, starch or sawdust. Suitable amounts of filler can be from 0.5 to 50% by weight, depending on the end product. Films can be formed from the polylactide compositions of the present invention by the blown method, which is one of the greatest benefits of the present invention. In addition, cast films or sheets can, of course, also be formed, but these do not usually have a high demand on materials. The thickness of the blown or cast film can be adjusted according to the final product by using different molecular weight polymers and by varying the amount of peroxide and also by adding appropriate plasticizers and / or fillers. It can be easily finished. The purpose of the use of the film is for all conventional uses of the film, and in particular for those wishing to minimize the amount of waste and to treat it, for example by composting. Such applications are, for example, various packaging materials such as pouches, films, bags, sanitary products such as diapers, and agricultural films. Sheets formed from polylactide can be processed into various packaging trays or lids, or shallow agricultural containers or flower pots. Many different types of products can be made from the polymer compositions of the present invention. One such application is called twist film, which refers to a wrap used for, for example, a candy, where the wrap is twisted at both ends to wrap around an object and close the package. This twist remains closed and does not open before use by the consumer. Not many polymers have good torsional properties. One of the best torsion materials is cellophane. It is also characteristic of the film or sheet formed from the polymer composition of the present invention that it can be easily sealed by either heat sealing or high frequency sealing. Various printing inks, even when soluble in water, adhere very well to the film. The following examples illustrate the invention in more detail. In Examples 1-3, two different poly (L-lactic acids) were used, their weight average molecular weights Mw were 160,000 and 140,000 g / mol, respectively, and the number average molecular weights Mn were about 70,000 and 60,000 respectively. g / mol. Therefore, the molecular weight ratio Mw / Mn was about 2.3. The polymer was manufactured by Nesta Oy and used as such in the experiments. The following peroxides: Dibenzoyl peroxide (Fluka), half-life 0.742 sec. B. di-tert-butyl peroxide (Akzo), half-life 20.5 seconds D. Dicumyl peroxide (Akzo), half-life 14.7 seconds Tert-butyl peroxybenzoate (Akzo), a half-life of 4.47 seconds, was used for stabilization in the experiments. All peroxides were commercial products and were used as such. In other examples, polylactides having molecular weights (Mw) of 115,000, 130,000, and 145,000, manufactured by Neste Oy, were used. The molecular weight was measured by a GPC (gel permeation chromatograph) using a polystyrene standard. DSC (differential scanning calorimetry) measurements were performed on a Perkin Elmer DSC7 and METTLER DSC-30S instrument. The sample weight in these measurements was 10 mg. The heating and cooling rates were 10 ° C./min and the measurement was for two cycles. Thermogravimetric analysis (TGA) was performed using a Mettler TG50 instrument. The size of the sample during the measurement was 10 mg, the sample was heated to 500 ° C. under a nitrogen atmosphere, and the heating rate was 10 ° C./min. The Kel content of the polymer was determined by the method of ASTM D2765 using chloroform as solvent. Embodiment 1 FIG. The stabilization of the film polylactic acid was investigated using a Brabender mixer (Plasticoder® pL2000), which also allowed the melt viscosity of the compound to be monitored directly from the machine torque. 40 g of polylactide having a Mw of 160,000 was mixed with 0 to 3% of dibenzoyl peroxide (A) at 180 ° C. for 5 minutes. Assuming all peroxide had reacted, the DSC measurement did not show any out-of-range peaks. Polymer samples were pressed between PET films for 15 seconds at a pressure of 200 bar and a temperature of 180 ° C. After molding, the film was rapidly cooled to room temperature. Film thickness was 250-300 μm. The film was dissolved in chloroform and no gel was visually detectable. The amount of peroxide added affected the melt viscosity, as can be seen from FIG. Addition of the peroxide in an amount of 0-0.5% by weight increased the melt viscosity, but the difference was small between the 0.5% and 3.0% by weight additions. Without peroxide, the melt viscosity decreased rapidly during processing. Embodiment 2. FIG. Polylactide having a Mw of 140,000 tape was mixed with the peroxides AD. The peroxide was dissolved in a small amount of cyclohexane before addition. However, when peroxide A was used, toluene was used as the solvent because A was insoluble in cyclohexane. The solvent was evaporated from the polymer before processing. All experiments were performed under a stream of nitrogen. The experimental batch size was 40 g of polylactic acid. The samples were then processed to tape on a Brabender Plasticoder® PL E651 single screw extruder. The zone temperatures were 190 ° C, 200 ° C, and 200 ° C, and the nozzle temperature was 200 ° C. The rotation speed of the screw was 50 rpm. The residence time of the extruder was about 1.5 minutes. The molecular weight Mw of the unstabilized reference sample of polylactide dropped during processing to at least one third of its initial value. Mw / Mn dropped from an initial value of 2.3 to about 1.9. According to DSC analysis, the reference sample had a glass transition temperature of about 50 ° C. Tg, the melting point Tm of about 1 70 ° C., and about 50% crystallinity C _r. According to thermogravimetric analysis, the decomposition temperature (T _D ) was about 303 ° C. Table 1 shows the molecular weights when different peroxides were used, and Table 2 shows the DSC / TGA results of the corresponding experiments. The results in Table 1 show that peroxides B and C did not achieve the desired stabilizing effect, while peroxides A and D reduced the molecular weight only slightly. Example 3 Gel formation Possible cross-linking of polylactide was investigated by measuring the gel content of the polymer after peroxide treatment. Polylactide was blended with various amounts of dibenzoyl peroxide in the manner of Example 1. Gel content was measured according to ASTM D2765, but chloroform was used instead of xylene. No gel formation was observed when the peroxide content was 0.25% by weight or less, and gel formation was low even when the peroxide content was less than 3% by weight. When the results were further examined on a particle size analyzer Malvern 2600c, the amount of very small particles was noticeable at low peroxide content, and the amount of large particles increased with increasing peroxide content. The results are shown in Table 3. Embodiment 4. FIG. Melting Characteristics of Stabilized Polylactide Poly-L-lactide (PLLA) was stabilized by the method described in the previous example, ie, the polymer was treated with dibenzoyl peroxide (Fluka, half-life 0.742 seconds) for 5 minutes 180 minutes. The mixture was melt mixed at ℃. The equipment used to measure the melting properties was a Getfeld extruder, with a screw diameter of 30 mm and a length of 20D, equipped with a melting pump and a capillary die, and L / D = 100/3. The take-off device is for uniaxial stretching of the polymer melt The reamer melt strand was gripped between two co-rotating wheels and stretched at a constant speed or constant acceleration until the strand broke. In this experiment, a constant acceleration was used. The tensile force used to stretch the polymer melt was recorded as a function of stretched strand speed. The extruder temperature profile was 160-180-180-180, and the melt pump and die temperatures were 180 ° C. Die pressure was adjusted by the melt pump rpm to avoid melt fracture of the polymer strand. Table 4 shows the tensile strength of the melt at various speeds. The stabilized polylactide was compared to the unstabilized polylactide and also to a film grade low density polyethylene with a melt index of 4.5. These results indicate that 0.5% peroxide stabilized polylactide is comparable to film grade polyethylene. Embodiment 5 FIG. Melt Strength Properties of Stabilized Polylactide Blown films of various grades of polylactide were produced on a Brabender extruder with a screw diameter of 19 mm and a length of 25D. The extruder was equipped with a blown film die with a diameter of 25 mm and a die gap of 1.0 mm. The extruder temperature profile was set at 170-180-190 ° C and at the die at 190 ° C. The screw speed was set at 30 rpm. The expansion ratio was 2: 1. The thickness of the film was varied from 10 μm to 150 μm and adjusted by the speed of the unloader. Subsequent to the extrusion process, a visual inspection of the foam stability corresponding to the melt strength and elasticity of the extruded polymer, which is the main criterion for a suitable blown process, was performed. The steady state extrusion was held for 1 hour. Table 5 shows the film extrusion properties of stabilized and unstabilized polylactides of various molecular weights. Blown films cannot be formed from unstabilized polylactide. These results show that the appropriate amount of stabilizer is higher for polylactides with lower molecular weights to form a suitable blown film. From Examples 4 and 5, it is clear that polylactide compositions can be effectively prepared by varying the molecular weight of the polymer and the amount of stabilizer to apply a variety of films from thin to thick films. Embodiment 6 FIG. Physical Properties of Blown Films of Stabilized Polylactide Compared to Unstabilized Polylactide As mentioned above, blown films of unstabilized polylactide could not be formed due to the lack of melt strength of the polymer. However, it was possible to make blown films of unstabilized blown films by coextrusion. A coextruded film with a layer of polylactide between the two layers of polyethylene was formed with the die temperature set at 190 ° C. The polyethylene used was a film grade LDPE, NCPE 4024 made from Borealis polymer Oy with a melt index of 4.0. The polylactide film was peeled from the polyethylene layer. This is possible because the adhesion between polylactide and polyethylene is relatively low. Coextruded films can, of course, be formed from stabilized polylactide. This can be a good method in some special cases where a sterile film is needed for special purposes. The physical properties of the stabilized and unstabilized polylactide films are shown in Table 6. The high flexibility of films made from stabilized polylactide can be clearly seen from the results. Embodiment 7 FIG. Addition of Plasticizer to Stabilized Polylactide Films formed from stabilized polylactide are already flexible by themselves, but can still be finished by further adding a plasticizer to the polymer. A commercial stabilizer was used in the experiments: Emuldan SHR60, a blend of glycerol monooleate and dioleate (manufacturer Grindstead Products AS, Denmark). The film was formed as described in Example 5. Table 7 shows the stress at peak and the elongation at break. The results show that the addition of the plasticizer further improves the film properties and, in particular, the properties in the machine and transverse directions are more uniform. Embodiment 8 FIG. Addition of filler to polylactide Various amounts of commercial filler were added to the stabilized polylactide composition. Fillers and plasticizers can be used simultaneously. A film was produced by the process described in Example 5. The results are shown in Table 8. These results show that a small amount of talc gives a very strong and hard film, whereas a large amount of kaolin gives a flexible film, which can be further softened by small amounts of some plasticizers. Embodiment 9 FIG. Twisting properties of stabilized polylactide film For example, when candy is wrapped in individual wraps, the ends are closed by twisting about once and a half. One of the best twisting materials is cellophane, which was used for comparative testing. The twist properties of the polylactide composition according to the invention were very good. Twist properties were tested on an in-house developed device that wrapped a film around a candy substitute and twisted both ends 1.6 turns. The force required to open the twist with this machine, and the angle at which the twist was opened by itself, were also measured. The results for polylactide and cellophane are shown in Table 9. Embodiment 10 FIG. Sealability and printability of polylactide film The sealability of the film formed in Example 6 was investigated. The sealing property of this film was good. Heat sealing was performed at 105 ° C. with a sealing time of 0.5 seconds. During sealing, only one seal rod was heated. A high frequency seal was formed at 60 ° C. The seal in both cases was perfect. The printability of the film was tested and it was found that the film could be printed in both solvent and water based inks without corona treatment. This print had very good adhesion to the film when tested by the tape method. Embodiment 11 FIG. Degradation of polylactide buried in soil Injection molding of test bars with various levels of stabilizers to show that stabilized polylactide as well as unstabilized polylactide may at least biodegrade did. The samples were buried in the soil, removed at regular intervals, and tested for mechanical properties. From the results summarized in Table 10, all samples could be seen to be embrittled after 6-8 weeks. Embodiment 12 FIG. Decomposition of stabilized polylactide product at constant humidity The test bar of Example 11 was stored under constant conditions of a temperature of 23 ° C and a humidity of 50%. This was done to test the assumption that the first stage of biodegradation was hydrolysis with water. Table 11 shows the mechanical properties. The molecular weight was also measured and the results are shown in Table 12. The results showed that the hydrolysis rate was higher for the stabilized samples than for the non-stabilized ones. This is probably due to a different crystal structure. As can be seen from the above examples, the polylactide compositions with good melt strength and the possibility of producing them have enabled their use in a wide variety of different applications.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI // A01G 9/10 ZAB 9318-2B A01G 9/10 ZABC 9/14 9318-2B 9/14 S 13/02 9318-2B 13/02 D B29C 55/28 7639-4F B29C 55/28 B29K 67:00 B29L 7:00 (72) Inventor Niemi, Maria Finland, FFIEN-0250 Helsinki, Helsinki, Minna Kanthinkatu 24 a 25 (72) Inventor Johansson, Karl Johan, Fien-06100 Porvo, Wadenströminkya, Finland 32 (72) Inventor Mayandel, Kerstin Efien-06100 Porvo, Ticantier, Finland 6

Claims (1)

[Claims] 1. Processable poly (hydroxy acid) composition having a number average molecular weight of at least 10,000 Wherein the melt strength and the elasticity of the polymer are poly (hydroxy acid), organic, Processable poly characterized by being achieved by reactive extrusion with peroxide (Hydroxy acid) composition. 2. During the melt processing stage, the organic peroxy compound in an amount of 0.05-3% by weight is added to the polymer. And the decomposition thereof produces one or several acid free radicals. The processable poly (hydroxy acid) composition according to claim 1. 3. The poly (hydroxy acid) has a number average molecular weight of 10,000 to 200,000 The processable poly (hydroxy acid) composition according to claim 1 or 2. 4. Characterized in that the amount of peroxide is 0.05-0.8% by weight of the amount of polymer The processable poly (hydroxy acid) composition according to claim 1. 5. The half-life of the peroxide used is less than 10 seconds at a temperature of 200 ° C. The processable poly (hydr) according to any one of claims 1 to 4, wherein Roxyacid) compositions. 6. If the peroxide is tert-butylperoxybenzoate or dibenzoylpe 6. The oxide according to claim 1, wherein An engineered poly (hydroxy acid) composition. 7. 2. The poly (hydroxy acid) is poly-L-lactide. Item 7. The processable poly (hydroxy acid) composition according to any one of Items 6 to 6. 8. Melt strength and elasticity are suitable for blown film production. The poly (hydroxy acid) composition according to claim 1. 9. That the melt strength and elasticity are appropriate for the production of cast films or sheets. A poly (hydroxy acid) set according to any one of claims 1 to 8, characterized in that: Adult. 10. The method according to claim 1, further comprising 0.5 to 30% by weight of a plasticizer. A poly (hydroxy acid) composition according to any one of the preceding paragraphs. 11. Plasticizers are di- and tricarboxylic esters, epoxy oils and esters , High molecular weight polyester, aliphatic diester, alkyl ether mono and die Selected from the group consisting of ter and glycerin esters or mixtures thereof The poly (hydroxy acid) composition according to claim 10, wherein 12. The method as claimed in claim 1, wherein the filler is contained in an amount of 0.1 to 50% by weight. A poly (hydroxy acid) composition according to any one of the preceding paragraphs. 13. Filler is calcium carbonate, kaolin, mica, talc, silicon dioxide, zeo Selected from the group consisting of lights, glass fibers or spheres, starch or sawdust 13. The poly (hydroxy acid) composition according to claim 12, wherein 14． A poly (hydroxy acid) composition according to any one of claims 1 to 13. A film or sheet formed from an object. 15. 15. The film according to claim 14, produced by blown film extrusion. 16. 15. The film or sheet according to claim 14, which is produced by casting extrusion. 17． It can be sealed by heat seal or high frequency seal. A film or sheet according to any one of claims 14 to 16, characterized in that: 18. Printable with solvent or water-based ink A film or sheet according to any one of claims 14 to 16. 19. 19. It has good twist characteristics. The film or sheet according to any one of the above items. 20. Sanitary products such as diapers, agricultural films, bags, pouches, shrink or 20. A packaging material, such as a twisted film packaging, according to any one of claims 14 to 19. Use of the film described in 1. 21. Thermoformed packaging articles such as trays or lids and cultivation trays or flowerpots Use of a sheet according to any one of claims 14 to 19 in agriculture products . 22. 22. Hydrolyzable and biodegradable. A film, sheet and product according to any one of the preceding claims.