Polylactic acid composition as well as preparation method and application thereof

Abstract

The invention provides a polylactic acid composition as well as a preparation method and application thereof, and relates to the field of high polymer materials. The polylactic acid composition comprises polylactic acid and a polyester block copolymer, the general formula of the polyester block copolymer is A-B-A, and the A segment comprises a lactic acid unit; and the segment B comprises a caprolactone unit and a trimethylene carbonate unit which are arranged randomly. According to the polylactic acid composition provided by the invention, the polylactic acid is subjected to toughening modification by adopting the polyester block copolymer. A soft segment in the polyester block copolymer is a random copolymer of caprolactone and trimethylene carbonate, and introduction of trimethylene carbonate can destroy crystallization of a caprolactone polymerization chain segment, so that the soft segment is softer. The hard segment of the polyester block copolymer is polylactic acid, and the segment can improve the compatibility between the polyester block copolymer and polylactic acid. The polyester block copolymer plays a role in toughening the polylactic acid, and the polyester block copolymer also has biodegradability, so that the whole composition has biodegradability.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, specifically to a polylactic acid composition, its preparation method, and its application. Background Technology

[0002] Polylactic acid (PLA) is a widely used biodegradable material with advantages such as renewable raw materials, high strength, high hardness, and biocompatibility. However, its brittleness limits its applications, making toughening modification of PLA a focus of attention. For example, CN109608843A discloses a scheme for toughening PLA with polyester-type thermoplastic polyurethane, CN114957941A discloses a scheme for toughening PLA with modified carboxylated butadiene-acrylonitrile rubber, CN10459097B discloses a scheme for toughening PLA with polyester elastomer, and CN105315631A discloses a scheme for toughening PLA with polyisobutylene, etc. However, most of the toughening components added in these schemes are non-biodegradable, which affects the overall biodegradability of PLA materials. Therefore, it is necessary to develop PLA technologies that possess both overall biodegradability and improved toughening performance. Summary of the Invention

[0003] In view of the above analysis, the present invention aims to provide a polylactic acid composition, a method for preparing the same, and its application, in order to solve at least one of the following problems: improving the toughness of polylactic acid, thereby making toughened polylactic acid biodegradable.

[0004] The objective of this invention is mainly achieved through the following technical solutions:

[0005] In a first aspect, the present invention provides a polylactic acid composition comprising polylactic acid and a polyester block copolymer, wherein the polyester block copolymer has the general formula ABA, wherein segment A comprises lactic acid units; and segment B comprises randomly arranged caprolactone units and trimethylene carbonate units.

[0006] Preferably, the polyester block copolymer comprises 5%-30% by weight of the total composition, more preferably 10%-25%.

[0007] Preferably, in the polyester block copolymer, the molar percentage of lactic acid units is 5%-33%; the molar percentage of trimethylene carbonate units is 7%-57%; and the molar percentage of caprolactone units is 27%-86%.

[0008] Preferably, in segment B, the molar ratio of caprolactone units to the sum of caprolactone units and trimethylene carbonate units is 40%-90%.

[0009] Preferably, the randomness value of the distribution of caprolactone units and trimethylene carbonate units in segment B is greater than 0.9, and more preferably 0.95-1.1.

[0010] Preferably, in the polyester block copolymer, the molar ratio of lactic acid units to the sum of caprolactone units and trimethylene carbonate units is 5%-50%.

[0011] Preferably, the molecular weight of the polyester block copolymer is greater than 10,000, and more preferably 15,000-100,000.

[0012] In a second aspect, the present invention provides a method for preparing the polylactic acid composition, comprising: melt blending polylactic acid and polyester block copolymer.

[0013] Preferably, the melt blending conditions include: a temperature of 180-210℃, a rotation speed of 30-80 rpm, and a time of 2-5 min.

[0014] Preferably, the method for preparing the polyester block copolymer includes:

[0015] Step 1: Obtain a mixture of caprolactone, trimethylene carbonate, initiator, catalyst, and solvent, and carry out the reaction;

[0016] Step 2: Add lactide and react to obtain a polyester block copolymer.

[0017] Preferably, in step 1, the initiator includes at least one of ethylene glycol and butanediol.

[0018] Preferably, in step 1, the catalyst includes at least one of 1,5,7-triazadicyclo(4.4.0)dec-5-ene, 1,8-diazobisspirocyclo[5.4.0]undec-7-ene and 7-methyl-1,5,7-triazadicyclo[4.4.0]dec-5-ene.

[0019] Preferably, in step 1, the solvent includes at least one of tetrahydrofuran, dichloromethane, toluene, N,N-dimethylformamide, N,N-dimethylacetamide, xylene, diphenyl ether, and acetone.

[0020] Thirdly, the present invention provides an application of the polylactic acid composition, wherein the polylactic acid composition is applied to at least one of injection molded articles, films, and fibers.

[0021] Beneficial effects:

[0022] The polylactic acid (PLA) composition provided by this invention utilizes a polyester block copolymer to toughen and modify PLA. The soft segment of the polyester block copolymer is a random copolymer of caprolactone and trimethylene carbonate. The introduction of trimethylene carbonate disrupts the crystallization of the caprolactone polymer chain, thus making the soft segment softer. The hard segment of the polyester block copolymer is PLA, which improves the compatibility between the polyester block copolymer and PLA. This polyester block copolymer toughens PLA and is also biodegradable; therefore, the entire composition is biodegradable. Attached Figure Description

[0023] Figure 1 The polyester block copolymer of Example 1 provided by the present invention 1 H NMR spectrum.

[0024] Figure 2 Differences in tensile failure of the spline of the composition provided by the present invention. Detailed Implementation

[0025] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0026] In a first aspect, the present invention provides a biodegradable polylactic acid composition with improved toughness, comprising polylactic acid and a polyester block copolymer, wherein the general formula of the polyester block copolymer is ABA, wherein segment A is the two end segments, which are polylactic acid segments including lactic acid units; segment B is the middle segment, which is a random copolymer of caprolactone and trimethylene carbonate, including randomly arranged caprolactone units and trimethylene carbonate units.

[0027] The polylactic acid (PLA) composition provided by this invention utilizes a polyester block copolymer to toughen and modify PLA. The soft segment of the polyester block copolymer is a random copolymer of caprolactone and trimethylene carbonate. The introduction of trimethylene carbonate disrupts the crystallization of the caprolactone polymer chain, thus making the soft segment softer. The hard segment of the polyester block copolymer is PLA, which improves the compatibility between the polyester block copolymer and PLA. This polyester block copolymer toughens PLA and is also biodegradable; therefore, the entire composition is biodegradable.

[0028] In a specific embodiment of the present invention, the mass percentage of the polyester block copolymer, based on the total weight of the composition, is 5%-30%, for example 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc., preferably 10%-25%.

[0029] In a specific embodiment of the present invention, the molar percentage of lactic acid units in the polyester block copolymer ranges from 5% to 33%, for example, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, etc.; the molar percentage of trimethylene carbonate units ranges from 7% to 57%, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, etc.; and the molar percentage of caprolactone units ranges from 27% to 86%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, etc.

[0030] In a specific embodiment of the present invention, in segment B, the molar ratio of caprolactone units to the sum of caprolactone units and trimethylene carbonate units is 40%-90%, for example 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, etc. It should be noted that when the molar ratio of caprolactone units to the sum of caprolactone and trimethylene carbonate units is too high, for example, above 90%, the amount of trimethylene carbonate copolymer is too low. The effect of trimethylene carbonate in disrupting the crystallization of caprolactone polymer segments is limited, and the soft segments are not soft enough. When mixed with polylactic acid, the increase in elongation at break is not significant. When the molar ratio of caprolactone units to the sum of caprolactone and trimethylene carbonate units is too low, for example, below 40%, that is, the proportion of trimethylene carbonate units is above 60%, the soft segments will harden again because the glass transition temperature of trimethylene carbonate is higher than that of caprolactone. This will lead to a decrease in the elongation at break of the block copolymer and polylactic acid composition.

[0031] In a specific embodiment of the present invention, the randomness value of the distribution of caprolactone units and trimethylene carbonate units in segment B is greater than 0.9, preferably 0.95-1.1.

[0032] In a specific embodiment of the present invention, the molar ratio of the total number of all lactic acid units, caprolactone units, and trimethylene carbonate units in the polyester block copolymer is 5%-50%, for example, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, etc., preferably 15%-30%, more preferably 20%-25%.

[0033] In a specific embodiment of the present invention, the molecular weight of the polyester block copolymer is greater than 10,000, preferably 15,000-100,000.

[0034] In this invention, the molecular weight of polylactic acid in the composition is not limited, for example, it can be 20,000-200,000.

[0035] In a second aspect, the present invention provides a method for preparing the above-mentioned toughened biodegradable polylactic acid composition, comprising: melt blending polylactic acid and polyester block copolymer.

[0036] In a specific embodiment of the present invention, the conditions for melt blending include: a temperature of 180-210°C, a rotation speed of 30-80 rpm, and a time of 2-5 min.

[0037] In a specific embodiment of the present invention, the method for preparing the polyester block copolymer includes:

[0038] Step 1: Obtain a mixture of monomer caprolactone, monomer trimethylene carbonate, initiator, catalyst and solvent, and carry out the reaction;

[0039] Step 2: Add lactide and allow the reaction to proceed.

[0040] In a specific embodiment of the present invention, in step 1, the initiator includes at least one of ethylene glycol and butanediol.

[0041] In a specific embodiment of the present invention, in step 1, the catalyst includes at least one of 1,5,7-triazidobicyclo(4.4.0)dec-5-ene, 1,8-diazobispyrocyclo[5.4.0]undec-7-ene and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene.

[0042] In a specific embodiment of the present invention, in step 1, the solvent is at least one selected from tetrahydrofuran, dichloromethane, toluene, N,N-dimethylformamide, N,N-dimethylacetamide, xylene, diphenyl ether, and acetone.

[0043] In this invention, there are no restrictions on the amount of initiator, catalyst, and solvent used, as long as the preparation of polyester block copolymer can be achieved.

[0044] Thirdly, the present invention provides applications of the above-mentioned polylactic acid composition in injection molded products, films, fibers, etc.

[0045] The following detailed description of preferred embodiments of the present invention illustrates the principles of the invention and is not intended to limit the scope of the invention.

[0046] The test conditions are as follows:

[0047] Molecular weight characterization of polyester block copolymers: Analysis was performed using a GPC 1260 Infinity II (Agilent Technologies) gel permeation chromatography system with a 2×PLgel 5µm MIXED-C column (300mm×7.5mm, Agilent Technologies). The solvent and mobile phase were tetrahydrofuran (containing 0.025% antioxidant 2,6-dibutyl-p-cresol), column temperature 40°C, flow rate 1.0 mL / min. Narrow-distribution polystyrene standards were used for universal standardization. The sample concentration was 2 mg / mL. The number-average molecular weight of the samples was determined.

[0048] Nuclear magnetic resonance characterization of polyester block copolymers: performed on an Agilent DD2 600MHz nuclear magnetic resonance spectrometer, using CDCl3 as solvent, at room temperature.

[0049] Tensile test conditions for the composite tensile specimens: The Instron 5965 tensile tester was used. The tensile test was performed at a rate of 50 mm / min at room temperature of 23°C with a clamp spacing of 50 mm. The gauge length was 25 mm when calculating the elongation at break.

[0050] Methods for calculating the proportions of caprolactone (CL), trimethylene carbonate (TMC), and lactic acid (LA) monomers in polyester block copolymers ABA: (e.g.) Figure 1 The NMR spectrum is shown below. 1 The peak with chemical shifts in the 1.90–2.10 ppm range in the 1H NMR spectrum is assigned to the proton on the methylene group in the TMC unit. This peak is selected as the characteristic peak of TMC, and its integrated area is denoted as A. TMC The peak with a chemical shift between 2.20 and 2.45 ppm is attributed to the proton on the methylene group attached to the carbonyl group in the CL unit. This peak is selected as the characteristic peak of CL, and its integrated area is denoted as A. CL The peak with a chemical shift between 5.00 and 5.35 ppm is assigned to the proton on the methine group in the LA unit, and this peak is selected as the characteristic peak of LA. The integrated area is denoted as A. LA The formulas for calculating the molar content of different monomers are as follows:

[0051]

[0052]

[0053]

[0054] Methods for calculating the randomness values ​​of caprolactone (CL) and trimethylene carbonate (TMC) monomers in segment B of block copolymer ABA: Four segmental structures exist in the CL and TMC copolymers: the CL-CL binary sequence consists of two linked caprolactone units; the CL-TMC binary sequence consists of a linked caprolactone unit and a trimethylene carbonate unit; the TMC-CL binary sequence consists of a linked trimethylene carbonate unit and a linked caprolactone unit; and the TMC-TMC binary sequence consists of two linked trimethylene carbonate units. Different sequence structures will affect the proton... 1 The 1H NMR spectrum peaks split, and the binary sequence distribution in the copolymer was calculated using the peaks in the 4.0–4.3 ppm region of the 1H NMR spectrum. For example... Figure 1 As shown, the peak at 4.00–4.10 ppm is the proton peak (a) of the methylene group bonded to the oxygen atom in the caprolactone unit of the CL-CL sequence, and the integrated area is denoted as A. a The peak at 4.10–4.15 ppm is the proton peak of the methylene group bonded to the oxygen atom in the caprolactone unit of the TMC-CL sequence (b), and the integrated area is denoted as A. b The peak at 4.15–4.19 ppm is the proton peak (c) of the methylene group in the TMC unit of the CL-TMC sequence, which is bonded to an oxygen atom and located near the CL unit. The integrated area is denoted as A. c The peaks at 4.19–4.27 ppm represent the proton peaks (c') of two methylene groups (d) attached to oxygen atoms in the TMC unit of the TMC-TMC sequence and the methylene group (c') attached to oxygen atoms and far from the CL unit in the TMC unit of the CL-TMC sequence. The integrated area is denoted as A. d+c’ The probability P of connecting another structural unit to a CL or TMC structural unit. TMC-CL and P CL-TMC It can be obtained from the following formula:

[0055]

[0056]

[0057] Randomness R = P TMC-CL +P CL-TMC ,

[0058] Wherein, the length of the number-mean sequence L nCL and L nTMC Can be made by P TMC-CL and P CL-TMC L is obtained by reciprocal. nCL and L nTMCThe larger the value, the stronger the block copolymerization; conversely, the smaller the value, the stronger the alternation copolymerization. The randomness R value reflects the type of copolymer: R=1 indicates that the CL and TMC in the copolymer are randomly distributed; R=0 indicates that the polymer is a blend of homopolymers or a long block copolymer; and R=2 indicates a completely alternating sequence distribution.

[0059] The preparation conditions for the composition are as follows:

[0060] Melt blending conditions for polylactic acid and polyester block copolymers: Blending was carried out using a Haake polylab OS small internal mixer at a temperature of 190℃, a mixing speed of 50 r / min, and a mixing time of 3 min.

[0061] Preparation conditions for the tensile test strips of the composition: A CAVER 4533 laboratory hot press was used, with a PTFE membrane as the separator. The pressure was 3000 kgs, preheated for 10 min, held for 3 min, and then cold-pressed at 20°C for 3 min. A dumbbell-shaped sample mold was used for preparation. The dumbbell-shaped sample was 1 mm thick, with a width and length of 6 mm and 30 mm for the narrow parallel section, an end width of 10 mm, and a total sample length of 100 mm.

[0062] Preparation Example 1

[0063] Preparation method of polyester block copolymer (PLA-P(CL-co-TMC)-PLA): In an ampoule after high-temperature dehydration, monomers caprolactone (CL), trimethylene carbonate (TMC), ethylene glycol as initiator, and 1,5,7-triazidobicyclo(4.4.0)dec-5-ene and tetrahydrofuran as catalysts are added separately under nitrogen protection. The temperature of the heating stirrer is adjusted to 25℃, and the reaction is stirred for 24 hours. Then, lactide (LA) is added, and the reaction is carried out for 8 hours. The reaction solution is collected, and an appropriate amount of benzoic acid is added to quench the reaction. Excess methanol is added to precipitate the polymer. The precipitate is collected by centrifugation and then vacuum dried for 48 hours to obtain pure block copolymer (PLA-P(CL-co-TMC)-PLA). The specific amounts used are adjusted according to the desired block copolymer structure ratio.

[0064] Preparation Example 2

[0065] Preparation method of polyester block copolymer (PLA-PCL-PLA): In an ampoule after high-temperature dehydration, under nitrogen protection, monomer caprolactone (CL), initiator ethylene glycol, catalyst 1,5,7-triazidobicyclo(4.4.0)dec-5-ene and tetrahydrofuran were added respectively. The temperature of the heating stirrer was adjusted to 25℃ and the reaction was stirred for 24h. Then, lactide (LA) was added. After reacting for 8h, the reaction solution was collected, and an appropriate amount of benzoic acid was added to quench the reaction. Excess methanol was added to precipitate the polymer. After centrifugation, the precipitate was collected and vacuum dried for 48h to obtain pure block copolymer (PLA-PCL-PLA).

[0066] Preparation Example 3

[0067] Preparation method of polycaprolactone-polytrimethylene carbonate block copolymer (PCL-PTMC): In an ampoule after high-temperature dehydration, caprolactone (CL), benzyl alcohol as an initiator, 1,5,7-triazidobicyclo(4.4.0)dec-5-ene as a catalyst, and tetrahydrofuran were added separately under nitrogen protection. The temperature of the heating stirrer was adjusted to 25℃, and the reaction was stirred for 24 h. Then, trimethylene carbonate (TMC) and tetrahydrofuran were added. After reacting for another 24 h, the reaction solution was collected, and an appropriate amount of benzoic acid was added to quench the reaction. Excess methanol was added to precipitate the polymer. After centrifugation, the precipitate was collected and vacuum dried for 48 h to obtain the pure block copolymer PCL-PTMC.

[0068] Preparation Example 4

[0069] Preparation method of polyester block copolymer (PLA-P(CL-co-TMC)): In an ampoule after high-temperature dehydration, monomers caprolactone (CL), trimethylene carbonate (TMC), initiator benzyl alcohol, catalyst 1,5,7-triazidobicyclo(4.4.0)dec-5-ene, and tetrahydrofuran were added separately under nitrogen protection. The temperature of the heating stirrer was adjusted to 25℃, and the reaction was stirred for 24 h. Then lactide (LA) was added. After reacting for 8 h, the reaction solution was collected, and an appropriate amount of benzoic acid was added to quench the reaction. Excess methanol was added to precipitate the polymer. After centrifugation, the precipitate was collected and vacuum dried for 48 h to obtain pure block copolymer PLA-P(CL-co-TMC).

[0070] Example 1

[0071] 92% polylactic acid (Total Luminy L130, Thailand) and 8% polyester block copolymer S1 (prepared using the method in Preparation Example 1) were melt-blended at 190°C. The resulting dumbbell-shaped specimens were then pressed at 190°C, and their tensile properties were tested. GPC analysis showed that the molecular weight of polyester block copolymer S1 was 2.5 x 10⁻⁶. 4 NMR analysis revealed that caprolactone units comprised 51% of the total caprolactone and trimethylene carbonate units in S1, while lactic acid units comprised 8%. The randomness value for the distribution of caprolactone and trimethylene carbonate monomers in S1 was 0.95. Details are shown in Table 1. Performance parameters are shown in Table 2.

[0072] Example 2

[0073] 90% polylactic acid (Total Luminy L130, Thailand) and 10% polyester block copolymer S2 (prepared using the method in Preparation Example 1) were melt-blended at 190°C. The resulting dumbbell-shaped specimens were then pressed at 190°C, and their tensile properties were tested. The molecular weight of the polyester block copolymer S2, as determined by GPC, was 1.8 x 10⁻⁶. 4 NMR analysis revealed that caprolactone units accounted for 50% of the total number of caprolactone and trimethylene carbonate units in S2, while lactic acid units accounted for 23%. The randomness value of the distribution of caprolactone and trimethylene carbonate monomers in S2 was 1.04. Details are shown in Table 1. Performance parameters are shown in Table 2.

[0074] Example 3

[0075] 80% polylactic acid (Total Luminy L130, Thailand) and 20% polyester block copolymer S3 (prepared using the method in Preparation Example 1) were melt-blended at 190°C. The resulting dumbbell-shaped specimens were then pressed at 190°C, and their tensile properties were tested. The molecular weight of polyester block copolymer S3 was determined to be 1.6 x 10⁻⁶ by GPC testing. 4 NMR analysis revealed that caprolactone units comprised 49% of the total caprolactone and trimethylene carbonate units in S3, while lactic acid units comprised 8%. The randomness value for the distribution of caprolactone and trimethylene carbonate monomers in S3 was 1.01. Details are shown in Table 1. Performance parameters are shown in Table 2.

[0076] Example 4:

[0077] 93% polylactic acid (Total Luminy L130, Thailand) and 7% polyester block copolymer S4 (prepared using the method in Preparation Example 1) were melt-blended at 190°C. The resulting dumbbell-shaped specimens were then pressed at 190°C, and their tensile properties were tested. The molecular weight of the polyester block copolymer S4, as determined by GPC, was 1.9 x 10⁻⁶. 4 NMR analysis revealed that caprolactone units accounted for 90% of the total number of caprolactone and trimethylene carbonate units in S4, while lactic acid units accounted for 6%. The randomness value of the distribution of caprolactone and trimethylene carbonate monomers in S4 was 1.06. Details are shown in Table 1. Performance parameters are shown in Table 2.

[0078] Example 5

[0079] This embodiment is basically the same as Example 3, except that the mass percentage of polyester block copolymer S3 in the composition is 15%.

[0080] Example 6

[0081] This composition is essentially the same as Example 3, except that the mass percentage of polyester block copolymer S3 in the composition is 25%.

[0082] Comparative Example 1:

[0083] Polylactic acid (Total Luminy L130 from Thailand) was melt-blended in an internal mixer at 190°C, and then pressed into dumbbell-shaped specimens at 190°C to test their tensile properties. The performance parameters are shown in Table 2. Figure 2 The difference between the tensile specimens of Example 2 and Comparative Example 1 after tensile fracture is shown. Comparative Example 1 shows brittle fracture, while Example 2 shows ductile fracture.

[0084] Comparative Example 2

[0085] Polylactic acid (Total Luminy L130, Thailand) was melt-blended with 10% of polyester block copolymer D2 (prepared using the method in Preparation Example 1) at 190°C. The resulting dumbbell-shaped specimens were then pressed at 190°C, and their tensile properties were tested. GPC analysis showed that the molecular weight of polyester block copolymer D2 was 7000. NMR analysis showed that the proportion of caprolactone units in D2 to the total number of caprolactone and trimethylene carbonate units was 50%, and the proportion of lactic acid units in D2 to the total number of caprolactone and trimethylene carbonate units was 23%. The randomness value of the distribution of caprolactone and trimethylene carbonate monomers in D2 was 1.03. Details are shown in Table 1. Performance parameters are shown in Table 2.

[0086] Comparative Example 3:

[0087] This comparative example is basically the same as Example 1, except that the mass percentage of polyester block copolymer S1 in the composition is 4%.

[0088] Comparative Example 4:

[0089] Polylactic acid (Total Luminy L130, Thailand) was melt-blended with 7% polyester block copolymer D4 (prepared using the method in Preparation Example 2) at 190°C. The resulting dumbbell-shaped specimens were then pressed at 190°C, and their tensile properties were tested. GPC analysis showed that the molecular weight of polyester block copolymer D4 was 1.7 x 10⁻⁶. 4 NMR analysis revealed that block copolymer D4 contained only caprolactone units; the proportion of lactic acid units to caprolactone units in D4 was 4%. Details are shown in Table 1. Performance parameters are shown in Table 2.

[0090] Comparative Example 5:

[0091] Polylactic acid (Total Luminy L130, Thailand) was melt-blended with 8% of polyester block copolymer D5 (prepared using the method in Preparation Example 1) at 190°C. The resulting dumbbell-shaped specimens were then pressed at 190°C, and their tensile properties were tested. The molecular weight of polyester block copolymer D5, as determined by GPC, was 2.5 x 10⁻⁶. 4 NMR analysis revealed that caprolactone units comprised 28% of the total caprolactone and trimethylene carbonate units in D5, while lactic acid units comprised 8%. The randomness value for the distribution of caprolactone and trimethylene carbonate monomers in D5 was 0.71. Details are shown in Table 1. Performance parameters are shown in Table 2.

[0092] Comparative Example 6:

[0093] Polylactic acid (Total Luminy L130, Thailand) was melt-blended with 7% of polyester block copolymer D6 (prepared using the method in Preparation Example 3) at 190°C. The resulting dumbbell-shaped specimens were then pressed at 190°C, and their tensile properties were tested. Polyester block copolymer D6 is a two-block copolymer of polycaprolactone and polytrimethylene carbonate, and its molecular weight, determined by GPC, is 1.9 x 10⁻⁶. 4 NMR analysis revealed that caprolactone units accounted for 37% of the total number of caprolactone and trimethylene carbonate units in D6. The randomness value of the distribution of caprolactone and trimethylene carbonate monomers in D6 was 0.24. See Table 1 for details.

[0094] Comparative Example 7:

[0095] Polylactic acid (Total Luminy L130, Thailand) was melt-blended with 8% polyester block copolymer D7 at 190°C, and then dumbbell-shaped specimens were obtained by pressing at 190°C. The tensile properties were then tested. GPC analysis showed that the molecular weight of polyester block copolymer D7 was 2.5 x 10⁻⁶. 4 NMR analysis revealed that caprolactone units accounted for 49% of the total number of caprolactone and trimethylene carbonate units in D7, while lactic acid units accounted for 55%. The randomness value of the distribution of caprolactone and trimethylene carbonate monomers in D7 was 1.02. See Table 1 for details.

[0096] Comparative Example 8:

[0097] Polylactic acid (Total Luminy L130, Thailand) was melt-blended with 8% polyester block copolymer D8 at 190°C, and then dumbbell-shaped specimens were obtained by pressing at 190°C. The tensile properties were then tested. GPC analysis showed that the molecular weight of polyester block copolymer D8 was 2.4 x 10⁻⁶. 4 NMR analysis revealed that caprolactone units accounted for 50% of the total number of caprolactone and trimethylene carbonate units in D8, while lactic acid units accounted for 2%. The randomness value of the distribution of caprolactone and trimethylene carbonate monomers in D8 was 1.02. See Table 1 for details.

[0098] Comparative Example 9

[0099] This comparative example is basically the same as Example 1, except that the polyester block copolymer D9 is PLA-P (CL-co-TMC) prepared in Preparation Example 4, with a molecular weight of 2.4 x 10⁻⁶. 4 The proportion of caprolactone units to the total number of caprolactone and trimethylene carbonate units was 50%; the proportion of lactic acid units to the total number of caprolactone and trimethylene carbonate units was 8%. The randomness value of the distribution of the two monomers, caprolactone and trimethylene carbonate, was 1.02.

[0100] Table 1. Molar content of each monomer in each polyester block copolymer ABA, and number mean sequence length and randomness value of the distribution of caprolactone and trimethylene carbonate monomers in segment B.

[0101]

[0102]

[0103] Table 2. Elongation at break and tensile stress of spline tensile curves

[0104] Elongation at break (%) Tensile stress (MPa) Example 1 18 51.7 Example 2 32 46.4 Example 3 54 38.8 Example 4 14 46.1 Example 5 38 45.6 Example 6 62 34.1 Comparative Example 1 8 59.9 Comparative Example 2 9 51.4 Comparative Example 3 7 56.7 Comparative Example 4 9 51.2 Comparative Example 5 7 55.8 Comparative Example 6 9 51.6 Comparative Example 7 7 53.6 Comparative Example 8 7 54.6 Comparative Example 9 10 51.0

[0105] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A polylactic acid composition, characterized in that, It includes polylactic acid and polyester block copolymers, wherein the general formula of the polyester block copolymer is ABA, wherein, Section A includes lactate units; Segment B consists of randomly arranged caprolactone units and trimethylene carbonate units.

2. The composition according to claim 1, characterized in that, The polyester block copolymer comprises 5%-30% by weight of the total composition, preferably 10%-25%.

3. The composition according to claim 1 or 2, characterized in that, In the polyester block copolymer The molar percentage of lactic acid units is 5%-33%; And / or, the molar percentage of trimethylene carbonate units is 7%-57%; And / or, the molar percentage content of caprolactone units is 27%-86%.

4. The composition according to any one of claims 1-3, characterized in that, In segment B, the molar ratio of caprolactone units to the sum of caprolactone units and trimethylene carbonate units is 40%-90%.

5. The composition according to any one of claims 1-4, characterized in that, The randomness value of the distribution of caprolactone units and trimethylene carbonate units in segment B is greater than 0.9, preferably 0.95-1.

1.

6. The composition according to any one of claims 1-5, characterized in that, In the polyester block copolymer, the molar ratio of lactic acid units to the sum of caprolactone units and trimethylene carbonate units is 5%-50%.

7. The composition according to any one of claims 1-6, characterized in that, The molecular weight of the polyester block copolymer is greater than 10,000, preferably 15,000-100,000.

8. A method for preparing a polylactic acid composition according to any one of claims 1-7, characterized in that, include: Polylactic acid and polyester block copolymers are melt-blended. Preferably, the melt blending conditions include: a temperature of 180-210℃, a rotation speed of 30-80 rpm, and a time of 2-5 min.

9. The preparation method according to claim 8, characterized in that, The method for preparing the polyester block copolymer includes: Step 1: Obtain a mixture of caprolactone, trimethylene carbonate, initiator, catalyst, and solvent, and carry out the reaction; Step 2: Add lactide and react to obtain a polyester block copolymer; Preferably, in step 1, the initiator includes at least one of ethylene glycol and butanediol; Preferably, in step 1, the catalyst includes at least one of 1,5,7-triazadicyclo(4.4.0)dec-5-ene, 1,8-diazobisspirocyclo[5.4.0]undec-7-ene, and 7-methyl-1,5,7-triazadicyclo[4.4.0]dec-5-ene; Preferably, in step 1, the solvent includes at least one of tetrahydrofuran, dichloromethane, toluene, N,N-dimethylformamide, N,N-dimethylacetamide, xylene, diphenyl ether, and acetone.

10. The application of a polylactic acid composition according to any one of claims 1-7 or a polylactic acid composition prepared by the method according to any one of claims 8-9, characterized in that, The polylactic acid composition is used in at least one of injection molded products, films, and fibers.

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