Polylactic acid copolymer as well as preparation method and application thereof

Abstract

The invention relates to a polylactic acid copolymer as well as a preparation method and application thereof. Polymeric monomers of the polylactic acid copolymer provided by the invention comprise lactic acid, polyol and polyacid. The preparation method of the polylactic acid copolymer provided by the invention comprises the following steps: in an inert atmosphere, carrying out polymerization reaction on polymeric monomers in the presence of a catalyst to obtain the polylactic acid copolymer, and the polymeric monomers comprise lactic acid, polyol and polyacid. The polylactic acid copolymer provided by the invention is relatively high in molecular weight, the hardness of the product can be adjusted according to needs, and meanwhile, the preparation method also has the characteristics of low production cost, convenience in operation and large-scale production.

Description

Technical Field

[0001] The present application relates to the technical field of polymer materials, and in particular to a polylactic acid copolymer and a preparation method and application thereof. Background Art

[0002] In recent years, the research interest in biodegradable polymer materials has become increasingly strong at home and abroad. Biodegradable polymer materials involve various aspects such as industrial and agricultural production, medical fields, etc. Polylactic acid (PLA) is a popular biodegradable aliphatic polyester. PLA has good biodegradability and processing performance, is renewable, has good biocompatibility, and has a high melting temperature. It can also be made into fibers by melt spinning. The raw material lactic acid can be prepared by fermentation of starch, etc. The final decomposition products of the prepared PLA in nature are carbon dioxide and water, which does not pollute the ecological environment and is a green and environmentally friendly polymer.

[0003] There are usually two ways to synthesize polylactic acid: direct polycondensation and ring-opening polymerization. Polylactic acid prepared by the lactide ring-opening polymerization process has high molecular weight and controllable operating conditions, and has been used in industrial production. However, the production process of the ring-opening polymerization method is lengthy and complicated to operate, especially in terms of the purification of lactide, which leads to the high price of polylactic acid, thus limiting the industrial production of polylactic acid. Direct polycondensation methods include solution polymerization, melt polycondensation, melt-solid phase polycondensation, etc. The solution polycondensation method usually uses solvents such as diphenyl ether with high boiling points for water-carrying agents. Although this method can prepare high molecular weight polylactic acid, there are problems with solvent recovery and difficulty in removing solvents from the product. The melt polycondensation method has the problem that the water generated in the late stage of polycondensation is difficult to discharge from the system, and polylactic acid and its oligomers are easily decomposed at high temperature, resulting in a low molecular weight of polylactic acid. The product of the melt polycondensation of lactic acid can be subjected to solid phase condensation to increase the molecular weight, but how to effectively reduce the vapor pressure of the system and inhibit the side reaction of lactide generation is very critical.

[0004] Although there are improvements on the synthesis method of polylactic acid in the prior art, there are still problems such as harsh reaction conditions, many side reactions, low molecular weight of the prepared polylactic acid, and high cost. Summary of the invention

[0005] In order to solve the problems existing in the existing production process, the present application proposes a polylactic acid copolymer and a preparation method and application thereof.

[0006] In a first aspect, the present application provides a polylactic acid copolymer, wherein the polymerization monomers thereof include lactic acid, polyol and polyacid.

[0007] In some embodiments, the mass content of the structural unit derived from the lactic acid monomer is 55-99% (w / w) based on the mass of the polylactic acid copolymer. In some embodiments, the mass content of the structural unit derived from the lactic acid monomer is 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or any value therebetween.

[0008] The polylactic acid copolymer of the present application uses lactic acid, polyol and polyacid as polymerization monomers, which not only has a higher molecular weight, but also can adjust the hardness of the product according to actual needs, thus better meeting the material processing requirements.

[0009] In some embodiments, in the polymerized monomer, the molar ratio of hydroxyl to carboxyl in the polyol and the polyacid is (1-1.5):1, for example, 1.11:1, 1.13:1, 1.15:1, 1.17:1, 1.19:1, 1.2:1, 1.21:1, 1.23:1, 1.25:1, 1.27:1, 1.29:1, 1.3:1, 1.31:1, 1.33:1, 1.35:1, 1.37:1, 1.39:1, 1.4:1, 1.41:1, 1.43:1, 1.45:1, 1.47:1, 1.49:1 or any value therebetween.

[0010] In some embodiments, the polyol is selected from one or more of C2-C8 divalent or polyvalent fatty alcohols, polyether polyols and polyester polyols. In some embodiments, the polyol is selected from one or more of ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, hexylene glycol, glycerol, trimethylolpropane, pentaerythritol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran, polycaprolactone polyol and polycarbonate polyol.

[0011] In some embodiments, the polyacid is selected from one or more of a C2-C12 dibasic organic acid and a C4-C12 tribasic organic acid. In some embodiments, the polyacid is selected from one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, undecanedicarboxylic acid, dodecanedioic acid, malic acid, citric acid, phthalic acid and trimesic acid.

[0012] In some embodiments, the lactic acid is selected from one or more of L-lactic acid, D-lactic acid and DL-lactic acid.

[0013] In some embodiments, the weight average molecular weight of the polylactic acid copolymer is 80,000-200,000, for example, 90,000, 100,000, 105,000, 110,000, 115,000, 120,000, 125,000, 130,000, 135,000, 140,000, 145,000, 150,000, 155,000, 160,000, 165,000, 170,000, 175,000, 180,000, 185,000, 190,000, 195,000 or any value therebetween.

[0014] In some embodiments, the number average molecular weight of the polylactic acid copolymer is 20,000-60,000, for example, 21,000, 23,000, 25,000, 27,000, 29,000, 30,000, 31,000, 33,000, 35,000, 37,000, 39,000, 40,000, 41,000, 43,000, 45,000, 47,000, 49,000, 50,000, 51,000, 53,000, 55,000, 57,000, 59,000 or any value therebetween.

[0015] In a second aspect, the present application provides a method for preparing a polylactic acid copolymer, comprising: in an inert atmosphere, allowing polymerization monomers to undergo a polymerization reaction in the presence of a catalyst to obtain the polylactic acid copolymer, wherein the polymerization monomers include lactic acid, a polyol, and a polyacid.

[0016] The present application adopts lactic acid, polyol and polyacid as polymerization monomers, and obtains polylactic acid copolymer by dehydration polymerization in the presence of a catalyst. Polyol and polyacid are added to copolymerize with lactic acid to form a copolymer, so that the toughness of the polylactic acid material is improved, and it is more conducive to film formation during the stirring process, thereby accelerating the removal of water molecules, improving polymerization efficiency, and increasing the molecular weight of the polymer. The polymer obtained at the same time can better meet the material processing requirements. The preparation method of the present invention also has the characteristics of low production cost, convenient operation, and large-scale production. The prepared polylactic acid copolymer can be applied to food packaging, tableware, ground film, shopping bags, etc.

[0017] In some embodiments, based on the mass of the polymerized monomer, the mass content of the polyol is 0.5%-25%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or any value therebetween. In some embodiments, the mass content of the polyol is 1%-15%. In some embodiments, the mass content of the polyol is 3%-10%.

[0018] In some embodiments, based on the mass of the polymerized monomer, the mass content of the polyacid is 0.5%-25%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or any value therebetween. In some embodiments, the mass content of the polyacid is 1%-15%. In some embodiments, the mass content of the polyacid is 3%-10%.

[0019] In some embodiments, in the polymerized monomer, the molar ratio of hydroxyl to carboxyl in the polyol and the polyacid is (1-1.5):1, for example, 1.11:1, 1.13:1, 1.15:1, 1.17:1, 1.19:1, 1.2:1, 1.21:1, 1.23:1, 1.25:1, 1.27:1, 1.29:1, 1.3:1, 1.31:1, 1.33:1, 1.35:1, 1.37:1, 1.39:1, 1.4:1, 1.41:1, 1.43:1, 1.45:1, 1.47:1, 1.49:1 or any value therebetween.

[0020] In some embodiments, based on the mass of the polymerized monomer, the mass content of the catalyst is 50ppm-5000ppm, for example, 100ppm, 300ppm, 500ppm, 700ppm, 1000ppm, 1100ppm, 1300ppm, 1500ppm, 1700ppm, 2000ppm, 2100ppm, 2300ppm, 2500ppm, 2700ppm, 3000ppm, 3500ppm, 4000ppm or 4500ppm. In some embodiments, the mass content of the catalyst is 200ppm-3000ppm.

[0021] In some embodiments, the polyol is selected from one or more of C2-C8 divalent or polyvalent fatty alcohols, polyether polyols and polyester polyols. In some embodiments, the polyol is selected from one or more of ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, hexylene glycol, glycerol, trimethylolpropane, pentaerythritol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran, polycaprolactone polyol and polycarbonate polyol.

[0022] In some embodiments, the polyacid is selected from one or more of a C2-C12 dibasic organic acid and a C4-C12 tribasic organic acid. In some embodiments, the polyacid is selected from one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, undecanedicarboxylic acid, dodecanedioic acid, malic acid, citric acid, phthalic acid and trimesic acid.

[0023] In some embodiments, the lactic acid is selected from one or more of L-lactic acid, D-lactic acid and DL-lactic acid.

[0024] In some embodiments, the catalyst is selected from one or more of zinc-based catalysts, titanium-based catalysts, bismuth-based catalysts, and tin-based catalysts. In some embodiments, the catalyst is selected from one or more of stannous octoate, zinc acetate, tetrabutyl titanate, and stannous chloride.

[0025] In some embodiments, the polymerization temperature is 120°C-200°C, for example, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C or any value therebetween. In some embodiments, the polymerization temperature is 130°C-185°C.

[0026] In some embodiments, the polymerization reaction time is 2h-50h, for example, 3h, 6h, 8h, 12h, 16h, 20h, 22h, 24h, 28h, 32h, 36h, 40h, 44h, 48h or any value therebetween. In some embodiments, the polymerization reaction time is 5h-30h.

[0027] In some embodiments, the polymerization reaction is carried out under vacuum. In some embodiments, the vacuum degree is 0.1 kPa-4.0 kPa, for example, 0.3 kPa, 0.5 kPa, 0.7 kPa, 1.0 kPa, 1.3 kPa, 1.5 kPa, 1.7 kPa, 2.0 kPa, 2.3 kPa, 2.5 kPa, 2.7 kPa, 3.0 kPa, 3.3 kPa, 3.5 kPa, 3.7 kPa or any value therebetween. In some embodiments, the vacuum degree is 0.3 kPa-3.0 kPa.

[0028] In some embodiments, the preparation method of the polylactic acid copolymer provided in the present application comprises the following steps:

[0029] S1: in an inert atmosphere, allowing the polymerization monomer to undergo a first polymerization reaction in the presence of a catalyst to obtain a first polymerization reactant;

[0030] S2: In an inert atmosphere, subjecting the first polymer reactant in step S1 to a second polymerization reaction to obtain the polylactic acid copolymer.

[0031] In some embodiments, in step S1, the temperature of the first polymerization reaction is 120°C-160°C, for example, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C or 155°C. In some embodiments, in step S1, the temperature of the first polymerization reaction is 130°C-150°C.

[0032] In some embodiments, in step S1, the first polymerization reaction is carried out under vacuum conditions. In some embodiments, in step S1, the vacuum degree is 1.0 kPa-4.0 kPa, such as 1.3 kPa, 1.5 kPa, 1.7 kPa, 2.0 kPa, 2.3 kPa, 2.5 kPa, 2.7 kPa, 3.0 kPa, 3.3 kPa, 3.5 kPa, 3.7 kPa or any value therebetween. In some embodiments, in step S1, the vacuum degree is 2.0 kPa-3.0 kPa.

[0033] In some embodiments, in step S1, the first polymerization reaction time is 2h-20h, for example, 3h, 6h, 8h, 12h or 16h. In some embodiments, in step S1, the first polymerization reaction time is 8h-14h.

[0034] In some embodiments, in step S2, the temperature of the second polymerization reaction is 160°C-200°C, for example, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C or any value therebetween. In some embodiments, in step S2, the temperature of the second polymerization reaction is 175°C-185°C.

[0035] In some embodiments, in step S2, the second polymerization reaction is carried out under vacuum conditions. In some embodiments, in step S2, the vacuum degree is less than or equal to 1.0 kPa, such as 0.3 kPa, 0.5 kPa or 0.7 kPa. In some embodiments, in step S2, the vacuum degree is less than or equal to 0.5 kPa, such as 0.1 kPa, 0.2 kPa or 0.4 kPa.

[0036] In some embodiments, in step S2, the second polymerization reaction time is 2h-20h, for example, 3h, 6h, 8h, 12h or 16h. In some embodiments, in step S2, the second polymerization reaction time is 6h-14h.

[0037] In the present application, the inert atmosphere is provided by nitrogen and / or argon.

[0038] In some embodiments, the preparation method of the polylactic acid copolymer of the present application comprises the following specific steps:

[0039] Lactic acid, polyol, polyacid and catalyst are added into a reaction kettle, wherein the polyol accounts for 1wt%-25wt% of the total feed amount, and the polyacid accounts for 1wt%-25wt% of the total feed amount. Dehydration polymerization is first carried out at a temperature of 120°C-160°C and a vacuum degree of 1kpa-4kpa, and then dehydration polymerization is continued at a temperature of 160°C-200°C and a vacuum degree of less than or equal to 1kpa to obtain a polylactic acid copolymer product.

[0040] In a third aspect, the present application provides the use of the polylactic acid copolymer described in the first aspect or the polylactic acid copolymer prepared by the preparation method described in the second aspect in food containers, tableware and packaging, film bag products or injection molded tableware.

[0041] In some embodiments, the film bag product includes mulch film such as agricultural mulch film, garbage bag, etc.

[0042] Compared with the prior art, the advantages of this application are:

[0043] (1) The present application uses lactic acid, polyol, polyacid and catalyst as raw materials, and obtains polylactic acid copolymer through dehydration polymerization. The synthesized polylactic acid copolymer not only has a high molecular weight, but also can adjust the hardness of the product according to needs.

[0044] (2) The preparation method of the present application has the characteristics of low production cost, convenient operation, and large-scale production.

[0045] (3) The polylactic acid copolymer of the present application can be used in food containers, tableware and packaging, film bag products, injection molded tableware, etc. DETAILED DESCRIPTION

[0046] The preferred embodiments of the present application will be described in detail below in conjunction with the examples. It should be understood that the following examples are provided only for the purpose of illustration and are not intended to limit the scope of the present application. Various modifications and replacements made to the present application by those skilled in the art without departing from the purpose and spirit of the present application are considered to be the technical scope of the present application.

[0047] In the present application, the molecular weight of the polylactic acid copolymer was tested by gel permeation chromatography (GPC).

[0048] Example 1

[0049] Add 500g of polymerized monomer L-lactic acid, 6g of trimethylolpropane and 8g of adipic acid and 0.5g of catalyst stannous octoate into the reactor, evacuate and replace with nitrogen once, and start stirring. In the polymerized monomer, the molar ratio of the total number of hydroxyl groups to the total number of carboxyl groups in trimethylolpropane and adipic acid is 1.23:1. The reactor temperature is raised to 140°C, and decompression and dehydration are carried out for 8h under 2kpa vacuum conditions. Then, the temperature is continued to rise to 180°C under 0.3kpa vacuum conditions, and dehydration and polymerization are continued for 9h to obtain a polylactic acid copolymer product.

[0050] The GPC method measured the weight average molecular weight Mw of the polylactic acid copolymer product to be 156,000, and the number average molecular weight Mn to be 36,000.

[0051] Example 2

[0052] Add 500g of polymerized monomer L-lactic acid, 35g of trimethylolpropane and 42g of succinic acid and 0.58g of catalyst stannous octoate into the reactor, evacuate and replace with nitrogen twice, and start stirring. In the polymerized monomer, the molar ratio of total hydroxyl group to total carboxyl group in trimethylolpropane and succinic acid is 1.1:1. The reactor temperature is raised to 150°C, and decompression and dehydration are carried out for 8h under 2kpa vacuum conditions. Then, the temperature is continued to rise to 185°C under 0.3kpa vacuum conditions, and dehydration and polymerization are continued for 11h to obtain a polylactic acid copolymer product.

[0053] The GPC method measured the weight average molecular weight Mw of the polylactic acid copolymer product to be 135,000, and the number average molecular weight Mn to be 32,000.

[0054] Example 3

[0055] Add 500g of polymerized monomer L-lactic acid, 80g of trimethylolpropane, 110g of terephthalic acid and 1.75g ​​of catalyst zinc acetate into the reactor, evacuate and replace with nitrogen once, and start stirring. In the polymerized monomer, the molar ratio of total hydroxyl group to total carboxyl group in trimethylolpropane and terephthalic acid is 1.35:1. The reactor temperature is raised to 160°C, and decompression dehydration polymerization is carried out under 2kpa vacuum conditions for 10h. Then, under 0.3kpa vacuum conditions, continue to heat to 185°C, and continue dehydration polymerization for 13h to obtain a polylactic acid copolymer product.

[0056] The GPC method measured the weight average molecular weight Mw of the polylactic acid copolymer product to be 142,000, and the number average molecular weight Mn to be 37,000.

[0057] Example 4

[0058] Add 500g of polymerized monomers L-lactic acid, 35g of 1,4-butanediol and 40g (0.150mol) of succinic acid and 1.65g of catalyst zinc acetate into the reactor, evacuate and replace with nitrogen three times, and start stirring. In the polymerized monomers, the molar ratio of total hydroxyl groups to total carboxyl groups in 1,4-butanediol and succinic acid is 1.15:1. The reactor temperature is raised to 150°C, and decompression and dehydration are carried out for 8h under 2kpa vacuum conditions. Then, under 0.3kpa vacuum conditions, continue to heat to 175°C, and continue dehydration and polymerization for 11h to obtain a polylactic acid copolymer product.

[0059] The GPC method measured the weight average molecular weight Mw of the polylactic acid copolymer product to be 147,000, and the number average molecular weight Mn to be 29,000.

[0060] Example 5

[0061] Add 500g of polymerized monomer L-lactic acid, 20g of pentaerythritol and 30g of succinic acid and 1.65g of catalyst tetrabutyl titanate into the reactor, evacuate and replace with nitrogen once, and start stirring. In the polymerized monomer, the molar ratio of total hydroxyl to total carboxyl in pentaerythritol and succinic acid is 1.16:1. The reactor temperature is raised to 150°C, and decompression and dehydration are carried out under 2kpa vacuum conditions for 9h. Then, under 0.4kpa vacuum conditions, continue to heat to 180°C, and continue dehydration and polymerization for 12h to obtain a polylactic acid copolymer product.

[0062] The GPC method measured the weight average molecular weight Mw of the polylactic acid copolymer product to be 186,000, and the number average molecular weight Mn to be 51,000.

[0063] Example 6

[0064] Add 500g of polymerized monomer L-lactic acid, 100g of polycarbonate polyol (molecular weight 500), 18g of succinic acid and 1.3g of catalyst tetrabutyl titanate into the reactor, evacuate and replace with nitrogen twice, and start stirring. In the polymerized monomer, the molar ratio of total hydroxyl to total carboxyl in polycarbonate polyol (molecular weight 500) and succinic acid is 1.31:1. The reactor temperature is raised to 150°C, and decompression and dehydration are carried out under 2kpa vacuum conditions for 9h. Then, under 0.5kpa vacuum conditions, continue to heat to 190°C, and continue dehydration and polymerization for 16h to obtain a polylactic acid copolymer product.

[0065] The GPC method measured the weight average molecular weight Mw of the polylactic acid copolymer product to be 175,000, and the number average molecular weight Mn to be 48,000.

[0066] Example 7

[0067] Add 500g of polymerized monomers L-lactic acid, 50g of 1,6-hexanediol and 60g of citric acid and 0.3g of catalyst stannous chloride to the reactor, evacuate and replace with nitrogen once, and start stirring. In the polymerized monomers, the molar ratio of total hydroxyl to total carboxyl in 1,6-hexanediol and citric acid is 1.37:1. The reactor temperature is raised to 140°C, and decompression and dehydration are carried out for 8h under 2kpa vacuum conditions. Then, under 0.3kpa vacuum conditions, continue to heat to 180°C, and continue dehydration and polymerization for 9h to obtain a polylactic acid copolymer product.

[0068] The GPC method measured the weight average molecular weight Mw of the polylactic acid copolymer product to be 154,000, and the number average molecular weight Mn to be 38,000.

[0069] Example 8

[0070] Add 500g of polymerized monomer L-lactic acid, 180g of polycaprolactone polyol (molecular weight 1000), 22g of adipic acid and 0.5g of catalyst stannous chloride into the reactor, evacuate and replace with nitrogen once, and start stirring. In the polymerized monomer, the molar ratio of total hydroxyl to total carboxyl in polycaprolactone polyol (molecular weight 1000) and adipic acid is 1.2:1. The reactor temperature is raised to 150°C, and decompression and dehydration are carried out under 2kpa vacuum conditions for 6h. Then, under 0.3kpa vacuum conditions, continue to heat to 180°C, and continue dehydration and polymerization for 10h to obtain a polylactic acid copolymer product.

[0071] The GPC method measured the weight average molecular weight Mw of the polylactic acid copolymer product to be 128,000, and the number average molecular weight Mn to be 31,000.

[0072] Example 9

[0073] Add 500g of polymerized monomer L-lactic acid, 8g of trimethylolpropane, 16g of adipic acid and 0.5g of catalyst stannous octoate into the reactor, evacuate and replace with nitrogen once, and start stirring. In the polymerized monomer, the molar ratio of total hydroxyl group to total carboxyl group in trimethylolpropane and adipic acid is 0.82:1. The reactor temperature is raised to 140°C, and decompression and dehydration are carried out for 8h under 2kpa vacuum conditions. Then, the temperature is continued to rise to 180°C under 0.3kpa vacuum conditions, and dehydration and polymerization are continued for 9h to obtain a polylactic acid copolymer product.

[0074] The GPC method measured the weight average molecular weight Mw of the polylactic acid copolymer product to be 35,000, and the number average molecular weight Mn to be 17,000.

[0075] Example 10

[0076] Add 500g of polymerized monomer L-lactic acid, 8g of trimethylolpropane, 7g of adipic acid and 0.5g of catalyst stannous octoate into the reactor, evacuate and replace with nitrogen once, and start stirring. In the polymerized monomer, the molar ratio of total hydroxyl group to total carboxyl group in trimethylolpropane and adipic acid is 1.87:1. The reactor temperature is raised to 140°C, and decompression and dehydration are carried out for 8h under 2kpa vacuum conditions. Then, the temperature is continued to rise to 180°C under 0.3kpa vacuum conditions, and dehydration and polymerization are continued for 9h to obtain a polylactic acid copolymer product.

[0077] The GPC method measured the weight average molecular weight Mw of the polylactic acid copolymer product to be 37,000, and the number average molecular weight Mn to be 14,000.

[0078] Comparative Example 1

[0079] 500g of L-lactic acid with a purity of 85% was added to the reactor, nitrogen was introduced, heated to 100°C, the vacuum degree was controlled at 10000Pa, stirred and dehydrated for 2 hours, and after removing about 130g of water, 0.35g of stannous chloride was added. The temperature was gradually raised from 100°C to 140°C, the vacuum degree was controlled at 6000Pa, and polycondensation was performed for 20 hours to obtain a lactic acid oligomer with a weight average molecular weight of 3700. 11g of 1,6-hexanediol was added to the reaction bottle, the reaction was performed for 10 hours, and then 13g of terephthalic acid was added, and the reaction was continued for 10 hours to finally obtain a polylactic acid copolymer product.

[0080] The GPC method measured the weight average molecular weight Mw of the polylactic acid copolymer product to be 46,000, and the number average molecular weight Mn to be 21,000.

[0081] Although the present application has been described in detail above by means of general description, specific implementation methods and examples, it is obvious to those skilled in the art that certain supplements or improvements can be made to the discrimination model of the present method based on the present application. Therefore, these modifications or improvements made without departing from the spirit of the present application are within the scope of protection claimed by the present application.

Claims

1. A polylactic acid copolymer, wherein the polymerization monomers thereof include lactic acid, polyol and polyacid, and preferably, based on the mass of the polylactic acid copolymer, the mass content of the structural unit derived from the lactic acid monomer is 50-99%.

2. The polylactic acid copolymer according to claim 1, characterized in that In the polymerization monomer, the molar ratio of hydroxyl to carboxyl in the polyol and polyacid is (1-1.5):1; and / or The polyol is selected from one or more of C2-C8 divalent or polyvalent fatty alcohols, polyether polyols and polyester polyols, preferably selected from one or more of ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, hexylene glycol, glycerol, trimethylolpropane, pentaerythritol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran, polycaprolactone polyol and polycarbonate polyol; and / or The polyacid is selected from one or more of C2-C12 dibasic organic acids and C4-C12 tribasic organic acids, preferably selected from one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, malic acid, citric acid, phthalic acid and trimesic acid.

3. The polylactic acid copolymer according to claim 1 or 2, characterized in that: The lactic acid is selected from one or more of L-lactic acid, D-lactic acid and DL-lactic acid; and / or The weight average molecular weight of the polylactic acid copolymer is 50,000-200,000; the number average molecular weight of the polylactic acid copolymer is 5,000-60,000.

4. A method for preparing a polylactic acid copolymer, comprising: In an inert atmosphere, the polymerization monomers are subjected to a polymerization reaction in the presence of a catalyst to obtain the polylactic acid copolymer, wherein the polymerization monomers include lactic acid, polyols and polyacids.

5. The preparation method according to claim 4, characterized in that: Based on the mass of the polymerized monomer, the mass content of the polyol is 0.5%-25%, preferably 1%-15%, more preferably 3%-10%; and / or Based on the mass of the polymerized monomer, the mass content of the polyacid is 0.5%-25%, preferably 1%-15%, more preferably 3%-10%; and / or In the polymerization monomer, the molar ratio of hydroxyl to carboxyl in the polyol and polyacid is 1-1.5:1; and / or Based on the mass of the polymerized monomer, the mass content of the catalyst is 50 ppm-5000 ppm, preferably 200 ppm-3000 ppm.

6. The preparation method according to claim 4 or 5, characterized in that: The polyol is selected from one or more of C2-C8 divalent or polyvalent fatty alcohols, polyether polyols and polyester polyols, preferably selected from one or more of ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, hexylene glycol, glycerol, trimethylolpropane, pentaerythritol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran, polycaprolactone polyol and polycarbonate polyol; and / or The polyacid is selected from one or more of C2-C12 dibasic organic acids and C4-C10 tribasic organic acids, preferably one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, undecanedicarboxylic acid, dodecanedioic acid, malic acid, citric acid, phthalic acid and trimesic acid; and / or The lactic acid is selected from one or more of L-lactic acid, D-lactic acid and DL-lactic acid; and / or The catalyst is selected from one or more of zinc-based catalysts, titanium-based catalysts, bismuth-based catalysts and tin-based catalysts, and is preferably selected from one or more of stannous octoate, zinc acetate, tetrabutyl titanate and stannous chloride.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The following steps are involved: S1: in an inert atmosphere, allowing the polymerization monomer to undergo a first polymerization reaction in the presence of a catalyst to obtain a first polymerization reactant; S2: In an inert atmosphere, subjecting the first polymer reactant in step S1 to a second polymerization reaction to obtain the polylactic acid copolymer.

8. The preparation method according to claim 7, characterized in that: In step S1, the temperature of the first polymerization reaction is 120°C-160°C, preferably 130°C-150°C; and / or The first polymerization reaction is carried out under vacuum conditions, the vacuum degree is 1.0 kPa-4.0 kPa, preferably 2.0 kPa-3.0 kPa; and / or The first polymerization reaction time is 2h-20h, preferably 8h-14h.

9. The preparation method according to claim 7 or 8, characterized in that: In step S2, the temperature of the second polymerization reaction is 160°C-200°C, preferably 175°C-185°C; and / or The second polymerization reaction is carried out under vacuum conditions, wherein the vacuum degree is less than or equal to 1.0 kPa, preferably less than or equal to 0.5 kPa; and / or The second polymerization reaction time is 2h-20h, preferably 6h-14h.

10. Use of the polylactic acid copolymer according to any one of claims 1 to 3 or the polylactic acid copolymer prepared by the preparation method according to any one of claims 4 to 9 in food containers, tableware and packaging, film bag products or injection molded tableware.