阅读说明：本技术 一种聚乳酸可降解增韧改性剂及其制备方法 (Polylactic acid degradable toughening modifier and preparation method thereof ) 是由 高伟 陶志豪 王湘杰 李镓豪 彭友智 彭涛 于 2021-07-21 设计创作，主要内容包括：本发明提供一种聚乳酸可降解增韧改性剂及其制备方法。主要步骤如下：步骤(1)首先通过引发剂引发丙交酯开环聚合得到聚乳酸多元醇预聚物,步骤(2)将ε-己内酯单体和丙交酯单体混合均匀后加入到预聚物中,通过预聚物中的羟基引发己内酯与丙交酯的无规聚合,得到聚乳酸透明增韧改性剂。本发明中引入含有ε-己内酯与丙交酯进行无规共聚,在提高材料柔韧性的同时减少因结晶及相容性导致材料透明度下降的问题,与聚乳酸相容性良好,迁移率、渗透率低。(The invention provides a polylactic acid degradable toughening modifier and a preparation method thereof. The method mainly comprises the following steps: firstly, initiating lactide ring-opening polymerization through an initiator to obtain a polylactic acid polyol prepolymer, uniformly mixing an epsilon-caprolactone monomer and a lactide monomer, adding the mixture into the prepolymer, and initiating random polymerization of caprolactone and lactide through hydroxyl in the prepolymer to obtain the polylactic acid transparent toughening modifier. The invention introduces epsilon-caprolactone and lactide for random copolymerization, improves the flexibility of the material, reduces the problem of the reduction of the transparency of the material caused by crystallization and compatibility, and has good compatibility with polylactic acid and low mobility and permeability.)

1. The polylactic acid degradable toughening modifier is a copolymer with a polycaprolactone-lactide block and a random function, and the chain segment of the copolymer has the following schematic structure:

A-B-R-B-A

wherein R represents a carbon chain structure of small molecular polyol HO-R-OH;

wherein A represents a random chain segment part of the polylactic acid degradable toughening modifier, A is a random copolymer of lactide and epsilon-caprolactone, and the mass ratio of the lactide to the epsilon-caprolactone is 15-23: 25, the molecular weight of the random segment part is 29000-;

wherein B represents a polylactic acid block part of the polylactic acid degradable toughening modifier, and the molecular weight Mn range of the polylactic acid block part is 11700-23500.

2. The polylactic acid degradable toughening modifier according to claim 1, wherein the mass ratio of the prepolymer polylactic acid chain segment to the random chain segment is 1: 2-4, the polylactic acid chain segment accounts for 20-33% of the mass fraction of the whole copolymer; the molecular weight Mn range of the polylactic acid degradable toughening modifier is 41500-83500.

3. A preparation method of a polylactic acid degradable toughening modifier is characterized by comprising the following steps:

step (1): in a reaction kettle, firstly, lactide is melted, then micromolecular polyol is added, so that the micromolecular polyol and the lactide are uniformly mixed, a catalyst is added, and the ring opening polymerization of the lactide is initiated by the micromolecular polyol under the action of the catalyst to obtain a prepolymer; the ring-opening polymerization reaction is bulk polymerization;

step (2): completely dissolving a lactide monomer and an epsilon-caprolactone monomer mutually to obtain a lactide/epsilon-caprolactone solution, adding the lactide/epsilon-caprolactone solution into a reaction kettle through a feed inlet under the condition of isolating oxygen, uniformly mixing with a prepolymer, initiating ring-opening polymerization of the lactide and the epsilon-caprolactone through the prepolymer to obtain a copolymer, adding a terminator into the copolymer, uniformly stirring, performing devolatilization treatment, and discharging to obtain the polylactic acid degradable toughening modifier; the ring-opening polymerization reaction is bulk polymerization.

4. The preparation method of the polylactic acid degradable toughening modifier according to claim 3, wherein in the step (1), the mass ratio of the small molecular polyol to the lactide is 1.8-5.6:1000, or the amount of the small molecular polyol is 0.05-0.3% of the total mass of the epsilon-caprolactone and the lactide; the dosage of the catalyst is 0.05-0.1% of the total mass of the epsilon-caprolactone, the lactide and the micromolecule polyalcohol.

5. The method for preparing the polylactic acid degradable toughening modifier according to claim 3, wherein the ring-opening polymerization reaction is performed under the protection of an inert gas, and the inert gas comprises nitrogen.

6. The method for preparing the polylactic acid degradable toughening modifier according to claim 3, wherein the small molecular polyol is diol, and the diol comprises butanediol and diethylene glycol.

7. The preparation method of the polylactic acid degradable toughening modifier according to claim 3, wherein the catalyst comprises stannous octoate.

8. The method for preparing the degradable toughening modifier of polylactic acid according to claim 3, wherein in the step (1), the reaction temperature of the ring-opening polymerization is 100-220 ℃, and the reaction time is 5-7 h; in the step (2), the reaction temperature of the ring-opening polymerization is 170-210 ℃, and the reaction time is 5-10 h.

9. The preparation method of the polylactic acid degradable toughening modifier according to claim 4, wherein the terminating agent in the step (2) comprises 2-ethyl octanoic acid, and the weight ratio of the terminating agent to the total weight of the lactide and the caprolactone is (0.002-0.001): 1.

10. The method for preparing the polylactic acid degradable toughening modifier according to claim 3, wherein the devolatilization temperature in the step (2) is 100-210 ℃, the devolatilization pressure is 0.1-100kpa, and the devolatilization time is 0.5-5 h.

Technical Field

The invention relates to a material and a synthetic method in the technical field of high polymer materials, in particular to a polylactic acid degradable toughening modifier and a preparation method thereof.

Background

Today, the technological level is continuously developed, plastic products become common and indispensable things in people's life, and plastic films such as disposable plastic bags and express packaging bags are visible everywhere. Pollution caused by waste plastics is more and more serious, and the search for a substitute for general plastics is a research focus of all countries.

PLA is used as a fully biodegradable material, and has high tensile strength, high compression modulus and good transparency, so that PLA has extremely strong substituting capacity for traditional transparent hard materials such as PP, PET and the like. However, due to the characteristics of poor impact resistance and strong brittleness of PLA, a certain amount of toughening modifier is usually added when the PLA is used for preparing a full-biodegradable product, so that the impact resistance and the fracture growth rate of the PLA material are improved.

At present, the mainstream toughening methods for toughening and modifying PLA are divided into two major types, one is adding small molecular plasticizers, and the other is blending and modifying with high molecular toughness materials. The addition of the micromolecular plasticizer can achieve a good toughening effect, but the performance and stability of the material can be greatly reduced due to the fact that micromolecules are easy to separate out and migrate; the high molecular weight toughness material is usually flexible material such as PE, PBAT, PCL, PBS and the like, and the material is added into PLA to be blended and modified with PLA, wherein PE is difficult to biodegrade, PBAT, PCL, PBS and PLA have poor compatibility, the strength loss of PLA is large, PBAT, PCL and PBS all belong to semi-crystalline polymer with strong crystallinity, the transparency of the PBAT, PCL and PBS is very low, the transparency of the material is reduced after blending with PLA, and the application of PLA is limited.

A search of the prior art has found that Kelly s.anderson et al first synthesized a polylactic acid-polyethylene block copolymer (PLA-PE) and then blended a Linear Low Density Polyethylene (LLDPE) with PLA to toughen the PLA using the block copolymer as a solubilizer. Although the method can well solve the phenomenon of permeation and migration of the small-molecular plasticizer, the introduced polyethylene part is difficult to biodegrade.

The patent documents of Chinese mainland patent No. CN102675523B and CN201210120668.0 both describe a polylactic acid toughening modifier and a preparation method thereof, the two methods both adopt emulsion polymerization to obtain the polylactic acid degradable toughening modifier by introducing acrylic acid and methyl acrylate for polymerization, although the toughening agent prepared by the method has better toughening effect when being applied to polylactic acid, the acrylic acid and the methyl acrylate are not suitable for being applied in the degradable field because of no degradability.

The patent document of chinese continental patent No. CN104640903A discloses a preparation method of a segmented semi-crystalline poly (lactide-co-e-caprolactone) absorbable copolymer, and describes a copolymer with 40/60-25/75 mole ratio of caprolactone to lactide, which is semi-crystalline and has crystallinity of 34% -45%, and is not suitable for toughening modification of transparent polylactic acid due to reduction of copolymer transparency and light transmittance due to higher crystallinity.

Zhang culvert et al found that when the average length of lactide chain segments in the epsilon-caprolactone-lactide copolymer is less than 3.4, the copolymer has poor compatibility with PLA and phase separation occurs; the epsilon-caprolactone-lactide random copolymer prepared by a one-step copolymerization method cannot ensure enough long average segment length of lactide to meet the use requirement of polylactic acid degradable toughening modifier.

Disclosure of Invention

Based on the background current situation, in order to solve the technical problems, the invention provides the polylactic acid degradable toughening modifier and the preparation method thereof, and the toughening modifier is added into PLA, so that the problems of undegradability of the toughening agent, reduction of material transparency, poor compatibility and great material performance loss can be effectively solved.

The technical problem to be solved by the invention is realized by the following technical scheme:

in one aspect, the polylactic acid degradable toughening modifier is a copolymer combining a polycaprolactone-lactide block and a random block, and the chain segment schematic structure is as follows:

B-A-R-A-B

wherein R represents a carbon chain structure of small molecular polyol HO-R-OH;

wherein A represents a random chain segment part of the polylactic acid degradable toughening modifier, A is a random copolymer of lactide and epsilon-caprolactone, and the mass ratio of the lactide to the epsilon-caprolactone is 15-23: 25, the molecular weight of the random segment part is 29000-;

wherein A represents a polylactic acid block part of the polylactic acid degradable toughening modifier, and the molecular weight Mn range of the polylactic acid block part is 11700-23500.

Preferably, the mass ratio of the polylactic acid segment to the random segment is 1: 2-4, the polylactic acid chain segment accounts for 20-33% of the mass fraction of the whole copolymer; the molecular weight Mn range of the polylactic acid degradable toughening modifier is 41500-83500.

On the other hand, the preparation method of the polylactic acid degradable toughening modifier is provided, and comprises the following steps:

step (1): in a reaction kettle, firstly, lactide is melted, then an initiator is added, the initiator and the lactide are uniformly mixed, a catalyst is added, and the ring opening polymerization of the lactide is initiated by the initiator under the action of the catalyst to obtain a prepolymer; the ring-opening polymerization reaction is bulk polymerization;

step (2): completely dissolving a lactide monomer and an epsilon-caprolactone monomer mutually to obtain a lactide/epsilon-caprolactone solution, adding the lactide/epsilon-caprolactone solution into a reaction kettle through a feed inlet under the condition of isolating oxygen, uniformly mixing with a prepolymer, initiating ring-opening polymerization of the lactide and the epsilon-caprolactone through the prepolymer to obtain a copolymer, adding a terminator into the copolymer, and performing devolatilization and drying treatment to obtain the polylactic acid degradable toughening modifier; the ring-opening polymerization reaction is bulk polymerization.

Preferably, in the step (1), the mass ratio of the small molecular weight polyol to the lactide is 1.8:1000-5.6:1000, or the amount of the small molecular weight polyol is 0.05% -0.3% of the total mass of the epsilon-caprolactone and the lactide; the dosage of the catalyst is 0.05 to 0.1 percent of the total mass of the epsilon-caprolactone, the lactide and the micromolecule polyalcohol;

preferably, the stirring uniformly means stirring for 30-60min at the current temperature.

The principle of the reaction is as follows:

preferably, the polymerization reaction of step (1) and step (2) is carried out under the protection of inert gas, and the inert gas comprises nitrogen.

Preferably, the initiator in step (1) is a diol, and the diol comprises butanediol or diethylene glycol.

Preferably, the catalyst in step (1) comprises stannous octoate.

Preferably, in the step (1), the reaction temperature of the ring-opening polymerization is 100-220 ℃, and the reaction time is 5-7 h.

Preferably, in the step (2), the reaction temperature of the ring-opening polymerization is 170-210 ℃, and the reaction time is 5-10 h.

Preferably, the terminating agent in the step (2) is ring-opening polymerization containing 2-ethyl octanoic acid, and the weight ratio of the terminating agent to the total weight of (lactide and caprolactone) is (0.002-0.001): 1.

Preferably, the devolatilization temperature in the step (2) is 100-210 ℃, the devolatilization pressure is 0.1-100kpa, and the devolatilization time is 0.5-5 h.

The invention has the beneficial effects that:

1. the polylactic acid degradable toughening modifier provided by the invention is introduced with epsilon-caprolactone and lactide for random copolymerization, and has good compatibility with polylactic acid and low mobility and permeability.

2. The polylactic acid degradable toughening modifier provided by the invention has good elongation at break and light transmittance, improves the flexibility of the material, and reduces the problem of reduced transparency of the material caused by crystallization and compatibility.

Detailed Description

The invention is further illustrated by the following specific examples, which are not intended to be limiting and whose scope is indicated in the claims.

The test method comprises the following steps:

the number-average molecular weight Mn of the product was determined by GPC, with tetrahydrofuran as the mobile phase and polystyrene as the standard reference.

The monomer residue was determined using gas chromatography.

The crystallinity was measured by DSC.

Example 1

The method comprises the steps of melting 2000g of lactide in a 10L stainless steel oil jacket reaction kettle, adding 11.2g of Butanediol (BDO) into the reaction kettle, heating to 110 ℃, reducing the vacuum in the kettle to be below 1kpa, fully stirring for 10min, raising the pressure to be slightly higher than 0.1Mpa, adding 3.03g of stannous octoate, and replacing the gas in the kettle with nitrogen for 3 times. After the nitrogen replacement is finished, the temperature in the kettle is raised to 220 ℃, the prepolymer A1 is obtained after the reaction is carried out for 2 hours, and a small amount of prepolymer is taken for detection.

Completely dissolving 1500g of lactide and 2500g of epsilon-caprolactone at the temperature of 40-50 ℃, adding a lactide/epsilon-caprolactone solution into the reaction kettle through a feed inlet under the condition of isolating oxygen, uniformly stirring and mixing with the prepolymer, keeping the temperature in the kettle within the range of 180-190 ℃, continuously reacting for 6 hours, and raising the temperature to 210 ℃ for continuously reacting for 4 hours; adding 3.01g of 2-ethyl octanoic acid, keeping the temperature in the kettle at 100 ℃, uniformly stirring for 0.5h, reducing the pressure in the kettle to 0.1kpa, devolatilizing for 5h, discharging and drying to obtain a final product B1.

The lactide content of prepolymer a1, determined by gas chromatography after dissolution of the product with cyclohexanone, was 5.51% and the total content of lactide and epsilon-caprolactone of the final product B1 was 0.88%.

After dissolving the product in tetrahydrofuran, the number average molecular weight Mn of prepolymer product a1 was 11700, the number average molecular weight Mn of final product B1 was 41500, and the molecular weight Mn of the random segment was 29800, as determined by gel permeation chromatography.

Example 2

Adding 12.2DEG and 1500g of lactide into a reaction kettle, heating to 110 ℃, reducing the vacuum in the kettle to be below 1kpa, fully stirring for 10min, raising the pressure to be slightly higher than 0.1Mpa, adding 6.05g of stannous octoate, and replacing the gas in the kettle with nitrogen for 3 times. And after nitrogen replacement is finished, heating the temperature in the kettle to 150 ℃, reacting for 3 hours, heating the temperature in the kettle to 170 ℃, reacting for 2 hours to obtain prepolymer A2, and taking a small amount of prepolymer for detection.

Completely dissolving 2000g of lactide and 2500g of epsilon-caprolactone at the temperature of 40-50 ℃, adding a lactide/epsilon-caprolactone solution into a reaction kettle through a feed inlet under the condition of isolating oxygen, uniformly stirring and mixing with the prepolymer, keeping the temperature in the kettle at 170 ℃ for continuously reacting for 2 hours, then increasing the temperature to 190 ℃ for continuously reacting for 4 hours, adding 6.12g of 2-ethyl octanoic acid to finish the reaction, keeping the temperature in the kettle at 200 ℃ for stirring for 1 hour, reducing the pressure in the kettle to 100kpa, devolatilizing for 5 hours, discharging and drying to obtain a product B2.

The lactide content of prepolymer a2, determined by gas chromatography after dissolution of the product with cyclohexanone, was 3.42% and the total content of lactide and epsilon-caprolactone of the final product B2 was 0.98%.

After dissolving the product in tetrahydrofuran, the number average molecular weight Mn of prepolymer a2 was 13100, the number average molecular weight Mn of final product B2 was 42200, and the molecular weight Mn of the random segment was 29100, as determined by gel permeation chromatography.

Example 3

Adding 11.2g of BDO and 1200g of lactide into a reaction kettle, heating to 110 ℃, reducing the vacuum in the kettle to be below 1kpa, fully stirring for 10min, raising the pressure to be slightly higher than 0.1Mpa, adding 5.07g of stannous octoate, and replacing the gas in the kettle with nitrogen for 3 times. And after nitrogen replacement is finished, raising the temperature in the kettle to 150 ℃, reacting for 3 hours, raising the temperature in the kettle to 170 ℃, reacting for 2 hours to obtain prepolymer A3, and taking a small amount of prepolymer for detection.

Completely dissolving 2300g of lactide and 2500g of epsilon-caprolactone at the temperature of 40-50 ℃, adding the lactide/epsilon-caprolactone solution into a reaction kettle through a feed inlet under the condition of isolating oxygen, uniformly stirring and mixing with the prepolymer, keeping the temperature in the kettle at 170-180 ℃, continuing to react for 5 hours, raising the temperature in the kettle to 190 ℃, reacting for 3 hours, adding 5.01g of 2-ethyloctanoic acid, finishing the reaction, keeping the temperature in the kettle at 140 ℃, stirring for 0.5 hour, reducing the pressure in the kettle to 50kpa, devolatilizing for 5 hours, discharging and drying to obtain a product B3.

The lactide content of prepolymer a3, determined by gas chromatography after dissolution of the product with cyclohexanone, was 3.66% and the total content of lactide and epsilon-caprolactone of the final product B3 was 0.93%.

After dissolving the product in tetrahydrofuran, the number average molecular weight Mn of prepolymer a3 was 12900, the number average molecular weight Mn of final product B3 was 41800, and the molecular weight Mn of the random segment was 28900, as determined by gel permeation chromatography.

Example 4

Adding 7.2g of BDO and 2000g of lactide into a reaction kettle, heating to 110 ℃, reducing the vacuum in the kettle to be below 1kpa, fully stirring for 10min, raising the pressure to be slightly higher than 0.1Mpa, adding 6.12g of stannous octoate, replacing the gas in the kettle with nitrogen for 3 times, heating to 170 ℃ after completing nitrogen replacement, reacting for 5h to obtain prepolymer A4, and taking a small amount of prepolymer for detection.

The method comprises the steps of completely mutually dissolving 1500g of lactide and 2500g of epsilon-caprolactone at the temperature of 40-50 ℃, adding a lactide/epsilon-caprolactone solution into a reaction kettle through a feed inlet under the condition of isolating oxygen, uniformly stirring and mixing with a prepolymer, keeping the temperature in the kettle at 190 ℃ for continuous reaction for 3 hours, raising the temperature to 200 for continuous reaction for 2 hours, adding 6.07g of 2-ethyloctanoic acid for finishing the reaction, keeping the temperature in the kettle at 210 ℃, stirring for 1 hour, reducing the pressure in the kettle to 0.1kpa, devolatilizing for 0.5 hour, discharging and drying to obtain a final product B4.

The lactide content of prepolymer a4, determined by gas chromatography after dissolution of the product with cyclohexanone, was 3.37% and the total content of lactide and epsilon-caprolactone of the final product B4 was 0.91%.

After dissolving the product in tetrahydrofuran, the number average molecular weight Mn of prepolymer a4 was 17300, the number average molecular weight Mn of final product B4 was 58700, and the molecular weight Mn of the random segment was 41400, as determined by gel permeation chromatography.

Example 5

Adding 8.0g of DEG and 1500g of lactide into a reaction kettle, heating to 110 ℃, reducing the vacuum in the kettle to be below 1kpa, fully stirring for 10min, raising the pressure to be slightly higher than 0.1Mpa, adding 3.11g of stannous octoate, and replacing the gas in the kettle with nitrogen for 3 times. After nitrogen replacement is finished, the temperature in the kettle is raised to 150 ℃, after 4 hours of reaction, the temperature is raised to 170 ℃, and after 2 hours of reaction, prepolymer A5 is obtained, and a small amount of prepolymer is used for detection.

Completely dissolving 2000g of lactide and 2500g of epsilon-caprolactone at the temperature of 40-50 ℃, adding a lactide/epsilon-caprolactone solution into a reaction kettle through a feed inlet under the condition of isolating oxygen, uniformly stirring and mixing with the prepolymer, keeping the temperature in the kettle at 190 ℃ for continuous reaction for 6 hours, raising the temperature to 200 for continuous reaction for 2 hours, adding 3.05g of 2-ethyloctanoic acid for finishing the reaction, keeping the temperature in the kettle at 200 ℃ for stirring for 0.5 hour, reducing the pressure in the kettle to 0.1kpa for devolatilization for 3 hours, discharging and drying to obtain a final product B5.

The lactide content of prepolymer a5, determined by gas chromatography after dissolution of the product with cyclohexanone, was 3.87% and the total content of lactide and epsilon-caprolactone of the final product B5 was 0.61%.

After dissolving the product in tetrahydrofuran, the number average molecular weight Mn of prepolymer a5 was 17500, the number average molecular weight Mn of final product B5 was 60200, and the molecular weight Mn of the random segment was 42700, as determined by gel permeation chromatography.

Example 6

Adding 7.2g of BDO and 1200g of lactide into a reaction kettle, heating to 110 ℃, reducing the vacuum in the kettle to be below 1kpa, fully stirring for 10min, increasing the pressure to be slightly higher than 0.1Mpa, adding 4.88g of stannous octoate, and replacing the gas in the kettle with nitrogen for 3 times. After nitrogen replacement is finished, the temperature in the kettle is raised to 150 ℃, after 5 hours of reaction, the temperature is raised to 170 ℃, reaction is continued for 2 hours, prepolymer A6 is obtained, and a small amount of prepolymer is used for detection.

Completely dissolving 2300g of lactide and 2500g of epsilon-caprolactone at the temperature of 40-50 ℃, adding the lactide/epsilon-caprolactone solution into a reaction kettle through a feed inlet under the condition of isolating oxygen, stirring and mixing the lactide/epsilon-caprolactone solution with the prepolymer uniformly, keeping the temperature in the kettle at 180-190 ℃ for continuous reaction for 6 hours, raising the temperature to 200 for continuous reaction for 2 hours, adding 4.79g of 2-ethyloctanoic acid for finishing the reaction, keeping the temperature in the kettle at 200 ℃ for stirring for 1 hour, reducing the pressure in the kettle to 0.1kpa, devolatilizing for 2 hours, discharging and drying.

The lactide content of prepolymer a6, determined by gas chromatography after dissolution of the product with cyclohexanone, was 3.17% and the total content of lactide and epsilon-caprolactone of the final product B6 was 0.79%.

After dissolving the product in tetrahydrofuran, the number average molecular weight Mn of prepolymer a6 was 17100, the number average molecular weight Mn of final product B6 was 59500, and the molecular weight Mn of the random segment was 42400, as determined by gel permeation chromatography.

Example 7

Adding 5.2g of BDO and 2000g of lactide into a reaction kettle, heating to 110 ℃, reducing the vacuum in the kettle to be below 1kpa, fully stirring for 10min, raising the pressure to be slightly higher than 0.1Mpa, adding 6.12g of stannous octoate, replacing the gas in the kettle with nitrogen for 3 times, heating to 170 ℃ after completing nitrogen replacement, reacting for 5h to obtain prepolymer A7, and taking a small amount of prepolymer for detection.

The method comprises the steps of completely mutually dissolving 1500g of lactide and 2500g of epsilon-caprolactone at the temperature of 40-50 ℃, adding a lactide/epsilon-caprolactone solution into a reaction kettle through a feed inlet under the condition of isolating oxygen, uniformly stirring and mixing with a prepolymer, raising the temperature to 210, continuing to react for 2 hours, adding 6.07g of 2-ethyl octanoic acid to finish the reaction, keeping the temperature in the kettle at 180 ℃, stirring for 0.5 hour, reducing the pressure in the kettle to 1kpa, devolatilizing for 5 hours, discharging and drying to obtain a final product B7.

The lactide content of prepolymer a7, determined by gas chromatography after dissolution of the product with cyclohexanone, was 3.43% and the total content of lactide and epsilon-caprolactone of the final product B7 was 0.93%.

After dissolving the product in tetrahydrofuran, the number average molecular weight Mn of prepolymer a7 was 23300, the number average molecular weight Mn of final product B7 was 83500, and the molecular weight Mn of the random segment was 60200, as determined by gel permeation chromatography.

Example 8

Adding 5.8g of DEG and 1500g of lactide into a reaction kettle, heating to 110 ℃, reducing the vacuum in the kettle to be below 1kpa, fully stirring for 10min, raising the pressure to be slightly higher than 0.1Mpa, adding 3.11g of stannous octoate, and replacing the gas in the kettle with nitrogen for 3 times. After nitrogen replacement is completed, the temperature in the kettle is raised to 5 ℃, after 4 hours of reaction, the temperature is raised to 170 ℃, and after 2 hours of reaction, prepolymer A8 is obtained, and a small amount of prepolymer is used for detection.

Completely dissolving 2000g of lactide and 2500g of epsilon-caprolactone at the temperature of 40-50 ℃, adding a lactide/epsilon-caprolactone solution into a reaction kettle through a feed inlet under the condition of isolating oxygen, uniformly stirring and mixing with the prepolymer, keeping the temperature in the kettle at 190-195 ℃, continuing to react for 6 hours, raising the temperature to 210, continuing to react for 2 hours, adding 3.05g of 2-ethyloctanoic acid, finishing the reaction, keeping the temperature in the kettle at 180 ℃, stirring for 1 hour, reducing the pressure in the kettle to 0.1kpa, devolatilizing for 3 hours, discharging and drying to obtain a final product B8.

The lactide content of prepolymer A8, determined by gas chromatography after dissolution of the product with cyclohexanone, was 3.66% and the total content of lactide and epsilon-caprolactone of the final product B8 was 0.73%.

After dissolving the product in tetrahydrofuran, the number average molecular weight Mn of prepolymer A8 was 23500, the number average molecular weight Mn of final product B8 was 80200, and the molecular weight Mn of the random segment was 56700, as determined by gel permeation chromatography.

Example 9

Adding 5.3g of BDO and 1200g of lactide into a reaction kettle, heating to 60 ℃, reducing the vacuum in the kettle to be below 1kpa, fully stirring for 10min, raising the pressure to be slightly higher than 0.1Mpa, adding 4.88g of stannous octoate, and replacing the gas in the kettle with nitrogen for 3 times. After nitrogen replacement is finished, the temperature in the kettle is raised to 150 ℃, after 5 hours of reaction, the temperature is raised to 170 ℃, reaction is continued for 2 hours, prepolymer A6 is obtained, and a small amount of prepolymer is used for detection.

Completely dissolving 2300g of lactide and 2500g of epsilon-caprolactone at the temperature of 40-50 ℃, adding the lactide/epsilon-caprolactone solution into a reaction kettle through a feed inlet under the condition of isolating oxygen, stirring and mixing the lactide/epsilon-caprolactone solution with prepolymer uniformly, keeping the temperature in the kettle at 190-195 ℃, continuing to react for 6 hours, raising the temperature to 210, continuing to react for 2 hours, adding 4.79g of 2-ethyloctanoic acid, ending the reaction, keeping the temperature in the kettle at 180 ℃, stirring for 0.5 hour, reducing the pressure in the kettle to 0.1kpa, devolatilizing for 2 hours, discharging and drying.

The lactide content of prepolymer a9, determined by gas chromatography after dissolution of the product with cyclohexanone, was 3.27% and the total content of lactide and epsilon-caprolactone of the final product B9 was 0.69%.

After dissolving the product in tetrahydrofuran, the number average molecular weight Mn of prepolymer a9 was 22900, the number average molecular weight Mn of final product B9 was 82100, and the molecular weight Mn of the random segment was 59200, as determined by gel permeation chromatography.

Example 10

The products of examples 1 to 9 were pressed into test specimens using a press machine, and the tensile strength, elongation at break and impact strength were measured by an universal tensile machine in accordance with GB/T1040-1992, and the light transmittance of the samples was measured in accordance with the national standard GB 2410-80.

The results of the tests for the ratios of the amounts of different starters, lactide and epsilon-caprolactone are as follows:

as can be seen from the table above, the crystallinity of examples 1-9 is lower than 25%, the crystallization ability is weaker, the light transmittance of the prepared sample wafer is greater than 90%, the sample wafer has good elongation at break and light transmittance, and all indexes are favorable for being used as transparent toughening agents.

Example 11

The control group 1 was set as a PLA blank control group, PLA was NatureWorks 4060D brand, and test specimens were prepared by press-molding using a press vulcanizer.

The control group 2 was a blend obtained by blending and extruding PLA and PCL in a mass ratio of 9:1 by a single screw extruder, and the blend was pressed by a plate vulcanizer to prepare a test sample strip, wherein PCL is a PCL-6500 brand of new materials science and technology company, Inc., of kernel-gathering chemical industry in Hunan province.

The products obtained in examples 1 to 9 were co-extruded with PLA in a ratio of PLA: P (CL-LA)9:1 by means of a single-screw extruder and were laminated using a press vulcanizer to prepare test specimens.

The tensile strength, elongation at break and impact strength were measured by a universal tensile machine according to GB/T1040-1992, and the light transmittance of the sample was measured according to the national standard GB 2410-80.

The test results were as follows:

as can be seen from the above table, examples 1-9 all improved the elongation at break of PLA by more than 200% without decreasing the transparency when the toughening agent was added at 10%. While the elongation at break of the PCL and PLA blend of control 2 was only improved by 60% and the transparency was reduced by 7%. The toughening agent has good gain effect on the flexibility and the transparency of PLA and is superior to the pure PCL master batch.

The above-described series of detailed descriptions are merely specific to possible embodiments of the present invention, and they are not intended to limit the scope of the present invention, and various changes made without departing from the gist of the present invention within the knowledge of those skilled in the art are included in the scope of the present invention.