阅读说明：本技术 聚乳酸共聚物及其制备方法和应用、共混薄膜的制备方法 (Polylactic acid copolymer, preparation method and application thereof, and preparation method of blended film ) 是由 董同力嘎 胡健 云雪艳 孙滔 刘博� 白佳鑫 于 2021-09-14 设计创作，主要内容包括：本发明提供了一种聚乳酸共聚物及其制备方法和应用、共混薄膜的制备方法,该聚乳酸共聚物主链上包括不饱和二元酸和二元醇的共聚链段；其中,不饱和二元酸包括马来酸、富马酸和衣康酸中的至少一种；二元醇为碳原子数为4～10的二元醇。本发明的聚乳酸共聚物,其相比纯聚乳酸(PLLA),引入不饱和二元酸和二元醇的共聚物后,聚乳酸共聚物具有极高的柔性,其薄膜的断裂伸长率可达300％以上,约是纯PLLA的55倍；本发明的柔性聚乳酸共混薄膜(与PBAT和PLLA共混)的断裂伸长率为纯聚对苯二甲酸-己二酸丁二醇酯和PLLA的3.8和2.8倍,均表现出良好的柔性。(The invention provides a polylactic acid copolymer, a preparation method and application thereof, and a preparation method of a blend film, wherein the main chain of the polylactic acid copolymer comprises a copolymerization chain segment of unsaturated dibasic acid and dihydric alcohol; wherein the unsaturated dibasic acid comprises at least one of maleic acid, fumaric acid and itaconic acid; the dihydric alcohol is dihydric alcohol with 4-10 carbon atoms. Compared with pure polylactic acid (PLLA), after the copolymer of unsaturated dibasic acid and dihydric alcohol is introduced, the polylactic acid copolymer has extremely high flexibility, and the elongation at break of a film of the polylactic acid copolymer can reach more than 300 percent, which is about 55 times of that of the pure PLLA; the elongation at break of the flexible polylactic acid blended film (blended with PBAT and PLLA) is 3.8 times and 2.8 times of that of pure polybutylene terephthalate-adipate (PBT-adipate (PBAT)) and PLLA, and the flexible polylactic acid blended film shows good flexibility.)

1. A polylactic acid copolymer is characterized in that the main chain of the polylactic acid copolymer comprises a copolymerization block of unsaturated dibasic acid and dihydric alcohol;

wherein the unsaturated dibasic acid comprises at least one of maleic acid, fumaric acid, and itaconic acid;

the dihydric alcohol is dihydric alcohol with 4-10 carbon atoms.

2. The polylactic acid copolymer according to claim 1, wherein the mass fraction of the copolymer of an unsaturated dibasic acid and a diol in the polylactic acid copolymer is 4 to 20%.

3. A preparation method of polylactic acid copolymer is characterized by comprising the following steps:

carrying out polycondensation reaction on lactic acid or a lactic acid water solution to obtain a polylactic acid oligomer;

carrying out polycondensation reaction on unsaturated dibasic acid and dihydric alcohol to obtain a copolymer of the unsaturated dibasic acid and the dihydric alcohol;

mixing the copolymer of unsaturated dibasic acid and dihydric alcohol with polylactic acid oligomer, and carrying out further polycondensation reaction under the action of a catalyst to obtain polylactic acid copolymer;

wherein the unsaturated dibasic acid comprises at least one of maleic acid, fumaric acid, and itaconic acid;

the dihydric alcohol is dihydric alcohol with 4-10 carbon atoms.

4. The method for preparing the polylactic acid copolymer according to claim 3, wherein the polylactic acid oligomer obtained by subjecting lactic acid or an aqueous solution of lactic acid to polycondensation reaction is specifically: drying lactic acid or a lactic acid water solution, and then placing the lactic acid or the lactic acid water solution at the temperature of 80-150 ℃ and the vacuum degree of 1-100 KPa for polycondensation reaction for 1-8 h to obtain the polylactic acid oligomer.

5. The method for preparing a polylactic acid copolymer according to claim 3, wherein the unsaturated dibasic acid and the glycol are subjected to polycondensation reaction to obtain the unsaturated dibasic acid-glycol copolymer, and the method comprises the following steps: and mixing unsaturated dibasic acid and dihydric alcohol, and then carrying out polycondensation reaction for 3-7 h at the temperature of 100-150 ℃ and the vacuum degree of 10-300 Pa to obtain the copolymer of the unsaturated dibasic acid and the dihydric alcohol.

6. The method for preparing the polylactic acid copolymer according to claim 3, wherein the copolymer of the unsaturated dibasic acid and the dihydric alcohol is mixed with the polylactic acid oligomer, and the mixture is reacted for 16 to 60 hours at a temperature of 160 to 200 ℃ and a vacuum degree of 10 to 300Pa under the action of a catalyst to obtain the polylactic acid copolymer.

7. The preparation method of the polylactic acid copolymer as claimed in claim 3, wherein the catalyst is a mixture of stannous chloride dihydrate and p-toluenesulfonic acid monohydrate, and the molar ratio of the stannous chloride dihydrate to the p-toluenesulfonic acid monohydrate is 1 (1-3);

and/or the lactic acid is L-lactic acid or D-lactic acid;

and/or the molar ratio of the unsaturated dibasic acid to the dihydric alcohol is (0.25-1) to (1-0.25);

and/or the mass of the catalyst is 0.3-0.5% of the sum of the mass of the copolymer of the unsaturated dibasic acid and the dihydric alcohol and the mass of the polylactic acid oligomer.

8. Use of the polylactic acid copolymer according to any one of claims 1 to 2 or the polylactic acid copolymer prepared by the preparation method according to any one of claims 3 to 7 as a plasticizer in the preparation of a polymer material.

9. A preparation method of a blend film is characterized by comprising the following steps:

granulating the polylactic acid copolymer according to any one of claims 1 to 2 or the polylactic acid copolymer prepared by the preparation method according to any one of claims 3 to 7;

mixing the poly terephthalic acid-adipic acid-butanediol ester or polylactic acid with the pelletized polylactic acid copolymer, adding the mixture into an extruder for casting extrusion, and cooling, drawing or blow molding to obtain the blend film.

10. The method for preparing the blend film according to claim 9, wherein the poly (terephthalic acid) -butylene adipate or the poly (lactic acid) and the pelletized poly (lactic acid) copolymer are added into a mixer and mixed for 5-10 min at a rotation speed of 100-200 rpm/min;

the mass ratio of the poly (terephthalic acid) -butanediol adipate or the poly (lactic acid) to the poly (lactic acid) copolymer is (10-90): 90-10);

the heating temperature of the extruder is 160-230 ℃, and the die head temperature is 180-230 ℃.

Technical Field

The invention relates to the technical field of polylactic acid materials, in particular to a polylactic acid copolymer, a preparation method and application thereof, and a preparation method of a blend film.

Background

Plastic is the most common and convenient packaging material, and worldwide annual production of plastic has exceeded one hundred million tons, with about 30% being used for packaging. As the largest plastic production country and consumer country in the world, the yield of plastic products in China is about 7500 ten thousand tons, the annual usage amount of plastic bags is over 400 ten thousand tons, wherein about 80 percent of the plastic bags are discarded in one year, the recovery benefit is low, and the degradation period is generally as long as one hundred years. The white pollution produced by these packages has been a hazard to human health, the natural environment and the national economy. Biodegradable materials will become a key to solving white pollution.

Among many biodegradable materials, polylactic acid (PLA) is derived from renewable plant resources, and the raw material thereof is lactic acid, which is mainly prepared by fermenting starch (such as corn and rice) and the like, and can be recycled in nature, and is consistently regarded as the most promising new green ecological material in the industry. After being used, the product made of PLA raw material can be automatically degraded into carbon dioxide and water under the composting condition, and the degraded product can form substances such as starch and the like again through the photosynthesis of plants, thereby realizing clean carbon cycle. While PLA also has excellent physical properties as well as biocompatibility and bioabsorbability, these properties are strongly influenced by its stereochemistry and molecular weight.

Currently, the most common route for the industrial production of PLA is the ring-opening polymerization of lactide, the reaction principle of which is shown below:

firstly, lactic acid intermolecular dehydration generates low molecular weight oligomer, cracking generates cyclic lactide at 180-230 ℃, and PLA is prepared by lactide ring-opening polymerization. The PLA prepared by the method has high molecular weight, good mechanical strength and higher cost. The ring-opening polymerization production process of lactide is long and complex, and particularly, the lactide needs to be purified and recrystallized for multiple times in the refining process, a large amount of solvent is consumed, and the product efficiency is low.

The prior art also discloses a direct polycondensation method for synthesizing PLA, and the specific reaction principle is as follows:

the direct polymerization of PLA is a typical polycondensation reaction, and there is a balance of free lactic acid, water, oligomers, and lactide in the reaction system. However, the conventional polycondensation of lactic acid does not sufficiently increase the molecular weight unless azeotropic distillation of condensed water is performed using an organic solvent and the polymerization time is very long. The melt polycondensation method can obtain PLA with high molecular weight and certain mechanical property, has simple process, and avoids the problem caused by using an organic solvent in solution polycondensation, thereby greatly reducing the production cost of the PLA. However, compared with the ring-opening polymerization method, the molecular weight of the PLA material obtained by melt polycondensation is still not high enough, and the melt strength, flexibility and toughness are poor, so that it is difficult to meet the application requirements.

There is a need to improve this based on the deficiencies of current polylactic acid (PLA) materials.

Disclosure of Invention

In view of the above, the invention provides a polylactic acid copolymer, a preparation method and an application thereof, and a preparation method of a blend film, so as to solve or partially solve the problems in the prior art.

In a first aspect, the present invention provides a polylactic acid copolymer comprising a copolymerized block of an unsaturated dibasic acid and a diol in a main chain;

wherein the unsaturated dibasic acid comprises at least one of maleic acid, fumaric acid, and itaconic acid;

the dihydric alcohol is dihydric alcohol with 4-10 carbon atoms.

Preferably, the mass fraction of the copolymer of unsaturated dibasic acid and dihydric alcohol in the polylactic acid copolymer is 4-20%.

In a second aspect, the present invention also provides a preparation method of a polylactic acid copolymer, comprising the following steps:

carrying out polycondensation reaction on lactic acid or a lactic acid water solution to obtain a polylactic acid oligomer;

carrying out polycondensation reaction on unsaturated dibasic acid and dihydric alcohol to obtain a copolymer of the unsaturated dibasic acid and the dihydric alcohol;

mixing the copolymer of unsaturated dibasic acid and dihydric alcohol with polylactic acid oligomer, and carrying out further polycondensation reaction under the action of a catalyst to obtain polylactic acid copolymer;

wherein the unsaturated dibasic acid comprises at least one of maleic acid, fumaric acid, and itaconic acid;

the dihydric alcohol is dihydric alcohol with 4-10 carbon atoms.

Preferably, the preparation method of the polylactic acid copolymer comprises the following steps of carrying out polycondensation reaction on lactic acid or a lactic acid aqueous solution to obtain a polylactic acid oligomer: drying lactic acid or a lactic acid water solution, and then placing the lactic acid or the lactic acid water solution at the temperature of 80-150 ℃ and the vacuum degree of 1-100 KPa for polycondensation reaction for 1-8 h to obtain the polylactic acid oligomer.

Preferably, the preparation method of the polylactic acid copolymer comprises the following steps of carrying out polycondensation reaction on unsaturated dibasic acid and dihydric alcohol to obtain the unsaturated dibasic acid and dihydric alcohol copolymer: and mixing unsaturated dibasic acid and dihydric alcohol, and then carrying out polycondensation reaction for 3-7 h at the temperature of 100-150 ℃ and the vacuum degree of 10-300 Pa to obtain the copolymer of the unsaturated dibasic acid and the dihydric alcohol.

Preferably, the preparation method of the polylactic acid copolymer comprises the steps of mixing the copolymer of unsaturated dibasic acid and dihydric alcohol with the polylactic acid oligomer, and reacting for 16-60 hours at the temperature of 160-200 ℃ and the vacuum degree of 10-300 Pa under the action of a catalyst to obtain the polylactic acid copolymer.

Preferably, in the preparation method of the polylactic acid copolymer, the catalyst is a mixture of stannous chloride dihydrate and p-toluenesulfonic acid monohydrate, and the molar ratio of the stannous chloride dihydrate to the p-toluenesulfonic acid monohydrate is 1 (1-3);

and/or the lactic acid is L-lactic acid or D-lactic acid;

and/or the molar ratio of the unsaturated dibasic acid to the dihydric alcohol is (0.25-1) to (1-0.25);

and/or the mass of the catalyst is 0.3-0.5% of the sum of the mass of the copolymer of the unsaturated dibasic acid and the dihydric alcohol and the mass of the polylactic acid oligomer.

In a third aspect, the invention also provides an application of the polylactic acid copolymer or the polylactic acid copolymer prepared by the preparation method as a plasticizer in preparing a high polymer material.

In a fourth aspect, the present invention also provides a preparation method of a blend film, comprising the following steps:

granulating the polylactic acid copolymer or the polylactic acid copolymer prepared by the preparation method;

mixing the poly terephthalic acid-adipic acid-butanediol ester or polylactic acid with the pelletized polylactic acid copolymer, adding the mixture into an extruder for casting extrusion, and cooling, drawing or blow molding to obtain the blend film.

Preferably, the preparation method of the blend film comprises the steps of adding the poly (terephthalic acid) -butanediol adipate or the polylactic acid and the granulated polylactic acid copolymer into a mixer, and mixing for 5-10 min at the rotating speed of 100-200 rpm/min;

the mass ratio of the poly (terephthalic acid) -butanediol adipate or the poly (lactic acid) to the poly (lactic acid) copolymer is (10-90): 90-10);

the heating temperature of the extruder is 160-230 ℃, and the die head temperature is 180-230 ℃.

Compared with the prior art, the polylactic acid copolymer, the preparation method and the application thereof, and the preparation method of the blend film have the following beneficial effects:

(1) compared with pure polylactic acid (PLLA), the polylactic acid copolymer contains unsaturated dibasic acid and dihydric alcohol, and has extremely high flexibility after the unsaturated dibasic acid and the dihydric alcohol copolymer are introduced, and the elongation at break of a film can reach more than 300 percent, which is about 55 times of that of the pure polylactic acid (PLLA);

(2) the polylactic acid copolymer prepared by the invention can be used as a plasticizer to be applied to the preparation of high polymer materials, and the flexibility of the high polymer materials can be greatly improved;

(3) according to the preparation method of the blend film, the prepared polylactic acid copolymer is used as a plasticizer to be added into the polybutylene terephthalate-adipate-butanediol or the polylactic acid, the blend film material is prepared in an extrusion casting or blow molding mode, the breaking elongation of the blend film is 3.8 times and 2.8 times of that of the pure polybutylene terephthalate-adipate-butanediol and the polylactic acid, and the blend film material shows good flexibility.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.

FIG. 1 is a graph showing the storage modulus versus scanning frequency of the polylactic acid copolymer prepared in examples 1 to 3 of the present invention and the PLLA prepared in comparative example 1;

FIG. 2 is a graph showing the loss modulus and scanning frequency of the polylactic acid copolymers prepared in examples 1 to 3 of the present invention and the PLLA prepared in comparative example 1;

FIG. 3 is a graph showing the apparent viscosity versus scanning frequency of the polylactic acid copolymers prepared in examples 1 to 3 of the present invention and the PLLA prepared in comparative example 1;

FIG. 4 is a drawing graph showing the tensile strength of the polylactic acid copolymer prepared in examples 2 to 3 and 8 to 9 of the present invention and the tensile strength of the PLLA prepared in comparative example 2;

FIG. 5 is a drawing graph showing the tensile strength of the blend films prepared in examples 10 to 11 of the present invention and the poly (butylene terephthalate-adipate-terephthalate) (PBAT) used in the blend films;

FIG. 6 is a drawing graph showing the tensile strength of the blend film prepared in example 12 of the present invention and the PLLA used.

Detailed Description

In the following, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

The embodiment of the application provides a polylactic acid copolymer, wherein the main chain of the polylactic acid copolymer comprises a copolymerization chain segment of unsaturated dibasic acid and dihydric alcohol;

wherein the unsaturated dibasic acid comprises at least one of maleic acid, fumaric acid and itaconic acid;

the dihydric alcohol is dihydric alcohol with 4-10 carbon atoms.

The polylactic acid copolymer according to the embodiment of the present invention includes a copolymer of an unsaturated dibasic acid and a diol, and a polymer produced by polycondensation of an unsaturated dibasic acid and a diol. Specifically, the polylactic acid copolymer is polymerized by polylactic acid and a copolymer of unsaturated dibasic acid and dihydric alcohol. The chemical structural formula (taking L-lactic acid, itaconic acid and 1, 4-butanediol as examples to synthesize a polylactic acid copolymer P (LA-BI)) is as follows:

the unsaturated dibasic acid includes maleic acid and fumaric acidAt least one of acid and itaconic acid, wherein maleic acid is also called maleic acid, and the molecular formula is C₄H₄O₄Is a dicarboxylic acid having the structural formulaFumaric acid is also called fumaric acid and has the chemical formula C₄H₄O₄Having a structural formula ofThe itaconic acid is known as methylene succinic acid and methylene succinic acid, is unsaturated dibasic organic acid and has a structural formulaThe dihydric alcohol is a dihydric alcohol having 4-10 carbon atoms, and specifically, the dihydric alcohol can be 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 7-heptanediol 1, 8-octanediol, 1, 9-nonanediol, 1, 10-decanediol, and the like. Compared with pure polylactic acid (PLLA), the polylactic acid copolymer contains unsaturated dibasic acid and dihydric alcohol, and has extremely high flexibility after the unsaturated dibasic acid and the dihydric alcohol are introduced, and the elongation at break of a film can reach more than 300 percent and is about 55 times of that of the pure polylactic acid (PLLA).

In some embodiments, the mass fraction of the copolymer of unsaturated dibasic acid and dihydric alcohol in the polylactic acid copolymer is 4-20%.

Based on the same inventive concept, the embodiment of the application also provides a preparation method of the polylactic acid copolymer, which comprises the following steps:

s11, carrying out polycondensation reaction on lactic acid or a lactic acid water solution to obtain a polylactic acid oligomer;

s12, carrying out polycondensation reaction on unsaturated dibasic acid and dihydric alcohol to obtain a copolymer of the unsaturated dibasic acid and the dihydric alcohol;

s13, mixing the copolymer of unsaturated dibasic acid and dihydric alcohol with the polylactic acid oligomer, and reacting under the action of a catalyst to obtain the polylactic acid copolymer;

wherein the unsaturated dibasic acid comprises at least one of maleic acid, fumaric acid and itaconic acid;

the dihydric alcohol is dihydric alcohol with 4-10 carbon atoms.

In the preparation method of the polylactic acid copolymer in the embodiment of the present application, the lactic acid or the aqueous solution of lactic acid is dried and then subjected to a polycondensation reaction to obtain a polylactic acid oligomer, which has a chemical formula shown below:then the copolymer of unsaturated dibasic acid and dihydric alcohol and polylactic acid oligomer are prepared by polycondensation reaction under the catalysis of a catalyst.

In some embodiments, the polylactic acid oligomer obtained by subjecting lactic acid or an aqueous lactic acid solution to a polycondensation reaction is specifically: and (3) placing lactic acid or a lactic acid water solution at the temperature of 80-150 ℃ and the vacuum degree of 1-100 Kpa for polycondensation reaction for 1-8 h to obtain the polylactic acid oligomer. Furthermore, the vacuum degree is preferably 4 to 40KPa, the temperature is preferably 100 to 150 ℃, and the reaction time is preferably 5 to 7 hours.

In some embodiments, the aqueous lactic acid solution has a mass concentration of 90-99%.

In some embodiments, the unsaturated diacid and diol copolymer obtained by polycondensation reaction of the unsaturated diacid and diol is specifically: mixing unsaturated dibasic acid and dihydric alcohol, and then carrying out polycondensation reaction for 3-7 h at the temperature of 100-150 ℃ and the vacuum degree of 10-300 Pa to obtain a copolymer of the unsaturated dibasic acid and the dihydric alcohol; furthermore, the vacuum degree is preferably 50-100 Pa, the temperature is preferably 120-140 ℃, and the reaction time is preferably 4-5 h.

In some embodiments, the copolymer of unsaturated dibasic acid and dihydric alcohol is mixed with the polylactic acid oligomer, and the mixture reacts for 16-60 hours at the temperature of 160-200 ℃ and the vacuum degree of 10-300 Pa under the action of a catalyst to obtain the polylactic acid copolymer. Furthermore, the vacuum degree is preferably 10-50 Pa, the temperature is preferably 170-190 ℃, and the reaction time is preferably 15-30 h.

In some embodiments, the catalyst is a mixture of stannous chloride dihydrate and p-toluenesulfonic acid monohydrate, and the molar ratio of the stannous chloride dihydrate to the p-toluenesulfonic acid monohydrate is 1 (1-3).

In some embodiments, the lactic acid is L-lactic acid or D-lactic acid, and the poly-lactic acid oligomer is obtained after polycondensation, wherein the molecular weight of the copolymer is 1000-2000.

In some embodiments, the molar ratio of unsaturated dibasic acid to glycol is (0.25-1): 1-0.25.

In the embodiment of the application, the unsaturated dibasic acid and the dihydric alcohol are subjected to polycondensation reaction to obtain a copolymer of the unsaturated dibasic acid and the dihydric alcohol, and the molecular weight of the copolymer is 500-1000.

In some embodiments, the mass of the catalyst is 0.3 to 0.5% of the sum of the mass of the copolymer of the unsaturated dibasic acid and the glycol and the polylactic acid oligomer.

In some embodiments, all of the reactions in steps S1-S3 may be performed under the protection of nitrogen or other inert gas.

According to the preparation method of the polylactic acid copolymer, the copolymer of unsaturated dibasic acid and dihydric alcohol is mixed with polylactic acid, and the polylactic acid copolymer is obtained through reaction under the action of a catalyst, wherein the polylactic acid copolymer has extremely high flexibility, and the elongation at break of a film of the polylactic acid copolymer can reach more than 300 percent and is about 55 times of that of pure PLLA.

Based on the same inventive concept, the embodiment of the application also provides the application of the polylactic acid copolymer or the polylactic acid copolymer prepared by the preparation method as a plasticizer in preparing a high polymer material.

Based on the same inventive concept, the embodiment of the application also provides a preparation method of the blend film, which comprises the following steps:

s21, granulating the polylactic acid copolymer or the polylactic acid copolymer prepared by the preparation method;

and S22, mixing the poly (terephthalic acid) -butanediol adipate or the polylactic acid with the pelletized polylactic acid copolymer, adding the mixture into an extruder for casting extrusion, and cooling, drawing or blow molding to obtain the blend film.

It should be noted that, in the preparation method of the blended film, the prepared polylactic acid copolymer is used as a plasticizer to be added into the polybutylene terephthalate-adipate-butanediol or the polylactic acid to prepare the blended film material in an extrusion casting or blow molding mode, the elongation at break of the blended film is 3.8 times and 2.8 times of that of the pure polybutylene terephthalate-adipate and the polylactic acid, and the blended film material shows good flexibility.

In some embodiments, the poly (butylene terephthalate) -adipate or the poly (lactic acid) and the pelletized poly (lactic acid) copolymer are added into a mixer to be mixed for 5-10 min at the rotating speed of 100-200 rpm/min;

in some embodiments, the mass ratio of the poly (butylene terephthalate) -adipate or the poly (lactic acid) to the poly (lactic acid) copolymer is (10-90): 90-10);

in some embodiments, the casting extruder heating temperature is 160 to 230 ℃ and the die temperature is 180 to 230 ℃.

In some embodiments, in step S21, the polylactic acid copolymer is pelletized to have a particle size of 50 to 70 mesh.

In some embodiments, step S22 further includes, before mixing the polybutylene terephthalate-adipate or the polylactic acid with the pelletized polylactic acid copolymer: and (3) drying the poly (terephthalic acid) -adipic acid-butanediol ester or the polylactic acid at room temperature for 24-48 h in vacuum.

The following further describes a method for producing the polylactic acid copolymer and a method for producing a blend film according to the present invention.

Example 1

The embodiment of the application provides a preparation method of a polylactic acid copolymer, which comprises the following steps:

s11, adding 700g of L-lactic acid aqueous solution with the mass fraction of 90% into 2000mL of a reaction kettle provided with a mechanical stirrer and a condensation reflux device, gradually reducing the vacuum degree of the reaction system from normal pressure to 50KPa within 20 minutes, carrying out polycondensation reaction for 1h at 110 ℃, then heating to 150 ℃, carrying out reaction for 2h at 15KPa, and finally continuing to react for 3h at 5KPa to prepare polylactic acid oligomer;

s12, mixing maleic acid and 1, 4-butanediol, and then placing the mixture at the temperature of 130 ℃ and the vacuum degree of 60Pa for polycondensation reaction for 5 hours to obtain a copolymer of unsaturated dibasic acid and dihydric alcohol; wherein the molar ratio of the maleic acid to the 1, 4-butanediol is 1: 1;

s13, after the reaction kettle in the step S11 is returned to normal pressure, 34.1g of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12, 2.8g of stannous chloride dihydrate and 2.4g of p-toluenesulfonic acid monohydrate are added, then the temperature is raised to 180 ℃, the pressure in the reaction kettle is reduced to 30Pa within 60 minutes, and then the melt polycondensation reaction is continued for 20 hours, so that the polylactic acid copolymer is obtained.

Wherein the polylactic acid oligomer obtained in step S11 of example 1 has a number average molecular weight M measured by GPC_nIs 1500; the number average molecular weight M of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12 was measured by GPC_nIs 800; the polylactic acid copolymer prepared in the step S13 has a number average molecular weight M measured by GPC_n31567 and a molecular weight distribution of 2.33.

Example 2

The embodiment of the application provides a preparation method of a polylactic acid copolymer, which comprises the following steps:

s11, adding 700g of L-lactic acid aqueous solution with the mass fraction of 90% into 2000mL of a reaction kettle provided with a mechanical stirrer and a condensation reflux device, gradually reducing the vacuum degree of the reaction system from normal pressure to 50KPa within 20 minutes, carrying out polycondensation reaction for 1h at 110 ℃, then heating to 150 ℃, carrying out reaction for 2h at 15KPa, and finally continuing to react for 3h at 5KPa to prepare polylactic acid oligomer;

s12, mixing fumaric acid and 1, 4-butanediol, and performing polycondensation reaction for 5 hours at the temperature of 130 ℃ and the vacuum degree of 60Pa to obtain a copolymer of unsaturated dibasic acid and dihydric alcohol; wherein the molar ratio of the fumaric acid to the 1, 4-butanediol is 1: 1;

s13, after the reaction kettle in the step S11 is returned to normal pressure, 34.1g of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12, 2.8g of stannous chloride dihydrate and 2.4g of p-toluenesulfonic acid monohydrate are added, then the temperature is raised to 180 ℃, the pressure in the reaction kettle is reduced to 30Pa within 60 minutes, and then the melt polycondensation reaction is continued for 20 hours, so that the polylactic acid copolymer is obtained.

Wherein the polylactic acid oligomer obtained in step S11 of example 2 has a number average molecular weight M measured by GPC_nIs 1400; the number average molecular weight M of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12 was measured by GPC_nIs 900; the polylactic acid copolymer prepared in the step S13 has a number average molecular weight M measured by GPC_n46891, molecular weight distribution 2.02.

Example 3

The embodiment of the application provides a preparation method of a polylactic acid copolymer, which comprises the following steps:

s11, adding 700g of L-lactic acid aqueous solution with the mass fraction of 90% into 2000mL of a reaction kettle provided with a mechanical stirrer and a condensation reflux device, gradually reducing the vacuum degree of the reaction system from normal pressure to 50KPa within 20 minutes, carrying out polycondensation reaction for 1h at 110 ℃, then heating to 150 ℃, carrying out reaction for 2h at 15KPa, and finally continuing to react for 3h at 5KPa to prepare polylactic acid oligomer;

s12, mixing itaconic acid and 1, 4-butanediol, and then placing the mixture at the temperature of 130 ℃ and the vacuum degree of 60Pa for polycondensation reaction for 5 hours to obtain a copolymer of unsaturated dibasic acid and dihydric alcohol; wherein the molar ratio of the itaconic acid to the 1, 4-butanediol is 1: 1;

s13, after the reaction kettle in the step S11 is returned to normal pressure, 36.6g of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12, 2.9g of stannous chloride dihydrate and 2.4g of p-toluenesulfonic acid monohydrate are added, then the temperature is raised to 180 ℃, the pressure in the reaction kettle is reduced to 30Pa within 60 minutes, and then the melt polycondensation reaction is continued for 20 hours, so that the polylactic acid copolymer is obtained.

Wherein the polylactic acid oligomer obtained in step S11 of example 3 has a number average molecular weight M measured by GPC_nIs 1300; the number average molecular weight M of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12 was measured by GPC_nIs 600; the number of the polylactic acid copolymer produced in the step S13 measured by GPCAverage molecular weight M_n48947, molecular weight distribution 1.94.

Example 4

The embodiment of the application provides a preparation method of a polylactic acid copolymer, which comprises the following steps:

s11, adding 700g of L-lactic acid aqueous solution with the mass fraction of 90% into 2000mL of a reaction kettle provided with a mechanical stirrer and a condensing reflux device, gradually reducing the vacuum degree of the reaction system from normal pressure to 50KPa within 20 minutes, carrying out polycondensation reaction for 1h at 110 ℃, then heating to 150 ℃, and then carrying out reaction for 2h at 15KPa to prepare polylactic acid oligomer;

s12, mixing fumaric acid and 1, 8-octanediol, and then carrying out polycondensation reaction for 5 hours at the temperature of 130 ℃ and the vacuum degree of 60Pa to obtain a copolymer of unsaturated dibasic acid and dihydric alcohol; wherein the molar ratio of fumaric acid to 1, 8-octanediol is 1: 1;

s13, after the reaction kettle in the step S11 is returned to normal pressure, 46.5g of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12, 1.7g of stannous chloride dihydrate and 1.5g of p-toluenesulfonic acid monohydrate are added, then the temperature is raised to 180 ℃, the pressure in the reaction kettle is reduced to 30Pa within 60 minutes, and then the melt polycondensation reaction is continued for 20 hours, so that the polylactic acid copolymer is obtained.

Wherein the polylactic acid oligomer obtained in step S11 of example 4 has a number average molecular weight M measured by GPC_nIs 1400; the number average molecular weight M of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12 was measured by GPC_nIs 700; the polylactic acid copolymer prepared in the step S13 has a number average molecular weight M measured by GPC_n44067, molecular weight distribution 2.15.

Example 5

The embodiment of the application provides a preparation method of a polylactic acid copolymer, which comprises the following steps:

s11, adding 700g of L-lactic acid aqueous solution with the mass fraction of 90% into 2000mL of a reaction kettle provided with a mechanical stirrer and a condensation reflux device, gradually reducing the vacuum degree of the reaction system from normal pressure to 50KPa within 20 minutes, carrying out polycondensation reaction for 1h at 110 ℃, then heating to 150 ℃, carrying out reaction for 2h at 15KPa, and finally continuing to react for 3h at 5KPa to prepare polylactic acid oligomer;

s12, mixing itaconic acid and 1, 6-hexanediol, and then placing the mixture under the conditions that the temperature is 130 ℃ and the vacuum degree is 60Pa for polycondensation reaction for 5 hours to obtain a copolymer of unsaturated dibasic acid and dihydric alcohol; wherein the molar ratio of the itaconic acid to the 1, 6-hexanediol is 1: 1;

s13, after the reaction kettle in the step S11 is returned to normal pressure, 73.0g of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12, 1.8g of stannous chloride dihydrate and 1.5g of p-toluenesulfonic acid monohydrate are added, then the temperature is raised to 180 ℃, the pressure in the reaction kettle is reduced to 30Pa within 60 minutes, and then the melt polycondensation reaction is continued for 20 hours, so that the polylactic acid copolymer is obtained.

Wherein the polylactic acid oligomer obtained in step S11 of example 5 has a number average molecular weight M measured by GPC_nIs 1500; the number average molecular weight M of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12 was measured by GPC_nIs 800; the polylactic acid copolymer prepared in the step S13 has a number average molecular weight M measured by GPC_n46309, molecular weight distribution 1.98.

Example 6

The embodiment of the application provides a preparation method of a polylactic acid copolymer, which comprises the following steps:

s11, adding 700g of L-lactic acid aqueous solution with the mass fraction of 90% into 2000mL of a reaction kettle provided with a mechanical stirrer and a condensation reflux device, gradually reducing the vacuum degree of the reaction system from normal pressure to 50KPa within 20 minutes, carrying out polycondensation reaction for 1h at 110 ℃, then heating to 150 ℃, carrying out reaction for 2h at 15KPa, and finally continuing to react for 3h at 5KPa to prepare polylactic acid oligomer;

s12, mixing itaconic acid and 1, 8-octanediol, and then carrying out polycondensation reaction for 5 hours at the temperature of 130 ℃ and the vacuum degree of 60Pa to obtain a copolymer of unsaturated dibasic acid and dihydric alcohol; wherein the molar ratio of the itaconic acid to the 1, 8-octanediol is 1: 1;

s13, after the reaction kettle in the step S11 is returned to normal pressure, 22.3g of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12, 2.8g of stannous chloride dihydrate and 2.4g of p-toluenesulfonic acid monohydrate are added, then the temperature is raised to 180 ℃, the pressure in the reaction kettle is reduced to 30Pa within 60 minutes, and then the melt polycondensation reaction is continued for 20 hours, so that the polylactic acid copolymer is obtained.

Wherein the polylactic acid oligomer obtained in step S11 of example 6 has a number average molecular weight M measured by GPC_nIs 1600; the number average molecular weight M of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12 was measured by GPC_nIs 700; the polylactic acid copolymer prepared in the step S13 has a number average molecular weight M measured by GPC_n47135, molecular weight distribution 2.06.

Example 7

The embodiment of the application provides a preparation method of a polylactic acid copolymer, which comprises the following steps:

s11, adding 700g of L-lactic acid aqueous solution with the mass fraction of 90% into 2000mL of a reaction kettle provided with a mechanical stirrer and a condensation reflux device, gradually reducing the vacuum degree of the reaction system from normal pressure to 50KPa within 20 minutes, carrying out polycondensation reaction for 1h at 110 ℃, then heating to 150 ℃, carrying out reaction for 2h at 15KPa, and finally continuing to react for 3h at 5KPa to prepare polylactic acid oligomer;

s12, mixing maleic acid and 1, 4-butanediol, and then placing the mixture at the temperature of 130 ℃ and the vacuum degree of 60Pa for polycondensation reaction for 5 hours to obtain a copolymer of unsaturated dibasic acid and dihydric alcohol; wherein the molar ratio of the maleic acid to the 1, 4-butanediol is 1: 1;

s13, after the reaction kettle in the step S11 is returned to normal pressure, 34.1g of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12, 2.8g of stannous chloride dihydrate and 2.4g of p-toluenesulfonic acid monohydrate are added, then the temperature is raised to 180 ℃, the pressure in the reaction kettle is reduced to 30Pa within 60 minutes, and then the melt polycondensation reaction is continued for 20 hours; then continuously keeping the vacuum degree of 30Pa, reducing the system temperature to 100 ℃, reacting for 2.5h, then heating to 132 ℃, and continuously reacting for 36h to obtain the polylactic acid copolymer.

Wherein the polylactic acid oligomer obtained in step S11 of example 7 has a number average value by GPCMolecular weight M_nIs 1600; the number average molecular weight M of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12 was measured by GPC_nIs 800; the polylactic acid copolymer prepared in the step S13 has a number average molecular weight M measured by GPC_n50543 and molecular weight distribution 2.04.

Example 8

The embodiment of the application provides a preparation method of a polylactic acid copolymer, which comprises the following steps:

s11, adding 700g of L-lactic acid aqueous solution with the mass fraction of 90% into 2000mL of a reaction kettle provided with a mechanical stirrer and a condensation reflux device, gradually reducing the vacuum degree of the reaction system from normal pressure to 50KPa within 20 minutes, carrying out polycondensation reaction for 1h at 110 ℃, then heating to 150 ℃, carrying out reaction for 2h at 15KPa, and finally continuing to react for 3h at 5KPa to prepare polylactic acid oligomer;

s12, mixing fumaric acid and 1, 4-butanediol, and performing polycondensation reaction for 5 hours at the temperature of 130 ℃ and the vacuum degree of 60Pa to obtain a copolymer of unsaturated dibasic acid and dihydric alcohol; wherein the molar ratio of the fumaric acid to the 1, 4-butanediol is 1: 1;

s13, after the reaction kettle in the step S11 is returned to normal pressure, 34.1g of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12, 2.8g of stannous chloride dihydrate and 2.4g of p-toluenesulfonic acid monohydrate are added, then the temperature is raised to 180 ℃, the pressure in the reaction kettle is reduced to 30Pa within 60 minutes, and then the melt polycondensation reaction is continued for 20 hours; then continuously keeping the vacuum degree of 30Pa, reducing the system temperature to 95 ℃, reacting for 2.5h, then heating to 137 ℃, and continuously reacting for 36h to obtain the polylactic acid copolymer.

Wherein the polylactic acid oligomer obtained in step S11 of example 8 has a number average molecular weight M measured by GPC_nIs 1400; the number average molecular weight M of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12 was measured by GPC_nIs 900; the polylactic acid copolymer prepared in the step S13 has a number average molecular weight M measured by GPC_n81793 and a molecular weight distribution of 1.80.

Example 9

The embodiment of the application provides a preparation method of a polylactic acid copolymer, which comprises the following steps:

s11, adding 700g of L-lactic acid aqueous solution with the mass fraction of 90% into 2000mL of a reaction kettle provided with a mechanical stirrer and a condensation reflux device, gradually reducing the vacuum degree of the reaction system from normal pressure to 50KPa within 20 minutes, carrying out polycondensation reaction for 1h at 110 ℃, then heating to 150 ℃, carrying out reaction for 2h at 15KPa, and finally continuing to react for 3h at 5KPa to prepare polylactic acid oligomer;

s12, mixing itaconic acid and 1, 4-butanediol, and then placing the mixture at the temperature of 130 ℃ and the vacuum degree of 60Pa for polycondensation reaction for 5 hours to obtain a copolymer of unsaturated dibasic acid and dihydric alcohol; wherein the molar ratio of the itaconic acid to the 1, 4-butanediol is 1: 1;

s13, after the reaction kettle in the step S11 is returned to normal pressure, 36.6g of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12, 2.9g of stannous chloride dihydrate and 2.4g of p-toluenesulfonic acid monohydrate are added, then the temperature is raised to 180 ℃, the pressure in the reaction kettle is reduced to 30Pa within 60 minutes, and then the melt polycondensation reaction is continued for 20 hours; and then continuously maintaining the vacuum degree of 30Pa, reducing the system temperature to 105 ℃, reacting for 2.5h, then heating to 132 ℃, and continuously reacting for 36h to obtain the polylactic acid copolymer.

Wherein the polylactic acid oligomer obtained in step S11 of example 9 has a number average molecular weight M measured by GPC_nIs 1500; the number average molecular weight M of the copolymer of unsaturated dibasic acid and dihydric alcohol prepared in the step S12 was measured by GPC_nIs 600; the polylactic acid copolymer prepared in the step S13 has a number average molecular weight M measured by GPC_n83905 and a molecular weight distribution of 1.75.

Example 10

The embodiment of the application provides a preparation method of a blend film, which comprises the following steps:

s21, pelletizing the polylactic acid copolymer prepared in example 2;

s22, putting 80 parts by weight of poly (butylene terephthalate) -adipate and 20 parts by weight of the polylactic acid copolymer pelletized in the step S21 into a mixer to be mixed for 5min at the rotating speed of 150 rpm/min; adding the mixed materials into a double-screw extruder (PPT-3/SJ 2 Co., Ltd., common laboratory analytical instruments, Guangzhou city) to perform casting extrusion, cooling, traction and rolling to obtain a film material; wherein, the temperature of the double-screw extruder charging barrel is as follows: cartridge 1: 170 ℃, cartridge 2: 175 ℃, cartridge 3: 180 ℃, barrel 4-5: 190 ℃, cartridge 6-9: 195 ℃ and a die temperature of 210 ℃.

Example 11

The embodiment of the application provides a preparation method of a blend film, which comprises the following steps:

s21, pelletizing the polylactic acid copolymer prepared in example 3;

s22, putting 80 parts by weight of poly (butylene terephthalate) -adipate and 20 parts by weight of the polylactic acid copolymer pelletized in the step S21 into a mixer to be mixed for 5min at the rotating speed of 150 rpm/min; adding the mixed materials into a double-screw extruder, performing casting extrusion, cooling, traction and rolling to obtain a film material; wherein, the temperature of the double-screw extruder charging barrel is as follows: cartridge 1: 170 ℃, cartridge 2: 175 ℃, cartridge 3: 180 ℃, barrel 4-5: 190 ℃, cartridge 6-9: 195 ℃ and a die temperature of 210 ℃.

Example 12

The embodiment of the application provides a preparation method of a blend film, which comprises the following steps:

s21, pelletizing the polylactic acid copolymer prepared in example 2;

s22, putting 70 parts by weight of poly (butylene terephthalate) -adipate and 30 parts by weight of the polylactic acid copolymer pelletized in the step S21 into a mixer to be mixed for 5min at the rotating speed of 150 rpm/min; adding the mixed materials into a double-screw extruder (PPT-3/SJ 2 Co., Ltd., common laboratory analytical instruments, Guangzhou city) to perform casting extrusion, cooling, traction and rolling to obtain a film material; wherein, the temperature of the double-screw extruder charging barrel is as follows: cartridge 1: 180 ℃, cartridge 2: 185 ℃, barrel 3: 190 ℃, barrel 4-5: 200 ℃, cartridge 6-9: 210 ℃ and a die temperature of 225 ℃.

Comparative example 1

The present comparative example provides a method of preparing polylactic acid (PLLA), comprising the steps of:

adding 700g of L-lactic acid aqueous solution with the mass fraction of 90% into a 2000mL reaction kettle provided with a mechanical stirrer and a condensation reflux device, gradually reducing the vacuum degree of the reaction system from normal pressure to 50KPa within 20 minutes, carrying out polycondensation reaction for 1h at 110 ℃, then heating to 150 ℃, then carrying out reaction for 2h at 15KPa, and finally continuing to react for 3h at 5KPa to prepare polylactic acid Oligomer (OLA); and further, after the reaction kettle is restored to the normal pressure, adding 2.7g of stannous chloride dihydrate and 2.3g of p-toluenesulfonic acid monohydrate, then heating to 180 ℃, reducing the pressure in the reaction kettle to 30Pa within 60 minutes, and continuing to perform melt polycondensation reaction for 20 hours to obtain polylactic acid (PLLA).

Wherein the polylactic acid Oligomer (OLA) obtained by the preparation has a number average molecular weight M measured by GPC_nIs 1600; the polylactic acid (PLLA) finally obtained was measured for its number average molecular weight M by GPC_n28215, molecular weight distribution 2.41.

Comparative example 2

The present comparative example provides a method of preparing polylactic acid (PLLA), comprising the steps of:

adding 700g of L-lactic acid aqueous solution with the mass fraction of 90% into a 2000mL reaction kettle provided with a mechanical stirrer and a condensation reflux device, gradually reducing the vacuum degree of the reaction system from normal pressure to 50KPa within 20 minutes, carrying out polycondensation reaction for 1h at 110 ℃, then heating to 150 ℃, then carrying out reaction for 2h at 15KPa, and finally continuing to react for 3h at 5KPa to prepare polylactic acid Oligomer (OLA); further returning the reaction kettle to normal pressure, adding 2.7g of stannous chloride dihydrate and 2.3g of p-toluenesulfonic acid monohydrate, heating to 180 ℃, reducing the pressure in the reaction kettle to 30Pa within 60 minutes, and continuing to perform melt polycondensation for 20 hours; and then continuously maintaining the vacuum degree of 30Pa, reducing the system temperature to 97 ℃, reacting for 2.5h, then heating to 147 ℃, and continuously reacting for 36h to obtain polylactic acid (PLLA).

Wherein the polylactic acid Oligomer (OLA) obtained by the preparation has a number average molecular weight M measured by GPC_nIs 1600; the polylactic acid (PLLA) finally prepared had its number average molecular weight measured by GPCM_n53472, molecular weight distribution 2.09.

Performance testing and analysis

1. Molecular weight measurement

The molecular weight and molecular weight distribution of the synthesized polylactic acid copolymer were measured by high performance liquid chromatography (Shimadzu) LC20, japan). Mobile phase: THF; the method comprises the following steps: narrow distribution polystyrene is used as a relative calibration method of a standard curve. And (3) testing conditions are as follows: the flow rate of the mobile phase was 1.0mL/min, and the column temperature was 35 ℃.

2. Rheological Property test

The rheological properties of the polymers were tested using a flat plate structure rotational rheometer (Sammerfo USA, RS 6000). Sample preparation: after being crushed, the polylactic acid copolymer sample is placed under a hot press and is hot-pressed to a sheet with the thickness of about 1 mm. And (3) testing conditions are as follows: setting the temperature at 180 ℃, setting the strain at 50 and the frequency at 1-10 Hz, and respectively testing the storage modulus, the loss modulus and the apparent viscosity of the sample.

3. Mechanical Property test

According to the national standard GB/T13022-1991, an intelligent electronic tensile testing machine (XLW (EC) Jinan light) is used for testing the mechanical properties of the smooth, non-damaged and uniform-thickness film. Each set was tested on 10 replicates and the test results (tensile strength, elongation at break, young's modulus) were directly derived by the equipment. Test conditions of 23 stand-by temperature, 50% RH humidity and effective stretching length of the film: 28mm and 5mm in width.

The polylactic acid copolymers prepared in examples 1 to 9 and comparative examples 1 to 2, the polylactic acid number average molecular weight, and the molecular weight distribution were measured, and the results are shown in table 1 below.

TABLE 1 polylactic acid copolymers prepared in different examples and polylactic acid copolymers prepared in different comparative examples have number average molecular weights and molecular weight distributions

Examples	Number average molecular weight	Molecular weight distribution
			Example 1	31567	2.33
Example 2	46891	2.02
			Example 3	48947	1.94
Example 4	44067	2.15
			Example 5	46309	1.98
Example 6	47135	2.06
			Example 7	50543	2.04
Example 8	81793	1.80
			Example 9	83905	1.75
Comparative example 1	28215	2.41
			Comparative example 2	53472	2.09

As can be seen from Table 1, the polylactic acid copolymers prepared by the methods of examples 2 to 6 have a relatively high molecular weight, and the number average molecular weight is between 4.4 and 4.9 ten thousand. Meanwhile, the molecular weight distribution is narrow and is 1.94-2.15. After further controlling the reaction temperature and reaction time (examples 8 to 9), the molecular weight of the polylactic acid copolymer was further increased to 8 ten thousand or more, and the molecular weight distribution was decreased to 1.80 or less. Whereas the molecular weight of the polylactic acid prepared in comparative example 1 was only 28215, and the molecular weight distribution was 2.41. The use performance of the material is seriously influenced by the lower molecular weight and wider molecular weight distribution, so that the material does not have film forming property, thereby limiting the application of the material in the field of packaging materials. Only after the reaction temperature and the reaction time are further regulated and controlled, the molecular weight of the polylactic acid reaches the molecular weight close to that of the polylactic acid copolymer prepared by the method of the embodiment 2-6 with shorter reaction time, and the film-forming property is achieved.

The rheological properties of the polylactic acid copolymers prepared in examples 1 to 3 and the PLLA prepared in comparative example 1 were measured, and the results are shown in fig. 1 to 3.

FIG. 1 shows the storage modulus versus sweep frequency curves for different copolymers, FIG. 2 shows the loss modulus versus sweep frequency curves for different copolymers, and FIG. 3 shows the apparent viscosity versus sweep frequency curves for different copolymers.

The polymer material exhibits dynamic viscoelasticity under the action of an alternating stress, wherein the storage modulus and the loss modulus are one of important parameters for describing the dynamic rheological property of the polymer under the action of a dynamic load. The contribution of elasticity of a material is reflected in the storage modulus and the contribution of viscosity is reflected in the loss modulus, i.e. a measure of the conversion of the mechanical energy of the material into thermal energy.

It can be seen from the graph of fig. 1 that, as the frequency increases, the storage moduli of examples 1 to 3 are all higher than that of PLLA, which is mainly because the synthetic polylactic acid copolymer has an unsaturated double bond structure, and promotes a crosslinking reaction between molecular chain segments at high temperature to form a more compact network structure, so that the storage modulus of the copolymer increases, wherein BI molecules are easier to promote a crosslinking reaction between molecular chain segments because of the double bond structure with higher activity, so that the storage moduli of example 3 are all higher than those of other samples. The general trend of fig. 2 is consistent with fig. 1, and the entanglement between example 1 and example 3 is tighter, so that a larger external force is required for the migration between the molecular segments, and thus the direct flow loss of the molecular segments is increased.

FIG. 3 shows the variation of apparent viscosity at 180 ℃ with the scanning frequency of PLLA and examples 1 to 3 in comparative example 1, and it can be seen from FIG. 3 that the apparent viscosity of PLLA is the lowest and the apparent viscosities of examples 1 to 3 are successively higher. Among them, the apparent viscosity of example 3 is the largest because the apparent viscosity of the copolymer is larger than that of PLLA due to the flow frictional resistance caused by the mutual entanglement between the molecular segments by the crosslinked structure in example 3, which is consistent with the change in storage modulus and loss modulus.

The mechanical properties of the polylactic acid copolymers prepared in examples 2 to 3 and 8 to 9 and the PLLA in comparative example 2 were measured, and the results are shown in table 2 below.

TABLE 2 mechanical Properties of polylactic acid copolymer prepared in different examples and PLLA in comparative example 2

The tensile curves of the polylactic acid copolymers prepared in examples 2 to 3 and 8 to 9 and the PLLA prepared in comparative example 2 were measured, and the results are shown in FIG. 4.

In fig. 4, a represents a stretching curve of PLLA, b represents a stretching curve of the polylactic acid copolymer prepared in example 2, c represents a stretching curve of the polylactic acid copolymer prepared in example 3, d represents a stretching curve of the polylactic acid copolymer prepared in example 8, and e represents a stretching curve of the polylactic acid copolymer prepared in example 9. As can be seen from table 2 and fig. 4, the elongation at break of PLLA prepared in comparative example 2 was 5.6%, and the material exhibited brittle fracture; secondly, the Young modulus and tensile strength of PLLA are 2314.8MPa and 68.7MPa respectively, and the material rigidity is higher. The elongation at break for examples 2 and 3 compared to pure PLLA was 252.2% and 308.9%, which are 45 and 55 times that of PLLA, respectively. In addition, the decrease in young's modulus and tensile strength of examples 2 and 3 was significant, and it can be shown that the flexibility of the polylactic acid copolymer prepared was greatly improved as compared with PLLA. After further controlling the reaction temperature and the reaction time, the elongation at break of the polylactic acid copolymers prepared in examples 8 and 9 were 70.3% and 63.4%, respectively, which both reached more than 10 times of PLLA. In addition, the young's modulus of the polylactic acid copolymers prepared in examples 8 and 9 is 1131.2MPa and 897.7MPa, which are lower than pure PLLA and are obviously improved compared with examples 2 and 3, and it can be shown that the polylactic acid copolymers prepared in examples 8 and 9 have flexibility and toughness.

Test examples 10 to 11 were conducted to obtain blend films and poly (butylene terephthalate-adipate-co-terephthalate) (PBAT) used therein_n≈1.7×10⁵Supplied by hangzhou xin fukejiu co., ltd) and the results are shown in table 3 below.

TABLE 3 mechanical Properties of blend films and PBAT prepared in different examples

The tensile curves of the blend films prepared in examples 10 to 11 and the poly (butylene terephthalate-adipate-terephthalate) (PBAT) used were measured, and the results are shown in FIG. 5.

In FIG. 5, a represents a stretching curve of polybutylene terephthalate-adipate-terephthalate (PBAT), b represents a stretching curve of the blended film prepared in example 10, and c represents a stretching curve of the blended film prepared in example 11.

As can be seen from Table 3 and FIG. 5, the flexibility of the film material is further improved by adding a certain proportion of polylactic acid copolymer. Compared to pure PBAT, the elongation at break for examples 10 and 11 was 774.5% and 571.9%, which are 2.8 and 3.8 times higher than pure PBAT, respectively; in addition, the Young's modulus and tensile strength are further reduced, which may indicate that the flexibility of the blended film material is further improved.

The mechanical properties of the blend film prepared in example 12 and PLLA (obtained from Nature Works, usa, model 4032D) were tested, and the results are shown in table 4 below.

TABLE 4 mechanical Properties of the blend film prepared in example 12 and PLLA

Examples	Thickness (μm)	Young's modulus (MPa)	Tensile strength (MPa)	Elongation at Break (%)
					Example 12	18±1.7	3756.5±128.4	89.0±3.7	63.4±5.6
PLLA	16±1.9	4220.8±156.5	71.9±4.1	22.5±2.7

The tensile curve of the blended film prepared in example 12 and PLLA (model 4032D from Nature Works) was tested and shown in fig. 6.

In FIG. 6, a represents the stretch curve of the blend film obtained in example 12, and b represents the stretch curve of PLLA.

As can be seen from Table 4 and FIG. 6, the flexibility of the film material is further improved by adding a certain proportion of polylactic acid copolymer. Example 12 had an elongation at break of 63.4%, which was 2.8 times that of pure PLLA; in addition, the Young's modulus of example 12 is 3756.5MPa, which is 11% lower than that of pure PLLA, and it can be shown that the flexibility of the blended film material is further improved while the toughness of the pure PLLA film is maintained.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.