A kind of degradable expandable polylactic acid polymer foam material and preparation method thereof

Abstract

The present application relates to the field of new polymer materials, and specifically discloses a degradable expandable polylactic acid polymer foam material and a preparation method thereof, comprising the following raw materials: a polylactic acid-starch-polyamide blended modified mixture, polylactic acid foam material waste scraps, a foaming agent, a nucleating agent, and an activator; the preparation method comprises the following steps: melt-mixing polylactic acid, acylated starch, and polyamide in proportion to obtain a polylactic acid-starch-polyamide blended modified mixture, weighing the polylactic acid-starch-polyamide blended modified mixture, the polylactic acid foam material waste scraps, a foaming agent, a nucleating agent, and an activator, mixing them, extruding and pelletizing to obtain a foaming masterbatch, and foaming and molding; the present application has the characteristics of improving the expandability of the polylactic acid material, and obtaining a polylactic acid foam material with a more uniform pore size distribution, a small pore size, and excellent mechanical properties.

Description

Technical Field

[0001] The present application relates to the field of new polymer materials, and more specifically, to a degradable and expandable polylactic acid polymer foam material and a preparation method thereof. Background Art

[0002] As environmental problems become increasingly serious, the white pollution caused by traditional petroleum-based plastics due to their difficulty in degradation has attracted widespread attention. In recent years, a variety of new green packaging materials have been developed, among which polylactic acid, as an important biomass-derived polymer, has great potential in replacing petrochemical products. It not only has good processing and molding properties and certain mechanical strength, but also can be biodegraded under certain conditions and return to the natural circulation system, which meets the requirements of the concept of sustainable development and is more environmentally friendly.

[0003] In recent years, polylactic acid has begun to be used in the field of polymer foam materials. Polylactic acid foam materials not only have the advantages of light weight, high specific strength, good toughness, good thermal insulation and sound insulation properties, but also have biodegradability and biocompatibility. They have great application potential in food packaging, biomedicine and other fields.

[0004] At present, the most common method for polylactic acid foaming is physical foaming, which uses gas for direct foaming, such as nitrogen, carbon dioxide, etc., and also includes the use of supercritical gas. However, the use of gas foaming has high requirements on equipment. A gas inlet needs to be added at the die, and the barrel design needs to prevent gas leakage. The process cost is high. In addition, the physical foaming method uses a foaming agent that will volatilize, making the foamed material unsuitable for long-term storage.

[0005] Polylactic acid can also be foamed by chemical foaming. Chemical foaming agents are generally in powder form, and there will be no problem of foaming agent volatilization. However, chemical foaming is prone to poor dispersion uniformity. In addition, since polylactic acid is prone to oxidation fracture during processing, its melt strength is very low. During the foaming process, bubble rupture and merging are prone to occur, resulting in larger bubble size, low bubble density, and mechanical properties that cannot meet the use requirements.

[0006] How to improve the expandability of polylactic acid materials and regulate the polylactic acid pore structure are the difficulties in preparing polylactic acid foam materials. Summary of the invention

[0007] In order to improve the expandability of polylactic acid materials and obtain a polylactic acid foam material with more uniform pore size distribution, small pore size and excellent mechanical properties, the present application provides a degradable expandable polylactic acid polymer foam material and a preparation method thereof.

[0008] In the first aspect, the present application provides a degradable expandable polylactic acid polymer foam material, which adopts the following technical solution:

[0009] A degradable and expandable polylactic acid polymer foam material, comprising the following raw materials in parts by weight:

[0010] 100-120 parts of polylactic acid-starch-polyamide blended modified mixture, 20-30 parts of polylactic acid foam material waste scraps, 8-15 parts of foaming agent, 0.5-0.8 parts of nucleating agent, 0.1-0.3 parts of activator;

[0011] The polylactic acid-starch-polyamide blended modified mixture is prepared by melt mixing polylactic acid, acylated starch and polyamide according to a mass ratio of 10: (0.2-0.3): (0.05-0.1).

[0012] By adopting the above technical scheme, the raw material base material in the present application uses polylactic acid-starch-polyamide blended modified mixture and polylactic acid foamed material waste scraps as main raw materials, the polylactic acid-starch-polyamide blended modified mixture uses polylactic acid as the main material, and is modified by acylation of starch and polyamide. Starch is a completely degradable material, and starch contains a large number of hydroxyl groups, while polyamide contains amide bonds. Hydroxyl groups and amide bonds can form a hydrogen bond network after blending with polylactic acid, thereby improving the melt strength of polylactic acid, and the starch particles are uniformly dispersed in the polylactic acid matrix to play a certain reinforcing role. These particles are fixed on the polylactic acid molecular chain like anchor points to prevent the molecular chain from excessively slipping and flowing in the molten state, thereby improving the melt strength. The blend has a higher melt strength, and can better withstand the pressure in the subsequent foaming process during the cell growth process, thereby reducing the rupture and merging of cells, and obtaining a polylactic acid foam material with higher cell density, smaller size and more uniformity, and better mechanical properties.

[0013] In addition, the acylated starch in the present application helps to improve the compatibility between starch and polylactic acid, which is more conducive to the uniform dispersion of starch particles in the polylactic acid matrix, reduces the agglomeration line phenomenon of starch particles in the polylactic acid, and thus enhances the overall strength. Moreover, the interaction force between the polyamide molecular chains is strong, and a tighter network structure can be formed. Finally, the acylated starch and polyamide play a complementary effect when modifying polylactic acid. The acylated starch improves the compatibility between starch and polylactic acid, has better dispersion performance and better improves its melt strength. The reinforcing effect of polyamide significantly improves the melt strength of polylactic acid, and also makes the formed bubbles more stable, which ultimately helps to obtain a foaming material with higher bubble density, smaller size and more uniformity.

[0014] On the other hand, a portion of waste scraps of polylactic acid foaming materials are added to the raw materials in the present application. The pore structure existing in the waste scraps is retained during the melt mixing process, and the pore structure existing in the waste scraps provides more sites for the nucleation of bubbles, becoming the nucleation points of bubbles. Compared with a uniform melt without a pore structure, a melt containing a pore structure can form a large number of bubble nuclei faster during foaming, and the pore structure itself provides more sites for the nucleation of bubbles, so that the number of bubbles increases and the distribution is more uniform, and the growth space of the bubbles is relatively reduced, thereby reducing the risk of bubble rupture and merging. Finally, after the bubble nuclei are formed, as the gas diffuses and the melt cools, the bubbles gradually grow and finally take shape. The obtained polylactic acid foaming material has a higher bubble density and a smaller bubble size. At the same time, due to the uniform distribution of bubbles, the overall foaming of the foaming material is also more uniform, thereby improving the foaming structure of the foaming material.

[0015] Optionally, the acylated starch is prepared by the following method:

[0016] 1) Mix starch and water, raise the temperature to 78-85°C, keep warm for 20-30 minutes, then adjust the pH value to 5-6 to obtain a mixed solution;

[0017] 2) Mix maleic anhydride and dimethylformamide to prepare a modifier solution;

[0018] 3) Add the modifier solution dropwise to the mixed solution prepared in step 1), react for 20-30 minutes, add peracetic acid, continue to react for 40-60 minutes, cool, adjust the pH to neutral, then add ethanol for precipitation, wash the precipitate with acetone solution, and dry to obtain acylated starch.

[0019] By adopting the above technical scheme, the starch is first mixed with water and heated at a high temperature to achieve gelatinization of the starch. During the gelatinization process, the crystalline region of the starch is destroyed, and the crystallinity decreases to form a looser molecular structure. On the one hand, the starch molecules with a non-crystalline structure are more compatible with polylactic acid and are more evenly dispersed. On the other hand, the starch with a loose non-crystalline structure is more conducive to the subsequent acylation reaction of maleic anhydride and the subsequent in-depth modification, and finally the modification effect on polylactic acid is better, and the foaming structure of the obtained polylactic acid foam material is more uniform and the bubbles are smaller.

[0020] Optionally, when preparing acylated starch, the acylated starch obtained in step 3) is further treated by the following steps:

[0021] 4) Immerse the acylated starch in a treatment solution for 30-40 minutes. The treatment solution is prepared by mixing 1-carboxymethyl-3-methylimidazolium tetrafluoroborate, 1-ethylmethyl-3-methylimidazolium tetrafluoroborate and water in a mass ratio of 10: (0.2-0.3): (0.1-0.2).

[0022] By adopting the above technical scheme, in the present application, after the acylation modification treatment of starch is achieved by maleic anhydride, the acylated starch is also treated in carboxymethyl and ester ionic liquids. The carboxyl groups in the carboxymethyl ionic liquids can react with the hydroxyl groups on the starch to introduce carboxyl groups, introduce more polar interactions, and interfere with the orderly arrangement of the starch, thereby reducing its crystallinity. When blended with polylactic acid, more amorphous regions can be formed, which is more conducive to the nucleation and growth of bubbles during the foaming process. In addition, the treatment with ester ionic liquids helps to improve the compatibility of acylated starch with polylactic acid. It is found that the acylated starch after the above treatment forms a more uniform dispersed phase with polylactic acid, which can further improve the pore structure of the polylactic acid foaming material.

[0023] Optionally, when preparing acylated starch, gas is introduced during the impregnation process in step 4), wherein the gas is nitrogen or air, and the gas flow rate is 1-3 L / min.

[0024] By adopting the above technical solution, gas is introduced during the immersion treatment of acylated starch in ionic liquid, which, on the one hand, helps to improve and add the penetration and modification process of ionic liquid on acylated starch, promotes uniform distribution on the surface of starch particles, and improves the treatment effect; on the other hand, the introduction of gas forms a microporous structure inside the starch particles, and finally the acylated starch has a certain pore structure, which, on the one hand, improves the compatibility with polylactic acid, and more importantly, provides nucleation points and growth points of pores in the subsequent pore forming process, which helps to obtain a polylactic acid foaming material with a better pore structure.

[0025] Optionally, during the preparation of acylated starch, the added mass ratio of starch to water in step 1) is 1:(5-7);

[0026] In step 2), the mass ratio of maleic anhydride to dimethylformamide is 1:(2-4);

[0027] In step 3), the mass ratio of the modifier solution to the mixed solution is 1:(3-5), and the amount of peracetic acid added is 1-3wt% of the amount of maleic anhydride added.

[0028] Optionally, the foaming agent is an AC foaming agent;

[0029] The nucleating agent is selected from one or more of montmorillonite, nano titanium dioxide, and TMC series nucleating agents;

[0030] The activator is a mixture of octadecyltrimethylammonium bromide and zinc oxide in a mass ratio of 1:(2-3).

[0031] By adopting the above technical scheme, the addition of nucleating agent can increase the crystallization rate and expand the polymer crystallization window, thereby indirectly improving the melt strength. The addition of zinc oxide in the activator can reduce the decomposition temperature of AC foaming agent and increase its gas emission. Octadecyltrimethylammonium bromide reduces the agglomeration of the foaming agent.

[0032] Optionally, the foaming agent is added after being prepared into a microcapsule foaming agent by microencapsulation treatment, and the microcapsule foaming agent is prepared by the following method:

[0033] Chitosan and acetic acid solution are mixed, and heated until chitosan is completely dissolved to form a uniform chitosan solution; AC foaming agent is dissolved in sodium hydroxide solution to form a core material solution, and then the core material solution is added to the chitosan solution, and a mixture of sodium dodecyl sulfate and polyethylene glycol is added, and the mixture is stirred to form a microcapsule suspension, and then the microcapsule suspension is dripped into a polyurethane prepolymer, and then glutaraldehyde is dripped at the same time, and the reaction is carried out at 45-55°C for 2-4 hours, followed by centrifugation, washing and drying to obtain a microcapsule foaming agent.

[0034] By adopting the above technical scheme, in the present application, chitosan is dissolved in an acetic acid solution and heated to achieve complete dissolution of the chitosan, and then the AC foaming agent is dissolved in a sodium hydroxide alkaline solution, and the interfacial tension between the core material and the wall material is reduced under the action of an emulsifier to promote the formation of microcapsules, and finally the microcapsule suspension is dripped into a polyurethane prepolymer, and glutaraldehyde is dripped as a curing agent. Glutaraldehyde can react with amino groups or hydroxyl groups in chitosan to form covalent bonds, thereby curing the chitosan wall material, and the polyurethane prepolymer can also form a cross-linked network structure with chitosan, promote the curing of chitosan, and achieve the curing of the AC foaming agent core material to form a microcapsule foaming agent.

[0035] Finally, the foaming agent in this application is added in the form of a microcapsule foaming agent, which can achieve a sustained release of the foaming agent, making the foaming process more uniform, and combined with the nucleation point effect of the pore structure in the waste scraps of the polylactic acid foaming material, the polylactic acid polymer foaming material finally prepared in this application has a more uniform size distribution and a smaller pore size, and at the same time has excellent mechanical properties.

[0036] In addition, chitosan and polylactic acid have good biocompatibility. The microcapsule foaming agent with chitosan as the wall material is more easily compatible with the polylactic acid matrix, which is beneficial to the dispersion and stability of the microcapsules in the polylactic acid matrix. Chitosan and polylactic acid are both degradable materials. Therefore, the microcapsule foaming agent with chitosan as the wall material is more easily degraded by the natural environment after disposal, which is beneficial to reduce environmental pollution.

[0037] Optionally, during the preparation of the microcapsule foaming agent, the mass ratio of chitosan to acetic acid solution is 1:(4-6), and the mass concentration of the acetic acid solution is 5-10%; the mass ratio of AC foaming agent to sodium hydroxide solution is 1:(3-5), and the mass concentration of sodium hydroxide solution is 5-10%; the mass ratio of core material solution to chitosan solution is 1:(1.1-1.3), and the mass ratio of sodium dodecyl sulfate to polyethylene glycol is 1:(0.6-0.8), and the amount of sodium dodecyl sulfate added is 0.3-0.8wt% of the amount of chitosan added, the amount of polyurethane prepolymer added is 10-15wt% of the amount of chitosan added, and the amount of glutaraldehyde added is 5-10wt% of the amount of chitosan added.

[0038] Optionally, during the preparation of the microcapsule foaming agent, chitosan and acetic acid solution are mixed and heated to dissolve, and then ammonium bicarbonate is added after the temperature is cooled to 40-50° C., and the amount of ammonium bicarbonate added is 5-10wt% of the amount of chitosan added.

[0039] By adopting the above technical solution, when the foaming agent is microencapsulated, sodium bicarbonate is also added and dispersed in the wall material chitosan. Subsequently, the sodium bicarbonate can be decomposed to form gas at a lower temperature. When it is added to the polylactic acid system for foaming treatment, it can first decompose to generate gas and simultaneously form a foaming agent channel to achieve the slow release of the foaming agent.

[0040] In a second aspect, the present application provides a method for preparing a degradable expandable polylactic acid polymer foam material, using the following technical solution:

[0041] A method for preparing a degradable expandable polylactic acid polymer foam material comprises the following steps:

[0042] Polylactic acid, acylated starch and polyamide are melt-mixed in proportion to obtain a polylactic acid-starch-polyamide blended modified mixture, and then the polylactic acid-starch-polyamide blended modified mixture is weighed and mixed with polylactic acid foam material waste scraps, a foaming agent, a nucleating agent and an activator. The mixing temperature is 90-120° C., the mixing time is 30-40 minutes, and then the foaming masterbatch is extruded and pelletized to obtain the foaming masterbatch. The foaming masterbatch is then molded and foamed. The foaming temperature is 160-165° C. and the foaming time is 50-70 minutes.

[0043] By adopting the above technical solution, the preparation method provided in the present application is simple, convenient and easy to realize industrialization, and the foamed material finally obtained has small pores and is evenly distributed.

[0044] In summary, this application has the following beneficial effects:

[0045] 1. In the present application, the raw material base material is mainly composed of a polylactic acid-starch-polyamide blended modified mixture and waste scraps of polylactic acid foaming materials. The polylactic acid-starch-polyamide blended modified mixture is mainly composed of polylactic acid, which is modified by acylation of starch and polyamide. Starch is a completely degradable material, and starch contains a large number of hydroxyl groups, while polyamide contains amide bonds. Hydroxyl groups and amide bonds can form a hydrogen bond network after blending with polylactic acid, thereby improving the melt strength of polylactic acid. In addition, the starch particles are uniformly dispersed in the polylactic acid matrix, which plays a certain reinforcing role. These particles are fixed on the polylactic acid molecular chain like anchor points to prevent the molecular chain from slipping and flowing in a molten state, thereby improving the melt strength. The blend has a higher melt strength, and can better withstand the pressure in the subsequent foaming process during the cell growth process, thereby reducing the rupture and merging of cells, and obtaining a polylactic acid foam material with a higher cell density, smaller size and more uniformity, and better mechanical properties;

[0046] 2. In the present application, a portion of waste scraps of polylactic acid foaming materials are added to the raw materials. The pore structure existing in the waste scraps is retained during the melt mixing process, and the pore structure existing in the waste scraps provides more sites for the nucleation of bubbles, becoming the nucleation points of bubbles. Compared with a uniform melt without a pore structure, a melt containing a pore structure can form a large number of bubble nuclei faster during foaming, and the pore structure itself provides more sites for the nucleation of bubbles, so that the number of bubbles increases and the distribution is more uniform, and the growth space of the bubbles is relatively reduced, thereby reducing the risk of bubble rupture and merging. Finally, after the bubble nuclei are formed, with the diffusion of gas and the cooling of the melt, the bubbles gradually grow and finally take shape. The obtained polylactic acid foaming material has a higher bubble density and a smaller bubble size. At the same time, due to the uniform distribution of bubbles, the overall foaming of the foaming material is more uniform, thereby improving the foaming structure of the foaming material. DETAILED DESCRIPTION

[0047] The present application is further described in detail below in conjunction with the examples. It is particularly noted that if no specific conditions are specified in the following examples, the experiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources.

[0048] In the following embodiments and preparation examples, the polylactic acid is 8052D foaming grade PLA produced by NatureWorks;

[0049] The polyamide is PA66 with the grade of 102L;

[0050] The polyurethane prepolymer is a polyurethane prepolymer of model 103837-45-2 produced by Hubei Langbowan Biopharmaceutical Co., Ltd.;

[0051] The waste scraps of polylactic acid foam material are the waste scraps generated during the subsequent cutting and other sizing processes of the polylactic acid foam material.

[0052] The following preparation example is an example of the preparation of acylated starch

[0053] Preparation Example 1

[0054] A method for preparing acylated starch comprises the following steps:

[0055] 1) Mix corn starch and water in a mass ratio of 1:6, heat to 80°C, keep warm for 25 minutes, and adjust the pH value to 5 to obtain a mixed solution;

[0056] 2) Mix maleic anhydride and dimethylformamide in a mass ratio of 1:3 to prepare a modifier solution;

[0057] 3) Add the modifier solution dropwise to the mixed solution prepared in step 1), the reaction temperature is 80°C, and after reacting for 25 minutes, add peracetic acid, continue the reaction for 50 minutes, cool, adjust the pH to neutral, and then add ethanol for precipitation. Wash the precipitate with acetone solution and dry to obtain acylated starch, wherein the mass ratio of the modifier solution to the mixed solution is 1:4, and the amount of peracetic acid added is 2wt% of the amount of maleic anhydride added.

[0058] Preparation Example 2

[0059] A method for preparing acylated starch comprises the following steps:

[0060] 1) Mix corn starch and water in a mass ratio of 1:5, heat to 78°C, keep warm for 30 minutes, and adjust the pH value to 5 to obtain a mixed solution;

[0061] 2) Mix maleic anhydride and dimethylformamide in a mass ratio of 1:2 to prepare a modifier solution;

[0062] 3) Add the modifier solution dropwise to the mixed solution prepared in step 1), the reaction temperature is 85°C, and after reacting for 20 minutes, add peracetic acid, continue the reaction for 40 minutes, cool, adjust the pH to neutral, and then add ethanol for precipitation. Wash the precipitate with acetone solution and dry to obtain acylated starch, wherein the mass ratio of the modifier solution to the mixed solution is 1:3, and the amount of peracetic acid added is 1-3wt% of the amount of maleic anhydride added.

[0063] Preparation Example 3

[0064] A method for preparing acylated starch comprises the following steps:

[0065] 1) Mix corn starch and water in a mass ratio of 1:7, heat to 85°C, keep warm for 20 minutes, and adjust the pH value to 6 to obtain a mixed solution;

[0066] 2) Mix maleic anhydride and dimethylformamide in a mass ratio of 1:4 to prepare a modifier solution;

[0067] 3) Add the modifier solution dropwise to the mixed solution prepared in step 1), the reaction temperature is 75°C, and after reacting for 30 minutes, add peracetic acid, continue the reaction for 60 minutes, cool, adjust the pH to neutral, and then add ethanol for precipitation. Wash the precipitate with acetone solution and dry to obtain acylated starch, wherein the mass ratio of the modifier solution to the mixed solution is 1:5, and the amount of peracetic acid added is 3wt% of the amount of maleic anhydride added.

[0068] Preparation Example 4

[0069] A method for preparing acylated starch is carried out according to the method in Preparation Example 1, except that the acylated starch prepared in step 3) is further treated by the following steps:

[0070] 4) Immerse the acylated starch in the treatment solution for 35 minutes at a temperature of 40°C. The mass ratio of acylated starch to the treatment solution is 1:9. During the immersion process, gas is introduced, wherein nitrogen gas has a gas flow rate of 2 L / min. The treatment solution is prepared by mixing 1-carboxymethyl-3-methylimidazole tetrafluoroborate, 1-ethylmethyl-3-methylimidazole tetrafluoroborate and water in a mass ratio of 10:0.2:0.1.

[0071] Preparation Example 5

[0072] A method for preparing acylated starch is carried out according to the method in Preparation Example 1, except that the acylated starch prepared in step 3) is further treated by the following steps:

[0073] 4) Immerse the acylated starch in the treatment solution for 30 minutes at a temperature of 45°C. The mass ratio of acylated starch to the treatment solution is 1:8. During the immersion process, gas is introduced, the gas is air, and the gas flow rate is 1 L / min. The treatment solution is prepared by mixing 1-carboxymethyl-3-methylimidazole tetrafluoroborate, 1-ethylmethyl-3-methylimidazole tetrafluoroborate and water in a mass ratio of 10:0.2:0.1.

[0074] Preparation Example 6

[0075] A method for preparing acylated starch is carried out according to the method in Preparation Example 1, except that the acylated starch prepared in step 3) is further treated by the following steps:

[0076] 4) Immerse the acylated starch in the treatment solution for 40 minutes at a temperature of 40°C. The mass ratio of acylated starch to the treatment solution is 1:10. During the immersion process, gas is introduced, wherein nitrogen gas has a gas flow rate of 3 L / min. The treatment solution is prepared by mixing 1-carboxymethyl-3-methylimidazolium tetrafluoroborate, 1-ethylmethyl-3-methylimidazolium tetrafluoroborate and water in a mass ratio of 10:0.3:0.2.

[0077] Preparation Example 7

[0078] A method for preparing acylated starch is carried out according to the method in Preparation Example 4, except that no gas is introduced during the impregnation process.

[0079] Example 1

[0080] A method for preparing a degradable expandable polylactic acid polymer foam material comprises the following steps:

[0081] The polylactic acid, the acylated starch prepared in Preparation Example 1 and the polyamide were melt-mixed in a mass ratio of 10:0.2:0.08 to prepare a polylactic acid-starch-polyamide blended modified mixture;

[0082] Then, 110 kg of the polylactic acid-starch-polyamide blended modified mixture was weighed and mixed with 25 kg of polylactic acid foam material waste scraps, 12 kg of foaming agent, 0.6 kg of nucleating agent and 0.2 kg of activator. The mixing temperature was 100°C and the mixing time was 35 minutes. Then, the foaming masterbatch was extruded and pelletized through a twin-screw extruder (the temperature of each section of the extruder was set to 145°C). The foaming masterbatch was then molded and foamed into shape using a flat vulcanizer. The foaming temperature was 162°C and the foaming time was 60 minutes.

[0083] The foaming agent is AC foaming agent, the nucleating agent is TMC-300, and the activator is a mixture of octadecyltrimethylammonium bromide and zinc oxide in a mass ratio of 1:2.5.

[0084] Example 2

[0085] A method for preparing a degradable expandable polylactic acid polymer foam material comprises the following steps:

[0086] The polylactic acid, the acylated starch prepared in Preparation Example 2 and the polyamide were melt-mixed in a mass ratio of 10:0.2:0.05 to prepare a polylactic acid-starch-polyamide blended modified mixture;

[0087] Then, 100 kg of the polylactic acid-starch-polyamide blended modified mixture was weighed and mixed with 20 kg of polylactic acid foam material waste scraps, 8 kg of foaming agent, 0.5 kg of nucleating agent and 0.1 kg of activator. The mixing temperature was 90°C and the mixing time was 40 minutes. Then, the foaming masterbatch was extruded and pelletized through a twin-screw extruder (the temperature of each section of the extruder was set to 145°C). Then, the foaming masterbatch was molded and foamed into shape using a flat vulcanizer. The foaming temperature was 160°C and the foaming time was 70 minutes.

[0088] The foaming agent is AC foaming agent, the nucleating agent is montmorillonite, and the activating agent is a mixture of octadecyltrimethylammonium bromide and zinc oxide in a mass ratio of 1:2.

[0089] Example 3

[0090] A method for preparing a degradable expandable polylactic acid polymer foam material comprises the following steps:

[0091] The polylactic acid, the acylated starch prepared in Preparation Example 3 and the polyamide were melt-mixed in a mass ratio of 10:0.3:0.1 to prepare a polylactic acid-starch-polyamide blended modified mixture;

[0092] Then, 120 kg of the polylactic acid-starch-polyamide blended modified mixture was weighed and mixed with 30 kg of polylactic acid foam material waste scraps, 15 kg of foaming agent, 0.8 kg of nucleating agent and 0.3 kg of activator. The mixing temperature was 120°C and the mixing time was 30 minutes. Then, the foaming masterbatch was extruded and pelletized through a twin-screw extruder (the temperature of each section of the extruder was set to 145°C). The foaming masterbatch was then molded and foamed into shape using a flat vulcanizer. The foaming temperature was 165°C and the foaming time was 50 minutes.

[0093] The foaming agent is AC foaming agent, the nucleating agent is TMC-300, and the activator is a mixture of octadecyltrimethylammonium bromide and zinc oxide in a mass ratio of 1:3.

[0094] Embodiment 4-7

[0095] A method for preparing a degradable expandable polylactic acid polymer foam material is carried out according to the method in Example 1, except that when preparing the polylactic acid-starch-polyamide blended modified mixture, the acylated starch is selected from the acylated starch prepared in Preparation Examples 4-7.

[0096] Example 8

[0097] A method for preparing a degradable expandable polylactic acid polymer foam material is carried out according to the method in Example 4, except that the AC foaming agent is added after being prepared into a microcapsule foaming agent by microencapsulation treatment, and the microcapsule foaming agent is prepared by the following method:

[0098] Mix chitosan and acetic acid solution in a mass ratio of 1:5, the mass concentration of the acetic acid solution is 5-10%, and heat until the chitosan is completely dissolved to form a uniform chitosan solution;

[0099] The AC foaming agent is dissolved in a sodium hydroxide solution with a mass concentration of 8%, and the mass ratio of the AC foaming agent to the sodium hydroxide solution is 1:4 to form a core material solution;

[0100] Then the core material solution is added to the chitosan solution, and a mixture of sodium dodecyl sulfate and polyethylene glycol is added, and the mixture is stirred to form a microcapsule suspension. The microcapsule suspension is then dropped into the polyurethane prepolymer, and then glutaraldehyde is dropped at the same time. After reacting at 50°C for 3 hours, the mixture is centrifuged, washed, and dried to obtain a microcapsule foaming agent.

[0101] The addition mass ratio of the core material solution to the chitosan solution is 1:1.2, and the addition mass ratio of sodium dodecyl sulfate to polyethylene glycol is 1:0.7, and the addition amount of sodium dodecyl sulfate is 0.5wt% of the addition amount of chitosan, the addition amount of polyurethane prepolymer is 12wt% of the addition amount of chitosan, and the addition amount of glutaraldehyde is 8wt% of the addition amount of chitosan.

[0102] Example 9

[0103] A method for preparing a degradable expandable polylactic acid polymer foam material is carried out according to the method in Example 4, except that the AC foaming agent is added after being prepared into a microcapsule foaming agent by microencapsulation treatment, and the microcapsule foaming agent is prepared by the following method:

[0104] Chitosan and acetic acid solution were mixed in a mass ratio of 1:4, the mass concentration of the acetic acid solution was 5%, and heated until the chitosan was completely dissolved to form a uniform chitosan solution;

[0105] The AC foaming agent is dissolved in a sodium hydroxide solution with a mass concentration of 5%, and the mass ratio of the AC foaming agent to the sodium hydroxide solution is 1:3 to form a core material solution;

[0106] Then the core material solution is added to the chitosan solution, and a mixture of sodium dodecyl sulfate and polyethylene glycol is added, and the mixture is stirred to form a microcapsule suspension. The microcapsule suspension is then dropped into the polyurethane prepolymer, and then glutaraldehyde is dropped at the same time. After reacting at 45°C for 4 hours, the mixture is centrifuged, washed, and dried to obtain a microcapsule foaming agent.

[0107] The addition mass ratio of the core material solution to the chitosan solution is 1:1.1, and the addition mass ratio of sodium dodecyl sulfate to polyethylene glycol is 1:0.6, and the addition amount of sodium dodecyl sulfate is 0.3wt% of the addition amount of chitosan, the addition amount of polyurethane prepolymer is 10wt% of the addition amount of chitosan, and the addition amount of glutaraldehyde is 5wt% of the addition amount of chitosan.

[0108] Example 10

[0109] A method for preparing a degradable expandable polylactic acid polymer foam material is carried out according to the method in Example 4, except that the AC foaming agent is added after being prepared into a microcapsule foaming agent by microencapsulation treatment, and the microcapsule foaming agent is prepared by the following method:

[0110] Chitosan and acetic acid solution were mixed in a mass ratio of 1:6, the mass concentration of the acetic acid solution was 10%, and heated until the chitosan was completely dissolved to form a uniform chitosan solution;

[0111] The AC foaming agent is dissolved in a sodium hydroxide solution with a mass concentration of 10%, and the mass ratio of the AC foaming agent to the sodium hydroxide solution is 1:5 to form a core material solution;

[0112] Then the core material solution is added to the chitosan solution, and a mixture of sodium dodecyl sulfate and polyethylene glycol is added, and the mixture is stirred to form a microcapsule suspension. The microcapsule suspension is then dropped into the polyurethane prepolymer, and then glutaraldehyde is dropped at the same time. After reacting at 55°C for 2 hours, the mixture is centrifuged, washed, and dried to obtain a microcapsule foaming agent.

[0113] The addition mass ratio of the core material solution to the chitosan solution is 1:1.3, and the addition mass ratio of sodium dodecyl sulfate to polyethylene glycol is 1:0.8, and the addition amount of sodium dodecyl sulfate is 0.8wt% of the addition amount of chitosan, the addition amount of polyurethane prepolymer is 15wt% of the addition amount of chitosan, and the addition amount of glutaraldehyde is 10wt% of the addition amount of chitosan.

[0114] Embodiment 11

[0115] A method for preparing a degradable expandable polylactic acid polymer foam material is carried out according to the method in Example 8, except that, during the preparation of the microcapsule foaming agent, after chitosan and acetic acid solution are mixed and heated to dissolve, ammonium bicarbonate is added after the temperature is cooled to 45°C, and the amount of ammonium bicarbonate added is 8wt% of the amount of chitosan added.

[0116] Example 12

[0117] A method for preparing a degradable expandable polylactic acid polymer foam material is carried out according to the method in Example 8, except that, during the preparation of the microcapsule foaming agent, after chitosan and acetic acid solution are mixed and heated to dissolve, ammonium bicarbonate is added after the temperature is cooled to 40°C, and the amount of ammonium bicarbonate added is 5wt% of the amount of chitosan added.

[0118] Example 13

[0119] A method for preparing a degradable expandable polylactic acid polymer foam material is carried out according to the method in Example 8, except that, during the preparation of the microcapsule foaming agent, after chitosan and acetic acid solution are mixed and heated to dissolve, ammonium bicarbonate is added after the temperature is cooled to 50°C, and the amount of ammonium bicarbonate added is 10wt% of the amount of chitosan added.

[0120] Comparative Example 1

[0121] A method for preparing a degradable expandable polylactic acid polymer foam material is carried out according to the method in Example 1, except that an equal amount of the polylactic acid-starch-polyamide blended modified mixture is replaced by a polylactic acid raw material.

[0122] Comparative Example 2

[0123] A method for preparing a degradable expandable polylactic acid polymer foam material is carried out according to the method in Example 1, except that an equal amount of acylated starch is replaced by starch during the preparation of the polylactic acid-starch-polyamide blended modified mixture.

[0124] Comparative Example 3

[0125] A method for preparing a degradable and expandable polylactic acid polymer foam material is carried out according to the method in Example 1, except that no waste scraps of the polylactic acid foam material are added to the raw materials.

[0126] Comparative Example 4

[0127] A method for preparing a degradable and expandable polylactic acid polymer foam material is carried out according to the method in Example 1, except that an equal amount of waste scraps of polylactic acid foam material in the raw material is replaced by polylactic acid raw material.

[0128] Performance Testing

[0129] A polylactic acid foamed plate was prepared according to the method in the above embodiments and comparative examples, and the foamed sample was analyzed and processed using image analysis software ImagePro Plus6.0 to calculate the average pore diameter and pore density (the average number of pores per unit volume (cubic centimeter)). In addition, the pore size variance of the uniformity of pore size distribution was calculated. The statistical results are shown in Table 1 below.

[0130] Table 1:

[0131]

[0132] According to the test results in Table 1 above, the average pore size of the polylactic acid foamed material obtained in the examples of the present application reaches the micron level, and the cell density is large, the variance is small, and the cell distribution is more uniform. Combined with the test results of Example 1 and Examples 4-6, it can be seen that when the acylated starch in the raw material is treated in the ionic liquid and aerated at the same time, its cell diameter is smaller, the cell density is larger, and the cell distribution is more uniform. Combined with the test results of Example 7, when the acylated starch is immersed in the ionic liquid without aeration, its cell diameter increases, and the uniformity of cell dispersion is also reduced.

[0133] Referring to the test results of Example 1 and Examples 8-10, when the foaming agent is added in the form of microcapsules, a foaming slow-release effect is achieved, and the final foaming effect is better, the obtained pore diameter is smaller, the density is large, and the pore distribution is more uniform. In combination with the test results of Examples 11-13, when ammonium bicarbonate is added during microencapsulation, the expandability of the polylactic acid foam material is further improved, and the foaming effect is better. Referring to the test results of Comparative Example 1, the addition of modified polylactic acid significantly improves its foaming performance. In combination with the test results of Comparative Example 2, starch is more conducive to uniform foaming after acylation. Referring to the test results of Comparative Examples 3 and 4, the addition of waste edge materials of polylactic acid foam material as raw materials has a significant positive promoting effect on the foaming performance of polylactic acid.

[0134] Finally, the tensile strength and impact strength of the polylactic acid foamed plates prepared in the examples and comparative examples of the present application were tested, and the test results are shown in Table 2 below.

[0135] Table 2:

[0136]

[0137] Referring to the test results in Table 2 above, the polylactic acid foamed board prepared in the examples of the present application has excellent mechanical properties.

[0138] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A degradable expandable polylactic acid polymer foam material, characterized in that: It includes the following raw materials in parts by weight: 100-120 parts of polylactic acid-starch-polyamide blended modified mixture, 20-30 parts of polylactic acid foam material waste scraps, 8-15 parts of foaming agent, 0.5-0.8 parts of nucleating agent, 0.1-0.3 parts of activator; The polylactic acid-starch-polyamide blended modified mixture is prepared by melt mixing polylactic acid, acylated starch and polyamide according to a mass ratio of 10: (0.2-0.3): (0.05-0.1); the acylated starch is prepared by the following method: 1) Mix starch and water, raise the temperature to 78-85°C, keep warm for 20-30 minutes, then adjust the pH value to 5-6 to obtain a mixed solution; 2) Mix maleic anhydride and dimethylformamide to prepare a modifier solution; 3) Add the modifier solution dropwise to the mixed solution prepared in step 1), react for 20-30 minutes, add peracetic acid, continue to react for 40-60 minutes, cool, adjust the pH to neutral, then add ethanol for precipitation, wash the precipitate with acetone solution, and dry to obtain acylated starch; The activator is a mixture of octadecyltrimethylammonium bromide and zinc oxide in a mass ratio of 1:(2-3).

2. The degradable expandable polylactic acid polymer foam material according to claim 1, characterized in that: When preparing acylated starch, the acylated starch obtained in step 3) is further processed by the following steps: 4) Immerse the acylated starch in a treatment solution for 30-40 minutes. The treatment solution is prepared by mixing 1-carboxymethyl-3-methylimidazolium tetrafluoroborate, 1-ethylmethyl-3-methylimidazolium tetrafluoroborate and water in a mass ratio of 10: (0.2-0.3): (0.1-0.2).

3. The degradable expandable polylactic acid polymer foam material according to claim 2, characterized in that: When preparing acylated starch, gas is also introduced during the impregnation process in step 4), and the gas is nitrogen or air, and the gas flow rate is 1-3 L / min.

4. The degradable expandable polylactic acid polymer foam material according to claim 1, characterized in that: In the preparation process of acylated starch, the added mass ratio of starch to water in step 1) is 1:(5-7); In step 2), the mass ratio of maleic anhydride to dimethylformamide is 1:(2-4); In step 3), the mass ratio of the modifier solution to the mixed solution is 1:(3-5), and the amount of peracetic acid added is 1-3wt% of the amount of maleic anhydride added.

5. The degradable expandable polylactic acid polymer foam material according to claim 1, characterized in that: The foaming agent is AC foaming agent; The nucleating agent is selected from one or more of montmorillonite, nano titanium dioxide, and TMC series nucleating agents.

6. The degradable expandable polylactic acid polymer foam material according to claim 1, characterized in that: The foaming agent is added after being prepared into a microcapsule foaming agent by microencapsulation treatment. The microcapsule foaming agent is prepared by the following method: Chitosan and acetic acid solution are mixed, and heated until chitosan is completely dissolved to form a uniform chitosan solution; AC foaming agent is dissolved in sodium hydroxide solution to form a core material solution, and then the core material solution is added to the chitosan solution, and a mixture of sodium dodecyl sulfate and polyethylene glycol is added, and the mixture is stirred to form a microcapsule suspension, and then the microcapsule suspension is dripped into a polyurethane prepolymer, and then glutaraldehyde is dripped at the same time, and the reaction is carried out at 45-55°C for 2-4 hours, followed by centrifugation, washing and drying to obtain a microcapsule foaming agent.

7. The degradable expandable polylactic acid polymer foam material according to claim 6, characterized in that: In the preparation process of the microcapsule foaming agent, the addition mass ratio of chitosan to acetic acid solution is 1: (4-6), and the mass concentration of the acetic acid solution is 5-10%; the addition mass ratio of AC foaming agent to sodium hydroxide solution is 1: (3-5), and the mass concentration of sodium hydroxide solution is 5-10%; the addition mass ratio of core material solution to chitosan solution is 1: (1.1-1.3), and the addition mass ratio of sodium dodecyl sulfate to polyethylene glycol is 1: (0.6-0.8), and the addition amount of sodium dodecyl sulfate is 0.3-0.8wt% of the addition amount of chitosan, the addition amount of polyurethane prepolymer is 10-15wt% of the addition amount of chitosan, and the addition amount of glutaraldehyde is 5-10wt% of the addition amount of chitosan.

8. The method for preparing the degradable expandable polylactic acid polymer foam material according to any one of claims 1 to 7, characterized in that: The following steps are involved: Polylactic acid, acylated starch and polyamide are melt-mixed in proportion to obtain a polylactic acid-starch-polyamide blended modified mixture, and then the polylactic acid-starch-polyamide blended modified mixture is weighed and mixed with polylactic acid foam material waste scraps, a foaming agent, a nucleating agent and an activator. The mixing temperature is 90-120° C., the mixing time is 30-40 minutes, and then the foaming masterbatch is extruded and pelletized to obtain the foaming masterbatch. The foaming masterbatch is then molded and foamed. The foaming temperature is 160-165° C. and the foaming time is 50-70 minutes.

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