Foaming biodegradable polymer sheet and preparation method thereof

Abstract

The invention relates to a foamed biodegradable polymer sheet and a preparation method thereof, and belongs to the technical field of foamed materials, the foamed biodegradable polymer sheet is prepared from the following raw materials in parts by weight: 100 parts of polylactic acid, 0.5-2 parts of modified graphene oxide, 10-40 parts of cellulose, 1-5 parts of a foaming agent, 2-5 parts of a compatibilizer and 1-1.5 parts of an antioxidant, the raw materials are dried, mixed, extruded, granulated and molded, and the foamed biodegradable polymer sheet is obtained. A foamed biodegradable polymer sheet is obtained; the polymer sheet prepared by the invention not only has the advantages of uniform foam pore distribution, complete foam pore structure and the like, but also has excellent mechanical properties and controllable biological decomposition rate, and has wide application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of foaming materials, and in particular relates to a foaming biodegradable polymer sheet and a preparation method thereof. Background Art

[0002] Polylactic acid (PLA), a biodegradable polymer made from renewable plant resources, exhibits excellent biocompatibility and compostability, showing broad application prospects in packaging, building materials, daily necessities, and other fields. However, pure PLA suffers from two inherent drawbacks that significantly limit its application prospects. First, PLA is highly brittle and has poor impact resistance, making it susceptible to thermal degradation at high temperatures, resulting in insufficient mechanical properties. Second, pure PLA has low melt strength, a slow crystallization rate, and low crystallinity, resulting in poor uniformity after foaming and a tendency for cell collapse or merging in traditional foaming processes.

[0003] To overcome the above technical defects, existing technologies mainly innovate from the following two dimensions: 1) material composite modification, such as significantly improving the mechanical properties of materials through the design of PLA / PBAT or PLA / PBS blend systems; 2) foaming process optimization, such as using supercritical CO2 foaming technology combined with chemical foaming agent compounding strategies to achieve precise control of the foam structure; however, existing technologies still find it difficult to take into account both foam uniformity and excellent mechanical properties. Therefore, the development of a foamed polymer sheet with uniform foam structure and excellent mechanical properties is of great significance to promoting the development of green packaging and cushioning materials. Summary of the Invention

[0004] In order to solve the technical problems of poor cell uniformity and insufficient mechanical properties mentioned in the background art, the present invention provides a foamed biodegradable polymer sheet and a preparation method thereof.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts of polylactic acid, 0.5-2 parts of modified graphene oxide, 10-40 parts of cellulose, 1-5 parts of a foaming agent, 2-5 parts of a compatibilizer, and 1-1.5 parts of an antioxidant.

[0006] Furthermore, the modified graphene oxide comprises the following raw materials in parts by weight: 100 parts of graphene oxide and 40-60 parts of L-cysteine.

[0007] Furthermore, the modified graphene oxide comprises the following steps: Graphene oxide (GO) is ultrasonically dispersed in deionized water, and the pH is adjusted to 10 with KOH solution to obtain a GO dispersion. L-cysteine ​​(L-Cys) is dissolved in deionized water to obtain an L-Cys solution. The L-Cys solution is added dropwise to the GO dispersion, and the reaction is carried out at 40-60°C under inert atmosphere for 5-12 hours. After the reaction product is cooled to room temperature, it is centrifuged and washed with deionized water and dried to obtain modified graphene oxide. The process mainly utilizes the nucleophilic substitution reaction between the epoxy groups on GO and the amino groups on L-Cysteine ​​to successfully connect cysteine ​​to the graphene sheets, thereby obtaining L-cysteine-modified graphene oxide, i.e., modified graphene oxide.

[0008] Furthermore, the usage ratio of the graphene oxide and deionized water is (2-4) mg:1 mL.

[0009] Furthermore, the usage ratio of L-cysteine ​​to deionized water is (20-40) mg:1 mL.

[0010] Furthermore, the molar concentration of the KOH solution is 0.1-0.3 mol / L.

[0011] Furthermore, the cellulose is any one or both of microcrystalline cellulose and nanocellulose.

[0012] Furthermore, the foaming agent is supercritical carbon dioxide.

[0013] Furthermore, the compatibilizer is maleic anhydride.

[0014] Furthermore, the antioxidant is any one or both of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris[2,4-di-tert-butylphenyl]phosphite.

[0015] A method for preparing a foamed biodegradable polymer sheet comprises the following steps: S1. Drying polylactic acid and cellulose at 60-80° C. for 1-12 h; S2, the dried polylactic acid, cellulose, a compatibilizer, modified graphene oxide and an antioxidant were mixed to obtain a mixture A; S3, adding mixed material A into a twin-screw extruder for blending and granulation, and injecting a foaming agent through the supercritical fluid injection port of the twin-screw extruder during the granulation process; The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain a foamed biodegradable polymer sheet.

[0016] Furthermore, in step S3, the temperature of each zone of the twin-screw extruder is 160-190°C.

[0017] Furthermore, in step S3, the rotation speed of the twin-screw extruder is 200-250 rpm.

[0018] Furthermore, in step S3, the supercritical fluid injection pressure is 12-20 MPa.

[0019] Beneficial effects of the present invention: 1. The present invention uses L-cysteine-modified graphene oxide as a nucleating agent for foamed biopolymer sheets, and significantly improves the foaming performance and mechanical properties of the polymer sheets through a dual optimization mechanism. In terms of foaming performance, since graphene oxide itself has a large specific surface area and rich functional groups, after modification with L-cysteine, its surface active sites are further increased, which can serve as the nucleation center of more bubbles and greatly improve the bubble nucleation density; in terms of mechanical properties, on the one hand, since the two-dimensional lamellar structure of graphene oxide can form a rigid network in the polylactic acid matrix, it can effectively disperse the stress through the slip between the lamellar layers and its own deformation under the action of external force, thereby improving the mechanical properties of the polymer sheet while maintaining its lightweight characteristics; on the other hand, since L-cysteine ​​contains polar groups such as thiol and amino groups, it can combine with graphene oxide through covalent or non-covalent interactions, improve its dispersibility in biopolymers, ensure the uniform distribution of nucleation sites, and the interface interaction between the modified graphene oxide and biopolymers is stronger, which can effectively reduce bubble merging, stabilize the foaming structure, and give the polymer sheet higher mechanical properties.

[0020] 2. The present invention introduces L-cysteine-modified graphene oxide. Since its structure contains a large number of amino and carboxyl groups, these groups can generate strong van der Waals forces with CO2 molecules, thereby increasing the solubility of CO2 in the polymer system, and then promoting the rapid nucleation of pores in the polymer melt, effectively inhibiting the merging of pores and delaying gas escape, ultimately forming a structurally complete pore wall, and significantly improving the mechanical properties of the material.

[0021] 3. The present invention adds cellulose as a filler to the polymer sheet. On the one hand, the compatibility of cellulose and polymer is improved by the compatibilizer maleic anhydride, enhancing interfacial bonding and significantly improving the mechanical properties of the polymer sheet. On the other hand, the preferential degradation of cellulose can expand the contact area between the polymer sheet and microorganisms, providing more attachment sites for microorganisms and increasing the degradation rate of the polymer. In addition, cellulose and the introduced L-cysteine ​​can provide a nutrient source and energy for microorganisms, promoting their growth, thereby enhancing the degradation rate of the polymer. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] Unless otherwise specified, the experimental methods in the following examples are conventional methods and were performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials and reagents used in the following examples, unless otherwise specified, were all commercially available.

[0024] Example 1

[0025] A modified graphene oxide is prepared by the following steps: 1 g of graphene oxide (GO) was ultrasonically dispersed in 500 mL of deionized water, and the pH was adjusted to 10 with 0.1 mol / L KOH solution to obtain a GO dispersion. 0.4 g of L-cysteine ​​(L-Cys) was dissolved in 20 mL of deionized water to obtain an L-Cys solution. The L-Cys solution was added dropwise to the GO dispersion, and the reaction was carried out at 50°C for 12 h under inert atmosphere. After the reaction product was cooled to room temperature, it was centrifuged and washed with deionized water and dried to obtain modified graphene oxide.

[0026] Example 2

[0027] A modified graphene oxide is prepared by the following steps: 1 g of graphene oxide (GO) was ultrasonically dispersed in 250 mL of deionized water, and the pH was adjusted to 10 with 0.2 mol / L KOH solution to obtain a GO dispersion. 0.6 g of L-cysteine ​​(L-Cys) was dissolved in 15 mL of deionized water to obtain an L-Cys solution. The L-Cys solution was added dropwise to the GO dispersion, and the reaction was carried out at 50°C for 12 h under inert atmosphere. After the reaction product was cooled to room temperature, it was centrifuged and washed with deionized water and dried to obtain modified graphene oxide.

[0028] Example 3

[0029] A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts of polylactic acid, 1 part of modified graphene oxide prepared in Example 1, 30 parts of cellulose, 3 parts of a foaming agent, 3 parts of a compatibilizer, and 1 part of an antioxidant; wherein the cellulose is microcrystalline cellulose, the foaming agent is supercritical carbon dioxide, the compatibilizer is maleic anhydride, and the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0030] The foamed biodegradable polymer sheet is made by the following steps: S1, drying polylactic acid and cellulose at 70°C for 12h; S2, the dried polylactic acid, cellulose, a compatibilizer, modified graphene oxide and an antioxidant were mixed to obtain a mixture A; S3. Add mixed material A into a twin-screw extruder for blending and granulation. The temperature of each zone of the twin-screw extruder is 160°C → 170°C → 180°C → 180°C → 180°C → 180°C → 185°C → 185°C → 185°C → 185°C → 180°C → 175°C. The speed of the twin-screw extruder is 220rpm. The foaming agent is injected into the twin-screw melt through the supercritical fluid injection port in the 5th zone of the twin-screw extruder using a mass plunger pump. The injection pressure is 16 MPa. The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain a foamed biodegradable polymer sheet.

[0031] Example 4

[0032] A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts of polylactic acid, 0.5 parts of modified graphene oxide prepared in Example 2, 30 parts of cellulose, 3 parts of a foaming agent, 3 parts of a compatibilizer, and 1 part of an antioxidant; wherein the cellulose is microcrystalline cellulose, the foaming agent is supercritical carbon dioxide, the compatibilizer is maleic anhydride, and the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0033] The foamed biodegradable polymer sheet is made by the following steps: S1, drying polylactic acid and cellulose at 70°C for 12h; S2, the dried polylactic acid, cellulose, a compatibilizer, modified graphene oxide and an antioxidant were mixed to obtain a mixture A; S3. Add mixed material A into a twin-screw extruder for blending and granulation. The temperature of each zone of the twin-screw extruder is 160°C → 170°C → 180°C → 180°C → 180°C → 180°C → 185°C → 185°C → 185°C → 185°C → 180°C → 175°C. The speed of the twin-screw extruder is 220rpm. The foaming agent is injected into the twin-screw melt through the supercritical fluid injection port in the 5th zone of the twin-screw extruder using a mass plunger pump. The injection pressure is 16 MPa. The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain a foamed biodegradable polymer sheet.

[0034] Example 5

[0035] A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts of polylactic acid, 1.5 parts of modified graphene oxide prepared in Example 1, 30 parts of cellulose, 3 parts of a foaming agent, 3 parts of a compatibilizer, and 1 part of an antioxidant; wherein the cellulose is nanocellulose, the foaming agent is supercritical carbon dioxide, the compatibilizer is maleic anhydride, and the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0036] The foamed biodegradable polymer sheet is made by the following steps: S1, drying polylactic acid and cellulose at 70°C for 12h; S2, the dried polylactic acid, cellulose, a compatibilizer and modified graphene oxide and an antioxidant were mixed to obtain a mixture A; S3. Add mixed material A into a twin-screw extruder for blending and granulation. The temperature of each zone of the twin-screw extruder is 160°C → 170°C → 180°C → 180°C → 180°C → 180°C → 185°C → 185°C → 185°C → 185°C → 180°C → 175°C. The speed of the twin-screw extruder is 220rpm. The foaming agent is injected into the twin-screw melt through the supercritical fluid injection port in the 5th zone of the twin-screw extruder using a mass plunger pump. The injection pressure is 16 MPa. The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain a foamed biodegradable polymer sheet.

[0037] Example 6

[0038] A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts of polylactic acid, 1 part of modified graphene oxide prepared in Example 1, 40 parts of cellulose, 3 parts of a foaming agent, 3 parts of a compatibilizer, and 1 part of an antioxidant; wherein the cellulose is microcrystalline cellulose, the foaming agent is supercritical carbon dioxide, the compatibilizer is maleic anhydride, and the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0039] The foamed biodegradable polymer sheet is made by the following steps: S1, drying polylactic acid and cellulose at 70°C for 12h; S2, the dried polylactic acid, cellulose, a compatibilizer and modified graphene oxide and an antioxidant were mixed to obtain a mixture A; S3. Add mixed material A into a twin-screw extruder for blending and granulation. The temperature of each zone of the twin-screw extruder is 160°C → 170°C → 180°C → 180°C → 180°C → 180°C → 185°C → 185°C → 185°C → 185°C → 180°C → 175°C. The speed of the twin-screw extruder is 220rpm. The foaming agent is injected into the twin-screw melt through the supercritical fluid injection port in the 5th zone of the twin-screw extruder using a mass plunger pump. The injection pressure is 16 MPa. The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain a foamed biodegradable polymer sheet.

[0040] Example 7

[0041] A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts of polylactic acid, 1 part of modified graphene oxide prepared in Example 1, 10 parts of cellulose, 3 parts of a foaming agent, 3 parts of a compatibilizer, and 1 part of an antioxidant, wherein the cellulose is microcrystalline cellulose, the foaming agent is supercritical carbon dioxide, the compatibilizer is maleic anhydride, and the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0042] The foamed biodegradable polymer sheet is made by the following steps: S1, drying polylactic acid and cellulose at 70°C for 12h; S2, the dried polylactic acid, cellulose, a compatibilizer and modified graphene oxide and an antioxidant were mixed to obtain a mixture A; S3. Add mixed material A into a twin-screw extruder for blending and granulation. The temperature of each zone of the twin-screw extruder is 160°C → 170°C → 180°C → 180°C → 180°C → 180°C → 185°C → 185°C → 185°C → 185°C → 180°C → 175°C. The speed of the twin-screw extruder is 220rpm. The foaming agent is injected into the twin-screw melt through the supercritical fluid injection port in the 5th zone of the twin-screw extruder using a mass plunger pump. The injection pressure is 16 MPa. The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain a foamed biodegradable polymer sheet.

[0043] Comparative Example 1

[0044] The method of Example 3 was used for preparation, except that the weight portion of the modified graphene oxide was 3 parts.

[0045] Comparative Example 2

[0046] The method of Example 3 was used for preparation, except that no modified graphene oxide was added.

[0047] Comparative Example 3

[0048] The method of Example 3 was used for preparation, except that the modified graphene oxide was replaced with an equal weight portion of graphene oxide.

[0049] Comparative Example 4

[0050] The method of Example 3 was used for preparation, except that the modified graphene oxide was replaced with L-cysteine ​​in equal parts by weight.

[0051] Comparative Example 5

[0052] The method of Example 3 was used for preparation, except that the weight portion of cellulose was 5 parts.

[0053] Comparative Example 6

[0054] The method of Example 3 was used for preparation, except that the weight portion of cellulose was 45 parts.

[0055] In order to more intuitively and clearly demonstrate the differences between the embodiments of the present invention and the comparative examples in terms of various key performance indicators, and to facilitate understanding of the significant advantages of the technical solution of the present invention, the formulas of key materials and experimental results of Examples 3-7 and Comparative Examples 1-6 are listed in Table 1. The specific test method is: Cell density: Tested using a density meter in accordance with the standard GB / T 27868-2011 Tensile strength: tested according to the method of standard GB / T 9614-2008; Elongation at break: tested according to the method of GB / T 9614-2008; Impact strength: tested according to the method of standard GB / T 9614-2008; Biodegradation rate: The biodegradation rate of polymer sheets under industrial composting conditions for 180 days is tested in accordance with the standard GB / T 41010-2021 "Degradation performance and labeling requirements of biodegradable plastics and products".

[0056] Table 1

[0057] As can be seen from Table 1, under the preferred formulation conditions (Examples 3-7), the prepared biopolymer sheets exhibit excellent comprehensive properties: the pore density reaches 6.13×1 The results show that the modified graphene oxide has a surface area of ​​1000 nm and a surface area of ​​1000 nm, a tensile strength of 11.4 MPa or higher, a notched impact strength of 64.8 kJ / m² or higher, and a 180-day biodegradability of over 90.6%. In contrast, the test results of Comparative Examples 1 and 2, and Example 3 show that when an excessive amount of modified graphene oxide is added, the cell density and mechanical properties decrease significantly due to particle agglomeration. When no modified graphene oxide is added, the mechanical properties significantly deteriorate due to the lack of nucleation and nano-enhancement effects. The test results of Comparative Examples 3 and 4, and Example 3, show that when an equal amount of graphene oxide is added, the lack of L-cysteine ​​modification reduces its surface active sites, lowers CO2 solubility in the polymer system, and results in relatively poor dispersion of graphene oxide in the polymer system, leading to decreased cell density and mechanical properties. When an equal amount of L-cysteine ​​is added, the lack of nucleation and nano-enhancement effects of the graphene oxide also lead to decreased cell density and mechanical properties. Combining the test results of Comparative Examples 5, 6 and Example 3, it can be seen that although excessive cellulose can increase the degradation rate, it will destroy the continuity of the matrix, resulting in an increase in surface defects and a decrease in mechanical properties; when insufficient cellulose is added, the mechanical properties and degradation rate will decrease simultaneously due to insufficient interface toughening and degradation promotion.

[0058] The above results show that by precisely controlling the addition ratio of modified graphene oxide and cellulose, the synergistic optimization of the material's mechanical properties and degradation rate can be achieved, providing an important basis for the development of high-performance, controllable, and degradable biopolymer materials.

[0059] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0060] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A foamed biodegradable polymer sheet, characterized in that: The invention comprises the following raw materials in parts by weight: 100 parts of polylactic acid, 0.5-2 parts of modified graphene oxide, 10-40 parts of cellulose, 1-5 parts of foaming agent, 2-5 parts of compatibilizer, and 1-1.5 parts of antioxidant; The preparation of the modified graphene oxide includes the following raw materials in parts by weight: 100 parts of graphene oxide and 40-60 parts of L-cysteine.

2. The foamed biodegradable polymer sheet according to claim 1, characterized in that: The modified graphene oxide comprises the following steps: Graphene oxide was ultrasonically dispersed in deionized water, and the pH was adjusted to 10 with a KOH solution to obtain a GO dispersion. L-cysteine ​​was dissolved in deionized water to obtain an L-Cys solution. The L-Cys solution was added dropwise to the GO dispersion, and the reaction was carried out at 40-60°C under an inert atmosphere for 5-12 hours. After the reaction product was cooled to room temperature, it was centrifuged and washed with deionized water and dried to obtain modified graphene oxide.

3. The foamed biodegradable polymer sheet according to claim 1, characterized in that: The cellulose is any one or both of microcrystalline cellulose and nanocellulose.

4. The foamed biodegradable polymer sheet according to claim 1, characterized in that: The foaming agent is supercritical carbon dioxide.

5. The foamed biodegradable polymer sheet according to claim 1, characterized in that: The compatibilizer is maleic anhydride.

6. The foamed biodegradable polymer sheet according to claim 1, characterized in that: The antioxidant is any one or both of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and [2,4-di-tert-butylphenyl]phosphite.

7. A method for preparing a foamed biodegradable polymer sheet according to any one of claims 1 to 6, characterized in that: The steps include: S1. Drying polylactic acid and cellulose at 60-80° C. for 1-12 h; S2, the dried polylactic acid, cellulose, a compatibilizer, modified graphene oxide and an antioxidant were mixed to obtain a mixture A; S3, adding mixed material A into a twin-screw extruder for blending and granulation, and injecting a foaming agent through the supercritical fluid injection port of the twin-screw extruder during the granulation process; The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain a foamed biodegradable polymer sheet.

8. The method for preparing a foamed biodegradable polymer sheet according to claim 7, wherein: In step S3, the temperature of each zone of the twin-screw extruder is 160-190°C.

9. The method for preparing a foamed biodegradable polymer sheet according to claim 7, wherein: In step S3, the twin-screw extruder rotates at a speed of 200-250 rpm.

10. The method for preparing a foamed biodegradable polymer sheet according to claim 7, wherein: In step S3, the supercritical fluid injection pressure is 12-20 MPa.

Images