A foamed biodegradable polymer sheet and a method for preparing the same

Abstract

The application relates to a foamed biodegradable polymer sheet and a preparation method thereof, and belongs to the technical field of foamed materials, which 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; the raw materials are dried, mixed, extruded, granulated and molded to obtain the foamed biodegradable polymer sheet; the polymer sheet prepared by the application not only has the advantages of uniform bubble distribution, complete bubble structure and the like, but also has excellent mechanical properties and controllable biodegradation rate, and has wide application prospects.

Description

Technical Field

[0001] This invention belongs to the field of foamed materials technology, specifically, it relates to a foamed biodegradable polymer sheet and its preparation method. Background Technology

[0002] Polylactic acid (PLA), a biodegradable polymer prepared from renewable plant resources, possesses excellent biocompatibility and compostability, showing broad application prospects in packaging, building materials, and daily necessities. However, pure PLA has two inherent defects that significantly limit its application prospects: firstly, PLA is highly brittle and has poor impact resistance, easily undergoing thermal degradation at high temperatures, resulting in insufficient mechanical properties; secondly, pure PLA has low melt strength, slow crystallization rate, and low crystallinity, leading to poor uniformity after foaming, and easily causing cell collapse or merging in traditional foaming processes.

[0003] To overcome the aforementioned technical deficiencies, existing technologies mainly innovate from the following two dimensions: 1) Material composite modification, such as significantly improving the mechanical properties of materials through PLA / PBAT or PLA / PBS blending system design; 2) Foaming process optimization, such as using supercritical CO2 foaming technology combined with chemical foaming agent compounding strategy to achieve precise control of cell structure. However, existing technologies still struggle to balance cell uniformity and excellent mechanical properties. Therefore, developing a foamed polymer sheet with uniform cell structure and excellent mechanical properties is of great significance for promoting the development of green packaging and cushioning materials. Summary of the Invention

[0004] To address the technical problems of poor cell uniformity and insufficient mechanical properties mentioned in the background art, this invention provides a foamed biodegradable polymer sheet and its preparation method.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts polylactic acid, 0.5-2 parts modified graphene oxide, 10-40 parts cellulose, 1-5 parts foaming agent, 2-5 parts compatibilizer, and 1-1.5 parts antioxidant.

[0007] Furthermore, the modified graphene oxide comprises the following raw materials in parts by weight: 100 parts graphene oxide and 40-60 parts L-cysteine.

[0008] Furthermore, the modified graphene oxide is prepared by the following steps:

[0009] Graphene oxide (GO) was ultrasonically dispersed in deionized water, and the pH was adjusted to 10 with KOH solution to obtain a GO dispersion. L-cysteine ​​(L-Cys) 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℃ for 5-12 hours under an inert atmosphere. After the reaction product was cooled to room temperature, it was washed by centrifugation with deionized water and dried to obtain modified graphene oxide. The main process involved the nucleophilic substitution reaction between the epoxy groups on GO and the amino groups on L-Cysteine, which allowed cysteine ​​to be successfully attached to the graphene sheets, thus obtaining L-cysteine-modified graphene oxide, i.e., modified graphene oxide.

[0010] Furthermore, the ratio of graphene oxide to deionized water is (2-4) mg: 1 mL.

[0011] Furthermore, the ratio of L-cysteine ​​to deionized water is (20-40) mg: 1 mL.

[0012] Furthermore, the molar concentration of the KOH solution is 0.1-0.3 mol / L.

[0013] Furthermore, the cellulose is any one or both of microcrystalline cellulose and nanocellulose.

[0014] Furthermore, the foaming agent is supercritical carbon dioxide.

[0015] Furthermore, the compatibilizer is maleic anhydride.

[0016] Furthermore, the antioxidant is any one or two of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris[2,4-di-tert-butylphenyl]phosphite.

[0017] A method for preparing a foamed biodegradable polymer sheet includes the following steps:

[0018] S1. Dry polylactic acid and cellulose at 60-80℃ for 1-12 hours;

[0019] S2. Mix the dried polylactic acid, cellulose, compatibilizer, modified graphene oxide, and antioxidant to obtain mixture A;

[0020] S3. Add mixture A to a twin-screw extruder for co-blending and granulation. During the granulation process, inject the foaming agent through the supercritical fluid injection port of the twin-screw extruder.

[0021] The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain foamed biodegradable polymer sheets.

[0022] Furthermore, in step S3, the temperature of each zone of the twin-screw extruder is 160-190℃.

[0023] Furthermore, in step S3, the twin-screw extruder rotates at a speed of 200-250 rpm.

[0024] Furthermore, in step S3, the supercritical fluid injection pressure is 12-20 MPa.

[0025] The beneficial effects of this invention are:

[0026] 1. This 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, graphene oxide has a large specific surface area and abundant functional groups. After modification with L-cysteine, its surface active sites are further increased, which can serve as nucleation centers for more bubbles, thus significantly improving the bubble nucleation density. In terms of mechanical properties, on the one hand, the two-dimensional sheet structure of graphene oxide can form a rigid network in the polylactic acid matrix. Under external force, it can effectively disperse stress through interlayer slippage and self-deformation, 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, improving its dispersibility in biopolymers and ensuring uniform distribution of nucleation sites. The modified graphene oxide has a stronger interfacial interaction with biopolymers, which can effectively reduce bubble coalescence, stabilize the foaming structure, and endow the polymer sheet with higher mechanical properties.

[0027] 2. This invention introduces L-cysteine-modified graphene oxide, which contains a large number of amino and carboxyl groups in its structure. These groups can generate strong van der Waals forces with CO2 molecules, thereby increasing the solubility of CO2 in the polymer system. This promotes the rapid nucleation of cells in the polymer melt, effectively inhibits cell merging and delays gas escape, and finally forms a structurally complete cell wall, significantly improving the mechanical properties of the material.

[0028] 3. This invention adds cellulose as a filler for polymer sheets. On the one hand, the compatibilizer maleic anhydride improves the compatibility between cellulose and polymer, enhances interfacial bonding, and significantly improves the mechanical properties of the polymer sheets. On the other hand, the preferential degradation of cellulose can expand the contact area between the polymer sheets 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 nutrients and energy for microorganisms, promote microbial growth, and thus enhance the degradation rate of the polymer. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0031] Example 1

[0032] A modified graphene oxide is prepared by the following steps:

[0033] 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 an inert atmosphere. After the reaction product was cooled to room temperature, it was washed by centrifugation with deionized water and dried to obtain modified graphene oxide.

[0034] Example 2

[0035] A modified graphene oxide is prepared by the following steps:

[0036] 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 an inert atmosphere. After the reaction product was cooled to room temperature, it was washed by centrifugation with deionized water and dried to obtain modified graphene oxide.

[0037] Example 3

[0038] A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts polylactic acid, 1 part modified graphene oxide prepared in Example 1, 30 parts cellulose, 3 parts foaming agent, 3 parts compatibilizer, and 1 part 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] This foamed biodegradable polymer sheet is made by the following steps:

[0040] S1. Dry polylactic acid and cellulose at 70°C for 12 hours;

[0041] S2. Mix the dried polylactic acid, cellulose, compatibilizer, modified graphene oxide, and antioxidant to obtain mixture A;

[0042] S3. Add mixture A to a twin-screw extruder for co-blending and granulation. The temperature of each zone of the twin-screw extruder is 160℃→170℃→180℃→180℃→180℃→180℃→185℃→185℃→185℃→180℃→175℃. The speed of the twin-screw extruder is 220 rpm. The foaming agent is injected into the twin-screw melt through the supercritical fluid injection port of the fifth zone of the twin-screw extruder using a mass plunger pump at an injection pressure of 16 MPa.

[0043] The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain foamed biodegradable polymer sheets.

[0044] Example 4

[0045] A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts polylactic acid, 0.5 parts modified graphene oxide prepared in Example 2, 30 parts cellulose, 3 parts foaming agent, 3 parts compatibilizer, and 1 part 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].

[0046] This foamed biodegradable polymer sheet is made by the following steps:

[0047] S1. Dry polylactic acid and cellulose at 70°C for 12 hours;

[0048] S2. Mix the dried polylactic acid, cellulose, compatibilizer, modified graphene oxide, and antioxidant to obtain mixture A;

[0049] S3. Add mixture A to a twin-screw extruder for co-blending and granulation. The temperature of each zone of the twin-screw extruder is 160℃→170℃→180℃→180℃→180℃→180℃→185℃→185℃→185℃→180℃→175℃. The speed of the twin-screw extruder is 220 rpm. The foaming agent is injected into the twin-screw melt through the supercritical fluid injection port of the fifth zone of the twin-screw extruder using a mass plunger pump at an injection pressure of 16 MPa.

[0050] The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain foamed biodegradable polymer sheets.

[0051] Example 5

[0052] A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts polylactic acid, 1.5 parts modified graphene oxide prepared in Example 1, 30 parts cellulose, 3 parts foaming agent, 3 parts compatibilizer, and 1 part 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].

[0053] This foamed biodegradable polymer sheet is made by the following steps:

[0054] S1. Dry polylactic acid and cellulose at 70°C for 12 hours;

[0055] S2. The dried polylactic acid, cellulose, compatibilizer, modified graphene oxide, and antioxidant are mixed to obtain mixture A;

[0056] S3. Add mixture A to a twin-screw extruder for co-blending and granulation. The temperature of each zone of the twin-screw extruder is 160℃→170℃→180℃→180℃→180℃→180℃→185℃→185℃→185℃→180℃→175℃. The speed of the twin-screw extruder is 220 rpm. The foaming agent is injected into the twin-screw melt through the supercritical fluid injection port of the fifth zone of the twin-screw extruder using a mass plunger pump at an injection pressure of 16 MPa.

[0057] The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain foamed biodegradable polymer sheets.

[0058] Example 6

[0059] A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts polylactic acid, 1 part modified graphene oxide prepared in Example 1, 40 parts cellulose, 3 parts foaming agent, 3 parts compatibilizer, and 1 part 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].

[0060] This foamed biodegradable polymer sheet is made by the following steps:

[0061] S1. Dry polylactic acid and cellulose at 70°C for 12 hours;

[0062] S2. The dried polylactic acid, cellulose, compatibilizer, modified graphene oxide, and antioxidant are mixed to obtain mixture A;

[0063] S3. Add mixture A to a twin-screw extruder for co-blending and granulation. The temperature of each zone of the twin-screw extruder is 160℃→170℃→180℃→180℃→180℃→180℃→185℃→185℃→185℃→180℃→175℃. The speed of the twin-screw extruder is 220 rpm. The foaming agent is injected into the twin-screw melt through the supercritical fluid injection port of the fifth zone of the twin-screw extruder using a mass plunger pump at an injection pressure of 16 MPa.

[0064] The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain foamed biodegradable polymer sheets.

[0065] Example 7

[0066] A foamed biodegradable polymer sheet comprises the following raw materials in parts by weight: 100 parts polylactic acid, 1 part modified graphene oxide prepared in Example 1, 10 parts cellulose, 3 parts foaming agent, 3 parts compatibilizer, and 1 part 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].

[0067] This foamed biodegradable polymer sheet is made by the following steps:

[0068] S1. Dry polylactic acid and cellulose at 70°C for 12 hours;

[0069] S2. The dried polylactic acid, cellulose, compatibilizer, modified graphene oxide, and antioxidant are mixed to obtain mixture A;

[0070] S3. Add mixture A to a twin-screw extruder for co-blending and granulation. The temperature of each zone of the twin-screw extruder is 160℃→170℃→180℃→180℃→180℃→180℃→185℃→185℃→185℃→180℃→175℃. The speed of the twin-screw extruder is 220 rpm. The foaming agent is injected into the twin-screw melt through the supercritical fluid injection port of the fifth zone of the twin-screw extruder using a mass plunger pump at an injection pressure of 16 MPa.

[0071] The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain foamed biodegradable polymer sheets.

[0072] Comparative Example 1

[0073] The modified graphene oxide was prepared according to the method of Example 3, except that the modified graphene oxide was prepared in 3 parts by weight.

[0074] Comparative Example 2

[0075] Prepared according to the method of Example 3, except that no modified graphene oxide is added.

[0076] Comparative Example 3

[0077] Prepared according to the method of Example 3, except that the modified graphene oxide was replaced with an equal part by weight of graphene oxide.

[0078] Comparative Example 4

[0079] Prepared according to the method of Example 3, except that the modified graphene oxide was replaced with an equal part by weight of L-cysteine.

[0080] Comparative Example 5

[0081] Prepared according to the method of Example 3, except that the weight parts of cellulose are 5 parts.

[0082] Comparative Example 6

[0083] Prepared according to the method of Example 3, except that the weight parts of cellulose are 45 parts.

[0084] To more intuitively and clearly demonstrate the differences between the embodiments of the present invention and the comparative examples in various key performance indicators, and to facilitate understanding of the significant advantages brought by the technical solution of the present invention, the formulations and experimental results of the key materials of Examples 3-7 and Comparative Examples 1-6 are listed in Table 1. The specific test methods are as follows:

[0085] Cell density: Tested using a density meter according to the method in standard GB / T 27868-2011.

[0086] Tensile strength: Tested according to the method of standard GB / T 9614-2008;

[0087] Elongation at break: Tested according to the method of standard GB / T 9614-2008;

[0088] Impact strength: Tested according to the method of standard GB / T 9614-2008;

[0089] Biodegradability: The biodegradability of polymer sheets under industrial composting conditions for 180 days was tested according to standard GB / T 41010-2021 "Degradation Performance and Labeling Requirements of Biodegradable Plastics and Products".

[0090] Table 1

[0091]

[0092] As shown in Table 1, under the preferred formulation conditions (Examples 3-7), the prepared biopolymer sheets exhibit excellent overall performance: a cell density of 6.13 × 10⁻⁶. The particle density was above 100 cells / cm³, the tensile strength was ≥11.4 MPa, the notched impact strength was ≥64.8 kJ / m², and the biodegradability after 180 days exceeded 90.6%. In contrast, based on the test results of Comparative Examples 1, 2, and 3, it can be seen that when excessive modified graphene oxide was added, the particle agglomeration led to a significant decrease in cell density and mechanical properties; while without addition, the lack of nucleation and nano-reinforcement effects resulted in a significant deterioration in mechanical properties. Based on the test results of Comparative Examples 3, 4, and 3, it can be seen that when an equal weight of graphene oxide was added, the lack of L-cysteine ​​modification reduced its surface active sites, decreased the solubility of CO2 in the polymer system, and resulted in relatively poor dispersibility of graphene oxide in the polymer system, thus leading to a decrease in cell density and mechanical properties; when an equal weight of L-cysteine ​​was added, the lack of nucleation and nano-reinforcement effects of graphene oxide led to a decrease in cell density and mechanical properties. Based on the test results of Comparative Example 5, Comparative Example 6 and Example 3, it can be seen that although excessive cellulose can improve the degradation rate, it will destroy the continuity of the matrix, leading to an increase in surface defects and a decrease in mechanical properties; while when the addition is insufficient, the mechanical properties and degradation rate will decrease simultaneously due to insufficient interface toughening and degradation promotion.

[0093] The above results demonstrate that by precisely controlling the addition ratio of modified graphene oxide and cellulose, the mechanical properties and degradation rate of the material can be synergistically optimized, providing an important basis for the development of high-performance, controllable degradable biopolymer materials.

[0094] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above 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 one or more embodiments or examples.

[0095] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A foamed biodegradable polymer sheet, characterized in that, The raw materials include the following parts by weight: 100 parts polylactic acid, 0.5-2 parts modified graphene oxide, 10-40 parts cellulose, 1-5 parts foaming agent, 2-5 parts compatibilizer, and 1-1.5 parts 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. The modified graphene oxide It is made by the following steps: Graphene oxide was ultrasonically dispersed in deionized water, and the pH was adjusted to 10 with 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℃ for 5-12 hours under an inert atmosphere. After the reaction product was cooled to room temperature, it was washed by centrifugation with deionized water and dried to obtain modified graphene oxide. The foaming agent is supercritical carbon dioxide; The compatibilizer is maleic anhydride; The antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

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

3. A method for preparing a foamed biodegradable polymer sheet as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Dry polylactic acid and cellulose at 60-80℃ for 1-12 hours; S2. Mix the dried polylactic acid, cellulose, compatibilizer, modified graphene oxide, and antioxidant to obtain mixture A; S3. Add mixture A to a twin-screw extruder for co-blending and granulation. During the granulation process, inject the foaming agent through the supercritical fluid injection port of the twin-screw extruder. The particles extruded from S4 and S3 are shaped by a sheet mold and cooled to obtain foamed biodegradable polymer sheets.

4. The method for preparing the foamed biodegradable polymer sheet according to claim 3, characterized in that, In step S3, the temperature of each zone of the twin-screw extruder is 160-190℃.

5. The method for preparing the foamed biodegradable polymer sheet according to claim 3, characterized in that, In step S3, the twin-screw extruder rotates at a speed of 200-250 rpm.

6. The method for preparing the foamed biodegradable polymer sheet according to claim 3, characterized in that, In step S3, the supercritical fluid injection pressure is 12-20 MPa.

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