Degradable film modified by blending and cross-linking or copolymerization of pseudo-carboxymethyl chitosan and preparation method thereof

Abstract

The present application relates to a method for preparing a composite film by blending and cross-linking pseudo-carboxymethyl chitosan / polyvinyl alcohol (PVA) or copolymerizing with lactic acid. The raw materials of the film material include: 30-54 parts of polyvinyl alcohol, 6-30 parts of pseudo-carboxymethyl chitosan, 10-30 parts of cross-linking agent, and 10-30 parts of plasticizer. After adding pseudo-carboxymethyl chitosan in a suitable proportion and compounding and cross-linking, the performance of the composite film is significantly improved. The production cost of pseudo-carboxymethyl chitosan synthesized by replacing calcium cellulose sulfonate and glycine is less than 6000 yuan / ton, and about 30% of polyvinyl alcohol can be replaced under the premise of maintaining performance, and the tensile strength performance of the composite resin coating film with paper base is also improved by 5-10 times. Similarly, the pseudo-carboxymethyl chitosan / lactic acid graft copolymer prepared by copolymerizing pseudo-carboxymethyl chitosan with lactic acid has better reinforcing and water resistance effect on polylactic acid (PLA) film, and even if the thickness of the composite film is reduced by about 37%, the mechanical strength of the pure PLA film can also be achieved. This achievement shows great application prospect in the cost reduction and strength improvement of degradable plastics and packaging materials.

Description

Technical Field

[0001] This invention relates to the field of biodegradable plastic films. Specifically, it relates to biodegradable films modified by crosslinking or copolymerizing carboxymethyl chitosan analogs—pseudocarboxymethyl chitosan—obtained from sulfonation products of biomass, and methods for preparing such films. Background Technology

[0002] Traditional plastic films such as polypropylene and polyethylene are widely used in agricultural films, food, and pharmaceutical packaging due to their excellent mechanical properties and low production costs. However, because traditional plastic products are difficult to degrade, large amounts of plastic waste float on water surfaces, severely polluting oceans and rivers. Microplastic particles are now ubiquitous, causing serious environmental pollution and ecological impacts. In particular, agricultural film residues in the soil can severely affect crop absorption of water and nutrients, leading to reduced yields. Developing biodegradable plastics to combat white pollution has become urgent. Since 2020, my country has begun a comprehensive ban on the production, use, and sale of traditional plastic films, ushering in a golden age for the development of biodegradable plastic films.

[0003] Biodegradable plastic films are mainly classified into two categories: bio-based and petroleum-based. The most widely used are bio-based modified starch and polylactic acid (PLA), petroleum-based polybutylene terephthalate (PBAT), and polyvinyl alcohol (PVA). PLA and PBAT are priced as high as 25,000-27,000 yuan / ton, while the relatively cheaper PVA is still as high as 18,000 yuan / ton. In contrast, traditional plastic films such as polyethylene (PE) and polypropylene (PP) are priced at only around 10,000 yuan / ton. Furthermore, while PLA has high tensile strength, its toughness and barrier properties are relatively poor. PBAT has an elongation rate 120 times that of PLA and good heat resistance and impact resistance, but its mechanical strength is relatively low. PVA has excellent mechanical properties but suffers from poor moisture resistance and a significant decrease in performance after moisture absorption. Therefore, the application and promotion of biodegradable plastic films are constrained by high raw material costs and performance defects. Currently, the global production capacity of PVA is approximately 1.3 million tons per year, while the global production capacity of PLA and PBAT is only around 500,000 tons per year, far from meeting market demand. Clearly, developing inexpensive green raw materials and high-performance biodegradable plastic films has significant economic, social, and environmental benefits. Preparing composite films by blending with biopolymers to reduce production costs and improve the strength of biodegradable plastic films should be the primary focus.

[0004] Chitosan is a natural high-molecular-weight polysaccharide with many advantages, including good biocompatibility and degradability, safety and non-toxicity, and good film-forming properties. Carboxymethyl chitosan, as a water-soluble derivative of chitosan, has a wider range of applications. However, the application of chitosan and carboxymethyl chitosan is limited by the difficulty in collecting raw materials, the serious pollution during the extraction process, and the high production cost. On the other hand, chitosan and carboxymethyl chitosan have poor strength and water resistance as film materials, requiring composite modification. Chitosan has good compatibility with polyvinyl alcohol (PVA), which has attracted the attention of researchers. Patent CN109867823A discloses a method for preparing a chitosan / PVA composite film, using chitosan, polyethanol, and glycerol as raw materials to improve the mechanical properties of the film to a certain extent. However, the strength of the resulting composite film is still limited, and in this process, PVA dissolves in water, while chitosan needs to be dissolved in a certain concentration of acetic acid solution, which greatly increases the complexity of the process and the cost of film preparation.

[0005] Our research team invented a new method for semi-synthesizing pseudocarboxymethyl chitosan using cellulose or straw as raw materials in CN112175096A. This method solves the problem of high production cost of carboxymethyl chitosan. The resulting pseudocarboxymethyl chitosan is also easily soluble in water, has excellent performance, and has the advantage of low cost. It is expected that using pseudocarboxymethyl chitosan as a raw material to form a composite film with polyvinyl alcohol will significantly reduce the cost of the film and improve its strength and water resistance. Summary of the Invention

[0006] Based on the above situation and research foundation, we optimized the formulation and process conditions, including crosslinking agents and plasticizers, and obtained a composite film material with significantly improved water resistance and strength, thus completing this invention.

[0007] As previously mentioned, chitosan and carboxymethyl chitosan are hydrophilic, while most biodegradable resins are hydrophobic. This invention innovatively provides a method for crosslinking or copolymerizing carboxymethyl chitosan with polyvinyl alcohol or polylactic acid in an optimized ratio, which improves the hydrophobicity of the membrane, increases the membrane strength, reduces the membrane cost, and expands the application of bio-based carboxymethyl chitosan in biodegradable films, forming the characteristics and highlights of this invention.

[0008] Specifically, this invention relates to a composite biodegradable material prepared by crosslinking degradable polyvinyl alcohol with pseudocarboxymethyl chitosan, which can reduce production costs and improve membrane strength performance. The composite biodegradable material comprises, by weight, the following raw materials: 30-54 parts polyvinyl alcohol, 6-30 parts pseudocarboxymethyl chitosan, 10-30 parts crosslinking agent, and 10-30 parts plasticizer. The specific preparation steps are as follows:

[0009] Weigh out the prescribed amounts of polyvinyl alcohol and pseudocarboxymethyl chitosan, place them separately in water, stir and heat until completely dissolved. The heating and dissolution temperature is 100-120℃, and the heating time is 0.5-1h. Mix the obtained 3% polyvinyl alcohol and 3% pseudocarboxymethyl chitosan solution in proportion to obtain a film-forming solution. Then add the prescribed amounts of plasticizer and crosslinking agent, and carry out the crosslinking reaction at a crosslinking temperature of 40-80℃ for 10-30 minutes. After ultrasonic defoaming of the film-forming solution, pour it into a mold and dry it at a temperature of 40-80℃ to form a film, thus obtaining the composite biodegradable material described in this invention.

[0010] In one embodiment of the present invention, the method for preparing pseudocarboxymethyl chitosan refers to the previous patent application CN112175096A of our research team, the entire contents of which are incorporated herein by reference. Specifically, a bio-based calcium sulfonate intermediate is synthesized by sulfonation using abundant and inexpensive raw materials such as fiber or straw, and then replaced with calcium glycine. This allows for low-cost and large-scale synthesis of pseudocarboxymethyl chitosan, with a production cost of only about 6,000 yuan / ton, which is more cost-effective than traditional plastics, providing a raw material guarantee for reducing the cost and improving the performance of plastic films.

[0011]

[0012] Based on the above-mentioned innovative achievements in the synthesis of pseudocarboxymethyl chitosan, the focus of this invention is to use pseudocarboxymethyl chitosan and PVA (polyvinyl alcohol) to form a composite film. Since the cost of pseudocarboxymethyl chitosan is much lower than that of PVA, increasing the addition ratio can reduce the film production cost.

[0013] Studies have found that when the proportion of pseudocarboxymethyl chitosan added is low, the mechanical properties of the composite film are significantly improved compared with those of pure PVA film; when the proportion of pseudocarboxymethyl chitosan added is 30%, the mechanical properties of the composite film do not decrease significantly.

[0014] The degree of carboxymethyl amino substitution in the pseudocarboxymethyl chitosan is 0.31-0.63. The proportion of pseudocarboxymethyl chitosan is 10%-50% of the total solute mass.

[0015] In one embodiment of the present invention, the polyvinyl alcohol raw material is not particularly limited, and commonly used polyvinyl alcohols in the art can be selected, such as polyvinyl alcohol with a degree of polymerization of 1750.

[0016] In one embodiment of the present invention, the crosslinking agent may be any one of glutaraldehyde, boric acid, benzoyl oxide, etc. The preferred amount of the crosslinking agent is 20 parts. Both carboxymethyl chitosan and polyvinyl alcohol macromolecules have a large number of hydroxyl groups, which enhance the water resistance and strength of the composite film through crosslinking into a network.

[0017] In one embodiment of the present invention, the plasticizer may be any one of glycerol, propylene glycol, polyethylene glycol, etc. The amount of plasticizer used is preferably 20 parts. The plasticizer molecules can form bonds with macromolecules, increasing the flexibility of the film.

[0018] This invention relates to a method for preparing a composite biodegradable material, as described above, which reduces production costs and improves membrane strength by crosslinking degradable polyvinyl alcohol with carboxymethyl chitosan. The specific preparation steps are as follows:

[0019] Weigh out the prescribed amounts of polyvinyl alcohol and carboxymethyl chitosan, place them in water, stir and heat until completely dissolved. The heating and dissolution temperature is 100-120℃, and the heating time is 0.5-1h. Prepare 3% polyvinyl alcohol and 3% carboxymethyl chitosan solutions by mass fraction, respectively. Mix them in proportion to obtain a film-forming solution, then add the prescribed amounts of plasticizer and crosslinking agent. Carry out the crosslinking reaction at a crosslinking temperature of 40-80℃ for 10-30 minutes. After ultrasonic defoaming of the film-forming solution, pour it into a mold and dry it at a temperature of 40-80℃ to form a film, thus obtaining the composite biodegradable material of the present invention.

[0020] In the preparation method described in this invention, the limitations on each raw material and its dosage are the same as above.

[0021] On the other hand, the present invention relates to a paper-based coated material further prepared using the above-mentioned composite biodegradable material, wherein the preparation method of the paper-based coated material is as follows:

[0022] Weigh 54 parts by weight of polyvinyl alcohol and 6 parts by weight of pseudocarboxymethyl chitosan, and prepare pseudocarboxymethyl chitosan solution and polyvinyl alcohol solution with a mass fraction of 3% respectively. Mix the obtained solutions, add 20 parts by weight of glycerol as plasticizer and 20 parts by weight of glutaraldehyde as crosslinking agent, crosslink at 70℃ for 15 min to obtain film-forming solution. Then, use paper (including but not limited to household paper, ordinary A4 paper, kraft paper, corrugated paper and any other paper products) to fully soak in film-forming solution, take it out and dry it to obtain crosslinked polyvinyl alcohol / carboxymethyl chitosan paper-based coating material.

[0023] The restrictions on each raw material are the same as above.

[0024] The strength of the paper-based coated material obtained by this invention can be increased by 5-10 times. In particular, the strength of the coating on A4 paper with very little adsorption has exceeded that of pure resin, showing its application potential in high-strength packaging materials.

[0025] Furthermore, our research team discovered that using the copolymerization modification method of pseudocarboxymethyl chitosan and low-polymerization-degree lactic acid can improve the hydrophilicity of pseudocarboxymethyl chitosan, significantly reduce the production cost of polylactic acid films, and improve the film strength performance.

[0026] Therefore, the present invention also relates to a pseudocarboxymethyl chitosan / lactic acid graft copolymer having a structural unit as shown in formula (I):

[0027]

[0028] The viscosity-average molecular weight (Mi) of the pseudocarboxymethyl chitosan / lactic acid graft copolymer is... v ) = 2 × 10 4 ~5×10 4 ;

[0029] m = 70 - 200;

[0030] n = 2 - 10:

[0031] The grafting rate is approximately 15%-30%.

[0032] Another aspect of the present invention relates to a method for preparing the pseudocarboxymethyl chitosan / lactic acid graft copolymer, the method specifically comprising:

[0033] (1) First, add a certain amount of lactic acid to the reaction vessel, heat to 80-120℃ for prepolymerization for 1-2 hours, and at the same time, vacuum the system to remove the water generated in the reaction system.

[0034] (2) After dehydration, add pseudocarboxymethyl chitosan and catalyst. The mass ratio of lactic acid to pseudocarboxymethyl chitosan is 2:1-20:1. The amount of catalyst is 0.5%-1% of the mass of lactic acid. Raise the temperature to 140-180℃ and react for 6-10 hours.

[0035] (3) After the reaction is completed, the crude product of pseudocarboxymethyl chitosan / lactic acid graft copolymer can be obtained by dissolving, filtering and drying. The crude product can be purified by Soxhlet extractor to remove lactic acid homopolymer impurities.

[0036] The catalyst is selected from stannous chloride or stannous octoate, etc.

[0037] In the above method, some of the lactic acid and its oligomers that are vacuum distilled can be recycled.

[0038] The method of this invention can improve the hydrophilicity of carboxymethyl chitosan, expand the application of carboxymethyl chitosan in polylactic acid biodegradable materials, reduce membrane costs, and improve membrane strength performance.

[0039] Specifically, another aspect of the present invention relates to a method for preparing a composite film of polylactic acid and carboxymethyl chitosan / lactic acid graft copolymer, the method comprising:

[0040] The finished polylactic acid and the above-obtained graft copolymer were dissolved together in dichloroethane to make the mass fraction of the film-forming solution 3%. After ultrasonic degassing, the solution was poured into a film-forming mold and dried to form a film.

[0041] The mass ratio of polylactic acid to the graft copolymer is 9:1 to 1:1.

[0042] Among them, the performance of the composite film is significantly improved when the copolymer addition ratio is low.

[0043] The biodegradable composite film material provided by this invention can be applied in various fields such as food, medical, chemical, and agriculture. Furthermore, pseudocarboxymethyl chitosan and its grafted modifiers can also be used as reinforcing or filling materials for other biodegradable resins.

[0044] Beneficial effects of the present invention

[0045] 1. Carboxymethyl chitosan and its graft copolymers can enhance the properties of representative biodegradable films such as polyvinyl alcohol and polylactic acid, reduce the thickness of composite films, and maintain the strength performance even at a high addition level, resulting in significant benefits in reducing film production costs.

[0046] 2. When the proportion of carboxymethyl chitosan added to the composite film is 10%, the composite film exhibits the highest tensile strength, which is 37% higher than that of pure polyvinyl alcohol film. When the proportion of carboxymethyl chitosan added reaches 30%, the tensile strength of the composite film is still superior to that of pure polyvinyl alcohol film.

[0047] 3. This invention provides a method for improving the hydrophobicity of pseudocarboxymethyl chitosan through copolymerization. The obtained pseudocarboxymethyl chitosan / lactic acid graft copolymer has better reinforcement effect and better hydrophobicity. When the proportion of pseudocarboxymethyl chitosan added to the composite film is 10%, the tensile strength is increased by nearly 56% compared with pure polylactic acid film. Attached Figure Description

[0048] Figure 1 Flowchart of the preparation process of pseudocarboxymethyl chitosan / polyvinyl alcohol composite membrane

[0049] Figure 2 Scanning electron microscopy (SEM) images of chitosan / polyvinyl alcohol composite films with different carboxymethyl chitosan loading amounts

[0050] Figure 3 Flowchart of the preparation process of pseudocarboxymethyl chitosan / lactic acid graft copolymer

[0051] Figure 4 Infrared spectrum of pseudocarboxymethyl chitosan / lactic acid graft copolymer

[0052] Figure 5Scanning electron microscopy analysis of the pseudocarboxymethyl chitosan / lactic acid graft copolymer

[0053] Figure 6 The 1H NMR spectrum of the pseudocarboxymethyl chitosan / lactic acid graft copolymer

[0054] Figure 7 Thermogravimetric analysis diagram of the pseudocarboxymethyl chitosan / lactic acid graft copolymer Detailed Implementation

[0055] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art. It should be noted that these embodiments are descriptive and not limiting, and should not be construed as limiting the scope of protection of the present invention.

[0056] In the following embodiments of the present invention, the degree of polymerization of the polyvinyl alcohol used is 1750; and the degree of nitrogen substitution of the pseudocarboxymethyl chitosan used is 0.33.

[0057] Example 1

[0058] Weigh 54 parts by weight of polyvinyl alcohol and 6 parts by weight of carboxymethyl chitosan, and prepare 3% (w / w) carboxymethyl chitosan solution and polyvinyl alcohol solution respectively. Mix the resulting solutions, add 20 parts by weight of glutaraldehyde as a crosslinking agent, and vary the amount of plasticizer glycerin. Crosslink at 70℃ for 15 minutes, remove bubbles, and dry in a film mold to form a film. Investigate the effect of different plasticizer dosages on the mechanical properties and water resistance of the film. The obtained film was tested for mechanical properties using a universal testing machine according to GB13022-91. Water resistance was tested using the solubility analysis method. The film was cut into 5×5cm squares, dried at 50℃ for 24 hours, and weighed as m1. After soaking in distilled water at 25℃ for 24 hours, it was dried again and weighed as m2. The results can be calculated as follows:

[0059]

[0060] Table 1 Effect of Plasticizer (Glycerin) Dosage on Composite Film Properties

[0061] 0 27.93 9.07 42.53 10 31.97 349.91 37.39 20 38.83 474.35 31.33 30 32.91 506.23 31.47 40 28.86 442.08 34.61 50 16.07 306.20 36.43

[0062] As shown in Table 1, with the increase of glycerol content, the tensile strength and elongation at break of the film first increase and then decrease. This is because glycerol, as a small molecule polyol, can penetrate into the interior under stirring, which is conducive to the entanglement of pseudocarboxymethyl chitosan and PVA and the formation of secondary valence bonds. Therefore, the tensile strength and elongation at break of the film both show an increasing trend. However, when the amount of glycerol added is too high, the relative content of pseudocarboxymethyl chitosan and PVA in the film will decrease, the intermolecular forces will become weaker, the film density will decrease, and thus the mechanical properties will decrease.

[0063] The water resistance of the film initially increases and then decreases with increasing glycerol content. This is mainly because the addition of glycerol forms hydrogen bonds, strengthening the hydrogen bond between the carboxymethyl chitosan and PVA, thus improving the film's water resistance. However, excessive glycerol content leads to a decrease in water resistance due to its hydrophilic nature. In summary, the composite film exhibits optimal performance with a plasticizer content of 20 parts, achieving a tensile strength of 38.83 MPa and an elongation at break of 474.35%.

[0064] Example 2

[0065] like Figure 1 As shown in the process flow diagram, 54 parts by weight of polyvinyl alcohol and 6 parts by weight of carboxymethyl chitosan were weighed and prepared into a 3% carboxymethyl chitosan solution and a polyvinyl alcohol solution, respectively. The resulting solutions were mixed, and 20 parts by weight of glycerol were added as a plasticizer. The amount of crosslinking agent glutaraldehyde was changed, and crosslinking was carried out at 70°C for 15 minutes. After defoaming, the membrane was placed in a membrane mold and dried to form a film. The effect of glutaraldehyde addition on the performance of the composite membrane is shown in Table 2.

[0066] Table 2 Effect of crosslinking agent (glutaraldehyde) dosage on the properties of composite films

[0067] 0 24.11 351.14 43.71 10 31.75 450.08 34.76 20 38.83 474.35 31.46 30 29.82 449.62 31.17 40 28.62 376.63 32.15 50 25.31 353.51 32.89

[0068] As shown in Table 2, with the increase of the crosslinking agent glutaraldehyde, the tensile strength and elongation at break of the composite film first increase and then decrease. When the amount of glutaraldehyde is small, the aldehyde groups in glutaraldehyde, the carboxymethyl chitosan, and the hydroxyl groups in PVA undergo a condensation reaction, crosslinking to form a network structure. This enhances the intermolecular forces between the carboxymethyl chitosan and PVA macromolecules, increasing the strength of the molecular chains and thus improving the mechanical properties. In addition, crosslinking reduces the number of hydrophilic hydroxyl groups in the molecules, and the formed network structure reduces the solubility of the film in water, thus improving the water resistance of the film. However, when the amount of glutaraldehyde is high, excessive crosslinking between molecules occurs. A large number of crosslinking bonds restrict the sliding between the macromolecules, making it difficult for the molecular chains to orient, thus reducing the elongation at break of the film. Furthermore, uncrosslinked glutaraldehyde fills the film in the form of small molecules, reducing the relative composition of carboxymethyl chitosan and polyvinyl alcohol in the composite film, thus reducing the tensile strength of the film. Since glutaraldehyde itself is a hydrophilic substance, excessive glutaraldehyde will lead to a deterioration in the water resistance of the film. In summary, the optimal dosage of glutaraldehyde is 20 parts.

[0069] Example 3

[0070] like Figure 1As shown in the process flow diagram, 54 parts by weight of polyvinyl alcohol and 6 parts by weight of carboxymethyl chitosan were weighed and prepared into 3% (w / w) carboxymethyl chitosan solution and polyvinyl alcohol solution, respectively. The resulting solutions were mixed, and 20 parts by weight of glycerol and 20 parts by weight of glutaraldehyde were added as crosslinking agents. The crosslinking temperature was 70℃, and the crosslinking time was varied. After defoaming, the membrane was placed in a membrane mold and dried to form a film. The effect of crosslinking time on the performance of the composite membrane is shown in Table 3.

[0071] Table 3 Effect of crosslinking time on the properties of composite films

[0072] 5 32.64 385.72 36.63 10 37.04 466.47 33.91 15 38.83 474.35 31.32 20 39.02 420.61 30.88 25 37.54 396.33 30.69 30 36.81 382.15 31.98

[0073] Table 3 shows that with the extension of crosslinking time, the degree of crosslinking increases, and the tensile strength and elongation at break of the film both improve. However, further extension of crosslinking time leads to a decrease in the mechanical properties of the film. Furthermore, the water resistance of the film initially increases and then decreases with increasing crosslinking time. In summary, the film exhibits the best performance when the crosslinking time is 15 min.

[0074] Example 4

[0075] like Figure 1 As shown in the process flow diagram, the total amount of pseudocarboxymethyl chitosan and polyvinyl alcohol was maintained at 60 parts. The proportion of pseudocarboxymethyl chitosan was varied to prepare 3% (w / w) solutions of pseudocarboxymethyl chitosan and polyvinyl alcohol, respectively. 20 parts of glycerol and 20 parts of glutaraldehyde were added as crosslinking agents. The crosslinking temperature was 70℃, and the crosslinking time was 15 min. After defoaming, the membrane was placed in a membrane mold and dried to form a film. The effect of the pseudocarboxymethyl chitosan filling ratio on the composite membrane performance is shown in Table 4.

[0076] Table 4. Effect of carboxymethyl chitosan filling ratio on composite membrane performance

[0077]

[0078]

[0079] Table 4 shows that when the proportion of pseudocarboxymethyl chitosan is 10%, the tensile strength reaches 38.83 MPa, which is nearly 37% higher than that of pure PVA film, and the film toughness is also improved. At this point, if the strength of pure PVA film is used as the standard, the composite film thickness can be reduced by about 30%, that is, the amount of PVA can be reduced by more than 30%, and the overall cost of the composite film is significantly reduced. When the proportion of pseudocarboxymethyl chitosan is 30%, the film performance is still slightly better than that of pure PVA film. However, when the proportion of pseudocarboxymethyl chitosan exceeds 30%, the mechanical properties of the film decrease significantly, the solubility of the film in water also increases, and the water resistance decreases. In summary, when the proportion of pseudocarboxymethyl chitosan is around 10%, the composite film has the best overall performance, and when the proportion of pseudocarboxymethyl chitosan is around 30%, the composite film has the lowest cost.

[0080] Example 5

[0081] First, add 50 parts by weight of lactic acid to the reaction vessel, heat to 120℃ for prepolymerization for 1 hour, and simultaneously remove water from the lactic acid and water generated during the prepolymerization process under vacuum to prevent hydrolysis of the pseudocarboxymethyl chitosan during the subsequent copolymerization process, which would reduce the yield of the modified product. After dehydration, add 10 parts by weight of pseudocarboxymethyl chitosan and 0.25 parts by weight of stannous octoate catalyst, raise the temperature to 180℃, and react for 8 hours. Dissolve in dichloroethane, remove insoluble impurities by centrifugation or filtration, and back-precipitate with ethanol. Filter to obtain the pseudocarboxymethyl chitosan / lactic acid graft copolymer.

[0082] The 1H NMR spectrum of the pseudocarboxymethyl chitosan / lactic acid graft copolymer is shown below. Figure 6 At chemical shifts of 1.58 ppm and 5.20 ppm, hydrogen elution peaks corresponding to methyl and methine groups in the polylactic acid structure are visible. This is based on thermogravimetric analysis. Figure 7 It is also easy to see that there is only one weight loss peak in the figure, indicating that the product obtained is a pseudocarboxymethyl chitosan / lactic acid graft copolymer, rather than a simple mixture of pseudocarboxymethyl chitosan and polylactic acid.

[0083] Example 6

[0084] The filling ratio of the pseudocarboxymethyl chitosan / lactic acid graft copolymer in polylactic acid was varied. Both were dissolved in dichloroethane to achieve a total mass fraction of 3%. After ultrasonic degassing, the mixture was poured into a film-forming mold and dried in a fume hood to form a film. The comprehensive properties of the films formed by combining the pseudocarboxymethyl chitosan / lactic acid graft copolymer with polylactic acid at different ratios are shown in Table 5.

[0085] Table 5. Effect of the proportion of pseudocarboxymethyl chitosan / lactic acid graft copolymer on the properties of the composite membrane.

[0086]

[0087] As shown in Table 5, when the filler ratio of the pseudocarboxymethyl chitosan / lactic acid graft copolymer is 10%, the tensile strength of the film reaches 46.73 MPa, which is nearly 56% higher than that of the pure polylactic acid film. This indicates that the pseudocarboxymethyl chitosan / lactic acid graft copolymer has a good reinforcing effect on the film. At this point, if the strength of the pure PLA film is used as the standard, the thickness of the composite film can be reduced by about 37%, which means that the amount of PLA used can be reduced by more than 40% without sacrificing performance. In addition, when the filler ratio of the pseudocarboxymethyl chitosan / lactic acid graft copolymer is large, the composite film can still maintain excellent performance, indicating that the copolymerization of this graft copolymer with polylactic acid largely solves the problem of uneven dispersion of pseudocarboxymethyl chitosan-based biodegradable hydrophilic polymers in hydrophobic biodegradable resins such as polylactic acid.

[0088] Example 7

[0089] Weigh 54 parts by weight of polyvinyl alcohol and 6 parts by weight of pseudocarboxymethyl chitosan, and prepare pseudocarboxymethyl chitosan solution and polyvinyl alcohol solution with a mass fraction of 3% respectively. Mix the obtained solutions, add 20 parts by weight of glycerol as crosslinking agent and 20 parts by weight of glutaraldehyde as crosslinking agent, crosslink at 70℃ for 15 min to obtain film-forming solution. Then, use household paper, ordinary A4 paper and kraft paper to fully soak in the film-forming solution, take them out and dry them to obtain crosslinked polyvinyl alcohol / carboxymethyl chitosan paper-based coating material.

[0090] Table 6 Performance of Paper-Based Coated Materials

[0091]

[0092]

[0093] Table 6 shows that the loosely structured tissue paper has the highest resin adsorption capacity, while ordinary A4 paper and kraft paper have lower resin adsorption capacities. The strength of paper-based coated materials can be increased by 5 to 10 times. In particular, the strength of A4 paper with very low resin adsorption has exceeded that of pure resin, demonstrating its application prospects in high-strength packaging materials.

[0094] It should be emphasized that the embodiments described in this invention are illustrative and not limiting. Therefore, this invention is not limited to the embodiments shown in the implementation. Any equivalent structural or procedural transformations made based on the content of this specification and drawings, or direct or indirect applications in other related technical fields, are included within the scope of patent protection of this invention.

Claims

1. A composite biodegradable material prepared by crosslinking polyvinyl alcohol with carboxymethyl chitosan, which can reduce production costs and improve membrane strength, characterized in that, By weight, the composite biodegradable material comprises the following raw materials: 48-54 parts of polyvinyl alcohol, 6-12 parts of carboxymethyl chitosan, 10-30 parts of crosslinking agent, and 10-20 parts of plasticizer; The preparation steps are as follows: Weigh out the prescribed amounts of polyvinyl alcohol and carboxymethyl chitosan, and place them separately in water. Stir and heat until completely dissolved. The heating and dissolution temperature is 100-120℃, and the heating time is 0.5-1h. Prepare 3% polyvinyl alcohol solution and 3% carboxymethyl chitosan solution by mass fraction. Mix them in proportion to obtain a film-forming solution. Then add the prescribed amounts of plasticizer and crosslinking agent. Carry out the crosslinking reaction at a crosslinking temperature of 40-80℃ for 10-25 minutes. After ultrasonic defoaming of the film-forming solution, pour it into a mold and dry it at a temperature of 40-80℃ to form a film. The crosslinking agent is glutaraldehyde, and the plasticizer is glycerol.

2. The composite biodegradable material according to claim 1, characterized in that, The degree of carboxymethyl amino substitution in the pseudocarboxymethyl chitosan is 0.31-0.63; the proportion of the pseudocarboxymethyl chitosan is 10%-20% of the total solute mass, and the total solute mass is the sum of the masses of the pseudocarboxymethyl chitosan and polyvinyl alcohol.

3. The composite biodegradable material according to claim 1, characterized in that, The amount of the crosslinking agent used is 20 parts.

4. The composite biodegradable material according to claim 1, characterized in that, The amount of plasticizer used is 20 parts.

5. A method for preparing a composite biodegradable material prepared by crosslinking polyvinyl alcohol with pseudocarboxymethyl chitosan according to any one of claims 1-4, which can reduce production costs and improve membrane strength, characterized in that, The preparation steps include the following: Weigh out the prescribed amounts of polyvinyl alcohol and pseudocarboxymethyl chitosan, place them separately in water, stir and heat until completely dissolved. The heating and dissolution temperature is 100-120℃, and the heating time is 0.5-1h, to obtain 3% polyvinyl alcohol solution and 3% pseudocarboxymethyl chitosan solution by mass fraction. Mix them in proportion to obtain a film-forming solution, then add the prescribed amounts of plasticizer and crosslinking agent, and carry out the crosslinking reaction at a crosslinking temperature of 40-80℃ for 10-25 minutes. After ultrasonic defoaming of the film-forming solution, pour it into a mold and dry it at a temperature of 40-80℃ to form a film.

6. A paper-based coated material, characterized in that, The preparation method of the paper-based coated material is as follows: Weigh 54 parts by weight of polyvinyl alcohol and 6 parts by weight of carboxymethyl chitosan, and prepare 3% polyvinyl alcohol solution and 3% carboxymethyl chitosan solution by weight respectively. Mix the obtained solutions, add 20 parts by weight of glycerol as plasticizer and 20 parts by weight of glutaraldehyde as crosslinking agent, crosslink at 70℃ for 15 min to obtain film-forming solution. Then, after fully immersing the paper in the film-forming solution, it is removed and dried to obtain a cross-linked polyvinyl alcohol / carboxymethyl chitosan paper-based coating material.

7. The paper-based coated material according to claim 6, characterized in that, The paper is selected from household paper, ordinary A4 paper, kraft paper, and corrugated paper.

Images