Preparation process of a highly extensible cellulose-based plastic packaging film

Abstract

The invention discloses a preparation process of a cellulose-based plastic packaging film with high extensibility, belonging to the technical field of packaging film processing, and is used to solve the technical problem that the cellulose-based plastic packaging film in the prior art needs to further improve the mechanical strength and degradation performance; the invention comprises the following steps: putting composite cellulose polylactic acid, ethanol and auxiliary additives into a reaction kettle, heating to 50-60 °C, stirring until dissolved, pouring the solution onto one end of a glass substrate, and evenly casting the solution on the surface of the glass substrate with a scraper of a certain thickness, and performing stretching after cooling and shaping to obtain a plastic packaging film; the invention uses lignocellulose as the base material, modified polylactic acid as the reinforcing material, and through a casting method with auxiliary additives and ethanol to obtain a plastic packaging film, effectively improving the mechanical strength and degradation performance of the cellulose-based plastic packaging film.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging film processing, and particularly relates to a preparation process of a cellulose-based plastic packaging film with high extensibility. Background Art

[0002] At present, the packaging materials for food are mainly plastics. The raw materials for plastic production are generally petroleum-based and are difficult to degrade. The waste plastics brought by waste packaging have led to increasingly serious white pollution. Therefore, packaging films made of biodegradable polymer materials with biomass as raw materials have become a research hotspot. Biodegradable biopolymers can be derived from crops, microorganisms, algae, animals, etc. Currently, the biopolymers that have been studied more are mainly cellulose and its derivatives derived from plants. Preparing plastic packaging films with them as the base material is the current research hotspot.

[0003] A large number of hydrogen bonds interact between cellulose molecules to form a highly crystalline structure. These hydrogen bonds endow cellulose with high rigidity and stability, but also limit the free movement of molecular chains. When the plastic packaging film prepared from cellulose is stretched, the molecular chains cannot be effectively extended, resulting in poor extensibility. Because of its poor toughness and large brittleness, it is easy to break during stretching or bending and cannot meet the requirements of daily packaging for the toughness of materials.

[0004] To increase the toughness and extensibility of cellulose packaging films, cellulose is often mixed with polyolefins and polyurethanes to prepare packaging films. Although this method can improve their mechanical properties, it also reduces the degradation performance of the packaging films. Moreover, the compatibility between cellulose and non-degradable polyesters is poor, further resulting in insufficient extensibility, toughness and impact resistance of the prepared packaging films.

[0005] In view of the technical defects in this regard, a solution is proposed now. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation process of a cellulose-based plastic packaging film with high extensibility, which is used to solve the technical problems that the cellulose-based plastic packaging films in the prior art need to be further improved in terms of extensibility, toughness, impact resistance and degradation performance.

[0007] The purpose of the present invention can be achieved by the following technical solutions: A preparation process of a cellulose-based plastic packaging film with high extensibility, comprising the following steps:

[0008] S1. Put the pretreated lignocellulose, modified polylactic acid and N-N-dimethylformamide into a reaction kettle, stir for 1-2 h, dropwise add a glutaraldehyde solution, heat up to 35-45 °C, keep warm and react for 3-5 h, and perform post-treatment to obtain composite cellulose polylactic acid;

[0009] The preparation reaction formula of the composite cellulose polylactic acid is as follows:

[0010]

[0011] The preparation reaction principle of the composite cellulose polylactic acid is as follows:

[0012] Glutaraldehyde can form a Schiff base with the amino group of the modified polylactic acid, and form a hemiacetal with the hydroxyl group on the cellulose molecule at the other end, obtaining the composite cellulose polylactic acid cross-linked by the modified polylactic acid and the xylose residue cellulose.

[0013] S2. Place the composite cellulose polylactic acid, ethanol and auxiliary additives in a reaction kettle, heat up to 50 - 60 °C, stir until dissolved, pour the solution onto one end of a glass substrate, and use a scraper with a certain thickness to evenly cast the solution on the surface of the glass substrate. After cooling and shaping, perform stretching to obtain a plastic packaging film.

[0014] Furthermore, in step S1, the concentration of the glutaraldehyde solution is 50%, and the dosage ratio of the pretreated xylose residue fiber, modified polylactic acid, N - N - dimethylformamide and glutaraldehyde solution is 10 - 15 g : 8 - 12 g : 200 - 300 mL : 40 - 50 mL. The post - treatment includes: after the reaction is completed, wait for the reaction kettle to cool to room temperature, add ethyl acetate and pure water, wash and extract, transfer the organic phase to a rotary evaporator at a temperature of 40 - 50 °C, and rotate and evaporate until no liquid is collected to obtain the composite cellulose polylactic acid.

[0015] Furthermore, in step S2, the dosage ratio of the composite cellulose polylactic acid, deionized water and auxiliary additives is 10 - 15 g : 100 - 150 mL : 3 - 4 g. The auxiliary additives are composed of a lubricant, a mildew preventive, a dispersant, an antioxidant and an antioxygen agent according to a weight ratio of 1 : 1 : 2 : 4 : 1. The lubricant is one or more of polyethylene wax and polypropylene wax, the mildew preventive is one or more of... (the original text seems incomplete here for the mildew preventive), the dispersant is one or more of zinc stearate, calcium stearate, magnesium stearate, cadmium stearate, the antioxidant is one or more of diphenyl - p - phenylenediamine (DPPD), phenyl - β - naphthylamine (PPD), antioxidant H; the antioxygen agent is one or more of butylated hydroxyanisole (BHA), dibutylhydroxytoluene (BHT), tert - butylhydroquinone (TBHQ).

[0016] Furthermore, the preparation method of the pretreated xylose residue cellulose is as follows:

[0017] A1. Place the xylose residue powder, benzene and ethanol in a Soxhlet extractor, heat up to 90 - 100 °C, keep the temperature for reaction for 4 - 6 h, and perform suction filtration to obtain the crude xylose residue cellulose.

[0018] The preparation reaction principle of the crude xylose residue cellulose is as follows:

[0019] Benzene is a non-polar solvent with strong hydrophobicity and can dissolve some non-polar or low-polar organic substances. Ethanol is a polar solvent and has good solubility for polar substances. Benzene and methanol form a mixed solvent system. Under heating conditions, benzene and methanol are continuously evaporated and condensed, and part of the lignin and hemicellulose in the lignocellulosic residue powder are dissolved in the mixed solvent and removed after filtration.

[0020] A2. Place the crude lignocellulosic residue cellulose, dimethyl sulfoxide, and ionic solution in a reaction kettle, heat up to 80 - 100 °C, hold the temperature for reaction for 1 - 2 h, and filter to obtain a pretreated lignocellulosic residue cellulose solution.

[0021] The reaction principle for the preparation of the pretreated lignocellulosic residue cellulose solution is as follows:

[0022] The ionic liquid prepared from 1-ethylimidazole and triethyl phosphate has strong polarity and can form hydrogen bonds with the hydroxyl groups in cellulose through its cations and anions, destroying the hydrogen bond network between cellulose molecules, causing its molecular chains to separate and dissolve in the solution. Due to the polar and hydrophilic characteristics of cellulose, the dissolution effect of the ionic liquid is mainly concentrated on cellulose. The structure of hemicellulose is more loose. Although it also contains some hydroxyl groups, due to its high degree of branching and the mixed nature of polysaccharides, it is difficult to break its hydrogen bonds. The chemical structure of lignin is very complex and hydrophobic, and the polar solvents in the ionic liquid cannot effectively dissolve these highly hydrophobic substances. Therefore, the ionic liquid will not have the same dissolution effect on hemicellulose and lignin when dissolving cellulose.

[0023] A3. Drop the pretreated lignocellulosic residue cellulose solution into deionized water to regenerate the lignocellulosic residue cellulose, and perform post-treatment to obtain the pretreated lignocellulosic residue fiber.

[0024] The reaction principle for the preparation of the pretreated lignocellulosic residue cellulose is as follows:

[0025] When the pretreated lignocellulosic residue cellulose solution is dropped into deionized water, the polarity of deionized water is strong, and water molecules will compete with the hydrogen bonds between lignocellulosic residue cellulose molecules, resulting in a decrease in the solubility of lignocellulosic residue cellulose and precipitation. The pretreated lignocellulosic residue cellulose is obtained.

[0026] Furthermore, in step A1, the dosage ratio of the lignocellulosic residue powder, benzene, and ethanol is 5 - 10 g : 130 - 200 mL : 70 - 100 mL; in step A2, the dosage ratio of the crude lignocellulose and the ionic mixture is 5 - 10 g : 100 - 200 mL : 150 - 200 mL; in step A3, the post-treatment includes: after regeneration is completed, filter, wash the filter cake with deionized water 1 - 2 times, transfer it to a drying oven at a temperature of 80 - 90 °C and dry to a constant weight to obtain the pretreated lignocellulosic residue cellulose.

[0027] Further, the preparation method of the ionic solution is as follows: 1-ethylimidazole and triethyl phosphate are placed in a reaction kettle, heated to 120-140 °C, kept warm for reaction for 8-12 h, and then post-treated to obtain the ionic solution.

[0028] The preparation reaction formula of the ionic solution is:

[0029]

[0030] The preparation reaction principle of the ionic solution is:

[0031] The nitrogen atom of 1-ethylimidazole has a lone pair of electrons and is nucleophilic. It attacks the ethyl group of triethyl phosphate to form a hydrogen bond, obtaining an ionic liquid containing paired cations and anions.

[0032] Further, the dosage ratio of 1-ethylimidazole to triethyl phosphate is 1-2 g: 2-4 mL. The post-treatment includes: after the reaction is completed, when the reaction drops to room temperature, ethyl acetate is added for extraction. The lower-layer organic phase is transferred to a rotary evaporator and rotary-evaporated until no liquid is produced. Then it is transferred to a drying oven and dried to constant weight to obtain the ionic solution.

[0033] Further, the preparation method of the modified polylactic acid includes the following steps:

[0034] B1. 3-Methylglutaric acid, 2,5-furandicarboxylic acid, 1,4-butanediol, tetrabutyl titanate and N,N-dimethylformamide are placed in a reaction kettle protected by a nitrogen atmosphere, heated to 140-150 °C, kept warm for reaction for 4-6 h, and then post-treated to obtain intermediate Ⅰ;

[0035] The preparation reaction formula of intermediate Ⅰ is:

[0036]

[0037] The preparation reaction principle of intermediate Ⅰ is:

[0038] Under the catalytic action of tetrabutyl titanate, 3-methylglutaric acid, 2,5-furandicarboxylic acid and 1,4-butanediol undergo esterification and condensation reactions to generate intermediate Ⅰ with a flexible chain segment.

[0039] B2. Intermediate Ⅰ, polylactic acid, toluene and stannous octoate are added to a reaction kettle protected by nitrogen and stirred. The temperature of the reaction kettle is raised to 120-130 °C, kept warm for reaction for 8-10 h. Then the temperature of the reaction kettle is lowered to 75-85 °C, and toluene-2,4-diisocyanate is added to the reaction kettle, and kept warm for treatment for 3-4 h, and then post-treated to obtain the modified polylactic acid.

[0040] The preparation reaction formula of the modified polylactic acid is:

[0041]

[0042] In the formula:

[0043]

[0044] The preparation reaction principle of the modified polylactic acid is as follows:

[0045] Under the catalysis of stannous octoate, the terminal carboxyl group of polylactic acid reacts with the terminal hydroxyl group on the molecular chain of intermediate I, and is introduced into the polylactic acid chain to form a polylactic acid-intermediate I molecular chain. The two isocyanate groups contained in toluene-2,4-diisocyanate molecules can react with the hydroxyl groups on the intermediate I chain to extend the length of the polymer chain and form a modified polylactic acid capped with isocyanate groups. The isocyanate groups form amino groups in an aqueous environment, and through high-temperature vacuum distillation, impurities with small molecular structures are removed to obtain the modified polylactic acid.

[0046] Further, in step B1, the dosage ratio of 3-methylglutaric acid, 2,5-furandicarboxylic acid, 1,4-butanediol, tetrabutyl titanate and N-N-dimethylformamide is 5-7 g: 10-11 g: 28-32 g: 0.5-1 mL: 300 mL. The post-treatment includes: after the reaction is completed, when the reaction kettle cools to room temperature, ethyl acetate and pure water are added for washing and extraction. The organic phase is transferred to a rotary evaporator at a temperature of 40-50 °C and rotary evaporated until no liquid is collected to obtain intermediate I. In step B2, the dosage ratio of intermediate I, toluene, stannous octoate and toluene-2,4-diisocyanate is 25-30 g: 300-400 mL: 0.5-0.8 g: 6-8 g. The dosage of polylactic acid is calculated according to the molar ratio of carboxyl groups in the polylactic acid molecule to hydroxyl groups in the intermediate I molecule of 1:2. The post-treatment steps include: after the reaction is completed, purified water is added to the reaction kettle, the temperature of the reaction kettle is raised to 120-130 °C, and vacuum distillation is carried out until no liquid is collected to obtain the modified polylactic acid.

[0047] The present invention has the following beneficial effects:

[0048] 1. In the process of preparing a highly extensible cellulose-based plastic packaging film, using lignocellulose as the base material, modified polylactic acid as the reinforcing material, together with auxiliary additives and ethanol, a plastic packaging film is prepared by the casting method. An ionic liquid is prepared from 1-ethylimidazole and triethyl phosphate to remove impurities from lignocellulose, increasing the hydroxyl content of cellulose and providing more active sites for grafting modified polylactic acid, thereby improving the extensibility and degradation performance of the plastic packaging film. A bio-polyester with flexibility and ductility is introduced into polylactic acid through esterification and condensation reactions, enhancing the extensibility and environmental friendliness of the plastic packaging film. A crosslinking agent, glutaraldehyde, reacts with the amino group of the modified polylactic acid to form a Schiff base, and the other end reacts with the hydroxyl group on the cellulose molecule to form a hemiacetal, resulting in a composite cellulose-polylactic acid with crosslinked modified polylactic acid and lignocellulose, strengthening the bonding force between the fiber material and the polylactic acid material and improving the mechanical properties of the plastic packaging film.

[0049] 2. In the process of preparing a highly extensible cellulose-based plastic packaging film, 3-methylglutaric acid, 2,5-furandicarboxylic acid, and 1,4-butanediol react through esterification and condensation reactions to form intermediate Ⅰ. Intermediate Ⅰ has a long molecular flexible chain segment, enabling it to move and deform more easily under external forces, possessing good ductility and toughness, further reducing the glass transition temperature of the plastic packaging film and maintaining high impact resistance at room temperature. By linking toluene-2,4-diisocyanate, polylactic acid, and intermediate Ⅰ, a crosslinked structure is formed. Polylactic acid has good degradation performance, and the polymerization of the two can further improve the extensibility, toughness, impact resistance, and degradation performance of the plastic packaging film.

[0050] 3. In the process of preparing a highly extensible cellulose-based plastic packaging film, after the pretreated lignocellulose is washed with an ionic solution, it has high reprocessing ability. Using the crosslinking agent glutaraldehyde, the modified polylactic acid and the pretreated lignocellulose are crosslinked by covalent bonds to obtain a composite cellulose-polylactic acid with a complex network structure, improving the extensibility, toughness, and impact resistance of the plastic packaging film. Moreover, the composite cellulose-polylactic acid is uniformly dissolved with ethanol and auxiliary additives, and after casting, cooling, and stretching, a packaging film is prepared. This packaging film is composed of nanofibers, enhancing the toughness and extensibility of the plastic packaging film. Additionally, the production process of the casting method is simple, the equipment cost is relatively low, and the process parameters can be easily adjusted during production, reducing the cost of producing the plastic packaging film. Detailed implementation methods

[0051] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0052] Example 1

[0053] This example provides a preparation process for a highly extensible cellulose-based plastic packaging film, including the following steps:

[0054] S1. Prepare pretreated xylose residue cellulose

[0055] Weigh: 50 g of xylose residue powder, 1.3 L of benzene, and 700 mL of ethanol and place them in a Soxhlet extractor. Heat to 90 °C and hold for 4 h, then filter to obtain the crude xylose residue cellulose.

[0056] Weigh: 10 g of 1-ethylimidazole and 20 mL of triethyl phosphate and place them in a reaction kettle. Heat to 120 °C and hold for 8 h. After the reaction is completed, wait for the reaction kettle to cool to room temperature, add ethyl acetate for extraction, transfer the lower organic phase to a rotary evaporator, evaporate until no liquid is collected, and then transfer it to a drying oven and dry to constant weight to obtain an ionic solution.

[0057] Weigh: 50 g of the crude xylose residue cellulose, 1 L of dimethyl sulfoxide, and 1.5 L of the ionic solution and place them in a reaction kettle. Heat to 80 °C and hold for 1 h, then filter to obtain a pretreated xylose residue cellulose solution.

[0058] Drop the pretreated xylose residue cellulose solution into deionized water to regenerate the xylose residue cellulose. After regeneration is completed, filter, wash the filter cake with deionized water twice, transfer it to a drying oven at 80 °C and dry to constant weight to obtain the pretreated xylose residue cellulose.

[0059] S2. Prepare modified polylactic acid

[0060] Weigh: 50 g of 3-methylglutaric acid, 100 g of 2,5-furandicarboxylic acid, 280 g of 1,4-butanediol, 5 mL of tetrabutyl titanate, and 3 L of N-N-dimethylformamide and place them in a reaction kettle under nitrogen atmosphere protection. Heat to 140 °C and hold for 4 h. After the reaction is completed, wait for the reaction kettle to cool to room temperature, add ethyl acetate and pure water for washing and extraction, transfer the organic phase to a rotary evaporator at 40 °C, evaporate until no liquid is collected to obtain Intermediate I.

[0061] Weigh: Add 250 g of Intermediate I, 3 L of toluene, and 5 g of stannous octoate into a reaction kettle protected by nitrogen and stir. Calculate the addition amount of polylactic acid according to 1 / 2 of the molar amount of hydroxyl groups in Intermediate I, and add it into the reaction kettle. Raise the temperature of the reaction kettle to 120 °C, keep the temperature for reaction for 8 h, then lower the temperature of the reaction kettle to 75 °C. Add 60 g of toluene-2,4-diisocyanate into the reaction kettle and keep the temperature for treatment for 3 h. After the reaction is completed, add purified water into the reaction kettle, raise the temperature of the reaction kettle to 120 °C, and distill under reduced pressure until no liquid is collected, obtaining modified polylactic acid.

[0062] S3. Prepare the cellulose-based plastic packaging film

[0063] Weigh: Put 100 g of pretreated xylose residue cellulose, 80 g of modified polylactic acid, and 2 L of N,N-dimethylformamide into a reaction kettle, stir for 2 h, dropwise add 300 mL of 50% glutaraldehyde solution, raise the temperature to 35 °C, keep the temperature for reaction for 3 h. After the reaction is completed, wait for the reaction kettle to cool to room temperature, add ethyl acetate and pure water, wash and extract. Transfer the organic phase to a rotary evaporator at 40 °C and rotary evaporate until no liquid is collected, obtaining composite cellulose polylactic acid;

[0064] Mix polyethylene wax, benzimidazole, butylated hydroxyanisole, zinc stearate, and antioxidant PPD evenly according to the weight ratio of 1:1:2:4:1 to obtain an auxiliary additive;

[0065] Weigh: Put 100 g of composite cellulose polylactic acid, 1 L of ethanol, and 30 g of auxiliary additive into a reaction kettle, raise the temperature to 50 °C, stir until dissolved, pour the solution onto one end of a glass substrate, and use a scraper with a certain thickness to evenly cast the solution on the surface of the glass substrate. After cooling and shaping, stretch it to obtain a plastic packaging film.

[0066] Example 2

[0067] This example provides a preparation process for a highly extensible cellulose-based plastic packaging film, including the following steps:

[0068] S1. Prepare pretreated xylose residue cellulose

[0069] Weigh: Put 75 g of xylose residue powder, 1.6 L of benzene, and 800 mL of ethanol into a Soxhlet extractor, raise the temperature to 95 °C, keep the temperature for reaction for 5 h, and filter by suction to obtain the crude product of xylose residue cellulose;

[0070] Weigh: Put 15 g of 1-ethylimidazole and 30 mL of triethyl phosphate into a reaction kettle, raise the temperature to 130 °C, keep the temperature for reaction for 10 h. After the reaction is completed, wait for it to cool to room temperature, add ethyl acetate, extract, transfer the lower-layer organic phase to a rotary evaporator, rotary evaporate until no liquid is collected, transfer it to a drying oven, and dry to constant weight to obtain an ionic solution;

[0071] Weigh: 75 g of crude lignocellulose, 1.5 L of dimethyl sulfoxide and 1.5 L of ionic solution, place them in a reaction kettle, heat up to 90 °C, keep the temperature for reaction for 2 h, carry out suction filtration to obtain a pretreated lignocellulose solution;

[0072] Drop the pretreated lignocellulose solution into deionized water to regenerate lignocellulose. After regeneration is completed, carry out suction filtration, wash the filter cake with deionized water twice, transfer it to a drying oven at 85 °C and dry it to constant weight to obtain pretreated lignocellulose.

[0073] S2. Prepare modified polylactic acid

[0074] Weigh: 60 g of 3-methylglutaric acid, 105 g of 2,5-furandicarboxylic acid, 300 g of 1,4-butanediol, 7 mL of tetrabutyl titanate and 3 L of N-N-dimethylformamide, place them in a reaction kettle protected by a nitrogen atmosphere, heat up to 140 °C, keep the temperature for reaction for 5 h. After the reaction is completed, wait for the reaction kettle to cool to room temperature, add ethyl acetate and pure water for washing and extraction. Transfer the organic phase to a rotary evaporator at 45 °C and rotary evaporate until no liquid is collected to obtain intermediate I;

[0075] Weigh: 270 g of intermediate I, 3.5 L of toluene and 7 g of stannous octoate, add them to a reaction kettle protected by nitrogen and stir. Calculate the addition amount of polylactic acid according to 1 / 2 of the molar amount of hydroxyl groups in intermediate I and add it to the reaction kettle. Raise the temperature of the reaction kettle to 125 °C, keep the temperature for reaction for 9 h. Lower the temperature of the reaction kettle to 80 °C, add 70 g of toluene-2,4-diisocyanate to the reaction kettle, keep the temperature for treatment for 3.5 h. After the reaction is completed, add purified water to the reaction kettle, raise the temperature of the reaction kettle to 125 °C, and carry out vacuum distillation until no liquid is collected to obtain modified polylactic acid.

[0076] S3. Prepare a cellulose-based plastic packaging film

[0077] Weigh: 130 g of pretreated lignocellulose, 100 g of modified polylactic acid and 2.5 L of N-N-dimethylformamide, place them in a reaction kettle, stir for 2 h, drop 350 mL of 50% glutaraldehyde solution, heat up to 40 °C, keep the temperature for reaction for 4 h. After the reaction is completed, wait for the reaction kettle to cool to room temperature, add ethyl acetate and pure water for washing and extraction. Transfer the organic phase to a rotary evaporator at 45 °C and rotary evaporate until no liquid is collected to obtain composite cellulose polylactic acid;

[0078] Mix polyethylene wax, benzimidazole, butyl hydroxyanisole, zinc stearate and antioxidant PPD evenly according to the weight ratio of 1:1:2:4:1 to obtain an auxiliary additive;

[0079] Weigh: 130 g of composite cellulose polylactic acid, 1.3 L of ethanol and 35 g of auxiliary additive and place them in a reaction kettle. Heat up to 55 °C and stir until dissolved. Pour the solution onto one end of a glass substrate, and use a scraper with a certain thickness to evenly cast the solution on the surface of the glass substrate. After cooling and shaping, perform stretching to obtain a plastic packaging film.

[0080] Example 3

[0081] This example provides a preparation process for a cellulose-based plastic packaging film with high extensibility, including the following steps:

[0082] S1. Prepare pretreated xylose residue cellulose

[0083] Weigh: 100 g of xylose residue powder, 2 L of benzene and 1 L of ethanol and place them in a Soxhlet extractor. Heat up to 100 °C and hold for a reaction for 6 h. Perform suction filtration to obtain crude xylose residue cellulose;

[0084] Weigh: 20 g of 1-ethylimidazole and 40 mL of triethyl phosphate and place them in a reaction kettle. Heat up to 140 °C and hold for a reaction for 12 h. After the reaction is completed, wait for the reaction to cool to room temperature, add ethyl acetate, perform extraction. Transfer the lower organic phase to a rotary evaporator, and rotary evaporate until no liquid is produced. Transfer it to a drying oven and dry to constant weight to obtain an ionic solution;

[0085] Weigh: 100 g of crude xylose residue cellulose, 2 L of dimethyl sulfoxide and 2 L of ionic solution and place them in a reaction kettle. Heat up to 100 °C and hold for a reaction for 2 h. Perform suction filtration to obtain a pretreated xylose residue cellulose solution;

[0086] Drop the pretreated xylose residue cellulose solution into deionized water to regenerate xylose residue cellulose. After regeneration is completed, perform suction filtration. Wash the filter cake with deionized water twice, transfer it to a drying oven at 90 °C and dry to constant weight to obtain pretreated xylose residue cellulose.

[0087] S2. Prepare modified polylactic acid

[0088] Weigh: 70 g of 3-methylglutaric acid, 110 g of 2,5-furandicarboxylic acid, 320 g of 1,4-butanediol, 10 mL of tetrabutyl titanate and 3 L of N-N-dimethylformamide and place them in a reaction kettle protected by a nitrogen atmosphere. Heat up to 150 °C and hold for a reaction for 6 h. After the reaction is completed, wait for the reaction kettle to cool to room temperature, add ethyl acetate and pure water, perform washing and extraction. Transfer the organic phase to a rotary evaporator at 50 °C and rotary evaporate until no liquid is produced to obtain Intermediate Ⅰ;

[0089] Weigh: 300 g of Intermediate I, 4 L of toluene and 8 g of stannous octoate were added to a reaction kettle protected by nitrogen and stirred. Calculate the addition amount of polylactic acid according to 1 / 2 of the molar amount of hydroxyl groups in Intermediate I, and add it to the reaction kettle. The temperature of the reaction kettle was raised to 130 °C, and the reaction was carried out for 10 h under insulation. Then the temperature of the reaction kettle was lowered to 85 °C, and 8 g of toluene-2,4-diisocyanate was added to the reaction kettle, and the reaction was carried out for 4 h under insulation. After the reaction was completed, purified water was added to the reaction kettle, the temperature of the reaction kettle was raised to 130 °C, and the mixture was distilled under reduced pressure until no liquid was collected, and the modified polylactic acid was obtained.

[0090] S3. Preparation of cellulose-based plastic packaging film

[0091] Weigh: 150 g of pretreated xylose residue cellulose, 120 g of modified polylactic acid and 3 L of N,N-dimethylformamide were placed in a reaction kettle and stirred for 2 h. Then 400 mL of 50% glutaraldehyde solution was added dropwise, and the temperature was raised to 45 °C, and the reaction was carried out for 5 h under insulation. After the reaction was completed, when the reaction kettle cooled to room temperature, ethyl acetate and pure water were added for washing and extraction. The organic phase was transferred to a rotary evaporator at 50 °C and rotary evaporated until no liquid was collected, and the composite cellulose polylactic acid was obtained.

[0092] Mix polyethylene wax, benzimidazole, butylhydroxyanisole, zinc stearate and antioxidant PPD evenly according to the weight ratio of 1:1:2:4:1 to obtain an auxiliary additive.

[0093] Weigh: 150 g of composite cellulose polylactic acid, 1.5 L of ethanol and 40 g of auxiliary additive were placed in a reaction kettle, and the temperature was raised to 60 °C and stirred until dissolved. The solution was poured onto one end of a glass substrate, and a scraper with a certain thickness was used to evenly cast the solution on the surface of the glass substrate. After cooling and shaping, it was stretched to obtain a plastic packaging film.

[0094] Comparative Example 1

[0095] The difference between this comparative example and Example 3 is that step S1 was cancelled, and wood sugar residue powder was used in step S3 to equally replace pretreated wood sugar residue cellulose.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 3 is that step S2 was cancelled, and polylactic acid was used in step S3 to equally replace modified polylactic acid.

[0098] Comparative Example 3

[0099] The difference between this comparative example and Example 3 is that in the step of preparing the cellulose-based plastic packaging film in step S3, the use of glutaraldehyde solution was cancelled, and pretreated wood sugar residue cellulose and modified polylactic acid were blended to obtain composite cellulose polylactic acid.

[0100] Performance test:

[0101] With reference to the standard GB / T 10654-2001 "Determination of Tensile Strength and Elongation at Break of High Polymer Porous Elastic Materials", the elongation at break and tensile strength of the plastic packaging film specimens prepared in Examples 1-3 and Comparative Examples 1-3 were tested respectively;

[0102] With reference to the standard GB / T 41762.2-2022 "Fiber Reinforced Plastic Composites - Determination of In-Plane Properties of Laminates - Part 2: Flexural Test to Determine the Elastic Modulus, Strength and Weibull Size Effect of Carbon Fiber Unidirectional Laminates", the elastic modulus of the plastic packaging film specimens prepared in Examples 1-3 and Comparative Examples 1-3 was tested respectively;

[0103] With reference to the standard GB / T 41010-2021 "Degradation Performance and Labeling Requirements for Biodegradable Plastics and Products", the disintegration rate at 12 weeks and the biodegradation rate at 180 days of the plastic packaging film specimens prepared in Examples 1-3 and Comparative Examples 1-3 under industrial composting conditions were tested respectively. The specific test results are shown in Tables 1-2 below.

[0104] Table 1 - Physical Property Detection Data Table of Each Specimen

[0105] Table 2 - Biodegradation Performance Detection Data Table of Specimens

[0106] Data Analysis:

[0107] By comparing and analyzing the data in Tables 1-2 above, the elongation at break of the highly extensible cellulose-based plastic packaging film prepared in the present invention is 391%, the tensile strength is 59 MPa, the elastic modulus is 2.8 Mpa, and the impact strength is KJ / m -2 , and the disintegration rate of the prepared highly extensible cellulose-based plastic packaging film reaches 81.3% at 12 weeks and the biodegradation rate reaches 78.4% under industrial composting conditions. All performance parameters are better than those of the comparative examples, indicating that the present invention dissolves and regenerates pretreated xylose residue cellulose with an ionic solution, crosslinks it with modified polylactic acid to prepare a composite cellulose polylactic acid, and obtains a highly extensible cellulose-based plastic packaging film by the casting method, which not only effectively improves its mechanical properties but also improves its degradation performance.

[0108] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only the specific embodiments. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A preparation process of a highly extensible cellulose-based plastic packaging film, characterized in that, It includes the following steps: S1. Place the pretreated lignocellulose residue fiber, modified polylactic acid, and N-N-dimethylformamide in a reaction kettle, stir for 1 - 2 h, add a glutaraldehyde solution dropwise, heat up to 35 - 45 °C, keep the temperature for reaction for 3 - 5 h, and perform post-treatment to obtain composite cellulose polylactic acid; S2. Place the composite cellulose polylactic acid, ethanol, and auxiliary additives in a reaction kettle, heat up to 50 - 60 °C, stir until dissolved, pour the solution onto one end of a glass substrate, and use a scraper with a certain thickness to evenly cast the solution on the surface of the glass substrate. After cooling and shaping, perform stretching to obtain a plastic packaging film; The preparation method of the pretreated lignocellulose residue fiber is as follows: A1. Place the lignocellulose residue powder, benzene, and ethanol in a Soxhlet extractor, heat up to 90 - 100 °C, keep the temperature for reaction for 4 - 6 h, and perform suction filtration to obtain crude lignocellulose; A2. Place the crude lignocellulose, dimethyl sulfoxide, and ionic solution in a reaction kettle, heat up to 80 - 100 °C, keep the temperature for reaction for 1 - 2 h, and perform suction filtration to obtain a pretreated lignocellulose residue fiber solution; A3. Drop the pretreated lignocellulose solution into deionized water to regenerate lignocellulose, and perform post-treatment to obtain the pretreated lignocellulose residue fiber; The preparation method of the modified polylactic acid includes the following steps: B1. Place 3-methylglutaric acid, 2,5-furandicarboxylic acid, 1,4-butanediol, tetrabutyl titanate, and N-N-dimethylformamide in a reaction kettle under nitrogen atmosphere protection, heat up to 140 - 150 °C, keep the temperature for reaction for 4 - 6 h, and perform post-treatment to obtain intermediate Ⅰ; B2. Add intermediate Ⅰ, polylactic acid, toluene, and stannous octoate to a reaction kettle under nitrogen protection and stir. Raise the temperature of the reaction kettle to 120 - 130 °C, keep the temperature for reaction for 8 - 10 h, lower the temperature of the reaction kettle to 75 - 85 °C, add toluene-2,4-diisocyanate to the reaction kettle, keep the temperature for treatment for 3 - 4 h, and perform post-treatment to obtain modified polylactic acid.

2. The preparation process of a highly extensible cellulose-based plastic packaging film according to claim 1, characterized in that, In step S1, the concentration of the glutaraldehyde solution is 50%, and the dosage ratio of the pretreated lignocellulose residue fiber, modified polylactic acid, N-N-dimethylformamide, and glutaraldehyde solution is 10 - 15 g: 8 - 12 g: 200 - 300 mL: 40 - 50 mL; in step S2, the dosage ratio of the composite cellulose polylactic acid, deionized water, and auxiliary additives is 10 - 15 g: 100 - 150 mL: 3 - 4 g, and the auxiliary additives are composed of a lubricant, a mildew preventive, a dispersant, an anti-aging agent, and an antioxidant in a weight ratio of 1:1:2:4:

1.

3. The preparation process of a highly extensible cellulose-based plastic packaging film according to claim 1, characterized in that, In step A1, the dosage ratio of the lignocellulose residue powder, benzene, and ethanol is 5 - 10 g: 130 - 200 mL: 70 - 100 mL.

4. The preparation process of a highly extensible cellulose-based plastic packaging film according to claim 1, characterized in that, The preparation method of the ionic solution is: Place 1-ethylimidazole and triethyl phosphate in a reaction kettle, heat up to 120 - 140 °C, keep the temperature for reaction for 8 - 12 h, and perform post-treatment to obtain the ionic solution.

5. The preparation process of a highly extensible cellulose-based plastic packaging film according to claim 4, characterized in that, The dosage ratio of 1-ethylimidazole and triethyl phosphate is 1 - 2 g: 2 - 4 mL.

6. The preparation process of a highly extensible cellulose-based plastic packaging film according to claim 1, characterized in that, In step B1, the dosage ratio of 3-methylglutaric acid, 2,5-furandicarboxylic acid, 1,4-butanediol, tetrabutyl titanate and N-N-dimethylformamide is 5-7 g: 10-11 g: 28-32 g: 0.5-1 mL: 300 mL; in step B2, the dosage ratio of intermediate I, toluene, stannous octoate and toluene-2,4-diisocyanate is 25-30 g: 300-400 mL: 0.5-0.8 g: 6-8 g, and the dosage of the polylactic acid is calculated based on the molar ratio of the carboxyl group in the polylactic acid molecule to the hydroxyl group in the intermediate I molecule being 1:2.

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