Preparation process of high-extensibility cellulose-based plastic packaging film

Abstract

The invention discloses a preparation process of a high-extensibility cellulose-based plastic packaging film, belongs to the technical field of packaging film processing, and is used for solving the technical problem that the mechanical strength and degradation performance of a cellulose-based plastic packaging film in the prior art need to be further improved. The preparation method comprises the following steps: putting composite cellulose polylactic acid, ethanol and an auxiliary additive into a reaction kettle, heating to 50-60 DEG C, stirring until the mixture is dissolved, pouring the solution to one end of a glass substrate, uniformly casting the solution on the surface of the glass substrate by using a scraper with a certain thickness, cooling, sizing, and drafting to obtain a plastic packaging film; according to the invention, the wood sugar residue cellulose is used as a base material, the modified polylactic acid is used as a reinforcing material, and the plastic packaging film is prepared from the base material, the reinforcing material, the auxiliary additive and the ethanol through a tape casting method, so that the mechanical strength and the degradation performance of the cellulose-based plastic packaging film are effectively improved.

Description

Technical Field

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

[0002] At present, food packaging is mainly made of plastic. The raw materials for plastic production are generally petroleum-based and difficult to degrade. The waste plastics brought by discarded packaging have led to increasingly serious white pollution. Therefore, packaging films made of degradable polymer materials using biomass as raw materials have become a research hotspot. Degradable bio-based polymers can be derived from crops, microorganisms, algae, animals, etc. Currently, the most studied bio-based polymers are mainly derived from plant cellulose and its derivatives. Using them as the substrate to prepare plastic packaging films is a current research hotspot.

[0003] Cellulose molecules interact with each other through a large number of hydrogen bonds to form a highly crystalline structure. These hydrogen bonds give cellulose high rigidity and stability, but also limit the free movement of the molecular chains. When the plastic packaging film made of cellulose is stretched, the molecular chains cannot be effectively stretched, resulting in poor extensibility. Because of its poor toughness and high brittleness, it is easy to break when stretched or bent, and cannot meet the material toughness requirements of daily packaging;

[0004] In order to increase the toughness and elongation of cellulose packaging films, cellulose is often mixed with polyolefins and polyurethanes to prepare packaging films. Although this method can improve its mechanical properties, it also reduces the degradation performance of the packaging film. In addition, cellulose and non-degradable polyesters have poor compatibility, which further leads to insufficient elongation, toughness and impact resistance of the prepared packaging film.

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

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

[0007] The object of the present invention can be achieved by the following technical scheme: A process for preparing a high-extensibility cellulose-based plastic packaging film, comprising the following steps:

[0008] S1, placing pretreated wood sugar residue cellulose, modified polylactic acid and NN-dimethylformamide in a reaction kettle, stirring for 1-2 hours, adding glutaraldehyde solution dropwise, heating to 35-45°C, keeping the temperature for reaction for 3-5 hours, and post-treating to obtain composite cellulose polylactic acid;

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

[0010]

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

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

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

[0014] Furthermore, in step S1, the concentration of the glutaraldehyde solution is 50%, the amount ratio of the pretreated wood sugar residue fiber, modified polylactic acid, NN-dimethylformamide and glutaraldehyde solution is 10-15g:8-12g:200-300mL:40-50mL, and the post-treatment includes: after the reaction is completed, the reaction kettle is cooled to room temperature, ethyl acetate and pure water are added, washed, and the organic phase is transferred to a rotary evaporator at a temperature of 40-50°C, and rotary evaporated until no liquid is extracted to obtain composite cellulose polylactic acid.

[0015] Furthermore, in step S2, the amount ratio of the composite cellulose polylactic acid, deionized water and auxiliary additives is 10-15g:100-150mL:3-4g, the auxiliary additives are lubricants, mildew inhibitors, dispersants, antioxidants and antioxidants in a weight ratio of 1:1:2:4:1, the lubricant is one or more of polyethylene wax and polypropylene wax, the mildew inhibitor is one or more of chlorobenzene, the dispersant is one or more of zinc stearate, calcium stearate, magnesium stearate, and cadmium stearate, the antioxidant is one or more of antioxidant DPPD, antioxidant PPD, and antioxidant H; the antioxidant is one or more of butylated hydroxyanisole, dibutylhydroxytoluene, and tert-butylhydroquinone.

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

[0017] A1. Place wood sugar residue powder, benzene and ethanol in a Soxhlet extractor, heat to 90-100°C, keep warm for 4-6 hours, and filter to obtain a crude wood sugar residue cellulose product;

[0018] The reaction principle for preparing crude cellulose from wood sugar residue is as follows:

[0019] Benzene is a non-polar solvent with strong hydrophobicity and can dissolve some non-polar or low-polar organic matter. Ethanol is a polar solvent with 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 wood sugar residue powder are dissolved in the mixed solvent and removed after filtration.

[0020] A2, placing crude lignocellulose, dimethyl sulfoxide and ion solution in a reaction kettle, heating to 80-100° C., keeping the temperature for 1-2 hours, and filtering to obtain a pretreated lignocellulose solution;

[0021] The reaction principle for preparing the pretreated lignocellulosic 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 detach and dissolve into the solution. Due to the polarity and hydrophilicity of cellulose, the dissolving effect of ionic liquids is mainly concentrated on cellulose. The structure of hemicellulose is looser. Although it also contains some hydroxyl groups, it is difficult to destroy its hydrogen bonds due to its high branching structure and the mixed nature of polysaccharides. The chemical structure of lignin is very complex and hydrophobic. The polar solvents in ionic liquids cannot effectively dissolve these highly hydrophobic substances. Therefore, ionic liquids will not have the same dissolving effect on hemicellulose and lignin when dissolving cellulose.

[0023] A3. The pretreated wood sugar residue cellulose solution is added dropwise into deionized water to regenerate the wood sugar residue cellulose, and then post-processed to obtain the pretreated wood sugar residue fiber.

[0024] The preparation reaction principle of pretreated wood sugar residue cellulose is:

[0025] The pretreated lignocellulosic cellulose solution is added dropwise to deionized water. The deionized water has a strong polarity, and the water molecules compete with the hydrogen bonds between the lignocellulosic cellulose molecules, so that the solubility of the lignocellulosic cellulose is reduced and precipitated, thereby obtaining the pretreated lignocellulosic cellulose.

[0026] Furthermore, in step A1, the usage ratio of the wood sugar residue powder, benzene and ethanol is 5-10g:130-200mL:70-100mL; in step A2, the usage ratio of the crude wood cellulose and the ion mixed solution is 5-10g:100-200mL:150-200mL; in step A3, the post-treatment includes: after regeneration is completed, filtering, washing the filter cake with deionized water 1-2 times, transferring to a drying oven at a temperature of 80-90°C and drying to constant weight to obtain pretreated wood sugar residue cellulose.

[0027] Furthermore, the preparation method of the ionic solution is: 1-ethylimidazole and triethyl phosphate are placed in a reaction kettle, the temperature is raised to 120-140° C., the reaction is kept warm for 8-12 hours, and the ionic solution is obtained by post-treatment.

[0028] The reaction formula for preparing the ionic solution is:

[0029]

[0030] The reaction principle for preparing ionic solution is:

[0031] The nitrogen atom of 1-ethylimidazole has a lone electron pair and is nucleophilic, attacking the ethyl group of triethyl phosphate to form a hydrogen bond, thereby obtaining an ionic liquid containing an anion-cation pair.

[0032] Furthermore, the dosage ratio of 1-ethylimidazole and triethyl phosphate is 1-2g:2-4mL, and the post-treatment includes: after the reaction is completed, the reaction temperature is cooled to room temperature, ethyl acetate is added, extraction is performed, the lower organic phase is transferred to a rotary evaporator, rotary evaporated until no liquid is extracted, transferred to a drying oven, and dried to constant weight to obtain an ionic solution.

[0033] Furthermore, the preparation method of the modified polylactic acid comprises the following steps:

[0034] B1, 3-methylglutaric acid, 2,5-furandicarboxylic acid, 1,4-butanediol, tetrabutyl titanate and NN-dimethylformamide are placed in a reactor protected by a nitrogen atmosphere, the temperature is raised to 140-150°C, the reaction is kept at this temperature for 4-6 hours, and the intermediate I is obtained by post-treatment;

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

[0036]

[0037] The reaction principle for the preparation 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 of the flexible chain segment.

[0039] B2. Add intermediate I, polylactic acid, toluene and stannous octoate into a nitrogen-protected reactor and stir. Raise the temperature of the reactor to 120-130°C and keep the reaction for 8-10 hours. Lower the temperature of the reactor to 75-85°C, add toluene-2,4-diisocyanate into the reactor, keep the reaction for 3-4 hours, and post-treat to obtain modified polylactic acid.

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

[0041]

[0042] Where:

[0043]

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

[0045] Under the catalysis of stannous octoate, the terminal carboxyl group of polylactic acid undergoes esterification reaction with the terminal hydroxyl group on the intermediate I molecular chain and is introduced into the polylactic acid chain to form a polylactic acid-intermediate I molecular chain. The two isocyanate groups contained in the toluene-2,4-diisocyanate molecule can react with the hydroxyl group on the intermediate I chain to extend the length of the polymer chain to form an isocyanate-terminated modified polylactic acid. The isocyanate group forms an amino group in an aqueous environment. The impurities of the small molecular structure are removed by high-temperature and reduced-pressure distillation to prepare the modified polylactic acid.

[0046] Further, in step B1, the amount ratio of 3-methylglutaric acid, 2,5-furandicarboxylic acid, 1,4-butanediol, tetrabutyl titanate and NN-dimethylformamide is 5-7g:10-11g:28-32g:0.5-1mL:300mL, and the post-treatment includes: after the reaction is completed, the reaction kettle is cooled to room temperature, ethyl acetate and pure water are added, washed, and the organic phase is transferred to a rotary evaporator at a temperature of 40-50°C, and rotary evaporation is performed until no liquid is extracted to obtain intermediate I; in step B2, The dosage ratio of the intermediate I, toluene, stannous octoate and toluene-2,4-diisocyanate is 25-30g:300-400mL:0.5-0.8g:6-8g, and the dosage of the polylactic acid is calculated by the molar ratio of the carboxyl group in the polylactic acid molecule to the hydroxyl group in the intermediate I molecule of 1:2. The post-treatment step includes: after the reaction is completed, adding purified water to the reactor, raising the temperature of the reactor to 120-130°C, and distilling under reduced pressure until no liquid is produced to obtain modified polylactic acid.

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

[0048] 1. In the process of preparing a cellulose-based plastic packaging film with high extensibility, the present invention uses wood sugar residue cellulose as a basic material, modified polylactic acid as a reinforcing material, and prepares the plastic packaging film through a casting method with auxiliary additives and ethanol, prepares an ionic liquid through 1-ethylimidazole and triethyl phosphate, removes impurities from the wood sugar residue cellulose, increases the hydroxyl content of the cellulose, provides more active sites for grafting modified polylactic acid, improves the extensibility and degradation performance of the plastic packaging film, introduces flexible and ductile biopolyester into polylactic acid through esterification and condensation reactions, improves the extensibility and environmental protection of the plastic packaging film, uses cross-linking agent glutaraldehyde to form a Schiff base with the amino group of the modified polylactic acid, and the other end forms a hemiacetal with the hydroxyl group on the cellulose molecule, thereby obtaining a composite cellulose polylactic acid cross-linked with the wood sugar residue cellulose, strengthens the bonding force between the fiber material and the polylactic acid material, and improves 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 are subjected to esterification and condensation reactions to generate intermediate I. Intermediate I has a relatively long molecular flexible chain segment, which makes it easier for it to move and deform under the action of external force, has good ductility and toughness, further reduces the glass transition temperature of the plastic packaging film, and can maintain a high impact resistance at room temperature. A cross-linked structure is formed by linking toluene-2,4-diisocyanate, polylactic acid and intermediate I. Polylactic acid has good degradation properties. The polymerization of the two can further improve the extensibility, toughness, impact resistance and degradation properties of the plastic packaging film.

[0050] 3. In the process of preparing a cellulose-based plastic packaging film with high extensibility, the pretreated wood sugar residue cellulose has a high reprocessing capacity after being washed with an ion solution. The cross-linking agent glutaraldehyde is used to cross-link the modified polylactic acid and the pretreated wood sugar residue cellulose through covalent bonds to obtain a composite cellulose polylactic acid with a complex network structure, which improves the extensibility, toughness and impact resistance of the plastic packaging film. The composite cellulose polylactic acid is evenly dissolved with ethanol and auxiliary additives, and the film is stretched after cooling and casting to prepare a packaging film. The packaging film is composed of nano-scale fibers, which improves the toughness and extensibility of the plastic packaging film. The production process of the casting method is simple, the equipment cost is relatively low, the process parameters can be easily adjusted during production, and the cost of producing the plastic packaging film can be reduced. DETAILED DESCRIPTION

[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 part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] Example 1

[0053] This embodiment provides a process for preparing a cellulose-based plastic packaging film with high extensibility, comprising the following steps:

[0054] S1. Preparation of pretreated lignocellulosic residue

[0055] Weigh: 50 g of wood sugar residue powder, 1.3 L of benzene and 700 mL of ethanol, put them into a Soxhlet extractor, heat to 90°C, keep the temperature for 4 hours, and filter to obtain the crude wood sugar residue cellulose;

[0056] Weigh: 10 g of 1-ethylimidazole and 20 mL of triethyl phosphate, place in a reaction kettle, heat to 120°C, keep warm for 8 hours, after the reaction is completed, wait for the reaction to cool to room temperature, add ethyl acetate, extract, transfer the lower organic phase to a rotary evaporator, evaporate until no liquid is extracted, transfer to a drying oven, dry to constant weight, and obtain an ion solution;

[0057] Weigh: 50 g of crude lignocellulosic cellulose, 1 L of dimethyl sulfoxide and 1.5 L of ion solution into a reaction kettle, heat to 80° C., keep warm for 1 hour, and filter to obtain a pretreated lignocellulosic cellulose solution;

[0058] The pretreated lignocellulosic cellulose solution was added dropwise to deionized water to regenerate the lignocellulosic cellulose. After the regeneration was completed, the filter cake was filtered and washed twice with deionized water, and then transferred to a drying oven at a temperature of 80° C. and dried to constant weight to obtain the pretreated lignocellulosic cellulose.

[0059] S2. Preparation of 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 NN-dimethylformamide, place in a reactor protected by a nitrogen atmosphere, heat to 140°C, and keep warm for 4 hours. After the reaction is completed, wait for the reactor to cool to room temperature, add ethyl acetate and pure water, wash, transfer the organic phase to a rotary evaporator at a temperature of 40°C, and evaporate until no liquid is extracted to obtain intermediate I;

[0061] Weigh: 250g of intermediate I, 3L of toluene and 5g of stannous octoate, add to a nitrogen-protected reactor and stir, calculate the amount of polylactic acid added according to 1 / 2 of the molar amount of hydroxyl groups in intermediate I, and add it to the reactor, raise the temperature of the reactor to 120°C, keep the reaction for 8h, lower the temperature of the reactor to 75°C, add 60g of toluene-2,4-diisocyanate to the reactor, keep the reaction for 3h, after the reaction is completed, add purified water to the reactor, raise the temperature of the reactor to 120°C, and distill under reduced pressure until no liquid is produced to obtain modified polylactic acid.

[0062] S3. Preparation of cellulose-based plastic packaging film

[0063] Weigh: 100 g of pretreated lignocellulosic cellulose, 80 g of modified polylactic acid and 2 L of NN-dimethylformamide, place in a reactor, stir for 2 h, dropwise add 300 mL of 50% glutaraldehyde solution, raise the temperature to 35 ° C, and keep the temperature for 3 h. After the reaction is completed, wait for the reactor to cool to room temperature, add ethyl acetate and pure water, wash, transfer the organic phase to a rotary evaporator at a temperature of 40 ° C, and rotary evaporate until no liquid is extracted to obtain composite cellulose polylactic acid;

[0064] The polyethylene wax, benzimidazole, butylated hydroxyanisole, zinc stearate and antioxidant PPD are uniformly mixed in a weight ratio of 1:1:2:4:1 to obtain an auxiliary additive;

[0065] Weigh: 100g of composite cellulose polylactic acid, 1L of ethanol and 30g of auxiliary additives, place them in a reaction kettle, heat to 50°C, stir until dissolved, pour the solution onto one end of a glass substrate, use a scraper of a certain thickness to evenly cast the solution on the surface of the glass substrate, cool and shape it, and then stretch it to obtain a plastic packaging film.

[0066] Example 2

[0067] This embodiment provides a process for preparing a cellulose-based plastic packaging film with high extensibility, comprising the following steps:

[0068] S1. Preparation of pretreated lignocellulosic residue

[0069] Weigh: 75 g of wood sugar residue powder, 1.6 L of benzene and 800 mL of ethanol, put them into a Soxhlet extractor, heat to 95°C, keep the temperature for 5 hours, and filter to obtain the wood sugar residue cellulose crude product;

[0070] Weigh: 15 g of 1-ethylimidazole and 30 mL of triethyl phosphate, place in a reaction kettle, heat to 130°C, keep warm for 10 hours, wait until the reaction is cooled to room temperature, add ethyl acetate, extract, transfer the lower organic phase to a rotary evaporator, evaporate until no liquid is extracted, transfer to a drying oven, dry to constant weight, and obtain an ion solution;

[0071] Weigh: 75 g of crude lignocellulosic cellulose, 1.5 L of dimethyl sulfoxide and 1.5 L of ion solution into a reactor, heat to 90° C., keep warm for 2 h, and filter to obtain a pretreated lignocellulosic cellulose solution;

[0072] The pretreated lignocellulosic cellulose solution was added dropwise to deionized water to regenerate the lignocellulosic cellulose. After the regeneration was completed, the filter cake was filtered and washed twice with deionized water, and then transferred to a drying oven at a temperature of 85° C. and dried to constant weight to obtain the pretreated lignocellulosic cellulose.

[0073] S2. Preparation of 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 NN-dimethylformamide, place in a reactor protected by a nitrogen atmosphere, heat to 140°C, and keep warm for 5 hours. After the reaction is completed, wait for the reactor to cool to room temperature, add ethyl acetate and pure water, wash, transfer the organic phase to a rotary evaporator at a temperature of 45°C, and evaporate until no liquid is extracted to obtain intermediate I;

[0075] Weigh: 270g of intermediate I, 3.5L of toluene and 7g of stannous octoate, add to a nitrogen-protected reactor and stir, calculate the amount of polylactic acid added according to 1 / 2 of the molar amount of hydroxyl groups in intermediate I, and add it to the reactor, raise the temperature of the reactor to 125°C, keep the reaction for 9h, lower the temperature of the reactor to 80°C, add 70g of toluene-2,4-diisocyanate to the reactor, keep the reaction for 3.5h, after the reaction is completed, add purified water to the reactor, raise the temperature of the reactor to 125°C, and distill under reduced pressure until no liquid is produced to obtain modified polylactic acid.

[0076] S3. Preparation of cellulose-based plastic packaging film

[0077] Weigh: 130 g of pretreated lignocellulosic cellulose, 100 g of modified polylactic acid and 2.5 L of NN-dimethylformamide, place in a reactor, stir for 2 h, dropwise add 350 mL of 50% glutaraldehyde solution, raise the temperature to 40 ° C, keep warm for 4 h, after the reaction is completed, wait for the reactor to cool to room temperature, add ethyl acetate and pure water, wash, transfer the organic phase to a rotary evaporator at a temperature of 45 ° C, and rotary evaporate until no liquid is extracted to obtain composite cellulose polylactic acid;

[0078] The polyethylene wax, benzimidazole, butylated hydroxyanisole, zinc stearate and antioxidant PPD are uniformly mixed in a weight ratio of 1:1:2:4:1 to obtain an auxiliary additive;

[0079] Weigh: 130g of composite cellulose polylactic acid, 1.3L of ethanol and 35g of auxiliary additives, place them in a reactor, heat to 55°C, stir until dissolved, pour the solution onto one end of a glass substrate, use a scraper of a certain thickness to evenly cast the solution on the surface of the glass substrate, cool and shape, and then stretch to obtain a plastic packaging film.

[0080] Example 3

[0081] This embodiment provides a process for preparing a cellulose-based plastic packaging film with high extensibility, comprising the following steps:

[0082] S1. Preparation of pretreated lignocellulosic residue

[0083] Weigh: 100 g of wood sugar residue powder, 2 L of benzene and 1 L of ethanol, put them into a Soxhlet extractor, heat them to 100°C, keep them warm for 6 hours, and filter to obtain the crude wood sugar residue cellulose;

[0084] Weigh: 20 g of 1-ethylimidazole and 40 mL of triethyl phosphate are placed in a reaction kettle, heated to 140°C, and kept warm for 12 hours. After the reaction is completed, wait for the reaction to cool to room temperature, add ethyl acetate, extract, transfer the lower organic phase to a rotary evaporator, evaporate until no liquid is extracted, transfer to a drying oven, and dry to constant weight to obtain an ion solution;

[0085] Weigh: 100 g of crude lignocellulosic cellulose, 2 L of dimethyl sulfoxide and 2 L of ion solution, put them into a reaction kettle, heat them to 100° C., keep them warm for 2 h, and filter them to obtain a pretreated lignocellulosic cellulose solution;

[0086] The pretreated lignocellulosic cellulose solution was added dropwise to deionized water to regenerate the lignocellulosic cellulose. After the regeneration was completed, the filter cake was filtered and washed twice with deionized water, and then transferred to a drying oven at a temperature of 90° C. and dried to constant weight to obtain the pretreated lignocellulosic cellulose.

[0087] S2. Preparation of 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 NN-dimethylformamide, place in a reactor protected by a nitrogen atmosphere, heat to 150°C, and keep warm for 6 hours. After the reaction is completed, wait for the reactor to cool to room temperature, add ethyl acetate and pure water, wash, transfer the organic phase to a rotary evaporator at a temperature of 50°C, and evaporate until no liquid is extracted to obtain intermediate I;

[0089] Weigh: 300g of intermediate I, 4L of toluene and 8g of stannous octoate, add to a nitrogen-protected reactor and stir, calculate the amount of polylactic acid added according to 1 / 2 of the molar amount of hydroxyl groups in intermediate I, and add it to the reactor, raise the temperature of the reactor to 130°C, keep the reaction for 10h, lower the temperature of the reactor to 85°C, add 8g of toluene-2,4-diisocyanate to the reactor, keep the reaction for 4h, after the reaction is completed, add purified water to the reactor, raise the temperature of the reactor to 130°C, and distill under reduced pressure until no liquid is produced to obtain modified polylactic acid.

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

[0091] Weigh: 150g of pretreated lignocellulosic cellulose, 120g of modified polylactic acid and 3L of NN-dimethylformamide, put them in a reactor, stir for 2h, add 400mL of 50% glutaraldehyde solution, heat to 45°C, keep warm for 5h, after the reaction is completed, cool the reactor to room temperature, add ethyl acetate and pure water, wash, transfer the organic phase to a rotary evaporator at 50°C, and rotary evaporate until no liquid is extracted to obtain composite cellulose polylactic acid;

[0092] The polyethylene wax, benzimidazole, butylated hydroxyanisole, zinc stearate and antioxidant PPD are uniformly mixed in a weight ratio of 1:1:2:4:1 to obtain an auxiliary additive;

[0093] Weigh: 150g of composite cellulose polylactic acid, 1.5L of ethanol and 40g of auxiliary additives, place them in a reaction kettle, heat to 60°C, stir until dissolved, pour the solution onto one end of a glass substrate, use a scraper of a certain thickness to evenly cast the solution on the surface of the glass substrate, cool and shape it, and then stretch it to obtain a plastic packaging film.

[0094] Comparative Example 1

[0095] The difference between this comparative example and Example 3 is that step S1 is omitted, and in step S3, an equal amount of wood sugar residue powder is used to replace the pretreated wood sugar residue cellulose.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 3 is that step S2 is eliminated, and in step S3, an equal amount of polylactic acid is used to 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 is omitted, and the pretreated wood sugar residue cellulose and the modified polylactic acid are blended to obtain composite cellulose polylactic acid.

[0100] Performance Testing:

[0101] The elongation at break and tensile strength of the plastic packaging film samples prepared in Examples 1-3 and Comparative Examples 1-3 were tested respectively with reference to the standard GB / T 10654-2001 "Determination of tensile strength and elongation at break of polymer porous elastic materials";

[0102] The elastic modulus of the plastic packaging film samples prepared in Examples 1-3 and Comparative Examples 1-3 were tested respectively with reference to the standard GB / T 41762.2-2022 "Determination of thickness direction properties of fiber reinforced plastic composite laminates Part 2: Determination of elastic modulus, strength and Weibull size effect of carbon fiber unidirectional laminates by bending test";

[0103] With reference to the standard GB / T 41010-2021 "Degradation performance and labeling requirements of biodegradable plastics and products", the 12-week disintegration rate and 180-day biodegradation rate of the plastic packaging film samples prepared in Examples 1-3 and Comparative Examples 1-3 were tested under industrial composting conditions. The specific test results are shown in Tables 1-2 below.

[0104] Table 1- Physical properties test data of each sample

[0105] Table 2-Biodegradation performance test data of samples

[0106] Data Analysis:

[0107] Comparing and analyzing the data in Tables 1-2 above, the high-extensibility cellulose-based plastic packaging film prepared by the present invention has a breaking elongation of 391%, a tensile strength of 59 MPa, an elastic modulus of 2.8 MPa and an impact strength of KJ / m -2 The prepared high-extensibility cellulose-based plastic packaging film has a one-week disintegration rate of 81.3% and a biodegradation rate of 78.4% under industrial composting conditions, and all performance parameters are better than those of the comparative example, indicating that the present invention dissolves and regenerates pretreated wood sugar residue cellulose through ion solution, cross-links it with modified polylactic acid to prepare composite cellulose polylactic acid, and the composite cellulose polylactic acid is used to obtain a high-extensibility cellulose-based plastic packaging film through a 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 explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A process for preparing a highly extensible cellulose-based plastic packaging film, characterized in that: The following steps are involved: S1, placing pretreated wood sugar residue fiber, modified polylactic acid and NN-dimethylformamide in a reaction kettle, stirring for 1-2 hours, adding glutaraldehyde solution dropwise, heating to 35-45°C, keeping the temperature for reaction for 3-5 hours, and post-treating to obtain composite cellulose polylactic acid; S2. Place composite cellulose polylactic acid, ethanol and auxiliary additives in a reaction kettle, heat to 50-60°C, stir until dissolved, pour the solution onto one end of a glass substrate, use a scraper of a certain thickness to evenly cast the solution on the surface of the glass substrate, cool and shape, and then stretch to obtain a plastic packaging film.

2. The process for preparing 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 wood sugar residue fiber, modified polylactic acid, NN-dimethylformamide and glutaraldehyde solution is 10-15g:8-12g:200-300mL:40-50mL; in step S2, the dosage ratio of the composite cellulose polylactic acid, deionized water and auxiliary additives is 10-15g:100-150mL:3-4g, and the auxiliary additives are lubricants, mildew inhibitors, dispersants, antioxidants and antioxidants in a weight ratio of 1:1:2:4:

1.

3. The process for preparing a highly extensible cellulose-based plastic packaging film according to claim 1, characterized in that: The preparation method of the pretreated wood sugar residue fiber is as follows: A1. Place wood sugar residue powder, benzene and ethanol in a Soxhlet extractor, heat to 90-100°C, keep warm for 4-6 hours, and filter to obtain crude wood cellulose; A2, placing the crude lignocellulose, dimethyl sulfoxide and ion solution in a reaction kettle, heating to 80-100° C., keeping the temperature for 1-2 hours, and filtering to obtain a pretreated lignocellulose fiber solution; A3. The pretreated wood sugar residue cellulose solution is added dropwise into deionized water to regenerate the wood sugar residue cellulose, and then post-processed to obtain the pretreated wood sugar residue fiber.

4. The process for preparing a highly extensible cellulose-based plastic packaging film according to claim 3, characterized in that: In step A1, the usage ratio of the wood sugar residue powder, benzene and ethanol is 5-10g:130-200mL:70-100mL; in step A2, the usage ratio of the lignocellulose crude product and the ion mixed solution is 5-10g:100-200mL:150-200mL.

5. The process for preparing a highly extensible cellulose-based plastic packaging film according to claim 3, characterized in that: The preparation method of the ionic solution is as follows: 1-ethylimidazole and triethyl phosphate are placed in a reaction kettle, the temperature is raised to 120-140° C., the reaction is carried out by heat preservation for 8-12 hours, and the ionic solution is obtained by post-processing.

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

7. The process for preparing a highly extensible cellulose-based plastic packaging film according to claim 1, characterized in that: The preparation method of the modified polylactic acid comprises the following steps: B1, 3-methylglutaric acid, 2,5-furandicarboxylic acid, 1,4-butanediol, tetrabutyl titanate and NN-dimethylformamide are placed in a reactor protected by a nitrogen atmosphere, the temperature is raised to 140-150°C, the reaction is kept at this temperature for 4-6 hours, and the intermediate I is obtained by post-treatment; B2. Add intermediate I, polylactic acid, toluene and stannous octoate into a nitrogen-protected reactor and stir. Raise the temperature of the reactor to 120-130°C and keep the reaction for 8-10 hours. Lower the temperature of the reactor to 75-85°C, add toluene-2,4-diisocyanate into the reactor, keep the reaction for 3-4 hours, and post-treat to obtain modified polylactic acid.

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

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