A degradable material for food packaging box and a preparation method thereof

Abstract

The application discloses a degradable material for food packaging boxes and a preparation method thereof, and belongs to the technical field of environment-friendly materials. Grafting polylactic acid, a reactive solubilizer and glycerol modified fiber are mixed according to a weight ratio of 60-70:5-8:25-30, and are subjected to a blending reaction at 160-170 DEG C for 8-9 min to obtain a blending crosslinking material; and the blending crosslinking material is subjected to a hot-pressing treatment at 130-140 DEG C and 8-9 MPa for 8-10 min to obtain the material for food packaging boxes. The reactive solubilizer, i.e., epoxy soybean oil, is used to crosslink the glycerol modified fiber and the grafting polylactic acid at high temperature, so that the material for food packaging boxes with good heat resistance and mechanical properties is obtained.

Description

Technical Field

[0001] This invention belongs to the field of environmentally friendly materials technology, specifically relating to a biodegradable food packaging material and its preparation method. Background Technology

[0002] In the development of the entire food industry chain, food packaging boxes, as the core carrier between food and consumers, undertake multiple key functions such as food safety protection, quality preservation, transportation and storage, information transmission, and brand display. They are an indispensable and important component in all stages of food production, distribution, and sales. Food packaging boxes are not merely containers; they are functional carriers that ensure food quality, regulate distribution, and safeguard food safety, spanning the entire life cycle of food from factory to transportation, storage, sales, and consumption. Their core functions can be divided into four dimensions: protective function, distribution function, commercial function, and safety traceability function.

[0003] Paper packaging boxes are the most widely used traditional packaging material, mainly including white cardboard, kraft paper, corrugated paper, and specialty food paper. They are widely used in packaging pastries, bread, snacks, fast food, and gift foods due to their advantages such as low cost, good printability, recyclability, and no pollution. Paper packaging boxes occupy a large market share due to their environmental friendliness, low cost, and ease of processing. However, limited by the characteristics of their natural fiber structure, they have many performance shortcomings and cannot meet the needs of mid-to-high-end, high-preservation, and special-scenario food packaging. The core defects are concentrated in four aspects: barrier properties, weather resistance, mechanical properties, and safety stability. First, barrier properties are severely insufficient. Paper has a porous hydrophilic fiber structure and naturally possesses air and water permeability. Unmodified paper packaging boxes have extremely poor barrier effects against moisture, oxygen, and oils. Moisture easily penetrates the paper, causing the packaging to become damp and soften; oxygen penetrates the packaging, accelerating food oxidation and spoilage; and oils quickly penetrate the paper surface, contaminating the packaging and affecting food hygiene. Second, weather resistance and temperature resistance are weak. Paper packaging boxes have extremely poor resistance to both high and low temperatures. In high-temperature environments, they easily absorb water, deform, soften, and break, making them unsuitable for hot food packaging and high-temperature sterilization. In low-temperature cold chain environments, condensation easily forms on the packaging surface, causing the paper to absorb moisture, become brittle, crack, and break, seriously affecting the safety of cold chain food transportation and storage. Furthermore, the structural strength of paper packaging decreases significantly when exposed to water or oil, making it prone to deformation, collapse, and leakage. Thirdly, its mechanical protection performance is limited. Paper materials have poor toughness, tear resistance, and compressive strength, making them susceptible to deformation and breakage during stacking, storage, and long-distance transportation. This provides insufficient physical protection for food, easily leading to food breakage and crushing damage. Increasing the thickness of the cardboard to improve strength would increase packaging volume, raw material consumption, and logistics costs, significantly reducing cost-effectiveness and failing to meet the packaging protection needs of heavy and delicate foods. Fourthly, there are potential hygiene and stability risks. The plant fibers and starch in paper raw materials provide conditions for microbial growth, making them highly susceptible to mold and bacteria growth in humid environments, posing a food safety risk. Meanwhile, recycled paper raw materials may contain residual printing ink, chemical additives and other impurities. If the processing is not up to standard, harmful substances may migrate, failing to meet the high safety standards required for high-end foods and ready-to-eat foods.

[0004] Compared to the numerous performance shortcomings of paper packaging, plastic food packaging boxes, with their superior comprehensive performance, have become an indispensable packaging material in the modern food industry, supporting the rapid development of cold chain food, pre-prepared food, and airtight food. Plastic packaging boxes are the core material of modern food packaging, with mainstream raw materials including polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polyester (PET). They are mostly formed through processes such as injection molding, thermoforming, and extrusion, possessing characteristics such as strong barrier properties, high mechanical strength, water and oil resistance, and lightweight and impact resistance. They are widely used in food sectors with high requirements for freshness and protection, such as fresh fruits and vegetables, pre-prepared dishes, beverages, frozen foods, and cooked foods, making them the preferred material for cold chain and airtight food packaging. Although traditional plastic food packaging boxes have excellent comprehensive performance and outstanding economic benefits, they also have unavoidable degradation defects, leading to serious ecological and environmental problems, which is a core pain point in the current green transformation of the food packaging industry. Ordinary food packaging plastics such as PE, PP, and PET can take up to a hundred years to fully degrade in natural soil, water, and atmospheric environments. Large quantities of discarded plastic packaging boxes accumulate in the natural environment, unable to decompose for extended periods, continuously occupying land resources and polluting water and soil. Furthermore, their inability to completely degrade under normal conditions easily leads to microplastic pollution. Polylactic acid (PLA) is currently a widely used bio-based biodegradable material. However, directly processing its resin into food packaging boxes presents several inherent technical defects. First, its heat resistance is extremely poor; the glass transition temperature of pure PLA is only around 60°C. Second, the material itself is brittle and lacks toughness, making directly processed packaging boxes prone to cracking and damage. Its mechanical properties are weaker than traditional plastic packaging materials such as PP and PET, resulting in lower yield rates and poorer stability in use.

[0005] Therefore, improving the heat resistance and mechanical properties of polylactic acid to enable its effective application in food packaging materials is of great significance for the development of environmentally friendly packaging boxes. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention utilizes reactive solubilizer epoxidized soybean oil to crosslink glycerol-modified fibers and grafted polylactic acid at high temperatures, resulting in a food packaging material with excellent heat resistance and mechanical properties, thus solving the technical problems mentioned in the background art. Specifically, the technical solution of this invention includes the following:

[0007] One objective of this invention is to provide a method for preparing a biodegradable food packaging material, the method comprising the following steps:

[0008] Grafted polylactic acid, reactive solubilizer and glycerol modified fiber are mixed in a weight ratio of 60~70:5~8:25~30 and reacted at 160℃~170℃ for 8min~9min to obtain a cross-linked blend.

[0009] The blended crosslinked compound is hot-pressed at 130℃~140℃ and 8MPa~9MPa for 8min~10min to obtain the material for food packaging boxes.

[0010] Furthermore, the preparation method of the grafted polylactic acid includes the following steps:

[0011] L-lactic acid and stannous chloride are mixed and heated to 140℃~145℃ for 30min~40min and kept at this temperature. Then, a polyol is added and the reaction continues for another 30min~40min. The vacuum is then controlled to 0.08MPa~0.09MPa and the temperature is raised to 160℃~170℃ for 7h~8h to obtain the grafted polylactic acid.

[0012] Furthermore, the polyol includes D-mannitol.

[0013] Furthermore, the weight ratio of L-lactic acid:stannous chloride:polyol is 1:0.006~0.007:0.01~0.02.

[0014] Furthermore, the reactive solubilizer includes epoxidized soybean oil.

[0015] Furthermore, the epoxy value of the epoxidized soybean oil is 6%.

[0016] Furthermore, the method for preparing the glycerol-modified fiber includes the following steps:

[0017] Biomass fibers are pretreated by plasma etching at 80W~100W for 5min~8min.

[0018] Pretreated fibers, diisocyanate and tetramethylpropylenediamine are mixed and heated to 45℃~50℃ for 55min~65min, then kept at this temperature. Plasticizer is then added and the reaction continues for 40min~45min to obtain glycerol-modified fibers.

[0019] Furthermore, the biomass fiber is bamboo fiber with a length of 38 mm and a fineness of 1.56 dtex.

[0020] Furthermore, the plasma etching uses oxygen gas with a flow rate of 200 mL / min to 300 mL / min.

[0021] Furthermore, the diisocyanate includes hexamethylene diisocyanate, and the plasticizer includes glycerol.

[0022] Furthermore, the weight ratio of the pretreated fiber, diisocyanate, tetramethylpropylenediamine, and plasticizer is 10:2~3:0.07~0.08:0.2~0.3.

[0023] A second objective of this invention is to provide a biodegradable material for food packaging boxes.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention uses biomass fibers as a toughness-enhancing material. Biomass fibers can enhance the toughness of composite materials through fiber pull-out mechanisms and crack deflection, making the materials less prone to fracture due to brittleness. Pretreated fibers are obtained by plasma etching of biomass fibers. This process destroys impurities such as lignin and hemicellulose, reducing the tightly packed structure of cellulose and promoting hydroxyl group exposure, thus increasing reactivity. It also creates a micro-rough structure, increasing the contact area and enhancing mechanical interlocking. The pretreated fibers are then condensed with diisocyanate, followed by the addition of glycerol as a plasticizer to obtain glycerol-modified fibers. The role of glycerol as a plasticizer is twofold: firstly, it increases interfacial bonding through multiple hydroxyl reaction sites during subsequent polymerization with polylactic acid; secondly, it improves the toughness of the polymerized material, compensating for the performance degradation of the fibers caused by plasma treatment. Next, grafted polylactic acid (PLA) was obtained by introducing polyols with multiple hydroxyl branching points as grafting structures during the PLA synthesis process. The grafting structure can, on the one hand, disrupt the tight packing between PLA molecular chains, reducing PLA's brittleness; on the other hand, the hydroxyl groups introduced by the grafting structure can improve the polarity of PLA and enhance its interfacial compatibility with fibers. Finally, using epoxidized soybean oil containing polyepoxy groups as a reactive solubilizer, the glycerol-modified fibers and grafted PLA were covalently cross-linked at high temperature through the hydroxyl groups in the fiber structure and the epoxy groups in the epoxidized soybean oil, forming a three-dimensional cross-linked network structure. This not only improved the interfacial bonding but also enhanced the mechanical strength and heat resistance of the cross-linked structure. This prevented defects such as excessive toughness modification resulting in low mechanical strength or poor PLA modification due to performance degradation caused by plasma treatment of the fibers. Through this modification, the prepared material not only possesses good heat resistance but also exhibits improved mechanical properties. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below through embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise stated, all raw materials and reagents used in this invention are commercially available or can be prepared by known methods.

[0028] Preparation Example 1

[0029] The preparation method of grafted polylactic acid includes the following steps:

[0030] Before use, L-lactic acid is first removed by vacuum distillation to remove moisture. Then, 500g of dried L-lactic acid and 3g of stannous chloride are weighed and mixed into a reaction vessel. Nitrogen gas is introduced to purge the air from the vessel, and the mixture is heated to 140℃. The pressure inside the vessel is adjusted to atmospheric pressure, and the mixture is stirred at 200 rpm for 30 minutes (water generated during the reaction is discharged through a water separator). After the reaction is complete, the temperature is maintained, and then 5g of D-mannitol is added, with the mixture stirred at 140℃ for another 30 minutes. The temperature is then further increased to 160℃, and a vacuum is drawn to a degree of 0.09 MPa. The mixture is stirred at 150 rpm for 7 hours under this reaction environment. After the reaction is complete, the pressure is restored to atmospheric pressure, and the grafted polylactic acid is discharged.

[0031] Preparation Example 2

[0032] The preparation method of grafted polylactic acid includes the following steps:

[0033] Before use, L-lactic acid is first removed by vacuum distillation to remove moisture. Then, 500g of dried L-lactic acid and 3.2g of stannous chloride are weighed and mixed into a reaction vessel. Nitrogen gas is introduced to purge the air from the vessel, and the mixture is heated to 140℃. The pressure inside the vessel is adjusted to atmospheric pressure, and the mixture is stirred at 200 rpm for 35 minutes (water generated during the reaction is discharged through a water separator). After the reaction is complete, the temperature is maintained, and then 7g of D-mannitol is added, with the mixture stirred at 140℃ for another 35 minutes. The temperature is then further increased to 160℃, and a vacuum is drawn to a degree of 0.09 MPa. The mixture is stirred at 150 rpm for 7.5 hours under this reaction environment. After the reaction is complete, the pressure is restored to atmospheric pressure, and the grafted polylactic acid is discharged.

[0034] Preparation Example 3

[0035] The preparation method of grafted polylactic acid includes the following steps:

[0036] Before use, L-lactic acid was first removed by vacuum distillation to remove moisture. Then, 500g of dried L-lactic acid and 3.4g of stannous chloride were weighed and mixed into a reaction vessel. Nitrogen gas was introduced to purge the air from the vessel, and the mixture was heated to 145℃. The pressure inside the vessel was adjusted to atmospheric pressure, and the mixture was stirred at 200 rpm for 35 minutes (water generated during the reaction was discharged through a water separator). After the reaction was completed, the temperature was maintained, and then 8g of D-mannitol was added, with the mixture stirred at 145℃ for another 35 minutes. The temperature was then further increased to 165℃, and a vacuum was drawn to a degree of 0.09 MPa. The mixture was stirred at 150 rpm for 8 hours under this reaction environment. After the reaction was completed, the pressure was restored to atmospheric pressure, and the grafted polylactic acid was discharged.

[0037] Preparation Example 4

[0038] The preparation method of grafted polylactic acid includes the following steps:

[0039] Before use, L-lactic acid is first removed by vacuum distillation to remove moisture. Then, 500g of dried L-lactic acid and 3.5g of stannous chloride are weighed and mixed into a reaction vessel. Nitrogen gas is introduced to purge the air from the vessel, and the mixture is heated to 145℃. The pressure inside the vessel is adjusted to atmospheric pressure, and the mixture is stirred at 200 rpm for 40 minutes (water generated during the reaction is discharged through a water separator). After the reaction is complete, the temperature is maintained, and then 10g of D-mannitol is added, with the mixture stirred at 145℃ for another 40 minutes. The temperature is then further increased to 170℃, and a vacuum is drawn to a degree of 0.08 MPa. The mixture is stirred at 150 rpm for 8 hours under this reaction environment. After the reaction is complete, the pressure is restored to atmospheric pressure, and the grafted polylactic acid is discharged.

[0040] Preparation Example 5

[0041] The preparation method of grafted polylactic acid includes the following steps:

[0042] The amount of D-mannitol used in Preparation Example 4 was increased to 20g, while the rest of the preparation process remained the same as in Preparation Example 4.

[0043] Preparation Example 6

[0044] The preparation method of grafted polylactic acid includes the following steps:

[0045] In Preparation Example 4, D-mannitol was replaced with pentaerythritol, and the rest of the preparation process remained the same as in Preparation Example 4.

[0046] Preparation Example 7

[0047] The preparation method of polylactic acid includes the following steps:

[0048] Before use, L-lactic acid is first removed by vacuum distillation to remove moisture. Then, 500g of dried L-lactic acid and 3.5g of stannous chloride are weighed and mixed into a reaction vessel. Nitrogen gas is introduced to purge the air from the vessel, and the mixture is heated to 145℃. The pressure inside the vessel is adjusted to atmospheric pressure, and the reaction is carried out with stirring at 200 rpm for 40 minutes (water produced during the reaction is discharged through a water separator). The temperature is then further increased to 170℃, and a vacuum is drawn to a degree of 0.08 MPa. The reaction is carried out under this environment with stirring at 150 rpm for 8 hours. After the reaction is complete, the pressure is restored to atmospheric pressure, and the product is discharged to obtain polylactic acid.

[0049] Preparation Example 8

[0050] The preparation method of glycerol-modified fiber includes the following steps:

[0051] Bamboo fibers with a length of 38 mm and a fineness of 1.56 dtex were placed in a plasma chamber, using oxygen as the plasma treatment gas at a flow rate of 200 mL / min. The bamboo fibers were then etched at 80 W for 5 minutes to obtain pretreated fibers. 200 g of the pretreated fibers were added to 200 mL of N,N-dimethylformamide and mixed at high speed until evenly dispersed. The speed was then adjusted to 400 r / min, and the temperature was controlled at 45℃. At this point, 40 g of hexamethylene diisocyanate and 1.4 g of tetramethylpropylenediamine were added and the mixture was stirred for 55 minutes, maintaining the temperature at 45℃. Then, 4 g of glycerol was added, and the reaction was continued for another 40 minutes. After the reaction, the mixture was filtered, rinsed with deionized water, and then dried in a vacuum oven at 55℃ for 24 hours to obtain glycerol-modified fibers.

[0052] Preparation Example 9

[0053] The preparation method of glycerol-modified fiber includes the following steps:

[0054] Bamboo fibers with a length of 38 mm and a fineness of 1.56 dtex were placed in a plasma chamber, using oxygen as the plasma treatment gas at a flow rate of 240 mL / min. The bamboo fibers were then etched at 80 W for 6 minutes to obtain pretreated fibers. 200 g of the pretreated fibers were added to 200 mL of N,N-dimethylformamide and mixed at high speed until evenly dispersed. The speed was then adjusted to 400 rpm, and the temperature was controlled at 45 °C. At this point, 45 g of hexamethylene diisocyanate and 1.5 g of tetramethylpropylene diamine were added and the mixture was stirred for 58 minutes, maintaining the temperature at 45 °C. Then, 5 g of glycerol was added, and the reaction was continued for another 40 minutes. After the reaction, the mixture was filtered, rinsed with deionized water, and then dried in a vacuum oven at 55 °C for 24 hours to obtain glycerol-modified fibers.

[0055] Preparation Example 10

[0056] The preparation method of glycerol-modified fiber includes the following steps:

[0057] Bamboo fibers with a length of 38 mm and a fineness of 1.56 dtex were placed in a plasma chamber, using oxygen as the plasma treatment gas at a flow rate of 280 mL / min. The bamboo fibers were then etched at 90 W for 7 minutes to obtain pretreated fibers. 200 g of the pretreated fibers were added to 200 mL of N,N-dimethylformamide and mixed at high speed until evenly dispersed. The speed was then adjusted to 400 r / min, and the temperature was controlled at 50 °C. At this point, 55 g of hexamethylene diisocyanate and 1.6 g of tetramethylpropylene diamine were added and the mixture was stirred for 62 minutes, maintaining the temperature at 50 °C. Then, 5 g of glycerol was added, and the reaction was continued for another 45 minutes. After the reaction, the mixture was filtered, rinsed with deionized water, and then dried in a vacuum oven at 55 °C for 24 hours to obtain glycerol-modified fibers.

[0058] Preparation Example 11

[0059] The preparation method of glycerol-modified fiber includes the following steps:

[0060] Bamboo fibers with a length of 38 mm and a fineness of 1.56 dtex were placed in a plasma chamber, using oxygen as the plasma treatment gas at a flow rate of 300 mL / min. The bamboo fibers were then etched at 100 W for 8 minutes to obtain pretreated fibers. 200 g of the pretreated fibers were added to 200 mL of N,N-dimethylformamide and mixed at high speed until evenly dispersed. The speed was then adjusted to 400 r / min, and the temperature was controlled at 50 °C. At this point, 60 g of hexamethylene diisocyanate and 1.6 g of tetramethylpropylene diamine were added and stirred for 65 minutes, maintaining the temperature at 50 °C. Then, 6 g of glycerol was added, and the reaction was continued for another 45 minutes. After the reaction, the mixture was filtered, rinsed with deionized water, and then dried in a vacuum oven at 55 °C for 24 hours to obtain glycerol-modified fibers.

[0061] Preparation Example 12

[0062] The preparation method of glycerol-modified fiber includes the following steps:

[0063] The bamboo fiber in Preparation Example 11 was replaced with bamboo fiber with a length of 38 mm and a fineness of 5.56 dtex, and the rest of the preparation process was the same as in Preparation Example 11.

[0064] Preparation Example 13

[0065] The preparation method of glycerol-modified fiber includes the following steps:

[0066] Bamboo fibers with a length of 38 mm and a fineness of 1.56 dtex were placed in a plasma chamber, using oxygen as the plasma treatment gas at a flow rate of 200 mL / min. The bamboo fibers were then etched at 50 W for 3 minutes to obtain pretreated fibers. 200 g of the pretreated fibers were added to 200 mL of N,N-dimethylformamide and mixed at high speed until evenly dispersed. The speed was then adjusted to 400 r / min, and the temperature was controlled at 50 °C. At this point, 60 g of hexamethylene diisocyanate and 1.6 g of tetramethylpropylene diamine were added and the mixture was stirred for 65 minutes, maintaining the temperature at 50 °C. Then, 6 g of glycerol was added, and the reaction was continued for another 45 minutes. After the reaction, the mixture was filtered, rinsed with deionized water, and then dried in a vacuum oven at 55 °C for 24 hours to obtain glycerol-modified fibers.

[0067] Preparation Example 14

[0068] The preparation method of glycerol-modified fiber includes the following steps:

[0069] Bamboo fibers with a length of 38 mm and a fineness of 1.56 dtex were placed in a plasma chamber, using oxygen as the plasma treatment gas at a flow rate of 400 mL / min. The bamboo fibers were then etched at 150 W for 15 minutes to obtain pretreated fibers. 200 g of the pretreated fibers were added to 200 mL of N,N-dimethylformamide and mixed at high speed until evenly dispersed. The speed was then adjusted to 400 r / min, and the temperature was controlled at 50 °C. At this point, 60 g of hexamethylene diisocyanate and 1.6 g of tetramethylpropylenediamine were added and the mixture was stirred for 65 minutes, maintaining the temperature at 50 °C. Then, 6 g of glycerol was added, and the reaction was continued for another 45 minutes. After the reaction, the mixture was filtered, rinsed with deionized water, and then dried in a vacuum oven at 55 °C for 24 hours to obtain glycerol-modified fibers.

[0070] Preparation Example 15

[0071] The method for preparing pretreated fibers includes the following steps:

[0072] Bamboo fibers with a length of 38 mm and a fineness of 1.56 dtex were placed in a plasma chamber, and oxygen was used as the plasma treatment gas, with the oxygen flow rate adjusted to 300 mL / min. The bamboo fibers were then etched for 8 minutes using a power of 100 W to obtain pre-treated fibers.

[0073] Example 1

[0074] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0075] First, 300g of grafted polylactic acid obtained from Preparation Example 1 and 125g of glycerol-modified fiber obtained from Preparation Example 8 were premixed in a mixer at 60°C at a speed of 80r / min for 5min. Then, 25g of epoxidized soybean oil with an epoxy value of 6% was added and the mixture was blended at 160°C for 8min before being discharged to obtain a cross-linked blend. The cross-linked blend was placed in a flat vulcanizing machine at a temperature of 130~140°C and hot-pressed at a pressure of 8~9MPa for 8~10min to obtain a material for food packaging boxes.

[0076] Example 2

[0077] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0078] First, 320g of grafted polylactic acid obtained from Preparation Example 2 and 135g of glycerol-modified fiber obtained from Preparation Example 9 were premixed in a mixer at 60°C at a speed of 80r / min for 5min. Then, 30g of epoxidized soybean oil with an epoxy value of 6% was added and the mixture was blended at 160°C for 9min before being discharged to obtain a cross-linked blend. The cross-linked blend was placed in a flat vulcanizing machine at a temperature of 135°C and hot-pressed at a pressure of 8MPa for 8min to obtain a material for food packaging boxes.

[0079] Example 3

[0080] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0081] First, 340g of grafted polylactic acid obtained from Preparation Example 3 and 145g of glycerol-modified fiber obtained from Preparation Example 10 were premixed in a mixer at 60°C at a speed of 80r / min for 5min. Then, 35g of epoxidized soybean oil with an epoxy value of 6% was added and the mixture was blended at 165°C for 9min before being discharged to obtain a cross-linked blend. The cross-linked blend was placed in a flat vulcanizing machine at a temperature of 135°C and hot-pressed at a pressure of 9MPa for 9min to obtain a material for food packaging boxes.

[0082] Example 4

[0083] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0084] First, 350g of grafted polylactic acid obtained from Preparation Example 4 and 150g of glycerol-modified fiber obtained from Preparation Example 11 were premixed in a mixer at 60°C at a speed of 80r / min for 5min. Then, 40g of epoxidized soybean oil with an epoxy value of 6% was added and the mixture was blended at 170°C for 9min before being discharged to obtain a cross-linked blend. The cross-linked blend was placed in a flat vulcanizing machine at 140°C and hot-pressed at a pressure of 9MPa for 10min to obtain a material for food packaging boxes.

[0085] Comparative Example 1

[0086] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0087] The grafted polylactic acid in Example 4 was replaced with the grafted polylactic acid obtained in Preparation Example 5, and the rest of the preparation process was the same as in Example 4.

[0088] Comparative Example 2

[0089] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0090] The grafted polylactic acid in Example 4 was replaced with the grafted polylactic acid obtained in Preparation Example 6, and the rest of the preparation process was the same as in Example 4.

[0091] Comparative Example 3

[0092] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0093] The grafted polylactic acid in Example 4 was replaced with the polylactic acid obtained in Preparation Example 7, and the rest of the preparation process was the same as in Example 4.

[0094] Comparative Example 4

[0095] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0096] The glycerol-modified fiber in Example 4 was replaced with the glycerol-modified fiber obtained in Preparation Example 12, and the rest of the preparation process was the same as in Example 4.

[0097] Comparative Example 5

[0098] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0099] The glycerol-modified fiber in Example 4 was replaced with the glycerol-modified fiber obtained in Preparation Example 13, and the rest of the preparation process was the same as in Example 4.

[0100] Comparative Example 6

[0101] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0102] The glycerol-modified fiber in Example 4 was replaced with the glycerol-modified fiber obtained in Preparation Example 14, and the rest of the preparation process was the same as in Example 4.

[0103] Comparative Example 7

[0104] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0105] The glycerol-modified fiber in Example 4 was replaced with the pretreated fiber obtained in Preparation Example 15, and the rest of the preparation process was the same as in Example 4.

[0106] Comparative Example 8

[0107] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0108] The epoxidized soybean oil in Example 4 was replaced with epoxidized soybean oil with an epoxy value of 5%, and the rest of the preparation process remained the same as in Example 4.

[0109] Comparative Example 9

[0110] A method for preparing a biodegradable food packaging material, specifically including the following steps:

[0111] The amount of epoxidized soybean oil used in Example 4 was increased to 50g, while the rest of the preparation process remained the same as in Example 4.

[0112] The softening temperatures of the food packaging box materials obtained in Examples 1-4 and Comparative Examples 1-9 were tested using a Vicat softening point temperature measuring instrument. The results are shown in Table 1 below.

[0113] Table 1 Vicat softening temperature

[0114] Source of materials Vicat softening temperature (°C) Example 1 86.1 Example 2 88.5 Example 3 90.2 Example 4 90.6 Comparative Example 1 89.3 Comparative Example 2 70.3 Comparative Example 3 68.3 Comparative Example 4 70.2 Comparative Example 5 69.3 Comparative Example 6 61.1 Comparative Example 7 68.3 Comparative Example 8 72.1 Comparative Example 9 88.9

[0115] The food packaging box materials obtained in Examples 1-4 and Comparative Examples 1-9 were used to prepare 100mm×20mm×1mm specimens. The tensile speed was controlled at 100mm / min, and the tensile strength was measured by a universal testing machine. The results are shown in Table 2 below.

[0116] Table 2 Mechanical Strength

[0117] Source of materials Tensile strength (MPa) Example 1 12.3 Example 2 14.4 Example 3 15.6 Example 4 16.1 Comparative Example 1 7.2 Comparative Example 2 6.8 Comparative Example 3 5.3 Comparative Example 4 6.4 Comparative Example 5 6.1 Comparative Example 6 4.8 Comparative Example 7 5.9 Comparative Example 8 9.1 Comparative Example 9 8.2

[0118] The following conclusions can be drawn from Tables 1 and 2 above:

[0119] (1) As can be seen from Examples 1 to 4, the food packaging box material prepared by the present invention has good heat resistance and mechanical strength.

[0120] (2) Comparative Example 1 shows that the mechanical properties of the prepared food packaging box material are poor. This may be due to the excessive amount of mannitol. When it is crosslinked with glycerol-modified fiber, there are too many hydroxyl groups participating in the crosslinking, which may make the crosslinking too strong and result in high material brittleness and a decrease in mechanical strength.

[0121] (3) Comparative Example 2 shows that the heat resistance and mechanical properties of the prepared food packaging box material are poor. This may be because in this system, hydroxyl groups are active groups that improve the interfacial bonding between polylactic acid and glycerol modified fiber. If the content is low, on the one hand, the interfacial bonding between the two may be poor, and on the other hand, the cross-linking effect through reactive solubilizers is poor, thus affecting the material properties.

[0122] (4) Comparative Example 3 shows that the heat resistance and mechanical properties of the prepared food packaging box material are poor. This may be because in this system, polylactic acid does not introduce polyols that can generate multiple hydroxyl branching points. On the one hand, it may not be conducive to improving polarity and making it difficult to crosslink with glycerol modified fibers in the future. On the other hand, the arrangement of polylactic acid is too dense, which may result in poor toughening and modification effect by relying solely on glycerol modified fibers, thus affecting the material properties.

[0123] (5) Comparative Example 4 shows that the heat resistance and mechanical properties of the prepared food packaging box material are poor. This may be because when the bamboo fiber is too coarse in this system, the modification effect is poor, which may lead to poor interfacial bonding between the bamboo fiber and the grafted polylactic acid, resulting in poor material performance.

[0124] (6) Comparative Example 5 shows that the heat resistance and mechanical properties of the prepared food packaging box material are poor. This may be because when the plasma treatment intensity is low in this system, the surface modification effect on bamboo fiber is poor, which may be unfavorable for subsequent grafting of glycerol, and thus unfavorable for improving the interfacial bonding force with grafted polylactic acid, resulting in poor material performance.

[0125] (7) Comparative Example 6 shows that the heat resistance and mechanical properties of the prepared food packaging box material are poor. This may be because when the plasma treatment intensity is too high in this system, it causes serious damage to the structure of bamboo fiber, which may cause the bamboo fiber to lose its toughening properties of polylactic acid, resulting in poor material performance.

[0126] (8) Comparative Example 7 shows that the heat resistance and mechanical properties of the prepared food packaging box material are poor. This may be because the structure of bamboo fiber was damaged to a certain extent after plasma treatment in this system. The introduction of plasticizer glycerin can make up for the defects caused by plasma modification. Without the modification of plasticizer glycerin, the toughening properties of bamboo fiber are poor and it is not conducive to the subsequent construction of a three-dimensional cross-linked system through cross-linking of hydroxyl and epoxy groups, which may be detrimental to the improvement of heat resistance.

[0127] (9) Comparative Example 8 shows that the heat resistance and mechanical properties of the prepared food packaging box material are poor. This may be because the low epoxy value in this system is not conducive to the cross-linking reaction, which in turn affects the material properties.

[0128] (10) Comparative Example 9 shows that the mechanical properties of the prepared food packaging box materials are all poor. This may be because when the amount of epoxidized soybean oil in this system is large, the degree of cross-linking of the system is too large, which may make the material too brittle and affect the mechanical strength.

[0129] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A method for preparing a biodegradable food packaging material, characterized in that, The preparation method includes the following steps: Grafted polylactic acid, reactive solubilizer and glycerol modified fiber are mixed in a weight ratio of 60~70:5~8:25~30 and reacted at 160℃~170℃ for 8min~9min to obtain a cross-linked blend. The blended crosslinked compound is hot-pressed at 130℃~140℃ and 8MPa~9MPa for 8min~10min to obtain the material for food packaging boxes.

2. The method for preparing a biodegradable food packaging material according to claim 1, characterized in that, The preparation method of the grafted polylactic acid includes the following steps: L-lactic acid and stannous chloride are mixed and heated to 140℃~145℃ for 30min~40min and kept at this temperature. Then, a polyol is added and the reaction continues for another 30min~40min. The vacuum is then controlled to 0.08MPa~0.09MPa and the temperature is raised to 160℃~170℃ for 7h~8h to obtain the grafted polylactic acid.

3. The method for preparing a biodegradable food packaging material according to claim 2, characterized in that, The polyols include D-mannitol.

4. The method for preparing a biodegradable food packaging material according to claim 2, characterized in that, The weight ratio of L-lactic acid:stannous chloride:polyol is 1:0.006~0.007:0.01~0.

02.

5. The method for preparing a biodegradable food packaging material according to claim 1, characterized in that, The reactive solubilizer includes epoxidized soybean oil.

6. The method for preparing a biodegradable food packaging material according to claim 1, characterized in that, The preparation method of the glycerol-modified fiber includes the following steps: Biomass fibers are pretreated by plasma etching at 80W~100W for 5min~8min. Pretreated fibers, diisocyanate and tetramethylpropylenediamine are mixed and heated to 45℃~50℃ for 55min~65min, then kept at this temperature. Plasticizer is then added and the reaction continues for 40min~45min to obtain glycerol-modified fibers.

7. The method for preparing a biodegradable food packaging material according to claim 6, characterized in that, The biomass fiber is bamboo fiber with a length of 38 mm and a fineness of 1.56 dtex.

8. The method for preparing a biodegradable food packaging material according to claim 6, characterized in that, The diisocyanate includes hexamethylene diisocyanate, and the plasticizer includes glycerol.

9. The method for preparing a biodegradable food packaging material according to claim 6, characterized in that, The weight ratio of the pretreated fiber, diisocyanate, tetramethylpropylenediamine and plasticizer is 10:2~3:0.07~0.08:0.2~0.

3.

10. A biodegradable material for food packaging boxes, characterized in that, The food packaging box material is prepared by any one of the preparation methods of a biodegradable food packaging box material according to claims 1 to 9.