Method for manufacturing biodegradable fiber plastic-substitute packaging bag

Abstract

The invention discloses a method for making a plastic-substitute packaging bag made of degradable fiber, which belongs to the technical field of packaging bags and comprises the following steps: S1, mixing deionized water, starch, chitosan and sodium carboxymethyl cellulose and gelatinizing the mixture to obtain a gelatinized solution; S2, mixing an organic solvent, polylactic acid, an emulsifier and a functional additive to obtain a polylactic acid solution; S3, mixing the gelatinized solution with the polylactic acid solution and emulsifying the mixture to obtain a starch-based polylactic acid emulsion; S4, processing a pulp raw material into papermaking stock; S5, laying starch-based polylactic acid fibers formed by spraying the starch-based polylactic acid emulsion on the surface of the papermaking stock in a mesh curtain, and then drying the fibers to form a base paper layer and a toughening layer; S6, forming a heat-sealing layer and a barrier layer on the surface of the base paper layer and the surface of the toughening layer respectively to obtain plastic-substitute packaging paper; S7, making the plastic-substitute packaging paper into a plastic-substitute packaging bag; the plastic-substitute packaging bag of the invention is degradable and provides better protection for the packaged products.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging bags, and in particular to a method for manufacturing a plastic-substitute packaging bag made of degradable fiber. Background Art

[0002] At present, the outer packaging bags of products commonly seen in life are made of non-degradable plastic materials, which are prone to bring a series of hazards of microplastics (plastic debris and particles with a diameter of less than 5mm), which can further evolve into microplastics, submicron plastics, and nanoplastics. Due to their tiny size and difficult-to-degrade properties, microplastics have been enriched in some marine organisms and gradually enter the human body through the food chain, posing potential hazards to human health. Some of the outer packaging currently on the market is made of degradable plastics such as polylactic acid, polycaprolactone, and polypropylene succinate, but the production cost of these materials is high, making it difficult for them to widely replace difficult-to-degrade plastics and be used in the production of product outer packaging.

[0003] Wood pulp paper, as a product made from natural raw materials, is completely biodegradable, making it an ideal packaging material. However, the strength and barrier properties of current paper packaging bags are significantly different from those of plastic packaging bags. Paper packaging bags are easily damaged during product transportation and are easily corroded by water vapor in humid environments. As a result, paper packaging bags are difficult to use for products with high protection requirements and it is difficult to maintain the original protection strength for a long time. Therefore, most paper packaging bags are used to package products with low protection requirements or only short-term protection. It is still difficult for them to replace plastic packaging on a large scale and be used for products with high protection requirements or long-term protection.

[0004] A Chinese patent with publication number CN110451067A discloses a waterproof paper-plastic composite packaging bag and a method for making the same, wherein the preparation materials of the waterproof paper-plastic composite packaging bag include a paper layer and a plastic layer, and the plastic layer includes the following components: fluorocarbon resin, reflective glass microbeads, hollow glass microbeads, talcum powder, silane coupling, sodium montmorillonite, polyhexamethylene biguanide, and amino resin; the prepared plastic layer is compounded with the paper layer to form a composite paper-plastic layer, which is then processed into a waterproof paper-plastic composite packaging bag; the composite paper-plastic layer has good waterproof properties based on the plastic layer, and has higher strength than common packaging paper, but the plastic layer uses fluorocarbon resin as one of its main components. Fluorocarbon resin has stable chemical properties and is not easy to degrade. If the packaging bag is abandoned in the environment, the non-degradable fluorocarbon resin is prone to produce a series of microplastic hazards, thereby affecting the environment. Therefore, the above packaging bag still has room for improvement. Summary of the Invention

[0005] In view of the technical defects existing in the background technology, the present invention proposes a method for manufacturing a plastic-substitute packaging bag made of biodegradable fiber, which solves the above technical problems and meets practical needs. The specific technical solution is as follows:

[0006] A method for manufacturing a plastic-substitute packaging bag made of biodegradable fiber comprises the following steps:

[0007] S1. Dispersing starch, chitosan, and sodium carboxymethyl cellulose in deionized water and stirring evenly, heating the obtained dispersion to gelatinize to obtain a gelatinized solution;

[0008] S2, dissolving polylactic acid, an emulsifier, and a functional additive in an organic solvent to obtain a polylactic acid solution;

[0009] S3, mixing the gelatinized solution and the polylactic acid solution and stirring them uniformly, and then emulsifying them to obtain a starch-based polylactic acid emulsion;

[0010] S4, crushing, desanding, and grinding the pulp raw material to obtain papermaking pulp, and then subjecting the papermaking pulp to primary slurrying, desanding, and secondary slurrying to obtain papermaking raw pulp;

[0011] S5. Spreading papermaking pulp on the surface of a mesh curtain through a headbox, then spraying a starch-based polylactic acid emulsion with high pressure and rapidly drying it to form starch-based polylactic acid fibers, evenly spreading the starch-based polylactic acid fibers on the surface of the papermaking pulp in the mesh curtain by airflow, shaping them through a finishing roller, and then drying them so that the papermaking pulp forms a base paper layer and the starch-based polylactic acid fibers form a toughening layer on the surface of the base paper layer;

[0012] S6. Coating a heat-sealing material on the surface of the base paper layer and drying it to form a heat-sealing layer; coating a barrier material on the surface of the toughening layer and drying it to form a barrier layer; the heat-sealing layer, base paper layer, toughening layer, and barrier layer together constitute the plastic-substitute packaging paper;

[0013] S7, folding the plastic-substitute packaging paper and bonding the edges thereof by heating the heat-sealing layer to form a plastic-substitute packaging bag.

[0014] As a further technical solution of the present invention, the gelatinization solution includes the following components by mass percentage: 50% to 70% deionized water, 20% to 40% starch, 5% to 9% chitosan, and 2% to 4% sodium carboxymethyl cellulose.

[0015] As a further technical solution of the present invention, the starch is selected from one or more of oxidized starch, phosphate starch, enzymatically cross-linked starch, and cross-linked etherified starch.

[0016] As a further technical solution of the present invention, in step S1, the gelatinization temperature of the gelatinization solution is 70-90° C., and the gelatinization time is 20-100 min.

[0017] As a further technical solution of the present invention, the polylactic acid solution includes the following components by mass percentage: 75% to 85% organic solvent, 12% to 22% polylactic acid, 1% to 3% emulsifier, and 0.5% to 2% functional additive; the organic solvent is selected from one of dichloromethane and ethyl acetate; the emulsifier is selected from one of polyvinyl alcohol and polyoxyethylene sorbitan fatty acid ester.

[0018] As a further technical solution of the present invention, the functional additive includes the following components by mass percentage: 40% to 60% of an emulsifier and 40% to 60% of a stabilizer; the emulsifier is selected from one of n-butanol, ethylene glycol, ethanol, propylene glycol, and glycerol; and the stabilizer is selected from one or more of xanthan gum, montmorillonite, and nano-silica.

[0019] As a further technical solution of the present invention, in step S3, the gelatinized solution and the polylactic acid solution are mixed in a mass ratio of 1:1 to 3:1.

[0020] As a further technical solution of the present invention, the pulp raw material includes the following components by mass percentage: 50% to 70% coniferous wood pulp, 15% to 30% broadleaf wood pulp, 10% to 25% cotton pulp, 1% to 2% polyamide-epichlorohydrin resin, and 0.1% to 0.2% polyethylene oxide.

[0021] As a further technical solution of the present invention, the heat sealing material is selected from a starch-based heat sealing material and a cellulose-based heat sealing material, and the heat sealing layer completely or partially covers the side of the base paper layer away from the toughening layer.

[0022] As a further technical solution of the present invention, the barrier material is selected from a starch-based barrier material and a cellulose-based barrier material, and the barrier layer completely covers the side of the toughening layer away from the base paper layer.

[0023] The beneficial effects of the present invention are:

[0024] The present invention forms starch-based polylactic acid fibers through high-pressure spraying of starch-based polylactic acid emulsion, and evenly spreads the starch-based polylactic acid fibers on the surface of pulp fibers after papermaking with wood pulp paper. The starch in the starch-based polylactic acid fibers has good compatibility with the pulp fibers, and can form a base paper layer and a toughening layer that are firmly bonded to each other after drying. The toughening layer can increase the toughness inside the plastic-substitute packaging paper and maintain its degradable properties, thereby improving the environmental friendliness of the plastic-substitute packaging paper. In addition, the heat-sealing layer allows the plastic-substitute packaging paper to be formed into a plastic-substitute packaging bag through heat bonding, and the barrier layer can prevent the plastic-substitute packaging paper from being penetrated by gas and liquid, and combined with the higher toughness of the plastic-substitute packaging paper, the plastic-substitute packaging bag has more excellent protective properties. DETAILED DESCRIPTION

[0025] The following describes the implementation of the present invention in conjunction with relevant embodiments. The implementation of the present invention is not limited to the following embodiments, and the present invention relates to relevant necessary components in this technical field and should be regarded as a well-known technology in this technical field, which can be known and mastered by technical personnel in this technical field.

[0026] A method for manufacturing a plastic-substitute packaging bag made of biodegradable fiber comprises the following steps:

[0027] S1. Dispersing starch, chitosan, and sodium carboxymethyl cellulose in deionized water and stirring uniformly, and heating the obtained solution to gelatinize to obtain a gelatinized solution; wherein the gelatinization temperature of the gelatinized solution is 70-90° C. and the gelatinization time is 20-100 min;

[0028] S2, dissolving polylactic acid, an emulsifier, and a functional additive in an organic solvent to obtain a polylactic acid solution;

[0029] S3, mixing the gelatinized solution and the polylactic acid solution and stirring them uniformly, and then emulsifying them to obtain a starch-based polylactic acid emulsion;

[0030] S4, crushing, desanding, and grinding the pulp raw material to obtain papermaking pulp, and then subjecting the papermaking pulp to primary slurrying, desanding, and secondary slurrying to obtain papermaking raw pulp;

[0031] S5. Spreading papermaking pulp on the surface of a mesh curtain through a headbox, then spraying a starch-based polylactic acid emulsion with high pressure and rapidly drying it to form starch-based polylactic acid fibers, evenly spreading the starch-based polylactic acid fibers on the surface of the papermaking pulp in the mesh curtain by airflow, shaping them through a finishing roller, and then drying them so that the papermaking pulp forms a base paper layer and the starch-based polylactic acid fibers form a toughening layer on the surface of the base paper layer;

[0032] S6. Coating a heat-sealing material on the surface of the base paper layer and drying it to form a heat-sealing layer; coating a barrier material on the surface of the toughening layer and drying it to form a barrier layer; the heat-sealing layer, base paper layer, toughening layer, and barrier layer together constitute the plastic-substitute packaging paper;

[0033] S7, folding the plastic-substitute packaging paper and bonding the edges thereof by heating the heat-sealing layer to form a plastic-substitute packaging bag.

[0034] The invention discloses a method for manufacturing a plastic-substitute packaging bag made of degradable fiber. The main base material of the packaging bag is plastic-substitute packaging paper, the internal skeleton of the plastic-substitute packaging paper is mainly composed of starch-based polylactic acid fiber and pulp fiber. Steps S1 to S3 are preparatory steps for manufacturing starch-based polylactic acid fiber. Step S1 prepares a gelatinized solution and uses it as the water phase of a starch-based polylactic acid emulsion. Step S2 prepares a polylactic acid solution and uses it as the oil phase of the starch-based polylactic acid emulsion. In step S3, the water phase and the oil phase are mixed and then emulsified into a starch-based polylactic acid emulsion by ultrasonic emulsification or homogenization. The starch-based polylactic acid emulsion is a system in which the water phase envelops the oil phase, that is, the polylactic acid solution forms a plurality of small droplets uniformly dispersed in the gelatinized solution.

[0035] In step S4, the pulp raw materials use wood pulp and additives commonly used in making wood pulp paper. The pulp raw materials are pulped to refine the pulp fibers, desanded to remove impurities, and polished to improve the uniformity of the pulp fibers to obtain papermaking coarse pulp. Then, the papermaking coarse pulp is beaten in the post-beating pulp pool, and the pulp beating degree ranges from 50 to 70oSR. The papermaking coarse pulp is refined with a higher beating degree, and its pulp fibers are more effectively dispersed during the refining process, and the entanglement and aggregation between the pulp fibers are reduced, so that the pulp fibers are more evenly distributed in the papermaking coarse pulp, which is beneficial to the interweaving and combination of the pulp fibers in the subsequent papermaking process, and improves the uniformity of the wood pulp paper. The papermaking coarse pulp retains the effective components of papermaking and improves the purity of the pulp fibers during the beating and punching process, thereby obtaining papermaking raw pulp, so that the pulp fibers in the papermaking raw pulp are formed into wood pulp paper through papermaking in the subsequent process.

[0036] In step S5, the papermaking pulp is spread on the surface of the mesh curtain through the pulping box, and the pulp fibers therein are randomly spread on the surface of the mesh curtain to form the precursor structure of wood pulp paper. The dry weight of the pulp fibers on the surface of the mesh curtain needs to be maintained at more than 20g / m2. If the dry weight is too low, the produced matrix layer is too thin and not suitable for use as packaging paper. The actual dry weight is adaptively adjusted according to demand; at the same time, the starch-based polylactic acid emulsion is formed into filaments through high-pressure injection technology and then continuously formed by air traction. The traction airflow can be heated to properly dry the filaments to remove the solvent on their surface, and solid starch is obtained after drying. The starch-based polylactic acid fiber is cut into short fibers after being formed and laid evenly and disorderly on the pulp fiber surface of the mesh curtain under the action of airflow. Since the pulp fiber still contains a certain amount of moisture, the starch-based polylactic acid fiber will absorb part of the moisture in the pulp fiber and adhere to its surface. Then the pulp fiber and the starch-based polylactic acid fiber are smoothed by the finishing roller. In the subsequent drying process, the moisture in the pulp fiber is dried to form a base paper layer. At the same time, the solvent in the starch-based polylactic acid fiber is dried to form a toughening layer. The matrix layer and the toughening layer are firmly bonded to each other and together form the plastic-substitute paper for making plastic-substitute packaging paper.

[0037] The above-mentioned plastic-substitute paper is composed of pulp fibers and starch-based polylactic acid fibers. The pulp fibers and starch-based polylactic acid fibers are dried and formed on the surface of the mesh curtain at the same time and form a base paper layer and a toughening layer respectively. During the drying and forming process of the plastic-substitute paper, the starch-based polylactic acid fibers are laid flat on the surface of the pulp fibers and are dried with solvent at the same time. The adjacent fibers will adhere to each other and be fixed, so that the dried and formed base paper layer and the toughening layer can be fixed to each other without applying an adhesive; in addition, the starch-based polylactic acid fibers have good toughness due to the addition of polylactic acid, which can improve the tear resistance and tensile strength of the plastic-substitute paper. At the same time, polylactic acid is easily decomposed and metabolized by a variety of microorganisms in nature or enzymes in animals and plants under conditions such as composting and contact with specific microorganisms, and finally decomposed into carbon dioxide and water. Its easy degradation property can ensure the environmental friendliness of the packaging bag.

[0038] In steps S6 and S7, heat-sealing material and barrier material are coated on both sides of the plastic-substitute paper respectively to form heat-sealing layer and barrier layer respectively. The heat-sealing layer becomes sticky after being heated, so that the plastic-substitute packaging paper can be folded and bonded through its own heat-sealing layer or spliced ​​and bonded with another plastic-substitute packaging paper to form a plastic-substitute packaging bag. The interior of the plastic-substitute packaging bag has space to accommodate the product, and the bonding position of the plastic-substitute packaging bag bonded by the heat-sealing layer has high firmness, which can prevent the plastic-substitute packaging bag from opening; the plastic-substitute packaging paper is provided with a barrier layer on one side as the outer surface of the plastic-substitute packaging bag, and the barrier layer can prevent external gas, liquid and other impurities from penetrating into the interior of the plastic-substitute packaging paper or the interior of the plastic-substitute packaging bag, and avoid the reduction of strength of the interior of the plastic-substitute packaging paper due to liquid penetration, thereby improving the protective strength of the plastic-substitute packaging bag. At the same time, a more sealed space can be formed inside the plastic-substitute packaging bag, thereby isolating the product inside the plastic-substitute packaging bag from contact with the outside world, thereby improving the shelf life of the product.

[0039] In summary, the present invention forms starch-based polylactic acid fibers through high-pressure spraying of starch-based polylactic acid emulsion, and evenly spreads the starch-based polylactic acid fibers on the surface of pulp fibers after papermaking using wood pulp paper. The starch in the starch-based polylactic acid fibers has good compatibility with the pulp fibers, and after drying, a base paper layer and a toughening layer that are firmly bonded to each other can be formed. The toughening layer can increase the toughness inside the plastic-substitute packaging paper and maintain its degradable properties, thereby improving the environmental friendliness of the plastic-substitute packaging paper. In addition, the heat-sealing layer allows the plastic-substitute packaging paper to form a plastic-substitute packaging bag through heat bonding, and the barrier layer can prevent the plastic-substitute packaging paper from being penetrated by gas and liquid, and combined with the higher toughness of the plastic-substitute packaging paper, the plastic-substitute packaging bag has better protective properties.

[0040] As one of the preferred embodiments of the present invention, the gelatinization solution includes the following components by mass percentage: 50% to 70% deionized water, 20% to 40% starch, 5% to 9% chitosan, and 2% to 4% sodium carboxymethyl cellulose; the gelatinization solution is mainly composed of starch in deionized water by heating to break the hydrogen bonds between ordered and disordered molecules in the starch granules and disperse them in deionized water to form a colloidal solution. Chitosan can improve the compatibility of the gelatinization solution, so that starch can better form starch-based polylactic acid fibers with polylactic acid. Chitosan has an inhibitory and killing effect on a variety of bacteria, which can improve the antibacterial properties of plastic-substitute packaging bags and avoid starch-based polylactic acid. The starch in the fiber deteriorates, and chitosan can also enhance the tensile strength and toughness of starch-based polylactic acid fibers, making the starch-based polylactic acid fibers more stable and less likely to break when subjected to external forces; sodium carboxymethyl cellulose can quickly dissolve in water to form a viscous colloidal solution, which can prevent the precipitation and stratification of starch in the gelatinized solution and improve the dispersion uniformity of the gelatinized solution in the starch-based polylactic acid emulsion. Sodium carboxymethyl cellulose can increase the viscosity of the gelatinized solution, which helps to improve the flexibility of the starch-based polylactic acid fibers, making the starch-based polylactic acid fibers easier to shape during processing, thereby improving the processing performance and molding quality of the starch-based polylactic acid fibers.

[0041] As one of the preferred embodiments of the present invention, starch is selected from one or more of oxidized starch, phosphate starch, enzymatically cross-linked starch, and cross-linked etherified starch; oxidized starch has the advantages of low viscosity, high stability, and good film-forming properties, which can make starch-based polylactic acid fibers easier to process and form and form a uniform and dense film on the fiber surface, thereby improving the mechanical properties and durability of starch-based polylactic acid fibers; phosphate starch has good dispersing, emulsifying, and anti-aging capabilities, which is beneficial to the formation of starch-based polylactic acid emulsions through emulsification, and enables starch-based polylactic acid fibers to maintain good stability for a long time; enzymatically cross-linked starch has good acid resistance, shear resistance, and processing performance, which is beneficial to starch-based polylactic acid fibers maintaining good stability and durability under harsh environmental conditions; cross-linked etherified starch has good resistance to acid environments, high temperature resistance, and processing performance, which is beneficial to starch-based polylactic acid fibers maintaining good stability and durability under harsh environmental conditions.

[0042] As one of the preferred embodiments of the present invention, the polylactic acid solution includes the following components by mass percentage: 75% to 85% organic solvent, 12% to 22% polylactic acid, 1% to 3% emulsifier, and 0.5% to 2% functional additive; the organic solvent is selected from one of dichloromethane and ethyl acetate; the emulsifier is selected from one of polyvinyl alcohol and polyoxyethylene sorbitan fatty acid ester.

[0043] In the polylactic acid solution of the present invention, the organic solvent functions to dissolve solid polylactic acid to form a solution. During the polylactic acid dissolution process, water bath heating can be used to assist dissolution and improve dissolution efficiency. Both dichloromethane and ethyl acetate can dissolve polylactic acid, and dichloromethane and ethyl acetate have low mutual solubility with deionized water, which is conducive to emulsifying the polylactic acid solution and the gelatinized solution into a starch-based polylactic acid emulsion through an emulsification operation. During the emulsification process, an emulsion system in which the water phase envelops the oil phase is formed under the action of an emulsifier. Both polyvinyl alcohol and polyoxyethylene sorbitan fatty acid ester have excellent emulsification, dispersion and stability properties, and can form a stable and thick interfacial film at the oil-water interface to prevent coalescence and stratification of oil droplets.

[0044] As one of the preferred embodiments of the present invention, the functional additives include the following components by mass percentage: 40% to 60% of an emulsifier and 40% to 60% of a stabilizer; the emulsifier is selected from one of n-butanol, ethylene glycol, ethanol, propylene glycol, and glycerol; and the stabilizer is selected from one or more of xanthan gum, montmorillonite, and nano-silica.

[0045] The functional additive of the present invention is used to improve the emulsification efficiency of the starch-based polylactic acid emulsion and improve the stability of the emulsion. The co-emulsifier adopts a short-chain alcohol. The short-chain alcohol can be adsorbed on the interface between the water phase and the oil phase and work together with the emulsifier to form an interfacial film. The film helps to reduce the interfacial tension between oil and water, so that the originally immiscible oil phase and water phase can be mixed more easily. The short-chain alcohol can also enhance the fluidity of the interfacial film and prevent the coalescence of droplets, so that the interfacial film can better maintain its integrity and stability when subjected to external disturbances. Among the stabilizers, xanthan gum has excellent suspension, emulsification and stability, can increase the viscosity of the emulsion and improve the stability of the emulsion. Montmorillonite has excellent adsorption and stability, can prevent the coalescence and stratification of the oil phase droplets by adsorbing charges or molecules on the surface of the oil phase droplets. Nano-silica has a large specific surface area and surface energy, can form a stable adsorption layer at the interface between the water phase and the oil phase, and enhance the stability of the emulsion.

[0046] As one of the preferred embodiments of the present invention, in step S3, the mass ratio of the gelatinized solution and the polylactic acid solution is 1:1~3:1; the mass ratio of the gelatinized solution and the polylactic acid solution is preferably 2:1. The ratio of starch to polylactic acid in the starch-based polylactic acid fiber is controlled by controlling the mixing ratio of the gelatinized solution and the polylactic acid solution. The effect of the amount of polylactic acid added on the production cost and performance of the packaging bag is comprehensively considered, and the mixing ratio of the gelatinized solution and the polylactic acid solution is adaptively adjusted according to actual needs.

[0047] As one of the preferred embodiments of the present invention, the pulp raw material includes the following components by mass percentage: 50% to 70% coniferous wood pulp, 15% to 30% broadleaf wood pulp, 10% to 25% cotton pulp, 1% to 2% polyamide-epichlorohydrin resin, and 0.1% to 0.2% polyethylene oxide.

[0048] Among the pulp raw materials of the present invention, softwood pulp, hardwood pulp, and cotton pulp are common raw materials in the papermaking process and are the main components of the pulp, providing the pulp with a large amount of components such as cellulose and lignin, so that the pulp can be made into pulp paper through a series of processing steps; polyamide-epichlorohydrin resin is mainly used as a wet strength agent in the pulp, and the polyamide-epichlorohydrin resin reacts with hydroxyl groups, aldehyde groups, etc. on the surface of pulp fibers through functional groups such as amino groups and epoxy groups to form a cross-linked structure and enhance the bonding force between pulp fibers, thereby improving the wet strength of the final pulp paper and enabling the pulp paper to maintain good physical properties in a humid environment; polyethylene oxide is mainly used as a dispersant in the pulp. During the papermaking process, pulp fibers and other components are insoluble in water and tend to aggregate in water. Adding a dispersant can form a double-layer structure on the surface of solid particles. The outer layer dispersant has a strong affinity with water, which increases the degree to which the solid particles are wetted by water and improves the dispersion effect of the pulp fibers.

[0049] As one of the preferred embodiments of the present invention, the heat-sealing material is selected from one of a starch-based heat-sealing material and a cellulose-based heat-sealing material, and the heat-sealing layer completely or partially covers the side of the base paper layer away from the toughening layer; the starch-based heat-sealing material and the cellulose-based heat-sealing material both have the advantages of being environmentally friendly, degradable, and renewable, ensuring the degradability and environmental friendliness of the plastic-substitute packaging bag, and the heat-sealing material can be intermittently coated so that the heat-sealing layer can be arranged along the edge of the plastic-substitute packaging paper, which not only ensures that the plastic-substitute packaging paper can be bonded into a plastic-substitute packaging bag through the heat-sealing layer, but also reduces the amount of heat-sealing material used; in addition, the heat-sealing material can be completely coated on the surface of the base paper layer. Since the heat-sealing material has certain waterproof and oil-proof properties, the plastic-substitute packaging bag can be used to package products containing a certain amount of moisture or other liquids, thereby improving the scope of application of the plastic-substitute packaging bag.

[0050] As one of the preferred embodiments of the present invention, the barrier material is selected from one of a starch-based barrier material and a cellulose-based barrier material, and the barrier layer completely covers the side of the toughening layer away from the base paper layer; the starch-based barrier material and the cellulose-based barrier material both have the advantages of being environmentally friendly, degradable, and renewable, ensuring the degradability and environmental friendliness of the plastic-substitute packaging bag. The barrier layer that completely covers the base paper layer can prevent external gases, liquids, etc. from penetrating into the interior of the plastic-substitute packaging bag, thereby improving the protective effect of the plastic-substitute packaging bag on the internally packaged products.

[0051] The present invention is further described below by way of examples and comparative examples.

[0052] Example 1

[0053] S1, mixing 60% deionized water, 30% enzymatically cross-linked starch, 7% chitosan, and 3% sodium carboxymethyl cellulose, and stirring uniformly, and then heating and gelatinizing to obtain a gelatinized solution;

[0054] S2. Mix 82% of dichloromethane, 15% of polylactic acid, 2% of polyvinyl alcohol, 0.5% of glycerol, and 0.5% of xanthan gum, and stir to obtain a polylactic acid solution;

[0055] S3, mixing the gelatinized solution and the polylactic acid solution in a mass ratio of 1:1, stirring uniformly, and then emulsifying by ultrasonication to obtain a starch-based polylactic acid emulsion;

[0056] S4. Add appropriate amount of water to 60% of softwood pulp, 20% of hardwood pulp, 18.3% of cotton pulp, 1.5% of polyamide-epichlorohydrin resin, and 0.2% of polyethylene oxide, and subject the mixture to pulping, sand removal, and grinding to obtain papermaking rough pulp. The papermaking rough pulp is subjected to primary pulping, sand removal, and secondary pulping to obtain papermaking stock pulp, wherein the moisture content of the papermaking stock pulp is 90%;

[0057] S5. Spreading papermaking pulp on the surface of a mesh curtain through a headbox, then spraying a starch-based polylactic acid emulsion with high pressure and rapidly drying it to form starch-based polylactic acid fibers, evenly spreading the starch-based polylactic acid fibers on the surface of the papermaking pulp in the mesh curtain by airflow, and shaping them through a finishing roller, and then drying the papermaking pulp to form a base paper layer and the starch-based polylactic acid fibers to form a toughening layer on the surface of the base paper layer, the base paper layer and the toughening layer together forming a plastic-substitute paper, the plastic-substitute paper having a grammage of 60 gsm, and a mass ratio of the base paper layer to the toughening layer of 2:1;

[0058] S6. Coating a heat-sealing material on the surface of the base paper layer and drying it to form a heat-sealing layer; coating a barrier material on the surface of the toughening layer and drying it to form a barrier layer; the heat-sealing layer, base paper layer, toughening layer, and barrier layer together constitute the plastic-substitute packaging paper;

[0059] S7, folding the plastic-substitute packaging paper and bonding the edges thereof by heating the heat-sealing layer to form a plastic-substitute packaging bag.

[0060] Example 2

[0061] The difference between this embodiment and the above-mentioned embodiment 1 is that in step S3, the mass ratio of the gelatinized solution to the polylactic acid solution is 2:1, and the remaining operation steps are the same.

[0062] Example 3

[0063] The difference between this embodiment and the above-mentioned embodiment 1 is that in step S3, the mass ratio of the gelatinized solution and the polylactic acid solution is 3:1, and the remaining operation steps are the same.

[0064] Comparative Example 1

[0065] S1. Take wood pulp paper with a gram weight of 60gsm, and coat heat-sealing material and barrier material on both sides of the wood pulp paper to form a heat-sealing layer and a barrier layer respectively. The heat-sealing layer, wood pulp paper, and barrier layer together constitute the plastic substitute packaging paper;

[0066] S2, folding the plastic-substitute packaging paper and bonding the edges thereof by heating the heat-sealing layer to form a plastic-substitute packaging bag.

[0067] Comparative Example 2

[0068] S1. Take wood pulp paper with a gram weight of 120gsm, and coat heat-sealing material and barrier material on both sides of the wood pulp paper to form a heat-sealing layer and a barrier layer respectively. The heat-sealing layer, wood pulp paper, and barrier layer together constitute the plastic substitute packaging paper;

[0069] S2, folding the plastic-substitute packaging paper and bonding the edges thereof by heating the heat-sealing layer to form a plastic-substitute packaging bag.

[0070] Comparative Example 3

[0071] S1. Take wood pulp paper with a gram weight of 180gsm, and coat heat-sealing material and barrier material on both sides of the wood pulp paper to form a heat-sealing layer and a barrier layer respectively. The heat-sealing layer, wood pulp paper, and barrier layer together constitute the plastic substitute packaging paper;

[0072] S2, folding the plastic-substitute packaging paper and bonding the edges thereof by heating the heat-sealing layer to form a plastic-substitute packaging bag.

[0073] The tensile strength and elongation at break of the plastic-substitute packaging bags obtained in all the above examples and comparative examples were tested. The test results are shown in Table 1 below:

[0074]

[0075] Table 1

[0076] According to the data in Table 1, it can be seen that by comparing the plastic-substitute packaging bags made of the same gram weight plastic-substitute paper and wood pulp paper, the plastic-substitute packaging bags made of the plastic-substitute paper have better tensile strength. By adjusting the mixing ratio of the gelatinization solution and the polylactic acid solution, the tensile strength of the plastic-substitute packaging bags made of 60gsm plastic-substitute paper is comparable to that of the plastic-substitute packaging bags made of 180gsm wood pulp paper; in addition, since the plastic-substitute paper contains a certain amount of polylactic acid and has higher toughness, the elongation at break of the plastic-substitute packaging bags made of the plastic-substitute paper is significantly improved; from the test performance of the plastic-substitute packaging bags obtained in Examples 1 to 3 based on the technical solution of the present invention, it can be seen that the plastic-substitute packaging bags of the present invention have excellent protective performance.

[0077] The above description is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for making a plastic-substitute packaging bag made of biodegradable fiber, characterized in that: The following steps are involved: S1. Dispersing starch, chitosan, and sodium carboxymethyl cellulose in deionized water and stirring evenly, heating the obtained dispersion to gelatinize to obtain a gelatinized solution; S2, dissolving polylactic acid, an emulsifier, and a functional additive in an organic solvent to obtain a polylactic acid solution; S3, mixing the gelatinized solution and the polylactic acid solution and stirring them uniformly, and then emulsifying them to obtain a starch-based polylactic acid emulsion; S4, crushing, desanding, and grinding the pulp raw material to obtain papermaking raw pulp, and then subjecting the papermaking raw pulp to primary pulping, desanding, and secondary pulping to obtain papermaking raw pulp; S5. Spreading papermaking pulp on the surface of a mesh curtain through a headbox, then spraying a starch-based polylactic acid emulsion with high pressure and rapidly drying it to form starch-based polylactic acid fibers, evenly spreading the starch-based polylactic acid fibers on the surface of the papermaking pulp in the mesh curtain by airflow, shaping them through a finishing roller, and then drying them so that the papermaking pulp forms a base paper layer and the starch-based polylactic acid fibers form a toughening layer on the surface of the base paper layer; S6. Coating a heat-sealing material on the side of the base paper layer away from the toughening layer and drying the layer to form a heat-sealing layer. Coating a barrier material on the surface of the toughening layer and drying the layer to form a barrier layer. The heat-sealing layer, base paper layer, toughening layer, and barrier layer together constitute the plastic-substitute packaging paper. S7, folding the plastic-substitute packaging paper and bonding the edges thereof by heating the heat-sealing layer to form a plastic-substitute packaging bag; The gelatinization solution comprises the following components by mass percentage: 50% to 70% deionized water, 20% to 40% starch, 5% to 9% chitosan, and 2% to 4% sodium carboxymethyl cellulose; The starch is selected from one or more of oxidized starch, phosphate starch, enzymatic cross-linked starch, and cross-linked etherified starch; The polylactic acid solution comprises the following components by mass percentage: 75% to 85% organic solvent, 12% to 22% polylactic acid, 1% to 3% emulsifier, and 0.5% to 2% functional additive; the organic solvent is selected from one of dichloromethane and ethyl acetate; the emulsifier is selected from one of polyvinyl alcohol and polyoxyethylene sorbitan fatty acid ester; In step S3, the gelatinized solution and the polylactic acid solution are mixed in a mass ratio of 1:1 to 3:

1.

2. The method for making a plastic-substitute packaging bag made of biodegradable fiber according to claim 1, characterized in that: In step S1, the gelatinization temperature of the gelatinization solution is 70-90° C., and the gelatinization time is 20-100 min.

3. The method for making a plastic-substitute packaging bag made of biodegradable fiber according to claim 1, characterized in that: The functional additives include the following components by mass percentage: 40% to 60% of an emulsifier and 40% to 60% of a stabilizer; the emulsifier is selected from one of n-butanol, ethylene glycol, ethanol, propylene glycol, and glycerol; and the stabilizer is selected from one or more of xanthan gum, montmorillonite, and nano-silica.

4. The method for making a plastic-substitute packaging bag made of biodegradable fiber according to claim 1, characterized in that: The pulp raw material includes the following components by mass percentage: 50% to 70% of softwood pulp, 15% to 30% of hardwood pulp, 10% to 25% of cotton pulp, 1% to 2% of polyamide-epichlorohydrin resin, and 0.1% to 0.2% of polyethylene oxide.

5. The method for making a plastic-substitute packaging bag made of biodegradable fiber according to claim 1, characterized in that: The heat sealing material is selected from one of a starch-based heat sealing material and a cellulose-based heat sealing material, and the heat sealing layer completely or partially covers the side of the base paper layer away from the toughening layer.

6. The method for making a plastic-substitute packaging bag made of biodegradable fiber according to claim 1, characterized in that: The barrier material is selected from one of a starch-based barrier material and a cellulose-based barrier material, and the barrier layer completely covers the side of the toughening layer away from the base paper layer.

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