High-strength plant cellulose-based composite paperboard and method for manufacturing the same

Abstract

The application discloses a high-strength plant cellulose-based composite paperboard and a preparation method thereof, and belongs to the technical field of paperboard materials, and is used for solving the technical problem that the strength and wet strength maintenance rate of a plant fiber-based composite paperboard in the prior art need to be further improved, and specifically comprises a plurality of composite plant fiber layers, wherein the composite plant fiber layer is composed of a plant fiber layer and interface layers modified on both sides of the plant fiber layer. The plant fiber layer is prepared by using CMC modified plant cellulose, PEG modified inorganic reinforcing agent and bio-based toughening agent to reinforce the plant fiber, the composite structure of the interface layer, the fiber layer and the interface layer is formed by arranging the double interface layers containing lignin nanoparticles / carboxylated nanocellulose, and the heat pressing and curing process is combined, so that the strength and toughness of the plant fiber-based composite paperboard are effectively improved, and the wet strength maintenance rate of the material is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of paperboard materials technology, specifically to a high-strength plant cellulose-based composite paperboard and its preparation method. Background Technology

[0002] Paper and paperboard, as traditional packaging and load-bearing materials, have been widely used in food packaging, electronic product packaging, logistics and transportation, and protective padding due to their advantages such as wide availability of raw materials, easy recycling and biodegradability. Paperboard materials based on plant cellulose are gradually being regarded as an important direction to replace highly polluting materials such as plastics and foams. Traditional plant fiber paperboard is mainly made by simply forming and compacting wood pulp or non-wood pulp fibers. In order to improve the strength and burst resistance of paperboard, methods such as increasing the degree of beating, increasing the proportion of long fibers, adding some dry strength agents, or coating the surface are usually adopted.

[0003] Currently, while over-beating can increase the number of bonding points between fibers, it significantly reduces the porosity and elasticity of paper, leading to increased rigidity and brittleness of the paperboard. This also results in higher energy consumption, hindering energy conservation and cost reduction. Furthermore, commonly used dry strength agents are mostly petroleum-based polymers, and their usage is limited by cost, environmental concerns, and fiber compatibility. Simply increasing the amount of dry strength agent often makes it difficult to balance tear toughness and overall structural stability. In traditional paperboard, inorganic fillers are often used to reduce costs and improve optical properties, resulting in weak interfacial bonding with fibers. These fillers are prone to detachment and peeling during load-bearing, failing to effectively support the load and instead becoming stress concentration sources, weakening the overall strength and durability of the material. In terms of wet strength, conventional plant fiber paperboard experiences a sharp decline in strength after water immersion, making it difficult to simultaneously meet the comprehensive requirements of high strength, high toughness, high wet strength, and high bio-based content.

[0004] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a high-strength plant cellulose-based composite paperboard and its preparation method, which solves the technical problem that the strength and wet strength retention rate of plant fiber-based composite paperboard in the prior art need to be further improved.

[0006] The objective of this invention can be achieved through the following technical solution: a high-strength plant cellulose-based composite paperboard, comprising a plurality of composite plant fiber layers, wherein the composite plant fiber layers are composed of plant fiber layers and interface layers modified on both sides of the plant fiber layers;

[0007] The plant fiber layer comprises the following components by weight: 60-70 parts plant fiber, 30-40 parts CMC-modified plant cellulose, 15-20 parts inorganic reinforcing agent, 6-8 parts bio-based toughening agent, and 2-3 parts additives.

[0008] The interface layer comprises the following components by weight: 40-60 parts of lignin nanoparticles, 30-50 parts of carboxylated nanocellulose, 5-7 parts of crosslinking agent, and 2-3 parts of additives.

[0009] The crosslinking agent is composed of polyvalent metal ions and oxidized soybean polysaccharides in a weight ratio of 2:6-7.

[0010] Furthermore, the bio-based toughening agent is composed of sodium alginate and carboxymethyl starch in a weight ratio of 3:1, and the polyvalent metal ions are composed of calcium chloride, magnesium chloride and aluminum chloride in a weight ratio of 7:3:1.

[0011] Furthermore, the preparation method of the CMC modified plant cellulose is as follows: nanocellulose, lignocellulose and deionized water are mixed and stirred, hydrochloric acid is added to the reaction system to adjust the pH of the system to 3, the reaction system is heated to 70-80℃, carboxymethyl cellulose solution is added dropwise to the reaction system, the mixture is kept warm and stirred for 50-70 min, and then post-processed to obtain CMC modified plant cellulose.

[0012] Furthermore, the ratio of the nanocellulose, lignocellulose, deionized water, and carboxymethyl cellulose solution is 7g:3-4g:80mL:20mL. The carboxymethyl cellulose solution is composed of carboxymethyl cellulose, glyoxal, and deionized water at a ratio of 1g:0.4-0.5g:20mL. The post-treatment includes: after the reaction is complete, the reaction system is cooled to room temperature, filtered, the filter cake is washed with purified water until neutral, dried, and the filter cake is transferred to a drying oven at a temperature of 70-80℃ and dried to constant weight to obtain CMC modified plant cellulose.

[0013] Furthermore, the inorganic reinforcing agent is obtained by the following steps:

[0014] A1. Mix kaolin, nano silica, KH-560 and anhydrous ethanol, ultrasonically disperse for 30-50 min, heat the reaction system to 50-60℃, add sodium hydroxide solution to the reaction system, keep the reaction at the temperature for 60-80 min, and then perform post-treatment to obtain epoxy modified filler.

[0015] A2. Mix and stir epoxy-modified filler, polyethylene glycol, deionized water and sodium hydroxide. Heat the reaction system to 70-80℃ and keep it at that temperature for 50-70 minutes. After post-treatment, the inorganic reinforcing agent is obtained.

[0016] Further, in step A1, the ratio of kaolin, nano-silica, KH-560, anhydrous ethanol, and sodium hydroxide solution is 6g:1.1-1.3g:1g:70mL:10mL, and the concentration of the sodium hydroxide solution is 2-3mol / L. The post-treatment includes: after the reaction is complete, the reaction system is cooled to room temperature, filtered, the filter cake is washed with purified water until neutral, dried, and the filter cake is transferred to a drying oven at 60-70℃ and dried to constant weight to obtain epoxy modified filler.

[0017] Further, in step A2, the ratio of epoxy modified filler, polyethylene glycol, deionized water and sodium hydroxide is 10g:3-4g:100mL:2g, the polyethylene glycol is PEG-800, and the post-treatment includes: after the reaction is completed, the reaction system is cooled to room temperature, filtered, the filter cake is washed with purified water until neutral and then dried, the filter cake is transferred to a drying oven at a temperature of 70-80℃ and dried to constant weight to obtain the inorganic reinforcing agent.

[0018] Furthermore, the preparation method of the oxidized soybean polysaccharide is as follows: under light-protected conditions, soybean polysaccharide and deionized water are mixed and stirred for 20-30 minutes, the reaction system is cooled to 25-30°C, sodium periodate solution is added dropwise to the reaction system, the reaction is kept at the temperature for 8-12 hours, and then post-processed to obtain oxidized soybean polysaccharide.

[0019] Furthermore, the ratio of soybean polysaccharide, deionized water, and sodium periodate solution is 5-6g:50mL:6-7mL, and the sodium periodate solution is composed of sodium periodate and deionized water at a ratio of 1g:5mL. The post-treatment includes: after the reaction is completed, the reaction solution is placed in a 1000Da dialysis bag, and then the dialysis bag is placed in deionized water. Dialysis is performed at room temperature for 20 hours, and the deionized water is replaced every 2 hours. The substance in the dialysis bag is then freeze-dried in a freeze dryer at a temperature of -30℃ to obtain oxidized soybean polysaccharide.

[0020] This invention also proposes a method for preparing high-strength plant cellulose-based composite paperboard, comprising the following steps:

[0021] S1. Mix and stir plant fiber, CMC-modified plant cellulose, inorganic reinforcing agent, bio-based toughening agent, additives and deionized water to obtain a fiber pulp with a solid content of 3-4 wt%.

[0022] The fiber slurry is evenly coated on a dewatering screen and dewatered to form a plant fiber layer with a thickness of 0.3±0.02mm and a water content of 30-40wt%.

[0023] S2. Mix and stir lignin nanoparticles, carboxylated nanocellulose, crosslinking agent, additives and deionized water to obtain an interface layer slurry with a solid content of 1-2 wt%.

[0024] The interface layer slurry is evenly coated on the dewatering screen to form an interface layer one with a thickness of 0.05±0.01mm. Then, a plant fiber layer is laid flat on the interface layer one. The interface layer slurry is then evenly sprayed onto the plant fiber layer to form an interface layer two with a thickness of 0.05±0.01mm on top of the plant fiber layer. After dewatering, a composite plant fiber layer with a water content of 30-40wt% is obtained.

[0025] S3. After stacking several composite plant fiber layers, place them into a cardboard mold and heat press them to obtain a composite cardboard with a thickness of 2-3mm.

[0026] Furthermore, the additives are composed of polyacrylamide, melamine-formaldehyde resin, alkyl ketone dimer, sodium lignosulfonate, ethylenediaminetetraacetic acid, polyether defoamer, and fatty acid salt in a weight ratio of 6-7:4-5:3:2:1:0.3:0.5. The hot-pressing pressure is 2-3 MPa, the hot-pressing temperature is 95-105℃, and the hot-pressing time is 20-30 min.

[0027] The present invention has the following beneficial effects:

[0028] 1. This invention involves preparing a plant fiber layer of a certain thickness from a fiber pulp containing plant fibers, CMC-modified cellulose, inorganic reinforcing agents, and bio-based toughening agents. An interface layer rich in lignin nanoparticles, carboxylated nanocellulose, and a crosslinking agent is then placed above and below this layer, resulting in a multi-layered board structure with "high surface stiffness and strong core support." In the interface layer, nano-lignin and nanocellulose form a high-strength interfacial bond with the fiber layer under the action of the crosslinking agent, effectively preventing interlayer delamination and local instability. By increasing the solid content of the fiber layer and interface layer, strengthening the amount of inorganic reinforcing agents and crosslinking agents, and gradually increasing the pressure and temperature and extending the holding time during hot pressing, the fibers, nanofillers, and resin are fully rearranged, compacted, and cured in three-dimensional space. This reduces internal porosity, creates a denser and more uniform structure, and significantly improves dimensional stability and fatigue resistance. This not only ensures the performance of the board under tensile, tear, bursting, and wet conditions but also improves the consistency and repeatability of the composite board's performance, making it suitable for large-scale application.

[0029] 2. This invention utilizes glyoxal to perform acetal crosslinking of carboxymethyl cellulose, plant nanocellulose, and micronized cellulose under acidic conditions, constructing a three-dimensional network on the fiber surface consisting of CMC flexible segments and a rigid cellulose skeleton. This is further enhanced by combining this with kaolin / nano silica inorganic reinforcing agents modified with KH-560 and PEG-800, forming a composite structure with rigid particles, a flexible organic shell, and a fiber skeleton tightly bonded together. Simultaneously, the organic crosslinking system of oxidized soybean polysaccharides and multivalent metal ion crosslinking agents further constructs a high-density covalent crosslinking and hydrogen bond network between fibers and between fibers and fillers, enabling efficient load transfer between long fibers, nanofibers, inorganic particles, and crosslinked resins; improving the tensile strength and bursting index of the material; and introducing bio-based toughening agents such as sodium alginate / carboxymethyl starch and a PEG flexible layer, providing energy-dissipating mechanisms such as segment stretching and interfacial slippage on top of high crosslinking degree and high stiffness, effectively suppressing embrittlement and achieving a balance between high strength and high toughness.

[0030] 3. This invention utilizes the acetal structure of CMC and glyoxal, as well as the acetal bonds and Schiff base bonds formed between oxidized soybean polysaccharides, cellulose, and CMC, to provide a covalent skeleton for paperboard that is not easily decoupled in water, exhibiting good stability in a neutral water environment. Furthermore, the multivalent metal ions form ionic gels and coordination crosslinks with carboxylated polysaccharides such as sodium alginate, CMC, and carboxylated nanocellulose, maintaining a continuous skeleton structure even when absorbing water and swelling. This provides a soft skeleton for wet paperboard that can maintain its shape, enabling the material to retain a high effective load-bearing network even under immersion conditions, thus significantly improving the retention rate of tensile strength. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] In this invention, the plant fiber is poplar wood powder with a mesh size of 40, an effective ingredient content of 99%, and a density of 2.3 g / cm³. 3 ;

[0033] In this invention, the effective component content of nanocellulose is 99%, the particle size is 0.1-1μm, and it is selected from commercially available products of Hubei Maidehao Biotechnology Co., Ltd.

[0034] In this invention, the lignocellulose is ball-milled bamboo powder with a particle size of 5-10 μm and an effective ingredient content of 99%, selected from commercially available products of Hubei Maidehao Biotechnology Co., Ltd.

[0035] In this invention, the particle size of nano-silica is 30-50 nm;

[0036] In this invention, KH-560 is γ-glycidyl etheroxypropyltrimethoxysilane, CAS number 2530-83-8;

[0037] In this invention, the soybean polysaccharide is a soluble soybean polysaccharide with an effective ingredient content of 99%, selected from commercially available products of Sichuan Huanxu Biotechnology Co., Ltd.

[0038] In this invention, the effective component content of carboxymethyl starch is 99%, the viscosity is 76 cps, and it is selected from commercially available products of Zhonghe Chemical (Shandong) Co., Ltd.

[0039] Example 1

[0040] This embodiment provides a method for preparing high-strength plant cellulose-based composite paperboard, specifically including the following steps:

[0041] Step 1: Preparation of CMC-modified plant cellulose

[0042] Carboxymethyl cellulose, glyoxal, and deionized water were mixed evenly at a ratio of 1g:0.4g:20mL to obtain a carboxymethyl cellulose solution.

[0043] Weigh out 70g of nanocellulose, 30g of lignocellulose, and 800mL of deionized water and add them to a reaction flask. Stir the mixture and add 1mol / L hydrochloric acid to adjust the pH of the system to 3. Heat the reaction flask to 70℃ and add 200mL of carboxymethyl cellulose solution dropwise. Keep the mixture warm and stir for 50min. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain CMC-modified plant cellulose.

[0044] In the reaction, a carboxymethyl cellulose (CMC), glyoxal, and water were prepared into a CMC solution. This solution was then added dropwise to a fiber dispersion system composed of plant nanocellulose and micronized cellulose under weak acid and high temperature conditions. Glyoxal is a typical small molecule dialdehyde. Since the system contains CMC chains, hydroxyl groups on the surface of nanocellulose, and hydroxyl groups on the surface of micronized cellulose, glyoxal can act as a bridge between CMC and cellulose, and between cellulose fibers, constructing a cross-linked network with CMC as flexible segments and cellulose as a rigid skeleton. This introduces a certain density of covalent cross-linking points and a reactive layer rich in carboxyl and hydroxyl groups on the fiber surface and between fibers.

[0045] CMC modification significantly increases the effective binding sites between fibers and between fibers and subsequent polysaccharides / resins. This results in fiber bonding points formed during papermaking containing both hydrogen bonds and covalent bonds such as acetals, thereby improving tensile strength and burst index. Acetal bonds have a low hydrolysis rate in neutral water, and the carboxyl groups on the CMC chains facilitate further complexation or crosslinking with subsequent polyvalent metal ions and crosslinking agents, improving the material's performance retention rate after immersion in water. Nanocellulose provides high specific surface area and high modulus, while micronized cellulose provides a long fiber skeleton. The two are organically connected through a CMC / glyoxal network, enabling effective load transfer between fibers of different sizes and laying a skeletal foundation for subsequent overall mechanical properties.

[0046] Step 2: Preparation of inorganic reinforcing agent

[0047] Weigh out 60g of kaolin, 11g of nano-silica, 10g of KH-560, and 700mL of anhydrous ethanol and add them to a reaction flask. Mix and ultrasonically disperse for 30min. Fix the reaction flask on an iron stand with mechanical stirring. Heat the reaction flask to 50℃ and add 100mL of 2mol / L sodium hydroxide solution. Keep the reaction at this temperature for 60min. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 60℃ and dry it to constant weight to obtain epoxy modified filler.

[0048] In the reaction, kaolin, nano-silica, and KH-560 are mixed in anhydrous ethanol and ultrasonically dispersed. Then, sodium hydroxide solution is added and the temperature is raised to react. KH-560 undergoes hydrolysis to generate silanol, which then condenses with the hydroxyl groups on the surface of kaolin or nano-silica to form chemical bonds. This firmly fixes the silane with organic chains and terminal epoxy groups on the surface of inorganic particles, thus preparing an epoxy-modified filler.

[0049] Weigh out 70g of epoxy modified filler, 21g of PEG-800, 700mL of deionized water and 14g of sodium hydroxide and add them to the reaction flask. Stir the mixture and heat the reaction flask to 70℃. Keep the temperature for 50min. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain the inorganic reinforcing agent.

[0050] In the reaction, the PEG-800 molecular chain contains hydroxyl groups at its end, which can act as nucleophiles under alkaline conditions to attack the epoxy groups on the epoxy-modified filler and undergo ring-opening etherification reaction. Flexible and hydrophilic PEG segments are grafted onto the surface of inorganic particles to obtain an inorganic reinforcing agent.

[0051] Kaolin and nano-silica, as rigid frameworks, can improve the overall modulus and compressive strength in paper structures, which is beneficial to the improvement of tensile strength and bursting index. Through silane and PEG grafting modification, a large number of hydrogen bonds and physical entanglements are formed between the particle surface and organic components such as cellulose and CMC, avoiding the problems of easy agglomeration and easy peeling from the fiber surface of traditional unmodified fillers. This ensures that the load can be effectively transferred to the inorganic phase. The PEG chain segments themselves are flexible. Under dynamic loads such as tearing, the interface region can dissipate energy through the stretching and a certain degree of slippage of the PEG chain, thereby slowing down the increase in material brittleness caused by the increase of inorganic fillers and improving the tear index of the material.

[0052] Step 3: Preparation of crosslinking agent

[0053] Sodium periodate and deionized water were mixed evenly at a ratio of 1g:5mL to obtain a sodium periodate solution.

[0054] Weigh out 10g of soybean polysaccharide and 100mL of deionized water and add them to a brown light-proof reaction flask. Stir for 20min. Cool the reaction flask to 25℃ and add 12g of sodium periodate solution dropwise. Keep the reaction at this temperature for 8h. Place the reaction solution in a 1000Da dialysis bag and then place the dialysis bag in deionized water. Dialyze at room temperature for 20h, changing the deionized water every 2h. Place the substance in the dialysis bag in a freeze dryer at -30℃ to freeze dry and obtain oxidized soybean polysaccharide.

[0055] In the reaction, sodium periodate, a reagent with selective oxidizing properties for polysaccharides, performs ring-opening oxidation on the 1,2-vicinal diol structure of the polysaccharide chain, converting two adjacent hydroxyl groups into two aldehyde groups. Soybean polysaccharides, oxidized under the action of sodium periodate, become oxidized soybean polysaccharides with a high density of aldehyde groups. These aldehyde groups can subsequently undergo acetal reactions with the hydroxyl groups of polysaccharides such as cellulose, CMC, sodium alginate, and carboxymethyl starch in the pulp system, thereby forming new covalent crosslinking points between the fiber, polysaccharide, and resin.

[0056] Calcium chloride, magnesium chloride and aluminum chloride were mixed evenly in a weight ratio of 7:3:1 to obtain polyvalent metal ions.

[0057] A cross-linking agent is obtained by mixing polyvalent metal ions and oxidized soybean polysaccharides at a weight ratio of 2:6.

[0058] By mixing calcium chloride, magnesium chloride, and aluminum chloride to obtain polyvalent metal ions, and then mixing them with oxidized soybean polysaccharides, the polyvalent metal ions can coordinate with the carboxyl and hydroxyl groups on the oxidized soybean polysaccharides, improving the stability of the crosslinking agent itself. On the other hand, when subsequently added to the interface layer slurry, these metal ions can further form ionic crosslinking structures with carboxylated polysaccharides such as sodium alginate, CMC, and carboxylated nanocellulose, resulting in a product that combines the functions of polyaldehyde polysaccharides and polyvalent metal ions. This generates additional covalent crosslinking points on the fiber surface and within the interface layer, significantly enhancing the bonding strength between fibers and between fibers and nanofillers in the dry state, and improving tensile strength and bursting index. Moreover, the gel network formed by the polyvalent metal ions and sodium alginate, CMC, etc., can still maintain spatial continuity under water immersion conditions, and does not completely disintegrate even when it absorbs water and swells, providing skeletal support for wet paperboard. Its water-resistant acetal and Schiff base network improves the retention rate of tensile strength after water immersion.

[0059] Step 4: Preparation of composite plant fiber layer

[0060] Sodium alginate and carboxymethyl starch were mixed in a weight ratio of 3:1 to obtain a bio-based toughening agent;

[0061] Polyacrylamide, melamine-formaldehyde resin, alkyl ketone dimer, sodium lignosulfonate, ethylenediaminetetraacetic acid, polyether defoamer, and fatty acid salt were mixed in a weight ratio of 6:4:3:2:1:0.3:0.5 to obtain the additive.

[0062] Weigh out the following components by weight: 60 parts of plant fiber, 30 parts of CMC-modified plant cellulose, 15 parts of inorganic reinforcing agent, 6 parts of bio-based toughening agent, and 2 parts of auxiliary agent. Mix them together and add them to a mixing tank containing deionized water. Stir to obtain a fiber slurry with a solid content of 3 wt%.

[0063] Weigh out the following by weight: 40 parts of lignin nanoparticles, 30 parts of carboxylated nanocellulose, 5 parts of crosslinking agent and 2 parts of additives, mix them and add them to a mixing tank containing deionized water and stir to obtain an interface layer slurry with a solid content of 1 wt%.

[0064] The fiber slurry is evenly coated on a dewatering screen and dewatered to form a plant fiber layer with a thickness of 0.3±0.02mm and a water content of 30wt%.

[0065] The interface layer slurry is evenly coated on the dewatering screen to form interface layer one with a thickness of 0.05±0.01mm. Then, a plant fiber layer is laid flat on interface layer one. Then, the interface layer slurry is evenly sprayed on the plant fiber layer to form interface layer two with a thickness of 0.05±0.01mm on top of the plant fiber layer. After dewatering, a composite plant fiber layer with a water content of 30wt% is obtained.

[0066] Step 5: Prepare plant cellulose-based composite paperboard

[0067] Several composite plant fiber layers are stacked and placed into a cardboard mold, then hot-pressed. The hot-pressing pressure is set to 2 MPa, the hot-pressing temperature is 95℃, and the hot-pressing time is 20 min, resulting in a composite cardboard with a thickness of 2 mm.

[0068] Example 2

[0069] This embodiment provides a method for preparing high-strength plant cellulose-based composite paperboard, specifically including the following steps:

[0070] Step 1: Preparation of CMC-modified plant cellulose

[0071] Carboxymethyl cellulose, glyoxal, and deionized water were mixed evenly at a ratio of 1g:0.45g:20mL to obtain a carboxymethyl cellulose solution.

[0072] Weigh out 70g of nanocellulose, 35g of lignocellulose, and 800mL of deionized water and add them to a reaction flask. Stir the mixture and add 1.5mol / L hydrochloric acid to adjust the pH of the system to 3. Heat the reaction flask to 75℃ and add 200mL of carboxymethyl cellulose solution dropwise. Keep the mixture warm and stir for 60min. Cool the reaction flask to room temperature and filter it. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 75℃ and dry it to constant weight to obtain CMC-modified plant cellulose.

[0073] Step 2: Preparation of inorganic reinforcing agent

[0074] Weigh out 60g of kaolin, 12g of nano-silica, 10g of KH-560, and 700mL of anhydrous ethanol and add them to a reaction flask. Mix and ultrasonically disperse for 40min. Fix the reaction flask on an iron stand with mechanical stirring. Heat the reaction flask to 55℃ and add 100mL of 2.5mol / L sodium hydroxide solution. Keep the reaction at this temperature for 70min. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 65℃ and dry it to constant weight to obtain epoxy modified filler.

[0075] Weigh out 70g of epoxy modified filler, 24.5g of PEG-800, 700mL of deionized water and 14g of sodium hydroxide and add them to the reaction flask. Stir the mixture and heat the reaction flask to 75℃. Keep the mixture at this temperature for 60min. Cool the reaction flask to room temperature and filter the mixture. Wash the filter cake with purified water until it is neutral and then dry it. Transfer the filter cake to a drying oven at 75℃ and dry it to constant weight to obtain the inorganic reinforcing agent.

[0076] Step 3: Preparation of crosslinking agent

[0077] Sodium periodate and deionized water were mixed evenly at a ratio of 1g:5mL to obtain a sodium periodate solution.

[0078] Weigh out 11g of soybean polysaccharide and 100mL of deionized water and add them to a brown, light-proof reaction flask. Stir for 25 minutes. Cool the reaction flask to 27℃ and add 13g of sodium periodate solution dropwise. Keep the reaction at this temperature for 10 hours. Place the reaction solution in a 1000Da dialysis bag and then place the dialysis bag in deionized water. Dialyze at room temperature for 20 hours, changing the deionized water every 2 hours. Place the substance in the dialysis bag in a freeze dryer at -30℃ to freeze dry and obtain oxidized soybean polysaccharide.

[0079] Calcium chloride, magnesium chloride and aluminum chloride were mixed evenly in a weight ratio of 7:3:1 to obtain polyvalent metal ions.

[0080] A crosslinking agent is obtained by mixing polyvalent metal ions and oxidized soybean polysaccharides at a weight ratio of 2:6.5.

[0081] Step 4: Preparation of composite plant fiber layer

[0082] Sodium alginate and carboxymethyl starch were mixed in a weight ratio of 3:1 to obtain a bio-based toughening agent;

[0083] Polyacrylamide, melamine-formaldehyde resin, alkyl ketone dimer, sodium lignosulfonate, ethylenediaminetetraacetic acid, polyether defoamer, and fatty acid salt were mixed in a weight ratio of 6.5:4.5:3:2:1:0.3:0.5 to obtain the additive.

[0084] Weigh out the following components by weight: 65 parts plant fiber, 35 parts CMC modified plant cellulose, 17.5 parts inorganic reinforcing agent, 7 parts bio-based toughening agent, and 2.5 parts additives. Mix them and add them to a mixing tank containing deionized water. Stir to obtain a fiber slurry with a solid content of 3.5 wt%.

[0085] Weigh out the following by weight: 50 parts of lignin nanoparticles, 40 parts of carboxylated nanocellulose, 6 parts of crosslinking agent and 2.5 parts of additives, mix them and add them to a mixing tank containing deionized water and stir to obtain an interface layer slurry with a solid content of 1.5 wt%.

[0086] The fiber slurry is evenly coated on a dewatering screen and dewatered to form a plant fiber layer with a thickness of 0.3±0.02mm and a water content of 30-40wt%.

[0087] The interface layer slurry is evenly coated on the dewatering screen to form interface layer one with a thickness of 0.05±0.01mm. Then, a plant fiber layer is laid flat on interface layer one. Then, the interface layer slurry is evenly sprayed on the plant fiber layer to form interface layer two with a thickness of 0.05±0.01mm on top of the plant fiber layer. After dewatering, a composite plant fiber layer with a water content of 35wt% is obtained.

[0088] Step 5: Prepare plant cellulose-based composite paperboard

[0089] Several composite plant fiber layers are stacked and placed into a cardboard mold, then hot-pressed. The hot-pressing pressure is set to 2.5 MPa, the hot-pressing temperature is 100℃, and the hot-pressing time is 25 min, resulting in a composite cardboard with a thickness of 2.5 mm.

[0090] Example 3

[0091] This embodiment provides a method for preparing high-strength plant cellulose-based composite paperboard, specifically including the following steps:

[0092] Step 1: Preparation of CMC-modified plant cellulose

[0093] Carboxymethyl cellulose, glyoxal, and deionized water were mixed evenly at a ratio of 1g:0.5g:20mL to obtain a carboxymethyl cellulose solution.

[0094] Weigh out 70g of nanocellulose, 40g of lignocellulose, and 800mL of deionized water and add them to a reaction flask. Stir the mixture and add 2mol / L hydrochloric acid to adjust the pH of the system to 3. Heat the reaction flask to 80℃ and add 200mL of carboxymethyl cellulose solution dropwise. Keep the mixture warm and stir for 70min. Cool the reaction flask to room temperature and filter it. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 80℃ and dry it to constant weight to obtain CMC-modified plant cellulose.

[0095] Step 2: Preparation of inorganic reinforcing agent

[0096] Weigh out 60g of kaolin, 13g of nano-silica, 10g of KH-560, and 700mL of anhydrous ethanol and add them to a reaction flask. Mix and ultrasonically disperse for 50min. Fix the reaction flask on an iron stand with mechanical stirring. Heat the reaction flask to 60℃ and add 100mL of 3mol / L sodium hydroxide solution. Keep the reaction at this temperature for 80min. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain epoxy modified filler.

[0097] Weigh out 70g of epoxy modified filler, 28g of PEG-800, 700mL of deionized water and 14g of sodium hydroxide and add them to the reaction flask. Stir the mixture and heat the reaction flask to 80℃. Keep the temperature for 70min. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 80℃ and dry it to constant weight to obtain the inorganic reinforcing agent.

[0098] Step 3: Preparation of crosslinking agent

[0099] Sodium periodate and deionized water were mixed evenly at a ratio of 1g:5mL to obtain a sodium periodate solution.

[0100] Weigh out 12g of soybean polysaccharide and 100mL of deionized water and add them to a brown, light-proof reaction flask. Stir for 30min. Cool the reaction flask to 30℃ and add 14g of sodium periodate solution dropwise. Keep the reaction at this temperature for 12h. Place the reaction solution in a 1000Da dialysis bag and then place the dialysis bag in deionized water. Dialyze at room temperature for 20h, changing the deionized water every 2h. Place the substance in the dialysis bag in a freeze dryer at -30℃ to freeze dry and obtain oxidized soybean polysaccharide.

[0101] Calcium chloride, magnesium chloride and aluminum chloride were mixed evenly in a weight ratio of 7:3:1 to obtain polyvalent metal ions.

[0102] A crosslinking agent is obtained by mixing polyvalent metal ions and oxidized soybean polysaccharides at a weight ratio of 2:7.

[0103] Step 4: Preparation of composite plant fiber layer

[0104] Sodium alginate and carboxymethyl starch were mixed in a weight ratio of 3:1 to obtain a bio-based toughening agent;

[0105] Polyacrylamide, melamine-formaldehyde resin, alkyl ketone dimer, sodium lignosulfonate, ethylenediaminetetraacetic acid, polyether defoamer, and fatty acid salt were mixed in a weight ratio of 7:5:3:2:1:0.3:0.5 to obtain the additive.

[0106] Weigh out the following components by weight: 70 parts plant fiber, 40 parts CMC modified plant cellulose, 20 parts inorganic reinforcing agent, 8 parts bio-based toughening agent and 3 parts auxiliary agent. Mix them and add them to a mixing tank containing deionized water. Stir to obtain a fiber slurry with a solid content of 4 wt%.

[0107] Weigh out the following by weight: 60 parts of lignin nanoparticles, 50 parts of carboxylated nanocellulose, 7 parts of crosslinking agent and 3 parts of additives, mix them and add them to a mixing tank containing deionized water and stir to obtain an interface layer slurry with a solid content of 2wt%.

[0108] The fiber slurry is evenly coated on a dewatering screen and dewatered to form a plant fiber layer with a thickness of 0.3±0.02mm and a water content of 40wt%.

[0109] The interface layer slurry is evenly coated on the dewatering screen to form an interface layer one with a thickness of 0.05±0.01mm. Then, a plant fiber layer is laid flat on the interface layer one. The interface layer slurry is then evenly sprayed onto the plant fiber layer to form an interface layer two with a thickness of 0.05±0.01mm on top of the plant fiber layer. After dewatering, a composite plant fiber layer with a water content of 40wt% is obtained.

[0110] Step 5: Prepare plant cellulose-based composite paperboard

[0111] Several composite plant fiber layers are stacked and placed in a cardboard mold, then hot-pressed. The hot-pressing pressure is set to 3 MPa, the hot-pressing temperature is 105℃, and the hot-pressing time is 30 min, resulting in a composite cardboard with a thickness of 3 mm.

[0112] Comparative Example 1

[0113] The difference between this comparative example and Example 3 is that carboxymethyl cellulose solution was not added in step 1.

[0114] Comparative Example 2

[0115] The difference between this comparative example and Example 3 is that the epoxy-modified filler in step 2 is used instead of the inorganic reinforcing agent in step 4.

[0116] Comparative Example 3

[0117] The difference between this comparative example and Example 3 is that step 2 is omitted, and the inorganic reinforcing agent in step 4 is replaced by a mixture of kaolin and nano-silica in a ratio of 60:13.

[0118] Comparative Example 4

[0119] The difference between this comparative example and Example 3 is that, in step 3, soybean polysaccharide is used instead of oxidized soybean polysaccharide to prepare the crosslinking agent.

[0120] Performance testing:

[0121] The tensile strength of the composite paperboards prepared in Examples 1-3 and Comparative Examples 1-4 was determined according to the standard GB / T 12914-2018 "Determination of tensile strength of paper and paperboard - constant speed tensile method (20 mm / min)".

[0122] The tear index of the composite paperboards prepared in Examples 1-3 and Comparative Examples 1-4 was determined in accordance with the standard GB / T 455-2002 "Determination of tear strength of paper and paperboard".

[0123] The bursting index of the composite paperboards prepared in Examples 1-3 and Comparative Examples 1-4 was determined in accordance with the standard GB / T 454-2020 "Determination of bursting strength of paper".

[0124] The tensile strength retention rate of the composite paperboards prepared in Examples 1-3 and Comparative Examples 1-4 after immersion in water was determined according to the standard GB / T 465.2-2008 "Determination of tensile strength of paper and paperboard after immersion in water". The specific test data are shown in Table 1 below.

[0125] Table 1 - Performance Test Data of Samples

[0126]

[0127] Data Analysis:

[0128] Comparative analysis of the data in Table 1 shows that the composite paperboard samples prepared by this invention have a tensile strength of 26.5-47.3 kN / m and a tear index of 16.7-19.4 mN·m. 2 / g, with a bursting index of 6.12-8.11 kPa·m. 2 The tensile strength retention rate reached 71.5-66.1% per g, and all performance test data were better than those of the comparative example. This indicates that the present invention strengthens plant fibers by CMC-modified plant cellulose, PEG-modified inorganic reinforcing agents, and bio-based toughening agents to prepare a plant fiber layer. By setting a double interface layer containing lignin nanoparticles / carboxylated nanocellulose, a composite structure of interface layer, fiber layer, and interface layer is formed. Combined with hot pressing curing process, a plant cellulose-based composite paperboard with high strength, high toughness, and high wet strength retention rate is constructed.

[0129] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A high-strength plant cellulose-based composite paperboard, characterized in that, It includes several composite plant fiber layers, each of which consists of a plant fiber layer and an interface layer modified on both sides of the plant fiber layer. The plant fiber layer comprises the following components by weight: 60-70 parts plant fiber, 30-40 parts CMC-modified plant cellulose, 15-20 parts inorganic reinforcing agent, 6-8 parts bio-based toughening agent, and 2-3 parts additives. The interface layer comprises the following components by weight: 40-60 parts of lignin nanoparticles, 30-50 parts of carboxylated nanocellulose, 5-7 parts of crosslinking agent, and 2-3 parts of additives. The crosslinking agent is composed of polyvalent metal ions and oxidized soybean polysaccharides in a weight ratio of 2:6-7; The preparation method of CMC modified plant cellulose is as follows: nanocellulose, lignocellulose and deionized water are mixed and stirred, hydrochloric acid is added to the reaction system to adjust the pH of the system to 3, the reaction system is heated to 70-80℃, carboxymethyl cellulose solution is added dropwise to the reaction system, the system is kept warm and stirred for 50-70 min, and then post-processed to obtain CMC modified plant cellulose. The inorganic reinforcing agent is obtained by the following steps: A1. Mix kaolin, nano silica, KH-560 and anhydrous ethanol, ultrasonically disperse for 30-50 min, heat the reaction system to 50-60℃, add sodium hydroxide solution to the reaction system, keep the reaction at the temperature for 60-80 min, and then perform post-treatment to obtain epoxy modified filler. A2. Mix and stir epoxy-modified filler, polyethylene glycol, deionized water and sodium hydroxide. Heat the reaction system to 70-80℃ and keep it at that temperature for 50-70 minutes. After post-treatment, the inorganic reinforcing agent is obtained.

2. The high-strength plant cellulose-based composite paperboard according to claim 1, characterized in that, The bio-based toughening agent is composed of sodium alginate and carboxymethyl starch in a weight ratio of 3:1, and the polyvalent metal ions are composed of calcium chloride, magnesium chloride and aluminum chloride in a weight ratio of 7:3:

1.

3. The high-strength plant cellulose-based composite paperboard according to claim 1, characterized in that, The ratio of the amount of nanocellulose, lignocellulose, deionized water and carboxymethyl cellulose solution is 7g:3-4g:80mL:20mL, and the carboxymethyl cellulose solution is composed of carboxymethyl cellulose, glyoxal and deionized water at a ratio of 1g:0.4-0.5g:20mL.

4. The high-strength plant cellulose-based composite paperboard according to claim 1, characterized in that, In step A1, the ratio of kaolin, nano-silica, KH-560, anhydrous ethanol, and sodium hydroxide solution is 6g:1.1-1.3g:1g:70mL:10mL, and the concentration of sodium hydroxide solution is 2-3mol / L; in step A2, the ratio of epoxy modified filler, polyethylene glycol, deionized water, and sodium hydroxide is 10g:3-4g:100mL:2g, and the polyethylene glycol is PEG-800.

5. The high-strength plant cellulose-based composite paperboard according to claim 1, characterized in that, The preparation method of the oxidized soybean polysaccharide is as follows: under light-protected conditions, soybean polysaccharide and deionized water are mixed and stirred for 20-30 minutes, the reaction system is cooled to 25-30℃, sodium periodate solution is added dropwise to the reaction system, the reaction is kept at the temperature for 8-12 hours, and then post-processed to obtain oxidized soybean polysaccharide.

6. The high-strength plant cellulose-based composite paperboard according to claim 5, characterized in that, The ratio of soybean polysaccharide, deionized water and sodium periodate solution is 5-6g:50mL:6-7mL, and the sodium periodate solution is composed of sodium periodate and deionized water at a ratio of 1g:5mL.

7. A method for preparing a high-strength plant cellulose-based composite paperboard according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Mix and stir plant fiber, CMC-modified plant cellulose, inorganic reinforcing agent, bio-based toughening agent, additives and deionized water to obtain a fiber pulp with a solid content of 3-4 wt%. The fiber slurry is evenly coated on a dewatering screen and dewatered to form a plant fiber layer with a thickness of 0.3±0.02mm and a water content of 30-40wt%. S2. Mix and stir lignin nanoparticles, carboxylated nanocellulose, crosslinking agent, additives and deionized water to obtain an interface layer slurry with a solid content of 1-2 wt%. The interface layer slurry is evenly coated on the dewatering screen to form an interface layer one with a thickness of 0.05±0.01mm. Then, a plant fiber layer is laid flat on the interface layer one. The interface layer slurry is then evenly sprayed onto the plant fiber layer to form an interface layer two with a thickness of 0.05±0.01mm on top of the plant fiber layer. After dewatering, a composite plant fiber layer with a water content of 30-40wt% is obtained. S3. After stacking several composite plant fiber layers, place them into a cardboard mold and heat press them to obtain a composite cardboard with a thickness of 2-3mm.

8. The method for preparing a high-strength plant cellulose-based composite paperboard according to claim 7, characterized in that, The additives are composed of polyacrylamide, melamine-formaldehyde resin, alkyl ketone dimer, sodium lignosulfonate, ethylenediaminetetraacetic acid, polyether defoamer, and fatty acid salt in a weight ratio of 6-7:4-5:3:2:1:0.3:0.

5. The hot-pressing pressure is 2-3 MPa, the hot-pressing temperature is 95-105℃, and the hot-pressing time is 20-30 min.

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