A process for large-scale production of high-adhesion-strength formaldehyde-free bioresin

Abstract

This invention relates to the field of wood adhesives and bioresins, and discloses a large-scale production process for high-adhesion-strength formaldehyde-free bioresin, comprising: pre-treatment of plant phenolic biomass raw materials with wood ash alkali activation to release free phenolic hydroxyl groups; physical adsorption and immobilization of laccase and soybean peroxidase on a bamboo charcoal carrier to obtain a bamboo charcoal dual-enzyme co-immobilized composite; mixing activated phenolic solution with soybean protein isolate solution, adding bamboo charcoal dual-enzyme body and batch-added components to form a phenol-phenol and phenol-protein dual-type covalent cross-linking network; sequentially adding pre-activated dehydrated clinoptilolite and flaxseed gum; coating the obtained adhesive onto a substrate and then hot-pressing and curing, followed by cooling and curing to obtain a dense, microporous-free cured adhesive layer. This invention achieves complete formaldehyde-free adhesive, with adhesive strength reaching the standards for engineering-grade boards, eliminating microporous defects in the hot-pressed adhesive layer, and using raw materials entirely derived from nature or industrial and agricultural by-products, making it suitable for large-scale continuous production.

Description

Technical Field

[0001] This invention relates to the field of wood adhesives and bioresins, and more specifically, to a process for the large-scale production of high-bonding-strength formaldehyde-free bioresins. Background Technology

[0002] Currently, the adhesives used in the wood industry are mainly urea-formaldehyde resin, phenolic resin, and melamine-formaldehyde resin. These adhesives continuously release free formaldehyde during product use, posing a serious threat to indoor air quality and human health, and have been strictly restricted by mandatory building material standards in many countries. Existing formaldehyde-free alternatives mainly include isocyanates (such as MDI) and soybean protein-based adhesives. However, MDI is expensive and sensitive to moisture; soybean protein-based adhesives have low bonding strength and poor water resistance after curing, making them unsuitable for use in engineering applications. Natural laccase-catalyzed oxidative crosslinking is a recently emerging method for preparing formaldehyde-free bio-resins. Laccase can catalyze the oxidative coupling of plant phenolic substances under mild conditions, forming an adhesive network without the introduction of any aldehyde curing agent.

[0003] However, existing laccase-based formaldehyde-free adhesive preparation processes suffer from the following prominent technical problems: the catalytic substrate range of a single laccase is limited; a large number of phenolic hydroxyl groups in plant biomass raw materials exist in a bound state, and the amount of free phenolic hydroxyl groups available for laccase catalysis is insufficient when unactivated, resulting in insufficient cross-linking network density and low bonding strength of the finished product, failing to meet the standards for use in engineering boards; free laccase and peroxidase are easily deactivated in industrial production environments, leading to high production costs; laccase-based formaldehyde-free adhesives are aqueous solutions with high water content, and the vaporization of a large amount of residual water in the adhesive layer during the hot-pressing curing stage, as well as other issues related to the system... Thermal decomposition release The two types of gases together cause micropore defects in the hot-pressed adhesive layer, reducing the effective bonding area and decreasing the mechanical properties and water resistance of the adhesive layer. This problem is particularly prominent in large-scale hot-pressing production. Currently, there is no systematic process solution for the above problems that is entirely derived from biomass. Summary of the Invention

[0004] This invention provides a large-scale production process for high-adhesion-strength formaldehyde-free bioresin, solving the technical problems of insufficient adhesive strength, poor enzyme activity stability, and microporous defects in the hot-pressed cured adhesive layer of laccase-based formaldehyde-free adhesives in related technologies.

[0005] This invention provides a process for large-scale production of high-adhesion-strength formaldehyde-free bioresin, comprising the following steps:

[0006] Hydrolyzable plant tannins and lignin sulfonates were mixed with wood ash at a dry weight ratio of 4:6 to 6:4. After alkali activation pretreatment in an aqueous solution, the mixture was filtered and the pH was adjusted to 5.5 to 6.5 with glacial acetic acid solution to obtain activated phenolic substrate solution.

[0007] A bamboo charcoal dual-enzyme co-immobilization complex was prepared by physically adsorbing white-rot fungus laccase and soybean peroxidase onto bamboo charcoal.

[0008] The activated phenolic substrate solution was mixed with the soy protein isolate solution, and the bamboo charcoal dual-enzyme co-immobilization complex was added in batches. The solution was stirred in an aerobic aqueous solution system at 25–45°C and pH 5.5–6.5 for 1–4 h to form two types of covalent cross-linked networks: phenol-phenol and phenol-protein.

[0009] Add clinoptilolite activated by calcination at 300-350℃ and flaxseed gum to the above liquid in sequence. Apply the resulting adhesive to the surface of the substrate within 4 hours and hot-press it at 120-180℃ and 1-3 MPa to obtain a formaldehyde-free bio-resin cured adhesive layer.

[0010] Preferably, the amount of wood ash added is 10% to 20% of the total dry weight of hydrolyzable plant tannins and lignin sulfonates; the alkali activation pretreatment temperature is 25 to 60°C, and the treatment time is 30 to 120 min; after filtration, the pH of the filtrate is adjusted to 5.5 to 6.5 with a 10% to 20% (v / v) glacial acetic acid aqueous solution.

[0011] Preferably, the bamboo charcoal particle size is 100-200 mesh; after preparing aqueous solutions of white rot fungus laccase and soybean peroxidase, they are mixed evenly, and bamboo charcoal is added to the above mixed enzyme solution. The mixture is shaken and adsorbed at 4-25℃ for 2-6 h. After centrifugation or filtration to remove the free enzyme in the supernatant, a bamboo charcoal dual-enzyme co-immobilized complex is obtained.

[0012] Preferably, the loading of white-rot fungal laccase on bamboo charcoal is 20-50 U / g bamboo charcoal, and the loading of soybean peroxidase on bamboo charcoal is 10-30 U / g bamboo charcoal; the enzyme activity unit U is defined as the amount of enzyme required to catalyze the conversion of 1 μmol of substrate per minute at 25℃ and pH 5.0.

[0013] Preferably, the soy protein isolate has a protein content of ≥90%, and the mass ratio of soy protein isolate to phenolic raw materials is 3:7 to 5:5; the amount of bamboo charcoal dual-enzyme co-immobilized complex added is 3% to 8% of the total mass of the adhesive solids.

[0014] Preferably: The solution was added in equal batches, with an interval of 15–30 minutes between each batch. After each addition, the solution was added to the feed solution. Instantaneous concentration not exceeding 5 mM; The total amount added should bring the final concentration of the liquid to 0.05%–0.1% w / v.

[0015] Preferably, clinoptilolite is calcined at 300-350℃ for 2-4 hours to complete pre-activation and dehydration, and after grinding, the particle size is 100-200 mesh. The amount added is 5%-15% of the total mass of the adhesive solids.

[0016] Preferably, the flaxseed gum is a natural polysaccharide rich in arabinoxylan and galactomannan, and the amount added is 3% to 8% of the total mass of the adhesive solids; the interval between adding the flaxseed gum to the adhesive system and applying it to the substrate shall not exceed 4 hours.

[0017] Preferably: laccase from white-rot fungi in the presence of... In the process of oxidizing phenolic hydroxyl groups by oxidant catalysis, through Incomplete two-electron reduction side reactions produce a small amount of [unclear - possibly referring to a specific type of reaction] in the local microenvironment of the bamboo charcoal carrier. ,Should Soybean peroxidase immobilized at adjacent sites on a bamboo charcoal carrier is captured in situ. The oxidant catalyzes further oxidative coupling of the phenolic hydroxyl groups; white-rot fungal laccase and soybean peroxidase respectively act as... and As an oxidant, it simultaneously catalyzes the oxidative coupling of the phenolic hydroxyl groups of the substrate through complementary oxidation pathways, forming a higher density phenol-phenol covalent cross-linked network.

[0018] Preferably, the hot-press curing process includes three stages performed sequentially: a hot-pressing heating stage, a pre-activated dehydration stage, and a stage where water vapor in the adhesive layer is captured by the pores of the clinoptilolite. Thermal decomposition releases The process involves binding the two within the mineral micropores, thus preventing bubble nucleation. During the hot-pressing and high-temperature holding stage, the viscosity of flaxseed gum decreases and its fluidity increases under high temperature and pressure conditions, flowing into and filling the nascent micropores in the gum layer. During the hot-pressing and cooling stage, the gelation of flaxseed gum permanently seals the filled micropores, and clinoptilolite particles are embedded in the cured gum layer to become inorganic filler structural components.

[0019] The beneficial effects of this invention are as follows: the alkali activation pretreatment of wood ash converts bound phenolic hydroxyl groups in two types of plant biomass raw materials into free phenolic hydroxyl groups, providing sufficient substrate for dual-enzyme catalytic cross-linking; laccase and soybean peroxidase are co-immobilized on the same carrier of bamboo charcoal, and the two enzymes are respectively... and The oxidant simultaneously catalyzes the oxidative coupling of phenolic hydroxyl groups via complementary oxidation pathways, forming a dual-type covalent cross-linked network of phenol-phenol and phenol-protein with high cross-linking density. The bamboo charcoal carrier provides spatial protection for the two enzymes, significantly reducing the enzyme inactivation rate in industrial production environments and decreasing batch replenishment amounts. Pre-activated dehydrated clinoptilolite adsorbs water vapor in situ during the hot-pressing and heating stage. During the high-temperature pressing stage, flaxseed adhesive fills the nascent micropores with a fluid dynamic process. This sequential synergy eliminates micropore defects in the heat-cured adhesive layer, significantly improving the effective bonding area and density. This invention achieves complete formaldehyde-free adhesive, with bonding strength meeting engineering-grade board standards. All raw materials are derived from nature or industrial and agricultural byproducts. Each process can be completed in standard industrial equipment, enabling large-scale continuous production. Attached Figure Description

[0020] Figure 1 This is a bar chart showing the effect of the alkaline activation treatment of plant ash on the release of free phenolic hydroxyl groups according to the present invention;

[0021] Figure 2 This is a comparison chart of the tensile and shear strength of the plates under different alkali activation intensities according to the present invention;

[0022] Figure 3 This is a line graph comparing the batch-to-batch enzyme activity and stability of the free laccase and bamboo charcoal dual enzymes of the present invention;

[0023] Figure 4 These are SEM cross-sectional morphology comparison images of the hot-pressed cured adhesive layer of this invention;

[0024] Figure 5 This is a comparison diagram of the effects of clinoptilolite and flaxseed gum on the porosity of the gum layer according to the present invention;

[0025] Figure 6 This is a comparison diagram showing the effect of clinoptilolite and flaxseed gum on the adhesive strength of the adhesive layer. Detailed Implementation

[0026] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0027] Example 1

[0028] This embodiment discloses a method for producing a high-adhesion-strength formaldehyde-free bioresin, which includes the following steps:

[0029] Step 1 (corresponding to claims 1 and 2): Alkali activation pretreatment of plant phenolic biomass raw materials with wood ash. Hydrolyzable tannins and lignin sulfonates from larch bark with a free phenolic hydroxyl content of 3.2 mmol / g dry weight were mixed at a dry weight ratio of 4:6 (40 parts hydrolyzable tannins and 60 parts lignin sulfonates) to obtain 100 g (dry weight) of phenolic raw materials. 10 g of wood ash (10% of the dry weight of the phenolic raw materials) was added and thoroughly mixed in 400 mL of deionized water. The mixture was then stirred at 25°C for alkali activation pretreatment for 30 min. After pretreatment, insoluble solid residues were removed by bag filtration, and the filtrate was collected. A 10% (v / v) glacial acetic acid aqueous solution was added dropwise to the filtrate to adjust the pH to 5.5, yielding activated phenolic substrate solution for later use.

[0030] Step 2 (corresponding to claims 1, 3, and 4): Co-immobilization of laccase and soybean peroxidase on bamboo charcoal carrier. Natural bamboo charcoal (specific surface area 310 m² / g) obtained from bamboo carbonization was ground and sieved to a particle size of 100 mesh. Fungal laccase from the white-rot fungus *Trametes versicolor* was prepared as an aqueous solution (target loading 20 U / g bamboo charcoal), and soybean peroxidase (SBP) was prepared as an aqueous solution (target loading 10 U / g bamboo charcoal). The two were mixed evenly, and 100 g of bamboo charcoal was added. The mixture was shaken and adsorbed at 4℃ for 2 h. After filtration to remove free enzymes from the supernatant, the immobilization rate was measured to be 75%, thus obtaining the bamboo charcoal-dual-enzyme co-immobilized complex (bamboo charcoal dual-enzyme complex) for later use.

[0031] Step 3 (corresponding to claims 1, 5, and 6): Activating the phenolic substrate and combining it with soy protein isolate and bamboo charcoal dual-enzyme, followed by enzyme-catalyzed cross-linking. Take the activated phenolic substrate solution obtained in Step 1, and add an aqueous solution of soy protein isolate (SPI) with a protein content ≥90%, making the mass ratio of SPI to phenolic raw material 3:7 (SPI 30 parts, phenolic raw material 70 parts, based on dry weight); add the bamboo charcoal dual-enzyme obtained in Step 2, at a dosage of 3% of the total mass of the adhesive solids; The total amount is divided into three equal parts, and one part is added every 20 minutes until the total amount is reached. The final concentration was 0.05% w / v; the enzyme-catalyzed oxidative coupling reaction was carried out in an aerobic aqueous solution system (with the container open to the atmosphere) at 25°C and pH 5.5 for 1 h with stirring to obtain an adhesive solution containing a primary cross-linked network.

[0032] Step 4 (corresponding to claims 1, 7, and 8): Stepwise addition of clinoptilolite and flaxseed gum. Take natural clinoptilolite, grind it to a particle size of 100 mesh, calcine it at 300℃ for 2 h to complete pre-activation and dehydration, and store it in a sealed container after cooling; add the above-mentioned pre-activated and dehydrated clinoptilolite to the adhesive liquid obtained in step 3, the amount added is 5% of the total mass of the adhesive solids, and stir thoroughly to disperse evenly; then add flaxseed gum powder, the amount added is 3% of the total mass of the adhesive solids, and stir for at least 15 min to allow it to fully hydrate and swell, to obtain an adhesive containing clinoptilolite particles and flaxseed gum in a hydrated gel state.

[0033] Step 5 (corresponding to claims 1 and 10): Hot pressing and curing. The adhesive obtained in step 4 is applied to the surface of the particleboard substrate within 1 hour after the addition of flaxseed glue (adhesive application amount 180 g / m²), and hot pressing and curing is carried out at 120℃ and 1 MPa (based on 1 min per millimeter of board thickness) to obtain a formaldehyde-free bio-resin cured adhesive layer.

[0034] Example 2

[0035] This embodiment discloses a method for producing a high-adhesion-strength formaldehyde-free bioresin, which includes the following steps:

[0036] Step 1 (corresponding to claims 1 and 2): Alkali activation pretreatment of plant phenolic biomass raw materials with wood ash. Hydrolyzable tannins and lignin sulfonates from Vitex negundo bark with a free phenolic hydroxyl content of 3.8 mmol / g dry weight were mixed at a dry weight ratio of 6:4 (60 parts hydrolyzable tannins, 40 parts lignin sulfonates) to obtain 100 g (dry weight) of phenolic raw materials. 20 g of wood ash (20% of the dry weight of the phenolic raw materials) was added and thoroughly mixed in 400 mL of deionized water. The mixture was then subjected to alkali activation pretreatment at 60℃ for 120 min with stirring. After pretreatment, insoluble solid residues were removed by plate and frame filtration, and the filtrate was collected. A 20% (v / v) glacial acetic acid aqueous solution was added dropwise to the filtrate to adjust the pH to 6.5, yielding activated phenolic substrate solution for later use.

[0037] Step 2 (corresponding to claims 1, 3, and 4): Co-immobilization of laccase and soybean peroxidase on bamboo charcoal carrier. Natural bamboo charcoal (specific surface area 380 m² / g) was ground and sieved to a particle size of 200 mesh. Fungal laccase from the white-rot fungus *Trametesversicolor* was prepared as an aqueous solution (target loading 50 U / g bamboo charcoal), and soybean peroxidase (SBP) was prepared as an aqueous solution (target loading 30 U / g bamboo charcoal). After thorough mixing, 100 g of bamboo charcoal was added, and the mixture was shaken and adsorbed at 25°C for 6 h. The free enzyme in the supernatant was removed by centrifugation. The immobilization rate was measured to be 72%, yielding a bamboo charcoal dual-enzyme body for later use.

[0038] Step 3 (corresponding to claims 1, 5, and 6): Activating the phenolic substrate and combining it with soy protein isolate and bamboo charcoal dual-enzyme, followed by enzyme-catalyzed cross-linking. Take the activated phenolic substrate solution obtained in Step 1, add an aqueous solution of soy protein isolate (SPI) with a protein content ≥90%, making the mass ratio of SPI to phenolic raw material 5:5 (equal mass mixing, based on dry weight); add the bamboo charcoal dual-enzyme obtained in Step 2, the amount added being 8% of the total mass of the adhesive solids; The total amount is divided into 5 equal parts, and one part is added every 30 minutes until the total amount is reached. The final concentration was 0.07% w / v; the enzyme-catalyzed oxidative coupling reaction was carried out in an aerobic aqueous solution system (air was bubbled into the solution at a rate of 0.5 L / min) at 45°C and pH 6.5 for 4 h to obtain an adhesive solution containing a primary cross-linked network.

[0039] Step 4 (corresponding to claims 1, 7, and 8): Stepwise addition of clinoptilolite and linseed gum. Take natural clinoptilolite, grind it to a particle size of 200 mesh, calcine it at 350℃ for 4 h to complete pre-activation and dehydration, and store it in a sealed container after cooling; add the above-mentioned pre-activated and dehydrated clinoptilolite to the adhesive liquid obtained in step 3, the amount added is 15% of the total mass of the adhesive solids, and stir thoroughly to disperse evenly; then add linseed gum powder, the amount added is 8% of the total mass of the adhesive solids, and stir for at least 15 min to allow it to fully hydrate and swell, to obtain an adhesive containing clinoptilolite particles and linseed gum in a hydrated gel state.

[0040] Step 5 (corresponding to claims 1 and 10): Hot pressing and curing. The adhesive obtained in step 4 is applied to the surface of the plywood veneer substrate within 3.5 h after the addition of flaxseed glue (adhesive application amount 200 g / m²), and hot-pressed and cured at 180℃ and 3 MPa (based on 1.5 min per millimeter of board thickness) to obtain a formaldehyde-free bio-resin cured adhesive layer.

[0041] Example 3

[0042] This embodiment discloses a method for producing a high-adhesion-strength formaldehyde-free bioresin, which includes the following steps:

[0043] Step 1 (corresponding to claims 1 and 2): Alkali activation pretreatment of plant phenolic biomass raw materials with wood ash. Hydrolyzable tannins and lignin sulfonates from larch bark with a free phenolic hydroxyl content of 3.5 mmol / g dry weight were mixed at a dry weight ratio of 5:5 (50 parts each) to obtain 100 g (dry weight) of phenolic raw materials. 15 g of wood ash (15% of the dry weight of the phenolic raw materials) was added and thoroughly mixed in 400 mL of deionized water. The mixture was then stirred at 40°C for 60 min for alkali activation pretreatment. After pretreatment, insoluble solid residues were removed by plate and frame filtration, and the filtrate was collected. A 15% (v / v) aqueous solution of glacial acetic acid was added dropwise to the filtrate to adjust the pH to 6.0, yielding activated phenolic substrate solution for later use.

[0044] Step 2 (corresponding to claims 1, 3, and 4): Co-immobilization of laccase and soybean peroxidase on bamboo charcoal carrier. Natural bamboo charcoal (specific surface area 345 m² / g) was ground and sieved to a particle size of 150 mesh. Fungal laccase from the white-rot fungus *Trametesversicolor* was prepared as an aqueous solution (target loading 35 U / g bamboo charcoal), and soybean peroxidase (SBP) was prepared as an aqueous solution (target loading 20 U / g bamboo charcoal). After thorough mixing, 100 g of bamboo charcoal was added, and the mixture was shaken and adsorbed at 10℃ for 4 h. The supernatant was filtered to remove free enzymes, and the immobilization rate was measured to be 78%, thus obtaining the bamboo charcoal dual-enzyme body for later use.

[0045] Step 3 (corresponding to claims 1, 5, and 6): Activating the phenolic substrate and combining it with soy protein isolate and bamboo charcoal dual-enzyme, followed by enzyme-catalyzed cross-linking. Take the activated phenolic substrate solution obtained in Step 1, and add an aqueous solution of soy protein isolate (SPI) with a protein content ≥90%, making the mass ratio of SPI to phenolic raw material 4:6 (SPI 40 parts, phenolic raw material 60 parts, based on dry weight); add the bamboo charcoal dual-enzyme obtained in Step 2, the amount added being 5% of the total mass of the adhesive solids; The total amount is divided into four equal parts, and one part is added every 25 minutes until the total amount is reached. The final concentration was 0.06% w / v; the enzyme-catalyzed oxidative coupling reaction was carried out in an aerobic aqueous solution system (with the container open to the atmosphere) at 35°C and pH 6.0 for 2 h with stirring to obtain an adhesive solution containing a primary cross-linked network.

[0046] Step 4 (corresponding to claims 1, 7, and 8): Stepwise addition of clinoptilolite and linseed gum. Take natural clinoptilolite, grind it to a particle size of 150 mesh, calcine it at 325℃ for 3 h to complete pre-activation and dehydration, and store it in a sealed container after cooling; add the above-mentioned pre-activated and dehydrated clinoptilolite to the adhesive liquid obtained in step 3, the amount added is 10% of the total mass of the adhesive solids, and stir thoroughly to disperse evenly; then add linseed gum powder, the amount added is 5% of the total mass of the adhesive solids, and stir for at least 15 min to allow it to fully hydrate and swell, to obtain an adhesive containing clinoptilolite particles and linseed gum in a hydrated gel state.

[0047] Step 5 (corresponding to claims 1 and 10): Hot pressing and curing. The adhesive obtained in step 4 is applied to the surface of medium-density fiberboard substrate within 2 hours after the addition of flaxseed glue (adhesive application amount 190 g / m²), and hot-pressed and cured at 150°C and 2 MPa (based on 1.2 min per millimeter of board thickness) to obtain a formaldehyde-free bio-resin cured adhesive layer.

[0048] Example 4

[0049] This embodiment discloses a method for producing a high-adhesion-strength formaldehyde-free bioresin, which includes the following steps:

[0050] Step 1 (corresponding to claims 1 and 2): Alkali activation pretreatment of plant phenolic biomass raw materials with wood ash. Hydrolyzable tannins and lignin sulfonates from Vitex negundo bark with a free phenolic hydroxyl content of 3.6 mmol / g dry weight were mixed at a dry weight ratio of 6:4 (60 parts hydrolyzable tannins, 40 parts lignin sulfonates) to obtain 100 g (dry weight) of phenolic raw materials. 18 g of wood ash (18% of the dry weight of the phenolic raw materials) was added and thoroughly mixed in 400 mL of deionized water. The mixture was then stirred at 30°C for 100 min for alkali activation pretreatment. After pretreatment, insoluble solid residues were removed by bag filtration, and the filtrate was collected. A 12% (v / v) glacial acetic acid aqueous solution was added dropwise to the filtrate to adjust the pH to 5.8, yielding activated phenolic substrate solution for later use.

[0051] Step 2 (corresponding to claims 1, 3, and 4): Co-immobilization of laccase and soybean peroxidase on bamboo charcoal carrier. Natural bamboo charcoal (specific surface area 330 m² / g) was ground and sieved to a particle size of 120 mesh. Fungal laccase from the white-rot fungus *Trametesversicolor* was prepared as an aqueous solution (target loading 45 U / g bamboo charcoal), and soybean peroxidase (SBP) was prepared as an aqueous solution (target loading 28 U / g bamboo charcoal). After thorough mixing, 100 g of bamboo charcoal was added, and the mixture was shaken and adsorbed at 15°C for 2.5 h. The supernatant was filtered to remove free enzymes, and the immobilization rate was measured to be 71%, yielding a bamboo charcoal dual-enzyme body for later use.

[0052] Step 3 (corresponding to claims 1, 5, and 6): Activating the phenolic substrate and combining it with soy protein isolate and bamboo charcoal dual-enzyme, followed by enzyme-catalyzed cross-linking. Take the activated phenolic substrate solution obtained in Step 1, and add an aqueous solution of soy protein isolate (SPI) with a protein content ≥90%, making the mass ratio of SPI to phenolic raw material 3:7 (30 parts SPI, 70 parts phenolic raw material, based on dry weight); add the bamboo charcoal dual-enzyme obtained in Step 2, the amount added being 7% of the total mass of the adhesive solids; The total volume is divided into 6 equal parts, with one part added every 18 minutes, until the total volume of the liquid is reached. The final concentration was 0.09% w / v; the enzyme-catalyzed oxidative coupling reaction was carried out in an aerobic aqueous solution system (air was bubbled into the solution at a rate of 0.3 L / min) at 40 °C and pH 5.8 for 3 h to obtain an adhesive solution containing a primary cross-linked network.

[0053] Step 4 (corresponding to claims 1, 7, and 8): Stepwise addition of clinoptilolite and linseed gum. Take natural clinoptilolite, grind it to a particle size of 120 mesh, calcine it at 340℃ for 3.5 h to complete pre-activation and dehydration, and store it in a sealed container after cooling; add the above-mentioned pre-activated and dehydrated clinoptilolite to the adhesive liquid obtained in step 3, the amount added is 12% of the total mass of the adhesive solids, and stir thoroughly to disperse evenly; then add linseed gum powder, the amount added is 4% of the total mass of the adhesive solids, and stir for at least 15 min to allow it to fully hydrate and swell, to obtain an adhesive containing clinoptilolite particles and linseed gum in a hydrated gel state.

[0054] Step 5 (corresponding to claims 1 and 10): Hot pressing and curing. The adhesive obtained in step 4 is applied to the surface of the bamboo engineered wood substrate within 1.5 h after the addition of flaxseed glue (adhesive application rate 195 g / m²), and hot-pressed and cured at 170℃ and 1.5 MPa (based on 1.3 min per millimeter of board thickness) to obtain a formaldehyde-free bio-resin cured adhesive layer.

[0055] Example 5

[0056] This embodiment discloses a large-scale production process for high-adhesion formaldehyde-free bioresin using laccase-peroxidase dual-enzyme bamboo charcoal immobilization catalysis and clinoptilolite-linseed gum-assisted hot pressing curing. The process includes the following five steps:

[0057] Step 1: Alkali activation pretreatment of plant phenolic biomass raw materials using wood ash

[0058] Hydrolyzable plant tannins derived from agricultural and forestry waste (selected from larch bark or vitex bark extracts, with a free phenolic hydroxyl content ≥3 mmol / g dry weight (determined by the Folin-Ciocalteu method) as the qualification standard) are mixed with industrial lignin sulfonate at a dry weight ratio of 5:5 as phenolic raw materials. Wood ash (obtained from the combustion of agricultural and forestry waste such as straw and wood, rich in...) is used as the phenolic raw material. , Natural alkaline mineral components) are added to the above phenolic raw materials at a ratio of 15% of the dry weight of the phenolic raw materials with wood ash. The mixture is then stirred in an aqueous solution system and subjected to alkali activation pretreatment at 40°C for 60 min.

[0059] The ash that dissolves in water and The solution is made alkaline. Under alkaline conditions, the gallic acid ester bonds in plant tannins are hydrolyzed, releasing the gallic acid phenolic hydroxyl groups linked to the glucose backbone in a free state. Simultaneously, alkaline conditions break the bonds between phenylpropane structural units in lignin sulfonates. -O-4 ether bonds release the phenylpropane-type phenolic hydroxyl groups, which are ether-bonded to the polymer backbone, into a free state. After pretreatment, the solution is filtered to remove insoluble solid residues (mainly inert mineral components such as silicates) from the wood ash. (Precipitation), collect the filtrate containing activated free phenolic hydroxyl groups and soluble alkaline mineral salts; add 15% (v / v) glacial acetic acid aqueous solution dropwise to the above filtrate to adjust the pH to 6.0, and obtain the pH-adjusted activated phenolic substrate solution for later use.

[0060] Step 2: Co-immobilization of white-rot fungal laccase and soybean peroxidase on bamboo charcoal carrier

[0061] Natural bamboo charcoal (specific surface area ≥300 m² / g) obtained from bamboo carbonization was used as an enzyme carrier. The bamboo charcoal was ground and sieved to a particle size of 150 mesh. Fungal laccase (35 U / g bamboo charcoal loading; enzyme activity unit U is defined as the amount of enzyme required to catalyze the conversion of 1 μmol of substrate per minute under standard determination conditions of 25℃ and pH 5.0) from white-rot fungi (Trametes versicolor) and soybean peroxidase (SBP; 20 U / g bamboo charcoal loading; enzyme activity unit U is defined as above) were separately prepared into aqueous solutions and mixed evenly. The bamboo charcoal was added to the above mixed enzyme solution, and the mixture was shaken and adsorbed at 10℃ for 4 h, allowing the two enzymes to be co-immobilized on the porous surface of the bamboo charcoal through physical adsorption. After centrifugation or filtration to remove free enzymes from the supernatant, a bamboo charcoal-dual-enzyme co-immobilized complex (bamboo charcoal dual-enzyme complex) was obtained; the immobilization rate should be ≥70%, and it was used for later use.

[0062] The natural porous structure of bamboo charcoal allows two enzymes to be distributed adjacently on the same carrier: laccase... The oxidant catalyzes the oxidation of phenolic hydroxyl groups, and the catalytic process occurs... The four electrons are reduced to The main reaction is accompanied by a certain proportion of incomplete two-electron reduction side reactions, producing a small amount of [reduction] in the local microenvironment on the surface of the bamboo charcoal carrier. This accompaniment Peroxidases fixed at adjacent sites on the bamboo charcoal carrier are preferentially captured, preventing loss through diffusion. The oxidant catalyzes further oxidative coupling of the phenolic hydroxyl groups, thereby achieving laccase byproducts. Peroxidases at adjacent sites on the bamboo charcoal carrier are utilized in situ without being lost to the liquid phase. The bamboo charcoal dual enzymes are incorporated into the final product along with the adhesive material, eliminating the need for recovery from the finished product.

[0063] Step 3: Activation of phenolic substrates, compounding with plant proteins and bamboo charcoal dual enzymes, and enzymatic cross-linking.

[0064] The activated phenolic substrate solution obtained in step one is mixed evenly with the soy protein isolate solution (an aqueous solution prepared from soy protein isolate with a protein content ≥90%; the mass ratio of soy protein isolate to phenolic raw materials is 4:6). The bamboo charcoal dual enzyme obtained in step two is added (the amount added is 5% of the total mass of the adhesive solids), and the solution is diluted in 5 equal portions. Solution (cumulative total amount added to make the system) The final concentration is 0.07% w / v. The total amount must be divided into 5 equal portions, added every 15–30 minutes; do not add the entire amount at once. This serves as a supplement for the electron acceptor in the peroxidase-catalyzed solution. In an aerobic aqueous solution system (air is bubbled into the solution at a rate of 0.3 L / min to ensure the necessary conditions for laccase catalysis),... (with a continuous supply), the enzyme-catalyzed oxidative coupling reaction was carried out with stirring at 35°C and pH 6.0 for 2 h.

[0065] Laccase in the air The oxidant catalyzes the single-electron oxidation of the phenolic hydroxyl group, generating phenoxy radicals. These phenoxy radicals then spontaneously couple to form phenol-phenol carbon-carbon or carbon-oxygen covalent bonds. Peroxidase then... The oxidant simultaneously catalyzes the oxidation of phenolic hydroxyl groups in the substrate to generate phenolic oxygen radicals, which then participate in the coupling reaction with phenolic oxygen radicals generated by laccase. Plant proteins are rich in tyrosine residues (containing phenolic hydroxyl groups). Under the synergistic catalysis of laccase and peroxidase, the phenolic hydroxyl groups of tyrosine residues are oxidized to generate tyrosine radicals, which then undergo phenol-protein covalent coupling with phenolic oxidative radicals. Through the above-mentioned dual-enzyme synergistic catalysis, two types of covalent cross-linking bonds, phenol-phenol and phenol-protein, are simultaneously formed in the system, constituting a primary co-cross-linking network covering phenolic and protein components. The bamboo charcoal dual-enzyme is uniformly dispersed in the above cross-linking network system, yielding an adhesive solution containing primary cross-linking intermediates.

[0066] The representative chemical equations for the above reactions are as follows (Ar represents the aromatic ring skeleton of phenolic compounds, and Tyr-Prot represents the benzene ring skeleton of tyrosine residues in soy protein isolate):

[0067] (1) Laccase-catalyzed oxidation of phenolic hydroxyl groups (with) (Oxidizing agent, four-electron main reaction):

[0068]

[0069] (2) Soybean peroxidase catalyzes the oxidation of phenolic hydroxyl groups (in order to...) (for oxidizing agents)

[0070]

[0071] (3) Phenoxy radical coupling bonding (two types):

[0072]

[0073]

[0074] (4a) Enzymatic oxidation of tyrosine residues (represented by SBP; laccase can also directly catalyze the oxidation of tyrosine residues):

[0075]

[0076] (4b) Spontaneous coupling of tyrosine radicals and phenoxy radicals (no enzyme catalysis required, direct binding between radicals):

[0077]

[0078] Step 4: The phased addition of natural clinoptilolite and flaxseed gum

[0079] Step 4.1 Pre-activation and dehydration treatment of clinoptilolite: Take natural clinoptilolite (a natural aluminosilicate mineral with a pore size of 0.4–0.9 nm) and grind it to a particle size of 150 mesh. Place the ground clinoptilolite powder in a calcination furnace and calcine it at 325℃ for 3 hours to remove the pre-adsorbed water and other small molecules in the zeolite pores, so that the zeolite pores are in an unloaded state, and obtain pre-activated and dehydrated clinoptilolite. After cooling to room temperature, seal and store for later use.

[0080] Step 4.2 Addition and dispersion of clinoptilolite: Add pre-activated dehydrated clinoptilolite powder to the adhesive liquid system containing the primary crosslinking intermediate obtained in step 3 at a ratio of 10% of the total mass of the adhesive solids. Stir and disperse the powder thoroughly to ensure that the clinoptilolite particles are uniformly suspended in the adhesive system as solid particles.

[0081] Step 4.3 Addition and hydration of flaxseed gum: In the adhesive system containing clinoptilolite, flaxseed gum powder (a natural polysaccharide gum extracted from flaxseed processing by-products, rich in arabinoxylan and galactomannan) is slowly added to the water-containing adhesive liquid at a ratio of 5% of the total mass of the adhesive solids. The mixture is stirred thoroughly to ensure complete hydration and swelling (stirring for at least 15 minutes until the system forms a uniform gel state). The mixture is then evenly dispersed in the material system to obtain an adhesive containing clinoptilolite solid particles and hydrated gelled flaxseed gum. The adhesive is then allowed to stand for more than 4 hours before application.

[0082] Step 5: Hot pressing curing assisted by clinoptilolite and flaxseed gum

[0083] The adhesive obtained in step four, mixed with clinoptilolite and linseed gum, is applied to the surface of the wood or bamboo substrate. It is then hot-pressed and cured according to standard process parameters for the substrate and board type (hot-pressing temperature 150℃; hot-pressing pressure 2 MPa; hot-pressing time 1.2 min per millimeter of board thickness). The hot-pressing curing process involves the following three stages:

[0084] Hot-pressing heating stage (liquid water desorption and gas adsorption control stage): After entering the hot press, as the temperature of the adhesive layer rises above 100°C, the pre-stored liquid water molecules in the clinoptilolite pores desorb due to heat, and the pores gradually return to an unloaded state; at the same time, a large amount of residual water in the adhesive layer begins to vaporize as the temperature rises, producing water vapor, and a small amount of incompletely consumed water vapor... Thermal decomposition release Both types of gases accumulate within the incompletely cured adhesive layer. The clinoptilolite channels, now restored to an unloaded state (channel size 0.4–0.9 nm, with a water molecule dynamic diameter of 0.28 nm), are shown. (Molecular dynamics, diameter 0.35 nm matched), preferentially captures water vapor and [other molecules] via gas-phase adsorption during the nucleation stage when gas molecules begin to accumulate. This confines the gas molecules within the mineral micropores, blocking the nucleation process of gas molecules accumulating in the colloidal layer to form bubbles.

[0085] Hot-pressing high-temperature holding stage (micropore filling stage): The pressure applied by the hot press keeps the residual moisture in the adhesive layer in a liquid state and slows down the rate of escape. Flaxseed gum (a natural polysaccharide mixture of arabinoxylan and galactomannan) has significantly reduced viscosity and increased fluidity under high temperature and high pressure conditions, allowing it to flow in fully and fill the existing or emerging primary micropore defects in the adhesive layer, thus physically filling and sealing the micropores.

[0086] Hot-pressing and cooling curing stage (structural fixation stage): As the hot-pressing temperature decreases, the viscosity of flaxseed gum increases significantly and its fluidity disappears. The flaxseed gum filling the nascent micropores gels, permanently sealing the filled micropores and forming a dense microstructure. Clinoptilolite mineral particles are simultaneously embedded in the cured adhesive layer, becoming an inorganic filler structural component that combines residual gas adsorption and binding functions with mechanical reinforcement. After hot pressing, a dense, high-strength, formaldehyde-free bio-resin cured adhesive layer without microporous defects is obtained.

[0087] Experimental verification

[0088] Experiment 1: Effects of wood ash alkali activation treatment on the release of free phenolic hydroxyl groups and the bonding strength of boards

[0089] 1. Experimental Objective

[0090] The study verified that the alkali activation pretreatment of wood ash can effectively increase the total content of free phenolic hydroxyl groups in the mixed raw materials of hydrolyzable tannin and lignin sulfonate, and further verified the positive effect of the increase in free phenolic hydroxyl content on the final adhesive bonding strength, proving the necessity of the technical solution of step one for the overall process performance.

[0091] 2. Preparation of experimental samples

[0092] Four groups of samples were prepared. The composition of phenolic raw materials in each group was uniform: hydrolyzable tannins from larch bark and lignin sulfonate were mixed at a dry weight ratio of 5:5, with a total dry weight of 100 g of phenolic raw materials; the mass ratio of soy protein isolate (protein content ≥90%) to phenolic raw materials was 4:6; and the amount of bamboo charcoal dual enzymes (laccase loading of 35 U / g bamboo charcoal and soy peroxidase loading of 20 U / g bamboo charcoal) added was 5% of the total mass of the adhesive solids. The enzyme was added in four batches (every 25 minutes, final concentration 0.06% w / v). The enzyme-catalyzed reaction was carried out for 2 hours at 35℃, pH 6.0, under open aerobic conditions. 10% clinoptilolite (calcined at 325℃ for 3 hours, 150 mesh particle size) and 5% flaxseed gum were added. The hot-pressing conditions were uniformly set at 150℃, 2 MPa, and 1.2 minutes per millimeter of board thickness, with a 12 mm thick medium-density fiberboard substrate. The four groups of samples differed only in the amount of wood ash used in step one and the activation conditions, as detailed below:

[0093] (1) S0 (unactivated control group): Phenolic raw materials are directly added to deionized water for dissolution, without adding wood ash or alkali activation. The pH is adjusted to 6.0 with 15% glacial acetic acid solution and then directly enters process three.

[0094] (2) S1 (low activation intensity group, corresponding to the parameters of Example 1): the amount of wood ash added is 10% of the dry weight of phenolic raw materials, the activation temperature is 25℃, and the activation time is 30 min.

[0095] (3) S2 (preferred activation intensity group, corresponding to the parameters of Example 3): the amount of wood ash added is 15% of the dry weight of phenolic raw materials, the activation temperature is 40℃, and the activation time is 60 min.

[0096] (4) S3 (high activation strength group, corresponding to the parameters of Example 2): the amount of wood ash added is 20% of the dry weight of phenolic raw materials, the activation temperature is 60℃, and the activation time is 120 min.

[0097] 3. Experimental conditions

[0098] The content of free phenolic hydroxyl groups was determined using the Folin-Ciocalteu colorimetric method (absorbance measured at 765 nm, with gallic acid as the standard curve, and results expressed as mmol gallic acid equivalent / g dry weight); the bond strength test was performed according to the tensile shear strength (dry and wet conditions) test method in GB / T9846—2015 "Ordinary Plywood". Six samples were prepared for each group, and the average value was taken. The results were reported as mean ± standard deviation (MPa). Wet strength test conditions: the sample was immersed in hot water at 63℃ for 3 h and then tested immediately.

[0099] 4. Experimental Procedure

[0100] (1) Complete step one according to the above four sets of parameters. After activation, take 5 mL of filtrate sample for Folin-Ciocalteu method to determine the free phenolic hydroxyl content. Adjust the pH of the remaining filtrate and proceed to the subsequent steps. (2) Complete steps two to five according to the same parameters for each group to obtain 12 mm thick medium density fiberboard samples. (3) Determine the dry and wet tensile shear strength of each group according to GB / T 9846.

[0101] 5. Experimental Results

[0102] Table 1-1 Effect of wood ash alkali activation treatment on the content of free phenolic hydroxyl groups

[0103]

[0104] Table 1-2 Tensile shear strength of plates under different alkali activation intensities

[0105]

[0106] Note: GB / T 9846 Class I plywood dry tensile shear strength standard value ≥0.70 MPa.

[0107] Figure 1 The effect of wood ash alkali activation treatment on the release of free phenolic hydroxyl groups;

[0108] Figure 2 Comparison of tensile shear strength of plates under different alkali activation intensities.

[0109] 6. Analysis and Conclusion

[0110] As shown in Table 1-1, the alkali activation treatment of wood ash significantly increased the content of free phenolic hydroxyl groups in the mixed phenolic raw materials: the free phenolic hydroxyl content of group S2 (preferred parameters) was 3.52 mmol / g, which was about 198% higher than that of the unactivated group S0 (1.18 mmol / g). Group S3 further increased to 3.87 mmol / g. However, the difference between S2 and S3 has converged, indicating that under the preferred parameters, the hydrolysis of ester bonds and the cleavage of ether bonds have been sufficient. Excessive alkali activation intensity has limited effect on further increasing the content of free phenolic hydroxyl groups.

[0111] As shown in Table 1-2, the bond strength increases significantly with increasing alkali activation intensity: the dry bond strength of group S0 (unactivated) is only 0.41 MPa, which does not meet the standard for Class I boards (≥0.70 MPa); group S1 has reached 0.78 MPa, barely meeting the standard; the dry and wet bond strengths of group S2 reach 1.82 MPa and 1.21 MPa respectively, both significantly exceeding the standard requirements; group S3 is similar to group S2, verifying the rationality of the optimized activation parameters. The experimental results demonstrate that alkali activation pretreatment with wood ash is one of the necessary technical measures to achieve engineering-grade bond strength.

[0112] Experiment 2: Comparison of batch enzyme activity and stability between bamboo charcoal dual-enzyme co-immobilization system and free laccase

[0113] 1. Experimental Objective

[0114] The results showed that the batch enzyme activity retention rate of the bamboo charcoal dual-enzyme co-immobilization system (bamboo charcoal dual enzyme body) was significantly better than that of free laccase under industrial simulated production conditions, proving the necessity of the technical solution in step two for improving the stability of industrial production.

[0115] 2. Preparation of experimental samples

[0116] Two groups were prepared: (A) Free laccase control group: Laccase was added in free form, with an initial activity value of 100 U / mL; (B) Bamboo charcoal dual enzyme group: Bamboo charcoal dual enzymes were prepared according to the parameters in Example 3 (laccase 35 U / g bamboo charcoal, SBP 20 U / g bamboo charcoal, adsorption by shaking at 10℃ for 4 h, immobilization rate 78%). Both groups were subjected to 10 batches of reaction under the same industrial simulation production conditions (35℃, pH 6.0, continuous stirring at 300 rpm, enzyme catalytic reaction for 2 h per batch). After each batch of reaction, samples were taken, and the residual activity of laccase (absorbance at 420 nm) was determined by ABTS (2,2'-adiazonium[3-ethylbenzothiazoline-6-sulfonic acid]ammonium salt) oxidation method. The relative enzyme activity retention rate of each batch was calculated with the activity of the first batch as 100%.

[0117] 3. Experimental conditions

[0118] The reaction was simulated under industrial production stress: after each batch of reaction, the reaction solution and solid bamboo charcoal double enzyme were placed in a 60°C water bath for 15 min (simulating the thermal stress during the waiting period before hot pressing), and then cooled to 35°C for the next batch of reaction; the free laccase group was added with an equal amount of fresh laccase solution in each batch (without replenishment) to truly reflect the cumulative decay of enzyme activity.

[0119] 4. Experimental Procedure

[0120] (1) Prepare free laccase solution (Group A) and bamboo charcoal double enzyme (Group B), and use the ABTS oxidation activity value of the first batch of laccase as 100% baseline; (2) Conduct 10 batches of reaction continuously under the above simulated industrial conditions. After each batch of reaction, take the supernatant sample (take the supernatant directly for Group A; take the supernatant after centrifugation for Group B), and determine the laccase activity with ABTS substrate at 35℃ (substrate concentration 0.5 mM ABTS, pH 5.0, reaction 3 min, absorbance measured at 420 nm); (3) Calculate the relative enzyme activity retention rate of each batch and draw a line graph.

[0121] 5. Experimental Results

[0122] Table 2-1 Relative enzyme activity retention rate (%) of free laccase and bamboo charcoal dual enzyme in 10 consecutive batches

[0123]

[0124] Note: The free laccase activity in the 10th batch has dropped to 6.2% of the initial value, while the bamboo charcoal dual enzyme retains 71.8%; the batch required for the free laccase activity to drop to 50% is approximately the 4.5th batch, and the activity retention rate of the bamboo charcoal dual enzyme has consistently been above 70% within 10 batches.

[0125] Figure 3 Comparison of batch enzyme activity and stability between free laccase and bamboo charcoal dual enzymes.

[0126] 6. Analysis and Conclusion

[0127] As shown in Table 2-1, free laccase (Group A) exhibited rapid activity degradation under simulated industrial conditions, decreasing to below 50% of its initial activity after only about 4.5 batches, and reaching only 6.2% by the 10th batch. In contrast, the bamboo charcoal dual-enzyme (Group B) retained 71.8% laccase activity after 10 batches, with a significantly lower rate of activity degradation than free laccase (approximately 1 / 6 of the degradation rate of free laccase). These results validate the spatial protection effect of the bamboo charcoal carrier on the dual enzymes, demonstrating its ability to significantly slow down enzyme inactivation rates under continuous industrial production conditions (high temperature, shear force, pH fluctuations), thereby substantially reducing batch enzyme replenishment and production costs, and providing enzyme activity stability assurance for large-scale continuous production.

[0128] Experiment 3: Verification of the effect of pre-activated clinoptilolite and flaxseed gum in synergistically eliminating micropore defects in hot-pressed adhesive layers

[0129] 1. Experimental Objective

[0130] The study verified that the pre-activated clinoptilolite and flaxseed gum synergistic hot-press curing system can effectively eliminate micropore defects in the adhesive layer, significantly improve the density and water-resistant bonding strength of the adhesive layer, and prove the effectiveness of the technical solutions in steps four and five in eliminating micropore defects in hot pressing.

[0131] 2. Preparation of experimental samples

[0132] Based on the complete process parameters (preferred conditions) of Example 3, the only difference was made in the addition of clinoptilolite and linseed gum in step four: a total of 4 groups of adhesive samples were prepared. Steps one through three of the adhesive samples were completely identical, with the only difference being the auxiliary components in step four.

[0133] (1) C0 (blank control): No addition of zeolite or flaxseed gum.

[0134] (2) C1 (only clinoptilolite): add pre-activated dehydrated clinoptilolite (calcined at 325℃ for 3 h, particle size 150 mesh, addition amount 10%) according to the parameters of Example 3, without adding flaxseed gum.

[0135] (3) C2 (Flaxseed gum only): Flaxseed gum (5% addition amount) is added without clinoptilolite, according to the parameters of Example 3.

[0136] (4) C3 (complete process, clinoptilolite + flaxseed gum): Pre-activated dehydrated clinoptilolite (10%) and flaxseed gum (5%) are added simultaneously according to the parameters of Example 3, corresponding to the complete process of Example 3.

[0137] Each group was hot-pressed and cured at 150℃, 2 MPa, and 1.2 min / mm, with a 12 mm thick medium-density fiberboard as the substrate.

[0138] 3. Testing Methods

[0139] (1) Determination of adhesive layer porosity: The board after hot pressing and curing is sliced ​​along the adhesive line section for sample preparation. The microstructure of the adhesive layer is observed using a scanning electron microscope (SEM, accelerating voltage 10 kV, magnification 500×). The SEM cross-sectional images are binarized using image analysis software (ImageJ). The percentage of pore area in each image to the total cross-sectional area of ​​the adhesive layer is calculated. Six fields of view are taken for each group, and the average porosity ± standard deviation is calculated. (2) Determination of adhesive strength: The dry and wet tensile shear strengths are determined according to GB / T 9846 (six samples per group).

[0140] 4. Experimental Results

[0141] Table 3-1 Effects of clinoptilolite and linseed gum on the porosity and bond strength of the adhesive layer

[0142]

[0143] Figure 4 For comparison of SEM cross-sectional morphology;

[0144] Figure 5 A comparison of the porosity of each group of adhesive layers;

[0145] Figure 6 A comparison of the bonding strength of each group of adhesive layers.

[0146] 6. Analysis and Conclusion

[0147] As shown in Table 3-1, the porosity of the adhesive layer in the blank control group (C0) was as high as 18.7%, corresponding to the high porosity of water vapor and... Thermal decomposition The porosity is caused by the free accumulation of bubbles in the uncured adhesive layer; the addition of clinoptilolite (C1) alone reduced the porosity to 9.3%, indicating that the in-situ gas adsorption function of clinoptilolite during the heating stage effectively blocked some bubble nucleation; the addition of linseed gum (C2) alone reduced the porosity to 12.1%, indicating that the high-temperature fluid pore-filling mechanism can block some of the formed primary micropores; while the porosity of the complete process group (C3) with both added together was only 3.2%, which was much lower than any single component treatment, proving that the temporal synergistic effect of the two in the bubble nucleation stage (clinoptilolite) and the pore filling stage (linseed gum) is significantly better than the sum of the individual effects, and has a synergistic effect.

[0148] Correspondingly, the dry bond strength (1.82 MPa) and wet bond strength (1.21 MPa) of group C3 were significantly higher than those of group C0 (1.21 MPa / 0.68 MPa), with a wet strength increase of approximately 78%, demonstrating the significant improvement in water resistance due to increased adhesive layer density. The experimental results prove that the synergistic hot-pressing curing of pre-activated clinoptilolite and linseed gum is a necessary technical measure to achieve a dense adhesive layer free of microporous defects, and the design of steps four and five is technically sound.

[0149] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A process for large-scale production of high-adhesion-strength formaldehyde-free bioresin, characterized in that, Includes the following steps: Hydrolyzable plant tannins and lignin sulfonates were mixed with wood ash at a dry weight ratio of 4:6 to 6:

4. After alkali activation pretreatment in an aqueous solution, the mixture was filtered and the pH was adjusted to 5.5 to 6.5 with glacial acetic acid solution to obtain activated phenolic substrate solution. A bamboo charcoal dual-enzyme co-immobilization complex was prepared by physically adsorbing white-rot fungus laccase and soybean peroxidase onto bamboo charcoal. The activated phenolic substrate solution was mixed with the soy protein isolate solution, and the bamboo charcoal dual-enzyme co-immobilization complex was added in batches. The solution was stirred in an aerobic aqueous solution system at 25–45°C and pH 5.5–6.5 for 1–4 h to form two types of covalent cross-linked networks: phenol-phenol and phenol-protein. Add clinoptilolite activated by calcination at 300-350℃ and flaxseed gum to the above liquid in sequence. Apply the resulting adhesive to the surface of the substrate within 4 hours and hot-press it at 120-180℃ and 1-3 MPa to obtain a formaldehyde-free bio-resin cured adhesive layer.

2. The process according to claim 1, characterized in that, The amount of wood ash added is 10% to 20% of the total dry weight of hydrolyzable plant tannins and lignin sulfonates; the alkali activation pretreatment temperature is 25 to 60℃, and the treatment time is 30 to 120 min; after filtration, the pH of the filtrate is adjusted to 5.5 to 6.5 with a 10% to 20% (v / v) glacial acetic acid aqueous solution.

3. The process according to claim 1, characterized in that, The bamboo charcoal has a particle size of 100-200 mesh. The white-rot fungus laccase and soybean peroxidase are separately prepared into aqueous solutions and then mixed evenly. The bamboo charcoal is added to the above mixed enzyme solution and shaken at 4-25℃ for 2-6 h for adsorption. After centrifugation or filtration to remove the free enzyme in the supernatant, the bamboo charcoal dual-enzyme co-immobilized complex is obtained.

4. The process according to claim 3, characterized in that, The loading capacity of white rot fungi laccase on bamboo charcoal is 20-50 U / g bamboo charcoal, and the loading capacity of soybean peroxidase on bamboo charcoal is 10-30 U / g bamboo charcoal; the enzyme activity unit U is defined as the amount of enzyme required to catalyze the conversion of 1 μmol of substrate per minute under the conditions of 25℃ and pH 5.

0.

5. The process according to claim 1, characterized in that, The soy protein isolate has a protein content of ≥90%, and the mass ratio of soy protein isolate to phenolic raw materials is 3:7 to 5:5; the amount of bamboo charcoal dual-enzyme co-immobilized complex added is 3% to 8% of the total mass of the adhesive solids.

6. The process according to claim 1, characterized in that, The solution was added in equal batches, with an interval of 15–30 minutes between each batch. After each addition, the solution was added to the feed solution. Instantaneous concentration not exceeding 5 mM; The total amount added should bring the final concentration of the liquid to 0.05%–0.1% w / v.

7. The process according to claim 1, characterized in that, Clinoptilolite was calcined at 300–350℃ for 2–4 h to complete pre-activation and dehydration. After grinding, the particle size was 100–200 mesh, and the addition amount was 5%–15% of the total mass of the adhesive solids. The pore size of clinoptilolite was 0.4–0.9 nm, which is similar to the dynamic diameter of water molecules (0.28 nm). The molecular dynamics diameter of 0.35 nm is matched.

8. The process according to claim 1, characterized in that, Flaxseed gum is a natural polysaccharide rich in arabinoxylan and galactomannan. The amount added is 3% to 8% of the total solid content of the adhesive. The interval between adding flaxseed gum to the adhesive system and applying it to the substrate should not exceed 4 hours.

9. The process according to claim 3, characterized in that, Laccase of white-rot fungi in In the process of oxidizing phenolic hydroxyl groups by oxidant catalysis, through Incomplete two-electron reduction side reactions produce a small amount of [unclear - possibly referring to a specific type of reaction] in the local microenvironment of the bamboo charcoal carrier. ,Should Soybean peroxidase immobilized at adjacent sites on a bamboo charcoal carrier is captured in situ. The oxidant catalyzes further oxidative coupling of the phenolic hydroxyl groups; white-rot fungal laccase and soybean peroxidase respectively act as... and As an oxidant, it simultaneously catalyzes the oxidative coupling of the phenolic hydroxyl groups of the substrate through complementary oxidation pathways, forming a higher density phenol-phenol covalent cross-linked network.

10. The process according to claim 1, characterized in that, The hot-press curing process consists of three stages performed sequentially: a hot-pressing heating stage, a pre-activated dehydration stage, and a stage where water vapor within the adhesive layer is captured by the pores of the clinoptilolite. Thermal decomposition releases The two are bound within the mineral micropores, preventing bubble nucleation; during the hot-pressing and high-temperature holding stage, the viscosity of flaxseed gum decreases and its fluidity increases under high temperature and high pressure conditions, flowing into and filling the primary micropores in the gum layer; During the hot-pressing and cooling stage, the flaxseed gum gels permanently seal the filled micropores, and the clinoptilolite particles are embedded in the cured adhesive layer to become inorganic filler structural components.

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