Preparation method and application of konjac bio-based adhesive

Abstract

The application belongs to the technical field of biological adhesives, and particularly relates to a preparation method of a konjac bio-based adhesive and application thereof. The application constructs a high-performance konjac bio-based adhesive through a multi-step aqueous process: firstly, a PVA mother liquor is prepared, high shear is introduced to form a hydrogen bond interpenetrating network with konjac glucomannan, so as to guarantee wettability and early holding force; then, a reversible thixotropic sub-network is constructed by sodium lignosulfonate, tannic acid and kaolin, so as to realize shear thinning and stress buffering; a pre-hydrolyzed silane forms a Si-O-C bridge under weak acid conditions, so as to realize the transition of the interface from physical intercalation to chemical anchoring; a latent crosslinking agent (BTCA / SHP) ensures storage stability, and activates esterification reaction to strengthen the bulk phase when used; silane modified nano-SiO2 forms an inorganic lattice, which cooperates with energy consumption to inhibit cracks; finally, a dense glue line is obtained through vacuum degassing and filtration.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of biological adhesives, and particularly relates to a preparation method of a konjac bio-based adhesive and application thereof. BACKGROUND

[0002] Adhesives, especially wood processing panel adhesives, are indispensable key materials in modern industry and life. However, for a long time, this field has been dominated by petroleum-based tri-aldehyde adhesives such as urea-formaldehyde resin, phenol-formaldehyde resin and melamine-formaldehyde resin. Although such adhesives have excellent bonding performance and cost advantages, their core raw materials rely on non-renewable fossil resources. To address the above challenges, developing an environmentally friendly, low-carbon, bio-based adhesive new system using renewable resources as raw materials has become a core issue that needs to be solved by the academic and industrial communities.

[0003] Among the many biomass candidate materials, the natural polymer konjac glucomannan derived from konjac tubers is considered a highly potential adhesive matrix material due to its rich active hydroxyl groups on the molecular chain, good water solubility and film-forming potential. However, despite its promising prospects, the existing konjac glucomannan-based adhesive solutions still face a series of severe technical bottlenecks. First, its rheological properties are difficult to control, often exhibiting high viscosity and lacking sufficient thixotropy, resulting in difficulties in leveling and spreading during coating and application, and prone to sagging and edge collapse after standing, which cannot form a uniform and dense adhesive layer. Second, its bonding action mainly relies on physical hydrogen bonding and chain entanglement, and the interfacial bonding force, especially the water and moisture resistance, is severely insufficient, and the strength of the bonded area will rapidly decrease in a humid environment. In addition, the large shrinkage rate during drying easily causes internal stress concentration and micro-crack initiation, resulting in a brittle adhesive layer with poor creep resistance and morphology stability. Finally, the chemical cross-linking components introduced to enhance performance often create conflicts between storage stability and user-side curing efficiency, making it difficult to balance the long shelf life of the production end and the convenient and efficient curing requirements of the user end. Therefore, although existing research has made many attempts, simple physical blending or local modification cannot systematically solve the above problems, resulting in obvious deficiencies in the comprehensive performance of konjac bio-based adhesives, especially in early wetting, construction adaptability, strong and durable interfacial bonding, and long-term morphology stability. SUMMARY

[0004] In view of the defects of the prior art, the purpose of the present application is to provide a preparation method of konjac bio-based adhesive and its application. In order to solve the problems of uneven wetting, narrow construction window, easy interface peeling and performance fluctuation of wood-based panel water-based adhesive, the present application proposes a synergistic strategy of water phase step-by-step construction and latent toughening. First, a reproducible PVA mother liquor is prepared by high-temperature dissolution and low-dose pre-foaming, and then konjac glucomannan is introduced by high-shear dispersion and mild hydration to construct a dense hydrogen bond interpenetrating network, which ensures early wetting, holding force and self-adaptive spreading of wood channels; then, water-soluble lignin sulfonate is used to construct a reversible thixotropic sub-network with tannic acid and sheet kaolin, realizing shear thinning, standing rebound, inhibiting sagging and buffering drying shrinkage stress. Under weak acid conditions, pre-hydrolyzed silane is introduced into the system, and stable silicon-oxygen bridges are formed with hydroxyl-containing substrates, realizing the transition from physical intercalation to chemical anchoring and enhancing the interface durability. Multivalent acid / catalyst is incorporated in a latent form, which remains inert during the glue preparation stage to ensure storage stability and open time, and can be activated under subsequent application conditions to complete the conversion from physical network to chemical network; finally, silane modified nano-SiO2 sol is introduced to form a uniform inorganic lattice, which cooperates with the energy consumption of organic segments to inhibit crack propagation and hygrothermal rebound; combined with vacuum degassing and step-by-step filtration, the defect source is eliminated, and the glue line density and consistency are improved.

[0005] The technical effects of the present application are realized by the following technical scheme: a preparation method of konjac bio-based adhesive, specifically comprising the following steps:

[0006] S1: add deionized water to the reaction container, start stirring at 300-400 rpm, heat to 90-95℃, add pre-foaming agent, stir for 1-2 min, then slowly add polyvinyl alcohol, stir for 45-60 min, cool to 70-75℃, obtain the mother liquor;

[0007] S2: cool the mother liquor of step S1 to 25-30℃, start stirring at 2000-3000 rpm, slowly and uniformly add konjac glucomannan in a rain-like manner, uniformly disperse for 10-15 min, then heat to 75-85℃ for 10-20 min, obtain mixed solution A;

[0008] S3: add lignin sulfonate and tannic acid to equal mass volume of 60℃ deionized water, pre-slurry for 10 min, then add the mixed solution A of step S2, stir at 400-500 rpm for 15 min; reduce the temperature to 45-55℃, slowly add powder kaolin, mix at 400 rpm for 10 min, adjust the pH to 4.8-5.2 with citric acid-sodium citrate buffer, obtain mixed solution B;

[0009] S4: γ-glycidoxypropyltrimethoxysilane is added to deionized water, and the pH is adjusted to 4.5-5 with a citric acid-sodium citrate buffer solution. Pre-hydrolysis is carried out at room temperature for 25-40 min to obtain a 10 wt% pre-hydrolysis solution. Then, the pre-hydrolysis solution is slowly added to the mixed solution B of step S3, the temperature is controlled at 45-55°C, and stirring is carried out at 400 rpm for 20-30 min to obtain a mixed solution C;

[0010] S5: Butane tetracarboxylic acid is added to deionized water, heated to 60-70°C in a water bath, and stirred to dissolve uniformly to obtain a 40 wt% BTCA solution. Sodium hypophosphite is added to deionized water, stirred to dissolve uniformly to obtain a 40 wt% SHP solution. The BTCA solution and the SHP solution are sequentially added to the mixed solution C of step S4, the temperature is controlled at 55-65°C, and stirring is carried out at 400-600 rpm for 20-30 min. The pH is adjusted to 4.8-5.3 with a citric acid-sodium citrate buffer solution to obtain a mixed solution D;

[0011] S6: Silane-modified nano-silicon dioxide is added to deionized water, stirred to disperse uniformly to obtain a 20-30 wt% sol. The sol is slowly added to the mixed solution D of step S5, the temperature is controlled at 45-50°C, and stirring is carried out at 400 rpm for 20-30 min. The pH is adjusted to 4.8-5.2 with a citric acid-sodium citrate buffer solution to obtain a mixed solution E;

[0012] S7: The temperature of the mixed solution E of step S6 is controlled to 35-45°C, vacuum defoaming treatment is carried out at -0.06 to -0.08 MPa for 10-15 min, and 80 mesh and 120 mesh filters are sequentially used to obtain a konjac bio-based adhesive;

[0013] Preferably, in step S1, the pre-defoaming agent is prepared by mixing polyether 1740 and hydrogenated castor oil at a mass ratio of 30-40:60-70, heating at 85-90°C, shearing at 2000-3000 rpm for 20-30 min, maintaining the temperature, adding 5% of the total mass of hydrophobic fumed silica, and shearing for another 10 min. The temperature is then cooled to 40-45°C at a rate of 5°C / min, 2% of the total mass of stearyl alcohol is added, and shearing is carried out at 1000-1500 rpm for 10-15 min.

[0014] Preferably, in step S1, the deionized water, pre-defoaming agent, and polyvinyl alcohol are used in a ratio of 50 mL:0.05-0.1 g:8-10 g.

[0015] Preferably, in step S2, the viscosity of the konjac glucomannan is 15000-20000 mPa·s, and the test conditions are a 2% aqueous solution at 25°C.

[0016] Preferably, in step S2, the ratio of the amount of konjac glucomannan to the amount of deionized water in step S1 is 1.5-2 g:50 mL;

[0017] Preferably, in step S3, the ratio of the amount of sodium lignosulfonate, tannic acid, kaolin to the amount of deionized water in step S1 is 3.5-4 g:1.5-2 g:0.35-0.4 g:50 mL;

[0018] Preferably, in step S4, the ratio of the amount of γ-glycidyl ether oxypropyl trimethoxysilane to the amount of deionized water in step S1 is 0.25-0.3 g:50 mL;

[0019] Preferably, in step S5, the ratio of the amount of butane tetracarboxylic acid, sodium hypophosphite to the amount of deionized water in step S1 is 1-1.5 g:0.1-0.15 g:50 mL;

[0020] Preferably, in step S6, the silane-modified nano-silica is obtained by conventional modification of KH560 silane coupling agent, and the specific preparation process is as follows:

[0021] A1: nano-silica is added to a 70% ethanol solution, the pH is adjusted to 4.5-5 with glacial acetic acid, and ultrasonic dispersion is performed to obtain a 10 wt% nanosol;

[0022] A2: γ-glycidyl ether oxypropyl trimethoxysilane is added to a 70% ethanol solution, the pH is adjusted to 4.5-5, and pre-hydrolysis is performed at room temperature for 25-30 min to obtain a 10 wt% silane solution;

[0023] A3: the silane solution of step A2 is slowly added to the nanosol of step A1, kept at 45-55°C, and treated with 200W ultrasonic for 60-90 min with a working time of 3s / stop time of 3s; centrifuged, washed with ethanol and deionized water in turn, and dried at 60°C under vacuum to constant weight to obtain silane-modified nano-silica;

[0024] Preferably, in step A3, the ratio of the volume of the silane solution to the volume of the nanosol is 4-6 mL:100 mL;

[0025] Preferably, in step S6, the ratio of the amount of silane-modified nano-silica to the amount of deionized water in step S1 is 2-3 g:50 mL;

[0026] Preferably, another aspect of the present application is to provide an application of the konjac bio-based adhesive; specifically, the konjac bio-based adhesive of the present application is applied at 120-180 g / m 2 The amount of coating is 120-180 g / m Preheated at 60-80°C for 5 min after opening for 5-10 min, heated to 120-140°C, 0.6-1 MPa warm pressure for 10-25 min, and then placed at room temperature for 16-24 h after decompression.

[0027] The beneficial effects of the present application are as follows:

[0028] Compared with the prior art, the present application builds a continuous and stable glue layer in an aqueous phase system through multi-scale synergy: first, the dissolution by heating and low-dose pre-foaming make polyvinyl alcohol fully dissociate and establish a good film-forming basis; then introduce konjac glucomannan (KGM) by high shear dispersion first and then mild hydration, both of which form a dense interpenetrating network in the aqueous phase through dense hydrogen bonding and chain entanglement, significantly improving wetting and spreading, early holding force, and adaptability to wood ring differences and pore heterogeneity. On this body phase skeleton, by introducing water-soluble sodium lignosulfonate and tannic acid synergistically, and cooperating with the lamellar bridging and electrical neutralization of sheeted kaolin, a reversible thixotropic secondary support subnetwork is built: the viscosity decreases with shear, which is conducive to flow and spread, and the skeleton strength recovers quickly after standing to inhibit sagging and edge collapse, and provides deformation buffer during drying shrinkage, reducing internal stress concentration and micro-crack initiation. On the interface level, γ-glycidyloxypropyltrimethoxysilane is pre-hydrolyzed to active silanol under weak acid conditions, which slowly incorporates into the glue phase and the surface of the hydroxyl-containing substrate to form stable Si-O-Si / Si-O-C bridges, realizing the transition from physical intercalation to chemical anchoring, and making the interface failure mode evolve from brittle peeling to substrate-dominated cooperative fracture, balancing interface strength and water resistance durability. In terms of body phase reinforcement, butane tetracarboxylic acid (BTCA) and catalyst sodium hypophosphite (SHP) are incorporated in a low-dose latent manner, remaining inert during the gel preparation stage to ensure storage stability and controllable viscosity; in a suitable drying / warming environment at the user end, this latent system can be converted into active intermediates and undergo region-selective esterification with polysaccharide / PVA hydroxyl groups, thereby providing activatable chemical network support for subsequent durability and swelling resistance without interfering with the preparation process. The terminal introduction of silane-modified nano-silicon dioxide is uniformly dispersed in the form of sol, forming an inorganic lattice support, and the surface silane layer and organic chain segments establish a multi-level energy consumption channel through hydrogen bonding and van der Waals interaction, deflecting, branching, and passivating crack propagation, significantly improving creep resistance and hygrothermal morphology stability. On the formulation level, by selecting sodium lignosulfonate, controlling the pH in a weak acid environment, and inhibiting excessive ionic strength, the risk of salting out and agglomeration between polyphenols and inorganics is reduced; on the process level, vacuum defoaming and step-by-step fine filtration are used to remove microbubbles and coarse particles, eliminating stress peaks and ensuring the density and repeatability of the glue line. In summary, the present application uses water as the medium, is low in VOC and free of free formaldehyde release, and achieves time and structural synergy in early wetting and pore filling, medium-term thixotropic self-shaping, interface chemical anchoring, latent chemical toughening, and inorganic lattice shaping, balancing initial workability, interface bonding strength, water resistance, and hygrothermal cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1is a shearing strength test result chart of the konjac bio-based adhesive of the present application examples 1-3 and comparative examples 1-4;

[0030] Figure 2 is a wood failure rate test result chart of the konjac bio-based adhesive of the present application examples 1-3 and comparative examples 1-4;

[0031] Figure 3 is a durability shearing strength test result chart of the konjac bio-based adhesive of the present application examples 1-3 and comparative examples 1-4;

[0032] Figure 4 is a durability wood failure rate test result chart of the konjac bio-based adhesive of the present application examples 1-3 and comparative examples 1-4;

[0033] Figure 5 is a long-term stability test result chart of the konjac bio-based adhesive of the present application examples 1 and comparative examples 1-4. DETAILED DESCRIPTION

[0034] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments; without special description, the raw materials involved in the present application are purchased through the conventional commercial channel; the experimental methods without specific conditions are the conventional methods and conventional conditions familiar to the field, or according to the conditions suggested by the instrument manufacturer.

[0035] Example 1: A preparation method of a konjac bio-based adhesive, specifically comprising the following steps:

[0036] S1: 500 mL of deionized water was added to the reaction container, the stirring was started at 350 rpm, the temperature was raised to 92℃, 0.8 g of pre-foaming agent was added, stirring for 1.5 min, then 90 g of polyvinyl alcohol was slowly added, stirring for 55 min, and cooling to 72℃, to obtain a mother liquor;

[0037] S2: The mother liquor of step S1 was cooled to 28℃, the stirring was started at 2500 rpm, 18 g of konjac glucomannan was slowly and evenly added in a rain-like manner, and after uniform dispersion by shearing treatment for 12 min, the temperature was raised to 80℃ and hydrated for 15 min to obtain a mixed solution A;

[0038] S3: 38 g of sodium lignosulfonate and 18 g of tannic acid were added to 56 mL of 60℃ deionized water, pre-slurried for 10 min, then added to the mixed solution A of step S2, stirred at 450 rpm for 15 min; the temperature was lowered to 50℃, 3.8 g of powder kaolin was slowly added, stirred at 400 rpm for 10 min for mixing, and the pH was adjusted to 5 by citric acid-sodium citrate buffer to obtain a mixed solution B;

[0039] S4: 2.8 g of γ-glycidoxypropyltrimethoxysilane was added to 28 mL of deionized water, and the pH was adjusted to 4.8 with a citric acid-sodium citrate buffer. Pre-hydrolysis was performed at room temperature for 35 min to obtain a 10 wt% pre-hydrolysis solution. Then, the pre-hydrolysis solution was slowly added to the mixed solution B of step S3, and stirring was performed at 50°C and 400 rpm for 25 min to obtain a mixed solution C;

[0040] S5: 12 g of butane tetracarboxylic acid was added to 30 mL of deionized water, and stirring was performed to obtain a 40 wt% BTCA solution. 1.2 g of sodium hypophosphite was added to 3 mL of deionized water, and stirring was performed to obtain a 40 wt% SHP solution. The BTCA solution and the SHP solution were sequentially added to the mixed solution C of step S4, and stirring was performed at 60°C and 500 rpm for 25 min. The pH was adjusted to 5 with a citric acid-sodium citrate buffer to obtain a mixed solution D;

[0041] S6: 2.5 g of silane-modified nano-silica was added to 10 mL of deionized water, and stirring was performed to obtain a 25 wt% sol. The sol was slowly added to the mixed solution D of step S5, and stirring was performed at 48°C and 400 rpm for 25 min. The pH was adjusted to 5 with a citric acid-sodium citrate buffer to obtain a mixed solution E;

[0042] S7: The temperature of the mixed solution E of step S6 was controlled to 40°C, and vacuum defoaming was performed at -0.07 MPa for 12 min. Filtration was sequentially performed at 80 mesh and 120 mesh to obtain a konjac bio-based adhesive;

[0043] The pre-defoaming agent was prepared by mixing polyether 1740 and hydrogenated castor oil at a mass ratio of 30:70, heating at 88°C, shearing at 2500 rpm for 25 min, maintaining the temperature, adding 5 g of hydrophobic fumed silica, and shearing for another 10 min. The temperature was cooled to 42°C at a rate of 5°C / min, 2 g of stearyl alcohol was added, and shearing was performed at 1200 rpm for 12 min.

[0044] The silane-modified nano-silica was prepared according to the following procedure:

[0045] A1: 10 g of nano-silica was added to 100 mL of 70% ethanol solution, and the pH was adjusted to 4.7 with glacial acetic acid. Ultrasonic dispersion was performed to obtain a 10 wt% nano-sol;

[0046] A2: 1 g of γ-glycidoxypropyltrimethoxysilane was added to 10 mL of 70% ethanol solution, and the pH was adjusted to 4.7. Pre-hydrolysis was performed at room temperature for 28 min to obtain a 10 wt% silane solution;

[0047] A3: 5 mL silane solution of step A2 was slowly added into 100 mL nanosol of step A1, kept at 50℃, 200W ultrasonic treatment for 80 min, work 3s / stop 3s; centrifuged, washed with ethanol and deionized water in turn, vacuum dried at 60℃ to constant weight, to obtain silane modified nanosilica.

[0048] Example 2: A preparation method of a konjac bio-based adhesive, specifically comprising the following steps:

[0049] S1: 500 mL of deionized water was added to the reaction vessel, the stirring was started at 400 rpm, the temperature was raised to 95℃, 1 g of pre-foaming agent was added, stirred for 2 min, then 100 g of polyvinyl alcohol was slowly added, stirred for 60 min, and cooled to 75℃ to obtain a mother liquor;

[0050] S2: The mother liquor of step S1 was cooled to 25℃, the stirring was started at 3000 rpm, 20 g of konjac glucomannan was slowly and evenly added in a rain-like manner, and shearing treatment was carried out for 10 min to disperse evenly, then the temperature was raised to 85℃ and hydrated for 10 min to obtain a mixed solution A;

[0051] S3: 40 g of sodium lignosulfonate and 20 g of tannic acid were added to 60 mL of deionized water at 60℃, pre-slurried for 10 min, then added to the mixed solution A of step S2, stirred at 500 rpm for 15 min; the temperature was lowered to 55℃, 4 g of powder kaolin was slowly added, stirred at 400 rpm for 10 min to mix, and the pH was adjusted to 5.2 with citric acid-sodium citrate buffer to obtain a mixed solution B;

[0052] S4: 3 g of γ-glycidoxypropyltrimethoxysilane was added to 30 mL of deionized water, the pH was adjusted to 4.5 with citric acid-sodium citrate buffer, and pre-hydrolysis was carried out at room temperature for 40 min to obtain a 10 wt% pre-hydrolysis solution; then slowly added to the mixed solution B of step S3, the temperature was controlled at 55℃, and stirred at 400 rpm for 30 min to obtain a mixed solution C;

[0053] S5: 15 g of butane tetracarboxylic acid was added to 37.5 mL of deionized water, heated to 70℃ in a water bath, and stirred to dissolve uniformly to obtain a 40 wt% BTCA solution; 1.5 g of sodium hypophosphite was added to 3.75 mL of deionized water, stirred to dissolve uniformly to obtain a 40 wt% SHP solution; the BTCA solution and the SHP solution were added to the mixed solution C of step S4 in turn, the temperature was controlled at 65℃, and stirred at 600 rpm for 20 min, and the pH was adjusted to 5.3 with citric acid-sodium citrate buffer to obtain a mixed solution D;

[0054] S6: 30 g of silane-modified nano-silica was added into 100 mL of deionized water, stirred and dispersed uniformly to obtain a 30 wt% sol; the sol was slowly added into the mixed solution D of step S5, the temperature was controlled at 50°C, 400 rpm stirring was performed for 30 min, the pH was adjusted to 5.2 by citric acid-sodium citrate buffer to obtain a mixed solution E;

[0055] S7: the temperature of the mixed solution E of step S6 was controlled to 45°C, vacuum defoaming treatment was performed for 15 min at -0.08 MPa, and 80 mesh and 120 mesh step-by-step filtration was performed to obtain a konjac bio-based adhesive;

[0056] The pre-foaming agent was prepared by mixing polyether 1740 and hydrogenated castor oil at a mass ratio of 35:65, heating at 90°C, shearing at 3000 rpm for 20 min, maintaining the temperature, adding 4.5 g of hydrophobic fumed silica with a total mass, and shearing for 10 min again, cooling to 40°C at a speed of 5°C / min, adding 1.8 g of stearyl alcohol, and shearing at 1500 rpm for 10 min;

[0057] The silane-modified nano-silica was prepared according to the following process:

[0058] A1: 10 g of nano-silica was added into 100 mL of 70% ethanol solution, the pH was adjusted to 4.5 by glacial acetic acid, and ultrasonic dispersion was performed to obtain a 10 wt% nano-sol;

[0059] A2: 1 g of γ-glycidyl ether propyltrimethoxysilane was added into 10 mL of 70% ethanol solution, the pH was adjusted to 4.5, and pre-hydrolysis was performed at room temperature for 30 min to obtain a 10 wt% silane solution;

[0060] A3: 6 mL of the silane solution of step A2 was slowly added dropwise into 100 mL of the nano-sol of step A1, the temperature was maintained at 55°C, 200 W ultrasonic treatment was performed for 90 min with a working time of 3 s and a stop time of 3 s; centrifugation, ethanol and deionized water were sequentially washed, and vacuum drying was performed at 60°C until the weight was constant to obtain silane-modified nano-silica.

[0061] Example 3: A preparation method of a konjac bio-based adhesive, specifically comprising the following steps:

[0062] S1: 500 mL of deionized water was added into a reaction container, stirring was started at 300 rpm, the temperature was raised to 90°C, 0.5 g of pre-foaming agent was added, stirring was performed for 1 min, then 80 g of polyvinyl alcohol was slowly added, stirring was performed for 45 min, and the temperature was cooled to 70°C to obtain a mother liquor;

[0063] S2: The mother liquor of step S1 is cooled to 30°C, stirring is started at 2000 rpm, 15 g of konjac glucomannan is added slowly and evenly in a rain-like manner, and after uniform dispersion by shearing treatment for 15 min, the temperature is raised to 75°C and hydrated for 20 min to obtain mixed solution A;

[0064] S3: 35 g of sodium lignosulfonate and 15 g of tannic acid are added to 50 mL of deionized water at 60°C, pre-slurried for 10 min, and then added to the mixed solution A of step S2, stirred at 400 rpm for 15 min; the temperature is lowered to 45°C, 3.5 g of powder kaolin is slowly added, stirred at 400 rpm for 10 min, mixed, the pH is adjusted to 4.8 with citric acid-sodium citrate buffer, and mixed solution B is obtained;

[0065] S4: 2.5 g of γ-glycidoxypropyltrimethoxysilane is added to 25 mL of deionized water, the pH is adjusted to 5 with citric acid-sodium citrate buffer, and pre-hydrolysis is carried out at room temperature for 25 min to obtain a 10 wt% pre-hydrolysis solution; then slowly dropwise added to the mixed solution B of step S3, control the temperature at 45°C, 400 rpm stirring for 20 min, to obtain mixed solution C;

[0066] S5: 10 g of butane tetracarboxylic acid is added to 25 mL of deionized water, heated to 60°C in a water bath, and stirred to dissolve evenly to obtain a 40 wt% BTCA solution; 1 g of sodium hypophosphite is added to 2.5 mL of deionized water, stirred to dissolve evenly to obtain a 40 wt% SHP solution; the BTCA solution and the SHP solution are sequentially added to the mixed solution C of step S4, the temperature is controlled at 55°C, 400 rpm stirring for 30 min, the pH is adjusted to 4.8 with citric acid-sodium citrate buffer, and mixed solution D is obtained;

[0067] S6: 20 g of silane-modified nano-silica is added to 100 mL of deionized water, stirred and dispersed evenly to obtain a 20 wt% sol; the sol is slowly added to the mixed solution D of step S5, the temperature is controlled at 45°C, 400 rpm stirring for 20 min, the pH is adjusted to 4.8 with citric acid-sodium citrate buffer, and mixed solution E is obtained;

[0068] S7: The temperature of the mixed solution E of step S6 is controlled to 35°C, vacuum degassing treatment is carried out at -0.06 MPa for 10 min, and 80 mesh and 120 mesh are sequentially filtered to obtain a konjac bio-based adhesive;

[0069] The pre-antifoaming agent is prepared by mixing polyether 1740 and hydrogenated castor oil at a mass ratio of 40:60, heating at 85°C, shearing at 2000 rpm for 30 min, maintaining the temperature, adding 4.5 g of hydrophobic fumed silica with a total mass, shearing again for 10 min, cooling to 45°C at a speed of 5°C / min, adding 1.8 g of stearyl alcohol, shearing at 1000 rpm for 15 min, and preparing;

[0070] The silane-modified nano-silica is prepared according to the following specific process:

[0071] A1: 10 g of nano-silica is added to 100 mL of 70% ethanol solution, the pH is adjusted to 5 with glacial acetic acid, and ultrasonic dispersion is performed to obtain a 10 wt% nano-sol;

[0072] A2: 1 g of γ-glycidoxypropyltrimethoxysilane is added to 10 mL of 70% ethanol solution, the pH is adjusted to 5, and pre-hydrolysis is performed at room temperature for 25 min to obtain a 10 wt% silane solution;

[0073] A3: 4 mL of the silane solution of step A2 is slowly added to the 100 mL nano-sol of step A1, 45°C is maintained, 200 W ultrasonic treatment is performed for 60 min with a working time of 3 s and a stop time of 3 s; centrifugation, ethanol and deionized water are sequentially washed, and vacuum drying is performed at 60°C until a constant weight is obtained to obtain silane-modified nano-silica.

[0074] Comparative Example 1: The process route and parameters of Comparative Example 1 are basically the same as those of Example 1, the main difference being that in step S2 of Comparative Example 1, the high-shear dispersion and hydration conditions are adjusted to: the stirring speed is reduced to 800 rpm, and the hydration temperature is adjusted to 60°C; the remaining steps and parameters remain the same as those of Example 1.

[0075] Comparative Example 2: The process route and parameters of Comparative Example 2 are basically the same as those of Example 1, the main difference being that in step S3 of Comparative Example 2, the sodium lignosulfonate is replaced with an equal amount of lignin, and the same pre-slurry time as in Example 1 is used; the remaining steps and parameters remain the same as those of Example 1.

[0076] Comparative Example 3: The process route and parameters of Comparative Example 3 are basically the same as those of Example 1, the main difference being that in step S4 of Comparative Example 3, the pre-hydrolysis process of γ-glycidoxypropyltrimethoxysilane is cancelled, and an equal amount of silane is directly added to the mixed solution B; the remaining steps and parameters remain the same as those of Example 1.

[0077] Comparative Example 4: The process route and parameters of Comparative Example 4 are basically the same as those of Example 1, the main difference being that in step S6, the silane-modified nano-silica is replaced with nano-silica; the remaining steps and parameters remain the same as those of Example 1.

[0078] Performance Testing: It should be noted that the specific parameters within the above application range can be selected according to the heat resistance of the substrate and the capabilities of the equipment. To ensure that all test samples are compared under the same process conditions, the following adhesive application and temperature-pressing conditions are uniformly adopted in both the embodiments and comparative examples of this invention; the konjac bio-based adhesive of this invention is applied at 160 g / m³. 2 Apply the coating solution, open for 10 minutes, preheat at 70°C for 5 minutes, then pressurize at 130°C and 0.8MPa for 20 minutes, depressurize, and let stand and cool for 24 hours.

[0079] Volatilization Test: Total Volatilization Loss on Drying Test: The film samples (100mm×100mm) of Examples 1-3, which had been cured for 24 hours, were dried in an oven at 105℃ for 60 minutes (weighed before drying after 24 hours of curing), cooled to room temperature, and weighed. The total volatile matter (TVS) was calculated as (mass before drying - mass after drying) / mass before drying × 100%. At the same time, the content of volatile organic compounds (VOCs), formaldehyde, and total benzene compounds in the konjac bio-based adhesive samples of Examples 1-3 were measured according to GB / T 14074-2017 (results of formaldehyde <0.05mg / kg were marked as not detected, and results of total benzene compounds <0.01mg / kg were marked as not detected). The test results are shown in Table 1 below.

[0080] Table 1. Volatilization test results of konjac bio-based adhesives in the examples.

[0081]

[0082] Based on the results in Table 1, the konjac bio-based adhesive prepared in this invention possesses excellent environmental protection characteristics; the total amount of formaldehyde and benzene compounds was undetectable, while the content of volatile organic compounds (VOCs) was controlled at an extremely low level, and the total volatile matter (TVS) was also kept at a low level; these results are highly consistent with the formaldehyde-free, water-based formulation design concept adopted in this invention, and fully meet the safety and environmental protection requirements for high-performance bio-based adhesives.

[0083] Adhesion test: The test samples were the konjac bio-based adhesives of Examples 1-3 and Comparative Examples 1-4; lap joints were prepared using wood samples of the same tree species (poplar), with dimensions of 100mm×20mm×5mm and an overlap area of ​​10mm×20mm; after sample preparation, the samples were placed in an environment of 25℃ and 50%RH for 24 hours to equilibrate; dry strength (with an unactivated control group, i.e., the konjac bio-based adhesive of this invention at 160g / m²) was measured. 2The amount of coating, after 10 min open 50 ℃ preheating 5 min, 80 ℃, 0.8 MPa warm pressure 20 min, after pressure relief and cooling for 24 h, on the universal testing machine with 5 mm / min crosshead speed to stretch to break, record the shear strength (MPa) and wood failure rate WFP (%) =(wood failure area / total bonding area) x 100%; wet strength, the sample is immersed in 20 ℃ deionized water for 24 h, after taking out, with filter paper to absorb the surface excess water, within 10 min to complete the shear strength test, record the shear strength (MPa) and wood failure rate WFP (%); high temperature strength, the sample is balanced in 80 ℃ constant temperature box for 2 h, then directly shear test under this high temperature condition with 5 mm / min loading speed, record the shear strength (MPa) and wood failure rate WFP (%), shear strength test results as shown in Figure 1 Figure 2, wood failure rate test as shown in Figure 2 Figure 3.

[0084] Based on Figure 1 and Figure 2The results show that the konjac bio-based adhesive prepared by the application has excellent shear strength and wood failure rate in dry state / wet state / high temperature test. After the BTCA / SHP latent system is activated and regionally selective esterification with PVA / KGM hydroxyl, the dense PVA / KGM interpenetrating framework and the uniform glue line provided by the polyphenol-kaolin thixotropic subnetwork form a stronger binding force. The shear strength and wood failure rate of Comparative Example 1 are significantly reduced at the S2 stage, that is, the dispersion and hydration intensity are reduced. Even if the BTCA / SHP is activated at 130 DEG C, the loose interpenetrating network and fisheye defects caused by insufficient hydration of konjac glucomannan (KGM) still become weak bands irreversibly. In wet state and high temperature shear, these areas are prone to water softening and stress concentration, thereby limiting the benefits brought by esterification, and finally showing a significant decrease in wet state shear strength and WFP. In Comparative Example 2, the unsulfonated lignin is used to replace sodium lignosulfonate, and the dry state, wet state and high temperature strength and WFP are systematically inferior to those of Example 1. This may be due to the poor solubility and dispersion stability of unsulfonated lignin in weakly acidic water, which easily causes local aggregation, hinders the uniform coupling of tannic acid and the matrix network, and finally forms a rough and uneven thixotropic network. This structural defect leads to a decrease in glue application uniformity, an increase in micro defects in the glue layer and an interface stress concentration, thereby causing a comprehensive decline in bonding performance. In Comparative Example 3, the silane pre-hydrolysis step is cancelled, and the high temperature shear strength and WFP decrease most significantly. This may be due to the fact that the unprehydrolyzed silane is more prone to self-condensation, thereby reducing the density and efficiency of the Si-O-Si / Si-O-C covalent bridge formed with the wood surface. Although the esterification can improve the bulk cohesion, the interface anchoring is still mainly physical embedding. This weak interface structure is more prone to failure at high temperatures, so its high temperature performance is the worst. In Comparative Example 4, unmodified nano-SiO2 is used, and its wet state and high temperature strength are significantly inferior to those of Example 1. This may be due to the fact that in a weakly acidic and ion environment containing carboxylic acid / buffer salt, the unmodified SiO2 sol is more prone to aggregation, causing thixotropic abnormalities and viscosity fluctuations, and forming local stress concentration points. At the same time, due to the lack of Si-O-C interface synergy mediated by silane, the system is difficult to build a uniform and effective inorganic-organic hybrid energy dissipation network. Therefore, the glue layer has insufficient anti-creep and anti-crack propagation ability when immersed in water or heated, resulting in a significant decrease in performance.

[0085] Durability test: the tested samples are konjac bio-based adhesives of Examples 1-3 and Comparative Examples 1-4; wet-heat cycle: 40℃, 95%RH to 23℃, 50%RH, 24h for each cycle, 5 cycles in total (10 days in total), after the cycle, 2h at 25℃, 50%RH and test the shear strength and wood failure rate WFP(%); hot water boiling cycle: the sample is boiled in 100℃ hot water for 2h, dried at 60℃ for 16h, then boiled in 100℃ hot water for 2h, after the cycle, 2h at 25℃, 50%RH and test the shear strength and wood failure rate WFP(%), the test results are shown in Figure 3 and Figure 4 .

[0086] Based on the results of analysis, Figure 3 and Figure 4 , the konjac bio-based adhesives prepared by the present application have excellent durability, and still maintain high residual shear strength and WFP in the wet-heat cycle and hot water boiling cycle. The short board of Comparative Example 1 is still concentrated in the wet-heat cycle; the network loosening and fisheye / micellar caused by insufficient hydration of konjac glucomannan in the early stage become the preferential channel and the starting point of crack initiation in the circulating water, even if esterification occurs, the gain is offset by these structural defects, and the residual strength and WFP after wet-heat are limited in the improvement range. Comparative Example 2 still shows a systematic decline in the two types of durability tests: poor compatibility and phase separation caused by unsulfonated lignin destroy the continuity of the polyphenol-high clay thixotropic subnetwork, the rigid particle / phase interface becomes a stress concentration point under the coupling of wet-heat and boiling water, limiting the improvement range of esterification on water resistance and durability, and finally showing lower residual strength and WFP than Example 1. The durability short board of Comparative Example 3 is particularly obvious in the boiling cycle; although the bulk phase is enhanced due to esterification, the low interface chemical anchoring density is still the decisive factor, in the 100℃ boiling water condition, the interface first micro-detaches and guides the rapid expansion of the crack, and the WFP and strength decrease synchronously, verifying the key role of pre-hydrolysis silane-interface bridging in durability. Comparative Example 4 lags behind Example 1 in both wet-heat and boiling cycles; the colloidal stability of unmodified SiO2 and the lack of interface synergy cause local agglomeration and rigidity defects, reducing the efficiency of inorganic-organic synergistic energy consumption and cross-scale stress dispersion, even if the bulk phase esterification is enhanced, it is also difficult to make up for this short board, so the residual strength and WFP improvement range is still less than that of Example 1.

[0087] Long-term stability test: the tested samples are konjac bio-based adhesives of Examples 1 and Comparative Examples 1-4; 10g of liquid adhesive sample is stored at 50℃, 80%RH for 6 months, and sampled at 1st, 2nd, 3rd and 6th month, and the change of volatile organic compounds VOCs content in the glue is analyzed by gas chromatography-mass spectrometry, the results are shown in Figure 5 .

[0088] Based on the results of analysis, Figure 5The results show that the konjac bio-based adhesive prepared in the embodiment of the present application has a significantly reduced tendency of continuous release in the subsequent storage stage after the pre-hydrolysis of GPTMS is basically completed in the weak acid window, and the overall performance shows excellent stability. In the comparative example 1, the PVA / KGM interpenetrating network framework formed is loose and has uneven microstructure due to insufficient hydration of konjac glucomannan, and the fish eyes and micelles are more prone to slow degradation and interface desorption under high temperature and high humidity storage conditions, which promotes the gradual release of small molecules (such as residual ethanol, organic acid salt byproducts, etc.) coated therein; at the same time, the thixotropic network reconstruction ability is weak and the internal free volume fraction is large, which together cause the VOCs content to increase significantly with storage time. In the comparative example 2, the unsulfonated lignin used has poor compatibility and charge stability in the weak acid aqueous phase, and is prone to form coarse particles and phase separation; these interface regions not only become desorption sites for small molecules during storage, but also serve as a secondary source of slow oxidation and hydrolysis reactions, continuously releasing trace amounts of phenolic and low molecular organic substances, resulting in VOCs content higher than that of the embodiment 1 since the first month, and showing a continuous growth trend. In the comparative example 3, the silane pre-hydrolysis step is cancelled, and the unhydrolyzed silane continuously undergoes self-condensation and side reactions during storage, constantly generating low molecular alcohol, ether volatile substances; at the same time, due to the insufficient interface chemical anchoring effect, the desorption rate of the interface adsorbed components is increased, and both of them together cause the VOCs content of this group to have the highest initial value and the largest growth rate. In the comparative example 4, the unmodified nano-SiO2 has poor colloidal stability in the weak acid and high ionic strength system, and there is a dynamic process of aggregation-redispersion, which is accompanied by the desorption-adsorption cycle of interface adsorbed molecules; in addition, the lack of Si-O-C covalent bridging and strong hydrogen bond synergistic effect causes the local free volume and interface energy to increase, which together promotes the monthly increase of VOCs content.

[0089] Although embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a konjac bio-based adhesive, characterized in that, Specifically comprising the following steps: S1: adding deionized water to the reaction vessel, starting stirring, warming up, adding pre-foaming agent, stirring, then slowly adding polyvinyl alcohol, stirring, cooling, obtaining mother liquor; S2: cooling the mother liquor of step S1 to 25-30℃, starting stirring at 2000-3000 rpm, slowly and evenly adding konjac glucomannan in a rain-like manner, uniformly dispersing after shearing treatment for 10-15 min, warming up to 75-85℃, hydrating for 10-20 min, obtaining mixed solution A; S3: adding sodium lignosulfonate and tannic acid to deionized water, pre-slurrying, then adding mixed solution A of step S2, stirring; reducing temperature, slowly adding powder kaolin, stirring and mixing, adjusting pH with citric acid-sodium citrate buffer, obtaining mixed solution B; S4: adding γ-glycidyl ether oxypropyl trimethoxysilane to deionized water, adjusting pH with citric acid-sodium citrate buffer, pre-hydrolyzing at room temperature, obtaining pre-hydrolysis solution; then slowly adding to mixed solution B of step S3, controlling temperature, stirring, obtaining mixed solution C; S5: adding butane tetracarboxylic acid to deionized water, heating to 60-70℃ in water bath, stirring to dissolve uniformly, obtaining 40wt% BTCA solution; adding sodium hypophosphite to deionized water, stirring to dissolve uniformly, obtaining 40wt% SHP solution; adding BTCA solution and SHP solution to mixed solution C of step S4 in sequence, controlling temperature to 55-65℃, stirring at 400-600 rpm for 20-30 min, adjusting pH to 4.8-5.3 with citric acid-sodium citrate buffer, obtaining mixed solution D; S6: adding silane-modified nano-silicon dioxide to deionized water, stirring to disperse uniformly, obtaining 20-30wt% sol; slowly adding the sol to mixed solution D of step S5, controlling temperature to 45-50℃, stirring at 400 rpm for 20-30 min, adjusting pH to 4.8-5.2 with citric acid-sodium citrate buffer, obtaining mixed solution E; S7: controlling temperature of mixed solution E of step S6 to 35-45℃, vacuum degassing at -0.06 to -0.08 MPa for 10-15 min, filtering step by step at 80 mesh and 120 mesh, obtaining konjac bio-based adhesive.

2. The method for preparing a konjac bio-based adhesive according to claim 1, characterized in that, In step S1, the pre-foaming agent is prepared by mixing polyether 1740 and hydrogenated castor oil at a mass ratio of 30-40:60-70, heating at 85-90℃, shearing at 2000-3000 rpm for 20-30 min, maintaining temperature, adding 5% of total mass of hydrophobic fumed silica, shearing for another 10 min, cooling to 40-45℃ at a speed of 5℃ / min, adding 2% of total mass of stearyl alcohol, shearing at 1000-1500 rpm for 10-15 min.

3. The method for preparing a konjac bio-based adhesive according to claim 2, characterized in that, In step S1, the amount ratio of deionized water, pre-foaming agent and polyvinyl alcohol is 50 mL:0.05-0.1 g:8-10 g.

4. The method for preparing a konjac bio-based adhesive according to claim 3, characterized in that, In step S2, the viscosity of the konjac glucomannan is 15000-20000 mPa·s, the test condition is 2% aqueous solution, 25℃; the ratio of the amount of the konjac glucomannan to the deionized water in step S1 is 1.5-2 g:50 mL.

5. The method for preparing a konjac bio-based adhesive according to claim 4, characterized in that, In step S3, the ratio of the amount of sodium lignosulfonate, tannic acid, kaolin and the deionized water in step S1 is 3.5-4 g:1.5-2 g:0.35-0.4 g:50 mL.

6. The method for preparing a konjac bio-based adhesive according to claim 5, characterized in that, In step S4, the ratio of the amount of γ-glycidyl ether oxypropyl trimethoxysilane and the deionized water in step S1 is 0.25-0.3 g:50 mL.

7. The method for preparing a konjac bio-based adhesive according to claim 6, characterized in that, In step S5, the ratio of the amount of butane tetracarboxylic acid, sodium hypophosphite and the deionized water in step S1 is 1-1.5 g:0.1-0.15 g:50 mL.

8. The method for preparing a konjac bio-based adhesive according to claim 7, characterized in that, In step S6, the silane-modified nano-silica is prepared according to the following procedure: A1: nano-silica is added into 70% ethanol solution, the pH is adjusted to 4.5-5 with glacial acetic acid, and ultrasonic dispersion is performed to obtain 10 wt% nano-sol; A2: γ-glycidyl ether oxypropyl trimethoxysilane is added into 70% ethanol solution, the pH is adjusted to 4.5-5, and pre-hydrolysis is performed at room temperature for 25-30 min to obtain 10 wt% silane solution; A3: the silane solution in step A2 is slowly added dropwise into the nano-sol in step A1, 200 W ultrasonic treatment is performed at 45-55℃ for 60-90 min with 3 s working and 3 s stopping, centrifugation is performed, ethanol and deionized water are sequentially washed, and 60℃ vacuum drying is performed to constant weight to obtain silane-modified nano-silica; In step A3, the volume ratio of the amount of the silane solution to the nano-sol is 4-6 mL:100 mL.

9. The method for preparing a konjac bio-based adhesive according to claim 8, characterized in that, In step S6, the ratio of the amount of the silane-modified nano-silica to the deionized water in step S1 is 2-3 g:50 mL.

10. The application of the konjac bio-based adhesive prepared by the preparation method in any one of claims 1-9 in wood processing adhesive.

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