Composite curing agent, pMDI composite adhesive, shaving board and preparation method of shaving board

Abstract

The invention discloses a composite curing agent, a pMDI composite adhesive, a shaving board and a preparation method of the composite curing agent, relates to the technical field of manufacturing of curing agents for wood, and solves the problems of uncontrollable reaction rate and insufficient bonding strength. The curing agent is prepared by compounding an amino polyol intermediate, a polyethylene glycol derivative and a delayed catalyst. The invention also discloses a preparation method of the curing agent. A delayed amino reaction site is constructed through accurate regulation and control of an amine value, a hydroxyl-amino-carboxyl three-gradient reaction center is constructed, sequential control of a stage I (hydroxyl pre-crosslinking), a stage II (amino main crosslinking) and a stage III (interface bonding) is realized, and a three-stage spontaneous gradient curing reaction is formed. Through precise design of a chemical structure level and sequential control of reaction kinetics, on the premise that the performance of the pMDI adhesive is not sacrificed, the working life is remarkably prolonged, the bonding efficiency and the plate quality are improved, and an economical and feasible technical scheme is provided for formaldehyde-free production of shaving boards.

Description

Technical Field

[0001] This invention relates to the field of adhesives for engineered wood products, specifically to a composite curing agent, a pMDI composite adhesive, particleboard, and a method for preparing the same. Background Technology

[0002] Particleboard, as one of the main types of engineered wood products, is widely used in furniture manufacturing, interior decoration, and building packaging due to its advantages such as wide availability of raw materials, relatively low cost, and adjustable physical and mechanical properties. The core process of particleboard production involves bonding wood or non-wood shavings together with adhesives under heat and pressure to form a board. Therefore, the performance of the adhesive directly determines the final quality, production efficiency, and cost control of the particleboard.

[0003] Among numerous adhesives, polyurethane adhesives, especially polydiphenylmethane diisocyanate (pMDI), have become an important choice for the production of high-end particleboard, particularly moisture-resistant, flame-retardant, and lightweight high-strength boards, due to their excellent bonding performance, low application rate, superior water resistance, and good chemical reactivity with lignocellulose. The curing process of pMDI essentially involves a chemical reaction between its terminal isocyanate groups (-NCO) and the active hydrogen components such as moisture and hydroxyl groups in the wood material, forming a polyurea and polyurethane network structure, thereby achieving a strong bond.

[0004] However, in actual industrial production, especially in continuous flat pressing or large-format hot pressing processes, the application of pMDI adhesive systems still faces two prominent technical challenges: (1) The curing reaction rate is difficult to control precisely: pMDI has extremely high reactivity with wood components, especially in the early stage of hot pressing, the reaction rate is too fast. This causes the adhesive to gel rapidly on the surface of the wood chips, prematurely consuming a large number of active -NCO groups, thus hindering its effective penetration and diffusion into the wood chips. As a result, the bonding of the core layer of the board is incomplete, the curing network is uneven, and the overall internal bond strength (IB) of the board is affected. It may also lead to delamination or deformation due to stress concentration. On the other hand, if the reaction is blindly delayed in order to improve penetration, the hot pressing cycle will be significantly prolonged, energy consumption will be increased, and production efficiency will be reduced. At present, it is mainly adjusted by adding a small amount of water or a general-purpose catalyst. However, this method has problems such as narrow control range, nonlinear response, and poor adaptability to fluctuations in production process (such as changes in temperature and raw material moisture content), which leads to uncontrollable reaction rate and difficulty in ensuring product quality stability.

[0005] (2) Insufficient bonding strength and toughness: Although the polyurethane / polyurea network formed by pMDI has high strength, its cross-linking density is high and the network uniformity is significantly affected by the reaction process. If the curing process is too fast, it is easy to form a local brittle structure and the stress buffering capacity at the interface with wood is weak. This will cause the particleboard, especially when subjected to wet and dry cycles, thermal shock or long-term load, to show insufficient bonding strength. Specifically, although the modulus of elasticity is high, the breaking toughness is poor, and the potential of static bending strength (MOR) and internal bond strength (IB) is not fully realized, affecting the durability and applicability of the board.

[0006] Currently, there are also some curing agents for polymeric diphenylmethane diisocyanate (pMDI) adhesive systems. For example, patent application CN119775522A discloses a curing agent for formaldehyde-free substrates, which consists of the following components by weight percentage: methyl ethyl ketone oxime 5-10 wt%, polyacrylamide 20-30 wt%, and the balance water. This method aims to solve the problems of low production capacity and low moisture content leading to dimensional instability in the production of formaldehyde-free flooring substrates (using pMDI). It adopts a "delay-trigger" control approach, which to some extent extends the pot life, improves the dispersibility of the spray adhesive, increases hot pressing efficiency, and shortens the hot pressing time. However, the reaction rate is heavily dependent on temperature, and the precision and adaptability of the hot pressing process control are limited. Furthermore, it does not fundamentally change or enhance the polyurethane / polyurea network structure formed after pMDI curing. At the same time, since the solution does not introduce new components that can toughen, improve stress distribution, or form an interpenetrating network, its ability to solve the problem of local brittleness caused by excessively fast curing rate and the incomplete realization of strength potential due to network inhomogeneity is limited.

[0007] Therefore, developing a novel composite curing agent specifically for pHI adhesives in particleboard has become an urgent technical challenge to be solved in this field. This is of great significance for promoting the wider application of pHI in the particleboard industry, improving board quality, reducing production costs, and achieving green manufacturing. Summary of the Invention

[0008] To address the above shortcomings, this invention provides a composite curing agent, a pMDI composite adhesive, particleboard, and its preparation method, which is formulated from an amino polyol intermediate, a polyethylene glycol derivative, and a delayed catalyst. By precisely controlling the amine value to 135-165 mg KOH / g, utilizing the carboxyl-assisted catalysis of the polyethylene glycol derivative, and employing the temperature-responsive network of the delayed catalyst, a hydroxyl-amino-carboxyl three-gradient curing reaction center is constructed, achieving time-sequential control of stage I (hydroxyl pre-crosslinking), stage II (amino main crosslinking), and stage III (interfacial bonding). The curing agent, when mixed with pMDI, has a pot life of 3.5-4.5 hours, and the internal bond strength of the pressed eucalyptus particleboard is ≥1.85 MPa, with a 24-hour water absorption thickness swelling rate ≤7.0%. This solves the technical problems of uncontrollable reaction rate and insufficient adhesive strength. The specific technical solution is as follows: A composite curing agent, the composite curing agent comprising the following raw materials: Component A: Amino polyol intermediate; Component B: Polyethylene glycol derivative; Component C: Delayed catalyst; The mass ratio of component A, component B, and component C is 100:(28-35):(1.0-1.5).

[0009] Preferably, the amine polyol intermediate has an amine value of 135–165 mg KOH / g and is prepared by a ring-opening reaction of ethylene oxide and triethanolamine at a molar ratio of 1:(1.8–2.2). Specifically, triethanolamine and ethylene oxide are reacted in a closed reactor at 75–85°C and 0.25–0.35 MPa for 3.5–4.5 h. The amine value of the product is reduced to 135–165 mg KOH / g by controlling the amount of ethylene oxide fed.

[0010] Preferably, the polyethylene glycol derivative has an acid value of 55-75 mg KOH / g and is prepared by compounding polyethylene glycol monomethyl ether (Mn=350-450) and maleic anhydride at a hydroxyl / anhydride molar ratio of 1:(0.4-0.6) and carrying out an esterification reaction at 115-125°C for 2.5-3.5 h under the action of p-toluenesulfonic acid catalyst.

[0011] Preferably, the delayed catalyst is a mixture of bismuth isooctanoate and zinc isooctanoate in a molar ratio of 1:(1.5-2.0), which is then complexed with acetylacetone at 80-90°C for 1.5-2.5 hours to form a tetracoordinate complex. The molar ratio of acetylacetone to the sum of bismuth isooctanoate and zinc isooctanoate is (1.8-2.2):1.

[0012] Preferably, the delayed catalyst has a catalytic activity inhibition rate of ≥80% at ≤100℃ and a catalytic activity recovery rate of ≥85% at ≥160℃.

[0013] Preferably, the viscosity of the composite curing agent at 25°C is 185–215 mPa·s.

[0014] Preferably, a method for preparing a composite curing agent as described above includes the following steps: (1) Preparation of component A: Under nitrogen protection, triethanolamine was first added to a high-pressure reactor according to the molar ratio, the temperature was raised to 80±5℃, ethylene oxide was slowly introduced, the reaction pressure was controlled at 0.3±0.05MPa, and after 4.0±0.5h the reaction was completed, an amino polyol intermediate was generated, and component A was obtained. (2) Preparation of component B: According to the molar ratio, polyethylene glycol monomethyl ether and maleic anhydride were added to the reactor, and p-toluenesulfonic acid 0.8-1.2wt% was added. The temperature was raised to 120±5℃ and reacted for 3±0.5h to generate polyethylene glycol derivative. The temperature was then lowered to obtain component B. (3) Preparation of component C: Bismuth isooctanoate and zinc isooctanoate were added to the reactor according to the molar ratio and subjected to complexation reaction with acetylacetone at 80-90℃ for 2±0.5h to form a delayed catalyst of tetracoordinate complex, thus obtaining component C; (4) According to the mass ratio, the component A of step (1) and the component B of step (2) are stirred and mixed at 40-50°C for 13-17 minutes, and the component C of step (3) is added. After homogenization treatment, the composite curing agent is obtained.

[0015] Preferably, a pMDI composite adhesive comprises a composite curing agent prepared by the above-described preparation method and pMDI, wherein the mass ratio of the composite curing agent to pMDI is (20-25):100; the pMDI composite adhesive system has an initial viscosity of 680-750 mPa·s at 25°C and a pot life of 3.5-4.5 h.

[0016] Preferably, the composite curing agent, when mixed with pMDI, forms a three-stage curing system, as follows: First stage: At a temperature of 25–60℃, the hydroxyl groups of component A react with the -NCO groups of pMDI, with a reaction rate constant k1 = 0.8–1.2 × 10⁻⁶. -3 L·mol -1 ·s -1 ; Second stage: At a temperature of 60–140℃, under the catalysis of the carboxyl group of component B, the amino group of component A reacts with -NCO, with a reaction rate constant k2 = 2.5–3.5 × 10⁻⁶. -2 L·mol -1 ·s -1 ; The third stage: at a temperature of 140–180℃, a delayed catalyst is used for decomplexing activation, and -NCO reacts with the hydroxyl groups in wood, with a reaction rate constant k3 = 1.8–2.2 × 10⁻⁶. -1 L·mol -1 ·s -1 .

[0017] Preferably, a particleboard comprises wood raw material and pMDI composite adhesive, wherein the pMDI composite adhesive is used to shape the wood raw material; the pMDI composite adhesive is the pMDI composite adhesive described above.

[0018] Preferably, a method for preparing particleboard as described above includes the following steps: applying a pMDI composite adhesive mixture to the surface of wood shavings, wherein the application amount, based on the oven-dry condition of pMDI, is 105–125 g / m². 3 The particleboard is obtained by hot pressing at a temperature of 160–180°C and a hot pressing factor of 0.9–1.2 min / mm.

[0019] The present invention achieves at least the following beneficial effects: 1. This invention's composite curing agent achieves a three-stage spontaneous gradient curing reaction through precise control of the amine value of the amine polyol intermediate, carboxyl-assisted catalysis of the polyethylene glycol derivative, and temperature-responsive decomplexation of the delayed catalyst. This solves the technical problems of uncontrollable reaction rates and insufficient adhesive strength in existing curing agents. Through precise design at the chemical structure level and sequential control of reaction kinetics, the pot life is significantly extended without sacrificing the performance of the pMDI adhesive, while improving bonding efficiency and board quality. This provides an economical and feasible technical solution for the formaldehyde-free production of particleboard.

[0020] 2. This invention reduces the amine value to 135-165 mg KOH / g by ring-opening with ethylene oxide, converting 35-40% of the amino groups in triethanolamine into hydroxyl groups, forming a delayed amine structure. This achieves the temporal separation of stage I and stage II, allowing for precise control of the amine value to construct delayed amine reaction sites. The carboxyl group of the polyethylene glycol derivative forms a transient acid-base pair with the amine group, reducing the activation energy ΔE≈15 kJ / mol through proton transfer in the 60-140℃ range, achieving temperature-selective activation. This enables carboxyl-assisted catalysis to achieve mid-temperature activation of the amine group. The delayed catalyst exhibits precise temperature response, with a bismuth isooctanoate / zinc complex coordination bond energy of 85-95 kJ / mol, matching the hot pressing process of wood shavings. The activity inhibition rate is >80% below 140℃, and the recovery rate is >85% above 160℃.

[0021] 3. This invention, through precise control of amine value and synergy of multiple functional groups, achieves for the first time gradient matching of the three-stage reaction rate constants (k1 / k2 / k3≈1:30:200) in a pMDI curing system, extending the pot life from 0.6 hours of traditional polyamine curing agents to 3.5-4.5 hours, while shortening the hot-press curing time from 1.8 min / mm to 0.9-1.2 min / mm. It breaks through the reaction kinetics sequence to achieve precise control and solves the industry problem of being unable to achieve both long pot life and rapid curing.

[0022] 4. This invention utilizes a hydroxyl pre-crosslinked-amine main crosslinked-interfacial bonded triple gradient network constructed from a composite curing agent and a pMDI-prepared adhesive. This network enables the internal bonding strength of eucalyptus particleboard to reach 1.85-1.94 MPa, which is 20% higher than that of the pure pMDI system. The 24-hour water absorption thickness swelling rate is ≤7.0%, the wet static bending strength retention rate is ≥65%, and the crosslinking density of the adhesive layer reaches 320 mol / m³, which is significantly better than that of a single functional group curing agent (crosslinking density <280 mol / m³). Both the bonding strength and water resistance are improved.

[0023] 5. The viscosity of the curing agent in this invention is precisely controlled at 185-215 mPa·s. After mixing with pMDI, it forms an application window of 680-750 mPa·s, which reduces the CV value of eucalyptus wood shavings application uniformity from 26.3% to 12.8%, and increases the pre-compression strength of the board to 0.13 MPa, meeting the requirements of continuous pre-compression conveyors. This invention solves the technical contradiction of high-viscosity curing agent droplet agglomeration and low-viscosity curing agent excessive penetration, fundamentally improving the process compatibility problem.

[0024] 6. This invention converts 35-40% of the amine groups into hydroxyl groups through ring-opening of ethylene oxide, forming a delayed amine structure (¹H NMR characterization); the carboxyl and amine groups of the polyethylene glycol derivative form a transient acid-base pair, reducing the activation energy of the stage II reaction by 15 kJ / mol (DSC verification); the bismuth / zinc complex of the delayed catalyst dissociates at 140℃ (coordination bond enthalpy change 88 kJ / mol), achieving precise temperature response. The synergistic effect of the chemical structure of the three-stage curing system of the adhesive of this invention produces a gradient curing effect that cannot be achieved by a single component. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1This is a schematic diagram of the "dual active center-three-stage kinetics" reaction system formed by mixing the composite curing agent of the present invention with pMDI; Figure 2 The DSC analysis charts of six curing agents, namely 1070, A, B, G01, G03, and G201, are shown in the screening experiment of the technical solution of this invention. Figure 3 Infrared spectra of six curing agents—glycerol, polyvinyl alcohol, triethanolamine, ethylene glycol, tartaric acid, and polyethylene glycol monomethyl ether—during the screening experiment for the technical solution of this invention. Figure 4 The DSC analysis charts for fourteen curing agents, namely pure MDI, water, A, B, G01, G03, G20A, polyvinyl alcohol, triethanolamine, glycerol, monomethyl ether, tartaric acid, ethylene glycol, and 1070, are shown in the figure. Detailed Implementation

[0027] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] Currently, in the pHMDI adhesive system for particleboard, the performance of the curing agent directly determines the bonding efficiency and the quality of the board. Through long-term research, the inventors of this application have discovered that in actual industrial production, especially in continuous flat pressing or large-format hot pressing processes, the application of the pHMDI adhesive system still faces the following prominent technical challenges: (1) The contradiction between reactivity and pot life: the reaction rate constant between polyamine curing agents such as triethanolamine and isocyanates (-NCO) reaches 10. -1 L·mol -1 ·s -1 The magnitude of the reaction caused the viscosity to increase by more than 300% within 30 minutes after mixing, which could not meet the glue application process requirements of the continuous particleboard production line.

[0030] (2) The contradiction between the single functional group and the bonding strength: a single polyethylene glycol compound only provides hydroxyl reaction sites, and the density of urethane bonds formed after reacting with pMDI is insufficient. The internal bonding strength (IB) of the pressed particleboard is only 1.33 MPa, and the water resistance is poor.

[0031] (3) Uncontrollable reaction sequence: Existing curing agents cannot accurately control the multi-stage curing temperature of pMDI, resulting in prolonged hot pressing time (>1.5min / mm) or insufficient curing.

[0032] Therefore, the inventors are dedicated to developing a novel composite curing agent specifically for pMDI adhesives in particleboard, enabling intelligent and controllable adjustment of the curing reaction rate to ensure that the adhesive completes penetration and curing within the optimal time window. Simultaneously, it optimizes the cross-linked network structure of the final adhesive layer, significantly improving bond strength and overall toughness. Prior to creating this invention, the inventors conducted the following experimental explorations.

[0033] I. Experimental exploration of the design scheme of this invention, i.e., partial screening experiment 1. Experimental Background: 1.1 Summary of previous experiments Previous experiments are summarized in Table 1 below.

[0034] Table 1 1.2 Usage of formaldehyde-free adhesive curing agent in each trial plant The usage of formaldehyde-free adhesive curing agent in each trial factory during particleboard preparation is shown in Table 2 below.

[0035] Table 2 2. Experimental objective: By analyzing the curing kinetics of different types of curing agents mixed with MDI and studying the curing effect, this study explores the influence of the optimal curing agent on the curing effect and physicochemical properties of MDI, and develops a lower-cost formaldehyde-free adhesive curing agent.

[0036] 3. Price of experimental materials and samples: Material prices: 1070 > G03 >> G01 > G20A > Wanhua. The specific prices of experimental materials and samples are shown in Table 3 below.

[0037] Table 3 4. Test Plan Hardener, factory-made MDI adhesive.

[0038] 4.1 pH value, viscosity, and solid content testing Based on the supply department's purchase orders and contracts, pH value, viscosity, and solid content tests were conducted on the six types of curing agents currently purchased by the group.

[0039] 4.2 Molecular weight, type and number of chemical functional groups tested The above six curing agents were sent to external testing facilities to determine their molecular weight, type and quantity of chemical functional groups.

[0040] 4.3 Curing Kinetics Analysis The curing agent was prepared as a 10% aqueous solution and added to MDI. After thorough mixing (stirring for 5 min), DSC and TG analyses were performed. A curing agent addition gradient was set, based on the MDI dosage and according to the product process sheet and factory usage. The curing agent addition gradients were set to 3%, 8%, and 15%. The DSC parameters were set to 350℃ and 10℃ / min. The TG parameters were set to 600℃ and 15℃ / min.

[0041] 4.4 Study on Curing Effect Using MDI as an adhesive, fiberboard was pressed with different curing agents and without curing agents, and its physical and chemical properties were tested (Fy testing was not required).

[0042] The adhesive application rate for milling plates in the factory is 38±2 kg / m 3 Foundation / Ordinary 28±2kg / m 3 about.

[0043] The curing agent is applied at a rate of 1 kg / m². 3 Add the curing agent to a 10% aqueous solution to increase uniformity. That is, dilute the curing agent at a concentration of 10 kg / m³. 3 Add it.

[0044] 1kg / m 3 Hardener = 1.72g, prepares 10% aqueous solution = 17.2g, 30kg / m 3 Formaldehyde-free adhesive = 51.6g.

[0045] 5. Experimental Results 5.1 The basic chemical properties of the above six curing agents are as follows: pH: Wanhua > G20A > 1070 > G03 > G01. Overall, the MDI curing agent used for fiberboard is alkaline.

[0046] Viscosity and solid content: Wanhua > 1070 >> G20A > G03 > G01. Wanhua and 1070 curing agents have higher viscosity and are more oily.

[0047] The details are shown in Table 4 below.

[0048] Table 4 5.2 Infrared Test Results Based on the board material test results, among the six curing agents, curing agent 1070 showed the best performance. Comparing the compatibility of curing agent 1070 with the following substances: triethanolamine > ethylene glycol > polyethylene glycol monomethyl ether > glycerol, polyvinyl alcohol and tartaric acid showed low compatibility. Based on this, the inventors of this application make a bold conjecture: a blend of triethanolamine and polyethylene glycol monomethyl ether may achieve a compatibility of over 90% with curing agent 1070. The results are as follows... Figure 2 , Figure 3 As shown.

[0049] 5.3 DSC Test Results like Figure 4 As shown, based on the analysis of MDI adhesive and curing mechanism, the DSC curve results are compared with those of pure MDI and MDI-water mixture: First-stage curing temperature: water < G20A < monomethyl ether = ethylene glycol; Two-stage curing temperature: Ethylene glycol < Water < Polyvinyl alcohol < Triethanolamine; Three-stage curing temperature: G03 < Wanhua < Triethanolamine; Four-stage curing temperature: 1070 < Wanhua < G20A < Ethylene glycol; Conclusion: Based on the combined results of the small-scale test on the later-stage pressing plate, 1070, ethylene glycol, and monomethyl ether showed better performance. This indicates that improving the first and second stage curing temperatures of MDI in fiberboard is crucial, and it does not mean that lower temperatures are always better. The curing curves of monomethyl ether, ethylene glycol, and 1070 are similar.

[0050] 5.4 Results of small-scale test of the pressure plate Application of adhesive: 1 kg / m³ of curing agent = 1.72 g, 10% aqueous solution = 17.2 g, 30 kg / m³ of formaldehyde-free adhesive = 51.6 g.

[0051] Sample preparation: Take the average value of 8 samples for internal bonding and the average value of 6 samples for density and moisture content.

[0052] 0#: Add 17.2g of water to MDI and apply. See Table 5 for details.

[0053] Table 5 Based on the above and many other experimental studies, the inventors discovered that a multi-functional group gradient reaction system needs to be constructed through creative design to achieve precise matching of the kinetic parameters of each reaction stage to the particleboard hot pressing process. After summarizing many failed creative experiments and further creative design, the inventors finally developed the technical solution of this invention.

[0054] A composite curing agent comprising the following raw materials: Component A: Amino polyol intermediate; Component B: Polyethylene glycol derivative; Component C: Delayed catalyst; The mass ratio of component A, component B, and component C is 100:(28-35):(1.0-1.5); the delayed catalyst has a catalytic activity inhibition rate of ≥80% at ≤100℃ and a catalytic activity recovery rate of ≥85% at ≥160℃; the composite curing agent has a viscosity of 185-215 mPa·s at 25℃.

[0055] Specifically, a method for preparing the composite curing agent as described above includes the following steps: (1) Preparation of component A: Under nitrogen protection, the mixture of ethylene oxide and triethanolamine was prepared in a molar ratio of 1:(1.8-2.2). Triethanolamine was first added to a high-pressure reactor and heated to 80±5℃. Ethylene oxide was slowly introduced and the reaction pressure was controlled at 0.3±0.05MPa. After reacting for 4.0±0.5h, an amino polyol intermediate was generated, and component A was obtained. The amine value of the product was reduced to 135-165mg KOH / g by controlling the amount of ethylene oxide fed. (2) Preparation of component B: Polyethylene glycol monomethyl ether (Mn=350~450) and maleic anhydride were mixed according to a molar ratio of hydroxyl to anhydride of 1: (0.4~0.6). Polyethylene glycol monomethyl ether and maleic anhydride were added to the reaction vessel, and p-toluenesulfonic acid 0.8~1.2wt% was added. The temperature was raised to 120±5℃ and reacted for 3±0.5h to generate a polyethylene glycol derivative with an acid value of 55~75mg KOH / g. The temperature was then lowered to obtain component B. (3) Preparation of component C: The bismuth isooctanoate and zinc isooctanoate were prepared according to a molar ratio of 1:(1.5~2.0). Bismuth isooctanoate and zinc isooctanoate were added to the reactor and subjected to a complexation reaction with acetylacetone (the molar ratio of acetylacetone to the sum of bismuth isooctanoate and zinc isooctanoate was (1.8~2.2):1) at 80~90℃ for 2±0.5h to form a delayed catalyst of a four-coordinate complex, thus obtaining component C; (4) According to the mass ratio, the component A of step (1) and the component B of step (2) are stirred and mixed at 40-50°C for 13-17 minutes, and the component C of step (3) is added. After homogenization treatment, the composite curing agent is obtained.

[0056] Specifically, a pMDI composite adhesive comprises a composite curing agent prepared by the above-described preparation method and pMDI, wherein the mass ratio of the composite curing agent to pMDI is (20-25):100; the pMDI composite adhesive system has an initial viscosity of 680-750 mPa·s at 25°C and a pot life of 3.5-4.5 h.

[0057] Specifically, such as Figure 1 As shown, after the composite curing agent is mixed with pMDI, a "dual-active-center-three-stage kinetics" reaction system is formed. The three-stage reaction kinetic parameters are as follows: Stage I (sizing period): The hydroxyl groups react slowly with -NCO, k1≈10 -3 Applicable period > 3.5 hours; Phase II (Pre-compression period): Amine group reaction under carboxyl catalysis, k2≈10 -2 Provides slab strength; Stage III (Hot-pressing period): Catalyst activation, k3≈10 -1 It can rapidly increase the degree of cross-linking.

[0058] More specifically, the three-stage curing system formed by mixing the composite curing agent with pMDI is as follows: First stage: At a temperature of 25–60℃, the hydroxyl groups of component A react with the -NCO groups of pMDI, with a reaction rate constant k1 = 0.8–1.2 × 10⁻⁶. -3 L·mol -1 ·s -1 ; Second stage: At a temperature of 60–140℃, under the catalysis of the carboxyl group of component B, the amino group of component A reacts with -NCO, with a reaction rate constant k2 = 2.5–3.5 × 10⁻⁶. -2 L·mol -1 ·s -1 ; The third stage: at a temperature of 140–180℃, a delayed catalyst is used for decomplexing activation, and -NCO reacts with the hydroxyl groups in wood, with a reaction rate constant k3 = 1.8–2.2 × 10⁻⁶. -1 L·mol -1 ·s -1 .

[0059] Specifically, a particleboard includes wood raw materials and a pMDI composite adhesive, wherein the pMDI composite adhesive is used to shape the wood raw materials; and the pMDI composite adhesive is the pMDI composite adhesive described above.

[0060] Specifically, a method for preparing particleboard as described above includes the following steps: applying a pMDI composite adhesive mixture to the surface of wood shavings, wherein the amount of adhesive applied is 105–125 g / m² based on the oven-dry condition of the pMDI. 3 The particleboard is obtained by hot pressing at a temperature of 160–180°C and a hot pressing factor of 0.9–1.2 min / mm.

[0061] Example 1 A composite curing agent comprising the following raw materials: Component A: 100g of amino polyol intermediate; Component B: 32g of polyethylene glycol derivative; Component C: 1.2 g of delayed catalyst; The delayed catalyst exhibits a catalytic activity inhibition rate of ≥80% at ≤100℃ and a catalytic activity recovery rate of ≥85% at ≥160℃.

[0062] A method for preparing the composite curing agent as described above includes the following steps: (1) Preparation of component A: Under nitrogen protection, 149g (1.0mol) of triethanolamine was first added to a high-pressure reactor, heated to 80℃, and after nitrogen replacement, 79.2g (1.8mol) of ethylene oxide was slowly introduced. The reaction temperature was controlled at 80℃ and the pressure at 0.28MPa. After 4.0h of reaction, an amino polyol intermediate was obtained with an amine value of 148mg KOH / g and a viscosity of 185mPa·s at 25℃, which is component A. The amine value of the product was reduced to 148mg KOH / g by controlling the amount of ethylene oxide fed. (2) Preparation of component B: 200g (0.5mol) of polyethylene glycol monomethyl ether (Mn=400) and 29.4g (0.3mol) of maleic anhydride were added to the reaction vessel, and 2.3g of p-toluenesulfonic acid catalyst was added. After esterification reaction at 120℃ for 3h, a polyethylene glycol derivative with an acid value of 62mg KOH / g was generated. After cooling, component B was obtained. (3) Preparation of component C: 0.65 g of bismuth isooctanoate and 0.975 g of zinc isooctanoate were added to the reactor and subjected to a complexation reaction with acetylacetone (the molar ratio of acetylacetone to the sum of bismuth isooctanoate and zinc isooctanoate was 2.0:1) at 85°C for 2 h to form a delayed catalyst of a four-coordinate complex, thus obtaining component C; (4) According to the mass ratio, 100g of component A in step (1) and 32g of component B in step (2) are stirred and mixed at 45°C for 15min. Then, 1.2g of component C in step (3) is added. After homogenization, a composite curing agent with a viscosity of 198mPa·s at 25°C, pH=9.8 and solid content of 40.5% is obtained.

[0063] A pMDI composite adhesive comprises 22g of composite curing agent and 100g of pMDI prepared by the above preparation method.

[0064] Specifically, after the composite curing agent is mixed with pMDI, a "dual-active-center-three-stage kinetics" reaction system is formed. The three-stage curing system formed after the composite curing agent is mixed with pMDI is as follows: First stage (sizing period): The temperature is 45℃. The hydroxyl groups of component A react slowly with the -NCO groups of pMDI, and the reaction rate constant k1 = 1.0 × 10⁻⁶.-3 L·mol -1 ·s -1 ; Second stage (pre-compression period): At a temperature of 95℃, under the catalysis of the carboxyl groups of component B, the amine groups of component A react with -NCO to increase the strength of the slab. The reaction rate constant k2 = 3.0 × 10⁻⁶. -2 L·mol -1 ·s -1 ; The third stage (hot pressing period): the temperature is 160℃, the delayed catalyst is activated by decomposition, -NCO reacts with the hydroxyl groups of wood, rapidly increasing the degree of cross-linking, and the reaction rate constant k3 = 2.0 × 10⁻⁶. -1 L·mol -1 ·s -1 .

[0065] A particleboard comprising wood raw material and pMDI composite adhesive, wherein the pMDI composite adhesive is used to shape the wood raw material; the pMDI composite adhesive is the pMDI composite adhesive described above.

[0066] A process for gluing and pressing particleboard as described above includes the following steps: (1) Mix 22g of composite curing agent with 100g of pMDI to obtain pMDI composite adhesive with an initial viscosity of 720mPa·s and a pot life of 3.6 hours at 25℃; (2) Apply the pMDI composite adhesive mixture to the surface of 1000g of eucalyptus wood shavings (moisture content 8.2%), with an application rate of 110g / m². 3 (Based on the absolute dryness of pMDI), the mixer speed is 300 rpm and the application time is 2 minutes; (3) After paving, the pre-compression strength of the slab is 0.13MPa, the hot-compression temperature is 173℃, the pressure is 4.0MPa, and the hot-compression factor is 1.1min / mm, to prepare 18mm thick particleboard.

[0067] This embodiment verifies the reaction mechanism: Stage I conversion rate: 18% (hydroxyl pre-crosslinking); Stage II conversion rate: 42% (amino main crosslinking); Phase III conversion rate: 32% (interface bonding); Total crosslinking density: 320 mol / m³ (determined by swelling method).

[0068] Example 2 A composite curing agent, in this embodiment, adjusts the amount of ethylene oxide added to the amine polyol intermediate. The composite curing agent comprises the following raw materials: Component A: 100g of amino polyol intermediate; Component B: 35g of polyethylene glycol derivative; Component C: 1.5g of delayed catalyst; The delayed catalyst exhibits a catalytic activity inhibition rate of ≥80% at ≤100℃ and a catalytic activity recovery rate of ≥85% at ≥160℃.

[0069] A method for preparing the composite curing agent as described above includes the following steps: (1) Preparation of component A: Under nitrogen protection, 149g (1.0mol) of triethanolamine was first added to a high-pressure reactor, heated to 75℃, and 96.8g (2.2mol) of ethylene oxide was slowly introduced. The reaction pressure was controlled at 0.25MPa. After 3.5h of reaction, an amino polyol intermediate was generated, and component A was obtained. By controlling the amount of ethylene oxide fed, the amine value of the product was reduced to 135mg KOH / g, and the viscosity at 25℃ was 185mPa·s. (2) Preparation of component B: 200g (0.5mol) of polyethylene glycol monomethyl ether (Mn=400) and 29.4g (0.3mol) of maleic anhydride were added to the reaction vessel, and 2.3g of p-toluenesulfonic acid catalyst was added. After esterification reaction at 120℃ for 3h, a polyethylene glycol derivative with an acid value of 62mg KOH / g was generated. After cooling, component B was obtained. (3) Preparation of component C: 0.65 g of bismuth isooctanoate and 1.30 g of zinc isooctanoate were added to the reaction vessel and subjected to a complexation reaction with acetylacetone (the molar ratio of acetylacetone to the sum of bismuth isooctanoate and zinc isooctanoate was 2.2:1) at 80 °C for 2 h to form a delayed catalyst of a four-coordinate complex, thus obtaining component C; (4) According to the mass ratio, 100g of component A from step (1) and 35g of component B from step (2) are stirred and mixed at 40°C for 13min. Then, 1.5g of component C from step (3) is added. After homogenization, the composite curing agent is obtained.

[0070] A pMDI composite adhesive comprises 25g of composite curing agent and 100g of pMDI prepared by the above-described preparation method.

[0071] Specifically, after the composite curing agent is mixed with pMDI, a "dual-active-center-three-stage kinetics" reaction system is formed. The three-stage curing system formed after the composite curing agent is mixed with pMDI is as follows: First stage (sizing period): The temperature is 25℃. The hydroxyl groups of component A react slowly with the -NCO groups of pMDI, and the reaction rate constant k1 = 0.8 × 10⁻⁶. -3 L·mol -1 ·s -1 ; Second stage (pre-compression period): At 60℃, under the catalysis of the carboxyl groups of component B, the amine groups of component A react with -NCO to increase the strength of the slab. The reaction rate constant k2 = 2.5 × 10⁻⁶. -2 L·mol -1 ·s -1 ; The third stage (hot pressing period): the temperature is 140℃, the delayed catalyst is activated by decomposition, -NCO reacts with the wood hydroxyl groups, rapidly increasing the degree of cross-linking, and the reaction rate constant k3 = 1.8 × 10 -1 L·mol -1 ·s -1 .

[0072] In this embodiment, the conversion rate in Stage II is increased to 45%, and the hot pressing time is shortened to 0.9 min / mm.

[0073] A particleboard comprising wood raw material and pMDI composite adhesive, wherein the pMDI composite adhesive is used to shape the wood raw material; the pMDI composite adhesive is the pMDI composite adhesive described above.

[0074] A process for gluing and pressing particleboard as described above includes the following steps: (1) Mix 25g of composite curing agent with 100g of pMDI to obtain pMDI composite adhesive with an initial viscosity of 720mPa·s and a pot life of 4.0 hours at 25℃; (2) Apply the pMDI composite adhesive mixture to the surface of 1000g of eucalyptus wood shavings (moisture content 8.2%), with an application rate of 105g / m². 3 (Based on the absolute dryness of pMDI), the mixer speed is 300 rpm and the application time is 2 minutes; (3) After paving, the pre-compression strength of the slab is 0.13MPa, the hot-compression temperature is 165℃, the pressure is 3.8MPa, and the hot-compression factor is 1.0min / mm, to prepare 18mm thick particleboard.

[0075] Example 3 A composite curing agent, wherein the amount of delayed catalyst is adjusted in this embodiment, comprises the following raw materials: Component A: 100g of amino polyol intermediate; Component B: 30g of polyethylene glycol derivative; Component C: 1.4 g of delayed catalyst; The delayed catalyst exhibits a catalytic activity inhibition rate of ≥80% at ≤100℃ and a catalytic activity recovery rate of ≥85% at ≥160℃.

[0076] A method for preparing the composite curing agent as described above includes the following steps: (1) Preparation of component A: Under nitrogen protection, 149g (1.0mol) of triethanolamine was first added to a high-pressure reactor, heated to 80℃, and after nitrogen purging, 79.2g (1.8mol) of ethylene oxide was slowly introduced. The reaction temperature was controlled at 85℃ and the pressure at 0.35MPa. After reacting for 4.5h, an amino polyol intermediate was obtained with an amine value of 165mg KOH / g and a viscosity of 185mPa·s at 25℃, which is component A. The amine value of the product was reduced by controlling the amount of ethylene oxide fed. (2) Preparation of component B: 200g (0.5mol) of polyethylene glycol monomethyl ether (Mn=450) and 29.4g (0.3mol) of maleic anhydride were added to the reaction vessel, and 2.3g of p-toluenesulfonic acid catalyst was added. After esterification reaction at 125℃ for 3.5h, a polyethylene glycol derivative with an acid value of 75mg KOH / g was generated. After cooling, component B was obtained. (3) Preparation of component C: 0.8 g of bismuth isooctanoate and 1.6 g of zinc isooctanoate were added to the reaction vessel and subjected to a complexation reaction with acetylacetone (the molar ratio of acetylacetone to the sum of bismuth isooctanoate and zinc isooctanoate was 1.8:1) at 90 °C for 2.5 h to form a delayed catalyst of a four-coordinate complex, thus obtaining component C; (4) According to the mass ratio, 100g of component A in step (1) and 30g of component B in step (2) are stirred and mixed at 50°C for 17min. Then, 1.4g of component C in step (3) is added and homogenized to obtain a composite curing agent.

[0077] Specifically, a pMDI composite adhesive comprises 20g of a composite curing agent prepared by the above preparation method and 100g of pMDI.

[0078] Specifically, after the composite curing agent is mixed with pMDI, a "dual-active-center-three-stage kinetics" reaction system is formed. The three-stage curing system formed after the composite curing agent is mixed with pMDI is as follows: First stage (sizing period): The temperature is 60℃. The hydroxyl groups of component A react slowly with the -NCO groups of pMDI. The reaction rate constant k1 = 1.2 × 10⁻⁶. -3 L·mol -1 ·s -1 ; The second stage (pre-compression period): at a temperature of 140℃, under the catalysis of the carboxyl groups of component B, the amine groups of component A react with -NCO to increase the strength of the slab. The reaction rate constant k2 = 3.5 × 10⁻⁶. -2 L·mol -1 ·s -1 ; The third stage (hot pressing period): the temperature is 180℃, the delayed catalyst is activated by decomplexing, -NCO reacts with the hydroxyl groups of wood, rapidly increasing the degree of cross-linking, and the reaction rate constant k3 = 2.2 × 10⁻⁶. -1 L·mol -1 ·s -1 It meets the requirements of high-speed continuous production lines.

[0079] A particleboard comprising wood raw material and pMDI composite adhesive, wherein the pMDI composite adhesive is used to shape the wood raw material; the pMDI composite adhesive is the pMDI composite adhesive described above.

[0080] A process for gluing and pressing particleboard as described above includes the following steps: (1) Mix 20g of composite curing agent with 100g of pMDI to obtain pMDI composite adhesive with an initial viscosity of 720mPa·s and a pot life of 3.2 hours at 25℃; (2) Apply the pMDI composite adhesive mixture to the surface of 1000g of eucalyptus wood shavings (moisture content 8.2%), with an application rate of 125g / m². 3 (Based on the absolute dryness of pMDI), the mixer speed is 300 rpm and the application time is 2 minutes; (3) After paving, the pre-compression strength of the slab is 0.13MPa, the hot-pressing temperature is 180℃, the pressure is 4.0MPa, the hot-pressing factor of the rapid press is 0.9min / mm, and 18mm thick particleboard is prepared.

[0081] Example 4 A composite curing agent using polyethylene glycol monomethyl ether of different molecular weights, comprising the following raw materials: Component A: 100g of amino polyol intermediate; Component B: 28g of polyethylene glycol derivative; Component C: 1.0 g of delayed catalyst; The delayed catalyst exhibits a catalytic activity inhibition rate of ≥80% at ≤100℃ and a catalytic activity recovery rate of ≥85% at ≥160℃.

[0082] A method for preparing the composite curing agent as described above includes the following steps: (1) Preparation of component A: Under nitrogen protection, 149g (1.0mol) of triethanolamine was first added to a high-pressure reactor, heated to 80℃, and after nitrogen purging, 79.2g (1.8mol) of ethylene oxide was slowly introduced. The reaction temperature was controlled at 82℃ and the pressure at 0.32MPa. After reacting for 4.1h, an amino polyol intermediate was obtained with an amine value of 150mg KOH / g and a viscosity of 185mPa·s at 25℃, which is component A. The amine value of the product was reduced by controlling the amount of ethylene oxide fed. (2) Preparation of component B: 200g (0.5mol) of polyethylene glycol monomethyl ether (Mn=350) and 29.4g (0.3mol) of maleic anhydride were added to the reaction vessel, and 2.3g of p-toluenesulfonic acid catalyst was added. After esterification reaction at 122℃ for 3.2h, a polyethylene glycol derivative with an acid value of 65mg KOH / g was generated. The mixture was then cooled to obtain component B. (3) Preparation of component C: 0.65 g of bismuth isooctanoate and 1.17 g of zinc isooctanoate were added to the reactor and subjected to a complexation reaction with acetylacetone (the molar ratio of acetylacetone to the sum of bismuth isooctanoate and zinc isooctanoate was 2.0:1) at 90 °C for 2 h to form a delayed catalyst of a four-coordinate complex, thus obtaining component C; (4) According to the mass ratio, 100g of component A in step (1) and 28g of component B in step (2) are stirred and mixed at 42°C for 16min. Then, 1.0g of component C in step (3) is added. After homogenization, a composite curing agent with a viscosity of 185 mPa·s at 25°C is obtained.

[0083] A pMDI composite adhesive comprises 20g of a composite curing agent prepared by the above method and 100g of pMDI.

[0084] Specifically, after the composite curing agent is mixed with pMDI, a "dual-active-center-three-stage kinetics" reaction system is formed. The three-stage curing system formed after the composite curing agent is mixed with pMDI is as follows: First stage (sizing period): The temperature is 50℃. The hydroxyl groups of component A react slowly with the -NCO groups of pMDI. The reaction rate constant k1 = 1.1 × 10⁻⁶. -3 L·mol -1 ·s -1 ; Second stage (pre-compression period): At 100℃, under the catalysis of the carboxyl groups of component B, the amine groups of component A react with -NCO to increase the strength of the slab. The reaction rate constant k2 = 3.0 × 10⁻⁶. -2 L·mol -1 ·s -1 ; The third stage (hot pressing period): the temperature is 170℃, the delayed catalyst is activated by decomposition, -NCO reacts with the hydroxyl groups of wood, rapidly increasing the degree of cross-linking, and the reaction rate constant k3 = 2.1 × 10⁻⁶. -1 L·mol -1 ·s -1 .

[0085] A particleboard comprising wood raw material and pMDI composite adhesive, wherein the pMDI composite adhesive is used to shape the wood raw material; the pMDI composite adhesive is the pMDI composite adhesive described above.

[0086] A process for gluing and pressing particleboard as described above includes the following steps: (1) Mix 20g of composite curing agent with 100g of pMDI to obtain pMDI composite adhesive with an initial viscosity of 720mPa·s and a pot life of 4.0 hours at 25℃; (2) Apply the pMDI composite adhesive mixture to the surface of 1000g of eucalyptus wood shavings (moisture content 8.2%), with an application rate of 120g / m². 3 (Based on the absolute dryness of pMDI), the mixer speed is 300 rpm and the application time is 2 minutes; (3) After paving, the pre-compression strength of the slab is 0.13MPa, the hot-compression temperature is 175℃, the pressure is 4.0MPa, and the hot-compression factor is 1.1min / mm, to prepare 18mm thick particleboard.

[0087] Comparative Example 1 The difference from Example 1 is that, in the preparation of particleboard, the mass ratio of composite curing agent to pMDI in the pMDI composite adhesive is 15:100, and the initial viscosity of the pMDI composite adhesive system at 25°C is 600 mPa·s, while other conditions remain unchanged.

[0088] Comparative Example 2 The difference from Example 1 is that, in the preparation of particleboard, the mass ratio of components A, B, and C of the composite curing agent in the pMDI composite adhesive is 100:22:3, while other conditions remain unchanged.

[0089] Comparative Example 3 The difference from Example 1 is that, more specifically, the composite curing agent, when mixed with pMDI, forms a three-stage curing system: First stage: At 80℃, the hydroxyl groups of component A react with the -NCO groups of pMDI, with a reaction rate constant k1 = 2 × 10⁻⁶. -3 L·mol -1 ·s -1 ; Second stage: At 160℃, under the catalysis of the carboxyl group of component B, the amino group of component A reacts with -NCO, and the reaction rate constant k2 = 4 × 10⁻⁶. -2 L·mol -1 ·s -1 ; Third stage: At 200℃, the delayed catalyst is decomplexed and activated, and -NCO reacts with the hydroxyl groups of wood. The reaction rate constant k3 = 2.8 × 10⁻⁶. -1 L·mol -1 ·s -1 All other conditions remain unchanged.

[0090] II. Effect Test According to the requirements of GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", some performance tests were conducted on the particleboard samples prepared by the methods of Examples 1-4 and Comparative Examples 1-3. The experimental results are shown in Table 6 below.

[0091] Table 6 Experimental data shows that the formaldehyde release rate of the method of this invention reaches the ENF level.

[0092] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A composite curing agent, characterized in that, The composite curing agent comprises the following raw materials: Component A: Amino polyol intermediate; Component B: Polyethylene glycol derivative; Component C: Delayed catalyst; The mass ratio of component A, component B, and component C is 100:(28-35):(1.0-1.5).

2. The composite curing agent according to claim 1, characterized in that, The amine polyol intermediate has an amine value of 135–165 mg KOH / g and is prepared by ring-opening reaction of ethylene oxide and triethanolamine in a molar ratio of 1:(1.8–2.2). Specifically, triethanolamine and ethylene oxide are reacted in a closed reactor at 75–85 °C and 0.25–0.35 MPa for 3.5–4.5 h.

3. The composite curing agent according to claim 1, characterized in that, The polyethylene glycol derivative has an acid value of 55-75 mg KOH / g and is prepared by compounding polyethylene glycol monomethyl ether and maleic anhydride at a hydroxyl / anhydride molar ratio of 1:(0.4-0.6) and carrying out an esterification reaction at 115-125°C for 2.5-3.5 h under the action of p-toluenesulfonic acid catalyst.

4. The composite curing agent according to claim 1, characterized in that, The delayed catalyst is prepared by complexing bismuth isooctanoate and zinc isooctanoate in a molar ratio of 1:(1.5-2.0) with acetylacetone at 80-90°C for 1.5-2.5 hours to form a four-coordinate complex. The molar ratio of acetylacetone to the sum of bismuth isooctanoate and zinc isooctanoate is (1.8-2.2):

1. The delayed catalyst exhibits a catalytic activity inhibition rate of ≥80% at ≤100°C and a catalytic activity recovery rate of ≥85% at ≥160°C.

5. The composite curing agent according to claim 1, characterized in that, The viscosity of the composite curing agent at 25°C is 185–215 mPa·s.

6. A method for preparing a composite curing agent as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Preparation of component A: Under nitrogen protection, triethanolamine was first added to the high-pressure reactor according to the molar ratio, the temperature was raised to 80±5℃, ethylene oxide was slowly introduced, the reaction pressure was controlled at 0.3±0.05MPa, and after reacting for 4.0±0.5h, component A was obtained; (2) Preparation of component B: According to the molar ratio, polyethylene glycol monomethyl ether and maleic anhydride were added to the reactor, and 0.8-1.2 wt% p-toluenesulfonic acid was added. The mixture was heated to 120±5℃ and reacted for 3±0.5 h. Then the mixture was cooled to obtain component B. (3) Preparation of component C: Bismuth isooctanoate and zinc isooctanoate were added to the reactor according to the molar ratio and subjected to complexation reaction with acetylacetone at 80-90℃ for 2±0.5h to form a four-coordinate complex, thus obtaining component C; (4) According to the mass ratio, the component A of step (1) and the component B of step (2) are stirred and mixed at 40-50°C for 13-17 minutes, and the component C of step (3) is added. After homogenization treatment, the composite curing agent is obtained.

7. A pMDI composite adhesive, characterized in that, The composite curing agent prepared by the method described in claim 6 and pMDI are included, wherein the mass ratio of the composite curing agent to pMDI is (20-25):100; the initial viscosity of the pMDI composite adhesive system at 25°C is 680-750 mPa·s, and the pot life is 3.5-4.5 h.

8. The pMDI composite adhesive according to claim 7, characterized in that, The composite curing agent, when mixed with pMDI, forms a three-stage curing system, as detailed below: First stage: At a temperature of 25–60℃, the hydroxyl groups of component A react with the -NCO groups of pMDI, with a reaction rate constant k1 = 0.8–1.2 × 10⁻⁶. -3 L·mol -1 ·s -1 ; Second stage: At a temperature of 60–140℃, under the catalysis of the carboxyl group of component B, the amino group of component A reacts with -NCO, with a reaction rate constant k2 = 2.5–3.5 × 10⁻⁶. -2 L·mol -1 ·s -1 ; The third stage: at a temperature of 140–180℃, a delayed catalyst is used for decomplexing activation, and -NCO reacts with the hydroxyl groups in wood, with a reaction rate constant k3 = 1.8–2.2 × 10⁻⁶. -1 L·mol -1 ·s -1 .

9. A type of particleboard, characterized in that: The particleboard comprises wood raw material and pMDI composite adhesive, wherein the pMDI composite adhesive is used to shape the wood raw material; the pMDI composite adhesive is the pMDI composite adhesive as described in claim 7 or 8.

10. A method for preparing particleboard as described in claim 9, characterized in that, Includes the following steps: The pMDI composite adhesive mixture was applied to the surface of wood shavings, with an application rate of 105–125 g / m² based on the oven-dry condition of the pMDI. 3 The particleboard is obtained by hot pressing at a temperature of 160–180°C and a hot pressing factor of 0.9–1.2 min / mm.

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