Research And Application Of Formaldehyde-free Adhesive For Green Household Materials

Indoor household products are primarily produced using wood-based panels as raw materials.However,the production of these panels typically involves the use of formaldehyde adhesives,which can release harmful free formaldehyde during the production and ultilization process,posing health risks to users.In response to the national goal of building a healthy China during the 14th Five-Year Plan,the green household materials industry has been focusing on developing formaldehyde-free wood-based panels and adhesives.Among these,sucrose-based adhesives have gained attention due to their excellent adhesive properties and renewable biomass sources.However,the sucrose-based adhesives present challenges,such as bleeding-through during the preparation of wood-based panels and low production efficiency due to harsh curing conditions.This paper addresses the above issues by focusing on the preparation conditions,modification,and application of sucrose-based adhesives for green household materials.The main research findings are as follows:（1）Study on the preparation conditions of SADP/DCP adhesive by using sucrose and dephenolized cottonseed proteinBy studying the type and preparation method of the sucrose-based solution of the adhesive and the mass ratio of dephenolic cottonseed protein（DCP）to sucrose-based solution,the best preparation conditions were determined to be as follows:sucrose-ammonium dihydrogen phosphate（SADP）solution was mixed with DCP at room temperature,and the mass ratio of DCP to SADP was 1/3.The adhesive prepared under the optimal conditions was used to press the plywood,and there was no significant bleed-through phenomenon.The wet shear strength of the plywood reached 1.17 MPa,67.1%higher than the requirement of the China National Standard GB/T 9846-2015（≥0.7 MPa）.The results of the insoluble mass proportion showed that the SADP/DCP adhesive formed 62.7%insoluble mass when heated at 170℃for 7 min.The thermal analysis results revealed that the SADP/DCP adhesive experienced rapid weight loss at 166.2℃and an endothermic peak at 170.6℃,indicating that both thermal decomposition and polymerization of the SADP/DCP adhesive occur at about 170℃,resulting in the formation of a water-insoluble polymer.By studying the hot pressing temperature and time of the SADP/DCP adhesive,the optimal hot pressing parameter of the three-layer plywood was determined to be170℃and 7 min.The ATR-FTIR analysis results showed that during the high-temperature curing process of the SADP/DCP adhesive,the molecules in the SADP solution were transformed into furan compounds.The active groups of furan compounds（e.g.,hydroxymethyl and aldehyde groups）underwent Maillard reactions with amino acids in DCP to form water-insoluble polymers with dimethyl ether bridge（C-O-C）as the main bonding bond.The SEM analysis results demonstrated that the SADP/DCP adhesive modified by DCP increased the surface flatness and reduced porosity.（2）Optimization of the SADP/DCP adhesive by using TsOH/MDI（p-toluenesulfonic acid/Methylenediphenyl Diisocyanate）By studying the catalyst type,catalyst addition amount,synthesis temperature and time of sucrose-base solution,the optimal synthesis conditions of sucrose-based solution were determined as using 5%TsOH as a catalyst,synthesizing sucrose-based solution at 100℃for 3h.The best preparation conditions of the optimal adhesive（SADP/DCP-TsOH/MDI）were determined by using 20%MDI as a curing agent.Under these conditions,the wet shear strength of the SADP/DCP-TsOH/MDI adhesive was 0.79 MPa,meeting the China National Standard GB/T 9846-2015（≥0.7 MPa）.Compared to the unoptimized SADP/DCP adhesive,the SADP/DCP-TsOH/MDI adhesive showed an improvement of 132.4%under the same hot pressing conditions.The thermal curing behavior of the adhesive was studied by insoluble mass proportion and thermal analysis.The insoluble mass proportion of the SADP/DCP-TsOH/MDI adhesive reached 61.2%（150℃for 7 min）,which was 141.9%higher than the unoptimized SADP/DCP adhesive（25.3%）.The rapid weight loss temperature and endothermic reaction temperature of the optimized adhesive were 145.1℃and 148.4℃,respectively,which were about 20℃lower than those of the unoptimized SADP/DCP adhesive（166.2、170.6℃）.The synthesis mechanism of SADP-TsOH solution under optimal conditions was studied by ¹³C NMR and HPLC analysis.TsOH promoted the conversion of sucrose to 5-HMF,and the content of 5-HMF in SADP-TsOH solution was 44.0 g/L,which was 158.8%higher than before modification（SADP solution）.The results obtained from ATR-FTIR and Py-GC/MS analysis indicated that the use of TsOH as a catalyst resulted in a higher conversion rate of sucrose into furan compounds.These furan compounds possess active groups,such as aldehyde and hydroxymethyl,which undergo Maillard reaction with DCP.During the curing process,the MDI curing agent increased the reactivity of the SADP/DCP adhesive system,leading to the formation of an insoluble polymer with a dimethyl ether bridge as the main bonding bond.The SEM analysis of the cured adhesive revealed changes in surface morphology due to TsOH/MDI optimization.The formation of irregular holes and bubbles could be attributed to the reaction between the hydroxyl-containing compounds in SADP/DCP-TsOH/MDI adhesive and the subsequent release of carbon dioxide.（3）Formulation optimization and application of SADP/DCP-TsOH/MDI adhesiveThe study focused on optimizing the formulation and application of SADP/DCP-TsOH/MDI adhesive material.By exploring the solid content of the adhesive and filler type,the researchers identified the optimal formula,which involved adjusting the solid content of the SADP/DCP-TsOH/MDI adhesive to 70%and using 10%Ca₂CO₃ filler to replace 10%MDI.The adhesive with the optimized formula was used to prepare three-layer plywood under hot pressing at 150℃for 7 min,resulting in a wet shear strength of 0.83 MPa,which met the China National Standard GB/T 9846-2015（≥0.7 MPa）.In addition,the optimized formula SADP/DCP-TsOH/MDI adhesive had a lower viscosity value with better fluidity,and a higher p H value which would help prevent excessive acid corrosion of wood veneer.According to the cost analysis,the raw material cost of the optimized formula SADP/DCP-TsOH/MDI adhesive was 3307 yuan/ton,which was39.2%lower than that of the unoptimized adhesive（5442 yuan/ton）.Additionally,the adhesive had a shelf life of up to four weeks without significant decreases in wet shear strength or signs of mildew or deterioration.Using the SADP/DCP-TsOH/MDI adhesive with the optimized formula to prepare multilayer plywood,the wet shear strength till met the China National Standard GB/T9846-2015（≥0.7 MPa）.In a formaldehyde emission test,the plywood prepared with optimized formula SADP/DCP-TsOH/MDI adhesive had a formaldehyde emission of 0.05 mg/L,which was lower than the formaldehyde emission classification E₀≤0.4 mg/L specified in T/CNFPIA 1001-2019 Formaldehyde Emission Limit for Wood-based Panels.