异氰酸酯改性大豆油基木材胶黏剂的制备与性能

环氧大豆油丙烯酸酯（Acrylated Epoxidized Soybean Oil, AESO）具有原料来源丰富、环境友好、耐水性好等优点，以AESO为原料制备新型无醛木材胶黏剂是降低当前甲醛系胶黏剂用量的重要途径。针对AESO同时含双键、羟基和环氧基的结构特点，以六亚甲基二异氰酸酯（Hexamethylene Diisocyanate, HDI）为改性剂、过氧化苯甲酸叔丁酯为自由基引发剂，制备了改性大豆油基木材胶黏剂及其杨木胶合板材，分析了胶黏剂的化学结构、流变性、固化行为、胶合机理及其对胶合板物理力学性能的影响。结果表明：HDI改性后的胶黏剂具有更高的交联密度、内聚力和胶接力，其杨木胶合板的耐水胶合强度可达1.18 MPa；HDI可与AESO的羟基、环氧基反应生成氨基甲酸酯结构，同时HDI的加入降低了AESO树脂的黏度和最大固化温度，提高了胶黏剂的加工性能；HDI改性显著提高胶合板的物理力学性能（P<0.05），当HDI与AESO的质量比为1∶9时，胶合板的横向静曲强度和弹性模量分别为57.6和5 920 MPa，且板材在120°C下2 h不开裂。该研究为以生物质大豆油为原料制备无醛胶黏剂提供了一种可行路径，有利于木材工业的绿色与可持续发展。

Effects of isocyanate usage on the properties of soybean oil-based adhesives and their plywoods

Engineered wood-based products including plywood, fiberboard, and particleboard have been largely used in interior furnishing and construction fields, which promotes the rapidly increased consumption of wood adhesives. Formaldehyde-based adhesives such as urea formaldehyde and phenol formaldehyde are the most widely used wood adhesives because of their low cost, excellent bonding performance, and water resistance. Many biomass materials including cellulose, tannin, and lignin have been utilized as main components for developing biobased adhesives, but they mostly show high cost, week bonding strength, and poor water resistance. Plant oils are composed of triglycerides that are intrinsically water resistance, and thus are perfect materials for preparing water-resistant adhesives. As one of the main commercially available plant oil derivatives, Acrylated Epoxidized Soybean oil (AESO) is derived from soybean oil via an epoxidization and acrylation process. AESO possesses the advantages of abundance, water resistance, and environmental friendliness. The development of AESO-based wood adhesives is a novel approach to reduce the consumption of aldehyde-based adhesives. AESO contains carbon-carbon double bonds and hydroxyl groups as well as epoxy groups. Thus, Hexamethylene Diisocyanate (HDI) was introduced as a modifier and tert-butyl Peroxybenzoate (TBPB) was used as a free-radical initiator to prepare the formaldehyde-free AESO wood adhesives and their poplar plywoods. The chemical structure, rheological and curing behaviors, water-resistance, and bonding mechanism of the modified AESO adhesives and their effects on the physical and mechanical properties of the plywoods were investigated. FTIR and NMR analyses confirmed that HDI could react with both the hydroxyl and epoxy groups of AESO to form carbamate structure, hence leading to improved crosslinking density of the adhesives and interfacial bonding between wood and the adhesives. Due to the improved cohesion and bonding force of the adhesives, and the water-resistant bonding strength of poplar plywood was up to 1.18 MPa, which meets the requirement of Chinese standard. The addition of HDI significantly reduced the viscosity and the maximum curing temperature of AESO resins, and improved the processibility of the adhesives. The HDI modification significantly increased the physical and mechanical properties of the plywoods (P<0.05). The bonding strength, flexural strength, elastic modulus, and water resistance of the plywoods significantly increased with the increased mass ratio of HDI to AESO from 0.5:9.5 to 1:9, and then leveled off as the further increased HDI usage. The optimum mass ratio of HDI to AESO was considered as 1:9, in which the transverse flexural strength and elastic modulus of the plywood reached 57.6 MPa and 5 920 MPa, respectively, and the plywood did not crack at 120 °C for 2 h. SEM images indicated that the HDI modification significantly increased the interfacial adhesion between wood and adhesives due to the formation of covalent bonds. The work provides a feasible way to prepare formaldehyde-free adhesives by using biomass soybean oil as raw materials, which is beneficial for the green and sustainable development of wood industry.