高含水率状态下桦木与异氰酸酯的胶接化学反应历程

The Chemical Reaction Process of Bonding Birch with Isocyanate at the Condition of High Moisture Content

对湿固化异氰酸酯胶黏剂粘接高含水率桦木的胶接机理进行系统研究。利用计算化学方法这一崭新的手段,采用Material Studio软件中DMol3模块,采用基于密度泛函理论的量子化学程序,通过模拟胶接体系中异氰酸酯基团(NCO)与自由水(H2O)及桦木中不同化学环境羟基(—OH)的反应历程,搜索反应的过渡态,计算反应活化能以及反应总能量,判定反应进行的难易以及先后次序。研究结果表明胶接体系中—NCO基团与自由水反应的活化能与—NCO基团与纤维素中—OH的反应活化能相接近,反应存在竞争关系。胶接体系中—NCO与纤维素上—OH相对来说较容易反应,且反应进行的顺序是C6>C3>C1>C2,均为放热反应;与木质素上—OH不容易反应,反应进行的顺序是紫丁香基丙烷(Lig-S)>愈创木基丙烷(Lig-G)>对羟苯基丙烷(Lig-H),其中羟基与Lig-S和Lig-G的反应是放热反应,与Lig-H的反应是吸热反应。

The bonding mechanism of birch in high moisture content glued with moisture curing isocyanate adhesive was investigated in this paper. The reaction processes between isocyanate groups （--NCO） in glued systems and free water or hydroxyl （--OH） in different chemical environment of birch were simulated using DMol3 program of Material Studio software. The difficulty and order of reaction were determined by searching the transition state and computation of the activation energy and the total energy of reaction. The investigations showed that the activation energy of reaction between --NCO groups and free water was closed to that between --NCO groups and -OH of cellulose. This indicated that these were a couple of competitive reactions. The reaction between --NCO and --OH of cellulose in the glued system occurs relatively easier than the reaction of --NCO and --OH of lignin. Furthermore, the order of reaction in cellulose is C6 〉 C3 〉 C1 〉 C2 and all of reactions in cellulose are exothermic. The order of reaction in lignin is lilac propane （Lig-S） 〉 guaiacyl propane （Lig-G） 〉p-hydroxyphenyl propane （Lig-H）. The reactions of Lig-S and Lig-G are exothermic, but the reaction of Lig-H was an endothermic reaction.