聚合物的分子结构与吸声性能研究

以甲苯二异氰酸酯和聚乙二醇为原料合成了聚氨酯,同时以乙烯基聚二甲基硅氧烷和含氢硅油为原料合成了硅橡胶.然后,以上述合成的硅橡胶和聚氨酯橡胶分别作为消声涂层的基体材料,研究了聚合物分子结构对涂层吸声性能的影响.采用傅利叶变换红外光谱(FTIR)表征了聚合物的分子结构,用驻波管法测量了涂层的吸声系数,用拉伸法和剪切法测定涂层的拉伸模量和剪切模量,并利用有限元程序ANSYS8.0模拟分析了涂层在水压下的形变.测试结果表明,不同结构的聚合物,在常压和高压下呈现出不同的吸声性能.具有柔性链状结构的硅橡胶基涂层,在水压作用下形变较大,吸声系数随水压增大而迅速减小;而含氢键结构的聚氨酯基涂层,在水压作用下形变较小,吸声系数随水压增大而升高.分析认为聚合物自由体积的大小和运动可能是影响涂层吸声性能的重要因素.橡胶体积压缩后,在一定程度上减少了自由体积的大小,限止了自由体积的运动,因此,选择刚性结构的聚合物作为涂层基体,调节自由体积,是制备在高压下具有高吸声性能涂层的重要途径.

STUDIES ON THE RELATIONSHIP BETWEEN SOUND ABSORPTION AND MOLECULAR STRUCTURE OF POLYMERS

Two coating matrix materials, polyurethane and silicone rubber were used for investigating the relationship between absorption and molecular structure of polymers under hydraulic pressure. The polyurethane was synthesized with toluene diisocyanate and polyethylene glycol as main raw materials, and the silicone rubber was prepared with vinyl polydimethyl siloxane and hydrogen-containing silicone fluid. The molecular structure of polymers was analyzed by using Fourier transform infrared spectroscopy. The sound absorption performance was measured by the standing wave tube method. The mechanical performance of coating films was characterized by tensile and shear moduli measurements, and their volume change under hydraulic pressure was simulated by using a file ANSYS 8.0. The different polymer presented different sound absorption performance under ordinary and hydraulic pressure. As frequency ranged from 3 to 30 kHz under ordinary pressure, the average absorption coefficient of silicone rubber-based coatings was 92.6%, and that of polyurethane-based coatings was 68.5%. The sound absorption performance of coatings changed noticeably with hydraulic pressure increased. The sound absorption performance of silicone rubber with flexible molecule chain structure decreased rapidly when the hydraulic pressure increased. The average absorption coefficient changed from 26.9% under 0.5 MPa down to 13% under 3 MPa. The sound absorption ability of polyurethane with rigid molecule chain structure increased when the hydraulic pressure increased. The average absorption coefficient changed from 75.2% under 0.5 MPa to 87.6% under 3 MPa. The results of finite element analysis showed that the volume compressibility of silicone rubber-based coatings increased from 0.55% to 3.29%, and that of polyurethane-based coatings changed from 0.03% to 0.20% when the hydraulic pressure increased from 0.5 MPa to 3 MPa. The polymer of polyurethane-based coatings was a polyether-type polyurethane with a large number of intermolecular hydrogen bonds and carbonate polar groups from TDI and hydroxyl groups. The cohesive power of the carbonate groups was very large, the total power of interaction of the rigid molecule chains with large numbers of carbonate groups was powerful,which engendered network-like structure among linear chains. The free volume of polyurethane with rigid molecule chains changed slightly as the volume compressibility was less under hydraulic pressure. The flexible molecule chains of silicone rubber were easy to slide under hydraulic pressure, which resulted in rapid decrease of free volume, and the molecular motion was blocked. The sound absorption performance was affected by the size free volume and the movement of polymer molecules. These results indicate the importance of molecular structure and free volume adjusting in preparing excellent anechoic coatings under high hydraulic pressure.