Ultrasonic weld (USW) techniques for thermoplastics are used to be limited identical polymers, which obstruct the increasingly development of dissimilar polymers joining. In this study, as a direct-joining method without using environmentally unfriendly adhesives, ultrasonic thermal welding by the third phase (TWTP) was successfully proposed to join the immiscible thermoplastics. Poly(methyl methacrylate) (PMMA) and polyformaldehyde (POM) were chosen as the work piece (WP) materials. The third phase of functionally graded material (FGM) were prepared from PMMA, POM and polylactic acid (PLA). The optimal welded strength of 47 MPa (approximately 80 % of tensile strength of POM matrix) was achieved, which is satisfied to the lightweight demand in automotive industry. Meanwhile, the welded interfacial morphology can be divided into four parts, which is related to the diffusion depths of interposed sheet (IPS) and WP molecules, respectively. Based on the interdiffusion analysis, the interdiffusion chains can give the similar configuration as that of the IPS due to the steric hindrance and Van der Waals force.

用于热塑性塑料的超声波焊接 (USW) 技术被用于限制相同的聚合物，这阻碍了不同聚合物连接的日益发展。在这项研究中，作为一种不使用对环境不友好的粘合剂的直接连接方法，成功地提出了第三阶段超声波热焊接 (TWTP) 来连接不混溶的热塑性塑料。选择聚（甲基丙烯酸甲酯）（PMMA）和聚甲醛（POM）作为工件（WP）材料。第三相功能梯度材料 (FGM) 由 PMMA、POM 和聚乳酸 (PLA) 制备。达到了47 MPa的最佳焊接强度（约为POM基体抗拉强度的80%），满足了汽车行业的轻量化需求。同时，焊接界面形态可分为四个部分，这分别与插入片 (IPS) 和 WP 分子的扩散深度有关。根据相互扩散分析，由于空间位阻和范德华力，相互扩散链可以提供与 IPS 相似的配置。