Ultrasonic thermal welding of immiscible thermoplastics via the third phase.

[Display omitted] 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. [ABSTRACT FROM AUTHOR]