Thermal Welding by the Third Phase Between Polymers: A Review for Ultrasonic Weld Technology Developments

Ultrasonic welding (USW) is a promising method for the welds between dissimilar materials. Ultrasonic thermal welding by the third phase (TWTP) method was proposed in combination with the formation of a third phase, which was confirmed as an effective technology for polymer welding between the two dissimilar materials compared with the traditional USW. This review focused on the advances of applying the ultrasonic TWTP for thermoplastic materials. The research development on the ultrasonic TWTP of polycarbonate (PC) and polymethyl methacrylate (PMMA), polylactic acid (PLA) and polyformaldehyde (POM), and PLA and PMMA are summarized according to the preparation of the third phase, welded strength, morphologies of rupture surfaces, thermal stability, and others. The review aimed at providing guidance for using ultrasonic TWTP in polymers and a basic understanding of the welding mechanism, i.e., interdiffusion and molecular motion mechanisms between the phases.

Heat Affected Zone in Microwave Polymer Welding

This paper aims to present some specific aspects regarding the heat affected zone in microwave polymer welding. It presents several results of investigation of the physical and mechanical modification of the HDPE100 polymer when the microwave heating is applied. Burst stress, elongation and relaxation modulus are subject of this research, as well as the information regarding the crystallization rate and elongation viscosity. To reveal the type of the structure and its transformation, Differential Scanning Calorimetry (DSC) was used. The recorded values for rate of crystallization are appropriate for the welding process, but it has negative effect when plastic deformation at high temperature (as in the extrusion process) is applied. The microwave heating produced a 12-20% decreasing of the plasticity with the increasing of the amount of heat introduced into the material (from 65 W power and 10 s heating to 130 W and 40 s). After the microwave heating, the material showed low values for the elongation viscosity, which means not very fluid material and a necessity to apply high temperatures during the processing by welding or plastic deformation.