Thermo-expandable microcapsule as a blowing agent for producing thermoplastic elastomer vulcanized syntactic foam

Thermoplastic Elastomer Vulcanized (TPE-V) syntactic foams made by Thermo-Expandable Microcapsules (TEMs) are becoming of a large interest for automotive industry. TPE-Vs combine advantages of class rubber compound properties with an easier manufacture process and are recyclable. Therefore, TPE-Vs are more and more used to manufacture automotive sealing system by an extrusion process, which is the focus of this research. Due to the two-phase structure of TPE-V, classical extrusion foaming technologies, such as chemical and physical foaming, are complex to be controlled. Thus, TEMs show an outstanding ability to be effective and produce repeatable microstructure with standard extrusion equipment. TEMs consist in a mixture of liquid hydrocarbons, encapsulated by a gas-proof polymeric shell. Exposed to elevated temperatures, the internal pressure drives the dilation of the TEMs, as a result a TPE-V syntactic foam is produced. The aim of this study is to understand where the expansion occurs and how can it be affected by extrusion process parameters. Temperature is a well-known key parameter to control final expansion of TEMs. Hence, measurements at high pressure and temperature were done to find out the location of expansion during extrusion process. Additionally, we have designed three groups of three dies to apply different pressure drops, pressure drop rates and residence time, inside the die. Under these process conditions, density, cell microstructure and viscosity have been investigated.