Mechanical performance of thermoplastic elastomers for two-component injection moulding
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The thesis is based on studies of the mechanical properties of thermoplastic elastomers (TPEs). A TPE is a soft thermoplastic polymer material with rubber-like properties. Vulcanizate TPEs (TPVs) were selected as the main model material and a styrenic TPE (TPS) was selected as a comparative material. These are subfamilies of TPEs with competitive properties. TPVs are essentially composites of thermoplastic and dispersed crosslinked rubber while TPSs are triblock copolymers. The TPEs (including TPVs and TPSs) may be injection moulded directly on a hard polymer in an integrated process, using two component injection moulding. The melt processing and the possibility for in-mould assembly are major reasons for a seen rise in market volume of TPEs. Another reason is that the performance of the TPEs, has been incrementally improved as the scientific knowledge has matured. The mechanical properties of thermoplastic elastomers are a wide topic, this work is limited to two subtopics: (i) Behaviour of a TPV in compression and (ii) the adhesion between soft (TPV or TPS) and hard material (polyamide-12). These investigated topics represents important performance criteria for usage of TPEs in demanding applications. The behaviour of TPV in cyclic compression was studied in a large temperature interval. The temperature effect was strong on some characteristics of the behaviour and weak on others. The TPV was also studied in cyclic compression side by side with a few crosslinked rubbers in order to elaborate on differences and similarities. The adhesion between soft and hard polymer was studied with a special focus on the effect of glass fibre concentration in the substrate. Additionally, the effect of ageing (hot and humid) on the adhesion strength was studied. Common for both subtopics is that they complement the existing scientific studies and add novelty due to both the selected model materials and the chosen experimental techniques. Explanations of the TPE behaviour was sought in the morphology.