Two-component injection moulding of thermoset elastomer and rigid thermoplastic

Abstract

This project is a collaboration between the University of Malta and Trelleborg Sealing Solutions Malta. The main aim of this dissertation was to investigate the bond strength in two-component (2K) injection moulding (IM) through the use of different roughness values at the interface between the rigid thermoplastic and the thermoset elastomer materials. This encompasses various tasks, firstly through the machining of metal inserts with different roughnesses using EDM machining. Then the production of the rubber to plastic products using two-component injection moulding process. Finally, the fabricated 2K samples were tensile tested to determine the correlation of surface roughness with the bond strength. 2K IM allows the production of components made from two material types without the use of conventional over-moulding process or post-processing, such as assembly. This technique would help in potential saving on the rubber, the elimination of costs related to the assembly process and better interface properties. However, there are various challenges when using such a process, since it involves different processing temperatures for the injection of the thermoplastic and thermoset elastomer materials. The 0.31µm, 4.1 µm and 6.3 µm roughness values were machined on metal stopper inserts, and then replicated on the thermoplastic and thermoset elastomer interface during injection moulding. After the samples were moulded, tensile testing and microscopic analysis were performed to determine how different roughness values and ageing relate to the bond strength. The thermoplastic side of the dumbbells were also analysed to verify that the roughnesses from the metal inserts were being replicated. Results from the experimental investigation revealed that high roughness values affect the adhesion of the material combination, due to higher mechanical interlocking resulting in higher amount of residue at the interface of the fabricated samples. From the tensile test results obtained, strong adhesion was achieved between the 4.1 µm and 6.3 µm roughnesses, however, high interface roughness does not significantly alter the adhesion due to increase in air inclusion at the interface. This was further confirmed through microscopic analysis at the interface of the samples after tensile testing. Furthermore, from the results obtained the bond strength also changes depending on the ageing process conducted.