Thermoplastic elastomer vulcanizate (TPV) and liquid silicone rubber (LSR) are replacement candidates for ethylene-propylene-diene rubbers (EPDM), as they offer the possibility for two-component injection moulding. In this study, these material types were compared side by side in cyclic compression tests. The materials were also characterized to provide details on the formulations. Compared to the rubbers, the TPV had higher compression set (after a given cycle) and hysteresis loss, and a stronger Mullins effect. This is due to the thermoplastic matrix in the TPV. The LSR had lower compression set (after a given cycle) than the EPDM, but stronger Mullins effect and higher relative hysteresis loss. These differences between the LSR and the EPDM are likely due to differences in polymer network structure and type of filler. Methods for quantifying the Mullins effect are proposed, and correlations between a Mullins index and parameters such as compression set are discussed. The EPDMs showed a distinct trend in compression set, relative hysteresis loss and relaxed stress fraction vs. strain amplitude; these entities were almost independent of strain amplitude in the range 15–35%, while they increased in this range for the TPV and the LSR. The difference between the compression set values of the LSR and the EPDM decreased with increasing strain amplitude and increasing strain recovery time.

The usage of thermoplastic elastomers (TPEs) is increasing, and integrated hard‐soft parts can be mass produced by two‐component injection molding (or sequential molding). A key property of such parts, the adhesion between the two materials, is the topic of this study. The hard part (the first molded component) in this study was polyamide‐12 with 0 to 50 wt% glass fibers (PA12‐GF). As the second component, two TPEs were used: a vulcanized TPE and a styrenic TPE, both modified for adhesion to polyamides. The adhesion, assessed by 90° peel tests, increased with increasing melt temperatures and TPE injection rate, while it decreased with increasing glass fiber fraction in the PA12‐GF. Based on characterization of cross‐sections and fiber distributions near the interface, we propose some hypotheses for the effect of fiber fraction on the fusion between PA12‐GF and TPE. These hypotheses involve the near‐surface properties of the PA12‐GF materials, microstructure, thermo‐mechanical properties, and thermal properties. A direct effect of increasing the glass fiber fraction, that is, a reduction in adhesion as more fibers are present at the interface, does not seem to be a major effect, since few fibers are in direct contact with the TPE for any fiber fraction.