Adhesion between thermoplastic elastomers and polyamide‐12 with different glass fiber fractions in two‐component injection molding

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.