Metal–thermoplastic urethane hybrids in environmental exposure

The long-term properties of injection moulded metal–thermoplastic urethane (TPU) hybrids were studied. The hybrids manufactured with different metal substrates, namely copper, stainless steel and aluminium, were compared, using two surface modifications for copper and stainless steel. N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane was used as coupling agent. It is concluded that the bond mechanism of the silane on different substrate differs, affecting the long-term behaviour of the respective hybrids. The thick layers of silane coupling agent on copper and stainless steel are sensitive to hydrolysis; thus the resistance in humid conditions is quite low. The high temperature exposure increased the bond strength and the fraction of cohesive failure in TPU in copper–TPU, aluminium–TPU and polished steel–TPU hybrids. The last one has native mixed oxide, contrary to controlled oxidised stainless steel, where adhesion decreased after any long-term experiments. This is suggested to derive from hydrogen bonding of the coupling agent to the surface Fe2O3 oxide.