Chemical structure of amino-terminated alkyl silanes influencing the strength of aluminum-polyamide joints

Organo-functional silane coupling agents are widely used to promote adhesion in between inorganic and organic materials. Amino-functional silanes can improve bonding with polyamide. Aiming on a mechanically performant aluminum-polyamide joints, the effect of six amino silanes of different chemical structure, namely number and type of amine groups and alkyl spacers lengths, on the joint strength is investigated by means of lap-shear testing. Higher shear strengths are found along with a more pronounced capability of the amine group to form hydrogen bonds with polyamide. The results show that an additional amine group within the organo-functional group can increase joint strength, whereas long alkyl spacers reduce the observed joint strength. It is shown that high lap-shear strengths, in maximum about 15 MPa for N-(2-aminoethyl)-3-aminopropyltrimethoxysilane are achieved and that the high reproducibility can be assured when using right processing routines.