Silane adhesion promoters

A model polyurethane (PUr) adhesive has been modified by the addition of various silane adhesion promoters and used to bond PVC, ABS, a polyblend and glass. Inverse gas chromatography (IGC) data showed that epoxy silane substantially increased the surface reactivity of the adhesive while maintaining its amphoteric character. An aminosilane shifted the PUr surface to basicity, while vinyl, mercapto and chlorosilanes promoted surface acidity. Lap-shear data identified the amphoteric epoxy silane as the most successful adhesion promoter in all polymer and glass assemblies, increasing their initial bond strengths and also their residual bond strengths following accelerated aging. Elsewhere, the success of silane additives reflected the strength of interfacial acid/base interactions, the aminosilane being favored for bonding PVC, the others being preferred for the basic ABS and polyblend substrates. Correlations were developed between residual bond strength and initial bond properties of the assemblies and also between these system characteristics and an acid/base interaction parameter. The correlations may be useful as guidelines to the formulation of superior adhesives for bonding with substrates of known acid/base interaction potential.