The use of silane reagents as primers to enhance the adhesion of chromium tanned heavy-duty leather (Salz leather)

This paper investigates the use of silane reagents in a non-traditional role as a primer for modifying the chemical characteristics of chromium (Cr) tanned heavy-duty leather (Salz leather). The silanes investigated were 3-aminopropyltriethoxysilane (APES) and 3-(2-aminoethylamino)propyltriethoxysilane (AEAPES), applied as a polymer solution to leather surfaces treated with an isocyanate monomer to create an interpenetrating polymer network (IPN), prior to bonding with the polyurethane adhesive. The assembled strengths of APES and AEAPES samples were measured using the T-peel test against 2-hydroxyethyl methacrylate samples and conventionally treated samples (abrasion, chloroform and surfactant washing), under dry and wet testing conditions. The physical structure of leather surfaces was investigated using scanning electron microscopy (SEM) and the chemical composition by electron dispersive X-ray spectroscopy (EDX) for Cr, Si and Al impurities. The results indicate that APES and AEAPES treatments significantly enhance surface adhesion with respect to abrasion alone and in the latter case by 179% (dry) and 52% under wet conditions. The adhesive joints tested showed cohesive failure indicating that the improvements in adhesion were due to the generation of a consistent network across the interface due to increased physical adsorption of the silane polymer with the leather surface and interaction with the polyurethane adhesive via van der Waals forces and/or hydrogen bonding.