A comparative study on the use of photoreagents for the enhancement of adhesion on heavy-duty leather (Salz leather)

This paper aims to expand on work presented by us in previous publications regarding the enhancement of adhesion on leather substrates with photoreagent type primers. Two new reagents were synthesized: 3,5-dihydroxyphenyl-4-azidobenzoate (7) and 4,4′-ethylene-1,1′-diphenyl azide (8) and used as an intimate mixture with commercial polyurethane adhesive (Solibond PU39), to enhance the adhesion of Salz leather surfaces. The molecular design of the primer molecule was intended to provide 2- and 3-point fixation between the substrate and adhesive. The strength of adhesive joints do not seem to be highly dependent on the molecular structure of the primers investigated in respect to the type of OH groups present (aliphatic or aromatic), both confer high adhesive strengths under dry and wet testing conditions. Cyanuric chloride (CNCl)3 a commercially used primer when tested under the same conditions for comparison purposes, gave good results but with a high standard deviation. Overall, the azide primers generate good, reliable joint strengths under extreme testing conditions and we believe they present negligible technological problems to industrial scale implementation.