Chemical nature of adhesion: Plasma modified styrene-butadiene elastomer and polyurethane adhesive joints

A study of the mechanism of gluing between plasma-modified styrene-butadiene elastomer (SBS) surfaces and polyurethane (PU) adhesives is presented in this paper. The plasma treatment was carried out employing low-pressure O₂ plasma generated by an RF discharge (13.56 MHz). FTIR-ATR spectroscopy and peel tests were utilized to characterize the SBS surfaces before and after the plasma treatment. It was found that hydroxyl groups are mainly created on the SBS surface by the plasma treatment and their concentration reveals very good linear correlation with the peel strength of the SBS-PU joints. The grafting of phenyl isocyanate (analog of the PU curing agent) into the plasma-treated SBS surface was also investigated. The process was performed at 353 K, that is at temperature in which the adhesive-bonded joints were made. It was shown that all hydroxyl groups on the SBS surface react with isocyanate groups forming carbamate bonds. The results obtained in this work strongly confirm the conception of the adhesion by chemical bonding between SBS and PU.