Treatment of a styrene-butadiene-styrene rubber with corona discharge to improve the adhesion to polyurethane adhesive

A styrene–butadiene–styrene (S6) rubber was treated with corona discharge to increase its surface energy and adhesion to polyurethane (PU) adhesive. The influence of the length of treatment (the speed of the upper plate was varied from 80 to 900 cm/min) during corona discharge was analyzed. The corona energy applied to S6 rubber surface ranged from 0.4 to 4.6 J/cm2. The surface modifications produced as a consequence of the corona discharge were characterized immediately after treatment was carried out and were monitored by means of different surface analysis techniques, mainly contact angle measurements (ethylene glycol, 25°C), ATR-IR spectroscopy, XPS and Scanning Electron Microscopy (SEM). T-peel tests of corona-discharge-treated S6-rubber/polyurethane (PU) adhesive/leather joints (72 h after joint formation) were carried out to evaluate the influence of the surface modifications produced by the corona discharge on the adhesion properties of the treated S6 rubber. rona discharge improved the wettability of the S6 rubber due to the formation of polar moieties, mainly C–O, C=O and COO− groups. These chemical modifications were not detected by ATR-IR spectroscopy (depth of analysis about 5 μm), indicating that a nanometer-range oxidized layer was created on the S6 rubber surface by treatment with corona discharge. Besides, surface cleaning and removal of rubber contaminants (mainly silicon moieties) were produced but roughness was not created as a consequence of the treatment. These modifications were enhanced when a low speed treatment (long treatment and high corona energy) was carried out. Peel strength values of corona-discharge-treated S6 rubber/PU adhesive/leather joints only moderately increased (mainly for long length of the corona discharge). Although corona treatment chemically modified the surface of the S6 rubber, the absence of surface roughness might likely be responsible for the slight improvement in its adhesion properties.