Addition of ozone in the UV radiation treatment of a synthetic styrene-butadiene-styrene (SBS) rubber

Abstract The effect of exposure to different ozone concentrations, in conjunction with UV radiation, on the surface modification and adhesion properties of a block synthetic styrene-butadiene-styrene (S6) rubber was studied. The treatment time varied between 10 s and 30 min. Three different surface treatments were investigated: ozone only (O3), UV radiation in the presence of air, and UV radiation in the presence of externally generated, supplemental ozone (UV/O3). The surface modified S6 rubber was characterized using contact angle measurements (ethylene glycol, 25 °C), Fourier transform infrared spectroscopy using an attenuated total reflection attachment (ATR-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). T-peel tests of surface modified S6 rubber/polyurethane (PU) adhesive/leather joints were carried out to quantify the changes in the adhesion properties. The O3, UV and UV/O3 treatment of S6 rubber improved wettability, created oxygen-containing moieties at the surface, and resulted in ablation of the surface (removal of a thin rubber layer from the treated S6 rubber surface). Different surface modifications were produced using each treatment and these modifications were enhanced with increasing treatment time. Whereas the UV and UV/O3 treatments created C O and COO− moieties on the S6 rubber surface, the O3 treatment produced a lower degree of oxidation (predominantly O–H moieties). For short treatment time, O–H and C–O moieties were dominant, and the increase in the length of treatment lead to more oxidized moieties (C O, COO−). Lower degree of oxidation was obtained with O3 treatment as compared to that obtained with UV and UV/O3 treatments. Adhesion was highly improved after UV and UV/O3 treatments of S6 rubber, more markedly with increasing treatment time. A moderate increase in peel strength of the joints produced with O3-treated S6 rubber was produced and an adhesion/cohesive failure in a thin rubber layer was observed irrespective of treatment time. On increasing the treatment time with UV and UV/O3, the adhesive joints showed different loci of failure: adhesion+cohesive failure in a thin rubber layer for the S6 rubber treated for 2 min with UV or UV/O3, and cohesive failure in the S6 rubber treated for 30 min with UV or UV/O3 treatments.