SURFACE MODIFICATION OF SYNTHETIC VULCANIZED RUBBER

Surface modifications produced by treatments (mainly halogenation) of synthetic vulcanized styrene-butadiene rubber (SBR) leading to increas ed adhesion properties with polyurethane adhesives have been studied. T-peel tests, scanning electron microscopy (SEM), advancing contact an gle measurements, infra-red (IR) spectroscopy, X-ray photoelectron spe ctroscopy (XPS) and differential scanning calorimetry (DSC) were used to analyze the nature of surface modifications produced in the rubber. Although some surface heterogeneities were created, physical treatmen ts (ultrasonic cleaning, solvent wiping, abrasion) did not noticeably increase the adhesion strength because certain abhesive substances (e. g. zinc stearate, paraffin wax) cannot be removed from the rubber surf ace by such treatments. Chemical treatment (chlorination) was carried out using ethyl acetate solutions of trichloroisocyanuric acid (TCI) ( 1,3,5-trichloro-1,3,5-triazine-2,4,6-trione). Chlorination of SBR with trichloroisocyanuric acid produced a significant improvement in T-pee l strength, due to the contribution of mechanical (surface roughness, microcracks), thermodynamical (increase of polar contribution to the s urface energy) and chemical (removal of abhesive substances, creation of polar groups) rubber surface modifications. The strong adhesion bet ween the chlorinated SBR surface and the polyurethane adhesive was due to the presence of oxidized species of >C=O, -C-OH and -COR type. Chl orination of SBR is a fast reaction which needs only a small concentra tion of chlorination agent (< 1 wt% TCI/ethyl acetate) to produce high adhesion levels. An increased amount of TCI facilitated the chlorinat ion reaction progressing from the exterior to the internal rubber bulk ; however, although a thicker layer of chlorinated rubber created no f urther increase in adhesion strength was obtained.