Chlorination of vulcanized styrene-butadiene rubber using solutions of trichloroisocyanuric acid in different solvents

Abstract

The chlorination of vulcanized styrene-butadiene rubbers (SBRs) with trichloroisocyanuric acid (TCI) has been studied. The solvent used to apply the TCI chlorinating solutions on the rubber plays an important role in the effectiveness of the treatment since the solvent determined the degree of penetration of TCI into the rubber and also different chlorinating species were produced depending on the nature of the solvent. Surface modifications produced on a synthetic sulfur-vulcanized SBR using TCI solutions in ethyl acetate (EA), methyl ethyl ketone (MEK), and EA + MEK mixtures have been compared. Furthermore, the effects of a solvent wipe with EA or MEK prior to the chlorination process were also considered. Surface modifications produced by the treatments were analyzed using ATR-IR spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Adhesion was obtained from the T-peel strength of treated rubber/polyurethane adhesive joints. TCI/MEK solutions produced a higher degree of surface modification than TCI/EA solutions, but TCI/EA solutions were more effective in removing zinc stearate from the rubber surface. When high TCI percentages (5-7 wt%) in EA solutions were used, a weak boundary layer (WBL) was created on the rubber surface as a consequence of the deposition of an excess of chlorinating agent on the rubber surface and of by-products (cyanuric and/or isocyanuric acid). The formation of the WBL led to a lack of adhesion in the rubber towards the polyurethane adhesive. When MEK was used as a solvent for TCI, this WBL was not produced on the rubber surface, and thus adhesion was considerably higher even when high concentrations of TCI/MEK were used. Similar effects were produced using EA + MEK mixtures as the solvent for TCI. The wiping of the rubber surface with MEK prior to the chlorination treatment led to good adhesion, irrespective of the percentage of TCI and the solvent used in the chlorinating solution.