Influence of the nature and formulation of sty rene-butadiene rubber on the effects produced by surface treatment with trichloroisocyanuric acid

The nature and formulation of two synthetic sulfur-vulcanized styrene-butadiene rubbers affected the extent, but not the nature, of the surface modification produced by halogenation with different amounts (1-7 wt%) of trichloroisocyanuric acid (TCI) solutions in ethyl acetate. R1 rubber had a low oil and plasticizer content, whereas R2 rubber contained a smaller amount of styrene than R1, and a relatively significant amount of oil and plasticizer. Chlorination of the rubbers decreased their tensile strength (more markedly in R2) without noticeable changes in elongation at break, and heterogeneities and cracks were created on the rubber surface (mainly in R2). The surface modifications were not influenced by the manner in which the post-chlorination agent was removed (air or vacuum). Chlorination with TCI created C-Cl, C-O, and COO- moieties on the rubber surface which were responsible for its enhanced acid-base contribution to the surface energy. The extent of chlorination was more extensive in R1 (the rubber with a smaller butadiene content). The surface modification was less effective for R2, due to its noticeable amount of oil and plasticizer. On the other hand, when the chlorination was carried out with 7 wt% TCI, removal of the excess of the post-chlorination agent in vacuum prevented the formation of weak boundary layers (due to isocyanuric acid + mechanically damaged surface) in the treated surfaces. The nature and formulation of the rubber determined the thickness of the weak boundary layer (thinner in R1). On the other hand, a relatively deep penetration (at least 10 nm) of the chlorination agent into the rubber bulk was produced.     

UV treatment of synthetic styrene-butadiene-styrene rubber

The effectiveness of the treatment with ultraviolet light (UV) on several polymeric surfaces has previously been established. In this study, a low pressure mercury vapour lamp was used as a source of UV radiation for the surface treatment of a difficult-to-bond block styrenebutadiene-styrene rubber (S6), the treatment time ranging from 10 s to 30 min. The UV-treated S6 rubber surfaces were characterized by contact angle measurements (ethylene glycol, 25°C), ATR-IR spectroscopy, XPS, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). T-peel tests on UV-treated S6 rubber/polyurethane (PU) adhesive/ leather joints (before and after ageing) were carried out to quantify adhesion strengths. The UV treatment of S6 rubber produced improved wettability, the formation of C—O, C=O and COO^- moieties, and ablation (removal of a thin rubber layer from the surface). The extent of these modifications increased with increasing treatment time. The extended UV treatment produced greater surface modifications, as well as the incorporation of nitrogen moieties at the surface. Furthermore, noticeable ablation of S6 rubber surface occurred. Peel strength values increased with increased treatment time of UV treatment of S6 rubber. Also, with increasing treatment time, the adhesive joints showed different loci of failure: adhesional failure for the as-received and 2 min-UV treated S6 rubber/polyurethane adhesive/leather joints changed to mixed failure (cohesive in the treated S6 rubber + adhesional failure) for the 30 min-UV treated S6 rubber/polyurethane adhesive/leather joint.     

Addition of Silica to Polyurethane Adhesives

The influence of the addition of silica (Aerosil-200) (5-25 wt%) to polyurethane adhesives on their adhesion properties with non-chlorinated and surface-chlorinated rubbers has been studied. The chlorinating agent was Trichloroisocyanuric acid (TIC) in 2-butanone solution at a concentration of between 1 and 9 wt%. In general, silica produced an increase in the adhesive viscosity and an improvement of green (immediate) peel strength (especially with chlorinated rubber). The best results were obtained for a silica content of 10-20 wt%. However, the addition of silica did not improve the peel strength after a thermal ageing process. Polyurethane adhesives containing silica undergo an improvement in their resistance to degradation by chlorine on the rubber surface. On the other hand, the chlorination of silica produces the rupture of Si-O bonds and the formation of Si-H and Si-Cl groups. Furthermore, the stirring speed (directly related to the dispersion) of silica into the adhesive is an important parameter which affects the viscosity and peel strength. A stirring speed of 1000 rpm gives the best silica dispersion.     

Addition of Silica to Polyurethane Adhesives

The influence of the addition of silica (Aerosil-200) (5-25 wt%) to polyurethane adhesives on their adhesion properties with non-chlorinated and surface-chlorinated rubbers has been studied. The chlorinating agent was Trichloroisocyanuric acid (TIC) in 2-butanone solution at a concentration of between 1 and 9 wt%. In general, silica produced an increase in the adhesive viscosity and an improvement of green (immediate) peel strength (especially with chlorinated rubber). The best results were obtained for a silica content of 10-20 wt%. However, the addition of silica did not improve the peel strength after a thermal ageing process. Polyurethane adhesives containing silica undergo an improvement in their resistance to degradation by chlorine on the rubber surface. On the other hand, the chlorination of silica produces the rupture of Si-O bonds and the formation of Si-H and Si-Cl groups. Furthermore, the stirring speed (directly related to the dispersion) of silica into the adhesive is an important parameter which affects the viscosity and peel strength. A stirring speed of 1000 rpm gives the best silica dispersion.