Interfacial adhesion in sisal fiber/SBR composites: an investigation by the restricted equilibrium swelling technique

Short sisal fiber-reinforced styrene butadiene rubber (SBR) composites were prepared and characterized by the restricted solvent swelling technique. T he solvent swelling characteristics of SBR composites containing untreated and bonding agent-added mixes were investigated in a series of aromatic sol vents, such as benzene, toluene, and xylene. The diffusion experiments were conducted by the sorption gravimetric method. The adhesion between the rub ber and short sisal fibers was evaluated from the restricted equilibrium sw elling measurements. The anisotropy of swelling of the composite was confir med by this study. The effect of fiber orientation in controlling the aniso tropy of restricted swelling was also demonstrated. As the fiber content in creased, the solvent uptake decreased, due to the increased hindrance and g ood fiber-rubber interactions. Bonding agent-added mixes showed enhanced re striction to swelling, due to the strong interfacial adhesion. The bonding system containing hexa-resorcinol in the mix produces an in-situ resin, whi ch binds the fiber and the rubber matrix firmly. In addition, as the penetr ant size increases from benzene to xylene, the uptake decreases. The swelli ng index values of the composites support this observation. Due to the impr oved adhesion between the short sisal fiber and SBR, the ratio of the volum e fraction of rubber in the dry composite sample to the swollen sample (V-T ) decreases. The extent of fiber orientation of the composites was also ana lysed from the restricted swelling method. SEM studies of the composite rev ealed the orientation of short fibers. The sorption data support the Fickia n diffusion trend, which is typical in the case of cross-linked rubbers.