Studying the effect of untreated and treated rice straw on different properties of carbon black filled styrene-butadiene rubber composites

Extensive investigations have been performed on Egyptian rice straw (RS) fibre residues to be employed as a supplementary reinforcement material in polymer composites. In this study, two identical groups based on carbon black (CB) filled styrene butadiene rubber (SBR) vulcanisates were prepared by incorporating different proportions (10–50 phr) of treated and untreated rice straw (TRS/ URS) in the SBR composites to examine their effects on some of the demanded properties in rubber applications. Maleic anhydride (MA), as a coupling agent, was added to improve the interfacial bonding between the hydrophilic RS natural fibre and the hydrophobic SBR matrix. The TRS and URS were selectively grinded through a grinding machine to obtain RS fine powder with a selective grain size distribution ranging from about 20–180 μm. Some important physico-mechanical properties of the rubber vulcanisates were studied. The prepared samples were analysed by using X- ray diffractometer (XRD) and scanning electron microscopy (SEM). The tensile strength (TS), modulus (M100) and hardness values of TRS filled composites were almost superior compared to the URS ones, and 20 phr of TRS was found to be the optimum filling in SBR vulcanisates and this was obviously revealed through all the mechanical properties results as well as in the percentage swelling findings. The SEM analysis indicates that the presence of MA increases the interfacial interaction between SBR, and the alkali treated rice straw fibres, as well it was found to be in complete agreement with the TS findings. The XRD analysis reveals that the alkaline pretreatment of RS fibres was found to yield a higher crystallinity index for the SBR vulcanisates. The results indicate the potential of using TRS as filler in the rubber industry for cost reduction and raising the environmental credentials of the product.