Characteristics of natural rubber – carbonized pawpaw seed composites

The search for eco-friendly and less expensive fillers and additives has necessitated the use of renewable natural resources of plant origin in rubber compounding. This research work utilized carbonized pawpaw (Carica papaya) seeds as filler in natural rubber compounds in a bid to determining the reinforcing potentials. The carbonized pawpaw seeds (CPS) and dried raw pawpaw seeds (RPS) were separately pulverized, screened with a 75 μm sized test sieve and incorporated into natural rubber, Standard Nigerian Rubber (SNR 10), loaded between 0 – 50 parts per hundred (Phr) of the rubber. The cure characteristics, physicomechanical properties as well as the percentage swelling characteristics of vulcanizates were measured as a function of filler loading and compared with the values obtained using industrial grade carbon black (N330) as a standard reinforcing filler. Results showed that the CPS and RPS filled SNR 10 influenced the cure characteristics and physicomechanical properties of rubber vulcanizates. The scorch and cure times of the vulcanizates decreased as filler loading is increased while maximum torque increased with increase in filler loading. Tensile strength and modulus at 100% strain for all SNR 10 filled vulcanizates increased to optimum level at 40 phr respectively, thereafter decreased, and elongation at break decreased as filler loading is increased. The hardness and abrasion resistance of the vulcanizates increased with increase in filler loading, while compression set and percentage swelling in both petroleum and aromatic solvents decreased as filler loading is increased. The vulcanizates tend to swell more in aromatic solvents than in petroleum solvents. Percentage swelling of the vulcanizates (N330 – SNR 10 < CPS – SNR 10 < RPS – SNR 10) and in the order benzene > toluene > kerosene > diesel solvents. The research work showed that CPS and RPS fillers exhibited considerable reinforcing potentials but somewhat inferior to carbon black, N330. Keywords: Natural rubber, pawpaw seeds, fillers, vulcanizates and reinforcement