by Abbas Ghanbari, Ali Vahidifar, Zia Chawdhry, Joy Spandler, Steven Yu – Airboss of America
Natural rubber (NR) is used in manufacturing various products such as pneumatic passenger vehicle tires and those used under heavy conditions for aircraft and off-the-road vehicles, conveyor belts, footwear, water and fire hoses, gloves, dock fenders and o-rings. The wide application range of NR is due to its unique combination of properties, including low heat build-up, good crack growth resistance and tear strength, high extensibility, remarkable strength, good bonding tack and resilience at low temperatures, and abrasion resistance. Inclusion of various ingredients is inevitable in the proper formulation design of NR based products with desired performance. Dispersion of the incorporated chemicals, fillers and additives in NR compounds is challenging due to the extremely high molecular weight of the polymer, which also requires high energy during compounding. Therefore, NR is usually masticated for viscosity reduction through breakdown of the long molecular chains to facilitate subsequent processing steps (e.g., extrusion and calendering) and improve rheological properties, such as die swell, shrinkage and building tack.