Tensile Strength of Protein-free Natural Rubber and its Vulcanizate Soaked in Water

Vulcanization, tensile strength and water-resistance of protein-free natural rubber (PFNR) were investigated in a viewpoint of application to a seal-product. The PFNR was prepared by incubation of high ammonia natural rubber (HANR) latex with urea, sodium dodecyl sulfate and acetone followed by washing with a centrifuge, twice. It was vulcanized with sulfur, zinc oxide, accelerator, stearic acid and anti-aging agent at 150 °C. Optimum vulcanization time and crosslink density were prolonged and lowered by removing proteins, respectively. The resulting vulcanized PFNR was characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) and nuclear magnetic resonance spectroscopy (NMR). After soaking in water, stress at break of vulcanized HANR decreased, whereas that of vulcanized PFNR did not. The PFNR in water was proved to be superior in the stress at break due to improvement of water-resistance that was a drawback of natural rubber.