The role of model fatty acid and protein on thermal aging and ozone resistance of peroxide vulcanized natural rubber

Natural rubber (NR) contains cis-1,4-polyisoprene and many kinds of non-rubber components, e.g., proteins, lipids and phospholipids, which are believed to affect the properties of NR. Oxidative degradation is one of the problems for rubber performance, which shorten the service life of the product. To overcome this problem, the influence of fatty acids and proteins on the cure properties, heat-ageing behaviours, and ozone resistance of NR vulcanizates were investigated. The peroxide vulcanization was chosen to avoid the effect of essential fatty acid and proteins. The purified NR, deproteinized NR (DPNR) and lipids-removed NR (LRNR) were mixed with model fatty acid (stearic acid) and amino acid (alanine). It was found that the cure behaviour of these mixed samples showed almost the same trend. After removing proteins, the rate of oxidative degradation was faster than that of the lipid-removal samples. Lower lipid content would result in less oxidative degradation of the rubber. These findings can infer that the endogenous proteins in NR act as natural antioxidants, while the endogenous lipids are pro-oxidants.