The role of non-rubber components acting as endogenous antioxidants on thermal-oxidative aging behavior of natural rubber

Natural rubber (NR) with complex compositions has more excellent thermo-oxidative resistance properties compared to synthetic high cis -1,4-polyisoprene (IR), although synthetic IR owns similar molecular chain structure to NR. Compared with synthetic IR, the existence of non-rubber components is an obvious characteristic of NR. In this study, we pay attention to the non-rubber components acting as endogenous antioxidants, causing significant impact on thermo-oxidative resistance of NR. After removal of non-rubber components, the retention of tensile strength of NR exhibits a 2.7-fold decrease (from 84.29% to 31.29%) after 24 h of aging at 100 °C. The effect of non-rubber components on improving thermo-oxidative resistance of NR can be verified and mimicked through additional acetone extract or δ-tocopherol. The results show that the retention of tensile strength of purified NR (PNR) increases from 3.06% to 64.31% and retention of elongation at break of PNR increases from 60.61% to 92.59% after 48 h of aging after adding 0.6% δ-tocopherol, which can be comparable to or even exceed some traditional antioxidants. Furthermore, the antioxidative mechanism of endogenous antioxidant is explored. This work reveals another characteristic of non-rubber components and provides a rational design for the new biomimetic rubber with unique compositions and excellent properties similar to NR.