Mechanical and Aging Properties of Hydrogenated Epoxidized Natural Rubber and Its Lifetime Prediction

Abstract

Natural rubber (NR) has restricted its application due to its potential for thermal- and oil-resistant materials. The weakness of NR can be eliminated by chemical modification to enhance aging properties. Formic acid and hydrogen peroxide have been used to prepare partially epoxidized natural rubber (ENR) in the latex state. Its residual unsaturated units were then modified using hydrazine and hydrogen peroxide to obtain hydrogenated ENR (HENR). 1H-NMR characterized the resulting products. NR and modified NRs were compounded and then vulcanized using a conventional milling process. This paper compares NR, ENR having 49.5% epoxide group content, and HENR having 49.5% epoxide group content and 24% hydrogenation degree in terms of tensile, thermal, oil, and ozone properties. Morphology and lifetime prediction were studied. Overall results show that the tensile strength of the HENR composite (14.7 MPa) was 79 and 71% lower than that of ENR (18.6 MPa) and NR (20.8 MPa) composites, respectively. In contrast, the modulus at 100% elongation of the HENR composite (2.0 MPa) was 167 and 200% higher than that of ENR (1.2 MPa) and NR (1.0 MPa) composites, respectively. Morphological studies of the tensile fractured surface of the vulcanizates, using scanning electron microscopy, confirmed a shift from ductility failure to brittle with the presence of the epoxide groups and low unsaturated bonds in the backbone chain. The results demonstrated that HENR could act as an ideal material, providing better thermal, oil, and ozone resistances while maintaining the mechanical properties of the rubber. The kinetic analyses of the thermal degradation of NR, ENR, and HENR were studied using thermogravimetric analysis (TGA) at three heating rates. Kissinger-Akahira-Sunose (KAS) was employed to calculate the activation energy (Ea). The obtained data were used to predict the lifetime under the established temperature range and 0.05 conversion level. Overall, the results represented that HENR had a longer lifetime than NR and ENR for a temperature range between 25 and 200 °C, indicating that HENR had excellent thermal stability than NR and ENR. Therefore, the HENR should extend the applications to include gaskets and seals, especially for the automotive and oil industries.