To assess and predict the functional life of a natural rubber engine mount compound, the mechanical property changes were determined under accelerated aging conditions. The rubber was aged at temperatures ranging from 70 to 1108C for times ranging from 1 h to 5 weeks. Tensile and fatigue measurements were used to characterize the aging trends and mechanisms of the engine mount compound. With the time-temperature superposition approach, the activation energy was found to be about 98 kJ/mol for the elongation at break, 93 kJ/mol for the tensile strength, and 60 kJ/mol for the fatigue life. The tensile strength after aging for 13 weeks at 508C was predicted to be 18.73 MPa, which was very close to the experimental value of 19.04 6 2.25 MPa. With a 50% reduction in the tensile strength used as the failure criterion, it was predicted that the tensile strength of the engine mount compound would take 80 days to decrease by 50% at 708C. At 238C, it would last approximately 140 times (31 years) its lifetime at 708C.

Most unfilled elastomers exhibit a high electrical resistance. Fillers are usually added to elastomers to enhance their mechanical properties. Frequently the filler type used is an electrically conductive carbon black and the inclusion of such fillers reduces the resistivity of the elastomer compound. Previous work has shown that for elastomers containing high abrasion furnace, carbon black fillers such as N330 (or N300 series) at a volume fraction above the percolation threshold the resistivity changes with strain, the precise resistivity versus strain behavior being nonlinear and irreversible for conventional carbon black fillers. A strain-measuring device, deriving strain directly from a measure of the resistivity, requires that the behavior be reversible and reproducible from cycle to cycle. This work presents the electrical resistivity behavior of a natural rubber (NR) compound filled with Printex XE2 carbon black. This type of filler has a significantly different morphology to the N300 series blacks examined previously. The Printex was incorporated into the rubber at a volume fraction above its percolation threshold and its behavior is contrasted to that observed with N300 series carbon black-filled NR. Here, and for the first time, reversible electrical resistivity dependence with strain is reported for an elastomer filled with Printex XE2. This reversible behavior under strain opens up the possibility of applications, such as a flexible load sensor, pressure sensor, or switch.

No abstract

Natural rubber (NR) undergoes chemical changes on heat and air ageing. These changes affect its physical properties and as such, affect the service life of the rubber compound. In this study, a vulcanized NR compound of a typical engine mount composition was subjected to thermooxidative ageing at temperatures from 70 to 1108C, to assess the effect on the tensile properties. The kinetics of degradation of the rubber compound, in terms of changes in these properties, was investigated. A fractional rate law was used to describe the kinetics of ageing in terms of its effect on modulus. Rates of ageing, in terms of effect on modulus, passed through a minimum at about 808C, indicating the danger of trying to extrapolate in-service ageing behavior from high temperature ageing data. The activation energy of ageing in terms of its effect on modulus, determined for temperatures of 90-1108C, was 151 kJ mol À1. A second order rate law was used to describe the kinetics of ageing in terms of its effect on tensile strength and elongation at break, with activation energies of 88.32 and 74.3 kJ mol À1, respectively. According to Ahagon's (Ahagon et al., Rubber Chem Technol, 1990, 63, 683) classification of ageing mechanisms, Type I and Type III ageing mechanisms were predominant.

The effect of a large amount of precipitated amorphous white silica nanofiller, pre-treated with bis[3-triethoxysilylpropyl-)tetrasulfide (TESPT), on the mechanical properties of a sulfur-cured natural rubber (NR) was studied. TESPT chemically adheres silica to rubber and also prevents silica from interfering with the reaction mechanism of sulfur-cure. The silica particles were fully dispersed in the rubber, which was cured primarily by using sulfur in TESPT, or, by adding a small amount of elemental sulfur to the cure system. The cure was also optimized by incorporating sulphenamide accelerator and zinc oxide into the rubber. The hardness, tear strength, tensile strength, and stored energy density at break of the vulcanizate were substantially improved when the filler was added. Interestingly, these properties were also enhanced when the rubber was cured primarily by using sulfur in TESPT.