Influence of the cure systems on long time thermal aging behaviors of NR composites

Abstract

NR composites with different curing systems were aged thermally at 60, 70, 80, and 90 o C for 2-185 days in a convection oven, and the changes in the crosslink density were investigated as a function of the accelerated thermal aging. The overall crosslink densities increased with increasing aging time irrespective of the aging temperatures and curing systems. The changes in crosslink density were enhanced by increasing the aging temperature. The degree of the increased crosslink density was in the following order: "the conventional cure system > the semi-EV system > the EV system". For short term thermal aging, the change in crosslink density with the aging time was complicated, particularly for low temperature aging. The activation energies of the change in crosslink density with thermal aging using the conventional and semi-EV cure systems increased and then remained relatively constant with increasing aging time, whereas that of the specimen with an EV cure system tended to increase linearly. The experimental results were explained by the dissociation of the existing polysulfidic linkages and the formation of new crosslinks through the crosslinking-related chemicals remaining in the sample.

Study on the Aging Behavior of Natural Rubber/Butadiene Rubber (NR/BR) Blends Using a Parallel Spring Model

“…This is because, as the aging proceeds [29], the molecular weight of the rubber increases and chain molecules are generated, thereby widening the molecular-weight distribution. Thus, the rubber molecules have reduced flexibility [30], which limits the intermolecular slippage and reduces the swelling [31]. In the case of unaged specimens, the initial crosslink density is about 4.5 × 10 −5 mol/cm 3 , and it can be confirmed that the crosslink density increases up to 14.5 × 10 −5 mol/cm 3 as the aging progresses.…”

Thermal Aging Behaviors of Weather Resistant Rubber Composites of EPDM, IIR, and BIIR

“…The values are relatively much lower than those of general R group rubbers such as NR, BR, SBR, and NBR. [2][3][4][5][6][7][8][9][10] The crosslink densities of the EPDM composite increased after thermal aging irrespective of the aging temperatures and the aging times. The crosslink densities of the BIIR composite also increased after thermal aging except the long-term thermal aging at high temperatures.…”

“…For the long-term themal aging of the IIR and BIIR compo- [5][6][7] The crosslink densities of the IIR and BIIR composites after thermal aging at 90 ℃ for a long time above 100 days also decreased as shown in Figure 4(b). This may be due to the chain scissions of the IIR and BIIR by oxidation.…”

“…Amounts of HPPD remained in the rubber samples after thermal aging at 90 ℃ for 35 days were negligible as shown in Figures. [5][6][7] Activation energies for the ΔXcs by thermal aging were obtained from the Arrhenius plot of lnk vs 1/T, where k is the ΔXc and T is the aging temperature, to compare the thermal aging behaviors of the EPDM, IIR, and BIIR composites. The activation energies varied with the aging time as shown in Figure 8.…”

“…1 Hence, degrees of crosslink density changes of the R group rubber composites by themal aging are relatively high, and their physical and chemical properties are also changed. [2][3][4][5][6][7][8][9][10] Of R group rubbers, isobutene-isoprene rubber (butyl rubber, IIR) has relatively good thermal resistance properties since it has only isoprene content with less than 3 wt%. 11,12 Crosslink type and degree of crosslink density of a rubber vulcanizate determine the physical properties such as modulus, hardness, resilience, elongation at break, heat build-up, and so forth.…”