Journal of Elastomers & Plastics

The curing and mechanical properties of nitrile (NBR) and natural rubber (NR) blends were carried out. Two series of blends were prepared, i.e., NBR/SMR L and NBR/ENR 50 blends. Blends were prepared using a Brabender at a temperature of 60°C. Results indicate that the scorch time, t ₂ and cure time, t ₉₀ increase with increasing NBR content in both blends. In NBR/ENR 50 blends the increasing content of NBR increases the maximum elastic torque, torque difference, tan δ @ MH and viscous torque. However, in NBR/SMR L blends the opposite trend is observed for maximum elastic torque and torque difference. In both blends modulus at 100% elongation (M100) and at 300% elongation (M300) increases with increasing NBR content, whereas tensile strength and elongation at break show a decreasing trend.

In the present work, the effect of different network structures, created in natural rubber vulcanizates by different curing systems, on the fatigue behavior was studied. The accompanying changes in the physico-mechanical properties of unfilled and filled rubber vulcanizates was also studied. It was found that the physico-mechanical properties greatly depend on the curing system used. Scanning electron microscopy (SEM) was used to study the failure mechanism of rubber. The SEM results show the changes in network structure of the natural rubber vulcanizates, which have undergone fatigue failure via flexing. On the other hand the loading of rubber compounds with reinforcing filler increases stiffness, improves the mechanical properties and decreases the resistance to fatigue of the resultant vulcanizates.

The fatigue properties of [±20°] steel cord-rubber laminated composite under tension-tension (T-T) loading are studied in this paper. The results show that the variation of the cycle strain in the fatigue process under the constant cycle loading exhibits three stages which correspond to damage initiation, steady damage propagation and catastrophic failure. Two-step experiments demonstrate that the strain variation in step-2 generally follows the similar regularity, indicating that the three-stage behavior also exists in that of the defected specimens. The S-N data in the fatigue-life diagram follow a linear trend. Studies on the effect of the frequency on the fatigue properties show that the higher the frequency of loading, the faster the cycle strain increases and the shorter the fatigue life is. The hysteretic loss caused by the viscoelasticity of the constituent materials remains constant during the steady propagation stage of the damage. Both the surface temperature and its increasing rate go up as the maximum stress and the frequency increase.

Die swell measurements were performed on low density polyethylene, polypropylene, and polystyrene, in a Randcastle microtruder over a range of shear rate, length/diameter ratio (L_i/D_i) of die, and polymer melt temperature to accelerate efforts to develop reliable quantitative description of die swell phenomena observed in practical polymer processing operations. Die swell of these polymers increased with increasing shear rates. An increase in polymer melt temperature and the length/diameter ratio of the Microtruder die decreased the die swell of the polymers. A comparison of the experimental data with predictions from various existing models such as the ones reported by Bagley and Duffey, Mendelson et al., Tanner, White and Roman, Vinogradov and Malkin, Macosko and Kumar et al. revealed that existing models are not capable of accurately predicting the die swell of the materials. Therefore, a theoretical model based on strain energy density function, Gaussian network theory, and first normal stress difference with no adjustable parameters appropriate for determining die swell has been developed for Newtonian fluid. The experimental data for the polymers studied conformed excellently well with predictions from this proposed model. Thus for the first time a suitable quantitative model for exploring die swell phenomena in actual polymer processing equipment, such as an extruder, is established. Further, a special linear relationship between die swell and maximum recoverable deformation and a nonlinear relationship between die swell, storage and loss moduli have been established for these polymers. The first normal stress difference, calculated from the maximum recoverable deformation, has been found to vary strongly with shear stress and shear rate but independent of temperature for a specific polymer. Flow activation energies of the polymer melts decrease with increasing frequencies, indicating increased mobility of polymer chains at such frequencies.