Characterization of the Viscoelastic and Vulcanization Behavior of Natural Rubber Nanocomposites Having Different Levels of Nano Silicate/Black

Abstract

The effects of various loadings of nano layered silicate (NS) and black (BK) were investigated on the cure and stress relaxation behavior of natural rubber (NR), for both uncured and cured states. The changes in elastic (S′) and viscous (S″) vulcanization torques were meaningfully different. The drop in S″_max (D_S″) was larger for NS than BK; and lowered when the amounts of reinforcements increased. As the nano particles concentration increased, peak of S″ happened in shorter time and higher conversion of cure. Relaxation curves were divided into two viscous and elastic regions at short and long times. With increasing nano filler content, elastic (A_e) and viscous (A_v) slopes of relaxation increased. A_v was bigger than A_e for uncured compounds while after cure the reverse trend was observed. Vulcanized samples had higher A_e, which clearly confirmed different viscoelastic behavior caused by curing. Comparing with BK, NS had more significant effect on the rate of falling of the relaxation modulus, especially after curing.

The ratio of drop in relaxation modulus in the viscous zone to the elastic zone (ΔGv/ΔGe) decreased as a function of NS/BK content for uncured samples; and increased with NS and BK level after cure. In both cured and uncured samples, NS was more effective on ΔGv/ΔGe than BK. An interesting correlation was found between viscoelastic parameters obtained from cure and stress relaxation studies.