The effect of mastication time on the physical properties and structure of natural rubber

Abstract

The effect of mastication time in an internal mixer on the physical properties and microstructure of natural rubber (NR) was studied. The Mooney viscosity, plasticity, and complex viscosity reduced with increases in the mastication time due to the molecular breakdown of the rubber. The microstructural changes in the NR were studied using small-angle X-ray scattering. The results revealed that a reduction in the physical properties correlated with the structural changes, which occurred due to mastication. Increases in mastication time affected the distribution and size of the nonrubber component aggregations and the uniformity of the molecular structure of the NR.

Tensile and structural properties of natural rubber vulcanizates with different mastication times

“…This study suggests not only the variation of crosslinked structures with decreasing molecular weight caused by mastication, but also suggests reduction in size of crosslinked structures with decreasing molecular weight. As compared to NR without vulcanization [9] , the size of R g for the vulcanized rubber was larger. This is due to the fact that the R g in unvulcanized NR was attributed to the aggregation of impurities (non-rubber components) [35] , but the R g in the vulcanized sample was due to crosslinking of clusters by all impurities, activating agents and crosslinking agents [36] .…”

“…The I(q) in all cases decreased continuously with increasing q and the I(q) was almost constant when the value of q approached 0.2. However, the lowest intensity was observed for the sample with 5 min of mastication, suggesting a homogeneous distribution of the crosslinked networks throughout the rubber matrix [9] . The homogeneity of crosslinked networks clearly contributed to the tensile properties and thus the highest tensile strength was obtained for the sample with 5 min mastication.…”

“…The M L is usually proportional to the uncured physical crosslinking or chain entanglement [10] and to molecular weight of rubber. It is well-known that mastication mechanically breaks and shortens long rubber molecular chains [8,9,19] . A longer mastication then corresponds to greater molecular weight reduction.…”

“…Considering T s1 and T c90 , it was found that the T s1 appeared to be independent of the mastication time, but the shortest curing time (T c90 ) was observed when the rubber was initially masticated for 5 min. Previously, it was demonstrated that non-rubber components in the masticated rubber were more homogeneously distributed throughout the rubber matrix when the rubber was masticated for a comparatively short time (e.g., for less than 5 min) [9] . These impurities may be involved in the crosslinking reactions, possibly acting as natural accelerators [20,21] .…”

“…It is well accepted that mastication affects NR viscosity due to molecular weight reduction [8,9] . Previously, the effect of mastication time on the physical properties and microstructure of uncrosslinked NR was reported [9] . Unfortunately, the contributions of mastication time to the network structure and the deformation-induced crystallization behavior of NR after vulcanization were not included.…”