Strain-Induced Crystallization of Fractionated Natural Rubber from Fresh Latex

Abstract

Effects of non-rubber contents on strain-induced crystallization and tensile mechanical properties were investigated using fractionated samples from fresh latex of natural rubber (NR). The upper fraction (UF) was mostly composed of cis-1,4-polyisoprene (namely, NR molecules), while the bottom fraction (BF) contained non-rubber contents of more than 13%. Vulcanized samples were prepared from the UF and the BF. Wide-angle X-ray diffraction patterns and tensile stress data were collected during 6 cycles of uniaxial deformation for the vulcanized samples. Both UF and BF samples showed the similar degree of the strain softening (the Mullins effect) in the tensile stress-strain behavior. On the other hand, the larger depression of crystallization in the 2nd cycle compared with the 1st cycle was observed for the sample prepared from the BF. The strain ratio at which crystalline reflections disappeared was almost unchanged regardless to the number of deformation cycles and the difference of the samples. On the basis of these results, the non-rubber contents in the BF were suspected to suppress strain-induced crystallization not by reducing thermodynamic driving force but by affecting the kinetic factors of crystallization.