Strain-induced crystallization of blends of natural rubber and ultra high cis polybutadiene as studied by synchrotron X-ray diffraction

Strain-induced crystallization of a series of natural rubber (NR) and ultra high cis polybutadiene (UBR) blend was studied by the in situ synchrotron wide angle X-ray diffraction. X-ray diffraction peaks from the oriented rubber were decomposed into the three phases (isotropic amorphous (IA), oriented amorphous (OA), and crystalline (CR)) to probe the structure changes upon stretching. Overall chain orientation of the blend upon stretching was speeded up, which was found to be associated with the UBR chains. The strain-induced crystallization was retarded by the UBR chains. It was found out that 100% UBR did not show crystallization and the crystallization in the blend was only associated with NR chains. Furthermore, the early oriented UBR chains do not play a role as nucleation sites for the NR chains to crystallize. The crystallite size became larger with the UBR content, which was attributed to the small number of nuclei formation by the presence of UBR chains.