Wide-angle X-ray scattering study on shear-induced crystallization of propylene-1-butylene random copolymer: Experiment and diffraction pattern simulation

Shear-induced crystallization of a propylene-1-butylene random copolymer with low butylene content (5.7 mol %) was studied using time-resolved wide-angle X-ray scattering (WAXS) techniques. Polymorphism, preferred crystal orientation, crystallization kinetics, and disorder effect were investigated based on WAXS 2D whole pattern analysis. It was found that at 100 °C, the crystallite of P-B copolymer was a mixture of 80% γ-form and 20% α-form of isotactic polypropylene (iPP) crystals. The application of a step shear (shear rate = 100 s^-1, shear duration =3s) induced γ-form crystals with c-axis oriented perpendicular to the shear direction. In contrast, the c-axis of α-form crystals was normally in parallel to the shear direction. Both crystallization kinetics and crystallinity were greatly enhanced by shear. The disorder effect was found to play an important role in the crystallization behavior of P-B copolymer. In the early stage crystallization, the chosen copolymer contained a large amount of structure defects, where crystals became more ordered upon annealing. The degree of crystal orientation was also found to decrease during crystallization due to the relaxation after shear.