Thermal analysis of shear induced crystallization by the shear flow thermal rheometer: isothermal crystallization of polypropylene

In situ differential thermal analysis during steady shear induced crystallization of polypropylene were performed by the shear flow thermal rheometer. Time development of crystallinity was obtained and analyzed by the Avrami equation; Xc(t)=1−exp{−k(t−t0)n}, where Xc is relative crystallinity, k the kinetic constant, t0 the induction time and n the Avrami exponent. With an increase of shear rate, k decreases slightly and t0 decreases drastically. The increase of n was also observed but the magnitude of the change was insignificant. The observed value of n suggested the spherulite growth and inhomogeneous nucleation of the crystal even under shear. Against the crystallization temperature, the parameters behaved similar to those under quiescent conditions except that t0 increases extremely with the increase in t0.