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 crystalli zation of polypropylene were performed by the shear flow thermal rheometer. Time development of crystallinity was obtained and analyzed by the Avrami equation; X-c(t) = 1 - exp{ - k(t - t(0))(n)} where X-c is relative crystal linity, k the kinetic constant, to the induction time and n the Avrami expo nent. With an increase of shear rate, k decreases slightly and t(0) decreas es drastically. The increase of n was also observed but the magnitude of th e change was insignificant. The observed value of n suggested the spherulit e growth and inhomogeneous nucleation of the crystal even under shear. Agai nst the crystallization temperature, the parameters behaved similar to thos e under quiescent conditions except that to increases extremely with the in crease in to. (C) 2001 Elsevier Science Ltd. All rights reserved.