The memory effect of shear history was studied with poly(ethylene terephthalate) (PET) prepared under different shear conditions of 11.7 to 1168 s−1 in a capillary rheometer. The shear history of PET resin led to a memory effect, which in turn affected the crystallization kinetics. The crystallization rate increased with increasing shear rate. Double peaks of heating crystallization exotherms and a low value of Avrami exponent appeared at low shear rates, which was attributed to the existence of crystallization processes with different rates; one was the fast process involving the disentangled molecules that persisted during melting, and the other was the slow process involving the highly entangled molecules. The change of instantanenous Avrami exponent and overall crystallization rate constant was in good agreement with the expected trends assuming coexistence of the two crystallization processes. The crystallization kinetics of PET with shear history could be regarded as a growth rate decrease problem to be interpreted by the modified Avrami equation, 1 − Vc = exp[− K·f(t)n], when the fast process dominated the overall crystallization. The effect of shear history was reduced because of the relaxation process as the holding time in melt state before crystallization was increased.

A new crystallization kinetic equation has been derived considering the decrease in growth rate. The average linear growth rate of spherulite was assumed to be proportional to the m-th order of the uncrystallized fraction of the crystallizing material. A modified Avrami equation, 1 -V , = exp[-Kf(t)"], was used where f ( t ) is the integral of the growth function, (1 -Vc)"'. The validity of the equation was tested by analyzing the isothermal crystallization kinetic data of poly(ethy1ene terephthalate) from the melt using differential scanning calorimetry.