The isothermal flow induced crystallization (FIC) of isotactic polypropylene (iPP) under large amplitude oscillation shear fields was studied by rotational rheometer. The sinusoidal-strain dynamic shear flow of different amplitudes was performed on the undercooling iPP melts. Experimental results showed that

in comparison with the case for a small amplitude oscillation

the storage modulus of the melt would increase within a short period when a large amplitude oscillation was performed on the melts. This fact is attributed to that the large amplitude oscillation shear field is able to accelerate the crystallization kinetics of iPP significantly. Moreover

the larger strain performed on the melts would inevitably result in a more prominent acceleration of the iPP’s crystallization kinetics. Thus the rapid rise of the crystallinity of the melt directly gives rise to a more evident change of storage modulus. The Fourier transformation method was employed to analysis the stress waveform during the crystallization of iPP melts under large amplitude oscillation shear. It was found that the transition change of the ratio (I3/I1) of the peak value at triple-fundamental frequency I3 to the peak value at fundamental frequency I1 was sensitive in characterizing the FIC process of iPP melts when the change of the non-linear mechanical property occurred in the melt during crystallization. In addition

at a crystallization temperature of 140℃

the onset time corresponding to the abrupt increase in I3/I1

a little longer than the time when the storage modulus increased remarkably

decreased from 2500 s to 600 s as the amplitude of strain increased from 10% to 30%.