SHEAR-INDUCED CRYSTALLIZATION OF ISOTACTIC POLYPROPYLENE
SHEAR-INDUCED CRYSTALLIZATION OF ISOTACTIC POLYPROPYLENE
复制标题
作者：
Chen Qing
Shear-induced crystallization behavior of isotactic polypropylene(iPP)was investigated using a rotational rheometry covering a shear rate range of 1.2×10-4～1 s-1 and temperatures between 135℃ and 145℃.As the specimen was sheared at a constant rate,the viscosity and normal force were constant at first,then started to increase sharply after a certain time.At higher shear rates the transition of the normal force occurred considerably earlier than that of the viscosity,and at medium shear rates the two transition times were coincident.However at extremely low shear rates the data of normal force became noisy and only the data of viscosity was reliable.It was suggested that the earlier time in transitions for the normal force and viscosity was used to define an onset time(t_ on)which characterized the crystallization process.Furthermore,it is proposed that the plot of t_ on versus shear rate can be converted into a temperature-invariant curve by dividing the y axis by quiescent onset time t_ on,q and multiplying the x axis by t_ on,q.
