Direct Evidence of Nucleation During the Induction Period of Polyethylene Crystallization by SAXS

Abstract

Direct evidence that nuclei are formed during the induction period of crystallization is obtained for the first time by means of small-angle X-ray scattering (SAXS). Polyethylene (PE) was used as a model crystalline polymer. The nucleating agent was mixed with PE in order to increase the scattering intensity I x from nuclei as large as 104 times bigger than usual. I x increased soon after quenching to the crystallization temperature from the melt and saturated after some time. A new theory is proposed to estimate the size of the nuclei N, the number density distribution of nuclei with N at time t, f(t,N), and the induction time τ i, by analyzing the SAXS scattering intensity. The volume-averaged size of the nuclei was nearly the same as that of critical nuclei and does not change so much with time during the induction period. Lamellae start stacking much later than nuclei start forming.