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 10 4 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 t 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.

Acceleration Mechanism of Nucleation of Polymers by Nano-sizing of Nucleating Agent

“…3 Therefore the proposed relationship in eq 10 is expected to be valid for any polymers. The universality of eq 10 for any NAs will be soon reported in our succeeding paper by showing increase of I of iPP mixed with three NAs.…”

“…CONCLUSIONS 1. Theoretical prediction proposed in our previous study 3 that I / C NA a NA À1 was experimentally confirmed on iPP, where I is nucleation rate of polymer crystals, C NA is concentration of NA in the mixture of NA and polymers and a NA is the longest lateral size of NA crystal. a NA and C NA were changed in order from nm to mm and from 10 À3 to 1 wt %, respectively.…”

“…Reduction of processing time is also attributed to the effect of NA. Hikosaka et al 3 showed that the number density of crystals of polyethylene (PE) increased by 10 4 times after adding NA, which enabled direct observation of nucleation by means of small angle X-ray scattering (SAXS). In this study sodium 2,2 0 -methylene-bis-(4,6-di-t-butylphenylene)phosphate (ADEKA Corp., NA-11) was mixed with PE.…”

Nucleation kinetics of polymer formation on nucleation agent

“…Imai et al [1] on the basis of experimental data about the crystallization process of poly(ethylene terephthalate) suggested that the formation of a new phase is a type of phase separation process occurring during some induction period. Recently, Hikosaka et al [2] showed that the formation of crystalline phase occurs by mechanism of formation of nuclei.…”

Viscoelasticity as a tool to investigate the early stage of the quiescent crystallization process of poly(lactic acid)

“…The classic nucleation theory predicted that the concentration of nuclei approached a steady state when its rate of formation was equal to that of transformation into crystallites [34,35]. Therefore, the increase in viscoelasticity slowed down in the second stage.…”