Crystallization of filled Nylon 6 II. Isothermal crystallization

Summary

Isothermal crystallization kinetics from the melt of nylon 6 containing various amounts of untreated glass beads and Aerosil (series GB and A) and aminosilane-treated glass beads (series GBA) was studied by DSC method. Treatment of experimental data in terms of Kolmogorov-Avrami equation has shown that time exponentn is relatively insensitive to presence of GBA filler, whereas it was found to decrease gradually with increasing filler content in samples of GB and A series to value as low as 0.5 for sample A–67. Nucleation free energy was the same in pure nylon 6 and filled samples of GBA series, but dropped suddenly in samples of GB series when mean interparticle separation x decreased below “critical” value ξ_crit =(5–10) x 10⁻⁶ m. Taking into account the concomitant drop of equilibrium melting temperature, it was concluded that these effects are a consequence of specific structural change in polymer phase accompanying transition into a “boundary state”. Temperature dependence of polyer crystallization rate in highly filled samples of A series at small supercoolings was found to obey them=4 law, which is characteristic of transformations in strained media. Experimental data seem to be consistent with the idea that the postulated strain energy might originate from negative capillary pressure between high-surface energy solid particles wette d by polymer melt. Quantitative analysis of overall crystallization rate dependence on interparticle distance x has shown that ξ_crit may be identified with change of growth morphology from a three-dimensional to a two-dimensional one, while slowing down of growth rate at lower values of ξ was attributed to increase of nucleation free energy due to increasing contribution from capillary forces.