Enthalpy Relaxation in the Cooling/Heating Cycles of Polyamide 6/Organoclay Nanocomposites. II. Melting Behavior

Abstract

Nonisothermally crystallized samples of the neat polyamide 6 homopolymer (PA 6) and of a series of commercial nanocomposites (PNC) containing up to 7.5 wt.% of exfoliated organoclay nanoparticles were characterized at room temperature by wide‐angle and small‐angle X‐ray scattering, while their melting behavior was studied in the temperature‐modulated differential scanning calorimetry (DSC) mode at three underlying heating rates and five modulation frequencies. Both α‐ and γ‐crystal modifications of PA 6 were invariably formed during cooling from the melt, the ratio α‐form/γ‐form tending to decrease the higher the organoclay content and/or the cooling rate. Strongly scattering organoclay platelets within the PNC were spatially organized into two different, mass fractal‐like structures in the ranges of characteristic structural scales of ca. 14–100 nm and ca. 5–14 nm, respectively. The patterns of melting endotherms in both the neat PA 6 and the PNC could be semiquantitatively characterized by a simple Debye model with a single, temperature‐ and underlying heating rate‐dependent characteristic time. The mechanisms of structural rearrangements in the melting intervals of the neat PA 6 sample and the PNC were basically similar; however, the spatial scale of such rearrangements in the latter samples was significantly reduced due to severe steric constraints on the PA 6 chain mobility in the melt state from the infinite cluster of nanoparticles.