Crystal morphology and isothermal crystallization kinetics of short carbon fiber/poly(ethylene 2,6‐naphthalate) composites

Abstract

AbstractIsothermal crystallization kinetics, subsequent melting behavior, and the crystal morphology of short carbon fiber and poly(ethylene 2,6‐naphthalate) composites (SCF/PEN) were investigated by using differential scanning calorimetry and polarized optical microscopy. The crystal morphology of the composites isothermally crystallized at Tc = 220°C is predominantly banded spherulites observed under polarizing micrographs, while the pattern of banded spherulites changed from ring to serration as the SCF content added into the PEN. Moreover, nonbanded spherulites formed at Tc = 210°C. The commonly used Avrami equation was used to fit the primary stage of the isothermal crystallization. The Avrami exponents n are evaluated to be 2.6–3.0 for the neat PEN and 3.7–4.0 for SCF/PEN composites, and the SCF acting as nucleation agents in composites accelerates the crystallization rate with decreasing the half‐time of crystallization, and the sample with SCF component of 2% has the fastest crystallization rate. The crystallization activation energy calculated from the Arrhenius formula suggests that the adding SCF component improved the crystallization ability of the PEN matrix greatly, and the sample with of 2% SCF component has the most crystallization ability. Subsequent melting scans of the isothermally crystallized composites exhibited triple melting endotherms, in which the more the component of SCF, the lower temperature of the melting peak, indicating the less perfect crystallites formed in those composites. Furthermore, the melting peaks of the same sample are shifted to higher temperature with increasing Tc, suggesting the more perfect crystallites formed at higher Tc. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008