Blends of poly(ethylene 2,6-naphthalate) with liquid-crystalline polymers: crystallization behavior and morphology

The isothermal crystallization behavior and morphology of blends of Poly(ethylene 2,6-naphthalate) (PEN) with two types of liquid-crystalline polymers (LCP) (rigid and semiflexible) have been studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and scanning electron microscopy (SEM). The blends posses a two-phase morphology due to immiscibility of the two components. The dispersion of the minor LCP phase is favored at a low LCP concentration (7 wt%). The PEN overall crystallization rate is enhanced strongly by the addition of LCPs. The maximum enhancing effect has been found to occur at a LCP concentration of ca. 7 wt%. The POM observations show that PEN spherulite dimensions decrease in the presence of LCPs. These results have been interpreted on the basis of a heterogeneous nucleation played by the crystallized LCP particles on the molten PEN matrix. The nucleation mechanism and the equilibrium melting temperature of PEN are not changed by the presence of a dispersed LCP phase. The relationship between blend morphology and nucleation phenomena has been discussed.