SIMULTANEOUS MEASUREMENTS OF SMALL-ANGLE X-RAY-SCATTERING, WIDE-ANGLE X-RAY-SCATTERING AND HEAT-EXCHANGE DURING CRYSTALLIZATION AND MELTING OF POLYMERS

Experimental equipment was constructed for simultaneous measurements of wide angle X-ray scattering (WAXS), small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) using synchrotron radiation as a strong source of X-rays. The crystallization occurring during heating of an initially amorphous sample with constant heating rate was investigated. Poly(ethylene naphthalene-2,6-dicarboxylate) (PEN), poly(ethylene terephthalate) (PET) and the copolymer PEN-co-PHB (90:10), where PHB stands for poly(p-hydroxybenzoic acid), were used as materials. By comparing the change of the degree of crystallinity as measured by WAXS and DSC with the change of the SAXS power Q, it was shown that the primary crystallization, during which morphological units like spherulites axe growing, is followed by a secondary crystallization during which the degree of crystallinity within the lamellar stacks in the spherulites is increased. Assuming a two-phase system for the semicrystalline structure, consisting of crystals and amorphous regions, three different processes were shown to be responsible for this increase: The formation of new crystal lamellae within the already existing lamellar stacks, the thickening of already existing crystals at the expense of the amorphous regions, and the complete melting of crystals followed by formation of new, thicker, crystals.