M. Bark et Hg. Zachmann, SIMULTANEOUS MEASUREMENTS OF SMALL-ANGLE X-RAY-SCATTERING, WIDE-ANGLEX-RAY-SCATTERING AND HEAT-EXCHANGE DURING CRYSTALLIZATION AND MELTINGOF POLYMERS, Acta polymerica, 44(6), 1993, pp. 259-265
Experimental equipment was constructed for simultaneous measurements o
f wide angle X-ray scattering (WAXS), small angle X-ray scattering (SA
XS) and differential scanning calorimetry (DSC) using synchrotron radi
ation as a strong source of X-rays. The crystallization occurring duri
ng 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 (90:1
0), where PHB stands for poly(p-hydroxybenzoic acid), were used as mat
erials. By comparing the change of the degree of crystallinity as meas
ured by WAXS and DSC with the change of the SAXS power Q, it was shown
that the primary crystallization, during which morphological units li
ke spherulites axe growing, is followed by a secondary crystallization
during which the degree of crystallinity within the lamellar stacks i
n the spherulites is increased. Assuming a two-phase system for the se
micrystalline structure, consisting of crystals and amorphous regions,
three different processes were shown to be responsible for this incre
ase: The formation of new crystal lamellae within the already existing
lamellar stacks, the thickening of already existing crystals at the e
xpense of the amorphous regions, and the complete melting of crystals
followed by formation of new, thicker, crystals.