Correct determination of crystal lamellar thickness in semicrystalline poly(ethylene terephthalate) by small-angle X-ray scattering

For the purpose of resolving an uncertainty over the correct determination of the crystalline lamellar thickness in semicrystalline poly(ethylene tere phthalate), PET, via small-angle X-ray scattering (SAXS) analysis, a gel-cr ystallization method from oligomeric poly(ethylene glycol) solution was use d to prepare samples with high crystallinity (57%). By using simultaneous s ynchrotron SAXS and wide-angle X-ray diffraction (WAXD) measurements, the h eating and cooling processes of the gel-crystallized PET sample were monito red. Results support the assignment of the larger thickness value from the SAXS correlation function analysis as the lamellar crystal thickness. Analy sis of WAXD 011 reflection line broadening gives the minimum lamellar thick ness (in the chain axis) and verifies the thickness assignment for gel and melt crystallized samples. This assignment is critical as it affects the co rrect interpretation of the crystallization behavior in semicrystalline pol ymers of relatively low crystallinity. (C) 1999 Elsevier Science Ltd. All r ights reserved.