CHARACTERIZATION OF THE TWO-PHASE STRUCTURE IN SEMICRYSTALLINE POLY(ETHYLENE TEREPHTHALATE)

The X-ray diffraction whole pattern (XDWP) data of semicrystalline poly (ethylene terephthalate)PET2 sample were collected in the symmetric reflection geometry on a diffractometer, employing a copper target(Kα wavelength=0.15418nm).The XDWP was fitted by combining the Rietveld method and Fourier filtering technique,Rietveld structure refinement for PET2 crystalline phase was done,the unit-cell parameters obtained being a=0.445,b=0.592,c=1.072 nm,α=99.6,β=116.9,γ=111.9(°),and the density of the sample being dc=1.495(g/cm3).Meanwhile, the XDWP was separated into two parts,CR2 crystalline region and AM2 non-crystalline region in PET2.The reduced radial distribution function G2(r) was calculated from AM2, finding three main peaks,G21(r)=0.150,G22(r)=0.254,G23(r)=0.460 nm, which characterize the structure of the non-crystalline phase in PET2.We suggest that the amorphous curve is best taken as the sum of several non-crystalline scattering peaks.Reliability and reasonableness of the structural parameters of the crystalline phase and the non-crystalline phase are discussed.In conclusion,it is a very effective method that the combination based on the Fourier filtering technique and the full-pattern diffraction least-squares refinement (Rietveld method) and the radial distribution function analyses to study the two-phase structure in semi-crystalline polymers.