The application of Raman spectroscopy to three-phase characterization of polyethylene crystallinity

The crystallinity of polyethylenes of various densities was studied by applying the Raman spectroscopy technique. Raman spectra were decomposed into the following three components: the orthorhombic crystalline phase, the melt-like amorphous phase and the interfacial phase, which is located between the crystalline and amorphous phases, with possibly highly oriented or ordered chain segments but not in orthorhombic packing. It was found that the amorphous fraction obtained by the Raman method has a small deviation, and it is more reliable to define the crystallinity of polyethylene samples as (1 − amorphous fraction)×100% rather than by using the orthorhombic crystalline fraction itself. The calculated results show good linear correlation with the crystallinities derived from other methods - by density, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) measurements.