Study of the pre-melting behavior of polyethylene using Raman spectroscopy combined with two-dimensional (2D) correlation spectroscopy

The thermal behavior of polyethylene (PE) below its melting temperature (Tm) in relation to the density variation was studied by Raman spectroscopy combined with two-dimensional (2D) correlation analysis. The Raman spectra of homo and 1-octene copolymerized PEs were collected by varying the sample temperature from 30 to 100 °C, where pre-melting would occur. The spectral variation upon temperature perturbation was dependent on the density. For a deeper understanding of the thermal behaviors, 2D hetero correlation analysis was performed for the temperature-dependent Raman spectra of homo and 1-octene copolymerized PEs. The hetero-sample correlation analysis revealed that even below Tm, co-monomer side chains excluded from the crystalline lattice of the PE underwent partial fusion, indicating that such a conformational defect was closely related to the pre-melting of PE.