Effects of heat treatment on the structure of LDPE-derived solid carbons

Heat treatment of spherical solid carbons produced by pyrolysis of low-density polyethylene (LDPE) gave faceted particles with spherical geometry. The changes in the structure of the heat-treated (HT) carbons in the temperature range 1300-2600°C were characterized by elemental analysis, X-ray diffraction (XRD), temperature-programmed oxidation (TPO), Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) which was also used in conjunction with the focused ion beam (FIB) thinning. The HT carbons gave interlayer spacing (d ₀₀₂) values close to that of graphite, however, the maximum values of L _a and L _c (around 20nm) were significantly lower than those of graphite. The TPO profiles showed that the HT carbons contain domains with different structural order and that the contribution of the more ordered domains increases with the increasing treatment temperature. The SEM and TEM examination showed faceting of the initial spherules and FIB analysis showed concentric carbon aromatic layers in a core shell structure. The extent of ordering in the coherent domains increased in the radial direction suggesting that the growth of crystallites was constrained by the size of the initial carbon spherules.