Mechanism of carbonization under pressure, part I: Influence of aromaticity (polyethylene and anthracene)

Abstract

Carbonization under pressure (30 MPa) of polyethylene (purely aliphatic) and anthracene (purely aromatic) leads to carbonaceous material having a radial texture. The two samples were heattreated up to 650°C at a 3.5°C min −1 heating rate, during 1 hour and 20 hours residence time in sealed gold tubes. Morphological and microtextural characterizations were carried out by scanning electron microscopy, optical microscopy and transmission electron microscopy. Carbonization of polyethylene yields two phases, the matrix and drops getting a radial texture. Carbonization of anthracene yields only one phase (matrix) getting also a radial texture. The drops are precursors of radial single spheres. This radial growth of aromatic layers initiates from the external free surfaces or interfaces and is disrupted by any wall such as the gold tube wall. Carbonization of polyethylene favors the formation of single spheres whereas carbonization of anthracene does not. It is the H C atomic ratio which governs the drop demixtion and then the single sphere formation. The proper range of H C ratios can be obtained when any impurity such as oxygenated functional groups or aromatic groups or other functional groups plays the role of “heterogeneities” in a mainly aliphatic compound.