Thermal analysis and other techniques were employed to characterize two expandable
graphite samples. The expansion onset temperatures of the expandable graphite’s were ca.
220 °C and 300 °C respectively. The key finding is that the commercial products are not just
pure graphite intercalation compounds with sulfuric acid species intercalated as guest ions
and molecules in between intact graphene layers. A more realistic model is proposed where
graphite oxide-like layers are also randomly interstratified in the graphite flakes. These
graphite oxide-like layers comprise highly oxidized graphene sheets which contain many
different oxygen-containing functional groups. This model explains the high oxygen to sulfur
atomic ratios found in both elemental analysis of the neat materials and in the gas generated
during the main exfoliation event.