Convenient preparation of expanded graphite and graphite nanosheets as well as improvement of electrical conductivity of polyurethane by filling graphite nanosheets

Abstract

Expandable graphite precursors were firstly prepared by the oxidative intercalation of natural flake graphite powders with mean lateral particle sizes of 25–100 μm in concentrated sulfuric acid solutions using Ca(ClO)2 as an oxidant. Higher oxidative intercalation extent increased the thermal expansion of expandable graphite to obtain expanded graphite with a larger volume ratio of 162 mL⋅g−1. Graphite nanosheet samples were facilely and eco-friendly prepared by sand milling of expanded graphite in an aqueous solution. The thicknesses of as-prepared graphite nanosheets could be decreased from 15–20 to 4.8–5.5 nm with the prolonging of sand milling time from 4 to 12 h. As compared with polyurethane/natural flake graphite composite films, the electric conductivity of polyurethane/graphite nanosheet composite films was increased by 6 orders of magnitude at a lower filler content of 5 wt%. The filling of graphite nanosheets endows polyurethane with good electrical conductivity.