Study on the interface of phenolic resin/expanded graphite composites prepared via in situ polymerization

Phenolic resin/expanded graphite (EG) composites were synthesized via in situ condensation polymerization of the monomers in the presence of foliated graphite. SEM observation showed that the graphite flakes were well dispersed in the phenolic resin matrix. The electrical conductivity of the composites was investigated as a function of the foliated graphite fraction. The composites containing graphite sheets exhibited an electrical conductivity percolation threshold with 3.2 wt% graphite content in polymer matrix. Inverse gas chromatography (IGC) measurements were carried out to characterize the surface of the foliated graphite before and after condensation polymerization of phenolic resin using a series of both non-polar and polar acid–base probe gases. The data obtained indicated that the character of graphite surface changed after the polymerization of phenolic resin. The dispersive component of surface free energy decreased greatly. Before polymerization the graphite surface is predominantly acidic while the surface turns to basic after polymerization. The increased polarity of surface contributed to the stronger interactions between graphite and phenolic resin and the fine dispersion of expanded graphite in the matrix, and resulted in the low conductivity percolation threshold.