Mechanical and flame‐resistance properties of polyurethane‐imide foams with different‐sized expandable graphite

Abstract

AbstractPolyurethane‐imide (PUI) composite foams with expandable graphite (EG) of different sizes were prepared by a polyimide prepolymer method. EG particles were treated with a silane coupling agent to improve compatibility with the foam. The effect of EG particle size on cell morphology, thermal degradation, flame‐resistance and mechanical properties of PUI foams was investigated. Results showed that the mean cellular diameter of foams with EG particle was much higher than that of foams with surface‐modified EG particle at the same filler loading. When filler particle diameter increased from 20 to 90 μm, the compressive strength, density and closed‐cell ratio of foams increased, and then decreased when filler particle diameter further increased from 90 to 150 μm. Thermal stability of foams increased with the increasing filler particle diameter from 20 to 50 μm, and decreased with the increasing filler particle diameter from 50 to 90 μm. The limited oxygen index (LOI) value of foams with surface‐modified EG increased from 24.8% to 32.1% when EG particle diameter was below 90 μm. Foams with surface‐modified EG exhibited enhanced mechanical properties, thermal stability and flame resistance than foams with neat EG at the same loading.