Effects of Expandable Graphite on Thermal and Mechanical Properties of Rigid Polyurethane Foams
AbstractPolyurethane rigid foams are commonly used for insulation purposes as advanced materials in defense industry because they have better thermal properties than thermoplastic foams or other common insulation materials. Their low thermal conductivity is due to a unique combination of blowing agent properties, cell size, and closed cell morphology. [1] The expandable graphite is a good instumescent flame retardant for rigid polyurethane foam. The structure of graphite consists of layers and chemicals sucs as sulfuric acid may be inserted between these carbon layers. With the heat effect expandable graphite expands and voluminous insulative layer is occurred. When EG content increases in rigid polyurethane foam, significant improvement in fire reaction is observed. [2] Series of flame-retardant polyurethane foams were prepared using various concentrations (0–10% by weight) of expandable graphite. The effect of these additives on the properties of the polyurethane foams, including physico- mechanical, morphological, flame retardancy and thermal stability, was studied. The effects of expandable graphite on the performance of composites were characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), optical microscopy(OM) other mechanical and thermal analysis techniques.