Thermal and flame properties of calcium borate and intumescent ammonium polyphosphate in epoxy/glass fiber composites

The thermal and flammability properties of halogen-free flame retardants, calcium borate and intumescent ammonium polyphosphate, were evaluated on epoxy/glass fiber composites. The evolved volatile products under thermal stresses were analyzed accordingly, and the thermal decomposition of the composites was studied. It was determined that ammonium polyphosphate and calcium borate releases water vapor and carbon dioxide during their thermal decomposition, as a method to overcome the fire. Ammonium polyphosphate that achieved the V-0 rating at 5 vol% loading had showed better fire resistance than calcium borate that failed to achieve any rating even at high loading of 20 vol%. However, the calcium borate had recorded higher residual content. The combination of 1 vol% calcium borate and 4 vol% ammonium polyphosphate exhibited a synergistic performance by mass producing more char as a protection for the composites. Nevertheless, this synergism was not observed with the other combination, which comprised a 50:50 ratio of ammonium polyphosphate–calcium borate.