Fire retardant mechanism analysis between ammonium polyphosphate and triphenyl phosphate in unsaturated polyester resin

Ammonium polyphosphate (APP) and triphenyl phosphate (TPP) were added in a dicyclopentadiene (DCPD) modified unsaturated polyester resin (UPR) as intumescent flame retardant (IFR) and the combustion resistance effects were investigated. Flammability and thermal stability were investigated through limiting oxygen index (LOI) test and UL-94 vertical burning test and by using thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). When 57.6 wt.% of the flame retardant was added, the LOI value increased from 20.9 to 27.2 and a V-0 rating in UL-94 test was obtained. The fire-resistant time reached to 26∼34 min. The TGA and DSC analyses showed that the char yield was increased by the introduction of APP and TPP system and decomposition of the phosphorous additives yielded strongly phosphoric acids which effectively promoted the cross-linking reaction during the burning process. So, a profound flame retardant effect was obtained as APP and TPP were added to the unsaturated polyester resin.