Synergistic effect of aluminum hypophosphite and intumescent flame retardants in polylactide

Aluminum hypophosphite (AHP) was introduced into polylactide/intumescent flame retardant (PLA/IFR) systems by melt blending. The flame retardant and thermal properties of the PLA composites were investigated. The results suggest that a synergistic effect exists between IFR and AHP on the char formation and anti-dripping behavior of PLA composites. The PLA/IFR composites containing 10wt% IFR can pass the UL-94V-0 rating but the test is accompanied by heavy melt dripping. For the PLA/AHP a UL-94V-2 rating is obtained for the same loading of IFR. However, the composites containing 7wt% IFR and 3wt% AHP pass the UL-94V-0 rating with modified dripping behavior. Moreover, the char from combustion of PLA/IFR is flexible but of poor quality. That for PLA/AHP is brittle with many cracks. In contrast, that for PLA/IFR/AHP is strong and compact. Thus it can resist the erosion due to heat and gas formation and protect the inside of the matrix. In addition, AHP causes the crosslinking among APP, which promotes the char formation and prevents the melt dripping. This is the main reason for the good flame retardant properties of PLA composites. Copyright (c) 2015 John Wiley & Sons, Ltd.