The Flame Retardancy Performance of Aluminum Hypophosphite and its Synergistic Effect with Expandable Graphite in Carbon Fiber Reinforced Poly (Lactic Acid) Composites

Abstract

The aim of this study is to investigate the effects of both aluminum hypophosphite (AHP) and its synergistic effect with expandable graphite (EG) on the thermal and flame retardant properties of carbon fiber reinforced polylactic acid (PLA) composites. The composites were produced by melt blending method by keeping the carbon fiber (CF) ratio (30 wt.%) constant. The flame retardancy effect of AHP was studied at three different concentrations (10, 15, 20 wt.%). The synergic effect studies were also carried out using mixture formulations of 7 wt.% AHP and 3 wt.% EG, 5 wt.% AHP and 5 wt.% EG. The characterization of the composites was performed using thermogravimetric analysis (TGA), mass loss cone (MLC), limiting oxygen index (LOI) and vertical burning tests (UL-94 V). The TGA results showed that only the addition of AHP decreased the thermal stability, while the addition of AHP and EG combination did not affect the thermal properties much. From the LOI and UL-94 V test results, it was determined that only the addition of AHP significantly increased the LOI values and the composites passed to UL-94 V0 rating. It was found that the LOI values increased with the addition of AHP and EG combination, but this increase was less compared to the composite containing only AHP (20 wt.%). However, these composites failed the UL-94 V test. The MLC test results showed that only the addition of AHP significantly reduced the pHRR values, while the combination of AHP and EG was close to these values. As a result, only the addition of AHP improved the thermal and flame retardant properties of carbon fiber reinforced PLA more than the combination of AHP and EG.