Flammability and thermal degradation studies of PVA/rice husk composites

Biodegradable poly(vinyl alcohol)/rice husk (PVA/RH) unplasticized composites are prepared by blending 10 wt%, 20 wt%, and 30 wt% of RH with PVA via solvent-casting technique. Composites are also prepared using boric acid as cross-linking agent. Tensile properties of PVA improved, though slightly, on adding RH and boric acid. Flammability of composites is evaluated using limiting oxygen index (LOI) and Underwriters Laboratory test (UL 94), while thermal stability is determined by employing TG/DTA. Thermal stability of PVA increases on adding RH and boric acid. PVA/RH composite with only 10 wt% RH loading passes HB rating (UL 94) and LOI values increase from 20.5% to 23.5% for 30 wt% RH loading. Better flame retardancy of PVA/RH composites is explained on the basis of ‘heat shielding’ and ‘barrier’ theories. Besides, degradation activation energy calculated by model-free methods favors the flammability data. Silica present in RH is the core substance responsible for the improved flame retardancy of PVA.