Synergistic Effect of Intumescent Flame Retardant and Organically Modified Montmorillonite on Flame-Retardant and Foaming Properties of High Density Polyethylene/Walnut Shell Powder Biocomposites

The synergistic effects of organic montmorillonite (OMMT) and ammonium polyphosphate (APP) on flame retardant enhancement of High density polyethylene/walnut shell powder (HDPE/WSP) biocomposite were investigated by using the limiting oxygen index (LOI), thermogravimetric analysis (TGA) and Cone calorimeter test. The LOI data show that OMMT has a synergistic flame retardant effect with APP and the LOI value reaches 28%for the samples containing 9 phr OMMT and 15 phr APP. The TGA and Cone calorimeter data demonstrate that the incorporation of OMMT and APP is very effective in enhancing the thermal stability ofHDPE/WSP/OMMT/APP system. Based on The results of the thermogravimetric analysis all samples decomposed in two decomposition stages. Addition of OMMT and APP alsocatalyzed the first stage of decomposition, and produced morechar residual. The second decomposition stage conductedin higher temperature. These transitionsare due to the OMMTincorporates with APP to produce a charred layer and prevents the heatand mass transfer between surface and melting polymer, lead toimprovethe fire resistance of the composites.Addition of OMMT and APP and consequently production of charred layer also decreased HRR and MLR values.Microcellular HDPE/WSP biocomposite foams were prepared with batch foaming apparatus using nitrogen as blowing agent. In microcellular biocomposites, therelative density and cell size were a strong function of APP and OMMT contentand processing conditions. With increasing of APP content, the relative density decreased and then increased and the cell size increased.Addition of OMMTresulting in smaller cell size and higher relative density. The relative density decreased with increasing of saturation temperature and pressure.