Phosphorylated avocado seed: A renewable biomaterial for preparing a flame retardant biofiller

Avocado seed was first washed, dehydrated, and pulverized, and thereafter, chemically modified with phosphoric acid in the presence of urea, to obtain a low density and sustainable fire retarding filler. Infrared spectroscopy, nuclear magnetic resonance, and X-Ray photoelectron spectroscopy were used in order to determine the resulting chemical structure and confirm the presence of the proposed functional groups. In addition, scanning electron microscopy and elemental analysis were used to establish the resulting morphological changes, as well as the elements present on the modified material. Thermogravimetric analysis was also carried out in order to establish the thermal stability of the material and predict the effect on the flame retardancy due to the mentioned chemical modification. It was also determined that chemical modification greatly increased the thermal stability of the avocado seed. The flame-retardant effect of the modified avocado seed was assessed in polyethylene/ethylene-vinyl-acetate (PE/EVA) composites via cone calorimeter tests. It was observed by DSC, that the incorporation of avocado seed, does not affect the melting temperature of the PE/EVA polymer blend. The results showed that the modified avocado seed decreased the peak of the heat release rate (pHRR) by 54% and the total heat released (THR) by 15%. The UL-94 and LOI tests of the modified avocado biocomposites showed an improvement in the flame retardant properties, and reached a UL-94 V-1 classification. Tensile tests showed that the bio-composites with unmodified and modified avocado seed exhibit similar tensile strength and modulus than the LDPE/EVA blend, but a lower elongation. These results suggest that phosphorylated avocado seed could be a good option as a renewable biofiller for polymer composites with enhanced flame-retardant properties.