Partially Bio-Derived Phosphazene-Tannic Acid Microspheres as Fire Retardant Additives for an Epoxy Tannic Acid Resin System

Abstract

In this work, partially bio-derived colloidal microspheres are synthesised from tannic acid (TA) and hexachloro-cyclophosphazene (HCCP), then investigated for their effectiveness as a fire-retardant additive to a partially bioderived epoxy resin system. The epoxy resin system is based upon diglycidyl ether of bisphenol A (DGEBA) and tannic acid (TA), itself a highly aromatic phenolic curative noted for its inherent fire retardancy. This study reports on the impact of increasing the concentration of the phosphazene-TA microspheres (TAPZ) and varying the DGEBA-TA stoichiometry to determine the optimum formulation displaying the greatest improvement in fire retardancy. At a concentration of 15wt% of TAPZ, the DGEBA-TA resin, easily achieves a V-0 rating using the UL-94 vertical burn test, had an LOI value of 29% and displays a 61.9% reduction in PHHR compared with the unmodified DGEBA-TA network using cone calorimetry. TAPZ addition, however, does reduce Tg, flexural and modulus strength, and increases viscosity significantly. The effect of the additional hydroxyl groups from the surface of the TAPZ modifier accelerates the DGEBA-TA reaction while also enhancing interfacial reaction between residual epoxide groups of the cure epoxy network. These results present a promising approach to the development of a highly fire retardant, high performance, and highly bio-derived epoxy network.

Keywords: fire retardant, micro-spheres, epoxy resin, tannic acid, phosphazene