Fabrication of Anisotropic Polyphosphazene/Bio-based Poly(urethane-acrylate) composite foams with High Thermal Insulation and Flame Retardancy

Abstract

Developing renewable porous materials with low thermal conductivity and high flame retardancy is of great significance in energy saving and fire safety. Herein, a series of bio-based anisotropic composite foams were fabricated from oil-in-water (o/w) high internal phase Pickering emulsions (Pickering HIPEs) stabilized by both bio-based poly (urethane-acrylate) (PUA) and poly (cyclotriphosphazene-co-4,4ʹ-sulfonyldiphenol) (PZS) particles. All Pickering HIPEs have good stability originated from the two kinds of particles irreversible adsorption at the oil-water interface and the formation of a “3D networks” of PUA particles aggregates in the aqueous phase. The microstructures and rheology of the double-particles stabilized HIPEs were adjusted by changing the contents of particles and the internal phase volume fractions. Then the anisotropic PZS/PUA composite foams with high porosity (up to 93.9%) and low thermal conductivity (down to 48.4 mW m−1∙K−1) were prepared by unidirectional freeze-drying these Pickering HIPEs. The anisotropic structure enhanced the mechanical strength in axial direction and thermal insulation property in radial direction. Compared with the PUA foam, loading only PZS of 10.7 wt%, the values of average heat release rate, total heat release and average effective heat of combustion of the composite foams were reduced by 19.3%, 12.8%, and 40.2%, respectively. Meanwhile, the value of limiting oxygen index was also increased from 16.3% to 18.2%, which was resulted from PZS functioned in the condensed phases during the combustion process. This work provides a strategy to prepare a kind of bio-based anisotropic foams which would find uses in the fields of fire safety and thermal insulation.