Loading an organophosphorous flame retardant into halloysite nanotubes for modifying UV-curable epoxy resin

Abstract

Novel flame-resistant UV-curable epoxy (EP) composites were prepared using the organophosphorous flame retardant dimethyl methylphosphonate (DMMP) which was loaded into halloysite nanotubes (HNTs). We used a cone calorimeter to investigate the flame retardancy of the UV-curable epoxy resin containing DMMP-loaded halloysite nanotubes (HNT-D). It was found that compared with the neat epoxy resin the EP/HNT-D system exhibited better flame retardancy with an obvious decrease in the heat release rate (HRR), total heat release (THR), total smoke release (TSR), mass loss rate (MLR) and smoke production rate (SPR). Exploring the flame retardant mechanism revealed two reaction steps in the process of the flame retardant: DMMP gasification followed by a polyphosphoric-HNT carbon layer generating on the condensed phase. It was revealed through measuring the dynamic mechanical properties and tensile properties of the UV-cured EP materials that adding DMMP-loaded halloysite nanotubes (HNT-D) into EP obtained better mechanical properties than adding a simple mixture of halloysite clay and DMMP. With DMMP loaded in HNTs, the HNT-D could reduce the softening influence of DMMP. This method may potentially be applied to improve the flame retardancy of UV-curable epoxy resin in the future.