Aluminum–organophosphorus hybrid nanorods for simultaneously enhancing the flame retardancy and mechanical properties of epoxy resin

Abstract

New aluminum–organophosphorus hybrid nanorods (AOPH-NR) have been prepared by reacting aluminum hydroxide (ATH) with dibenzylphosphinic acid (DBPA) with aluminum hydroxide (ATH) and used to prepare nanocomposites with epoxy resin. In order to determine the structure–property relationship of these composites, several other phosphinic acids of the general formula (R(CH₂)_n)₂POOH (R = ester, allyl, nitrile, n = 1 or 2), and corresponding AOPHs were synthesized. FTIR, Raman, TGA, and XRD examinations showed that only AOPH-NR possesses a highly hybrid structure and high thermostability. SEM and TEM confirmed the nanorod morphology of AOPH-NR. The formation mechanism can be described as a decomposing–reforming process. This characteristic causes AOPH-NR to exhibit superior properties. Limiting oxygen index (LOI) determination and cone calorimeter analysis showed that the incorporation of only 4.25 wt% AOPH-NR remarkably improved the LOI value to as much as 28.0 and led to a 23% reduction in peak heat release rate (PHRR). Dynamic mechanical analysis (DMA) indicated that the mechanical properties of epoxy resin were also improved by incorporating AOPH-NR. In this way, the aluminum–organophosphorus hybridization via reacting ATH with specific organophosphinic acids shows promise as a means of improving flame retardancy and mechanical properties simultaneously. The thermal and anti-flaming properties of composites, combined with the properties of AOPHs, allowed us to discover the important role that the release and migration of phosphorus species plays in fire-retarding materials. This provides a new insight into the design of high-performance flame retardants.