Functionalized layered double hydroxide-based epoxy nanocomposites with improved flame retardancy and mechanical properties

Functionalized layered double hydroxides (LDHs) based on a multi-modifier system composed of hydroxypropyl-sulfobutyl-beta-cyclodextrin sodium (sCD), dodecylbenzenesulfonate (DBS) and taurine (T) have been designed and fabricated in this paper, aiming at developing high performance fire retardant epoxy nanocomposites. In this multi-modifier system, sCD was utilized to improve the char yield, DBS was used to enlarge the inter-layer distance of LDH and T was used to enhance the interaction between the epoxy matrix and LDH layers. Based on these functionalized LDHs, bisphenol A epoxy resin and diamino diphenyl sulfone (DDS), a series of functionalized LDH/epoxy nanocomposites have been developed. The structural morphologies of the LDH/epoxy nanocomposites were investigated by transmission electron microscopy (TEM) and wide-angle X-ray scattering (WAXS), revealing that sCD-DBS-T-LDH/EP shows a much better dispersion state than the epoxy composites containing unmodified LDHs or single modifier modified LDHs. Importantly, with only 6 wt% functionalized LDH, the sCD-DBS-T-LDH/EP nanocomposite reached V0 rating in the UL-94 vertical burning test. Furthermore, the incorporation of sCD-DBS-T-LDH into epoxy resins led to a significant reduction in peak heat release rate, total heat release and total smoke production, which exhibited superior fire resistance over its counterparts at the equivalent filler loading. The notably improved fire resistance could be attributed to the formation of the consolidated and compact char layers during combustion which significantly suppressed heat and mass transfer between the polymer matrix and flame zone. Additionally, sCD-DBS-T-LDH/EP showed the best impact and tensile strength compared to those of other LDH/epoxy composites. This work offers a new approach to develop high performance fire retardant polymer/LDH nanocomposites.