Insight into the flame-retardant mechanism of different organic-modified layered double hydroxide for epoxy resin

Aiming to enhance the flame-retardant efficiency of layered double hydroxide (LDH) in epoxy resin (EP), positively charged LDH was modified by incorporating various anionic modifiers, resulting in a series of organically modified LDH. These modifiers were selected based on the length of nonpolar tails with and without aromatic ring such as sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS) and sodium benzene sulfonate (SBS). The chemical composition, structure and hydrophobicity of organic-modified LDH were characterized and the flame-retardant efficiency of organic-modified LDH in EP were investigated. The incorporation of organic-modified LDH into EP resulted in improved Tg and flame retardancy, which depended on the type of modifiers used as well as the structure and loading amount of LDH. Particularly, LDH@DBS exhibited higher improvement efficiency in flame retardancy and Tg than that of LDH@BS and LDH@DS due to the enlarged interlayer spacing, which facilitated the homogeneous dispersion and compatibility in the epoxy matrix. These results demonstrated that good compatibility between organic-modified LDH and polymer was advantageous to enhance the flame-retardancy efficiency and thermal mechanical properties of polymer.