Hierarchical core–shell TiO₂@LDH@Ni(OH)₂ architecture with regularly-oriented nanocatalyst shells: Towards improving the mechanical performance, flame retardancy and toxic smoke suppression of unsaturated polyester resin

Due to poor interfacial interaction between titanium dioxide (TiO₂) and polymers, the fabrication of high-performance polymer/TiO₂ composites is still a big challenge. To improve and fully utilize the catalytic efficiency of TiO₂ for flame retardant application, in this work, a hierarchical core–shell TiO₂-based architecture was constructed, composed by TiO₂ nanospheres (core) and oriented-growth Co-Al layered double hydroxide (LDH)@Ni(OH)₂ nano-catalyst (shell). As-fabricated hybrids with a fine frame construction improved the interfacial interaction with unsaturated polyester resin (UPR) matrix, contributed by increased contact area and interpenetration between two phases. Through well-contacted interface, the external force can be transferred smoothly to the rigid filler, and thus improved mechanical performance of UPR/TiO₂@LDH@Ni(OH)₂ nanocomposites. Theoretically, the well-designed structures and optimization of the chemical composition for transition metal compounds are important to effectively reduce fire hazards of UPR composites. Compared with pure UPR, the heat release, flammable pyrolysis products and toxic smoke emission were clearly reduced during the combustion of UPR/TiO₂@LDH@Ni(OH)₂, which can be attributed to the adsorption effect of core–shell hybrids and the barrier effect of thermostable char layers. Moreover, the total CO release experienced a maximum 53.33% decrease. Herein, this work expands the thinking of the preparation of multifunctional high-performance composites, and designs a novel hierarchical core–shell architecture with multiple regularly oriented shell layers.