Valorization of Salt Lake Waste Magnesium Res: Facet-Controlled Mg(OH)2 with Optimized Acidity and Basicity for Enhanced Flame Retardancy and Smoke Suppression in EVA

Ethylene–vinyl acetate copolymer (EVA) is widely used but limited by its high flammability and smoke emission. Magnesium hydroxide (MH), derived from sustainable Qinghai Salt Lake byproducts, offers a green solution for improving EVA’s fire safety. However, conventional MH suffers from random facet exposure and low efficiency. Here, a facet-engineering strategy is reported to selectively expose the (001) plane of MH by tuning hydrothermal temperature and polyethylene glycol (PEG) content. The optimized MH-3/EVA displays markedly enhanced flame-retardant and smoke-suppression behavior, with the LOI rising from 21.5% to 30.3%, and pHRR, THR, pSPR, TSP reduced by 41.8%, 26.7%, 51.5%, and 33.3%, respectively; Ds,max decreases by 51.1%. The enhanced fire-safety performance is attributed to the tailored surface acid–base sites on the (001)-facet-exposed MH, which capture acidic pyrolysis intermediates and catalyze the deep oxidation of volatile fragments. The synergistic action of CO2 capture, acid–base-catalyzed oxidation, and surface carbonation promotes the formation of a dense MgO/MgCO3/carbon barrier, thereby hindering heat and volatile transfer and inhibiting smoke precursor formation. This study synchronously enhances the flame-retardant and smoke-suppression efficiency of MH in EVA through crystal facet regulation, providing a new approach for the development of sustainable, green, and high-efficiency halogen-free flame-retardant polymer composites with excellent smoke suppression.