Yong Guo, Xiaoning Song, Qingshan Yang, Boyou Hou, Asim Mushtaq, Peng Hong, Siqi Huo, Pingan Song
Epoxy resin (EP) is widely used in electronic and electrical applications, but its inherent flammability significantly restricts further use in these fields. Phosphorus-based flame retardants, such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), provide efficient halogen-free flame retardancy and good compatibility with epoxy matrices, but their practical application is limited by high cost, reduced glass transition temperature, and increased smoke production. In this work, Australian red mud was upcycled to prepare high-purity Al 2 O 3 fillers, which were subsequently surface-modified with a silane coupling agent and grafted with DOPO to fabricate multifunctional Al-Si-DOPO. Epoxy composites containing both 5 wt% Al-Si-DOPO and 5 wt% DOPO (EP/5Al-Si-DOPO/5DOPO) were successfully prepared, exhibiting significantly high glass transition temperature, enhanced flame retardancy, suppressed smoke generation, and well-maintained mechanical properties. The EP/5Al-Si-DOPO/5DOPO composite exhibited a limiting oxygen index (LOI) of 31.3% and achieved a UL-94 V-0 rating, while its peak heat release rate (pHRR) and total hear release (THR) were reduced by 19.1% and 23.9%, respectively, compared with EP/DDM. Compared with the commercial DOPO price, the theoretically calculated price of Al-Si-DOPO decreased by 62.5%, indicative of superior cost-effectiveness. Thus, this strategy enables high-value utilization of industrial waste and offers a sustainable approach for designing environmentally friendly, cost-effective, high-performance epoxy composites.