Synthesis of Aluminum Phosphate from Aluminum Dross and Its Application as a Flame-Retardant Additive for Polymer Composites

Abstract

In this study, an aluminum phosphate–based material (denoted as AlPO) was synthesized from aluminum dross waste and investigated as a flame-retardant additive for unsaturated polyester (UPE) composites reinforced with glass fiber and pineapple fiber. Aluminum dross was first dissolved in NaOH solution, followed by CO₂ bubbling to precipitate aluminum hydroxide, which was subsequently reacted with phosphoric acid to form an aluminum phosphate–based material. The synthesized AlPO was incorporated into UPE composites at different loadings, and its effects on curing behavior, flame retardancy, and mechanical properties were evaluated.

XRD analysis indicated that the synthesized AlPO mainly exhibited an amorphous structure, while FTIR spectra confirmed the formation of Al–O–P bonds characteristic of aluminum phosphate–based materials. DSC results revealed that the presence of AlPO retarded the curing reaction of the UPE matrix, leading to a shift of the curing exotherm toward higher temperatures and a reduction in released heat. Flame retardancy tests showed that the incorporation of AlPO effectively improved the fire performance of the composites, with samples containing 8 wt.% AlPO achieving UL94 V-1 classification. Although the addition of AlPO resulted in a reduction in mechanical strength, the composites maintained acceptable mechanical properties at moderate AlPO loadings. These results demonstrate that aluminum phosphate–based material synthesized from aluminum dross is a promising flame-retardant additive for polymer composite applications, while also contributing to the recycling and valorization of industrial aluminum waste.