Preparation of microencapsulated aluminum hypophosphite and its flame retardancy of the unsaturated polyester resin composites

A novel microencapsulated flame retardant (CP@AHP), aluminum hypophosphite (AHP) as the core material and chlorinated paraffin (CP) as the shell material, was successfully prepared and applied in unsaturated polyester resin (UPR) to prepare the UPR composites in this paper. The aim of microencapsulation AHP was to enhance the fire safety of the UPR composites. The structure, morphology and thermal behavior of CP@AHP were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and thermogravimetric analysis (TG), respectively. The thermal and flame-retardant properties of the UPR composites were evaluated by TG and cone calorimetry test (CCT), respectively. At the same time, the tensile and flexural properties of UPR composites were tested. Compared with pure UPR, the residue at 800 °C of UPR/CP@AHP-1:2 (UPR/CP@AHP with the mass ratio of CP:AHP = 1:2) under nitrogen atmosphere is from 6.9 to 31.6. The CCT results showed that the peak heat release rate (pHRR) and total heat release of UPR/CP@AHP-1:2 decreased by 58.4 and 46.1%, respectively, in comparison with pure UPR. The results of TG and CCT indicated that CP@AHP could improve the thermal stability and flame retardancy of the UPR composites. Finally, based on the above results, the flame retardancy mechanism of CP@AHP was proposed.