Enhancement of flame retardancy and mechanical properties of unsaturated polyester resin through organic-inorganic hybrid flame retardant composites

In order to fill the gap in the application of organic-inorganic flame retardant systems for flame-retarding unsaturated polyester resin (UPR) and develop highly efficient flame-retarded UPR composites to meet market demands, an organic-inorganic flame retardant system named PHAO@KL is proposed. A comprehensive analysis is conducted on the impacts of PHAO@KL on the flame-retardant and mechanical properties of unsaturated polyester, as well as its flame-retardant mechanism. The results obtained from the cone calorimeter demonstrated that the combination of 15 wt% PHAO and 15 wt% kaolin (KL) led to a reduction of 45.7 % and 38.9 % in the peak of the maximum heat release rate and the total heat release of the UPR composites, respectively. The PHAO@KL flame retardant system enhanced the mechanical properties of the UPR composites. Specifically, the tensile and flexural strengths of UPR/15PHAO@15KL reached 35.6 and 56.9 MPa, respectively, which were increased by 36.4 % and 31.4 % compared with those of pure UPR. Furthermore, the flame-retardant mechanism of PHAO@KL was investigated through X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM). The results indicated that the catalytic char-forming effect of PHAO interacted with the fragmented KL generated during combustion to form a stable heat-insulating barrier, thereby significantly strengthening the flame retardancy of the UPR composites and providing a reference for the development of organic-inorganic flame retardant systems.