Incorporating a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-based derivative (1,4-bis(diphenoxyphosphoryl)piperazine, DIDOPO) in combination with modified calcium sulfate whiskers (MCSWs) improved the flame retardancy, thermal stability, and rheological properties of a polyethylene oxide (PEO) composite. The synergistic flame-retardant effect of DIDOPO and MCSW on the PEO system was investigated. After introducing 5 wt.% MCSW and 10 wt.% DIDOPO into PEO, the UL-94 rating of the composite reached V-0, and the limiting oxygen index was increased to 26.5%. Additionally, the peak and average heat release rates and total heat release of the PEO/10% DIDOPO/5% MCSW composite decreased by 38.9%, 22%, and 20.07%, respectively. The results of a thermogravimetric analysis (TGA) revealed that PEO/10% DIDOPO/5% MCSW displayed an improved initial thermal stability and rate of char formation compared to those of the PEO matrix. The results of TGA/Fourier transform infrared analysis indicated that the composites exhibited phosphorus-containing groups during thermal degradation, based on the characteristic absorption peaks, and increased amounts of gas-phase volatiles. The morphologies and structures of the residues indicated that the PEO/10% DIDOPO/5% MCSW blend was less stable than PEO during combustion. The MCSW mixture formed a denser, more continuous carbon layer on the composite surface during combustion. The rheological behavior indicated that the high complex viscosity and moduli of PEO/10% DIDOPO/5% MCSW promoted the cross-linking network structure of the condensed phase during combustion. MCSW exhibited an excellent flame retardancy and improved thermal stability, which are potentially promising for use in fire safety applications.

The morphology and composition of inorganic particles play a vital role in controlling the flame-retardant characteristics of polymers. Halogen-free flame-retardant polymers have also become a current research hotspot. Boron nitride (BN), phytic acid (PA), and chitosan (CS), a natural polysaccharide with a nitrogen content of approximately 6.8–7.5%, show great promise as flame retardants owing to their high thermal stability, P-based flame retardancy, and natural polysaccharide properties, respectively. In this study, BN (BN@PA-CS) particles coated with PA and CS were designed and prepared via a facile modification strategy. The effect of BN@PA-CS on the mechanical and flame-retardant properties of polyvinylidene fluoride (PVDF) was further investigated, and it was found that both characteristics were improved. Compared to pure PVDF, the PVDF composite films exhibited a significantly lower peak heat release rate and total heat release. With a BN@PA-CS content of 20%, the peak was the lowest at 18.25 W/g, corresponding to a decrease of 77.83%. This phenomenon may be attributed to the synergistic effect of the BN nanosheets and PA-CS in the BN@PA-CS particles. This work describes a facile and effective method of modifying the morphology and composition of inorganic particles, thereby controlling the properties of polymers, and provides a new approach to improving the safety of PVDF battery separators.