Investigation on flame retardancy, combustion and pyrolysis behavior of flame retarded unsaturated polyester resin with a star-shaped phosphorus-containing compound

•The star-shaped phosphorus-containing flame retardant was synthesized.•TRIPOD-DOPO can impart excellent flame retardant properties to UPR.•TRIPOD-DOPO acted in the gas and condensed phase at the same time.

The phosphorus-containing star-shaped flame retardant (TRIPOD-DOPO) was synthesized, while the flame retardant unsaturated polyester resins (FR-UPRs) composites with various amounts of TRIPOD-DOPO were prepared. The thermogravimetric analysis (TGA) and oxygen index (OI) results showed that the incorporation of TRIPOD-DOPO improves the thermal stability and flame retardancy of UPR. The combustion properties of composites were evaluated by microscale combustion calorimeter (MCC), and the results indicated that TRIPOD-DOPO decreased the peak heat release rate (pHRR) and total heat release (THR) of UPR. Fourier transform infrared coupled with the thermogravimetric analyzer (TG–IR) revealed that UPR and TRIPOD-DOPO decomposed independently of each other. Flame inhibition was expected to occur in the gas phase. Under the air condition, TRIPOD-DOPO showed a more obviously condensed phase interaction increasing charring from the TG results. The SEM results showed that the residual char of composites were more compact and continuous, which could prevent mass and thermal transfer.