Strategic design unsaturated polyester resins composites with excellent flame retardancy and high tensile strength

Unsaturated polyester resin (UPR) composites with excellent flame retardancy and high mechanical property is a great challenge to its widely application. In present work, a highly efficient flame retardant (MA-DOPO) containing nitrogen, sulfur and phosphorus elements was designed via a nucleophilic substitution reaction of amino and aldehyde groups. For the UPR/MA-DOPO 15 composites, its tensile strength was 28.3 MPa, which was 19.9 % higher than that of neat UPR attributing to the formation of hydrogen bonds with UPR. It should be noted that tensile strength of UPR/MA-DOPO 20 composites reached the highest 39.6 MPa, showing a growth trend with the enhancement of incorporation amount of MA-DOPO. Meanwhile, the UPR/MA-DOPO 15 composites passed the UL-94 V-0 rating with a LOI of 27.0%, and the peak heat release rate (PHRR) and total heat release rate (THR) were reduced by 35.1% and 41.6% in cone calorimeter (CC) test comparing to that of neat UPR respectively. Moreover, the detailed flame-retarding mechanism of MA-DOPO was investigated by the thermogravimetric infrared spectroscopy (TG-IR), Raman spectrum, X-ray photoelectron spectroscopy (XPS) and pyrolysis-gas chromatography/mass spectrometry (PY-GC/MS), in which the releasement of inert gas in gas-phase and the catalytic carbonation in condensed phase jointly taking effect.