A DOPO based reactive flame retardant constructed by multiple heteroaromatic groups and its application on epoxy resin: curing behavior, thermal degradation and flame retardancy

• Published in: Polymer degradation and stability Vol. 167; pp. 10 - 20
• Main Authors: Zhang, Qianqian, Yang, Shuang, Wang, Jun, Cheng, Jianwen, Zhang, Qiaoxin, Ding, Guoping, Hu, Yefa, Huo, Siqi
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.09.2019; Elsevier BV
• Subjects: Charring; Chemical bonds; Combustion; Crosslinking; Curing; Curing agents; Curing behavior; Enthalpy; epoxides; Epoxy resin; Epoxy resins; fire hazard; Flame retardant; Flame retardants; Fourier transform infrared spectroscopy; Fourier transforms; Free radicals; gases; Glass transition temperature; heat; Heat release rate; Heat transfer; Heteroaromatic; Imidazole; mass spectrometry; NMR; Nuclear magnetic resonance; nuclear magnetic resonance spectroscopy; Organic chemistry; oxygen; phosphorus; phosphorus content; Pyrolysis behavior; stable isotopes; Thermal degradation; Thermal stability; Thermogravimetric analysis; thermogravimetry; Thermosetting resins; Epoxy resin; Flame retardant; Heteroaromatic; Pyrolysis behavior; Curing behavior
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2019.06.020

A high-efficiency flame retardant composed of phosphaphenanthrene, benzothiazole and imidazole groups (PBI) was synthesized and served as flame retardant co-curing agent to reduce the fire hazard of epoxy resin (EP). The chemical structure of PBI was characterized by Fourier transform infrared spectroscopy (FTIR), high-resolution mass spectroscopy (HR-MS), 1H and 31P nuclear magnetic resonance (NMR). The curing behavior, thermal stability and flame retardant properties of the prepared EP systems were investigated. The curing behavior study disclosed that PBI accelerated the crosslinking reaction of EP and was chemically bonded with EP matrix to obtain intrinsic flame retardant thermoset. The resulting EP thermosets showed only slight decrease in glass transition temperature (Tg). The thermogravimetric analysis (TGA) results indicated both the catalytic decomposition and catalytic charring effects of PBI demonstrated by decreased thermal stability and enhanced charring capability of EP/DDS/PBI thermosets. The combustion test results showed remarkable improvement in the flame retardant properties of EP/DDS/PBI thermosets. When the phosphorus content was only 0.75 wt%, EP/DDS/PBI-0.75 thermoset achieved a limiting oxygen index (LOI) value of 34.6% and passed UL94 V-0 rating. Moreover, the peak of heat release rate (pk-HRR), average of heat release rate (av-HRR) and total heat release (THR) values were decreased by 48.7%, 31.1% and 28.3%, respectively, in comparison with those of the EP/DDS thermoset. The flame retardant effect of PBI on EP was attributed to the catalytic charring effect to form protective char layer in condensed phase and release of free radicals with quenching effect and nonflammable gases with diluting effect in gaseous phase. •A DOPO based reactive flame retardant (PBI) constructed by multiple heteroaromatic groups was successfully synthesized.•PBI accelerated the crosslinking reaction of EP.•Blowing-out effect was observed for EP/DDS/PBI thermosets.•PBI exhibited bi-phase flame retardant effect on EP.