Performance comparison of flame retardant epoxy resins modified by DPO–PHE and DOPO–PHE

• Published in: Polymer degradation and stability Vol. 156; pp. 89 - 99
• Main Authors: Zhao, Junjing, Dong, Xu, Huang, Shan, Tian, Xiujuan, Song, Liang, Yu, Qing, Wang, Zhongwei
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.10.2018; Elsevier BV
• Subjects: Bisphenol A; burning; calorimetry; Curing agent; Curing agents; Diaminodiphenylsulfone; Diphenylphosphine oxide; DOPO; epoxides; Epoxy resin; Epoxy resins; Flame retardant; Flame retardants; Gas chromatography; gases; Mass spectrometry; oxides; oxygen; Phosphine oxide; Polymers; Pyrolysis; pyrolysis gas chromatography; resins; Scanning electron microscopy; Submerging; Thermal stability; Thermogravimetric analysis; thermogravimetry; Thermosetting resins; Water absorption; water uptake; Epoxy resin; Flame retardant; Curing agent; Diphenylphosphine oxide; DOPO
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2018.08.007

Two phosphorus-containing flame retardants, (bis(4-hydroxyphenyl)methyl)diphenyl phosphine oxide (DPO–PHE) and 1-(bis(4-hydroxyphenyl)methyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO–PHE) were synthesized and characterized. The two target compounds both were used as a flame retardant and a co-curing agent of 4,4′-diaminodiphenylsulfone of bisphenol A diglycidyl ether to prepare flame-retardant epoxy resins (EP/DPO–PHE and EP/DOPO–PHE). The thermal and flame-retardant properties of the thermosets were investigated by thermogravimetric analysis (TGA), limited oxygen index (LOI) measurement, and UL-94 vertical burning testing (UL-94). The results indicated that both flame retardants can improve the flame retardancy of epoxy thermosets. TGA results indicated that the char yields of EP/DPO–PHE–P-0.9 and EP/DOPO–PHE–P-0.9 thermosets were increased from 19.1% of EP/P-0 to 25.3% and 27.8%, respectively. Compared with that of EP/P-0, the LOI of the EP/DPO–PHE–P-0.5 thermoset increased from 23.7% to 30.1%, and the sample reached UL-94 V-0. Meanwhile, the LOI of the EP/DOPO–PHE–P-0.7 thermoset increased from 23.7% to 28.9%, and the sample reached UL-94 V-0. Cone calorimetry test, scanning electron microscopy of burning residues, and pyrolysis–gas chromatography/mass spectrometry indicated that both flame retardants mainly act through the gas–phase mechanism. In addition, no condensed-phase activity of DPO–PHE was observed, whereas the condensed-phase activity of DOPO–PHE was negligible. Immersion experiments showed that the water absorption activity of flame retardant epoxy resins fluctuates. Compared with DOPO–PHE, DPO–PHE was more effective as a higher flame-retardant and exhibited better characteristics for improving the Tg, thermal stability, and water absorption of modified resins. •DPO-PHE and DOPO-PHE were used as a flame retardant and a co-curing agent of DDS of DGEBA to prepare flame-retardant epoxy resins.•Both flame retardants can improve the flame retardancy of epoxy thermosets, and act mainly through gas-phase activity mechanism.•Study showed that DPO-PHE have higher flame-retardant effectiveness than DOPO-PHE.•DPO–PHE exhibited better characteristics for improving the Tg, thermal stability, and water absorption of modified resins.