A novel curing agent based on diphenylphosphine oxide for flame-retardant epoxy resin

Abstract

A phosphorous/nitrogen-containing diphenylphosphine oxide (DPO) derivative (DPO-SS) was designed and synthesized via a two-step reaction of 4,4′-diaminodiphenylsulfone, 2-hydroxy-benzaldehyde, and DPO. The structure of DPO-SS was confirmed by Fourier transform infrared spectroscopy (FTIR), 1H and 31P nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry (MS). DPO-SS was used as a flame retardant and curing agent for copolymerizing with diglycidyl ether of bisphenol-A. Thermal and flame-retardant properties of the obtained flame-retardant epoxy resin (F-EP) were investigated by thermogravimetric analysis, dynamic thermomechanical analysis, limited oxygen index (LOI) measurement, vertical burning test (UL-94), and cone calorimeter test. Results indicated that all F-EP samples exhibited excellent thermal stability and flame-retardant property. Especially for F-EP with P content of 0.7 wt% (denoted as EP/P-0.7), it achieved high LOI values (32.4%) and UL-94 V-0 rating. Compared with pure EP, all F-EP samples showed lower heat release rate, total heat release, total smoke produce, and little Tg fluctuation. In order to study the flame-retardant mechanism, the char residues were investigated by FTIR, scanning electron microscopy, and energy-dispersive spectrometer analysis. The results manifested that DPO-SS acted as flame retardant in both gas phase and condensed phase. Water absorption properties of pure EP and F-EP were also compared through immersion experiments. Results showed that EP/P-0.7 sample had apparently lower water absorptivity than pure EP.

Effect of ethyl‐bridged diphenylphosphine oxide on flame retardancy and thermal properties of epoxy resin

“…The data presented in Figure A,C,E reveal that under a nitrogen atmosphere, all thermosets show a similar decomposition process. The introduction of EDPO, HTP‐6123, and HPCTP leads to a decrease in decomposition temperature of EP, which was also mentioned in other reports . The T 5% , T 10% , and T max of EP/EDPO‐P‐0.9 are 364°C, 374°C, and 409°C, respectively, while those for EP/HTP‐6123‐P‐0.9 are 365°C, 374°C, and 400°C, respectively, and those for EP/HPCTP‐P‐0.9 are 349°C, 358°C, and 378°C, respectively.…”

“…Recently, diphenylphosphine oxide (DPO) and its derivatives have been used as flame retardants for EP in our group, and the performance of the flame retardant EPs were investigated . It was found that DPO or its derivatives modified diglycidyl ether of bisphenol A (DGEBA) EPs and led to good flame retardance performance.…”

Performance comparison of epoxy resins modified with diphenylphosphine oxide and DOPO

“…At 25°C, the peaks at 3400, 2960, 2863, 1510, 1460, 1362, 1245, 1181, 1037, and 829 cm −1 are assigned to the typical absorptions of the epoxy matrix. 35 The relative intensity of the characteristic peaks of the epoxy resin declines sharply between 300°C and 500°C, indicating that the degradation of the epoxy thermosets occurred mainly in this temperature range. This phenomenon is consistent with the TGA results.…”

“…[32][33][34] In our previous works, we concentrated on finding DPO derivatives-modified diglycidyl ether of bisphenol A (DGEBA) epoxy resins that showed apparent different properties compared with a similarly modified DOPO derivatives. 35,36 We realized that the molecular structure of DPO is similar to that of DOPO (Scheme 1), and each compound has an active P─H bond. The phosphorus content of DPO (15.32%) is a slightly higher than that of DOPO (14.33%), which means that lower dosage would be needed if DPO were to replace DOPO in the modification of epoxy resins.…”

Synthesis of Diphenylphosphine Oxide Derivative and Its Flame Retardant Application in Epoxy Resin

“…Although phosphaphenanthrene flame retardants generally have high flame-retardant efficiency, low smoke and toxicity, they can influence the thermostability of epoxy resin significantly [11,15,22]. Recently, Wang et al applied DPO and its derivatives to flame retardants [23][24][25]. And Tian et al also applied DPO derivatives to flame retarded poly(ethylene terephthalate) [26].…”