The bisphenol F epoxy resin (DGEBF) reacted with 10-(2,5-Dihydroxyphenyl)-10H-9-oxa-10-phospha-phenantbrene-10-oxide (ODOPB) and phenyltrimethoxysilane (PTMS) to obtain a novel epoxy resin containing both phosphorus and silicon (EP-P/Si). EP-P/Si exhibited evidently improved flame retardancy, with a limited oxygen index value of 33.4% and UL-94 V-1 rating acquired. In cone calorimeter test, its peak heat release rate (PHRR), total heat release (THR), average effective heat of combustion (av-EHC), and total smoke production (TSP) were reduced by 36.0%, 19.5%,11.5%, and 7.2% compared with neat epoxy resin (EP), respectively, indicating that the P/Si synergistic effect not only improved the flame retardancy but also inhibited the smoke release. The flame retardancy mechanism was studied by analysis of char residue and pyrolysis behavior in gas phase. Scanning electron microscopy (SEM) results exhibited that EP-P/Si formed a dense and compact carbon layer acting as a barrier to inhibit further combustion. And the Fourier transform infrared (FTIR) spectra, laser Raman spectroscopy (LRS), and X-ray photoelectron spectroscopy (XPS) results indicated that it had good thermal stability. In addition, the pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) results suggested that the phosphorus-containing radicals (·PO2) that had quenching effect existed in the gas phase. While the flame retardancy got improved, EP-P/Si also exhibited excellent mechanical properties, with an improvement of 31.8%, 6.2%, and 369.7% in tensile strength, flexural strength, and impact strength compared with EP, respectively.
A phosphorous/silicon/triazine-containing flame retardant named DTD is synthesized and provides epoxy resin with enhanced flame retardancy and mechanical properties simultaneously. The modified epoxy with the DTD content of 18.1 wt% shows excellent flame retardancy, manifested in the limited oxygen index (LOI) value of 36.6% with UL-94 V-0 rating obtained. In the cone calorimeter test, its peak heat release rate (PHRR), total heat release (THR) and average effective heat of combustion (av-EHC) are reduced by 43.7%, 45.0%, and 38.1% compared with neat epoxy resin, respectively. Besides, DTD exhibits a good charring capability, indicated by observation of an expanded char layer structure and the 160.3% increment in char residue after the cone calorimeter test. The mode of action of DTD is explained by the analysis of char residue and the pyrolysis behavior in the gas phase. In addition, DTD has good compatibility with epoxy resin, confirmed by single spike of tan delta and similar half-peak width in dynamic mechanical analysis. While improving the flame retardancy, DTD also enhances the mechanical properties of epoxy resin. With 8.8 wt% of DTD content, the modified epoxy resin possesses desirable mechanical properties, with 36.0% and 18.9% increase in tensile strength and flexural strength, respectively.
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