Abstract
A novel liquid phosphorous-containing flame retardant anhydride (LPFA) with low viscosity was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and methyl tetrahydrophthalic anhydride (MeTHPA) and further cured with bisphenol-A epoxy resin E-51 for the preparation of the flame retardant epoxy resins. Both Fourier transform infrared spectroscopy (FT-IR), mass spectrometry (MS) and nuclear magnetic resonance (NMR) measurements revealed the successful incorporation of DOPO on the molecular chains of MeTHPA through chemical reaction. The oxygen index analysis showed that the LPFA-cured epoxy resin exhibited excellent flame retardant performance, and the corresponding limiting oxygen index (LOI) value could reach 31.2%. The UL-94V-0 rating was achieved for the flame retardant epoxy resin with the phosphorus content of 2.7%. With the addition of LPFA, the impact strength of the cured epoxy resins remained almost unchanged, but the flexural strength gradually increased. Meanwhile, all the epoxy resins showed good thermal stability. The glass transition temperature (Tg) and thermal decomposition temperature (Td) of epoxy resin cured by LPFA decreased slightly compared with that of MeTHPA-cured epoxy resin. Based on such excellent flame retardancy, low viscosity at room temperature and ease of use, LPFA showed potential as an appropriate curing agent in the field of electrical insulation materials.
Highlights
The results showed the initial decomposition temperature and limiting oxygen index were elevated while the residue decreased with the increase in MMDOPO
Bisphenol-A epoxy resin E-51 was cured by liquid phosphorous-containing flame retardant anhydride (LPFA) and methyl tetrahydrophthalic anhydride (MeTHPA) using N, N-dime-dimethylbenzylamine (0.5% by mass of anhydride) as an accelerator according to the thylbenzylamine (0.5% by mass of anhydride) as an accelerator according to the stoichiostoichiometric ratio under mechanical stirring at 60 ◦ C for 30 min
Liquid anhydride (LPFA) with excellent flame retardancy was synthesized with DOPO
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The epoxy resins cured in the common way are flammable with a low limiting oxygen index (LOI, about 19.8%) [5,6,7], which greatly limit the application in the electric and electronic fields. Flame retardant epoxy resins containing bromine are extensively used in the field of electronic and electrical materials because of their good flame retardancy. Schäfer et al [23] prepared two flame retardant epoxy resins with 0.81–1.66% phosphorus contents that reached UL-94V-0 level and exhibited high LOI values from 31.6 to 39.2. The results showed the cured epoxy resin passed V-0 rating of UL 94 test with the limiting oxygen index of 32.7% when the phosphorus content was only 1.5 wt%. We believed the research will contribute meaningful information to find a facile method for the flame retardant epoxy resins
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