Preparation of phosphorus-nitrogen flame retardant DOPO-DBAPh and its flame retarded epoxy-based composites

Novel double DOPO-grafted phthalonitrile flame retardant (DOPO-DBAPh) has been successfully synthesized via solution reaction with amino-substituted phthalonitrile monomer, bisphenol A, paraformaldehyde and 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as initial materials. The molecular structure of DOPO-DBAPh was investigated by FT-IR and H-1-NMR spectrum. Then, the DOPO-DBAPh was added into epoxy (EP) to construct DOPO-DBAPh/EP fire-retarding composites by casting forming method. The effect of different proportions of DOPO-DBAPh/EP fire-retarding composites on the microstructure, thermal, mechanical, flame retardancy and combustion behavior was investigated. It was found that the DOPO-DBAPh/EP fire-retarding composites have a high glass transition temperature (T-g = 156 similar to 179 degrees C), and also have excellent thermal stability (T-5% = 331.4 similar to 365.4 degrees C) and high flexural strength (96.1-139.8 MPa). When DOPO-DBAPh content is 5 wt%, the vertical burning grade and limiting oxygen index (LOI) of DOPO-DBAPh/EP composites reached V-0 and 29.6%, respectively. Furthermore, the cone calorimeter testing results showed that the addition of DOPO-BAPh can obviously inhibit the decom-position rate of cured substance at high temperature and accelerated the formation of dense carbon layer. When DOPO-BAPh content was 20 wt%, the total heat release rate (THR) and peak heat release rate (PHRR) of the DOPO-DBAPh/EP fire-retarding composites were decreased by 38.55% and 35.81% compared with that of cured EP. In a word, this work presents a good way for synthesizing economical and highly efficient flame retardant for use in the preparation of EP-based fire-retarding composites with excellent comprehensive performance. Highlights center dot Novel phosphorus-nitrogen flame retardant (DOPO-DBAPh) is developed. center dot 5 wt% DOPO-DBAPh significantly improves the fire safety of EP resin. center dot The DOPO-DBAPh/EP composites exhibit good thermal and mechanical properties.