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

Abstract

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 1H-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 (Tg = 156∼179°C), and also have excellent thermal stability (T5% = 331.4∼365.4°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 decomposition 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: Novel phosphorus-nitrogen flame retardant (DOPO-DBAPh) is developed. 5 wt% DOPO-DBAPh significantly improves the fire safety of EP resin. The DOPO-DBAPh/EP composites exhibit good thermal and mechanical properties.