A DOPO modified cyclosiloxane reactive diluent as an effective flame retardant for a high-performance epoxy network
Houlei Gan, Seyed Mohsen Seraji, Rusheni Bhagya Senanayake, Samuel Swan, Juan Zhang, Russell J. Varley
Abstract
A novel phosphorus-siloxane containing liquid flame retardant epoxy resin was synthesized and incorporated into an epoxy amine network, maintaining low viscosity and rapid cure characteristics, good mechanical and thermal properties, and affording excellent flame retardancy at low concentration. The synthesized flame retardant incorporated a tetra-functional glycidyl ether cyclosiloxane substructure which was substituted with two DOPO segments to obtain a liquid bi-functional flame-retardant epoxy resin (BGTS-DOPO). At only 10 wt% BGTS-DOPO, the modified epoxy amine resin had a viscosity of less than 210 mPa s at 90 °C, gelled rapidly at 150 °C, (9.3 min at 150 °C), exhibited a T g of 198.7 (extrapolated onset of E’) and 233.0 °C (tan δ max), and possessed improved flexural strength (4.5 %), modulus (4.1 %), strain (7.7 %) and fracture toughness (26.1 %). The self-extinguishing behaviour easily achieved a UL-94 V0 rating, exhibited a maximum limiting oxygen index of 36.7 %, while cone calorimetry produced a 24 % improvement in combustion behaviour of the carbon fibre composite. Presented here therefore is a new highly fire-retardant epoxy resin system that exhibited fast cure, low viscosity and excellent mechanical and thermal properties. • A liquid novel hybrid cyclosiloxane-DOPO (Si/P) reactive diluent (BGTS-DOPO) was synthesized then used to modify a high Tg epoxy amine resin. • The resin displayed low viscosity, rapid cure, but also high T g improved modulus, strength, failure strain and toughness. • UL-94, LOI and cone calorimetry also highlighted excellent improvements in flame retardancy at only 10 wt% addition.