A New DOPO-Eugenol Adduct as an Effective Flame Retardant for Epoxy Thermosets with Improved Mechanical Properties

Abstract

The development of efficient green flame retardants is an important way to realize more sustainable epoxy thermosets and downstream materials. In this work, a monoepoxide is synthesized through O-glycidylation of eugenol, and then reacted with DOPO (9,10-dihydro-9-oxa-10-phosphophenanthrene-10-oxide) to obtain a new bio-based flame retardant, DOPO-GE. DOPO-GE is blended with a bisphenol A epoxy prepolymer exhibiting good compatibility and DDS (4,4′-diaminodiphenylsulfone) is used as the curing agent to afford epoxy thermosets. Although DOPO-GE leads to the reduced glass transition temperature of the thermosets, the storage modulus increases considerably. The DOPO-GE-modified thermosets exhibit the high thermal stability with the onset thermal decomposition temperature in nitrogen and air exceeding 300°C. When the phosphorus content in the thermoset is 1.0%, the residual yield of the thermosets at 750°C in nitrogen increases from 13.9% to 30.6%, due to the increased charring ability. More interestingly, when the phosphorus content is only 0.5%, the limiting oxygen index is as high as 30.3% with UL94 V0 achieved. Cone calorimeter results reveals the significantly decreased heat release rate, total heat release, mass loss and total smoke production. Furthermore, DOPO-GE can notably improve the flexural strength, flexural modulus and fracture toughness, whereas the shear and impact strength are reduced to varied extents. In short, DOPO-GE can be obtained via a facile way, and shows the good flame-retardant effect on the epoxy thermosets with an application potential.