Abstract
The aim of this work was an investigation of the ability of gallic (GA) and ellagic (EA) acids, which are phenolic compounds encountered in various plants, to act as flame retardants (FRs) for epoxy resins. In order to improve their fireproofing properties, GA and EA were treated with boric acid (to obtain gallic acid derivatives (GAD) and ellagic acid derivatives (EAD)) to introduce borate ester moieties. Thermogravimetric analysis (TGA) highlighted the good charring ability of GA and EA, which was enhanced by boration. The grafting of borate groups was also shown to increase the thermal stability of GA and EA that goes up respectively from 269 to 528 °C and from 496 to 628 °C. The phenolic-based components were then incorporated into an epoxy resin formulated from diglycidyl ether of bisphenol A (DGEBA) and isophorone diamine (IPDA) (72, 18, and 10 wt.% of DGEBA, IPDA, and GA or EA, respectively). According to differential scanning calorimetry (DSC), the glass transition temperature (Tg) of the thermosets was decreased. Its values ranged from 137 up to 108 °C after adding the phenolic-based components. A cone calorimeter was used to evaluate the burning behavior of the formulated thermosets. A significant reduction of the peak of heat release rate (pHRR) for combustion was detected. Indeed, with 10 wt.% of GA and EA, pHRR was reduced by 12 and 44%, respectively, compared to that for neat epoxy resin. GAD and EAD also induced the decrease of pHRR values by 65 and 33%, respectively. In addition, a barrier effect was observed for the resin containing GAD. These results show the important influence of the biobased phenolic compounds and their boron derivatives on the fire behavior of a partially biobased epoxy resin.
Highlights
Due to their intrinsic characteristics, such as mechanical and electrical insulating properties, chemical resistance under both acidic and basic conditions, and adhesive properties, epoxy resins are widely used for structural applications, as well as in the coating, electronic, and adhesive industries [1]
Gallic acid derivatives (GAD) were recovered by freeze-drying of the treatment solution
A sample of freeze-dried GAD powder was dissolved in methanol prior to electrospray ionization (ESI)–Mass spectrometry (MS) analysis
Summary
Due to their intrinsic characteristics, such as mechanical and electrical insulating properties, chemical resistance under both acidic and basic conditions, and adhesive properties, epoxy resins are widely used for structural applications (in association with glass or carbon fibers), as well as in the coating, electronic, and adhesive industries [1]. Low thermal and fire resistance of epoxy resins are drawbacks limiting their use in some applications. To improve these properties, the addition of flame retardants (FRs) has been practiced for many years. Among others, halogenated FRs have been extensively used [2,3]. The harmful effects on both environment and human beings are an impediment to their use [4]. The development of Molecules 2019, 24, 4305; doi:10.3390/molecules24234305 www.mdpi.com/journal/molecules
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
