Abstract
Epoxy resins are characterized by excellent properties such as chemical resistance, shape stability, hardness and heat resistance, but they present low flame resistance. In this work, the synthesized derivatives, namely hexacyclohexylamino-cyclotriphosphazene (HCACTP) and novel diaminotetracyclohexylamino-cyclotriphosphazene (DTCATP), were applied as curing agents for halogen-free flame retarding epoxy materials. The thermal properties and combustion behavior of the cured epoxy resins were investigated. The obtained results revealed that the application of both derivatives significantly increased flame resistance. The epoxy resins cured with HCACTP and DTCATP exhibited lower total heat release together with lower total smoke production compared to the epoxy materials based on conventional curing agents (dipropylenetriamine and ethylenediamine). Comparing both derivatives, the HCACTP-cured epoxy resin was found to provide a higher flame resistance. The designed novel class of epoxy materials may be used for the preparation of materials with improved flame resistance properties in terms of flame spreading and smoke inhibition.
Highlights
In the modern polymer industry, epoxy resins have been extensively used as advanced composite matrices in a wide field of applications due to their attractive properties such as high adhesion, excellent mechanical properties, good chemical and corrosion resistance, damage tolerance, impact resistance, outstanding dimensional stability and remarkable electric insulating properties [1,2,3,4,5,6]
The results revealed that DTCATP was a more reactive curing agent than HCACTP
The results revealed that the DTCATP-cured epoxy resin exhibited the highest total smoke production (TSP)
Summary
In the modern polymer industry, epoxy resins have been extensively used as advanced composite matrices in a wide field of applications due to their attractive properties such as high adhesion, excellent mechanical properties, good chemical and corrosion resistance, damage tolerance, impact resistance, outstanding dimensional stability and remarkable electric insulating properties [1,2,3,4,5,6]. Phosphazene-based compounds bearing simultaneously phosphorus and nitrogen atoms in their structure have attracted a great attention [13,14,15,16,17,18,19,20,21,22] This class of products brings a synergistic flame retarding effect: phosphorus atoms act as radical scavengers and quenchers [23] and nitrogen atoms release inert gaseous by-products that create a porous network providing thermal insulation during the combustion [24,25,26]. Considerable efforts have been focused on the development of halogen-free flame retardants for epoxy resins [32,33,34,35] such as a spiro-phosphorus (P)based compound [36] or phosphaphenanthrene/benzimidazole-based agent [37]. Another phosphorus-based flame retardant was melamine phenyl phosphate [38] which greatly enhanced the flame retardancy and suppressed smoke evolution during burning of cured epoxy resin
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