Abstract
Epoxy resin (EP) has widespread applications in thermosetting materials with great versatility and desirable properties such as high electrical resistivity and satisfactory mechanical properties. At present, 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is widely applied to EP matrix for high flame resistance. Nevertheless, EP/DOPO composites acquire highly toxic decomposition products and smoke particles produced during combustion due to the gaseous fire-inhibition mechanism, which will be a major problem. To address this concern, an effective hyper-branched aluminum phosphonate (AHPP) was rationally designed and then coupled with DOPO into EP matrix to fabricate the fire-safe epoxy resin composites. On the basis of the results, significant increment in limiting oxygen index value (an achievement of 32% from 23.5% for pristine EP) and reduction in peak heat release rate and total heat release (59.4% and 45.6%) with the DOPO/AHPP ratio of 2:1 were recorded. During the cone calorimeter test, both the smoke production and total CO yield of EP-4 composite with the DOPO/AHPP ratio of 1:2 were dramatically decreased by 42.7% and 53.6%, which was mainly associated with the excellent catalytic carbonization of AHPP submicro-particles for EP composite. Future applications of submicro-scaled flame-retardant with various phosphorus oxidation states will have good prospects for development.
Highlights
Epoxy resin (EP) belongs to an outstanding class of thermosetting polymers, which has been considered to be a widely used material owing to its multiple and unique properties, for instance low shrinkage, superior solvent resistance, remarkable electrical insulation, excellent adhesive strength and ease of curing and processing [1,2,3,4]
Compared with the corresponding samples, the results show that the synergy between aluminum phosphonate phosphonate (AHPP) and DOPO reduces the heat release for the epoxy matrix during combustion, which is beneficial for decreasing the thermal hazard
A fire hazard suppression mode containing phosphorus oxidation states of −1, +1, and +3 the incorporation of reactive organic and unreactive inorganic additives was successfully applied to EP, through the incorporation of reactive organic and unreactive inorganic additives was successfully resulting in the construction of a very thick and non-inflammable char layer and tremendous reduction applied to EP, resulting in the construction of a very thick and non-inflammable char layer and tremendous reduction of TSP and toxic CO during combustion
Summary
Epoxy resin (EP) belongs to an outstanding class of thermosetting polymers, which has been considered to be a widely used material owing to its multiple and unique properties, for instance low shrinkage, superior solvent resistance, remarkable electrical insulation, excellent adhesive strength and ease of curing and processing [1,2,3,4]. Qiu et al [19] demonstrated that the simultaneous existence of TDBA (phosphaphenanthrene derivative) and DOPO structure in the EP composites produced more pyrolysis products and formed large-scale smoke particles, signifying the prominent gas phase action of DOPO present in inhibiting the transformation of the matrix to fuel. Braun et al [20] compared the effect of phosphorus valence on the fire behavior of EP and found that the flame inhibition effect, i.e., gas phase action decreased with the increasing oxidation state. Owning phosphorus-rich groups, hyper-branched polymers possess interesting architecture and a large number of active terminal groups compared to their linear counterparts [22,23], and have attracted increasing attention in constructing highly-efficient flame retardants. To obtain EP composites with simultaneous excellent flame retardance and smoke hazard suppression, a novel and submicro-scaled hyper-branched aluminum phosphonate (AHPP) was successfully prepared.
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