Phenethyl-bridged DOPO derivative (DiDOPO) was combined with organo-modified aluminum hydroxide (OATH) in an epoxy resin (EP) to improve its flame retardancy. The results indicated that the introduction of only 10 wt% DiDOPO/60 wt% OATH in EP increased the limited oxygen index from 21.8% to 39.2%, thus the material met the UL 94 V-0 rating. Thermogravimetric analysis revealed that char yield increased in the presence of OATH to form thermally stable carbonaceous char. The evaluation of flame-retardant effect by cone calorimetry demonstrated that OATH improved the protective-barrier effect of the fire residue of EP/DiDOPO/OATH.

In this paper, phosphorus-based compouds, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and hexa-phenoxy-cyclotriphosphazene (HPCP), and expandable graphite (EG) were adopted as flame retardants for epoxy resin (EP). The resulting EP composites were investigated using thermogravimeric analysis (TGA), limited oxygen index (LOI), vertical burning (UL94), cone calorimeter, pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), Fourier Transform Infrared (FTIR) and scanning electron microscope/energy dispersive X-ray (SEM-EDX). The results disclosed that EG affected the thermal decomposition process of EP composites and led to the earlier arisen pk-HRR and later lower HRR due to its high thermal conductivity and strong barrier effect. The further enhanced flame retardancy of EP composites containing both EG and phosphorus-containing compounds indicated the synergy between different flame retardant components. The morphology study showed that the residual char of EP/EG exhibited an intumescent but fluffy and wormlike structure with low adhesion. However, those of EP/EG/DOPO and EP/EG/HPCP revealed compact and tough structures composed of wormlike graphite and carbonized EP matrix. The strong interfacial bonding between these two different carbon residues strengthened the integrality and continuity of the intumescent char layers, leading to a stronger barrier effect in condensed phase. In addition, DOPO and HPCP provided flame retardant effect in gaseous phase for EG-containing epoxy resin.

A novel reactive flame-retarded epoxy resin system was prepared by copolymerizing diglycidyl ether of bisphenol-A (DGEBA) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), N,N'-bis-maleimide-4,4'-diphenylmethane (BDM) and 4,4'-diamino-diphenyl sulfone (DDS). Curing behavior, thermal and flame-retardant properties of the cured epoxy resins were investigated by differential scanning calorimeter (DSC), thermogravimeric analysis (TGA), limited oxygen index (LOI) measurement, UL94 test and cone calorimeter. The results indicated that phosphaphenanthrene group was introduced into the multicomponent system by addition reaction of DOPO with BDM. Compared with traditional DOPO-DGEBA systems, the EP/DDS/BDM/DOPO thermosets showed greatly improved glass transition temperatures (210-223 degrees C). The results of combustion tests indicated that the addition of BDM or DOPO into DGEBA could improve the flame resistance of the thermosets. Most importantly, the flame-retardant property was further improved when BDM and DOPO coexisted in the epoxy resin systems. For example, compared to the control samples, the EP/DDS/BDM/DOPO-15 thermoset displayed better flame retardancy with higher LOI value and UL94 rating, lower peak of heat release rate (pk-HRR) and average of effective heat of combustion (av-EHC) under the same content of BDM and phosphorus, strongly confirming the synergistic effect of BDM and DOPO. In addition, in a particular proportion, BDM and DOPO synergistically functioned in the condensed-phase and gaseous-phase at the same time. The flame retardant mechanism was studied by TGA and cone calorimeter coupled with the analysis of the char residues. (C) 2015 Elsevier Ltd. All rights reserved.

A novel additive, tri(phosphaphenanthrene-maleimide-phenoxyl)-triazine (DOPO-TMT), was successfully synthesized. The chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance. DOPO-TMT was blended with epoxy resins to prepare flame-retardant thermosets. The flame-retardant properties were evaluated using limited oxygen index (LOT), vertical burning (UL94), and cone calorimeter tests. The results indicated that DOPO-TMT exhibited excellent flame-retardant effect. The flame-retardant mechanism was studied by thermogravimeric analysis (TGA), pyrolysis-gas chromatography/mass spectrometry, and thermogravimetric analysis/infrared spectrometry (TGA-FTIR) coupled with the morphology and chemical analysis of the char residues. The results disclosed that DOPO-TMT exerted biphase flame-retardant effect. In gaseous-phase, DOPO-TMT released phosphorus- and nitrogen-containing free radicals with quenching effect under thermal decomposition. The morphologies of the char residues exhibited intumescent and honeycombed structure with a small number of holes on the surfaces. The honeycombed char structure served as an excellent protective layer. A few number of holes on the surface facilitated the concentrated release of free radicals to implement a strong quenching effect. The functional groups of DOPO-TMT synergistically interacted to endow epoxy resin with excellent flame retardancy.

Triazine derivative with active maleimide group (TMT) was synthesized via nucleophilic substitution reaction between N-(4-hydroxyphenyl) maleimide (HPM) and cyanuric chloride using a new method, and higher yield of TMT was obtained. The investigated flame-retardant epoxy resins were then prepared by copolymerizing diglycidyl ether of bisphenol-A (DGEBA) with TMT, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 4,4'-diamino-diphenyl methane (DDM). The study on the reactivity disclosed that DOPO was exclusively grafted on TMT. The glass transition temperatures (T(g)s) of EP/TMT/DOPO thermosets (154-160 degrees C) were much higher than that of the traditional EP/DOPO thermoset (122 degrees C). Flame-retardant properties of the cured products were evaluated using limited oxygen index (LOI), vertical burning (UL94) and cone calorimeter tests. The results indicated that the flame retardancy of EP/TMT/DOPO thermosets was dramatically enhanced with low loading of phosphorus content. EP/TMT/DOPO-1.0 sample with phosphorus content of only 1.0 wt.% achieved a LOI value of 40.3% with UL94 V-0 rating, and the average of heat release rate (av-HRR), average of effective heat of combustion (av-EHC) and total heat release (THR) were decreased by 37%, 31.9% and 35.4%, respectively, compared with those of the neat EP. The excellent flame-retardant properties of EP/TMT/DOPO thermosets were ascribed to bi-phase flame-retardant effect. The morphologies of the char residues showed honeycombed and intumescent structures with a small number of holes on the surfaces. The char barrier served as protective layer. The small number of holes on the surface facilitated the concentrated release of free radicals to implement an intensive quenching effect. The enhanced flame retardancy was achieved by means of carbonization, swelling and high concentration of free radicals. (C) 2015 Elsevier Ltd. All rights reserved.

A phosphorous/nitrogen-containing reactive phenolic derivative (DOPO HPM) was synthesized via the addition reaction between 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and N-(4-hydroxyphenyl) maleimide (HPM). The structure of DOPO HPM was characterized by Fourier transform infrared spectroscopy (FTIR), H-1 and P-31 nuclear magnetic resonance (NMR) and elemental analysis (EA). The studied flame-retardant epoxy resin systems were prepared by copolymerizing diglycidyl ether of bisphenol-A (DGEBA) with DOPO HPM, triglycidyl isocyanurate (TGIC) and 4,4'-diamino-diphenyl sulfone (DDS). Thermal and flame retardant properties of the cured epoxy resins were investigated by differential scanning calorimeter (DSC), thermogravimeric analysis (TGA), limited oxygen index (LOI) measurement, UL94 test and cone calorimeter. The DSC results indicated that the modified epoxy resins showed little fluctuation in glass transition temperatures (197-205 degrees C). The results of combustion tests indicated that the modified epoxy resin systems exhibited excellent flame retardant properties. The P-1 and P-1.25 systems acquired LOI values of 37% and 38.5%, respectively, and achieved a UL94 V-0 rating. Compared with the P-0 system, the peak of heat release rate (pk-HRR), average of effective heat of combustion (av-EHC) and total heat release (THR) of P-1.25 system decreased by 61.4%, 234% and 34.9%, respectively. In addition, the total smoke production (TSP) of the modified epoxy resin systems decreased with the increasing content of flame retardants, indicating the smoke suppression effect of the flame-retardant systems. Through visual observation, the char residues after cone calorimetry test exhibited intumescent structures with continuous and compact surfaces. The flame retardant mechanism was studied by FTIR, scanning electron microscope (SEM), cone calorimeter and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). (C) 2015 Elsevier Ltd. All rights reserved.