| Epoxy resin (EP) is one of the well-known thermosetting polymers and has been used in surface coating, adhesives, composites, etc., due to superior toughness, low shrinkage on curing, outstanding adhesion, and excellent mechanical properties. However, the flammability of EP-limits its application in some areas. Therefore,flame retardant (FR) EP have been attracting increasing attention Considering the generation of toxic and corrosive gases of the halogenated flame retardants during combustion, there is a trend toward using halogen-free FRs in EPs.’Phosphorus-and nitrogen-containing compounds are considered to be promising "green" FRs, due to their high efficiency. In this dissertation, different 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-phosphonamidates were synthesized by the way of molecular design to improve flame retardancy of EP. Considering the advantages of 2-dimensional graphene, DOPO-phosphonamidate functionalized and phosphoramide wrapped graphene were prepared to enhance mechanical and flame retardant properties of EP. Combining nanocomposite technique with DOPO-phosphonamidates, the optimization of mechanical properties and flame retardancy of EP was achieved by the addition of DOPO-phosphonamidate/graphene hybrids. To reduce non-thermal hazards of EP during combustion, highly efficient smoke and toxic gases suppression agent, transition metal molybdates, were successfully prepared. Research work of this dissertation is composed of the following parts:1. Three DOPO-phosphonamidates were successfully synthesized and the influence of these DOPO-phosphonamidates on fire performance of EP was comparatively investigated, and flame retardant mechanism was proposed. The results mdicated that DOPO-phosphonamidates exbAied superior fire performance. The EP composite containing extremely bw bading of PiP-DOPO (0.5 wt%P) may pass die UL-94 V-0 rating and the LOI was as high as 28.0%. The PHRR and THR values for flame retarded EP system were significantly reduced. Only a very small residue was observed at 800℃ for all the EP formulations, indicating the limited condensed phase interaction Large amount of gas products during the combustion of PiP-DOPO rapidly released in a short time, promoting flame inhibition, which may explain its superior flame retardant efficiency.2. Reactive DOPO-based phosphonamidate oligomers, including branched (BFR) and linear (LFR) structures were prepared via nucleophilic substitution reaction and incorporated into EP. The flame retardancy and the thermal properties of the EP composites were investigated by TGA, LOI, UL-94 and cone calorimeter. Results indicated the addition of BFR and LFR catalyzed the degradation of EP, promoting the formation of thermally stable char layers. BFR and LFR increased the LOI value and effectively reduced PHRR and THR.7% loading of BFR was enough to achieve the UL-94 VO rating, while 4% LFR is available, indicating higher efficiency. During the thermal degradation process, PO radicals released from DOPO trapped H and OH radicals in the gaseous phase of the fire, which retarded polymer degradation and combustion. Meanwhile, the pyrolysis products of acid source catalyzed the formation of the char layer, protecting the inner polymer matrix from further burning;3. DOPO-phosphonamidate fimctionalized graphene was achieved by the reaction of GO with PEI and subsequently with DOPO. Graphene wrapped with phosphoramide (FRGO) was successfully prepared by in situ reaction of 4-4’diamino dphenyl methane, phosphorus oxychloride and reduced graphene oxide. Owing to the strong interfacial interaction between the functionalized rGO and epoxy, f-rGO and FRGO were dispersed well in the matrix. The addition of f-rGO and FRGO increased the thermal stability at the elevated temperature. Moreover, the addtion of 3 wr%f-rGO resulted in 31%and 34.3%reduction on PHRR and THR, respectively, compared to those of neat EP, while 43.0%reduction in PHRR for 2 wt%FRGO/EP nanocomposite. These notable reductions in fire hazards were mainly due to the synergistic effect of functionalized graphene:the flame retardant promoted the formation of additional char residues and improved the thermal oxidative resistance of the graphene; highly thermal-stability char layer, consisting of graphene sheets, retarded the permeation of heat and the escape of volatile degradation products.4. PiP-DOPO/piperazine-modified graphene hybrids (PD-rGO) were successfully prepared via in situ synthesis, and incorporated into EP to fabricate EP composites. The presence of PD-rGO significantly reduced the PHRR and THR values by 43.0% and 30.2% over neat EP, respectively. PD-rGO exhibited higher LOI value and excellent UL-94 results than PiP-DOPO. Moreover, the storage modulus was increased, due to the high stiffness of graphene. The enhanced fire resistance was mainly attributed to the combination of flame inhibition in the gas phase and the barrier effect of graphene in the condensed phase, which reduced the release of flammable volatile components and promoted the formation of additional graphitized carbons.5. The toxic gases of EP composites filled with DOPO-phosphonamidates and FRGO were evaluated by steady state tube furnace. The results indicated the addition of DOPO-phosphonamidates increased the CO production and reduced the release of CO2, due to the incomplete combustion However, the presence of FRGO had negligible impact on the CO and CO2 yields. Three types of transition metal molybdates (AMOO4) nanocrystallines were prepared via a hydrothermal method for reducing the release of toxic gases of EP during combustioa Adding AMoO4 promoted the early degradation of EP, resulting in the formation of additional char residues. Moreover, the amount of organic volatiles of EP was significantly reduced and the toxic CO was suppressed, implying the reduced fire hazards. CoMoO4 and CuMoO4 performed better results than the NMoO4.The catalytic oxidation of CO and catalytic carbonization by AMoO4 was the possible mechanism for the smoke suppression. |
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