Synthesis And Properties Of Flame-retardant Latent Curing Agent For Epoxy Resins

Epoxy Resin is an important thermosetting with excellent properties such asstrong adhesion, electrical insulation properties, chemical stability, and so on.It is widelyused as adhesives, coatings and composite materials and widely used in construction,machinery, electrical and electronic, aerospace and many other fields. Only the curedepoxy resin can be used as useful materials with excellent properties. Add appropriatecuring agents in epoxy resin, curing reaction under certain conditions, to generate athree-dimensional mesh structure product. So the curing agent plays a decisive role inthe application of epoxy resin.The LOI of epoxy resin is19.8，flammability is the greatest disadvantage of it. Inthis thesis，DOPO derivatives（ODOPM）was synthesized，and was introduced toboron amine latent curing agents. Synthesized a latent flame retardant curing agentcontaining phosphorus, boron, nitrogen, wherein the phosphorus, boron, nitrogen,having a flame retardancy; epoxy resin can be easily cured by nitrogen-containinggroups curing agent. The complexation of boron and nitrogen, decreased the curingactivities of the curing agent at ambient temperature, therefore the curing agent can belatent.Acording to the controlled experiment, the optimum molar ratio of P/B/N was1.2:1:2and the hydrolytic stability of the synthesized boric acid ester was measuredby saturated vapor method and exposure method. The result of the exposureobservation test is above720h, and it is consistent with the BN boric acid esterscontaining aromatic ring structure reported in the literature. The result of the saturatedvapor method is better than the boric acid ester of the same type.The curing agent was heated and blended with the epoxy resin. By differentialscanning calorimetry (DSC),we have studied the curing properties of the premixtures.BN-EP system’s curing peak is closed to PBN-EP system’s first curing peak, but ismuch lower than the second curing peak temperature, which shows that the epoxycuring activity of the boron-amine complex was reduced because of the introductionof phosphorus. And the increase in the amount of the curing agent can improve thecuring rate of the system.ODOPM-BN: BGE (epoxy diluent): E51=20:20:80, thestorage life of the premix system at60℃achieved10days and the viscosity growthrate during48h was236%. It is clear to say the curing agent shows good curingability. In ODOPM-BN curing system, with the increases theoretical phosphorus content,the limiting oxygen index (LOI) increased, and also there’s a corresponding increase inthe level of the vertical combustion. The phosphorus content of PBN-EP3is1.38percent, and it could achieve UL-94V-0level, LOI was34.2.The thermal stability of PBN-EP series was tested by thermal gravimetricanalysis. Compared to only one weightless interval in the nitrogen atmosphere, thereare two weightless interval in an air atmosphere, and this is due to the secondweightlessness caused by oxidative decomposition. So the thermal stability in air issignificantly decreased. The introduction of phosphorus causes the decrease of theinitial decomposition temperature.With the use of ODOPM-BN increased, the charyield (800℃, N2) of PBN-EP system increased. The char yield(800℃, N2) ofBN-PBN is only3.76%, while the PBN-EP2which has the same content ofphosphorus is as high as16.32%. PBN-EP1and PN-EP, although close to thephosphorus content, but char yield of PBN-EP1is significantly higher than that ofPN-EP. It shows that PBN-EP is a good flame flame retardant, and it belongs to thecondensed phase flame retardant mechanism.The FTIR of PBN-EP3maximum decomposition rate proved the generate ofphosphate ester during the decomposition. The polyvinylidene phosphate was viscousliquid film and covered the surface of the combustible which made a good flameretardant effect. Further, since the phosphoric acid and metaphosphoric acid are strongacids, with a strong dehydrating, so that the polymer surface to form a carbonized filmplay a flame retardant.Through EDS and the PBN-EP3FTIR spectra before and afterVertical burning, it is confirmed that the content of phosphorus element in carbonresidue increased, so the series was condensed phase flame retardant mechanism.