The Effect Of Ammonium Polyphosphate Microcapsules/expanded Graphite On The Flame Retardancy Of Epoxy Resin

Epoxy resin(EP)as one of the most commonly used thermosetting resins in the composite industry has good mechanical properties,electrical properties,adhesive performance and resistance to chemical corrosion,etc.It is widely used as adhesive,coatings,sealants and composites for machinery manufacturing,electrical and electronic materials,aerospace and wind power generation and so on.However,with the increase of crosslinking density,the poor toughness become the fatal flaws for EP.Meanwhile,the molecular structure of EP only contains C,H and O elements,leading to burning easily and burning with a large number of black smoke and toxic gases,which causes serious damage to ecological environments.The brittleness and flammability of EP have restricted its further development in industrial applications.Based on the background and requirements above,in this paper,the allyl-containing benzoxazine(Bala)was synthesized,considered by the perspective of molecular design.Ammonium polyphosphate microcapsules(BMAPP)were prepared by the in-situ polymerization.And the functional epoxy was prepared by blending with the BMAPP and expanded graphite(EG).The combustion behaviors and mechanism of flame retardant were discussed deeply,and the toughening mechanism had also been detailed in this paper through mechanics properties tests.The main research work is as follows:(1)The Bala was synthesized via Mannich condensation reaction using paraformaldehyde,allylamine and phenol as raw materials.The chemical structure of Bala was confirmed by 1H nuclear magnetic resonance(1H-NMR).The coated polymer layer had been seen clearly by scanning electron microscopy(SEM).Polybenzoxazine(PBala)modified ammonium polyphosphate microcapsules(BMAPP)were prepared by the in-situ ring-opening polymerization of Bala on the surfaces of APP.Fourier transform infrared spectroscopy(FTIR)and static contact angle test showed that Bala polymerized successfully,and enhanced the hydrophobicity of’ the APP effectively.The static contact angle of BMAPP microcapsules increased from 10.8° to 71.3° compared to the APP.The results of thermogravirmetric analysis(TGA)showed that the PBala could improve the initial decomposition temperature(Tinitial)of APP.(2)The thermal properties and combustion performance of EP and its composites(EP/BMAPP)investigated by thermogravimetric analysis(TGA),vertical combustion test(UL-94),limiting oxygen index(LOI),cone calorimeter(CONE)and dynamic thermal mechanical analysis(DMA).The results showed the LOI value of EP increased from 22.6%to 33.6%,and passed the UL 94 V-0 level with the addition of 10%BMAPP.Residue char of EP/BMAPP-10%was as high as 26.3%at 600℃.Meanwhile,the incorporation of BMAPP microcapsules leaded to great decrease of smoke production rate and heat release rate of EP during combustion process,along with an increase of glass transition temperature(Tg)and storage modulus of EP.The peak of heat release rate(PHRR)of EP/BMAPP-10%reduced from 1247KW·m-2 to 434 KW·m-2 due to the synergistic flame retardant effects of PBala and APP in BMAPP.Smoke production rate of EP/BMAPP-10%was approximately 67%lower than that of EP.The Tg of EP/BMAPP-10%increased from 169℃ to 173℃ with respect to EP.(3)The ultrasonic dissection of expanded graphite(EG)was added to the EP/BMAPP system,and the synergistic flame retardant epoxy(EP/BMAPP/EG)were prepared successfully.The flame retardant performance,thermal degradation and combustion behaviors were analyzed by TGA,UL-94,LOI,CONE and thermogravimetric-infrared spectrometry(TG-FTIR).Combined with the results of SEM and FTIR of carbon layer,the mechanism of flame retardant had been discussed.EG could improve the flame retardant effect,and the EP/BMAPP-10%/EG-1%had the best flame retardant performance.The LOI value reached at 34.1%,and residue char was 26.3%at 600℃.The initial thermal degradation temperature(Tintial)of EP increased from 338℃ to 345℃,comparing to EP/BMAPP-10%.The AHRR value was reduced by 10.9%and the SPR value was 0.26 m2·s-1 significantly lower than EP/BMAPP-10%.The characteristic absorption peak of P-O chemical bonds and NH3 could be detected in residue char and pyrolysis gas phase compounds respectively.And BMAPP/EG could promote EP to form high-quality char layer on the surface of composites.In conclusion,the BMAPP/EG synergies system had the characteristic of condensed phase and gas phase flame retardant.(4)Mechanical performance test results showed that the tensile strength of EP composites materials increased,with the increase of the content of BMAPP.And the elongation at break showed a trend of decrease after the first increase.EP/BMAPP-15%had the best tensile strength,arrived at 45.5MPa.The K,c value respectively increased at 61.8%,76.3%and 80.3%,comparing to pure EP.When adding EG toEP/BMAPP-15%as the compound materials,EP/BMAPP-10%/EG-0.3%had the largest tensile strength,the value was 47MPa,but the Young’s modulus and Elongation at break could reduced.In a degree,the increase of the content of EG could lead to the decrease of mechanical properties.EP/BMAPP-10%/EG-0.5%had the largest Young’s modulus,and the value reached at 3889MPa,and had the best comprehensive mechanical properties.Meanwhile,the value of Kic also gradually increased,arriving at 1.54 MPa·m1/2,1.56 MPa·m1/2,1.92 MPa·m1/2 respectively.EG could play to a role of synergistic toughening to improve the toughness of EP.