Study On Flame Retardant Epoxy Resin Composites With Boron Phosphate/Nanofiller

The combination of catalyzing carbonization technology and nano-technology is an important research field of enhancing non-halogen efficiency and developing environmentally friendly flame retardant materials.Bisphenol-A epoxy resin(EP)is widely used in many fields such as electrical and electronic materials,coatings and adhesives due to its superior adhesion properties,good mechanical strength,chemical resistance and insulating property.However,the application of EP composites is limited by their flammability.Meanwhile,EP has benzene and oxygen-containing groups in its molecular structure,which impart EP with charring ability during the pyrolysis process.Consequently,it serves as a suitable model to study the catalyzing degradation and carbonization mechanism.Boron phosphate(BP)possesses plenty of Br?nsted acid sites and Lewis acid sites in the three-dimensional structure of BP which are formed by tetrahedral phosphorus-oxygen and tetrahedral boron-oxygen sharing oxygen atoms and these sites.Researches on the relations between the surface acidity and catalyzing carbonization effect are performed to unravel the mechanism and acquire the data of applying catalyzing carbonization agents.One-dimensional nanofillers with high aspect ratio(such as sepiolite,halloysite,modified MCNTs)can enhance the mechanical properties of polymer matrix.With the combination of nanofillers and BP,the technical methods of enhancing mechanical property for catalyzing carbonization flame retardant polymer materials are explored.In this paper,the following researches are carried out.(1)Boron phosphates(BPs)with different acidities were prepared by regulating the calcination temperatures for reaction products of boric acid and phosphoric acid.The influences of surface acidities on fire properties and thermal degradation behavior for EP/BP composites are explored.The morphology,crystal structure,surface acidity and thermal stability were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),chemical absorbed apparatus and thermogravimetric analysis(TG).LOI,UL 94 vertical test and Cone calorimetry test are carried out to characterize the combustion behavior of composites.The results showed the surface acidities decreased with the increase of calcination temperatures and the flame retardancy of composites decreased with decrease of BP surface acidity.Compared with pure EP,when 3 wt%/5 wt% BP was loaded,LOI of composites increased by 0.9%~3.2% and UL 94 reached V-1.With the addition of 5 wt% BP prepared at 300 ?C,PHRR of EP/BP composites decreaed by 43%,average specific extinction area(ASEA)decreased by 25%.(2)The influences of BP surface acidity on volatile products and condensed phase products have been explored.TG-FTIR,TG,Raman spectra and XPS test results indicated that BP1 with higher surface acidity and relatively more Br?nsted acid sites catalyzed the degradation of EP matrix at lower temperature and promote the cross-linking reaction which leads to the higher char yield of composites.T he presence of BP provided homogeneous and dense char layer with an enhanced graphitization degree.Meanwhile,the existence of more non-oxidized carbon(C-C,C=C,et al)groups in the residues signifies improved thermal-oxidation resistant capabilities.TG-FTIR results suggested that volatile products of EP/BP composites released at lower temperature and the quantity of flammable gases decreased obviously.(3)With the combination of inorganic nanofiller and BP,the combustion behaviour and mechanical properties are studied.Combustion test showed that EP composites possess higher LOI values than pure EP.However,the c ontinued burning time in the UL 94 test became longer.CONE test showed that the peak heat release rate(PHRR)and total heat release(THR)are highe r than EP/BP composites.Meanwhile,the yield,height and compactness of the char residue were obviously decreased.Mechanical test proved that the presence of inorganic nanofillers improved the tensile and flexural strength of EP composites,wherein the EP/4 wt%BP/1 wt%MMCNTs showed the best improvement which can be explained by one-dimensional nanofillers having stronger interfacial interaction with EP matrix and transferring the external forces to the maximum degree.