Loading LDH On Sepiolite Nanofiber And Its Application In Flame Retardant Epoxy Resin

Epoxy resin(EP)has been used almost 100 years in industry since its discovery.However,the flammable behavior is a common feature for all polymer materials and likewise for EP.Recently,the phosphorus and nitrogen-based fillers with well char formation property are the most popular epoxy flame retardant.Unfortunately,the fire safety and mechanical properties as well as thermal resistance of those EP composites frequently fails to be balanced and thus limits the application of EP in some fields,for instance,in aeronautic and automobile applications withstanding the wide temperature variations and many kinds of mechanical stresses.With the development of nano-technology,the flame retardant in nano-size owns low-feeding and multifunctional characteristics due to its nanoscale effect.The inorganic nano-fillers with catalytic charring effect are mainly chosen as the nano-flame-retardant for EP.However,the catalytic charring ability of nano-flame-retardant is influenced by many factors,hence the nano-flame-retardant EP systems show inconsistent fire performances in different fire scenarios.The underlying reason is attributed to the limited flame retardancy of nano-flame-retardant.Therefore,the phosphorus and nitrogen elements are usually introduced into nano-flame-retardant EP system.Based on this,to endow EP with flame retardancy and enhanced mechanical properties as well as thermal resistance,herein a multifunctional flame retardant a-SEP@LDH is prepared through the layered double hydroxide nanosheets containing transition metals(Ni-Fe LDH)self-assembled on the surface of sepiolite nanofiber.Taking advantage of the unique structure of a-SEP@LDH,the dispersion of LDH in EP matrix can be relatively improved.The effects of a-SEP@LDH in flame retardancy,mechanical properties and thermal resistance performances of EP and EP composites composed of PAMA nanosheets have been studied.Additionally,the related mechanism also investigated.With addition of 2.3 wt% a-SEP@LDH,EP/a-SEP@LDH possesses V-1 rating and 31.1% of limiting oxygen index(LOI).In addition,EP/a-SEP@LDH shows a certain fire retardancy in cone calorimeter test,reflecting in decreased peak heat release rate,total smoke production and carbon monoxide production.The flame-retardant mechanism of EP/a-SEP@LDH is ascribed to the high-quality char formation and the details are drawn as follows: a)physical solidified char residue by sepiolite nanofiber;b)the catalytic charring effect of both Ni/Fe alloy catalyst(originated from partially thermal decomposed LDH)and Br?nsted acid sites in sepiolite.Excitedly,the tensile strength and impact strength of EP/a-SEP@LDH are enhanced and almost maintained,respectively.Meanwhile,the glass transition temperature of EP/a-SEP@LDH in DMA(dynamic mechanical analysis)has been greatly increased.To further increase the fire-retardant efficiency of EP/a-SEP@LDH,the PAMA nanosheets(melamine phytate)made in our laboratory was used as a flame retardant synergist for a-SEP@LDH.Adding 3.0 wt% flame retardants(the mass ration between a-SEP@LDH and PAMA is 1:3),the EP composite reaches V-0 rating and possesses 34.2% of LOI.The excellent fire retardancy of EP composite is ascribed to the synergistic effect among a-SEP@LDH and PAMA.In detail,the PAMA is able to increase the aromatic degree of char residue for EP composite,and the a-SEP@LDH mainly plays a strengthening residual char role.Noticeably,the tensile strength and glass transition temperature in differential scanning calorimeter test are simultaneously increased.