Study On Preparation And Porperties Of Hydroxyapatite/silica Aerogel Nanocomposite Heat Insulating Paper

Thermal insulating materials with remarkable ability to reduce heat radiation,reflection and conduction are of great social and economic significance in industrial and civilian application due to excellent energy-saving performance in this age of energy shortage.Humans have been developing insulating materials for thousands of years,trying to obtain high thermal insulation performance.The organic heat insulating materials commonly used in the construction industry have good heat insulating performance.But they are inflammable and may release harmful substances under high temperature,which brings great potential risks to the use.Thermos-stable organic insulation materials with poorer thermal insulation performance and formability are easy to be off the slags and absorb water,which would destroy and pollute the situation.Even asbestos are carcinogenic.Hence,preparing a new thermal insulating inorganic material with low thermal conductivity,prominent fire retardancy and good flexibility is extremely necessary at present.In this work,novel nanocomposite paper with low thermal conductivity,flame retardancy and good mechanical property was prepared by employing ultralong hydroxyapatite（HAP）nanowires as scaffolds for silica aerogels.The paper studied the influence of the silica aerogel contents on the mechanical properties,thermal insulation perfoemance,thermal stability and fire retardancy of nanocomposite heat insulating paper by adjusting the content of silica aerogels to optimize the formulation of the nanocomposite heat insulating paper,and finally obtained the nanocomposite paper with excellent comprehensive performance.Some conclusions have been drwn:（1）Silica aerogel particles distributed well into the 3D network weaved by HAP nanowires,and all the papers showed high flexibility.With the increase of silica aerogel loading,ultimate tensile strength of nanocomposite paper decreased from 329.3±16.4kPa to 140±5.7 kPa due to the decrease in interactions among HAP nanowires and the increase in defects inside the nanocomposite paper,but the tensile strength was still higher than that of most fiber-reinforced heat insulating composites;（2）With the increase of silica aerogel content,the thermal conductivity of the nanocomposite paper decreased from 0.0564 W·m^-1K^-1 to 0.0448 W·m^-1K^-1 at room temperature,which indicated that the addition of silica aerogel could greatly enhance the thermal insulation performance of nanocomposite paper.Theoretical analyses showed that the improved thermal insulating performance could be contributed to the fibrous network structure constructed by the HAP nanowires,intrinsic low thermal conductivity of HAP nanowires and silica aerogels and the complicated heat transfer path;（3）The weight losses of all the nanocomposite papers with different contents of silica aerogels were less than 10 wt%even at 800°C,which showed that the nanocomposite paper possessed prominent thermal stability;The temperature where the methyls on surface of silica aerogels inside nanocomposite paper were oxidized increased by 131°C than that of pure silica aerogels,which indicated that the existence of hydroxyapatite nanowires could greatly improve the thermal stability of the internal silica aerogel inside the paper.（4）Meanwhile,the tests of UL-94 vertical burning and microgravity combustion showed that nanocomposite heat insulating papers exhibited good fire retardant properties with UL94V-0 and poor heat release capacity.Therefore,the as-prepared HAP/silica aerogel nanocomposite paper is promising for applications in the protection layer of insulation materials,fire-retardant wallpaper,specialty fire clothing,pipe insulate and so on.