The In Situ Synthesis And Structure Characterization Of Cellulose/Silica Aerogels

SiO2aerogels are a kind of low thermal conductivity functional materials. Theirslight porous network structures, however, result in high brittleness, which is aserious restriction for the practical applications. Therefore, it is very valuable andsignificative to realize the flexibility of aerogels. As new third generation materials,cellulose aerogels possess many excellent performances besides traditional featuresof aerogels. In this paper, based on the features of silica and cellulose aerogels, thecellulose/silica aerogels were in-situ synthesized and the structural characteristicsand mechanical behavior were analyzed.The cellulose/silica aerogels were in-situ synthesized by means of freeze-dryingmethod. In the preparative process, the original celluloses were dissolved in alkalisolution. The silica aqueous solution and alcoholic solution were chosen asregenerative coagulants, respectively. The influences of the cellulose content,regenerative time, the types of coagulants and drying methods were discussed. Theresults show that the cellulose/silica aerogels possess porous characteristics. Whenthe content of the cellulose is3.2%, the cellulose/silica aerogels present highporosity. With the increase of the cellulose contents, more silica particles wereintroduced into the cellulose/silica aerogels. The addition of inorganic silicaparticles can improve the thermal stability of cellulose materials. The cellulosesrender the optimal crosslink ing network structures when the regenerative time is6h.It is an easier process to obtain the cellulose/silica aerogels by using silicaalcoholic solution as a regenerative coagulant and by means of freeze-dryingmethod.It is noted that two kinds of crystal structure of cellulose I and II co-exist in thecellulose/silica aerogels. The amorphous silica particles increase and the bondingactions between silica and cellulose strengthen with the extension of regenerativetime. The microcrystalline celluloses self-assemble and then render parallelarrangements under the actions of hydrogen bonds in intra-and inter-molecular.Ultimately, the layered porous structures are formed. The dehydration andcondensation between Si–OH groups originating from silica gels and–OH groupson the surfaces of cellulose are the main actions to realize organic- inorganic hybrids. The cellulose/silica aerogels possess high specific surface areaand small average pore diameter, which is related with the filling of silica particlesinto cellulose gels.The mechanical properties of the cellulose/silica aerogels were improved by theintroduction of the silica particles. In the condition of short regenerative time, thestrengths of the cellulose/silica aerogels mainly generate from skeleton structures ofmicrocrystalline celluloses. The silica particles wrapping on the surfaces ofcellulose and the condensation among silica particles are the main reasons to furtherimprove the strength of aerogels. In the condition of long regenerative time, seriousaccumulational silica particles result in the brittleness of aerogels, which decreasedthe mechanical characteristics of the cellulose/silica aerogels.