Preparation And Characterization Of Cellulose Acetate Aerogels

Cellulose-based aerogel,a new kind of materials from abundant and reproducible resource,possesses low density,high porosity and specific surface area,which has already become a hot topic in the fields of template material,hydrophobicity,hydrophilcity and electrochemistry.However,study on cellulose-based aerogel in the field of building insulation system is still rare.In this work,cellulose acetate aerogel was prepared with cellulose acetate as resource,2,4-toluene diisocyanate as cross-linker and pyridine as catalyst in acetone solvent,via sol-gel,aging and dioxide carbon supercritical drying process.The structure,compression,thermal insulation and hydrophobization properties of as-prepared aerogel were studied,and compression model was established.Besides,radiative conductivity of cellulose acetate aerogel was calculated.The main results are as follows:The influence of reactant dosage and aging process on the structure of as-prepared cellulose acetate-based aerogel was studied,and growth process of skeletons was also analyzed in the procedure of aging treatment.The obtained results show that cellulose acetate aerogel has three-dimensional nanoscale network with fiber-liked skeleton,pores of 10 to 200 nm in diameter,and specific surface area of 286~466 m~2/g.When cellulose acetate dosage is increased,skeletons of network grow wider with narrower pore size distribution and smaller average pore size,and some lamellas start to appear.While the addition of cross-linker dosage can cause the growth of secondary skeletons cross pores in obtained network,leading to narrower pores with smaller pore volume.When aging duration lasts longer,skeletons also turn to be wider with narrower pore size distribution,and pore size firstly goes up from 18 nm to 24 nm,then falls down to14 nm.Besides,the elevated aging temperature can cause pores size decrease,skeletons and lamellas grow wide.The influence of reactant dosage and aging process on the shrinkage in drying and compression property was investigated,compression model of cellulose actatea aerogel with high strenght was constructed.The obtained results show that gel shrinks at shrinkage ratio of 12%~42%after supercritical drying process and aerogel obtained has the cylindrical shape with the middle shrinking more than that of border region.When cellulose acetate and cross-linker dosage are decreased,drying shrinkage ratio and density fall down with the minimum of 12%and 0.056 g/cm~3,respectively.And the lomger aging duration and higher temperature can cause decrease of drying shrinkage ratio.Compression strength of cellulose acetate aerogel is 0.03~1.29 MPa and modulus is 0.51~21.86 MPa.Compression strength and modulus of as-prepared aerogel increased with the increase of reactants dosage,and the optimal value are 1.29 MPa,21.86 MPa,respectively,which is attributed to the self-reinforced network structure with fiber-liked skeleton as basic structural unit and lamellas as reinforce.Meanwhile,longer aging time can cause compression strength and modulus of as-preparedd aerogel firstly falling down and then going up,and higher aging temperature can also cause compression strength and modulus decrease.The influence of reactant dosage on thermal insulation property was researched,and riaditive conductivity and thermal conductivity composition of cellulose actate aeogel were calculated and dicussed,respectively.The obtained results show that the increase of cellulose acetate can cause thermal conductivity increase from 0.0361W/m·K to 0.0510 W/m·K.When cellulose acetate is kept at 1.5 g,the increase of cross-linker dosage can indicate that thermal conductivity firstly decreases and then increases with the minimum value of 0.0313 W/m·K.Radiative thermal conductivity of as-prepared aerogel was calculated as 0.0012~0.0054 W/m·K.The increase of reactant can cause the transition of thermal conductivity from gaseous part-leaded to solid part-leaded,and the thermal conductivity composition in the minimum value is 39.30%for solid part,48.24%for gaseous part and 12.46%for radiant part,respectively.Hydrophobization property of cellulose acetate aerogel was studied.Surface modification of cellulose acetate for hydrophobization was conducted with perfluorodecyltriethoxysilane as hydrophobing agent via chemical vapor deposition.The optimal caondition for hydrophobization treatment is hydrophobing agent/aerogel mass ratio of 0.3 and treated duration of 3 days.After hydrophobization treatment,aerogel obtains water contact angle of 136° and saturated weight moisture absorption of4%,along with good stability for hydrophobization.Compared with other hydrophobing agent with alkyl groups,perfluorodecyltriethoxysilane has better hydrophobization property for cellulose acetate aerogel.