Preparation Of Nanofibrillated Cellulose Gel Via Solution/Solvent Exchange And Research Of Hygroscopic Performance

With the increasing of global attention on renewable resources,efficient utilization of forest resource is also increasing emphasis.The nanofibrillated cellulose exfoliate from the wood cell wall.Because nanofibrillated cellulose has merits such as fine scale?high aspect ratio?high specific surface area and biodegradable,they are expected to obtain hydrogel and aerogel with different properties.It is solution exchangement that the solution was directly added into the nanocellulose suspensions to obtain gel.And it has virtues such as simple operation?tunable and increase the stiffness of gel.Thus,we systematically researched the structure and performance of these hydro/aerogels for a better understanding of the effect of these exchange treatments.We use exchange treatment to prepare the nanocomposite aerogel desiccant,and the hygroscopic performance and water harvesting performance were studied.The paper mainly studies five different solutions/solvents including two types of dilute acids,alkali,salt,and organic solvent were used for the exchange treatment to produce nanofibrillated cellolose gels.And the dimension,porosity,density,were measured.The morphologies,structures and properties were evaluated by rotary rheometer,mechanical testing,transmission electronic microscope,scanning electronic microscope,X-ray diffraction,Thermogravimetric analysis and thermal conductivity tester.And we use exchange treatment to prepare the nanocomposite aerogel desiccant(NCAD).The structures were observed by the scanning electronic microscope and X-ray 3D microscope;The hygroscopic performance,regenerability were measured.The water absorption process on the surface and vertical section of NCAD were recorded by the steremicroscope and contact angle meter.And the efficiency and reproducibility of water collection were investigated.The main results are as follows:(1)The NaOH-hydrogel has the high storage modulus(36.4 kPa)and good mechanical property with compressive modulus(37.6 kPa).All aerogels were lightweight and highly porous.The packing density and pore structure varied among different aerogels.The NaOH-aerogel had a 2D sheet-like structure with densely packed micrometer-sized pores uniformly distributed within the aerogel network;it thus illustrated high compressive strength.However,the structures of other aerogels were relative loose,leading to the relative weak compressive strength.These aerogels showed a high thermal stability and demonstrated a great potential in thermal insulation applications.(2)NCAD prepared by 5%LiCI solution has the highest water uptake(1.2 g/g),compared with commercially desiccants such as silica gel and molecular sieve;Good renewable performance and low reproducibility temperature(60?).(3)The LiCl was mainly stacked in the surface of NCAD with porous network structure.The LiCl condense water vapour on the surface and formed liquid water,the liquid was storage in the network of the NCAD under the synergistic effect of hydrophilic group and osmotic pressure.NCAD has fast air dehumidification capacity and controlled the required humidity.(4)The collected water was colorless,pure and drinkable for human.The water collection rate of desiccant is as high as 1.32 g/g NCAD in relative humidity of 30%.Moreover,the distilled salt was repeated utilized for fabrication of NCAD,and reduced the cost greatly.