Synthesis Of Functional Cellulose Nanofibril Aerogels And Their Applications

Cellulose is the most abundant biopolymer on the earth.Meanwhile,cellulose could be easily obtained from the large-scale production of pulp and paper industry.Nano cellulose prepared by chemical mechanical methods has a larger specific surface area and strength compared with conventional cellulose fibers.Cellulose nanofibril aerogel is a sponge like material which composed of interlaced nano cellulose fibers.Due to the porous structure and large surface area,cellulose nanofibril aerogel has become a new kind of adsorption material.Compared with the traditional inorganic aerogels materials,CNF aerogel materials have better ductility and it is easier to be chemical modified.Hereby,nano cellulose aqueous suspension was used as the raw material,CNF aerogel graft cyclodextrin was prepared first,and its phenol removal capacity was investigated.However,the phenol removal efficiency was limited by grafting efficiency.Afterwards,spherical CNF aerogel was prepared as skeleton structure for preparing polymer-modified CNF aerogel spheres.These spherical absorbents have drawbacks of uneven and big particle sizes which limited their performance as absorbents.It was found that nanocellulose aerogel microspheres prepared through ultrasonic atomization method and the particle size distribution of the prepared microspheres mainly in the range of 3-7 μm.The microspheres could be used as microreactors used for W/O/W extraction and water/oil separation.The details are shown as follows:(1)Cellulose nanofibril aerogels with grafted beta-cyclodextrin(β-CD)were prepared for adsorbing phenols pollutants from water.Compared with regular wood fibers,CNF aerogel cannot only immobilize more β-CDs but also provide higher porosity and larger specific surface area for phenol absorption.The CNF-CD aerogel becomes mechanically robust through chemical crosslinking.It can be easily separated from water after adsorbing phenol pollutants without complicated centrifugation or filtration.A series studies of phenol adsorption were conducted.The results indicated that CNF-CD aerogel prepared with the suspension concentration of 3%(w/w)has the highest adsorption capability.In addition,the CNF-CD aerogel showed an excellent reusability.The results indicated that CNF-CD aerogel is an environmentally friendly and promising adsorbent for removing phenols pollutants from water.(2)A novel method for synthesizing temperature sensitive polymer modified cellulose nanofibril(CNF)aerogel microspheres was reported.The pristine aerogel microspheres were first prepared using a spray-freeze dry method in the presence of chemical crosslinker.Afterwards,NIPAm(n-isopropylacrylamide),a temperature sensitive monomer,was polymerized and grafted to the cellulose aerogel microspheres through an in-situ free radical polymerization method.The morphology,chemical structure,thermal sensitivity,bulk density and water uptake capacity of the hybrid microspheres were characterized.The CNF-PNIPAmhybrid microspheres exhibited a good temperature responsibility in water around 32 oC.The swelling behavior and drug release capability of CNF-PNIPAm hybrid microspheres were also investigated.The microspheres with PNIPAm exhibited a controllable drug release rate.The temperature effect on the drug release rate was also observed.These results indicated that porous CNF-PNIPAm hybrid microspheres could serve as a new type of template for controlled drug release.Also,we have reported a facile method for synthesizing poly(sodium acrylate)(PAANa)modified TEMPO-oxidized cellulose nanofibril(TOCN)aerogel spheres.The water absorbent capacity of the spheres could be as high as 1030 g/g,which has never been reported before.Practically,1 wt% TOCN suspension was simply dropped into an HCl solution to prepare physical crosslinked TOCN hydrogel spheres.Afterwards,PAANa,an anionic monomer,was added into TOCN gel spheres by solution replacement,and the monomer was polymerized and grafted to the TOCN spheres in the presence of N,N-methylenebisacrylamide as a crosslinker through in-situ free radical polymerization.The physical crosslinking(through hydrogen bonding)of the spheres was replaced by chemical crosslinking after washing the gel spheres to neutral,which resulted in high volume expansion(about 27 times v/v)of the washed sphere.The expansion rate and morphologies of the obtained hybrid gel spheres were strongly depended on the dosage of crosslinker and monomer.The structure and morphologies of the hybrid spheres were characterized by FTIR,TGA and SEM.The water absorbing behaviors of the hybrid spheres were depend on the pH,concentration of the salt solution and the crosslinker content.The freeze-dried aerogel spheres are highly porous(approximately 99.88%)with density as low as 1.5 mg/cm3.All results indicated that TOCN-PAANa hybrid aerogel spheres could serve as a new type of superabsorbent.(3)Cellulose nanofirbril aerogel-based W/O/W microreactor system that can be used for fast and high efficient molecule or ions extraction and separation.The ultra-light cellulose nanofibril based aerogel microspheres with high porous structure and water storage capacity were prepared.The aerogel microspheres that were saturated with stripping solution were dispersed in an oil phase to form a stable water-in-oil(W/O)suspension.This suspension was then dispersed in large amount of external waste water to form W/O/W microreactor system.Similar to a conventional emulsion liquid membrane(ELM),the molecules or ions in external water can quickly transport to the internal water phase.However,the microreactor is also significantly different from traditional ELM: the water saturated nanocellulose cellulose aerogel microspheres can be easily removed by filtration or centrifugation after extraction reaction.The condensed materials in the filtrated aerogel particles can be squeezed and washed out and aerogel microspheres can be reused.This novel process overcomes the key barrier step of demulsification in traditional ELM process.Our experimental indicates the novel microreactor was able to extract 93% phenol and 82% Cu2+ from external water phase in a few minutes,suggesting its great potential for industrial applications.(4)By tailoring the surface chemistry,cellulose nanofibril aerogel microspheres coated filter paper could be used to filtrate either oil or water from their mixture solution.Suchprepared filter papers show unique “micro-nano” structure.Because of abundant hydroxyl groups on the paper surface,the microspheres coated filter paper was superhydrophilic,but it became superhydrophobic when treated with methyltrimethoxysilane(MTMS)through vapor deposition.The as-prepared papers also showed unique under-water superoleophobicic or under-oil superhydrophobic properties.Also,with superhydrophobic properties in the air,the water contact angle is larger than 150 o.The water or oil separation showed a high water/oil separation efficiency of more than 96.8%.