Cellulose Nanofibril Aerogel Research Articles

Ambient‐Dried Cellulose Nanofibril Aerogel Membranes with High Tensile Strength and Their Use for Aerosol Collection and Templates for Transparent, Flexible Devices

The application potential of cellulose nanofibril (CNF) aerogels has been hindered by the slow and costly freeze‐ or supercritical drying methods. Here, CNF aerogel membranes with attractive mechanical, optical, and gas transport properties are prepared in ambient conditions with a facile and scalable process. Aqueous CNF dispersions are vacuum‐filtered and solvent exchanged to 2‐propanol and further to octane, followed by ambient drying. The resulting CNF aerogel membranes are characterized by high transparency (>90% transmittance), stiffness (6 GPa Young's modulus, 10 GPa cm3 g−1 specific modulus), strength (97 MPa tensile strength, 161 MPa m3 kg−1 specific strength), mesoporosity (pore diameter 10–30 nm, 208 m2 g−1 specific surface area), and low density (≈0.6 g cm−3). They are gas permeable thus enabling collection of nanoparticles (for example, single‐walled carbon nanotubes, SWNT) from aerosols under pressure gradients. The membranes with deposited SWNT can be further compacted to transparent, conductive, and flexible conducting films (90% specular transmittance at 550 nm and 300 Ω ◻−1 sheet resistance with AuCl3‐salt doping). Overall, the developed aerogel membranes pave way toward use in gas filtration and transparent, flexible devices.

Synthesis of Cyclodextrin-functionalized Cellulose Nanofibril Aerogel as a Highly Effective Adsorbent for Phenol Pollutant Removal

Cellulose nanofibril (CNF) aerogels with grafted beta-cyclodextrin (β-CD) were prepared for the adsorption of phenol pollutants from water. Compared with regular wood fibers, CNF aerogel not only can immobilize more β-CDs, but also it provides higher porosity and a 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 of studies on phenol adsorption was conducted. The results indicated that the CNF-CD aerogel prepared with a suspension concentration of 3% (w/w) had the highest adsorption capability. In addition, the CNF-CD aerogel showed an excellent reusability. The results indicated that the CNF-CD aerogel is an environmentally friendly and promising adsorbent for removing phenol pollutants from water.

Preparation of cross-linked cellulose nanofibril aerogel with water absorbency and shape recovery

Cellulose nanofibril (CNF) aerogels are promising materials for various applications because of their highly porous and ultralight characteristics. The fiber network of CNF aerogels held together by hydrogen bonding and mechanical entanglement of adjacent fibers is easily destroyed when it is exposed to water. In this study, cross-linked CNF aerogels were prepared using maleic acid and sodium hypophosphite as cross-linking agents. In the first step of treatment, CNF dispersed in water was reacted with maleic acid to form an ester linkage. Sodium hypophosphite was then added to the maleic acid-functionalized CNF suspension and the suspension was rapidly frozen using liquid nitrogen. CNF aerogel was obtained after freeze drying. The cross-linking of the cellulose was formed by the reaction between the carbon–carbon double bond of maleic acid-functionalized CNF and hypophosphite. The cross-linked CNF aerogel exhibited good network stability in water and springiness after compression.

Poly(vinyl alcohol)/cellulose nanofibril hybrid aerogels with an aligned microtubular porous structure and their composites with polydimethylsiloxane.

Superhydrophobic poly(vinyl alcohol) (PVA)/cellulose nanofibril (CNF) aerogels with a unidirectionally aligned microtubular porous structure were prepared using a unidirectional freeze-drying process, followed by the thermal chemical vapor deposition of methyltrichlorosilane. The silanized aerogels were characterized using various techniques including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and contact angle measurements. The structure of the aerogels fully filled with polydimethylsiloxane (PDMS) was confirmed by SEM and optical microscopy. The mechanical properties of the resulting PDMS/aerogel composites were examined using both compressive and tensile tests. The compressive and tensile Young's moduli of the fully filled PDMS/aerogel composites were more than 2-fold and 15-fold higher than those of pure PDMS. This study provides a novel alternative approach for preparing high performance polymer nanocomposites with a bicontinuous structure.

Ultralight and hydrophobic nanofibrillated cellulose aerogels from coconut shell with ultrastrong adsorption properties

ABSTRACTUltralight aerogels based on nanofibrillated cellulose (NFC) isolated from coconut shell were successfully prepared via a mild fast method, which included chemical pretreatment, ultrasonic isolation, solvent exchange, and tert‐butanol freeze drying. The as‐prepared NFC aerogels with complex three‐dimensional fibrillar networks had a low bulk density of 0.84 mg/cm3 (specific surface area = 9.1 m2/g and pore volume = 0.025 cm3/g), maintained a cellulose I crystal structure, and showed more superior thermal stability than the coconut shell raw materials. After the hydrophobic modification by methyl trichlorosilane (MTCS), the NFC aerogels exhibited high water repellency properties, an ultrastrong oil‐adsorption capacity (542 times that of the original dry weight of diesel oil), and superior oil–water separation performance. Moreover, the absorption capabilities of the MTCS‐treated NFC aerogels were as high as 296−669 times their own weights for various organic solvents and oil. Thus, this class of high‐performance adsorbing materials might be useful for dealing with chemical leaks and oil spills. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42037.

Polyethylenimine-grafted cellulose nanofibril aerogels as versatile vehicles for drug delivery.

Aerogels from polyethylenimine-grafted cellulose nanofibrils (CNFs-PEI) were developed for the first time as a novel drug delivery system. The morphology and structure of the CNFs before and after chemical modification were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Water-soluble sodium salicylate (NaSA) was used as a model drug for the investigation of drug loading and release performance. The CNFs-PEI aerogels exhibited a high drug loading capability (287.39 mg/g), and the drug adsorption process could be well described by Langmuir isotherm and pseudo-second-order kinetics models. Drug release experiments demonstrated a sustained and controlled release behavior of the aerogels highly dependent on pH and temperature. This process followed quite well the pseudo-second-order release kinetics. Owing to the unique pH- and temperature-responsiveness together with their excellent biodegradability and biocompatibility, the CNFs-PEI aerogels were very promising as a new generation of controlled drug delivery carriers, offering simple and safe alternatives to the conventional systems from synthetic polymers.

Sol–gel synthesis highly porous titanium dioxide microspheres with cellulose nanofibrils-based aerogel templates

Highly porous titanium dioxide microspheres had been prepared via a template-assisted sol–gel process with cellulose nanofibril aerogel microsphere template. The modified porous titanium dioxide microspheres showed a typical super-hydrophobic property. The method reported in this study may be applied to fabricate other inorganic materials with desired porous structure.

Super water absorbing and shape memory nanocellulose aerogels from TEMPO-oxidized cellulose nanofibrils via cyclic freezing–thawing

Mechanically robust cellulose nanofibril (CNF) aerogels with ultralow density (8 mg cm−3), superior porosity (99.5%), super water absorbency (104 g g−1 water/dried mass), high crystallinity (68.5%) as well as exceptional wet resilience and water activated shape recovery were facilely fabricated for the first time by ice-crystal templated self-assembly of TEMPO oxidized CNFs via cyclic freezing–thawing. With ultrathin widths (1–2 nm), high aspect ratios (several hundreds) and numerous surface polar hydroxyls and carboxyls, TEMPO oxidized CNFs behaved similar to aqueous soluble polymers to form strong freestanding hydrogels by repetitive freezing (−20 °C, 15 h) and thawing (room temperature, 9 h). The spaces occupied by the several hundred microns wide ice crystals were well preserved upon freeze-drying, deriving macroporous CNF aerogels with over 99% porosity of interconnected pores. The freezing induced self-assembling of CNFs was observed at a low concentration of 0.05%, whilst more ordered macroporous honeycomb structures were observed at and above 0.2%. Exchanging water in the CNF hydrogel with tert-butanol generated hierarchical CNF aerogels containing several hundred microns sized macroscopic as well as mesoscopic pores ranging from 2 to 90 nm with further improved specific surface area (117.8 m2 g−1), pore volume (1.19 cm3 g−1) and water absorption (116 g g−1). All CNF aerogels demonstrated super water absorbency, fast water-activated shape recovery in 4 s and reusability for at least 20 times.

Mechanosorptive creep in nanocellulose materials

The creep behavior of nanocellulose films and aerogels are studied in a dynamic moisture environment, which is crucial to their performance in packaging applications. For these materials, the creep rate under cyclic humidity conditions exceeds any constant humidity creep rate within the cycling range, a phenomenon known as mechanosorptive creep. By varying the sample thickness and relative humidity ramp rate, it is shown that mechanosorptive creep is not significantly affected by the through-thickness moisture gradient. It is also shown that cellulose nanofibril aerogels with high porosity display the same accelerated creep as films. Microstructures larger than the fibril diameter thus appear to be of secondary importance to mechanosorptive creep in nanocellulose materials, suggesting that the governing mechanism is found between molecular scales and the length-scales of the fibril diameter.

Electroactive nanofibrillated cellulose aerogel composites with tunable structural and electrochemical properties

This work presents conductive aerogel composites of nanofibrillated cellulose (NFC) and polypyrrole (PPy) with tunable structural and electrochemical properties. The conductive composites are prepared by chemically polymerizing pyrrole onto TEMPO-oxidized cellulose nanofibers dispersed in water and the various nanostructures are obtained employing different drying methods. Supercritical CO2 drying is shown to generate high porosity aerogel composites with the largest surface area (246 m2 g−1) reported so far for a conducting polymer–paper based material, whereas composites produced by ambient drying attain high density structures with mechanical properties significantly surpassing earlier reported values for cellulose–conducting polymer composites when normalized with respect to the content of reinforcing cellulose (Young's modulus = 0.51 GPa, tensile strength = 10.93 MPa and strain to failure = 2.5%). Electrochemical measurements clearly show that differences in the porosity give rise to dramatic changes in the voltammetric and chronoamperometric behavior of the composites. This indicates that mass transport rate limitations also should be considered, in addition to the presence of a distribution of PPy redox potentials, as an explanation for the shapes of the voltammetric peaks. A specific charge capacity of ∼220 C g−1 is obtained for all composites in voltammetric experiments performed at a scan rate of 1 mV s−1 and this capacity is retained also at scan rates up to 50 mV s−1 for the high porosity composites. The composites should be applicable as electrodes in structural batteries and as membranes in ion exchange applications requiring exchange membranes of high mechanical integrity or high porosity.

Making flexible magnetic aerogels and stiff magnetic nanopaper using cellulose nanofibrils as templates

Nanostructured biological materials inspire the creation of materials with tunable mechanical properties. Strong cellulose nanofibrils derived from bacteria or wood can form ductile or tough networks that are suitable as functional materials. Here, we show that freeze-dried bacterial cellulose nanofibril aerogels can be used as templates for making lightweight porous magnetic aerogels, which can be compacted into a stiff magnetic nanopaper. The 20-70-nm-thick cellulose nanofibrils act as templates for the non-agglomerated growth of ferromagnetic cobalt ferrite nanoparticles (diameter, 40-120 nm). Unlike solvent-swollen gels and ferrogels, our magnetic aerogel is dry, lightweight, porous (98%), flexible, and can be actuated by a small household magnet. Moreover, it can absorb water and release it upon compression. Owing to their flexibility, high porosity and surface area, these aerogels are expected to be useful in microfluidics devices and as electronic actuators.