Jiangqi Zhao

Uniaxially Aligned Electrospun All-Cellulose Nanocomposite Nanofibers Reinforced with Cellulose Nanocrystals: Scaffold for Tissue Engineering

Uniaxially aligned cellulose nanofibers with well oriented cellulose nanocrystals (CNCs) embedded were fabricated via electrospinning using a rotating drum as the collector. Scanning electron microscope (SEM) images indicated that most cellulose nanofibers were uniaxially aligned. The incorporation of CNCs into the spinning dope resulted in more uniform morphology of the electrospun cellulose/CNCs nanocomposite nanofibers (ECCNN). Polarized light microscope (PLM) and transmission electron microscope (TEM) showed that CNCs dispersed well in ECCNN nonwovens and achieved considerable orientation along the long axis direction. This unique hierarchical microstructure of ECCNN nonwovens gave rise to remarkable enhancement of their physical properties. By incorporating 20% loading (in weight) of CNCs, the tensile strength and elastic modulus of ECCNN along the fiber alignment direction were increased by 101.7 and 171.6%, respectively. Their thermal stability was significantly improved as well. In addition, the ECCNN nonwovens were assessed as potential scaffold materials for tissue engineering. It was elucidated from MTT tests that the ECCNN were essentially nontoxic to human cells. Cell culture experiments demonstrated that cells could proliferate rapidly not only on the surface but also deep inside the ECCNN. More importantly, the aligned nanofibers of ECCNN exhibited a strong effect on directing cellular organization. This feature made the scaffold particularly useful for various artificial tissues or organs, such as blood vessel, tendon, nerve, and so on, in which cell orientation was crucial for their performance.

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.

A super biosorbent from dendrimer poly(amidoamine)-grafted cellulose nanofibril aerogels for effective removal of Cr(VI)

Over the past decades, heavy metal ions, especially hexavalent chromium [Cr(VI)], have substantially ravaged the aquatic environment and human health. Thus, the development of new, more efficient, and environmentally friendly methods to tackle this problem becomes very urgent. In this study, a novel dendrimer poly(amidoamine)-grafted cellulose nanofibril (PAMAM-g-CNF) aerogel was synthesized for Cr(VI) removal. The morphology, structure and adsorption properties of the PAMAM-g-CNF aerogel were investigated in detail. The results indicated that the aerogel bore abundant functional groups with a bimodal pore structure and a high specific surface area, all of which are essential for an efficient adsorbent. The maximum Cr(VI) removal capacity of the aerogel reached 377.36 mg g−1, the highest one ever reported for biosorbents. It was interesting to note that part of Cr(VI) ions had been reduced to Cr(III) during the adsorption process, which meant that PAMAM-g-CNFs could detoxify Cr(VI).

Extraction of cellulose nanofibrils from dry softwood pulp using high shear homogenization

The objective of this study was to extract cellulose nanofibrils (CNFs) from dry softwood pulp through a simple and environmentally friendly physical method of refining pretreatment coupled with high shear homogenization. An optical microscopy (OM) clearly showed the morphological development from the cellulose fibers to CNFs under repeated shear forces. The morphology, structure and properties of the obtained CNFs were comprehensively investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared (FTIR) spectra, X-ray diffraction (XRD) and thermogravimetric (TG) analysis. The results indicated that the CNFs had diameters mainly ranged from 16 to 28nm. Compared with the pulp fibers, the CNFs exhibited a slightly higher crystallinity and a lower thermal stability. Moreover, a novel nanopaper with high optical transparency was prepared from the obtained CNFs, and a possible mechanism for the high optical transparency was discussed.

Reinforcement of all-cellulose nanocomposite films using native cellulose nanofibrils

All-cellulose nanocomposite films were prepared using native cellulose nanofibrils (CNFs) as fillers and lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) dissolved regenerated cellulose as the matrix. The CNFs, with diameters in the range of 15-40 nm were obtained by combined physical methods of ultrasonic treatment and high shear homogenization. The morphology, structure, and properties of the nanocomposite films were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), optical transmittance, thermal gravimetric analysis (TGA), and mechanical testing. The nanocomposite films exhibited good optical transparency, thermal stability, and remarkably enhanced mechanical properties compared to the regenerated cellulose matrix. By varying the CNFs content, the tensile strength of the nanocomposite films increased from 61.56 MPa to 99.92 MPa and the Youngs modulus increased from 0.76 GPa to 4.16 GPa. This work provided a promising pathway for manufacturing high performance and environmental-friendly all-cellulose nanocomposites.

Aerogels from quaternary ammonium-functionalized cellulose nanofibers for rapid removal of Cr(VI) from water.

An efficient heavy metal adsorbent from quaternary ammonium-functionalized cellulose nanofiber aerogels was successfully developed. The highly porous aerogel could well retain its large specific surface area, which allowed rapid and effective removal of Cr(VI) from contaminated water. The aerogel adsorbent became mechanically robust after chemical crosslinking. It could be easily separated from water after adsorption without complicated centrifugation or filtration process. With only 1g of aerogel, more than 99% of Cr(VI) in 1L of 1mg/L solution could be removed in 50 min. Besides, the aerogel also exhibited excellent reusability.

Synthesis of a ferric hydroxide-coated cellulose nanofiber hybrid for effective removal of phosphate from wastewater

Ferric hydroxide-coated cellulose nanofibers (Fe(OH)3@CNFs) were synthesized for the removal of phosphate from wastewater. The maximum sorption capacity of Fe(OH)3@CNFs for phosphate was estimated to be 142.86mg/g, demonstrating a superior adsorption capacity compared with many adsorbents reported in the literature. Batch experiments were performed to investigate various adsorption conditions on the adsorption performance. It was discovered that an increased solution ionic strength would remarkably enhance the adsorption. Additionally, Fe(OH)3@CNFs achieved a favorable adsorption performance over a wide range of pH conditions, which could result in operation cost savings. The adsorption of phosphate can be described by both the Langmuir isotherm and pseudo-second-order models. The phosphate adsorbed by Fe(OH)3@CNFs was characterized using XPS, SEM, SBET and EDS. The data obtained revealed that the electrostatic attraction and ligand exchange constituted the major forces in phosphate adsorption. This work suggested that Fe(OH)3@CNFs are a promising adsorbent for phosphate removal.

Effective dispersion and crosslinking in PVA/cellulose fiber biocomposites via solid-state mechanochemistry

A mechanochemical approach to improve the dispersion and the degree of crosslinking between cellulose fiber and polymer matrix is presented herein to create high performance poly(vinyl alcohol) (PVA)/cellulose biocomposites in a solvent-free and catalyst-free system. During a pan-milling process, the hydrogen bonds in both cellulose and PVA were effectively broken up, and the released hydroxyl groups could react with succinic anhydride (SA) to form covalent bonds between the two components. This stress-induced chemical reaction was verified by fourier transform infrared spectroscopy. The reaction kinetics was discussed according to the conversion rate of SA during the pan-milling process. Soxhlet extraction with hot water showed that the crosslinked PVA/cellulose retained more PVA in the composites due to the homogeneous and heterogeneous crosslinking. Scanning electron microscope images indicated the dispersion and interfacial interactions between PVA and cellulose were largely improved. The resulting composites exhibited remarkably enhanced mechanical properties. The tensile strength increased from 8.8 MPa (without mechanochemical treatment) to 18.2 MPa, and elongation at break increased from 76.8 to 361.7% after the treatment. Their thermal stability was also significantly improved.

Acrylic acid grafted and acrylic acid/sodium humate grafted bamboo cellulose nanofibers for Cu2+ adsorption

Bamboo cellulose nanofibers-graft-poly (acrylic acid) (BCN-g-PAA) and bamboo cellulose nanofibers-graft-poly (acrylic acid)/sodium humate (BCN-g-PAA/SH) were synthesized for the first time and sequentially utilized as biosorbents for removal of Cu2+ from aqueous solutions. The chemical structure and morphology of both modified nanofibers were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. Batch adsorption experiments were conducted to elucidate their adsorption behaviors on Cu2+. The influencing factors, such as pH, contact time and initial Cu2+ concentration, on Cu2+ adsorption were investigated in detail. It was discovered that pH strongly influenced the Cu2+ adsorption. When pH increased from 2.0 to 4.5, the adsorption capacities of both modified nanofibers were improved significantly. Adsorption isotherm studies indicated that the Cu2+ adsorption could be described well by the Freundlich equation. Meanwhile, their adsorption kinetics was more likely to follow the pseudo-second-order model. These nanocellulose-based adsorbents exhibited very fast adsorption rates. The calculated adsorption capacities at equilibrium (qcale) for BCN-g-PAA and BCN-g-PAA/SH were 0.727 and 0.709 mmol g−1, significantly higher than that of BCN (0.286 mmol g−1). Adsorption/desorption cycling tests suggested that the introduced SH segments allowed for improved reusability of BCN-g-PAA/SH.

Grafting of polyethylenimine onto cellulose nanofibers for interfacial enhancement in their epoxy nanocomposites

Cellulose nanofibers (CNFs) were surface-modified with polyethyleneimine (PEI), which brought plentiful amine groups on the surface of CNFs, leading to a reduced hydrogen bond density between CNFs and consequently less CNFs agglomerates. The amine groups could also react with the epoxy as an effective curing agent that could increase the interfacial crosslinking density and strengthen interfacial adhesion. The tensile strength and Youngs modulus of CNFs-PEI/Epoxy nanocomposites were 88.1% and 237.6% higher than those of neat epoxy, respectively. The tensile storage modulus of the nanocomposites also increased significantly at the temperature either below or above the Tg. The coefficient of thermal expansion for the CNFs-PEI/Epoxy nanocomposites was 22.2ppmK-1, much lower than that of the neat epoxy (88.6ppmK-1). In addition, the thermal conductivity of the nanocomposites was observed to increase as well. The exceptional and balanced properties may provide the nanocomposites promising applications in automotive, construction and electronic devices.