Aji P. Mathew

Nanoporous membranes with cellulose nanocrystals as functional entity in chitosan: Removal of dyes from water

Fully biobased composite membranes for water purification were fabricated with cellulose nanocrystals (CNCs) as functional entities in chitosan matrix via freeze-drying process followed by compacting. The chitosan (10 wt%) bound the CNCs in a stable and nanoporous membrane structure with thickness of 250-270 μm, which was further stabilized by cross-linking with gluteraldehyde vapors. Scanning electron microscopy (SEM) studies revealed well-individualized CNCs embedded in a matrix of chitosan. Brunauer, Emmett and Teller (BET) measurements showed that the membranes were nanoporous with pores in the range of 13-10nm. In spite of the low water flux (64 Lm(-2) h(-1)), the membranes successfully removed 98%, 84% and 70% respectively of positively charged dyes like Victoria Blue 2B, Methyl Violet 2B and Rhodamine 6G, after a contact time of 24h. The removal of dyes was expected to be driven by the electrostatic attraction between negatively charged CNCs and the positively charged dyes.

Electrospun chitosan-based nanocomposite mats reinforced with chitin nanocrystals for wound dressing

The aim of this study was to develop electrospun chitosan/polyethylene oxide-based randomly oriented fiber mats reinforced with chitin nanocrystals (ChNC) for wound dressing. Microscopy studies showed porous mats of smooth and beadless fibers with diameters between 223 and 966 nm. The addition of chitin nanocrystals as well as crosslinking had a positive impact on the mechanical properties of the mats, and the crosslinked nanocomposite mats with a tensile strength of 64.9 MPa and modulus of 10.2 GPa were considered the best candidate for wound dressing application. The high surface area of the mats (35 m(2)g(-1)) was also considered beneficial for wound healing. The water vapor transmission rate of the prepared mats was between 1290 and 1,548 gm(-2)day(-1), and was in the range for injured skin or wounds. The electrospun fiber mats showed compatibility toward adipose derived stem cells, further confirming their potential use as wound dressing materials.

Nanocelluloses and their phosphorylated derivatives for selective adsorption of Ag+, Cu2+ and Fe3+ from industrial effluents

The potential of nanoscaled cellulose and enzymatically phosphorylated derivatives as bio-adsorbents to remove metal ions (Ag(+), Cu(2+) and Fe(3+)) from model water and industrial effluents is demonstrated. Introduction of phosphate groups onto nanocelluloses significantly improved the metal sorption velocity and sorption capacity. The removal efficiency was considered to be driven by the high surface area of these nanomaterials as well as the nature and density of functional groups on the nanocellulose surface. Generally, in the solutions containing only single types of metal ions, the metal ion selectivity was in the order Ag(+)>Cu(2+)>Fe(3+), while in the case of mixtures of ions, the order changed to Ag(+)>Fe(3+)>Cu(2+), irrespective of the surface functionality of the nanocellulose. In the case of industrial effluent from the mirror making industry, 99% removal of Cu(2+) and Fe(3+) by phosphorylated nanocellulose was observed. The study showed that phosphorylated nanocelluloses are highly efficient biomaterials for scavenging multiple metal ions, simultaneously, from industrial effluents.

A comparative study on properties of micro and nanopapers produced from cellulose and cellulose nanofibres.

Cellulose nanocrystals (CNCs) and cellulose nanofibres (CNFs) were successfully extracted from cellulose obtained from maize stalk residues. A variety of techniques, such as Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used for characterization and the experimental results showed that lignin and hemicellulose were removed to a greater extent by following the chemical methods. Atomic force microscopy (AFM) results confirmed that the diameters of CNCs and CNFs were ranging from 3 to 7 nm and 4 to 10nm, respectively, with their lengths in micro scale. CNCs suspension showed a flow of birefringence, however, the same was not observed in the case of suspension containing CNFs. XRD analysis confirmed that CNCs had high crystallinity index in comparison to cellulose and CNFs. Nanopapers were prepared from CNCs and CNFs by solvent evaporation method. Micropapers were also prepared from cellulose pulp by the same technique. Nanopapers made from CNFs showed less transparency as compared to nanopapers produced from CNCs whereas high transparency as compared to micropaper. Nanopapers produced from CNFs provided superior mechanical properties as compared to both micropaper and nanopapers produced from CNCs. Also, nanopapers produced from CNFs were thermally more stable as compared to nanopapers produced from CNCs but thermally less stable as compared to micropapers.

Crosslinked fibrous composites based on cellulose nanofibers and collagen with in situ pH induced fibrillation

Collagen and cellulose nanofiber based composites were prepared by solution casting followed by pH induced in situ partial fibrillation of collagen phase and crosslinking of collagen phase using gluteraldehyde. Microscopy studies on the materials confirmed the presence of fibrous collagen and cellulose nanofibers embedded in the collagen matrix. The cellulose nanofiber addition as well as collagen crosslinking showed significant positive impact on the nanocomposite’s mechanical behaviour. The synergistic performance of the nanocomposites indicated stabilization and reinforcement through strong physical entanglement between collagen and cellulose fibres as well as chemical interaction between collagen matrix and collagen fibrils. The mechanical performance and stability in moist conditions showed the potential of these materials as implantable scaffolds in biomedical applications. The collagen-cellulose ratio, crosslinking agent and crosslinking level of collagen may be further optimised to tailor the mechanical properties and cytocompatibility of these composites for specific applications such as artificial ligament or tendon.

Dry-Spun Single-Filament Fibers Comprising Solely Cellulose Nanofibers from Bioresidue

We demonstrated that low-cost and environmentally friendly filaments of native cellulose can be prepared by dry spinning an aqueous suspension of cellulose nanofibers (CNF). The CNF were extracted from banana rachis, a bioresidue from banana cultivation. The relationship between spinning rate, CNF concentration, and the mechanical properties of the filaments were investigated and the results showed that the modulus of the filaments was increased from 7.8 to 12.6 GPa and the strength increased from 131 to 222 MPa when the lowest concentration and highest speed was used. This improvement is believed to be due to an increased orientation of the CNF in the filament. A minimum concentration of 6.5 wt % was required for continuous filament spinning using the current setup. However, this relatively high concentration is thought to limit the orientation of the CNF in the filament. The process used in this study has a good potential for upscaling providing a continuous filament production with well-controlled speed, but further work is required to increase the orientation and subsequently the mechanical properties.

Biocompatible Fibrous Networks of Cellulose Nanofibres and Collagen Crosslinked Using Genipin: Potential as Artificial Ligament/Tendons

Bio-based fibrous nanocomposites of cellulose nanofibres and non-crosslinked/crosslinked collagen were prepared by in situ pH-induced fibrillation of collagen phase and sterilized using gamma rays at 25 KGy. Collagen phase is crosslinked using genipin, a bio-based crosslinker that introduces flexible crosslinks. Microscopy studies of the prepared materials showed nanostructured fibrous collagen and cellulose dispersed in collagen matrix. Mechanical performance of the sterilized nanocomposites was close to that of natural ligament and tendon, in simulated body conditions. Cytocompatibility studies indicated that these nanocomposites allowed human ligament cell and human endothelial cell adhesion, growth, and differentiation; which is eminently favourable to ligament tissue engineering.

Poly(methyl vinyl ether-co-maleic acid)−Polyethylene Glycol Nanocomposites Cross-Linked In Situ with Cellulose Nanowhiskers

Nanocomposites were developed by cross-linking cellulose nanowhiskers with poly(methyl vinyl ether-co-maleic acid) and polyethylene glycol. Nuclear magnetic resonance (NMR) studies showed cross-linking occurs between the matrix and cellulose nanowhiskers via an esterification reaction. Proton NMR T(2) relaxation experiments provided information on the mobility of the polymer chains within the matrix, which can be related to the structure of the cross-linked nanocomposite. The nanocomposite was found to consist of mobile chain portions between cross-linked junction points and immobilized chain segments near or at those junction points, whose relative fraction increased upon further incorporation of cellulose nanowhiskers. Atomic force microscopy images showed a homogeneous dispersion of nanowhiskers in the matrix even at high nanowhisker content, which can be attributed to cross-linking of the nanowhiskers in the matrix. Relative humidity conditions were found to affect the mechanical properties of the composites negatively while the nanowhiskers content had a positive effect. It is expected that the cross-links between the matrix and the cellulose nanowhiskers trap the nanowhiskers in the cross-linked network, preventing nanowhisker aggregation subsequently producing cellulose nanocomposites with unique mechanical behaviors. The results show that in situ cross-linking of cellulose nanowhiskers with a matrix polymer is a promising route to obtain nanocomposites with well dispersed nanowhiskers, tailored nanostructure, and mechanical performance.

All-cellulose nanocomposite fibers produced by melt spinning cellulose acetate butyrate and cellulose nanocrystals

Bio-based continuous fibers were prepared by melt spinning cellulose acetate butyrate (CAB), cellulose nanocrystals (CNC) and triethyl citrate. A CNC organo-gel dispersion technique was used and the prepared materials (2 and 10 wt% CNC) were melt spun using a twin-screw micro-compounder and drawn to a ratio of 1.5. The microscopy studies showed that the addition of CNC in CAB resulted in defect-free and smooth fiber surfaces. An addition of 10 wt% CNC enhanced the storage modulus and increased the tensile strength and Young’s modulus. Fiber drawing improved the mechanical properties further. In addition, a micromechanical model of the composite material was used to estimate the stiffness and showed that theoretical values were exceeded for the lower concentration of CNC but not reached for the higher concentration. In conclusion, this dispersion technique combined with melt spinning can be used to produce all-cellulose nanocomposites fibers and that both the increase in CNC volume fraction and the fiber drawing increased the mechanical performance.

Surface adsorption and self-assembly of Cu(II) ions on TEMPO-oxidized cellulose nanofibers in aqueous media.

TEMPO-mediated oxidized cellulose nanofibers (TOCNFs) have shown potential in the bioremediation of metal ions from contaminated water due to their interaction with positively charged metal ions via electrostatic interactions involving surface carboxyl groups. Copper is one of the most common pollutants in industrial effluents and is thus the target metal in the current study. The specific surface adsorption of Cu(II) was similar for TOCNFs with different degrees of functionalization and directly impacted the zeta potential. SEM imaging of the TOCNF after Cu(II) adsorption revealed interesting nanostructured clusters that were attributable to Cu(II) ions first being adsorbed by carboxylate groups on the TOCNF and subsequently being reduced and self-assembled to Cu(0) nanoparticles (NPs) or copper oxide NPs by microprecipitation. TOCNF turned superhydrophilic and resulted in faster water filtration after copper adsorption due to the stronger polarity of the copper ions or the self-assembled Cu(0) NPs creating voids or highly water-permeable channels at the interface between the interconnected TEMPO-oxidized nanofibers. Thus, the adsorption of Cu(II) ions and self-assembly into the Cu NPs on TOCNF favors a faster water purification process and provides a viable route to reuse/recycle TOCNFs studded with Cu nanoparticles as biocidal materials.