TEMPO-oxidized Nanocellulose Research Articles

Structural properties and foaming of plant cell wall polysaccharide dispersions

Water suspensions of cellulose nanofibres with xylan, xyloglucan and pectin were studied for foaming and structural properties as a new means for food structuring. The dispersions were analysed with rheological measurements, microscopy and optical coherence tomography. A combination of xylan with TEMPO-oxidized nanocellulose produced a mixture with well-dispersed air bubbles, while the addition of pectin improved the elastic modulus, hardness and toughness of the structures. A similar structure was observed with native nanocellulose, but the elastic modulus was not as high. Shear flow caused cellulose nanofibres to form plate-like flocs in the suspension that accumulated near bubble interfaces. This tendency could be affected by adding laccase to the dispersion, but the effect was opposite for native and TEMPO-oxidized nanocellulose. Nanocellulose type also influenced the interactions between nanofibers and other polysaccharides. For example, xyloglucan interacted strongly with TEMPO-oxidized nanocellulose (high storage modulus) but not with native nanocellulose.

New insights into the material chemistry of polycaprolactone-grafted cellulose nanofibrils/polyurethane nanocomposites

Polycaprolactone (PCL) was grafted to TEMPO-oxidized nanocellulose (TONCs) through a classical ring-opening polymerization reaction mediated by the surface TONC hydroxyl and carboxyl groups. The PCL increased the thermal stability and hydrophobicity without compromising the crystallinity. When TONCs and PCL-grafted TONCs (PTONC) were compared with respect to their perfusion within a segmented polyurethane matrix (CLPU), PTONC dispersed far better as evidenced by increased storage modulus and Young’s modulus. The mechanical strength of the PTONC nanocomposites was nearly that of unmodified TONCs while at a low content (<3 wt%). Furthermore, PTONC in CLPU promoted micro-phase separation of the matrix leading to a smaller decrease in loss factor and elongation at break for the nanocomposites, highly superior to unmodified TONCs. Thus, PTONC as a reinforcement agent enhanced the mechanical properties and ductility of CLPU.

Dynamic mechanical analysis of layer-by-layer cellulose nanocomposites

Natural composites like wood are scale integrated structures from molecular to the macroscopic scale. Inspired by this design, layer-by-layer (LbL) deposition technique was used to create lignocellulosic composites from isolated wood polymers with an ordered architecture from the nano to the microscale level. The objective of this study was to investigate the effect of the LbL ordering versus a cast film composed of a blended mixture of the same polymers using dynamic mechanical analysis (DMA). The composites were made from TEMPO-oxidized nanocellulose (TONc) obtained by fibrillation of TEMPO mediated oxidized pulp fibers, organosolv lignin (OL), and a cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) used as a linking layer. DMA was performed on thin films that were saturated with ethylene glycol, utilizing a parallel-plate compression-torsion geometry. In the temperature range that was studied (0–120°C), a single tan δ peak was observed in the 30–40°C region for both nanocomposite films. A neat NC cast film was tested under similar conditions that displayed a similar relaxation in this region. The peak was seen to disappear in case of LbL films in the second heat, whereas it was recurring in case of cast films of the blended mixture, and neat NC films. Heating of the samples under a compressive force produced an opposite effects in the two films; the LbL films exhibited swelling, whereas the cast films showed densification Furthermore, the tan δ peak in the second heat of cast films was found to be frequency dependent, while the LbL film did not show the same behavior. The apparent activation energies calculated (65–80kJmol−1) for these film based on the Arrhenius equation was found to be coincident to those reported for the β transition of cellulose.

Study of the Effect of Grafting Method on Surface Polarity of Tempo-Oxidized Nanocellulose Using Polycaprolactone as the Modifying Compound: Esterification versus Click-Chemistry.

Esterification and click-chemistry were evaluated as surface modification treatments for TEMPO-oxidized nanocelluloses (TONC) using Polycaprolactone-diol (PCL) as modifying compound in order to improve the dispersion of nanofibers in organic media. These two grafting strategies were analyzed and compared. The first consists of grafting directly the PCL onto TONC, and was carried out by esterification between hydroxyl groups of PCL and carboxyl groups of TONC. The second strategy known as click-chemistry is based on the 1,3-dipolar cycloaddition reaction between azides and alkyne terminated moieties to form the triazole ring between PCL and TONC. The grafted samples were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Thermogravimetry analysis (TGA). Further, the effects of the two treatments on the surface hydrophobization of TONC were investigated by contact angle measurements. The results show that both methods confirm the success of such a modification and the click reaction was significantly more effective than esterification.

Transparent, Conductive, and Printable Composites Consisting of TEMPO-Oxidized Nanocellulose and Carbon Nanotube

Ultrastrong, transparent, conductive and printable nanocomposites were successfully prepared by mixing single-walled carbon nanotubes (CNTs) with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs) with abundant sodium carboxyl groups on the crystalline nanocellulose surfaces. The surface-anionic cellulose nanofibrils had reinforcing and nanodispersing effects on the CNTs both in water used as the dispersed medium and in the dried composite film, providing highly conductive and printable nanocomposites with a small amount of CNTs. TOCNs are therefore expected as an effective flexible matrix that can be used as an alternative to conventional polymers for various electrical materials, when nanocomposited with CNTs and also graphene. Our findings provide a promising route to realize green and flexible electronics.

TEMPO-Oxidized Nanocellulose Participating as Crosslinking Aid for Alginate-Based Sponges

Crosslinked polysaccharide sponges have been prepared by freeze-drying of amorphous alginate-oxidized nanocellulose in the presence of a Ca(2+) ionic crosslinking agent. The new carboxyl groups on the surface of nanocellulose induced by the chemical oxidization provided the possibility of participating in the construction of an alginate-based sponge's structure and played a fundamental role in the structural and mechanical stability of ensuing sponges. Furthermore, enhanced mechanical strength induced by oxidized cellulose nanocrystals and the formation of a semi-interpenetrating polymer network from oxidized microfibrillated cellulose were reported. Together with the facile and ionic crosslinking process, the ultrahigh porosity, promising water absorption and retention, as well as the improved compression strength of the crosslinked sponges should significantly extend the use of this soft material in diverse practical applications.

Nanocomposites prepared by in situ enzymatic polymerization of phenol with TEMPO-oxidized nanocellulose

The objective of this study was to prepare nanocomposites based on polyphenols and nanocellulose fibers using relatively benign processing. To accomplish this, phenol was polymerized using horseradish peroxidase in the presence of TEMPO-oxidized nanocellulose. The polyphenol-nanocellulose composite was insoluble in organic solvents but the individual components were soluble. SEM imaging of fracture surfaces of polyphenol, nanocellulose, and composite indicated brittle failure in polyphenol and nanocellulose but ductile failure in the composite pointing to a potential synergistic effect from the addition of the components. Polyphenol existed as spherical or near-spherical “clusters” that were ca. 10 μm in the absence of nanocellulose and ca. 0.1 μm in the presence of nanocellulose. The observed change in structure corresponded to changes in the thermal stability because the composite was more thermally stable than the components. FT-IR analysis of polyphenol-nanocellulose composites showed physical and chemical interactions between the fiber and matrix. This study is a significant improvement in forming nanocomposites without the intensive processing usually required for dispersion.