CNF Films Research Articles

High-performance cellulose nanofibril composite films

Cellulose nanofibril/phenol formaldehyde (CNF/PF) composite films with high work of fracture were prepared by filtering a mixture of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized wood nanofibers and water-soluble phenol formaldehyde with resin contents ranging from 5 to 20 wt%, followed by hot pressing. The composites were characterized by tensile testing, dynamic mechanical analysis, scanning electron microscopy, atomic force microscopy, thermo-gravimetric analysis, and moisture/water absorption. Neat CNF films had tensile stress and Young’s modulus of 232 MPa and 4.79 GPa, respectively. PF resin was found to be well dispersed in the composites, although the resin increased the roughness of the film surfaces. Hygroscopic capacities of the composites were dramatically reduced, as compared to neat films, in both high humidity environments and when soaked in water. The composites exhibited slightly reduced tensile strength with modestly increased storage modulus compared to neat CNF films. Remarkably, the work of fracture ranged from 20 to 27 MJ/m3, making these films among the toughest reported for cellulose nanocomposites.

Piezoresistive polypropylene–carbon nanofiber composites as mechanical transducers

This paper describes a strain sensor based on a polypropylene–carbon nanofiber (PP–CNF) composite film, fabricated by twin screw extrusion and compression molding, which is an inexpensive industrial polymer production technique. Its working principle is based on the piezoresistive effect showed by this kind of composites. Strain sensing by variation of the electrical resistance of the sensor was tested by a four-point bending method. Furthermore, the dependence of the gauge factor as a function of the deformation and velocity of deformation was calculated. The reproducibility of the electrical response of the material was also tested by applying up to forty loading–unloading cycles. The experimental results showed that PP–CNF films have an overall appropriate response for being used as piezoresistive deformation sensors, with a small non-linear response, typical of composites within the percolation threshold. Finally, electrical equivalent model of the sensor was developed and the experimental data was tested against it, showing good agreement.

Dielectric properties at microwave frequencies of poly(ɛ-caprolactone)/CNF films and electrospun mats

The electromagnetic (EM) properties of hybrid poly(ɛ-caprolactone)/carbon nanofiber films and electrospun mats at microwave frequencies (8.2–12.4 GHz) were assessed by means of wave guide measurements. It was found that, on equal composition, the two systems present very different permittivities, that in the case of electrospun mats is far lower than that of films. These results are explained in view of the different microstructures. In particular, the massive presence of porosity is demonstrated to be the major parameter affecting the EM properties of mats. Shielding effectiveness was evaluated and was found to be poor for both systems, despite the relative large amount of conductive nanofiller. This results was attributed, in the case of films, to the presence of multiple reflections among CNF, while in the case of mats to their porous microstructure that let the waves easily pass through.

Regeneration of carbon nanotube and nanofibre composite film electrode for electrical removal of cupric ions

Low cost and large scale carbon nanotube and nanofibre (CNT-CNF) composite films have been fabricated and employed as electrodes for electrosorption of cupric ions. The regeneration of the saturated CNT-CNF film electrode has been investigated. Three methods (short-circuiting, short-circuiting and then reversing voltage, reversing voltage and then short-circuiting) are used for regeneration. The results show that low regeneration efficiency of CNT-CNF film electrode due to electrodeposition of Cu on the electrode surface can be highly improved by regeneration applying reverse voltage combined with short circuit. 93% regeneration efficiency can be achieved when 0.8 V reverse voltage is applied before short-circuiting during regeneration of CNT-CNF film electrode.

Electrosorption of anions with carbon nanotube and nanofibre composite film electrodes

The electrosorption of different salt solutions with carbon nanotube and nanofibre (CNT–CNF) composite film electrodes was studied. The electrochemical properties of CNT–CNF film were systematically investigated using ac impedance spectroscopy and cyclic voltammetry, and it was found that capacitive deionization (CDI) of CNT–CNF composite film electrodes is mainly due to Coulombic interaction on the electrical double-layer. Several experiments were conducted to determine the ion removal capacity and selectivity of CNT–CNF composite film electrodes, showing that smaller hydrated anions exhibit better CDI capacities.