Flexible cellulose and ZnO hybrid nanocomposite and its UV sensing characteristics.

This paper reports the synthesis and UV sensing characteristics of a cellulose and ZnO hybrid nanocomposite (CEZOHN) prepared by exploiting the synergetic effects of ZnO functionality and the renewability of cellulose. Vertically aligned ZnO nanorods were grown well on a flexible cellulose film by direct ZnO seeding and hydrothermal growing processes. The ZnO nanorods have the wurtzite structure and an aspect ratio of 9 ~ 11. Photoresponse of the prepared CEZOHN was evaluated by measuring photocurrent under UV illumination. CEZOHN shows bi-directional, linear and fast photoresponse as a function of UV intensity. Electrode materials, light sources, repeatability, durability and flexibility of the prepared CEZOHN were tested and the photocurrent generation mechanism is discussed. The silver nanowire coating used for electrodes on CEZOHN is compatible with a transparent UV sensor. The prepared CEZOHN is flexible, transparent and biocompatible, and hence can be used for flexible and wearable UV sensors.

Transparent and flexible cellulose nanocrystal/reduced graphene oxide film for proximity sensing.

The rapid development of touch screens as well as photoelectric sensors has stimulated the fabrication of reliable, convenient, and human-friendly devices. Other than sensors that detect physical touch or are based on pressure sensing, proximity sensors offer controlled sensibility without physical contact. In this work we present a transparent and eco-friendly sensor made through layer-by-layer spraying of modified graphene oxide filled cellulose nanocrystals on lithographic patterns of interdigitated electrodes on polymer substrates, which help to realize the precise location of approaching objects. Stable and reproducible signals generated by keeping the finger in close proximity to the sensor can be controlled by humidity, temperature, and the distance and number of sprayed layers. The chemical modification and reduction of the graphene oxide/cellulose crystal composite and its excellent nanostructure enable the development of proximity sensors with faster response and higher sensitivity, the integration of which resolves nearly all of the technological issues imposed on optoelectronic sensing devices.

Possibility of cellulose-based electro-active paper energy scavenging transducer.

In this paper, a cellulose-based Electro-Active Paper (EAPap) energy scavenging transducer is presented. Cellulose is proven as a smart material, and exhibits piezoelectric effect. Specimens were prepared by coating gold electrodes on both sides of cellulose film. The fabricated specimens were tested by a base excited aluminum cantilever beam at resonant frequency. Different tests were performed with single and multiple parallel connected electrodes coated on the cellulose film. A maximum of 131 mV output voltage was measured, when three electrodes were connected in parallel. It was observed that voltage output increases significantly with the area of electrodes. From these results, it can be concluded that the piezoelectricity of cellulose-based EAPap can be used in energy transduction application.

Tannic-Acid-Cross-Linked and TiO2-Nanoparticle-Reinforced Chitosan-Based Nanocomposite Film.

A chitosan-based nanocomposite film with tannic acid (TA) as a cross-linker and titanium dioxide nanoparticles (TiO2) as a reinforcing agent was developed with a solution casting technique. TA and TiO2 are biocompatible with chitosan, and this paper studied the synergistic effect of the cross-linker and the reinforcing agent. The addition of TA enhanced the ultraviolet blocking and mechanical properties of the chitosan-based nanocomposite film. The reinforcement of TiO2 in chitosan/TA further improved the nanocomposite film's mechanical properties compared to the neat chitosan or chitosan/TA film. The thermal stability of the chitosan-based nanocomposite film was slightly enhanced, whereas the swelling ratio decreased. Interestingly, its water vapor barrier property was also significantly increased. The developed chitosan-based nanocomposite film showed potent antioxidant activity, and it is promising for active food packaging.

Environment-Friendly Zinc Oxide Nanorods-Grown Cellulose Nanofiber Nanocomposite and Its Electromechanical and UV Sensing Behaviors.

This paper reports a genuine environment-friendly hybrid nanocomposite made by growing zinc oxide (ZnO) nanorods on cellulose nanofiber (CNF) film. The nanocomposite preparation, characterizations, electromechanical property, and ultraviolet (UV) sensing performance are explained. CNF was extracted from the pulp by combining the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidation and the aqueous counter collision (ACC) methods. The CNF film was fabricated using doctor blade casting, and ZnO nanorods were grown on the CNF film by seeding and by a hydrothermal method. Morphologies, optical transparency, mechanical and electromechanical properties, and UV sensing properties were examined. The nanocomposite's optical transparency was more than 80%, and the piezoelectric charge constant d31 was 200 times larger than the CNF film. The UV sensing performance of the prepared ZnO-CNF nanocomposites was tested in terms of ZnO concentration, UV irradiance intensity, exposure side, and electrode materials. A large aspect ratio of ZnO nanorods and a work function gap between ZnO nanorods and the electrode material are essential for improving the UV sensing performance. However, these conditions should be compromised with transparency. The use of CNF for ZnO-cellulose hybrid nanocomposite is beneficial not only for electromechanical and UV sensing properties but also for high mechanical properties, renewability, biocompatibility, flexibility, non-toxicity, and transparency.

Alignment Effect on the Piezoelectric Properties of Ultrathin Cellulose Nanofiber Films.

This study aims at evaluating the piezoelectric property of an ultrathin cellulose nanofiber (CNF) film in a thickness direction. Cellulose is known to have piezoelectric properties. However, its measurement is not easy. By making an ultrathin CNF film and eliminating space charges, the pure piezoelectric property of CNF is intended to be measured. A 600 nm thick ultrathin CNF film was prepared using a microfabrication process. The effect of alignment methods on the piezoelectric property of the ultrathin CNF film in the thickness direction was investigated with the three alignment methods: corona poling, electrical in-plane alignment, and high magnetic field (HiMA) alignment. Piezoresponse force microscopy (PFM) was utilized to analyze the piezoelectric property. By applying AC voltages using PFM, the vertical displacement on the ultrathin CNF film surface was recorded and converted into the piezoelectric coefficient, d33. The aligned ultrathin CNF films show different piezoelectric coefficients. The corona-poled ultrathin CNF film shows the largest piezoelectric coefficient among the three alignment methods. Water contact angle measurement proves that the piezoelectric constant in the thickness direction is associated with hydroxyl groups in cellulose chains appearing on the surface of the ultrathin CNF films.

Simple centrifugal fractionation to reduce the size distribution of cellulose nanofibers.

Since cellulose nanofiber (CNF) has unique characteristics in terms of renewability, high specific elastic modulus and strength and transparency, it is attractive for a building block of future materials. CNF can be extracted from various natural resource by several means. However, the size of the extracted CNF is very broad and uniformity of the extracted CNF is very important for many applications. Thus, a fractionation process is necessary to obtain a uniformly sized CNF. In this paper, a simple centrifugal fractionation was carried out to reduce the size distribution of the extracted CNF suspension from hardwood pulp by the combination of TEMPO oxidation and aqueous counter collision methods. The original CNF suspension was diluted and centrifuged under low speed to remove cellulose microfibers then centrifuged under high speed to separate very small CNF. The centrifugation condition is 10 k rpm for 1 h followed by 45 k rpm for 4 h. The fractionated CNF was analyzed by an atomic force microscopy, and the length and width distribution histogram analysis was utilized. UV-visible analysis, FT-IR and XRD crystallinity analysis were carried out to analyze all fractionated CNFs and the original CNF. After centrifugal fractionation, the width and length distribution range were reduced by 62% and 70%, respectively. It is shown that the centrifugal fractionation is an easy and efficient method to fractionate a uniform CNF suspension.

Green nanocomposite made with chitin and bamboo nanofibers and its mechanical, thermal and biodegradable properties for food packaging.

This paper reports a green nanocomposite made by simply blending chitin nanofibers and bamboo cellulose nanofibers without chemically dissolving chitin and cellulose raw materials. Good biodegradability and biocompatibility of chitin in conjunction with good mechanical properties of cellulose are beneficial for developing green nanocomposite applicable for food packaging. The bamboo cellulose nanofiber (BACNF) is isolated by using a TEMPO-oxidation followed by an aqueous counter collision (ACC) method. Chitin nanofiber (CTNF) is isolated by using the ACC method. A simple blending is used to prepare the nanocomposite with different CTNF and BACNF concentration. Morphologies, mechanical properties, chemical interactions, thermal properties, water contact angles and biodegradability of the nanocomposite are investigated. The tensile strength and Young's modulus of the prepared nanocomposite increased up to 3 and 1.3 times, respectively as the BACNF concentration increase. The nanocomposite exhibites better thermal stability than the pure BACNF. Furthermore, the nanocomposite is fully biodegradable within a week. Good mechanical, thermal properties as well as biodegradability of the nanocomposite are promising for possible food packaging application.

Preparation and characterization of synthetic melanin-like nanoparticles reinforced chitosan nanocomposite films.

This paper reports the preparation, characterization and properties of synthetic melanin-like nanoparticle (MNP) reinforced chitosan nanocomposite films. The MNP was prepared using dopamine hydrochloride and sodium hydroxide which followed by spontaneous oxidation. The prepared MNP was spherical in shape and in the size range of ∼100 nm. The MNP was used as a functional nanofiller to produce the chitosan/MNP nanocomposite films using simple solution mixing and casting method. The MNP are evenly dispersed and biocompatible with chitosan to form the nanocomposite films. The incorporation of MNP enhances the ultraviolet blocking, mechanical properties, swelling ratio, and hydrophobicity of the nanocomposite films. The reinforcement of MNP in chitosan does not deteriorate the thermal stability and water vapor barrier property of the nanocomposite films. Furthermore, the prepared nanocomposite films show strong antioxidant activity. The developed chitosan/MNP nanocomposite films can applied to active food packaging and biomedical packaging.

Chitosan Nanofiber and Cellulose Nanofiber Blended Composite Applicable for Active Food Packaging.

This paper reports that, by simply blending two heterogeneous polysaccharide nanofibers, namely chitosan nanofiber (ChNF) and cellulose nanofiber (CNF), a ChNF-CNF composite was prepared, which exhibited improved mechanical properties and antioxidant activity. ChNF was isolated using the aqueous counter collision (ACC) method, while CNF was isolated using the combination of TEMPO oxidation and the ACC method, which resulted in smaller size of CNF than that of ChNF. The prepared composite was characterized in terms of morphologies, FT-IR, UV visible, thermal stability, mechanical properties, hygroscopic behaviors, and antioxidant activity. The composite was flexible enough to be bent without cracking. Better UV-light protection was shown at higher content of ChNF in the composite. The high ChNF content showed the highest antioxidant activity in the composite. It is the first time that a simple combination of ChNF-CNF composites fabrication showed good mechanical properties and antioxidant activities. In this study, the reinforcement effect of the composite was addressed. The ChNF-CNF composite is promising for active food packaging application.

Steered Pull Simulation to Determine Nanomechanical Properties of Cellulose Nanofiber.

Cellulose nanofiber (CNF) exhibits excellent mechanical properties, which has been extensively proven through experimental techniques. However, understanding the mechanisms and the inherent structural behavior of cellulose is important in its vastly growing research areas of applications. This study focuses on taking a look into what happens to the atomic molecular interactions of CNF, mainly hydrogen bond, in the presence of external force. This paper investigates the hydrogen bond disparity within CNF structure. To achieve this, molecular dynamics simulations of cellulose I ß nanofibers are carried out in equilibrated conditions in water using GROMACS software in conjunction with OPLS-AA force field. It is noted that the hydrogen bonds within the CNF are disrupted when a pulling force is applied. The simulated Young's modulus of CNF is found to be 161 GPa. A simulated shear within the cellulose chains presents a trend with more hydrogen bond disruptions at higher forces.

Cellulose nanofibers isolated by TEMPO-oxidation and aqueous counter collision methods.

In this research, cellulose nanofiber (CNF) was isolated by the combination of chemical 2,2,6,6-tetramethylpiperidine-1-oxylradical (TEMPO)-oxidation and physical aqueous counter collision (ACC) methods The combination of TEMPO-oxidation and ACC is an efficient method to isolate CNFs by reducing chemical usage in TEMPO-oxidation and saving energy in ACC along with controlling the size of CNFs. Two cellulose sources, hardwood bleached kraft pulp (HW) and softwood bleached kraft pulp (SW), were used for the CNF isolation with different TEMPO oxidation time and a defined number of ACC pass. The CNF properties were investigated and compared in term of morphology, crystallinity index, transparency and birefringence. The width of the isolated CNFs from HW is in the range of 15.1 nm-17.5 nm, and that of the SW CNFs is between 18.4 nm and 22 nm depending on the TEMPO oxidation time. This difference is due to the fact that SW is less oxidized than HW under the same chemical dosage, which results in larger width of SW-CNFs than HW-CNFs. The HW-CNF treated with TEMPO for over 2 h and isolated using ACC with 5 pass offers almost 90% transparency. Birefringence of CNFs exhibits that HW-CNFs show better birefringence phenomenon than SW-CNFs. The combination of TEMPO-oxidation and ACC methods is useful for isolating CNFs with its size control.

Fabrication Method Study of ZnO Nanocoated Cellulose Film and Its Piezoelectric Property.

Recently, a cellulose-based composite material with a thin ZnO nanolayer-namely, ZnO nanocoated cellulose film (ZONCE)-was fabricated to increase its piezoelectric charge constant. However, the fabrication method has limitations to its application in mass production. In this paper, a hydrothermal synthesis method suitable for the mass production of ZONCE (HZONCE) is proposed. A simple hydrothermal synthesis which includes a hydrothermal reaction is used for the production, and the reaction time is controlled. To improve the piezoelectric charge constant, the hydrothermal reaction is conducted twice. HZONCE fabricated by twice-hydrothermal reaction shows approximately 1.6-times improved piezoelectric charge constant compared to HZONCE fabricated by single hydrothermal reaction. Since the fabricated HZONCE has high transparency, dielectric constant, and piezoelectric constant, the proposed method can be applied for continuous mass production.

Cellulose long fibers fabricated from cellulose nanofibers and its strong and tough characteristics.

Cellulose nanofiber (CNF) with high crystallinity has great mechanical stiffness and strength. However, its length is too short to be used for fibers of environmentally friendly structural composites. This paper presents a fabrication process of cellulose long fiber from CNF suspension by spinning, stretching and drying. Isolation of CNF from the hardwood pulp is done by using (2, 2, 6, 6-tetramethylpiperidine-1-yl) oxidanyl (TEMPO) oxidation. The effect of spinning speed and stretching ratio on mechanical properties of the fabricated fibers are investigated. The modulus of the fabricated fibers increases with the spinning speed as well as the stretching ratio because of the orientation of CNFs. The fabricated long fiber exhibits the maximum tensile modulus of 23.9 GPa with the maximum tensile strength of 383.3 MPa. Moreover, the fabricated long fiber exhibits high strain at break, which indicates high toughness. The results indicate that strong and tough cellulose long fiber can be produced by using ionic crosslinking, controlling spinning speed, stretching and drying.

Electroactive and Optically Adaptive Bionanocomposite for Reconfigurable Microlens.

This paper introduces an electroactive bionanocomposite based on poly(diethylene glycol adipate) (PDEGA) and cellulose nanocrystals (CNCs). The bionanocomposites were made using CNCs extracted from cotton and by optimizing its concentration in terms of the optical transmittance and viscosity. The characteristic properties of the materials were analyzed using contact angle measurements and Fourier transformation infrared spectra. Using the PDEGA/CNC bionanocomposite at a very low concentration of CNCs, a configurable lens having a robust, self-contained tunable optical structure was developed. The shape and curvature of the soft PDEGA/CNC device were controlled by applying voltage, and the focal length was measured. The simple structure, high optical transparency, biodegradability, thermal stability, high durability, and low power consumption make the new material particularly useful in fabricating a reconfigurable lens for future electronic and optical devices.