Cellulose Nanofiber Film Research Articles

Spray Coated Cellulose Nanofiber (CNF) Film as an Eco-Friendly Substrate for Flexible and Printed Electronics

Cellulose nanofiber is an eco-friendly nanomaterial used for fabricating various functional materials. It is an alternative for synthetic plastic and other petroleum derived materials. Due to demand of CNF film, fast and rapid method for fabrication of CNF film is required. A new method on spray coating to prepare smooth cellulose nanofiber (CNF) films was developed. In this method, spraying CNF suspension onto a smooth and polished metal surface was carried out and then allowed the spray coated wet film to dry in air under standard laboratory conditions. Spraying has notable advantages such as contour coating and contactless coating with the base substrate. The basis weight and thickness of the CNF film is tailorable by adjusting CNF suspension in spraying process. CNF film prepared via spray coating has unique two-sided surface roughness with the surface in contact with the base substrate or metal side much smoother than the air-contact side. The surface roughness is one of the controlling parameter in the application of the CNF film as a substrate for flexible and printed electronics. The RMS roughness of the two surfaces investigated by Optical Profilometry [OP] was found to be 2087 nm on the rough side and 389 nm on the spray coated side, respectively. The spray coated CNF film has ultra-high smoothness on the side exposed to the polished stainless steel surface. The factors including the size of cellulose fibrils and surface smoothness of base surface that control the roughness of the film are currently being investigated and will be discussed in this chapter. The surface smoothness requirements for substrate applications in flexible and printed electronics will be discussed.

Transparent nanocellulose paper-based biodegradable colorimetric nerve agent detectors

Transparent cellulose nanofiber (t-CNF) films were prepared by succinylation and an aqueous collision counter system treatment, and used for the colorimetric detection of diethyl chlorophosphate (DCP), a nerve agent mimic in the vapor phase. DCP receptor with an oxime residue was anchored on the surface of succinylated CNF films, resulting in the target probe (CNF-Azo films). CNF-Azo films exhibited selective detection behavior toward DCP in the vapor phase. The oxime groups of CNF-Azo film reacted with DCP upon exposure to DCP vapor, which was accompanied by a color change from yellow to purple. Significantly, the film's transparency was preserved throughout the detection process, allowing it to identify objects behind the film during DCP detection. This property could apply to any detection system in which the color change caused by detection does not interfere with the film's transparency. The CNF-based film sensor was biodegradable, allowing it to be disposable after use.

Cellulose Nanofiber-Based Ethylene Scavenging Antimicrobial Films Incorporated with Various Types of Titanium Dioxide Nanoparticles to Extend the Shelf Life of Fruits

TiO2 nanotubes (TNTs) were synthesized hydrothermally and modified by Cu2O using a sol–gel method to provide photocatalytic activity in visible light. Cellulose nanofiber (CNF)-based films were prepared by adding TiO2, TNTs, and Cu2O-modified TNT (TNT-Cu2O). The TiO2-based nanoparticles (TiO2, TNTs, and TNT-Cu2O) were uniformly distributed in the base polymer to make compatible and flexible films. The incorporation of nanoparticles significantly enhanced the UV-shielding properties of the film while slightly decreasing the transparency. Incorporating nanofillers improved the film’s mechanical and water resistance properties depending on the nanoparticle type. The TNT-Cu2O-added CNF film (CNF/TNT-Cu2O) showed the strongest antibacterial activity in visible light, followed by CNF/TNT and CNF/TiO2 films. The CNF-based films were used for tomato packaging to evaluate the ethylene scavenging property of the films. The CNF/TNT-Cu2O film scavenged ethylene gas produced in the headspace during storage, delaying the tomatoes’ discoloration, softening, and weight loss. CNF/TNT-Cu2O films are expected to be excellent composite films for the active packaging application of fruits and vegetables.

Atmosphere‐free activation methodology for holey graphene/cellulose nanofiber‐based film electrode with highly efficient capacitance performance

AbstractAn efficient chamber‐induced activation method was applied for the preparation of holey graphene/cellulose nanofiber‐based film with high specific surface area (SSA) and multiple channels through the graphene nanosheets. With the cellulose nanofiber (CNF) simultaneously serving as “dispersing agent,” “spacer,” and “activating agent,” the graphene oxide (GO) nanosheets are perforated by the pyrolysis gas from CNF in the confined space inside the hybrid films, uniformly dispersed, and sandwiched between CNF networks with less agglomeration and restacking. Additionally, we have proved that H2O and H2 are primarily responsible for the activation and etching of GO/CNF film. As the CNF content increases, the mesoporosity of the activated reduced GO/CNF (A‐RGO/CNF) film increases, and the graphene nanosheets show more nanopore perforations. Benefitting from the high SSA, high density, moderate mesoporosity, and abundant channels for ion diffusion through the graphene nanosheets, the A‐RGO/CNF film exhibits the highest specific capacitance of 323 (236) F g−1 (F cm−3) at 1 A g−1. For the A‐RGO5/CNF5 film containing half CNF and half GO, an excellent comprehensive electrochemical performance including superior rate performance (208 (160) F g−1 (F cm−3) at 60 A g−1) is exhibited. Moreover, the A‐RGO5/CNF5 electrode in an all‐solid‐state flexible symmetric supercapacitor delivers a high specific capacitance of 250 (193) F g−1 (F cm−3) at 1 A g−1. This study provides a novel idea for the preparation of holey graphene‐based film for supercapacitor electrodes. The strategy of simultaneously employing CNF as “dispersing agent,” “spacer,” and “activating agent” also offers a new vision for the assembly of homogeneous nanohybrid material and the utilization of pyrolysis gas.

Preparation of ZnO/NiO-loaded flexible cellulose nanofiber film electrodes and their application to dye-sensitized solar cells

Since flexible solar cells are demanded portable purposes, materials are requested to be light and soft. Hence the present work focused on the preparation of metal oxide-based flexible dye-sensitized solar cells (DSSCs) using sustainable, eco-friendly TEMPO-oxidized cellulose nanofiber (TOCNF) films as substrates and their performances were compared. When nanorod (NR), nanowire (NW), and nanoparticle (NP) of ZnO or NiO as photovoltaic materials and carbon dot (Cdot) and N719 dye as photosensitizers were used, the coating of ZnONP (50 wt%) incorporated Cdot on ZnONW/Cdot/TOCNF substrate revealed the better photovoltaic conversion efficiency (PCE) (1.34%) and the lower charge transfer resistance property. A NiONP/Cdot-coated NiONW/TOCNF electrode also achieved a good PCE, but the hydrophobic treatment of TOCNF improved the efficiency to be 1.45%. Although the flexible working electrodes for DSSCs were successfully manufactured from a biodegradable and sustainable TOCNF, more effort is still required at least to achieve the performance (4.43%) of conventional non-biodegradable polyethylene terephthalate substrate.

Flexible MXene/copper/cellulose nanofiber heat spreader films with enhanced thermal conductivity

Abstract To deal with the heat dissipation problem produced by a high integrated circuit, the preparation of heat spreaders with excellent heat transportation performance is increasing in demand. The Ti3C2 MXene sheets and copper particles were fully contacted with cellulose nanofibers by a high-speed mixer, and the composite film was prepared as a heat spreader under the action of the vacuum-assisted filtration. The MXene sheets are connected by the esterification of the carboxyl group in MXene and the hydroxyl group in cellulose nanofibers to form a chemical bond and consist of the main skeleton of the composite film. Due to the synergistic effects of MXene and copper particles, the in-plane and out-of-plane thermal conductivities of the composite film reach 24.96 and 2.46 W m−1 K−1, respectively. Compared with the pure cellulose nanofiber films, the thermal conductivity of composite films increased by 2819.2 and 187.6%, respectively. By designing two applications of composite films in the actual use process, the excellent heating conduction abilities in two directions have been proved. This measure to improve the thermal conductivities of composite films by MXene-copper binary fillers also provides ideas for the novel heat spreader.

Construction and Performance of a Nanocellulose–Graphene-Based Humidity Sensor with a Fast Response and Excellent Stability

Humidity sensors have been widely applied in environmental monitoring, respiratory monitoring, electronic skin, noncontact switch, etc. However, weak interface interactions between a flexible substrate and conductive fillers will deteriorate the sensing performance. Herein, a flexible, rapid-response, and durable humidity sensor was proposed via employing cellulose nanofiber (CNF)-dispersed graphene (Gr) as a humidity sensing layer, which could be easily filtered onto a coessential CNF film (CNFF) to form the humidity sensor. CNFs as a dispersant and bonder strengthened the adhesion of graphene on the surface of the CNFF substrate. Simultaneously, CNFs as a reservoir provided abundant adsorption sites to capture water molecules and promoted electron transfer from adsorbed water molecules to graphene, further amplifying electrical signals by a hygroscopic expansion of the sensing layer under humidity conditions. Benefiting from this unique composition and structure, the prepared humidity sensor exhibited a rapid response (45 s) and recovery time (33 s), low hysteresis (4%), wide RH detection range (15–99%), and long-term stability (15 days). Further, the sensor could monitor the humidity of human skin and human breath, indicating a versatile noncontact humidity sensing function by altering its component proportion of CNF-to-Gr on demand.

Green in situ immobilization of gold and silver nanoparticles on bacterial nanocellulose film using Punica granatum peels extract and their application as reusable catalysts.

In this study, Punica granatum peels extract induced in situ deposition was applied to prepare Au and Ag nanoparticles on bacterial nanocellulose film. Bacterial nanocellulose provided as an eco-friendly and excellent support for the interaction of P. granatum peel biomolecules and further reduction of Au and Ag ions. Meanwhile, a possible in situ growth mechanism of Au and Ag on bacterial cellulose by P. granatum peel extract biomolecules was presented. Further, the metal nanoparticles incorporated bacterial cellulose films were used to catalyze the reduction of 4-nitrophenol. The results of the present study indicated excellent catalytic reduction properties of Au and Ag nanocellulose films for 4 consecutive cycles. In addition, Au and Ag incorporated cellulose nanofiber films exhibited superior antioxidant activity and improved mechanical properties compared to pristine cellulose nanofiber film. The findings of this study may provide new insights and broad application of bacterial cellulose and green synthesis method for the development of various metal-cellulose composites.

Functionalization of spray coated cellulose nanofiber sheet with montmorillonite (MMT) and silver nanoparticles (AgNPs) to biomedical nanocomposite as wound regeneration scaffold

Cellulose nanofiber is one of the predominant biomaterials in carbohydrate polymers and is excellent in recyclability and biodegradability. Due to excellence in mechanical properties, CNF film can be used as a base biomaterial for the fabrication of nanocomposite. The spray-coated cellulose nanofiber was characterized and investigated by UV-VIS absorption spectroscopy, SEM, TGA, DSC, FTIR, and water absorption. The structure of sprayed cellulose nanofiber sheet was observed to be 70 nm in size. The AgNPs absorption peak was recorded around 452 nm in the absorption spectroscopy. To improve the mechanical strength and water absorption of cellulose nanofiber film, Montmorillonite (MMT) was impregnated on the sheet by spraying. The AgNPs were synthesized from the plant extract Cassia alata which shows good antioxidant and antimicrobial activity. The cell viability assay of the composite film was analyzed using the 3T3 fibroblast cell by MTT assay. The anti-diabetic assay for the plant extract and AgNPs was observed to be 56% and 61% in the alpha-amylase inhibitory assay. The dressing material made from CNF-MMT- AgNP scan be used in medical treatment to cure various wounds due to its good biocompatibility and cost-effective nature.

Chemical and molecular structure transformations in atomistic conformation of cellulose nanofibers under thermal environment

The structural changes of the glucopyranose chain and the chemical compositional response of cellulose nanofibers (CNFs) under thermal exposure (at 190 °C for 5 h) have remained a significant gap in the understanding of the long-term performance of nanocellulose. Herein, CNF films with different chemical compositions were investigated to confirm the structural transformation of glucopyranose (coupling constant of OH groups changed up to 50%) by nuclear magnetic resonance (NMR) analysis. Remarkably, the glucopyranose rings underwent partial dehydration during the thermal exposure resulting in enol formation. This study confirms the chain mobility that could lead to the conformational and dimensional changes of the CNFs during thermal exposure. The broad range of conformations was defined by the dihedral angles that varied from ±27° to ±139° after thermal exposure. Investigation into the mechanism involving chemical transformation of the substrates during heating is important for the fabrication of the next generation of flexible electrical materials.

Improvement of thermal conductivity and latent heat of cellulose film using surfactant and surface-treated CNT with stearic acid

The formation of a thermal path greatly contributes to the improvement of the thermal management performance of the polymer composite material. In particular, 3D thermally conductive networks are effective in building fast conductive paths in polymer composites. We fabricated a stearic acid (SA) carbon nanotube (CNT)/cellulose nanofiber (CNF) film with a 3D network. The film consisted of a filler loading of 70 wt% and demonstrated a thermal conductivity that was higher than that of neat CNFs by 259%. Furthermore, an X-ray diffraction test showed that the crystallinity of the composite changed during the foam structure formation owing to freeze-casting. Our results indicate that composites prepared with surface-modified CNTs showed high thermal conductivity and heat latent. This study proposes a process to significantly improve the thermal conductivity of polymer composite films through a simple system.

Novel CNFs-based organic UV-adsorber intercalated ZnAl-LDHs composited films with superior photothermal stability and mechanical properties

The improvement of the photothermal stability and mechanical properties for cellulose nanofibers (CNFs) is a highly desirable yet challenging research topic due to its wide applications. Featuring the 2D-organized structure and various characteristics, layered double hydroxides (LDHs) shows tremendous potential in improving the photothermal stability and mechanical properties of CNFs matrix. Herein, a series of ZnAl-LDHs nanosheets intercalated with different organic molecules were synthesized and subsequently doped into CNFs matrix for preparing CNFs/LDHs composited films. It was showed that doping UV-adsorber intercalated ZnAl-LDHs into the CNFs matrix can significantly enhance UV-shielding ability of CNFs/LDHs composited films due to the synergistic effect between organic anions and the interaction between organic anions and metal cations in LDHs laminates. And the CNFs/HUL (HUL = HALS/UV-P-LDHs) composited film exhibited outstanding UV-shielding ability (UV-shielding rate > 60%) among the considered films, which is comparable to that of the reported materials. Compared with the pristine CNFs film, compositing with HUL rendered the increasing of tensile strength from 80 to 110 MPa. The superior photothermal stability and mechanical properties of CNFs/HUL composited film highlight its great application potential in the fields of coating and packaging.

Cellulose nanofiber-based coating film integrated with nitrogen-functionalized carbon dots for active packaging applications of fresh fruit

Carbon dots were synthesized using a hydrothermal method with glucose as the carbon source (GCD) and functionalized with nitrogen. The GCD and N-functionalized carbon dots (NGCD) were used to prepare cellulose nanofiber (CNF)-based composite films. GCD and NGCD provided high UV blocking properties to the CNF film without changing the transparency, reducing the T280 by 91–98 % and T660 by 12−10 %. The addition of GCD and NGCD did not affect the mechanical properties but increased the film's water vapor permeability (WVP) and water contact angle (WCA). The composite films also showed high antioxidant activity with 99−99 % of ABTS and 80–85 % of DPPH radical scavenging activities. The CNF-based films with GCD generated reactive oxygen species (ROS) to exhibit high antimicrobial activity; however, the CNF/NGCD film showed stronger antibacterial and antifungal activity than the CNF/GCD film. In addition, the CNF-based films incorporated with GCDs showed negligible cytotoxicity. When tangerine and strawberry fruit were coated with the CNF-based coating solutions, the fruit coated with CNF/NGCD inhibited fungal growth on the fruit surface, extending their shelf life by more than 10 and 2 d, respectively. The CD-added CNF films with high antioxidant, antimicrobial, and low cytotoxicity are likely to be used for antifungal coating of fresh fruit and active packaging applications.

Hydrogen Bonding Crosslinking of Starch‐Polyvinyl Alcohol Films Reinforced by Ultrasound‐Assisted and Cellulose Nanofibers Dispersed Cellulose Nanocrystals

AbstractThe study reports the effects of cellulose nanofibers (CNF) and an ultrasound‐assisted method dispersed cellulose nanocrystals (CNC) on the mechanical and water resistance properties of starch‐polyvinyl alcohol (PVA) films. Starch‐PVA (SP) based films are prepared by casting method, compared with the original SP films, the ultrasound‐assisted and CNF are beneficial to the dispersion of CNC in nanocomposites, and the tensile strength (TS) of the ultrasound treatment starch/PVA/CNC/CNF (USPCF) film is increased to 10.63 MPa, an increase by 60%. The cross‐section morphology of the USPCF film is smoother and more homogeneous, indicating the particle size of CNC is small. The structure of blend films is homogeneous and compact due to the CNC full playing to the nano‐effect, which is the main reason for the improvement of SP‐based films in mechanical properties. Fourier Transform Infrared spectroscopy shows the hydrogen bonding is formed between SP and the fillers, while X‐ray diffraction shows that the crystallinity of nanocomposite films is decreased with ultrasonication. From the results, it can be concluded that CNF and ultrasound‐assisted dispersed nanoparticles could reinforce the SP‐based films efficiently to prepare green nanocomposite films.

Optimization of Spraying Process via Response Surface Method for Fabrication of Cellulose Nanofiber (CNF) Film

Cellulose nanofiber (CNF) is a sustainable bionanomaterial which has fibril’s width varying from 5 nm to ~73 nm with an average length of 8 μm. It can be used as a base material for various functional materials such as barrier, flexible electronic substrates, and membrane etc. Though several methods such as solvent casting and vacuum filtration are available for the production of CNF film in laboratory scale, the major constraints are film formation time, shrinkage on the film, and poor uniformity. Spraying CNF suspension is one of the emerging methods which forms the film rapidly. The present investigation deals with the optimization of critical parameters such as CNF suspension concentration, velocity of the conveyor, and spray distance involved in the spraying process via central composite design (CCD) in the response surface methodology (RSM). The influence of these parameters on the basis weight and thickness of the CNF film was evaluated from the linear models. It concludes that the CNF suspension concentration is a strong parameter for controlling the basis weight and the thickness of the CNF film. The developed linear models were validated with experimental data confirming that it was a good fit. Given this correspondence, these models may be used for scaling up the spraying process for the fast production of CNF film.

Flexible Ag NCs/CNFs film for colorimetric and SERS dual-mode ultrasensitive detection of mercury ions (II)

As toxic heavy metal ions, mercury ions seriously affect environmental safety and human health. Therefore, prepare a rapid and sensitive sensor for mercury ions detection is of great significance. In this work, dual-mode colorimetric/SERS Ag nanocrystals (NCs)/cellulose nanofibers (CNFs) film nanosensor for ultrasensitive detection of mercury ions (II) was constructed by simple filtration method with Ag NCs and CNFs mixture. Ag NCs/CNFs film was immersed into mercury ions solutions and separated for the following experiments. Mercury ions react with Ag, reducing the content of Ag in the film, which would depress the peroxidase-like activity and SERS properties of Ag NCs/CNFs film, achieving the ultrasensitive detection of mercury ions. 3,3′,5,5′-tetramethylbenzidine (TMB) was used both as the chromogenic substrate and SERS probe. The linear detection range of the colorimetric method is 100 nM - 1 mM and the limit of detection (LOD) is 33 nM. The sensitivity of SERS method is 10 times higher than that of colorimetry. Moreover, Ag NCs/CNFs film is also proved to be an ultrasensitive SERS sensor for malachite green (MG) detection (LOD 1.1 nM). The results suggest that Ag NCs/CNF film can realize rapid and in-situ detection of pollutants, which should have a good application prospect in environmental monitoring.

Wettability of cellulose nanofiber films and their nanoscale observation

Wettability of cellulose nanofiber films and their nanoscale observation

Sustainable Cellulose Nanofiber Films from Carrot Pomace as Sprayable Coatings for Food Packaging Applications

Sustainable Cellulose Nanofiber Films from Carrot Pomace as Sprayable Coatings for Food Packaging Applications

Modulation of interfacial interactions toward strong and tough cellulose nanofiber-based transparent thin films with antifogging feature

Cross-linking is often performed to overcome the weak mechanical properties of native polymer films in order to expand their functional properties and applications. While this approach offers enhanced strength to the film, the film also suffers from low flexibility, low toughness and high brittleness. However, in view of the growing demand for strong and tough transparent thin films, this article reported our study to develop films made from cellulose nanofiber (CNF) via tailoring the interfacial bonding interactions through the application of glycerol (Gly) and glutaraldehyde (GA), which functioned as a plasticizer and cross-linking agent, respectively. Among the prepared films, the 10GA-8Gly-CNF film exhibited the best results with regard to the enhancement in the tensile strength (21.1%), Young's modulus (10.6%), elongation at break (100%) and toughness (32.7%), as compared to the native CNF film. Importantly, treating the surface of the film to radiofrequency oxygen plasma endowed the film with antifogging property, without compromising the optical clarity.

Cellulose nanofiber networked bamboo particle‐based biocomposites

AbstractThis paper deals with preparation and characterization of cellulose nano fibers (CNF) extracted from the bamboo pulp using TEMPO (2,2,6,6,‐Tetramethyl‐1‐piperidinyloxy) oxidization method. The CNF was used as a binder to prepare biocomposites (particleboards) from bamboo particles. The specimens were fabricated using an industrial oven and further hot pressing. Morphological analysis of bamboo pulp and CNF was carried out using scanning electron microscope (SEM), confirming fiber formation in nanoscale. Dynamic Mechanical Analysis (DMA) of the pure CNF film shows storage modulus of 121.58 GPa. Composite specimens prepared were subjected to tensile and flexural tests to characterize the mechanical properties. The tensile strength was found to be 0.19 MPa for oven‐dried (OD) samples and 0.661 MPa for hot‐pressed (HP) samples. The modulus of elasticity (MOE) for OD samples was 121.8 and 1065.5 MPa for HP samples, respectively. Modulus of rupture (MOR) was found to be 0.77 and 3.25 MPa, for OD and HP samples, respectively. The present study results show that the CNF extracted from the bamboo pulp can be used as a sole binder in making biocomposites.