Nanofibril Films Research Articles

Mechanical enhancement of cellulose nanofibril (CNF) films through the addition of water-soluble polymers

In this work, water-soluble polymers were screened through solution casting and polyvinyl alcohol (PVA) and poly(2-ethyl-2-oxazoline) (PEOX) were found as reinforcement agents for cellulose nanofibril (CNF) films. Mechanical property increases of 99% in elastic modulus, 93% in the ultimate tensile strength (UTS) and 134% in the work of failure (WOF) were reported for TEMPO-oxidized cellulose nanofibrils (TOCNFs) with 0.44 mmol/g carboxylate groups and 15 wt% PVA. PEOX had a higher elastic modulus increase of 113%, yet lower UTS and WOF increases were found at 63% and 28%, respectively. Additionally, increases in UTS and elastic modulus were also seen in mechanically fibrillated CNFs and TOCNFs with higher carboxylate contents (1.5 mmol/g). The toughening mechanism was attributed to the formation of strong hydrogen bonding between the CNFs and the hydrophilic polymers added. The presence of such mechanisms was indirectly confirmed by tensile testing, zeta potential and rheology.

Self-Standing Lignin-Containing Willow Bark Nanocellulose Films for Oxygen Blocking and UV Shielding

Developing the bio-based barrier material to substitute the petroleum-based one is the trend in functional packaging applications. Utilization of the abundantly underappreciated bark biomass is attractive from the sustainability point of view; however, an upgraded approach is required to maximize the performances of the lignin-containing cellulose nanofibril (LCNF) films from willow bark. Herein, hot water extraction (HWE) and microfluidization were studied for their effect on the yield of LCNF and its film performance after treatment of aqueous p-toluenesulfonic acid. The resultant HWE films were superior to the nontreated ones regarding yield, moisture, and oxygen barrier properties. In particular, the HWE films achieved an oxygen permeability of 3 cm3·μm/m2·kPa·day at 50% relative humidity, which is among the lowest achieved for single bio-based materials and comparable to commercially available synthetic barrier films. The LCNF films attained complete blocking of UV light transmission within the wavelength range of 290–400 nm. Overall, this study shows that HWE pretreatment not only allows the recovery of high-value extracts, but also significantly improves the yield of LCNF and its barrier performances. The biocompatible, lignin-containing, and self-standing hydrophobic nanocellulose films show promise as a barrier layer against UV radiation and oxygen permeation in food packaging and other applications.

Wood-inspired strategy to toughen transparent cellulose nanofibril films

The simultaneous attainment of high strength and high toughness of transparent cellulose nanofibril (CNF) film can expedite its uses in advanced applications. In this work, a wood-inspired strategy is proposed to address the conflict between strength and toughness by using natural derived lignosulfonic acid (LA) as a reinforcing additive. Only 1 wt% LA addition can double the toughness (11.0±1.3 MJ/m3) of pure CNF film. Consequently, the as-prepared CNF/LA-1 nanocomposite film not only exhibits superior mechanical properties (23.6±1.3 MJ/m3 toughness, 249±6 MPa strength, and 15.4±1.4 % strain), but also maintains an excellent optical transparency of 91.2 % (550 nm). Furthermore, the mechanism for simultaneously enhancing strength and toughness is essentially attributed to the improved hydrogen bonding between CNF-OH and LA-SO3H and effective energy dissipation system. This work provides a green and effective approach to prepare strong yet tough and transparent biodegradable CNF film for high-end applications.

Surface Charges Control the Structure and Properties of Layered Nanocomposite of Cellulose Nanofibrils and Clay Platelets.

The interfacial bonding and structure at the nanoscale in the polymer–clay nanocomposites are essential for obtaining desirable material and structure properties. Layered nanocomposite films of cellulose nanofibrils (CNFs)/montmorillonite (MTM) were prepared from the water suspensions of either CNFs bearing quaternary ammonium cations (Q-CNF) or CNFs bearing carboxylate groups (TO-CNF) with MTM nanoplatelets carrying net surface negative charges by using vacuum filtration followed by compressive drying. The effect of the ionic interaction between cationic or anionic charged CNFs and MTM nanoplatelets on the structure, mechanical properties, and flame retardant performance of the TO-CNF/MTM and Q-CNF/MTM nanocomposite films were studied and compared. The MTM nanoplatelets were well dispersed in the network of TO-CNFs in the form of nanoscale tactoids with the MTM content in the range of 5–70 wt %, while an intercalated structure was observed in the Q-CNF/MTM nanocomposites. The resulting TO-CNF/MTM nanocomposite films had a better flame retardant performance as compared to the Q-CNF/MTM films with the same MTM content. In addition, the effective modulus of MTM for the TO-CNF/MTM nanocomposites was as high as 129.9 GPa, 3.5 times higher than that for Q-CNF/MTM (37.1 GPa). On the other hand, the Q-CNF/MTM nanocomposites showed a synergistic enhancement in the modulus and tensile strength together with strain-to-failure and demonstrated a much better toughness as compared to the TO-CNF/MTM nanocomposites.

Cellulose nanostructured films from pretreated açaí mesocarp fibers: physical, barrier, and tensile performance

ABSTRACT Background: During de-pulping of acai (Euterpe oleracea) for juice production in the Amazonia, large amounts of fibrous waste are daily discarded, a promising substrate for production of high-value cellulose nanofibrils. Therefore, this study sought to evaluate the modifications of acai surface fibers submitted to chemical pretreatment steps and compare the quality of nanostructured films produced with different cycles of mechanical nanofibrillation. Results: A 2-hour pretreatment (at 5% of NaOH) followed by two NaOH/H2O2 bleaching steps resulted in fibers with increased length and reduced diameter compared to raw fibers while preserving fiber integrity and cellulose I structure. The increase of fibers’ grinding cycles from 3 (minimum to gel point) to 21 (maximum suspension thickness) resulted in nanofibril films with higher crystallinity properties, uniform thickness, compacted morphology, and smoother surface. Nanofibril films formed after different numbers of passages exhibited similar mechanical strength, but distinct barrier properties. Conclusion: Acai waste films produced with fibers submitted to 3 grinding cycles can be recommended for packaging applications that demand easily dissolving, such as instantaneous food. Oppositely, acai fibers subjected to 21 cycles in grinder provide films suitable for water-resistant packaging, ideal for secondary coatings of papers and paperboards.

Electron-Ion Coupling Mechanism to Construct Stable Output Performance Nanogenerator.

Recently, triboelectric nanogenerators (TENGs) have been promoted as an effective technique for ambient energy harvesting, given their large power density and high energy conversion efficiency. However, traditional TENGs based on the combination of triboelectrification effect and electrostatic induction have proven susceptible to environmental influence, which intensively restricts their application range. Herein, a new coupling mechanism based on electrostatic induction and ion conduction is proposed to construct flexible stable output performance TENGs (SOP-TENGs). The calcium chloride doped-cellulose nanofibril (CaCl2-CNF) film made of natural carrots was successfully introduced to realize this coupling, resulting from its intrinsic properties as natural nanofibril hydrogel serving as both triboelectric layer and electrode. The coupling of two conductive mechanisms of SOP-TENG was comprehensively investigated through electrical measurements, including the effects of moisture content, relative humidity, and electrode size. In contrast to the conventional hydrogel ionotronic TENGs that require moisture as the carrier for ion transfer and use a hydrogel layer as the electrode, the use of a CaCl2-CNF film (i.e., ion-doped natural hydrogel layer) as a friction layer in the proposed SOP-TENG effectively realizes a superstable electrical output under varying moisture contents and relative humidity due to the compound transfer mechanism of ions and electrons. This new working principle based on the coupling of electrostatic induction and ion conduction opens a wider range of applications for the hydrogel ionotronic TENGs, as the superstable electrical output enables them to be more widely applied in various complex environments to supply energy for low-power electronic devices.

Ultrathin, biomimetic multifunctional leaf-like silver nanowires/Ti3C2Tx MXene/cellulose nanofibrils nanocomposite film for high-performance electromagnetic interference shielding and thermal management

Herein, we reported an ultrathin, flexible and super conductive silver nanowires (Ag NWs) doped Ti3C2Tx/Cellulose nanofibrils (CNFs) films by constructing biomimetic leaf-vein scaffolds via a facile vacuum-assisted filtration. Leaf-vein structure was built by Ti3C2Tx nanosheets and Ag NWs, offering numerous junctions and forming 3D conductive skeletons. The Ag NWs doped Ti3C2Tx/CNFs film with 85 wt% Ti3C2Tx and 5 wt% Ag NWs exhibited extremely high electrical conductivity and superior electromagnetic interference shielding effectiveness (EMI SE) value with a small thickness of 6 µm in X-bands (8.2–12.4 GHz). Synergetic effect on the mechanical property was observed for film with 70 wt% Ti3C2Tx and 10 wt% Ag NWs, exhibiting EMI SSE/t of 19,613.5 dB cm2 g−1, much higher than Ti3C2Tx/CNFs film. The electron migrating and hopping in the leaf-like conductive networks would lead to the massive ohmic and dielectric losses on the dipole-rich surface of Ti3C2Tx nanosheets. Additionally, the proof-of-concept of the proven film used as a Joule heater for thermal management was ascertained, which possessed fast response, aging stability, high-precision and ultralow voltage supply (1–3 V). Due to those preferential characteristics, the biomimetic Ag NWs doped Ti3C2Tx/CNFs materials can be integrated into the emerging applications, such as intelligent garments, thermotherapy and wearable devices.

Natural lignocellulosic nanofibril film with excellent ultraviolet blocking performance and robust environment resistance

Due to the current state of ozone layer depletion and potential risk of skin cancer, researches on sustainable cellulose-based films with ultraviolet (UV) blocking capabilities has attracted widespread attention. However, pure cellulose-based film required UV absorbent to be incorporated because of its poor UV blocking ability. In this work, natural lignocellulosic nanofibril (LCNF) film was fabricated by vacuum filtration and pressing process without any complex chemical modification or adding UV absorbers. The residual lignin retained in LCNF was found to act as natural macro-molecular UV absorber. LCNF film with lignin content of 4.89–15.68% exhibited excellent thermal stability, and their UVA and UVB blocking were in the range of 81.4–99.5% and 96.7–100%, respectively. Moreover, LCNF film exhibited stable UV shielding performance under high temperature, UV irradiation, acidic or alkaline conditions, providing LCNF film with a long-term use capacity. Overall, LCNF film is more environmentally friendly and harmless, which shows high potentials in anti-counterfeiting materials, UV protection, and windshields for vehicles.

High-Throughput Tailoring of Nanocellulose Films: From Complex Bio-Based Materials to Defined Multifunctional Architectures.

This paper demonstrates a high-throughput approach to fabricate nanocellulose films with multifunctional performance using conventionally existing unit operations. The approach comprises cast-coating and direct interfacial atmospheric plasma-assisted gas-phase modification along with the microscale patterning technique (nanoimprint lithography, NIL), all applied in roll-to-roll mode, to introduce organic functionalities in conjunction with structural manipulation. Our strategy results in multifunctional cellulose nanofibrils (CNF) films in which the high optical transmittance (∼90%) is retained while the haze can be adjusted (2–35%). Concomitantly, the hydrophobic/hydrophilic balance can be tuned (50–21 mJ/m2 with the water contact angle ranging from ∼20 up to ∼120°), while intrinsic hygroscopicity of CNF films is not significantly compromised. Therefore, a challenge to produce multifunctional bio-based materials with properties defined by various high-performance applications conjoined to the lack of efficient processing strategies is elucidated. Overall, economically and ecologically viable strategy, which was realized by facile and upscalable unit operations using the R2R technology, is introduced to expand the properties’ spaces and thus offer a vast variety of interesting applications for CNF films.

TEMPO-oxidized cellulose nanofibril film from nano-structured bacterial cellulose derived from the recently developed thermotolerant Komagataeibacter xylinus C30 and Komagataeibacter oboediens R37–9 strains

Bacterial cellulose (BC), prepared from two recently developed thermotolerant bacterial strains (Komagataeibacter xylinus C30 and Komagataeibacter oboediens R37–9), were used as a raw material to synthesize nanofibril films. Field-emission scanning electron microscope (FE-SEM) observations confirmed the ultrafine nano-structure of BC pellicle (BCP) with average fibril widths between 50 and 60 nm. The BC was directly oxidized in a TEMPO/NaBr/NaClO system at pH of 10 for 2 h. TEMPO-oxidized bacterial cellulose nanofibrils (TOBCN) were obtained by a mild mechanical treatment and the TOBCN films were prepared through heat-drying. The oxidation yielded a recovery ratio between 70 and 80% by weight with an increase in the carboxylate content of 0.9–1.0 mmol g −1. Nanofibrillation yields were more than 90% and the resulting high aspect ratio TOBCNs were ~6 nm in average width with >800 nm in lengths, when observed under transmission electron microscope (TEM). TOBCN film of K. xylinus C30 exhibited high transparency (79%), tensile strength (142 MPa), Young's modulus (7.13 GPa), elongation around failure (3.89%), and work of fracture (2.29 MJ m−3), when compared to the TOBCN films of K. oboediens R37–9 at 23 °C and 50% RH. Coefficients of thermal expansion of both the TOBCN films were low at around 6 ppm K−1.

Procuring the nano-scale lignin in prehydrolyzate as ingredient to prepare cellulose nanofibril composite film with multiple functions

Cellulose is lack of UV-blocking and antibacterial properties, which have limited its application. In this work, the nanoscale lignin with high content of hydroxyl groups and small particle size in prehydrolysate was isolated and used as a green reinforcement ingredient for fabrication of cellulose nanofibril (CNF) films with excellent mechanical properties, as well as UV protection and antibacterial capabilities. Cryogenic transmission electron microscopy (Cryo-TEM) and nuclear magnetic resonance analyses showed that the resulting lignin was in the form of nanoparticles (6–12 nm) with high phenolic hydroxyl contents (4.9 mmol/g). The optimum lignin inclusion rate of 5% allowed it to reinforce CNF composite film, increasing its tensile strength from 108.5 to 143.3 MPa. In addition, the film exhibited excellent UV protection capabilities. It blocked 91.5% of UV-A and 99.9% of UV-B light. Finally, the resulting lignin-based CNF films exhibited antibacterial activities against both Escherichia coli and Streptococcus hemolyticus. This work demonstrates the utility of nanoscale lignin from prehydrolysate can be used to produce cellulose-based composite films with valuable properties.

Favorable combination of foldability and toughness of transparent cellulose nanofibril films by a PET fiber-reinforced strategy

Transparent cellulose nanofibril (CNF) films have been considered a promising sustainable alternative for nonrenewable and nonbiodegradable petroleum-based plastic films. However, their relatively low toughness and poor folding endurance are two remaining challenges for commercial application. In this work, inspired by fiber-reinforced polymer, a transparent CNF film with favorable combination of toughness and folding endurance is demonstrated by a facile and scalable polyethylene terephthalate (PET) fiber-reinforced strategy. The as-prepared PET fiber-reinforced CNF film not only exhibits a maximum average toughness of 13.7 ± 2.4 MJ/m3 that is nearly 4 times stronger than that of pure CNF film (3.7 ± 1.1 MJ/m3), but also presents superior bending flexibility with a folding endurance of over 104 times that is an order of magnitude higher than that of pure CNF film (~4 × 103 times). Moreover, its underlying principle for the enhanced toughness and foldability is explored. This work provides a facile strategy to prepare tough yet foldable CNF film and could promote its industrial uses in the fields of energy storage devices, packaging, and electronic devices.

Binding affinity of family 4 carbohydrate binding module on cellulose films of nanocrystals and nanofibrils

The binding affinity and thermodynamics of family 4 carbohydrate-binding module (CBM4), belonging to type B CBM, on model surfaces of cellulose nanocrystals (CNC) and nanofibrils (CNF) were investigated by quartz crystal microbalance with dissipation monitoring (QCM-D) technology in real-time at different temperatures. The thermodynamic parameters associated with the interaction, such as Gibbs free energy, enthalpy change, entropy change and heat capacity were obtained using the van’t Hoff analysis via a nonlinear parameter estimation. The results demonstrated CBM4 binds preferentially to both CNF and CNC, whereas the driving forces behind them were very different. The former was related to the hydrogen bonds formed in the CBM4 clefts, resulting in a favorable enthalpy but compensated by unfavorable entropy change; on the contrary, the latter was mainly driven by favorable entropy but compensated by unfavorable enthalpic change due to water rearrangement.

Modification of cellulose degree of polymerization by superheated steam treatment for versatile properties of cellulose nanofibril film

Cellulose from oil palm empty fruit bunch (OPEFB) was subjected to superheated steam (SHS) treatment at 150 °C for 1 and 2 h to produce cellulose with different degree of polymerization (DP). The treated OPEFB cellulose was subjected to a wet disc milling process to produce cellulose nanofibrils (CNFs), followed by nanocellulose film production using casting-evaporation technique. Reduction of DP by 23 and 40% were recorded after SHS treatment of OPEFB cellulose for 1 h (SHS1) and 2 h (SHS2), respectively, as compared to the untreated OPEFB cellulose. CNFs produced from treated cellulose (CNF-SHS1 and CNF-SHS2) exhibited smaller diameter and were less entangled compared to CNF from untreated cellulose (CNF-UT). These contributed to smoother CNF-SHS films. The highest light transmittance was recorded for CNF-SHS2 film, followed by CNF-SHS1 and CNF-UT films. The increment in transmittance value is in accordance with the reduction in cellulose DP. Lower DP also caused CNF-SHS films to have less wetting property as a result of smoother film surface. Mechanical properties were affected by DP values suggesting the possibility to control mechanical properties of CNF films in relation to DP. Overall, SHS is an efficient treatment method to reduce cellulose DP with the advantage of controlling CNF film properties towards the production of a versatile CNF film.

In-Situ Growth of Metal Oxide Nanoparticles on Cellulose Nanofibrils for Dye Removal and Antimicrobial Applications

Nanocellulose is known to act as a platform for the in-situ formation of metal oxide nanoparticles, where the multiple components of the resultant hybrids act synergistically toward specific applications. However, typical mineralization reactions require hydrothermal conditions or addition of further reducing agents. Herein, we demonstrate that carboxylated cellulose nanofibril-based films can spontaneously grow functional metal oxide nanoparticles during the adsorption of heavy metal ions from water, without the need of any further chemicals or temperature. Despite the apparent universality of this behavior with different metal ions, this work focuses on studying the in-situ formation of copper oxide nanoparticles on TOCNF films as well as the resultant hybrid films with improved functionality toward dye removal from water and antimicrobial activity. Using a combination of cutting-edge techniques (e.g., in-situ SAXS and QCMD) to systematically follow the nanoparticle formation on the nanocellulosic films in real time, we suggest a plausible mechanism of assembly. Our results confirm that carboxylated cellulose nanofibril films act as universal substrate for the formation of metal oxide nanoparticles, and thus hybrid nanomaterials, during metal ion adsorption processes. This phenomenon enables the upcycling of nanocellulosic materials through multistage applications, thus increasing its sustainability and efficiency in terms of an optimal use of resources.

Transparent tempo oxidized cellulose nanofibril (TOCNF) composites with increased toughness and thickness by lamination

The favorable mechanical properties and performance of TEMPO-oxidized cellulose nanofibril (TOCNF) films has been limited by their brittleness and the incapability of obtaining thick enough materials for self-supported applications. In this study, lamination with room temperature curable epoxy was used to combat brittleness, increase thickness, and produce a more damage tolerant material. The effect of the volume fraction and layer thickness of both phases (e.g., TOCNF, epoxy), the number of layers, and the overall total thickness of the laminate, on the tensile and flexural properties are investigated. Lamination was successful at increasing the toughness and thickness of TOCNF composites, resulting in an increased work of fracture that was associated with fracture retardation by crack digression in three-point bending specimens. The ultimate tensile strength and Young’s modulus were higher for laminates with low volume fractions of epoxy although not statistically different than the neat TOCNF films, but decreased with increasing volume fraction of epoxy, and with increasing number of TOCNF layers.

A Comparative Analysis of the Characteristics of Cellulose Nanofibril Films Fabricated by Batch-Wise Mode

A Comparative Analysis of the Characteristics of Cellulose Nanofibril Films Fabricated by Batch-Wise Mode

High-performance flexible freestanding polypyrrole-coated CNF film electrodes for all-solid-state supercapacitors

Nowadays, supercapacitors based on cellulose nanofibril (CNF) films have attracted extensive interest due to their excellent flexibility, light weight, and unique structure. Herein, we report that highly conductive films are prepared through polypyrrole (PPy) coating on CNF films by a simple and low-cost “soak and polymerization” method. The optimized flexible film features a high electrical conductivity of 23.77 S cm−1, a superior tensile strength of 71.4 MPa, outstanding conductance stability, and a good thermal stability. Additionally, the hybrid film as a freestanding and binder-free supercapacitor electrode can provide a high areal capacitance (2.26 F cm−2 at 2 mA cm−2) and good cyclic stability (a capacitance retention of 70.5% after 5000 cycles). Remarkably, an all-solid-state flexible supercapacitor assembled by two pieces of the optimized PPy-coated CNF (PPy/CNF) film electrodes delivers an excellent areal capacitance of 1.39 F cm−2 at 0.1 mA cm−2, revealing an ultrahigh energy density of 16.95 mWh cm−3 at a power density of 1.2 mW cm−3.

Hydrophobization, smoothing, and barrier improvements of cellulose nanofibril films by sol–gel coatings

Single-layer films from cellulose nanofibrils on a plastic support were coated with sol–gel coated with inorganic–organic copolymers (ORMOCER®s), consisting of inorganic Si–O–Si-based networks combined with ceramic (Al–O– and Zr–O–) groups and special organic fluoroalkyl chain containing functional groups. Sol–gel coatings decreased the surface hydrophilicity and water vapor transmission rate. The water contact angle of uncoated films was 24°, indicating high affinity between water and the cellulose nanofibrils. All sol–gel coatings tested increased the surface hydrophobicity with the contact angles ranging between 54° and 102°. The water vapor transmission rates varied between 230 and 410 g/m2/day. With UV curable highly organically crosslinked coating, the water vapor transmission rate was decreased by 77% as compared to uncoated film. The uncoated film had oxygen transmission rates of 0.7 and 107 cc/m2/day at 50% and 80% RH, respectively. At high humidity conditions, the films tended to swell, thus allowing permeation to increase. Sol–gel coatings significantly improved the oxygen barrier properties especially at 80% RH. The transmission rates varied between 0.4 and 0.5 cc/m2/day (50% RH) and between 51 and 86 cc/m2/day (80% RH).

Tannin-stabilized silver nanoparticles and citric acid added associated to cellulose nanofibrils: effect on film antimicrobial properties

The aim of this work was to evaluate the potential of cellulose nanofibrils (CNFs) films treated with commercial solution of Ag nanoparticles stabilized with natural tannin and silane groups in the bacteria growth inhibition. The films were produced with commercial pulps of pine and eucalyptus treated with sodium hydroxide (5% w/v) and calcium hydroxide (10% w/v), respectively. The bacteria selected for the inhibition test were the gram-positive Listeria monocytogenes and gram-negative Salmonella enteriditis. The films performance was investigated by the antimicrobial activity using disc diffusion. In addition, the pulps were evaluated by their chemical composition, water retention index (WRI) and X-ray diffraction (XRD). The content of hemicelluloses in the treated pine pulp (11.32%) was lower in comparison to the found in the treated eucalyptus pulp (14.46%). The XRD diffractogram presented higher crystallinity index for the treated eucalyptus pulp (70%) with a characteristic peak of calcium carbonate. The treated eucalyptus pulp showed higher WRI and viscosity values in relation to the treated pine pulp. Growth inhibitory halos were more expressive when the treatment with both antimicrobial solutions were proceeded in the films produced with pine CNFs with addition of the citric acid. The effect of the nanoparticles stabilized with tannin must be highlighted, mainly on the bacterium S. enteriditis.