Nanocellulose Films Research Articles

Some Practical Aspects of Nanocellulose Film: Characterization, Expansion and Shrinking Tests, and Techniques to Create Remoistenable Nanocellulose

Abstract Microfibrillated cellulose (MFC), commonly referred to as nanocellulose, is an emerging conservation material with significant potential for application in a wide range of conservation treatments. Due to its properties of transparency and mechanical strength, nanocellulose film offers novel potential when thin tissues may not be suitable. However, when water or aqueous adhesives are applied to nanocellulose, it loses stability and becomes pulpy, making practical use problematic. Additionally, nanocellulose film can shrink upon drying, causing planar deformation. For these reasons, adhesives used with nanocellulose are limited in published treatments to date. The nanocellulose film used in this study was characterized and expansion and shrinking tests were conducted to better understand how nanocellulose film reacts when water and ethanol are introduced. The potential of using nanocellulose film in a remoistenable form is also explored. Results found that nanocellulose film behaved differently than Japanese tissue when water was introduced. While each expanded when water was introduced, the nanocellulose film shrunk 11 % from its initial size when dry, whereas the Japanese tissue returned to its initial size. Practical techniques are recommended to create remoistenable nanocellulose film with a selection of adhesives. Notably, remoistenable nanocellulose films created with methylcellulose and gelatine showed promising initial results.

Tailoring the performance of nanocellulose-based multilayer-barrier paperboard using biodegradable-thermoplastics, pigments, and plasticizers

In this work a multilayer barrier paperboard was produced in a roll-to-roll process by slot-die coating of nanocellulose (microfibrillated cellulose or carboxymethylated cellulose nanofibrils) followed by extrusion coating of biodegradable thermoplastics (polylactic acid, polybutylene adipate terephthalate and polybutylene succinate). Hyperplaty kaolin pigments were blended in different ratios into nanocellulose to tailor the barrier properties of the multilayer structure and to study their influence on adhesion to the thermoplastic top layer. Influence of a plasticizer (glycerol) on flexibility and barrier performance of the multilayer structure was also examined. Water vapor permeance for the multilayer paperboard was below that of control single-layer thermoplastic materials, and oxygen permeance of the coated structure was similar or lower than that of pure nanocellulose films. Glycerol as a plasticizer further lowered the oxygen permeance and kaolin addition improved the adhesion at the nanocellulose/thermoplastic interface. The results provide insight into the role played by nanocelluloses, thermoplastics, pigments, and plasticizers on the barrier properties when these elements are processed together into multilayer structures, and paves the way for industrial production of sustainable packaging.

CO2 Escaping In Situ Endowed the Antimicrobial Nanocellulose Packaging Film with a Microporous Structure

The atmosphere and the mold under high humidity severely determine the shelf-life of fruits and vegetables. The microporous structure is helpful to regulate the atmosphere in the package. In this study, we designed a nanocellulose film with a microporous structure by CO2 escaping in situ. The microporous structure provided a pathway that enhanced the gas transmission rate, with the porosity of the film reaching 79.60% and O2 and CO2 transmission reaching 115.57 ± 1.81 cm3/m2 day bar and 145.91 ± 11.71 cm3/m2 day bar, respectively. Polyethyleneimine was exposed around the micropores accompanied by CO2 escaping in situ, which endowed the film with excellent antimicrobial property. The film could regulate the atmosphere and inhibit the microbial growth to maintain the color and taste of green plums and loquats for a long time. CO2 escaping in situ provides a green and sustainable strategy for the development of packaging materials of the microporous structured nanocellulose films with antimicrobial property.

UV-blocking composite films containing hydrophilized spruce kraft lignin and nanocellulose: Fabrication and performance evaluation

The development of biodegradable films with good UV-blocking and mechanical properties is of great significance for the alleviation of plastic pollution and the establishment of a sustainable society. Given that most natural biomass–derived films have poor mechanical and UV aging properties and are therefore of limited applicability, additives capable of mitigating these drawbacks are highly sought after. In particular, industrial alkali lignin, which is a byproduct of the pulp and paper industry, features a benzene ring–dominated structure with abundant active functional groups and is therefore a promising natural anti-UV additive and composite reinforcing agent. However, the commercial applications of alkali lignin are hindered by its structural complexity and polydispersity. Herein, spruce kraft lignin was fractionated and purified using acetone, subjected to structural characterization, and then quaternized based on the obtained structural data to increase water solubility. TEMPO-oxidized cellulose was supplemented with quaternized lignin at different loadings, and the mixtures were homogenized under high pressure to obtain uniform and stable lignin-containing nanocellulose dispersions, which were subsequently converted into films through suction filtration–based dewatering under pressure. The quaternization of lignin improved its compatibility with nanocellulose and endowed the corresponding composite films with excellent mechanical properties as well as high visible light transmission and UV-blocking performance. The film with a quaternized lignin loading of 6 % had UVA and UVB shielding efficiencies of 98.3 and 100 %, respectively, and featured a tensile strength (175.2 MPa) and elongation at break (7.6 %) that were 50.4 % and 72.7 % higher than those of the pure nanocellulose (CNF) film prepared under the same conditions, respectively. Thus, our work provides a cost-effective and viable method of preparing fully biomass–derived UV-blocking composite films.

Highly hydrophobic and moisture barrier nanocellulose based films produced via spray deposition

Nanocellulose (NC) films are gaining popularity in recent years owing to their recyclability and biodegradability; however, the commercialization of this material is limited by environmental and moisture barrier constraints. The incorporation of carboxymethyl cellulose (CMC) with NC significantly improved the barrier performance but the resultant films were quite hydrophilic and hence completely disintegrated in water. The aim of this study is to produce hydrophobic NC/CMC films without compromising their barrier characteristics. For this purpose, the optimized content of alkyl ketene dimer (AKD) was spray-deposited on the fully and partially dried NC/CMC films and their hydrophobic, barrier and mechanical properties were assessed. The deposition of AKD has improved the hydrophobicity and flexibility while maintaining the barrier properties of the films. However, their tensile index values decreased by 26–29% as compared with the neat NC/CMC films, but the values remained in acceptable range. Additionally, the partially dried spray deposited AKD-NC/CMC films have shown superior results as they showed higher hydrophobicity (θ = 127° ± 3), while lower percentage of mass loss after immersion for 48 h in water (15%) as compared with the fully dried spray deposited AKD-NC/CMC films.Graphical abstract

Resilient high oxygen barrier multilayer films of nanocellulose and polylactide

Nanocelluloses are promising high gas barrier materials for biobased food packaging, but they must be protected from water to preserve high performance. The respective O2 barrier properties of different types of nanocelluloses were compared (nanofibers (CNF), oxidized nanofibers (CNF TEMPO) and nanocrystals (CNC)). The oxygen barrier performance for all types of nanocelluloses was similarly high. To protect the nanocellulose films from water, a multilayer material architecture was used with poly(lactide) (PLA) on the outside. To achieve this, a biobased tie layer was developed, using Corona treatment and chitosan. This allowed thin film coating with nanocellulose layers between 60 and 440 nm thickness. AFM images treated with Fast Fourier Transform showed the formation of locally-oriented CNC layers on the film. Coated PLA(CNC) films performed better (3.2 × 10−20 m3.m/m2.s.Pa) than PLA(CNF) and PLA(CNF TEMPO) (1.1 × 10−19 at best), because thicker layers could be obtained. The oxygen barrier properties were constant during successive measurements at 0 % RH, 80 % RH and again at 0 % RH. This shows that PLA is sufficiently shielding nanocelluloses from water uptake to keep high performance in an extended range of RH and opens the way to high oxygen barrier films which are biobased and biodegradable.

Diffusion of Thyme, Cinnamon and Oregano essential oils in different nanocellulose matrices

Solubility and diffusivity of Thyme, Cinnamon and Oregano essential oils in nanocellulose films, with different carboxymethylation degree, were investigated in view of potential use in active packaging applications.Solubility of liquid essential oils resulted to increase with the carboxymethylation degree for both Oregano and Thyme, while it was non-monotonous for Cinnamon. Thyme showed the higher solubility (about 20%wt) followed by Cinnamon and Oregano.The sorption kinetics of liquid essential oils was substantially Fickian. The diffusivity also increased with the increase of the carboxymethylation degree, going from 9.6 × 10−9 cm2⁄s, observed for oregano in pure nanocellulose, to 2.0 × 10−8 cm2⁄s, measured for Cinnamon in the most charged one.The release in vapor phase showed two different kinetics: a faster one dominating at short times and a slower one visible at long times. Fickian diffusion described the behaviour of most of the samples even if in some case data were better fitted by using exponential functions. In general, Diffusivities values ranged from 10−9 to 10−11 cm2⁄s for the fast process and from 10−11 to 10−13 cm2⁄s, for the slow one.Carboxymethylation degree also affected the release kinetics of antimicrobial essential oils, which therefore can be tuned by appropriate choice of the nanocellulose material.

Capacitive and Resistive Humidity Sensors Based on Flexible Nanocellulose Film for Wearable Electronics

Capacitive and Resistive Humidity Sensors Based on Flexible Nanocellulose Film for Wearable Electronics

Effect of bonding on the structure and properties of nanocellulose films

In this study, cellulose nanofibers (CNF) were obtained by chemical pretreatment using a rubberwood substrate. Different forms of drying were used to prepare three CNF film variants. Each of the films was rehydrated and hot-pressed to introduce more hydrogen bonds, and the films were characterized in terms of density and porosity, micromorphology, and mechanical properties. The mechanical properties of the films improved substantially after rehydration and hot-press drying. The tensile strengths of the films increased to approximately two to three times that of the original CNF films. These results with micromorphological observations suggest that adjusting the water content during CNF drying can significantly improve the formation of 3D networks in the films, thus imparting higher hydrogen bonding content to the films and improving the mechanical properties of the substrates. This study provides a theoretical basis for the formation of high-strength materials through water molecule-induced assembly and broadens the application of biomass cellulose materials in emerging fields.

Understanding viscoelastic behavior of hybrid nanocellulose film based on rheological and electrostatic observation in blended suspension

The effects of TEMPO-mediated oxidized cellulose nanofibril (TOCN) on the viscoelastic behavior and phase of cellulose nanocrystal (CNC) in suspension and film were investigated using polarized optical microscopy, rotational rheometry, and dynamic mechanical analysis. The sodium cation from TOCN changed the electrostatic state of CNC by screening the CNC surface charge. The volume inflation of TOCN locally increased the CNC concentration in the suspension. In turn, the CNC–CNC interactions increased the viscosity and the yield stress. Based on the experimental observation, the changing mechanisms of electrostatic state and particular interaction in the TOCN/CNC suspensions were suggested. In the hybrid film, the time dependency of complex moduli was changed owing to the different networking between CNCs and TOCNs. The CNC–CNC contacts easily collapsed by strain, while the TOCN–TOCN entanglements were slowly altered. This study provides a fundamental understanding of CNC behavior for optimizing processes and composite properties.

Study of nano cellulose-based membrane tailorable biodegradability for use in the packaging application of electronic devices

With a growing demand for packaging materials and witnessing many landfills and huge garbage islands floating in the Pacific oceans, the need for an alternative material such as bio-degradable plastics has risen. Cellulose-based materials are already in use in several packaging industries. Nanocellulose, a processed cellulose with a specific nanostructure, have several advantages such as high specific strength, modulus, high surface area and unique optical properties. By varying the crosslinking percentages, the kinetics of degradation can be tailored. In this work, extracted cellulose from sugarcane bagasse was hydrolyzed to obtain nanocellulose, which was used to fabricate packaging films (membrane) with PVA as matrix and nanocellulose. Variations of PVA and nanocellulose loadings, and crosslinking agent ratios. In the fabricated films were investigated for chemical, mechanical, optical, thermal, and topographical properties. Results from the degradation tests under appropriate physically simulated environments have suggested that the crosslinking has enhanced the mechanical properties, extent of degradation was dependent on percentages of crosslinking. A real-world device packaging application was demonstrated by encapsulation of perovskite solar cells with the fabricated nanocellulose film revealed that the lifetime of the devices improved which might be indicative of the film having lower permeability for oxygen and moisture.

Three-dimensional bioprinting and electrospinning of cellulose nanocrystal/polycaprolactone for tracheal scaffolds

Three-dimensional printing (3DP) has high flexibility and controllability, and has attracted extensive attention in the biomedical field. However, the scaffolds prepared only by 3D bioprinting have poor mechanical properties, and they cannot effectively carry the required drugs. At the same time, compared with the size of cells, the pore size of 3D printed scaffolds is relatively large, and the efficiency of cell inoculation and tissue formation are still limited by the pore resolution of scaffolds. Therefore, a new method of forming 3D printing trachea composites is proposed. When combined, 3D bioprinting and electrospinning (ESP) can overcome the issues associated with scaffolds prepared by 3D bioprinting alone. Nanofibers create a suitable environment for cell growth. In terms of material use, Polycaprolactone (PCL) is commonly used as an ideal material source for 3D printing, but its biomechanical properties are insufficient. Cellulose nanocrystals (CNC) can effectively improve the properties of polymers such as PCL. Therefore, the inner layer of the scaffold used in tracheal surgery is created from PCL/CNC composite by 3D bioprinting, and the outer nano-cellulose film is deposited on the inner surface by electrospinning. Mechanical properties and cell adhesion/growth of scaffolds prepared by 3D bioprinting combined with electrospinning were found to be superior to those of scaffolds prepared by 3D bioprinting.

Multimode Anticounterfeiting Labels Based on a Flexible and Water-Resistant NaGdF4Yb3+,Er3+@Carbon Dots Chiral Fluorescent Cellulose Film.

Advanced fluorescent anticounterfeiting technology has attracted a great deal of attention and inspired researchers to develop reliable fluorescent materials with multimodal luminescence. Herein, hydrophobic NaGdF4:Yb3+,Er3+ nanoparticles with dual-mode luminescence were prepared through a one-step solvothermal method using oleic acid as a chelating agent and octadecene as a solvent. The as-synthesized sample was found to provide both green upconversion luminescence and blue downconversion luminescence at excitation wavelengths of 365 and 980 nm. The structure and composition analysis showed that the as-obtained samples were spherical NaGdF4:Yb3+,Er3+@carbon dots (CDs) with a 14.5 ± 0.2 nm particle size and good dispersity in nonpolar solvents. Subsequently, NaGdF4:Yb3+,Er3+@CDs were coated on a cholesteric nanocellulose film with structural color to prepare multimode circularly polarized fluorescent materials. The prepared composite film is flexible and water-resistant, meaning that it is very suitable for anticounterfeiting labels, not only providing a simple and rapid synthesis method with which to prepare multimode fluorescent materials but also presenting a novel anticounterfeiting technology.

Water-soluble polysaccharides promoting production of redispersible nanocellulose

To date, the energy-intensive production and high-water content severely limits nanocellulose applications on a large scale off-site. In this study, adding water-soluble polysaccharides (PS) to achieve an integrated process of water-redispersible nanocellulose production was well established. The addition of PS, in particular carboxymethylated-galactoglucomannan (cm-GGM), facilitates fibre fibrillation enabling homogenization at a higher solid content at 1.5 wt% compared with around 0.4 wt% for neat fibre. More importantly, the addition of cm-GGM saved 73 % energy in comparison without PS addition. Good water redispersibility of thus-prepared nanocellulose was validated in viewpoints of size distribution, morphology, viscosity and film properties as compared with neat nanocellulose. The tensile strength and optical transmittance of nanocellulose films increased to 116 MPa and 77 % compared to those without PS addition of 62 MPa and 74 %, respectively. Collectively, this study provides a new avenue for large-volume production of redispersible nanocellulose at a high solid content with less energy-consumption.

Paraffin particle dispersion costabilized by W-doped VO2 nanoparticles and chitosan for the fabrication of functional nanocellulose film

The development of functional window films for energy savings and privacy protection has attracted considerable attention. Herein, a functional nanocellulose film was fabricated via a papermaking technique by using the naturally formed network structure of nanocellulose film to obtain privacy protection and to encapsulate paraffin particles stabilized by W-doped VO2 nanoparticles and chitosan. The paraffin particles stabilized by W-doped VO2 nanoparticles and chitosan were prepared via an emulsion approach without using surfactant. The incorporation of paraffin into the nanocellulose film not only enhances the latent heat and lowers the forward transmittance of the nanocellulose film but also improves its hydrophobicity. The presence of a small amount of W-doped VO2 nanoparticles in the paraffin particle dispersion further increases the forward transmittance and latent heat of the nanocellulose film, especially at elevated temperatures. Meanwhile, the introduction of chitosan in the paraffin particle dispersion significantly improves the toughness of the nanocellulose film. Consequently, the incorporation of paraffin particles endows the nanocellulose film with hydrophobicity and toughness as well as good privacy protection and thermal insulation for energy savings at both room and elevated temperatures, making the as-prepared nanocellulose film a promising functional window film.

Preparation of hemp nanocellulose and its use to improve the properties of paper for food packaging

The study describes the preparation of nanocellulose from organosolv hemp pulp and its application in the production of food packaging paper as an alternative to petroleum products. OHP was obtained from renewable plant materials hemp fibers by extraction with NaOH solution and cooking using a mixture of acetic acid and hydrogen peroxide. A stable transparent nanocellulose gel was extracted from OHP by acid hydrolysis followed by ultrasonic treatment. It was found that an increase in the consumption of sulfuric acid, temperature and duration of the OHP hydrolysis process improved the quality indicators of hemp nanocellulose. A linear dependence of the tensile strength and transparency of nanocellulose films on their density has been established. Morphological (SEM), structural (FTIR and XRD) and thermal analysis (TGA) of hemp fibers, OHP and nanocellulose were carried out. Nanocellulose films had a density of up to 1.56 g/cm3, a tensile strength of up to 66.7 MPa, a transparency of up to 87.3%. Atomic force microscopy method showed that the transverse dimension of nanocellulose particles is from 8 to 23 nm. Hemp nanocellulose had a higher crystallinity index (87.2%) than OHP (72.0%), but lower thermal stability. The positive effect of adding nanocellulose from hemp on improving all quality parameters of paper for food packaging has been shown. The addition of 2% hemp nanocellulose makes it possible to obtain paper that exceeds the breaking force requirements of premium grade paper by 40%, and the breaking length increases by 42% compared to paper without chemical additives.

Highly Aligned Bacterial Nanocellulose Films Obtained During Static Biosynthesis in a Reproducible and Straightforward Approach.

Bacterial nanocellulose (BNC) is usually produced as randomly‐organized highly pure cellulose nanofibers films. Its high water‐holding capacity, porosity, mechanical strength, and biocompatibility make it unique. Ordered structures are found in nature and the properties appearing upon aligning polymers fibers inspire everyone to achieve highly aligned BNC (A‐BNC) films. This work takes advantage of natural bacteria biosynthesis in a reproducible and straightforward approach. Bacteria confined and statically incubated biosynthesized BNC nanofibers in a single direction without entanglement. The obtained film is highly oriented within the total volume confirmed by polarization‐resolved second‐harmonic generation signal and Small Angle X‐ray Scattering. The biosynthesis approach is improved by reusing the bacterial substrates to obtain A‐BNC reproducibly and repeatedly. The suitability of A‐BNC as cell carriers is confirmed by adhering to and growing fibroblasts in the substrate. Finally, the thermal conductivity is evaluated by two independent approaches, i.e., using the well‐known 3ω‐method and a recently developed contactless thermoreflectance approach, confirming a thermal conductivity of 1.63 W mK−1 in the direction of the aligned fibers versus 0.3 W mK−1 perpendicularly. The fivefold increase in thermal conductivity of BNC in the alignment direction forecasts the potential of BNC‐based devices outperforming some other natural polymer and synthetic materials.

A biodegradable cellulose-based flame-retardant triboelectric nanogenerator for fire warning

Triboelectric nanogenerator (TENG) is a type of disruptive high-entropy energy technology for the era of internet of things that drives the ubiquitous innovations of flexible/wearable electronics and sensor networks. However, developing a flexible TENG with a high sensitivity temperature response and fire warning capabilities is challenging. Here, we demonstrate a flexible, biodegradable, single electrode cellulose-based TENG with flame retardancy (FR-TENG) that is fabricated by biocompatible black phosphorus (BP) and phytic acid (PA) as flame retardants. The corresponding peak heat release rate and the total heat release rate values of FR-TENG are reduced by 64.6% and 47.6% compared with pure nanocellulose film, respectively, and the limiting oxygen index is increased to 39.1%. The FR-TENG exhibits an output of 116 V and 3.02 mA·m−2 at 2 Hz, indicating the application prospect of source for wearable electronics. An exciting feature of the FR-TENG is its resistance response to temperature with a high thermal index of 3779.16 K in the range of 35–150 ℃, which can be used as a temperature sensor to achieve quickly respond to temperature changes and fire warnings within 5 s. Therefore, the cellulose-based FR-TENG provides an idea to develop advanced multifunctional wearable electronics with potential applicability as sensors and fire alarms for firefighting and industrial applications.

Preparation of coumarin polymer grafted nanocellulose films to form high performance, photoresponsive barrier layers

AbstractHydrophobically modified cellulose is prepared in this research by conducting atom transfer radical polymerization (ATRP) of methacrylate substituted coumarin monomer on initiator grafted cellulose. The photocrosslinking of uniformly grafted coumarin on cellulose surface is applied to improve the water vapor barrier property of the film. The water vapor transmission rate (WVTR) of films prepared from modified cellulose with varying grafting density, grammage, and photocrosslinking time is studied. By increasing the amount of crosslinking within the grafted cellulose film, we succeeded in reducing WVTR. The WVTR is reduced from 160 to 20 g/m2/day using a sheet of 60 g/m2 after crosslinking. The effect of grafting density on WVTR is also analyzed to observe that the higher the grafting density, lower the WVTR of the sheet both before and after crosslinking. Furthermore, free ATRP polymerization (without cellulose) and polymerization using a sacrificial initiator of the monomer are conducted to estimate the dispersity of the polymer on cellulose. The monomer, free polymer and cellulose grafted polymers are analyzed for the composition, thermal, morphology, photoresponsive behavior, and polymerization quantification using NMR, FTIR, UV–Vis, TGA DSC, GPC, SEM, ICP‐MS. It is concluded that the inter and intramolecular photo dimerization of coumarin molecules forms a hydrophobic crosslinked hyper network in the polymer sheet, which improves its barrier property.

Wood based quasi-solid-state Zn-air battery with dual honeycomb-like porous carbon and cationic nanocellulose film

Conversion of low-value biomass to hierarchically porous carbon-based materials for oxygen reduction reactions (ORR), without using conventional template methods, is of particular significant for energy storage technology. Herein, dual honeycomb-like porous carbon inspired by multiscale structure of wood was assembled with cationic nanocellulose film into Zn-air battery. Nitrogen-doped hierarchically porous carbon was obtained by a simple two-step process involving alkaline extraction and pyrolysis with NH4Cl. Alkaline extraction was utilized for partially degrading lignin and heterosaccharide from unprocessed wood to create a porous wood with numerous nanopores and 3D loose structure. The inner and outer parts of obtained porous wood were further pore-optimized and doped with NH4Cl by a consequent pyrolysis step. The resulting carbon-based material (AHWC) possessed high specific surface area (1601.8 m2 g−1), well-developed hierarchical porosity, and high N content enabled excellent electrocatalytic oxygen reduction performance. Compared with commercial Pt/C catalysts in KOH electrolyte, AHWC exhibits nearly two times higher kinetic currents in the low overpotential region, comparable number of transferred electrons, and significantly higher operating stability. This carbon-based material also showed an excellent capacity and energy density equal to 792 mA h g−1 and 927 W h kg−1, together with superior long-term durability (200 h at the current density of 10 mA cm−2) when assembled as the active electrode material into a Zn-air battery. Additionally, cationic modified nanocellulose film (C-CNF-M), acting as a solid electrolyte, was assembled with AHWC for a quasi-solid-state Zn-air battery which exhibited excellent specific capacity (672.2 mA h g−1), energy density (644.11 W h kg−1) and cycling stability (500 min at 1 mA cm−2). The AHWC establish a bridge between papermaking and the field of energy storage by green conversion of biomass and fabrication of porous carbon-based materials and cellulose based electrolyte with excellent properties applicable to electrochemical energy devices.