TEMPO-oxidized nanocellulose films derived from coconut residues: Physicochemical, mechanical and electrical properties

Nanocellulose-stabilized nanocomposites for effective Hg(II) removal and detection: a comprehensive review

Mercury pollution, with India ranked as the world's second-largest emitter, poses a critical environmental and public health challenge and underscores the need for rigorous research and effective mitigation strategies. Nanocellulose is derived from cellulose, the most abundant natural polymer on earth, and stands out as an excellent choice for mercury ion remediation due to its remarkable adsorption capacity, which is attributed to its high specific surface area and abundant functional groups, enabling efficient Hg(II) ion removal from contaminated water sources. This review paper investigates the compelling potential of nanocellulose as a scavenging tool for Hg(II) ion contamination. The comprehensive examination encompasses the fundamental attributes of nanocellulose, its diverse fabrication techniques, and the innovative development methods of nanocellulose-based nanocomposites. The paper further delves into the mechanisms that underlie Hg removal using nanocellulose, as well as the integration of nanocellulose in Hg detection methodologies, and also acknowledges the substantial challenges that lie ahead. This review aims to pave the way for sustainable solutions in mitigating Hg contamination using nanocellulose-based nanocomposites to address the global context of this environmental concern.

A High-Stretching, Rapid-Self-Healing, and Printable Composite Hydrogel Based on Poly(Vinyl Alcohol), Nanocellulose, and Sodium Alginate

Hydrogels with excellent flexibility, conductivity, and controllable mechanical properties are the current research hotspots in the field of biomaterial sensors. However, it is difficult for hydrogel sensors to regain their original function after being damaged, which limits their practical applications. Herein, a composite hydrogel (named SPBC) of poly(vinyl alcohol) (PVA)/sodium alginate (SA)/cellulose nanofibers (CNFs)/sodium borate tetrahydrate was synthesized, which has good self-healing, electrical conductivity, and excellent mechanical properties. The SPBC0.3 hydrogel demonstrates rapid self-healing (<30 s) and achieves mechanical properties of 33.92 kPa. Additionally, it exhibits high tensile strain performance (4000%). The abundant internal ions and functional groups of SPBC hydrogels provide support for the good electrical conductivity (0.62 S/cm) and electrical response properties. In addition, the SPBC hydrogel can be attached to surfaces such as fingers and wrists to monitor human movements in real time, and its good rheological property supports three-dimensional (3D) printing molding methods. In summary, this study successfully prepared a self-healing, conductive, printable, and mechanically superior SPBC hydrogel. Its suitability for 3D-printing personalized fabrication and outstanding sensor properties makes it a useful reference for hydrogels in wearable devices and human motion monitoring.

TEMPO-Oxidized Nanocellulose Films Modified by Tea Saponin Derived from Camellia oleifera: Physicochemical, Mechanical, and Antibacterial Properties

Nanocellulose materials have been widely used in biomedicine, food packaging, aerospace, composite material, and other fields. In this work, cellulose obtained from Camellia shells through alkali boiling and subbleaching was micro-dissolved and regenerated using the DMAc (N,N-Dimethylacetamide)/LiCl system, and TOCNs (TEMPO-oxidized cellulose nanofibers) with different degrees of oxidation. The membrane was prepared by filtration of polytetrafluoroethylene (pore size 0.1 μm), and the oxidized nanocellulose film was obtained after drying, Then, the crystallinity, mechanical properties and oxygen barrier properties of the TOCN film were investigated. Furthermore, based on TS (tea saponin) from Camellia oleifera seed cake and TOCNs, TS-TOCN film was prepared by the heterogeneous reaction. The TS-TOCN film not only shows excellent oxygen barrier properties (the oxygen permeability is 2.88 cc·m-2·d-1) but also has good antibacterial effects on both Gram-negative and Gram-positive bacteria. The antibacterial property is comparable to ZnO-TOCN with the same antibacterial content prepared by the in-situ deposition method. Antioxidant activity tests in vitro showed that TS-TOCN had a significant scavenging effect on DPPH (2,2-Diphenyl-1-picrylhydrazyl) radicals. This design strategy makes it possible for inexpensive and abundant Camellia oleifera remainders to be widely used in the field of biobased materials.

A new strategy to improve the dielectric properties of cellulose nanocrystals (CNCs): Surface modification of small molecules

Nanocellulose finds various applications in advanced electrical devices due to its impressive mechanical properties, thermal stability, and degradability. Cellulose nanocrystals (CNCs) with excellent dielectric properties may act as a fresh dielectric plastic. In this study, a new strategy of small molecule modification was used to improve the dielectric constant, breakdown strength, and band gap of the CNCs. The dipole moments, dipole density, and the anisotropic impact of surface groups on the dielectric constant were studied. The number of sulfates in the CNCs showed a gradient due to alkali treatment and sulfonation, which allowed for a controlled range of the dielectric constant of nanocellulose between 4.9 and 11.9. TEMPO oxidation (2,2,6,6-tetramethylpiperidine-1-oxyl) and cyanoethylation of the CNCs further increased the dielectric constant to 11.1 and 13.2, respectively, and the dielectric loss 10-1. By understanding and innovating organic polymer dielectrics, we can provide significant benefits to the electronics and device industries.

Flexoelectric and piezoelectric effects in micro- and nanocellulose films

In this work, we evaluated the flexoelectric and piezoelectric contributions to the overall macroscopic polarization in cellulose films. To this end, the flexoelectric μ31 and transverse effective piezoelectric e31,f coefficients of cellulose films were determined using cantilever beam bending. The experiments were based on theoretical developments allowing to separate the flexoelectric from the piezoelectric contribution, represented by an effective flexoelectric coefficient, μeff, depending on both e31,f and μ31. Five free-standing and stainless steel/cellulose bilayer films were prepared from cellulose showing different morphologies and surface charge degrees: two almost neutral cellulose microfibers (CMF) and three (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose micro- (TCMF) and nanofibers (TCNF) bearing negative charged groups on the surface. The dielectric properties of the films indicated a low dielectric constant for unmodified CMF, and a huge increase for TEMPO-oxidized samples, which were up to 9 times higher than poly(vinylidene fluoride)-based polymers. TEMPO-oxidized cellulose films exhibited the largest flexoelectric coefficients (almost 7 times higher than those of synthetic polymer dielectrics), which evidenced that the presence of polar groups and surface charge boosted both flexoelectricity and piezoelectricity in unpoled cellulose films. These findings pave the way towards sustainable cellulose-based curvature sensors with large effective flexoelectric coefficients, without the need of preliminary energy consuming poling step.

Cellulose Dissolution, Modification, and the Derived Hydrogel: A Review

The cellulose-based hydrogel has occupied a pivotal position in almost all walks of life. However, the native cellulose can not be directly used for preparing hydrogel due to the complex non-covalent interactions. Some literature has discussed the dissolution and modification of cellulose but has yet to address the influence of the pretreatment on the as-prepared hydrogels. Firstly, the "touching" of cellulose by derived and non-derived solvents was introduced, namely, the dissolution of cellulose. Secondly, the "conversion" of functional groups on the cellulose surface by special routes, which is the modification of cellulose. The above-mentioned two parts were intended to explain the changes in physicochemical properties of cellulose by these routes and their influences on the subsequent hydrogel preparation. Finally, the "reinforcement" of cellulose-based hydrogels by physical and chemical techniques was summarized, viz., improving the mechanical properties of cellulose-based hydrogels and the changes in the multi-level structure of the interior of cellulose-based hydrogels.

Current advances of nanocellulose application in biomedical field

Nanocellulose (NC) is a natural fiber that can be extracted in fibrils or crystals form from different natural sources, including plants, bacteria, and algae. In recent years, nanocellulose has emerged as a sustainable biomaterial for various medicinal applications including drug delivery systems, wound healing, tissue engineering, and antimicrobial treatment due to its biocompatibility, low cytotoxicity, and exceptional water holding capacity for cell immobilization. Many antimicrobial products can be produced due to the chemical functionality of nanocellulose, such disposable antibacterial smart masks for healthcare use. This article discusses comprehensively three types of nanocellulose: cellulose nanocrystals (CNC), cellulose nanofibrils (CNF), and bacterial nanocellulose (BNC) in view of their structural and functional properties, extraction methods, and the distinctive biomedical applications based on the recently published work. On top of that, the biosafety profile and the future perspectives of nanocellulose-based biomaterials have been further discussed in this review.

Surface-Modified Carboxylated Cellulose Nanofiber Hydrogels for Prolonged Release of Polyhexamethylene Biguanide Hydrochloride (PHMB) for Antimicrobial Applications

The surface modification of cellulose nanofibers (CNFs) using a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)/sodium bromide (NaBr)/sodium hypochlorite (NaClO) system was successful in improving their hydrophilicity. Following that, we fabricated hydrogels containing carboxylated cellulose nanofibers (c-CNFs) and loaded them with polyhexamethylene biguanide (PHMB) using a physical crosslinking method, aiming for efficient antimicrobial uses. The morphological and physicochemical properties of all hydrogel formulations were characterized, and the results revealed that the 7% c-CNFs-2 h loaded with PHMB formulation exhibited desirable characteristics such as regular shape, high porosity, good mechanical properties, suitable gel content, and a good maximum swelling degree. The successful integration of PHMB into the c-CNF matrix was confirmed by FTIR analysis. Furthermore, the 7% c-CNFs-2 h loaded with the PHMB formulation demonstrated PHMB contents exceeding 80% and exhibited a prolonged drug release pattern for up to 3 days. Moreover, this formulation displayed antibacterial activity against S. aureus and P. aeruginosa. In conclusion, the novel approach of c-CNF hydrogels loaded with PHMB through physical crosslinking shows promise as a potential system for prolonged drug release in topical drug delivery while also exhibiting excellent antibacterial activity.

Amino carboxymethyl chitosan//dialdehyde starch/polyvinyl alcohol double-layer film loaded with ε-polylysine

To develop food packaging with good antibacterial activity and mechanical performance, four amino carboxymethyl chitosan (ACC)//dialdehyde starch (DAS) /polyvinyl alcohol (PVA) films were prepared by Schiff base and hydrogen bond interactions for efficient loading and release of ε-polylysine (ε-PL). The effects of the Schiff base reaction on the physicochemical properties of the films were explored based on the different aldehyde group contents in DAS. The ACC//DAS₄/PVA film exhibited a tensile strength of 62.5 MPa, and the water vapor and oxygen permeability was 8.77 × 10^-3·g·mm/m²·d·kPa and 0.15 × 10³·cm³·mm/m²·d, respectively. By leveraging the Schiff base reaction, the film swelling properties were improved by adjusting the cross-link density, mesh size, and molecular mass between the cross-links. The ACC//DAS₄/PVA film could efficiently load ε-PL with a value of 98.44% and long-term release in a food simulant of 10% ethanol at 25 °C for 120 min. Moreover, the ACC-ε-PL//DAS₄/PVA film was successfully used for salmon preservation.

A mini-review on the dielectric properties of cellulose and nanocellulose-based materials as electronic components

Cellulose-based materials have the advantages of renewable, non-toxic, flexible, and strong mechanical properties, so it of is great significance to study the dielectric properties of cellulose-based materials. In this paper, we summarized the factors influencing the dielectric properties of cellulose and nanocellulose-based dielectric and the ways to change the dielectric properties, mainly exploring the methods to improve the dielectric constant of cellulose-based dielectric materials. Cellulose and nanocellulose-based dielectric need to improve the hygroscopic property, increase the flexibility and reduce dielectric loss of the composite materials. This review summarizes the current state-of-art progress of new dielectric materials for green energy storage and flexible electronic devices.

Bacterial nanocellulose as green support of platinum nanoparticles for effective methanol oxidation

Bacterial nanocellulose, BNC, has emerged as a new class of nanomaterials recognized as renewable, biodegradable, biocompatible and material for versatile applications. BNC also proved as a perfect support matrix for metallic nanoparticle synthesis and appeared as suitable alternative for widely used carbon based materials. Following the idea to replace commonly used carbon based materials for platinum supports with the green and sustainable one, BNC appeared as an excellent candidate. Herein, microwave assisted synthesis has been reported for the first time for platinum nanoparticles supported on BNC as green material. Bacterial nanocelullose-platinum catalyst, Pt/BNC, was investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), atomic force microscopy (AFM), X-ray diffractometry (XRD) and transmission-electron microscopy (TEM) analysis. The obtained results confirmed successful synthesis of new Pt-based catalyst. It was found that Pt/BNC catalyst has high electrocatalytic performance in methanol oxidation reaction. Green/sustainable catalytic system is highly desirable and provided by the elegant microwave assisted synthesis of Pt/BNC will pave the way for a larger scale application and expedite the market penetration of such fuel cells.

Isolation of Cellulose Nanocrystals from Banana Peel Using One-Pot Microwave and Mild Oxidative Hydrolysis System

The current investigation deals with the application of a one-pot system to facilitate the production of cellulose nanocrystals (CNCs) from banana peel by a combination of microwave pre-treatment and mild oxidative hydrolysis with hydrogen peroxide (H₂O₂, 0-30 wt%) and sulfuric acid (H₂SO₄, 0-10%). H₂O₂ causes decolorization of the banana peel suspension from dark brown to light yellow, while further treatment with H₂SO₄ produces a white suspension, indicating successful removal of the non-cellulosic components from the banana peel. This finding was further supported by Fourier Transform Infrared (FTIR) spectroscopic analysis, which showed the gradual disappearance of lignin and hemicellulose peaks with increasing H₂O₂ and H₂SO₄ concentrations. The CNCs has considerably high crystallinity, with the highest crystallinity (~85%) being obtained at 6% H₂SO₄. Therefore, CNCs obtained at 6% H₂SO₄ were selected for further characterization. Scanning Electron Microscope (SEM) analysis confirmed the disintegration of the cellulose fibres into small fragments after hydrolysis. Transmission Electron Microscope (TEM) and Atomic Force Microscope (AFM) analyses revealed the spherical shape of the CNCs with an average size of approximately 20 nm. The CNCs have good stability with zeta potential of -42.9 mV. Findings from this study suggest that the combination of microwave pre-treatment and oxidative hydrolysis with 30 wt% H₂O₂ and 6% H₂SO₄, which is about 11 times lower than the commonly used H₂SO₄ concentration, is proven effective for the isolation of CNCs from banana peel. These observations are expected to provide insight into a facile and environmentally benign alternative to the conventional CNCs isolation method, using abundant and underutilized agricultural waste as feedstock.

Production of Nanocellulose Film from Abaca Fibers

Abaca fibers were subjected to a TEMPO mediated oxidation to extract nanocellulose on a 500 L capacity locally fabricated reactor. A yield of 46.7% white gel material with 2.23% solid content was obtained from an overnight reaction. Transmission electron microscopy scan of the white gel material confirms the production of relatively short highly individualized cellulose nanofibril (CNF) as the diameter of abaca fiber was reduced from 16.28 μm to 3.12 nm with fiber length in the range of 100 nm to 200 nm. Nanocellulose film was prepared using air drying (CNF-VC) and vacuum oven drying (CNF-OD). The effect of CNF concentration on the physical, morphological, thermal and mechanical properties were evaluated. FTIR spectra showed cellulose I spectra between abaca fiber with both the CNF-VC film and CNF-OD film with two distinct peaks at 1620 cm−1 and 1720 cm−1 attributed to the carboxyl group resulting from the TEMPO oxidation. In addition, the carboxyl group decreases in thermal stability of cellulose. Moreover, the XRD scan showed a decrease in crystallinity index of CNF films compared to abaca fibers. CNF-VC film showed the highest tensile strength at 0.4% concentration with 88.30 MPa, while a 89.72 MPa was observed for CNF-OD film at 0.8% concentration.

Insights into structure and properties of cellulose nanofibrils (CNFs) prepared by screw extrusion and deep eutectic solvent permeation

To achieve the balance on economy and ecology, it is indispensable to explore the greener and more inexpensive method for the production of cellulose nanofibrils (CNFs). Herein, a deep eutectic solvent (DES) system based on choline chloride (ChCl) and ethylene glycol (EG) was employed as the swollen solvent, combining with screw extrusion and permeant, to fabricate unmodified CNFs with high yield and thermal stability. The proposed method in this work was simple, convenient, and industrially viable. The hydrous DESs were applied in the process of CNFs preparation and dispersion to reduce the cost and viscosity of DES. To reveal the principle of CNFs preparation, the impact of sulfuric acid and water content of DES system on the chemical, physical, morphological, thermal, and dispersive properties of CNFs was systematically studied. Properties of the dispersed solvents were characterized by solvatochromic parameters and viscosity parameters to evaluate the potential influence on the preparation and dispersion of CNFs. In general, this work would play valuable guidance in realizing the preparation and dispersion of CNFs via a versatile DES solvent system, thus endowing cellulose materials high-value utilization.

Scalable Preparation of Cellulose Nanofibers from Office Waste Paper by an Environment-Friendly Method

Waste paper is often underutilized as a low-value recyclable resource and can be a potential source of cellulose nanofibers (CNFs) due to its rich cellulose content. Three different processes, low acid treatment, alkali treatment and bleaching treatment, were used to pretreat the waste paper in order to investigate the effect of different pretreatments on the prepared CNFs, and CNFs obtained from bleached pulp boards were used as control. All sample fibers were successfully prepared into CNFs by 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) oxidation. It was quite obvious that the bleached CNFs samples showed dense fibrous structures on a scanning electron microscopy (SEM), while needle-like fibers with width less than 20 nm were observed on a transmission electron microscopy (TEM). Meanwhile, the bleaching treatment resulted in a 13.5% increase in crystallinity and a higher TEMPO yield (e.g., BCNF, 60.88%), but a decrease in thermal stability. All pretreated CNFs samples showed narrow particle size distribution, good dispersion stability (zeta potential less than −29.58 mV), good light transmission (higher than 86.5%) and low haze parameters (lower than 3.92%). This provides a good process option and pathway for scalable production of CNFs from waste papers.