Wood-inspired strategy to toughen transparent cellulose nanofibril films

Permeable, Stretchable, and Recyclable Cellulose Aerogel On-Skin Electronics for Dual-Modal Sensing and Personal Healthcare

Flexible on-skin electronics present tremendous popularity in intelligent electronic skins (e-skins), healthcare monitoring, and human-machine interfaces. However, the reported e-skins can hardly provide high permeability, good stretchability, and large sensitivity and are limited in long-term stability and efficient recyclability when worn on the human body. Herein, inspired from the human skin, a permeable, stretchable, and recyclable cellulose aerogel-based electronic system is developed by sandwiching a screen-printed silver sensing layer between a biocompatible CNF/HPC/PVA (cellulose nanofiber/hydroxypropyl cellulose/poly(vinyl alcohol)) aerogel hypodermis layer and a permeable polyurethane layer as the epidermis layer. The cellulose aerogel displays a high tensile strength of 1.14 MPa and tensile strain of 43.5% while maintaining good permeability. The cellulose aerogel-based electronics embrace appealing sensing performances with high sensitivity (gauge factor ≈ 238), ultralow detection limit (0.1%), and fast response time (18 ms) under strain stimulus. Owing to the disconnection and reconnection of microcracks in the sensing layer, both strain/humidity sensing and thermal healthcare can be easily achieved. The permeable electronics can be further integrated into an electronic mask for patient-centered healthcare with a power supply system, switching control device, and wireless Bluetooth module. Moreover, the prepared electronic system enables long-term wearing on human skin without skin irritation, and all components of the electronics can be recaptured/reused in water. This material strategy highlights the potential of next-generation on-skin electronics with high permeability and good environmental friendliness.

Supramolecular Scale Hydrophilicity Regulation Enabling Efficient Dewatering and Assembly of Nanocellulose into Dense and Strong Bulk Materials as Sustainable Plastic Substitutes

Cellulose nanofibers (CNFs) are ideal building blocks for creating lightweight and strong bulk structural materials due to their unique supramolecular structure and exceptional mechanical properties within the crystalline regions. However, assembling CNFs into dense bulk structural materials with customizable shape and functionalities remains a great challenge, hindering their practical applications. Here, the dewatering issue of aqueous CNF dispersions is addressed by regulating supramolecular scale hydrophilicity using lactic acid, combined with hot-press molding. This approach enables the fabrication of transparent CNF bulk structural materials with a density of up to 1.426 g cm-3. The mechanical properties, including isotropic in-plane tensile strength (75.5 ± 4.5 MPa), flexural strength (198 ± 20 MPa), and hardness (≈300 MPa), surpass most engineering plastics. Moreover, unlike conventional CNF based materials, the CNF bulk structural materials exhibit remarkable water stability and flame retardancy. These unique advantages open a new avenue to bottom-up assembly of CNFs into high-performance multifunctional eco-friendly structural materials, dedicating to substitution of plastics and easing the consumption of petrochemical resources.

Synchronously enhanced breakdown strength and energy storage ability of cellulose acetate flexible films via introducing ultra-low content of carbonized polymer dots

Developing green and environmentally friendly biomass materials for energy storage and application is of great significance to sustainable development. Novel composite films containing cellulose acetate (CA) and carbonized polymer dots (CPDs) are reported herein. The CPDs have strong hydrogen bonding interactions with CA matrix, in which CPDs act as the physical crosslinking points and enhance the entanglement density of the matrix. And the composite films demonstrate a significant enhancement in breakdown strength (Eb), reaching up to 520.58 MV/m with the addition of 0.1 wt% CPDs (1.62 times higher than 321.94 MV/m of pure CA). Furthermore, the discharging energy density (Ud) achieves 2.55 J/cm3 at 450 MV/m, which is 1.36 times higher than that of the pure CA film (1.87 J/cm3 at 400 MV/m) and simultaneously, the energy efficiency (η) is maintained at 73.3 %. The Coulomb-blockade effect induced by the ultra-low content of CPDs effectively inhibiting carrier migration, and the enhanced entanglement density of the matrix improving mechanical properties and reducing polarization loss, mainly contribute to the enhanced dielectric performances. Furthermore, CPDs also improve the mechanical properties of the composite films apparently. This work provides some references for the fabrication of the next generation of environmentally friendly dielectric composite films.

High aspect ratio cellulose nanofibrils with low crystallinity for strong and tough films

Cellulose nanofibril (CNF) films with both high strength and high toughness are attractive for applications in energy, packaging, and flexible electronics. However, simultaneously achieving these mechanical properties remains a significant challenge. Herein, a multiscale structural optimization strategy is proposed to prepare high aspect ratio CNFs with reduced crystallinity for strong and tough films. Carboxymethylation coupled with mild mechanical disintegration is employed to modulate the multiscale structure of CNFs. The as-prepared CNFs feature an aspect ratio of >800 and a crystallinity of <60 %. The film prepared using CNFs with a high aspect ratio (~1100) and reduced crystallinity (~54 %) exhibits a tensile strength of 229.9 ± 9.9 MPa and toughness of 22.2 ± 1.4 MJ/m3. The underlying mechanism for balancing these mechanical properties is unveiled. The high aspect ratio of the CNFs facilitates the transfer and distribution of local stress, thus endowing the corresponding film with high strength and toughness. Moreover, the low crystallinity of the CNFs permits the movement of the cellulose chains in the amorphous regions, thereby dissipating energy and finally increasing the film toughness. This work introduces an innovative and straightforward method for producing strong and tough CNF films, paving the way for their broader applications.

A facile method to fabricate sustainable bamboo ethanol lignin/carboxymethylcellulose films with efficient anti-ultraviolet and insulation properties

Given the environmental concerns related to the non-degradability of conventional petroleum-based polymer films, the synthesis of biodegradable films utilizing natural polymers derived from biomass has emerged as a promising alternative, garnering significant attention in recent research endeavors. This research introduced an environmentally friendly and efficient method, utilizing extract liquid from the green ethanol pulping process as the solvent to completely dissolve carboxymethylcellulose into the film-forming liquid, and employing the solution pouring technique to successfully fabricate bamboo ethanol lignin/carboxymethylcellulose films (LCF). The findings revealed that the lignin content significantly influenced the LCF, endowing them with tunable mechanical properties, effective UV-blocking, and thermal insulation capabilities. With a lignin addition of 3.75 %, LCF-3.75 exhibited enhanced mechanical properties, characterized by a tensile strength of 19.4 MPa, along with superior UV-blocking efficiency, blocking 100 % of UVB and 99.81 % of UVA rays. Furthermore, relative to LCF-0, LCF-3.75 had been shown to possess enhanced hydrophobicity and thermal stability, culminating in the development of the composite films that showcased exceptional thermal insulation properties and biodegradability. The films not only harbored extensive application prospects as an anti-ultraviolet and heat-insulating glass films but also represented a potential avenue for the efficient utilization of lignin, thereby contributing to sustainable development.

Hydrogen Bond-Mediated Strong Plasticization for High-Performance Alginate Plastics

The increasingly severe plastic pollution has urged an inevitable trend to develop biodegradable plastic products that can take over synthetic plastics. As one of the most abundant natural polymers, polysaccharides are an ideal candidate to substitute synthetic plastics. The rigidity of polysaccharide chains principally allows for high strength and stiffness of their materials, however, challenges the facile orientation in material processing. Here, a general hydrogen bond-mediated plasticization strategy to regulate isotropic sodium alginate (SA) chains to a highly ordered state is developed, and alginate plastics with high performances are fabricated. It is revealed that hydroxyl groups in glycerol modulate the viscoelasticity of SA solids by forming strong hydrogen bonds with SA chains, achieving a large stretchability at a high solid content. Highly orientated alginate films exhibit a superior tensile strength of 575 MPa and toughness of 60.7 MJ m-3, outperforming most regenerated biomass films. The high solid content and large stretchability mediated by strong hydrogen bonding ensure plastic molding of solid-like SA with high fidelity. This hydrogen bond-mediated plasticity provides a facile but effective method to justify the high performances of polysaccharide-based plastics.

Nanotechnology in wood science: Innovations and applications

Application of nanomaterials is gaining tremendous interest in the field of wood science and technology for value addition and enhancing performance of wood and wood-based composites. This review focuses on the use of nanomaterials in improving the properties of wood and wood-based materials and protecting them from weathering, biodegradation, and other deteriorating agents. UV-resistant, self-cleaning (superhydrophobic) surfaces with anti-microbial properties have been developed using the extraordinary features of nanomaterials. Scratch-resistant nano-coatings also improve durability and aesthetic appeal of wood. Moreover, nanomaterials have been used as wood preservatives for increasing the resistance against wood deteriorating agents such as fungi, termites and borers. Wood can be made more resistant to ignition and slower to burn by introducing nano-clays or nanoparticles of metal-oxides. The use of nanocellulose and lignin nanoparticles in wood-based products has attracted huge interest in developing novel materials with improved properties. Nanocellulose and lignin nanoparticles derived/synthesized from woody biomass can enhance the mechanical properties such as strength and stiffness and impart additional functionalities to wood-based products. Cellulose nano-fibres/crystals find application in wide areas of materials science like reinforcement for composites. Incorporation of nanomaterials in resin has been used to enhance specific properties of wood-based composites. This review paper highlights some of the advancements in the use of nanotechnology in wood science, and its potential impact on the industry.

Recent Advances in Chemically Modified Cellulose and Its Derivatives for Food Packaging Applications: A Review

The application of cellulose in the food packaging field has gained increasing attention in recent years, driven by the desire for sustainable products. Cellulose can replace petroleum-based plastics because it can be converted to biodegradable and nontoxic polymers from sustainable natural resources. These products have increasingly been used as coatings, self-standing films, and paperboards in food packaging, owing to their promising mechanical and barrier properties. However, their utilization is limited because of the high hydrophilicity of cellulose. With the presence of a large quantity of functionalities within pristine cellulose and its derivatives, these building blocks provide a unique platform for chemical modification via covalent functionalization to introduce stable and permanent functionalities to cellulose. A primary aim of chemical attachment is to reduce the probability of component leaching in wet and softened conditions and to improve the aqueous, oil, water vapor, and oxygen barriers, thereby extending its specific use in the food packaging field. However, chemical modification may affect the desirable mechanical, thermal stabilities and biodegradability exhibited by pristine cellulose. This review exhaustively reports the research progress on cellulose chemical modification techniques and prospective applications of chemically modified cellulose for use in food packaging, including active packaging.

Eco-friendly chitosan@silver/plant fiber membranes for masks with thermal comfortability and self-sterilization

The surgical masks have been essential consumables for public in the COVID-19 pandemic. However, long-time wearing masks will make wearers feel uncomfortable and massive discarded non-biodegradable masks lead to a heavy burden on our environment. In this paper, we adopt degradable chitosan@silver (CS@Ag) core-shell fibers and plant fibers to prepare an eco-friendly mask with excellent thermal comfort, self-sterilization, and antiviral effects. The thermal network of CS@Ag core-shell fibers highly improves the in-plane thermal conductivity of masks, which is 4.45 times higher than that of commercial masks. Because of the electrical conductivity of Ag, the fabricated mask can be electrically heated to warm the wearer in a cold environment and disinfect COVID-19 facilely at room temperature. Meanwhile, the in-situ reduced silver nanoparticles (AgNPs) endow the mask with superior antibacterial properties. Therefore, this mask shows a great potential to address the urgent need for a thermally comfortable, antibacterial, antiviral, and eco-friendly mask.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10570-022-04582-x.