High yield production of microcrystalline cellulose by a thermo-mechano-solvolytic treatment

By thermally treating a commercial cellulose in ethylene glycol, celluloses of controlled low degree of polymerization, DP_r = 1000 to 70, can be derived. Two general behaviors are observed in the range studied. At first, the depolymerization reaction is predominant down to a DP equal to 130. Beyond this level, the depolymerization process leads to extensive solubilization of the cellulose. The treated celluloses have been analyzed by X-ray diffraction, FTIR, TGA, elemental analysis and enzymatic hydrolysis. No chemical change of the cellulose could explain the two different behaviors. A physical modification in the form of depolymerization and destructuration is suspected.     

Photoswitchable Superabsorbency Based on Nanocellulose Aerogels

Chemical vapor deposition of a thin titanium dioxide (TiO₂) film on lightweight native nanocellulose aerogels offers a novel type of functional material that shows photoswitching between water‐superabsorbent and water‐repellent states. Cellulose nanofibrils (diameters in the range of 5–20 nm) with native crystalline internal structures are topical due to their attractive mechanical properties, and they have become relevant for applications due to the recent progress in the methods of their preparation. Highly porous, nanocellulose aerogels are here first formed by freeze‐drying from the corresponding aqueous gels. Well‐defined, nearly conformal TiO₂ coatings with thicknesses of about 7 nm are prepared by chemical vapor deposition on the aerogel skeleton. Weighing shows that such TiO₂‐coated aerogel specimens essentially do not absorb water upon immersion, which is also evidenced by a high contact angle for water of 140° on the surface. Upon UV illumination, they absorb water 16 times their own weight and show a vanishing contact angle on the surface, allowing them to be denoted as superabsorbents. Recovery of the original absorption and wetting properties occurs upon storage in the dark. That the cellulose nanofibrils spontaneously aggregate into porous sheets of different length scales during freeze‐drying is relevant: in the water‐repellent state they may stabilize air pockets, as evidenced by a high contact angle, in the superabsorbent state they facilitate rapid water‐spreading into the aerogel cavities by capillary effects. The TiO₂‐coated nanocellulose aerogels also show photo‐oxidative decomposition, i.e., photocatalytic activity, which, in combination with the porous structure, is interesting for applications such as water purification. It is expected that the present dynamic, externally controlled, organic/inorganic aerogels will open technically relevant approaches for various applications.     

航空煤油的羟丙基纤维素凝胶力学性能研究

采用软固体测定仪，研究了胶凝剂、表面活性剂、稳定剂用量对航空煤油凝胶力学性能的影响。结果表明在实验条件下，随胶凝剂用量和表面活性剂OP-10用量的增加，凝胶的屈服应力增加。引入稳定剂C可使凝胶形成时间显著缩短，抗剪切能力显著增强。     

High‐Strength and High‐Toughness Double‐Cross‐Linked Cellulose Hydrogels: A New Strategy Using Sequential Chemical and Physical Cross‐Linking

Polysaccharide‐based hydrogels have multiple advantages because of their inherent biocompatibility, biodegradability, and non‐toxicic properties. The feasibility of using polysaccharide‐based hydrogels could be improved if they could simultaneously fulfill the mechanical property and cell compatibility requirements for practical applications. Herein, the construction of double‐cross‐linked (DC) cellulose hydrogels is described using sequential chemical and physical cross‐linking, resulting in DC cellulose hydrogels that are mechanically superior to single‐cross‐linked cellulose hydrogels. The formation and spatial distribution of chemically cross‐linked domains and physically cross‐linked domains within the DC cellulose hydrogels are demonstrated. The molar ratio of epichlorohydrin to anhydroglucose units of cellulose and the concentration of the aqueous ethanol solution are two critical parameters for obtaining mechanically strong and tough DC cellulose hydrogels. The mechanical properties of the DC cellulose hydrogels under loading‐unloading cycles are described using compression and tension models. The possible toughening mechanism of double‐cross‐linking is discussed.     

Re-Printable Chiral Photonic Paper with Invisible Patterns and Tunable Wettability

The construction of invisible patterns via high-resolution printing and the independent encoding/decoding of complex information can lead to promising applications in steganography and watermarking for optical encryption. Herein, a rewritable chiral photonic paper formed by cholesteric cellulose nanocrystals and polycation is reported. The chemically crosslinked polycation network interpenetrates in the cholesteric structure while retaining the optical properties of the photonic crystals. The film exhibits controllable wettability via anion exchange, leading to extremely low contrast in the dry state but high contrast by a rapid wetting response. Triple invisible information is independently encoded on the films, including invisible patterns caused by reversible counterion-controlled wettability, permanent fluorescent labels based on fluorescent counterions, and polarization-dependent structural colors based on cholesteric structures. Full color patterns can be reversibly constructed via inkjet printing, with a high resolution of 100 µm. In addition, the circular polarization characteristics of the cellulose nanocrystals, liquid crystals, endow the system with complex and independent responses, realizing a wetting/polarization double-key decryption. This work provides a simple and effective optical technique for coding complex information on a single material platform and expands the techniques available to achieve invisible patterns for sensing and anti-counterfeiting.     

Marrying Ester Group with Lithium Salt: Cellulose-Acetate-Enabled LiF-Enriched Interface for Stable Lithium Metal Anodes

The practical applications of high-energy-density lithium (Li) metal batteries (LMB) have been hindered by the formation and growth of Li dendrites. Homogenizing the Li-ion flux to suppress Li dendrites by regulating the solid electrolyte interphase (SEI) originating from electrolyte degradation is necessary but still challenging. Herein, ion-affiliative cellulose acetate (CA) with functional Li salts is prepared to generate the SEI with fast Li⁺ diffusion kinetics. First, the correlations between the functional ester group and LiN(CF₃SO₂)₂ (LiTFSI) are theoretically and experimentally identified, where CO strongly adsorbed N(CF₃SO₂)₂⁻ through electrostatic interaction to enhance the charge-transfer-promoted decomposition of LiTFSI. Furthermore, the CA with ex situ doped LiTFSI amplifies this fluorinated degradation effect, and the LiF-enriched SEI nanostructure is consequently established in situ, as confirmed by cryogenic transmission electron microscopy. As a result, the dendritic Li growth during cycling is efficiently suppressed, and the lifespan is prolonged by more than six times at a high current density of 3 mA cm⁻². This study provides insights into the interphase design for realizing ultrastable LMB.     

Triacetate cellulose gate dielectric organic thin-film transistors

Here, we report on the performance and the characterization of all solution-processable top-contact organic thin-film transistors (OTFTs) consisting of a natural-resourced triacetate cellulose gate dielectric and a representative hole-transport poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (pBTTT) semiconductor layer on rigid or flexible substrates. The bio-based triacetate cellulose layer has an important role in the OTFT fabrication because it provides the pBTTT semiconducting polymer with highly suitable gate dielectric properties including a low surface roughness, hydrophobic surface, appropriate dielectric constant, and low leakage current. The triacetate cellulose gate dielectric-based pBTTT OTFTs exhibit an average filed-effect mobility of 0.031 cm²/Vs similar to that obtained from a SiO₂ gate dielectric-based OTFT device in ambient conditions. Even after a bending stimulation of 100 times and in an outward bending state, the flexible triacetate cellulose gate pBTTT OTFT device still showed excellent electrical device performance without any hysteresis.     

Copper‐Based Nanostructured Coatings on Natural Cellulose: Nanocomposites Exhibiting Rapid and Efficient Inhibition of a Multi‐Drug Resistant Wound Pathogen,A. baumannii,and Mammalian Cell Biocompatibility In Vitro

This paper describes a layer‐by‐layer (LBL) electrostatic self‐assembly process for fabricating highly efficient antimicrobial nanocoatings on a natural cellulose substrate. The composite materials comprise a chemically modified cotton substrate and a layer of sub‐5 nm copper‐based nanoparticles. The LBL process involves a chemical preconditioning step to impart high negative surface charge on the cotton substrate for chelation controlled binding of cupric ions (Cu²⁺), followed by chemical reduction to yield nanostructured coatings on cotton fibers. These model wound dressings exhibit rapid and efficient killing of a multidrug resistant bacterial wound pathogen, A. baumannii, where an 8‐log reduction in bacterial growth can be achieved in as little as 10 min of contact. Comparative silver‐based nanocoated wound dressings–a more conventional antimicrobial composite material–exhibit much lower antimicrobial efficiencies; a 5‐log reduction in A. baumannii growth is possible after 24 h exposure times to silver nanoparticle‐coated cotton substrates. The copper nanoparticle–cotton composites described herein also resist leaching of copper species in the presence of buffer, and exhibit an order of magnitude higher killing efficiency using 20 times less total metal when compared to tests using soluble Cu²⁺. Together these data suggest that copper‐based nanoparticle‐coated cotton materials have facile antimicrobial properties in the presence of A. baumannii through a process that may be associated with contact killing, and not simply due to enhanced release of metal ion. The biocompatibility of these copper‐cotton composites toward embryonic fibroblast stem cells in vitro suggests their potential as a new paradigm in metal‐based wound care and combating pathogenic bacterial infections.     

Self‐Assembly of Mechanoplasmonic Bacterial Cellulose–Metal Nanoparticle Composites

Nanocomposites of metal nanoparticles (NPs) and bacterial nanocellulose (BC) enable fabrication of soft and biocompatible materials for optical, catalytic, electronic, and biomedical applications. Current BC–NP nanocomposites are typically prepared by in situ synthesis of the NPs or electrostatic adsorption of surface functionalized NPs, which limits possibilities to control and tune NP size, shape, concentration, and surface chemistry and influences the properties and performance of the materials. Here a self‐assembly strategy is described for fabrication of complex and well‐defined BC–NP composites using colloidal gold and silver NPs of different sizes, shapes, and concentrations. The self‐assembly process results in nanocomposites with distinct biophysical and optical properties. In addition to antibacterial materials and materials with excellent senor performance, materials with unique mechanoplasmonic properties are developed. The homogenous incorporation of plasmonic gold NPs in the BC enables extensive modulation of the optical properties by mechanical stimuli. Compression gives rise to near‐field coupling between adsorbed NPs, resulting in tunable spectral variations and enhanced broadband absorption that amplify both nonlinear optical and thermoplasmonic effects and enables novel biosensing strategies.     

Cellulose-based Interfacial Solar Evaporators: Structural Regulation and Performance Manipulation

The shortage of freshwater resources has become a major obstacle threatening human development, and directly utilizing solar energy by solar evaporators is emerging as a promising method to produce freshwater from the seawater. Compared to many synthetic polymer-based evaporators, cellulose-based evaporators are expected to offer more interesting features benefiting from the renewable feature and abundant reserves of cellulose-contained naturally occurring materials. First, according to the different fabrication methods, cellulose-based solar evaporators can be divided into two types, i.e., top-down utilization (wood-based) and bottom-up assembled (cellulose composite-based), respectively. The different fabrication schemes also bring their own unique advantages, such as the bimodal porous structure of wood-based evaporators and the artificial interconnection microporous network of cellulose composite-based evaporators. Subsequently, this review further summarizes the most recent advances and highlights of those cellulose-based solar evaporators, by focusing on their structural regulation strategies (e.g., drilled channel array, asymmetric wettability structure, delignification, 2D waterway, etc.) and evaporation performance improvements (e.g., salt resistance, high evaporation rate, etc.). Finally, the challenges in this field and potential solutions are also discussed, which are anticipated to provide new opportunities toward the future development of cellulose and other kinds of biomass-based evaporators.