Stretchable and compressible hydrogels based on natural polymers have received immense considerations for electronics. The feasibility of using pure natural polymer-based hydrogels could be improved ...if their mechanical behaviors satisfy the requirements of practical applications. Herein, we report highly stretchable (tensile strain ∼126%) and compressible (compression strain ∼80%) cellulose ionic hydrogels (CIHs) among pure natural polymer-based hydrogels including cellulose, chitin, and chitosan via chemical cross-linking based on free radical polymerization of allyl cellulose in NaOH/urea aqueous solution. In addition, the hydrogels have good transparency (transmittance of ∼89% at 550 nm) and ionic conductivity (∼0.16 mS cm–1) and can be worked at −20 °C without freezing and visual loss of transparency. Moreover, the CIHs can serve as reliable and stable strain sensors and have been successfully used to monitor human activities. Significantly, the various properties of hydrogel can be controlled through rationally adjusting the chemically cross-linked density. Our methodology will prove useful in developing the satisfied mechanical and transparent CIHs for a myriad of applications in flexible electronics.
All-cellulose composite films were prepared, for the first time, from native cellulose nanowhiskers and cellulose matrix regenerated from aqueous NaOH−urea solvent system on the basis of their ...temperature-dependent solubility. The cellulose whiskers retained their needlelike morphology with mean length and diameter of 300 and 21 nm as well as native crystallinity when added to the latter solution at ambient temperature. The structure and physical properties of the nanocomposite films were characterized by scanning electron microscope, X-ray diffraction, and tensile tests. The composite films were isotropic and transparent to visible light and showed good mechanical properties as a result of the reinforcement by the whiskers. By varying the ratio of the cellulose whiskers to regenerated cellulose matrix (cellulose II), the tensile strength and elastic modulus of the nanocomposite films could be tuned to reach 124 MPa and 5 GPa, respectively. The tensile strength of the nanocomposite films could reach 157 MPa through a simple drawing process, with the calculated Hermans’ orientation parameter of 0.30. This work provided a novel pathway for the preparation of biodegradable all-cellulose nanocomposites, which are expected to be useful as biomaterials and food ingredients.
Hemicellulose, one of the most abundant biopolymers next to cellulose, has been considered as a potential substitute to synthetic polymers. Film casting from water is the most basic route for ...material applications of xylan. However, depending on plant sources and separation methods, xylans do not always form films and the related mechanism is unclear, which significantly hinders their material applications. We extensively characterized various fractions of bagasse xylan to understand the molecular features promoting the film formation. The side groups of xylans or impurities contributed to the prevention of excessive aggregation or crystallization of xylan molecules, leading to the film-forming capacity. However, once the film is formed, the side groups do not seem to be necessarily contributing to the mechanical resistance.
Starch can be efficiently converted into the corresponding formates homogeneously using N-formyl imidazole obtained by the reaction of 1,1′-carbonyldiimidazole and formic acid in dimethyl sulfoxide ...as a solvent. Starch formates are soluble in polar aprotic solvents, not susceptible against hydrolysis, and not meltable. Thermoplastics could be generated by conversion of starch formates with long-chain fatty acids exemplified by the conversion with lauroyl chloride in N,N-dimethylacetamide, leading to mixed starch laurate formates. The mixed esters show melting temperatures mainly dependent on the amount of laurate ester moieties.
Dissolution of cellulose having different viscosity-average molecular weight (M η ) in 7 wt%NaOH/12 wt%urea aqueous solution at temperature from 60 to -12.6°C was investigated with optical ...microscope, viscosity measurements and wide X-ray diffraction (WXRD). The solubility (Sa) of cellulose in NaOH/urea aqueous solution strongly depended on the temperature, and molecular weight. Their Sa values increased with a decrease in temperature, and cellulose having M η below 10.0 x 10⁴ could be dissolved completely in NaOH/urea aqueous solution pre-cooled to -12.6°C. The activation energy of dissolution (Ea,s) of the cellulose dissolution was a negative value, suggesting that the cellulose solution state had lower enthalpy than the solid cellulose. The cellulose concentration in this system increased with a decrease of M η to achieve about 8 wt% for M η of 3.1 x 10⁴. Moreover, cellulose having 12.7 x 10⁴ could be dissolved completely in the solvent pre-cooled to -12.6°C as its crystallinity (χ c) decreased from 0.62 to 0.53. We could improve the solubility of cellulose in NaOH/urea aqueous system by changing M η , χ c and temperature. In addition, the zero-shear viscosity (η ₀ ) at 0°C for the 4 wt% cellulose solution increased rapidly with an increase of M η , as a result of the enhancement of the aggregation and entanglement for the relatively long chains.
Acetylation is a promising method for hydrophobic modification of cellulose-based materials. However, the current methods to prepare acetylated cellulose nanofibers (ACNFs) are often time- and ...energy-consuming. In this work, acetylated cellulose nanofibers (ACNFs) were fabricated by integrating acetylation and mechanical nano-defibrillation. The morphology and structure of the obtained ACNFs are characterized by means of atomic force microscope (AFM), Fourier transform infrared spectroscopy (FT-IR), solid state
13
C NMR spectra, X-ray diffraction (XRD), etc. The yield of ACNFs can be as high as 96.5% for acetylated cellulose with low degree of substitution (such as DS of 0.15). The diameter and length of ACNFs are in range of 3–7 nm and 200–1100 nm, respectively. Due to their amphiphilic property (the water contact angle is 62.5°), ACNFs can be used as stabilizers for Pickering emulsion. The features of the emulsion in this study can be controlled by varying the DS and concentration of ACNFs.
As an importance resource from domestic garbage, waste cotton textiles have great potential to be recycled for high value-added products. Herein, carboxymethyl cellulose nanofibers (CM-CNFs) were ...obtained from waste cotton fibers by carboxymethyl modification and followed mechanical nano-defibrillation. The high yield of 98% can be realized in our CM-CNFs. The morphology and properties of CM-CNFs were characterized by means of atomic force microscopy (AFM), Fourier infrared spectroscopy (FT-IR), X-ray diffraction (XRD) analysis, and UV−visible spectroscopy etc. The results showed CM-CNFs have the aspect ratio ranged from 32 to 340 and the degree of polymerization (DP) from 371 to 779, which could be tailored by the degree of substitution (DS, 0.13–0.70) during carboxymethyl modification process. The high zeta-potential (−78 – −95) endowed the CM-CNFs suspension with good chemical stability and it can be stored for several months. In addition, the CM-CNFs can be served as good dispersion for carbon nanotubes due to the highly charged groups on its surface.
This review article is dedicated to special polysaccharide esters – the polysaccharide toluenesulfonic acid esters (tosylates) and polysaccharide carbonate esters. After describing the specifics of ...the synthesis, particular emphasis is placed on the use of polysaccharide tosylates and polysaccharide phenyl carbonates for subsequent modification by nucleophilic substitution (SN) reactions. For this purpose, the advantages and limitations of the respective derivatives are discussed with regard to their application in chemical modification with nucleophiles containing functional groups. A few functional polysaccharide derivatives and their properties are presented. Finally, reactive derivatives for click chemistry approaches are featured. These can be prepared starting from the reactive intermediate of either polysaccharide tosylate or polysaccharide phenyl carbonate.
ZnO was added to the NaOH/urea aqueous solution to increase the solubility of cellulose at low temperature. The cellulose solution was characterized with
13C NMR, wide-angle X-ray diffraction (WAXD), ...transmission electron microscopy (TEM) and dynamic light scattering (DLS) to evaluate the interaction between solvent and cellulose and the dissolution mechanism. The results indicated that the solubility of cellulose in NaOH/urea solution was improved significantly by the introduction of a small amount of ZnO (0.5
wt%), which existed as Zn(OH)
4
2− in the alkali system. It has been demonstrated that Zn(OH)
4
2− could form stronger hydrogen bonds with cellulose than hydrated NaOH, leading to the enhancement of the dissolution power. The cellulose concentration could be achieved to 8
wt% with molecular weight of 5.7
×
10
4, and the solvent could dissolve cellulose with molecular weight of 1.7
×
10
5.
Cellulose/graphene oxide (GO)/iron oxide (Fe3O4) composites were prepared by coprecipitating iron salts onto cellulose/GO hydrogels in a basic solution. X-ray photoelectron spectroscopy (XPS), ...Fourier-transform infrared, and X-ray diffraction characterization showed that Fe3O4 was successfully coated on GO sheets and cellulose. Cellulose/GO/Fe3O4 composites showed excellent catalytic activity by maintaining almost 98% of the removal of acid orange 7 (AO7) and showed stability over 20 consecutive cycles. This performance is attributable to the synergistic effect of Fe3O4 and GO during the heterogeneous Fenton-like reaction. Especially, the cellulose/GO/Fe3O4 composites preserve their activity by keeping the ratio of Fe3+/Fe2+ at 2 even after 20 catalysis cycles, which is supported by XPS analysis.
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