Supramolecular Structure Characterization of Molecularly Thin Cellulose I Nanoparticles

Hydrophobization of nanofibrillated cellulose from Macaranga gigantea for binding of curcumin

Nanofibrillated cellulose (NFC) has found extensive potential and existing utilizations across various industries. Nonetheless, a notable constraint of NFC lies in its inherent hydrophilic nature, which restricts its suitability for non-aqueous application. This study aims at synthesising hydrophobic NFC through a two-step surface modification by reacting NFC with tannic acid and amine group. The study also investigated the effect of using various alkylamines on the properties of modified NFC. The hydrophobic NFC was characterized using various analytical techniques namely Thermogravimetric Analysis (TGA), X-Ray Diffraction analysis (XRD), Atomic Force Microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR), elemental analysis, and contact angle measurements. The present study also looked into the possible use of modified NFC as a pharmaceutical excipient for the delivery of water insoluble curcumin. The analysis of curcumin binding onto the modified NFC was conducted using UV-Visible spectrophotometry. The findings from the study indicated that the modified NFC effectively bound a substantial quantity of curcumin (80 % - 87 %) and the binding varied for samples of different degree of substitution.

Sulfuric acid solvolysis of cellulose in a butanol-1/benzene mixture for isolating cellulose nanocrystals

The absence of a universal method for isolating cellulose nanocrystals (CNCs) has prompted researchers to explore alternative approaches to traditional sulfuric acid hydrolysis. In this study, the authors continue their previous research by investigating CNC synthesis through cellulose solvolysis in an alcoholic environment. The CNCs were successfully obtained utilizing controlled sulfuric acid solvolysis of sulfate cellulose in a butanol-1/benzene mixture. The highest CNC yield (over 60 %) was achieved at strictly controlled acid-to-benzene ratios in a butanol-1/benzene/sulfuric acid reaction mixture, with a significant reduction in the optimal acid concentration. The study also analyzes the physicochemical properties of the isolated CNCs. No surface alkylation of the synthesized CNCs was observed during the cellulose solvolysis in the butanol-1/benzene mixture. Besides, the properties of these CNCs closely resembled those obtained through traditional sulfuric acid hydrolysis. The paper also discusses the potential mechanism of cellulose solvolysis in the process of CNC production.

Emergence of Amphiphilicity on Surfaces of Pure Cellulose Nanofibrils Directly Generated by Aqueous Counter Collision Process

The present paper describes a downsizing mechanism of an aqueous counter collision (ACC) process that enables the rapid preparation of cellulose nanofibrils (CNFs) as an aqueous dispersion solely by impinging a pair of water jets containing the raw materials. Extensive studies have revealed that the resulting CNFs by ACC have amphiphilic fiber surfaces, in which two kinds of faces with different natures are present along the entire fiber axis. They therefore have superior adsorption to surfaces of various conventional polymer plastics. These characteristic adsorption behaviors, which are totally different from those for other CNFs prepared by other means, are attributable to their hydrophobic surfaces. In the present study, high-resolution microscopy, including atomic force microscopy, confocal laser scanning microscopy, and scanning electron microscopy with broad argon ion beam milling, was used to determine how the emergence of such hydrophobic characteristics in a nanofibril face occurs in relation to the ACC nanopulverization mechanism due to the collision of the pair of water jets.

Microcrystalline cellulose from soybean hull as an excipient in solid dosage forms: Preparation, powder characterization, and tableting properties

Microcrystalline cellulose (MCC) is one of the essential functional excipients in the formulation of tablets. The need for cheaper MCC sources has drawn significant attention to exploring renewable sources. In this study, MCC was produced from soybean hull (SBH), the primary by-product of the soy industry, using a novel, simplified, and cost-effective approach. Various characterization techniques were used to study the physicochemical properties and micromeritics of the SBH-based MCC powders and compare them to those of the commercial Avicel PH-101. SBH MCCs had a larger particle size, a broader particle size distribution, a higher degree of polymerization, a higher degree of crystallinity, better thermal stability, and slightly superior flowability and compressibility than Avicel PH-101. The tableting blends (containing 60 % MCC) were prepared, and the post-compression out-of-die Heckel analysis showed that formulations with aggregated SBH MCCs were less ductile than those made with Avicel PH-101, resulting in a lower porosity (better compressibility) of the latter at higher compression pressures. The hardness values for all formulations were above 6 kg, with higher values for those made with Avicel PH-101. The lubricant sensitivity was lower for SBH MCCs. All tablets made using developed formulations showed very low friability (<0.1 %) and short disintegration times (<90 s), making them well-suited candidates for manufacturing orally disintegrating tablets (ODTs).

Radical electron-induced cellulose-semiconductors

Bio-semiconductors are expected to be similar to organic semiconductors; however, they have not been utilized in application yet. In this study, we show the origin of electron appearance, N- and S-type negative resistances, rectification, and switching effects of semiconductors with energy storage capacities of up to 418.5 mJ/m2 using granulated amorphous kenaf cellulose particles (AKCPs). The radical electrons in AKCP at 295 K appear in cellulose via the glycosidic bond C1-O1·-C4. Hall effect measurements indicate an n-type semiconductor with a carrier concentration of 9.89 × 1015/cm3, which corresponds to a mobility of 10.66 cm2/Vs and an electric resistivity of 9.80 × 102 Ωcm at 298 K. The conduction mechanism in the kenaf tissue was modelled from AC impedance curves. The light and flexible cellulose-semiconductors may open up new avenues in soft electronics such as switching effect devices and bio-sensors, primarily because they are composed of renewable natural compounds.

Preparation and functionalization of cellulose nanofibers using a naturally occurring acid and their application in stabilizing linseed oil/water Pickering emulsions

Finding efficient and environmental-friendly methods to produce and chemically modify cellulose nanofibers (CNFs) remains a challenge. In this study, lactic acid (LA) treatment followed by microfluidization was employed for the isolation and functionalization of CNFs. Small amounts of HCl (0.01, 0.1, and 0.2 M) were used alongside LA to intensify cellulose hydrolysis. FTIR spectroscopy and solid-state 13C NMR confirmed the successful functionalization of CNFs with lactyl groups during isolation, while SEM, AFM, and rheological tests revealed that the addition of HCl governed the fibers' sizes and morphology. Notably, the treatment with LA and 0.2 M HCl resulted in a more efficient defibrillation, yielding smaller nanofibers sizes (62 nm) as compared to the treatment with LA or HCl alone (90 and 108 nm, respectively). The aqueous suspension of CNFs treated with LA and 0.2 M HCl showed the highest viscosity and storage modulus. LA-modified CNFs were tested as stabilizers for linseed oil/water (50/50 v/v) emulsions. Owing to the lactyl groups grafted on their surface and higher aspect ratio, CNFs produced with 0.1 and 0.2 M HCl led to emulsions with increased stability (a creaming index increase of only 3 % and 1 %, respectively, in 30 days) and smaller droplets sizes of 23.4 ± 1.2 and 35.5 ± 0.5 μm, respectively. The results showed that LA-modified CNFs are promising stabilizers for Pickering emulsions.

Effects of Ferric Ions on Cellulose Nanocrystalline-Based Chiral Nematic Film and Its Applications

Chiral nematic materials have been attracting attention in fields of advanced functional applications due to their unique iridescent colors and tunable helical structure. A precisely decreased pitch is of importance for construction and applications of chiral nematic materials; however, it remains a huge challenge. Herein, cellulose nanocrystal (CNC) is selected as a constructed matrix for chiral nematic films, and ferric chloride (FeCl3) is used as a modification agent. We investigate the effects of the ferric ion loads on the helical structure and optical characteristics of iridescent film. Subsequently, the influence of ferric ions on the assembly process of CNC liquid crystal and the regulation of the structure color of self-assembled monolayers are discussed. Therefore, the CNC/FeCl3 chiral nematic films showed a blueshifted structural color from orange to blue, which highlights a simple route to achieve the regulation of decreased pitch. Further, we have applied this CNC/FeCl3 chiral nematic film for benzene gas detection. The sensing performance shows that the CNC/FeCl3 chiral nematic film reacts to benzene gas, which can be merged into the nematic layer of the CNC and trigger the iron ions chelated on the CNC, consequently arousing the redshift of the reflected wavelength and the effective colorimetric transition. This CNC/FeCl3 chiral nematic film is anticipated to boost a new gas sensing mechanism for faster and more effective in-situ qualitative investigations.

Cellulose nanocrystals extracted from rice husk using the formic/peroxyformic acid process: isolation and structural characterization

Cellulose derived from biomass is a renewable resource with numerous applications. Using formic/peroxyformic acid at atmospheric pressure, cellulose nanocrystals (CNC) were isolated from rice husk (RH) in this study. This method was an excellent way to get rid of lignin and hemicelluloses from RH. The cellulose was subsequently acid hydrolyzed by H2SO4 (64%) for 30 minutes at 45 °C. The chemical and microstructure analysis showed that the lignin and hemicellulose contents of raw RH had been eliminated, and the crystallinity content of CNC was 67.16%. According to transmission electron microscopy (TEM) morphological analysis, CNC measured 19 ± 3.3 nm in diameter, 195 ± 24 nm in length, and 10.2 ± 6.8 in aspect ratio. The thermal stability of RH and CNC was also investigated using thermogravimetric analysis (TGA). These encouraging findings demonstrated the potential for reusing RH agricultural waste to create CNC and include nanocomposites as a reinforcing material.

Effect of pulp cell wall polysaccharides on citrus fruit with different mastication traits

Mastication trait is a primary quality attribute of citrus fruit, influencing consumer demands and industrial processing conditions. However, the underlying causes of differences in mastication traits of citrus remain unclear. In this study, microscopy, spectroscopy and diffraction techniques were applied to investigate the physicochemical properties of Hongmeiren (HMR), Satsuma (WM) and Nanfeng tangerine (NF) with superior, moderate and inferior mastication traits, respectively. Ultrastructure indicated that NF had more neatly arranged and regularly shaped cells than HMR and WM. The monosaccharide composition of NF revealed that multi-branched Na2CO3-soluble pectin (NSF) enhanced intercellular adhesion. Additionally, FT-IR analysis revealed more intense vibrations of O2-H····O6 intramolecular hydrogen bonds within NF cellulose, which resulted in a higher crystallinity of cellulose (73.75%) than HMR (32.53%) and WM (43.76%). Overall, the high content and crystallinity of cellulose, the multi-branched NSF and the high content of hemicellulose contributed to the inferior mastication trait of citrus fruit.

Plant-Derived Nanocellulose with Antibacterial Activity for Wound Healing Dressing

The medical sector is one of the biggest consumers of single-use materials, and while the insurance of sterile media is non-negotiable, the environmental aspect is a chronic problem. Nanocellulose (NC) is one of the safest and most promising materials that can be used in medical applications due to its valuable properties like biocompatibility and biodegradability, along with its good mechanical properties and high water uptake capacity. However, NC has no bactericidal activity, which is a critical need for the effective prevention of infections in chronic diabetic wound dressing applications. Therefore, in this work, a natural product, propolis extract (PE), was used as an antibacterial agent, in different amounts, together with NC to obtain sponge-like structures (NC/PE). The scanning electron microscope (SEM) images showed well-impregnated cellulose fibers and a more compact structure with the addition of PE. According to the thermogravimetric analysis (TGA), the samples containing PE underwent thermal degradation before the unmodified NC due to the presence of volatile compounds in the extract. However, the peak degradation temperature in the first derivative thermogravimetric curves was higher for all the sponges containing PE when compared to the unmodified NC. The antibacterial efficacy of the samples was tested against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, as well as on two clinically resistant isolates. The samples completely inhibited the development of Staphylococcus aureus, and Pseudomonas aeruginosa was partially inhibited, while Escherichia coli was resistant to the PE action. Considering the physical and biological properties along with the environmental and economic benefits, the development of an NC/PE wound dressing seems promising.

Extraction of the cellulose nanocrystals via ammonium persulfate oxidation of beaten cellulose fibers

The effect of beating starting pulp was investigated on the oxidation efficiency of ammonium persulfate (APS), the yield, and the properties of the CNCs. The beaten pulp and the subsequent CNCs were characterized, respectively, by different techniques. The CNCs were classified as CNC1 and CNC2, dependent on ultrasonication. It showed that the beating exposed more free OH groups in the pulp and enhanced the yield and surface charges of CNCs. Compared to the CNC2, the CNC1 had a higher surface charge, higher crystallinity, higher thermal stability, shorter length, smaller length distribution, and slightly larger width. The CNC1 and CNC2 had similar rheological properties. For the beaten pulp with a beating degree of 25°SR, the yields of the CNC1 and the total CNCs reached the maximum, 42.65 and 34.11 %, respectively. The surface charges of the CNC1 and the CNC2 also reached the maximum, -44.5 and - 33.6 mV, respectively. Their crystallinity indexes were 80.07 and 75.42 %, respectively. The lengths of the CNC1 and the CNC2 were 157.31 ± 30.61 and 214.92 ± 65.52 nm, and their widths were 10.13 ± 2.74 and 9.43 ± 2.99 nm, respectively. Therefore, proper beating enhanced the APS oxidation efficiency and influenced the CNCs properties.

High throughput disassembly of cellulose nanoribbons and colloidal stabilization of gel-like Pickering emulsions

We introduce a strategy to disintegrate cellulose microfibrils present in the cell walls of plant fibers. The process includes impregnation and mild oxidation followed by ultrasonication, which loosens the hydrophilic planes of crystalline cellulose while preserving the hydrophobic ones. The resultant molecularly-sized cellulose structures (cellulose ribbons, CR) retain a length of the order of a micron (1.47 ± 0.48 μm, AFM). A very high axial aspect ratio is determined (at least 190), considering the CR height (0.62 ± 0.38 nm, AFM), corresponding to 1-2 cellulose chains, and width (7.64 ± 1.82 nm, TEM). The new molecularly-thin cellulose proposes excellent hydrophilicity and flexibility, enabling a remarkable viscosifying effect when dispersed in aqueous media (shear-thinning, zero shear viscosity of 6.3 × 10⁵ mPa·s). As such, CR suspensions readily develop into gel-like Pickering emulsions in the absence of crosslinking, suitable for direct ink writing at ultra-low solids content.

Highly stretchable, fast self-healing nanocellulose hydrogel combining borate ester bonds and acylhydrazone bonds

Self-healing hydrogels have received considerable attention as a promising material for flexible electronic devices given their mechanical durability and structurally tunable properties. In this study, a highly stretchable self-healing hydrogel with dual cross-linking network was developed via borate ester bonds generated by polyvinyl alcohol and borax, and acylhydrazone bonds formed by aldehyde nanocellulose with adipic acid dihydrazide-modified alginate. Compared with the single network hydrogel composed of polyvinyl alcohol and borax, the introduction of dynamic acylhydrazone bonds greatly increases the flexibility of the hydrogel. The elongation rate increased from 480 % to approximately 1440 %, and the self-healing efficiency increased from 84.6 % to 92.7 % after healing for 60 min at ambient temperature without any stimulus. Moreover, the longer the self-healing time, the more evident the self-healing effect of the acylhydrazone bonds. In addition, electrical measurements confirmed a wide working strain range (ca.1000 %), durability, and reliability. Once assembled as a strain sensor, the hydrogel is able to monitor both large and subtle human motions. Besides, this hydrogel exhibited desirable biocompatibility, as demonstrated by in vitro cytotoxicity towards NIH 3T3 cells. These integrated properties make this nanocomposite hydrogel a promising candidate for future applications as green, flexible, and smart sensors.

Nanocellulose Sponges Containing Antibacterial Basil Extract

Nanocellulose (NC) is a valuable material in tissue engineering, wound dressing, and drug delivery, but its lack of antimicrobial activity is a major drawback for these applications. In this work, basil ethanolic extract (BE) and basil seed mucilage (BSM) were used to endow nanocellulose with antibacterial activity. NC/BE and NC/BE/BSM sponges were obtained from nanocellulose suspensions and different amounts of BE and BSM after freeze-drying. Regardless of the BE or BSM content, the sponges started to decompose at a lower temperature due to the presence of highly volatile active compounds in BE. A SEM investigation revealed an opened-cell structure and nanofibrillar morphology for all the sponges, while highly impregnated nanofibers were observed by SEM in NC/BE sponges with higher amounts of BE. A quantitative evaluation of the porous morphology by microcomputer tomography showed that the open porosity of the sponges varied between 70% and 82%, being lower in the sponges with higher BE/BSM content due to the impregnation of cellulose nanofibers with BE/BSM, which led to smaller pores. The addition of BE increased the specific compression strength of the NC/BE sponges, with a higher amount of BE having a stronger effect. A slight inhibition of S. aureus growth was observed in the NC/BE sponges with a higher amount of BE, and no effect was observed in the unmodified NC. In addition, the NC/BE sponge with the highest amount of BE and the best antibacterial effect in the series showed no cytotoxic effect and did not interfere with the normal development of the L929 cell line, similar to the unmodified NC. This work uses a simple, straightforward method to obtain highly porous nanocellulose structures containing antibacterial basil extract for use in biomedical applications.

Flow and assembly of cellulose nanocrystals (CNC): A bottom-up perspective - A review

Cellulosic sources, such as lignocellulose-rich biomass, can be mechanically or acid degraded to produce inclusions called cellulose nanocrystals (CNCs). They have several uses in the sectors of biomedicine, photonics, and material engineering because of their biodegradability, renewability, sustainability, and mechanical qualities. The processing and design of CNC-based products are inextricably linked to the rheological behaviour of CNC suspension or in combination with other chemicals, such as surfactants or polymers; in this context, rheology offers a significant link between microstructure and macro scale flow behaviour that is intricately linked to material response in applications. The flow behaviour of CNC items must be properly specified in order to produce goods with value-added characteristics. In this review article, we provide new research on the shear rheology of CNC dispersion and CNC-based hydrogels in the linear and nonlinear regime, with storage modulus values reported to range from ~10^-3 to 10³ Pa. Applications in technology and material science are also covered simultaneously. We carefully examined the effects of charge density, aspect ratio, concentration, persistence length, alignment, liquid crystal formation, the cause of chirality in CNCs, interfacial behaviour and interfacial rheology, linear and nonlinear viscoelasticity of CNC suspension in bulk and at the interface using the currently available literature.

Preparation of Cellulose Nanofibers from Corn Stalks by Fenton Reaction: A New Insight into the Mechanism by an Experimental and Theoretical Study

Agricultural biomass wastes are an abundant feedstock for biorefineries. However, most of these wastes are not treated in the right way. Here, corn stalks (CSs) were assigned as the raw material to produce cellulose nanofibers (CNFs) via in situ Fenton oxidation treatment. In order to probe the formation mechanism of an in situ Fenton reactor, the bonding interaction of hydrated Fe²⁺ ions and fiber has been systemically studied based on adsorption experiments, IR spectroscopy, density functional theory (DFT) calculations, and Raman spectroscopy. The results indicate that the coordination of the hydrated Fe²⁺ ion to the fiber generates a quasi-octahedral-coordinated sphere around the Fe center. The Jahn-Teller distortion effect of the Fe center promotes the Fe-O₂H₂ bonding interaction via reduction of the energy gap of the d_z² orbital of the Fe center and π_2py/π_2pz orbitals of the H₂O₂ molecule. The oxidation treatment of the pretreated CS by the in situ Fenton process shows the formation of a new carboxyl group on the fiber surface. The scanning electron microscopy image shows that the Fenton-treated fiber was scattered into the nanosized CNFs with a diameter of up to 50 nm. Both experimental and theoretical studies show that the pseudo-first-order kinetic reaction could describe the in situ Fenton kinetics well. Moreover, the proposed catalytic cycle shows that the large thermodynamic barrier is the cleavage of the O-O bond of H₂O₂ to generate the ^•OH radical, and the whole catalytic cycle is found to be spontaneous at room temperature.

Harvesting Electricity from Atmospheric Moisture by Engineering an Organic Acid Gradient in Paper

Moisture-activated electric generators (MEGs) that harvest clean energy from atmospheric humidity offer exciting opportunities for upgraded energy conversions. However, it is challenging to obtain MEGs that are both easy to fabricate and of high output power, due to the requirement for particular functional materials and the cumbersome manufacturing process. Herein, a simple and general method is adopted to prepare MEGs with chemically gradient structures. As a specific example, a gradient distribution of citric acid was successfully constructed inside an A4 printer paper by asymmetric drying, which can generate a continuous voltage of tens of millivolts by ambient humidity, and even to volts (275 mV and 7.6 μA cm^-2) under asymmetric humidity stimulation, and the maximum power density output was 2.1 μW cm^-2. The driving force behind this energy conversion is a self-maintained ionic gradient created within the paper by the asymmetric ionization of gradient organic acids when exposed to gradient or nongradient humid air. This work broadens the class of materials and possibilities for the rapid development of MEGs, shedding new light on the revolution of generators that harvest green and sustainable energy for power generation.

Sponges from Plasma Treated Cellulose Nanofibers Grafted with Poly(ethylene glycol)methyl Ether Methacrylate

In this work, cellulose nanofibers (CNF) were surface treated by plasma and grafted with poly(ethylene glycol)methyl ether methacrylate (PEGMMA) for increasing mechanical strength and hydrophobicity. The surface characteristics of the sponges were studied by scanning electron microscopy, micro-computed tomography, and Fourier transform infrared spectroscopy, which demonstrated successful surface modification. Plasma treatment applied to CNF suspension led to advanced defibrillation, and the resulting sponges (CNFpl) exhibited smaller wall thickness than CNF. The grafting of PEGMMA led to an increase in the wall thickness of the sponges and the number of larger pores when compared with the non-grafted counterparts. Sponges with increased hydrophobicity demonstrated by an almost 4 times increase in the water contact angle and better mechanical strength proved by 2.5 times increase in specific compression strength were obtained after PEGMMA grafting of plasma treated CNF. Cells cultivated on both neat and PEGMMA-grafted CNF sponges showed high viability (>99%). Remarkably, CNF grafted with PEGMMA showed better cell viability as compared with the untreated CNF sample; this difference is statistically significant (p < 0.05). In addition, the obtained sponges do not trigger an inflammatory response in macrophages, with TNF-α secretion by cells in contact with CNFpl, CNF-PEGMMA, and CNFpl-PEGMMA samples being lower than that observed for the CNF sample. All these results support the great potential of cellulose nanofibers surface treated by plasma and grafted with PEGMMA for biomedical applications.

Ultrasonic cavitation: An effective cleaner and greener intensification technology in the extraction and surface modification of nanocellulose

With rising consumer demand for natural products, a greener and cleaner technology, i.e., ultrasound-assisted extraction, has received immense attention given its effective and rapid isolation for nanocellulose compared to conventional methods. Nevertheless, the application of ultrasound on a commercial scale is limited due to the challenges associated with process optimization, high energy requirement, difficulty in equipment design and process scale-up, safety and regulatory issues. This review aims to narrow the research gap by placing the current research activities into perspectives and highlighting the diversified applications, significant roles, and potentials of ultrasound to ease future developments. In recent years, enhancements have been reported with ultrasound assistance, including a reduction in extraction duration, minimization of the reliance on harmful chemicals, and, most importantly, improved yield and properties of nanocellulose. An extensive review of the strengths and weaknesses of ultrasound-assisted treatments has also been considered. Essentially, the cavitation phenomena enhance the extraction efficiency through an increased mass transfer rate between the substrate and solvent due to the implosion of microbubbles. Optimization of process parameters such as ultrasonic intensity, duration, and frequency have indicated their significance for improved efficiency.

Single Molecular Layer of Chitin Sub-Nanometric Nanoribbons: One-Pot Self-Exfoliation and Crystalline Assembly into Robust, Sustainable, and Moldable Structural Materials

Sub-nanometric materials (SNMs) represent a series of unprecedented size-/morphology-related properties applicable in theoretical research and diverse cutting-edge applications. However, in-depth investigation and wide utilization of organic SNMs are frequently hindered, owing to the complex synthesis procedures, insufficient colloidal stability, poor processability, and high cost. In this work, a low-cost, energy-efficient, convenient, effective, and scalable method is demonstrated for directly exfoliating chitin SNMs from their natural sources through a one-pot "tandem molecular intercalation" process. The resultant solution-like sample, which exhibits ribbon-like feature and contains more than 85% of the single molecular layer (thickness <0.6 nm), is capable of being solution-processed to different types of materials. Thanks to the sub-nanometric size and rich surface functional groups, chitin SNMs reveal versatile intriguing properties that rarely observe in their nano-counterparts (nanofibrils), e.g., crystallization-like assembly in the colloidal state and alcoplasticity/self-adhesiveness in the bulk aggregate state. The finding in this work not only opens a new avenue for the high value-added utilization of chitin, but also provides a new platform for both the theoretical study and practical applications of organic SNMs.

Value-Added Utilization of Wheat Straw: From Cellulose and Cellulose Nanofiber to All-Cellulose Nanocomposite Film

To accelerate the high value-added usage of agricultural residue, cellulose and cellulose nanofibers (CNFs) were extracted from wheat straw and then formed into all-cellulose nanocomposite films. The acid-alkali method (AM) and the extraction method (EM) were respectively adopted to prepare wheat straw cellulose (WSC), and the TEMPO oxidation method was used to extract CNFs. The nanocomposite films were fabricated by dissolving WSC and adding different CNF contents of 0.0, 0.5, 1.5, and 3.0%. There was a better miscibility for the all-cellulose nanocomposite film prepared by EM (Composite-E) compared to that for the all-cellulose nanocomposite film prepared by AM (Composite-A). Composite-E also showed a better optical transparency than Composite-A. The thermal stability of the two RWSCs presented contrary results when the CNFs were added, indicating a higher thermal stability for Composite-E than for Composite-A. This should have determined the properties of the films in which Cellulose I and Cellulose II coexisted for the all-cellulose nanocomposite films, and the forming mechanism of Cellulose II and crystallinity were determined by the cellulose-extracting method. X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) spectroscopy also showed that there was more Cellulose I in Composite-E than in Composite-A. The results are expected to enrich the data for deep processing of agricultural residues.

The Influence of High-Intensity Ultrasonication on Properties of Cellulose Produced from the Hop Stems, the Byproduct of the Hop Cones Production

The goal of this work is to evaluate the hop stems, a byproduct of hop cones production, as a potential source of cellulose. Hop stems contain up to 29% of cellulose. The cellulose isolation was conducted through the thermochemical treatment. After high-speed blending, the cellulose was characterized by 67% of crystallinity degree obtained from X-ray diffraction and median diameter of 6.7 nm obtained from atomic force microscopy imaging. The high-intensity ultrasonication (HIUS) was applied to reach further disintegration of cellulose fibers. The longer HIUS treatment resulted in decrease in crystallinity degree even up to 60% and decrease in the fiber diameter up to 4 nm. The Fourier transform infrared spectroscopy (FTIR) spectra showed that HIUS treatment led to changes in intermolecular hydrogen bonds. The stability of cellulose dispersions versus length of HIUS treatment was monitored over 14 days with back dynamic light scattering and laser Doppler electrophoresis methods. Obtained results are evidence that the hop stems are a potential source of cellulose and that it is possible to obtain stable dispersions after HIUS treatment. This was the first time that the properties of hop cellulose have been described so extensively and in detail after the use of HIUS treatment.

Structural Evolution of Cellulose from Bamboo Fibers and Parenchyma Cells during Ionic Liquid Pretreatment for Enhanced Hydrolysis

Bamboo fibers and parenchyma cells, the two dominant types of cells in bamboo, exhibit some interesting differences in cellulose crystalline structures. In the present investigation, we further demonstrated that these structural differences affect their response during ionic liquid (IL) pretreatment and the sugar conversion yield, by tracking their changes in morphology, chemical, and crystalline structures. All of the results pointed to the fact that the cellulose from bamboo fibers exhibited higher recalcitrance to IL pretreatment, with a significantly lower change in crystallinity index, d spacings from the (110) and (11̅0) planes, crystallite sizes, and easier transformation from cellulose I to cellulose II after pretreatment, as compared to that from parenchyma cells. Furthermore, the crystalline parameters of (110) and (11̅0) lattice planes exhibited more changes compared to the (200) direction. This investigation highlights the significance of parenchyma cell wastes from bamboo processing plants as a competitive candidate for the biorefinery industry.

Preparation and Characterization of Nanocellulose/Chitosan Aerogel Scaffolds Using Chemical-Free Approach

Biopolymer-based aerogels are open three-dimensional porous materials that are characterized by outstanding properties, such as a low density, high porosity and high surface area, in addition to their biocompatibility and non-cytotoxicity. Here we fabricated pure and binary blended aerogels from cellulose nanofibers (CNFs) and chitosan (CS), using a chemical-free approach that consists of high-pressure homogenization and freeze-drying. The prepared aerogels showed a different porosity and density, depending on the material and mixing ratio. The porosity and density of the aerogels ranged from 99.1 to 90.8% and from 0.0081 to 0.141 g/cm³, respectively. Pure CNFs aerogel had the highest porosity and lightest density, but it showed poor mechanical properties and a high water absorption capacity. Mixing CS with CNFs significantly enhance the mechanical properties and reduce its water uptake. The two investigated ratios of aerogel blends had superior mechanical and thermal properties over the single-material aerogels, in addition to reduced water uptake and 2-log antibacterial activity. This green fabrication and chemical-free approach could have great potential in the preparation of biopolymeric scaffolds for different biomedical applications, such as tissue-engineering scaffolds.

Influence of TEMPO oxidation on the properties of ethylene glycol methyl ether acrylate grafted cellulose sponges

In this study, cellulose nanofibers (CNF) obtained via high-pressure microfluidization were 2,6,6-tetra-methylpiperidine-1-oxyl (TEMPO) oxidized (TOCNF) in order to facilitate the grafting of ethylene glycol methyl ether acrylate (EGA). FTIR and XPS analyses revealed a more efficient grafting of EGA oligomers on the surface of TOCNF as compared to the original CNF. As a result, a consistent covering of the TOCNF fibers with EGA oligomers, an increased hydrophobicity and a reduction in porosity were noticed for TOCNF-EGA. However, the swelling ratio of TOCNF-EGA was similar to that of original CNF grafted with EGA and higher than that of TOCNF, because the higher amount of grafted EGA onto oxidized cellulose and the looser structure reduced the contacts between the fibrils and increased the absorption of water. All these results corroborated with a good cytocompatibility and compression strength recommend TOCNF-EGA for applications in regenerative medicine.

Functional Materials from Nanocellulose: Utilizing Structure-Property Relationships in Bottom-Up Fabrication

It is inherently challenging to recapitulate the precise hierarchical architectures found throughout nature (such as in wood, antler, bone, and silk) using synthetic bottom-up fabrication strategies. However, as a renewable and naturally sourced nanoscale building block, nanocellulose-both cellulose nanocrystals and cellulose nanofibrils-has gained significant research interest within this area. Altogether, the intrinsic shape anisotropy, surface charge/chemistry, and mechanical/rheological properties are some of the critical material properties leading to advanced structure-based functionality within nanocellulose-based bottom-up fabricated materials. Herein, the organization of nanocellulose into biomimetic-aligned, porous, and fibrous materials through a variety of fabrication techniques is presented. Moreover, sophisticated material structuring arising from both the alignment of nanocellulose and via specific process-induced methods is covered. In particular, design rules based on the underlying fundamental properties of nanocellulose are established and discussed as related to their influence on material assembly and resulting structure/function. Finally, key advancements and critical challenges within the field are highlighted, paving the way for the fabrication of truly advanced materials from nanocellulose.

Synthesis of bio-inspired cellulose nanocrystals-soy protein isolate nanoconjugate for stabilization of oil-in-water Pickering emulsions

The development of hybrid polysaccharide-protein complexes as Pickering emulsion stabilizers has attracted increasing research interest in recent years. This work presents an eco-friendly surface modification strategy to functionalize hydrophilic cellulose nanocrystals (CNC) using hydrophobic soy protein isolate (SPI) via mussel adhesive-inspired poly (l-dopa) (PLD) to develop improved nanoconjugates as stabilizers for oil-in-water Pickering emulsion. The physicochemical properties of the CNC-PLD-SPI nanoconjugate were evaluated by solid-state 13C NMR, FT-IR, TGA, XRD, contact angle analysis, and TEM. The modified CNC (conjugation content of 38.22 ± 1.21%) had lowered crystallinity index, higher thermal stability, and more hydrophobic than unmodified CNC, with an average particle size of 309.9 ± 8.0 nm. Use of amphiphilic CNC-PLD-SPI nanoconjugate with greater conformational flexibility as Pickering stabilizer produced oil-in-water emulsions with greater physical stability.

The Effect of High Lignin Content on Oxidative Nanofibrillation of Wood Cell Wall

Wood from field-grown poplars with different genotypes and varying lignin content (17.4 wt % to 30.0 wt %) were subjected to one-pot 2,2,6,6-Tetramethylpiperidin-1-yl)oxyl catalyzed oxidation and high-pressure homogenization in order to investigate nanofibrillation following simultaneous delignification and cellulose oxidation. When comparing low and high lignin wood it was found that the high lignin wood was more easily fibrillated as indicated by a higher nanofibril yield (68% and 45%) and suspension viscosity (27 and 15 mPa·s). The nanofibrils were monodisperse with diameter ranging between 1.2 and 2.0 nm as measured using atomic force microscopy. Slightly less cellulose oxidation (0.44 and 0.68 mmol·g⁻¹) together with a reduced process yield (36% and 44%) was also found which showed that the removal of a larger amount of lignin increased the efficiency of the homogenization step despite slightly reduced oxidation of the nanofibril surfaces. The surface area of oxidized high lignin wood was also higher than low lignin wood (114 m²·g⁻¹ and 76 m²·g⁻¹) which implicates porosity as a factor that can influence cellulose nanofibril isolation from wood in a beneficial manner.

Fabrication and Characterization of Chitosan/Cellulose Nanocrystal/Glycerol Bio-Composite Films

Cellulose nanocrystal (CNC)-reinforced bio-composite films containing glycerol were produced using the solution casting technique. The influences of the addition of CNC (2, 4, and 8 wt%) and glycerol (10, 20, and 30 wt%) on the properties of the bio-composite films were studied in the present work. The resulting films were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetry analysis (TGA), and according to their tensile, water absorption, and light transmission behavior. The introduction of 4 wt% CNC into the chitosan film did not affect the thermal stability, but the presence of 20 wt% glycerol reduced the thermal stability. The addition of 4 wt% CNC to the chitosan film increased its tensile strength, tensile modulus, and elongation at break by 206%, 138%, and 277%, respectively. However, adding more than 8 wt% CNC resulted in a drastic reduction in the strength and ductility of the chitosan film. The highest strength and stiffness of the chitosan bio-composite film were attained with 4 wt% CNC and 20 wt% glycerol. The water absorption and light transmission of the chitosan film were reduced dramatically by the presence of both CNC and glycerol.

Contributions of Crystalline and Noncrystalline Cellulose Can Occur in the Same Spectral Regions: Evidence Based on Raman and IR and Its Implication for Crystallinity Measurements

Aggregated states of celluloses remain poorly understood, and therefore, the topic requires careful investigation. In this study, Raman, IR, and X-ray diffraction (XRDs) were used to study cotton microcrystalline cellulose (MCC) and MCC that has been ball-milled to various degrees. Raman and IR spectroscopy methods indicated that when these ball-milled samples were wet with water, most underwent conformational changes at the molecular level. Although formation of cellulose II was observed in longer duration ball-milled samples, the changes primarily gave rise to increased contributions in spectral and diffraction regions typically associated with the contributions of crystalline cellulose I. Moreover, when the wet samples were air-dried at 25 °C, the newly formed cellulose I-like structures partly reverted to the previous form present in the initial dry state. These findings explained for the previously reported XRD and NMR observations, where the addition of water resulted in increased crystallinities of cellulose samples. The implications of these findings to cellulose crystallinity measurements and other situations are discussed.

Characterization of an Amphiphilic Janus-Type Surface in the Cellulose Nanofibril Prepared by Aqueous Counter Collision

Cellulose nanofibrils, which attract extensive attention as a bio-based, sustainable, high-performance nanofibril, are believed to be predominantly hydrophilic. This study aimed to prove the presence of an amphiphilic "Janus-type fiber surface" in water with hydrophobic and hydrophilic faces in a cellulose nanofibril (ACC-CNF) that was prepared by the aqueous counter collision method. We clarified the surface characteristics of the ACC-CNF by confocal laser scanning microscopy with a carbohydrate-binding module and congo red probes for the hydrophobic planes on the cellulose fiber surfaces and calcofluor white as hydrophilic plane probes. The results indicated the presence of both characteristic planes on a single ACC-CNF surface, which verifies an amphiphilic Janus-type structure. Both hydrophobic probes adsorbed onto ACC-CNFs for the quantitative evaluation of the degree of ACC-CNF surface hydrophobicity by Langmuir's adsorption theory based on the optimal maximum adsorption amounts for various starting raw material types.

New insights into the autofluorescence properties of cellulose/nanocellulose

This work explored the fluorescence properties of nano/cellulose isolated from bleached softwood kraft pulp by TEMPO oxidation. Fluorescence spectra showed that all samples exhibited a typical emission peak at 574 nm due to the probabilistic formation of unsaturated bonds by glycosidic bonds independent of lignin. Increasing the excitation wavelengths (510-530 nm) caused red shift of fluorescence emission peaks (570-585 nm) with unchanged fluorescence intensity. Conversely, changing acid/alkaline conditions led to an increase of fluorescence intensity with no shifting of fluorescence emission peak. This can be attributed to an increase in the polarity of the solution environment but does not cause interaction of functional groups within the system identified by generalized two-dimensional correlation fluorescence spectroscopy. This study provides new insight in applying nano/cellulose with special luminous characteristics in biomedicine area such as multi-color biological imaging and chemical sensing.

Cellulose-based adsorbents loaded with zero-valent iron for removal of metal ions from contaminated water

Sawdust loaded with zero-valent iron (S-ZVI) was prepared using a liquid phase reduction method for removing heavy metal ions from contaminated water. Surface chemistry and morphology of adsorbents were characterized with Fourier transform infrared (FT-IR) spectrometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), SEM-mapping, EDX, and X-ray photoelectron spectrum (XPS). The results demonstrated that the zero-valent iron was successfully loaded onto the sawdust. The impact of various factors such as pH, initial metal ion concentration, temperature, and contact time on the removal capability of the adsorbents was systematically investigated. The equilibrium adsorption data showed that the adsorption of arsenic ions and Cr(III) followed the Langmuir model well, and the maximum adsorption reached 111.37 and 268.7 mg/g in an aqueous solution system. In addition, the adsorption kinetics was more accurately described by the pseudo-second-order model, suggesting the domination of chemical adsorption. Meanwhile, the results on recyclability indicated that the high performance of S-ZVI on the removal of arsenic ions was well maintained after three regeneration cycles. The adsorption mechanism revealed in this work suggested that S-ZVI improved the dispersion of ZVI by minimizing the agglomeration, thus leading to highly effective adsorption via chelation, electrostatic interaction, and redox reaction.

Effect of heat treatment on thermal resistance, transparency and antimicrobial activity of sonicated ginger cellulose film

Transparent film with high thermal resistance and antimicrobial properties has many applications in the food packaging industry particularly packaging for reheatable food. This work investigates the effects of heat treatment on the thermal resistance, stability of transparency and antimicrobial activity of transparent cellulose film. The film from ginger nanocellulose fibers was prepared with chemicals and ultrasonication. The dried film was heated at 150 °C for 30, 60, 90, or 120 min. The unheated and sonicated film had the lowest crystallinity index and the lowest thermal properties. After heating, the film became brownish-yellow resulting from thermal oxidation. The reheated film had higher thermal resistance than unheated film. Heating led to further relaxation of cellulose network evidenced by shifting of the XRD peak positions toward lower values. The antimicrobial activity decreased due to heating. Average opacity value increases after short heating durations. It was relatively stable for further heating.

Cellulose–water system’s state analysis by proton nuclear magnetic resonance and sorption measurements

Most cellulose-based materials’ manufacturing processes include processing this biopolymer in an aqueous medium. Sorption properties depend on cellulose supramolecular structure and nature of its change during moistening. Plenty of researchers’ efforts have been directed to the development of scientifically sound and commercially reliable processes over the past decade for the cellulose fibers’ dispersion in an aqueous medium. Therefore, it needs a more detailed study of the cellulose–water system components’ interaction. This study presents the supramolecular structure and sorption properties of native cotton cellulose research results obtained by 1H NMR relaxation, spectroscopy and sorption measurements. Hydrophilic properties of cellulose as an adsorbent are characterized, taking into account a porous system between its structural elements. We examine in detail water adsorption on the active surface of cellulose Iβ. We also demonstrate the approach for determining the entropy change in the first two layers of adsorbed water and estimate this value increased during adsorption. Cellulose moistening is accompanied by the decomposition of macrofibrils into microfibrils and is manifested in a crystallinity decrease and a specific surface area growth.

Bacterial Cellulose Nanocomposites: Morphology and Mechanical Properties

Bacterial cellulose (BC) is a promising material for biomedical applications due to its unique properties such as high mechanical strength and biocompatibility. This article describes the microbiological synthesis, modification, and characterization of the obtained BC-nanocomposites originating from symbiotic consortium Medusomyces gisevii. Two BC-modifications have been obtained: BC-Ag and BC-calcium phosphate (BC-Ca₃(PO₄)₂). Structure and physicochemical properties of the BC and its modifications were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and infrared Fourier spectroscopy as well as by measurements of mechanical and water holding/absorbing capacities. Topographic analysis of the surface revealed multicomponent thick fibrils (150–160 nm in diameter and about 15 µm in length) constituted by 50–60 nm nanofibrils weaved into a left-hand helix. Distinctive features of Ca-phosphate-modified BC samples were (a) the presence of 500–700 nm entanglements and (b) inclusions of Ca₃(PO₄)₂ crystals. The samples impregnated with Ag nanoparticles exhibited numerous roundish inclusions, about 110 nm in diameter. The boundaries between the organic and inorganic phases were very distinct in both cases. The Ag-modified samples also showed a prominent waving pattern in the packing of nanofibrils. The obtained BC gel films possessed water-holding capacity of about 62.35 g/g. However, the dried (to a constant mass) BC-films later exhibited a low water absorption capacity (3.82 g/g). It was found that decellularized BC samples had 2.4 times larger Young’s modulus and 2.2 times greater tensile strength as compared to dehydrated native BC films. We presume that this was caused by molecular compaction of the BC structure.

Adsorption and interfacial structure of nanocelluloses at fluid interfaces

Nanocelluloses (NCs), more specifically cellulose nanocrystals and nanofibrils, are a green alternative for the stabilization of fluid interfaces. The adsorption of NCs at oil-water interfaces facilitates the formation of stable and biocompatible Pickering emulsions. In contrast, unmodified NCs are not able to stabilize foams. As a consequence, NCs are often hydrophobized by covalent modifications or adsorption of surfactants, allowing also the stabilization of foams or functional inverse, double, and stimuli-responsive emulsions. Although the interfacial stabilization by NCs is readily exploited, the driving force of adsorption and stabilization mechanisms remained long unclear. Here, we summarize the recent advances in the understanding of NC adsorption regarding kinetics, isotherms, and energetic aspects, as well as their interfacial structure, surface coverage, and contact angle. We thereby distinguish unmodified NCs, covalently modified NCs, and surfactant enhanced adsorption.

Cellulose Nanocrystal Reinforced Chitosan Based UV Barrier Composite Films for Sustainable Packaging

In this study, green composite films based on cellulose nanocrystal/chitosan (CNC/CS) were fabricated by solution casting. FTIR, XRD, SEM, and TEM characterizations were conducted to determine the structure and morphology of the prepared films. The addition of only 4 wt.% CNC in the CS film improved the tensile strength and Young's modulus by up to 39% and 78%, respectively. Depending on CNC content, the moisture absorption decreased by 34.1-24.2% and the water solubility decreased by 35.7-26.5% for the composite films compared with neat CS film. The water vapor permeation decreased from 3.83 × 10-11 to 2.41 × 10-11 gm-1 s-1Pa-1 in the CS-based films loaded with (0-8 wt.%) CNC. The water and UV barrier properties of the composite films showed better performance than those of neat CS film. Results suggested that CNC/CS nanocomposite films can be used as a sustainable packaging material in the food industry.

Effect of Eco-Friendly Cellulose Nanocrystals on Physical Properties of Cement Mortars

Nanocellulose, being a material with nanodimensions, is characterized by high tensile strength, high modulus of elasticity, low thermal expansion, and relatively low density, as well as exhibiting very good electrical conductivity properties. The paper presents the results of research on cement mortars with the addition of nanocrystals cellulose, applied in three different amounts (0.5%, 1.0%, and 1.5%) by weight of cement, including: physical and mechanical properties, frost resistance and resistance against the detrimental effect of salt, and microstructure examination (SEM). Along with an increase in amount of admixture, the weight loss following frost resistance and salt crystallization tests is reduced. Studies have shown that the addition of nanocrystalline cellulose improves the compressive and flexural strength by 27.6% and 10.9%, respectively. After 50 freezing and thawing (F–T) cycles for the mortars with 1.5% nanocellulose admixture, an improvement in frost resistance by 98% was observed. In turn, the sulfate crystallization tests indicated a 35-fold decrease in weight loss following 1.5% nanopolymer addition to the mortar.

Effects of Cellulose Nanocrystals and Cellulose Nanofibers on the Structure and Properties of Polyhydroxybutyrate Nanocomposites

One of the major obstacles for polyhydroxybutyrate (PHB), a biodegradable and biocompatible polymer, in commercial applications is its poor elongation at break (~3%). In this study, the effects of nanocellulose contents and their types, including cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs) on the crystallization, thermal, and mechanical properties of PHB composites were systematically compared. We explored the toughening mechanisms of PHB by adding CNCs and cellulose CNFs. The results showed that when the morphology of bagasse nanocellulose was rod-like and its content was 1 wt %, the toughening modification of PHB was the best. Compared with pure PHB, the elongation at break and Young’s modulus increased by 91.2% and 18.4%, respectively. Cellulose nanocrystals worked as heterogeneous nucleating agents in PHB and hence reduced its crystallinity and consequently improved the toughness of PHB. This simple approach could potentially be explored as a strategy to extend the possible applications of this biopolymer in packaging fields.