Cross-Linked Nanocellulosic Materials and Their Applications

Fabrication and characterization of multifunctional bioactive aerogel pads as superabsorbent - Case study: Meat preservation

In this study cellulose nanofibrils (CNFs)/poly vinyl alcohol (PVA) aerogels were produced and the effect of the concentration of CNF/PVA on porosity, density, pore size, water absorption, water vapor absorption, and mechanical properties were studied. CNFs were developed using peanut shells as agricultural waste. Curcumin (CUR) was incorporated into the aerogel matrix at different concentrations (30 %, 40 %, and 50 %). The best bioactive aerogel pad was selected based on its encapsulation efficiency (80.57 ± 0.29 %), loading capacity (22.85 ± 0.22 %), and antioxidant properties (74.14 ± 0.31 %). The aerogels loaded with CUR were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The bioactive aerogel pads showed antibacterial properties against Staphylococcus aureus. The cumulative release (65 %) of CUR from the aerogel matrix for 8 days, indicates a sustained release in meat-simulated media, which is suitable for increasing the shelf life of meat. The kinetics of the release showed that the Ritger-Peppas and Peppas-Sahlin models are the best models for the meat-simulated media. The storage results indicated that the package containing the aerogels loaded with CUR could increase the shelf life of meat from 6 to 8 days compared to the package containing the aerogels without CUR and the control package. Finally, this research provides a suitable strategy in the field of food packaging to produce multifunctional antimicrobial pads based on biodegradable agricultural waste.

Nanocellulose Technologies: Production, Functionalization, and Applications in Medicine and Pharmaceuticals - A Review

This review provides a comprehensive analysis of nanocellulose production, characterization, and applications, with a particular focus on its use in membranes and films for healthcare applications. The diverse sources of nanocellulose, including wood-based materials, agricultural byproducts, algae, and bacteria, are explored, highlighting their renewability, environmental benefits, and adaptability for specialized applications. The review also examines various pretreatment and processing methods, such as mechanical, chemical, and enzymatic treatments, outlining their roles in achieving desirable nanocellulose properties. Additionally, surface modification techniques, including amidation and esterification, are discussed for enhancing compatibility, stability, and performance when nanocellulose is integrated into composite materials. A novel mechanochemical approach is highlighted as a sustainable and energy-efficient fibrillation technique that reduces the environmental impact of nanocellulose production. Furthermore, the chemical modification and functionalization of nanocellulose are analyzed to expand its capabilities in advanced biomedical applications, including tissue engineering scaffolds that provide structural support for cell growth, wound dressings that leverage nanocellulose's antimicrobial and moisture-retentive properties, and drug delivery systems that utilize its biocompatibility and tunable release characteristics. The review concludes with future research directions, emphasizing the need for continued optimization of processing techniques, hybrid material development, and stimuli-responsive nanocellulose systems to unlock new biomedical and industrial applications.

Thermoformed, thermostable, waterproof and mechanically robust cellulose-based bioplastics enabled by dynamically reversible thia-Michael reaction

Cellulose is a renewable biodegradable polymer derived from abundant natural resources. Substituting petroleum-based polymers with cellulose-based bioplastics is an effective way to alleviate environmental issues like resource depletion and white pollution. However, challenges such as poor thermostability, difficulty in thermoforming and water sensitivity seriously hinder the fabrication and use of cellulose-based bioplastics. Herein, a thermoformed, thermostable, waterproof and mechanically robust cellulose-based bioplastic (H-HEC) is fabricated by introducing thia-Michael-based reversible crosslinked structure into hydroxyethyl cellulose. This is the first instance of integrating thia-Michael-based crosslinked structure into cellulose derivatives. The resulting H-HEC can be thermoformed and remolded without adding any plasticizers. Besides, the obtained H-HEC exhibit excellent overall properties, such as a high thermal decomposition temperature of 366 °C, a high water contact angle of 108°, a high transmittance of 90 % and good mechanical properties. Additionally, H-HEC combines impressive transparency with effective UV-shielding properties. We envision that this work provides a novel method to prepare thermoformable cellulose-based bioplastics with good water resistance, thermostability, transparency and mechanical properties. The combined thermoformability and superior overall performances will promote the practical application of cellulose-based bioplastics and contribute to the replacement of petroleum-based polymer by cellulose-based bioplastics.

Recent perspective of synthesis and modification strategies of cellulose nanocrystals and cellulose nanofibrils and their beneficial impact in scaffold-based tissue engineering: A review

Outstanding properties of nanocellulose provide opportunities for novel applications in various fields, particularly tissue engineering. Despite of numerous useful characteristics of nanocellulose, its production methods suffer from the lack of control of morphology, high cost, and the use of organic solvents. On the other hand, hydrophilicity of nanocellulose is a significant challenge for its dispersion as a reinforcement in hydrophobic polymers matrix. Therefore, sustainable production methods and well-tuning interfacial characteristics of nanocellulose have been identified as critical steps in their development. This review article discusses the numerous preparation methods and surface modification strategies of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) to help nanocellulose users obtain the appropriate material for their desired application. We also cover various polymer/nanocellulose scaffolds that are reported in the literature and investigate the effect of CNC and CNF on their mechanical, thermal and biological properties. Moreover, we provide several scientific figures and tables for a better understanding of the explored topics. Finally, we evaluate the opportunities and challenges of nanocellulose industrialization in the field of tissue engineering. Overall, this review guides researchers towards a deeper understanding of nanocellulose production processes, changing their properties using surface modification methods, and subsequently their performance in scaffold-based tissue engineering.

Quantitative characterization of the crosslinking degree of hydroxypropyl guar gum fracturing fluid by low-field NMR

As a widely used water-based fracturing fluid, the performance of hydroxypropyl guar gum fracturing fluid is closely related to the degree of crosslinking, the quantitative characterization of which can reveal a detailed crosslinking mechanism and guide the preparation of fracturing fluid gels with an excellent performance. However, the commonly used high-temperature rheology method for evaluating the performance of fracturing fluids only qualitatively reflects the degree of crosslinking. In this study, low-field nuclear magnetic resonance (LF-NMR) was used to characterize the degree of crosslinking in guar gum fracturing fluid gels. The spin-spin relaxation time of the H proton in guar gum was molecularly analyzed using LF-NMR. The viscoelastic properties met the requirements when the crosslinking degree of the gel was 88-94 %. The transformation of the linear structure into a membrane structure during the crosslinking process of the guar gum fracturing fluid was confirmed by freeze-drying and scanning electron microscopy (SEM) from a microscopic perspective. The changing trend of the microstructure and viscoelastic properties of the fracturing fluid gel under different crosslinker dosages was consistent with changes in the degree of crosslinking. The LF-NMR test process is non-destructive to the gel structure, and the test results demonstrate good accuracy and repeatability.

Tailoring the Structure and Physico-Chemical Features of Cellulose-Based Hydrogels Using Multi-Epoxy Crosslinking Agents

Hydrogel features can be designed and optimized using different crosslinking agents to meet specific requirements. In this regard, the present work investigates the physico-chemical features of cellulose-based hydrogels, designed by using different epoxy crosslinkers from the same glycidyl family, namely epichlorohydrin (ECH), 1,4-butanediol diglycidyl ether (BDDE), and trimethylolpropane triglycidyl ether (TMPTGE). The effect of the crosslinker's structure (from simple to branched) and functionality (mono-, bi- and tri-epoxy groups) on the hydrogels' features was studied. The performances of the hydrogels were investigated through the gel fraction, as well as by ATR-FTIR, DVS, SEM, DSC, and TG analyses. Also, the swelling and rheological behaviors of the hydrogels were examined. The advantages and limitations of each approach were discussed and a strong correlation between the crosslinker structure and the hydrogel properties was established. The formation of new ether bonds was evidenced by ATR-FTIR spectroscopy. It was emphasized that the pore size is directly influenced by the crosslinker type, namely, it decreases with the increasing number of epoxy groups from the crosslinker molecule, i.e., from 46 ± 11.1 µm (hydrogel CE, with ECH) to 12.3 ± 2.5 µm (hydrogel CB, with BDDE) and 6.7 ± 1.5 µm (hydrogel CT, with TMPTGE). The rheological behavior is consistent with the swelling data and hydrogel morphology, such as CE with the highest Qmax and the largest pore size being relatively more elastic than CB and CT. Instead, the denser matrices obtained by using crosslinkers with more complex structures have better thermal stability. The experimental results highlight the possibility of using a specific crosslinking agent, with a defined structure and functionality, in order to establish the main characteristics of hydrogels and, implicitly, to design them for a certain field of application.

Fabrication of cellulose nanocrystals/carboxymethyl cellulose/zeolite membranes for methylene blue dye removal: understanding factors, adsorption kinetics, and thermodynamic isotherms

This study introduces environmentally-friendly nanocellulose-based membranes for AZO dye (methylene blue, MB) removal from wastewater. These membranes, made of cellulose nanocrystals (CNCs), carboxymethyl cellulose (CMC), zeolite, and citric acid, aim to offer eco-friendly water treatment solutions. CNCs, obtained from sugarcane bagasse, act as the foundational material for the membranes. The study aims to investigate both the composition of the membranes (CMC/CNC/zeolite/citric acid) and the critical adsorption factors (initial MB concentration, contact time, temperature, and pH) that impact the removal of the dye. After systematic experimentation, the optimal membrane composition is identified as 60% CNC, 15% CMC, 20% zeolites, and 5% citric acid. This composition achieved a 79.9% dye removal efficiency and a 38.3 mg/g adsorption capacity at pH 7. The optimized membrane exhibited enhanced MB dye removal under specific conditions, including a 50 mg adsorbent mass, 50 ppm dye concentration, 50 mL solution volume, 120-min contact time, and a temperature of 25°C. Increasing pH from neutral to alkaline enhances MB dye removal efficiency from 79.9% to 94.5%, with the adsorption capacity rising from 38.3 mg/g to 76.5 mg/g. The study extended to study the MB adsorption mechanisms, revealing the chemisorption of MB dye with pseudo-second-order kinetics. Chemical thermodynamic experiments determine the Freundlich isotherm as the apt model for MB dye adsorption on the membrane surface. In conclusion, this study successfully develops nanocellulose-based membranes for efficient AZO dye removal, contributing to sustainable water treatment technologies and environmental preservation efforts.

Biotechnological innovations in nanocellulose production from waste biomass with a focus on pineapple waste

New materials' synthesis and utilization have shown many critical challenges in healthcare and other industrial sectors as most of these materials are directly or indirectly developed from fossil fuel resources. Environmental regulations and sustainability concepts have promoted the use of natural compounds with unique structures and properties that can be biodegradable, biocompatible, and eco-friendly. In this context, nanocellulose (NC) utility in different sectors and industries is reported due to their unique properties including biocompatibility and antimicrobial characteristics. The bacterial nanocellulose (BNC)-based materials have been synthesized by bacterial cells and extracted from plant waste materials including pineapple plant waste biomass. These materials have been utilized in the form of nanofibers and nanocrystals. These materials are found to have excellent surface properties, low density, and good transparency, and are rich in hydroxyl groups for their modifications to other useful products. These materials are well utilized in different sectors including biomedical or health care centres, nanocomposite materials, supercapacitors, and polymer matrix production. This review explores different approaches for NC production from pineapple waste residues using biotechnological interventions, approaches for their modification, and wider applications in different sectors. Recent technological developments in NC production by enzymatic treatment are critically discussed. The utilization of pineapple waste-derived NC from a bioeconomic perspective is summarized in the paper. The chemical composition and properties of nanocellulose extracted from pineapple waste may have unique characteristics compared to other sources. Pineapple waste for nanocellulose production aligns with the principles of sustainability, waste reduction, and innovation, making it a promising and novel approach in the field of nanocellulose materials.

Tuning the water interactions of cellulose nanofibril hydrogels using willow bark extract

Cellulose nanofibrils (CNFs) are increasingly used as precursors for foams, films and composites, where water interactions are of great importance. In this study, we used willow bark extract (WBE), an underrated natural source of bioactive phenolic compounds, as a plant-based modifier for CNF hydrogels, without compromising their mechanical properties. We found that the introduction of WBE into both native, mechanically fibrillated CNFs and TEMPO-oxidized CNFs increased considerably the storage modulus of the hydrogels and reduced their swelling ratio in water up to 5-7 times. A detailed chemical analysis revealed that WBE is composed of several phenolic compounds in addition to potassium salts. Whereas the salt ions reduced the repulsion between fibrils and created denser CNF networks, the phenolic compounds - which adsorbed readily on the cellulose surfaces - played an important role in assisting the flowability of the hydrogels at high shear strains by reducing the flocculation tendency, often observed in pure and salt-containing CNFs, and contributed to the structural integrity of the CNF network in aqueous environment. Surprisingly, the willow bark extract exhibited hemolysis activity, which highlights the importance of more thorough investigations of biocompatibility of natural materials. WBE shows great potential for managing the water interactions of CNF-based products.

Understanding Nanocellulose-Water Interactions: Turning a Detriment into an Asset

Modern technology has enabled the isolation of nanocellulose from plant-based fibers, and the current trend focuses on utilizing nanocellulose in a broad range of sustainable materials applications. Water is generally seen as a detrimental component when in contact with nanocellulose-based materials, just like it is harmful for traditional cellulosic materials such as paper or cardboard. However, water is an integral component in plants, and many applications of nanocellulose already accept the presence of water or make use of it. This review gives a comprehensive account of nanocellulose-water interactions and their repercussions in all key areas of contemporary research: fundamental physical chemistry, chemical modification of nanocellulose, materials applications, and analytical methods to map the water interactions and the effect of water on a nanocellulose matrix.

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.

Mesenchymal stem cell-encapsulated cellulose nanofiber microbeads and enhanced biological activities by hyaluronic acid incorporation

Cell microencapsulation is a process to entrap viable and functional cells within a biocompatible and semi-permeable matrix to provide a favorable microenvironment to the cells. Cellulose nanofiber (CNF), a low-cost and sustainable cellulose-derived natural polymer, has been studied as a matrix for 3D stem cell culture in the form of a bulk hydrogel. Here, the preparation of CNF microbeads for the long-term 3D culture of human adipose-derived stem cells (hADSCs) was demonstrated. Furthermore, hyaluronic acid (HA) was physically incorporated into the stem cell encapsulated CNF microbeads with various molecular weights and concentrations to investigate its potential in enhancing the cellular bioactivities. The beneficial effects of HA incorporation on encapsulated cells were significant compared to CNF microbeads, especially with 700 kDa molecular weight and 0.2% in concentration in terms of cell proliferation (~2 times) and VEGF secretion (~2 times) while maintaining their stemness. All the results demonstrated that the HA-incorporated CNF microbeads could serve as a promising microencapsulation matrix for hADSCs.

Polysaccharide-based hydrogels crosslink density equation: A rheological and LF-NMR study of polymer-polymer interactions

A simple relation between pendant groups of polymers in hydrogels is introduced to determine the crosslink density of (complex) hydrogel systems (mixtures of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) modified nanocellulose, alginate, scleroglucan and Laponite in addition of crosslinking agents). Furthermore, the rheological properties and their great potential connection to design complex hydrogel systems with desired properties have been thoroughly investigated. Hydrogel structures governing internal friction and flow resistance were described by the predominant effect of ionic, hydrogen, and electrostatic interactions. The relationship between rheological properties and polymer-polymer interactions in the hydrogel network is explained and expressed in a new mathematical model for determining the crosslink density of (crosslinked) hydrogels based on single or mixture of polymer systems. In the end, the combined used of rheology and low field nuclear magnetic resonance spectroscopy (LF-NMR) for the characterization of hydrogel networks is developed.

Modification of naturally abundant resources for remediation of potentially toxic elements: A review

Water and soil contamination due to potentially toxic elements (PTEs) represents a critical threat to the global ecosystem and human health. Naturally abundant resources have significant advantages as adsorbent materials for environmental remediation over manufactured materials such as nanostructured materials and activated carbons. These advantages include cost-effectiveness, eco-friendliness, sustainability, and nontoxicity. In this review, we firstly compare the characteristics of representative adsorbent materials including bentonite, zeolite, biochar, biomass, and effective modification methods that are frequently used to enhance their adsorption capacity and kinetics. Following this, the adsorption pathways and sites are outlined at an atomic level, and an in-depth understanding of the structure-property relationships are provided based on surface functional groups. Finally, the challenges and perspectives of some emerging naturally abundant resources such as lignite are examined. Although both unamended and modified naturally abundant resources face challenges associated with their adsorption performance, cost performance, energy consumption, and secondary pollution, these can be tackled by using advanced techniques such as tailored modification, formulated mixing and reorganization of these materials. Recent studies on adsorbent materials provide a strong foundation for the remediation of PTEs in soil and water. We speculate that the pursuit of effective modification strategies will generate remediation processes of PTEs better suited to a wider variety of practical application conditions.

Cellulose-Based Materials for Water Remediation: Adsorption, Catalysis, and Antifouling

Cellulose-based materials have been advanced technologies that used in water remediation. They exhibit several advantages being the most abundant biopolymer in nature, high biocompatibility, and contain several functional groups. Cellulose can be prepared in several derivatives including nanomaterials such as cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidized cellulose nanofibrils (TOCNF). The presence of functional groups such as carboxylic and hydroxyls groups can be modified or grafted with organic moieties offering extra functional groups customizing for specific applications. These functional groups ensure the capability of cellulose biopolymers to be modified with nanoparticles such as metal-organic frameworks (MOFs), graphene oxide (GO), silver (Ag) nanoparticles, and zinc oxide (ZnO) nanoparticles. Thus, they can be applied for water remediation via removing water pollutants including heavy metal ions, organic dyes, drugs, and microbial species. Cellulose-based materials can be also used for removing microorganisms being active as membranes or antibacterial agents. They can proceed into various forms such as membranes, sheets, papers, foams, aerogels, and filters. This review summarized the applications of cellulose-based materials for water remediation via methods such as adsorption, catalysis, and antifouling. The high performance of cellulose-based materials as well as their simple processing methods ensure the high potential for water remediation.

The Manufacture and Characterization of Silver Diammine Fluoride and Silver Salt Crosslinked Nanocrystalline Cellulose Films as Novel Antibacterial Materials

There is an unmet need for biocompatible, anti-infective, and mechanically strong hydrogels. This study investigated the use of poly vinyl alcohol (PVA), polysaccharides, and nanocrystalline cellulose (CNC) to deliver silver in a controlled manner for possible use against oral or wound bacteria. Silver was included in solvent cast films as silver diammine fluoride (SDF) or as nitrate, sulphate, or acetate salts. Hydrogel formation was assessed by swelling determinations and silver release was measured using inductively coupled plasma methods. Antibacterial studies were performed using Gram-positive and negative bacteria turbidity assays. PVA formed homogenous, strong films with SDF and swelled gently (99% hydrolyzed) or vigorously with dissolution (88% hydrolyzed) and released silver slowly or quickly, respectively. CNC-SDF films swelled over a week and formed robust hydrogels whereas CNC alone (no silver) disintegrated after two days. SDF loaded CNC films released silver slowly over 9 days whereas films crosslinked with silver salts were less robust and swelled and released silver more quickly. All silver loaded films showed good antibacterial activity. CNC may be crosslinked with silver in the form of SDF (or any soluble silver salt) to form a robust hydrogel suitable for dental use such as for exposed periodontal debridement areas.

Sequential Oxidation on Wood and Its Application in Pb2+ Removal from Contaminated Water

Raw wood was subjected to sequential oxidation to produce 2,3,6-tricarboxycellulose (TCC) nanofibers with a high surficial charge of 1.14 mmol/g in the form of carboxylate groups. Three oxidation steps, including nitro-oxidation, periodate, and sodium chlorite oxidation, were successfully applied to generate TCC nanofibers from raw wood. The morphology of extracted TCC nanofibers measured using TEM and AFM indicated the average length, width, and thickness were in the range of 750 ± 110, 4.5 ± 1.8, and 1.23 nm, respectively. Due to high negative surficial charges on TCC, it was studied for its absorption capabilities against Pb2+ ions. The remediation results indicated that a low concentration of TCC nanofibers (0.02 wt%) was able to remove a wide range of Pb2+ ion impurities from 5–250 ppm with an efficiency between 709–99%, whereby the maximum adsorption capacity (Qm) was 1569 mg/g with R2 0.69531 calculated from Langmuir fitting. It was observed that the high adsorption capacity of TCC nanofibers was due to the collective effect of adsorption and precipitation confirmed by the FTIR and SEM/EDS analysis. The high carboxylate content and fiber morphology of TCC has enabled it as an excellent substrate to remove Pb2+ ions impurities.

Recent Developments in Nanocellulose-Based Aerogels in Thermal Applications: A Review

Naturally derived nanocellulose (NC) is a renewable, biodegradable nanomaterial with high strength, low density, high surface area, and tunable surface chemistry, which allows its interaction with other polymers and nanomaterials in a controlled manner. In recent years, NC aerogel has gathered a lot of attention due to environmental concerns. This review presents recent developments of NC-based aerogels and their controlled interactions with other polymers and nanomaterials for thermal applications that include electronic devices, the apparel industry, superinsulating materials, and flame-retardant smart building materials. After going through the distinctive properties of NC aerogels, they are orderly categorized and discussed as thermally insulated, thermally conductive, and flame-retardant materials.

Nanofibrillated Cellulose-Based Aerogels Functionalized with Tajuva (Maclura tinctoria) Heartwood Extract

Aerogels are 3-D nanostructures of non-fluid colloidal interconnected porous networks consisting of loosely packed bonded particles that are expanded throughout their volume by gas and exhibit ultra-low density and high specific surface area. Cellulose-based aerogels can be obtained from hydrogels through a drying process, replacing the solvent (water) with air and keeping the pristine three-dimensional arrangement. In this work, hybrid cellulose-based aerogels were produced and their potential for use as dressings was assessed. Nanofibrilated cellulose (NFC) hydrogels were produced by a co-grinding process in a stone micronizer using a kraft cellulosic pulp and a phenolic extract from Maclura tinctoria (Tajuva) heartwood. NFC-based aerogels were produced by freeze followed by lyophilization, in a way that the Tajuva extract acted as a functionalizing agent. The obtained aerogels showed high porosity (ranging from 97% to 99%) and low density (ranging from 0.025 to 0.040 g·cm^-3), as well a typical network and sheet-like structure with 100 to 300 μm pores, which yielded compressive strengths ranging from 60 to 340 kPa. The reached antibacterial and antioxidant activities, percentage of inhibitions and water uptakes suggest that the aerogels can be used as fluid absorbers. Additionally, the immobilization of the Tajuva extract indicates the potential for dentistry applications.

Recent advances in 3D printing of nanocellulose: structure, preparation, and application prospects

Emerging cellulose nanomaterials extracted from agricultural biomasses have recently received extensive attention due to diminishing fossil resources. To further reduce the carbon footprints and wastage of valuable resources, additive manufacturing techniques of new nanocellulosic materials have been developed. Studies on the preparation and characterization of 3D-printable functional nanocellulosic materials have facilitated a deeper understanding into their desirable attributes such as high surface area, biocompatibility, and ease of functionalization. In this critical review, we compare and highlight the different methods of extracting nanocellulose from biorenewable resources and the strategies for transforming the obtained nanocellulose into nanocomposites with high 3D printability. Optimistic technical applications of 3D-printed nanocellulose in biomedical, electronics, and environmental fields are finally described and evaluated for future perspectives.

Increasing straw surface functionalities for enhanced adsorption property

A simple low-temperature partial-oxidation process was demonstrated as an effective technology for reed straw modification towards environmental remediation. At an optimal temperature of 180 °C, the straw materials exhibited a remarkable colour change from light yellow to dark brown, increased methylene blue (MB) uptake by 1.8 times, enhanced removal efficiency from 34.5% to 92.8%, and a high yield of 77.2%. Spectroscopic characterization and Boehm titration proved that the amount of surface oxygen (O)-containing functional groups significantly increased after modification. A strong linear correlation (R² = 0.93) existed between total amounts of O-containing functional groups and MB uptake for modification temperatures below 180 °C, whereas blockage of the pore entrances and competition with metallic cations must be taken into account for samples generated from excess heating (>180 °C). These results provided insights into designing promising technologies for sustainable environmental management through reutilization of agricultural waste.

A mathematical model for pH-responsive ionically crosslinked TEMPO nanocellulose hydrogel design in drug delivery systems

Ionically crosslinked hydrogels based on TEMPO nanocelullose and alginate were prepared to develop a generalized pH value, temperature and biopolymer concentration dependent mathematical model. The distinctive attention was in the demonstration of hydrogen bonds effects in the mathematical model, prevailing especially in the field of low crosslink densities of TEMPO nanocellulose hydrogel in acid medium. Accordingly, alginate hydrogels were subjected to the research as comparable samples with less significant hydrogel bonds effect. The equation was built upon the determination of the average mesh size in a TEMPO nanocellulose and alginate hydrogel network and studying its changes in different pH release environments. Based on rheological measurements of TEMPO nanocellulose and alginate from the basic and acidic release environment, the mechanism of swelling and shrinkage was thoroughly discussed as well as the influence of substituent groups, ionic interactions and hydrogen bonds in different pH medium were evaluated. Due to the protonation of carboxylic groups, TEMPO nanocellulose and alginate hydrogels shrink in an acid environment. The presented approach will accelerate, improve and reduce the cost of research in the field of controlled release technology with target drug delivery.

Directionally-Grown Carboxymethyl Cellulose/Reduced Graphene Oxide Aerogel with Excellent Structure Stability and Adsorption Capacity

A novel three-dimensional carboxymethyl cellulose (CMC)/reduced graphene oxide (rGO) composite aerogel crosslinked by poly (methyl vinyl ether-co-maleic acid)/poly (ethylene glycol) system via a directional freezing technique exhibits high structure stability while simultaneously maintaining its excellent adsorption capacity to remove organic dyes from liquid. A series of crosslinked aerogels with different amounts of GO were investigated for their adsorption capacity of methylene blue (MB), which were found to be superb adsorbents, and the maximum adsorption capacity reached 520.67 mg/g with the incorporation of rGO. The adsorption kinetics and isotherm studies revealed that the adsorption process followed the pseudo-second-order model and the Langmuir adsorption model, and the adsorption was a spontaneous process. Furthermore, the crosslinked aerogel can be easily recycled after washing with dilute HCl solution, which could retain over 97% of the adsorption capacity after recycling five times. These excellent properties endow the crosslinked CMC/rGO aerogel’s potential in wastewater treatment and environment protection.

Strong Reinforcement Effects in 2D Cellulose Nanofibril-Graphene Oxide (CNF-GO) Nanocomposites due to GO-Induced CNF Ordering

Nanocomposites from native cellulose with low 2D nanoplatelet content are of interest as sustainable materials combining functional and structural performance. Cellulose nanofibril-graphene oxide (CNF-GO) nanocomposite films are prepared by a physical mixing-drying method, with focus on low GO content, the use of very large GO platelets (2-45μm) and nanostructural characterization using synchrotron x-ray source for WAXS and SAXS. These nanocomposites can be used as transparent coatings, strong films or membranes, as gas barriers or in laminated form. CNF nanofibrils with random in-plane orientation, form a continuous non-porous matrix with GO platelets oriented in-plane. GO reinforcement mechanisms in CNF are investigated, and relationships between nanostructure and suspension rheology, mechanical properties, optical transmittance and oxygen barrier properties are investigated as a function of GO content. A much higher modulus reinforcement efficency is observed than in previous polymer-GO studies. The absolute values for modulus and ultimate strength are as high as 17 GPa and 250 MPa at a GO content as small as 0.07 vol%. The remarkable reinforcement efficiency is due to improved organization of the CNF matrix; and this GO-induced mechanism is of general interest for nanostructural tailoring of CNF-2D nanoplatelet composites.

Towards an eco-friendly deconstruction of agro-industrial biomass and preparation of renewable cellulose nanomaterials: A review

There is an array of methodologies to prepare nanocellulose (NC) and its fibrillated form (CNF) with enhanced physicochemical characteristics. However, acids, bases or organosolv treatments on biomass are far from green, and seriously threaten the environment. Current approach to produce NC/CNF from biomass should be revised and embrace the concept of sustainability and green chemistry. Although hydrothermal process, high-pressure homogenization, ball milling technique, deep eutectic solvent treatment, enzymatic hydrolysis etc., are the current techniques for producing NC, the route designs remain imperfect. Herein, this review highlights the latest methodologies in the pre-processing and isolating of NC/CNF from lignocellulose biomass, by largely focusing on related papers published in the past two years till date. This article also explores the latest advancements in environmentally friendly NC extraction techniques that cooperatively use ball milling and enzymatic hydrolytic routes as an eco-efficient way to produce NC/CNF, alongside the potential applications of the nano-sized celluloses.

Chemically Cross-Linked Cellulose Nanocrystal Aerogels for Effective Removal of Cation Dye

In this study, porous aerogels were prepared by directional freeze-drying via cross-linking cellulose nanocrystals (CNCs) with poly(methyl vinyl ether-co-maleic acid) (PMVEMA) and poly(ethylene glycol) (PEG). The thermal properties and physical adsorption performance toward cation methylene blue dye of the obtained CNC aerogels were investigated. The maximum degradation temperature was increased from 324°C of CNCs to 355°C of cross-linked CNC aerogels. The dye adsorption isotherm results showed that the maximum methylene blue adsorption capacity of CNC aerogels was 116.2 mg g⁻¹, according to the Langmuir model, which was mainly due to the electrostatic attractions between negatively charged carboxyl groups or sulfonate groups on the CNC aerogles and cation MB molecules. The reusability test showed that the CNC aerogels contained the same dye adsorption performance in five adsorption/desorption cycles. Overall, this study described an ideal alternative for water purification with high dye adsorption capacity and enhanced physical performance.

Bottom-up assembly of nanocellulose structures

Nanocelluloses, both cellulose nanofibrils and cellulose nanocrystals, are gaining research traction due to their viability as key components in commercial applications and industrial processes. Significant efforts have been made to understand both the potential of assembling nanocelluloses, and the limits and prospectives of the resulting structures. This Review focuses on bottom-up techniques used to prepare nanocellulose-only structures, and details the intermolecular and surface forces driving their assembly. Additionally, the interactions that contribute to their structural integrity are discussed along with alternate pathways and suggestions for improved properties. Six categories of nanocellulose structures are presented: (1) powders, beads, and droplets; (2) capsules; (3) continuous fibres; (4) films; (5) hydrogels; and (6) aerogels and dried foams. Although research on nanocellulose assembly often focuses on fundamental science, this Review also provides insight on the potential utilization of such structures in a wide array of applications.

Best Practice for Reporting Wet Mechanical Properties of Nanocellulose-Based Materials

Nanocellulose-based materials and nanocomposites show extraordinary mechanical properties with high stiffness, strength, and toughness. Although the last decade has witnessed great progress in understanding the mechanical properties of these materials, a crucial challenge is to identify pathways to introduce high wet strength, which is a critical parameter for commercial applications. Because of the waterborne fabrication methods, nanocellulose-based materials are prone to swelling by both adsorption of moist air or liquid water. Unfortunately, there is currently no best practice on how to take the swelling into account when reporting mechanical properties at different relative humidity or when measuring the mechanical properties of fully hydrated materials. This limits and in parts fully prevents comparisons between different studies. We review current approaches and propose a best practice for measuring and reporting mechanical properties of wet nanocellulose-based materials, highlighting the importance of swelling and the correlation between mechanical properties and volume expansion.

Nanocellulose: From Fundamentals to Advanced Applications

Over the past few years, nanocellulose (NC), cellulose in the form of nanostructures, has been proved to be one of the most prominent green materials of modern times. NC materials have gained growing interests owing to their attractive and excellent characteristics such as abundance, high aspect ratio, better mechanical properties, renewability, and biocompatibility. The abundant hydroxyl functional groups allow a wide range of functionalizations via chemical reactions, leading to developing various materials with tunable features. In this review, recent advances in the preparation, modification, and emerging application of nanocellulose, especially cellulose nanocrystals (CNCs), are described and discussed based on the analysis of the latest investigations (particularly for the reports of the past 3 years). We start with a concise background of cellulose, its structural organization as well as the nomenclature of cellulose nanomaterials for beginners in this field. Then, different experimental procedures for the production of nanocelluloses, their properties, and functionalization approaches were elaborated. Furthermore, a number of recent and emerging uses of nanocellulose in nanocomposites, Pickering emulsifiers, wood adhesives, wastewater treatment, as well as in new evolving biomedical applications are presented. Finally, the challenges and opportunities of NC-based emerging materials are discussed.

3D printing of biomass-derived composites: application and characterization approaches

Biomass-derived 3D printing has attracted interests because of its developing technology and availability with renewable materials as well as compatible characteristics for many applications.