Improved thermal insulation and compressive property of bimodal poly (lactic acid)/cellulose nanocomposite foams

In this work, an innovative PLA/CNF nanocomposite foam with a bimodal cell structure is prepared by a simple one-step depressurization foaming process using only supercritical carbon dioxide (ScCO₂) as the foaming agent. Only at a specific foaming temperature, PLA/CNF nanocomposites foam with a bimodal cell structure could be obtained. According to the different crystallization kinetics and nucleation efficiency of samples, it was inferred that the crystallization rate and phase interface would affect the cell structure. The prepared PLA/CNF nanocomposite foam with a bimodal cell structure had an expansion ratio as high as 20 times and thermal conductivity of 0.041 w m^-1 k^-1, which exhibited low density and excellent thermal-insulation property. Meanwhile, the PLA/CNF nanocomposite foam exhibited excellent compression performance due to the presence of CNFs, which showed promising application in packaging and construction materials.

Regulation of hydrogen bonding network between cellulose nanofibers by rare earth ion Y(3)

Cellulose is regarded as the most abundant biomass, and nanocellulose derived from it has numerous applications in environmentally friendly materials. However, owing to the abundant hydroxyl groups on surface, nanocellulose is prone to agglomeration when transported, stored, or made into materials, which destroys material performance and limits its use. In this study, a feasible method was presented for regulating the hydrogen bonding strength between cellulose nanofibers (CNFs) by adding a minute quantity of rare earth ions Y³⁺ during cellulose nanofibrillation. It was found that the strength of hydrogen bonding between CNFs can be regulated by controlling the quantity of Y³⁺ in the system. The dispersibility and stability of CNFs, as well as the mechanical properties of CNFs films and CNFs-reinforced papers can be improved by 43.07 % and by 64.05 % after adding only 0.05 or 0.075 wt% Y³⁺. The possible mechanism of CNFs hydrogen bonding network reconstruction was proposed.

Nanocellulose-based electrodes and separator toward sustainable and flexible all-solid-state supercapacitor

Nanocellulose, as the most abundant natural nanomaterial with sustainability, biodegradability, and excellent mechanical properties, has been widely applied in modern electronic systems, particularly, in the flexible electrochemical energy storage devices. Herein, a reduced graphene oxide (RGO)/cellulose nanocrystal/cellulose nanofiber (RCC) composite membrane was prepared by using a one-pot method. Compared to the pure RGO membranes, the RCC composite membranes exhibited better mechanical properties and hydrophilicity. Furthermore, due to the synergistic effect of nanocellulose and RGO sheets, the RCC composite membrane exhibited a specific capacitance as high as 171.3 F·cm^-3. Consequently, a nanocellulose-based symmetric flexible all-solid-state supercapacitor (FASC) was constructed, in which two RCC composite membranes served as electrodes and a porous cellulose nanofiber membrane acted as separator. This fabricated FASC demonstrated a high volumetric specific capacitance of 164.3 F·cm^-3 and a satisfactory energy density of 3.7 mW·h·cm^-3, which exceeded that of many other FASCs ever reported. This work may open a new avenue in design of next-generation nanocellulose based, sustainable and flexible energy storage device.

Microalgae on distillery wastewater treatment for improved biodiesel production and cellulose nanofiber synthesis: A sustainable biorefinery approach

Sugarcane spent wash generates waste at a large scale that impacts the environment, hence the classic waste reuse technology needs to be implemented. An integrated approach of spent wash and microalgae cultivation to produce biodiesel has gained momentum in recent times. However, the microalgae technology lacks the functional utilization of de-oiled microalgae biomass (DOB). This study proposed the development of a microalgae-based advanced process for distillery spent wash treatment, biomass recovery for biodiesel and utilizing algal residue as a step towards waste management. A novel microalga Coelastrella sp KJ-04 grown in distillery spent wash represented with high biomass (4.61g/L) and lipid production (3.6 g/L). The significant reduction in Chemical Oxygen Demand (COD, 49.3%), Total Nitrogen (TN, 49.7%), Total Phosphorous (TP, 21.8%), Total Organic Carbon (TOC, 40.2%), Total Sulphur (S, 37.2%) and Potassium (K, 42.5%) were achieved in spent wash. The extracted lipids of Coelastrella sp KJ-04 were converted to Fatty acid methyl ester (FAME) and examined by Gas chromatography -mass spectrometry (GC-MS) to observe the suitability for biodiesel prospect. The de-oiled biomass (DOB) was utilized for the synthesis of Cellulose nanofibers (CNF), purified and estimated with a diameter ranging between 20 and 27 nm. The crystalline structure and functional group of CNF were analyzed by X-ray diffraction (XRD) and Fourier Transform infrared spectroscopy (FTIR). The unprecedented work demonstrated the microalgae biorefinery approach for spent wash remediation, biodiesel synthesis and simultaneous production of biodegradable CNF from algal residue to support waste-free technology. In future, CNF can be reinforced into material for concrete as it could be the smart alternative to replace synthetic cement plastics.

Effect of cellulose nanofibers on the fracture toughness mode II of glass fiber/epoxy composite laminates

Cellulose nanofibers (CNFs) were used to improve the fracture toughness of glass fiber reinforced epoxy composites (GFRPs). Different CNF suspensions were prepared and sprayed onto the surface of woven glass fiber laminates. The vacuum resin transfer molding (VaRTM) process was used to manufacture the GFRP composites. End notch flexure tests were conducted to evaluate the effect of CNFs on the critical energy release rate in mode II fracture toughness G_IIC. The results revealed that 0.05 wt% was the optimum concentration. The interlaminar fracture toughness G_IIC was improved by 28% with the addition of 0.05 wt% of CNFs to GF/epoxy composites. Whereas 0.1 wt% of CNFs resulted in decreasing G_IIC due to the uncomplete impregnation of GF with epoxy resin caused by the thicker CNF layer at the interfacial laminates. The toughening mechanisms were investigated using a field-emission electron microscope. Large epoxy deformations and shear hackles were predominant for improving the interlaminar fracture toughness of GFRP composites.

Study on cellulose nanofibers/aramid fibers lithium-ion battery separators by the heterogeneous preparation method

In this study, a heat-resistant and high-wettability lithium-ion batteries separator (PI-CPM-PI) composed of cellulose nanofibers (CNF) and aramid fibers (PMIA chopped fiber/PPTA pulp) with the reinforced concrete structure was fabricated via a traditional heterogeneous paper-making process. CNF played crucial roles in optimizing the pore structure and improving the wettability of PI-CPM-PI separator. The effects of composition on separator properties were investigated and the results indicated that the optimal compositions were 0.5 wt% CNF, 0.5 wt% PMIA chopped fiber/PPTA pulp (ratio of 5:5), 0.05 wt% diatomite and 1.5 wt% polyimide. Relevant tests demonstrated that the performance advantages of PI-CPM-PI separators were exhibited at the wettability and thermal stability compared to the commercial separator (PP). Additionally, batteries assembled with PI-CPM-PI separators showed excellent electrochemical and cycling performance (ionic conductivity of 1.041 mS.cm^-1, the first discharge capacity of 158.2 mAh.g^-1 at 0.2C and capacity retention ratio of 99.76 % after 100 cycles).

Preparation of antifouling and highly hydrophobic cellulose nanofibers/alginate aerogels by bidirectional freeze-drying for water-oil separation in the ocean environment

Oil spills frequently occur in the ocean, and adsorption is one of the effective ways to deal with oil spills. Compared with other adsorbent materials, biomass aerogel has superior selective adsorption capacity. CNF/SA aerogels with good mechanical properties (340 kPa at 90 % strain) and high adsorption capacity (88.91 g/g) were prepared by mixing cellulose nanofibers (CNF) with sodium alginate (SA) through bidirectional freeze-drying, ionic crosslinking, and surface modification to effectively solve the ocean oil spill problem. The bidirectional freeze-drying technology is a green and efficient technique for preparing layered microstructured composite aerogels. The prepared aerogels have a three-dimensional interpenetrating lamellar structure, low density (24.2 mg/cm³), high porosity (97.85 %), and high hydrophobicity (WCA = 144.5°), can be calibrated and used repeatedly. It has potential applications in water-oil separation and can be used as an absorbent for effectively treating oil spills in the ocean environment.

In vitro biodegradation, cytotoxicity, and biocompatibility of polylactic acid/napier cellulose nanofiber scaffold composites

This study aimed to evaluate the bioactivities and biocompatibilities of porous polylactic acid (PLA) reinforced with cellulose nanofiber (CNF) scaffolds. The in vitro degradation behaviors of the porous PLA/CNF scaffolds were systematically measured for up to 8 weeks in a phosphate-buffered saline medium at 37 °C. The reinforcement of CNF resisted the biodegradation of the scaffolds. The in vitro cytotoxicity and biocompatibility of the scaffolds were determined using the Beas2B American Type Culture Collection cells. The 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide cytotoxicity and proliferation tests showed that the scaffolds were non-toxic, and epithelial cells grew well on the scaffold after 7 days of culture, whereas the percentage of cell proliferation on the PLA/CNF₁₅ scaffold was the largest, 130 %. A scratch wound-healing assay was performed to evaluate the suitability of the scaffolds for cell migration. The results demonstrated that the scaffolds exhibited good cell migration towards nearly complete wound closure.

Superinsulating nanocellulose aerogels: Effect of density and nanofiber alignment

Cellulose aerogels are potential alternatives to silica aerogels with advantages in cost, sustainability and mechanical properties. However, the density dependence of thermal conductivity (λ) for cellulose aerogels remains controversial. Cellulose aerogels were produced by gas-phase pH induced gelation of TEMPO-oxidized cellulose nanofibers (CNF) and supercritical drying. Their properties are evaluated by varying the CNF concentration (5-33 mg·cm^-3) and by uniaxial compression (9-115 mg·cm^-3). The aerogels are transparent with specific surface areas of ~400 m²·g^-1, mesopore volumes of ~2 cm³·g^-1 and a power-law dependence of the E-modulus (α ~ 1.53, and the highest reported E of ~1 MPa). The dataset confirms that λ displays a traditional U-shaped density dependence with a minimum of 18 mW·m^-1·K^-1 at 0.065 g·cm^-3. For a given density, λ is ~5 mW·m^-1·K^-1 lower for compressed aerogels due to the alignment of nanofibers, confirmed by small angle X-ray scattering (SAXS).

Mesoporous cellulose nanofibers-interlaced PEDOT:PSS hybrids for chemiresistive ammonia detection

Chemiresistive ammonia (NH₃) detection at room temperature is highly desired due to the unique merits of easy miniaturization, low cost, and minor energy consumption especially for portable and wearable electronics. In this regard, poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) has sparked considerable attention due to the benign room-temperature conductivity and environmental stability, but it is undesirably impeded by limited sensitivity and sluggish reaction kinetics. To overcome these, we incorporated cellulose nanofibers (CNF) into PEDOT:PSS via a facile blending. The constituent-optimized composite sensor displayed sensitive (sensitivity of ∼7.46%/ppm in the range of 0.2-3 ppm), selective, and stable NH₃ sensing at 25 °C at 55% RH, with higher response and less baseline drift than pure PEDOT:PSS counterparts. Additionally, the response/recovery times (4.9 s/5.2 s toward 1 ppm NH₃) ranked the best cases of conducting polymers based NH₃ sensors. The humidity involved more than twofold response enhancement indicated a huge potential in exhaled breath monitoring. Furthermore, we observed an excellent flexible NH₃-sensing performance with bending-tolerant features. This work provides an alternative strategy for trace NH₃ sensing with low power consumption, superfast reaction, and high sensitivity.

Influence of hemicellulose content and cellulose crystal change on cellulose nanofibers properties

This study aimed to evaluate the properties of cellulose nanofibers (CNFs) with different hemicellulose contents and cellulose II polymorphs. A link was found between these polysaccharides and the properties of CNFs. A decrease in crystallinity (from 69 to 63%) and changes in the crystalline structure of cellulose subjected to an alkaline environment were observed, promoting the partial conversion of cellulose I to cellulose II (from 2 to 42%) and preventing CNFs production at NaOH concentrations higher than 5%. Most treatments showed pseudoplastic fluid behavior, except for the 10% NaOH treatment over 2 h, which showed Newtonian fluid behavior. The quality index of the reference CNFs (TEMPO-oxidized) was the highest (80 ± 3), followed by that of the 5% NaOH-treated (68 ± 3 and 22% energy savings compared to the untreated sample), and the untreated (63 ± 3) samples; and the 10% NaOH treatments had quality indices of 51 ± 3 and 32 ± 1, respectively.

Cellulose nanofibers/PVA blend polymeric beads containing in-situ prepared magnetic nanorods as dye pollutants adsorbents

Magnetic beads were developed from polyvinyl alcohol and different amounts of cellulose nanofibers (CNF) by in-situ preparation of iron oxide nanoparticles in an alkaline aqueous medium at room temperature. The CNF were isolated from wheat straw, whereas the magnetic nanoparticles (MNPs) precursors were simple iron salts. The complete characterization of all the obtained materials was conducted, and among some other outstanding results it showed that all the components were strongly interacting via hydrogen bonding, while the nano-rods and husks like MNPs were effectively acting as crosslinking dots. All the prepared materials had good magnetic responses, and they were able to remove not only cationic, but also anionic dye pollutants from aqueous model solutions.

Effect of oxalic acid and sulphuric acid hydrolysis on the preparation and properties of pineapple pomace derived cellulose nanofibers and nanopapers

Nanocellulose is the "green magnet" which attracts a wide spectrum of industries towards it due to its availability, biodegradability, and possible smart applications. For the first time, pineapple pomace was being explored as an economic precursor for cellulose nanofibers. Nanofiber isolation was accomplished using a chemo-mechanical method and solution casting was adopted for the development of nanopapers. Moreover, the study examines the structural, optical, crystalline, dimensional, and thermal features of nanofibers isolated using different acid hydrolysis (oxalic acid and sulphuric acid) methods. Fourier-transform infra-red spectroscopy, ¹³C solid-state nuclear magnetic resonance spectroscopy, and X-ray diffraction analysis indicated the presence of type I cellulose. The transmittance, crystallinity index, and thermal stability of PPNFS (sulphuric acid treated fiber) were greater than PPNFO (oxalic acid treated fiber). The transmission electron microscopy and dynamic light scattering analysis confirmed the nanodimension of PPNFO and PPNFS. While comparing the optical and mechanical properties of nanopapers, PPNFS outperforms PPNFO. The tensile strength of the prepared nanopapers (64 MPa (PPNFO) and 68 MPa (PPNFS)) was found to be high compared to similar works reported in the literature. The prepared nanopaper is proposed to be used for food packaging applications.

Eco-friendly laccase and cellulase enzymes pretreatment for optimized production of high content lignin-cellulose nanofibrils

Lignin-cellulose nanofibrils (LCNF) are of attracting an increasing interest due to the benefits of maintaining the lignin in the nanomaterial composition. The production of LCNF requires considerable energy consumption, which has been suppressed employing pretreatment of biomass, in which it highlights those that employ enzymes that have the advantage of being more environmentally friendly. Some negative aspects of the presence of lignin in the fiber to obtain cellulose nanofibrils is that it can hinder the delamination of the cell wall and act as a physical barrier to the action of cellulase enzymes. This study aimed to evaluate the impact of a combined enzymatic pretreatment of laccase and endoglucanase for high content lignin LCNF production. The morphological and chemical properties, visual aspect and stability, crystallinity, mechanical properties, rheology, barrier properties and quality index were used to characterize the LCNF. The laccase loading used was efficient in modifying the lignin to facilitate the action of the endoglucanase on cellulose without causing the removal of this macromolecule. This pretreatment improved the quality of LCNF (61 ± 3 to 71 ± 2 points) with an energy saving of 42% and, therefore, this pretreatment could be suitable for industrial production for a variety of applications.

Facile preparation of nanocellulose/Zn-MOF-based catalytic filter for water purification by oxidation process

Sulfate radical (SO₄^•-)-based advanced oxidation processes (SR-AOPs) have recently attracted much attention due to their potential in degrading organic pollutants. Metal-organic frameworks (MOFs) have been reported as effective materials to generate SO₄^•-. However, it is challenging to separate and recover the dispersed MOF particles from the reaction solution when MOFs are used alone. We used cellulose nanofibers (CNFs) as a porous filter template to immobilize Zn-based MOF, zeolitic imidazolate framework-8 (ZIF-8), and obtained a catalytic composite membrane having peroxymonosulfate (PMS) activating function to produce SO₄^•-. The CNF was effective in holding ZIF-8 nanoparticle and making a durable porous filter. The activated PMS-produced ^•OH and SO₄^•- radicals from ZIF-8 play an important role in the catalytic reaction. More than 90% of methylene blue and rhodamine B was degraded by ZIF-8/CNFs composite membrane in the PMS environment within 60 min. The ZIF-8/CNFs catalytic filters can be used several times without performance reduction for organic dye degradation. The results show that ZIF-8/CNFs catalytic membrane can be separated from organic pollution system quickly and used for the efficient separation and recovery of MOF particle-based catalytic materials. Therefore, this study provides a new perspective for fabricating the MOFs particles-immobilized catalytic filter by biomass nanocellulose-based materials for water purification. This method can be used for facile fabrication of the cellulose-based porous functional filter and open diverse applications.

Chlorine-free extraction and structural characterization of cellulose nanofibers from waste husk of millet (Pennisetum glaucum)

This study aims to extract cellulose nanofibers (CNFs) from a sustainable source, millet husk, which is considered as an agro-waste worthy of consideration. Pre-treatments such as mercerisation, steam explosion, and peroxide bleaching (chlorine-free) were applied for the removal of non-cellulosic components. The bleached millet husk pulp was subjected to acid hydrolysis (5% oxalic acid) followed by homogenization to extract CNFs. The extracted CNFs were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Dynamic Light Scattering (DLS), Energy Dispersive X-ray Spectroscopy (EDX), Thermogravimetry (TG and DTG), Differential scanning calorimetry (DSC), and Solid state ¹³C nuclear magnetic resonance spectroscopy (solid state ¹³C NMR). The isolated CNFs show a typical cellulose type-I structure with a diameter of 10-12 nm and a crystallinity index of 58.5%. The appearance of the specific peak at 89.31 ppm in the solid state ¹³C NMR spectra validates the existence of the type-I cellulose phase in the prepared CNFs. The prepared CNFs had a maximum degradation temperature (T_max) of 341 °C, that was 31 °C greater than raw millet husk (RMH). The outcome of the study implies that the nanofibers are prominent alternatives for synthetic fibers for assorted potential applications, especially in manufacturing green composites.

Critical comparison of the properties of cellulose nanofibers produced from softwood and hardwood through enzymatic, chemical and mechanical processes

Current knowledge on the properties of different types of cellulose nanofibers (CNFs) is fragmented. Properties variation is very extensive, depending on raw materials, effectiveness of the treatments to extract the cellulose fraction from the lignocellulosic biomass, pretreatments to facilitate cellulose fibrillation and final mechanical process to separate the microfibrils. Literature offers multiple parameters to characterize the CNFs prepared by different routes. However, there is a lack of an extensive guide to compare the CNFs. In this study, we perform a critical comparison of rheological, compositional, and morphological features of CNFs, produced from the most representative types of woody plants, hardwood and softwood, using different types and intensities of pretreatments, including enzymatic, chemical and mechanical ones, and varying the severity of mechanical treatment focusing on the relationship between macroscopic and microscopic parameters. This structured information will be exceedingly useful to select the most appropriate CNF for a certain application based on the most relevant parameters in each case.

Stimuli-responsive composite hydrogels with three-dimensional stability prepared using oxidized cellulose nanofibers and chitosan

Stimuli-responsive hydrogels have garnered the attention of the hydrogel industry, as they are able to change their physical and chemical properties based on changing external stimuli such as pH, temperature, ionic strength, electromagnetic fields, and light. However, stimuli-responsive hydrogel applications are hindered due to their inevitable swelling and shrinkage. Bacterial cellulose (BC), a natural hydrogel with tightly packed cellulose nanofibers (CNFs) was oxidized into dialdehyde BC (DABC) and was composited with chitosan (CS), a readily available natural polymer, to develop a mechanically adaptive hydrogel composite under different pH conditions. Composites exhibit pH sensitivity by presenting higher mechanical properties under acidic conditions and lower mechanical properties under basic conditions owing to the protonation of amino groups of the chitosan chains. Osmotic pressure is built up under acidic conditions, increasing the mechanical strength of the composites. The good three-dimensional stability of composites enables them to consistently maintain their volume when exposed to acidic or basic conditions.

Nanocelluloses as skin biocompatible materials for skincare, cosmetics, and healthcare: Formulations, regulations, and emerging applications

Nowadays, skin biocompatible products are fast-growing markets for nanocelluloses with increasing number of patents published in last decade. This review highlights recent developments, market trends, safety assessments, and regulations for different nanocellulose types (i.e. nanoparticles, nanocrystals, nanofibers, nanoyarns, bacterial nanocellulose) used in skincare, cosmetics, and healthcare. The specific properties of nanocelluloses for skincare include high viscosity and shear thinning properties, surface functionality, dispersion stability, water-holding capacity, purity, and biocompatibility. Depending on their morphology (e.g. size, aspect ratio, geometry, porosity), nanocelluloses can be used as formulation modifiers, moisturizers, nanofillers, additives, membranes, and films. Nanocellulose composite particles were recently developed as carriers for bioactive compounds or UV-blockers and platforms for wound healing and skin sensors. As toxicological assessment depends on morphologies and intrinsic properties, stringent regulation is needed from the testing of efficient nanocellulose dosages. The challenges and perspectives for an industrial breakthrough are related to optimization of production and processing conditions.

Intelligent hydrogel with both redox and thermo-response based on cellulose nanofiber for controlled drug delivery

The purpose of this study is to develop a hydrogel with temperature and redox response to control drug delivery. However, the strength of temperature sensitive N-isopropylacrylamide (NIPAM) hydrogel is weak. Therefore, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose nanofiber (CNF) is introduced to improve this problem. The compressive strength of hydrogels increased by 360% after CNF addition. Meanwhile, N,N'-bis(acryloyl)cystamine (BACy) is introduced into the hydrogels as a cross-linker, imparting redox responsive properties to the hydrogels. Tumor therapeutic drugs are used as model drugs for in vitro release studies. The drug release rate of hydrogel is regulated by temperature and reducing environment. The maximum cumulative release rate of doxorubicin (DOX) is 39.56%, and the Berberine (BBR) is 99.50% after 60 h. The swelling and transparency of hydrogels showed dramatic changes in the range of 30-40 °C. Cytotoxicity experiments demonstrated that the hydrogel had almost no cytotoxicity.

Modified cellulose nanofibers aerogels as a novel air filters; Synthesis and performance evaluation

Nanofilters made with high adsorption freeze-dried modified cellulose nanofiber (CNF) aerogel were produced. The modification was made using functional groups containing phthalimide, and then their ability to adsorb particulate matter (PM) was evaluated and compared with the control filter (HEPA). The results showed that the highest adsorption of PM_2.5 (99.95%) belonged to the nanofilters made of 1.5% phthalimide-modified CNF aerogel, and the lowest adsorption (76.66%) was related to the control samples. Moreover, based on the results, the nanofilter produced from freeze-dried phthalimide-modified CNF aerogel showed high filtration efficiency as well as excellent resistance to temperature and humidity. This modification enables the filter to operate in different environmental conditions, especially for particles less than 0.1 μm that are mainly responsible for reducing air quality, human health, air visibility, and climate change. In conclusion, we developed an environmentally friendly biodegradable nanofilter capable of high-performance filtration functions and structural stability in different environmental conditions.

A simultaneous strategy for the preparation of acetylation modified cellulose nanofiber/polypropylene composites

In this study, a simultaneous method with nano-fibrillation of acetylation modified fibers (A-cellulose) and preparation of cellulose nanofiber (CNF)/apolar polymer composites are proposed. The A-cellulose and isotactic polypropylene (iPP) were initially mixed and then melt-compounding in a twin-screw extruder. Due to the reduction of hydrogen bonding force inside A-cellulose and the high shear force provided by the extruder, acetylated cellulose nanofiber (A-CNF) distributed with the state of a three-dimensional network in PP composites (ACPP) were successful prepared. The scanning electron microscopy (SEM) images of A-CNF, dynamic mechanical analysis (DMA) and X-ray diffraction (XRD) results of ACPP showed that the A-CNF had good interface compatibility with PP matrix, and had the effects of inducing PP crystallization, decreasing crystal size and increasing the ratio of γ crystals in composites, which could improve the mechanical and thermodynamic properties of composites.

Promoted formation of stereocomplex in enantiomeric poly(lactic acid)s induced by cellulose nanofibers

Stereocomplex (SC) crystallization between enantiomeric poly(_L-lactic acid) (PLLA) and poly(_D-lactic acid) (PDLA) is believed to yield poly(lactic acid) (PLA) with superior physiochemical properties. However, homocrystallization (HC) crystallites are inevitably generated in the PLLA/PDLA blends. Herein, we report a simple approach to fabricate PLLA/PDLA racemic blends with high contents of SC crystallites by introducing cellulose nanofibers (CNFs). The isothermal crystallization results revealed that the half-crystallization time of the PLLA/PDLA blend was significantly decreased by adding CNFs. Additionally, with the incorporation of 3 wt% modified CNFs, the PLLA/PDLA blend was overwhelmingly crystallized into SC crystallites with no HC crystallite formation. Based on Fourier transform infrared spectroscopy findings, it was speculated that the preferred SC crystallization of PLLA/PDLA/CNF was caused by enhanced interchain molecular interactions between CNFs and PLA. This work presents a feasible and efficient method to fabricate PLA with exclusively SC crystallites, which possesses great potential for producing high-performance PLA materials.

The quality properties of frozen large yellow croaker fillets during temperature fluctuation cycles: improvement by cellobiose and carboxylated cellulose nanofibers

Frozen aquatic products undergo unavoidable quality changes owing to temperature fluctuations during frozen storage and distribution. This study investigated the effects of 1% cellobiose (CB), and 0.5 and 1% carboxylated cellulose nanofibers (CNF) on ice crystal growth and recrystallization of frozen large yellow croaker fillets exposed to temperature fluctuations. Denser and more uniformly distributed ice crystals were observed in the CB- and CNF-treated samples than in the water-treated samples. Furthermore, the addition of CB and CNF suppressed the conversion of bound water to frozen water in the samples during temperature fluctuation cycles, played a positive role in fixing the ionic and hydrogen bonds that stabilize the protein structure, limited the conformational transition from α-helix to β-sheet, and improved protein thermal stability. Based on turbidity, zeta potential, and confocal laser scanning microscopy (CLSM) analyses, the presence of CB and CNF restricted the protein aggregation. Compared with CB, CNF molecules with abundant carboxyl functional groups and longer morphology exhibited better cryoprotective effects. Moreover, the fillets were more improved protected from mechanical damage induced by large ice crystals at a higher CNF concentration. This study reveals the potential of CB and CNF as novel cryoprotectants.

Linear and nonlinear oscillatory rheology of chemically pretreated and non-pretreated cellulose nanofiber suspensions

Linear and nonlinear rheological properties of cellulose nanofiber (CNF) suspensions were measured under small and large amplitude oscillatory shear (SAOS and LAOS) flow. Four different CNFs were produced, two by only mechanical disintegration and two with chemical pretreatments. Linear viscoelastic properties distinguished chemically treated CNFs from two untreated fibers via a different scaling exponent of the elastic modulus. However, different mechanical fibrillation degree was not characterized via linear viscoelastic properties. In contrast, nonlinear viscoelastic properties reflected both effects of chemical pretreatments and mechanical fibrillation. More fibrillated CNFs exhibited nonlinear rheological phenomena at larger deformations. In addition, chemically treated CNFs exhibited greater network stiffness and higher network recovery rates due to the presence of charged functional groups on the fiber surfaces. A material-property co-plot showed that network stiffness and recovery rate were in a trade-off relationship.

Cellulose nanofibers aerogels functionalized with AgO: Preparation, characterization and antibacterial activity

In the experiment, a chemical oxidation method was used to prepare nano-divalent silver oxide powder with a particle size of about 10 nm. Compared with silver nanoparticles and monovalent silver compounds, nano‑silver oxide has better antibacterial properties. The cellulose antibacterial aerogel was prepared by combining it with cellulose nanofibrils and using freeze-thaw cycles and freeze-drying methods. The microscopic morphology, mechanical properties, in vitro release of silver ions, antibacterial properties and biodegradability of composite aerogels were studied. The porosity of the cellulose antibacterial aerogel can reach 94%, the swelling rate was greater than 1000%, and the pore size was between 13 and 15 nm, which showed a larger storage space and attachment site for the aerogel. The diameter of the inhibition zone of the aerogel against Escherichia coli and Staphylococcus aureus was 23 mm and 20 mm respectively, and the aerogels still exhibited significant antibacterial activities with more than 99.5% reductions in Escherichia coli and Staphylococcus aureus, which shows highly effective antibacterial properties. This research proposes an economical and novel preparation method of antibacterial cellulose aerogel, making it a candidate material with high efficiency, broad-spectrum antibacterial and more suitable for life needs.

A bionic cellulose nanofiber-based nanocage wound dressing for NIR-triggered multiple synergistic therapy of tumors and infected wounds

Tumor recurrence and drug-resistant bacterial infection are the main reasons that wounds heal with difficulty after skin tumor treatment. The near infrared- (NIR-) and pH-responsive, bionic, cellulose nanofiber-based (CNF-based) nanocage wound dressing with biocompatibility, bioviscosity, and shape adaptability is designed for dual NIR-triggered photothermal therapy of tumor and infection-induced wound healing. The wound dressing with the intertwining three dimensional (3D) nanocage network structure is skillfully constructed using NIR-responsive cellulose nanofibers and pH-responsive cellulose nanofibers as the skeleton, which endows the dressing with a high drug-loading capacity of doxorubicin (400 mg·g^-1), and indocyanine green (25 mg·g^-1). Moreover, the NIR- and pH-responsive bionic "On/Off" switches of the dressing enable a controllable and efficient drug release onto the wound area. The dual NIR-triggered wound dressing with excellent photothermal conversion performance possesses good antibacterial properties against Escherichia coli, Staphylococcus aureus, and drug-resistant Staphylococcus aureus. It could effectively eliminate bacterial biofilms and kill A375 tumor cells. Interestingly, the bionic wound dressing with shape adaptability could adapt and treat irregular postoperative skin tumor wounds and drug-resistant bacterial infection via the synergistic therapy of photothermal, photodynamic, and chemotherapy, which provides an ideal strategy for clinical intervention.

Facile fabrication of multifunctional citrus pectin aerogel fortified with cellulose nanofiber as controlled packaging of edible fungi

Citrus pectin was used as a precursor and cellulose nanofibers as a reinforcing agent, a mixed aerogel with enhanced structural properties was prepared. Pickering emulsion was a template for aerogel formation, embedding thymol. Its potential application in humidity regulating packaging has been investigated. Results showed that emulsion gel containing cellulose nanofibers has slightly larger droplet diameter, better viscoelasticity and emulsification. Composite aerogel has larger pore size and thinner pore wall. Additionally, its tensile and compressive properties have been significantly improved. Moisture absorption was close to 100% of its own weight, thymol was released slowly. Compared with Escherichia coli, aerogel has better resistance to Staphylococcus aureus. When applied on fresh Agaricus bisporus. It was found that relative humidity in package can be stabilized at about 97%. Hardness, color, total phenol content, cell membrane integrity and total antioxidant capacity of Agaricus bisporus were maintained and fresh-keeping period was extended to 5 days.

3D printed nanocellulose-based label for fruit freshness keeping and visual monitoring

Food packaging systems with a single function of freshness keeping or monitoring may not be able to meet all practical needs. Herein, cellulose nanofibers (CNF)-based labels with dual functions of fruit freshness keeping and visual monitoring were prepared by coaxial 3D printing. CNF-based ink with blueberry anthocyanin was used to create the shell of fibers, exhibiting high formability and print fidelity as well as sensitive visual pH-responsiveness for freshness monitoring. Chitosan containing 1-methylcyclopropene (1-MCP) was loaded into the hollow microchannels of fibers, in which 1-MCP was trapped by the electrostatic effect of chitosan and CNF and exhibited a sustained release behavior. The 3D printed labels prolonged the shelf life of litchis for 6 days, meanwhile, they sensitively indicated the changes in freshness and the accuracy was confirmed by Headspace-Gas Chromatography-Ion Mobility Spectrometry. The CNF-based integrated labels developed in this work provided a new idea for the development of food intelligent packaging.

Design of drug-loaded 3D printing biomaterial inks and tailor-made pharmaceutical forms for controlled release

Curcumin and chloramphenicol are drugs with different solubility properties in physiological conditions due to their hydrophobic and hydrophilic structure, respectively. In this work, sodium alginate-cellulose nanofibers (SA-CNF) based inks loaded with curcumin and/or chloramphenicol have been developed for syringe extrusion 3D printing technology. Printability and shape fidelity of the drug-loaded inks were analyzed through rheological characterization. Suitable drug-loaded inks were 3D printed showing shape fidelity, and samples were either freeze-dried or crosslinked with Ca²⁺ and air-dried to achieve functional pharmaceutical forms with different morphological characteristics. In vitro drug delivery tests were carried out from the resulted forms and it was observed that the release performed faster in freeze-dried than in Ca²⁺ crosslinked/air-dried ones for all cases, resulting in two different methods for controlling drug delivery over time. The differences in aqueous solubility of the drugs, the different CNF content of the inks and the surface area of the samples also played an important role during drug delivery, involving strategies to control the release over an extended duration.

Antimicrobial and antihemolytic properties of a CNF/AgNP-chitosan film: A potential wound dressing material

Cellulose nanofibers (CNFs), chitosan, and silver nanoparticles (AgNPs) are widely used to enhance the active functions and antibacterial properties of wound dressings. This study was conducted to prepare CNF/AgNP-chitosan using a straight incorporation method and to assess its antimicrobial activity. CNFs were isolated from oil palm empty fruit bunches (OPEFBs) using the pulping method and acid hydrolysis. AgNPs were synthesized using a green synthesis method. The wound dressing was produced by mixing a 10% CNF solution in LiCl/DMAc and AgNP-chitosan in a glass plate with various ratios of CNF/AgNP-chitosan, i.e., 100:0, 80:20, 60:40, and 50:50. UV-visible and TEM analyses were conducted to confirm the formation of AgNPs and CNFs at the nanoscale. The results showed particles with an absorption wavelength of 435 nm and spherical shapes. Based on the calculation using ImageJ software, the diameters of CNFs were approximately 50 nm, and the lengths were several micrometers. FTIR was used to analyze the chemical bonding of AgNP-chitosan and the incorporated AgNP-chitosan in CNFs. Based on the XRD analysis, the presence of AgNPs did not affect the crystallinity of the CNFs. SEM images showed that the addition of AgNPs resulted in the stretching of CNF pores on the pads. Thermal degradation of the film increased with the addition of AgNP-chitosan by up to 40%. Antimicrobial tests and hemocompatibility tests showed that the formed CNF/AgNP-chitosan film successfully inhibited bacterial growth and was classified as a nonhemolytic material; thus, its potential as a wound dressing should be further studied.

Development of a continuous fixed-bed column to eliminate cadmium(II) ions by starch-g-poly(acrylic acid)/cellulose nanofiber bio-nanocomposite hydrogel

This paper presents an experimental study on continuous adsorptive removal of Cd²⁺ from the water body using a bio-nanocomposite hydrogel within a fixed-bed column (FBC) system. The bio-nanocomposite hydrogel was synthesized based on starch grafted poly(acrylic acid) (St-g-PAA) reinforced by cellulose nanofibers (CNFs). The effects of processing conditions including pH, flow rate, and initial concentration of Cd²⁺ on adsorption efficiency were examined. Based on the results, the highest removal efficiency was achieved to be 82.5% at pH of 5, initial concentration of 10 mg L^-1, and flow rate of 5 mL min^-1. Furthermore, by applying isotherm models, it was uncovered that the Langmuir isotherm model was the most appropriate one, and the maximum adsorption capacity was 40.65 mg g^-1. Also, an adsorption process was carried out using the FBC system, and the outcome data were processed using Thomas and Yoon-Nelson models to find the characteristics of the column. In this study, the recovering capacity of the exhausted hydrogel was evaluated. Desorption process efficiencies of batch and continuous operations were obtained to be 91.9% and 90%, respectively.

Solution blowing spinning technology and plasma-assisted oxidation-reduction process toward green development of electrically conductive cellulose nanofibers

Cellulose fibers have been one of the most common fibers due to their biodegradability, excellent mechanical properties, biocompatibility, high absorption ability, cheapness and renewability. In this study, novel, simple and green method is concerned with the production of multifunctional cellulose nanofibers (CNFs). Nanocomposites consisting of silver nanoparticles (AgNPs) and polyaniline (PANi) were in situ synthesized into plasma-pretreated cellulosic nanofibers fabricated by solution blowing spinning technique. The produced cellulose acetate nanofibers were then subjected to deacetylation followed by plasma-activation followed by a treatment with aniline and silver nitrate (AgNO₃) in the presence of ammonium acetate. Plasma-assisted oxidation polymerization process of aniline into PANi associated with a reduction of Ag⁺ into AgNPs results in their permanent insolubility into the surface of the cellulose nanofibers. The morphologies and elemental contents were determined by polarizing optical microscope (POM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), energy-dispersive X-ray patterns and scanning electron microscopy (SEM). Additionally, transmission electron microscope (TEM) was applied to explore the morphologies of silver nanoparticles and PANi showing particle diameter between 12 and 25 nm. The antimicrobial Ag NPs were formed from an aqueous medium of silver nitrate by taking the reduction ability advantage of the electrically active PANi. The immobilization of polyaniline and silver nanoparticles into the surface of the cellulose nanofibers enhanced its electrical conductivity. The produced CNFs demonstrated a high UV protection as well as antibacterial activity.

Nanocellulose aerogel for highly efficient adsorption of uranium (VI) from aqueous solution

Cellulose nanofibers (CNFs) aerogel was prepared via simple covalent crosslinking and freeze-drying method. The porous cellulose aerogel possessed high specific surface area and high metal-chelating capacity, which showed fast adsorption kinetics and high adsorption capacity (440.60 mg g^-1) in static uranium adsorption process. In the dynamic filtration system, the maximum adsorption capacity reached 194 mg g^-1 with the initial concentration of 10 mg L^-1. In addition, the CNFs aerogel possessed excellent selectivity and good regeneration ability for uranium adsorption. The integrated analyses of attenuated total reflection Fourier transform infrared (ATR-FTIR), X-Ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) suggested that the predominant UO₂²⁺ species formed inner-sphere surface complexes with two active carboxyl groups in the coordination model. This strategy may provide a sustainable route for development of efficient biomass-based adsorbents for selective uranium removal from aqueous solution.

Curcumin doped functionalized cellulose nanofibers based edible chitosan coating on kiwifruits

The developed edible coating with curcumin facilitated iron functionalized cellulose nanofiber (f-CNF) reinforced chitosan (CS) were applied on kiwifruits for maintaining the quality during storage life. The f-CNF was fabricated via anchoring iron particles onto the surface of CNF as evident by FESEM, FETEM, and XRD analysis. The inclusion of f-CNF and curcumin as a component of edible coating can provide a synergistic effect in maintaining the quality of kiwifruits. The f-CNF (1.5 wt%) dispersed CS edible coating assisted by curcumin provided a lamellar and heterogonous surface morphology with a hazy appearance. The used edible coating materials were effective in reducing mass loss, firmness loss, respiration rate, and microbial count of the kiwifruits during storage life (10 days at 10 °C). Additionally, color, and physiological properties of kiwifruits can be modified by using the addressed edible coating materials.

Nanocellulose-derived carbon/g-C3N4 heterojunction with a hybrid electron transfer pathway for highly photocatalytic hydrogen peroxide production

Using oxygen reduction for the photocatalytic production of hydrogen peroxide (H₂O₂) has been considered a green and sustainable route. In the present study, to achieve high efficiency, graphitic carbon nitride (g-C₃N₄) was obtained using thermal polymerization from a bi-component precursor and was then assembled with cellulose nanofibers. It was found that a small quantity of cellulose nanofibers that generates carbon fibers upon pyrolysis greatly improves the photocatalytic activity compared with that of g-C₃N₄ alone. The well-defined carbon/g-C₃N₄ heterojunction-type material exhibits as high as 1.10 mmol L^-1h^-1 of photo-production of H₂O₂ under visible light, which is 4.2 times higher than that yielded by pristine g-C₃N₄ from a single precursor. A comprehensive characterization of the photocatalyst enables us to delineate the effect of the carbon nanofiber with respect to porosity, electron-hole separation, band gap regulation, and especially the electron transfer pathway. Our results demonstrate that nanocellulose-derived carbon, when precisely assembled with other functional material such as a photocatalyst, is a promising promoter of their activity.

TiO2/rectorite-trapped cellulose composite nanofibrous mats for multiple heavy metal adsorption

The anthropogenic release of highly toxic heavy metals into the environment presents a huge challenge for ecosystems and human society. Recoverable and efficient adsorption materials could be obtained by trapping inorganic adsorbents (e.g., TiO₂ nanoparticles and rectorite (REC)), in a natural polymer matrix. In this study, a series of cellulose-TiO₂/REC composite nanofibrous mats were fabricated via electrospinning. The interactions between inorganic adsorbents and cellulose molecules improved the thermal stability, surface area, tensile strength and adsorption capacity of the mats. We focused on the adsorption of Pb²⁺, Cu²⁺ and Cd²⁺ from acidic solutions onto cellulose-TiO₂/REC composite nanofibrous mats in multiple systems because the magnitudes of heavy metal concentrations in wastewater typically varied. The maximum total adsorption capacity of 69.81 mg/g was obtained by Cellulose-TiO₂/REC_2:1 nanofibrous mats. The composite nanofibrous mats successfully trapped TiO₂ nanoparticles, and the obtained cellulose-TiO₂/REC nanofibrous mats could be used to remove heavy metals from acidic wastewater.

Macroporous MnO2-based aerogel crosslinked with cellulose nanofibers for efficient ozone removal under humid condition

Atmospheric ozone pollution receives worldwide concerns, and it is a big challenge to search for the practical ozone-decomposition catalyst with good moisture resistance. Herein, a light-weight and high-porosity MnO₂-based hybrid aerogel was synthesized with cellulose nanofibers using a facile ice-template approach, followed by freeze-drying. In the three-dimensional framework, the cellulose nanofibers serve as the skeletons to disperse MnO₂ particles, improving the exposure of active sites on MnO₂. XPS, ¹H NMR and ATR-FTIR demonstrate that MnO₂ particles are effectively combined with cellulose nanofibers through hydrogen bonds, which originate from the abundant surface hydroxyl groups of both components. These consumed surface hydroxyl groups of MnO₂ not only reduce the water adsorption but also avoid the generation of surface-adsorbed H₂O via the reaction with ozone, thus alleviating the catalyst deactivation. In addition, the interconnected macroporous structure enables the rapid diffusion of ozone molecules and facilitates the passage of water molecules, which is conducive to the adsorption and decomposition of ozone on the active sites, i.e. surface oxygen vacancies. Thus, the high and stable ozone conversion was achieved for 150 ppb O₃ under the relative humidity of 50% and the space velocity of 600 L·g^-1·h^-1 within 10 days at room temperature.

Highly stretchable and self-healing cellulose nanofiber-mediated conductive hydrogel towards strain sensing application

HYPOTHESIS

Hydrogel-based sensors have attracted considerable attention due to potential opportunities in human health monitoring when both mechanical flexibility and sensing ability are required. Therefore, the integration of excellent mechanical properties, electrical conductivity and self-healing properties into hydrogels may improve the application range and durability of hydrogel-based sensors.

EXPERIMENTS

A novel composite hydrogel composed of polyaniline (PANI), polyacrylic acid (PAA) and 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNFs) was designed. The viscoelastic, mechanical, conductive, self-healing and sensing properties of hydrogels were studied.

FINDINGS

The TOCNF/PANI/PAA hydrogel exhibits a fracture strain of 982%, tensile strength of 74.98 kPa and electrical conductivity of 3.95 S m^-1, as well as good mechanical and electrical self-healing properties within 6 h at ambient temperature without applying any stimuli. Furthermore, owing to the high sensitivity of the TOCNF/PANI/PAA-0.6 hydrogel-based strain sensor (gauge factor, GF = 8.0), the sensor can accurately and rapidly detect large-scale motion and subtle localized activity. The proposed composite hydrogel is as a promising material for use as soft wearable sensors for health monitoring and smart robotics applications.

Anisotropic cellulose nanofiber/chitosan aerogel with thermal management and oil absorption properties

Attributed to low cost, renewable, and high availability, cellulose-based aerogels are desirable materials for various applications. However, mechanical robustness and functionalization remain huge challenges. Herein, we synthesized a recoverable, anisotropic cellulose nanofiber (CNF) / chitosan (CS) aerogel via directional freeze casting and chemical cross-link process. The chitosan was performed as strength polymers to prohibits the shrinkage and retains the structural stability of 3D cellulose nanofiber skeleton, endowing the composite aerogel with satisfactory deformation recovery ability (without loss under 60 % stress cycled 100 times). The CNF/CS composite aerogel has ultralow density (∼8.4 mg/cm³), high temperature-invariant (above 300 °C) and high porosity (98 %). The CNF/CS aerogel demonstrates anisotropic thermal insulation properties with low thermal conductivity (28 mWm^-1 K^-1 in rational direction and 36 mW m^-1 K^-1 in the axial direction). Moreover, the composite aerogel (water contact angle ∼148°) exhibited outstanding oil/water selectivity and high absorption capacity (82-253 g/g) for various oils and organic solvents. Therefore, the multifunctional CNF/CS composite aerogels are potential materials for thermal management and oil absorption applications.

Amylose/cellulose nanofiber composites for all-natural, fully biodegradable and flexible bioplastics

Thermoplastic, polysaccharide-based plastics are environmentally friendly. However, typical shortcomings include lack of water resistance and poor mechanical properties. Nanocomposite manufacturing using pure, highly linear, polysaccharides can overcome such limitations. Cast nanocomposites were fabricated with plant engineered pure amylose (AM), produced in bulk quantity in transgenic barley grain, and cellulose nanofibers (CNF), extracted from agrowaste sugar beet pulp. Morphology, crystallinity, chemical heterogeneity, mechanics, dynamic mechanical, gas and water permeability, and contact angle of the films were investigated. Blending CNF into the AM matrix significantly enhanced the crystallinity, mechanical properties and permeability, whereas glycerol increased elongation at break, mainly by plasticizing the AM. There was significant phase separation between AM and CNF. Dynamic plasticizing and anti-plasticizing effects of both CNF and glycerol were demonstrated by NMR demonstrating high molecular order, but also non-crystalline, and evenly distributed 20 nm-sized glycerol domains. This study demonstrates a new lead in functional polysaccharide-based bioplastic systems.

Lignin-mediated in-situ synthesis of CuO nanoparticles on cellulose nanofibers: A potential wound dressing material

Herein we present our research on the synthesis of CuO nanoparticles on the surface of electrospun cellulose (CE) nanofibers using alkali lignin as a reducing agent. Fascinatingly, CA nanofibers were deacetalized during alkali lignin treatment, which was verified by FTIR-ATR spectra. The morphology of the produced nanofibers was observed with SEM and TEM. The presence of CuO nanoparticles was verified by EDX, XRD, and XPS. The Cu/CE nanofibers showed low thermal stability. MVTR values of 2100-1900 g/m²/day are adequate for the transport of air and moisture from the wound surface. The Cu/CE showed faster release (80%) of copper ions to aqueous environment within 24 h and seemed to advance towards plateau for the next five days. The Cu/CE nanofibrous mats exhibited excellent antibacterial efficacy against both gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) bacteria. NIH3T3 fibroblast cells have excellent migrating and proliferating ability on our prepared nanofibrous mats. The presence of bound alkali lignin on the surface of nanofibers added a benefit of antioxidant activity. These findings revealed that such type of nanofibrous mats could be used as a potential wound dressing material.

Comparative analysis of physical and functional properties of cellulose nanofibers isolated from alkaline pre-treated wheat straw in optimized hydrochloric acid and enzymatic processes

Two methods, HCl and enzymatic treatments, were evaluated for diversification of morphological and functional properties of cellulose nanofibers (CNF) from two- stage-alkaline pre-treated wheat straw (WS). The extraction conditions were optimized by a central composite designed experimental approach varying time (4-8 h) and temperature (80-120 °C) for the HCl-based treatment and time (4-8 h), and FiberCare dosage (50-100 endo-1,4-β-glucanase unit/g) and Viscozyme (10-20 fungal β-glucanase units/g) for the enzyme-based treatment. The CNF yields, morphological (polydispersity index (PdI), length and diameter), and functional (crystallinity and thermal degradation) properties were compared. The CNF produced by the HCl (HCN) and enzymatically (ECN) attained diameters ~17 nm had PdI, length, and crystallinity of 0.53, 514 nm & 70%, and 0.92, 1.0 μm & 48%, respectively. Thus, the HCN morphology suits homogenous nano-applications, whereas that of the ECN, would suit heterogenous nano-applications. The HCN and ECN yields were similar (~20%) with optimal production time of 7.41 and 4.64 h, respectively. Both the HCN & ECN can be classified as thermally stable nanocolloids with maximum thermal degradation temperatures of ~380 °C and Zeta potential ~-16 mV. The two CNF production methods have potential synergetic effects on CNF production, morphological, and functional properties.

Environmentally friendly superabsorbent fibers based on electrospun cellulose nanofibers extracted from wheat straw

Superabsorbent polymers currently used in health and agricultural sectors are based on petroleum-based materials which led to serious concerns in the society. Here, superabsorbent fibers (SAFs) based on electrospun cellulose nanofibers (ECNFs) were prepared. Firstly, cellulose was removed from wheat straw, pre-treated with the TEMPO-mediated oxidation and subsequently dissolved into Trifluoroacetic acid for production of ECNFs through the electrospinning approach. The maximum swelling ratios of 225 g/g and 208 g/g in distilled water and 0.9 wt% NaCl solution were measured for ESAFs composed of oxidized ECNFs containing 15 % poly (sodium acrylate), respectively. The ESAFs were characterized using Fourier transform infrared spectroscopy and field emission scanning electron microscopy analysis. The FESEM showed that ESAFs formed high strength three-dimensional architecture networks. Also, the results showed that the ionic sensitivity of this ECNFs were low. The prepared ESAFs are attractive renewable alternatives for different applications, contributing to a reduction of plastic microspheres.

High crystallinity of tunicate cellulose nanofibers for high-performance engineering films

Tunicate cellulose nanofibers (CNFs) have received widespread attention as renewable and eco-friendly engineering materials because of their high crystallinity and mechanical stiffness. Here, we report the effects of disintegration process conditions on structure-property relationships of tunicate CNFs. By varying the hydrolysis time, we could establish a correlation between crystallinity of the CNFs with linearity and stiffness, which produces different molecular ordering within their nanostructured films. Despite having identical raw materials, tensile strength and thermal conductivity of the resulting layered films varied widely, ranging from 95.6 to 205 MPa and from 1.08 to 2.37 W/mK respectively. Furthermore, nanolayered CNF films provided highly anisotropic thermal conductivities with an in- and through-plane ratio of 21.5. Our systematic investigations will provide general and practical strategies in tailoring material properties for emerging engineering applications, including flexible paper electronics, heat sink adhesives and biodegradable, implantable devices.

Lignin containing cellulose nanofibers (LCNFs): Lignin content-morphology-rheology relationships

This study aims to investigate the relationship between lignin content, morphology, and rheology of lignin containing cellulose nanofibers (LCNFs). The morphology and rheology of LCNFs were dominated by lignin content. Lignin content had two-sides on mechanical fibrillation. At high lignin content (23.79 %), reduced efficiency of defibrillation resulted in large LCNFs connecting with lignin patches. LCNF suspensions exhibited low viscosity, weak gel behavior due to infirm fibril network. Small yield stress of 1.14 Pa suggested that fibril network was easily disrupted. At residual lignin of 6.52 %, fibril bundles were sensitive to defibrillation, producing long and flexible LCNFs with high capacity of entanglement. The entangled fibril network had high viscosity and strong gel like behavior. Creep compliance of 0.09 Pa^-1 and large yield stress of 4.25 Pa indicated excellent resistance to deformation. The desired rheology can be tailored by lignin content, providing practical guidance on novel rheology-dependent LCNF based materials.

Redispersion and structural change evaluation of dried microfibrillated cellulose

Commercializing dried microfibrillated cellulose (MFC) has always been a challenge mainly due to the tendency of MFC to aggregate. In this study MFC samples were submitted to drying/redispersion cycles at different temperatures. Morphology, crystallinity and mechanical performance of films were analyzed throughout the cycles. Microscopy images, particle size and stability in water showed that aggregation happens more severely with 5 drying/redispersion cycles and at drying temperatures of 75 and 100 °C. Particles once-dried at 20 °C formed the same size and web-like structure as the MFC-control. Crystallinity and crystallite sizes increased with drying/redispersion cycles especially when dried at 75 and 100 °C, however drying/redispersion cycles also led to a reduction in mechanical performance due to aggregation. While oven-drying is not the most suitable method, milder action at room temperature once-drying led to suspension stability in water, morphology and mechanical properties close to never-dried MFC, which makes this treatment a feasible option to maintain cellulose quality.

Ultra-fast heat dissipating aerogels derived from polyaniline anchored cellulose nanofibers as sustainable microwave absorbers

Electromagnetic (EM) pollution is ubiquitous and has soared to a great extent in the past few decades. The use of plant sourced cellulose nanofibers to fabricate sustainable and high performance electromagnetic shielding materials is foreseen as a green solution by the electronics industry to address this unseen pollutant. In this view, we report a facile and environmentally benign strategy to synthesize ultra-light and highly conductive aerogels derived from cellulose nanofibers (CNF) decorated with polyaniline (PANI) via a simple in-situ polymerization and subsequent freeze drying process devoid of any volatile organic solvents. The obtained conductive aerogels exhibited density as low as 0.01925 g/cc with a maximum EMI shielding value -32 dB in X band region. These porous shields demonstrated strong microwave absorption behavior (95 %) with minimal reflection (5 %) coupled with high specific EMI SE value ∼1667 dB.cm³. g^-1 which make these aerogels a potential candidate for use in telecommunication, military and defense applications.

Green and novel adsorbent from rice straw extracted cellulose for efficient adsorption of Hg (II) ions in an aqueous medium

Cellulose nanofibrils (CNF) were extracted from rice straw, a waste lignocellulosic biomass, using soda cooking, which resulted in a reduction of the recalcitrance of biomass, leading to hydrolysis of hemicellulose into sugars, which was subsequently washed, leaving a residue of cellulose. FTIR confirmed the removal of lignin and hemicellulose to yield pure CNF while XRD, DTG and TGA results showed increased crystallinity and thus higher thermal stability. CNFs were functionalized using l-methionine, a natural amino acid, to graft sulfides and amino functional groups onto the surface of fibers. Structural and morphological changes induced by grafting were confirmed by FTIR, XRD, TEM, Mapping and Elemental analysis. Modified fibers exhibited a high adsorption capacity of 131.86 mg/g for Hg (II) ions even at low concentration i.e. 300 ppm owing to sulfides. Optimization of pH on adsorption behavior was established through extensive pH studies and adsorption kinetics. Adsorption follows pseudo second order kinetic model indicating chemisorption for removal of Hg (II) ions from simulated wastewater.

Acid-free preparation and characterization of kelp (Laminaria japonica) nanocelluloses and their application in Pickering emulsions

Cellulose nanofibers (CNFs) from kelp were prepared by cellulase treatment with lengths greater than 3 μm. CNFs were further oxidized by TEMPO-oxidized system, and the lengths of the oxidized CNFs (TEMPO-CNFs) were 0.6-1 μm. AFM and TEM images showed that intertwined CNFs fibers were divided into individual nanofibrils. The crystallinity of TEMPO-CNFs increased to 66.5 %. TGA analysis indicated that TEMPO-CNFs were more sensitive to temperature than cellulose and CNFs. FT-IR spectra revealed no changes in the basic cellulose structures of CNFs and TEMPO-CNFs. In the sunflower oil/water (20/80, v/v) model emulsions, the oil droplet sizes were less than 20 μm in CNFs emulsions, which became smaller in TEMPO-CNFs emulsions. Delamination was found in CNFs emulsions after three days of storage. Addition of NaCl increased the volumes of TEMPO-CNFs emulsions but enlarged the oil droplets sizes. TEMPO-CNFs emulsions had the largest volume with smallest and most homogeneous oil droplets at pH 3. TEMPO-CNFs emulsions showed good stability after storage for 30 days. Further, TEMPO-CNFs could also emulsify 50 % (v/v) of sunflower oil. All these results indicated that TEMPO-CNFs can be used in preparing Pickering emulsions.