Cellulose Nanofibrils Research Articles

Thiol-Surface-Engineered Cellulose Nanocrystals in Favor of Copper Ion Uptake.

Cellulose, the most abundant natural polymer on earth, has recently gained attention for a large spectrum of applications. At a nanoscale, nanocelluloses (mainly involving cellulose nanocrystals or cellulose nanofibrils) possess many predominant features, such as highly thermal and mechanical stability, renewability, biodegradability and non-toxicity. More importantly, the surface modification of such nanocelluloses can be efficiently obtained based on the native surface hydroxyl groups, acting as metal ions chelators. Taking into account this fact, in the present work, the sequential process involving chemical hydrolysis of cellulose and autocatalytic esterification using thioglycolic acid was performed to obtain thiol-functionalized cellulose nanocrystals. The change in chemical compositions was attributed to thiol-functionalized groups and explored via the degree of substitution using a back titration method, X-ray powder diffraction, Fourier-transform infrared spectroscopy and thermogravimetric analysis. Cellulose nanocrystals were spherical in shape and ca. 50 nm in diameter as observed via transmission electron microscopy. The adsorption behavior of such a nanomaterial toward divalent copper ions from an aqueous solution was also assessed via isotherm and kinetic studies, elucidating a chemisorption mechanism (ion exchange, metal chelation and electrostatic force) and processing its operational parameters. In contrast to an inactive configure of unmodified cellulose, the maximum adsorption capacity of thiol-functionalized cellulose nanocrystals toward divalent copper ions from an aqueous solution was 4.244 mg g-1 at a pH of 5 and at room temperature.

Vascular bundle-inspired MXene ion-conducting microchannels enabled tough ionic hydrogels with high-sensitivity sensing and high-efficiency mechanical-electric conversion

High-sensitivity hydrogel-based sensors with self-powered functions are becoming more and more important in wearable electronics fields. However, traditional hydrogels cannot satisfy the application requirements for high-performance self-powered wearable sensors due to their low conductivity, poor sensitivity, and limited electric output performance. Inspired by the transport effect of vascular bundles in trees on inorganic salts, unique ion-conducting microchannels are assembled by MXene nanosheets as conductive materials, cellulose nanofibrils (CNFs) as cross-linking supports, and NH4HCO3 as an inducer, which exhibits high mechanical properties, excellent conductivity, and high-sensitivity sensing. The MXene microchannels contribute to the directional transport of free ions in the polyvinyl alcohol (PVA) hydrogel with poly(diallyl dimethyl ammonium chloride) (PDADMAC) as ion source, thus endowing the MXene-CNF-PDADMAC-PVA (MCPP) hydrogel with high-sensitivity sensing and high-efficiency mechanical-electric conversion performance. The MCPP hydrogel-based sensor possesses a low detection limit (200 mg) and fast response time (120 ms). The MCPP hydrogel-based triboelectric nanogenerator can generate a VOC of 159.1 V, ISC of 24.5 µA, and QSC of 32.5 nC, and the MCPP hydrogel-based piezoelectric nanogenerator can output a voltage of 1134.3 mV. Thanks to the excellent self-powered sensing performance, a self-powered sensing indicator and tiny pressure detector based on the hydrogel are developed to realize the visual sensing in an uncomfortable state of the elderly without an external power supply and detect the heartbeat and fluttering pulse. Therefore, this ionic hydrogel with high-sensitivity sensing and high-efficiency mechanical-electric conversion performance is very promising for applications in next-generation advanced wearable electronics.

Mechanically Adaptive Mixed Ionic-Electronic Conductors Based on a Polar Polythiophene Reinforced with Cellulose Nanofibrils.

Conjugated polymers with oligoether side chains are promising mixed ionic-electronic conductors, but they tend to feature a low glass transition temperature and hence a low elastic modulus, which prevents their use if mechanical robust materials are required. Carboxymethylated cellulose nanofibrils (CNF) are found to be a suitable reinforcing agent for a soft polythiophene with tetraethylene glycol side chains. Dry nanocomposites feature a Young's modulus of more than 400 MPa, which reversibly decreases to 10 MPa or less upon passive swelling through water uptake. The presence of CNF results in a slight decrease in electronic mobility but enhances the ionic mobility and volumetric capacitance, with the latter increasing from 164 to 197 F cm-3 upon the addition of 20 vol % CNF. Overall, organic electrochemical transistors (OECTs) feature a higher switching speed and a transconductance that is independent of the CNF content up to at least 20 vol % CNF. Hence, CNF-reinforced conjugated polymers with oligoether side chains facilitate the design of mechanically adaptive mixed ionic-electronic conductors for wearable electronics and bioelectronics.

Highly compressible and hydrophobic nanofibrillated cellulose aerogels for cyclic oil/water separation

Nanofibrillated cellulose (NFC)-based aerogels are ideal oil-sorbent materials, but the poor structural stability and hydrophilicity restrain their practical applications in the fields of oil/water separation. In the present work, we report a facile strategy for constructing a hydrophobic nanofibrillated cellulose aerogel for cyclic oil/water separation. Briefly, an aerogel matrix of C-g-PEI with multiple cross-linked network structures was constructed via the combined use of oxidized-NFC (ONC), polyethyleneimine (PEI), and ethylene glycol diglycidyl ether (EGDE), followed by rapid in situ deposition of poly(methyl trichlorosilane) (PMTS) through a low-temperature gas-solid reaction. The resulting ONC-based aerogel (C-g-PEI-PMTS) exhibits the advantages of ultralight (53.80 mg/cm3), high porosity (95.73 %), hydrophobicity (contact angle of 130.0°) and remarkable elasticity (95.86 %). Meanwhile, the composite aerogel of C-g-PEI-PMTS is extremely suitable for oil sorption-desorption by a simple mechanical squeezing method. After 10 cycles of sorption-desorption, the sorption capacity of the aerogel towards various oils reached almost the same level as in the first cycle. The filtration separation efficiency for the trichloromethane-water mixtures remained at 99 % after 50 cycles, demonstrating encouraging reusability. In summary, an efficient strategy to prepare NFC-based aerogel with highly compressible and hydrophobic properties is developed, which expands the applications of NFC in the fields of oil/water separation.

Extraction of Cellulose Nanofibrils (CNFs) from Pomelo Peel via Hydrothermal Auxiliary Alkali Treatment Combined with Ball-Milling

Extraction of Cellulose Nanofibrils (CNFs) from Pomelo Peel via Hydrothermal Auxiliary Alkali Treatment Combined with Ball-Milling

Simultaneously flame-retardant and antibacterial films from κ-carrageenan/carboxylated cellulose nanofibril/phytic acid for the preservation of cooked pork

Conventional polysaccharide films are flammable and susceptible to bacterial growth, decreasing the potential in practical applications such as bio-based and active food packaging. In this study, the nontoxic naturally occurring compound phytic acid (PA) was introduced to a blended film of κ-carrageenan (κC) and carboxylated cellulose nanofibrils (CCNF) to overcome these disadvantages. Compared with the κC-CCNF-PA0 film, the κC-CCNF-PA24 film possessed improved elongation at break (41%), water vapor permeability (3.46 g m−1 Pa−1 s−1 × 10−8) and oxygen permeability (1.50 cm3 mm−2 Pa−1 day−1 × 10−12). Thermogravimetric analysis, limiting oxygen index and actual flame-burning behaviors revealed good flame retardancy of the prepared films with the increase in PA. When the PA content reached 18% and 9%, the antibacterial rate against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) reached 100%, respectively. The cooked pork samples packaged by κC-CCNF-PA24 exhibited lower values of malondialdehyde (0.61 mg kg−1) and total viable count (8 CFU g−1) compared with those by κC-CCNF-PA0 film (0.99 mg kg−1, 447 CFU g−1). On the basis of these results, we believe that the sustainable and clean strategy provides an opportunity to improve and functionalize very brittle and flammable polysaccharide-based films.

Production and characterization of nanofibrillated cellulose gels simultaneously exhibiting thermally stable green color and oil-in-water emulsion stabilizing capability from Centella asiatica.

Nanofibrillated cellulose (NFC) gels simultaneously exhibiting Pickering stabilizing capability and thermally stable green color were developed for use as food additive in thermally processed food emulsion requiring the expression of color. Chopped Centella asiatica plant was mixed with zinc amino acid chelate solution and subject to autoclaving at 130°C for 2h to form zinc-chlorophylls complex and to remove noncellulosic components. Autoclaved sample was high-shear homogenized at 26,000rpm for 15min and microfluidized at either 80, 120, or 160MPa for 5 passes. An increase in microfluidization pressure resulted in a decrease in NFC diameters; microfluidization at 160MPa did not nevertheless yield any further reduction in the diameters when compared with that at 120MPa. From energy consumption point of view, microfluidization at 120MPa for 5 passes was then noted as optimal condition for preparation of NFC coloring gel; NFC with diameters of 8-42nm and crystallinity index of 35% was obtained. Freshly prepared gel exhibited gel-like behavior and dark green color. Heating at 121°C for 1h did not affect diameters, viscoelasticity, and color of the gel. Addition of the gel at 0.9% or 1.2% (w/w) into soybean oil-in-water emulsion, in combination with high-shear homogenization at 18,000rpm for 5min, resulted in adequate emulsion stability. The emulsion exhibited stable dark green color and no phase separation after heating at 121°C for 1h and during storage for 8 weeks. PRACTICAL APPLICATIONS: Information presented here can serve as a guideline for further development of a multifunctional food ingredient exhibiting thermally stable green color and oil-in-water emulsion stabilizing capability. In other words, one simple ingredient can serve at the same time as both natural food colorant and emulsion stabilizer.

Tuning topology towards stronger and tougher polymers inspired by semi-crystalline cellulose nanofibrils

A long-standing challenge in materials design is to overcome the conflict between strength and toughness, which generally contradict each other. Natural cellulose-enabled advanced materials are promising solutions due to their remarkable capabilities to increase toughness without sacrificing strength. Nevertheless, the lack of mechanistic understanding on their elementary building block, the semi-crystalline cellulose nanofibril, hinders the understanding and designing of stronger and tougher advanced polymeric materials where hydrogen bonds and chain topologies play critical roles. In this study, we address above challenges starting from molecular simulations of semi-crystalline cellulose nanofibrils. It is found that the strength and toughness of cellulose nanofibrils can simultaneously increase by tuning the semi-crystalline topologies, leading to simple topology engineering strategies to design ultra-strong and ultra-tough nanofibril and network structures. The fundamental mechanisms and designing concepts can be readily extended into material systems where secondary bonds are important, enabling a wide range of strong and tough advanced polymeric materials.

Inhibition of α-amylase and amyloglucosidase by cellulose nanofibrils with different surface charge and spectroscopic analysis of their interaction mechanism

We investigated the inhibition effect of carboxymethylated cellulose nanofibrils with four different surface chargeon α-amylase and amyloglucosidase via enzyme activity inhibition assay, fluorescence spectra and secondary structure change analysis. These results revealed that cellulose nanofibril with lowest surface charge displayed the greatest inhibition effects against α-amylase (9.81 mg/mL) and amyloglucosidase (13.16 mg/mL). All cellulose nanofibrils in starch model significantly (p < 0.05) inhibited the starch digestion, where the inhibition effect was negatively correlated with the magnitude of particle surface charge. Cellulose nanofibrils could bind α-amylase or amyloglucosidase to form new complex in the manner of static quenching. The thermodynamic parameters demonstrated that the cellulose nanofibrils-starch hydrolase (α-amylase or amyloglucosidase) complexes were formed spontaneously via hydrophobic effects. Additionally, Fourier transform Infrared spectra exhibited the changes in the fraction of secondary structures of starch hydrolase after the interactions with carboxymethylated cellulose nanofibrils. These data provide a convenient and simple method tailor gastrointestinal digestion of starch by changing cellulose surface charge, to control postprandial serum glucose upsurge.

Designing flexible CNT/CNF films with highly light-absorbing for solar energy harvesting: Seawater desalination, photothermal power generation and light- driven actuators

Green cellulose- based solar light capturing composite films made of carbon nanotubes (CNT) and cellulose nanofibrils (CNF), with high photothermal conversion performance, were designed and developed. Thanks to the strong electrostatic interactions between carboxyl- rich CNFs (obtained from 2, 2, 6, 6-tetramethylpiperidine-1-oxyl (TEMPO) mediated oxidation), and cationic-modified CNTs using cetyltrimethylammonium bromide, the resultant CNT/CNF composite (FTC) films are uniform and exhibit excellent mechanical properties. More importantly, the effect of CNT/CNF ratio in the FTC films on their photothermal conversion capacity and coefficient of thermal expansion (CTE) was investigated. The FTC film with 50 % CNT incorporation shows both high photothermal conversion capacity and high negative CTE, and its application for solar energy harvesting was explored, including seawater desalination, photothermal power generation and light- driven actuators. The FTC film exhibits high light-induced desalination capability, with water evaporation rate reaching 1.23 Kg m-2 h-1 at an irradiance of 1 kW m-2 (evaporation efficiency of 84.5 %) and ion concentrations in purified water decreasing by 4 orders of magnitude. The FTC film can also be assembled into photothermal power system, achieving an output voltage of 310 mV at an irradiance of 3 kW m-2. With the assistance of a boost module, it can be used to re-charge a cell phone. A light-driven FTC/polytetrafluoroethylene (PTFE) double- layered actuator was also designed. Benefiting from the negative CTE of the FTC film, the actuator has a high sensitivity and achieves a bending curvature of 3.3 cm-1 at an irradiance of 0.74 kW m-2. This study presents a scalable, yet simple strategy to design green/sustainable cellulose- based solar energy harvesting devices that can have multiple applications.

Endoglucanase pretreatment aids in isolating tailored-cellulose nanofibrils combining energy saving and high-performance packaging

Cellulose nanofibrils (CNFs) have emerged as a potential alternative to synthetic polymers in packaging applications owing to their oxygen and grease barrier performance, as well as their strong mechanical properties. However, the performance of CNF films relies on the inherent characteristics of fibers, which undergo changes during the CNF isolation process. Understanding these variations in characteristics during CNF isolation is crucial for tailoring CNF film properties to achieve optimum performance in packaging applications. In this study, CNFs were isolated by endoglucanase-assisted mechanical ultra-refining. The alterations in the intrinsic characteristics of CNFs and their impact on CNF films were systematically investigated by considering the degree of defibrillation, enzyme loading, and reaction time through a design of experiments. Enzyme loading had a significant influence on the crystallinity index, crystallite size, surface area, and viscosity. Meanwhile, the degree of defibrillation greatly affected the aspect ratio, degree of polymerization, and particle size. CNF films prepared from CNFs isolated under two optimized scenarios (casting and coating applications) exhibited remarkable properties, including high thermal stability (approximately 300 °C), high tensile strength (104 – 113 MPa), excellent oil resistance (kit n°12), and low oxygen transmission rate (1.00 – 3.17 cc·m−2.day−1). Therefore, endoglucanase pretreatment can aid in obtaining CNFs with lower energy consumption, resulting in films that possess higher transmittance, superior barrier performance, and reduced surface wettability compared to control samples without enzymatic pretreatment and other unmodified CNF films reported in the literature, all while maintaining mechanical and thermal performance without significant loss.

Dried water-redispersible bacterial nanocellulose with sorbitol as capping agent

In view of the economic and technical limitations associated with diluted aqueous suspensions of cellulose nanofibrils, in the present contribution sorbitol was assayed as capping agent in the drying of bacterial nanocellulose (BNC) for the first time. The effect of different sorbitol:BNC mass ratios (1:1, 3:1 and 5:1), drying strategies (freeze-drying versus oven-drying), and redispersion methods (high-speed homogenization and mechanical stirring) on the water redispersibility of dried BNC was studied. Sedimentation, specific surface area and rheology assays all demonstrated the suitability of sorbitol for significantly limiting irreversible hydrogen bonding between adjacent cellulose nanofibrils during dehydration, leading to redispersed BNC suspensions with characteristics similar to those of never-dried ones. In the case of freeze-dried samples, results showed that the lowest sorbitol:BNC mass ratio assayed (i.e., 1:1) was enough to prevent irreversible hydrogen bonding between adjacent cellulose fibrils, whereas for oven-dried BNC samples full redispersion was achieved by mechanical stirring when sorbitol:BNC mass ratios of at least 3:1 were used. The feasibility of easily removing sorbitol from the dried product upon redispersion was also verified.

Integrated enzyme hydrolysis assisted cellulose nanofibril (CNF) fabrication: A sustainable approach to paper mill sludge (PMS) management

The landfilling of paper mill sludge (PMS) has been restricted or even banned in many countries due to the raised concern about greenhouse gas (GHG) emissions and contamination of the soil and water, calling for a sustainable PMS management approach. The potential valorization of PMS to nanomaterials combined with traditional biorefinery was examined in this work. Three types of PMS-derived cellulose nanofibrils (CNFs) were prepared and evaluated: enzymatically assisted CNF (AU: with in-house produced enzyme and CT: with commercial enzyme), mechanically pretreated CNF (BT), and chemically pretreated CNF by TEMPO oxidation (TEMPO). It was found that enzyme-assisted mechanical fibrillation-derived CNFs had a comparable average diameter (27.9 nm for AU and 22.7 nm for CT) with that produced from mechanical pretreatment (26.5 nm for BT) and TEMPO oxidation pretreatment (20.0 nm for TEMPO), and they showed the best drainage properties among the three types of CNF. The CNFs resulting from enzymatic pretreatment reduced 15% of energy consumption compared to the mechanical method and had better thermostability than TEMPO oxidation method. In addition, the on-site produced enzyme showed similar performance to the commercial enzymes towards the CNF properties. These findings provide new insights into a promising integrated strategy in engineering CNF from PMS with on-site enzyme production as a novel and sustainable approach for PMS management and valorization.

Endoglucanase effects on energy consumption in the mechanical fibrillation of cellulose fibers into nanocelluloses

Enzymatic processing is considered a promising approach for advancing environmentally friendly industrial processes, such as the use of endoglucanase (EG) enzyme in the production of nanocellulose. However, there is ongoing debate regarding the specific properties that make EG pretreatment effective in isolating fibrillated cellulose. To address this issue, we investigated EGs from four glycosyl hydrolase (GH) families (5, 6, 7, and 12) and examined the roles of the three-dimensional structure and catalytic features, with a focus on the presence of a carbohydrate binding module (CBM). Using eucalyptus Kraft wood fibers, we produced cellulose nanofibrils (CNFs) through mild enzymatic pretreatment, followed by disc ultra-refining. Comparing the results with the control (without pretreatment), we observed that GH5 and GH12 enzymes (without CBM) reduced fibrillation energy by approximately 15 %. The most significant energy reduction, 25 and 32 %, was achieved with GH5 and GH6 linked to CBM, respectively. Notably, these CBM-linked EGs improved the rheological properties of CNF suspensions without releasing soluble products. In contrast, GH7-CBM exhibited significant hydrolytic activity, resulting in the release of soluble products, but did not contribute to a reduction in fibrillation energy. This discrepancy can be attributed to the large molecular weight and wide cleft of GH7-CBM, which led to the release of soluble sugars but had little impact on fibrillation. Our findings suggest that the improved fibrillation observed with EG pretreatment is primarily driven by efficient enzyme adsorption on the substrate and modification of the surface viscoelasticity (amorphogenesis), rather than hydrolytic activity or release of products.

Substitution of petrochemical compounds for polyphenols of natural origin reinforced with cellulose nanofibrils to formulate adhesives for wood bonding.

Vegetable tannins are excellent options to produce adhesives for the panel industry since they have the capacity to reduce formaldehyde emissions and are derived from renewable sources. They also allow for the possibility of increasing the resistance of the glue line through the use of natural reinforcements such as cellulose nanofibrils. Condensed tannins, polyphenols isolated from tree bark, are widely studied for the production of natural adhesives as an alternative to commercial synthetic adhesives. So, the purpose of our research is to show a natural adhesive alternative for wood bonding. Therefore, the objective of the study was to evaluate the quality of tannin adhesives of different species reinforced with different nanofibrils and thus predict which adhesive is the most promising at different concentrations of reinforcement and with different types of polyphenols. To meet this objective, polyphenols were extracted from the bark, nanofibrils were obtained, and both processes followed the current standards. Then, the adhesives were produced, their properties were characterized, and they were chemically analyzed via Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). A mechanical shear analysis of the glue line was also performed. According to the results, the addition of cellulose nanofibrils affected the physical properties of the adhesives, mostly the content of solids and the gel time. In the FTIR spectra, the OH band of the 5% Pinus and 5% Eucalyptus (EUC) TEMPO in the barbatimao adhesive and the 5% EUC of the cumate red adhesive were reduced, possibly due to their higher moisture resistance. Mechanical tests of the glue line showed that barbatimao with 5% Pinus and cumate red with 5% EUC performed best in the dry and wet shear tests. The control was the best-performing sample in the test of the commercial adhesives. The cellulose nanofibrils used as reinforcement did not change the thermal resistance of the adhesives. Therefore, the addition of cellulose nanofibrils to these tannins is an interesting means of increasing the mechanical strength, as occurred in commercial adhesive with 5% EUC. Thus, the physical and mechanical properties of tannin adhesives were better with reinforcement, making it possible to expand the use of these adhesives in the panel industry. At the industrial level, it is important to replace synthetic products with natural ones. Besides environmental and health issues, there is the question of the value of petroleum-based products, which have been widely studied so that they can be replaced.

Surface modification of cellulosic nanofibrils by spray drying: Drying yield and microstructural, thermal and chemical characterization

This study investigated the effect of the addition of cationic surfactant cetyltrimethylammonium bromide (CTAB) in cellulose nanofibril suspensions (CNF) on the efficiency of the spray drying process, as well as on the properties of the dried microparticles and on their water redispersibility. The results indicated that CNF pretreated with 10% sodium silicate and modified with surfactant resulted in higher drying yields. The particle sizes formed by drying depended on the characteristics of the precursor CNF, in general, the particles were smaller than 8 µm. The crystalline fraction of all particles produced was higher than that of never dried (ND) CNF, furthermore the powders were thermostable at elevated temperatures (>200 °C), which provides good evidence for applications in composites. Water stability showed that the rehydrated cellulose solutions were influenced by the treatments and the drying process. The addition of surfactant proves attractive to increase the spray drying yield of CNF, bringing prospects regarding cost reduction and expansion of CNF commercialization. Furthermore, the results provide fundamental insights into the relationship between the surface modification of CNF associated with the drying process with the characteristics of the spray-dried material.

A morphology control engineered strategy of Ti3C2Tx/sulfated cellulose nanofibril composite film towards high-performance flexible supercapacitor electrode

2D Ti3C2Tx MXene is an ideal material for fabricating supercapacitor electrodes due to its excellent physical-chemical properties. However, the inherent self-stacking, narrow interlayer spacing, and low general mechanical strength limit its application in flexible supercapacitors. Herein, facile structural engineering strategies by drying (vacuum drying, freeze drying, and spin drying) were proposed to fabricate 3D high-performance Ti3C2Tx/sulfated cellulose nanofibril (SCNF) self-supporting film supercapacitor electrodes. Compared with other composite films, the freeze-dried Ti3C2Tx/SCNF composite film exhibited a looser interlayer structure with more space which was conducive to charge storage and ion transport in the electrolyte. Therefore, the freeze-dried Ti3C2Tx/SCNF composite film exhibited a higher specific capacitance (220 F/g) compared to the vacuum-dried Ti3C2Tx/SCNF composite film (191 F/g) and the spin-dried Ti3C2Tx/SCNF composite film (211 F/g). After 5000 cycles, the capacitance retention rate of the freeze-dried Ti3C2Tx/SCNF film electrode was close to 100 %, showing excellent cycle performance. Meanwhile, the tensile strength of freeze-dried Ti3C2Tx/SCNF composite film (13.7 MPa) was much greater than that of the pure film (7.4 MPa). This work demonstrated a facile strategy for control of Ti3C2Tx/SCNF composite film interlayer structure by drying for fabricating well-designed structured flexible and free-standing supercapacitor electrodes.

Melanin and Polypyrrole-Coated Nanocellulose Hydrogel Networks for Environmental Sensing and Energy Storage

Melanins are black-brown pigments of a specific class of poly indolequinones found in nature and in the human body. They are responsible for photoprotection, radical scavenging, and metal ion chelation. Recently, there has been significant interest in eumelanin as a functional material due to its macromolecular structure and the exploitation of the quinone-hydroquinone redox equilibrium. While eumelanin can be used in many promising applications, it is insoluble in most solvents, limiting its processing into homogeneous materials and coatings. A promising approach is to use a carrier system to stabilize eumelanin by incorporating cellulose nanofibrils (CNFs), a nanoscopic material that originates from plant biomass. In this work, a flexible network consisting of CNFs coupled with vapor-phase polymerized conductive polypyrrole (PPy) is utilized to form a functional eumelanin hydrogel composite (MelaGel) for environmental sensing and battery applications. Flexible sensors for detecting pH or metal ions made from MelaGel can detect both pH values in a range from 4 to 10 and metal ions like zinc(II), copper(II), and iron(III), paving the way for environmental and biomedical sensor applications. The reduced internal resistance in the MelaGel leads to improved charge storage ability compared to synthetic eumelanin composite electrodes. Other noteworthy advantages of the MelaGel are the amphiphilic nature of PPy and the additionally offered redox centers. Lastly, this material was tested in aqueous electrolyte zinc coin cells, where it was shown to have charge/discharge stability for over 1200 cycles, showcasing this MelaGel composite as a promising eumelanin-based composite hybrid sensor/energy storage material.

The synergistic effects of lignin and cellulose nanofibers on the properties of starch/zein blends

The study aimed to develop cornmeal-based thermoplastic composites by using corn starch and zein (the two major components of cornmeal) as the matrix and lignin as the compatibilizer, while cellulose nanofibrils (CNFs) served as the reinforcement. The research examined the individual effects of lignin and CNFs on the mechanical properties of the composites. Two parts of lignin decreased the domain size of the blend and increased the strength and modulus by 31% and 44%, respectively. Six parts of CNFs led to a 137% and 399% increase in strength and modulus, respectively. The addition of two parts of powder lignin and six parts of CNFs resulted in the largest increases in strength (236%) and modulus (510%), suggesting a strong synergy between lignin and CNFs in reinforcing the corn-based thermoplastic. This study differentiates itself from previous research on thermoplastic starch composites by using a starch/zein blend as the matrix instead of pure starch. It demonstrates a novel method for producing cornmeal-based thermoplastics with significantly enhanced mechanical properties by separately controlling the contents of lignin and CNFs and optimizing the formulations to achieve desired composite properties. Furthermore, the research revealed the strong compatibilizing effect of lignin on the starch/zein blend. The results obtained in this research could facilitate the direct use of low-cost cornmeal as a feedstock for producing sustainable materials which could find application in the packaging and household plastic industries, among others.

Recent Advancements in the Valorization of Agro-Industrial Food Waste for the Production of Nanocellulose

The rising climate change concerns over the excessive exploitation of non-renewable sources have necessitated the need for alternative renewable and eco-friendly resources for the production of innovative materials, achieving the targets of bioeconomy. Lignocellulosic biomass (LB) constituted by polymeric sugars and lignin is an abundantly available plant-based renewable material in the form of agro-industrial food waste and crop residues that can be exploited for the production of an array of value-added chemicals and bioproducts. Cellulose is the most abundant natural and biodegradable organic polymer on earth derived from LB, with wide scale applications in the lignocellulosic biorefineries and food industries. The negative effects of food waste from agro-industrial activities could be reduced through the recovery of cellulose from these wastes and converting it into valuable forms. However, the extraction of cellulose from LB is a difficult task owing to the recalcitrant nature of biomass that restricts the easy accessibility of cellulose for value addition. Therefore, a suitable cellulose extraction method through the fractionation of LB is necessary for a better cellulose yield. Furthermore, owing to the enormous potential of nanocellulose (NC), researchers are keenly interested in developing ecologically acceptable cellulose extraction methods. Cellulose nanofibrils and nanocrystals confer excellent mechanical properties, non-toxic characteristics and biodegradability, due to which they possess wide-scale applications in diverse industrial sectors. The current review emphasizes the potential role of cellulose extraction and NC production from agro-food waste. The different pretreatment methods for their extraction from LB are outlined. The applications of nanocellulose in different areas are also discussed. The review also highlights the recent trends, challenges and future directions in the development of cellulose and NC-based commercial products.