Production Of Cellulose Nanofibers Research Articles

Kinetic study and real-time monitoring strategy for TEMPO-mediated oxidation of bleached eucalyptus fibers

The present work aims at glimpsing the rate-determinant process parameters of TEMPO-mediated oxidation of bleached kraft cellulose for developing kinetic models and real-time monitoring tools. This may contribute to the scaling up of this reaction, frequently used as precursor of the production of cellulose nanofibers. For this, the effect of temperature, TEMPO and NaBr contents, and surface area of the fibers was assessed by means of a total experimental batch of 18 combinations, monitoring the carboxyl content (CC) of the samples and the NaOH consumption during oxidation. The obtained data was used to calculate the kinetic constant as a function of the conditions, as well as correlating the CC with the NaOH consumption, obtaining a strong linear correlation between these parameters. It was found that similar correlations could be used regardless process conditions, except for the case of TEMPO, which was found to protect the fibers from depolymerization and, thus, having different behavior at increasing TEMPO contents. Overall, the obtained results in the present study reveal the suitability of upscaling TEMPO-mediated oxidation, as well as having a deeper understanding on how the key parameters involved in the reaction affect the reaction path and, thus, contributing to the industrial deployment of oxidized cellulose and nanofibers.

Nanocellulose from Spanish Harvesting Residues to Improve the Sustainability and Functionality of Linerboard Recycling Processes.

The hornification processes undergone by the fibers in the paper industry recycling processes lead to the loss of properties of the final products, which exhibit poor mechanical properties. Among the most promising solutions is the reinforcement of secondary fibers with cellulose nanofibers. The present work addresses two important issues: the efficient production of cellulose nanofibers from scarcely exploited agricultural wastes such as horticultural residues and vine shoots, and their application as a reinforcement agent in recycled linerboard recycling processes. The effect of the chemical composition and the pretreatment used on the nanofibrillation efficiency of the fibers was analyzed. Chemical pretreatment allowed a significantly higher nanofibrillated fraction (45-63%) than that produced by mechanical (18-38%), as well as higher specific surface areas (>430 m2/g). The application of the nanofibers as a reinforcing agent in the recycled linerboard considerably improved the mechanical properties (improvements of 15% for breaking length, 220-240% for Young's modulus and 27% for tear index), counteracting the loss of mechanical properties suffered during recycling when using chemically pretreated cellulose nanofibers from horticultural residues and vine shoots. It was concluded that this technology surpasses the mechanical reinforcement produced by conventional mechanical refining used in the industry and extends the number of recycling cycles of the products due to the non-physical modification of the fibers.

Comparative study of the production of cellulose nanofibers from agro-industrial waste streams of Salicornia ramosissima by acid and enzymatic treatment

The study of the suitability of two isolation processes to produce cellulose nanofibers (CNFs) from Salicornia ramosissima waste, with potential applicability as a reinforcing agent of polymeric composites was carried out. To separate the cellulose fibrils from the cell wall and obtain CNFs an alkaline treatment was applied followed by a bleaching treatment and, the insoluble residue was next hydrolyzed by either an acid treatment (AT) or an enzyme treatment (ET). SEM and TEM images indicated fiber exposure caused by both treatments. The diameter, length, aspect ratio, and polydispersity index, were measured for both CNFs. CNF (ET) showed high zeta potential values suggesting that ET produces more electrically stable and thinner nanofibers. The FTIR spectra revealed that both treatments effectively removed the amorphous components allowing the CNFs isolation, and XRD patterns evidenced the increase in the degree of crystallinity of both CNFs. Nonetheless, CNF(AT) presented a lower mechanical resistance due to its smaller particle size, compared to the CNF(ET). In summary, the (ET) could successfully isolate CNFs from the Salicornia waste, encouraging the use of this treatment, once when compared to (AT), it does not generate toxic residues, presents mild thermal conditions, and produces CNFs with higher-value applications.

High temperatures and pressures during cooking hinder the nanofibrillation of purified pulp

Kraft pulp is an abundant raw material for producing cellulose nanofibers. However, our previous study demonstrated that kraft cooking hinders the nanofibrillation of never-dried pulp. Therefore, this study aims to elucidate the specific factors of kraft cooking hindering nanofibrillation, particularly the effects of high temperature and pressure. Undried purified pulp, produced using the Wise method, was subjected to high temperature and pressure conditions, with and without subsequent alkali treatment. After fibrillating the pulps for different durations, the degree of nanofibrillation was evaluated by sedimentation tests. Undried Wise-based pulp, with excellent nanofibrillation ability, becomes less capable of nanofibrillation after cooking at high temperature and pressure. Thus, even in the undried state, harsh cooking is considered to have caused irreversible aggregation of microfibrils or hornification in the pulp cell wall. Moreover, high temperatures and pressure should be avoided when removing the matrix, e.g., lignin and hemicellulose, for producing pulp for cellulose nanofibers.

Isolation and Characterization of Cellulose Nanofibers from Wheat Straw and Their Application for the Supercapacitor

As a by-product of wheat planting, wheat straw is an abundant agricultural residue with the highest cellulose content of all agricultural fibers. Its resourceful utilization contributes to alleviating the environmental problems it caused. In this study, cellulose from wheat straw (WS) is used as a dispersing agent to prepare a novel multi-walled carbon nanotube-modified nickel foam (NF) electrode. The new electrode is investigated for electrochemical properties relevant to supercapacitors. The 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation is chosen to produce cellulose nanofibers (CNF) from wheat straw. The prepared CNF is used to facilitate the uniform dispersion of multi-walled carbon nanotubes (MWCNT) and favor the formation of a stable CNF-CNTs membrane on the nickel foam skeleton. The influence of dispersing materials and content of CNF on the electrochemical performance of electrodes is investigated. It is revealed that the incorporation of CNF can improve the electrochemical stability of electrodes. Moreover, it also exhibits optimum capabilities (70.2% capacitance retention from 1 to 40 mA cm−2) when CNF:MWCNT = 1:0.7. The areal capacity of the CNF-MWCNT/NF electrode for a scanning rate of 5 mV s−1 is twice that of the MWCNT/NF electrode and 30 times that of the NF electrode, indicating it is a promising candidate to ensure the synchronization of a green environment and energy development.

Using Experimental Design and Response Surface Methodology to Optimize Nanocellulose Production from Two Types of Pretreated Soybean Straw

AbstractThis study investigates how enzymatic activity (X1) and pretreated soybean straw concentration (X2) affect the production of cellulose nanofibers and reducing sugars using the Composite Central Rotational Design (CCRD). The soybean straw is subjected to alkaline pretreatment with either 5% NaOH (PT1) or 17.5% NaOH (PT2), followed by bleaching (4% H2O2) and enzymatic treatment. The mathematical model generated by Response Surface Methodology (RSM) predicts that increasing X1 and X2 simultaneously is necessary to increase the nanocellulose yield. On the other hand, to increase the sugar yield, it is necessary to increase the ratio X1:X2. The model also predicts that the lowest concentration of soybean straw (1.17%) resulted in more stable nanofiber suspensions, regardless of the enzyme activity (−25.0 and −19.4 mV for PT1 and PT2, respectively). The optimal condition for the simultaneous production of cellulose nanofibers and reducing sugars is 4.0 g of biomass and enzymatic activity of 600 CMCU, resulting for PT1 and PT2, respectively: 7.01 and 3.73 g of nanofibers/100 g of soybean straw; 11.34 and 14.30 g of reducing sugars/100 g of soybean straw. Therefore, the processing efficiency according to the pretreatment used can directly guide the production of cellulose nanofibers and reducing sugars.

Cellulose Nanofiber Preparation Combined with Bioethanol Production from Fermented Sweet Sorghum Bagasse

In order to achieve cost-competitive industrial production of cellulose nanofibers (CNFs), bioethanol extraction and lignocellulose pretreatment from fermented sweet sorghum bagasse were combined with alkaline distillation in this study. CNFs were further prepared from an alkaline-distilled substrate after washing, bleaching, and a high-pressure homogenization process. Lignin-containing cellulose nanofibers (LCNFs) were simultaneously prepared without bleaching. The effects of different alkali loadings on the ethanol quality and performances of CNFs and LCNFs were investigated. Results showed that only 12.94 mg/L of alkali residue was found in extracted ethanol at the highest alkali dosage, which can be removed in the subsequent purification process. Cellulose fibers can be prepared from sweet sorghum bagasse during alkaline distillation, and the crystallinity of pretreated samples increased from 37.2 to 59.5%. It is observed by transmission electron microscopy that the obtained nanofibrils aggregated and formed a network in suspension. The degradation temperature of the CNFs can be increased up to 352 °C, which is 34 °C higher than that of LCNFs due to less hemicellulose content. Wastewater was only generated in the washing process during alkali distillation, which is far less than that generated in a conventional pulping making process. The process scale-up simulation indicates that the coproduction of bioethanol and CNFs or LCNFs by alkaline distillation is environment-friendly and energy-efficient for industrialization.

Valorization of Pineapple Residues from the Colombian Agroindustry to Produce Cellulose Nanofibers

Cellulose nanofiber is the world’s most advanced biomass material. Most importantly, it is biodegradable. In this work, nanofibers were obtained from pineapple leaves, a large solid waste in Colombia, using a combined extraction method (chemical procedures and ultrasound). The native fibers were bleached, hydrolyzed, treated with ultrasound, and characterized by scanning electron microscopy (SEM), infrared analysis (FTIR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). As a comparison, a commercial microcrystalline cellulose sample was analyzed, which demonstrated the efficiency of cellulose extraction. The nanofibers had a diameter and a length of 18 nm and 237 nm, respectively, with a maximum degradation temperature of 306 °C. The analysis showed the efficiency of acid treatment combined with ultrasound to obtain nanofibers and confirmed that pineapple residues can be valorized by this method. These results indicate that lignocellulosic matrices from pineapple leaves have potential application for obtaining polymeric-type composite materials. Due to their morphology and characteristic physical properties, the cellulose nanofibers obtained in this work could be a promising material for use in a wealth of fields and applications such as filter material, high gas barrier packaging material, electronic devices, foods, medicine, construction, cosmetics, pharmacy, and health care, among others.

Optimization of reagent consumption in TEMPO-mediated oxidation of Eucalyptus cellulose to obtain cellulose nanofibers

Eucalyptus cellulose is usually pre-treated by oxidation with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), NaBr and NaClO at pH 10.5 and 25 °C before the mechanical process required to obtain cellulose nanofibers (CNFs). In this study, different aspects to improve the effectiveness and sustainability of the TEMPO-mediated oxidation are analyzed. The optimization was carried out at different reaction times by modifying both the concentration of the NaClO and the amount of the catalysts (TEMPO and NaBr). Results show that the carboxyl groups increased up to 1.1 mmol/g with 5 mmol NaClO/g after 50 min, and that the catalyst concentration can be reduced to 0.025 mmol TEMPO/g and 0.5 mmol NaBr/g to minimize costs while maintaining the high fibrillation degree of the CNFs. The kinetic of the reaction can be considered as zero-order with respect to NaClO, and as first order with respect to cellulose. As a result of this work, the catalyst doses are reduced up to 75% compared to the most widely used catalyst doses (0.1 mmol/g TEMPO and 1 mmol/g NaBr), obtaining highly fibrillated CNFs with a lower environmental impact. This reduction of catalyst doses will reduce the costs and facilitate the implementation of CNF production at industrial scale.Graphical abstract

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.

Sustainable production of cellulose nanofibrils from Kraft pulp for the stabilization of oil-in-water Pickering emulsions

Cellulose nanofibers (CNFs) have been shown to assemble at oil/water interface and act as Pickering emulsions stabilizers. Developing a simple approach to fabricate CNFs with tunable surface properties and elucidating the influence of the surface properties of the CNFs on their emulsifying performance are of great significance and highly demanded. Herein, a facile approach, namely FeCl3-catalyzed formic acid hydrolysis in combination with high pressure homogenization was reported to produce CNFs using industrial Kraft pulp as raw materials. The surface properties, especially the surface wettability of the CNFs could be easily adjusted by changing the hydrolysis time. Additionally, the emulsifying performance of the CNFs and the stability of CNF-stabilized Pickering emulsions were also evaluated. The obtained CNF-stabilized Pickering emulsions demonstrated great stability under various ionic strengths ranging from 0 to 1 M NaCl and high temperature of 80 °C. This work would greatly improve the possibility of sustainable production of CNFs for practical emulsions.

Water Hyacinth: A sustainable cellulose source for cellulose nanofiber production and application as recycled paper reinforcement

Water Hyacinth: A sustainable cellulose source for cellulose nanofiber production and application as recycled paper reinforcement

Production of Cellulose Nano-Fibers and Its Application in Poly-Lactic-Acid: Property Improvement by New Types of Coupling Agents

Poly-lactic-acid is a biopolymer that can be an attractive alternative to replace petroleum-based polymers. It has advanced mechanical properties, melts easily with less energy consumption, and can be used to produce biodegradable plastics using renewable sources. However, some of the properties of poly-lactic-acid are inferior to those of traditional polymers: e.g., intensive farming is necessary for high agricultural yield, the composting needs special conditions, it is difficult to blend with other commonly used plastics, expensive, high permeability, etc. Therefore, the present work seeks to improve the structure and mechanical properties of the poly-lactic-acid incorporated by cellulose nano-fibers obtained from rice straw by a chemical acidic treatment. The fibers were incorporated into the poly-lactic-acid polymer matrix in a concentration of 1% by two-roll mill. To improve the incorporation of the fibers in the matrix, different coupling agents were used: PE-g-MA, vinyl trimethoxy silane, polyethylene-glycol with different molecular weight, and two types of experimentally synthetized α-olefin-maleic anhydride-based copolymers. The properties of the final composite could be improved, however those depend on the coupling agent to be used. The improving effect of the tested chemicals had been depended on the temperature. Based on structure analysis, both chemical and physical interactions were proposed between the cellulose nanofiber and polymer matrix. The thermogravimetric and viscosity results well represented the softener effect of the used chemical agents.

Cellulose nanofibers prepared from pulp through ultrasound treatment followed semi-dry esterification and their application for transparent and anti-fingerprint coating

In order to facilitate nano-fibrillation via ultrasound to prepare cellulose nanofibers (CNFs) from flocculent pulp, a semi-dry esterification was carried out to modify the pulp with maleic anhydride. Small amount water addition improves mixing of the reactants and increases extent of esterification. The modification significantly enhances nano-fibrillation of the pulp in subsequent ultrasound treatment. CNFs with about 200–400 nm in length and about 20–25 nm in width are obtained from the esterified pulp. CNFs coating, prepared by casting CNFs aqueous dispersion on glass slide, gives rise to about 4% increase in transmittance of the slide and improves anti-fingerprint property of the slide. The results of this study provide a solution for production of CNFs from flocculent pulps and demonstrate the potential application of CNFs for anti-reflection and anti-fingerprint coatings.

Fabrication of cellulose nanofibers by the method of interfacial molecular films and the creation of organized soluble starch molecular films

This study investigated a new method for producing cellulose nanofibers (CNFs) at the air/water interface employing the monolayer on the water surface approach. The formation of hydrogen bonding networks in the two-dimensional plane facilitated the formation of the fibrous nanocellulose monolayer. The layered assembly of the interfacial cellulose monolayer exhibited periodic regularity, and its morphology changed with the subphase temperature. Further, insoluble starch was solubilized to create a spreading solvent for the monomolecular film on the water surface. The monolayer of the obtained soluble starch was particulate rather than sheetlike or fibrous. The hydrogen bonds might have been developed inside the particles. The subphase temperature dependency of the starch monolayer was also confirmed, revealing that these β- or α-glucose-derived natural polymer monolayers were affected by the molecular motion due to heating and the changes in their morphologies. Additionally, the introduction of the two natural polymers into the air/water interface, as well as the application of the repeated compression/expansion method ensured the formation of high-density NF/nanoparticle (NP) integrated monolayers.

Hydrothermal pretreatment of biomass-waste-garlic skins in the cellulose nanofiber production process

Hydrothermal pretreatment of biomass-waste-garlic skins in the cellulose nanofiber production process

MINI REVIEW ON NANOFIBRILLATION TECHNIQUES TO OBTAIN CELLULOSE NANOFIBER FROM LIGNOCELLULOSIC BIOMASS

Cellulose nanofiber (CNF) has been recognized as a new family of sustainable nanomaterials with significant mechanical, colloidal, low density, renewable and biodegradable properties. These properties make CNF a promising material either as an additive or primary material for the development of various applications such as for packaging, coatings, adsorbent, papermaking, biomedicine, cosmetic and automotive industries. Prior to CNF production, cellulose has to be isolated from various sources of lignocellulosic biomass such as oil palm, bamboo, flax bast, hemp, kraft pulp, and rutabagas. The isolated cellulose then can be nanofibrillated into CNF using several nanofibrillation treatments. However, the nanofibrillation treatment is one of the major factors that can influence the final characteristics of CNF. The selection of nanofibrillation treatment is important as each treatment produces CNF with different properties especially in terms of diameter sizes, lengths, thermal, crystalline and mechanical properties. The CNF properties have to comply with the requirement of the targeted application, as different applications require different specifications of CNF. Other external factors may also influence the properties of CNF. Hence, this review focused on discussing the current CNF production treatment as well as factors that may influence the nanofibrillation process of CNF production.

Populus alba L., an Autochthonous Species of Spain: A Source for Cellulose Nanofibers by Chemical Pretreatment.

In order to identify new sustainable sources for producing cellulose nanofibers (CNFs), fast-growing poplar (Populus alba L.) wood was evaluated herein. For that purpose, bleached poplar kraft pulp was produced and submitted to TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) mediated oxidation (TEMPO-ox) chemical pretreatment followed by microfluidization. The resulting CNFs were thoroughly characterized, including a rheological study at different pH values. Poplar CNFs showed properties comparable to eucalypt CNFs (reference material for CNFs production), showing high carboxylate content (1048 ± 128 µmol g−1), fibrillation yield (87.3% ± 8.1%), optical transmittance (83% at 700 nm) and thermal stability (up to more than 200 °C). Regarding the rheological study, whereas pH from 4 to 10 did not produce significant changes in rheological behavior, a reduction of pH down to 1 led to an order-of-magnitude increase on the viscoelastic functions. Therefore, poplar CNF shows potential in the pH-sensitive hydrogels application field. Finally, the possible ecotoxicity of poplar CNF was assessed. The decrease in cell viability was very low so that only concentrations causing a 10% cytotoxicity could be calculated for the assay detecting alterations in cell metabolism (10 µg mL−1) and plasma membrane integrity (60 µg mL−1).

Advances in nanotechnology and the benefits of using cellulose nanofibers in animal nutrition.

The production of cellulose nanofibers promotes the utilization of plant residues that are generated in agro-industries during food processing. The utilization of these plant by-products reduces environmental contamination. Cellulose nanofibers are used in several sectors, including the drug, food, and animal nutrition industries. Many sources of nanofibers used in animal diets can be used as potential fiber substitutes after being processed to improve efficiency. For instance, including nanometric particles of plant fibers (<100 nm) in animal feed may provide excellent physical properties such as high reactivity, a large surface area, and improved nutrient absorption from the diet. Nanotechnology improves the characteristics of fibers that are important for gastrointestinal transit and their utilization as energy sources and substrates for microbial fermentation in the digestive tract of animals. Nanofibers can improve the synthesis of volatile fatty acids and the blood lipid profile, with positive effects on the intestinal health of animals. Moreover, in vitro and in vivo studies have demonstrated promising effects in reducing blood glucose levels without toxic effects on the body. Supplying nanofibers in the diet improve animal performance, increase productivity, and work toward a more sustainable economic development of agribusinesses. The quality of animal products such as meat, milk, and eggs is also reported to be improved with the inclusion of nanominerals in the feed. Overall, the application of nanotechnology to harness the by-products of agro-industries can increase economic viability and sustainability in animal production systems. Therefore, this review presents a current survey on the main research and advances in the utilization of nanotechnology, focusing on cellulose nanofibers in animal feed to improve animal performance.

Facile isolation of cellulose nanofibers from soybean residue

The residue of soybean after extraction of oils, proteins, and soluble polysaccharides is rich in cellulose but not well utilized. Here, we exploited the soybean residue as a raw material to isolate cellulose nanofibers via a robust chemical-mechanical process. The soybean cellulose nanofibers (SCNFs) possessed ∼50 nm diameter and micrometer-scale length. They possessed a high degree of crystallinity (75.9%), negative surface charge (-22.5 mV), and high thermal stability. The hydrogel of SCNFs represented a typical shear-thinning behavior. The viscosity of the hydrogel was influenced by pH, ionic strength, ethanol, and temperature. SCNFs could also be made into flexible and transparent films with high tensile strength, which could be a raw material for food packages. Overall, soybean residue is a cost-effective source to produce cellulose nanofibers.