Editorial

2 pages, 185 KiB

Open AccessEditorial

Preparation, Characterization and Industrial Application of Nanocellulose

by Marc Delgado-Aguilar and Carlos Negro

Nanomaterials 2023, 13(10), 1592; https://doi.org/10.3390/nano13101592 - 10 May 2023

Cited by 1 | Viewed by 1238

The international research community has made significant efforts in the production, characterization, and application of cellulose nanofibers (CNFs) in many sectors [...] Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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16 pages, 4928 KiB

Open AccessArticle

Lignin-Containing Cellulose Nanofibrils from TEMPO-Mediated Oxidation of Date Palm Waste: Preparation, Characterization, and Reinforcing Potential

by Amira Najahi, Quim Tarrés, Pere Mutjé, Marc Delgado-Aguilar, Jean-Luc Putaux and Sami Boufi

Nanomaterials 2023, 13(1), 126; https://doi.org/10.3390/nano13010126 - 26 Dec 2022

Cited by 9 | Viewed by 2087

Abstract

Lignin-containing cellulose nanofibrils (LCNFs) have emerged as a new class of nanocelluloses where the presence of residual lignin is expected to impart additional attributes such as hydrophobicity or UV-absorption. In the present work, LCNFs with a lignin content between 7 and 15 wt% [...] Read more.

Lignin-containing cellulose nanofibrils (LCNFs) have emerged as a new class of nanocelluloses where the presence of residual lignin is expected to impart additional attributes such as hydrophobicity or UV-absorption. In the present work, LCNFs with a lignin content between 7 and 15 wt% were prepared via a TEMPO-mediated oxidation as chemical pretreatment followed by high-pressure homogenization. The impact of the carboxyl content (CC) on the properties of the resulting LCNF gel, in terms of lignin content, colloidal properties, morphology, crystallinity, and thermal stability, were investigated. It was found that lignin content was significantly decreased at increasing CC. In addition, CC had a positive effect on colloidal stability and water contact angle, as well as resulting in smaller fibrils. This lower size, together with the lower lignin content, resulted in a slightly lower thermal stability. The reinforcing potential of the LCNFs when incorporated into a ductile polymer matrix was also explored by preparing nanocomposite films with different LCNF contents that were mechanically tested under linear and non-linear regimes by dynamic mechanical analysis (DMA) and tensile tests. For comparison purposes, the reinforcing effect of the LCNFs with lignin-free CNFs was also reported based on literature data. It was found that lignin hinders the network-forming capacity of LCNFs, as literature data shows a higher reinforcing potential of lignin-free CNFs. Nonetheless, the tensile strength of the acrylic matrix was enhanced by 10-fold at 10 wt% of LCNF content. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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14 pages, 2090 KiB

Open AccessArticle

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

by Jorge De Haro-Niza, Esther Rincón, Zoilo Gonzalez, Eduardo Espinosa and Alejandro Rodríguez

Nanomaterials 2022, 12(24), 4447; https://doi.org/10.3390/nano12244447 - 14 Dec 2022

Cited by 7 | Viewed by 1456

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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28 pages, 3724 KiB

Open AccessArticle

Hexavalent Chromium Removal from Industrial Wastewater by Adsorption and Reduction onto Cationic Cellulose Nanocrystals

by Francisco de Borja Ojembarrena, Hassan Sammaraie, Cristina Campano, Angeles Blanco, Noemi Merayo and Carlos Negro

Nanomaterials 2022, 12(23), 4172; https://doi.org/10.3390/nano12234172 - 24 Nov 2022

Cited by 11 | Viewed by 1552

Abstract

Cationic cellulose nanocrystals (CCNC) are lignocellulosic bio-nanomaterials that present large, specific areas rich with active surface cationic groups. This study shows the adsorption removal of hexavalent chromium (Cr(VI)) from industrial wastewaters by the CCNC. The CCNC were synthetized through periodate oxidation and Girard’s [...] Read more.

Cationic cellulose nanocrystals (CCNC) are lignocellulosic bio-nanomaterials that present large, specific areas rich with active surface cationic groups. This study shows the adsorption removal of hexavalent chromium (Cr(VI)) from industrial wastewaters by the CCNC. The CCNC were synthetized through periodate oxidation and Girard’s reagent-T cationization. The high value of CCNCs cationic groups and anionic demand reveal probable nanocrystal-Cr(VI) attraction. Adsorption was performed with synthetic Cr(VI) water at different pH, dosage, Cr(VI) concentration and temperature. Fast removal of Cr(VI) was found while operating at pH 3 and 100 mg·L⁻¹ of dosage. Nevertheless, a first slower complete removal of chromium was achieved by a lower CCNC dosage (40 mg·L⁻¹). Cr(VI) was fully converted by CCNC into less-toxic trivalent species, kept mainly attached to the material surface. The maximum adsorption capacity was 44 mg·g⁻¹. Two mechanisms were found for low chromium concentrations (Pseudo-first and pseudo-second kinetic models and continuous growth multi-step intraparticle) and for high concentrations (Elovich model and sequential fast growth-plateau-slow growth intraparticle steps). The Sips model was the best-fitting isotherm. Isotherm thermodynamic analysis indicated a dominant physical sorption. The Arrhenius equation revealed an activation energy between physical and chemical adsorption. CCNC application at selected conditions in industrial wastewater achieved a legal discharge limit of 40 min. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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14 pages, 2696 KiB

Open AccessArticle

Improving the Barrier Properties of Paper to Moisture, Air, and Grease with Nanocellulose-Based Coating Suspensions

by André Mazega, Quim Tarrés, Roberto Aguado, Maria Àngels Pèlach, Pere Mutjé, Paulo J. T. Ferreira and Marc Delgado-Aguilar

Nanomaterials 2022, 12(20), 3675; https://doi.org/10.3390/nano12203675 - 19 Oct 2022

Cited by 6 | Viewed by 2609

Abstract

Food packaging manufacturers often resort to lamination, typically with materials which are neither non-biodegradable nor biobased polymers, to confer barrier properties to paper and cardboard. The present work considers a greener solution: enhancing paper’s resistance to moisture, grease, and air by aqueous coating [...] Read more.

Food packaging manufacturers often resort to lamination, typically with materials which are neither non-biodegradable nor biobased polymers, to confer barrier properties to paper and cardboard. The present work considers a greener solution: enhancing paper’s resistance to moisture, grease, and air by aqueous coating suspensions. For hydrophobization, a combined approach between nanocellulose and common esterifying agents was considered, but the water vapor transmission rate (WVTR) remained excessively high for the goal of wrapping moisture-sensitive products (>600 g m⁻² d⁻¹). Nonetheless, oil-repellant surfaces were effectively obtained with nanocellulose, illite, sodium alginate, and/or poly(vinyl alcohol) (PVA), reaching Kit ratings up to 11. Regarding air resistance, mineral-rich coatings attained values above 1000 Gurley s. In light of these results, nanocellulose, minerals, PVA, pullulan, alginate, and a non-ionic surfactant were combined for multi-purpose coating formulations. It is hypothesized that these materials decrease porosity while complementing each other’s flaws, e.g., PVA succeeds at decreasing porosity but has low dimensional stability. As an example, a suspension mostly constituted by nanocellulose, sizing agents, minerals and PVA yielded a WVTR of roughly 100 g m⁻² d⁻¹, a Kit rating of 12, and an air resistance above 300 s/100 mL. This indicates that multi-purpose coatings can be satisfactorily incorporated into paper structures for food packaging applications, although not as the food contact layer. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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21 pages, 6243 KiB

Open AccessArticle

Effect of Oxalic Acid Concentration and Different Mechanical Pre-Treatments on the Production of Cellulose Micro/Nanofibers

by Gabriela Adriana Bastida, Carla Natalí Schnell, Paulina Mocchiutti, Yamil Nahún Solier, María Cristina Inalbon, Miguel Ángel Zanuttini and María Verónica Galván

Nanomaterials 2022, 12(17), 2908; https://doi.org/10.3390/nano12172908 - 24 Aug 2022

Cited by 9 | Viewed by 1876

Abstract

The present work analyzes the effect of process variables and the method of characterization of cellulose micro/nanofibers (CMNFs) obtained by different treatments. A chemical pre-treatment was performed using oxalic acid at 25 wt.% and 50 wt.%. Moreover, for mechanical pre-treatments, a rotary homogenizer [...] Read more.

The present work analyzes the effect of process variables and the method of characterization of cellulose micro/nanofibers (CMNFs) obtained by different treatments. A chemical pre-treatment was performed using oxalic acid at 25 wt.% and 50 wt.%. Moreover, for mechanical pre-treatments, a rotary homogenizer or a PFI mill refiner were considered. For the mechanical fibrillation to obtain CMNFs, 5 and 15 passes through a pressurized homogenization were considered. The best results of nanofibrillation yield (76.5%), transmittance (72.1%) and surface charges (71.0 µeq/g CMNF) were obtained using the PFI mill refiner, 50 wt.% oxalic acid and 15 passes. Nevertheless, the highest aspect ratio (length/diameter) determined by Transmission Electron Microscopy (TEM) was found using the PFI mill refiner and 25 wt.% oxalic acid treatment. The aspect ratio was related to the gel point and intrinsic viscosity of CMNF suspensions. The values estimated for gel point agree with those determined by TEM. Moreover, a strong relationship between the intrinsic viscosity [η] of the CMNF dispersions and the corresponding aspect ratio (p) was found (ρ[η] = 0.014 p^2.3, R² = 0.99). Finally, the tensile strength of films obtained from CMNF suspensions was more influenced by the nanofibrillation yield than their aspect ratio. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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18 pages, 62227 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Micro-/Nanofibrillated Cellulose-Based Coating Formulations: A Solution for Improving Paper Printing Quality

by Mohit Sharma, Roberto Aguado, Dina Murtinho, Artur J. M. Valente and Paulo J. T. Ferreira

Nanomaterials 2022, 12(16), 2853; https://doi.org/10.3390/nano12162853 - 18 Aug 2022

Cited by 3 | Viewed by 1834

Abstract

The use of micro-/nanofibrillated celluloses (M/NFCs) is often considered for the enhancement of paper properties, while it is still challenging to use them in lower weight gain coatings. This work explores how they might be used on the paper surface to improve the [...] Read more.

The use of micro-/nanofibrillated celluloses (M/NFCs) is often considered for the enhancement of paper properties, while it is still challenging to use them in lower weight gain coatings. This work explores how they might be used on the paper surface to improve the printing quality. In this regard, M/NFCs were produced using different pre-treatment methods, including mechanical (m-MFC), enzymatic (e-MFC), TEMPO-mediated oxidation (t-NFC) and cationization (c-NFC), and uniform coating formulations were developed through the cooking of starch and M/NFCs simultaneously. The formulations, at 6–8% of total solid concentration, were applied to the paper surface by roll coating, resulting in a dry coating weight of 1.5 to 3 g/m

^{2}

. Besides M/NFCs, other components such as starch betainate (a cationic starch ester; SB), Pluronics^® (a triblock co-polymer), precipitated calcium carbonate (PCC) and betaine hydrochloride (BetHCl) were also used in the M/NFC-based coating formulations to observe their combined influence on the printing quality. The presence of M/NFCs improved the paper printing quality, which was further enhanced by the increase in cationic charge density due to the presence of BetHCl/SB, and also by Pluronics^®. The cationic charge of c-NFC was also found to be effective for improving the gamut area and optical density of coated papers, whereas whiteness was often reduced due to the quenching of the brightening agent. BetHCl, on the other hand, improved the printing quality of the coated papers, even though it was more effective when combined with M/NFCs, PCC and Pluronics^®, and also helped to retain paper whiteness. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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15 pages, 2528 KiB

Open AccessEditor’s ChoiceArticle

Micro- and Nanofibrillated Cellulose from Annual Plant-Sourced Fibers: Comparison between Enzymatic Hydrolysis and Mechanical Refining

by Roberto Aguado, Quim Tarrés, Maria Àngels Pèlach, Pere Mutjé, Elena de la Fuente, José L. Sanchez-Salvador, Carlos Negro and Marc Delgado-Aguilar

Nanomaterials 2022, 12(9), 1612; https://doi.org/10.3390/nano12091612 - 09 May 2022

Cited by 12 | Viewed by 1898

Abstract

The current trends in micro-/nanofibers offer a new and unmissable chance for the recovery of cellulose from non-woody crops. This work assesses a technically feasible approach for the production of micro- and nanofibrillated cellulose (MNFC) from jute, sisal and hemp, involving refining and [...] Read more.

The current trends in micro-/nanofibers offer a new and unmissable chance for the recovery of cellulose from non-woody crops. This work assesses a technically feasible approach for the production of micro- and nanofibrillated cellulose (MNFC) from jute, sisal and hemp, involving refining and enzymatic hydrolysis as pretreatments. Regarding the latter, only slight enhancements of nanofibrillation, transparency and specific surface area were recorded when increasing the dose of endoglucanases from 80 to 240 mg/kg. This supports the idea that highly ordered cellulose structures near the fiber wall are resistant to hydrolysis and hinder the diffusion of glucanases. Mechanical MNFC displayed the highest aspect ratio, up to 228 for hemp. Increasing the number of homogenization cycles increased the apparent viscosity in most cases, up to 0.14 Pa·s at 100 s⁻¹ (1 wt.% consistency). A shear-thinning behavior, more marked for MNFC from jute and sisal, was evidenced in all cases. We conclude that, since both the raw material and the pretreatment play a major role, the unique characteristics of non-woody MNFC, either mechanical or enzymatically pretreated (low dose), make it worth considering for large-scale processes. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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14 pages, 3259 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Influence of Dispersion and Orientation on Polyamide-6 Cellulose Nanocomposites Manufactured through Liquid-Assisted Extrusion

by Luísa Rosenstock Völtz, Shiyu Geng, Anita Teleman and Kristiina Oksman

Nanomaterials 2022, 12(5), 818; https://doi.org/10.3390/nano12050818 - 28 Feb 2022

Cited by 6 | Viewed by 1761

Abstract

In this study, the possibility of adding nanocellulose and its dispersion to polyamide 6 (PA6), a polymer with a high melting temperature, is investigated using melt extrusion. The main challenges of the extrusion of these materials are achieving a homogeneous dispersion and avoiding [...] Read more.

In this study, the possibility of adding nanocellulose and its dispersion to polyamide 6 (PA6), a polymer with a high melting temperature, is investigated using melt extrusion. The main challenges of the extrusion of these materials are achieving a homogeneous dispersion and avoiding the thermal degradation of nanocellulose. These challenges are overcome by using an aqueous suspension of never-dried nanocellulose, which is pumped into the molten polymer without any chemical modification or drying. Furthermore, polyethylene glycol is tested as a dispersant for nanocellulose. The dispersion, thermal degradation, and mechanical and viscoelastic properties of the nanocomposites are studied. The results show that the dispersant has a positive impact on the dispersion of nanocellulose and that the liquid-assisted melt compounding does not cause the degradation of nanocellulose. The addition of only 0.5 wt.% nanocellulose increases the stiffness of the neat polyamide 6 from 2 to 2.3 GPa and shifts the tan δ peak toward higher temperatures, indicating an interaction between PA6 and nanocellulose. The addition of the dispersant decreases the strength and modulus but has a significant effect on the elongation and toughness. To further enhance the mechanical properties of the nanocomposites, solid-state drawing is used to create an oriented structure in the polymer and nanocomposites. The orientation greatly improves its mechanical properties, and the oriented nanocomposite with polyethylene glycol as dispersant exhibits the best alignment and properties: with orientation, the strength increases from 52 to 221 MPa, modulus from 1.4 to 2.8 GPa, and toughness 30 to 33 MJ m⁻³ in a draw ratio of 2.5. This study shows that nanocellulose can be added to PA6 by liquid-assisted extrusion with good dispersion and without degradation and that the orientation of the structure is a highly-effective method for producing thermoplastic nanocomposites with excellent mechanical properties. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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19 pages, 3580 KiB

Open AccessArticle

Gel Point as Measurement of Dispersion Degree of Nano-Cellulose Suspensions and Its Application in Papermaking

by Jose Luis Sanchez-Salvador, Ana Balea, Carlos Negro, Maria Concepcion Monte and Angeles Blanco

Nanomaterials 2022, 12(5), 790; https://doi.org/10.3390/nano12050790 - 26 Feb 2022

Cited by 9 | Viewed by 1879

Abstract

The dispersion degree of cellulose micro and nanofibrils (CMFs/CNFs) in water suspensions is key to understand and optimize their effectiveness in several applications. In this study, we proposed a method, based on gel point (Ø_g), to calculate both aspect ratio and [...] Read more.

The dispersion degree of cellulose micro and nanofibrils (CMFs/CNFs) in water suspensions is key to understand and optimize their effectiveness in several applications. In this study, we proposed a method, based on gel point (Ø_g), to calculate both aspect ratio and dispersion degree. This methodology was validated through the morphological characterization of CMFs/CNFs by Transmission Electronic Microscopy. The influence of dispersion degree on the reinforcement of recycled cardboard has also been evaluated by stirring CMF/CNF suspensions at different speeds. Results show that as stirring speed increases, Ø_g decreased to a minimum value, in which the aspect ratio is maximum. Then, Ø_g increased again. Suspensions with lower Ø_g, in the intermediate region of agitation present very good dispersion behavior with an open and spongy network structure, in which nanofibril clusters are totally dispersed. Higher stirring speeds shorten the nanofibrils and the networks collapse. Results show that the dispersion of the nanocellulose at the minimum Ø_g before their addition to the pulp, produces higher mechanical properties, even higher than when CNFs and pulp are agitated together. This method allows for the determination of the CMF/CNF dispersion, to maximize their behavior as strength agents. This knowledge would be crucial to understand why some industrial trials did not give satisfactory results. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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16 pages, 6190 KiB

Open AccessEditor’s ChoiceArticle

Reinforcing Poly(methyl methacrylate) with Bacterial Cellulose Nanofibers Chemically Modified with Methacryolyl Groups

by Hiroyuki Kono, Haruto Tsujisaki and Kenji Tajima

Nanomaterials 2022, 12(3), 537; https://doi.org/10.3390/nano12030537 - 04 Feb 2022

Cited by 10 | Viewed by 2471

Abstract

Nanofibrillated bacterial cellulose (NFBC), a type of cellulose nanofiber biosynthesized by Gluconacetobacter sp., has extremely long (i.e., high-aspect-ratio) fibers that are expected to be useful as nanofillers for fiber-reinforced composite resins. In this study, we investigated a composite of NFBC and poly(methyl methacrylate) [...] Read more.

Nanofibrillated bacterial cellulose (NFBC), a type of cellulose nanofiber biosynthesized by Gluconacetobacter sp., has extremely long (i.e., high-aspect-ratio) fibers that are expected to be useful as nanofillers for fiber-reinforced composite resins. In this study, we investigated a composite of NFBC and poly(methyl methacrylate) (PMMA), a highly transparent resin, with the aim of improving the mechanical properties of the latter. The abundant hydroxyl groups on the NFBC surface were silylated using 3-(methacryloyloxy)propyltrimethoxysilane (MPTMS), a silane coupling agent bearing a methacryloyl group as the organic functional group. The surface-modified NFBC was homogeneously dispersed in chloroform, mixed with neat PMMA, and converted into PMMA composites using a simple solvent-casting method. The tensile strength and Young’s modulus of the composite increased by factors of 1.6 and 1.8, respectively, when only 0.10 wt% of the surface-modified NFBC was added, without sacrificing the maximum elongation rate. In addition, the composite maintained the high transparency of PMMA, highlighting that the addition of MPTMS-modified NFBC easily reinforce PMMA. Furthermore, interactions involving the organic functional groups of MPTMS were found to be very important for reinforcing PMMA. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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12 pages, 3586 KiB

Open AccessArticle

Electrospray Deposition of Cellulose Nanofibers on Paper: Overcoming the Limitations of Conventional Coating

by Quim Tarrés, Roberto Aguado, M. Àngels Pèlach, Pere Mutjé and Marc Delgado-Aguilar

Nanomaterials 2022, 12(1), 79; https://doi.org/10.3390/nano12010079 - 29 Dec 2021

Cited by 15 | Viewed by 2035

Abstract

While the potential of cellulose nanofibers to enhance the mechanical and barrier properties of paper is well-known, there are many uncertainties with respect to how to apply them. In this study, we use not only bulk addition of micro-/nanofibers and bar coating with [...] Read more.

While the potential of cellulose nanofibers to enhance the mechanical and barrier properties of paper is well-known, there are many uncertainties with respect to how to apply them. In this study, we use not only bulk addition of micro-/nanofibers and bar coating with oxidized nanofibers, but also a combination of these and, as a novel element, electrospray deposition of nanofiber dispersions. Characterization involved testing the strength of uncoated and coated paper sheets, their resistance to air flow, their Bendtsen roughness, and their apparent density, plus visualization of their surface and cross-sections by scanning electron microscopy. As expected, bulk addition to the unrefined pulp was sufficient to attain substantial strengthening, but this enhancement was limited to approximately 124%. Following this, surface addition by bar coating improved air resistance, but not strength, since, as applying nanocellulose at high consistency was technically unfeasible, this was performed several times with detrimental drying stages in between. However, replacing bar coating with electrospraying helped us overcome these apparent limitations, producing enhancements in both barrier and tensile properties. It is concluded that electrosprayed nanofibers, owing to their uniform deposition and favorable interactions, operate as an effective binder between fibers (and/or fines). Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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16 pages, 4077 KiB

Open AccessArticle

Facile Preparation and Characteristic Analysis of Sulfated Cellulose Nanofibril via the Pretreatment of Sulfamic Acid-Glycerol Based Deep Eutectic Solvents

by Weidong Li, Yu Xue, Ming He, Jiaqiang Yan, Lucian A. Lucia, Jiachuan Chen, Jinghua Yu and Guihua Yang

Nanomaterials 2021, 11(11), 2778; https://doi.org/10.3390/nano11112778 - 21 Oct 2021

Cited by 20 | Viewed by 3135

Abstract

A deep eutectic solvent (DES) composed of sulfamic acid and glycerol allowed for the sustainable preparation of cellulose nanofibrils (CNF) with simultaneous sulfation. The reaction time and the levels of sulfamic acid demonstrated that fibers could be swelled and sulfated simultaneously by a [...] Read more.

A deep eutectic solvent (DES) composed of sulfamic acid and glycerol allowed for the sustainable preparation of cellulose nanofibrils (CNF) with simultaneous sulfation. The reaction time and the levels of sulfamic acid demonstrated that fibers could be swelled and sulfated simultaneously by a sulfamic acid-glycerol-based DES and swelling also promoted sulfation with a high degree of substitution (0.12). The DES-pretreated fibers were further nanofibrillated by a grinder producing CNF with diameters from 10 nm to 25 nm. The crystallinity ranged from 53–62%, and CNF maintained the original crystal structure. DES pretreatment facilitated cellulose nano-fibrillation and reduced the energy consumption with a maximum reduction of 35%. The films prepared from polyvinyl alcohol (PVA) and CNF showed good UV resistance ability and mechanical properties. This facile and efficient method provided a more sustainable strategy for the swelling, functionalization and nano-fibrillation of cellulose, expanding its application to UV-blocking materials and related fields. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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19 pages, 13558 KiB

Open AccessArticle

Enhanced Morphological Characterization of Cellulose Nano/Microfibers through Image Skeleton Analysis

by Jose Luis Sanchez-Salvador, Cristina Campano, Patricio Lopez-Exposito, Quim Tarrés, Pere Mutjé, Marc Delgado-Aguilar, M. Concepcion Monte and Angeles Blanco

Nanomaterials 2021, 11(8), 2077; https://doi.org/10.3390/nano11082077 - 16 Aug 2021

Cited by 18 | Viewed by 2927

Abstract

The present paper proposes a novel approach for the morphological characterization of cellulose nano and microfibers suspensions (CMF/CNFs) based on the analysis of eroded CMF/CNF microscopy images. This approach offers a detailed morphological characterization and quantification of the micro and nanofibers networks present [...] Read more.

The present paper proposes a novel approach for the morphological characterization of cellulose nano and microfibers suspensions (CMF/CNFs) based on the analysis of eroded CMF/CNF microscopy images. This approach offers a detailed morphological characterization and quantification of the micro and nanofibers networks present in the product, which allows the mode of fibrillation associated to the different CMF/CNF extraction conditions to be discerned. This information is needed to control CMF/CNF quality during industrial production. Five cellulose raw materials, from wood and non-wood sources, were subjected to mechanical, enzymatic, and (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO)-mediated oxidative pre-treatments followed by different homogenization sequences to obtain products of different morphologies. Skeleton analysis of microscopy images provided in-depth morphological information of CMF/CNFs that, complemented with aspect ratio information, estimated from gel point data, allowed the quantification of: (i) fibers peeling after mechanical pretreatment; (ii) fibers shortening induced by enzymes, and (iii) CMF/CNF entanglement from TEMPO-mediated oxidation. Being mostly based on optical microscopy and image analysis, the present method is easy to implement at industrial scale as a tool to monitor and control CMF/CNF quality and homogeneity. Full article

(This article belongs to the Special Issue Preparation, Characterization and Industrial Application of Nanocellulose)

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