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Although cellulosic materials have been used as stabilizing agents for oil-in-water emulsions since the 1980s, their properties and the underlying mechanism are not universal regardless of the dispersed phase or of the treatments on cellulose. One case of unconventional organic phase is acetic acid-containing chloroform, which is known to be a good solvent system for the preservation of dithizone. In turn, dithizone is a long-known chromogenic reagent for the colorimetric detection of HgCl2. However, its usefulness is limited by its fast degradation in polar solvents. For instance, its dissolution in ethanol and the subsequent impregnation of paper strips allowed to quantify aqueous HgCl2 reliably and quickly (5.4 – 27 mg L–1), but only if they were used along the first 24 h after dip coating. Furthermore, those strips could not be used for sublimated HgCl2. The dithizone/chloroform-in-water emulsions presented in this work overcame these limitations. We opted for oxalic acid-treated cellulose nanofibers (ox-CNFs) as stabilizer, aiming at a proper balance between amphiphilic character and electrostatic repulsion. In this sense, ox-CNFs attained good gel-forming ability with a low content of carboxylate groups. The minimum ox-CNF concentration required was 0.35 wt%, regardless of the proportion of chloroform. This consistency implied yield stress values above 0.7 Pa. Nanocellulose also provided film-forming capabilities, which were exploited to produce visually responsive dipsticks and membranes. While quantification and reproducibility were hampered by the increase in the complexity of the system, dithizone/ox-CNF films were still a valid option for HgCl2 detection, outperforming solution coating in terms of stability, blank signal, and selectivity. [ABSTRACT FROM AUTHOR]

This study aims to provide a comprehensive understanding of the key factors influencing the rheological behavior and the mechanisms of natural polyelectrolyte complexes (PECs) as flocculation agents for cellulose microfibers (CMFs) and nanofibers (CNFs). PECs were formed by combining two polyelectrolytes: xylan (Xyl) and chitosan (Ch), at different Xyl/Ch mass ratios: 60/40, 70/30, and 80/20. First, Xyl, Ch, and PEC solutions were characterized by measuring viscosity, critical concentration (c*), rheological parameter, ζ-potential, and hydrodynamic size. Then, the flocculation mechanisms of CMF and CNF suspensions with PECs under dynamic conditions were studied by measuring viscosity, while the flocculation under static conditions was examined through gel point measurements, floc average size determination, and ζ-potential analysis. The findings reveal that PEC solutions formed with a lower xylan mass ratio showed higher intrinsic viscosity, higher hydrodynamic size, higher z-potential, and a lower c*. This is due to the high molecular weight, charge, and gel-forming ability. All the analyzed solutions behave as a typical non-Newtonian shear-thinning fluid. The flocculation mechanisms under dynamic conditions showed that a very low dosage of PEC (between 2 and 6 mg PEC/g of fiber) was sufficient to produce flocculation. Under dynamic conditions, an increase in viscosity indicates flocculation at this low PEC dosage. Finally, under static conditions, maximum floc sizes were observed at the same PEC dosage where minimum gel points were reached. Higher PEC doses were required for CNF suspensions than for CMF suspensions. [ABSTRACT FROM AUTHOR]

Beeswax is a bio-sourced, renewable, and even edible material that stands as a convincing option to provide paper-based food packaging with moisture resistance. Nonetheless, the difficulty of dispersing it in water limits its applicability. This work uses oxidized, negatively charged cellulose nanofibers along with glycerol to stabilize beeswax-in-water emulsions above the melting point of the wax. The synergistic effects of nanocellulose and glycerol granted the stability of the dispersion even when it cooled down, but only if the concentration of nanofibers was high enough. This required concentration (0.6–0.9 wt%) depended on the degree of oxidation of the cellulose nanofibers. Rheological hindrance was essential to prevent the buoyancy of beeswax particles, while the presence of glycerol prevented excessive aggregation. The mixtures had yield stress and showed pseudoplastic behavior at a high enough shear rate, with their apparent viscosity being positively influenced by the surface charge density of the nanofibers. When applied to packaging paper, the nanocellulose-stabilized beeswax suspensions not only enhanced its barrier properties towards liquid water (reaching a contact angle of 96°) and water vapor (<100 g m−2 d−1), but also to grease (Kit rating: 5) and airflow (>1400 Gurley s). While falling short of polyethylene-coated paper, this overall improvement, attained using only one layer of a biobased coating suspension, should be understood as a step towards replacing synthetic waxes and plastic laminates. [ABSTRACT FROM AUTHOR]

Measurements of nanocellulose size usually demand very high-resolution techniques and tedious image processing, mainly in what pertains to the length of nanofibers. Aiming to ease the process, this work assesses a relatively simple method to estimate the dimensions of nanocellulose particles with an aspect ratio greater than 1. Nanocellulose suspensions, both as nanofibers and as nanocrystals, are subjected to dynamic light scattering (DLS) and to field-emission scanning electron microscopy (FE-SEM). The former provides the hydrodynamic diameter, as long as the scatter angle and the consistency are adequate. Assays with different angles and concentrations compel us to recommend forward scattering (12.8°) and concentrations around 0.05–0.10 wt %. Then, FE-SEM with magnifications of ×5000–×20,000 generally suffices to obtain an acceptable approximation for the actual diameter, at least for bundles. Finally, length can be estimated by a simple geometric relationship. Regardless of whether they are collected from FE-SEM or DLS, size distributions are generally skewed to lower diameters. Width distributions from FE-SEM, in particular, are well fitted to log-normal functions. Overall, while this method is not valid for the thinnest fibrils or for single, small nanocrystals, it can be useful in lieu of very high-resolution techniques. [ABSTRACT FROM AUTHOR]

Anionic cellulose nanofibers (CNFs) were used to stabilize emulsions that combined water-soluble (and oil-soluble), strongly antioxidant extracts with a water-immiscible, notably antimicrobial essential oil. Specifically, the radical scavenging activity was primarily provided by aqueous extracts from olive fruit (Olea europaea L.), while the antimicrobial effects owed eminently to thyme oil (Thymus vulgaris L.). The resulting emulsions were highly viscous at low shear rate (4.4 Pa·s) and displayed yield stress. The addition of edible salts decreased the yield stress, the apparent viscosity and the droplet size, to the detriment of stability at ionic strengths above 50 mM. Once characterized, the antioxidant and antimicrobial emulsions were applied on packaging-grade paper. Coated paper sheets inhibited the growth of Listeria monocytogenes , a common foodborne pathogen, and acted as antioxidant emitters. In this sense, the release to food simulants A (ethanol 10 vol%), B (acetic acid 3 wt%), and C (ethanol 20 vol%) was assessed. A 24-hour exposure of 0.01 m2 of coated paper to 0.1 L of these hydrophilic simulants achieved inhibition levels of the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) in the 15–29 % range. All considered, the bioactive properties of thyme essential oil towards lipophilic food products can be complemented with the antioxidant activity of aqueous olive extracts towards hydrophilic systems, resulting in a versatile combination for active food packaging. • Nanocellulose-stabilized emulsions included thyme oil (lipophilic) and olive extract (water-soluble). • Thyme oil inhibited the growth of diverse foodborne pathogens and showed fair antioxidant activity. • Olive extract possessed stronger antioxidant properties and certain activity against L. monocytogenes. • Salt addition decreased yield stress, viscosity, and droplet size, to the detriment of stability. • Paper coated with these emulsions emitted antioxidant compounds to different food simulants. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cationic cellulose, despite its long history, has yet to find a place in the paper industry. However, recent research is evaluating the potential of its nanoscale forms. Likewise, the processes of Western manufacturers are optimized for wood pulps, relegating non-wood crops to specific products that, as also proposed by current research, could include nanocellulose. We combined these trends with the existing knowledge of the strong adsorption of poly(diallyldimethylammonium chloride) (polyDADMAC) on cellulosic fibers, which can be deemed a non-covalent kind of cationization. For that, polyDADMAC was first anchored to refined hemp pulps, under conditions that allowed the deprotonation of the primary hydroxyl groups of cellulose. The fiber surface remained positively-charged even after thoroughly washing the samples, owing not only to the small proportions of acidic hemicelluloses and lignin, but also to stable ion-dipole interactions. This non-covalent cationization was found to follow pseudo-second order kinetics, indicating that diffusion through the fiber was the rate-controlling step. PolyDADMAC-containing fibers were then fibrillated by high-pressure homogenization. The surface charge of cationic nanocellulose was greater than that of the starting fibers, as the specific surface area increased. Nonetheless, polyDADMAC caused agglomeration of fibrils to a certain extent. As a drawback, when applied in papermaking, cationic nanocellulose lowered air permeability to a lesser extent than non-cationized nanofibers. As an advantage, the tensile index increased by up to 57% in the absence of any retention agent. • Adsorption of polyDADMAC to hemp pulp fibers follows pseudo-second order kinetics. • Both refining and fibrillation increase the absolute value of the surface charge. • Strong binding of polyDADMAC: ionic in alkaline media, ion-dipole after neutralization. • The resulting nanofibers improve paper strength without the need of retention aids. [ABSTRACT FROM AUTHOR]

Partly inspired by the concept of masterbatch in plastics manufacturing, we developed a strategy to improve the technical viability, the economic feasibility, and the environmental performance of lignocellulosic micro-/nanofibers. Instead of investing strenuous efforts in dewatering and/or drying nanocellulose suspensions to maximize their consistency without significantly hampering redispersion, which still stands as an unresolved challenge, we used them in high proportions (up to 50 wt%) to reinforce a high-yield pulp. The suspension can be dewatered-pressed (0.70–1.75 MPa) to obtain wet laps of never-dried reinforced pulps, or dried to consistencies over 90% to produce dry boards, but at the cost of lower strengthening capability. In any case, both wet and dry reinforced boards succeeded in enhancing the breaking length of a recycled pulp by up to 62% and 56%, respectively. In light of these results, we proposed a tentative upscaling and subsequent assessment of the process, evaluating different scenarios. From the technical point of view, reinforced pulp boards are much easier to handle and to deliver than dilute aqueous suspensions. In economic terms, savings in transportation costs are worth remarking. Last but not least, this strategy fulfills at least three goals associated with the concept of cleaner production: water recovery (internal recycling), lower CO 2 emissions (especially if transportation takes place by road), and avoiding hazardous chemicals such as hypochlorite. [Display omitted] • The masterbatch strategy in plastics manufacturing is applied in papermaking. • Micro-/nanocellulose-enriched pulp boards were produced by dewatering-pressing and/or heating. • Reinforced pulp boards were used as an effective strengthening agent for packaging paper. • This novel approach to distribute lignocellulosic micro-/nanofibers minimizes volume and cost of transportation. • Water recycling is enhanced and CO 2 emissions in transport/delivery are lowered. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

Enzymatic pretreatment plays a crucial role in producing cellulose nanofibers (CNFs) before fibrillation. While previous studies have explored how treatment severity affects CNF characteristics, there remains a lack of suitable parameters to monitor real-time enzymatic processes and fully comprehend the link between enzymatic action, fibrillation, and CNF properties. This study focuses on evaluating the impact of enzyme charge (using a monocomponent endoglucanase) and treatment time on cellulose fiber morphology and reducing sugar generation. For the first time, a random forest (RF) model is developed to predict reducing sugar concentration based on easily measurable process conditions (e.g., stirrer power consumption) and fiber/suspension characteristics like fines content and apparent viscosity. Polarized light optical microscopy was found to be a suitable technique to evaluate the morphological changes that fibers experience during enzymatic pretreatment. The research also revealed that endoglucanases initially induce surface fibrillation, releasing fine fibers into the suspension, followed by fiber swelling and shortening. Furthermore, the effect of enzymatic pretreatment on resulting CNF characteristics was studied at two fibrillation intensities, indicating that a high enzyme charge and short treatment times (e.g., 90 min) are sufficient to produce CNFs with a nanofibrillation yield of 19–23 % and a cationic demand ranging from 220 to 275 μeq/g. This work introduces a well-modeled enzymatic pretreatment process, unlocking its potential and reducing uncertainties for future upscaling endeavors. [ABSTRACT FROM AUTHOR]