Nanocelluloses: Production, Characterization and Market.

Nanocelluloses are a very promising material that has been widely explored for the most diverse applications. The pursuit for sustainable and environmentally friendly materials is in line with the nature of nanocelluloses and therefore they have emerged as the perfect candidate for plastics substitution, food additive, rheology controller, 3D printing of diverse structures, among many other possibilities. This derives from their interesting characteristics, such as reduced size and high specific surface area, high tensile strength, crystallinity and transparency, and from the fact that, such as cellulose, they are obtained from renewable sources, with relative ease for functionalization in order to obtain desired specificities. Thus, the industry is trying to react and effectively respond to the exponential growth of published research in the last years, and therefore new facilities (not only lab and pilot plants but already industrial sites) have been producing nanocelluloses. This new fibrous materials can be obtained from different raw-materials by different methodologies, leading to different types of nanocelluloses with, obviously, different characteristics. Nonetheless, technical and economical constraints have been addressed, such as the high energy demand or the clogging of homogenizers/microfluidizers.This chapter intends to present a review addressing the main features related to the production, characterization and market of nanocelluloses and providing additional information regarding the vast literature published in these domains.

Rheology of Suspensions of TEMPO-Oxidised and Cationic Cellulose Nanofibrils-The Effect of Chemical Pre-Treatment.

Cellulose nanofibrils (CNFs) are particles with a high aspect ratio. Typically, chemically pre-treated CNFs (containing anionic or cationic charged groups) consist of long fibrils (up to 2 µm) with very low thickness (less than 10 nm). Derived from their high aspect ratio, CNFs form strong hydrogels with high elasticity at low concentrations. Thus, CNF suspensions appear as an interesting rheology modifier to be applied in cosmetics, paints, foods, and as a mineral suspending agent, among other applications. The high viscosity results from the strong 3D fibril network, which is related to the good fibrillation of the material, allowing the nanofibrils to overlap. The overlap concentration (c*) was found to vary from ca. 0.13 to ca. 0.60 wt.% depending on the type and intensity of the pre-treatment applied during the preparation of the CNFs. The results confirm the higher tendency for the fibres treated with (3-chloro-2-hydroxypropyl) trimethylammonium chloride (CHPTAC) and 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) to form a 3D network, resulting in the lowest c*. For the TEMPO-oxidised CNF suspensions, it was also found that aggregation is improved at acidic pH conditions due to lower charge repulsion among fibrils, leading to an increase in the suspension viscosity as well as higher apparent yield stresses. TEMPO CNF suspensions with a low content of carboxylic groups tend to precipitate at moderately acidic pH values.

Eco-Friendly Methods for Extraction and Modification of Cellulose: An Overview.

Cellulose is the most abundant renewable polymer on Earth and can be obtained from several different sources, such as trees, grass, or biomass residues. However, one of the issues is that not all the fractionation processes are eco-friendly and are essentially based on cooking the lignocellulose feedstock in a harsh chemical mixture, such as NaOH + Na2S, and water, to break loose fibers. In the last few years, new sustainable fractionation processes have been developed that enable the obtaining of cellulose fibers in a more eco-friendly way. As a raw material, cellulose's use is widely known and established in many areas. Additionally, its products/derivatives are recognized to have a far better environmental impact than fossil-based materials. Examples are textiles and packaging, where forest-based fibers may contribute to renewable and biodegradable substitutes for common synthetic materials and plastics. In this review, some of the main structural characteristics and properties of cellulose, recent green extraction methods/strategies, chemical modification, and applications of cellulose derivatives are discussed.

Impact of bacterial cellulose on the physical properties and printing quality of fine papers.

Bacterial nanocellulose (BNC), due to its inherent nanometric scale and strength properties, can be considered as a good candidate to be used in papermaking. This work explored the possibility of using it in the production of fine paper as a wet-end component and for the paper coating. Filler-containing handsheet production was performed with and without the presence of common additives typically used in the furnish of office papers. It was found that, under optimized conditions, BNC mechanically treated by high-pressure homogenization could improve all the evaluated paper properties (mechanical, optical and structural) without impairing the filler retention. However, paper strength was improved only to a small extent (increase in the tensile index of 8 % for a filler content of ca. 27.5 %). On the other hand, when used at the paper surface, remarkable improvements in the gamut area of >25 % in comparison to the base paper and of >40 % in comparison to starch-only coated papers were achieved for a formulation having 50 % BNC and 50 % of carboxymethylcellulose. Overall, the present results highlight the possibility of using BNC as a paper component, particularly when applied at the paper substrate as a coating agent aiming at improving printing quality.

Influence of dispersion of fibrillated cellulose on the reinforcement of coated papers.

The use of cellulose micro/nanofibrils (CMNFs) as reinforcement paper additive at industrial scale is delayed due to inconsistent results, suggesting a lack of proper consideration of some key parameters. The high influence of fibrillated nanocellulose dispersion has been recently identified as a key parameter for paper bulk reinforcement but it has not been studied for surface coating applications yet. This paper studies the effect of CMNF dispersion degree prior to their addition and during mixing with starch on the reinforcement of paper by coating. Results show that this effect depends on the type of CMNFs since it is related to the surface interactions. For a given formulation, a correlation is observed between the CMNF dispersion and the CMNF/starch mixing agitation with the rheology of the coating formulation which highly affects the paper properties. The optimal dispersion degree is different for each nanocellulose, but the best mechanical properties were always achieved at the lowest viscosity of the coating formulation. In general, the initial state of the nanocellulose 3D network, influences the mixing and smooth application of the coating and affects the reinforcement effect. Therefore, the CMNF industrial implementation in coating formulations will be facilitated by the on-line control of formulations prior to their surface application.

Assessing the Genotoxicity of Cellulose Nanomaterials in a Co-Culture of Human Lung Epithelial Cells and Monocyte-Derived Macrophages.

Cellulose micro/nanomaterials (CMNMs) are innovative materials with a wide spectrum of industrial and biomedical applications. Although cellulose has been recognized as a safe material, the unique properties of its nanosized forms have raised concerns about their safety for human health. Genotoxicity is an endpoint that must be assessed to ensure that no carcinogenic risks are associated with exposure to nanomaterials. In this study, we evaluated the genotoxicity of two types of cellulose micro/nanofibrils (CMF and CNF) and one sample of cellulose nanocrystals (CNC), obtained from industrial bleached Eucalyptus globulus kraft pulp. For that, we exposed co-cultures of human alveolar epithelial A549 cells and THP-1 monocyte-derived macrophages to a concentration range of each CMNM and used the micronucleus (MN) and comet assays. Our results showed that only the lowest concentrations of the CMF sample were able to induce DNA strand breaks (FPG-comet assay). However, none of the three CMNMs produced significant chromosomal alterations (MN assay). These findings, together with results from previous in vitro studies using monocultures of A549 cells, indicate that the tested CNF and CNC are not genotoxic under the conditions tested, while the CMF display a low genotoxic potential.

Effect of cationization pretreatment on the properties of cationic Eucalyptus micro/nanofibrillated cellulose.

Micro/nanofibrillated celluloses (M/NFCs) have attracted considerable research interest over the past few decades, with various pretreatments being used to reduce energy consumption and/or increase fibrillation. To date, few studies have considered cationization as a pretreatment for their preparation. In this work, quaternary ammonium groups were attached to cellulose fibers by a direct reaction with 2,3-epoxypropyltrimethylammonium chloride or by a two-step method (periodate oxidation + Girard's reagent T). The cationic fibers with degrees of substitution (DS) between 0.02 and 0.36, were subjected to homogenization treatment. The morphological properties, chemical composition, and rheological behavior were evaluated to assess the effect of DS and the effect of the cationization method (for samples with similar DS). The two-step cationization resulted in significant degradation of the cellulose structure, leading to the formation of short fibrils and solubilization of the material, ranging from 6% to almost complete solubilization at a DS of 0.36. Direct cationization resulted in longer fibrils with an average diameter of 1 µm, and no significant cellulose degradation was observed, leading to a more cohesive gel-like material (at 1 wt%). These observations clearly show the strong influence of the cationization method on the final properties of the cationic cellulosic materials.

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

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/m2. 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.

Assessment of the Performance of Cationic Cellulose Derivatives as Calcium Carbonate Flocculant for Papermaking.

Cationic polyacrylamides (CPAMs) are usually used as filler retention agents in papermaking formulations. However, increasing environmental restrictions and their non-renewable origin have driven research into bio-based alternatives. In this context, cationic lignocellulosic derivatives have been attracting considerable research interest as a potential substitute. In this work, distinct cationic celluloses with degrees of substitution of between 0.02 and 1.06 and with distinct morphological properties were synthesized via the cationization of bleached eucalyptus kraft pulp, using a direct cationization with (3-chloro-2-hydroxypropyl) trimethylammonium chloride (CHPTAC) or a two-step cationization, where the cellulose was first oxidized to form dialdehyde cellulose and was then made to react with Girard's reagent T (GT). Fibrillated samples were produced by subjecting some samples to a high-pressure homogenization treatment. The obtained samples were evaluated regarding their potential to flocculate and retain precipitated calcium carbonate (PCC), and their performance was compared to that of a commercial CPAM. The cationic fibrillated celluloses, with a degree of substitution of ca. 0.13-0.16, exhibited the highest flocculation performance of all the cationic celluloses and were able to increase the filler retention from 43% (with no retention agent) to ca. 61-62% (with the addition of 20 mg/g of PCC). Although it was not possible to achieve the performance of CPAM (filler retention of 73% with an addition of 1 mg/g of PCC), the results demonstrated the potential of cationic cellulose derivatives for use as bio-based retention agents.

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

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.

Genotoxicity of Three Micro/Nanocelluloses with Different Physicochemical Characteristics in MG-63 and V79 Cells.

(1) Background: Nanocellulose is an innovative engineered nanomaterial with an enormous potential for use in a wide array of industrial and biomedical applications and with fast growing economic value. The expanding production of nanocellulose is leading to an increased human exposure, raising concerns about their potential health effects. This study was aimed at assessing the potential toxic and genotoxic effects of different nanocelluloses in two mammalian cell lines; (2) Methods: Two micro/nanocelluloses, produced with a TEMPO oxidation pre-treatment (CNFs) and an enzymatic pre-treatment (CMFs), and cellulose nanocrystals (CNCs) were tested in osteoblastic-like human cells (MG-63) and Chinese hamster lung fibroblasts (V79) using the MTT and clonogenic assays to analyse cytotoxicity, and the micronucleus assay to test genotoxicity; (3) Results: cytotoxicity was observed by the clonogenic assay in V79 cells, particularly for CNCs, but not by the MTT assay; CNF induced micronuclei in both cell lines and nucleoplasmic bridges in MG-63 cells; CMF and CNC induced micronuclei and nucleoplasmic bridges in MG-63 cells, but not in V79 cells; (4) Conclusions: All nanocelluloses revealed cytotoxicity and genotoxicity, although at different concentrations, that may be related to their physicochemical differences and availability for cell uptake, and to differences in the DNA damage response of the cell model.

Analysis of the In Vitro Toxicity of Nanocelluloses in Human Lung Cells as Compared to Multi-Walled Carbon Nanotubes.

Cellulose micro/nanomaterials (CMNM), comprising cellulose microfibrils (CMF), nanofibrils (CNF), and nanocrystals (CNC), are being recognized as promising bio-nanomaterials due to their natural and renewable source, attractive properties, and potential for applications with industrial and economical value. Thus, it is crucial to investigate their potential toxicity before starting their production at a larger scale. The present study aimed at evaluating the cell internalization and in vitro cytotoxicity and genotoxicity of CMNM as compared to two multi-walled carbon nanotubes (MWCNT), NM-401 and NM-402, in A549 cells. The exposure to all studied NM, with the exception of CNC, resulted in evident cellular uptake, as analyzed by transmission electron microscopy. However, none of the CMNM induced cytotoxic effects, in contrast to the cytotoxicity observed for the MWCNT. Furthermore, no genotoxicity was observed for CNF, CNC, and NM-402 (cytokinesis-block micronucleus assay), while CMF and NM-401 were able to significantly raise micronucleus frequency. Only NM-402 was able to induce ROS formation, although it did not induce micronuclei. Thus, it is unlikely that the observed CMF and NM-401 genotoxicity is mediated by oxidative DNA damage. More studies targeting other genotoxicity endpoints and cellular and molecular events are underway to allow for a more comprehensive safety assessment of these nanocelluloses.

Novel approach on the synthesis of starch betainate by transesterification.

Transesterification of starch with methyl betainate was studied for the first time, both in aprotic media and in solid state, and both under alkaline and acidic conditions. Betaine hydrochloride was first esterified in methanol, attaining a conversion of 86%. Starch was then converted into starch betainate in either N,N-dimethylformamide or dimethyl sulfoxide, and using sulfuric acid as catalyst or pre-activating the polymer in NaOH/ethanol. Furthermore, solid-state transesterification was carried out in a ball mill, for which sulfuric acid was replaced with the less corrosive sulfamic acid. Cationic starch esters were characterised by 1H and 13C NMR spectroscopy, infrared spectroscopy, thermogravimetric analysis, viscometry, optical microscopy (in water) and scanning electron microscopy (dry). In solution, the process attained degrees of substitution up to 0.4. No by-products, dehydration, oxidation or colouring were detected, but starch underwent severe depolymerization in wet media. In solid state, whilst the resulting degree of substitution was lower, degradation was minimal. In any case, transesterification, with its variety of possibilities, yields cationic starches that offer a promising alternative to conventional ethers.

A review on cationic starch and nanocellulose as paper coating components.

Starch and derivatives thereof have proven their usefulness in paper coating processes. Among these derivatives, cationic starch has been widely used in the paper industry as a flocculation, dispersion and ink fixing agent. In another context, nanoscale cellulosic materials have been shown to improve the strength, retention of fillers, the barrier properties of packaging paper products, and printing qualities. This review summarizes the recent studies on the general components used in paper coating, describes the conventional and alternative synthetic processes of cationic starches and nanocellulose, and deals with their current and potential applications in papermaking, focusing primarily on surface treatments. Moreover, environmental applications have been considered to expand the understanding and usefulness of these materials. Further research on modified polysaccharides is encouraged to replace, in a feasible way, petro-based components of coating formulations, and to provide paper surfaces with new properties.

Enzymatic nanocellulose in papermaking - The key role as filler flocculant and strengthening agent.

Nanocelluloses have been increasingly used in composites since their reduced size, high aspect ratio and stiffness confer great strength to the materials. In papermaking, it has been proved that harsh and expensive chemical pre-treatments to generate nanofibrils, such as TEMPO-mediated oxidation, are not the most favourable and therefore the use of cellulose microfibrils (CMF) have gained extra attention, especially those produced with the aid of enzymatic hydrolysis. In the present work, strategies to improve filler flocculation and the papermaking properties, by using enzymatic CMF, are provided. The CMF degree of polymerization was found to be directly related to precipitated calcium carbonate flocculation, leading to higher retentions in the fibre matrix. Besides, the paper dry and wet strengths were much improved, allowing in return the production of high-filler loaded handsheets with reduced requirements for common paper additives.

Evaluating the genotoxicity of cellulose nanofibrils in a co-culture of human lung epithelial cells and monocyte-derived macrophages.

Cellulose nanofibrils (CNF) are manufactured nanofibres that hold impressive expectations in forest, food, pharmaceutical, and biomedical industries. CNF production and applications are leading to an increased human exposure and thereby it is of utmost importance to assess its safety to health. In this study, we screened the cytotoxic, immunotoxic and genotoxic effects of a CNF produced by TEMPO-mediated oxidation of an industrial bleached Eucalyptus globulus kraft pulp on a co-culture of lung epithelial alveolar (A549) cells and monocyte-derived macrophages (THP-1 cells). The results indicated that low CNF concentrations can stimulate A549 cells proliferation, whereas higher concentrations are moderately toxic. Moreover, no proinflammatory cytokine IL-1ß was detected in the co-culture medium suggesting no immunotoxicity. Although CNF treatment did not induce sizable levels of DNA damage in A549 cells, it leaded to micronuclei formation at 1.5 and 3 µg/cm2. These findings suggest that this type of CNF is genotoxic through aneugenic or clastogenic mechanisms. Noteworthy, cell overgrowth and genotoxicity, which are events relevant for cell malignant transformation, were observed at low CNF concentration levels, which are more realistic and relevant for human exposure, e.g., in occupational settings.

On the morphology of cellulose nanofibrils obtained by TEMPO-mediated oxidation and mechanical treatment.

The morphological properties of cellulose nanofibrils obtained from eucalyptus pulp fibres were assessed. Two samples were produced with the same chemical treatment (NaClO/NaBr/TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidation), but distinct mechanical treatment intensities during homogenization. It was shown that the nanofibrils production yield increases with the mechanical energy. The effect of mechanical treatment on the yield was confirmed by laser profilometry of air-dried nanocellulose films. However, no significant differences were detected regarding the nanofibrils width as measured by atomic force microscopy (AFM) of air-dried films. On the other hand, differences in size were found either by laser diffraction spectroscopy or by dynamic light scattering (DLS) of the cellulose nanofibrils suspensions as a consequence of the differences in the length distribution of both samples. The nanofibrils length of the more nanofibrillated sample was calculated based on the width measured by AFM and the hydrodynamic diameter obtained by DLS. A length value of ca. 600 nm was estimated. The DLS hydrodynamic diameter, as an equivalent spherical diameter, was used to estimate the nanofibrils length assuming a cylinder with the same volume and with the diameter (width) assessed by AFM. A simple method is thus proposed to evaluate the cellulose nanofibrils length combining microscopy and light scattering methods.