Obtained Cellulose Nanofibers Research Articles

Modulating digestibility and stability of Pickering emulsions based on cellulose nanofibers

Cellulose nanofibers (CNF) have been widely studied for their biodegradability and for their unique advantages as a stabilizer in Pickering-type emulsions. However, it is challenging to produce cellulose nanofibers from agroindustry waste with good techno-functional properties, without the use of harsh process conditions. Green alternatives (eco-friendly) have been studied to obtain nanofibers, such as enzymatic hydrolysis and/or application of mechanical processes. In this work, we used acid hydrolysis (as a control and example of an efficient method), enzymatic hydrolysis and a mechanical process (ultrasound) to obtain cellulose nanofibers. We also evaluated the effect of the presence of ethyl groups in the cellulosic matrix (ethylcellulose) on the stabilizing mechanism of emulsions. All cellulose nanofibers were able to produce Pickering emulsions at concentrations of 0.01–0.05% (w/w), although showing differences in emulsion stability and digestibility. Morphology of the different cellulose nanofibers affected the viscosity of the aqueous suspensions used as continuous phase. Emulsions with nanofibers obtained from cassava peel (without the presence of ethyl groups) were stabilized only by the Pickering-type mechanism, while ethylcellulose nanofibers also showed surface activity that contributed to the stability of the emulsion. Furthermore, these latter emulsions showed greater release of free fatty acids in in vitro digestion compared to emulsions stabilized by cellulose nanofibers. Despite these differences, in vitro digestion showed the potential of applying cellulose-stabilized emulsions to control the rate of lipid digestion, due to the low amount of free fatty acids released (<20%).

Assessment of cellulose nanofibers from bolaina blanca wood obtained at three shaft heights

This study evaluated cellulose nanofibers from bolaina blanca wood (Guazuma crinita) obtained at different heights of the longitudinal axis of the shaft of trees from a three-and-a-half-year-old plantation. The wood was subjected to pulping, bleaching and subsequent mechanical milling using a Changsha Samy XYQM-2L planetary ball mill to obtain cellulose nanofibers. The product was characterised using analytical techniques: scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy. Additionally, the degree of polymerisation was determined. The effect of longitudinal position on cellulose nanofibers characteristics was evaluated by comparing means using ANOVA and Kruskal–Wallis statistical tests. The yield of cellulose nanofibers production from the high, middle and basal sections was 32,1 %, 33,6 % and 31 %, respectively. The obtained cellulose nanofibers exhibited a significantly larger diameter for the high zone (84 nm) compared with the middle (75 nm) and basal (69 nm) zones; the length remained above the micrometre range. With respect to degree of polymerisation, a decrease was evidenced with respect to the increase in shaft height; the basal zone exhibited a degree of polymerisation of 300, a significantly higher value than the middle and high zones, which exhibited degree of polymerisation of 249 and 211, respectively. The product showed typical cellulose type I polymorphism and crystallinity indexes of 76 %, 93 % and 96 % for the high, middle and basal sections, respectively. Regarding the thermostability of cellulose nanofibers, the maximum degradation rate of cellulose nanofibers occurred between 335 °C and 341 °C, with cellulose nanofibers from the basal area being the most stable. The adsorption of the methylene blue dye on cellulose nanofibers was evaluated; an efficiency &gt; 60 % was found.

Exploring the feasibility of Babul-cellulose nanofiber nanocomposites as a sustainable alternative: Synthesis and properties analysis

Biodegradable polymers are a promising alternative to traditional, non-degradable polymers in various applications. Research into the use of primarily monosaccharides and natural tree gums has shown great potential in technology. Experiments on various gums, including Acacia nilotica (Babul), have revealed their excellent mechanical properties. In this study, biodegradable and water-soluble nanocomposites were synthesized using Acacia nilotica reinforced with different volume proportions (5 %, 10 %, 15 %, and 20 %) of cellulose nanofibers. The widely-used hydrothermal method was employed to obtain cellulose nanofibers (CNF), which were then used to create bubble gum. Sorbitol was used as a plasticizer during liquid metallurgy processes to form films. The properties of these films, including tensile strength, modulus of elasticity, contact angle, and moisture content were analyzed. The effect of reinforcement on the matrix was also analyzed using a scanning electron microscope (SEM). The low hydrophilicity and improved mechanical strength of these nanocomposites offer new possibilities for use in pharmaceutical and bio-edible coatings.

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

Bioactive Hydrogels: Design and Characterization of Cellulose-Derived Injectable Composites.

Cellulose represents a low cost, abundant, and renewable polysaccharide with great versatility; it has a hierarchical structure composed of nanofibers with high aspect ratio (3–4 nm wide, hundreds of μm long). TEMPO-mediated oxidation represents one of the most diffused methods to obtain cellulose nanofibers (CNFs): It is possible to obtain physically crosslinked hydrogels by means of divalent cation addition. The presence of inorganic components, such as calcium phosphates (CaP), can improve not only their mechanical properties but also the bioactivity of the gels. The aim of this work is to design and characterize a TEMPO-oxidized cellulose nanofibers (TOCNFs) injectable hydrogel embedded with inorganic particles, CaP and CaP-GO, for bone tissue regeneration. Inorganic particles act as physical crosslinkers, as proven by rheological characterization, which reported an increase in mechanical properties. The average load value registered in injection tests was in the range of 1.5–4.4 N, far below 30 N, considered a reasonable injection force upper limit. Samples were stable for up to 28 days and both CaP and CaP-GO accelerate mineralization as suggested by SEM and XRD analysis. No cytotoxic effects were shown on SAOS-2 cells cultured with eluates. This work demonstrated that the physicochemical properties of TOCNFs-based dispersions could be enhanced and modulated through the addition of the inorganic phases, maintaining the injectability and bioactivity of the hydrogels.

Evaluation of eco-friendly cellulose and lignocellulose nanofibers from rice straw using Multiple Quality Index

Huge amounts of rice straw are left every year in different areas of the world; these residues still cause environmental problems due to un-safe practices such as burning. Isolation of nanomaterials such as cellulose nanofibers represents an effective way for utilization of rice straw in advanced products. The current work aimed at evaluating the properties of rice straw cellulose nanofibers isolated from bleached and high-lignin unbleached pulps using a multi-criterion quality index, which allows a benchmarking analysis between different sources, processes and features. Rice straw was subjected to neutral sulfite pulping process to obtain the high-lignin unbleached pulp while the bleached pulp was obtained by bleaching the produced pulp with NaClO2/acetic acid mixture. Using mechanical pretreatment (Valley beater), and ultrafine friction grinder both bleached and unbleached pulps were used to obtain cellulose nanofibers with and without lignin (L-CNF and CNF, respectively). Nanopaper sheets were prepared from both types of nanofibers and characterized using tensile tests, optical microscopy, atomic force microscopy, electron scanning microscopy, water contact angle and surface energy. Cellulose nanofibers generated from rice straw were scored using a multi-criterion quality index depending on characterization using eight tests (nanosized and macro size fraction, turbidity, Young's modulus, porosity, transmittance, tear resistance, and homogeneity).

Nanofibrillation and characterization of sugarcane bagasse agro-waste using water-based steam explosion and high-pressure homogenization

Sugarcane bagasse waste, consisting of approximately 40–50% cellulose, has been widely used in a number of industries. The extraction and defibrillation of nanometer-scale cellulose fibers from such waste using strong chemical solutions have been extensively investigated. However, the using of strong chemical solutions can cause adverse effects to the fibers as well as negatively affect the environment. Some evidence has shown that mechanical treatments, such as steam explosion and high-pressure homogenization, are environmentally friendly when compared with chemical treatment techniques. This work aimed to isolate the cellulose nanofibers from sugarcane bagasse waste using steam explosion pretreatment at various temperatures (195, 200, 205, and 210 °C) and durations (5, 10, and 15 min) before passing through a microfluidizer within 12 passes of 200 mL cellulose suspension. The mean separation analysis using Duncan’s Multiple Range test showed that higher temperatures significantly improved the efficiency of non-cellulosic substances reduction, as evidenced by an increment of whiteness index (81.39–90.02), thermal degradation temperature (313.92–326.34 °C) and crystallinity index (74.27–81.42%). The obtained cellulose nanofibers exhibited very fine diameter within the range of 3–7 nm, had a high cellulose content (92.74 ± 0.14%) and a low density (0.8989 g/cm3). The obtained cellulose nanofibers could be applied in various fields such as medical, cosmetic, food packaging, and electronic device applications.

Fractionation of non-timber wood from Atlantic mixed forest into high-value lignocellulosic materials

The forestry industry in the Basque Country has experienced an abandonment of small-sized forests in which native and introduced species tend to regrow if unattended; thus, requiring an intervention under which proper forest management is implemented. This paper evaluates the potential fractionation of lignin and cellulose from six tree species coming from such mixed forests as a value-added use of wood discarded by logging within the frame of sustainable forest management. The species used were Northern red oak, common oak, common ash, Iberian white birch, sweet chestnut, and black locust. The different wood samples were treated with an Organosolv treatment and elemental chlorine-free bleaching to fractionate them to their main components, recovering the cellulose and the lignin. Cellulose was defibrillated via high-pressure homogenization to obtain cellulose nanofibers. The resulting lignin and cellulose nanofibers were analyzed. The results support the idea that this process offers the opportunity to treat different raw materials in the same process, with corresponding possible economic benefits.

Sustainable production of cellulose nanofiber gels and paper from sugar beet waste using enzymatic pre-treatment

Removal of non-cellulosic polymers from vegetable pulp to obtain cellulose nanofibers (CNF) is normally achieved by chemical pre-treatments which requires several washing steps. In the present study, it is demonstrated how incubation of sugar beet pulp at pH 9, followed by treatment with polysaccharide-degrading enzymes and subsequent bleaching can be done in a one-pot procedure to make CNF. The new method consumes 67% less water and removes non-cellulosic polysaccharides with similar efficiency as a chemical method. In addition, CNF produced by the new method contained slightly more pectin and formed gels with 2.7 times higher storage modulus. Nanopapers cast from chemically- and enzymatically produced CNF showed similar mechanical properties. However, without the pH 9 incubation step, the enzymes accessibility to cell-wall polymers was limited resulting in lower gel and paper strengths. In conclusion, the new method offers a sustainable route for producing high quality CNF from sugar beet waste.

Electron Beam Irradiation Isolates Cellulose Nanofiber from Korea "Tall Goldenrod" Invasive Alien Plant Pulp.

This work investigates the possibility of isolating cellulose nanofibers from pulps of tall goldenrod plant, which are invasive plants in Korea, by a convenient method, without strong acids or high-pressure homogenization, using electron beam irradiation (EBI). The obtained cellulose nanofibers were characterized by scanning electron microscopy (SEM), ultraviolet–visible (UV–vis) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and in terms of their mechanical properties. SEM showed that the initially isolated 10-μm-diameter cellulose fibers became more finely separated with increasing EBI dose, and that cellulose fibers treated with 300 kGy of EBI were separated into long cellulose nanofibers of around 160 nm in diameter. In addition, the paper samples prepared from more finely separated fibers generated by using higher doses of EBI had enhanced UV–vis transmittance. Via the XRD analysis, we observed that cellulose I in the EBI-treated cellulose fibers were gradually converted into a different type of cellulose similar to cellulose type II, as the EBI dose increased. Meanwhile, the TGA demonstrated that the finely separated cellulose fibers observed after administering the high EBI dose had lowered thermal stability due to the reduction of cellulose I but higher char yield. In addition, tensile strengths of paper samples increased with decreasing the diameters of their constituent fibers that result from the different EBI doses used in the preparation of the paper pulp.

Thiol-based chemistry as versatile routes for the effective functionalization of cellulose nanofibers

We demonstrate effective functionalization chemistry for cellulose nanofiber modification using thiol functionality. Electrospun cellulose acetate nanofibers were deacetylated to obtain cellulose nanofibers, which were modified further to incorporate thiol on their surface by the esterification of hydroxyl groups with 3,3′-dithiodipropionic acid and further reductive cleavage of the disulfide bond. The thiol functionality was highly versatile to bring simple and efficient chemical reactions to attain (i) Ag nanoparticle-adsorbed cellulose nanofibers by Ag ion reduction at surface, (ii) various amine (primary amine and quaternary amine) functionalized cellulose nanofibers by Michael addition, and (iii) complex polymer functionalized cellulose nanofibers by a radical-based thiol-ene reaction, under mild conditions, i.e. in any reaction media, at room temperature, and under ambient atmosphere, evidenced by a variety of characterization methods including a quantitative analysis with X-ray photoemission spectroscopy. These scalable thiol-based chemistries should offer a new generation of well-tailored cellulose nanofiber materials with complex inorganic, organic, and polymeric functionalities, potentially expanding to functionalized surfaces of other carbohydrate-based materials to achieve the desired properties.

Evaluation of different methods for extraction of nanocellulose from yerba mate residues

In this work, we evaluate the production of nanocellulose from yerba mate sticks (YMS) using soft chemical and steam explosion treatments. The nanocellulose is characterized by chemical characterization, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The main results showed that after the chemical treatment and steam explosion, the YMS fiber reached diameters of 11–15 nm and aspect ratios (L/D) of 12–24. The XRD results showed that there is an increase in the index of crystallinity of up to 35% when compared to raw YMS. We discover that it is possible to obtain cellulose nanofibers (CNF) from the YMS without the use of alkaline treatment, which reduces the generation of liquid waste. Thus, the production of CNF by means of acid hydrolysis, bleaching and steam explosion represents an alternative route.

Isolation and Characterization of Nanofibrillar Cellulose from Agave tequilana Weber Bagasse

The bagasse of Agave tequilana Weber is one of the most abundant agroindustrial wastes in the state of Jalisco. However, at the present time, there is no technical use for this waste, and its high availability makes it an environmental problem. The objective of this research was to take advantage of this waste and give it an added value to be used in the elaboration of advanced materials. In this sense, the agave bagasse cellulose was obtained using an organosolv method. To obtain the nanofibrils, the cellulose was passed through 6 cycles of a microfluidizer. The material was classified by FTIR, confirming the presence of the functional groups (O-H, C-H, C-C, and C-O-C), characteristics of cellulose, and the elimination of hemicellulose and lignin present in agave bagasse without treatment. The X-ray diffraction technique allowed the determination of the degree of crystallinity of the cellulose nanofibers, which was 68.5%, with a negative zeta potential of −42 mV. The images from the atomic force microscopy helped for the observation of the degree of fibrillation in the cellulose, and with the software ImageJ, the average diameter of the nanofibers was determined to be 75 ± 5 nm with a relatively uniform length of 1.0–1.2 μm. Finally, by means of thermogravimetric analysis, it was found that the obtained cellulose nanofibers (CNFs) supported high temperatures of thermal decomposition, so it was concluded that due to the diameter of the fibrils, the high resistance to pressure, and elasticity, the nanofibrils obtained in this investigation can be used in the elaboration of advanced materials.

Characterization of Nanocellulose Obtained from Cereus Forbesii (a South American cactus)

Crystalline cellulose nanofibers are obtained from the bark of Cereus Forbesii, a cactus native to the arid areas of South America. The obtaining of cellulose nanofibers was carried out in several steps: pretreatment of the raw material, elimination of hemicellulose and lignin to obtain cellulose, and an acid hydrolysis of cellulose to obtain crystalline cellulose nanofibers. The cellulose nanofibers obtained have a crystallinity index of 82% and a nanofiber diameter of 18 nm. An average crystallite size of 6 nm was calculated for the crystalline domains that form cellulose nanofibers. The high crystallinity of the obtained cellulose nanofibers makes the sample very homogeneous and decomposes in a relatively narrow temperature range (between 290°C and 375°C). The complete degradation of crystalline cellulose polymer chains takes place between 375°C and 600°C. The morphological and structural studies are carried out by scanning electron microscopy of field emission, infrared spectrometry with Fourier transform, and powder X-ray diffraction. The thermal stability of the samples is determined by thermogravimetric analysis.

Ball milling: a green technology for the preparation and functionalisation of nanocellulose derivatives.

Ball milling is a simple, fast, cost-effective green technology with enormous potential. One of the most interesting applications of this technology in the field of cellulose is the preparation and the chemical modification of cellulose nanocrystals and nanofibers. Although a number of studies have been reported in the literature, the potential of this technique in the field of cellulose nanoparticles has not been fully exploited. This minireview aims at putting existing work into perspective, highlighting the significance and the potential of this green, sustainable technique to facilitate the identification of areas of future development.

Production of cellulose nanofibers from Aspen and Bode chopsticks using a high temperature and high pressure steam treatment combined with milling

Holocellulose was generated from Aspen and Bode chopsticks by high temperature, high pressure steam treatment combined with milling. The steam treatment conditions were increased, the holocellulose component ratio in the treated sample as well as its molecular weight decreased. The treated holocellulose was subjected to grinder treatment to obtain cellulose nanofibers (CNF). Field-emission scanning electron micrographs indicated that CNF were successfully produced. The maximum tensile strength values of 86.9 and 109.9 MPa/(g/cm3) for Aspen and Bode, respectively, were obtained at a steam pressure of 15 atm and steaming time of 5 min. Furthermore, it was demonstrated that the optimal molecular weight of holocellulose to produce CNF with high tensile strength was around 1.2 × 105, while the optimal holocellulose recovery rate (HR; the degree of fibrillation was defined as HR in this study) was around 1.00.

(Invited) Transparent Electrode and Magnetic Permalloy Made from Novel2 Nanopaper

We report a novel partial dissolution strategy to liberate uniform cellulose nanofibers with diameter of 5-10 nm from macroscopic cellulose fibers and promote separation of nanofibers in an aqueous environment by forming water-soluble sodium carboxymethylcellulose (CMC) through heterogeneous sodium acetoxylation of cellulose. With the obtained cellulose nanofibers, we fabricated nanopapers which exhibit a high optical transparency of 90.5 % (550 nm) with promising mechanical properties and high thermal stability. By directly depositing Ag nanowires on a wet nanofiber sheet, we fabricated a flexible transparent electrode with 86.5 % (550 nm) transparency and 26.2 Ohm/sq sheet resistance (Rs). Meanwhile, we studied the magnetic properties of sputter deposited thin film of permalloy on nanopaper which exhibited a similar magnetic coercivity and a close saturation magnetization to conventional silicon dioxide-based permalloy.

Effect of Acid/Fiber Ratio on Physical Properties of Cellulose Nanofibers Extracted from Cassava Pulp

Cellulose nanofibers (CeNF) were extracted successfully from cassava pulp (CP) by submitting to alkali, bleaching and acid hydrolysis treatments. The raw CP was mercerized with NaOH solution and then followed by bleaching treatment using a solution made up of equal parts (v:v) of acetate buffer and aqueous chlorite. In order to obtain cellulose nanofibers, the acid hydrolysis treatment of bleached fibers was performed using a mixture of HCl/H2SO4 (1:2 v/v). In this acid treatment reaction, the effects of acid/fiber ratio (ml/g) on physical properties of obtained cellulose nanofibers were investigated. Nanofibers were morphologically characterized by transmission electron microscopy (TEM) revealing the nanofibers with diameter in the range of 12-24 nm and immeasurable length were obtained. An increase in crystallinity of fibers after treatments was revealed by X-ray diffraction (XRD). Due to the introduction of sulfate groups at the outer surfaces of fibers during the hydrolysis, thermal stability of nanofibers, characterized by thermogravimetric analysis (TGA), was lower than that of raw CP. The acid/fiber ratio of 150ml/2g was found to be a proper ratio for thermal stability of obtained nanofibers. The crystallinity of nanofibers increased with the increase of acid/fiber ratio.

Complete nanofibrillation of cellulose prepared by phosphorylation

In this work, we prepared phosphorylated pulp with a phosphorous content of 1.23 mmol/g by adding an aqueous solution of NH4H2PO4 and urea to softwood pulp sheets followed by drying and curing with hot air and obtained cellulose nanofibers (CNFs) with a uniform width of 3–4 nm in approximately 100% gravimetric yield by high-pressure homogenization of the phosphorylated pulp slurry. After phosphorylation, no significant decrease in the pulp recovery ratio was observed, and the viscosity-average degree of polymerization of phosphorylated pulp was almost equal to that of the original pulp. In addition, the crystal structure and crystallinity index were almost unchanged during phosphorylation. The obtained phosphorylated CNF dispersion was highly transparent, and the maximum total light transmittance was nearly 100% when the CNF content was 0.2 wt%. The maximum viscosity of the CNF dispersions was nearly 10–100 times greater than that of conventional thickeners. Furthermore, we found that not only insufficient but also excessive phosphorylation negatively affected the gravimetric yield, transparency and viscosity.

Thermoplastic Cassava Starch-PVA Composite Films with Cellulose Nanofibers from Oil Palm Empty Fruit Bunches as Reinforcement Agent

Thermoplastic starch-polyvinyl alcohol composite films were prepared by casting method with cellulose nanofibers as reinforcement agent and glycerol as plasticizer. The obtained cellulose nanofibers with a diameter of 27.23±8.21 nm were isolated from oil palm empty fruit bunches (OPEFBs) by mechanical treatment. The addition of cellulose nanofibers until 3 wt% increased tensile strength and crystallinity of the composite films. In contrast, it decreased their elongation at break and water vapor transmission rate. Meanwhile, the addition of glycerol increased elongation at break and water vapor transmission rate of film matrix but lowers tensile strength of composite films.