Production Of Cellulose Nanofibrils Research Articles

Nanofibrillated cellulose from Mahang gajah as thin film

Nanostructured cellulose has received tremendous attention due to its inherent unique properties. Being the most abundant organic polymer on earth, cellulose is the most suitable candidate for alternative replacement of petroleum-based products. Nanofibrillated cellulose (NFC) can be converted into thin films, aerogels and hydrogels. In particular, nanofibrillated cellulose suspension can form a neat and transparent thin film that has good film properties. Subsequently, this thin film can have numerous potential application areas such as in packaging, electronic etc. The objective of the study was to prepare nanofibrillated cellulose from local forest species namely Mahang gajah. After successful production of NFC, thin film was prepared from NFC and compared with commercial NFC. NFC was successfully produced from Mahang gajah possessing 19.7±17 nm width. Thin film produced from Mahang NFC showed comparable properties with commercial NFC such as thermal stability, porosity and wettability.

Combination of twin-screw extruder and homogenizer to produce high-quality nanofibrillated cellulose with low energy consumption

The commercialization of cellulose nanofibrils (CNF) is limited due to the high energy consumed during production. Twin-screw extrusion has recently been employed for the energy-efficient production of CNF with high solid content, but the method requires several passes. Cellulose nanofibrils have been produced by using both a twin-screw extruder and a homogenizer. Some combinations require a fewer number of passes thereby using less energy, while maintaining the desired CNF quality. The morphology and quality of CNF were characterized by optical microscopy, MorFi analysis, and with a recently developed quality index. The combination of one pass through the twin-screw extruder and two passes through the homogenizer decreases energy consumption by 45%. These CNF have a similar quality to CNF produced after five passes through the homogenizer alone.

Optimization of carboxymethylation reaction as a pretreatment for production of cellulose nanofibrils

We investigated the optimal reaction conditions for carboxymethylation as a pretreatment method for the production of cellulose nanofibrils (CNF). The influence of the reaction sequence, solvent composition, and presence of water in the reaction medium on the carboxymethylation of pulp was studied. We also investigated the effects of water in the reaction medium on CNF properties. The most effective carboxymethylation of pulp was achieved with non-solvent exchanged pulp and isopropanol. An increase in pulp consistency increased the carboxyl group content. The optimum reaction condition used only one-third the amounts of monochloroacetic acid and sodium hydroxide for the same level of carboxymethylation. The number of passes required for mechanical fibrillation of the pulp, the morphology and dispersion instability of CNF were all strongly influenced by the carboxyl content introduced during the carboxymethylation reaction. The number of mechanical treatment steps required to produce CNF decreased as the carboxyl content increased. Pulp with a high carboxyl content resulted in a more stable suspension due to the increased electrostatic repulsion between the fibrils.

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-1β 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.

Advances in cellulose nanomaterials

Research on nanocellulose has significantly increased over the past few decades, owing to the various attractive characteristics of this material, such as renewability, widespread availability, low density, excellent mechanical properties, economic value, biocompatibility, and biodegradability. Nanocellulose categorized into two main types, namely cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs). In this review, we present the recent advances made in the production of CNFs and CNCs. In addition to the conventional mechanical and chemical treatments used to prepare CNFs and CNCs, respectively, other promising techniques as well as pretreatment processes have been also proposed in recent times, in an effort to design an economically efficient and eco-friendly production route for nanocellulose. Further, while the hydrophilic nature of nanocellulose limits its use in polymeric matrices and in some industrial applications, the large number of hydroxyl groups on the surface of nanocellulose provides a suitable platform for various kinds of modification treatments. The various chemical and physical surface treatment procedures reported for nanocellulose have been reviewed in this paper. Finally, in this review, we summarize the life cycle assessment studies conducted so far on nanocellulose, which quantify the environmental impact of nanocellulose products. The current paper is a comprehensive review of the recent literature on nanostructured cellulose.

Production and Characterization of Cellulose Nanofibrils from Different Chemical and Mechanical Pulps

In this study, mechanical fibrillation for the production of cellulose nanofibrils (CNF) from chemical and mechanical pulps with different chemical compositions was studied. To investigate the effect of nanofibrillation on wood pulps by the grinder, the nanofibrils obtained from grinded pulp were characterized with morphology, particle size distribution, apparent viscosity in aqueous solution, degree of crystallinity, and water retention capacity. The results showed that the low lignin-containing unbleached kraft pulp (UKP) exhibited good performance for fibrillation, resulting in CNF with high viscosity, high water retention value, and small particle size. However, the fibrillation of high lignin-containing chemi-thermomechanical pulp was the most inefficient which resulted in heterogeneous materials with relatively low viscosity, low water retention value, and large particle size compared to chemical pulps. Furthermore, bleached softwood pulp from radiata pine was found to be much faster and for easier fibrillation compared to the bleached hardwood pulp from acacia due to the more rigid structure of hardwood fibers.

Pulping and Pretreatment Affect the Characteristics of Bagasse Inks for Three-dimensional Printing

Bagasse is an underutilized agro-industrial residue with great potential as raw material for the production of cellulose nanofibrils (CNF) for a range of applications. In this study, we have assessed the suitability of bagasse for production of CNF for three-dimensional (3D) printing. First, pulp fibers were obtained from the bagasse raw material using two fractionation methods, i.e. soda and hydrothermal treatment combined with soda. Second, the pulp fibers were pretreated by TEMPO-mediated oxidation using two levels of oxidation for comparison purposes. Finally, the CNF were characterized in detail and assessed as inks for 3D printing. The results show that CNF produced from fibers obtained by hydrothermal and soda pulping were less nanofibrillated than the corresponding material produced by soda pulping. However, the CNF sample obtained from soda pulp was cytotoxic, apparently due to a larger content of silica particles. All the CNF materials were 3D printable. We conclude that the noncytotoxic CNF pro...

Aqueous morpholine pre-treatment in cellulose nanofibril (CNF) production: comparison with carboxymethylation and TEMPO oxidisation pre-treatment methods

In this study, pulped cellulose fibres were pre-treated with aqueous morpholine prior to mechanical disruption in the production of cellulose nanofibrils (CNF). The properties of the morpholine pre-treated CNF (MCNF) were closely compared with CNF obtained from carboxymethylation (CMCNF) and TEMPO-oxidation (TCNF) pre-treatment methods. An investigation of the swelling behaviours of cellulose in varying concentrations of morpholine revealed that there is a synergistic behaviour between morpholine and water in its ability to swell cellulose. As a result, cellulose pulp dispersed in 1:1 mole ratio of morpholine to water was well swollen and readily fibrillated by mechanical shear. Surface chemistry analyses indicated that the surface of the MCNF remained unmodified, compared to the CMCNF and TCNF which were modified with anionic groups. This resulted in only a slight decrease in crystallinity index and a minimal effect on the thermal stability of MCNF, compared to CMCNF and TCNF which showed marked decreases in crystallinity indices and thermal stabilities. The average widths of MCNF, CMCNF and TCNF, as measured from electron microscopic images, were broadly similar. The higher polydispersity of MCNF widths however led to a differential sedimentation and subsequent lower aspect ratio in comparison with CMCNF and TCNF as estimated using the sedimentation approach. Also, the presence of electrostatic repulsive forces, physical interactions/entanglements and lower rigidity threshold of the CMCNF and TCNF resulted in higher storage moduli compared to the MCNF, whose elasticity is controlled by physical interactions and entanglements. Aqueous morpholine pre-treatment can potentially be regarded as an ecologically sustainable process for unmodified CNF production, since the chemical reagent is not consumed and can be recovered and reused.

A new method to produce cellulose nanofibrils from microalgae and the measurement of their mechanical strength

Despite the enormous potential of cellulose nanofibrils (CNFs) as a reinforcing filler in various fields, the use of them has been limited by high-energy mechanical treatments that require a lot of energy and time consumption. To reduce the demands of energy and time required for mechanical treatments, microalgae, in particular, Nannochloropsis oceanica, which has small size, rapid growth rate, and high productivity was used as a CNFs source. This study obtains the CNFs by lipid/protein extraction, purification, and TEMPO-mediated oxidation processes under gentle mixing without high-energy mechanical treatments. Furthermore, to evaluate the applicability of microalgal CNFs as a reinforcing filler, this study estimated the mechanical strength of the fibrils by the sonication-induced scission method. To achieve a precise estimation, an effective method to distinguish straight fibrils from buckled fibrils was also developed, and subsequently, only straight fibrils were used to calculate the mechanical strength in the sonication-induced scission method. Consequently, the tensile strength of the N. oceanica CNFs is around 3–4GPa on average which is comparable with the mechanical strength of general reinforcing fillers and even higher than that of wood CNFs. Thus, this study has shown that the newly proposed simplified method using N. oceanica is very successful in producing CNFs with great mechanical strength which could be used in various reinforcement fields.

Cellulose nanofibrils (CNFs) from Ammophila arenaria, a natural and a fast growing grass plant

The production of cellulose nanofibrils (CNFs) with a high yield from Ammophila arenariahas been explored and the ensuing CNFs were characterized in terms of morphology, crystallinity and rheological properties. Ammophila arenaria (marram grass) is a perennial grass plant with high tolerance to drought, which is growing naturally in nutritionally poor sand with low organic matter. Fibers were extracted from the plant by conventional alkaline pulping and bleaching with a yield around 50% based on the dry weight of the plant. A TEMPO-mediated oxidation and a cationization with glycidyltrimethylammonium chloride were performed as a pretreament to facilitate the fibrillation process and produced stable CNF suspension with high yield and controlled surface charge. High pressure homogenization was used for the mechanical disintegration of the pretreated fibers and nanosized CNFs with width around 5–8nm were produced with a yield exceeding 80%.

Improved thermal stability of cellulose nanofibrils using low-concentration alkaline pretreatment

The thermal stability of cellulose nanofibrils (CNFs) can be improved by converting cellulose crystalline structure to cellulose II using an alkaline treatment method. The conventional method requires around 20wt.% NaOH solutions and causes the cellulose interdigitation and aggregation, making CNFs production difficult. The objective of this study is to develop a new pretreatment method using a low-concentration alkaline solution to produce well-dispersed CNFs with improved thermal stability. CNFs with 90nm diameter were successfully prepared by treating cellulose powder with 2wt.% NaOH solution below 0°C, followed by homogenization through a French pressure cell press. The CNFs had relatively high thermal stability with the mean onset and maximum thermal decomposition temperature of 305°C and 343°C, respectively, compared with the CNFs prepared without the NaOH pretreatment (283°C and 310°C). The increased thermal stability can create new opportunities for the development of CNF-based bio-composites and electronics.

Impact of nanofibrillation degree of eucalyptus and Amazonian hardwood sawdust on physical properties of cellulose nanofibril films

The production of cellulose nanofibrils (CNFs) from Amazonian wood wastes could reduce pollution and raw material costs for cellulose industry. Further studies are required to analyze the feasibility of using hardwood sawdust for the production of high-quality CNF films. Therefore, the objective of this study was to evaluate the impact of various nanofibrillation degrees of waste sawdust generated from the primary processing of different hardwood species on the physical properties of CNF films. Raw sawdust was submitted to alkaline and bleaching pre-treatments. The chemical composition of the bleached fibers was determined. The CNFs were obtained by mechanical shearing of the bleached fibers using a grinder Super MassColloider after 10, 20, 30 and 40 passages. CNFs were evaluated by transmission electron microscopy. The CNF films were formed by the casting method. Residual lignin and hemicelluloses content greatly varied among species after bleaching. No clear influence of the number of passages on apparent density was observed. None of the films was degraded in significant amounts after water immersion. Water vapor absorption (WVA) consistently decreased with more passages through the Super MassColloider for Amazonian species until 30 passages. Residual hemicelluloses of the bleached fibers adversely affected WVA. Bleached fibers made of highly purified cellulose or containing residual lignin showed lower WVA after 30 and 40 passages. Water vapor permeability showed consistent relation with the apparent density of the films. For hardwood wastes, 10–30 passages through the grinder are recommended.

Mechanical pretreatment of cellulose pulp to produce cellulose nanofibrils using a dry grinding method

Cellulose nanofibrils (CNFs) are typically produced via wet milling pretreatment method to facilitate efficient disintegration of cellulose fibers by pre-fibrillation and fiber size reduction. However, the use of high energy and presence of water during wet milling methods leads to the increase in overall energy consumption during CNFs production and pose challenges during storage and handling. The objective of this study is to investigate the dry grinding of cellulose fluff pulp using the shear cutting method to determine the specific energy required to produce cellulose precursors and their characteristics for manufacturing CNFs. The specific energy required to grind cellulose fluff pulp with a screen size of 0.25mm in three cycles was measured. The ground sample received after each cycle was sampled to characterize its properties and its potential to produce CNF hydrogels. As the number of grinding cycles increased, the specific energy required per cycle decreased with an overall net energy consumption of 894kWh/Mg for three grinding cycles. The cellulose powder from the third grinding cycle was successfully disintegrated into cellulose nanofibrils with an average diameter of 119nm without any fiber clogging. In conclusion, the three-cycle shear cutting process was sufficient to produce dry cellulose precursors for CNFs production, while reducing the overall energy consumption and handling and storage problems.

Cellulose Nanofibrils from Nonderivatizing Urea-Based Deep Eutectic Solvent Pretreatments.

Deep eutectic solvents (DESs) are a fairly new class of green solvents applied in various fields. This study investigates urea-based DES systems as novel pretreatments for cellulose nanofibril production. In the experiments, deep eutectic systems having urea and ammonium thiocyanate or guanidine hydrochloride as a second component were formed at 100 °C and then applied to disintegrate wood-derived cellulose fibers. The DES-pretreated fibers were nanofibrillated into three different levels of mechanical treatments with a microfluidizer, and their properties were analyzed. Moreover, nanofibril films were fabricated by solvent casting method. Both DES systems were able to loosen and swell the cellulose fiber structure as indicated by the increase in the lateral dimension of the fibers. Nonpretreated birch cellulose fibers had difficulties in mechanical nanofibrillation as clogging of the chamber occurred often. However, cellulose nanofibrils with widths ranging from 13.0 to 19.3 nm were successfully fabricated from DES-pretreated fibers with both systems. Translucent nanofibril films generated from DES-pretreated cellulose nanofibrils had good thermal stability and mechanical properties, with tensile strengths of approximately 135-189 MPa and elastic modulus of 6.4-7.7 GPa. Consequently, both urea-based DESs showed a high potential as environmentally friendly solvents in the manufacture of cellulose nanofibrils.

On the nanofibrillation of corn husks and oat hulls fibres

Cellulose nanofibrils (CNF) were isolated from agro-industrial waste (corn husks and oat hulls) and market kraft pulp fibres, and a detailed comparative study was performed. Initially, the raw materials were subjected to a conventional pulping process to remove lignin and hemicelluloses. The chemical pre-treatment was based on 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidation and the mechanical treatment was carried out with a high-pressure homogenizer. An extensive characterization of the raw material and of the nanofibrillated celluloses was performed, considering structural and chemical aspects. CNF films were produced for their characterization by optical methods, laser profilometry (LP), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Considering the same pulping and chemical pre-treatment, the analyses indicated that the oxidized corn husks fibres had higher carboxylate content and thus a larger tendency to nanofibrillate compared to the oat hulls fibres. The obtained content of carboxylic acids was directly proportional to the content of cellulose in the assessed samples, confirming the selectivity of the TEMPO-mediated oxidation. The fibrillated corn husks material had a minor fraction of residual fibres (<4%) and homogeneous nanofibril width distribution (<20nm), which is a major achievement. The homogeneous CNF morphology was confirmed by AFM analysis. Hence, this study demonstrates that the assessed agro-industrial wastes are sustainable resources for production of CNF, which may have a wide range of value-added applications.

Understanding Longitudinal Wood Fiber Ultra-structure for Producing Cellulose Nanofibrils Using Disk Milling with Diluted Acid Prehydrolysis.

Here we used dilute oxalic acid to pretreat a kraft bleached Eucalyptus pulp (BEP) fibers to facilitate mechanical fibrillation in producing cellulose nanofibrils using disk milling with substantial mechanical energy savings. We successfully applied a reaction kinetics based combined hydrolysis factor (CHFX) as a severity factor to quantitatively control xylan dissolution and BEP fibril deploymerization. More importantly, we were able to accurately predict the degree of polymerization (DP) of disk-milled fibrils using CHFX and milling time or milling energy consumption. Experimentally determined ratio of fibril DP and number mean fibril height (diameter d), DP/d, an aspect ratio measurer, were independent of the processing conditions. Therefore, we hypothesize that cellulose have a longitudinal hierarchical structure as in the lateral direction. Acid hydrolysis and milling did not substantially cut the “natural” chain length of cellulose fibrils. This cellulose longitudinal hierarchical model provides support for using weak acid hydrolysis in the production of cellulose nanofibrils with substantially reduced energy input without negatively affecting fibril mechanical strength.

Enzyme-assisted Mechanical Fibrillation of Bleached Spruce Kraft Pulp for Producing Well-dispersed and Uniform-sized Cellulose Nanofibrils

Cellulose nanofibrils, as a bionanomaterial with many promising properties, have great potential in composite applications. Herein, well-dispersed and uniform-sized cellulose nanofibrils (CNF) was successfully obtained from commercial bleached softwood kraft pulp, with yields of 79.15% via enzyme-assisted hydrolysis and a subsequent homogenization process. Field emission scanning electron microscope (FE-SEM) confirmed the fiber morphology. Water retention value (WRV) was increased from 107.32% of original pulp to 1383.92% of the resulting CNFs, while crystallinity had no significant changes. Fourier transform infrared (FTIR) spectroscopy indicated the addition of enzyme resulted in the removal of hemicelluloses and lignin. CNFs subjected to enzymatic treatment and homogenization had less entangled network, larger aspect ratio and higher transmittance than those from pure mechanical treatment. They exhibited well-dispersed in aqueous solution and uniform-sized in morphology. These advantages revealed enzyme-assisted process had a remarkable effect on the production of CNFs and made CNFs attractive for nanotechnology and nanomaterial.

Evaluation of Electron Beam Irradiation as New Pretreatment for Cellulose Nanofibril Production

Many studies have reported that cellulose nanofibrils (CNFs) show high potential for use in many industries, but this material has been considered too costly for commercialization. An effective treatment is therefore needed to reduce the production costs of CNFs. This study describes the use of electron beam irradiation as a new pretreatment for the manufacture of CNFs and the effectiveness of electron beam irradiation in the refining process, which is a part of CNF production. Bleached kraft pulps were irradiated by an electron beam and subsequently refined, followed by measurement of the freeness and fiber properties. The strengths of treated pulps were identified by preparing handsheets and analyzing their strengths. Increases in the irradiation dose of the electron beam and in the beating time decreased the freeness and fiber length of the pulps. The images acquired with an optical microscope demonstrated fibrillation of pulps. The handsheets made from the pulps irradiated by the electron beam and beaten showed lower strengths because of the reduction in the degree of polymerization and crystallinity. Therefore, electron beam irradiation is concluded to reduce the amount of electric energy needed in the manufacturing process of CNFs, but the irradiation dose of electron beam must be controlled to avoid severe deterioration of the fiber strength.

Easy production of cellulose nanofibrils from corn stalk by a conventional high speed blender

Agricultural crop residues are an abundant and cheap source of cellulose fibers suitable for uses in composite, textile, pulp and paper manufacture. Besides, field crop fibers might be an attractive source for the production of value-added nanosized cellulose fibrils with a broad potential use. In this study, nanofibrillated cellulose (NFC) from corn stalk crop residues were produced with high yields using a simple high speed blender (HSB). It was shown that a full conversion of cellulose fibers into NFC was successfully achieved by disintegration during 30min of fibers produced via a NaClO2/acetic acid delignification mode and submitted to a TEMPO-mediated oxidation pre-treatment. The fibrillation yield, transparency degree, colloidal properties and morphological characteristics of the ensuing NFC were analyzed and compared according to the delignification mode and the carboxyl content. The reinforcing potential of the NFC produced with different carboxyl contents was investigated.

Influence of combined mechanical treatments on the morphology and structure of cellulose nanofibrils: Thermal and mechanical properties of the resulting films

The deconstruction of the hierarchical structure of cellulose results in the production of cellulose nanofibrils (CNFs). CNFs are commonly obtained by grinding and high-pressure homogenization processes and both treatments can be simultaneously used. Nevertheless, the influence of a two-stage high pressure homogenization of previously ground CNFs on the nanofibril diameter and the physical, thermal and mechanical properties of the resulting films has not been reported. The present study aims at understanding the changes exerted in cellulose after grinding and subsequent passing through the first and second stage of a high-pressure homogenizer. The films prepared from the resulting CNFs were analyzed by electron microscopy, infrared spectroscopy, X-ray diffraction, viscometry, thermal degradation and tensile tests. The data indicate that the initial grinding treatment prompted the most remarkable changes, resulting in enhanced mechanical properties of the films, while decreasing its thermal stability, intrinsic viscosity and crystallinity. Further fibrillation in a high-pressure homogenizer did not have a significant effect, except a decrease in thermal stability and intrinsic viscosity.