Production Of Cellulose Nanofibrils Research Articles

Optimization of Cellulose Nanofibril Production under Enzymatic Pretreatment and Evaluation of Dislocations in Plant Fibers

Dislocations are weak and discontinuous areas of plant cell walls. This study aims to evaluate the cellulase-mediated enzymatic pretreatment as a mechanical-chemical initiator of dislocations in unbleached and bleached fibers of commercial Eucalyptus kraft pulp, comparing both before and after the formation of micro/nanofibers in the mechanical process, in addition to evaluating the dislocations themselves. Four enzyme complexes were evaluated, of which three were endoglucanase (A, B and C) and one was a mixture of endoglucanase and exoglucanase (D), in addition to a control pretreatment. During the mechanical treatment of the fibers pretreated with enzyme B, samples were collected at pass/cycles 0, 5, 10, 15, 20, 25 and 30 in the mechanical fibrillator. The dislocations were evaluated using a polarized light microscope to analyze the index of dislocations (ID), dislocation angle and curvature index, while the crystallinity was analyzed by Raman spectroscopy. For bleached fibers, a reduction in the ID occurred with enzyme C and an increase with enzyme B, while for unbleached fibers, the ID did not change significantly. During the mechanical treatment, the enzyme did not cause a reduction in the fiber length (FL) but allowed a significant increase in the ID up to 20 passages for all pretreated fibers, with and without enzymes. The dislocation angle decreased with the enzymatic action and with the curvature index. The results show that the enzymatic pretreatment can affect the integrity of the fibers, increasing the number of dislocations and amorphous regions and decreasing the length of the cellulose chain.

Effect of the chemical and structural characteristics of pulps of Eucalyptus and Pinus on the deconstruction of the cell wall during the production of cellulose nanofibrils

The species Eucalyptus globulus, Eucalyptus nitens and Pinus radiata, are important supplies for the production of cellulose pulp in the world market, which can be used for the production of cellulose nanofibrils (CNFs). Understanding how the characteristics of different raw materials affect the production and final properties of nanofibrillated celluloses is very useful, both for the pulp industry and for the end user. The aim of this research was to determine how the chemical and structural differences of the commercial Kraft pulps of E. globulus, E. nitens and P. radiata affect the production and the morphological and rheological characteristics of the CNFs produced through an enzymatic-mechanical process. On one hand, the results showed that pine fibers were easier to deconstruct than eucalyptus fibers, however, pine CNFs were found to have the largest fibril width and a lower aspect ratio (length /width). On the other hand, the pulp of E. globulus, was the one that obtained a better aspect ratio and higher intrinsic viscosity.

Isolation and Characterization of Cellulose Nanofibrils from Banana Pseudostem, Oil Palm Trunk, and Kenaf Bast Fibers Using Chemicals and High-intensity Ultrasonication

ABSTRACT The adoption of high-intensity ultrasonication in the isolation process of cellulose nanofibrils (CNF) as an economical, timesaving, and environmental-friendly process has been explored. Three types of raw organic fibers, i.e., banana pseudostem, oil palm trunk, and kenaf bast were analyzed for the production of CNF using the process mentioned earlier. Before the raw organic fibers were subjected to a high-intensity ultrasonication process, it underwent an alkaline treatment to eliminate the non-cellulosic compounds. Field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) micrographs confirmed the presence of nanofibrils in all three different types of CNF. The frequency, amplitude, and duration of ultrasonication used in this study were sufficient to produce CNF. Fourier-transform infrared spectroscopy (FTIR) results indicated that the chemical treatment employed in this paper was effective in removing the compounds, especially lignin and hemicellulose. The increase in crystallinity, which is one of the advantages of CNF, was observed from the X-ray diffraction (XRD) results. Hence, it can be deduced that high-intensity ultrasonication could simplify the complex process of CNF isolation compared to the conventional method, widening the utilization and source of CNF in the industry.

Facile Extraction of Cellulose Nanofibrils (Cnfs) from Wood Using Acidic Ionic Liquid-catalyzed Organosolv Pretreatment Followed by Ultrasonic Processing

ABSTRACT Cellulose nanofibrils (CNFs) were successfully extracted from wood flour via atwo-step process involving acidic ionic liquid-catalyzed organosolv pretreatment and ultrasonic disintegration. Acomprehensive study was performed on the yield, morphology, crystallinity, chemical structure, and thermal stability of CNFs, as well as the mechanical properties and transparency of nanofilms. The results showed that 87.06% of the total lignin and 93.78% of hemicellulose were fractionated from lignocellulose after solvothermal pretreatment using 1, 4-butylene glycol. The isolated CNF maintained the type Icrystal lattice of native cellulose. Overall, the CNFs obtained after ultrasonication displayed asimilar morphology and crystallinity, but they had ahigher yield (41.82%), better thermal stability, and film-forming properties than those produced by concentrated acid hydrolysis. Solvothermal treatment using 1,4-butylene glycol alcohol/water followed by ultrasonication is an ideal alternative CNF production method with alow environmental impact.

Single-Step Fiber Pretreatment with Monocomponent Endoglucanase: Defibrillation Energy and Cellulose Nanofibril Quality

The combination of enzymatic pretreatment of cellulose fibers followed by mechanical defibrillation has become a green and low-energy route to obtain cellulose nanofibrils (CNF). However, the variability in the properties of the as-produced CNF remains a major challenge that needs to be addressed for any application to be realized. Herein, we study the effect of monocomponent endoglucanase (EG) on the energy consumed in defibrillation as well as the physical properties of the obtained CNF. This single-step enzymatic pretreatment (0.5–25 EGU/g cellulose fibers for 1–3 h) reduces the defibrillation energy (by up to 50%) at nearly 100% yield to obtain CNF of a similar morphology, size, and crystallinity compared to CNF obtained in the absence of pretreatment. Under mild conditions (5.6 EGU/g for 1 h), aiming to minimize energy consumption while preserving rheological properties, EG pretreatment increased the water retention value, reduced the molecular weight, and promoted structural surface modification (amorphogenesis), without significant cellulose solubilization. In addition, the carbohydrate binding module of the EG was found to improve the interaction of the catalytic core with the substrate. The combination of the factors considered here boosts the effect of the enzyme even if used at low loadings, facilitating high-yield, more sustainable production of CNF.

Production of cellulose nanofibrils and films from elephant grass using deep eutectic solvents and a solid acid catalyst.

A new strategy was developed to produce cellulose nanofibrils (CNFs) and films from raw elephant grass using deep eutectic solvents and a recyclable spent coffee-derived solid acid (SC-SO3H) catalyst with assistance of ultrasonic disintegration and a suction filtration film forming method. The effects of a solid acid and reused solid acid were comprehensively studied by comparing with catalyst-free conditions and using sulfuric acid as the catalyst. The CNF fibers obtained from this novel SC-SO3H catalyst method showed the longest fiber length. The corresponding films achieved the strongest tensile strength of 79.8 MPa and the elongation at break of 13.6%, and best thermostability. In addition, the performance of CNFs and films prepared by the fourth recovered SC-SO3H-4 catalyst was close to that obtained with the first use. The SC-SO3H could be reused by a simple decantation method, meaning this novel method has the potential for green and sustainable preparation of CNFs and films.

Extraction of Cellulose Nanofibrils with Ultraviolet Blocking from Agro-industrial Wastes: A Comparative Study

Cellulose nanofibrils (CNFs) were successfully isolated from agro-industrial waste (cornstalk, corn flesh, and corncob) by subjecting the raw materials to organosolv and peroxide treatment, followed by ultrasonication. A detailed comparative study was performed. Characterization results showed that the CNFs from cornstalk (CS) exhibited higher yield and lignin content (20.81%), compared with CNFs from corn flesh (CF) and corncob (CC). The CNFs from CF and CC exhibited similar morphology, particle size, crystallinity, and thermal stability but showed improved ultraviolet blocking ability and optical transparency relative to those of CS. The CNFs from CF showed higher dispersion stability and mechanical properties than those from CS and CC. Peroxide treatment negatively influenced crystallinity and thermal stability, but exerted no apparent effect on optical transparency and mechanical strength. Thus, this study demonstrates that agro-industrial wastes are sustainable resources for CNF production, which can potentially have a wide range of value-added applications. Ionic liquid-aided solvothermal treatment followed by ultrasonication is a facile and ideal method to produce CNFs with ultraviolet blocking ability.

Direct observation of endoglucanase fibrillation and rapid thickness identification of cellulose nanoplatelets using constructive interference

Better understanding through direct observation of the mechanisms involved in chemical and enzymatic hydrolysis of biomass is of great importance, to implement a substitute for the common cellulose standards. We report the hydrolysis of biomass, using exclusively the parenchyma, to isolate cellulose nanoplatelets using a less harsh pretreatment. Then, we show direct evidence of the effect of endoglucanase on the structure of cellulose nanoplatelets, finding that amorphous cellulose is exclusively digested, loosening the cellulose nanofibrils in the process. The analysis of micrographs demonstrates that when cellulose nanoplatelets are deposited on a silicon wafer, its thickness can be qualitatively measured by the interference color detected using an optical microscope. This finding facilitates further studies of mechanisms involved in lignin removal and cellulose nanofibrils production by specific enzymatic digestion.

From Cellulose to Cellulose Nanofibrils-A Comprehensive Review of the Preparation and Modification of Cellulose Nanofibrils.

This review summarizes the preparation methods of cellulose nanofibrils (CNFs) and the progress in the research pertaining to their surface modification. Moreover, the preparation and surface modification of nanocellulose were comprehensively introduced based on the existing literature. The review focuses on the mechanical treatment of cellulose, the surface modification of fibrillated fibers during pretreatment, the surface modification of nanocellulose and the modification of CNFs and their functional application. In the past five years, research on cellulose nanofibrils has progressed with developments in nanomaterials research technology. The number of papers on nanocellulose alone has increased by six times. However, owing to its high energy consumption, high cost and challenging industrial production, the applications of nanocellulose remain limited. In addition, although nanofibrils exhibit strong biocompatibility and barrier and mechanical properties, their high hydrophilicity limits their practical application. Current research on cellulose nanofibrils has mainly focused on the industrial production of CNFs, their pretreatment and functional modification and their compatibility with other biomass materials. In the future, with the rapid development of modern science and technology, the demand for biodegradable biomass materials will continue to increase. Furthermore, research on bio-based nanomaterials is expected to advance in the direction of functionalization and popularization.

Alkaline treatment combined with enzymatic hydrolysis for efficient cellulose nanofibrils production

Cellulose nanofibrils were efficiently produced from eucalyptus fibers using a combined NaOH and enzymatic treatment followed by a pilot scale grinding process. The structural changes of fibers were assessed after NaOH treatments at 5, 10 and 15 wt% concentrations. A progressive shift from a cellulose I to a cellulose II crystalline structure was observed with X-ray diffraction (XRD) and nuclear magnetic resonance (NMR). The further enzymatic hydrolysis was improved for the NaOH treated samples. The increase of crystallinity indices due to enzymatic hydrolysis was of + 4.7 %, + 3.5 %, and +10.3 % for samples treated with NaOH 5, 10 and 15 wt% respectively, and DP values were drastically reduced to 340, 190 and 166 respectively. A morphological analysis underlined an optimum with the combination of NaOH 10 wt% and enzymatic hydrolysis. This treatment followed by the grinding process resulted in CNF with a rigid structure, with diameters ranging from 10 to 20 nm and lengths between 150 and 350 nm. A multi-scale analysis enabled to study the impact of this combined treatment on CNF properties and energy consumption. A decrease in mechanical properties of nanopapers was observed for the combined treatment and NaOH treatment alone compared to enzymatic hydrolysis alone, with Young’s modulus of 8.94, 4.84 and 11.21 GPa respectively. However, optical properties were improved, with transmittance values of 42.2, 15.4 and 7.1 % respectively. This new pretreatment can therefore lead to CNF with tunable properties depending on the application, with possible industrialization thanks to the reduction of energy needs.

Effects of Phosphorylation Duration on the Jute Extracted Cellulose Nanofibrils Using Ultra‐sonication

AbstractThe pretreatment process for the extraction of cellulose nanofibrils (CNFs) has been attracting the awareness of researchers. However, toxicity, complicated multistep procedures, and the use of costly chemicals are still some problems for chemical modification of cellulose fibers during the CNFs production. In this work, the phosphorylation reaction is introduced to pretreat jute fibers to extract CNFs with tiny diameter, and then the physicochemical properties of the obtained CNFs are analyzed. Experimental results exhibit that the phosphorylation process can affect the overall defibrillation process and the structure as well as properties of the involved products. This study also reports that the phosphorylation efficiency can be influenced by the existence of water, absence of urea, high temperature, and reaction duration. Even at a low degree of substitution, the phosphorylated CNFs exhibit better thermal stability and higher residual char compared to raw jute at 700 °C.

Direct pretreatment of raw ramie fibers using an acidic deep eutectic solvent to produce cellulose nanofibrils in high purity

Due to biomass recalcitrance, the pulping and bleaching processes are usually needed to break down the resistance of the lignocellulosic matrix for nanocellulose extraction. In this study, an acidic deep eutectic solvent (DES) based on choline chloride-oxalic acid dihydrate was used to directly pretreat raw ramie fibers (RFs) without further bleaching/purification steps for producing cellulose nanomaterials. Raw RFs, DES pretreated RFs, and degummed RFs were comparatively studied as starting materials for the preparation of cellulose nanofibrils (CNFs) by ball milling. There was no significant difference between CNF samples prepared from the DES pretreated RFs after 6 h of ball milling and those from the degummed RFs after 12 h of ball milling. After 4 h DES pretreatment at 100 °C, the obtained CNFs had a high purity of glucan up to 90.31% and an average width of 14.29 nm. They also showed high crystallinity (79.17%) and high thermal stability (> 316.7 °C). The tensile strength and elastic modulus for the CNF films were 98.071 MPa and 2.749 GPa, respectively. Overall, with the choline chloride-oxalic acid dihydrate DES pretreatment, no additional pulping/bleaching processes were required for the preparation of nanocellulose from raw cellulosic fibers while the properties of the as-prepared nanocellulose were preserved.

Study of LCNF and CNF from pine and eucalyptus pulps

AbstractNanocelluloses produced from wood pulp are widely studied for various economic applications. Most studies of cellulose nanofibrils (CNF) use lignin-free fibres obtained from bleached pulps; however, unbleached fibres with residual lignin may also be used to obtain lignocelluloses nanofibrils (LCNF). Research on lignocellulose nanofibrils is a recent subject in the field; thus, the aim of the present study was to determine the ultrastructure of lignocellulose nanofibrils compared to cellulose nanofibrils produced from the same raw material. Understanding of nanoparticle properties is of great relevance for their various applications; therefore, complete characterisation of the chemical, physical, and morphological structures of LCNF and CNF produced from pine and eucalyptus woods was performed. Unbleached cellulosic fibres are a viable alternative for LCNF production, which has properties comparable to that of traditional CNF production that uses lignin-free fibres. LCNF from pine and eucalyptus were obtained with 4.0 % and 1.8 % residual lignin, respectively. The nanofibrils had high thermal stability because LCNF had a higher maximum degradation temperature. Due to the low interaction of lignin with water, LCNF had a lower water retention value than CNF.

Nanocomposite membranes with high-charge and size-screened phosphorylated nanocellulose fibrils for CO2 separation

In this study, cellulose nanofibrils (CNF) of high charge (H-P-CNF) and screened size (H-P-CNF-S) were fabricated by increasing the charge of phosphorylated cellulose nanofibrils (P-CNFs) during the pre-treatment step of CNF production. Results show that the H-P-CNF have a significantly higher charge (3.41 mmol g−1) compared with P-CNF (1.86 mmol g−1). Centrifugation of H-P-CNF gave a supernatant with higher charge (5.4 mmol g−1) and a reduced size (H-P-CNF-S). These tailored nanocelluloses were added to polyvinyl alcohol (PVA) solutions and the suspensions were successfully coated on porous polysulfone (PSf) supports to produce thin-film nanocomposite membranes. The humid mixed gas permeation tests show that CO2 permeability increases for membranes with the addition of H-P-CNF-S by 52% and 160%, compared with the P-CNF/PVA membrane and neat PVA membrane, respectively.

Preparation and characterization of nanofibrillated cellulose from waste sugarcane bagasse by mechanical force

The effect of different mechanical force application methods was investigated relative to the structure and properties of nanofibrillated cellulose (NFC) from sugarcane bagasse. The NFC was prepared by grinding, high pressure homogenization, and ultrasonication with chemical pretreatment. Fiber morphology, crystalline, chemical structures, and tensile property were analyzed to reveal the mechanisms of NFC production behind different mechanical treatments. The results showed that compared with grinding treatment, high pressure homogenization and ultrasonic treatment can obviously increase the aspect ratio and size uniformity of NFC. Ultrasonic treatment gave the best results. The combination of grinding, high pressure homogenization, and ultrasonic treatment resulted in NFC with the average diameter of 23.18 nm. With the shearing action of grinding, high pressure homogenization, and ultrasonic treatment, the mechanical properties, crystallinity and thermal stability of NFC were gradually enhanced. This results demonstrated that a very low-value agricultural waste product can be easily converted to a high performance nanocomposite with tensile strength of 153.6 MPa and strain at break of 8.83%.

Modification of cellulose degree of polymerization by superheated steam treatment for versatile properties of cellulose nanofibril film

Cellulose from oil palm empty fruit bunch (OPEFB) was subjected to superheated steam (SHS) treatment at 150 °C for 1 and 2 h to produce cellulose with different degree of polymerization (DP). The treated OPEFB cellulose was subjected to a wet disc milling process to produce cellulose nanofibrils (CNFs), followed by nanocellulose film production using casting-evaporation technique. Reduction of DP by 23 and 40% were recorded after SHS treatment of OPEFB cellulose for 1 h (SHS1) and 2 h (SHS2), respectively, as compared to the untreated OPEFB cellulose. CNFs produced from treated cellulose (CNF-SHS1 and CNF-SHS2) exhibited smaller diameter and were less entangled compared to CNF from untreated cellulose (CNF-UT). These contributed to smoother CNF-SHS films. The highest light transmittance was recorded for CNF-SHS2 film, followed by CNF-SHS1 and CNF-UT films. The increment in transmittance value is in accordance with the reduction in cellulose DP. Lower DP also caused CNF-SHS films to have less wetting property as a result of smoother film surface. Mechanical properties were affected by DP values suggesting the possibility to control mechanical properties of CNF films in relation to DP. Overall, SHS is an efficient treatment method to reduce cellulose DP with the advantage of controlling CNF film properties towards the production of a versatile CNF film.

Sustainable valorization of paper mill sludge into cellulose nanofibrils and cellulose nanopaper

As a kind of agro-industrial wastes, paper mill sludge (PMS) has posed serious environmental and economic challenges for disposal due to the more stringent regulations and diminishing land availability in recent years. The present study is aimed at providing a sustainable approach to efficiently convert PMS to cellulose nanofibrils (CNFs) and cellulose nanopaper (CNP) by formic acid (FA) hydrolysis pretreatment and the followed microfluidization. It is found that FA hydrolysis (4–6 h) could swell and shorten PMS fibers, and only two-pass microfluidization is sufficient to get uniform CNFs from the collected cellulose residual. Results indicate that the obtained CNFs show high thermal stability and crystallinity index, surface functionality (ester groups), as well as a high yield of over 75 wt.%. Notably, more than 90 % FA can be recovered and the hydrolyzed sugars could be potentially used to produce platform chemicals (e.g. lactic acid, furfural). Finally, transparent CNP is prepared from the CNFs suspension via a simple vacuum filtration technique. The resultant CNP shows good mechanical properties with the maximum tensile strength and toughness of 106.4 MPa and 6.62 MJ/m3, respectively. Therefore, the current work provides a green and sustainable method to valorize PMS for the production of valuable CNFs and CNP.

Cellulose nanofibrils prepared by twin-screw extrusion: Effect of the fiber pretreatment on the fibrillation efficiency

Twin-screw extrusion (TSE) is a rather recent method to produce cellulose nanofibrils (CNFs) at a high solid content under continuous feeding. Here, never-dried commercial eucalyptus pulp was used as starting material to produce CNFs by TSE after a chemical pretreatment to introduce carboxylic groups via TEMPO-mediated oxidation and carboxymethylation. Five samples with a carboxyl content ranging from 800 to 1300 μmol.g−1 were produced to explore how the carboxyl content affects the aptitude of cellulose fibers to be broken down to nanoscale. The properties of the resulting CNFs in terms of nanosized fraction, morphology and rheological properties were investigated. A critical carboxyl content of 700 μmol.g−1was a prerequisite for the successful conversion of cellulose fibers into a CNF gel by TSE, regardless the pretreatment method. The degree of swelling of the fibers was put forward to account for this critical parameter.

Properties of cellulose nanofibril produced from wet ball milling after enzymatic treatment vs. mechanical grinding of bleached softwood kraft fibers

Cellulose nanofibril (CNF) is a class of promising and renewable nanocellulosic material due to its unique dimensional characteristics and appealing properties. CNF preparations based on TEMPO pretreatment followed by high-pressure homogenization have been studied intensively, while the high energy consumption and the environmental issues remain challenges to their application. Mechanical refining processes have been commonly applied at the academic and industrial relevant scales for CNF production. In this study, bleached softwood kraft pulp was subjected to high-efficiency wet ball milling (following enzymatic pretreatment) and mechanical grinding to obtain CNF. The effects of ball milling time, grinding gap, and grinding passes on structure and properties of CNF were evaluated. Scanning electron microscopy images confirmed that the diameter of CNF was decreased with the increment of ball milling time and number of grinding passes. The results indicated that ball milling time, grinding gap, and grinding passes were important to increase the dispersity of CNF suspensions. The degree of polymerization and crystallinity index of CNF decreased with increasing ball milling time and grinding passes.

A Green Approach Based on Reactive Extrusion to Produce Nanofibrillated Cellulose from Oat Hull

The objectives of this study were (1) to produce nanofibrillated cellulose (NFC) from oat hull by employing simple processes based on reactive extrusion combined or not combined with previous bleaching with peracetic acid, with both processes followed by an ultrasonication step; and (2) to characterize the obtained materials according to their composition, morphology, crystallinity and thermal stability. Oat hull was submitted to two different process: (1) extrusion in three sequential steps: first, with NaOH (10% w/w); then, twice with H2SO4 (2% w/w); and finally, an ultrasonication step, which resulted in nanofibers with diameters of 100 ± 25 nm and a yield of 60%; (2) bleaching with peracetic acid, and then one-step extrusion with H2SO4 (2% w/w) followed by an ultrasonication step, which resulted in fibers with diameters of 12 ± 2 nm and a yield of 65%. Reactive extrusion and the combination of peracetic bleaching with reactive extrusion were effective in the production of NFC from oat hull, and the main advantages from the proposed methods were simplicity and generation of fewer effluents when compared with those of conventional methods that have been described in the literature.