Nanofibrils Production Research Articles

Influence of swelling on the efficiency of TEMPO reaction, nanofibril production and characterization

This paper studies the effect of three swelling pretreatment processes (glycerol, alkaline, and molten salt hydrate) to improve the efficiency of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO)-mediated oxidation (TMO) to produce cellulose nanofibrils (CNFs). The novelty of this research lies in the presentation of a new approach that increases the process`s sustainability. The new pretreatment results in the reduction of both chemical reagents and energy consumption. Results demonstrate that pulps pretreated with molten salt hydrate exhibit a crystallinity index up to 50 % lower than the original fibers, while the carboxyl groups obtained during oxidation increase up to 30 %. The increase in oxidation efficiency allows us to obtain a highly fibrillated CNF with a 50 % dose reduction of TEMPO and NaBr at the same time that the energy consumption (kWh/kg) is reduced by 15 %.

Upscaling cellulose oxidation: Integrating TEMPO-mediated oxidation in a pilot-plant twin-screw extruder for cellulose nanofibril production

(TEMPO)-mediated oxidation (TMO) is a widely recognized pretreatment for producing highly fibrillated cellulose nanofibrils (CNFs) because of its efficiency and selectivity. However, the challenges of scaling up this process is limiting its implementation. This study explores enhancing the production of oxidized pulps (OPs) by performing the TMO reaction within a pilot-plant twin-screw extruder (TSE). This approach aims to oxidize large volumes of cellulose at high concentrations while simultaneously applying a soft mechanical fibrillation, making the upscaling process more sustainable and feasible. OPs and CNFs were characterized and compared to those obtained from the traditional TMO pretreatment in a stirred reactor as well as those pretreated by mechanical TSE. Results demonstrate that TMO within the TSE is more efficient and increase the yield fibrillation using 0.8, 0.08 and 2 mmol/g pulp of NaBr, TEMPO and NaClO, respectively. Multiple TSE steps decrease polymerization degree, enhance the process yield, and reduce the number of large fibers. Gradual addition of oxidants in multiple TSE steps prevents harsh reaction conditions and avoids yellowing of the final products.

Improving sustainability of cellulose nanofibrils production: FTIR spectroscopy for online control of the synthesis of recyclable magnetic TEMPO catalyst

2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and its derivatives are well-established catalysts for various oxidation processes, despite its hazardous nature, causing harm to aquatic ecosystems. Thus, the reuse of TEMPO with a sustained high activity has gained significant importance for its industrial application, which has led to the development of supported TEMPO catalyst. In this context, the efficiency of the support process acquires high relevance. Therefore, this research is aimed at the improvement of the TEMPO supported on silica magnetically modified with Fe3O4 through the application of an online Fourier transform infrared spectroscopy (FTIR) probe to monitor its synthesis. FTIR effectively controlled the synthesis of supported TEMPO, by tracking online the concentration of 3-aminopropyltriethoxysilane (APTES) and tetraethyl orthosilicate (TEOS). Additionally, the presence of Fe3O4 particles in the core of the catalyst allowed its convenient recovery and subsequent reuse. Furthermore, the supported TEMPO catalyst was successfully applied in the oxidation of cellulose to produce nano/microfibrils. The carboxyl groups of the initial untreated cellulose increase from 0.05 mmol/g to 0.68 mmol/g with the supported TEMPO catalyst in presence of sodium hypochlorite and sodium bromide at 50 °C.

A facile route for concurrent fabrication and surface selective functionalization of cellulose nanofibers by lactic acid mediated catalysis

Celulose nanofibers are lightweight, recycable, biodegradable, and renewable. Hence, there is a great interest of using them instead of fossil-based components in new materials and biocomposites. In this study, we disclose an environmentally benign (green) one-step reaction approach to fabricate lactic acid ester functionalized cellulose nanofibrils from wood-derived pulp fibers in high yields. This was accomplished by converting wood-derived pulp fibers to nanofibrillated “cellulose lactate” under mild conditions using lactic acid as both the reaction media and catalyst. Thus, in parallel to the cellulose nanofibril production, concurrent lactic acid-catalyzed esterification of lactic acid to the cellulose nanofibers surface occured. The direct lactic acid esterification, which is a surface selective functionalization and reversible (de-attaching the ester groups by cleavage of the ester bonds), of the cellulose nanofibrils was confirmed by low numbers of degree of substitution, and FT-IR analyses. Thus, autocatalytic esterification and cellulose hydrolysis occurred without the need of metal based or a harsh mineral acid catalysts, which has disadvantages such as acid corrosiveness and high recovery cost of acid. Moreover, adding a mineral acid as a co-catalyst significantly decreased the yield of the nanocellulose. The lactic acid media is successfully recycled in multiple reaction cycles producing the corresponding nanocellulose fibers in high yields. The disclosed green cellulose nanofibril production route is industrial relevant and gives direct access to nanocellulose for use in variety of applications such as sustainable filaments, composites, packaging and strengthening of recycled fibers.

Effect of lignin on the morphological, rheological, and dielectric characteristics of lignocellulose nanofibrils from Pinus radiata

Lignocellulose nanofibrils (LCNFs) are a nanomaterial composed mainly of cellulose, hemicellulose, and lignin. The lignin and its chemical modification in fibrils affect the production process and the morphological and surface characteristics of the LCNFs. These differences in the LCNFs produce different rheological and dielectric properties, which are key to the potential uses of the nanomaterial. This work aims to understand the effect of lignin on the production process and characteristics of LCNFs. A smaller amount of lignin favored the nanofibril production process, producing fibrils with smaller widths and the same apparent length distribution (15 passes). Regarding the rheology of LCNFs, native lignin in the fibrils produced a minor resistance to flow. On the other hand, oxidized lignin had stronger and hydrated flocs of larger size due to higher specific surface area or surface charge of fibrils. Finally, the dielectric properties of LCNFs decreased with increasing crosslinking structures and increased with increasing polar groups.

Endo-Exoglucanase Synergism for Cellulose Nanofibril Production Assessment and Characterization.

A study to produce cellulose nanofibrils (CNF) from kraft cellulose pulp was conducted using a centroid simplex mixture design. The enzyme blend contains 69% endoglucanase and 31% exoglucanase. The central composite rotational design (CCRD) optimized the CNF production process by achieving a higher crystallinity index. It thus corresponded to a solid loading of 15 g/L and an enzyme loading of 0.974. Using the Segal formula, the crystallinity index (CrI) of the CNF was determined by X-ray diffraction to be 80.87%. The average diameter of the CNF prepared by enzymatic hydrolysis was 550-600 nm, while the one produced by enzymatic hydrolysis and with ultrasonic dispersion was 250-300 nm. Finally, synergistic interactions between the enzymes involved in nanocellulose production were demonstrated, with Colby factor values greater than one.

Cellulose nanofibril production by the combined use of four mechanical fibrillation processes with different destructuration effects

Cellulose nanofibril production by the combined use of four mechanical fibrillation processes with different destructuration effects

Response surface optimization of ionic liquid pretreatments for maximizing cellulose nanofibril production

Pretreatments with aqueous protic ionic liquid (PIL)–ethanolamine bis(oxalate) ([MEA][(HOA)(H2OA)]), combined with ultrasonic disintegration, were employed in cellulose nanofibril (CNF) production from pulp fibers.

Allomorphic regulation of bamboo cellulose by mild alkaline peroxide for holocellulose nanofibrils production

The exploration of sustainable lignocellulosic nanomaterials with unique properties and applicable functions is receiving growing interest. In this work, holocellulose nanofibrils (HCNFs) were prepared from moso bamboo using mild alkaline peroxide bleaching method (MAPB) followed by mechanical nanofibrillation. MAPB was proved to effectively remove lignin and retain hemicellulose. Meanwhile, partial allomorphic changes from cellulose I to cellulose II were revealed together with varying degrees of crystallinity. Thermogravimetric analysis (TGA) experiment showed an increasing thermal stability trend due to more allomorphic changes into anti-parallel cellulose II. Well-dispersed HCNFs suspensions were successfully prepared by homogenization and HCNFs films with high transparency and flexibility were fabricated. The films reached the maximum tensile strength of 55.8 MPa and tensile strain of 1.55 % along with a calculated toughness of 25 MJ/m3. Moreover, the prepared materials are biocompatible and completely non-toxic, which will theoretically support the application of HCNFs materials in fields of biology, medicine and food industry.

Cellulose Nanofibrils Production from Sugarcane Bagasse: A Comparative Study between Low Energy Selective Oxidation Method and Stone Milling Fibrillation

Sugarcane bagasse (SCB), an abundant agro-industrial residue in Vietnam, was used as a raw material to produce cellulose nanofibrils (CNF). First, SCB pulp was obtained from the raw material of bagasse using a two-fraction method, soda treatment followed by bleaching with Javel solution. Then, the SCB pulp was converted into nano-sized cellulose fibers by subjected to low energy, economical treatment of TEMPO-mediated oxidation. A traditional mechanical method of fibrillation SCB pulp, stone grinding was done for comparison, the produced nanocellulose is referred to as MeSCB. The nanocellulose fibers refer as TOSCB obtained from the TEMPO oxidation process were characterized in terms of carboxyl content, morphology, crystallinity and thermal stability. The degree of fibrillation and the dimension of the two obtained nanocelluloses was determined by applying FE-SEM observations combined with an image processing application, ImageJ. The results show that the MeSCB were much less nanofibrillated than the corresponding TOSCB material but less toxic.

DESIGN OF SHELL AND TUBE TYPE HEAT EXCHANGER FOR NANOFIBRIL CELLULOSE PRODUCTION PROCESS

Heat exchanger plays an important role in industry. In industrial applications, the type of heat exchanger that is often found is the shell and tube type heat exchanger. The aim of this paper is to of tube and shell type heat exchanger for nanofibril cellulose production applications. The method used is to design several assumptions and calculate parameters related to determining the performance of the heat exchanger. The parameters are calculated manually using the Microsoft Excel application. In this design, the TEMA standard is used as a reference. The result of this paper is the heat exchanger has 53 pcs of tubes with the effectiveness up to 89.21%. This indicates that the overall performance of the heat exchanger in cellulose nanofibril production applications can be further improved by selecting the right fluid, fluid flow rate, and other physical properties, as well as the number of tubes that will be required

Choline chloride based deep eutectic solvents for the lignocellulose nanofibril production from Mongolian oak (Quercus mongolica)

Choline chloride based deep eutectic solvents for the lignocellulose nanofibril production from Mongolian oak (Quercus mongolica)

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.

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.

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.

Comparison of Deep Eutectic Solvents on Pretreatment of Raw Ramie Fibers for Cellulose Nanofibril Production.

Deep eutectic solvents (DESs), featured as promising green solvents, were applied to examine their effectiveness in pretreating raw ramie fibers (RFs) for cellulose nanofibril (CNF) production. The pretreatment performance of three DESs, i.e., choline chloride–urea (CU), choline chloride–oxalic acid dihydrate (CO), and choline chloride–glycerol (CG), was evaluated based on chemical composition analysis and structural and morphological changes. CO attained the most dramatic morphological changes of RFs, followed by CG and CU. Its high structural disruption of RFs during the pretreatment process, shown in the results from scanning electron microscopy and atomic force microscopy, could be due to an outstanding ability to remove amorphous cellulose and noncellulosic components from raw RFs, confirmed by the results of chemical composition analysis, Fourier transform infrared spectroscopy, and X-ray diffractometry. Overall, this study provided an innovative and effective pretreatment process for fractionating raw cellulosic fibers, so as to promote the subsequent preparation of CNFs.

Enhanced ultrafine nanofibril biosynthesis of bacterial nanocellulose using a low-cost material by the adapted strain of Komagataeibacter xylinus MSKU 12

Bacterial nanocellulose (BNC) is a renewable and biodegradable biopolymer which has currently received considerable attention due to the rapid increase in environmental issues. In this study, a cost-effective strategy for BNC production was successfully improved in the adapted strain, C30, which was obtained from Komagataeibacter xylinus MSKU 12 by a repetitive cultivation in a low-cost coconut water containing acetic acid and ethanol (CW-AE medium) at 37 °C. The adaptive procedure allowed the strain C30 to be adapted to grow and produce BNC with a higher yield in a limiting nutrient CW-AE medium, than that in a standard HS-AE medium. This strain could produce a high yield of BNC (9.69 g/L dry weight) in a low-cost medium, a modified CW-AE medium supplemented with sucrose and ammonium sulfate. Moreover, SEM images showed that BNC pellicle produced by the strain C30 in the modified CW-AE medium exhibited finer nanofibrils with a narrower range of width compared with those of MSKU 12 while no significant differences in their physicochemical characteristics were detected among these BNCs produced. Therefore, this finding demonstrates, not only the potential strain for the cost-effective BNC production at high temperature, but also the superior ultrafine nanofibrils production useful for further applications.

Flax nanofibrils production via supercritical carbon dioxide pre‐treatment and enzymatic hydrolysis

AbstractFlax fibres are an agro‐industrial waste available in large quantities in several countries around the world. This resource can be properly used. The goal of this work was to extract lignocellulosic nanosized flax fibres using an environmentally friendly process based on a combination of supercritical carbon dioxide (SC‐CO2) pre‐treatment and enzymatic hydrolysis. Raw flax fibres (RFF) were submitted to a SC‐CO2 pre‐treatment at various temperatures (ie, 70°C and 80°C) and pressures (ie, 20 and 37.7 MPa) for 60 minutes. The enzymatic hydrolysis was performed at 40°C for 24 hours in a pH 4.0 buffer. Cellulase, xylanase, pectinase, and viscozyme were used as hydrolytic enzymes. The as‐received raw flax fibres, SC‐CO2 pretreated flax fibres, and extracted lignocellulosic nanofibrils (LCNF) were characterized by Fourier transformed infrared spectroscopy (FTIR), x‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was shown that the effect of the SC‐CO2 pre‐treatment of flax fibres was two‐fold. It helped to disorganize biomass without changing its chemical composition and it increased access to enzymes to extract LCNF. The FTIR analysis showed no changes in the functional groups after SC‐CO2 pre‐treatment. The XRD characterization revealed that the crystallinity increased with the SC‐CO2 pre‐treatment and LCNF extraction. SEM images showed holes, cracks, and erosion on the surface of the SC‐CO2 pretreated flax fibres (SC‐CO2‐PFF). TEM evidenced the production of nano/micro‐sized fibril and fibril aggregates.

Lignin containing cellulose nanofibril production from willow bark at 80 °C using a highly recyclable acid hydrotrope

We conducted the first comparative exploration on lignin containing cellulose nanofibril films prepared alternatively from willow bark and wood using a highly recyclable acid hydrotrope, aqueous p-toluenesulfonic acid, as a sustainable means for isolating the nanofibrils. The nanofibrils of willow bark were hydrophobic and produced dense films of high strength under hot pressing. The hydrophobicity resulted from condensation of the residual lignin with low molecular weight aromatic substances of the bark and hydroxymethylfurfural formed in situ from fructose that is also present in the bark.

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.