Fibrillation Of Fibers Research Articles

Preparation of micro-fibrillated cellulose fibers by a simple two-step refining process for paper- based flexible electronic devices

Cellulose micro/nano-materials are potential substrates for energy storage/ electronics applications. However, developing efficient/cost-effective technologies that can obtain these micro/nano-materials suited for flexible electronics continue to be a challenge. In this study, we report a simple process for extracting micro-fibrillated cellulose fibers from conventional bleached kraft pulp that are particularly applicable to flexible electronics applications. The process is made of two step refining: 1) refining in a Valley beater, and 2) further fibrillation in a ball mill. The Valley beater is to induce fibrillation of pulp fibers as a result of compression and shearing forces. Subsequently, the partially fibrillated cellulose fibers are further subjected to ball milling to obtain micro-fibrillated cellulose fibers (MFCs). These MFCs have a much higher specific surface area than the conventional pulp fibers due to fibrillation and reduction in fiber size, which leads to favorable properties to the as- prepared MFCs network, including high transparence, and high tensile strength. The MFCs paper exhibits excellent transparency of 82% at 550 nm (a significant increase of about 56% for the control), with exceptionally high tensile strength (35.16 MPa). Thanks to the high surface area of these MFCs, silver nanowires (AgNWs) can be well distributed into the MFCs network so that conductive paper with high conductivity was prepared. The MFCs/AgNWs composite paper was then assembled into the paper-based triboelectric nanogenerator (P-TENG) device, which shows excellent performance. The MFCs/AgNWs composite paper- based P-TENG system can also serve as self-powered sensors for monitoring human motions. This work provides a method for the production of micro- fibrillated cellulose fibers that can be applied for the production of flexible electronic devices.

Making positive use of the fibrillation of lyocell fibres in composite materials

The present study investigates the influence of surface fibrillation of lyocell fibres on the adhesion and resulting properties of short fibre-reinforced polypropylene (PP) and polylactide (PLA) composites. Fibrillation was shown to reduce the tensile strength and elongation at break of the fibres, while not affecting Young's modulus. It was demonstrated that fibrillation improved adhesion significantly compared to non-fibrillated (untreated) fibres, and the critical fibre length determined by microbond tests was reduced. Despite the reduced tensile strength of the fibrillated lyocell fibres, the tensile strength of the composites was increased by a factor of 1.15 for PP and 1.62 for PLA compared to composites produced with untreated fibres. The Young's modulus of the composites was increased using fibrillated fibres by a factor of 1.41 for PP and 1.20 for PLA. The impact strength was also improved by using fibrillated fibres by a factor of 1.38 for PP-based and 1.23 for PLA-based composites. Surface fibrillation of lyocell offers interesting application possibilities, particularly for short fibre-reinforced materials, as the higher specific fibre surface reduces the critical fibre length of lyocell, leading to improved stress transfer from the matrix to the fibre. These fibres seem particularly promising to enhance the mechanical properties of short-fibre reinforced composites for 3D printing applications.

Visualization of Fibrillated Cellulose in Polymer Composites Using a Fluorescent-Labeled Polymer Dispersant

The fibrillated cellulose embedded in the polymer matrix was visualized using confocal laser scanning microscopy (CLSM). A rhodamine-appended diblock copolymer (RhBCP) was used as a novel polymer dispersant to adsorb fibrillated celluloses and achieve fluorescent labeling and good dispersion in high-density polyethylene. The composite was produced through in situ fibrillation of wood pulp fibers during the process of melt compounding using urea as the fibrillation-accelerating agent. The length and width of the fiber, aspect ratio, and polydispersity values were determined using RhBCP and CLSM. The optimal RhBCP content to achieve good CLSM images and a high Young’s modulus was 2 wt %. The effects of urea concentration and kneading time on the fibrillation were investigated, indicating that the fiber length and aspect ratio were approximately 40 μm and 40, respectively, under optimal conditions. The maximum Young’s modulus was recorded under these conditions, and the recorded value agreed well with the value predicted by the Halpin–Tsai equation. Cellulose fibers fragmented under conditions of low urea concentration and prolonged kneading times. The method developed has the potential to analyze various cellulosic composite systems and improve their application prospects.

Inorganic fullerene-like tungsten disulfide/waterborne polyurethane reinforced Spectra® composites with improved mechanical properties and tensile energy absorption

Fiber-based nanocomposites play a significant role in bullet-resistant, anti-impact, and aerospace applications. This research was conducted to (1) determine the feasibility of preparing inorganic fullerene-like tungsten disulfide (IF-WS2)/waterborne-polyurethane (WPU) dispersions in varying water/ethanol mediums and (2) study the effects of IF-WS2/WPU impregnation on mechanical and tensile energy absorption properties of ultra-high molecular weight polyethylene (UHMWPE) fibers. The characterization results indicate that the WPU showed poor solubility in ethanol causing low distribution uniformity of IF-WS2 and WPU on fibers. Comparable mechanical properties were obtained for the optimal samples prepared with water and water/ethanol mediums. The maximum load, energy to break, and normalized energy to break increased by 26.5%, 44.9%, and 31.1% for the 2 wt% IF-WS2/10 wt% WPU/UHMWPE composite prepared with water medium, respectively. Neat UHMWPE fibers showed failure mechanisms of fiber breakage, delamination, fibrillation, and splitting, while additional ductile breakage and matrix debonding were observed on WPU/IF-WS2 incorporated UHMWPE composites.

Preparation of transparent fibroin nanofibril-reinforced chitosan films with high toughness and thermal resistance

Silk fibroin nanofibrils can be obtained through fibrillation of fibroin fibers using wet-mechanical methods with a strong shear force. These nanofibers possess favorable mechanical properties and high thermal stability due to the secondary β-sheet structure of native fibroin. Consequently, ductile chitosan composite films with high thermal stability and optical transparency were successfully fabricated through reinforcement with native fibroin nanofibrils. The crystallinity of the composite films increased with the fibroin nanofibril ratio. Furthermore, the swelling ratio of the composite film decreased with the increasing fibroin nanofibril ratio, suggesting the presence of interactions, such as hydrogen bonding and/or electrostatic interactions, between chitosan and fibroin nanofibrils. This composite film can be used in environments with high moisture content and high temperatures and is anticipated to be utilized in a wide range of applications (e.g., food packaging, cosmetics, and biomaterials).

A Numerical Model for Understanding the Development of Adhesion during Drying of Cellulose Model Surfaces

Adhesion is crucial for the development of mechanical properties in fibre-network materials, such as paper or other cellulose fibre biocomposites. The stress transfer within the network is possible through the fibre-fibre joints, which develop their strength during drying. Model surfaces are useful for studying the adhesive strength of joints by excluding other parameters influencing global performance, such as geometry, fibre fibrillation, or surface roughness. Here, a numerical model describes the development of adhesion between a cellulose bead and a rigid surface using an axisymmetric formulation, including moisture diffusion, hygroexpansion, and cohesive surfaces. It is useful for studying the development of stresses during drying. A calibration of model parameters against previously published contact and geometry measurements shows that the model can replicate the observed behaviour. A parameter study shows the influence of cohesive and material parameters on the contact area. The developed model opens possibilities for further studies on model surfaces, with quantification of the adhesion during pull-off measurements.

Oxidative treatment and nanofibrillation softwood kraft fibres with lytic polysaccharide monooxygenases from Trichoderma reesei and Podospora anserina

Cellulose oxidation and enzymatic treatments can be employed to reduce the energy consumption in production of cellulose nanofibrils (CNFs). Lytic polysaccharide monooxygenases (LPMOs) offer new biocatalytic tools for oxidative pretreatment of cellulosic fibres in this process. In this work the capability of LPMO enzymes to enhance fibrillation of bleached softwood kraft fibres was studied using two LPMO enzymes, i.e. C1/C4-oxidising AA9A from Trichoderma reesei (Tr AA9A) and C1-oxidising AA9E from Podospora anserina (Pa AA9E). The enzymatic treatments were carried out after mechanical pre-refining (grinding) of the pulp, which resulted in clear reduction of the intrinsic viscosity of the refined fibres compared to the previously published work, presumably due to better access of the enzymes on the fibre polysaccharides. The Tr AA9A treatments were carried out using different enzyme dosages (0.25–10 mg/g dry fibre) and fixed reaction time (24 h), resulting in fibres characterized by increased aldehyde content, which is in line with the C1/C4 oxidising activity of this enzyme. Comparison of the Tr AA9A to Pa AA9E with fixed enzyme dosage (2 mg/g dry fibre) and reaction time (24 h), showed that no remarkable increase in total charge of the cellulosic fibres could be obtained with either of the LPMO enzymes in these conditions. All the LPMO pretreatments improved fibrillation of mechanically refined fibres in microfluidization, seen as clearly lower residual fibre content and higher proportion nanosized material. In comparison of the Pa AA9E to Tr AA9A, clearly faster fibrillation was achieved with the Pa AA9E pretreatment. The mechanical and oxygen barrier properties of CNF films prepared from LPMO pretreated fibres were very similar to the reference CNF films while water vapour transmission rate was somewhat higher.

Upcycling cotton textile waste into bio-based building blocks through an environmentally friendly and high-yield conversion process

This work presents mechanical refining as a chemical-free pretreatment of cotton textile waste to be converted into glucose via enzymatic hydrolysis. Both Cellic® CTec2 and CTec3 cellulase enzymes were evaluated to perform the enzymatic hydrolysis. Mechanical refining enabled cotton fiber fibrillation, thus increasing its specific surface area, water swellability, enzyme adsorption, and the efficiency of cotton conversion into sugars. Compared to conventional pretreatments, mechanical refining promoted sugar yields above 90% after enzymatic hydrolysis at lower enzyme usage (4–6 FPU/O.D g). From experimental data, a non-linear model was developed to predict cotton conversion. The predictive model allowed the optimization of the conversion process, which resulted in maximum yields of 89.3 and 98.3% when CTec2 and CTec3 were respectively used. Results from this work open the window to deploy mechanical refining as a promising and more sustainable transformation approach to produce sugar-based building blocks within the circular economy framework of textile waste.

The experimental assessment of carbon nanotubes incorporation on the tensile and impact properties of fiber metal laminate fabricated by jute/basalt fabrics-aluminum layers: As hybrid structures

In this work, the simultaneous effect of different stacking sequences of basalt/jute fibers and adding the various weight fractions of carbon nanotubes (CNTs) on the mechanical features of fiber metal laminates (FMLs) under the tensile and impact conditions was assessed. According to the results, the FML had the highest performance under the mechanical tests, when the jute layers were sandwiched by the basalt fibers. In contrast, by sandwiching the basalt fibers with the jute fibers, the FML showed the weakest performance just under the tensile test. This configuration had the moderate performance under the impact test. Incorporating 0.3 wt.% CNTs in all configurations caused to reach the highest improvement in the tensile strength, elastic modulus and impact energy, which were 301 MPa, 50.9 GPa, and 12.3 J, respectively. Reinforcing an adhesion between skin/core and enhancing the mechanical properties of composite core were the effective factors for improving the tensile properties. The delamination of layers, fibrillation of jute fibers, creation of imprint phenomenon, and pull out the basalt fibers were the characterized wasting mechanisms under the impact conditions.

Morphology, structure and property of high consistency mechano-enzymatic fibrillated cellulose: Effect of treatment consistency of bamboo pulp fibers

High consistency mechano-enzymatic fibrillation of cellulose fibers is a desirable approach to producing high solid fibrillated cellulose (HSFC) materials in a green fashion, which can reduce water consumption and lower logistic costs as well as carbon footprint. Here, we mainly investigated the effects of various treatment consistencies (15–45%) of bamboo pulp fibers during the mechano-enzymatic processing on the morphology, structure, and property of the resulting HSFC materials. The results revealed that the 35% treatment consistency was the most favorable for producing fibrillated cellulose materials comprising the most nanoscale fibrils, despite a small fraction of unfibrillated microfibril bundles existing. The fibrillated cellulose obtained at the 35% consistency had the highest water retention value, yielding a cast film with the highest mechanical performance. The 15% treatment consistency generated HSFC materials with the least degree of fibrillation, in which most were shortened yet micro-sized fiber fragments. Regardless of treatment consistencies, the HSFC materials almost retained cellulose crystallinity and thermal stability. The results suggest that mechano-enzymatic fibrillation at a suitable treatment consistency is crucial to producing the most highly fibrillated cellulose.

Структурно-морфологические свойства вторичного волокна из влагопрочного сырья при мягком размоле. Часть 1. Характеристика волокон

The efficient use of papermaking potential of secondary fiber by gentle refining of recycled pulp is one of the basic principles for the recovered paper stock preparation. The use of mild refining modes for recycled fiber is more important in the case of wetstrength paper than for conventional waste paper. This is due to the fact that recycled fiber is weakened by hard conditions of wet-strength paper repulping, in particular, long repulping time, elevated temperature, the use of alkali and oxidizers. The study aims at evaluating the changes in the morphological characteristics of secondary fiber during gentle low-consistency refining of recycled pulp. The analysis of the secondary fiber morphological characteristics was carried out in two complementary directions, i.e. the analysis of the fibers (part 1) and the analysis of the fines (part 2). Recycled pulp (RP) was obtained from commercial wetstrength tissue paper consisting of 100 % bleached softwood kraft pulp (BSKP) made of pine (Pίnus sylvéstris L.). The wet-strength paper repulping was performed at 60 °C in three ways, namely, repulping with sodium hydroxide (indicated as RP(NaOH)), repulping with sodium hydroxide and sodium persulfate (RP(NaOH + Na2S2O8)), and finally repulping with sodium hydroxide and potassium monopersulfate (RP(NaOH + KHSO5)). Secondary fibers as well as primary fibers of BSKP had similar length distribution before and after gentle refining. Mean fiber length after first recycle reduced by 5–6 %. The calculated values of the fibershortening index showed that fiber cutting practically does not occur during gentle refiningof the recycled pulps. The increase in the refining degree of the pulps is mainly explained by the fibrillation of secondary fibers, rather than the formation of a large amount of fines. Secondary fibers obtained from the wet-strength paper have a high slenderness ratio ((L/W)l from 66.3 to 66.5 and (L/W)w from 83.6 to 84.3; where L – length, W – width) corresponding to pulp with good papermaking potential. The results showed that low-consistency gentle refining of the recycled pulp obtained by accelerated persulfate and monopersulfate repulping of the wet-strength paper leads to fiber straightening. The overall increase in the shape factor of secondary fibers was achieved due to a combination of accelerated repulping of the wetstrength waste paper (by ~ 60 %) and gentle refining of the pulp (by ~ 40 %).

Polyamide‐6/cellulose nanocomposites: Influence of fiber treatment and screw rotation on nanofibrillation of jute during extrusion process

The present work studied the preparation of nanocomposites of polyamide-6 (PA6) containing nanofibrillated cellulose by melt blending in a twin screw extruder at different screw rotations to verify the fibrillation of cellulose fibers. Initially, the jute fibers were purified, hydrolyzed, and modified with titanium isopropoxide and aminopropyl silane, as well as with the two chemical modifications. They were incorporated into the polymeric matrix aiming that the shear in processing further aids in fiber fibrillation. The scanning electron microscopy analysis images of the composites showed the presence of fibers with nanodiameters dispersed in the PA6 matrix. The doubly modified fibers resulted in more fibrillation during extrusion. Increasing the screw speed of the extruder improved the degree of crystallinity for the composites with the modified fibers. The thermogravimetric measurements showed that the composite containing the doubly modified fibers increased the maximum degradation temperature. The storage modulus increased for the composites with the insertion of the treated fibers, and the glass transition temperature decreased in some composites. The composites showed higher pseudoplastic behavior, especially at high shear rates.

EFFECT OF FIBRILLATION ON THE ABILITY OF CELLULOSE FIBERS TO SUPPRESS THE AGGREGATION OF QUINACRIDONE

Quinacridone is a red–violet pigment often used as a coloring agent. However, the aggregation of quinacridone needs to be resolved to avoid undesirable color changes. Cellulose nanofibers are a potential candidate for novel pigment dispersants, due to their ability to inhibit aggregation. In this study, the effect of the degree of fibrillation of cellulose fibers on their performance as dispersants was investigated. Four types of highly fibrillated cellulose particles (HFCPs) were prepared using a disk mill and a high-pressure homogenizer. The degree of fibrillation was evaluated using specific surface area measurements, scanning electron microscopy, and gravitational sedimentation analysis. Fibrillation of cellulose was found to increase its adsorption capacity toward quinacridone. Even partly fibrillated celluloses successfully inhibited the aggregation of quinacridone. Color measurements of the quinacridone–cellulose suspensions indicated that, although fibrillation of cellulose improves the chroma of the suspensions, excess fibrillation causes a decrease in the chroma.

Acoustic optimization of a flow through sonicator for fibrillation of cellulose fibers

Fibrillation is identified as the most energy intensive process step in pulp and paper manufacturing and improved energy efficiency is the motivation for development of alternative technologies. The aim of this study is to explore the potential of a new refining concept based on cavitation, focusing on the optimization of acoustic cavitation efficiency of the proposed flow-through sonicator concept. The simulations utilize the linearized wave equation in the frequency domain with an addition of nonlinear attenuation introduced by cavitation bubbles. Verification is made by pressure measurements, calorimetry, and foil tests. The fibrillation capability was validated on chemi-thermo mechanical pulp fibers at low consistencies. Fiber properties was characterized by ultrasonic spectroscopy, fiber analysis and SEM. The objective is to optimize the energy transfer efficiency from electrical input power to acoustic cavitation intensity for efficient fibrillation of cellulose fibers. Results showed changes in fiber dimensions and fiber morphology, however, improvements in tensile strength index, measured and predicted by ultrasonic spectroscopy, was limited to 20 % at an energy level of 804 kWh/bdt. To enhance energy efficiency and paper strength properties, it is suggested to add a hydrodynamic cavitation device prior to the sonicator to initiate cavitation bubbles and to increase turbulence intensity.

Water-soluble polysaccharides promoting production of redispersible nanocellulose

To date, the energy-intensive production and high-water content severely limits nanocellulose applications on a large scale off-site. In this study, adding water-soluble polysaccharides (PS) to achieve an integrated process of water-redispersible nanocellulose production was well established. The addition of PS, in particular carboxymethylated-galactoglucomannan (cm-GGM), facilitates fibre fibrillation enabling homogenization at a higher solid content at 1.5 wt% compared with around 0.4 wt% for neat fibre. More importantly, the addition of cm-GGM saved 73 % energy in comparison without PS addition. Good water redispersibility of thus-prepared nanocellulose was validated in viewpoints of size distribution, morphology, viscosity and film properties as compared with neat nanocellulose. The tensile strength and optical transmittance of nanocellulose films increased to 116 MPa and 77 % compared to those without PS addition of 62 MPa and 74 %, respectively. Collectively, this study provides a new avenue for large-volume production of redispersible nanocellulose at a high solid content with less energy-consumption.

Influences of fiber fibrillation degree on mechanical and tribological performances of aramid fiber/nitrile rubber composites

AbstractThree types of aramid fibers (AFs) with various surface fibrillation degrees were introduced into nitrile rubber (NBR) matrix to prepare the AF/NBR composites, respectively. Their impacts on the mechanical and tribological performances of the NBR composites were mainly studied. The results showed that, as the fiber content increased, the tensile strength of the AF/NBR composites increased after initially decreased, and the turning point moved toward the direction of lower AF content with the fiber fibrillation degree increase. In addition, when the AF content was low, the tensile strength decreased as the fibrillation degree increased, but the opposite trend was observed when the AF content became high. In addition, the tear strength increased with the increase of the fiber content and fibrillation degree. With the fiber fibrillation degree increase, the tan δmax of the composites decreased, indicating a stronger restriction on the NBR molecular chains. Furthermore, the surface fibrillation degree increase slightly decreased the friction coefficient (COF). The wear performance of the AF/NBR composites improved with the fiber content increase. The fibrillation degree increase further improved the wear resistance. It should be due to the tear strength increase and the enhanced interfacial interaction between the fiber and rubber matrix.

Production of lignin-containing cellulose nanofibrils by the combination of different mechanical processes

Due to its interesting properties, attention has been oriented to the production of cellulose nanofibrils. However, the cellulose isolation requires the combination of several steps which are generally very energy consuming. This is one of the main limitations for the use and industrialization of such materials. Trying to participate in the resolution of this probleme, lignin-containing cellulose nanofibrils are produced for the first time from Posidonia oceanica waste. Fibers are alkali-extracted by a conventional soda cooking in autoclave or by alkaline steam explosion. As conventional refining of unbleached fibers is difficult, a comparative study is carried out to test alternative processes for fiber fibrillation (twin-screw extrusion (1 pass) or steam explosion (during 3 times)). Actually, these two processes are known to be environmentally friendly and low energy consuming. For microfibrillation, an ultra-fine friction grinder is used to prepare lignin-containing cellulose nanofibrils. The obtained gels are characterized by several properties such as morphological analysis (Morfi, optical microscopy, scanning electron microscopy, transmission electron microscopy) and turbidity measurements. Papers and nanopapers are prepared by filtration to investigate the mechanical properties. All these analysis methods allow discussing the efficiency of the different process combinations. It is concluded that steam explosion could be an alternative method for Posidona fiber extraction, while for refining the process conditions should be optimized. Finally, it is found that LCNF produced from extruded pulps (whatever the fiber extraction method) exhibit promising properties comparing with other unbleached CNF.

The effect of repeated alkali pretreatments on the morphological characteristics of cellulose from oil palm empty fruit bunch fiber-reinforced epoxy adhesive composite

In this study, the effect of low-concentration (4 wt%) alkali and bleaching pre-treatments on the fibrillation of oil palm empty fruit bunch (OPEFB) fibers were evaluated. The OPEFB fibers were subjected to repeated weak alkali treatment and bleached by hydrogen peroxide in alkaline solution. Fibrillation was accomplished via mechanical process by a household blender. The obtained cellulose morphology was used to find paper-like sheets that were coated with epoxy resin to produce composites by sheet lamination. Fourier-transform infrared spectroscopy revealed that hemicellulose and lignin were partially removed and fiber dispersion strongly depended on the number of alkali treatment cycles. Scanning electron microscopy showed that fibers that underwent 12 alkali treatment cycles presented the most effective fibrillation. In addition, the blender fibrillation of cellulose fibers in a mild (6 wt%) alkali solution required less energy than blending in a neutral aqueous medium and improved fibrillation into nanofibrils. The obtained average diameters of the microfibrils and nanofibrils were approximately 7 μm and 89 nm, respectively. The tensile strength and Young's modulus of the composites were approximately 3.6 and 20 times higher, respectively, than those of neat epoxy resin. The proposed chemo-mechanical method could facilitate the use of micro-nanofibrils extracted from OPEFB for fiber-based materials and polymeric composites.

Fabrication of transparent paper devices from nanocellulose fiber

Green electronics devices based on nanocellulose fiber are acquiring increasing reorganization attributing to their excellent thermal stability (thermal degradation temperature at 370 °C), flexibility, and transparency (90% at 600 nm wavelength). Electronic and optoelectronic devices from cellulosic substrate have received thriving interest due to the unique properties, such as bendability and foldability (±180° folding). Nanocellulose is a fascinating material originating from woody (Softwood, Hardwood), non-woody (Sisal, Coir, Cotton), and bacterial sources. Mechanical isolation methods ensure better fibrillation of nanocellulose fiber. However, higher energy consumption is a major limitation to be tackled. Pretreatment facilitates lower energy demand and invokes irreversible changes in the fiber. Pretreatment accelerates the bonding potential by altering the size and morphology of nanocellulose fiber. This review summarizes the current fabrication methods of transparent paper from cellulose fiber and applications in transparent nanopaper devices such as transistors, touch sensors, electro chrome devices, solar cells.

Tear Resistance and Morphology Study of Tree Pruning Waste Papers: Effect of Soda Pulping Concentration

With the aim to explore the use of tree pruning waste as replacement material in papermaking, a study was conducted to investigate the effect of soda pulping concentration on the tear resistance and surface morphology of the fabricated papers. By varying the sodium hydroxide concentration from 5% to 25%, tree pruning waste papers with different tear resistance and surface morphology were fabricated. The tree pruning waste papers with the optimum tear resistance (73049.68 mN) was produced when the pulping medium was prepared at 20% sodium hydroxide concentration. As confirmed by the morphology study, the pulp fibres with improved interlocking surface morphology was produced at 20% sodium hydroxide concentration. Beyond that, fibre fibrillation had took place and exerted negative impact on the tear resistance of the papers. The present study confirms the use of tree pruning waste as an alternative in papermaking. Nonetheless, the soda pulping concentration must be properly regulated in order to maximize the performance of the fabricated paper products.