Regenerating “Clickable” Thiolated Cellulose Nanofibrils into Man-Made Cellulosic Composite Fibers: Effect on Properties and Spinnability

The constant worldwide increase in consumption of goods will also affect the textile market. The demand for cellulosic textile fibers is predicted to increase at such a rate that by 2030 there will be a considerable shortage, estimated at ~15 million tons annually. Currently, man-made cellulosic fibers are produced commercially via the viscose and Lyocell™ processes. Ionic liquids (ILs) have been proposed as alternative solvents to circumvent certain problems associated with these existing processes. We first provide a comprehensive review of the progress in fiber spinning based on ILs over the last decade. A summary of the reports on the preparation of pure cellulosic and composite fibers is complemented by an overview of the rheological characteristics and thermal degradation of cellulose–IL solutions. In the second part, we present a non-imidazolium-based ionic liquid, 1,5-diazabicyclo[4.3.0]non-5-enium acetate, as an excellent solvent for cellulose fiber spinning. The use of moderate process temperatures in this process avoids the otherwise extensive cellulose degradation. The structural and morphological properties of the spun fibers are described, as determined by WAXS, birefringence, and SEM measurements. Mechanical properties are also reported. Further, the suitability of the spun fibers to produce yarns for various textile applications is discussed.

Chemical functionalization of nano fibrillated cellulose by glycidyl silane coupling agents: A grafted silane network characterization study

Hydrophilic behaviour of carrageenan macroalgae biopolymer, due to hydroxyl groups, has limited its applications, especially for packaging. In this study, macroalgae were reinforced with cellulose nanofibrils (CNFs) isolated from kenaf bast fibres. The macroalgae CNF film was after that treated with silane for hydrophobicity enhancement. The wettability and functional properties of unmodified macroalgae CNF films were compared with silane-modified macroalgae CNF films. Characterisation of the unmodified and modified biopolymers films was investigated. The atomic force microscope (AFM), SEM morphology, tensile properties, water contact angle, and thermal behaviour of the biofilms showed that the incorporation of Kenaf bast CNF remarkably increased the strength, moisture resistance, and thermal stability of the macroalgae biopolymer films. Moreover, the films’ modification using a silane coupling agent further enhanced the strength and thermal stability of the films apart from improved water-resistance of the biopolymer films compared to unmodified films. The morphology and AFM showed good interfacial interaction of the components of the biopolymer films. The modified biopolymer films exhibited significantly improved hydrophobic properties compared to the unmodified films due to the enhanced dispersion resulting from the silane treatment. The improved biopolymer films can potentially be utilised as packaging materials.

The kinetics of the dissolution and swelling of different cellulose fibers in the ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) was studied by varying solvent power and temperature. Natural fiber, flax, and man-made fibers, Cordenka and Lyocell-type (Ioncell) were used with one Ioncell fiber containing lignin and hemicelluloses. Through the addition of water, the solvent power was modified from very good (neat ionic liquid), to moderate (with 5 wt% water) and weak (15 wt% water). The temperature was varied to correlate the fiber dissolution rate with the solvent viscosity. All fibers were characterized by chemical composition, crystallinity, molecular weight distribution and dynamic vapor sorption. It was demonstrated that while the rate of fiber dissolution in neat ionic liquid depends on fiber accessibility and solvent viscosity, the water-induced decreased solvent power dominates the general fiber behavior. Flax appeared to be the most “sensitive” to the solvent power due to its hierarchical structure. The fastest dissolution or swelling was recorded for Ioncell and the slowest for Cordenka.

With the goal of sustainable development, manufacturing continuous high-performance fibers based on sustainable resources is an emerging research direction. However, compared to traditional synthetic fibers, plant fibers have limited length/diameter and uncontrollable natural defects, while regenerated cellulose fibers such as viscose and Lyocell suffer from inferior mechanical properties. Wet-spun fibers based on nanocelluloses especially cellulose nanofibrils (CNFs) offer superior mechanical performance since CNFs are the fundamental high-performance building blocks of plant cell walls. This review aims to summarize the progress of making CNF wet-spun fibers, emphasizing on the whole wet spinning process including spinning suspension preparation, spinning, coagulation, washing, drying and post-stretching steps. By establishing the relationships between the nano-scale assembling structure and the macroscopic changes in the CNF dope from gels to dried fibers, effective methods and strategies to improve the mechanical properties of the final fibers are analyzed and proposed. Based on this, the opportunities and challenges for potential industrial-scale production are discussed.

Nanofibrillated cellulose (NFCs) are nanoscale fibers of high aspect ratio that can be isolated from a wide variety of cellulosic sources, including wood and bacterial cellulose. With high strength despite of their low density, NFCs are a promising renewable building block for the preparation of nanostructured materials and composites. To fabricate NFC-based materials with improved mechanical and chemical properties and additional new functionalities for different applications, it is essential to tailor the surface properties of individual NFCs. The surface structures control the interactions between NFCs and ultimately dictate the structure and macroscale properties of the bulk material. This research was focused on determining the feasibility of using hardwood residues from the Appalachian Hardwood Forest for the production of nanofibrillated cellulose (NFC). In addition, some modifications during the NFC production process were performed to evaluate their improvement to incorporate more antimicrobial copper in the cellulosic backbone. This thesis has been divided in the following main chapters: 1) Literature review regarding to nanocellulosic materials and their production processes, 2) Nanocellulose current and potential applications, 3) Nanofibrillated cellulose from the Appalachian Hardwood logging residues, 4) Modified nanofibrillated from the Appalachian Hardwood logging residues, 5) Preparation of nanocellulose using ionic liquids -- A review, 6) Nanocellulose-based drug delivery system -- A review, 7) Safety aspects on the utilization of lignocellulosic based materials - A review.

In Sri Lanka, a considerable percentage of agricultural waste such as rice straw and sugarcane bagasse is discharged to the environment without a commercial use and forms a huge organic environmental pollution. Therefore, the agricultural wastes can be used to extract cellulose and indirectly apply an additional value to the abundant priceless wastes. Nanocellulose is a cellulosic material which has at least one dimension in the nanometre range and has a potential for polymer reinforcement. Based on their structure nanocellulose extracted from plant species are categorised into two; nanofibrillated cellulose (NFC) and nanocrystalline cellulose (NCC). The present paper discussed the surface modification of NFC using Silane coupling agent (Si-69) and fabrication of silylated NFC reinforced polypropylene (PP) composites with different loadings of NFC from 0-5 wt. % by adding 0.5 wt. % per sample. The mechanical properties of the composite samples were compared with respect to neat PP and Scanning electron microscope (SEM), Fourier-transform infrared spectroscopy, X-ray diffraction, mechanical tests (tensile strength, percentage elongation at break, impact strength and hardness), percentage water absorption and melt flow index (MFI) were used to characterize the developed composites. The experimental results emphasize the wide improvement of mechanical properties with extremely narrow reduction of water absorption and processability of silylated NFC based PP than pure PP. The 3.5% silylated NFC reinforced PP composite indicated the highest improvement in mechanical properties such as hardness, tensile and impact strength, a 7.4%, 12.6%, and 86.1% higher than the neat PP, respectively.

Utilizing the elementary building blocks of plant cell walls, cellulose nanofibrils (CNFs), can give final materials excellent mechanical properties. For instance, CNF-based wet-spun fibers exhibit superior mechanical properties, surpassing their source materials, plant fibers. Such high mechanical performance is closely related to CNFs’ orientation; thus, most previous research has focused on optimizing spinning rates or introducing post-stretching to enhance this parameter. In this study, the effects of the CNF surface properties on CNF orientation were investigated, which are often neglected in the literature: 1) during extrusion, the CNF surface properties affect the rheological behaviors of the spinning suspension, which in turn influences CNFs’ orientation potential; 2) during coagulation, they govern the affinity between CNFs and antisolvents, thereby determining the shrinkage of CNF gels; 3) during drying, they directly impact capillary forces induced by the evaporation of antisolvents, which significantly determine the CNF orientation in the end products. Overall, this fundamental study provides deeper insights into the assembling behavior of colloidal nanoparticles such as CNFs, which can advance the development of high-performance man-made fibers.

Preparation of cellulose nanofibrils and their effects on the rheological properties and compressive strength of oil-well cement paste

All cellulose composites made of 100% cellulose nanofibrils (CNFs) were produced without the use of solvent, binders, chemicals and/or dissolution process. Specimens were produced by thermo-compression and compared with materials made with cellulosic fibers. Different compression conditions such as temperature, time and pressure were tested and their impacts were quantified regarding the mechanical properties of the obtained materials. After determining the optimal compressing conditions, different grades of CNFs were tested and characterized using several characterization methods such as bending properties, Charpy impact strength, water absorption or degree of polymerization. Specimens made of 100% CNFs present improved bending properties, lower Charpy impact strength and lower water sensitivity than samples made with cellulose fibers. CNFs with their smaller size and increased number of possible H-bonds, create samples of lower porosity and allow establishing a solid H-bonding network. However, the particle size of the dry CNF powder influences strongly the self-bonding of the CNFs and the mechanical resistance of the thermo-compressed objects. Objects made of 100% CNFs can now be produced using an environmentally friendly process. Schematic illustration of the study: production of 100% CNF objects by thermo-compression.

The aim of the present study was to determine the influence of sulphuric acid hydrolysis and high-pressure homogenization as an effective chemo-mechanical process for the isolation of quality nanofibrillated cellulose (NFC). The cellulosic fiber was isolated from oil palm empty fruit bunch (OPEFB) using acid hydrolysis methods and, subsequently, homogenized using a high-pressure homogenizer to produce NFC. The structural analysis and the crystallinity of the raw fiber and extracted cellulose were carried out by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The morphology and thermal stability were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric (TGA) analyses, respectively. The FTIR results showed that lignin and hemicellulose were removed effectively from the extracted cellulose nanofibrils. XRD analysis revealed that the percentage of crystallinity was increased from raw EFB to microfibrillated cellulose (MFC), but the decrease for NFC might due to a break down the hydrogen bond. The size of the NFC was determined within the 5 to 10 nm. The TGA analysis showed that the isolated NFC had high thermal stability. The finding of present study reveals that combination of sulphuric acid hydrolysis and high-pressure homogenization could be an effective chemo-mechanical process to isolate cellulose nanofibers from cellulosic plant fiber for reinforced composite materials.

We report for the first time the extraction of cellulose nano fibrils from Ficus natalensis barkcloth fibers by means of chemical treatments and catalytic oxidation of cellulose fibers by using 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO). After every stage of treatments, the structural properties of barkcloth fibers powder (BC-PW), cellulose fibers (BC-NB) and cellulose nano fibrils (BC-CNF) were carefully characterized by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for morphological analysis, Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction techniques for chemical analysis, and thermal properties were done by thermo-gravimetric analysis. FTIR results revealed the progressive removal of non-cellulosic contents and X-ray diffraction (XRD) analysis showed that the crystallinity increased with the successive alkali and bleaching treatments. Finally, by evaluating the TEM images, the average diameter of the nano-cellulose fibrils from Ficus natalensis barkcloth was also confirmed as 28 ± 0.6 nm and the length in hundred nano meters was recorded. The resultant cellulose nano fibrils maintaining the cellulose I structure had dimensional properties in nano-scale, higher crystallinity (68.5), and better thermal stability (305.62°C). The barkcloth cellulose nano fibrils can be used in nano technology like food packing material, nano composites and medical textiles.

Ionic liquids are used to dewater a suspension of birch Kraft pulp cellulose nanofibrils (CNF) and as a medium for water‐free topochemical modification of the nanocellulose (a process denoted as “WtF‐Nano”). Acetylation was applied as a model reaction to investigate the degree of modification and scope of effective ionic liquid structures. Little difference in reactivity was observed when water was removed, after introduction of an ionic liquid or molecular co‐solvent. However, the viscoelastic properties of the CNF suspended in two ionic liquids show that the more basic, but non‐dissolving ionic liquid, allows for better solvation of the CNF. Vibrio fischeri bacterial tests show that all ionic liquids in this study were harmless. Scanning electron microscopy and wide‐angle X‐ray scattering on regenerated samples show that the acetylated CNF is still in a fibrillar form. 1 D and 2 D NMR analyses, after direct dissolution in a novel ionic liquid electrolyte solution, indicate that both cellulose and residual xylan on the surface of the nanofibrils reacts to give acetate esters.

Cellulose nanofibrils from Euterpe oleracea residue extracted by acid hydrolysis and ultrasonic processing

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.