Lyocell Research Articles

Regenerated Cellulose by the Lyocell Process, a Brief Review of the Process and Properties

Lyocell fiber has emerged as an important class of regenerated cellulose that is produced based on the N-methyl morpholine-N-oxide (NMMO) dissolution method, and it has unique properties compared to viscose fiber. The NMMO technology provides a simple, resource-conserving, and environmentally friendly method for producing regenerated cellulose fiber. In this paper, the manufacturing process, environmental impact, and product quality of lyocell fiber are reviewed and compared with those of the conventional viscose fiber.

Factors affecting removal of bacterial pathogens from healthcare surfaces during dynamic wiping

Wiping of surfaces contaminated with pathogenic bacteria is a key strategy for combating the transmission of healthcare associated infections. It is essential to understand the extent to which removal of bacteria is modulated by fiber properties, biocidal liquid impregnation and applied hand pressure. The influence of intrinsic and extrinsic factors on the removal efficiencies of pathogenic bacteria was studied. Nonwoven wipes made of either hydrophobic (polypropylene) or hygroscopic (lyocell) fibers were manufactured and dynamic removal efficiency of bacteria studied. The single most important parameter affecting bacterial removal efficiency was impregnation with biocidal liquid ( p < 0.05). For inherently hygroscopic 100% regenerated cellulose (lyocell) wipes impregnated with biocidal liquid, removal of E. coli, S. aureus and E. faecalis improved by increasing the fabric surface density and wiping pressure to their maximal values – 150 g.m–2 and 13.80 kN.m–2, respectively. For inherently hydrophobic 100% polypropylene nonwoven wipes, the same conditions maximized the removal efficiency of S. aureus, but for E. coli and E. faecalis a reduction in the wiping pressure to 4.68 kN.m–2 was required. Best practice involves the use of higher surface density wipes (150 g.m–2) containing regenerated cellulose fibers loaded with liquid biocide, and applied with the greatest possible wiping pressure.

Properties of stretchable lyocell yarns developed using modified ring spinning frame

Stretchable fabrics provide a better fitting in addition to unhindered body movement. These stretchable fabrics are usually developed using composite yarns esp. core spun yarns having spandex as core. In the current research, stretchable yarns were developed using spandex and lyocell fibres. Spandex filaments were used as a core and lyocell fibres were used as a covering sheath. Two deniers of spandex were used in order to study the effect of deniers on the properties of yarns. Core spun yarns were developed by modified ring spinning frame at constant drawing ratio i.e. 3. Results of the study showed that presence of spandex, as well as change in its deniers, affected yarn count, tenacity, elongation and imperfection. However, breaking force and unevenness of yarns were remain unaffected by the presence of spandex as core in yarns.

From Cellulose Nanospheres, Nanorods to Nanofibers: Various Aspect Ratio Induced Nucleation/Reinforcing Effects on Polylactic Acid for Robust-Barrier Food Packaging.

The traditional approach toward improving the crystallization rate as well as the mechanical and barrier properties of poly(lactic acid) (PLA) is the incorporation of nanocelluloses (NCs). Unfortunately, little study has been focused on the influence of the differences in NC morphology and dimensions on the PLA property enhancement. Here, by HCOOH/HCl hydrolysis of lyocell fibers, microcrystalline cellulose (MCC), and ginger fibers, we unveil the preparation of cellulose nanospheres (CNS), rod-like cellulose nanocrystals (CNC), and cellulose nanofibers (CNF) with different aspect ratios, respectively. All the NC surfaces were chemically modified by Fischer esterification with hydrophobic formate groups to improve the NC dispersion in the PLA matrix. This study systematically compared CNS, CNC, and CNF as reinforcing agents to induce different kinds of heterogeneous nucleation and reinforce the effects on the properties of PLA. The incorporation of three NCs can greatly improve the PLA crystallization ability, thermal stability, and mechanical strength of nanocomposites. At the same NC loading level, the PLA/CNS showed the highest crystallinity (19.8 ± 0.4%) with a smaller spherulite size (33 ± 1.5 μm), indicating that CNS, with its high specific surface area, can induce a stronger heterogeneous nucleation effect on the PLA crystallization than CNC or CNF. Instead, compared to PLA, the PLA/CNF nanocomposites gave the largest Young's modulus increase of 350 %, due to the larger aspect ratio/rigidity of CNF and their interlocking or percolation network caused by filler-matrix interfacial bonds. Furthermore, taking these factors of hydrogen bonding interaction, increased crystallinity, and interfacial tortuosity into account, the PLA/CNC nanocomposite films showed the best barrier property against water vapor and lowest migration levels in two liquid food simulates (well below 60 mg kg-1 for required overall migration in packaging) than CNS- and CNF-based films. This comparative study was very beneficial for selecting reasonable nanocelluloses as nucleation/reinforcing agents in robust-barrier packaging biomaterials with outstanding mechanical and thermal performance.

Structural analysis of Ioncell-F fibres from birch wood

Quite recently, the Ioncell-F process, a novel and promising Lyocell fibre process, has been developed. The ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) utilized in this process, was identified as an excellent cellulose solvent for dry-jet wet fibre spinning. Fibres spun from cellulose-[DBNH]OAc solution have shown excellent mechanical properties. Herein, various structural features of these ionic liquid-based fibres were analyzed and correlated with their mechanical properties. The highest slope of tenacity increase of these Ioncell-F fibres (from birch wood) observed at low draw ratios (DRs), while a continuous but slower increase occurs to partly very high draws. The improvements in the mechanical properties do not seem to correlate with changes in the crystallite size or the crystalline orientation based on wide-angle X-ray scattering (WAXS) results. More significant differences were seen for the sample crystallinity, the amorphous orientation (measured by birefringence), the orientation of the voids, the specific surface (measured by small-angle X-ray scattering (SAXS)), and the sorption/desorption properties of the fibres.

Durable flame retardant cellulosic fibers modified with novel, facile and efficient phytic acid-based finishing agent

As a renewable, abundant, and eco-friendly bio-based compound, phytic acid (PA) possesses high phosphorus content, which is a potential flame retardant for cellulosic fibers. Generally, PA is not efficient for cellulosic fibers due to strong acidity that results in greatly reduced strength and lack of soft hand. As proved elsewhere, the compounds with phosphorous and nitrogen was reported to be an efficient flame retardant and exhibited synergistic effect for cellulosic fibers. Therefore, PA was firstly reacted with urea to synthesize a novel green flame retardant containing a high level of phosphorus and nitrogen elements, i.e., phytic acid ammonium, then it was employed for lyocell fibers through pad-dry-cure finishing process. As expected, flame retardancy and durability of finished lyocell fabrics were considerably improved, as evidenced by an increase of limiting oxygen index value up to 39.2% and still 29.7% after 30 laundering cycles. TG–MS and TG–FTIR coupled techniques demonstrate that the formation of carbonaceous residue and non-combustion gases preferably generated during thermal pyrolysis process of finished lyocell fibers.

Physical properties of lyocell-reinforced polypropylene composites from intermingled fibre with varying fibre volume fractions

Polypropylene (PP)-cellulose fibre blends exhibit substantial potential for the production of high-performance textile fibre–reinforced composites. The production of reinforced parts from PP-cellulose composites through thermal shaping of intermingled fibre blends is a strategy to form parts which exhibit superior mechanical properties. In this study, the use of intermingled fibre slivers with different ratios of lyocell fibres (CLY) and PP fibres as raw materials for thermally formed composites was investigated. Such a concept will maximize the interface between the reinforcement fibres and polymer matrix. The cellulose fibres remain oriented along the direction in which the drawing process was performed, which forms the basis for tailored fibre placement in technical production. Because of good surface contact between the cellulose fibre surface and PP matrix, no special coupling agents were required to improve the interfacial adhesion between the two different polymers. The share of CLY and PP fibres in the composite varied from 50% w/w CLY content, up to 70% w/w CLY. Besides analysis of the mechanical properties, such as tensile strength and E-modulus, attention was directed towards moisture sorption of the composites. The rate of sorption and amount of water bound in the composite were found to be dependent on the cellulose fibre content. Composites with a higher CLY content exhibited a more rapid and higher moisture uptake. In water saturated state, the ultimate tensile strength of composites reduced from 160 MPa to 90 MPa, which is an indicator for a reduced adhesion between the CLY surface and PP matrix. The results indicate the potential of the intermingled fibre concept blend for the efficient manufacturing of composite parts.

Surface chemical and colorimetric analysis of reactively dyed cellulosic fabric. The effect of ISO 105 CO9 laundering and the implications for waste cellulosic recycling

Previous studies have established that the application of crosslinking dyes and easy care finishes to cotton can significantly reduce the dissolution of waste cotton in solvents, such as N-Methylmorpholine oxide, and limit the potential recycling of cellulosic materials through the Lyocell fibre regeneration process. In this investigation the surface chemical compositions of three reactive dyed Tencel fabrics were studied using X-ray Photoelectron Spectroscopy (XPS) and the presence of the dye at the fibre surface demonstrated. The effect of the ISO 105 C09 oxidative-bleach fading test on the azo and anthraquinone chromophoric species was established by both surface chemical and colorimetric analyses. At low dye application levels the C. I. Reactive Black 5 and C. I. Reactive Red 228 dyed fabrics (azo chromophore) exhibited obvious colour fade while the anthraquinone-based C. I. Reactive Blue 19 dyed fabric was resistant to colour fade. However it is apparent that although some of the covalently bound dye will be removed during “first life” usage, most of the reactive colorant will remain bound to the cotton and will therefore need to be stripped from the waste garments to produce a white cellulosic feedstock prior to reprocessing through Lyocell fibre regeneration. A sequential acid, alkali and peroxide treatment completely removed the azo-based C. I. Reactive Black 5 and C. I. Reactive Red 228 colorants from the dyed cotton, however, the anthraquinone-based C. I. Reactive Blue 19 was highly resistant to removal and will require alternative chemical processing to remove the colorant.

Textile qualities of regenerated cellulose fibers from cotton waste pulp

Cotton is not the answer to meet the rapidly growing demand for textile fibers. Wood-based regenerated cellulose fibers are an attractive alternative. Since wood is a candidate to replace fossil raw materials in so many applications of the circular economy, other sources need investigation. Cotton linters work in the viscose process – can cotton waste be used to make dissolving pulp? We describe the textile qualities of lyocell fibers from (i) pure cotton waste pulp and (ii) blending with conventional dissolving pulp. The staple fibers were tensile tested, yarns spun and tensile tested and knitted, and tested for shrinkage, water and dye sorption, abrasion resistance, fuzzing and pilling, staining and fastness. TENCEL® staple fibers and off-the-shelf TENCEL® yarn were used as references. The results show that the two study fibers had tenacity and an E-modulus that exceeded the staple fiber reference. Also, the study yarns were at least as good as the spun reference yarn and the commercial off-the-shelf yarn in terms of wet tenacity. Single jerseys made from the study yarns shrunk less upon laundering, which is surprising since they could absorb at least as much water at a comparable rate as the references. Dyeability, staining and color fastness, durability and pilling tendency showed that the two study fiber tricots performed at least as good as the references. This study suggests that cotton waste is a promising candidate for special grade pulp to suit niche regenerated fiber products or to spice up conventional wood-based dissolving pulp.

Effect of Different Factors on the Fibrillation Degree of Lyocell Fiber Based on Homogenization Treatment

The homogenization treatment was performed to fibrillate Lyocell fiber, and then the effects of different factors including NaOH concentration, homogeneous time, temperature and bath ratio on the fibrillation degree of Lyocell fiber were investigated through the orthogonal experiment. Various characterization techniques were employed to compare the fibrillation degree of Lyocell fiber. The polarized light microscope (POM) and scanning electron microscope (SEM) were used to observe the appearance of the fiber after different treatment, and the results showed that it was a quick and efficient approach to obtain the fibrillated Lyocell fiber by homogenization treatment, and the fibrillation degree of fibers varied with different treatment conditions. The results of water retention value (WRV) and the characteristic parameter of the fibrillation degree revealed that the ranking of factors affecting the fibrillation degree of fibers was NaOH concentration > homogeneous time > temperature > bath ratio, using the extreme difference analysis and variance analysis methods. The degree of fibrillation was influenced dominantly by NaOH concentration, rather than any other three factors. By means of BET test, the specific surface area of treated fiber showed a similar trend with WRV, and they matched well with fibril amount on the fibers observed by SEM.

Dope dyeing of lyocell fiber with NMMO-based carbon black dispersion

NMMO-based carbon black (CB) dispersion was prepared and its properties as well as its compatibility with lyocell spinning solution were further investigated. Modified lignosulfonate (SP) was verified to be the preeminent dispersant for the preparation of NMMO-based CB dispersion with mass ratio of SP to CB 20% and water to NMMO 13%. The compatibility of NMMO-based CB dispersion with lyocell spinning solution had close relation with dispersant structure and CB content. Mass ratio of CB to cellulose affects the mechanical properties, color strength and crystallinity of lyocell fiber. 0.5% CB increased the breaking strength and elongation of lyocell fiber, whiles breaking strength and elongation of the lyocell fiber were reduced slightly when 2.0% CB was used. The dope dyed fiber showed excellent rubbing and washing fastness as well as migration resistance to water, ethanol and acetone.

Quantitative Analysis Method for Tencel A100 and Viscose Fiber Mixtures

This paper presents a quantitative analysis method for determining Tencel A100 (lyocell) fiber and viscose fiber content, and that of their blends, using a formic acid/zinc chloride dissolution procedure. Ultrasonic treatment was used in this procedure. A standard curve was generated to measure fiber content. This minimized errors caused by laboratory temperature changes, reagents and instruments used, and human factors.

Qualitative Analysis of Tencel A100 Fiber and Selected Regenerated Cellulose Fibers

This research studies the solubility properties of certain regenerated cellulose fibers in commonly-used acidic reagents, including formic acid/zinc chloride. A dissolution method for qualitative identification of Tencel A100 (lyocell) fiber in the presence of various other regenerated cellulose fibers was established. This qualitative method was simple, rapid, and had high sensitivity.

Permeability and Wicking Properties of Modal and Lyocell Woven Fabrics Used for Clothing

In this study, air permeability, water vapor permeability and wicking properties of certain woven fabrics, which are important comfort properties for clothes and garments, have been investigated. The effects of raw material (modal, Lyocell), weave pattern (plain, 2/2 twill, 1/3 twill, 2/2 matt) and weft yarn density (18, 22, 26) on these properties have been analysed graphically and statistically. The comfort characteristics of fabrics (permeability and wicking properties) are closely associated with the changes in their structural parameters: 2/2 matt and plain woven fabrics, where porosities are high, have better permeability and wicking properties. Increasing weft yarn density lead to decreases in porosity, resulting in decreased permeability and wicking properties. Increasing yarn twist increased the porosity of the fabrics. Lyocell fabrics showed improved permeability and wicking properties over modal fabrics due to Lyocell fibers’ high percentage of fibrillary structure.

Analysis of moisture sorption in lyocell-polypropylene composites

The preparation of composites by thermoforming of intermingled fibre slivers is an efficient method to receive high performance and lightweight materials. Cellulosic fibres have benefits like low density and sustainability but the sorption of water due to the high hydrophilicity of the cellulose requires attention. The swelling of the wet fibres changes the fibre-matrix adhesion and as a consequence, the mechanical strength of the composite is influenced negatively. In this study, the thermoplastic polypropylene was combined with lyocell fibres as reinforcement. Moisture sorption isotherms of cellulose/polypropylene composites were recorded as function of relative humidity. Additionally, the specific surface area was analysed by the Brunauer–Emmett–Teller model. It has been found, that the moisture sorption is influenced by the polypropylene (PP) ratio in the composites. At 60% relative humidity the moisture uptake of the lyocell fibres was reduced from 10.8 to 5.8% for lyocell embedded in a composite with 50% polypropylene. Besides the hysteresis between moisture sorption/desorption cycles was found to be proportional to the increased content of PP. The “Parallel Exponential Kinetics” (PEK) model was used to analyse the kinetics of moisture sorption of these composites in more detail. With the help of the PEK model the sorption/desorption kinetics were described by a fast and slow moisture sorption/desorption process. The capacity for rapid moisture sorption is reduced by the formation of PP layers on the lyocell surface. The share of slow moisture sorption increased with increasing PP content in the composite. The results support understanding of the interaction of water with cellulose containing composites.

Nonspecific protein adsorption on cationically modified Lyocell fibers monitored by zeta potential measurements

Nonspecific protein deposition on Lyocell fibers via a cationization step was explored by adsorption of two different N,N,N-trimethyl chitosan chlorides (TMCs). Both, the cationization and the subsequent protein deposition steps were performed and monitored in situ by evaluating the zeta potential using the streaming potential method. Both employed TMCs (degree of substitution with N+Me3Cl groups: 0.27 and 0.64) irreversibly adsorb on the fibers as proven by charge reversal (−12 to +7mV for both derivatives) after the final rinsing step. Onto these cationized fibers, BSA was deposited at different pH values (4, 5, and 7). Charge titrations revealed that close to the isoelectric point of BSA (4.7), BSA deposition was particularly favored, while at lower pH values (pH 4), hardly any adsorption took place due to electrostatic repulsion of the cationic fibers and the positively charged BSA. This work sets the foundation for further investigations to use zeta potential measurements for protein adsorption studies on fibrous materials.

Responses of fabric from lyocell/natural bamboo yarn to loading

With the growing demand for more comfortable, healthier and environmentally friendly products, research and development has been increasingly focusing on new environmentally friendly materials and products. One of the environmentally friendly materials is the bamboo fibre with its numerous favourable performing properties. The use of bamboo fibres increases every year, which was the main reason for choosing yarn from the mixture of lyocell fibres and natural bamboo fibres with the ratio 80/20 for the research. With the research, the tensile behaviour of woven fabrics with cotton yarn in warp and lyocell/natural bamboo yarn in the weft direction in comparison with cotton woven fabrics was studied. Twelve fabrics which differed in their construction properties were designed and produced. Two different weaves were chosen, i.e. plain and twill weave, and three different densities in weft. The results of the research show that the presence of lyocell/natural bamboo yarn in the weft direction improves the mechanical properties such as breaking stress, stress in the yield point, elasticity modulus in the weft direction of analysed fabrics, while in the warp direction, the weave type and weave density express a greater influence on the mechanical properties of analysed fabrics.

Steam explosion pretreatment used to remove hemicellulose to enhance the production of a eucalyptus organosolv dissolving pulp

The steam explosion (SE) pretreatment associated with the organosolv process was investigated to produce dissolving pulp from eucalyptus. Prehydrolysis Kraft (PHK) pulping was also done to produce viscose and acetate grade pulps as reference. The organosolv pulps were delignified in two steps with sodium chlorite. Viscose and acetate grade PHK pulps were bleached by OD0(EH)D1P and OD0(EP)D1PCCE sequences, respectively. Dilute acid-catalyzed (with acid addition) SE pretreatment dissolved more xylan than auto-catalyzed (no acid addition) SE pretreatment. Steam-exploded unbleached organosolv pulps showed lower residual lignin content and screened yield than unbleached organosolv pulps without SE pretreatment. Steam explosion pretreatment helped to decrease lignin content and damaged fiber length of unbleached organosolv pulps. The 1.0% H2SO4 organosolv pulp (organosolv dissolving pulp at bioconversion conditions) showed the highest reactivity. Even showing low viscosity for some applications, in general, the organosolv dissolving pulps produced in this study can be used for making lyocell fibers.

Lyocell fibers for textile processing derived from organically grown hemp

Because of world-wide persistent demand for cellulose man-made fibers suitable in textile processing and application and the predicted stagnation of cotton production, there is a strong need for innovative approaches to safeguard the future availability of dissolving pulps for cellulose fiber production. The paper will present the results of a national network project, which was focused on the development of an integrated process chain for the manufacturing of novel fabrics produced of man-made Lyocell fibers derived from organically grown hemp (OG hemp). The whole process line was established within the process studies starting from hemp cultivation, machine-aided harvesting and automatic peeling to isolate hemp bast stripes (HBS) from stems, pulp manufacturing and transfer into fibers by solution spinning up to processing to yarns and dyed and finished fabrics.More representative, the paper will specifically describe the transfer of almost free of shives extracted, retted hemp fibers and dried HBS into dissolving pulp by means of a specific adjusted pulp cooking process. The main challenges in that step were identification as well as practical development of suitable process approaches for degumming, DP adjustment and purification from contained light and heavy metal traces. Furthermore, the pulp had to be assessed for its usability in direct dissolution process. For that purpose dopes were prepared and characterized regarding optimal DP adjustment, the insoluble parts in dopes and the thermal dope stability at elevated temperatures. After identification and application of most favored process parameters the dissolved pulps could be converted into Lyocell fibers by solution spinning applying the most suitable dry-wet shaping procedure conditions. Manufactured fibers exhibit comparable properties in fineness, tensile strength, elongation and loop tenacity like common Lyocell fibers made of conventional wooden pulp. In project R&D activities obtained fibers had been further processed into yarns, fabrics and apparel demonstrators applying conventional processing parameter. The manufactured LyohempTM clothes offer excellent product qualities as well as wearing properties.

Cellulose Fiber-Reinforced PLA versus PP

The present study focuses on a comparison between different cellulose fiber-reinforced thermoplastics. Composites were produced with 30 mass-% lyocell fibers and a PLA or PP matrix with either an injection (IM) or compression molding (CM) process. Significant reinforcement effects were achieved for tensile strength, Young’s modulus, and Shore D hardness by using lyocell as reinforcing fiber. These values are significantly higher for PLA and its composites compared to PP and PP-based composites. Investigations of the fiber/matrix adhesion show a better bonding for lyocell in PLA compared to PP, resulting in a more effective load transfer from the matrix to the fiber. However, PLA is brittle while PP shows a ductile stress-strain behavior. The impact strength of PLA was drastically improved by adding lyocell while the impact strength of PP decreased. CM and IM composites do not show significant differences in fiber orientation. Despite a better compaction of IM composites, higher tensile strength values were achieved for CM samples due to a higher fiber length.