Lyocell Research Articles

Enhancing the flame retardancy of lyocell fabric finished with an efficient, halogen-free flame retardant.

A novel flame retardant (PNPG) containing phosphorus and nitrogen was synthesized through the reaction of neopentyl glycol, phosphoric acid and urea, and was then used for preparation of flame retardant lyocell fabric through a dip-dry-cure finishing process. The structure of the PNPG was confirmed by proton nuclear magnetic resonance spectroscopy (1H-NMR) and Fourier transform infrared spectroscopy (FT-IR). The flame retardancy and thermal stability of the treated fabric were evaluated by a cone calorimetry test and thermogravimetric analysis (TG), which showed that the char residue of the treated fabric at 800 °C was as high as 39.7% under a nitrogen atmosphere. At the same time, the peak heat release rate (PHRR) and total heat release (THR) were significantly reduced by 92.9% and 81.2%, respectively. Obviously, the presence of flame retardant can effectively improve the thermal stability and flame retardancy of lyocell fabrics. In addition, thermogravimetric analysis combined with Fourier transform infrared spectroscopy (TG-IR), scanning electron microscopy (SEM), and Raman spectroscopy indicated that the flame retardant mechanism was consistent with the condensed phase and gas phase mechanism. The limiting oxygen index (LOI) of the treated samples could reach 39.3%, moreover, even after 20 laundering cycles (LCs), the LOI values of the samples finished at 28.3% with 120 g L−1 flame retardant remaining, which confirmed the durability and high flame retardancy of the treated samples. In addition, the mechanical properties, whiteness, rigidity and flexibility of the fabrics treated with PNPG were insignificantly reduced within a more acceptable range than the original samples. In summary, the flame retardant described herein has excellent flame retardant properties and char-forming ability, and it is suitable for the preparation of flame retardant lyocell fibers.

Influence of cross-section shape on structure and properties of Lyocell fibers

Three kinds of Lyocell fibers with different cross-sections including circular, H-shape, and Y-shape (abbreviated as O-, H-, and Y-Lyocell) were prepared by a dry-jet wet spinning method. The effects of cross-sectional shape on structure and properties of Lyocell fibers were evaluated. The results showed H-Lyocell and Y-Lyocell exhibited triangular and dumbbell cross-sections, respectively, due to die swell. Both non-roundness factor and crystallinity of different cross-sectional Lyocell fibers were in the order of H-Lyocell > Y-Lyocell > O-Lyocell. All cross-sectional Lyocell fibers showed similar values of fineness and tensile strength. The profiled Lyocell fibers were superior to circular Lyocell fibers in terms of luster, dyeing properties, and moisture regain. The dye uptake and fixation rate of Lyocell fibers were influenced by shape in the order H-Lyocell > Y-Lyocell > O-Lyocell; while for luster and moisture regain the order was Y-Lyocell > H-Lyocell > O-Lyocell. Profiled Lyocell fibers are expected to open broader prospects in different textile or composite fields due to their various advantages versus conventional circular Lyocell fibers.

APPLICATION OF LYOCELL FIBER STRUCTURE FORMATION MECHANISM IN FLAME-RETARDANT MODIFICATION OF LYOCELL FIBER

In order to overcome the disadvantage of Lyocell fiber flammability, two types of flame-retardant finishing liquids, 2-carboxyethyl phenylphosphic acid (CEPPA) and N-hydroxymethyl-3-dimethoxyphosphoacyl propanamide (MDPA), were used in this study to treat Lyocell fiber in two different states: never-dried and dry. The results showed that CEPPA and MDPA can react with the hydroxyl groups of the cellulose and graft onto the Lyocell fiber under appropriate conditions, resulting in increased flame-retardant performance of the fiber, a slight reduction in crystallinity, and a significant decline in mechanical properties. Compared with the dry fiber, the P content and LOI of the fiber obtained by treating the as-spun never-dried Lyocell fiber rose significantly: the P content was higher by 38.9% (for CEPPA) and 20.5% (for MDPA), respectively, while the LOI increased by 6.0% (for CPPA) and 4.0% (for MDPA), respectively, which means that the fiber had better flame-retardant performance. Although the breaking strength of the fiber decreased, it still met the requirements for textiles. In addition, direct flame-retardant treatment of never-dried wet fiber can reduce energy consumption by avoiding repeated drying. Furthermore, the results of this study also have guiding significance for other post-processing procedures for Lyocell fibers, such as dyeing, catalyst infiltration during carbon fiber preparation etc

Quantification of N-methylmorpholine-N-oxide and its main degradation products by nuclear magnetic resonance spectroscopy

An important part of Lyocell fibers production is solvent recycling. Determining the content of the degradation products in the solvent will be helpful to select a reasonable solvent recovery process. However, a suitable method to simultaneously measure N-methylmorpholine-N-oxide and its main degradation products N-methylmorpholine and morpholine has not yet been reported, hence in this paper, a nuclear magnetic resonance spectroscopy method for quantitative analysis of N-methylmorpholine-N-oxide and its major degradation products was established. The feasibility of this nuclear magnetic resonance method was verified by using it to determine the contents of N-methyl morpholine-N-oxide, N-methylmorpholine, and morpholine in analytical samples and actual sample.

Superbase-based protic ionic liquids for cellulose filament spinning

Lyocell fibers have received increased attention during the recent years. This is due to their high potential to satisfy the rising market demand for cellulose-based textiles in a sustainable way. Typically, this technology adopts a dry-jet wet spinning process, which offers regenerated cellulose fibers of excellent mechanical properties. Compared to the widely exploited viscose process, the lyocell technology fosters an eco-friendly process employing green direct solvents that can be fully recovered with low environmental impact. N-methylmorpholine N-oxide (NMMO) is a widely known direct solvent that has proven its success in commercializing the lyocell process. Its regenerated cellulose fibers exhibit higher tenacities and chain orientation compared to viscose fibers. Recently, protic superbase-based ionic liquids (ILs) have also been found to be suitable solvents for lyocell-type fiber spinning. Similar to NMMO, fibers of high mechanical properties can be spun from the cellulose-IL solutions at lower spinning temperatures. In this article, we study the different aspects of producing regenerated cellulose fibers using NMMO and relevant superbase-based ILs. The selected ILs are 1,5-diazabicyclo[4.3.0]non-5-ene-1-ium acetate ([DBNH]OAc), 7-methyl-1,5,7-triazabicyclo[4.4.0] dec-5-enium acetate ([mTBDH]OAc) and 1,8-diazabicyclo[5.4.0]undec-7-enium acetate ([DBUH]OAc). All ILs were used to dissolve a 13 wt% (PHK) cellulose pulp. The study covers the fiber spinning process, including the rheological characterization of the various cellulose solutions. Moreover, we discuss the properties of the produced fibers such as mechanical performance, macromolecular properties and morphology.Graphic abstract

Interaction between N-Methylmorpholine N-Oxide, Water, and the Titanium Dioxide Surface in the Lyocell Process.

Interaction between N-methylmorpholine N-oxide (NMMO), H2O, and the titanium dioxide (TiO2) surface was studied by spectral tests and molecular dynamics simulations as the theoretical foundation for the development of functional lyocell. The molecular structure, movement, and arrangement of the NMMO and water molecules, as well as the interaction energies between them, were characterized. The results show that both water and NMMO molecules can interact with the TiO2 surface, and the water molecule is stronger, which makes the water molecules near the TiO2 surface different from that of the bulk solution. With the increase of the NMMO concentration, NMMO molecules compete with the water molecules adsorbed on the TiO2 surface, and two adsorption conformations of NMMO on the TiO2 surface were found. When the NMMO concentration is higher than 50%, the N-O bond of NMMO is the main position interacting with the TiO2 surface, forming a more stable and complex adsorption molecular layer and enhancing the interaction between TiO2 and the solution, and finally promote the dispersion of TiO2 particle and increase the zero-shear viscosity of the lyocell solution. At the same time, the strong interaction also weakens the N-O bond of the NMMO molecules near the TiO2 surface with the bond length increasing; however, the influence cannot cause instability of NMMO. UV spectra also shows that there is no NMMO decomposition due to the addition of TiO2 during the dissolution process. In conclusion, NMMO can promote the dispersion of the TiO2 nanoparticles in the solvent, and the stability of NMMO is not affected, which is the basis for the preparation of the functional lyocell fiber.

Luminescent Cellulose Fibers Modified with Poly((9-Carbazolyl)Methylthiirane).

This article presents the results of research related to the development of cellulose man-made fibers with luminescent properties. The fibers were obtained from regenerated cellulose with the use of the N-Methylmorpholine-N-Oxide (NMMO) method for lyocell (Tencel) fiber formation. The method is named after the cellulose solvent (NMMO) used to obtain the spinning solution. Fibers are formed by the dry–wet spinning method. Due to the characteristic of the lyocell process, the fibers were easily modified to achieve luminescent properties with star-shaped organic compound poly((9-carbazolyl)methylthiirane) (KMT). Fibers were examined on their mechanical parameters with the use of Zwick Z2.5/TN1S tensile testing machine, and the results show the influence of the KMT concentration in the fiber matrix on mechanical parameters of the fibers. The study also attempted to determine the concentration of the modifier in the fibers with the use of UV-VIS Spectrofluorometer JASCO. The luminescent properties of fibers were estimated as well, using Jobin–Yvon spectrofluorometer FLUOROMAX–4, and the results are very promising as the fibers emit blue light in the range of visible light spectrum even for small concentrations of KMT (about 0.1 wt.%).

ASSESSING WATER-RELATED COMFORT PERFORMANCE OF KNITTED FABRICS MADE OF RAYON MICROFIBERS AND LYOCELL FIBERS FOR INTIMATE WEAR

Comfort properties of knitted fabrics used for intimate wear is an important matter to be dealt with. Hence, the comfort issue of the knitted fabrics made of micro-rayon and lyocell fibers were examined in the current study after they were separately treated with the antibacterial and wicking finishes. Moreover, the effect of spandex was investigated. The fabric samples were analyzed in terms of vertical wicking capacity, transfer wicking, water vapor permeability and drying rate. According to the results, spandex incorporation and process history were found to be influential on the vertical wicking capacity of the fabric samples whereas, spandex incorporation was found as the main affecting parameter for the transfer wicking. Moreover, fiber type and spandex incorporation were both found to have significant effects on the water vapor permeability of the fabric samples. The best fabric option from its alternatives for intimate wear was chosen by the hybrid AHP-TOPSIS approach.

Comparison of Regenerated Cellulose Fibers Spun from Ionic Liquid Solutions with Lyocell Fiber

Comparison of Regenerated Cellulose Fibers Spun from Ionic Liquid Solutions with Lyocell Fiber

Influence of intensified cellulose dissolution process on spinning and properties of lyocell fibres

Effect of intensification of cellulose dissolution process on the spinning of lyocell fibers and their physical properties was systematically investigated. The cellulose dissolution process was intensified by pre-swelling of the pulps that benefited in bringing down the conventional process temperature of 75 °C to 50 °C as well as by assisting in good dissolution and formation of homogeneous dope. Further, effect of dopes prepared from pre-swelled and un-swelled pulps at a lower temperature (i.e. 50 °C) on spinnability and fiber properties, was thoroughly investigated and compared with dopes prepared at 75 °C. The resultant fibers were morphologically and structurally analyzed using SEM and XRD and correlated with their physical properties. It was observed that fibers regenerated from pre-swelled dope, showed increased overall molecular orientation (measured by birefringence) as well as high amorphous orientation that resulted in improved tenacity of the fibers. Finally, it has been observed that cellulose dissolution using pre-swelled method is an energy-efficient technique over un-swelled method (almost 35% at 50 °C and ∼20% at 75 °C of energy saving). Present work makes lyocell process more sustainable and simultaneously enhance fiber properties.

Fabrication of a high phosphorus–nitrogen content modifier with star structure for effectively enhancing flame retardancy of lyocell fibers

A novel phosphoramidate salt fire retardant (FR) with high phosphorus–nitrogen (P–N) content, tris(2-aminoethyl)amine phosphoramidate salt (TAEAPA), was synthesized by a simple design philosophy. A three-arm star-like structure FR with a high level of P or N content was obtained. Phosphorus and nitrogen contents of TAEAPA increased up to 8.6 at% and 14.5 at%, respectively. Subsequently, TAEAPA was employed to finish lyocell fibers through the classical dip-dry-cure technique. Consequently, the thermal stability and fire retardancy of finished lyocell fibers were improved significantly, as evidenced by thermogravimetric and vertical flammability test. Finished lyocell fibers exhibited higher char residues (39.2 wt%) and lower degradation rate (0.6%/°C) under nitrogen atmosphere. Besides, lyocell fabrics finished by 300 g/L of TAEAPA finishing solution only had a char length of 53 mm when exposed to flame more than 60 s, and immediately extinguished after the removal of flame. Thermogravimetry-infrared and pyrolysis gas chromatography/mass spectrometry coupled techniques confirmed that the high contents of P and N included in TAEAPA played a good synergistic effect on both condensed and gaseous phase during the thermal pyrolysis process of lyocell fibers.

The Effect of Alcohol Precipitants on Structural and Morphological Features and Thermal Properties of Lyocell Fibers

This research examines the possibilities of regulating the structure of cellulose precursor fibers spun from solutions in N-methylmorpholine-N-oxide when replacing aqueous coagulation baths with thermodynamically softer alcohol baths at different temperatures. The fibers were spun by the dry jet–wet method in isobutanol coagulation baths with a temperature of 25 °C and 70 °C. The study of the phase state of the solvent–coagulant system using viscometry and point cloud methods revealed the temperature-concentration regions of the single-phase and two-phase states of the system. Using elemental analysis, DSC (differential scanning calorimetry) and XRD (X-ray diffraction) methods, it was shown that just spun fibers, due to the presence of a residual amount of solvent and coagulant in them, regardless of the temperature of the precipitator, have an amorphous structure. Additional washing with water completely washed away the solvent and coagulant as well, however, the structure of cellulose changes slightly, turning into a defective amorphous-crystalline one. A relationship was found between the phase composition, structure, and properties of just spun fibers and precursors washed with water. Thus, the loss of structural ordering of both just spun and washed cellulose fibers leads to a decrease in strength characteristics and an increase in deformation. The thermal behavior of the fibers is determined by their phase composition. Fibers just spun into hot alcohol containing a coagulant and traces of solvent acquire thermal stability up to 330 °C. During the pyrolysis of the obtained precursors up to 1000 °C, the value of the carbon yield doubles. The amorphized structure of the obtained fibers allows us to consider it as a model when analyzing the transformation of the structure of precursors during thermolysis.

Preparation of durable and flame retardant lyocell fabrics by using a biomass-based modifier derived from vitamin C

Lyocell fibers, one of the green and regenerated cellulose fibers, are widely used in the textile fields. However, lyocell fibers are highly flammable which will cause fire accidents. Herein, a novel biomass-based flame retardant derived from vitamin C (VCFR) was designed and synthesized. Then, the lyocell fabrics were finished with VCFR through esterification to fabricate durable flame retardant lyocell fabrics (RF-lyocell). The structure of the different fabrics was characterized by X-ray photoelectron spectroscopy and Fourier transform infrared analysis analysis. The limiting oxygen index value of the FR-lyocell was as high as 39.8%, which still remained 26.4% after 30 washing cycles, indicating excellent flame retardancy and durability. Thermogravimetric-Fourier transform infrared analysis proved that non-combustion compounds, such as CO2 and water were generated, and provided an obvious flame retardant effect in the gas phase. Cone calorimeter tests showed that the peak of heat release rate and total heat release had a reduction of 89.5% and 54.5%, respectively. These results suggested that VCFR can be used as an effective biomass-based flame retardant for lyocell fabrics.

Synthesis and application of a new, facile, and efficient sorbitol-based finishing agent for durable and flame retardant lyocell fibers

In this paper, a simple and facile polyol sorbitol was employed to design and synthesize a novel flame retardant containing phosphorus and nitrogen by the reaction of sorbitol with phosphoric acid and urea. The obtained sorbitol-based flame retardant was then used to treat lyocell fibers by a pad-dry-cure procedure. Formaldehyde and other harmful substances were not used during the preparation of flame retardant and modified fibers. For this strategy, only water is used as solvent, and the conditions are mild, safe and environmentally friendly. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses show that the sorbitol-based flame retardant was successfully grafted onto lyocell fibers. Scanning electron microscopy analyses show that the surface morphology of the treated fibers remained unchanged. Thermogravimetric analyses imply that the residue of the treated fibers increases considerably. Vertical combustion and limit oxygen index results indicate that the treated fibers possess excellent flame retardant and durable properties. Based on the results of pyrolysis gas chromatography–mass spectrometry, thermogravimetric-infrared and Raman spectroscopy, the flame retardant operates in condensed phase and gas phase during burning of treated fibers.

Intensification of lyocell dissolution process and dope characteristics using pre-swelled cellulosic pulp

Transformation of pulp into regenerated lyocell fibre involves a critical step of cellulose dissolution in aqueous NMMO solution. The objective of this work is to investigate the effect of using pre-swelled pulps derived from hardwood kraft sulphate (H-KS) and softwood kraft sulphate (S-KS) process, on cellulose dissolution. Pre-swelling at temperatures follows from 30 °C to 75 °C results in lowering of pulp crystallinity, and hence, was hypothesized to form a homogeneous solution with lower power consumption during the dissolution process. Experimental torque moments (proportional to power consumption) of the un-swelled and pre-swelled pulps at different temperatures were compared and correlated with the cellulose dissolution process. Further, a time based morphological study of cellulose dissolution was performed with the help of a microscopic investigation method. The quality of the dissolved dope was evaluated by optical image analysis, refractive index (RI), dope composition and thermal analysis (TGA/DSC). It was observed that by using pre-swelled pulps, homogeneous cellulose solution could be formed at lower processing temperature, consuming less time and power thereby making the lyocell process more energy-efficient and sustainable.

PERFORMANCE AND CHARACTERIZATION OF ALOE VERA MICROCAPSULES ON SILK/LYOCELL BLENDED FABRIC

In this study, silk and lyocell fibers are blended in the ratio of 50:50 and used in warp and weft directions for the construction of a plain weave fabric. Aloe vera based microcapsules have been used to impart antibacterial finish and its performance on silk/lyocell blended fabrics have been assessed by scanning electron microscope, electron dispersive x-ray, fourier transform infrared spectrum, agar diffusion test, bacterial reduction test, and durability against washing. SEM analysis shows that the aloe vera capsules are impregnated in the fabric. EDX also proved the presence of aloe vera in the fabric by showing the presence of chemicals like Mg, Ca, K, Al and Fe which are not present in the untreated fabric. FTIR spectra of aloe vera treated samples showed an ether group, an alcohol secondary group, an aromatic group and a nitro group which shows the probable chromophoric groups likely to be present in the leaf, gel and root of aloe vera. The results of agar diffusion test clearly showed that aloe vera treated S/L 50:50 blended fabrics have very good antibacterial properties and do not allow the growth of bacteria under the treated fabric. The zone of inhibition was found to be very good and ranged from 28 mm to 30 mm. Bacterial reduction test showed the percentage reduction values of both the microorganisms S. aureus and E. coli to be more than 97%. The wash durability of aloe vera treated fabrics lasted up to 25 washes.

Green Solvent Processed Cellulose/Graphene Oxide Nanocomposite Films with Superior Mechanical, Thermal, and Ultraviolet Shielding Properties.

This study reports for the first time a green process to fabricate Lyocell fiber and graphene oxide (GO) based novel cellulose/graphene oxide nanocomposite (CGN) flexible films for ultraviolet (UV) shielding applications. A polyethelene glycol (PEG) mediated solvent system was utilized to make CGN films via solution casting route. To improve the dispersion of GO sheets in a cellulosic matrix, a reactive interface was formed in between cellulose and oxygenic functionalized groups of GO sheets via cross-linking them with epichlorohydrin (ECH). The addition of GO sheets in cellulose matrix leads to the synergistic changes, which were observed in the structure and surface morphology of CGN nanocomposite films. Enhanced dispersion of GO sheets in CGN films was observed in morphological investigations which is attributed to the adequate cellulose-GO interaction by hydrogen bonding and led to significant enhancement in the mechanical and thermal properties. The tensile strength and Young's modulus of CGN films with 2 wt % GO loading (CGN2) increased to 89 MPa and 4.3 GPa from 55.6 MPa and 2.1 GPa, respectively, as compared to the neat cellulosic film. Additionally, the CGN films exhibited remarkable UV shielding capability which increased with GO loading in a cellulose matrix. The CGN2 film (2 wt % GO loading) possessed outstanding absorbance in the wavelength range of 280 to 400 nm and showed almost complete shielding (∼99%) of UV rays in both the UV-B and the UV-A regions. Moreover, the ultraviolet protection factor of the CGN2 film demonstrated more than 80-fold increase compared to that of the neat cellulose film. The obtained CGN nanocomposite film has a high potential for applications in the field of UV protection.

라이오셀 섬유의 활성화 에너지 및 안정화 시 전처리 조건에 따른 열적 특성 분석

라이오셀 섬유의 활성화 에너지 및 안정화 시 전처리 조건에 따른 열적 특성 분석

Comparative Study on Dyeing of Cotton, Modal and Lyocell Fabrics Using Bifunctional and Polyfunctional Reactive Dyes

Polyfunctional reactive dyes have been introduced by the renowned dye manufacturers in the recent years for better exhaustion and fixation performance. This paper deals with evaluation of the dyeing performance of three cellulosic fibres namely cotton, modal and lyocell with polyfunctional (Avitera Cardinal SE) reactive dye in comparison a bifunctional-(Novacron Brilliant Red FN-3GL) reactive dye. The purpose of this study is to achieve a better understanding of exhaustion and fixation behaviour in dyeing of cotton, modal and lyocell fibres using these two types of reactive dyes. The dyeing was carried out at four different shade% (1%, 2%, 3%, and 4%). Besides studying exhaustion (%) and fixation (%) along with K/S values of dyed fabrics, several other quality parameters e.g. bursting strength, pilling resistance and colour fastness to wash were also examined. Finally, the optimum combination among the three types of cellulosic fabrics and two types of reactive dyes was observed. Lyocell fabric and polyfunctional reactive dyes have been found more sustainable.

Microstructural differences between Viscose and Lyocell revealed by in-situ studies of wet and dry fibers

Regenerated cellulose fibers manufactured using Lyocell and Viscose processes exhibit differences in their structural response to mechanical deformation. Here, we study the effect of stretching and stress relaxation on the orientation of crystal and amorphous phases. Our results show that on stretching, orientation in both crystal and amorphous phases increases linearly with strain, correlating with the increase in stress and with the stretching of the crystalline unit cell along the c-axis. On holding after stretching to a particular strain, the stress relaxes logarithmically in time, correlating with a decrease in the strain along the c-axis of the crystal unit cell. The stress relaxation is also correlated with a logarithmic increase in amorphous orientation, while crystalline orientation stays constant. We attribute the stress development during stretching to deformation of the crystal unit cell, while crystal reorientation in the fiber direction results in increase in the crystalline orientation parameter. On holding the fiber at a fixed total strain, the stress relaxes as strain is transferred from crystal to amorphous regions. Thus, the strain on the unit cell c-axis decreases and amorphous orientation increases. There are quantitative differences between the rate of increase in amorphous phase orientation during stress relaxation for Lyocell and Viscose fibers. For dry fibers, Lyocell shows a slower increase in orientation during stress relaxation. On wetting the fibers, their structural response changes qualitatively. We combine wide angle x ray diffraction and birefringence experiments with our model to infer that that on stretching the wet fiber, the crystalline phase is neither strained nor oriented. However, orientation develops in the amorphous phase. During stress relaxation in wet condition, Lyocell fibers shows a faster increase in amorphous orientation than Viscose fibers, in line with the comparison of relaxation time spectra for wet Viscose and Lyocell fibers.