As-spun Fibers Research Articles

Fabrication of melt-spun fibers from irradiation modified biocompatible PLA/PCL blends

The effect of electron induced reactive processing (EIReP) on the properties of biodegradable polylactide/masticated polycaprolactone (PLA/PCL) blends was firstly investigated without introducing any chemical additives. Subsequently, the melt spinnability of EIReP modified PLA/PCL blends was explored by a piston spinning. Different PCL concentrations (0, 5 and 10 wt%), applied dose (0, 12.5 and 25 kGy) and take up speeds (500 and 2000 m min−1) were evaluated in order to investigate their influences on the fiber morphology, thermal and mechanical properties. SEM investigation indicated that the non-irradiated PLA/PCL fibers demonstrated less uniform diameter. However, the EIReP modification leads to a homogenous fiber diameter distribution hence uniform as-spun fibers can be produced. The crystallinity of PLA phase increased concomitantly with increased PCL contents for all fibers, whereas it slightly reduced by increasing dose. In addition, the crystallinity degree of neat PLA raised from 6.19 to 36.05% by increasing take up speed from 500 to 2000 m min−1. Interestingly, the irradiated PLA/PCL blend fibers with 5 and 10 wt% PCL demonstrated an increased fracture strain of 48.7 and 34.4%, respectively, compared with their non-irradiated fibers. It can be due to the enhanced chain entanglements and interfacial bonding between two phases. However, the irradiated fibers demonstrated similar initial modulus and reduced tenacity compared with the non-irradiated fibers.

High-yield production of a super-soluble miniature spidroin for biomimetic high-performance materials

The mechanical properties of artificial spider silks are approaching a stage where commercial applications become realistic. However, the yields of recombinant silk proteins that can be used to produce fibers with good mechanical properties are typically very low and many purification and spinning protocols still require the use of urea, hexafluoroisopropanol, and/or methanol. Thus, improved production and spinning methods with a minimal environmental impact are needed. We have previously developed a miniature spider silk protein that is characterized by high solubility in aqueous buffers and spinnability in biomimetic set-ups. In this study, we developed a production protocol that resulted in an expression level of >20 g target protein per liter in an Escherichia coli fed-batch culture, and subsequent purification under native conditions yielded 14.5 g/l. This corresponds to a nearly six-fold increase in expression levels, and a 10-fold increase in yield after purification compared to reports for recombinant spider silk proteins. Biomimetic spinning using only aqueous buffers resulted in fibers with a toughness modulus of 74 MJ/m3, which is the highest reported for biomimetically as-spun artificial silk fibers. Thus, the process described herein represents a milestone for the economic production of biomimetic silk fibers for industrial applications.

Influence of the carbonization temperature on the properties of carbon fibers based on technical softwood kraft lignin blends

Lignin is an interesting renewable resource for carbon fibers. In this work we investigate the usage of unpurified softwood kraft lignin Indulin AT for melt-spinning of lignin-fibers and the properties of resulting lignin and carbon fibers. Indulin AT is blended with 10, 15 and 20 wt% polyethylene glycol (PEG) and melt-spun on a pilot plant. The obtained as-spun lignin fibers are stabilized in air and afterwards transformed to carbon fibers at carbonization temperatures of 900 °C, 1500 °C, 2000 °C and 2300 °C. Along the process chain the fibers are characterized by mechanical testing, scanning electron microscopy, X-ray diffraction (XRD) and Raman spectroscopy to provide insight into the structure and quality of the lignin and carbon fibers. Additionally, analytical studies show strong intermolecular interactions between Indulin AT and polyethylene glycol. Despite the high ash content the resulting carbon fibers exhibit promising mechanical properties. XRD and Raman show the increase in ordered carbon structures with an increasing carbonization temperature. Blends of unpurified Indulin AT and PEG are successfully used for melt-spinning of lignin fibers and production of low-cost carbon fibers thereof.

Electrospun Nickel Manganite (NiMn2O4) Nanocrystalline Fibers for Humidity and Temperature Sensing.

Nickel manganite nanocrystalline fibers were obtained by electrospinning and subsequent calcination at 400 °C. As-spun fibers were characterized by TG/DTA, Scanning Electron Microscopy and FT-IR spectroscopy analysis. X-ray diffraction and FT-IR spectroscopy analysis confirmed the formation of nickel manganite with a cubic spinel structure, while N2 physisorption at 77 K enabled determination of the BET specific surface area as 25.3 m2/g and (BJH) mesopore volume as 21.5 m2/g. The material constant (B) of the nanocrystalline nickel manganite fibers applied by drop-casting on test interdigitated electrodes on alumina substrate, dried at room temperature, was determined as 4379 K in the 20–50 °C temperature range and a temperature sensitivity of −4.95%/K at room temperature (25 °C). The change of impedance with relative humidity was monitored at 25 and 50 °C for a relative humidity (RH) change of 40 to 90% in the 42 Hzπ1 MHz frequency range. At 100 Hz and 25 °C, the sensitivity of 327.36 ± 80.12 kΩ/%RH was determined, showing that nickel manganite obtained by electrospinning has potential as a multifunctional material for combined humidity and temperature sensing.

Thermotropic liquid crystalline copolyester fibers according to various heat treatment conditions

Thermotropic liquid crystal copolyester (TLCP) was synthesized using a melt polymerization method, with a molar ratio composition of 2,5-diethoxy terephthalic acid (ETA), hydroquinone (HQ), and p-hydroxybenzoic acid (HBA) of 1:1:3. TLCP exhibited nematic liquid crystalline mesophase and maintained nematic textures under all heat treatment conditions applied. The synthesized TLCP was processed into fibers using a capillary rheometer. The liquid crystalline mesophase, thermo-mechanical properties, and morphology of TLCP fibers obtained under various heat treatment conditions were investigated. The thermo-mechanical properties of the heat-treated fibers were improved compared to those of the as-spun fibers. The best results were obtained for TLCP fibers annealed at 230 °C for 9 h. The heat-treated fibers showed a well-developed microfiber morphology compared to the as-spun fibers. In the spun fibers, a skin–core morphology was observed regardless of the heat treatment conditions, and a well-developed fiber morphology better than the core area was observed in the skin area. The diameter of the fiber heat-treated at 230 °C for 9 h was approximately 60–110 nm.

Transient Confinement of the Quaternary Tetramethylammonium Tetrafluoroborate Salt in Nylon 6,6 Fibres: Structural Developments for High Performance Properties.

A temporary confinement of the quaternary tetramethylammonium tetrafluoroborate (TMA BF4) salt among polyamide molecules has been used for the preparation of aliphatic polyamide nylon 6,6 fibres with high-modulus and high-strength properties. In this method, the suppression or the weakening of the hydrogen bonds between the nylon 6,6 segments has been applied during the conventional low-speed melt spinning process. Thereafter, after the complete hot-drawing stage, the quaternary ammonium salt is fully extracted from the drawn 3 wt.% salt-confined fibres and the nascent fibres are, subsequently, thermally stabilized. The structural developments that are acquired in the confined-nylon 6,6 fibres are ascribed to the developments of the overall fibres’ properties due to the confinement process. Surprisingly, unlike the neat nylon 6,6 fibres, the X-ray diffraction (XRD) patterns of the as-spun salt-confined fibres have shown diminishing of the (110)/(010) diffraction plane that obtained pseudohexagonal-like β’ structural phase. Moreover, the β’ pseudohexagonal-like to α triclinic phase transitions took-place due to the hot-drawing stage (draw-induced phase transitions). Interestingly, the hot-drawing of the as-spun salt-confined nylon 6,6 fibres achieved the same maximum draw ratio of 5.5 at all of the drawing temperatures of 120, 140 and 160 °C. The developments that happened produced the improved values of 43.32 cN/dtex for the tensile-modulus and 6.99 cN/dtex for the tensile-strength of the reverted fibres. The influences of the TMA BF4 salt on the structural developments of the crystal orientations, on the morphological structures and on the improvements of the tensile properties of the nylon 6,6 fibres have been intensively studied.

A comprehensive investigation on the chemical structure character of spinnable pitch for improving and optimizing the oxidative stabilization of coal tar pitch-based fiber

Oxidative stabilization is the critical step to maintain the fibrous morphology of pitch fiber and affects mechanical properties of resultant carbon fiber, but the detailed oxidation mechanism is still unclear because of the complex polycyclic aromatic hydrocarbons composition in pitch fiber. In here, pitch fiber was obtained from coal tar pitch followed by air-blowing and spinning. The chemical structure character of corresponding fibers before and after oxidative stabilization at different temperatures (260–320 °C) and durations (2–12 h) were analyzed. The results indicated that aromatic nucleus in spinnable pitch was gradually increased, while aliphatic chains were gradually shorten with prolongation of air-blowing time. The spinnable pitch obtained by air-blowing at 330 °C for 4 h showed excellent spinning performance, and the as-spun pitch fiber displayed a higher oxidative stabilization efficiency because the lower oxygen content was introduced and more C-O-C groups were formed in the resultant oxidative stabilized pitch fiber. The obtained pitch-based carbon fiber, after carbonizing at 1000 °C, showed excellent mechanical properties with tensile strength of 1068.7 ± 100.0 MPa and Young's modulus of 52.5 ± 9.8 GPa. This work provided a facile approach to improve and optimize the oxidative stabilization efficiency for pitch carbon fiber preparation.

Highly flexible and strong SiC fibre mats prepared by electrospinning and hot-drawing

ABSTRACT Silicon carbide (SiC) fibres are widely used as promising reinforcement in ceramic matrix composites due to their excellent mechanical and thermal properties. In this work, sub-micrometer SiC fibres were prepared by electrospinning using polycarbosilane as the precursor, followed by curing in air and pyrolysing at high temperatures. The effect of the microstructure of SiC fibres on mechanical properties was investigated and the SiC fibre mats prepared at 1300°C for 2 h exhibited a mechanical strength of 184.5 ± 19.4 MPa. Hot-drawing was conducted on as-spun fibres during the curing process and the strength, Young’s modulus, and flexibility of SiC fibre mats were improved. The strength with a drawing ratio of 200% reaches 243.0 ± 17.5 MPa. The enhancement of mechanical strength after hot-drawing is mainly attributed to the reduced defects in fibres, improvement in the orientation of the precursor fibres as well as the alignment of the molecular chains in the precursor fibres.

Fiber Formation and Structural Development of HBA/HNA Thermotropic Liquid Crystalline Polymer in High-Speed Melt Spinning.

High-speed melt spinning of thermotropic liquid crystalline polymer (TLCP) resin composed of 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-napthoic acid (HNA) monomers in a molar ratio of 73/27 was conducted to investigate the characteristic structure development of the fibers under industrial spinning conditions, and the obtained as-spun TLCP fibers were analyzed in detail. The tensile strength and modulus of the fibers increased with shear rate in nozzle hole, draft in spin-line and spinning temperature and exhibited the high values of approximately 1.1 and 63 GPa, respectively, comparable to those of industrial as-spun TLCP fibers, at a shear rate of 70,000 s−1 and a draft of 25. X-ray diffraction demonstrated that the mechanical properties of the fibers increased with the crystalline orientation factor (fc) and the fractions of highly oriented crystalline and non-crystalline anisotropic phases. The results of structure analysis indicated that a characteristic skin-core structure developed at high drafts (i.e., spinning velocity) and low spinning temperatures, which contributed to weakening the mechanical properties of the TLCP fibers. It is supposed that this heterogeneous structure in the cross-section of the fibers was induced by differences in the cooling rates of the skin and core of the fiber in the spin-line.

Mechanically Strong Proteinaceous Fibers: Engineered Fabrication by Microfluidics

Lightweight and mechanically strong natural silk fibers have been extensively investigated over the past decades. Inspired by this research, many artificial spinning techniques (wet spinning, dry spinning, electrospinning, etc.) have been developed to fabricate robust protein fibers. As the traditional spinning methods provide poor control over the as-spun fibers, microfluidics has been integrated with these techniques to allow the fabrication of biological fibers in a well-designed manner, with simplicity and cost efficiency. The mechanical behavior of the developed fibers can be precisely modulated by controlling the type iop and size of microfluidic channel, flow rate, and shear force. This technique has been successfully used to manufacture a broad range of protein fibers, and can accelerate the production and application of protein fibers in various fields. This review outlines recent progress in the design and fabrication of protein-based fibers based on microfluidics. We first briefly discuss the natural spider silk-spinning process and the microfluidics spinning process. Next, the fabrication and mechanical properties of regenerated protein fibers via microfluidics are discussed, followed by a discussion of recombinant protein fibers. Other sourced protein fibers are also reviewed in detail. Finally, a brief outlook on the development of microfluidic technology for producing protein fibers is presented.

Dual-function ZIF-8 membrane supported on alumina hollow fiber membrane for copper(II) removal

The as-spun alumina hollow fiber membrane was used as membrane support for the development of ZIF-8 membrane. The ZIF-8 layers were successfully grown on the support by using the in-situ solvothermal method and layer-by-layer method. The morphology and physicochemical properties of the membranes were characterized using the field emission scanning electron microscope (FESEM), X-ray diffraction spectrophotometer (XRD), Fourier-Transform Infrared Spectrophotometer (FTIR). The adsorption study revealed that the removal of copper(II) ion was pH-dependent. The adsorption capacity for copper(II) adsorption is 76.5 mg/g. The adsorption mechanism of copper(II) onto the ZIF-8 membrane was best fitted to the Freundlich isotherm and pseudo-second-order model. The filtration study showed that the membranes could remove up to 90% of copper(II) ions from the aqueous solution.

Melt-Spun Fibers from Bio-Based Polyester-Fiber Structure Development in High-Speed Melt Spinning of Poly(ethylene 2,5-furandicarboxylate) (PEF).

Poly(ethylene 2,5-furandicarboxylate) (PEF) is regarded as a bio-based alternative or complementary polyester for the widely used fossil resource-based polyester, poly(ethylene terephthalate) (PET). High-speed melt spinning of PEF of low and high molecular weight (L-PEF, H-PEF) was conducted, and the structure and properties of the resultant as-spun fibers were investigated. The occurrence of orientation-induced crystallization was confirmed for the H-PEF at the take-up velocity of 6.0 km/min, the highest speed for producing PET fibers in the industry. Molecular orientation and crystallinity of the as-spun fibers increased with the increase of take-up velocity, where the H-PEF fibers always showed a higher degree of structural development than the L-PEF fibers. The tensile modulus of the high-speed spun H-PEF fibers was relatively low at 5 GPa, whereas a sufficiently high tensile strength of approximately 500 MPa was measured. These values are adequately high for the application in the general semi-engineering fiber field.

The effect of various electrospinning parameter on preparation of alumina nanofibers

Alumina nanobers were successfully prepared via an electrospinning technique with combination of aluminum oxyhydroxide (AlOOH) as alumina precursor and Polyvinylpyrrolidone (PVP) as the polymer precursor. To produced alumina precursor, Aluminum Isopropoxide (AIP) was dissolved in distilled water under the constant stirring process at 80°C. Electrospinning solution was prepared by mixing Aluminum Oxyhydroxide (AlOOH) and Polyvinylpyrrolidone (PVP) aqueous solution for 2 hours under room temperature. Different concentrations of polymer precursor and various electrospinning parameters such as applied voltage, distance tip to collector, and flowrate of sol-gel were studied. The as-spun fibers were calcined at 1200°C and characterized by SEM. Results showed that the average fiber diameter decreases with decreasing of Polyvinylpyrrolidone (PVP) solution concentration, increasing of applied voltages and decreasing of electrospinning flow rate. At 10%wt Polyvinlpyrrolidone (PVP) concentration with 17.5v of applied voltages and 0.03 ml/min of flow rates, calcined fibers showed an average diameter of 100-200nm.

Preparation of poly(ethylene-2,6-naphthalate) nanofibers by CO2 laser supersonic drawing

Poly(ethylene-2,6-naphthalate) (PEN) nanofibers were prepared by carbon dioxide laser supersonic drawing (CLSD). The CLSD method was carried out by irradiating the as-spun PEN fiber with a laser in a low-temperature supersonic jet. The supersonic jet was generated by blowing the air from the fiber supplying orifice into a vacuum chamber. The thinnest nanofiber obtained at a laser power of 4 W and a chamber pressure of −98 kPa had an average fiber diameter of 0.249 μm. The DSC curve of this nanofiber showed two melting peaks: 260 °C and 285 °C. The higher melting temperature is 25 °C higher than the melting temperature of the original fiber. The higher melting peak is caused by an increase in the intermolecular forces in the crystallite and by the tie molecules connecting adjacent crystallites becoming fully extended. Thus, nanofibers produced by CLSD exhibit a higher melting peak, which is a unique feature. The increase in melting temperature is attributed to the supramolecular sequence effect, which is a nanoscale effect. CLSD is a new method for making nanofibers without the use of any solvent or removal of a second component. Poly(ethylene-2,6-naphthalate) (PEN) nanofibers were prepared by carbon dioxide laser supersonic drawing (CLSD). The CLSD method was carried out by irradiating the as-spun PEN fiber with a laser in a low-temperature supersonic jet, which was generated by blowing the air from the fiber supplying orifice into a vacuum chamber. The DSC curve of the PEN nanofibers produced by CLSD showed two melting peaks: 260 °C and 285 °C. The increase in melting temperature is attributed to the supramolecular sequence effect, which is a nanoscale effect.

Tentative Confinement of Ionic Liquids in Nylon 6 Fibers: A Bridge between Structural Developments and High-Performance Properties

A reversible confinement of ionic liquid (IL) among the amide segments has been carried out for the preparation of high-modulus and high-strength aliphatic semicrystalline nylon 6 fibers. In this research work, the suppression or the weakening of the hydrogen bonds during the conventional low-speed melt spinning process is followed by a hot-drawing stage and a subsequent IL extraction of the IL out of the 2% wt IL-confined fibers and an immediate thermal stabilization process for the improvement of the properties of the pristine nylon 6 fibers. The resulted crystal structural developments of the IL-confined fibers are attributed to ultimate molecular orientations, which have contributed to the developments of the overall fiber properties. Here, the influences of the IL on the γ and the α crystal phases, the γ-α transition, the morphological properties, and the tensile properties are investigated. The FTIR reported, experimentally, additional peaks at 1237 cm–1 for the γ crystal phase and at 1417 and 1476 cm–1 for the α crystal phase, in conformity with the theoretical computations. The XRD demonstrated that the conventional low-speed melt spinning can successfully be used to prepare as-spun IL-confined fibers having highly improved properties. The so prepared as-spun IL-confined fibers are found to have a γ phase structure that has a small crystal size and high crystal perfections. Fortunately, the γ-to-α crystal phase transition for the IL-confined nylon 6 fibers can be acquired during the hot-drawing stage (stress-induced phase transformation). Furthermore, the IL extraction process followed by a thermal stabilization process, interestingly, has led to significant increases in both of the tensile strengths and the tensile moduli of the reverted nylon 6 fibers. The values that are found are 8.46 cN/dtex for the tensile strength and 39.09 cN/dtex for the tensile modulus. The structure–property relationships between the IL-confined and the reverted nylon 6 fibers have also been discussed.

Integration of multivariate control charts and decision tree classifier to determine the faults of the quality characteristic(s) of a melt spinning machine used in polypropylene as-spun fiber manufacturing Part I: The application of the Taguchi method and principal component analysis in the processing parameter optimization of the melt spinning process

Melt spinning is the most extensively used method of fabricating polymeric fibers in the textile industry. This series of studies aimed to construct an automatic abnormality diagnosis system for polypropylene (PP) as-spun fiber produced by the melt spinning process. Part I of this study aimed to construct the processing parameter optimization for the PP as-spun fiber produced by the melt spinning machine. The product quality resulting from the processing parameters of the melt spinning process included six control factors: extruder temperature, gear pump temperature, die-head temperature, rotational speed of extruder, rotational speed of gear pump, and take-up speed. The quality characteristics included fiber fineness, breaking strength, breaking elongation, and modulus of resilience. The quality data were derived from the experiments, the design of which were based on the orthogonal array of the Taguchi method in order to calculate the signal-to-noise ratio, analysis of variance, and confidence interval. Principal component analysis was then applied to eliminate the multi-correlation of the output responses and transform the correlated responses into principal components, to obtain multi-quality optimum processing parameters. These optimum parameters, including the extruder temperature (180°C), gear pump temperature (220°C), die-head temperature (240°C), the rotational speed of the extruder (7.5 rpm), the rotational speed of the gear pump (15 rpm), and take-up speed (700 rpm) would later be used to build a prediction of an abnormality diagnosis system for identification of fault processing parameters in a melt spinning machine in Part II of this study.

Flexible Phase Change Material Fiber: A Simple Route to Thermal Energy Control Textiles.

A flexible hollow polypropylene (PP) fiber was filled with the phase change material (PCM) polyethylene glycol 1000 (PEG1000), using a micro-fluidic filling technology. The fiber’s latent heat storage and release, thermal reversibility, mechanical properties, and phase change behavior as a function of fiber drawing, were characterized. Differential scanning calorimetry (DSC) results showed that both enthalpies of melting and solidification of the PCM encased within the PP fiber were scarcely influenced by the constraint, compared to unconfined PEG1000. The maximum filling ratio of PEG1000 within the tubular PP filament was ~83 wt.%, and the encapsulation efficiencies and heat loss percentages were 96.7% and 7.65% for as-spun fibers and 93.7% and 1.53% for post-drawn fibers, respectively. Weak adherence of PEG on the inner surface of the PP fibers favored bubble formation and aggregating at the core–sheath interface, which led to different crystallization behavior of PEG1000 at the interface and in the PCM matrix. The thermal stability of PEG was unaffected by the PP encasing; only the decomposition temperature, corresponding to 50% weight loss of PEG1000 inside the PP fiber, was a little higher compared to that of pure PEG1000. Cycling heating and cooling tests proved the reversibility of latent heat release and storage properties, and the reliability of the PCM fiber.

Super-hydrophobic PTFE hollow fiber membrane fabricated by electrospinning of Pullulan/PTFE emulsion for membrane deamination

• PTFE hollow fiber membrane was fabricated via electrospinning with no organic solvent. • Pullulan was used as the carrier of the PTFE for electrospinning. • The prepared membrane shows high porous, superhydrophobicity and high LEP. • The K OE of the prepared membrane is 1.6–2.4 times higher than commercial membrane. Polytetrafluoroethylene (PTFE) is increasingly used in membrane applications due to its excellent thermal stability, resistance to chemical degradation and strong hydrophobicity. However, it is difficult to prepare high flux membranes by conventional technology due to its high melt viscosity and solvent resistance. Here, a environment-friendly technology is used to fabricate PTFE hollow fiber membrane via emulsion electrospinning. Pullulan is dope into the PTFE emulsion and employ as the binder of PTFE particles to facilitate the formation of the as-spun PTFE-Pullulan hollow fiber membrane. The expected PTFE hollow fiber membrane is obtained after sintering of the as-spun membrane. No organic solvent is used and no pollutant is discharged during the preparation process. The prepared PTFE hollow fiber membrane shows excellent properties such as superhydrophobicity (contact angle > 150°), high porosity (85%) and excellent mechanical properties (Young's modulus of 39 MPa and fracture strain of 245%). In the deamination test, the experimental mass transfer coefficient of the PTFE hollow fiber membrane reaches 2.4*10 −5 m/s when the pH is 11, which is 1.6–2.4 times as that of the commercial membrane. The self-made PTFE hollow fiber membrane shows great potential in the application of membrane deamination.

Effect of calcination temperatures on HfO2 fibers via electrospinning

Hafnium oxide (HfO2) fibers can be widely used in ultra-high temperature ceramics (UHTCs) as reinforced material in order to achieve better antioxidant performance and less cracks and flaking on surface of UHTCs in field of ultra-high temperature thermal protectors. Calcination temperature is one of essential parameters for forming HfO2 fiber. In this work, one-dimensional (HfO2) fibers were prepared through the electrospinning method and further post-calcination treatment. During the calcination treatment, the monoclinic-HfO2 (m-HfO2) was formed from as-spun HfO2 fibers at 432 °C, and only a small amount of m-HfO2 was converted into the tetragonal HfO2 at 1013 °C, which can increase the fiber density and decrease the grain size. However, the remaining m-HfO2 was directly converted into the cubic HfO2 at 1351 °C. The unique temperatures of forming monoclinic, tetragonal, cubic phase were much lower than the phase-transition temperature. The prepared HfO2 fiber could still maintain fibrous morphology after 10 times cyclic thermal shock in air. Moreover, the fibers calcined at 900 °C and 1200 °C have better thermal shock resistance for their stable phase and fibrous morphology with uniform grain growth after the thermal shock test.

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