Fiber Spinning Process Research Articles

Investigation into shear-thinning behavior in wet spinning of carbon nanotube fibers modeled by power law viscosity model

The wet spinning of carbon nanotube (CNT) fibers, a representative solution processing of CNTs, has been advanced through the integration of well-established polymer sciences into their field. However, the flow behavior of CNT dispersions in the narrow spinning line, where its characteristics undergo changes due to the high-shear rate regime, has not been utilized to determine their spinnability, despite being a commonly employed method in the wet spinning of polymer fibers. Herein, we employed the power law viscosity model to investigate the correlation between flow behavior and the spinnability of CNT dispersion through the power law index which approaches to 0 as the shear-thinning behavior strengthens. We suggest that the spinnability of CNT dispersion is proportional to the degree of shear-thinning behavior of the dispersion. We ascribe this correlation to the integrity of CNT fibers which predominantly rely on the strong van der Waals forces between CNTs. These findings offer new insights into the role of fiber integrity in spinnability and provide a framework for optimizing the wet spinning process of CNT fibers through detailed analysis of dispersion flow behavior.

One-step fabrication of hetero-structured polyethersulfone hollow fiber membranes through surface segregation for pervaporation desalination

Hollow fiber membranes (HFMs) are an ideal configuration for industrial applications of pervaporation desalination (PV) membranes. Currently, the efficient fabrication of PV HFMs is restricted by multi-step post-treatment processes on their outer surfaces to form the selective layer. Herein, we utilized the surface segregation strategy to fabricate a hetero-structured HFM in one step, simultaneously forming the hydrophilic dense outer layer and the porous support layer. During hollow fiber spinning process, the amphiphilic copolymer polyvinylpyrrolidone-polyvinyl acetate (PVP-PVAc) in polyether sulfone (PES) dope solution migrated towards water contacting interface in the coagulation bath and formed the hydrophilic layer by extending hydrophilic segment outwards. This fast in-situ hydrophilization well matched the spinning efficiency. The optimal PVP-PVAc content and phase inversion temperature were investigated and the spinning parameters on the structure and performance of HFMs were studied. The HFMs prepared realized a flux of 26.70 kg m−2 h−1 and the salt rejection of 99.98 %, along with adaptability to solutions with different salinities and excellent anti-organic fouling property. This study may provide a facile method to fabricate HFMs with desirable PV desalination performance and scaling-up potential.

Improved recyclability of the superbase ionic liquid [MTBNH][AcO] used in the lyocell fiber spinning process

In the research of new solvents for cellulose dissolution for textile fiber production, some ionic liquids offer high dissolving capacities making them attractive solvents for lyocell processes. One especially interesting group is superbase carboxylates. However, despite their excellent pulp dissolving abilities and good spinnability properties in a lyocell process, they have been lacking hydrolytic stability, which hinders their recyclability. In this article, a new type of superbase-based ionic liquid, [MTBNH][AcO], is aimed to provide higher hydrolytic stability than its structural relative predecessors. For evaluation of the hydrolysis behavior of [MTBNH][AcO], we have tested the ionic liquid in two sets of recycling experiments. The “blank-experiments” were applied to investigate hydrolytic behavior without the presence of pulp. These values were compared with the results from spinning trials with pulp. It was found that this new ionic liquid is not only more stable than its predecessor [MTBDH][AcO] in terms of hydrolysis but can also dissolve and spin cellulose at lower temperatures. The spun fibers were tested for their textile-physical properties and their performance was comparable to other lyocell fibers.

Effect of enhanced quenching on properties of melt spun multifilament poly[3-hydroxybutyrate] yarns

Bacterial poly-3-hydroxybutyrate is a thermoplastic biopolyester that is considered a potential alternative to traditional fossil-based plastics due to its rapid biodegradation performance in both soil and marine environments and its compostability. Due to problems in thermal and crystallization behaviors of the bacterial poly-3-hydroxybutyrate polymer, an improvement has been made in the cooling channel of the conventional fiber spinning process. Using an enhanced quench channel, named as a half tube on a conventional melt spinning line, melt spinning of the bacterial poly-3-hydroxybutyrate multifilament fibers is successfully carried out. The maximum crystallization temperature of polymers was taken into account while adjusting the quenching process. The study examined the impact of varying drawing ratios and the designed quenching apparatus on the thermal (differential scanning calorimetry), mechanical (tensile and drawing force tests), morphological, and crystal structure characteristics of fibers. The quenching apparatus has visibly created a homogeneous melt flow under the spinnerets. While it has a negative impact on fiber cross-sectional formation, raising the draw ratio greatly enhances mechanical properties.

Stabilization time and temperature influence on the evolution of the properties of mesophase pitch stabilized fibers and carbon fibers

The structure of a mesophase pitch carbon fiber is primarily developed during the fiber spinning process and is refined in stabilization and carbonization steps. Stabilization of mesophase pitch filaments was performed in a thermogravimetric apparatus (TGA) using a multivariate approach to investigate the influence of the initial and final temperature of stabilization and the step time on the changes that occur during the stabilization stage. Different levels of stabilization were observed: insufficient, proper, and over-oxidation. Through Fourier Transform Infrared Spectroscopy (FTIR), Energy-Dispersive X-ray Spectroscopy (EDX), and X-ray Photoelectron Spectroscopy (XPS), it was found that the chemical composition of the stabilized fibers was highly dependent on the mass evolution of this thermal treatment. Excessive stabilization induced defects in the structure of the fibers that negatively reflected on their tensile strength and modulus. Stabilization at lower final temperatures led to low mass increase but in turn provided carbon fibers with the highest modulus. Carbon fibers differing solely in their initial stabilization temperature did not exhibit statistically different tensile strength and modulus, proving that industrial stabilization can be shortened without compromising the fibers' properties.

Optimization of Fiber Laydown During the Fiber Spinning Process by Utilizing the Coanda‐Effect

AbstractThe laydown of aerodynamically stretched fibers during fiber spinning is a key feature of the non‐woven quality. The desired properties of the produced non‐woven are mostly determined by the mechanical properties of the single fiber and the homogeneity of the spunbond. While the former is studied widely, the homogeneity is mostly studied by simulations and not experimentally. Cloudiness or formation of non‐wovens is a known phenomenon that describes deviations from the ideal laydown. Thin areas have a huge impact on the mechanical properties of the spunbond; And subsequently, the investigation of the fiber laydown is of great interest. This work presents an experimental approach to optimize the fiber laydown of a pilot plant fiber spinning device consisting of two aerodynamic stretching devices (aspirators) that stretch eight single fibers each. Due to fiber accumulation on the lay‐down belt under each of the aspirators, a metal rod is placed in‐between to deflect the fibers into the center utilizing the Coanda‐effect to achieve a broad homogeneous fiber distribution.

Effects of Recycled Polymer on Melt Viscosity and Crystallization Temperature of Polyester Elastomer Blends.

As the world is paying attention to the seriousness of environmental pollution, the need for a resource circulation economy is emerging due to the development of eco-friendly industrial groups. In particular, the recycling of thermoplastic elastomers without cross-link has been highlighted in the plastics field, which has rapidly developed the industry. Growing interests have been directed towards the advancement of thermoplastic polyether-ester elastomer (TPEE) as a material suitable for the circular economy owing to its remarkable recyclability, both in terms of mechanical and chemical processes. Due to its excellent processability, simple mechanical recycling is easy, which is a driving force towards achieving price competitiveness in the process. In molding TPEE resin, it is essential to check the thermal properties of the resin itself because the thermal properties, including the melting and crystallization temperatures of the resin, depend on the design of the polymer. In this study, the thermal and mechanical performances of TPEE blends were evaluated by manufacturing compounds by changing the amount of recycled resin and additives. When the recycled resin was added, the melt flow index (MFI) changed rapidly as the temperature of the melt flow index measurement increased. Rapid changes in MFI make the fiber spinning process uncontrollable and must be controlled by optimizing the addition of compatibilizers. Based on the thermal property results, compatibilizers such as Lotader and Elvaloy series exhibited minimal change in glass transition temperature, even with greater amounts added. This makes them well-suited as compatibilizers for fiber spinning.

A novel structural design of cellulose-based conductive composite fibers for wearable e-textiles

Cellulose-based conductive composite fibers hold great promise in smart wearable applications, given cellulose's desirable properties for textiles. Blending conductive fillers with cellulose is the most common means of fiber production. Incorporating a high content of conductive fillers is demanded to achieve desirable conductivity. However, a high filler load deteriorates the processability and mechanical properties of the fibers. Here, developing wet-spun cellulose-based fibers with a unique side-by-side (SBS) structure via sustainable processing is reported. Sustainable sources (cotton linter and post-consumer cotton waste) and a biocompatible intrinsically conductive polymer (i.e., polyaniline, PANI) were engineered into fibers containing two co-continuous phases arranged side-by-side. One phase was neat cellulose serving as the substrate and providing good mechanical properties; another phase was a PANI-rich cellulose blend (50 wt%) affording electrical conductivity. Additionally, an eco-friendly LiOH/urea solvent system was adopted for the fiber spinning process. With the proper control of processing parameters, the SBS fibers demonstrated high conductivity and improved mechanical properties compared to single-phase cellulose and PANI blended fibers. The SBS fibers demonstrated great potential for wearable e-textile applications.

Toughening Effect of 2,5-Furandicaboxylate Polyesters on Polylactide-Based Renewable Fibers.

This work presents the successful preparation and characterization of polylactide/poly(propylene 2,5-furandicarboxylate) (PLA/PPF) and polylactide/poly(butylene 2,5-furandicarboxylate) (PLA/PBF) blends in form of bulk and fiber samples and investigates the influence of poly(alkylene furanoate) (PAF) concentration (0 to 20 wt%) and compatibilization on the physical, thermal, and mechanical properties. Both blend types, although immiscible, are successfully compatibilized by Joncryl (J), which improves the interfacial adhesion and reduces the size of PPF and PBF domains. Mechanical tests on bulk samples show that only PBF is able to effectively toughen PLA, as PLA/PBF blends with 5-10 wt% PBF showed a distinct yield point, remarkable necking propagation, and increased strain at break (up to 55%), while PPF did not show significant plasticizing effects. The toughening ability of PBF is attributed to its lower glass transition temperature and greater toughness than PPF. For fiber samples, increasing the PPF and PBF amount improves the elastic modulus and mechanical strength, particularly for PBF-containing fibers collected at higher take-up speeds. Remarkably, in fiber samples, plasticizing effects are observed for both PPF and PBF, with significantly higher strain at break values compared to neat PLA (up to 455%), likely due to a further microstructural homogenization, enhanced compatibility, and load transfer between PLA and PAF phases following the fiber spinning process. SEM analysis confirms the deformation of PPF domains, which is probably due to a "plastic-rubber" transition during tensile testing. The orientation and possible crystallization of PPF and PBF domains contribute to increased tensile strength and elastic modulus. This work showcases the potential of PPF and PBF in tailoring the thermo-mechanical properties of PLA in both bulk and fiber forms, expanding their applications in the packaging and textile industry.

Application of a Twin-Screw Extruder with an Ultra-High Length-to-Diameter Ratio in the Dry-Jet Wet Spinning Process of Polyacrylonitrile Nascent Fibers

The quality of nascent fiber is the primary factor determining the performance of polyacrylonitrile (PAN)-based carbon fibers. This work presented a novel twin-screw extruder (TSE) with an ultra-high screw length-to-diameter (L/D) ratio for the dry-jet wet spinning process of high-quality PAN nascent fibers. The TSE with an ultra-high L/D ratio of up to 150 enabled the homogeneous mixing of PAN powder and dimethyl sulfoxide (DMSO), resulting in improved dope concentration of up to 30 wt %, improved molecular chain disentanglement, and reduced void formation. Orthogonal experiments were conducted to analyze the influence of dope concentration, barrel temperature, and screw speed on the properties of the PAN nascent fibers. Especially, three L/D ratios of 64, 96, and 150 were established to clarify the influence of the L/D ratio. It was found that with the increase in the L/D ratio from 64 to 150, the average tensile strength and modulus of the PAN nascent fibers were improved by 42.1 and 67.2%, respectively, and the crystallinity was increased by 45.5%. The PAN nascent fibers produced using the TSE with the ultra-high L/D ratio were found to have dense and smooth surfaces and fewer microvoid defects. It demonstrated the innovativeness and potential industrial application of the ultra-high L/D technique in the manufacturing of high-quality PAN-based carbon fibers.

High consistency enzymatic pretreatment of eucalyptus and softwood kraft fibres for regenerated fibre products

Sustainability of regenerated cellulosic fibres could be improved by using paper grade pulp instead of dissolving pulp as a raw material in the fibre spinning process. However, the use of paper grade pulp calls for adjustment of the molar mass distribution (MMD) prior to dissolution to obtain good solubility and spinnability. The objective of this work was to adjust MMD of softwood and eucalyptus kraft pulps by enzymatic treatments at high pulp consistency. The reduction of the MMD of eucalyptus kraft pulp was found to require a nearly 30-fold higher dose of endoglucanase compared to the treatment of softwood pulp. Interestingly, when xylanase was used in combination with endoglucanase to treat eucalyptus kraft pulp, 27% of the xylan was dissolved and the required endoglucanase dose could be decreased from 0.57 to 0.06 mg/g. The endoglucanase dose could be further decreased to 0.028 mg/g when 67% of xylan was removed chemically before the enzymatic treatment. This suggests that xylan hinders endoglucanase action on eucalyptus kraft pulp. For softwood pulp, the addition of xylanase and mannanase had only a minor impact on the treatment efficiency. The different processabilities of softwood and eucalyptus kraft pulps are suggested to originate from the deviating cellulose accessibility which is affected by the fibre structures as well as their hemicellulose composition and localisation. The effect of the treatment consistency was further studied with softwood kraft pulp. Treatment at high consistency clearly enhanced the endoglucanase action whereas the effect of solid content on the hemicellulase action was modest.

Influence of DP and MMD of the pulps used in the Ioncell® process on processability and fiber properties

The Ioncell process is capable of producing high-quality regenerated cellulose fibers from dissolving pulps with a wide range of intrinsic viscosity and different molecular mass distributions.

Effects of coagulating conditions on the crystallinity, orientation and mechanical properties of regenerated cellulose fibers

Fabricating regenerated cellulose fibers using ionic liquids is a novel and green technology. Structural changes of regenerated fibers during forming process affect the macroscopic properties of regenerated fibers. The study of the regenerated fiber forming mechanisms in conditions relevant to fiber spinning processes, especially in the process of dry-wet spinning, is necessary and meaningful. In this work, regenerated cellulose fibers were prepared from wood pulp meal with 1-ethyl-3-methylimidazolium diethylphosphate ([Emim]DEP) under various coagulation bath compositions. The effect of coagulating conditions on the properties of regenerated fibers was investigated, and the internal structures and mechanical properties of regenerated fibers were characterized. The results indicated that regenerated cellulose fibers eventually developed differences in their internal structure and mechanical properties due to the different diffusion rates between spinning solution and coagulation bath. Ethanol significantly reduced the crystallinity and orientation, and elongation increased greatly. In addition, both the crystallinity and orientation of regenerated fibers increased with the decreased of ethanol content in coagulation bath when ethanol content >70 %, while the elongation was reversed. What's more, the scanning electron microscopy results revealed that the regenerated cellulose fibers' surfaces were homogeneous, indicating the regenerated fibers have great potential in the application of textile fabrics.

Direct Wet-Spun Single-Walled Carbon Nanotubes-Based p-n Segmented Filaments toward Wearable Thermoelectric Textiles.

Three-dimensional thermoelectric (TE) textiles (TETs) fabricated with TE filaments (TEFs) possess merits over other types such as thickness-direction thermal energy harvesting and excellent conformability with dynamic body curves, revealing the prospect of generating electricity for on-body application. Nonetheless, there is still a lack of a costless but scalable method to automatically and seamlessly produce in-series interconnected p-n segmented TEFs with high TE properties via conventional fiber spinning processes. Here, we developed an alternate wet-spinning strategy to continuously manufacture single-walled carbon nanotube-based p-n segmented TEFs at large scale. The TEF with high electrical conductivity (400-800 S cm-1) displays a low contact resistivity of 189.8 μΩ cm2 between the segments and interelectrode, showing 2 orders of magnitude smaller than that reported in the literature. More importantly, the power factors of p-type and n-type segments are 26.25 and 17.14 μW m-1 K-2, respectively, which are 3 and 4 orders of magnitude higher than those of advanced studies. We finally embroidered it into spacer fabric to fabricate a wearable TET, demonstrating an output power density of 501 nW m-2 at ΔT = 27.7 K. The methodology can inspire the development of fiber-based electronics such as wearable TEs and diodes and so forth.

Effect of hydrogen bond on phase transition behavior of polyamides during stretching process

During the fiber spinning process, the stretching process is the key to improve the mechanical properties of materials. It is very important to study the effect of hydrogen bond density on the aggregation structure evolution of polyamide for the preparation of high-performance fibers. In this paper, three kinds of polyamides (polyamide 6, polyamide 612 and polyamide 1212) were comparatively studied. In these three polyamides, the hydrogen bond density showed a gradient trend. With the increase of hydrogen bond density, the tensile strength and crystallinity of the materials gradually increased. The phase transition process of the three polyamides had significant difference. This was due to the difference of hydrogen bond density which resulted in different thermally stability of crystal blocks. Finally, the phase evolution schematic of polyamides depending on hydrogen bond density and stretching strains was established.

Rheological Properties and Melt Spinning Application of Controlled-Rheology Polypropylenes via Pilot-Scale Reactive Extrusion.

Based on pilot-scale twin-screw reactive extrusion, the structural and rheological properties of controlled-rheology polypropylenes (CR-PPs) are investigated, where the effects of peroxide content and extrusion conditions such as screw configuration, extrusion temperature, and screw speed are prioritized. The active chain cleavage reaction by a small peroxide content of less than 600 ppm inside the extruder gradually increases the melt index and narrows the molecular weight distribution of CR-PPs, thereby affording favorable properties that are applicable to the fiber spinning process. The mechanical properties of CR-PPs are slightly degraded owing to the generation of unsaturated chain ends during the reactive extrusion, which suppresses crystal growth. Under all extrusion conditions, the chain scission and thermal degradation of polypropylene samples occur actively in the harsh twin-screw extruder compared with those in the mild twin-screw extruder. Finally, it is confirmed that CR-PPs can be suitably applied to the melt-spinning process for staple fiber production, thereby guaranteeing a more stable spinning process window against draw resonance instability.

Dual role of nanoclay in the improvement of the in-situ nanofibrillar morphology in polypropylene/polybutylene terephthalate nanocomposites

The present study has addressed the effects of nanoclay on the properties of polypropylene (PP)/polybutylene terephthalate (PBT) blend fibers such as their dyeability and, rheological and resiliency behaviors which are produced by melt spinning. The results of the differential scanning calorimetry (DSC) analysis indicated that the presence of both nanoclay and PBT significantly influenced the crystallinity of PP which also confirmed their nucleating effects on the nanocomposite fibers. Compared to neat PP fibers, the incorporation of 0.5–1wt.% of nanoclay and 10 wt.% of PBT nanocomposite fibers caused approximately 23% and 52% enhancements in the resiliency and dye uptake respectively without using toxic carriers. The rheological analysis was carried out for investigating the viscoelastic behavior, and microstructural and dispersion of nanoclay in the nanocomposite fibers. The rheological behavior in the small amplitude oscillatory shear (SAOS) test demonstrated the percolation threshold network of the structure of PBT fibrils in the PP matrix. When the PBT domains are fibrillated, the storage modulus (G′) and complex viscosity increase compared to neat PP. Also, the nonterminal behavior at low frequencies indicates the uniform dispersion of nanoclay in fiber nanocomposites. These all cause the improvement of the melt strength of the PP matrix. Transmission electron microscopy (TEM) was used to study the dispersion and localization of nanoclay. Nanoclay has also played a compatibilizing role in the immisible PP/PBT blend and was localized mainly in the PBT disperse and interface, and therefore prevented coalescence. The role of the compatibility of nanoparticles is to decrease the mean diameter of the nano-fibrils to 75 nm, for the hot-drawn nanocomposite fibers, as measured by scanning electron microscopy (SEM). All of the above lead to increasing the melt strength and elasticity of the nanocomposites in the fiber spinning process.

Understanding the Dynamics of Cellulose Dissolved in an Ionic Liquid Solvent Under Shear and Extensional Flows.

Ionic liquids (ILs) hold great potential as solvents to dissolve, recycle, and regenerate cellulosic fabrics, but the dissolved cellulose material system requires greater study in conditions relevant to fiber spinning processes, especially characterization of nonlinear shear and extensional flows. To address this gap, we aimed to disentangle the effects of the temperature, cellulose concentration, and degree of polymerization (DOP) on the shear and extensional flows of cellulose dissolved in an IL. We have studied the behavior of cellulose from two sources, fabric and filter paper, dissolved in 1-ethyl-3-methylimidazolium acetate ([C2C1Im][OAc]) over a range of temperatures (25 to 80 °C) and concentrations (up to 4%) that cover both semidilute and entangled regimes. The linear viscoelastic (LVE) response was measured using small-amplitude oscillatory shear techniques, and the results were unified by reducing the temperature, concentration, and DOP onto a single master curve using time superposition techniques. The shear rheological data were further fitted to a fractional Maxwell liquid (FML) model and were found to satisfy the Cox-Merz rule within the measurement range. Meanwhile, the material response in the non-LVE (NLVE) regime at large strains and strain rates has special relevance for spinning processes. We quantified the NLVE behavior using steady shear flow tests alongside uniaxial extension using a customized capillary breakup extensional rheometer. The results for both shear and extensional NLVE responses were described by the Rolie-Poly model to account for flow-dependent relaxation times and nonmonotonic viscosity evolution with strain rates in an extensional flow, which primarily arise from complex polymer interactions at high concentrations. The physically interpretable model fitting parameters were further compared to describe differences in material response to different flow types at varying temperatures, concentrations, and DOP. Finally, the fitting parameters from the FML and Rolie-Poly models were connected under the same superposition framework to provide a comprehensive description within the wide measured parameter window for the flow and handling of cellulose in [C2C1Im][OAc] in both linear and nonlinear regimes.

Novel High‐Speed Elongation Rheometer

AbstractThe elongational viscosity of polymers can be determined by utilizing different devices such as extensional rheometer after Sentmanat (SER), oil bath rheometer after Meissner or tensile rheometer after Münstedt (MTR), with strain rates up to 10 s–1. Although these investigations are already complex, they do not depict real fiber spinning processes where higher elongation strain rates occur. Therefore, a novel method is developed to calculate the elongational viscosity of polymers during the fiber spinning process. To reduce the complexity of the system, two polymethylmethacrylates (PMMAs) with different molar masses are investigated using a capillary rheometer to exclude crystallization effects. The diameter of the polymeric strand is determined via a high‐speed camera from the die exit to the aspirator. In addition, simulations are carried out to describe the temperature profile of the polymeric strand along the spinline. It is possible to determine the elongational viscosity of the polymers in dependence of temperature and strain rates up to 100 s–1, by calibration of the force in an aerodynamic stretching device (aspirator).

Hydrolytic Degradation of Polylactic Acid Fibers as a Function of pH and Exposure Time.

Polylactic acid (PLA) is a widely used bioresorbable polymer in medical devices owing to its biocompatibility, bioresorbability, and biodegradability. It is also considered a sustainable solution for a wide variety of other applications, including packaging. Because of its widespread use, there have been many studies evaluating this polymer. However, gaps still exist in our understanding of the hydrolytic degradation in extreme pH environments and its impact on physical and mechanical properties, especially in fibrous materials. The goal of this work is to explore the hydrolytic degradation of PLA fibers as a function of a wide range of pH values and exposure times. To complement the experimental measurements, molecular-level details were obtained using both molecular dynamics (MD) simulations with ReaxFF and density functional theory (DFT) calculations. The hydrolytic degradation of PLA fibers from both experiments and simulations was observed to have a faster rate of degradation in alkaline conditions, with 40% of strength loss of the fibers in just 25 days together with an increase in the percent crystallinity of the degraded samples. Additionally, surface erosion was observed in these PLA fibers, especially in extreme alkaline environments, in contrast to bulk erosion observed in molded PLA grafts and other materials, which is attributed to the increased crystallinity induced during the fiber spinning process. These results indicate that spun PLA fibers function in a predictable manner as a bioresorbable medical device when totally degraded at end-of-life in more alkaline conditions.