Effect of Twist and Draw on Morphology and Tensile Property of Electrospun Nanofibrous Yarns

This study uses a nanofibrous membrane produced using electrospinning to undergo processing, to form a yarn with twist of 2.4, 4.0, 5.6, and 7.2 thermal pulsed currents (twist/cm). The optimum twist multiplier values are chosen and used to discuss the tendency of stress and strain. Furthermore, the draw ratios of 1.1, 1.2, 1.3, and 1.4 are applied, to determine which provides an optimum strength. The result showed that yarn with fineness of 40tex corresponding with twist multiplier of 36 and draw ratio of 1.4 have strength of 219.3 g (stress of 5.14 cN/tex). This result can be applied for the further study of continuous nanofibrous yarn.     

Shape memory polyurethane-based electrospun yarns for thermo-responsive actuation

Electrospun nanofibrous yarns of shape memory polyurethane (SMPU)-based nanofibers were successfully prepared. The electrospun yarns were analyzed to assess the dependence of mechanical and shape memory properties on the yarn twist angle. The yarn with a 60° twist angle has high compactness and density, leading to increased tensile strength, elastic modulus, and strain energy. In addition, this yarn shows a significant improvement in the shape memory recovery stress compared with the non-twisted SMPU nanofibers. Moreover, thermal stimuli allowed for the 60° twisted yarn to lift a load that is 103 times heavier than itself. This yarn had a shape recovery stress of 0.61 MPa and generated a 7.95 mJ recovery energy. The results suggest the electrospun yarns could be used as actuators and sensing devices in the medical and biological fields.     

Investigation of wicking phenomenon and tensile properties in three-layer composite nanofibrous PA/PLLA yarn

One critical property of a nanofibrous structure is the wicking behavior in contact with liquids. This work's purpose is fabrication and investigation of tensile and wicking properties of a newly designed three-layer nanofibrous yarn consisting of polyamide 6/poly(L-lactic acid) (PA/PLLA) with a similar idea to Bobtex spun yarn structure in which adhesion between core (PA) and sheath (PLLA) is provided with a thin layer of polymeric thin film. The tensile strength and strain decreased 32 and 46%, respectively, in a three-layer yarn compared with two-layer, that is, yarn without the adhesion film. In addition, the ultimate strength of the three-layer yarn was higher than a PLLA yarn. The vertical wicking test for three-layer nanofibrous yarn reveals that at short times, capillary rise kinetics follow the Lucas–Washburn law while increasing the take-up velocity of the take-up roller in yarn fabrication leads to increasing the maximum height of water in yarn.     

多异多重复合涤纶长丝的染色均匀度及检测方法研究 第一报·常压染色袜筒的目测判色和仪器测判色对比研究

对比多异多重复合涤纶长丝常压染色袜筒目光判色和测色仪测判色结果的差异以及有捻和无捻涤丝袜筒的测判色结果差异,指出了多异多重复合涤纶长丝染色均匀度差的原因,并提出现有测色仪尚不能用于复杂结构化纤的染色均匀度检测。     

Quality assessment of polyester chips and yarn by TMS-2

Penetration in polyester chips of different manufacturers and yarn (undrawn and drawn) was studied between 323 and 423 K on a thermomechanical system (TMS-2) using a penetration kit. It was observed that the penetration of the probe varied in the case of chips from manufacturer to manufacturer. The undrawn and drawn yarns from different batches and also within the same batch showed a clear variation in penetration curve, which may be attributed to the degree of crystallization. The same technique can be utilized for an assessment of the quality of yarn in continuous production and for differentiating the manufacturing process of polyester chips.     

Improving the tensile strength of carbon nanotube spun yarns using a modified spinning process

A modified process for the dry spinning of carbon nanotube (CNT) yarn is reported. The approach gives an improved structure of CNT bundles in the web drawn from the CNT forest and in the yarn produced from the twisted web leading to improved mechanical properties of the yarn. The process enables many different mechanical and physical treatments to be applied to the individual stages of the pure CNT spinning system, and may allow potential for the development of complex spinning processes such as polymer-CNT-based composite yarns. The tensile strength and yarn/web structure of yarn spun using this approach have been investigated and evaluated using standard tensile testing methods along with scanning electron microscopy. The experimental results show that the tensile properties were significantly improved. The effect of heat treatments and other yarn constructions on the tensile properties are also reported.     

Mechanical properties and morphology of hot drawn polyacrylonitrile nanofibrous yarn

In this study PAN nanofibrous yarn was produced by two‐nozzle conjugated electrospinning method. The nanofibrous yarns were drawn continuously in boiling water with drawing ratios of 1, 2, 3, and 4. The morphology of drawn yarns was investigated by scanning electron microscopy and tested for tensile properties as well as untreated yarn. The results showed that the nanofiber alignment in the yarn axis direction, the tensile strength, and tensile modulus of yarn increases as a result of drawing while the tensile strain and work of rapture decrease. X‐ray diffraction patterns of the produced yarns were analyzed as well. It was found that crystallinity index increases as the draw ratio increases. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

聚乳酸长丝与亚麻-黏胶纱的并捻工艺及性能

采用并捻联合纺纱方法,将聚乳酸长丝与亚麻-黏胶单纱直接并合加捻成复合纱线,并对影响其纱线结构和性能的因素(捻因数、张力、钢丝圈)进行了研究分析,随后通过捻因数与钢丝圈正交试验优化得出最佳的并捻纺纱工艺。研究分析得出:并捻纱的断裂强力随着捻因数的增大先增大后减小;钢丝圈号数对并捻纱断裂强力存在着较大的影响;并捻纱的纱线结构类似于包缠纱,一般张力大的组分为纱芯,另一组分在外层螺旋包覆纱芯。最佳并捻工艺参数为:捻因数220,钢丝圈选14号。     

Fabrication and characterization of hollow nanofibrous PA6 yarn reinforced with CNTs

Core-sheath nanofibrous yarns were obtained through electrospinning of polyamide 6 (PA6) solution containing different concentrations of multi-wall carbon nanotubes (MWNTs) as sheath and PVA multifilament as the yarn core. By dissolving PVA, for obtaining conductive hollow nanofibrous PA6/MWNTs yarn, two types of porosity could be obtained including hollow central tube due to the structure of hollow yarn and nano-porous areas embedded in electrospun nanofibers. SEM results showed that the diameters of nanofibers were varying in the range of 103–145 nm obeying MWNTs concentrations and TEM results revealed that the MWNTs were embedded in nanofiber matrix as straight and aligned form. DSC analysis showed that electrospinning process caused the formation of less-ordered γ phase in nanofibers. The electrical conductivity of yarns increased from 10^?13 S m^?1 to 2.4?×?10^?6 S m^?1 with increasing the concentration of nanotubes from 0 wt.% to 7 wt.%.     

Fabrication of continuous nanofiber yarn using novel multi‐nozzle bubble electrospinning

A novel multi‐nozzle bubble electrospinning apparatus, including spinning unit, metering pump, constant flow pump, metal funnel and yarn winder, was designed for the preparation of continuous twisted polyacrylonitrile nanofiber yarns, and the principle of nanofiber yarn spinning was studied. An innovative spinning unit consisting of nozzle and air chamber was used to improve the production of nanofibers. Double conjugate electrospinning was developed using two pairs of oppositely charged spinning units to neutralize the charges. The effects of applied voltage, air flow rate, overall solution flow rate and funnel rotary speed on the fiber diameter, production rate and mechanical properties of the nanofiber yarns were analyzed. Nanofibers could be aggregated stably and bundled continuously, then twisted into nanofiber yarns uniformly at an applied voltage of 34 kV, air flow rate of 1200 mL min^?1 and overall solution flow rate of 32 mL h^?1. With an increase in the funnel rotary speed, the twist angle of the nanofiber yarns gradually increased when the take‐up speed was constant. The yarn tensile strength and elongation at break showed an increasing trend with increasing twist angle. Nanofiber yarns obtained using this novel method could be produced at a rate from 2.189 to 3.227 g h^?1 with yarn diameters ranging from 200 to 386 µm. Nanofiber yarns with a twist angle of 49.7° showed a tensile strength of 0.592 cN dtex^?1 and an elongation at break of 65.7%. © 2013 Society of Chemical Industry     

Mechanical properties of twisted filaments

The knowledge of some mechanical properties of twisted filament is necessary to predict properties of continuous-filament yarns. Retraction, strength, strain, and elastic properties of filaments are the chief characteristics. Assuming that the filament can be considered as a yarn made of fibers bounded together and then twisted, formulas for prediction of those properties were elaborated and then compared with the experimentally received values. Satisfactory agreement of computed results with experimental values is obtained if the changes in volume of filament at strain is taken into account.     

Change in fine structure of nylon 6 gut yarn in twisting,annealing, and untwisting processes. I. Observation by WAXD,SAXD, and EM

To obtain information on the change in fine structure of nylon 6 taking place during practical false-twisting processes, the manner of change in the three elemental processes, i.e., twisting, annealing, and untwisting, was studied. For simplicity, nylon 6 gut yarn was used instead of multifilament yarn. Wide- and small-angle x-ray diffraction (WAXD and SAXD) together with electron microscopy (EM) were used here. The degree of molecular orientation in the crystalline region of the twisted yarn gradually decreases with increase of the twist number (TN) in the region of TN ? 100. The long spacing, determined by SAXD, of the twisted yarn increases with increases in TN. The increase in long spacing cannot be interpreted only by macroscopic strain or elongation of the yarn in the twisting process. This difference seems to arise from the contribution of the decrease of lateral size of lamellae to the average long spacing; therefore the increase in long spacing should be attributed to the elongation of the amorphous region, deduced from the crystallinity measured by WAXD and the long spacing diffraction. The angle between the streak line on the surface of twisted yarn observed by EM and the fiber axis agrees well with the twist angle of the yarn. The crystal lamellae are stacked normal to the streak line at the initial stage, i.e., at a low value of TN, but they begin to deviate from the normal direction with increase in TN, accompanied by their partial destruction. Based on SAXD and density measurements, the internal strain of yarn annealed after twisting is fully relaxed. When the yarn is untwisted after twisting and annealing, the crystal orientation recovers gradually to that of the untreated yarn. The chain axis within the lamellae in the center region of the yarn becomes nearly parallel to the fiber axis, but the chain axis in the outer region does not.     

Morphological and mechanical properties of drawn poly(l‐lactide) electrospun twisted yarns

In this study, the continuous twisted PLLA yarns were produced using an electrospinning device consists of two oppositely charged nozzles. The electrospinning process was performed at different twist rates. The electrospun twisted yarns were drawn at different extension ratios of 50% and 100% and their morphological and mechanical properties of post‐drawn yarns were investigated. The morphological studies at all twist rates shown that uniform and smooth fibers without any bead were formed. Increasing the twist rate up to 240 rpm resulted to a decrease in the average diameter of the fibers in the yarn structure. After uniaxially drawing of the yarns, the average diameter of fibers and thus the yarn diameter decreased. The post‐drawing process enhanced the crystallinity of the fibers in the yarn structure. Furthermore, by increasing the extension ratio, the tensile strength and modulus of yarns increased, while the elongation at break (%) decreased. POLYM. ENG. SCI., 58:1091–1096, 2018. © 2017 Society of Plastics Engineers     

Continuous yarns from electrospun fibers

A technique for making continuous uniaxial fiber bundle yarns from electrospun fibers is described. The technique consists of spinning onto a water reservoir collector and drawing the resulting non-woven web of fibers across the water before collecting the resulting yarn. Yarns from electrospun fibers of poly(vinyl acetate), poly(vinylidene difluoride) and polyacrylonitrile are used to illustrate the process of yarn formation and fiber alignment within the yarn. A theoretical production rate of 180 m of yarn per hour for a single needle electrospinning setup makes the process suitable for lab-scale production of electrospun yarns.     

以较低成本改善纱线质量的变形加工系统

研究了包括原料运送在内的变形纱生产工艺,讨论了变形纱加工过程中连续质量校制的几种构想,着重介绍了巴马格公司新近开发成功的UNITENS纱线张力检测系统、CD83型自动落筒机及AGV运输系统。利用UNITENS质量控制系统,人们不仅可以对每一个卷装实现真正的100%的检测,而且可以借助计算机系统了解到变形纱降等的各种原因。从而实现以较低的成本改善变形纱质量的目的。     

Color measurement of single yarn based on hyperspectral imaging system

This article proposed a novel approach to color measurement of a single yarn using hyperspectral imaging system (HIS). Due to the size of a single yarn, it is impossible for spectrophotometers to measure its color directly. The HIS can acquire the spectral reflectance of continuous bands within a region of interest on a yarn sample, which can achieve color measurement of a single yarn compared with traditional spectrophotometers. A single yarn is segmented from the background by a spectral matching method through adaptively setting threshold of Fréchet distance values. The spectral reflectance of single yarn is specified by a method that lightness of pixels used as weight. The experiment based on Pantone Cotton Chip Set shows that the interinstrument agreement between the HIS and a standard spectrophotometer Datacolor SF650 has a significant improvement after using the R-Model, and the average percentage improvement of the color difference is up to 54.99%. The yarn segmentation comparative experimental results show that the proposed method to segment single yarn from background is better in retaining the edge information of the yarn than the modified K-means clustering method, and the color of the yarn segmented by the proposed method is more similar to the actual color of single yarn.     

Strain dependence of electrical resistance in carbon nanotube yarns

Carbon nanotube forests or arrays can be drawn into a web and further twisted into threads. These carbon nanotube threads contain thousands of carbon nanotubes in their cross-sections and can be further composed into yarns that consist of one or more threads. The superior mechanical, thermal and electrical properties of carbon nanotubes are not translated into the carbon nanotube yarns. However, carbon nanotube yarns still exhibit relatively high mechanical stiffness and strength, and low electrical resistivity. More importantly, carbon nanotube yarns exhibit piezoimpedance that could be used for sensing purposes. In order to use carbon nanotube yarns as piezoimpedance-based sensors for structural health monitoring, it is necessary to determine the change in impedance of the yarn as a function of its mechanical strain or stress. This paper presents the results of an experimental study on the coupled mechanical response and electrical response in the direct current mode of the carbon nanotube yarn. A behavior consisting of a negative piezoresistive response was encountered during most of the deformation range of the yarn. This response was shown to exhibit a parabolic response and it was followed by a linear positive piezoresistive response that preceded the failure of the yarn.     

Tensile fatigue behavior of polyamide 66 nanofiber yarns

Nanofiber yarns with twisted and continuous structures have potential applications in fabrication of complicated structures such as surgical suture yarns, artificial blood vessels, and tissue scaffolds. The objective of this article is to characterize the tensile fatigue behavior of continuous Polyamide 66 (PA66) nanofiber yarns produced by electrospinning with three different twist levels. Morphology and tensile properties of yarns were obtained under static tensile loading and after fatigue loading. Results showed that tensile properties and yarn diameter were dependent on the twist level. Yarns had nonlinear time‐independent stress–strain behavior under the monotonic loading rates between 10 and 50 mm/min. Applying cyclic loading also positively affected the tensile properties of nanofiber yarns and changed their stress–strain behavior. Fatigue loading increased the crystallinity and alignment of nanofibers within the yarn structure, which could be interpreted as improved tensile strength and elastic modulus. POLYM. ENG. SCI., 55:1805–1811, 2015. © 2014 Society of Plastics Engineers     

Achievement of high surface charge in poly(vinylidene fluoride) fiber yarns through dipole orientation during fabrication

Electrospun fiber materials are of scientific interest for use in multiple application areas. Charged fiber structures show enhanced properties as desired for some of these applications. One factor influencing the charge on the fiber structure that has not been explored is fiber alignment. Electrospun fiber structures, such as membranes, typically consist of randomly oriented fibers. Structural properties of the membranes such as mechanical strength are known to be affected by the random orientation of the fibers. It is suspected that fiber orientation may also affect the charge capacity of charged fiber structures. A few approaches to form electrospun yarns have been reported. Some of these approaches can also cause fibers to preferentially align along the yarn axis instead of assembling into a random structure. In this work, a rotating metal cone was used to collect Poly(vinylidene fluoride) electrospun fibers from which stretched yarns were drawn and twisted into yarns. The alignment of the fibers in the yarns was controllable to a degree that allowed exploration of the effect of alignment on charge. Long continuous oriented or random yarns of relatively uniform thickness were produced at a rate of about 10 m/h. The yarns were polarized by methods of heating, stretching, and poling. The results show that the fiber yarn formation process endows more charges to the fibers compared to the normal fiber membrane electrospinning and post polarization. This provides a facile route for the preparation of enhanced charge-functionalized fiber structures for a wide range of applications.     

Application of nanofibers to improve the filtration efficiency of the most penetrating aerosol particles in fibrous filters

Conventional, mechanical fibrous filters made of microfibers exhibit a local minimum of fractional collection efficiency in the aerosol particle size-range between 100 and 500 nm, which is called the most penetrating particle size (MPPS). Simple theoretical calculations predict that this efficiency may be significantly increased using nanofibrous media. The main objective of this paper is an experimental verification of these expectations and simultaneously checking whether this anticipated gain in the filtration efficiency is not overpaid with an excessive pressure drop. For this purpose we developed a modified melt-blown technology, which allowed us to produce filters composed of micrometer as well as nanometer sized fibers. One conventional microfibrous filter and five nanofibrous filters were examined. The complete structural characteristics, pressure drop and efficiency of removal of aerosol particles with diameters 10-500 nm were determined for all media. The results of the experiments confirmed that using nanofibrous filters a significant growth of filtration efficiency for the MPPS range can be achieved and the pressure drop rises moderately. Simultaneously, we noticed a shift of the MPPS towards smaller particles. Consequently, the quality factor for bilayer systems composed of a microfibrous support and a nanofibrous facial layer was considerably higher than this one for a conventional microfibrous filter alone. Additionally, it was found that utilization of many-layer nanofibrous filters combined with a single microfibrous backing layer is even more profitable from the quality factor standpoint. Comparing experimental results with theoretical calculations based on the single-fiber theory we concluded that for microfibrous filters a fairly good agreement can be obtained if the resistance-equivalent fiber diameter is used in calculations instead of the mean count diameter determined from the SEM images analysis; in the latter case, filtration efficiency computed theoretically is slightly overestimated. This is even more evident for nanofibrous media, suggesting that in such case a structural filter inhomogeneity has a strong influence on the filter efficiency and its resistance and one should strive for minimization of this effect manufacturing nanofibrous filters as homogeneous as possible. We can finally conclude that fibrous filters containing nanofibers, which are produced using the melt-blown technique, are very promising and economic tools to enhance filtration of the most penetrating aerosol particles.