较细ZnS:Mn/PVP纳米纤维的制备及表征

采用静电纺丝的方法制备了ZnS:Mn/Polyvinylpyrrolidone复合纳米纤维.使用的溶剂为水、乙醇及DMF(N,N-Dimediylfommnide),的使用有助于制备较细的纤维,电纺溶液中随着聚合物PVP浓度降低,纤维的直径变小,当PVP质量分数为6.6%时,纤维的直径是80 nm,通过荧光显微镜和荧光...     

较细ZnS:Mn/PVP纳米纤维的制备及表征

采用静电纺丝的方法制备了ZnS:Mn/Polyvinylpyrrolidone复合纳米纤维.使用的溶剂为水、乙醇及DMF(N,N-Dimediylfommnide),的使用有助于制备较细的纤维,电纺溶液中随着聚合物PVP浓度降低,纤维的直径变小,当PVP质量分数为6.6%时,纤维的直径是80 nm,通过荧光显微镜和荧光光谱仪的测试可以知道,该纤维能够发光.基于纤维的发光及直径较小的特性,该纤维在一维纳米光电子领域有着潜在的应用.     

离子浓度对电纺纤维沉积形态及表面形貌的影响

通过采用传统电纺丝装置(接收板接地或连接负压电源)、逆向电场及非接触式电纺丝装置等4种不同的电纺丝装置,在相同电压、接收距离、纺针直径、温湿度条件下,对20%的聚乙烯醇溶液进行电纺丝实验,观察不同装置中制得的纤维的沉积形态与形貌.还采用ANSYS有限元模拟对电纺丝装置的场强分布进行分析,并引入电化学理论解释了采用不同电纺装置时离子浓度的不同对所得电纺纤维形貌的影响,分析了产生差异的原因.     

静电纺丝法制备PVP螺旋纤维及其机理研究

研究了电纺丝聚乙烯吡咯烷酮螺旋纤维的形成条件, 在9kV的电压下, 由于溶液质量分数的增加(12%-24%), 纤维形态呈现出直线→螺旋→折叠→无序的变化趋势; 在质量分数为20%时, 随着纺丝电压的增加, 纤维形态呈现出折叠→螺旋→无序的变化趋势, 同时对螺旋纤维的形成机理进行了讨论, 在纺丝过程中纤维束所带静电荷之间的库仑斥力是形成螺旋纤维的直接动力.     

聚(丙交酯-co-乙交酯)/β-磷酸三钙复合物的电纺研究

对生物可吸收聚(丙交酯-co-乙交酯)(poly(lactide-co-glycolide),PLGA)与β-磷酸三钙(-βTCP)复合物体系进行了电纺.研究了PLGA的浓度,-βTCP与PLGA比例,加料速度,电压,喷头与接收体之间的距离等因素对电纺过程的影响,制备出纳米纤维膜,并用扫描电镜(SEM)等对纤维膜进行表征.结果表明,电纺溶液浓度越高,或者加料速度越快,纳米纤维的直径越粗.力学实验显示,复合物中-βTCP的含量增加使纳米纤维膜的拉伸强度和杨氏模量下降.     

聚丙烯高速纺丝的研究

研究了分子量、分子量分布及纺丝工艺条件对聚丙烯高速纺得卷绕丝的结构及力学性质的影响。结果表明:改变聚丙烯树脂和调节纺丝工艺条件(如绕丝速度、纺丝温度和泵供量等)可以获得各种织构的聚丙烯纤维。适当选择上述参数以控制或改变卷绕丝的织构可提高高速纺出聚丙烯纤维的质量。     

聚甲醛电纺纤维表面孔结构的控制

研究了环境相对湿度、 温度、 溶液浓度、 纺丝电压和接收距离对聚甲醛(POM)电纺纤维表面孔形貌的影响. 结果表明, 空气中一定含量的水对孔的形成至关重要; 纺丝液浓度对孔的大小有影响. 并对POM 纤维表面成孔的可能机理进行了分析.     

静电纺丝制备图案化无机纳米纤维

静电纺丝技术近几年在制备纳米纤维领域得到了广泛的应用,被认为是批量制备纳米纤维材料最简单有效的方法。本文综述了近几年高压静电纺丝技术制备图案化无机物纳米纤维的纺丝装置和过程,特别详细综述了纺丝过程中纤维直径的变化,利用带电流体动力学(EHD)理论推导出纤维直径变化的运动方程,并对方程进行一定程度的修订,以符合电纺无机物纳米纤维直径的变化;并综述了取向纳米纤维、中空纳米纤维、壳-核结构纳米纤维、纳米线、纳米带、纳米管及多层次结构纳米纤维的构建及其基本性能。最后对电纺制备图案化无机纳米纤维未来发展方向,特别是功能化多层次结构电纺无机纳米纤维制备进行了展望。     

溶剂性质对两亲性聚肽静电纺丝的影响

通过对聚(γ-苄基L-谷氨酸酯)(PBLG)的亲水改性制备了两亲性聚(γ-苄基L-谷氨酸酯-co-羟乙谷酰胺)无规共聚肽(PBHG)用于静电纺丝制备超细纤维.通过傅里叶变换红外光谱、核磁共振氢谱表征了聚合物结构.通过测定溶液表面张力、黏度、电导率及扫描电镜观察纤维形貌考察了不同溶剂及PBHG浓度对纺丝溶液性质及电纺纤维的影响.通过水浸实验及MTT法评价了电纺纤维膜的亲水性及细胞相容性.研究发现在三氯甲烷(TCM)和四氢呋喃(THF)中PBHG采取α-螺旋构象,刚性分子链自取向排列,可获得直径为微米或亚微米的电纺纤维.以TCM为溶剂时,因溶液表面张力大、导电率低导致纤维品质较差,而以THF为溶剂可获得表面光洁、尺寸均匀的电纺纤维.当溶剂为三氟乙酸(TFA)时,PBHG采取无规线团构象,柔性分子链彼此缠结,同时溶液表面张力小、黏度低、电导率高,可获得纳米电纺纤维.但因TFA挥发性相对较差,易造成纤维粘连.将TFA与TCM复配后作为溶剂可改善纤维粘连问题.与PBLG电纺纤维相比,改性后的PBHG电纺纤维的亲水性得到了改善,可在水中保持纤维骨架而无需交联,并表现出良好的细胞相容性,能促进细胞在电纺纤维膜上的增殖.     

静电纺聚丙烯腈纳米纤维晶态结构及取向的形成

采用新型流动水浴收集方式制备出连续单向排列的静电纺聚丙烯腈(PAN)纳米初生纤维,收集静电纺丝不同阶段的静电纺PAN纳米纤维,并在热水中进行后牵伸,使其伸长至原长的2倍、3倍.通过扫描电子显微镜(SEM)、广角X射线衍射(WAXD)等方法对静电纺丝过程不同阶段的PAN纳米纤维的形貌、直径、致密性、晶态结构及取向进行了表征.研究表明,(1)在静电纺丝过程中PAN纺丝液射流受到牵伸作用,静电纺PAN纳米纤维的晶态结构形成并逐渐完善.纳米纤维的直径随着静电纺丝过程逐渐减小(从664 nm减小至353 nm),结晶度从42.55％增加至47.76％,晶区取向由37.48％提高至43.93％.纳米纤维致密性也逐渐提高(密度由1.1917 g/cm3增加至1.1943 g/cm3).(2)静电纺丝过程进入PAN射流溶剂含量较低的阶段后,继续通过静电纺丝过程提高纳米初生纤维晶态结构及取向的效果很有限,而通过热水后牵伸过程可进一步使晶态结构及取向得到有效果的完善.研究同时发现,静电纺初生纤维的晶态结构及取向与其在热水牵伸过程中的进一步完善具有相关性.     

Aligned and molecularly oriented semihollow ultrafine polymer fiber yarns by a facile method

In this work, aligned and molecularly oriented bone‐like PLLA semihollow fiber yarns were manufactured continuously from an optimized homogeneous polymer‐solvent‐nonsolvent system [PLLA, CH₂Cl₂, and dimethyl formamide (DMF)] by a single capillary electrospinning via self‐bundling technique. Here, it should be emphasized that the self‐bundling electrospinning technique, a very facile electrospinning technique with a grounded needle (which is to induce the self‐bundling of polymer nanofibers at the beginning of electrospinning process), is used for the alignment and molecular orientation of the polymer fiber, and the take‐up speed of the rotating drum for the electrospun fiber yarn collection is very low (0.5 m/s). PLLA can be dissolved in DMF and CH₂Cl₂ mixed solvent with different ratios. By varying the ratios of mixed solvent system, PLLA electrospun semihollow fiber with the porous inner structure and compact shell wall could be formed, the thickness of the shell and the size of inner pores could be adjusted. The results of polarized FTIR and wide angle X‐ray diffraction investigations verified that as‐prepared PLLA semihollow fiber yarns were well‐aligned and molecularly oriented. Both the formation mechanism of semihollow fibers with core‐shell structure and the orientation mechanism of polymer chains within the polymer fibers were all discussed. The as‐prepared self‐bundling electrospun PLLA fiber yarns possessed enhanced mechanical performance compared with the corresponding conventional electrospun PLLA fibrous nonwoven membranes. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1118–1125, 2010     

Uniaxially aligned carbon nanofibers derived from electrospun precursor yarns

Unlike conventional electrospun polymer fibers deposited on a target electrode as a randomly oriented mesh, poly(p‐xylenetetrahydrothiophenium chloride) was electrospun into centimeters‐long yarns vertically on the surface of the electrode but parallel to the electric field. The diameter of the yarn was strongly affected by the concentration, spinning rate, and viscosity of the polymer solution, but less dependent on the applied voltage. The subsequent carbonization of thus‐electrospun yarns at 600–1000 °C resulted in uniaxially aligned carbon nanofibers with average diameters of 127–184 nm. On the basis of Raman spectra, the graphitic crystallite size and the molar fraction of graphite were estimated to be 1.2–1.4 and 0.21–0.24 nm, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 305–310, 2008     

Effect of Blending Factors on Eri Silk and Cotton Blended Yarn and Fabric Characteristics

Eri cocoons were prepared into short fibers and subsequently blended with cotton fiber in order to develop the new fiber blended yarn in the short spinning system. The Eri and cotton fibers were blended using the drawframe blending with varying blending factors, viz. blending composition (0–100%) and yarn counts (30 and 50 tex). The results showed that Eri fiber which was longer and stronger than cotton fiber, affected the fiber distribution in the yarn cross-section. The mechanical properties of the blended fibers and yarns increased with increasing silk content. Longer fibers of Eri silk tended to move towards the yarn core, especially at silk content higher than 50%. Moreover, stronger and more extensible Eri silk fiber gave an advantage to the improvement of mechanical properties of those blended yarns with silk content higher than 50%. However, with increasing silk content, the blended yarns were more irregular as shown in %CV. Concerning the yarn count effect, the higher yarn count of 50 tex resulted in a more regular yarn with higher yarn strength than that of 30 tex. The plain-woven fabrics were prepared using the blended yarns as a weft yarn and the cotton yarn or silk yarn as a warp yarn. The mechanical properties of those woven fabrics were characterized in order to study the influence of silk contents. The results showed that tensile strength, %elongation and tear strength of woven fabrics using the blended yarn were increased with an increase in silk content. This is an advantage of Eri silk in the aspect of rendering the strength to the blended yarns and fabrics.     

Wicking in twisted yarns

This paper investigated vertical wicking in twisted yarns. A mathematical model was developed based on a capillary penetration mechanism. By using a macroscopic force balance approach, the wicking time was derived as a function of the capillary rise of the liquid. Packing of fibers in the yarn was assumed to be uniform. In order to validate our model, a series of experiments was conducted on polyester yarns. The results showed a good agreement between the experimental data and the theoretical predictions. The influence of twist level of the yarn on the capillary flow was also investigated.     

Novel antibacterial fibers of quaternized chitosan and poly(vinyl pyrrolidone) prepared by electrospinning

The preparation of continuous defect-free fibers from quaternized chitosan derivative (QCh) has been achieved by electrospinning of mixed aqueous solutions of QCh with poly(vinyl pyrrolidone) (PVP). The average fiber diameter significantly decreases from 2800 to 1500 nm on increasing the polyelectrolyte content. In order to impart to QCh/PVP electrospun fibers stability to water and water vapor, the fibers have been crosslinked by incorporation of photo-crosslinking additives into QCh/PVP spinning solutions and subsequent UV irradiation of the electrospun fibers. Photo-crosslinked QCh-containing electrospun mats show high antibacterial activity against the Gram-positive bacteria Staphylococcus aureus and Gram-negative bacteria Escherichia coli.     

EFFECT OF GAS FLOW RATE ON CRYSTAL STRUCTURES OF ELECTROSPUN AND GAS-JET/ELECTROSPUN POLY(VINYLIDENE FLUORIDE) FIBERS

The effect of gas flow rate on crystal structures of electrospun and gas-jet/electrospun poly(vinylidene fluoride) (PVDF) fibers was investigated.PVDF fibers were prepared by electrospinning and gas-jet/electrospinning of its N,N-dimethylformamide (DMF) solutions.The morphology of the PVDF fibers was investigated by scanning electron microscopy (SEM).With an increase of the gas flow rate,the average diameters of PVDF fibers were decreased.The crystal structures and thermal properties of the PVDF fibers w...     

Microstructural evolution and mechanical investigation of hot stretched graphene oxide reinforced polyacrylonitrile nanofiber yarns

To reveal the enhancement effect of graphene oxide (GO) in polymer nanofiber yarns, polyacrylonitrile (PAN)/GO nanofibers with different GO content (0.1‐0.5 wt%) were electrospun. The alignment of PAN chains and GO in nanofibers was enhanced by hot stretching of the yarn in dry conditions. The microstructure of the composite nanofiber yarns was investigated through X‐ray diffraction, polarized Fourier transform infrared spectroscopy and transmission electron microscopy. The results demonstrated that the hot stretching above T_g of PAN precursor lead to the increased orientation‐induced crystallization and alignment of PAN chain and GO. The yarn with 0.1 wt% GO and stretched by 4 times its length obtained the highest strength and modules (310.88 ± 24.68 MPa and 7.24 ± 0.55 GPa), which were 600% and 500% higher than those of the as‐electrospun pure PAN yarn. The most promising tensile properties found in hot stretched yarns with low GO content was because the strong interaction occurred between PAN molecules and oxygen‐containing functional groups. Indirect evidence of GO aggregation was also presented, which adversely affected the mechanical properties at higher GO content. Composite nanofiber yarns were sewable and weavable, and could be used as a new generation of composite reinforcement after pyrolysis.     

Effects of diameter and surface area of electrospun nanocomposite fibers on electromagnetic interference shielding

The effects of variation in average diameter and surface area of nanocomposite fibers on electromagnetic interference (EMI) shielding of multi-walled carbon nanotubes (MWCNTs)/polyvinylpyrrolidone (PVP) fibers were investigated in this paper. The EMI shielding effectiveness of electrospun nanocomposite fibers were measured in the X-band frequency range 8.2–12.4 GHz. The electrical conductivity and EMI shielding behaviors of the nanocomposite fibers were reported as function of average diameter and surface area of MWCNTs/PVP nanocomposite fibers. The electrical conductivity measurements demonstrate using thinner nanocomposite fibers results in a lower limit of electrical resistivity, better electrical conductivity performance. The EMI shielding efficiency of thinner nanocomposite fibers increased up to 42 dB. The EMI shielding data for MWCNTs/PVP nanocomposite fibers with various average diameter and surface area showed that absorption was the major shielding mechanism and reflection was the secondary shielding mechanism. It can be related to higher specific surface area of thinner electrospun MWCNTs/PVP nanocomposite fibers that means more surface area for radiative scatter and absorption leading to higher EMI shielding performance.     

Thermal shrinkage of electrospun PVP nanofibers

This paper outlines the shrinkage of electrospun polyvinylpyrrolidone (PVP) fiber mats during thermal treatment. The thermal behavior and phase changes within the fibers were investigated by DSC and TGA/DTA. Five precursors with different PVP loading in ethanol were electrospun. The mats shrinkage as function of temperature was measured in the RT–200 °C range. Shrinkage rate drastically increased above the polymer glass transition point, T_g (150–180 °C), due to increase in polymer chain mobility. Mats shrinkage at 200 °C as function of PVP concentration showed a minimum at ∼10%wt. Below 10% PVP the mats morphology is non‐uniform, consisting of beads and fibers. Above 10% PVP, only flat and uniform fibers were observed. This paper outlines the dominant mechanism governing the mats shrinkage during heating. In addition, the effect of PVP concentration on the expansion of fibers diameter was investigated and found to be consistent with the linear shrinkage observing a minimum at ∼10% PVP. The effect of applied voltage on mat shrinkage was investigated, and showed a minimum at 12 kV. Understanding the interplay between fibers morphology and thermal shrinkage allows precursor composition and system optimization needed for minimizing shrinkage negative effects on the structure and properties of electrospun fiber mats. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 248–254