丙烯腈-衣康酸基纳米纤维纱线的热稳定及碳化研究

碳纳米纤维主要以聚丙烯腈(PAN)作为前驱体,通过纺丝、热稳定、碳化等后处理工艺制备而得。但是,PAN基纳米纤维取向度低、致密性差,热稳定后环化度低,碳化后导电性差等缺点阻碍其在高性能碳纳米纤维领域的发展。因此,在PAN分子链中引入衣康酸(IA),通过溶液聚合法合成了P(AN-co-IA)共聚物并通过静电纺丝法制备了P(AN-co-IA)基纳米纤维纱线。研究了纱线中纳米纤维的取向度、致密性以及在热稳定后的环化反应程度。重点研究了P(AN-co-IA)基碳纳米纤维纱线的线电阻、微观结构与碳化温度的关系。用扫描电子显微镜(SEM)对纱线进行形貌表征。用X-射线衍射仪(XRD)、傅里叶显微红外仪(FT-IR)、拉曼光谱仪(Raman)对纱线进行结构分析。结果表明,P(AN-co-IA)基原丝纱线的结构较致密,取向度较高。热稳定后的P(AN-co-IA)基纳米纤维的环化度高于PAN基纳米纤维。当碳化温度升至1100℃时,P(AN-co-IA)基碳纳米纤维纱线的线电阻明显降低至14Ω/cm。当碳化温度继续升高至1400℃,纱线的线电阻没有明显变化,但通过Raman光谱分析其无序碳结构会大幅增加。本文的研究结果为制备高取向性、高致密性和高电导性的碳纳米纤维纱线提供了一定的理论及实验基础。     

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.     

Novel mechanism for spinning continuous twisted composite nanofiber yarns

Highly aligned and twisted composite Nylon 6 nanofibers incorporating multiwall carbon nanotubes (MWCNTs) were successfully electrospun, using a novel mechanism. It has been found that; ultrasound combined with high speed shearing is the simplest and most convenient method to improve the dispersion of MWCNTs into a polymer matrix with a certain loading. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were conducted to characterize the morphology of nanofibers, the dispersion of MWCNTs and their alignment inside the fiber body. By manipulating the electrical forces during electrospinning and applying mechanical stretching to the electrospun nanofibers, high polymer chain orientation and better alignment of the MWCNTs particles along the fiber axis was achieved. Twist was applied to the nanofibers for providing the required inter fiber lateral cohesion interaction and friction thus, spinning a continuous twisted composite yarn. SEM images show twisted yarns with diameters ranging between 5 and 10 μm. The twist effect of the parallel bundle was investigated by controlling the twist per unit length using a motor speed controller at values of 100, 250, 500, 750 and 1000 rpm. The paper also provides a comprehensive review of various yarn spinning mechanisms of electrospun nanofibers.     

Enhanced Mechanical Performance of Self‐Bundled Electrospun Fiber Yarns via Post‐Treatments

A new route to high‐performance electrospun polymer fibers was developed using a self‐bundling electrospinning technique combined with post‐treatments such as stretching and annealing under conditions similar to those used for conventional fibers. Self‐bundled electrospun PAN fiber yarns were characterized by SEM, mechanical tests, polarized FT‐IR spectroscopy and WAXD. The obtained results revealed that the PAN nanofiber yarns possessed enhanced alignment, a higher degree of crystallinity and higher molecular orientation after treatments, resulting in a remarkable improvement in mechanical performance, approaching the strength value of the corresponding conventional fibers.

     

Graphene oxide improved thermal and mechanical properties of electrospun methyl stearate/polyacrylonitrile form-stable phase change composite nanofibers

In the present work, a novel PAN-based form-stable composite phase change materials with the methyl stearate (MES) encapsulated in the supporting matrices of polyacrylonitrile (PAN) nanofibers were fabricated through electrospunning for the storage and retrieval of thermal energy. Influences of graphene oxide (GO) addition on the chemical properties, structural morphologies, mechanical properties, thermal energy storage properties, thermal stability, and thermal energy storage/retrieval rates of electrospun MES/PAN/GO phase change composite nanofibers were systematically investigated by FT-IR, FE-SEM, tensile testing, DSC, TG, and measurement of melting/freezing times, respectively. The results revealed that the incorporation of GO effectively enhanced the mechanical properties, thermal stability, as well as heat storage and release rates of the phase change composite nanofibers. The averaged tensile strength of electrospun MES/PAN/GO phase change composite nanofibers increased significantly by 573 % with 10 mass% loading of GO, while elongation at break had a maximum 107 % increment when adding 3 mass% of GO. The DSC results indicated that the electrospun PAN-based phase change composite nanofibers with various GO loadings had suitable phase transition temperatures with the latent heat ranging from about 92 to 109 kJ kg^?1 and exhibited good thermal reliability in terms of DSC measurements during 50 melting-freezing cycles. Moreover, the melting and freezing time were significantly decreased about 44 and 43 % for the MES/PAN/GO5, as well as 59 and 64 % for the MES/PAN/GO10 after introducing the GO into the composite nanofibers systems.     

Preparation of porous ultrafine polyacrylonitrile (PAN) fibers by electrospinning

A facile method for the preparation of porous ultrafine nanofibers was demonstrated. The PAN/NaHCO₃ composite nanofibers were electrospun, and then NaHCO₃ was removed by a selective dissolution and reaction with the solution of hydrochloric acid (10 wt%). The obtained PAN fibers showed highly porous surfaces after the extraction of NaHCO₃. The structure and properties of ultrafine PAN nanofibers were characterized by Fourier transform infrared (FT‐IR), X‐ray diffraction (XRD), and thermogravimetry (TG). The results indicated that NaHCO₃ could be introduced into the PAN solution and successfully electrospun. CO₂ is released and pores are formed on the fibers. The morphology image of the fibers was detected by scanning electron microscope (SEM) and showed that many pores aligned the nanofibers. Copyright © 2008 John Wiley & Sons, Ltd.     

Improving piezoelectric and pyroelectric properties of electrospun PVDF nanofibers using nanofillers for energy harvesting application

In this study, it was aimed to increase the piezoelectric and pyroelectric properties of electrospun polyvinylidene fluoride (PVDF) nanofibers simultaneously by using specific nanofillers. Graphene oxide (GO), graphene, and halloysite nanotubes with different concentrations (0, 0.05, 0.4, and 1.6% wt/wt) were combined with PVDF solution and were fabricated in the form of nanofibers through electrospinning. Pyroelectric properties of samples were measured by submerging sealed samples in hot water (360°K) and ice (270°K). The piezoelectric properties of the samples were evaluated through bending tests. The microstructural, mechanical, and thermal properties of the electrospun PVDF nanocomposite were investigated using scanning electron microscope, Instron instrument, and thermogravimetric analysis, respectively. To further support the experimental observations for generating electric voltage in the bended nanogenerator, the PVDF nanogenerator (PNG) was also modeled by a finite element analysis based on the theory of linear piezoelectricity using COMSOL Multiphysics simulation software. Experimental results showed that adding nanofillers could improve the piezoelectric and pyroelectric properties of all samples, associated with the increment of β‐phase in the nanofibers. It was concluded that adding nanofillers could increase pyroelectricity about 50% more than piezoelectricity in pristine PVDF nanofiber web. The PNG containing 1.6 wt% GO showed the highest efficiency in terms of piezoelectricity and pyroelectricity. In addition, the results showed that the ratio of piezoelectric to pyroelectric coefficients was constant (~1.5) and it was independent of the nanofiller type and content. The effect of external force and vibration frequency on the output voltage was also investigated. Increasing the compressive force and vibration frequency caused a greater output voltage. Finally, the fabricated nanogenerator was integrated on insole and elbow to investigate its energy harvesting capabilities from body movement.     

Functionalized carbon nanotube/polyacrylonitrile composite nanofibers: fabrication and properties

The functionalized multi‐walled carbon nanotubes (f‐MWCNTs) were obtained by Friedel–Crafts acylation, which introduced aromatic amine groups onto the sidewall. And the grafted yield was adjusted by controlling the concentration of the catalyst. The composite solutions containing f‐MWCNTs and polyacrylonitrile (PAN) were then prepared by in‐situ or ex‐situ solution polymerization. The resulting solutions were electrospun into composite nanofibers. In the in‐situ polymerization, morphological observation revealed that f‐MWCNTs was uniformly dispersed along the axes of the nanofibers and increased interfacial adhesion between f‐MWCNTs and PAN. Furthermore, two kinds of f‐MWCNTs/PAN composite nanofibers had a higher degree of crystallization and a larger crystal size than PAN nanofibers had, so the specific tensile strengths and modulus of the composite nanofibers were enhanced. And the thermal stability of f‐MWCNTs/PAN from in‐situ method was higher than that of ex‐situ system. When the f‐MWCNTs content was less than 1 wt%, the specific tensile strengths and modulus of nanofibers were enhanced with increase in the amounts of f‐MWCNTs, and f‐MWCNTs/PAN of in‐situ system provided better mechanical properties than that of ex‐situ system. Copyright © 2010 John Wiley & Sons, Ltd.     

Interplay of electrical forces for alignment of sub-100 nm electrospun nanofibers on insulator gap collectors

We present a quantitative design methodology for optimizing insulator gap width, gap resistivity, and collector to needle height for the alignment of sub-100 nm electrospun nanofibers at insulator gaps of metal collectors. Enhancement of the spatial extent of alignment forces at insulator gaps, due to the concerted action of attractive stretching forces from the modified electric fields and repulsive forces from residual charges on undischarged fibers in the gap, is studied. At gap widths considerably smaller than the collector to needle height (<2%), the spatial extent of stretching forces is large as evidenced by successive reduction in nanofiber size with gap width; however, the low magnitude of repulsive forces limits the degree of nanofiber alignment. At successively larger gap widths less than the needle height, the spatial extent of the stretching forces is gradually restricted toward the metal-insulator edges, while the influence of repulsive forces is gradually extended across the rest of the spatial extent of the gap, to cause enhanced nanofiber alignment through the concerted action of these forces. At gap widths greater than the needle height, the limited spatial extent and lowered maximum value of the stretching forces at the metal-insulator edge reduces their influence on fiber stretching and alignment. The collection of sub-100 nm electrospun poly(lactic acid-co-glycolic acid) nanofibers with a good degree of alignment (≤10° deviation) is found to require intermediate size gaps (～2% of needle height) of high resistivity (≥10(12) ohm-cm), to enhance the spatial extent of stretching forces while maintaining the dominance of repulsive forces due to residual charge across a majority of the spatial extent of the gap.     

Aligned electrospun nanofibers for ultra-thin layer chromatography

The fabrication and implementation of aligned electrospun polyacrylonitrile (PAN) nanofibers as a stationary phase for ultra-thin layer chromatography (UTLC) is described. The aligned electrospun UTLC plates (AE-UTLC) were characterized to give an optimized electrospun mat consisting of high nanofiber alignment and a mat thickness of ∼25 μm. The AE-UTLC devices were used to separate a mixture of β-blockers and steroidal compounds to illustrate the properties of AE-UTLC. The AE-UTLC plates provided shorter analysis time (∼2–2.5 times faster) with improved reproducibility (as high as 2 times) as well as an improvement in efficiency (up to100 times greater) relative to non-aligned electrospun-UTLC (E-UTLC) devices.     

Effect of CNT incorporation on PAN/PPy nanofibers synthesized by electrospinning method

In this study, carbon nanotubes (CNTs) added polyacrylonitrile/polypyrrole (PAN/PPy) electrospun nanofibers were produced. Average diameters of the nanofibers were measured as 268 and 153 nm for 10 and 25 wt% of PPy contents, respectively. A relatively higher strain to failure values (23.3%) were observed for the low PPy content. When as-grown CNTs (1 and 4 wt%) were added into the PAN/PPy blends, disordered nanofibers were observed to form within the microstructure. To improve the interfacial properties of CNTs/PAN/PPy composites, CNTs were functionalized with H₂SO₄/HNO₃/HCl solution. The functionalized CNTs were well dispersed within the nanofibers and aligned along the direction of nanofibers. Therefore, beads formation on nanofibers decreased. The impedance of the nanofibers was found to decrease with the PPy content and CNT addition. These nanofibers had a great potential to be used as an electrochemical actuator or a tissue engineering scaffold.     

Nanofiber Configuration of Electrospun Scaffolds Dictating Cell Behaviors and Cell-scaffold Interactions

Electrospun nanofibers are of the same length scale as the native extracellular matrix and have been extensively reported to facilitate adhesion and proliferation of cells and to promote tissue repair and regeneration. With a primary focus on tissue repair and regeneration using electrospun scaffolds, only a few studies involved electrospun nanofiber scaffolds directing cell behaviors have been reported. In this study, we prepared electrospun nanofiber scaffolds with distinct fiber configurations, namely, random and aligned orientations of nanofibers, as well as oriented yarns, and investigated their effects on cell behaviors. Our results showed that these scaffolds supported good proliferation and viability of murine fibroblasts. Fiber configuration profoundly influenced cell morpho-logy and orientation but showed no effects on cell proliferation rate. The yarn scaffold had comparable total protein accumulation with the random and aligned scaffolds, but it supported a greater pro-liferation rate of fibroblasts with significantly elevated collagen de-position due to its porous fibrous configuration. Cell-seeded yarn scaffolds showed a greater Young's modulus compared with cell-free controls as early as 1 week. Together with its unique fiber configuration similar to the native extracellular matrix of the myocardium, the yarn scaffold might be a suitable matrix material for modeling cardiac fibrotic disorders.     

浸润性可调的导电聚苯胺/聚丙烯腈同轴纳米纤维

聚苯胺(PANI)因其具有可调的导电性、优异的化学稳定性、简单的制备方法等特点, 在化学电源、抗静电涂层、电磁屏蔽材料、抗腐蚀、传感器等领域具有广泛的应用前景[^1~4]. 由于聚苯胺的刚性分子链使得聚苯胺几乎不溶不熔, 难以加工应用, 因此, 将导电聚合物直接制成纳米纤维一直是合成纤维界所希望的目标之一. 此外, 由于材料尺度的减小, 使纳米材料的表面与界面性质,尤其是表面浸润性变得更为突出.浸润性是固体表面的重要特征之一, 它主要由表面的化学组成和微观结构共同决定^[5,6]. 可调的浸润性在超疏水材料、药物传输、仿生材料和微流体等领域具有重要的应用价值^[7~10] , 引起人们广泛关注.     

A novel method for a high‐strength electrospun meta‐aramid nanofiber by microwave treatment

Electrospun nanofibers have attracted great attention as potential reinforcements in composite application due to their high specific surface area, high porosity, and versatility. Because the electrospun nanofibers exhibit relatively low mechanical strength due to low crystallinity and random alignment, many researchers have tried to enhance the mechanical strength through various approaches, such as heat treatment and fiber orientation control. These methods, however, are difficult to control and require the use of high temperatures and sophisticated apparatuses, and high costs. In this study, we investigate a novel microwave technique to fabricate high‐strength electrospun meta‐aramid nanofiber mats. To optimize the microwave irradiation conditions, the electrospun nanofiber was treated at varying levels of moisture and for different irradiation times. Field emission scanning electron microscopy was used to observe the surface morphology of the electrospun nanofiber mats at the different irradiation times. The changes in the crystallinity and thermal properties were investigated using X‐ray diffraction and thermogravimetric analysis measurements. Tensile tests were performed to measure the mechanical strength of the meta‐aramid nanofiber mats with respect to each parameter. As a result, any residual solvents and salts were removed, and the degree of crystallization was dramatically increased by microwave irradiation under wet conditions. These effects led to a 2.8‐fold increase in the tensile strength of the nanofiber mats compared with an untreated mat. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 807–814     

Electrospinning of polyurethane/organically modified montmorillonite nanocomposites

Polyurethane/organically modified montmorillonite (PU/O‐MMT) nanocomposites were electrospun and the effect of O‐MMT on the morphology and physical properties of the PU/O‐MMT nanofiber mats were investigated for the first time. The average diameters of the PU/O‐MMT nanofibers were ranged from 150 to 410 nm. The conductivities of the PU/O‐MMT solutions were linearly increased with increasing the content of O‐MMT, which caused a decrease in the average diameters of the PU/O‐MMT nanofibers. The as‐electrospun PU and PU/O‐MMT nanofibers were not microphase separated. The exfoliated MMT layers were well distributed within the PU/O‐MMT nanofibers and oriented along the fiber axis. When the PU/O‐MMT nanofibers were annealed, the exfoliated MMT layers hindered the microphase separation of the PU. The electrospinning of PU/O‐MMT nanocomposites resulted in PU nanofiber mats with improved Young's modulus and tensile strength. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3171–3177, 2005     

Antibacterial and wound healing properties of cellulose acetate electrospun nanofibers loaded with bioactive glass nanoparticles; in-vivo study

Bioactive glasses (BGs) have gained great attention owing to their versatile biological properties. Combining BG nanoparticles (BGNPs) with polymeric nanofibers produced nanocomposites of great performance in various biomedical applications especially in regenerative medicine. In this study, a novel nanocomposite nanofibrous system was developed and optimized from cellulose acetate (CA) electrospun nanofibers containing different concentrations of BGNPs. Morphology, IR and elemental analysis of the prepared electrospun nanofibers were determined using SEM, FT-IR and EDX respectively. Electrical conductivity and viscosity were also studied. Antibacterial properties were then investigated using agar well diffusion method. Moreover, biological wound healing capabilities for the prepared nanofiber dressing were assessed using in-vivo diabetic rat model with induced wounds. The fully characterized CA electrospun uniform nanofiber (100–200 nm) with incorporated BGNPs exhibited broad range of antimicrobial activity against gram negative and positive bacteria. The BGNP loaded CA nanofiber accelerated wound closure efficiently by the 10th day. The remaining wound areas for treated rats were 95.7?±?1.8, 36.4?±?3.2, 6.3?±?1.5 and 0.8?±?0.9 on 1st, 5th, 10th and 15th days respectively. Therefore, the newly prepared BGNP CA nanocomposite nanofiber could be used as a promising antibacterial and wound healing dressing for rapid and efficient recovery.

     

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     

Lignin bio-oil-based electrospun nanofibers with high substitution ratio property for potential carbon nanofibers applications

We reported a new approach for development of lignin bio-oil-based electrospun nanofibers (LENFs) that had high substitution ratio (up to 80 wt%) and good morphology. This approach was particularly unique and translatable as it used small molecule lignin bio-oil with high reactivity and low heterogeneity obtained via lignin depolymerization reaction to produce well-oriented LENFs. Firstly, effects of various blends solutions ratios and electrospinning parameters on the characteristics of the obtained LENFs were analyzed. The results showed that the optimal parameters that resulted in the best electrospun nanofibers were as follows: blend solution ratio, the 20 wt% blend solution containing 80 wt% straw lignin bio-oil (SLB) and 20 wt% polyacrylonitrile (PAN), flow rate, 1 mL/h, voltage, 20 kV, rotational speed, 500 r/min and the distance between needle and collection screen, 20 cm. Secondly, used the best LENFs, we also applied to prepare lignin bio-oil-based carbon nanofibers (LCNFs) and estimated its properties by scanning electron microscope (SEM), X-ray diffraction (XRD) patterns, Raman spectroscopy and tension testing. Our results demonstrated that compared with pure PAN carbon nanofibers (PCNFs), the as-prepared LCNFs had similar smooth surfaces, similar crystallinity and similar mechanical properties. This work can promote the utilization of lignin depolymerization main-products to produce lignin-based materials, while also help to reduce use of high-cost PAN.     

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     

Fabrication of random and aligned electrospun nanofibers containing graphene oxide for skeletal muscle cells scaffold

Graphene oxide (GO)‐based materials have been explored in biomedical applications as active engineered materials for diagnosis and therapy. Although a large number of studies have been carried out in the last years, aspects involving the orientation and elongation of cells on GO immobilized on polymeric nanofibers are still scarce. We investigated the interactions between skeletal muscle cells and GO immobilized on random and aligned electrospun nanofibers of poly(caprolactone) (PCL), a biocompatible and biodegradable polymer. Oxygen plasma was employed to modify the nanofiber polymer surface to enhance the interactions between the PCL fibers and GO. Scanning electron microscopy and confocal microscopy revealed the morphology and orientation of skeletal muscle cells (C2C12 cells) on random and aligned GO/PCL nanofibers. The approach employed here is useful to investigate the interaction of skeletal muscle cells with biocompatible polymer nanofibers modified with GO intended for cell scaffolds and tissue engineering.