掺杂羧基化碳纳米管的纳米碳纤维前驱体的制备及表征

为获得结构完整、 性能优良的纳米碳纤维前驱体, 采用静电纺丝法制备了掺杂羧基化多壁碳纳米管(MWCNTs)的聚丙烯腈(PAN)纳米纤维. 用扫描电子显微镜、 偏振红外光谱、 透射电子显微镜、 拉曼光谱及拉伸性能测试等对杂化纳米纤维的微观结构和力学性能进行了研究, 分析了MWCNTs含量的影响. 实验结果表明, 5%(质量分数)的MWCNTs掺杂量为杂化纳米纤维直径的突变点, 且MWCNTs的加入有利于PAN分子链的取向, MWCNTs在PAN纤维中大体上沿纤维轴向取向分布. 3%MWCNTs/PAN杂化纳米纤维的拉伸强度和拉伸模量分别达到88.6 MPa和3.21 GPa.     

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     

Fundamental study of crystallization,orientation, and electrical conductivity of electrospun PET/carbon nanotube nanofibers

The morphology, structure, and properties of polyethylene terephthalate (PET)/Carbon Nanotubes (CNT) conductive nanoweb were studied in this article. Nanocomposite nanofibers were obtained through electrospinning of PET solutions in trifluoroacetic acid (TFA)/dichloromethane (DCM) containing different concentrations and types of CNTs. Electrical conductivity measurements on nanofiber mats showed an electrical percolation threshold around 2 wt % multi‐wall carbon nanotubes (MWCNT). The morphological analysis results showed smoother nanofibers with less bead structures development when using a rotating drum collector especially at high concentrations of CNTs. From crystallographic measurements, a higher degree of crystallinity was observed with increasing CNT concentrations above electrical percolation. Spectroscopy results showed that both PET and CNT orientation increased with the level of alignment of the nanofibers when the nanotube concentration was below the electrical percolation threshold; while the orientation factor was reduced for aligned nanofibers with higher content in CNT. Considerable enhancement in mechanical properties, especially tensile modulus, was found in aligned nanofibers; at least six times higher than the modulus of random nanofibers at concentrations below percolation. The effect of alignment on the mechanical properties was less important at higher concentrations of CNTs, above the percolation threshold. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2052–2064, 2010     

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     

Solution Blowing of Poly（dimethylsiloxane）/Nylon 6 Nanofiber Mats for Protective Applications

A new strategy was developed to fabricate superhydrophobic nylon 6 nanofibers, in which the blend solutions of poly(dimethylsiloxane)(PDMS) prepolymer and nylon 6 was spun using an innovative solution blowing process, and then the PDMS prepolymer contianning nanofibers were cured to obtain PDMS/nylon 6 nanofiber mats. Morphology, surface composition, non-wetting property and protective performance were investigated. The results showed that the addition of PDMS prepolymer improved the spinnability of the spinning solutions, and the PDMS/nylon 6 nanofibers had smooth surfaces and diameters from 100 nm to 350 nm. The presence of PDMS effectively enhanced the hydrophobicity of the nanofiber mats, showing water contact angles of 132° to 161° for PDMS contents of 1 wt% to 3 wt%. The PDMS/nylon 6 mats also possessed excellent protective and transport properties. The results indicated the potential application of the novel nanofiber mats in protective clothing.     

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.     

Plasma-Electrospinning Hybrid Process and Plasma Pretreatment to Improve Adhesive Properties of Nanofibers on Fabric Surface

Electrospun nanofiber mats are inherently weak, and hence they are often deposited on mechanically-strong substrates such as porous woven fabrics that can provide good structural support without altering the nanofiber characteristics. One major challenge of this approach is to ensure good adhesion of nanofiber mats onto the substrates and to achieve satisfactory durability of nanofiber mats against flexion and abrasion during practical use. In this work, Nylon 6 nanofibers were deposited on plasma-pretreated woven fabric substrates through a new plasma-electrospinning hybrid process with the objective of improving adhesion between nanofibers and fabric substrates. The as-prepared Nylon 6 nanofiber-deposited woven fabrics were evaluated for adhesion strength and durability of nanofiber mats by carrying out peel strength and flex resistance tests. The test results showed significant improvement in the adhesion of nanofiber mats on woven fabric substrates. The nanofiber-deposited woven fabrics also exhibited good resistance to damage under repetitive flexion. X-Ray photoelectron spectroscopy and water contact angle analyses were conducted to study the plasma effect on the nanofibers and substrate fabric, and the results suggested that both the plasma pretreatment and plasma-electrospinning hybrid process introduced radicals, increased oxygen contents, and led to the formation of active chemical sites on the nanofiber and substrate surfaces. These active sites helped in creating crosslinking bonds between substrate fabric and electrospun nanofibers, which in turn increased the adhesion properties. The work demonstrates that the plasma-electrospinning hybrid process of nanofiber mats is a promising method to prepare durable functional materials.     

Mechanical and shape memory performance of shape memory polyurethane-based aligned nanofibers

In recent years, shape memory polyurethane (SMPU) as a smart material has been used in various applications owing to its desirable shape memory effect and biocompatibility. In this study, unidirectional SMPU nanofibers are innovated by electrospinning to clarify the mechanical and shape memory properties with nanofiber directions. The results showed that when the nanofiber alignment degree is 0° (parallel to the tensile direction), the aligned SMPU nanofibers achieved the obvious improvement of tensile strength (increased to 135%) and elastic modulus (increased to 313%), compared with the random SMPU nanofiber. Moreover, the developed aligned nanofibers exhibited good ability against stress relaxation and creep under constant strain or constant stress conditions in cyclic loading. The aligned SMPU nanofibers with a 0° alignment degree exhibited excellent shape memory properties with shape recovery rates larger than 93% and shape fixity rates larger than 90%, and a dramatic increase of shape recovery stress.     

A composite polyaniline/graphene–coated polyamide6 nanofiber mat for electrochemical applications

In this study, polyamide6 (PA6) nanofiber mats were fabricated through the electrospinning process. The nanofibers were coated by polyaniline (PANI) using the in situ polymerization of aniline in the presence of graphene oxide. The composite of the PANI/graphene oxide–coated nanofiber mat was treated with hydrazine monohydrate to reduce graphene oxide to graphene, and this was followed by the reoxidation of PANI. Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), wide angle X‐ray diffraction (WAXD), thermal gravimetric analysis (TGA), tensile strength tests, electrical conductivity measurements, cyclic voltammetry (CV), and charge/discharge measurements were conducted on the composite PA6/graphene nanofiber mats. It was found that the surface of the PA6 nanofibers was coated uniformly with the granular PANI and graphene oxide. Besides, the composite nanofibers showed good tensile and thermal properties. Their electrical conductivity and specific capacitance, when used as a separator in the cell, were 1.02 × 10^?4 S/cm and 423.28 F/g, respectively. Therefore, the composite PANI/reduced graphene oxide–coated PA6 nanofiber mats could be regarded as suitable candidates for application in energy storage devices.     

Investigation of nanomechanical and morphological properties of silane-modified halloysite clay nanotubes reinforced polycaprolactone bio-composite nanofibers by atomic force microscopy

There is remarkable interest in the fabrication of polymeric composite nano/micro-fibers by electrospinning for many applications ranging from bioengineering to water/air filtration. In almost all of these applications, the mechanical properties of both the polymer fibers and their assemblies, are significant. In this study, unmodified, 3-Glycidoxypropyltrimethoxysilane (GPTMS) or 3-Aminopropyltriethoxysilane (APTES) modified halloysite clay nanotube (HNT) reinforced polycaprolactone (PCL) nanofibers were successfully synthesized via the electrospinning. The morphology and mechanical features of the obtained electrospun fibers were investigated by atomic force microscopy (AFM) and AFM-based nanoindentation for single fibers in nanoscale, respectively. Besides, scanning electron microscopy and tensile strength tests were used to investigate whole fibrous structures in microscale. The AFMresults, accompanied by SEM and tensile strength, support the conclusion that silane-modification affected positively the morphology and mechanical characteristics of electrospun PCL nanofibers. Therefore, it was concluded that the morphological and mechanical features from the single fibers in the nanofiber mats were related to the whole fibrous structure.     

Electrospinning of biostable polyisobutylene-based thermoplastic polyurethanes

Electrospinning of a previously synthesized biostable polyisobutylene (PIB)-based thermoplastic polyurethanes (TPU) have been performed as materials with potential applications as vascular grafts. Electrospun mats were generated with fiber diameters in the submicron to 2 μm range as observed using scanning electron microscopy. Porosity of electrospun TPU fiber mats was investigated using Hg intrusion porosimetry. Fiber mats were found to have a distribution of pore sizes between 100 nm and 100 μm, with overall porosity between 50 and 70%. Thermal analysis of electrospun mats showed orientation of the TPU chains compared to the bulk as-synthesized material. Tensile failure properties were characterized, showing ultimate tensile strength of 1.6–6.5 MPa and ultimate elongation of ∼300–100% with TPUs of increasing hardness from Shore 60A to 100A. Strain-recovery experiments showed good recovery of tensile strain at significant stresses. The previously demonstrated biostability of these PIB-based TPUs, together with the excellent reported mechanical properties, indicates great promise for these materials as biostable vascular grafts. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Controlled release of doxorubicin from electrospun MWCNTs/PLGA hybrid nanofibers

In this study, multiwalled carbon nanotubes (MWCNTs) were used to encapsulate a model anticancer drug, doxorubicin (Dox). Then, the drug-loaded MWCNTs (Dox/MWCNTs) with an optimized drug encapsulation percentage were mixed with poly(lactide-co-glycolide) (PLGA) polymer solution for subsequent electrospinning to form drug-loaded composite nanofibrous mats. The structure, morphology, and mechanical properties of the formed electrospun Dox/PLGA, MWCNTs/PLGA, and Dox/MWCNTs/PLGA composite nanofibrous mats were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and tensile testing. In vitro viability assay and SEM morphology observation of mouse fibroblast cells cultured onto the MWCNTs/PLGA fibrous scaffolds demonstrate that the developed MWCNTs/PLGA composite nanofibers are cytocompatible. The incorporation of Dox-loaded MWCNTs within the PLGA nanofibers is able to improve the mechanical durability and maintain the three-dimensional structure of the nanofibrous mats. More importantly, our results indicate that this double-container drug delivery system (both PLGA polymer and MWCNTs are drug carriers) is beneficial to avoid the burst release of the drug and able to release the antitumor drug Dox in a sustained manner for 42 days. The developed composite electrospun nanofibrous drug delivery system may be used as therapeutic scaffold materials for post-operative local chemotherapy.     

Preparation of tough hydrogels based on β-chitin nanofibers via NaOH treatment

Cellulose and chitin exist in nature as highly crystalline nanofibers. Previously, we reported preparing unique hydrogels from cellulose nanofibers by a simple NaOH treatment without use of any specific solvents or cross-linking agents. In the present study, a similar gel preparation was applied to β-chitin nanofibers extracted from purified squid pen powder. The crystal structure of chitin nanofibers was transformed from β-chitin to α-chitin by NaOH(aq) treatment above 30 wt%. The crystal conversion involving the interdigitation among adjacent nanofibers caused the formation of stable hydrogels with a α-chitin nanofiber network. The use of ethanol voided the dissolution during neutralization and enabled preparation of a higher crystalline hydrogel with high mechanical strength. It achieved a Young’s modulus of 16.6 MPa, a tensile strength of 7 MPa and a strain at break of 52.2 %, on average. Finally, we note that the shrinkage of the cellulose I and β-chitin nanofibers in aqueous NaOH solutions was caused by the release of tensile residual stress due to the intracrystalline swelling in NaOH solutions.     

Solution‐blown nylon 6–chitosan core–shell nanofiber for highly efficient affinity adsorption

A facile spinning‐based strategy was developed to fabricate chitosan (CS) surface nanofiber‐based affinity membranes for protein adsorption. The core–shell nanofiber mat of nylon 6–CS was prepared via coaxial solution blowing process. The nanofibers have a diameter range of 60–300 nm. The core–shell structure was confirmed by transmission electron microscopy, and CS was observed as a thin layer that uniformly adhered to the core. The dye ligand of cibacron blue F3GA (CB F3GA) was further covalently immobilized on the nanofibers with a content of 425 µmol/g. The pristine and CB F3GA‐attached mats were studied in protein adsorption. High bovine serum albumin adsorption capacities of 91.9 and 219.6 mg/g were obtained for pristine and CB F3GA‐attached mats, respectively. Given its properties of high flux rate and low pressure drop, CB F3GA‐attached nylon 6–CS nanofiber mat meets the requirements of highly effective affinity membrane chromatography. Copyright © 2016 John Wiley & Sons, Ltd.     

Tensile versus AFM testing of electrospun PVA nanofibers: Bridging the gap from Microscale to nanoscale

Design and application of mechanically extraordinary nanofibers requires their full comprehension, based on conclusive testing methods. Electrospun polymer nanofibers, for instance, show a progressive and pronounced increase in their Young's moduli when diameters decrease below the µm scale. Measurement of mechanical properties in this diameter range is challenging and in the vast majority of reports, two classes of methods are commonly used: highly sensitive tensile testing and atomic force microscopy three‐point deformation testing. Despite the methods' inherent dissimilarity, we resolve their conformity for the first time, with respect to the determination of Young's moduli. Here, we benchmark them against each other for electrospun polyvinyl‐alcohol nanofibers, a well‐defined model system. Our results provide an experimental basis for a comprehensive understanding of nanofiber structures and its implications on their mechanical properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2418–2424     

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.     

Effect of constrained annealing on the mechanical properties of electrospun poly(ethylene oxide) webs containing multiwalled carbon nanotubes

In this work, flexible nanofibrous membranes (mats) of poly(ethylene oxide) (PEO) with and without multiwall carbon nanotubes (MWNTs) were fabricated by electrospinning. The effects of annealing and MWNT concentration on mat morphology, MWNT dispersion within the nanofibers, and the mechanical properties of electrospun mats were studied. Annealing temperatures ranged from 60 °C to 64 °C [near the melting temperature (64 °C via differential scanning calorimetry)] for 4 minutes. Samples were annealed with and without applied tension (constrained and unconstrained annealing). Annealing at the highest temperature (64 °C), before the loss of fibrous morphology, significantly improved fiber–fiber bonding and therefore the tensile strength of the mats. Compared with unconstrained annealing, constrained annealing introduced fiber alignment (and therefore molecular orientation) along the tensile axis (direction of constraint) during annealing and resulted in a significant increase in modulus for all samples (with and without MWNTs). The use of constrained annealing may be a facile approach to enhance modulus in nanofibrous mats while maintaining high porosity. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 787–796     

Tensile deformation of electrospun nylon‐6,6 nanofibers

Nylon‐6,6 nanofibers were electrospun at an elongation rate of the order of 1000 s^?1 and a cross‐sectional area reduction of the order of 0.33 × 10⁵. The influence of these process peculiarities on the intrinsic structure and mechanical properties of the electrospun nanofibers is studied in the present work. Individual electrospun nanofibers with an average diameter of 550 nm were collected at take‐up velocities of 5 and 20 m/s and subsequently tested to assess their overall stress–strain characteristics; the testing included an evaluation of Young's modulus and the nanofibers' mechanical strength. The results for the as‐spun nanofibers were compared to the stress–strain characteristics of the melt‐extruded microfibers, which underwent postprocessing. For the nanofibers that were collected at 5 m/s the average elongation‐at‐break was 66%, the mechanical strength was 110 MPa, and Young's modulus was 453 MPa, for take‐up velocity of 20 m/s—61%, 150 and 950 MPa, respectively. The nanofibers displayed α‐crystalline phase (with triclinic cell structure). © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1482–1489, 2006     

Double‐layered composite nanofibers and their mechanical performance

Continuous polymer nanofibers are available through electrospinning, but most have the same structure in their cross section. This article focuses on the fabrication and the structural and mechanical characterization of pencil‐like double‐layered composite nanofibers coaxially electrospun from solutions of two different biodegradable materials, i.e., gelatin and poly(ε‐caprolactone) (PCL). Transmission electron microscopy and water contact angle measurements confirmed that a gelatin inner fiber was wrapped with a PCL outer layer. Possible applications of such nanofibers include a controlled degradation rate when used as a medical device in human body. It has been found that the tensile performance of the composite nanofibers was better than those of both the pure constituent, i.e. gelatin and PCL, nanofibers alone. The ultimate strength and ultimate strain of the composite nanofibers with 7.5% w/v gelatin in the core and 10% w/v PCL as shell were at least 68% and 244% higher, respectively, than those of the same concentration pure gelatin and PCL nanofibers. Thus, a coaxial electrospinning technique as used in this article can be applicable, not only in developing functionalized nanofibers but also in elevating their mechanical property. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2852–2861, 2005     

Dissolution of MWCNTs by using polyoxadiazoles,and highly effective reinforcement of their composite films

Nonmodified multiwalled carbon nanotubes (MWCNTs)/sulfonated polyoxadiazole (sPOD) nanocomposites are successfully prepared by a facile solution route. The pristine MWCNTs are dispersed in a sPOD solution, and the mixtures are fabricated into thin films by solution casting. The homogeneous dispersion of nanotubes in the composites is confirmed by transmission electron microscopy. The mechanical properties, thermal stability, and electrical conductivity are investigated. Tensile strength, elongation at break, and tensile energy to break are shown to increase by more than 28, 45, and 73%, respectively, by incorporating up to 1.0 wt % pristine MWCNTs. The experimental values for sPOD/MWCNTs composite stiffness are compared with Halpin‐Tsai and modified Halpin‐Tsai predictions. The storage modulus is found to increase up to 10% at low CNT loading. The composite films, which have an outstanding thermal stability, show an increase of up to 57 °C in the initial degradation temperature. The addition of 1.0 wt % MWCNTs increases the electrical conductivity of the sPOD matrix by two orders of magnitude. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010