Chain conformation,crystallization behavior,electrical and mechanical properties of electrospun polymer-carbon nanotube hybrid nanofibers with different orientations

An improved electrospinning technique was used to produce poly(ethylene oxide) (PEO) and PEO-multi-walled carbon nanotube (MWCNT) hybrid nanofibers. By this technique, both the orientation of MWCNTs in the electrospun PEO nanofibers and the orientation of electrospun PEO–MWCNT hybrid nanofibers can be controlled. The morphologies of the as-spun PEO–MWCNT hybrid nanofibers and the dispersion and orientation of MWCNTs in the fiber matrix were observed by scanning and transmission electron microscopy. The effect of electrospinning process and the incorporation of MWCNTs on the chain conformation and semicrystalline framework of PEO were examined by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, and differential scanning calorimetry, and compared with pure PEO and PEO–MWCNT films prepared by casting. Finally, to investigate how the fiber assemblies affect the mechanical and electrical properties of the hybrid materials, tensile testing and impedance analysis were performed on randomly oriented, uniaxially and biaxially oriented PEO–MWCNT hybrid nanofiber mats. The results indicated that both the uniaxially and biaxially oriented assembled hybrid materials have better tensile strength, modulus, and electrical conductivity compared with random nanofibers.     

Conjugate electrospinning of continuous nanofiber yarn of poly(L‐lactide)/nanotricalcium phosphate nanocomposite

The continuous nanofiber yarns of poly(L ‐lactide) (PLLA)/nano‐β‐tricalcium phosphate (n‐TCP) composite are prepared from oppositely charged electrospun nanofibers by conjugate electrospinning with coupled spinnerets. The morphology and mechanical properties of PLLA/n‐TCP nanofiber yarns are characterized by scanning electron microscope, transmission electron microscope, and electronic fiber strength tester. The results show that PLLA/n‐TCP nanofibers are aligned well along the longitudinal axis of the yarn, and the concentration of PLLA plays a significant role on the diameter of the nanofibers. The thicker yarn of PLLA/n‐TCP composite with the weight ratio of 10/1 has been produced by multiple conjugate electrospinning using three pairs of spinnerets, and the yarn has tensile strength of 0.31cN/dtex. A preliminary study of cell biocompatibility suggests that PLLA/n‐TCP nanofiber yarns may be useable scaffold materials. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Composite chitosan/poly(ethylene oxide) electrospun nanofibrous mats as novel wound dressing matrixes for the controlled release of drugs

The aim of this study was to develop novel biomedical electrospun nanofiber mats for controlled drug release, in particular to release a drug directly to an injury site to accelerate wound healing. Here, nanofibers of chitosan (CS), poly(ethylene oxide) (PEO), and a 90 : 10 composite blend, loaded with a fluoroquinolone antibiotic, such as ciprofloxacin hydrochloride (CipHCl) or moxifloxacin hydrochloride (Moxi), were successfully prepared by an electrospinning technique. The morphology of the electrospun nanofibers was investigated by scanning electron microscopy. The functional groups of the electrospun nanofibers before and after crosslinking were characterized by Fourier transform infrared spectroscopy. X‐ray diffraction results indicated an amorphous distribution of the drug inside the nanofiber blend. In vitro drug‐release evaluations showed that the crosslinking could control the rate and period of drug release in wound‐healing applications. The inhibition of bacterial growth for both Escherichia coli and Staphylococcus aureus were achieved on the CipHCl‐ and Moxi‐loaded nanofibers. In addition, both types of CS/PEO and drug‐containing CS/PEO nanofibers showed excellent cytocompatibility in the cytotoxicity assays. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42060.     

Structure and process relationship of electrospun bioabsorbable nanofiber membranes

An electrospinning method was used to fabricate bioabsorbable amorphous poly(d,l-lactic acid) (PDLA) and semi-crystalline poly(l-lactic acid) (PLLA) nanofiber non-woven membranes for biomedical applications. The structure and morphology of electrospun membranes were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and synchrotron wide-angle X-ray diffraction/small angle X-ray scattering. SEM images showed that the fiber diameter and the nanostructured morphology depended on processing parameters such as solution viscosity (e.g. concentration and polymer molecular weight), applied electric field strength, solution feeding rate and ionic salt addition. The combination of different materials and processing parameters could be used to fabricate bead-free nanofiber non-woven membranes. Concentration and salt addition were found to have relatively larger effects on the fiber diameter than the other parameters. DSC and X-ray results indicated that the electrospun PLLA nanofibers were completely non-crystalline but had highly oriented chains and a lower glass transition temperature than the cast film.     

Characterization and cell response of electrospun Rana chensinensis skin collagen/poly(l‐lactide) scaffolds with different fiber orientations

Collagen was extracted from Rana chensinensis skin supplied from byproducts via an acid enzymatic extraction method. The R. chensinensis skin collagen (RCSC) and poly(l ‐lactide) (PLLA) were blended at a 3:7 ratio in 1,1,1,3,3,3‐hexafluoroisopropanol (HFIP) at a concentration of 10% (g/mL) and electrospun to produce nanofibers in an aligned and random orientation. For comparison, pure PLLA nanofibrous membranes with aligned and random nanofiber orientations were also produced. The secondary structure of the RCSC nanofibers was investigated by circular dichroism to confirm that the extracted substance was collagen. The presence of collagen in the blend nanofiber was verified by LSCM. The blended nanofibers showed uniform, smooth, and bead‐free morphologies and presented a smaller fiber diameter (278 and and 259 nm) than the pure the ones of PLLA (559 and and 439 nm) nanofibers. It was found that the addition of RCSC and the modification of the nanofiber's orientation affected the fiber's diameter and the crystallization of PLLA. The cell viability studies with human fibroblast cells demonstrated that the RCSC/PLLA nanofibrous membranes formed by electrospinning exhibited good biocompatibility and that the aligned scaffolds could regulate the cell morphology by inducing cell orientation. The empirical results in this study indicated that the aligned RCSC/PLLA nanofibrous membrane is a potential wound dressing candidate for skin regeneration. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45109.     

Biodegradable Electrospun Poly(lactic acid) Nanofibers for Effective PM 2.5 Removal

In addition to the rapid urbanization and industrialization around the world, air pollution due to particulate matter is a substantial threat to human health. A considerable research effort has been devoted to the development of electrospun polymer nanofibers for air filter applications. Among these new technologies, electrostatic charge‐assisted air filtration is a promising technology for removing small particulate matter (PM). In this investigation, biodegradable electrospun poly(l ‐lactic acid) (PLLA) polymer nanofibers are employed for air filter applications. Electrostatic charges generated from the PLLA nanofiber can significantly enhance air filter applications. Compared with a 3M commercial respirator filter, electrospun PLLA fibrous filters exhibit a high efficiency of 99.3%. Even after 6 h of filtration time, the PLLA filtration membrane still exhibits a 15% improvement in quality factor for PM 2.5 particles than the 3M respirator. This is mainly attributed to the electrostatic force generated from the electrospun PLLA nanofibers, which significantly benefit submicron particle absorption. Due to their biodegradability, ease of fabrication, and relatively high efficiency, electrospun PLLA nanofibers show great promise in applications such as air cleaning systems and personal air purifier applications.     

Synthesis and characterization of highly dispersed multi‐walled carbon nanotubes/polyvinylpyrrolidone composite nanofibers for EMI shielding application

Multi‐walled carbon nanotubes (MWCNTs)/polyvinylpyrrolidone (PVP) composite nanofibers having varying amounts of MWCNTs were fabricated with an aim to investigate the potential of such nanofibers as an effective light weight electromagnetic interference (EMI) shielding material in the frequency range of 8.2–12.4 GHz (X‐band). The state of dispersion of MWCNTs in PVP matrix was studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The TEM and SEM analyses confirmed the presence of individual dispersion MWCNTs encapsulated within the electrospun nanofibers and showed MWCNTs/PVP composite nanofiber morphologies with diameters of 150–600 nm. Moreover, the MWCNTs/PVP composite nanofibers were characterized by X‐ray diffraction and Raman spectrophotometer. The thermal stability of composite nanofibers studied from thermogravimetric analysis was increased after addition of MWCNTs to PVP matrix. The EMI shielding efficiency of MWCNTs/PVP composite nanofibers increased up to 42 dB. The MWCNTs/PVP composite nanofibers developed in this study have benefits in being light weight and having effective EMI shielding performance and can be best candidates for a broad range of electronic applications. POLYM. COMPOS., 38:2026–2034, 2017. © 2016 Society of Plastics Engineers     

Chain confinement in electrospun nanofibers of PET with carbon nanotubes

Composite nanofibers of poly(ethylene terephthalate), PET, with multiwalled carbon nanotubes (PET/MWCNT) were prepared by the electrospinning method. Confinement, chain conformation, and crystallization of PET electrospun (ES) fibers were analyzed as a function of the weight fraction of MWCNTs. For the first time, we have characterized the rigid amorphous fraction (RAF) in polymer electrospun fibers, with and without MWCNTs. The addition of MWCNTs causes polymer chains in the ES fibers to become more extended, impeding cold crystallization of the fibers, resulting in more confinement of PET chains and an increase in the RAF. The fraction of rigid amorphous chains greatly increased with a small amount of MWCNT loading: with addition of 2% MWCNTs, RAF increased to 0.64, compared to 0.23 in homopolymer PET ES fibers. Spatial constraints also inhibit the folding of polymer chains, resulting in a decrease in crystallinity of PET. For fully amorphous PET/MWCNT composites, MWCNTs do not affect the chain conformation of PET in the ES fibers. For cold crystallized PET/MWCNT composite nanofibers, more trans conformers were formed with the addition of MWCNTs. The increase of RAF (chain confinement) is associated with an increase of the concentration of the trans conformers in the amorphous region as the MWCNT concentration increases in the semicrystalline nanofibers.     

Oxidative solution polymerization of aniline hydrochloride onto electrospun nanofibers mats of polylactic acid: Preparation method and characterization

In this work, we present the preparation of polylactic acid (PLLA)/polyaniline (PANI) conductive composite nanofibers mats. They are prepared by bulk oxidative solution polymerization of PANI onto electrospun non‐woven fibers mats of PLLA. The PANI ratio in the composite is about 70%w/w. Scanning electron microscopy (SEM) shows that PLLA nanofibers are randomly oriented, beads free with diameters of 186 ± 85 nm, The PLLA/PANI composite nanofibers diameter values are 518 ± 128 nm with a good adherence between PANI and PLLA nanofibers. DSC and XRD measurements reveal an amorphous structure of the electrospun PLLA fibers due to the rapid evaporization of the solvent. FTIR and UV–vis spectra reflect good mutual interactions between PANI and PLLA chains. The DC‐conductivities ( ) far better than other published ones for similar composites prepared by bulk oxidative solution polymerization of PANI onto other electrospun nanofiber mats or with electrospun nanofibers from a solution mixture of PLLA and PANI. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41618.     

A new approach for conductive network formation in electrospun poly(vinylidene fluoride) nanofibers

Conductive nanofibers of poly(vinylidene fluoride) (PVDF) filled with polyaniline (PANi)‐coated multi‐wall carbon nanotubes (MWCNTs) were fabricated using the electrospinning technique. PANi is an intrinsically conductive polymer. The addition of PANi‐coated MWCNTs to PVDF created short conductive strands on the surface of the nanofibers, facilitating the formation of a conductive network in the transverse direction of the nanofibers. Piezoelectricity along with electric conductivity makes these PVDF nanofibers promising for applications such as sensors and actuators. Electrospun PVDF nanofiber mats had higher piezoelectricity than melt‐processed samples produced using traditional polymer processing techniques, such as compression molding. Spectroscopic imaging techniques were employed to study the effects of the filler and processing conditions on the nanofiber structure. X‐ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry results indicated a large increase in the β‐phase crystals of the PVDF nanofibers. This higher content of β‐phase crystals enhanced the piezoelectricity of the nanofibers. © 2015 Society of Chemical Industry     

Influence of silanized low‐dimensional carbon nanofillers on mechanical,thermomechanical, and crystallization behaviors of poly(L‐lactic acid) composites—A comparative study

Composites were investigated regarding the comparison of multi‐walled carbon nanotubes (MWCNTs) with exfoliated graphene(EG) in poly(L‐lactic acid) (PLLA) and the effect of silane‐treated carbon nanofillers on properties of PLLA composites. Solution blending method was used to prepare PLLA composites at a filler content of 0.5 wt %. Fourier transform infrared spectroscopy and X‐ray photoelectron spectra results indicated the attachment of silane molecules on the surface of these nanofillers. It was found that the addition of these nanofillers greatly enhanced the mechanical, thermomechanical, and crystallization behaviors of PLLA due to the heterogeneous nucleation effect. Moreover, the silane‐treated fillers further enhanced the breaking elongation moderately (although the materials are still brittle), modulus and thermal property of the nanocomposites, without sacrificing the tensile strength, compared with the pristine nanocomposites. On the other hand, composites reinforced with MWCNTs and EG perform almost the same mechanical property. And EG outperformed MWCNTs in thermomechanical properties of composites when being used as the reinforcement of PLLA. Conversely, composites reinforced with MWCNTs showed better crystallization properties than those reinforced with EG. Interestingly, no significant changes were observed for the crystallization properties of PLLA composites when MWCNTs and EG had been treated by silane coupling agent. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1194‐1202, 2013     

Effects of carbon nanofibers on the crystallization kinetics of polyethylene oxide

Differential scanning calorimetry (DSC) was used to investigate the crystallization behavior of polyethylene oxide (PEO) and carbon nanofiber (CNF) filled PEO systems under non-isothermal experimental conditions. The dispersion and distribution of CNF of the composites were studied using scanning electron microscopy. Studies showed the uniform segregation of CNFs in PEO. Different crystallization kinetic models were used to study the dependence of crystal nucleation on the filler content. Modified Avrami analysis showed that PEO undergoes change of crystallization from 3-D to 1-D crystal while going from primary to secondary crystallization. The crystallization kinetic of PEO reversed at CNF loading higher than 1 wt% of PEO. Based on modified Avrami and the combined approach of Avrami and Ozawa, it is concluded that the CNF retards the crystallization of PEO at all CNF loading under study.     

基于不同载药方式的同轴电纺纤维膜的制备与性能

通过同轴静电纺丝法制备了玉米醇溶蛋白(Zein)-聚乳酸(PLLA)载地塞米松(DEX)的纳米纤维膜,应用透射电子显微镜、扫描电子显微镜、差示扫描量热仪等分析观察纤维的微观结构并研究其性能。结果表明:Zein/PLLA-DEX纳米纤维膜的力学性能比Zein-DEX/PLLA纤维膜的好,其熔融温度受加入的DEX的质量分数影响较大;而Zein-DEX/PLLA纳米纤维膜的结晶温度受加入的DEX的质量分数影响大,并且随着DEX加入量的增大,结晶度降低,断裂强度也随之下降。     

Preparation and characterization of multi‐walled carbon nanotube/poly(ethylene terephthalate) nanoweb

Multi‐walled carbon nanotube (MWCNT)/Poly(ethylene terephthalate) (PET) nanowebs were obtained by electrospinning. For uniform dispersion of MWCNTs in PET solution, MWCNTs were functionalized by acid treatment. Introduction of carboxyl groups onto the surface of MWCNTs was examined by Fourier transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD) analysis. MWCNTs were added into 22 wt % PET solution in the ratio of 1, 2, 3 wt % to PET. The morphology of MWCNT/PET nanoweb was observed using field emission‐scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM). The nanofiber diameter decreased with increasing MWCNT concentration. The distribution of the nanofiber diameters showed a bi‐modal shape when MWCNTs were added. Thermal and tensile properties of electrospun MWCNT/PET nanowebs were examined using a differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA) and etc. Tensile strength, tensile modulus, thermal stability, and the degree of crystallinity increased with increasing MWCNT concentration. In contrast, elongation at break and cold crystallization temperature showed a contrary tendency. Electric conductivities of the MWCNT/PET nanowebs were in the electrostatic dissipation range. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of graphene oxide/poly(vinyl alcohol) composite nanofibers via electrospinning

Graphene oxide (GO) was well dispersed in poly(vinyl alcohol) (PVA) diluted aqueous solution, and then the mixture was electrospun into GO/PVA composite nanofibers. Electron microscopy and Raman spectroscopy on the as‐prepared and calcined samples confirm the uniform distribution of GO sheets in the nanofibers. The thermal and mechanical properties of the nanofibers vary considerably with different GO filler contents. The decomposition temperatures of the GO/PVA composite nanofiber dropped by 38–50°C compared with pure PVA. A very small loading of 0.02 wt % GO increases the tensile strength of the nanofibers by 42 times. A porous 3D structure was realized by postcalcining nanofibers in H₂. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fabrication of Core/Shell Nanofibers with Desirable Mechanical and Antibacterial Properties by Pickering Emulsion Electrospinning

To endow nanofibers with the desirable antibacterial and mechanical properties, a facile strategy using Pickering emulsion (PE) electrospinning is proposed to prepare functional nanofibers with core/shell structure for the first time. The water‐in‐oil (W/O) Pickering emulsion stabilized by oleic acid (OA)‐coated magnetite iron oxide nanoparticles (OA‐MIONs) is comprised of aqueous vancomycin hydrochloride (Van) solution and poly(lactic acid) (PLA) solution. The core/shell structure of the electrospun Van/OA‐MIONs‐PLA nanofibers is confirmed by scanning electron microscopy and transmission electron microscopy observation. Sustained release of Van from the PE electrospun nanofiber membrane is achieved within the time of 600 h. Compared with the neat PLA electrospun nanofiber membrane, 57% increase of tensile strength and 36% elevation of elongation at break are achieved on PE electrospun nanofiber membrane. In addition, the PE electrospun nanofiber membrane demonstrates excellent antibacterial property stemming from the combinational antibacterial activities of OA‐MIONs and Van. The Van‐loaded PE electrospinning nanofibers with sustained antibacterial performance possess potential applications in tissue engineering and drug delivery.

     

The influence of electrospinning parameters on the structural morphology and diameter of electrospun nanofibers

Electrospinning is a simple method of producing nanofibers by introducing electric field into the polymer solutions. We report an experimental investigation on the influence of processing parameters and solution properties on the structural morphology and average fiber diameter of electrospun poly ethylene oxide (PEO) polymer solution. Experimental trials have been conducted to investigate the effect of solution parameters, such as concentration, molecular weight, addition of polyelectrolyte in PEO solution, solvent effect, as well as governing parameter, such as applied voltage. The concentration of the aqueous PEO solution has shown noteworthy influence on the fiber diameter and structural morphology of electrospun nanofibers. At lower concentrations of PEO polymer solution, the fibers showed irregular morphology with large variations in fiber diameter, whereas at higher concentrations, the nanofibers with regular morphology and on average uniform fiber diameter were obtained. We find that the addition of polyelectrolytes, such as sodium salt of Poly acrylic acid (PAA) and Poly allylamine hydrochloride (PAH), increases the conductivity of PEO solutions and thereby decreases the bead formation in electrospun nanofibers. The increase in applied voltage has been found to affect the structural morphology of nanofiber while the addition of ethanol in PEO solution diminishes the bead defects. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of MIL‐53 (Al) MOF particles on the chain mobility and crystallization of poly(L‐lactic acid)

Polymer‐filler interactions significantly influence morphology, functionality, and various desirable properties of mixed matrix membranes (MMMs). In this study, chain mobility and crystallization of poly(l ‐lactic acid) (PLLA) MMM films prepared by solvent casting PLLA with 1, 5, 10, and 20% wt/wt of MIL‐53(Al) metal organic framework (MOF) were evaluated. The fabricated MMMs were characterized using differential scanning calorimetry, Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Differential scanning calorimetry studies indicated that the addition of MOF particles in the PLLA matrix reduces the polymeric chain mobility, which affects the crystallization process. The percent crystallinity of neat PLLA was found to decrease from 4% in neat PLLA to completely amorphous structures in PLLA‐10% and PLLA‐20% MMMs, as observed in the second heating cycle. Fourier transform infrared spectroscopy data supports these observations. Thermogravimetric analysis results showed that PLLA‐MOF films are thermally less stable than neat PLLA suggesting that MOF particles act as a depolymerization catalyst for PLLA. Partial agglomeration of MOF particles was observed in the samples using scanning electron microscopy studies. This study indicates strong PLLA‐MIL‐53(Al) MOF interactions. In addition, this study also provides insight into the effect of MOF particles on the segmental mobility and morphology of PLLA‐MIL‐53 (Al) composite films. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45690.     

Transformation of complex internal structures of poly(ethylene oxide)/chitosan oligosaccharide electrospun nanofibers

Electrospun nanofibers with a core–shell structure or an internal microphase‐separated structure were obtained from a homogeneous solution using a conventional single‐nozzle electrospinning setup. Because of the poor miscibility of poly(ethylene oxide) (PEO) and chitosan oligosaccharide (CS), the two polymers will separate into a core–shell structure (PEO as core, CS as shell) or an internal microphase‐separated structure (PEO as discrete phase, CS as continuous phase) depending on the fraction of each component in the solution. Moreover, the core–shell structure transforms to the internal microphase‐separated structure with a continuous decrease of the PEO fraction. The reason for the transition of these internal structures can be attributed to the different phase separation mechanisms. For the core–shell structure, phase separation proceeds in a mechanism of nucleation and growth; however, the internal microphase‐separated structure results from spinodal decomposition. Therefore, wide‐angle X‐ray diffraction and differential scanning calorimetry were employed to investigate PEO crystallization. Since both PEO and CS are biocompatible polymers, together with being able to control the fiber internal structure (core–shell or microphase separation), these electrospun nanofibers will have a great future in the biomedical field. Copyright © 2011 Society of Chemical Industry     

Electrospinning and crosslinking of zein nanofiber mats

Electrospinning processing can be applied to fabricate fibrous polymer mats composed of fibers whose diameters range from several microns down to 100 nm or less. In this article, we describe how electrospinning was used to produce zein nanofiber mats and combined with crosslinking to improve the mechanical properties of the as‐spun mats. Aqueous ethanol solutions of zein were electrospun, and nanoparticles, nanofiber mats, or ribbonlike nanofiber mats were obtained. The effects of the electrospinning solvent and zein concentration on the morphology of the as‐spun nanofiber mats were investigated by scanning electron microscopy. The results showed that the morphologies of the electrospun products exhibited a zein‐dependent concentration. Optimizing conditions for zein produced nanofibers with a diameter of about 500 nm with fewer beads or ribbonlike nanofibers with a diameter of approximately 1–6 μm. Zein nanofiber mats were crosslinked by hexamethylene diisocyanate (HDI). The tensile strength of the crosslinked electrospun zein nanofiber mats was increased significantly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:380–385, 2007