Effect of solvent and blended polymer on electrical conductivity of PEDOT:PSS/polymer blended nanofibers

Poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS) and polyethylene oxide (PEO) (or polyvinyl alcohol (PVA)) blended electrospun nanofibers were prepared in the presence of dimethyl sulfoxide (DMSO) and ethylene glycol (EG). The effects of added solvents (DMSO and EG) and blended polymers (PEO and PVA) on electrical conductivity and current-voltage (I-V) response were investigated. Electrical conductivity was dependent on both the additional solvent and blended polymers. PEDOT:PSS/PEO blended nanofibers showed a much higher electrical conductivity than PEDOT:PSS/PVA. EG blended PEDOT:PSS/PEO blended nanofibers showed much higher electrical conductivity than DMSO. The PEDOT:PSS/PEO/EG blended nanofibers web showed the highest value in I-V response.     

Properties and performance of polypyrrole (PPy)-coated silk fibers

Different silk substrates in form of spun silk tops, nonwoven web, yarn, and fabric were coated with electrically conducting doped polypyrrole (PPy) by in situ oxidative polymerization from an aqueous solution of pyrrole (Py) at room temperature using FeCl₃ as catalyst. PPy-coated silk materials were characterized by optical (OM) and scanning electron (SEM) microscopy, FT-IR spectroscopy, and thermal analysis (DSC, TG). OM and SEM showed that PPy completely coated the surface of individual silk fibers and that the polymerization process occurred only at the fiber surface and not in the bulk. Dendrite-like aggregates of PPy adhered to the fiber surface, with the exception of the sample first polymerized in the form of tops and then spun into yarn using conventional industrial machines. FT-IR (ATR mode) showed a mixed spectral pattern with bands typical of silk and PPy overlapping over the entire wavenumbers range. DSC and TG showed that PPy-coated silk fibers attained a significantly higher thermal stability owing to the protective effect of the PPy layer against thermal degradation. The mechanical properties of silk fibers remained unchanged upon polymerization of Py. The different PPy-coated silk materials displayed excellent electrical properties. After exposition to atmospheric oxygen for two years a residual conductivity of 10–20 % was recorded. The conductivity decreased sharply under the conditions of domestic washing with water, while it remained essentially unchanged upon dry cleaning. Abrasion tests caused a limited increase of resistance. PPy-coated silk tops were successfully spun into yarn either pure or in blend with untreated silk fibers. The resulting yarns maintained good electrical properties.     

Flexible VOC sensors using conductive polymers and porous membranes for application to textiles

In order to fabricate textile-based flexible VOC sensors, two conductive polymers such as polyaniline and poly(3,4-ethylenedioxythiophene)-poly(styrene-sulfonate) (PEDOT:PSS) were used as VOC-sensing materials, and various porous organic membranes were used as base substrates on which the conductive polymers were coated. Electrical resistance change of conductive polymers by adsorption of VOCs was measured. Polyaniline showed better sensitivity than PEDOT:PSS. Porous high density polyethylene membrane exhibited the most stable signal reproducibility and dimensional stability of membrane itself. Even after covering with additional high density polyethylene membrane to protect conductive polyaniline inside, the stable signals were still obtained during repeated measurement.     

Pervaporation separation of dimethyl carbonate/methanol binary mixtures with poly(vinyl alcohol)-perfluorslulfonic acid/poly(acrylonitrile) hollow fiber composite membranes

Using poly(vinyl alcohol) (PVA) and perfluorslulfonic acid (PFSA) as coating materials, poly(acrylonitrile) (PAN) hollow fiber ultrafiltration membrane as substrate, PVA-PFSA/PAN composite membranes were fabricated by dip-coating method. The fabricated composite membranes were used to the separation of dimethyl carbonate (DMC)/methanol (MeOH) binary mixtures by pervaporation process. SEM images verify that the coated layer is well combined with substrate and the thickness nearly linearly increases with the coating solution concentration. The separation factor increases but at cost of the decline of permeation flux when the concentration of the coating solution or its PVA mass fraction increase. The permeation flux increases and separation factor slightly increases with the feed temperature increasing at 30–60 °C. The increase of feed MeOH concentration leads to an improvement of permeation flux and a decline of separation factor.     

The effects of electrical discharge on the mechanical properties of <Emphasis Type="Italic">Bombyx mori</Emphasis> silk fibroin

Bombyx Mori is a representative of natural fibers which is known for its mechanical stability. In this study, electrical discharge of the fibers exposed to different voltages for certain periods was examined and mechanical lifetime was measured and also the structure parameters U _o and γ were calculated. We observed that crosslinks might be formed at the silk fibers exposed to high voltages and as a result, fibers become more resistant to mechanical effects.     

Development of energy generating photovoltaic textile structures for smart applications

The aim of this study is to develop a method with lower application temperature and a device structure to obtain reproducible photovoltaic textiles. Two different kinds of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) solutions over a silver (Ag) layer was used as anode, a blend of poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as light absorbing layer and a thin aluminum (Al)/Ag layer as semi-transparent cathode. These devices capable of generating electricity from sunlight were fabricated on polypropylene tapes that could be woven into a textile fabric. The short-circuit current density and power conversion efficiency of photovoltaic tapes were increased by using an Ag layer beneath the PEDOT:PSS electrode. The photovoltaic textile structure exhibited remarkable power conversion efficiency (0.29 %) by transmitting the light through the upper electrode. This approach may be used in industrial applications to develop photovoltaic textile materials.     

Silk grafting with chitosan and crosslinking agents

Chitosan grafting onto silk was tested with three crosslinking agents: trifunctional epoxy resin Araldite DY-T, PEG400 dimethacrylate, and glutaraldehyde in acetic as well as in tartaric acid solutions. Operating conditions were studied to obtain a significant silk weighting with satisfactory graft yields. With the epoxy crosslinker the weight gain was in the range from 1.8 to 8.8 % with graft yield from 8 to 23 %. In the case of PEG400DMA weight gain was 8–12 % with 22–24 % graft yield. With glutaraldehyde in tartaric acid solution a maximum weight gain of 8.4 % with 27.6 % graft yield was obtained. Results of determination of primary amino groups on the grafted silk showed that with epoxy and glutaraldehyde, unlike PEG400DMA, the amino groups of chitosan were only partially involved in crosslinking. Results of DSC analyses suggested that the modification of fibroin structure in chitosan-grafted silk was stronger with glutaraldehyde than with epoxy or dimethacrylate. FTIR-ATR spectra of grafted fibers were found very similar to that of control silk with an additional weak peak ascribable to chitosan in 1180–1080 cm⁻¹ range. Surface investigation through AFM showed clear morphology differences between chitosan-grafted silk with epoxy or dimethacrylate and that crosslinked with glutaraldehyde; the latter appears uneven and scale-like, the others slightly rougher than the original silk.     

Effects of Chemical Functionalization of MWCNTs on the Structural and Physical Properties of Elastomeric Copolyetherester-based Composite Fibers

Elastomeric copolyetherester (CPEE)-based composite fibers incorporating various neat and functionalized multiwalled carbon nanotubes (MWCNTs) were prepared through a conventional wet-spinning and coagulation process. The influence of functionalized MWCNTs on the morphological features, and the thermal, mechanical properties and electrical conductivity of CPEE/MWCNT (80/20, w/w) composite fibers were investigated. FE-SEM images show that a composite fiber containing poly(ethylene glycol)-functionalized MWCNTs (MWCNT-PEG) has a relatively smooth surface owing to the good dispersion of MWCNT-PEGs within the fiber, whereas composite fibers including pristine MWCNTs (p-MWCNT), acid-functionalized MWCNTs (a-MWCNT), and ethylene glycol-modified MWCNTs (MWCNT-EG) have quite a rough surface morphology owing to the presence of MWCNT aggregates. As a result, the CPEE/MWCNT-PEG composite fiber exhibits noticeably increased thermal and tensile mechanical properties as well as a faster crystallization behavior, which stems from an enhanced interfacial interaction between the CPEE matrix and MWCNT-PEGs.     

Surface characterization of aromatic thermotropic liquid crystalline fiber deposited by nanostructured silver

Nanostructured silver thin films were sputtered onto the aromatic thermotropic liquid crystalline fibers of Vectran by magnetron sputtering technology. Plasma treatment was used as pre-treatment in order to improve the deposition of the coating layer. Surface morphology of the coated fibers was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). A full energy dispersive X-ray analysis (EDX) was used to detect the elemental composition of the material. Its conductivity and mechanical properties were measured and analyzed as well. The study revealed that a very thin conductive silver deposition exhibited high electrical conductivity as well as less influence on the mechanical properties of the pre-treated Vectran fiber. The plasma treatment could improved the deposition of the coating layer, but the surface roughness caused by plasma treatment also affected the surface conductivity. It was found that the surface resistivity could reach very low value of 1.66×10⁻³ Ω·cm after sputtering deposition for 30 min.     

Effect of changing coating process parameters in the preparation of antimicrobial-coated silk sutures: An in vitro study

Braided silk sutures were coated using a combination of poly(ε-caprolactone) (PCL) and sulfamethoxazole trimethroprim (SMZ) to investigate their antimicrobial performance. SMZ (2500 μg/ml) was combined with different PCL concentrations, i.e., 2.5 %, 5 %, 7.5 %, and 10 % (w/v). Antimicrobial test results showed that SMZ and PCL-treated silk sutures exhibited increasing antimicrobial efficacy against Gram-negative (Escherichia coli) and -positive bacteria (Staphylococcus aureus) with increasing PCL concentrations. The tensile and knot strength of sutures coated with 10 % PCL were significantly higher than those of sutures coated with 7.5 %, 5 %, and 2.5 % PCL. Treatment with PCL exhibited a positive effect on drug release from the sutures. Significant traits of antibacterial activity were observed up to 4 days after instalment of 10 % PCL-coated silk sutures. Under a scanning electron microscope, untreated silk sutures showed a surface heavily coated with bacteria, whereas treated sutures showed a smooth surface without bacteria. The results of this study indicate that SMZ combined with high concentrations of PCL may afford a suitable antibacterial coating agent for braided silk sutures.     

Preparation of poly(acrylonitrile)-grafted silk fibers with antibacterial properties

This study is focused on investigating the feasibility of using silver(I) ions loaded poly(acrylonitrile)-grafted silk fibers as antibacterial dressing material. The optimum grafting conditions for ceric ammonium nitrate induced graft-copolymerization of acrylonitrile onto silk fibers were found to include initiator concentration of 35 mM, catalyst HNO₃ concentration of 0.40 M and initiation time of 10 min. The poly(acrylonitrile)-grafted silk fibers were loaded with silver(I) ions by equilibration method. The resulting fibers were investigated for their biocidal action against E. coli, by using zone inhibition and colonies counting method.     

An effective and simple process for obtaining high strength silkworm (Bombyx mori) silk fiber

This article describes a new process for strengthening natural silk fibers. This process is simple yet effective for mass production of high strength silk fibers, enabled by drawing at a lower temperature and immediately heat setting at a higher temperature. The processing conditions were investigated and optimized to improve the strength. Silk fibers drawn to the maximum ratio at room temperature and then heat set at 200 °C show best tensile properties. Some salient features of the resulting fibers are tensile strength at break reaching 533±10.2 MPa and Young’s modulus attaining 12.9±0.57 GPa. These values are significantly higher than those of natural silk fibers (tensile strength increased by 44 % and Young’s modulus by 135 %). Wide-angle X-ray diffraction and FTIR confirm the transformation of silk I to silk II crystalline structure for the fiber obtained from this process. DSC and TGA data also provide support for the structural change of the silk fiber.     

Surface modifications of natural Kanchipuram silk (pattu) fibers using glow discharge air Plasma

Experimental investigations have been carried out to modify the surface properties of natural Kanchipuram silk (pattu) fibers using a low temperature DC glow discharge air Plasma. Silk is an externally spun fibrous protein secretion formed into fibers. Plasma treatment is an eco-friendly, dry, and clean process over wet chemical method and does not suffer from any environmental and health concerns. Experiments have been performed considering three parameters such as discharge current, treatment time, and working pressure. The structural, thermal, morphological, optical, and mechanical studies of raw and plasma treated silk fibers have been obtained out using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) spectroscopy, X-ray diffraction (XRD), thermo gravimetric analyzer (TGA), scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS), diffuse absorbance spectroscopy, and tensile test. A comparative study has been done for the untreated and different treated fibers. Various characterization analyses reveal that surface roughness of the plasma treated silk fiber is increased and also crystallite size of treated samples is enhanced, plasma treated silk fibers maintain the whiteness effect and it is observed that UV transmittance region (A & B) is more for the treated fiber which signifies enhanced UV protection.     

Effect of Ni-coated short carbon fibers on the mechanical and electrical properties of epoxy composites

Ni-coated short carbon fibers (Ni-SCFs) were prepared using an electrodeposition method. Short carbon fiber (SCF) reinforced epoxy composites were prepared by changing the fiber content (0.1–0.7 wt%). To investigate the effect of Ni-coated short carbon fibers on the mechanical and electrical properties of the composites, we prepared two kinds of reinforcements: the short carbon fibers treated by 400 °C (400 °C treated SCFs) and Ni-SCFs. Fracture characteristics of the composites revealed the Ni coatings and the epoxy matrix had a better interface, so that the results of tensile and bending strength were better in epoxy/Ni-SCFs composites than those in epoxy/400 °C treated SCFs composites. The 400 °C treated SCFs decreased the electrical resistivity of the epoxy composites, compared to the pure epoxy. However the epoxy/Ni-SCFs composites had lower electrical resistivity than epoxy/400 °C treated SCFs with the same fiber content.     

Effect of pineapple protease on the characteristics of protein fibers

A pineapple protease, bromelain, was used to improve the dyeing properties of protein fibers such as wool and silk. The optimal condition for the activity of the pineapple protease was about 60 °C at pH 7. The wool and silk were treated with the protease extracted from a pineapple and the K/S values of the dyed wool and silk were measured using a spectrophotometer in order to compare the dye uptake. The protease treatment enhanced the dyeing properties of protein fibers without severe changes in mechanical properties. The surface appearances of protease-treated fibers were observed by microscopy.     

Effect of glycerol cross-linking and PDI on the shape memory effect and mechanical properties of polyurethane

A series of shape memory polyurethane (PU) copolymers synthesized from 1,4-phenyldiisocyanate (PDI), poly(tetramethyleneglycol) (PTMG), 1,4-butanediol (BD) as a chain extender, and glycerol as a cross-linking agent were tested for the mechanical properties and the shape memory effect at the temperature 20 °C above melting temperature (T _m), and were compared with other PUs synthesized from 4,4′-methylene-bis-phenyldiisocyanate (MDI), PTMG, and BD. Mechanical properties and shape memory effect were improved substantially by adopting both PDI and glycerol. Interestingly, enthalpy of melting and T _m were not affected by the glycerol content. Vibration and shock absorption ability was investigated by measuring both loss tan δ and storage modulus with dynamic mechanical analyzer (DMA).     

Fabrication of Biocompatible PLGA/PCL/PANI Nanofibrous Scaffolds with Electrical Excitability

Application of electrospun nanofibrous scaffolds has received immense attention in tissue engineering. Fabrication of scaffolds with appropriate electrical properties plays a key role in neural tissue engineering. Since fibers orientation in the scaffolds affects the growth and proliferation of the cells, this study aimed to prepare aligned electrospun conductive nanofibers by mixing 1 %, 10 % and 18 % (w/v) doped polyaniline (PANI) with polycaprolactone (PCL)/poly lactic-coglycolic acid (PLGA) (25/75) solution through the electrospinning process. The fibers diameter, hydrophilicity and conductivity were measured. In addition, the shape and proliferation of the nerve cells seeded on fibers were evaluated by MTT cytotoxicity assay and scanning electron microscopy. The results revealed that the conductive nanofibrous scaffolds were appropriate substrates for the attachment and proliferation of nerve cells. The electrical stimulation enhanced neurite outgrowth compared to those PLGA/PCL/PANI scaffolds that were not subjected to electrical stimulation. As polyaniline ratio increases, electric stimulation through nanofibrous PLGA/PCL/PANI scaffolds results in cell proliferation enhancement. However, a raise more than 10 % in polyaniline will result in cell toxicity. It was concluded that conductive scaffolds with appropriate ratio of PANI along with electrical stimulation have potential applications in treatment of spinal cord injuries.     

An adsorption study of alum-morin dyeing onto silk yarn

Silk yarn was dyed with morin (2′,3,4′,5,7-pentahydroxyflavone) by using alum as mordant. In order to optimize the process, three methods of dyeing involving: pre-mordanting, simultaneous mordanting, and post-mordanting were assessed and compared with a mordant-free process. The adsorption of alum-morin dye onto silk fibers indicated that the adsorption capacities were significantly affected by pH, the initial dye concentration, and temperature. The initial dye adsorption rates of alum-morin dye on silk before equilibrium was reached increased with higher dyeing temperatures. The pseudo second-order kinetic model was indicated for alum-morin dyeing (simultaneous mordanting) of silk at pH 4.0 with an activation energy (E _a ) of 45.26 kJ/mol. The value of the enthalpy of activation (ΔH ^#) for alum-morin dyeing on silk at pH 4.0 was −31.29 kJ/mol. Also, the free energy (ΔG ^o) and entropy changes (ΔS ^o) for alum-morin dyeing on silk were −17.73 kJ/mol and −45.7 J/molK, respectively, consistent with a spontaneous and exothermic adsorption process.     

Thermomechanical and Shape Memory Performances of Thermo-sensitive Polyurethane Fibers

This study is the first step to investigate usability of shape memory polyurethane (SMPU) fibers for smart garment applications. SMPU fibers were spun by wet spinning process and chemical/mechanical characterization was carried out. SMPU solutions were prepared with two different concentrations (20 % and 25 %) and three different coagulation bath concentrations (0 %, 1 % and 3 %) were used for determining optimum spinning parameters. For investigating influences of spinning process on crystal structure, mechanical, thermal and shape memory performances of fibers, X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM) and mechanical tests were conducted. DSC and DMA analysis results show that shape memory polyurethane fibers have a glass transition temperature about 35-40 oC which is suitable for body temperature. Moreover, SMPU fibers showed good tensile performance with an average tenacity of 1.38 cN/dtex and elongation at break of 350 %. Thermo mechanical test results showed that, all shape memory fibers have good shape memory effect with recovery and fixity ratios up to 91 % and 71 % respectively.     

One-step continuous coating of silver nanoparticles on well aligned fibers of PAI/PTACM

Highly aligned ultrafine fibers of Poly (amide-co-imide) PAI (torlon)/Poly (trimellitic anhydride chloride-co-4, 4′-methylene dianiline) (PTACM) blends have been prepared by using mechano-electrospinning. Employing a mixed solvent system of DMSO and THF alongwith water coagulation bath as a medium, continuous fibers with improved mechanical properties have been obtained. The continuity of the fibers is strongly dependent on the solvent mixing ratio of DMSO and THF (6:4). Continuous fibers with the most uniform diameter are obtained when a 30 % of PAI and PTACM (1:1) resins by weight is used in the blending solution. The aligned fibers are further coated with silver nanoparticles using a one-step process by passing the electrospunned fibers through PEG solution and a silver precursor solution followed by reduction in a continuous process. The advantage of our method lies in a uniform silver coating on a single fiber that can be coated continuously on a larger length scale (～Km). The mechanical properties of these fibers are dramatically improved after their alignment. Better electrical conductivity is obtained for these fibers after they are coated with silver nanoparticles. The highly aligned silver decorated fibers utilizes a novel electroless continuous process using Polyethylene glycol (PEG), which shows good binding properties and can be used for various bio and electronic applications.