Application of electrostatic force microscopy on characterizing an electret fiber: Effect of tip to specimen distance on phase shift

The application of Electrostatic Force Microscopy (EFM) on characterizing a corona charged polypropylene fiber by phase measurements was studied. Electrostatic force gradient images were obtained from the phase shifts with varied EFM tip bias voltages at a constant tip-to-sample distance, and with varied tip-to-sample distances at a constant tip bias voltage. Mathematical expressions were introduced to interpret the phase measurements in terms of the tip bias voltage and the tip-to-specimen distance. The phase measurements from EFM appeared feasible to provide the qualitative information of electrical properties of charged polymeric materials. The fit of mathematical expressions to the experimental measurements was discussed with regards to the effect of tip geometry on the interaction between the tip and the specimen.     

Large scaled fabrication of microfibers by air-suction assisted needleless melt electrospinning

A cone-shape spinneret with air-suction assisted was used for the production of ultrafine fibers by melt electrospinning. The influence of the applied voltages on the number of jets and the effects of the different types of air flow (air blowing and air suction) on the fiber bundle were studied. It was demonstrated that the breadth of the diameter distribution of the fibers decreases markedly and the production rate was also improved when air suction and higher applied voltages were applied. Therefore this new melt electrostatic spinning equipment can meet the need of some special applications and industrial mass production of nanofibers.     

Liquid sorption behavior of superabsorbent fiber based nonwoven media

Nonwovens are widely used as liquid absorbent media. Currently, superabsorbent fibers are used in nonwovens for making them less bulky yet very effective in absorbing liquids. In this work, a series of nonwovens were prepared by random mixing and layer-wise combining of superabsorbent fibers with fibers of different cross-sectional geometries. These nonwovens were studied for their liquid absorption behavior by using gravimetric testing absorption system. It was observed that in case of random mixing, the increase in weight fraction of superabsorbent fibers led to a tremendous increase in liquid sorption capacity and liquid sorption rate. When mixed randomly with superabsorbent fibers, the finer fibers exhibited better sorption characteristics than the coarser fibers, but the non-circular fibers displayed poorer sorption characteristics than the circular ones. In case of layer-wise combining, better sorption characteristics were obtained when the liquid was first challenged by the polypropylene fiber side as compared to that by superabsorbent fiber side. The superabsorbent fibers and the circular polypropylene fibers, when combined layer-wise, resulted in higher sorption capacity but lower sorption rate than those when mixed randomly.     

Study of charge decay in corona-charged fibrous electrets

In this work, a series of fibrous electrets was prepared by applying electrostatic charge onto a polypropylene nonwoven fabric using corona charging process. The charging process parameters were systematically varied and their effects on charge decay were examined. A double exponential function composed of two exponentials of very different characteristics explained the charge decay characteristics very well. It was hypothesized that two charges of different nature were present in corona-charged fibrous electrets. One of the charges could be ascribed to deposition of ions onto the electret surface and the other charge could be attributed to internal polarization caused by ionic displacement. The overall charge decay could be then explained by the quick decay of the surface charge in addition to the slow decay of the bulk charge. The slow-decay component was found to contribute more to the overall charge decay with respect to a change in applied voltage. With a decrease in applied voltage, the contribution of the slow-decay component was increased. The rate of quick-decay component as well as the rate of slow-decay component was found to increase with the increase in applied voltage. With respect to a change in charging time, the quick-decay and slow-decay components were found to contribute almost equally to the overall charge. This was also true with respect to a change in distance between electrodes, except at a very high distance. With an increase in charging time, the rate of quick-decay component as well as the rate of slow-decay component started decreasing till the minimum values were obtained and increased thereafter. A similar observation was made on the role of distance between electrodes in determining the rate of quick-decay as well as the rate of slow-decay components.     

Matrix-fibril morphology development of polypropylene/poly(butylenes terephthalate) blend fibers at different zones of melt spinning process and its relation to mechanical properties

Different shapes of dispersed phase such as sphere, laminar and fibrillar can form in the matrix phase of polymer blends. Production of blend fibers in melt spinning process can result more effective in fibrillar phase morphology formation than in other processes. In this research, the matrix-fibril morphology development during the melt spinning of polypropylene/poly(butylenes terephthalate) was studied. The shapes of blend dispersed phase collected from different zones of the melt spinning line were evaluated by scanning electron micrographs (SEM) and rheological mechanical spectra (RMS). The results showed that fibrillar shape could not be created in the PP/PBT blend fiber samples exited from the spinneret orifice (gravity spun fibers) at low contents (5 percent) of the PBT dispersed phase. However, a complete fibrillar structure was formed in all the as-spun PP/PBT blend fiber samples (melt drawn). The rheological evaluations confirmed a network structure resulting from fibril formation for the samples with high contents (20–40 %) of the PBT dispersed phase and the formation of spherical shape with low contents (5–10 %) of the PBT dispersed phase in matrix of the blend fibers. It was observed that the flow fields of processing zones and blend ratio, in producing the blend fibers, have intensive effects on morphological variations; besides there was a strong relation between the mechanical and morphological properties.     

The effects of UV irradiation exposure on the structure and properties of polypropylene/ZnO nanocamposite fibers

Unfilled polypropylene and polyropylene/ZnO nanocomposite fibers were produced using a melt spinning apparatus; then the fibers were exposed to UV irradiation. The structure and properties of the fibers were examined using scanning electron microscopy, tensile measurements, wide angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy, birefringence measurements and differential scanning calorimetry (DSC). Following 150 hours of exposure to UV irradiation, some transverse cracks on the surface of unfilled polypropylene fibers were observed. It was observed that both carbonyl and hydroperoxide indexes, which are the criteria for the detection of UV degradation of the fibers, were increased due to the increase in the UV irradiation exposure time and the increase in these indexes was smaller for nanocomposite fibers than those of unfilled Polypropylene fibers. It was also observed that crystallinity, crystallite size and total molecular orientation of UV irradiated nanocomposite fibers were increased in comparison with non-irradiated nanocomposite fibers. It was also found that the extent of increase in molecular orientation of the fibers was higher comparing to that for the nanocomposite fibers due to the UV irradiation exposure for the unfilled polypropylene fibers. Tensile properties of both unfilled and nanocomposite fibers were decreased after UV irradiation; this reduction correlated with the extent of the increase in molecular degradation of the fibers, as determined by measuring carbonyl and hydroperoxide indexes.     

Electrospinning of silk nanofibers. I. An investigation of nanofiber morphology and process optimization using response surface methodology

Ultra fine fibers were electrospun from regenerated silk fibroin/formic acid solution. Effect of some process parameters on the morphology, diameter and variation in fiber diameter of electrospun fibers were experimentally investigated. Scanning electron microscope was used for the measurement of fiber diameter. Fibers with diameter ranging from 80 to 210 nm were collected depending on the solution concentration and the applied voltages. Response surface methodology (RSM) was used to obtain a quantitative relationship between selected electrospinning parameters and the average fiber diameters and its distribution. It was shown that concentration of silk fibroin solution had a significant effect on the fiber diameter and the standard deviation of the fiber diameter. Applied voltage had no significant effect on the fiber diameter and its standard deviation.     

Effect of drying condition on the electrostatic characteristics of the laundry

This paper suggests the optimal conditions to prevent electrostatic charge in the laundry by the evaluation of the electrostatic characteristics during the drying process. Cotton, nylon, and polyester fabrics were used as test specimens, employing the standard washing cycle. The electrostatic characteristics of the laundry were measured after the automatic drying process. This paper investigates the optimal conditions for preventing electrostatic charges in laundry by evaluating the electrostatic characteristics that occur during the drying process. Cotton, nylon, and polyester fabrics were used as the test specimens, employing a standard washing cycle. The electrostatic characteristics of the laundry were measured immediately after the automatic drying process. The results, showed that the moisture content decreased and the electrostatic charge increased with drying time. The specimen fabrics had already dried up before completion of the standard drying cycle. Consequently, the excessive drying generated an electrostatic charge due to removal of the traces of remaining moisture and the resulting excessive friction. For cotton fabrics, the electrostatic charge was under 1000 V even for the maximum drying time due to the intrinsic high moisture regain of cotton. On the other hand, the electrostatic charge produced for nylon fabrics increased rapidly with the drying time, and amounted up to approximately 8000V after 120 minutes. The results also indicated that the electrostatic charge could be decreased by drying fabrics of only one kind. When mixed kinds of fabrics were dried, the electrostatic charge increased remarkably. Therefore, it is suggested that laundry be classified and washed according to the kinds of fiber, and not be dried excessively to reduce electrostatic charge. In addition, the proper use of a softener is effective in reducing the electrostatic charge.     

Modification and properties of polypropylene fibers using aluminosiloxane

Siloxylated polypropylene fibers composed of polypropylene (PP) and aluminosiloxane (AS) were prepared by melt blending followed by spinning. The effects of blend compositions on the thermal behaviors, surface and tensile properties of PP/AS blend fibers were investigated by DSC, WAXD, SEM, static honestometer, etc. The heat of fusion of PP/AS blends decreased with increasing AS contents. In addition, the peak intensity of PP/AS blends in X-ray diffraction patterns decreased with increasing AS contents. It was observed that the silicone molecules exist and well distribute on the surface of siloxylated polypropylene fibers. From the results of the half-life period measurements, the anti-static properties of PP fibers siloxylated with AS was found to be significantly modified.     

Modification of polypropylene fibers by electron beam irradiation. I. Evaluation of dyeing properties using cationic dyes

The dyeing properties of hydrophobic polypropylene fibers using cationic dyes were investigated to improve dyeability by electron beam irradiation and sulfonic acid incorporation. The color strength of polypropylene fibers after irradiation was examined according to the dyeing conditions including the pH of the dyebath, absorbed doses, and the introduction of a functional group to the fiber substrate. The best dyeing result was obtained when polypropylene fibers incorporated by sulfonic acid group after electron beam irradiation were dyed with cationic dyes at alkaline conditions and 30∼75 kGy irradiation ranges.     

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.     

Fabrication of long and discontinuous natural fiber reinforced polypropylene biocomposites and their mechanical properties

Natural fiber reinforced polypropylene (PP) biocomposites were fabricated by blending long-and-discontinuous (LD) natural fibers (NF) with LD PP fibers. Firstly, random fiber mats were prepared by mixing NFs and PP fibers using a carding process. Then, heat and pressure were applied to the mats, such that the PP fibers dispersed in the mats melted and flowed out, resulting in the formation of consolidated sheets upon subsequent cooling. The effect of the fiber volume fraction on the mechanical properties of the bio-composites was scrutinized by carrying out tensile and flexural tests and observing the interface between the fiber and matrix. It was observed that the natural LD fiber content needs to be maintained at less than the nominal fiber fraction of 40 % by weight for the composites fabricated using the current method, which is quite low compared to that of continuous or short fiber reinforced composites. The limited fiber fraction can be explained by the void content in the biocomposites, which may be caused by the non-uniform packing or the deficiency of the matrix PP fibers.     

Spray deposition in “tendone” vineyards when using a pneumatic electrostatic sprayer

The objective of this study was to evaluate the effect of electrostatic charge on foliar spray deposition in an Apulian “tendone” vineyard using an innovative pneumatic electrostatic sprayer. The sprayer was fitted with nozzles that linked the pneumatic atomization of the liquid, obtained using compressed air, to the electrostatic induction charge, thereby producing a stream of charged fine droplets. Furthermore, the sprayer was designed for low volume treatments, and the experimentation was carried out during a phenological stage with high leaf density to evaluate the performance of the machine under particularly challenging operative conditions.The sprayer was studied at three forward speeds (4, 5, and 6 km h⁻¹), and gave poor deposition inside the canopy, whether or not the electrostatic system was activated. Forward speed did not significantly affect the mean foliar spray deposition, whereas activation of the electrostatic system significantly increased the deposit only on the layer of foliage nearest to the sprayer (lower layer), but had no effect on deposition on the layer of foliage inside the canopy (upper layer). The ratio between the deposits on the two layers (lower:upper) was 6.5:1 when the electrostatic system was switched off, and 9.0:1 when it was switched on.However, this behaviour may allow targeted treatments on grapes, such as with Plant Protection Products (PPP) or bio growth stimulants. Furthermore, the small droplets produced by the machine are suitable for table grape protection because the droplets do not mark the grapes, which would reduce the quality of the product and its commercial value.     

Hydrophilic nonwovens by Forcespinning™ of isotactic polypropylene blended with amphiphilic surfactants

As a widely applied polymer, hydrophilic modification of polypropylene (PP) has been an important research field. Forcespinning? uses centrifugal force to fabricate nanofibers rather than electrostatic force as in conventional electrospinning. The absence of electric fields provides a board opportunity for low dielectric materials and the utilization of centrifugal forces significantly increases the yield compared to electrospinning. Hydrophilic nonwovens from isotactic polypropylene (iPP) melt blended with amphihilic surfactant TWEEN20 and TWEEN60 were obtained by Forcespinning?. The factors were investigated by SEM and DSC, which determined fiber diameter distribution and crystallinity. The meshes showed continuous homogeneity along the length of the fiber when the system was employed at 225 °C and the rotational speed at 14,000 rpm. Blending with surfactants bearing ethoxylate groups led to increased oxygen content of the meshes surface as confirmed by ATR-FTIR spectroscopy and X-ray photoelectron spectroscopy (XPS). XPS results indicated preferential distribution of additives on surfaces. The forcespun meshes exhibited excellent hygroscopicity even when the load of TWEEN20 was 10 %.     

Copper functionalization of polypropylene fabric surface in order to use in fog collectors

Polypropylene fabrics were coated with copper particles using electroless plating, screen printing and wire arc spray coating techniques. Surface morphology of the fabrics was studied using optical and scanning electron microscopes (SEM). Furthermore, tensile strength, electrical conductivity, thermal conductivity, air permeability, water contact angle and fog collection efficiency of the coated fabrics were measured and the obtained results were analyzed. SEM micrographs showed that a very thin and uniform layer of copper deposited on the surface of the electroless plated polypropylene fibers. In the printed or spray coated fabrics the copper particles filled the spaces between yarns and fibers. The polypropylene electroless copper plated fabrics showed higher tensile strength, electrical conductivity, air permeability and thermal conductivity when compared with the fabrics coated with copper screen printed and copper spray coated fabrics. Finally, the obtained results showed that copper electroless plating could increase the fog collection efficiency of polypropylene fabrics considerably. As a conclusion, the surface modified copper electroless polypropylene fabrics are good candidates for fog collection in appropriate regions which need further investigations.     

Acetylation of Jute fiber to improve oil absorbency

Raw Jute was modified by acetylation process with acetic anhydride using N-bromosuccinimide (NBS) as a catalyst in a solvent free system which was found to be effective catalyst. The reaction parameters were optimized which were found to be time 1 h, temperature 120 °C, catalyst concentration 2 %, and solid to liquid ratio 1:20. The product so formed was characterized by FT-IR and TG and its degree of acetylation was also evaluated. The extent of acetylation was measured by weight percent gain (WPG). Acetylation resulted in significant increase in hydrophobic properties of the jute fiber. The oil sorption capacity of the acetylated jute was higher than that of the commercial synthetic oil sorbents such as polypropylene fibers as well as raw jute. Therefore, these oil sorption-active materials which are also biodegradable can be used to substitute non-biodegradable synthetic materials in oil spill cleanup.     

Effect of multi walled carbon nanotube on the crystalline structure of polypropylene fibers

Polypropylene fibers containing varying amounts of multi walled carbon nanotube (MWCNT) have been spun using a conventional melt spinning and drawing apparatus. Changes in morphology and crystalline structure of composite fibers induced by addition of MWCNT were studied by small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR) and birefringence measurements. The results of SAXS experiments showed an increase in lamellar thickness, long period and crystallinity of the composite fibers in comparison to pure polypropylene fibers. Molecular orientation and helical content of the fibers were increased due to the addition of MWCNT to the polypropylene matrix. WAXS results, being in agreement with the SAXS results, also showed an increase in crystallinity of the composite fibers due to the increase in MWCNT content. This is probably because of nucleating effect of nanotubes in the fiber matrix, causing more crystallization and orientation of molecules to take place around them.     

Coating superfine down powder on polypropylene for the production of dyeable fibers

To develop dyeable isotactic polypropylene (iPP) fibers, superfine down powder (SDP) was coated on the surface of iPP fibers post melt-spinning. Optical micrographs showed that the surface of powder-coated iPP fibers was roughness, and the amount and dispersion of coated SDP were found entirely dependent on melt-spinning temperature. With the increase in coated SDP content, the moisture and water absorption of powder-coated iPP fibers increased. Powder-coated iPP fibers could be, respectively, dyed by reactive red dye and acid red dye, and the observed enhancement of color strength (K/S) and red value (a*) of powder-coated iPP fibers could be attributed to SDP coated on iPP fibers. It was worth noting that the removal of coated SDP affected the wet-washing fastness of powder-coated iPP fibers largely. In addition, the powder-coated iPP fibers were produced in a few minutes with lower cost and could have potential applications in textile industry.     

Relation between tacticity and fiber diameter in melt-electrospinning of polypropylene

Electrospun atactic polypropylene (PP) fibers are thicker than those obtained from isotactic PP, although the viscosity of molten PPs is almost same. Thus we focused on the effect of tacticity of PP on fiber diameters. The PP samples with various tacticity were prepared by changing the blend ratio of isotactic PP and atactic PP. Melt-electrospinning is performed by using blended samples, and then electrospun fibers were observed by scanning electron microscope to evaluate fiber diameter of obtained fibers. It is clear that the diameter of electrospun PP fibers decreases as high tacticity content of PP increases. This result suggests that tacticity of samples is an important factor to control the electrospun fiber diameter.     

Effect of electric fields on a novel enclosed air-jet electrospinning set-up

A novel enclosed air-jet electrospun set-up was described for fabricating nanofibers with high production rate. This study showed the components of the spinneret device, mainly including a spray nozzle, a liquid storage chamber, a connector and a gas storage chamber. By using this device, the polyacrylonitrile (PAN) nanofiber mats were fabricated with increased production rate of nearly more than ten times as compared with using single-needle electrospun set-up. The jets path, fibers morphology, mats throughput, along with forces acted on the bubbles in four positive electrodes were investigated in this report. The electric fields and equipotent lines distribution with corresponding positive electrodes were simulated with a second-dimension FEA (An-soft Maxwell) for analyzing experiment results. The simulated results showed that the strength of electric fields was related to the size of the charged area, and the uniform of electric fields depended on the mutual effects of electric fields from different charged position. The average diameter of fibers was the thinnest with about 280 nm and the standard deviation of fibers was 34.95 % with the top surface of the solution storage chamber and the nozzle charged. When the whole nozzle was charged, the diameter of fibers increased to 323.27 nm but the standard deviation reduced to 29.53 %. Especially, with the top surface of the solution storage chamber charged, the fibers showed thinner mean diameter of 290 nm and the most uniform standard deviation of 28.02 %. With further reduction of the charged area, a few beads-like fibers with the thickest diameter and the worst standard deviation were appeared.