Finer Fiber Diameter Research Articles

Aerosol filtration performance of nanofibrous mats produced via electrically assisted industrial‐scale solution blowing

AbstractHighly efficient polyamide 6 (PA6)‐based nanofibrous air filter media was developed for particulate matter (PM) removal in the ambient atmosphere. The PA6 nanofibrous mats exhibited 85% PM0.3 capture performance at a cost of 164 Pa pressure drop when the multiple‐nozzle solution blowing system was set to 8 m/h fabric winding speed. However, an increase in the winding speed at a constant feeding rate lowered the filtration efficiency to 62% due to the less amount of nanofibrous mats collected on the substrate. The application of electrical field at the same parameters allowed us to produce a filter media having FFP3‐level filtration performance, which means 99% PM0.3 capture performance. This was attributed to a fine fiber diameter (116 nm), higher solidity value (0.149), and lower average pore size (2.28 μm). These results show that the electrically assisted solution blowing provides a feasible route for the production of high‐quality nanofibrous filter media.

Correlation model for fiber diameter of the electro-spun membrane using KGM (1,N) model for nanofiltration

Nanofiltration is an important application for electro-spun fiber as it is well characterized by fine fiber diameter, huge density, high penetrability, and flexibility. In this paper, the poly-acrylonitrile fiber diameter is determined experimentally by varying four factors such as voltage, flow rate, the distance between spinneret and collector, and mass fraction in the electrospinning process. The fiber diameter is measured through SEM analysis. A highly accurate kernel-based non-linear multivariable grey model, KGM (1, 1) model is used for the prediction of nanofiber diameter for filtering particulate less than 500 nm. This is proved to be better when compared to the grey model first order one variable and multivariable grey model. Based on simulated outcomes, filtration membranes are prepared and tested for filtration efficiency for the airborne particles relating its air permeability, porosity and quality factor.

Simulating Study on Mechanical Properties of Rock Wool Board for Thermal Insulation on External Walls

Rock wool board (RWB) is widely used in construction of exterior insulation worldwide. Fiber diameter, solid volume fraction (SVF), and contact degree among the fibers significantly influence the RWB physical properties. Herein, the effects of these factors on the mechanical properties of RWB were investigated using the GeoDict software. First, the fiberization process resulted in a finer fiber diameter, and the SVF of RWB increased with decreasing pore sizes. In addition, both the fiber diameter and SVF significantly influenced the RWB shear strength. Furthermore, in compliance with the Chinese standards of compression, tensile, and shear strength, the SVF of RWB with a 10.5 μm fiber diameter did not exceed 4.72%, 4.04%, and 5.4%, respectively. The novel method proposed herein can be used for optimizing the RWB manufacturing process.

Development of composite filters with high efficiency, low pressure drop, and high holding capacity PM2.5 filtration

Many efforts are being made to develop filters with high efficiency and high holding capacity but remaining a low pressure drop. A two-layer composite filter to achieve the goal was developed, in which the first layer was a charged coarse fibers to provide large void space for particle loading and the second was a thin layer of charged melt-blown with finer fibers to enhance the overall efficiency. Experimental results showed that although the new composite media had a lower initial efficiency than the other two HEPA filters (PTFE and glass fiber filter), its figure of merit (FOM) was the highest. Besides, the composite media had a better holding capacity for PM2.5 than the other two. At a fixed mass load, i.e., 2 g m−2, the PTFE (ΔP = 380 Pa) and glass fiber (ΔP = 165 Pa) required around 7.6 and 3.3 times more power, respectively, than the composite media (ΔP = 50 Pa). Due to the low charge level of the coarse fiber layer and the fine fiber diameter of the melt-blown layer, resulted in no efficiency reduction along the loading process. Theoretical analysis showed that the charge shielding and the loss of efficiency in the successive top-down layers were timely compensated by the efficiency enhancement caused by the loading effects, which made the composite media a much uniform deposition of PM2.5 in layers. This was the main reason resulting in the high holding capacity and low pressure drop of the current composite media which acted like a perfect depth filtration media.

A comparison of transcriptomic patterns measured in the skin of Chinese fine and coarse wool sheep breeds

We characterised wool traits, and skin gene expression profiles of fine wool Super Merino (SM) and coarse wool Small Tail Han (STH) sheep. SM sheep had a significantly higher total density of wool follicles, heavier fleeces, finer fibre diameter, and increased crimp frequency, staple length and wool grease (lanolin) production. We found 435 genes were expressed at significantly different levels in the skin of the two breeds (127 genes more highly in SM and 308 genes more highly in STH sheep). Classification of the genes more highly expressed in SM sheep revealed numerous lipid metabolic genes as well as genes encoding keratins, keratin-associated proteins, and wool follicle stem cell markers. In contrast, mammalian epidermal development complex genes and other genes associated with skin cornification and muscle function were more highly expressed in STH sheep. Genes identified in this study may be further evaluated for inclusion in breeding programs, or as targets for therapeutic or genetic interventions, aimed at altering wool quality or yield. Expression of the lipid metabolic genes in the skin of sheep may be used as a novel trait with the potential to alter the content or properties of lanolin or the fleece.

Active generation of multiple jets for producing nanofibres with high quality and high throughput

Electrospinning is believed to be the most effective technique to produce micro- and nanofibre membrane which have been applied in various high-tech areas, including biomedical science, filtration, energy storage and electronic/optical devices, etc. A major challenge needing to surmount is the mass production of nanofibre membrane. Previous techniques such as multiple needle electrospinning and needleless electrospinning greatly improve the nanofibre throughput but bring about some problems simultaneously (poor quality of fiber, limit of polymer category). Here we present a novel technique using needle-disk as spinneret to enhance nanofibre throughput and maintain high quality nanofibre. Unlike previous researches of needleless electrospinning, needles on disk provide sites of jet initiation, showing an active and more controllable process of multiple jets generation. Simulation of electric field showed that electric field strongly concentrating on tip of every needle makes it easier to produce nanofibre with finer fiber diameter at relative low voltage. Moreover, this technique is capable of fabricating nanofibre from various materials with high quality as traditional single-needle electrospinning can do. This reliable technology with simple apparatus is not only convenient and efficient for laboratory use but also great practical for industrialization, suggesting profound significance for preparation and application of nano-materials.

Electrospun poly(butylene terephthalate) fibers: Entanglement density effect on fiber diameter and fiber nucleating ability towards isotactic polypropylene

Electrospun poly(butylene terephthalate) (PBT) fibers were prepared from trifluoroacetic acid (TFA)-based solvent. Rheological studies revealed the concentration (ϕ, volume fraction) dependence of zero-shear viscosity (ηo) to be ηo ∼ ϕ3.87 in the entangled solution regime, and the entanglement concentration (ϕe) was 7.84 vol.%. Effects of ηo on the straight jet-end diameter (dj) and fiber diameter (df) were investigated; two scaling laws existed for PBT/TFA solutions, i.e., dj ∼ ηo0.06 and df ∼ ηo0.73. Moreover, df can be scaled with entanglement density and solution plateau modulus (GN) through df ∼ (ϕ/ϕe)2.6 ∼ GN. Results of differential scanning calorimetry and wide-angle X-ray diffraction revealed that as-spun PBT fibers were not amorphous but contained imperfect small α crystallites. During stepwise annealing, crystal perfection gradually occurred, and well-ordered, α-form crystal was developed at temperatures above 160 °C. When electrospun PBT fibers were embedded in isotactic polypropylene (iPP) matrix, fiber surface-induced crystallization readily occurred to develop a transcrsytalline layer of iPP monoclinic crystals at the interface. Similar effects were found for electrospun fibers of poly(ethylene terephthalate) (PET) and poly(trimethylene terephthalate) (PTT). The conventional method of counting iPP nuclei occurring on the fiber surface to determine fiber nucleation rate was infeasible because of the fine fiber diameter. A new approach to characterize the nucleating ability of polyester fibers with submicron diameter was developed. By measuring the intensity of depolarized light during cooling from the melt, the initial temperature (Ti) for iPP transcrystallization was determined and compared. Based on the derived Ti, the nucleating ability of electrospun fibers toward iPP followed the order PBT > PET ∼ PTT. This finding was consistent with isothermal crystallization results. Moreover, the maximum temperature for PBT fiber to induce crystallization of iPP was ca. 157 °C, which was 20 °C higher than those of PET and PTT fibers. The remarkable nucleating ability of PBT fibers was likely associated with epitaxial crystallization and the large substrate crystal dimension in the matching direction, as revealed by atomic force microscopy.

Structure evolution of electrospun nanofibers probed by in-situ synchrotron X-ray scattering

To characterize the evolution of crystalline structure during heating of electrospun nanofibers is a challenging task due to the fine fiber diameter. In-situ X-ray scattering with synchrotron radiation sources are essentially powerful to trace the subtle structural variation. In this study, aligned syndiotactic polypropylene (sPP) nanofibers with an average diameter of 180 nm were obtained by means of high-temperature electrospinning of an 8 wt.% sPP/ortho-dichlorobenzene solution. The as-spun fibers were characterized to consist of the antichiral form I (11 %), mesophase (27 %) and amorphous phase (62 %), in the absence of isochiral form II. The aligned fibers were subjected to a progressive heating (either stepwisely or continuously at a rate of 4 °C/min) to fiber melting. During heating, structure evolution of the sPP chains was investigated by means of in-situ two-dimensional wide-angle and small-angle X-ray scattering. Upon heating, melting and phase transformation of the mesophase were detected; at 90 °C the processes were completed, giving rise to the annealed fibers of 27 % mixed form I/II and 73 % amorphous phase. In addition to directly producing amorphous phase, heating of the mesophase was accompanied with another two phase transitions, i.e. the solid-solid meso → II phase transition at 50–80 °C, as well as the formation of form I at 80–110 °C. The former is likely due to the chain reorganization in the mesomorphic solid, and the latter is associated with the crystallization of amorphous chains at high temperatures. These events were in accordance with the heating curve obtained from differential scanning calorimetry, which exhibited a small endotherm centered at T1 for the melting of mesophase, followed by a shallow exotherm centered at T2 associated with the formation of form I/II crystallites. Both T1 and T2 were found to increase with increasing heating rates. However, the melting enthalpy and the double melting temperatures of the sPP nanofibers are relatively independent of the heating rate applied (4 ~ 40 °C/min).

Characterization of camel fibers in regions of Kazakhstan and Uzbekistan

To generate information on Central Asian camel fiber quality, fiber samples of 712 camels from Kazakhstan and Uzbekistan were characterized. Fixed effects involved geographical location, animal age, sex, coat color and species. Camel species are Bactrians (Camelus bactrianus), dromedaries (Camelus dromedarius) and crosses between both species, hereafter referred as hybrids. Fiber traits included clean fine fiber yield (CY), mean fine fiber diameter (MFD), mean fine fiber diameter coefficient of variation (MFD CV), fine fiber curvature (Curv) and fine fiber staple length (SL). The arithmetic averages of CY, MFD, MFD CV, Curv and SL were respectively 37.3%, 18.0μm, 30.6%, 87.7°/mm and 46.0mm for Bactrians; 29.1%, 21.2μm, 30.3%, 78.2°/mm and 52.7mm for dromedaries; and 42.7%, 17.9μm, 29.5%, 89.9°/mm and 47.2mm for hybrids. Significant age by species interaction was detected for all traits. Overall, Bactrian camels had higher CY, lower MFD, higher Curv and lower SL than dromedaries (P<0.05). The geographical locations significantly differentiated CY and Curv but not the other traits; thus, for the locations studied little could be gained by looking into location variability when planning genetic improvement programs. There were no significant sex differences for all the studied traits, whereas significant differences due to the color of the coat were found only for Curv. The residual phenotypic correlations among CY, MFD and Curv were all high and would be favorable for selection purposes. Likewise, the residual phenotypic correlations between each of these variables with SL would be unfavorable if selection targets an increased SL. The study detected heterogeneity for most fiber quality traits, suggesting that a base is in place for fiber quality improvement.

Lignocellulosic nanofiber prepared by alkali treatment and electrospinning using ionic liquid

Nano-size fibers from lignocellulosic biomass were successfully obtained by akali-treatment and electrospinning using ionic liquid. The effects of the lignin and the hemicelluloses content on the spinnability, the web morphology, the micro-structure and the thermal stability of the electrospun fibers were investigated. The lower lignin content resulted in better spinnability, fine and uniform fiber diameter, higher crystallinity and decrease of thermal stability. This study reveals the possibility of the utilization for the lignocellulosic biomass other than pulp or cotton.

A numerical computation and experimental study of air drawing model of polymers in spunbonding nonwoven process

AbstractThe air drawing model of polyethylene terephthalate polymer and the model of the air jet flow field in spunbonding process are established. The air jet flow field model is simulated with the help of the finite difference method. The numerical simulation computation results of distributions of the air velocity and air temperature are in agreement with the experimental data. The air drawing model of polymer is solved with the aid of the distributions of the air velocity measured by a particle image velocimetry. The predicted fiber diameters tally with the experimental data well. It can be concluded that the higher initial air temperature can generate finer filament fiber diameter, and the higher initial air velocity can yield the finer fiber diameter as well. The experimental results show that the agreement between the predicted results and the experimental data is very good, which confirms the reliability and the accuracy of these mathematical models. Also, they reveal great prospects for this work in the field of computer assisted design of spunbonding process. POLYM. ENG. SCI., 2013. ©2012 Society of Plastics Engineers

Effect of co-solvent on the spinnability and properties of electrospun cellulose nanofiber

The effects of the type and the concentration of the co-solvent on the spinnability during cellulose electrospinning and the properties of the fiber were studied using cellulose dissolved in ionic liquid and co-solvent (DMF or DMAc). The prepared solution was electrospun onto a wired collector and coagulated in ethanol. As the weight ratio of co-solvent against ionic liquid increased, the spinnability was improved with stable whipping and splaying motion. Regardless of the co-solvent type, the higher co-solvent concentration resulted in finer fiber diameter, better web uniformity, higher crystallinity and better thermal stability. Comparing to DMAc, DMF showed more significant influence on the fiber diameter and the crystallinity.

Porphyrinated polyimide nanofibrous membrane for rapid detection of trace amount of methanol vapor

To prepare novel electrospun porphyrinated polyimide nanofibrous membrane for rapid detection of trace amount of methanol vapor. Porphyrin chromophore was copolymerized into polyimide backbones and the porphyrinated polyimide nanofibrous membrane was prepared by electrospinning technique. By optimizing the processing parameters, such as solution concentration and electrospinning voltage, nanofibrous membrane with three dimensional and large surface-to-area ratio structure was fabricated for trace amount of methanol vapor sensing applications. The obtained nanofibrous membrane preserved typical photophysical properties of porphyrin chromophores with uniformly fine and smooth fiber diameter. When exposed to methanol vapor, a red-shift of the absorption spectra and decrease in the emission intensities was observed, while no significant changes were seen when the membrane contacting with other common alcohols. After five times of 150 ppm methanol vapor quenching and nitrogen gas regeneration, the fluorescence of the membrane remained unchanged, indicating a good reversibility. Combining the specific optical properties of porphyrin with large surface-area-to-volume ratio of nanofibrous membranes, a porphyrinated polyimide nanofibrous membrane has been facilely fabricated for trace methanol vapor detection. The sensing membrane exhibits good sensitivity, selectivity and reproducibility.

Ionization-induced ultrarapid response behavior of fibrous and porous electrospun hydrogels containing carboxyl groups

Fibrous porous membranes composed of poly(N-isopropylacrylamide-co-acrylic acid) and poly(N-isopropylacrylamide-co-hydroxyethyl methacrylate) were prepared by electrospinning. The membranes behaved like hydrogels in water after being crosslinked at elevated temperatures. Investigations of the swelling and deswelling behavior indicated that the response rates significantly increased after the carboxyl and/or anhydride groups in the hydrogel membranes were ionized or neutralized with NaOH. It took them less than 60 s to reach equilibrium swelling and about 90 s to reach equilibrium deswelling. The response rates were much higher than those of the parent un-ionized membranes; this indicated that ionization played an important role in the ultrarapid response behavior. The response rate was also higher than that of most hydrogel materials previously reported and was even comparable to superporous hydrogels with high moisture contents. The mechanism of the ultrarapid response behavior of the ionized membranes was qualitatively analyzed. We believe that the fine fiber diameter, high porosity, and improved wettability with water contributed to the ultrarapid response behavior. This study presents a new and facile method for improving the response rate of hydrogel materials made by electrospinning. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The Effects of Cashmere Attributes on the Efficiency of Dehairing and Dehaired Cashmere Length

This study investigated the effects of raw cashmere attributes on the efficiency of dehairing and on dehaired cashmere length. The results show that the following attributes of raw cashmere were associated with more efficient processing and/or the production of longer cashmere: white color; longer raw cashmere; greater fiber curvature; lower vegetable matter; normal length guard hair; absence of visible cotting. Raw cashmere with a higher cashmere content and higher fiber diameter processed less efficiently than raw cashmere with a lower cashmere content and finer fiber diameter. This work identifies the value of using raw cashmere staple length and cashmere fiber curvature measurements, and shows that the variation explained by known attributes on cashmere processing efficiency was high. These results are applicable to cashmere classing, breeding, processing, and the value of the final product.

A review of the biology linking fibre diameter with fleece weight, liveweight, and reproduction in Merino sheep

There is increasing economic pressure on the Merino industry to grow finer wool and at the same time to turn off more sheep meat. Fleece weight generally decreases with finer fibre diameters, so theoretically, finer wool sheep should be able to partition more nutrients to reproduction and muscle growth. However, complex and often indirect mechanisms appear to prevent this in practice. This review summarises the available data on genetic and phenotypic relationships between wool fibre diameter and fleece weight, liveweight, fatness, and reproductive performance, and develops mechanistic hypotheses for these relationships that could be tested experimentally.Selection for reduced fibre diameter may decrease liveweight, fatness, and reproductive performance. These characteristics are also affected by the availability of nutrients, and finer fibre diameter may affect nutrient metabolism through 2 adaptations that tend to maintain fleece weight: an increase in follicle density and/or an increase in relative fibre length. These act in different ways. Follicle density may affect final body size through linkages established during fetal development. Increased fibre growth rate requires an increase in protein synthesis rate in the skin, which in turn may affect whole-body protein turnover rate and the sensitivity of tissues to insulin. Other pathways potentially affected by fibre diameter include the control of feed intake, prenatal programming of insulin sensitivity, and a reduced responsiveness of tissues to nutrient supply. However, none of these mechanisms accounts for the reports of an increased proportion of dry ewes in fine wool sheep, particularly if run in environments that experience periods of low quality pasture.Although associations between fibre diameter and growth rate, fatness, and reproduction rate are repeatable, there are not yet enough data for such associations to be realistically accounted for in breeding goals. More experimentation and a better knowledge of the causative relationships will facilitate development of finer wool sheep for environments where sheep turnoff normally provides a significant proportion of income from the sheep enterprise. Such mechanistic understanding will facilitate the development of molecular techniques for targetted selection, and the identification of more useful attributes for a quantitative genetics approach to improving simultaneously the profitability from both wool and meat.

Spider silk fibers spun from soluble recombinant silk produced in mammalian cells.

Spider silks are protein-based "biopolymer" filaments or threads secreted by specialized epithelial cells as concentrated soluble precursors of highly repetitive primary sequences. Spider dragline silk is a flexible, lightweight fiber of extraordinary strength and toughness comparable to that of synthetic high-performance fibers. We sought to "biomimic" the process of spider silk production by expressing in mammalian cells the dragline silk genes (ADF-3/MaSpII and MaSpI) of two spider species. We produced soluble recombinant (rc)-dragline silk proteins with molecular masses of 60 to 140 kilodaltons. We demonstrated the wet spinning of silk monofilaments spun from a concentrated aqueous solution of soluble rc-spider silk protein (ADF-3; 60 kilodaltons) under modest shear and coagulation conditions. The spun fibers were water insoluble with a fine diameter (10 to 40 micrometers) and exhibited toughness and modulus values comparable to those of native dragline silks but with lower tenacity. Dope solutions with rc-silk protein concentrations >20% and postspinning draw were necessary to achieve improved mechanical properties of the spun fibers. Fiber properties correlated with finer fiber diameter and increased birefringence.

Response to selection for ultrafine Merino sheep in New Zealand: I. Wool production and wool characteristics of ultrafine fibre diameter selected and control Merino yearlings

Merino ewes were screened for low fibre diameter from 15 000 yearlings within 12 flocks to establish a foundation flock in 1987, which was expanded to 500 ewes over the subsequent two years. Ewes were selected on fibre diameter BLUP breeding values. For comparison, a control flock of 100 ewes was randomly selected from the same sources. Data from approximately 2000 progeny over five birth years within 70 sire groups were analysed. Traits measured were live weight, greasy and clean fleece weight, yield, mean fibre diameter (FD), staple length, staple strength, staple crimp frequency, resistance to compression, Commission International de l'Eclairange (CIE) tristimulus value for scoured wool and coefficient of variation in fibre diameter. The ultrafine progeny had 2-μm finer FD, 0.6 units less yellow and had 0.6 more crimps/cm (all P<0.001) than their control counterparts. This experiment suggests that formation of an open nucleus breeding population by intensive screening for fibre diameter from a commercial population will improve selection response relative to traditional within flock selection without screening or to screening rams only.