Nonwoven Fiber Mats Research Articles

IMPREGNATED FIBROUS CHEMOSORBENTS OF ACID GASES FOR RESPIRATORY PURPOSE

The present review is dedicated to the analysis of scientific works carried out in Physico- Chemical Institute of Environment and Human Protection (Odessa, Ukrainie) and directed to the development of import-substituting sorption-filtering materials for respiratory purposes – impregnated fibrous chemisorbents (IFCS) of acid gases, which are manufactured using standard equipment, as well as affordable and inexpensive chemical reagents and carriers of domestic origin. The process of chemisorption of sulphur dioxide by hexamethylenetetramine (HMTA) modified nonwoven fibrous material resulted acid-catalyzed hydrolysis of HMTA to form aminomethanesulfonic acid and toxic formaldehyde. The IFCS with HMTA carried was recommended to use for air purification only from SiF4, HF, HCl and Cl2. Chemisorption of sulphur dioxide by fibrous materials impregnated by ethanolamines (monoethanolamine, diethanomamine, triethanomamine and N-methylethanolamine) and polyethylenepolyamine (PEPA) occurs only in the presence of “free” water with formation of “onium” sulphites, hydrosulphites and pyrosulphites. IFCS-PEPA (dynamic activity is 1,38 mmol(SO2)/g) are not inferior to the protective characteristics of IFCS with Na2CO3, HMTA, ethanolamines and the best foreign ionexchange fibrous chemisorbents brand VION and FIBAN (dynamic activity is 0,263 ÷0,422 mmol(SO2)/g) under conditions of respirators actual use (jAGM = 60 ÷ 90 %, TAGM = 297 K, VAGM = 2,0 sm/s, СSO2 = 20 ÷ 1000 mg/g3, QPEPA = 3,45 mmol/g). It is recommended to use the condensation products of primary alkylamines with formaldehyde (with large molar masses than the bases), complex compounds of amines with 3d-metals (Ni(II) and Cu(II)), salts of amine with aminoacids (glycine) and polybasic acids (orthophosphoric acid (pKa1 = 2,12) and citric acid (pKa1 = 3,13)) for manufacturing of IFCS of acid gases The IFCS with indication of dynamic absorptive capacity “wearing” (IVKS-I) was developed.

An In-Process Intervention to Mitigate the Effect of Built-Up Edges in Micromilling

This paper is focused on developing an in-process intervention technique that mitigates the effect of built-up edges (BUEs) during micromilling of aluminum. The technique relies on the intermittent removal of the BUEs formed during the machining process. This is achieved using a three-stage intervention that consists first of the mechanical removal of mesoscale BUEs, followed by an abrasive slurry treatment to remove the microscale BUEs. Finally, the tool is cleaned using a nonwoven fibrous mat to remove the slurry debris. An on-machine implementation of this intervention technique is demonstrated, followed by a study of its influence on key micromachining outcomes such as tool wear, cutting forces, part geometry, and burr formation. In general, all relevant machining measures are found to improve significantly with the intervention. The key attributes of this intervention that makes it viable for micromachining processes include the following: (i) an experimental setup that can be implemented within the working volume of the microscale machine tool; (ii) no removal of the tool from the spindle, which ensures that the intervention does not change critical process parameters such as tool runout and offset values; and (iii) implementation in the form of canned G-code subroutines dispersed within the regular micromachining operation.

Ultrathin Poly(3-hydroxybutyrate) Fibers Modified with the Iron(III) Complex of Tetraphenylporphyrin

New effective nonwoven fibrous materials with bactericidal activity were electrospun from poly(3-hydroxybutyrate) and the iron(III) complex of tetraphenylporphyrin. Fiber surface defects were found to disappear if the iron(III) complex of tetraphenylporphyrin was added to the polymer solution. The supramolecular structure of fibers with encapsulated iron(III) complexes of tetraphenylporphyrin was investigated by DSC and EPR spectroscopy (probe method). It was shown that the degree of crystallinity increased sharply and molecular motion slowed in amorphous regions of the ultrathin fibers if the complex was added to the poly(3-hydroxybutyrate) matrix. The resulting fibrous materials possessed bactericidal properties and should be directly applicable to the fabrication of antibacterial and antitumor therapy systems.

A monolithic “unibody” construction of structural assemblies through vacuum-assisted processing of agro-waste fibrous composites

This research explored the feasibility of using vacuum-assisted infusion process (VIP) and agricultural waste - based materials to in-situ build unitary (or “monolithic”) structural components and assemblies. Mechanical properties of the natural/synthetic hybrid fiber composite materials were studied. The experimental results show that in combination with a small amount of glass fiber, the nonwoven coconut coir fiber mats can be used as structural sheathing material to provide satisfactory strength and stiffness. In addition, five “unibody” light-frame composite shear panels sheathed with the coconut coir/fiberglass material and two plywood panels were fabricated; and three composite “I”-shape beams were prototyped using the vacuum infusion process. The structural behaviors of the composite shear panels and beams were tested and compared to those of conventional plywood constructions. The results indicate that structural members constructed through VIP have satisfactory stiffness and strength and they offer better structural integrity and energy dissipation over conventional constructions. The design and construction technique outlined in this paper provides a means to in-situ construct complex-shaped structural assemblies with minimal or no joint. The experimental data showed good agreement with results calculated through classical laminate theory (CLT).

Surface texturing of electrospun fibres by photoembossing using pulsed laser interference holography and its effects on endothelial cell adhesion

Electrospun fibres are nowadays extensively studied for biomedical applications such as tissue engineering and drug delivery. Here, fibres for such applications are electrospun from photopolymer blends using a volatile solvent. The obtained nonwoven fibre mats were textured using a photoembossing technique that uses the interference of two coherent UV laser beams followed by a thermal development step. AFM measurements revealed that the patterned exposure using pulsed laser interference holography resulted in a surface texture on the fibres. The effect of temperature and UV dosage on fibre texturing was studied and was similar to results seen in photoembossed films. Fibronectin and cell adhesion was evaluated on textured fibres of 1 μm diameter with relief structures of 60 nm height and 2 μm pitch. Initial results did not seem to indicate improved cell adhesion for photoembossed fibres compared to their non-embossed counterparts.

3D stochastic modeling, simulation and analysis of effective thermal conductivity in fibrous media

This paper develops a 3D stochastic model to describe porous metal fiber sintered sheet (PMFSS), which is a non-woven fiber mat composed of curved and partial overlapped sintered fibers. Firstly, single fibers of PMFSS are modeled based on morphology information involving curvature and orientation extracted from the actual structure employing the 3D micro-CT imaging. Secondly, since fibers are partially overlapped at sintered joints (fiber to fiber overlapping section) during sheet formation process, a graphics processing unit (GPU) accelerated force biased simulation is introduced, which turns the arbitrarily overlapped single fibers into partially overlapped ones, for the sake of making the virtual geometry more realistic. Finally, fibrous geometries resembling the microstructure of PMFSS with various porosities are established and further imported into the STAR-CCM+ CFD package (CD-adapco, London) to study the effective thermal conductivity. Results illustrate that the numerical effective thermal conductivity of PMFSS agrees well with the experimental results in the in-plane direction. Besides, the sensitiveness of effective thermal conductivity due to structural anisotropy is also verified.

Three-dimensional reconstruction of a random fibrous medium: Geometry, transport, and sound absorbing properties

The main purpose of this article is to present, within a unified framework, a technique based on numerical homogenization, to model the acoustical properties of real fibrous media from their geometrical characteristics and to compare numerical results with experimental data. The authors introduce a reconstruction procedure for a random fibrous medium and use it as a basis for the computation of its geometrical, transport, and sound absorbing properties. The previously ad hoc "fiber anisotropies" and "volume weighted average radii," used to describe the experimental data on microstructure, are here measured using scanning electron microscopy. The authors show that these parameters, in conjunction with the bulk porosity, contribute to a precise description of the acoustical characteristics of fibrous absorbents. They also lead to an accurate prediction of transport parameters which can be used to predict acoustical properties. The computed values of the permeability and frequency-dependent sound absorption coefficient are successfully compared with permeability and impedance-tube measurements. The authors' results indicate the important effect of fiber orientation on flow properties associated with the different physical properties of fibrous materials. A direct link is provided between three-dimensional microstructure and the sound absorbing properties of non-woven fibrous materials, without the need for any empirical formulae or fitting parameters.

Evaluation of nanofibrous scaffolds obtained from blends of chitosan, gelatin and polycaprolactone for skin tissue engineering

Polymer blending is a strategy commonly used to obtain hybrid materials possessing properties better than those of the individual constituents regarding their use in scaffolds for Tissue Engineering. In the present work, the scaffolds produced by electrospinning solutions of polymeric blends obtained using a polyester (polycaprolactone, PCL), a polysaccharide (chitosan, CS) and a protein (gelatin extracted from cold water fish skin, GEL), were investigated. Solutions conductivity, shear viscosity and surface tension were determined. GEL-containing scaffolds were crosslinked with vapour phase glutaraldehyde (GTA). The scaffolds were characterized physico-chemically regarding fibre morphology, porosity, water contact angle, mechanical properties, chemical bonds and fibre and dimensional stability upon immersion in water and cell culture medium. The scaffolds were further tested in vitro for cell adhesion, growth and morphology of human foetal fibroblasts (cell line HFFF2). Results show that the nanofibrous scaffolds are hydrophilic and display the typical porosity of non-woven fibre mats. The CS/PCL and CS/PCL/GEL scaffolds have the highest elastic modulus (48MPa). Dimensional stability is best for the CS/PCL/GEL scaffolds. FTIR spectra confirm the occurrence of cross-linking reactions of GTA with both GEL and CS. Cell adhesion ratio ranked from excellent (close to 100%) to satisfactory (around 50%) in the order PCL/GEL>CS/GEL>CS/PCL/GEL>CS/PCL. Cell populations show an extended lag phase in comparison with the controls but cell proliferation occurs on all scaffolds until confluence is reached. In conclusion, all scaffolds studied possess characteristics that enable them to be used in skin tissue engineering but the CS/PCL/GEL scaffolds have better physical properties whereas the PCL/GEL scaffolds support a higher cell adhesion.

Mutifunctional Electrospun Nonwoven Mats with Two‐Way Shape Memory Behavior Prepared from Sol–Gel Crosslinked Poly(ε‐Caprolactone)

Nonwoven fibrous mats based on semicrystalline networks are prepared starting from poly(ε‐caprolactone) and properly combining electrospinning and sol–gel reactions. The mats are obtained as continuous, randomly oriented micrometric fibers with different network densities. The systems are subjected to thermomechanical cycles to investigate their one‐way and two‐way shape memory behavior. One‐way tests aim at exploring the effects of the deformation temperature on the materials response, with particular interest to the less investigated cold‐working conditions (i.e., deformation temperature below T m). The materials display two‐way shape memory capabilities (i.e., the ability to change between two distinguished shapes upon heating and cooling under a fixed nonzero stress) and the effect of the applied stress is explored. The shape memory characterization is accompanied by an ex situ SEM analysis, to describe the concurrent microstructural evolution during the macroscopic shape variation, and by the assessment of their biocompatibility, to explore the suitability of the nonwovens for biomedical applications. image

Segmented imidazolium ionenes: Solution rheology, thermomechanical properties, and electrospinning

Segmented imidazolium ionenes with poly (tetramethylene oxide) (PTMO) soft segments and ionic, bis-imidazolium hard segments formed nonwoven fibrous mats upon electrospinning. The segmented imidazolium ionenes exhibited high thermal stability, excellent mechanical properties, and two glass transition temperatures indicative of microphase separation. Tensile analysis revealed strain-induced crystallization for ionenes with a 2 kg/mol PTMO soft segment and increased stress at break with increasing soft segment molecular weight. Solution rheology enabled the determination of solvent quality, overlap and entanglement concentrations, and the influence of ion content on solution properties. Fiber diameters for polymeric fibers electrospun from acetonitrile suggested solution polyelectrolyte behavior that was independent of the PTMO molecular weight. This work reports the successful electrospinning of segmented imidazolium-containing ionenes and an in-depth analysis of their thermomechanical and solution properties.

Preliminary Study on Tensile Properties of Electrospun Silica Fibers/Polypropylene Composites

Composites based on silica and glass fibers conventionally contain fibers with dimension in the range of a few micrometers to millimeters. Electrospinning technique allows fabrication of fibers in the submicron length scale. With smaller dimension, these fibers when applied as reinforcement in composites may yield interesting composite properties. In this paper, silica fibers fabricated via electrospinning were utilized as reinforcement in polypropylene-matrixed composites. The silica precursor was prepared by sol-gel reaction of tetraethyl orthosilicate, ethyl alcohol, de-ionized water and hydrochloric acid. Viscous silica precursor was made into fibers by electrospinning with electric field of 1 kV/cm. Electrospun non-woven fiber mats were stabilized at 200°C and calcined at 800°C to remove remaining organic residues. The fiber diameter average was 279±40 nm. In the process of making composites, the silica fiber mats were sandwiched between polypropylene sheets, and the layers were compression-molded together. The composite samples with varied silica fiber contents up to 2 wt% were mechanically tested. Tensile tests demonstrate slight increases in tensile modulus, tensile strength with increasing silica fiber content. However, silica fiber content within the experimental range does not have prominent effects on yield strength and strain at break.

Characterisation of unidirectional fibre reinforced grout as a strengthening material for RC structures

The main goal of the present research work is to characterise a unidirectional fibre reinforced grout (UFRG), developed as an alternative material to strengthen RC structures using small thickness jacketing.A high performance cementitious grout reinforced with continuous and unidirectional non-woven steel fibre mat has been developed for this purpose. It was expected that the optimization of the percentage and alignment of the steel fibres would yield a more efficient fibre grout. In fact, the composite should attain higher tensile strength with continuous fibres since the fibre embedment length is enough to prevent fibre pull-out.An experimental programme was carried out to characterise the UFRG’s mechanical properties. Compressive tests were conducted on small thickness tubular specimens to enable the determination of the compressive strength and the static modulus of elasticity. The tensile strength was obtained from splitting tests performed on cubic specimens (DIN 1048-5).Semi-empirical equations, based on the experimental results, are proposed to estimate UFRG’s modulus of elasticity, compressive strength and tensile strength.Two strengthening solutions for RC structures using small thickness CFRP jacketing are presented.

Characterization and application of zeolitic imidazolate framework-8@polyvinyl alcohol nanofibers mats prepared by electrospinning

In this study, Zeolitic imidazolate framework-8@polyvinyl alcohol (ZIF-8@PVA) nanofibers were creatively fabricated by electrospinning technique, and the nanofibers membranes were characterized by SEM, TEM, XRD, FTIR, TG, DSC, DTA, BET. Its thermal stability, mechanical property, water stability and adsorption nature were also performed. The optimized fabrication parameter of the ZIF-8@PVA was 10 wt% and the uniform diameters of the nanofibers has been obtained. In addition, the ZIF-8@PVA nanofibers displayed unique properties such as a water stable and flexible structure. The adsorption test for Congo red treatment revealed that the nanofibers had a great adsorption performance. The results indicated that the nonwoven fiber mats had a great potential as a new type of membrane adsorbents in wastewater purification. The possible mechanism of CR adsorption onto ZIF-8@PVA was researched.

Ozone Resistance of Nonwoven Polypropylene Fibrous Material

The efficiency of ozone absorption by nonwoven polypropylene fibrous material prepared by industrial spunbond technology and changes of its chemical composition and structure after ozone treatment were studied. The effects of ozone treatment at low (250 μg/m3) and high (25 g/m3) ozone concentrations were compared. It was found that oxidative destruction in both instances was localized primarily on the fiber surface. The conditions under which the propylene nonwoven spunbond material was resistant to ozone were determined.

Nonwoven materials obtained by electrospinning on the basis of epoxydated derivatives syndiotactic 1,2-PB

The production of chemical fibers is an urgent task. Non-woven ultra-thin materials based on thermoplastic elastomers have high physicomechanical and filtering properties. Of particular interest is the production of non-woven materials based on epoxidized derivatives of syndiotactic 1.2-polybutadiene. In this connection, the possibilities of obtaining nonwoven materials based on epoxy derivatives of syndiotactic 1.2-polybutadiene by the method of electrospinning and determining the main factors influencing the formation of fibers and the degree of orientation of fibers of syndiotactic 1.2-polybutadiene in non-woven materials were studied. Epoxidation of syndiotactic 1.2-PB was carried out by the action of tungsten oxo-peroxo complexes. The electro spinning method was used to orient oriented nonwoven materials based on syndiotactic 1.2-polybutadiene. Optimization of the process for obtaining fibers of syndiotactic 1.2-polybutadiene was carried out using the mathematical method of planning the Plaquette-Burman experiment. Investigation of the structure of nonwoven fibrous materials was carried out on a scanning electron microscope. The degree of orientation of the fibers of syndiotactic 1.2-polybutadiene was determined using the MBF program. With the use of the method of electrospinning, nonwoven materials with different degrees and variants of fiber orientation in the composition of nonwovens can be produced. The use of epoxidized derivatives of syndiotactic-1.2- polybutadiene with different content of oxirane groups allows to regulate the diameter of fibers in non-woven materials

Electrospun PVDF graphene oxide composite fibre mats with tunable physical properties

This article is aimed at a basic physical characterization of electrospun PVDF/graphene oxide (GO) composite non-woven fibre mats. The morphological characterization of the prepared fabrics was performed via SEM investigations. Introduction of the GO during the electrospinning process caused significant changes in the crystalline structure of PVDF, and a transformation from α- to β-crystalline phases was achieved. Addition of the GO particles into PVDF did not only improve the thermal stability of the polymer, but also acted as a reinforcing filler, giving rise to improved dynamic moduli and tensile strength. The dielectric properties were evaluated over a broad frequency range, and it was confirmed that the presence of small amounts of GO had little effect on the dielectric properties of the PVDF, since the GO has a dielectric character similar to that of the PVDF.

Ageing of fibre-laden aqueous foams

Fibre-laden liquid foams are used in the production process of novel non-woven fibrous materials, employed for example for thermal or acoustic insulation. Here we present an experimental investigation of the stability of such foams. We find that on a time-scale of a few minutes the presence of fibres does not alter the drainage properties of the foam. On a longer time-scale fibres slow down drainage, mainly due to their slowing down of coarsening. The drying of our aged samples leads to a fibre network with a fibre concentration profile that appears to be determined by gravity. Our experiments were performed using fibre concentrations of a few percent, as relevant also to the foam-laid forming of paper, where aqueous foam instead of water is used as a carrier medium for fibres .

Growth behavior of endothelial cells according to electrospun poly(D,L-lactic-co-glycolic acid) fiber diameter as a tissue engineering scaffold.

Investigating the effect of electrospun fiber diameter on endothelial cell proliferation provides an important guidance for the design of a fabric scaffold. In this study, we prepared biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) fibrous nonwoven mats with different fiber diameters ranged from 200 nm to 5 µm using the electrospinning technique. To control the fiber diameters of PLGA mats, 4 mixture solvents [hexafluoro-2-propanol, 2,2,2,-trifluoroethanol:dimethylformamide (9:1), 2,2,2,-trifluoroethanol:hexafluoro-2-propanol (9:1), chloroform] were used. Average diameters were 200 nm, 600 nm, 1.5 µm, and 5.0 µm, respectively. Stereoscopic structure and spatial characterization of fibrous PLGA mats were analyzed using atomic force microscopy and a porosimeter. The mechanical properties of PLGA mats were analyzed using a universal testing machine. The spreading behavior and infiltration of endothelial cells on PLGA mats were visualized by field emission scanning electron microscopy and hematoxylin and eosin staining. Cell proliferation on different PLGA fibers with different diameters was quantified using the MTT assay. Cells on 200 nm diameter PLGA mats showed rapid attachment and spreading. However, the cells did not penetrate the PLGA mat. Cells cultured on 600 nm and 1.5 µm diameter fibers could infiltrate the pores and cell proliferation was dramatically increased after 14 days. Secreted prostacyclin from endothelial cells on each mat was measured to examine the ability to inhibit platelet activation. This basic study on cell proliferation and fiber diameter with physical characterization provides a foundation for studies examining nonwoven fibrous PLGA mats as a tissue engineering scaffold.

Lateral crushing properties of non-woven kenaf (mat)-reinforced epoxy composite hexagonal tubes

The current study investigated the energy absorption capability and load carrying capacity of non-woven natural kenaf fiber (mat)/epoxy–hexagonal composite tubes subjected to a lateral quasi-static crushing test. The hexagonal composite tubes were manufactured by the hand lay-up technique. Natural non-woven kenaf (mat) was chosen as reinforcement due to low cost, low specific weight, easy processing, no need for tooling when dealing with the raw material, and no skin irritation and epoxy resin was used as the matrix to manufacture three configurations of β=40°, β=50° and β=60° of natural non-woven kenaf (mat)/epoxy laminate. The effects of hexagonal angles, supporting plate inside the tubes, and failure modes were studied by a lateral compression test. The crashworthiness of the tubes was evaluated by analysis of the specific energy absorption in quasi-static lateral compression. Specific energy absorption (SEA) was obtained from the load–displacement curve during testing. The failure mode of the tubes was analyzed from high-resolution photographs. Overall, the tube with β=40° had the best crashworthiness among the tubes. Furthermore, the results showed that the tubes with supporting plates have better specific energy absorption for all tested specimens and exhibited approximately 69% better crashworthiness than the non-supporting ones. The results also demonstrated that all specimens failed by the longitudinal failure mode.

Mechanical and electrical characterization of carbon nanofibers produced from water soluble precursors

This study presents the thermo-physical, electrical, and mechanical characterization of fine carbon fibers produced from water-soluble polymer precursors and low temperature processes. These fibers were developed utilizing the Forcespinning® technology which utilizes centrifugal force to spin fibers. Polyvinyl alcohol was used as the precursor material, and fibers were developed and deposited in a non-woven configuration. The resultant non-woven fiber mats were subjected to a dehydration process through exposure to sulfuric acid vapors. The partially carbonized mats were heat treated at 850°C. The produced porous nonwoven carbon fiber based mats have micro-and mesoporosity with a final fiber average diameter of 191nm. The electrical volume resistivity of the polymeric nanofibers was 8×1014Ωcm and it dropped to 165Ωcm for the chemically treated carbon fiber mat and to 0.407Ωcm for the subsequently heat treated fibers. The electromagnetic (EMI) shielding effectiveness (SE) was observed to be 20 and 40dB for the chemically treated fibers and heat treated fibers respectively. The tensile stress for the chemically treated fibers was 43MPa with a strain of 18% while the subsequently heat-treated fibers exhibited a stress of 124MPa and strain of 21%.