Comparison of tensile properties of co-woven-knitted and multi-layered biaxial weft-knitted fabric reinforced composites

The co-woven-knitted (CWK) fabric and multi-layered biaxial weft-knitted (MBWK) fabric were produced using glass filaments as warp and weft inserted yarns and high tenacity polyester as stitched yarns. Vacuum Assisted Resin Transfer Molding process was used to produce the two composites. Tensile tests were carried out in the course, wale and slanting directions of the composites, respectively. Specific stress-strain curves and failure modes of the two composites were investigated and compared. Results reveal that tensile strengths and elastic moduli of the two composites in the course and wale directions are better than those in the bias direction. All the composite samples fracture in the brittle damage mode. Furthermore, the buckling due to different inserted ways of the warp and weft yarns has a few influences on the tensile properties of the two composites. This research may lay a foundation for the establishment of the process windows for the co-woven-knitted reinforced composites.     

Prediction and interpretation of hydraulic permeability for nonwoven fabrics considering hypothetical 2-D layer

The permeability defined by Darcy’s law indicates the degree of ability that a fluid can flow through nonwoven media under a differential pressure in laminar flow. The permeability generally indicates the specific permeability or absolute permeability. On the other hand, if the fluid is water, the permeability indicates the hydraulic conductivity or permeability coefficient. The permeability is one of the important properties for nonwoven media and a prediction of the permeability acts as a bridge between the manufacturing technology and performance requirements. Because capillary channel theory aims to make the flow of fluid easier and more understandable, many models are based on capillary channel theory. On the other hand, the theory has a limitation in that it is unsuitable for high porosity media. In this study, a very thin downstream layer, which was suggested by Lifshutz [9], was introduced to derive a prediction model of hydraulic permeability. Needle-punched and spunbonded nonwoven fabrics with various basis weights were used in the cross-plain water permeability test. From this ‘thin layer’ model, reasonable agreement between the predicted and experimental results was obtained.     

Morphological aspects of polymer fiber mats obtained by air flow rotary-jet spinning

Fiber mats were obtained by using a modified rotary-jet spinning system, which allows a forced air flow produced by an air compressor to interfere with the polymer jets. The main focus of current studies rely on the range of morphological and dimensional characteristics of fibers that may be expected when using this new technical setup of a rotary-jet based spinning system. In fact, this work represents a proof of concept study regarding the potential of an air flow modified rotary-jet spinning for obtaining continuous fibers and nonwoven mats. The morphological examinations by scanning electron microscopy were proved the efficiency of this technique on obtaining relative homogeneous fiber mats from different raw compositions of pure and admixed, natural and synthetic polymers with different molecular masses and polydispersity degrees, like gelatin, polyurethane, and poly (vinyl chloride). The feasibility of air flow rotary-jet spinning was also tested for simultaneous independent deposition of mixed fiber mats from solutions of two polymers made in different solvents, and it was found that by carefully selecting the ratio of polymers through spinnerets number, this technique could be successfully used even in difficult solvent conditions otherwise incompatible with traditional spinning techniques. The distribution of fiber diameters was varying between nanometer scales (100–700 nm) in the case of pure polyurethane and micrometer ranges (2–12 µm) for gelatin-polyurethane mixed mats, which are convenient for various applications, from dressings and scaffolding to different filter systems. Besides the already known advantages of rotary-jet versus electrospinning, the air flow allows the control of solvent evaporation, extending the applicative range of this technique.     

A study of comfort performance in cotton and polyester blended fabrics. I. Vertical wicking behavior

Vertical wicking model was developed based on Darcy’s law. In the model, permeability coefficient, capillary pressure and fabric thickness were used as the key parameters to describe wicking behavior. For the simulation and test, fiber type and fabric structure were chosen as variables. In a highly porous knit fabric, gravitational effect during the wicking process was significant. The higher the capillary pressure was, the higher was the wicking rise. Surface wetting tension, i.e., the specific fluid affinity of material, was newly defined to characterize different capillary pressures in various types of fabric structures. The model, the methodology and the results could provide an insight into fabric design to produce fabric with an optimum wicking performance.     

Predicting the tensile strength of needle-punched nonwoven mats using X-ray computed tomography and a statistical model

As nonwoven mats are randomly oriented fiber assemblies, the tensile strength of nonwoven mats is determined by their microstructural factors, such as fiber orientation, fiber volume fraction, and fiber-fiber contact level. The complex microstructure of nonwoven mats must be reasonably simplified to properly predict their mechanical properties within affordable efforts. In this study, a new parameter, so called contact efficiency, is defined to describe the fiber-fiber contact level of nonwoven mats. Micro X-ray computer tomography (CT) is employed to characterize the microstructure of needlepunched nonwoven mats made of polypropylene short fibers. The fiber orientation and volume fraction are obtained by analyzing 2D sectional CT image of the nonwoven mat, while the contact efficiency is determined from 3D CT image. A statistical model, developed originally for staple yarns, is modified to predict the tensile strength of the nonwoven mat using the microstructural factors obtained from CT analysis. The prediction is then compared with experiments to validate that the current model incorporating the contact efficiency is highly suitable for predicting the tensile strength of nonwoven mats.     

Nitrogen transport and transformation in packed soil columns from paddy fields

Our understanding of nitrogen transformation in paddy fields or wetlands is limited due to the complex interactions between soil, water, and biomass. Therefore, we studied transformation patterns resulting from the oxic level in the soil, and studied saturated (anoxic) and unsaturated (oxic) flow conditions. We present a model designed to predict concentrations of nitrate and ammonium at several soil depths resulting from the processes of nitrification, denitrification, and ammonification. Model equations were obtained that describe NO₃-N and NH₄-N concentrations in terms of position, rate constant, and average flow velocity. Although many parameters were included in the model equations, some were determined from the literature and others were derived from experiments. A sensitivity analysis of the rate coefficients for NO₃-N and NH₄-N revealed that they are extremely sensitive to denitrification and ammonification respectively. Experimental results show that there were large differences in the transformations of NO₃-N and NH₄-N, the water pressure distributions, and the oxygen reduction potentials (ORP) between saturated and unsaturated pore water flow conditions. The performance of the model for sequential transformations during the transport of NO₃-N is well documented under both saturated and unsaturated flow conditions.     

Solution blowing nylon 6 nanofiber mats for air filtration

Solution blowing process is a new nanofiber fabricating method with high productivity. In the present study, nylon 6 nanofiber mats were solution blown and the effects of spinning conditions on nanofibers morphology were investigated. The fiber diameter ranged from 150 to 750 nm which was affected by solution concentration, gas pressure and solution feeding rate. The solution blown fibers were three-dimensional curly which made loose construction in bulk. The filtration performance of solution blown mats was evaluated. The tested solution blown nanofiber mats showed high filtration efficiency of 83.10 % to 93.45 % for 0.3 µm particles filtration and extremely low pressure drop of 15.37 to 30.35 Pa. The results indicate the solution blown nanofiber mats will find potential application of high efficiency and low resistance filter.     

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.     

Fatty acids of maize pollen – Quantification,nutritional and morphological evaluation

The aim of this work was to identify and quantify fatty acids presented in pollen samples collected from six different Serbian maize hybrids by GC capillary method. Due to great importance of fatty acids as food component potential nutritional value of maize pollen as food supplement in human diet was determined. It has been shown that pollen is a great source of different fatty acids, especially unsaturated fatty acids. In total, twenty eight fatty acids were quantify - the most abundant saturated FAs were palmitic and henicosanoic acid; the most prevalent monounsaturated FAs were oleic, elaidic and cis-10-heptadecenoic acid. Linoleic and cis-11,14-eicosadienoic acid were the most abundant polyunsaturated fatty acid. Also, it was found that FAs composition was significantly influenced by the type of maize hybrids. According to nutritional recommendations, four of six pollen samples had good nutritional quality with unsaturated/saturated fatty acids ratio higher than 1.6, but there is unsatisfied distribution of ω-6 and ω-3 fatty acids as the most important type of unsaturated fatty acids.     

The study on the air volume fraction of electrospun nanofiber nonwoven mats

Electrospinning is an efficient method to produce polymer fibers with a diameter range from nanometers to a few microns using an electrically driven jet. Electrospun nanofiber nonwoven fabrics can be applied into different areas with higher air volume fraction, especially applied into textile materials with good warmth retention property. In this article, the air volume fraction in nonwoven mats made of electrospun nanofibers was verified by studying fiber volume fraction in the mats. Then the relationship between fiber volume fraction and fiber diameter was derived, and the fiber volume fraction is in direct ratio to the square of fiber radius. By experimental verification, to get electrospun PAN nanofiber nonwoven mats with high air volume fraction about 99 %, it can fix the polymer concentration on 8 %. The voltage fixed on 20 kV, the tip-to-collector distance on 15 cm. The experiment is in accordance with the theory excellently.     

Electrospun poly(L-lactic)acid/nanoalumina (PLA/Al2O3) composite fiber mats with potential biomedical application — Investigation of cytotoxicity

PLA fibrous mats containing nanoalumina filler were fabricated by electrospinning method. The morphology of the mats was characterized by SEM, and TEM. In vitro biocompatibility of the electrospun fiber mats was also evaluated. Indirect cytotoxicity evaluation of the fiber mats with human skin fibroblasts revealed that the materials were non-toxic to living cells. The cells cultured on the fibrous mat exhibited normal cells shapes and were integrated well with surrounding fibers. The obtained results confirmed the potential for use of the electrosupun PLA/Al₂O₃ fiber mats for biomedical application.     

Data transmission textiles for smart clothing using conducting fibers

In this study, electrical properties and data transmission characteristics of 75D PET/silver composite filaments were measured and analyzed in order to explore the feasibility of “digital textiles” in terms of resistance, resonance frequency, dB loss, and Bandwidth. Those characteristics were measured and compared according to measurement length (10～50 cm) and number of strands (1～10) in order to provide a design guide line for smart clothing. According to the measurement results, electrical characteristics of conducting fiber can be enhanced by increasing the number of fiber strand. It was also demonstrated that multiple resonances could occur from conducting fiber when the fiber lengths are varied. Finally, it showed the delay time of conducting fiber reached the saturated value when the number of fiber strand exceeded five.     

Study of moisture and thermal transfer properties as a function of the fiber material variation

The properties of moisture transfer and the comfort of mesh-structured fabrics with various knit compositions and properties were investigated. The comfort effects of the double knitted fabrics combined with different cross-shaped fibers composed of dyeable-polypropylene (PPd) and regular polyester (PET) double-knitted fabrics were studied. A series of PET, PPd, Coolmax^® (Cm) with single knitted fabrics and PPd/Cm with double knitted fabrics were evaluated to determine the physical properties and wearing performance for comfortable clothing. To compare the structural properties involving the vapor transfer of 4 types of fabrics with different fiber compositions, fiber types, weights, and thicknesses, the surface structure and pore characteristics were evaluated by scanning electron microscopy and a capillary flow porometer. The properties of moisture transfer were tested using vertical wicking and gravimetric absorbent testing system (GATS). In addition, the comfort performance measured by the thermal insulation value (Rt) and moisture permeability index (im) with a thermal manikin in a conditioned walk-in environmental test chamber was predicted. The result showed that the PPd/Cm sample has potential applications as good comfort fabric materials.     

Prediction and measurement of residual stresses in injection molded parts

Residual stresses were predicted by a flow analysis in the mold cavity and residual stress distribution in the injection molded product was measured. Flow field was analyzed by the hybrid FEM/FDM method, using the Hele Shaw approximation. The Modified Cross model was used to determine the dependence of the viscosity on the temperature and the shear rate. The specific volume of the polymer melt which varies with the pressure and temperature fields was calculated by the Tait’s state equation. Flow analysis results such as pressure, temperature, and the location of the liquid-solid interface were used as the input of the stress analysis. In order to calculate more accurate gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise direction was predicted in two cases, the free quenching and the constrained quenching, under the assumption that the shrinkage of the injection molded product occurs within the mold cavity and that the solid polymer is elastic. Effects of the initial flow rate, packing pressure, and mold temperature on the residual stress distribution was discussed. Experimental results were also obtained by the layer removal method for molded polypropylene.     

Gallium arsenide (GaAs) nanofibers by electrospinning technique as future energy server materials

Gallium arsenide (GaAs) does have superior electronic properties compared with silicon. For instant, it has a higher saturated electron velocity and higher electron mobility. Weak mechanical properties and high production cost are the main drawbacks of this interesting semiconductor. In this study, we are introducing production of GaAs nanofibers by electrospinning methodology as a very low cost and yielding distinct product technique. In general, nano-fibrous shape is strongly improving the physical properties due to the high surface area to volume ratio of this nanostructure. The mechanical and environmental properties of the GaAs compound have been modified since GaAs nanofibers have been produced as a core inside a poly(vinyl alcohol) (PVA) shell. GaAs/PVA nanofibers were prepared by electrospinning of gallium nitrate/PVA solution in presence of arsenic vapor. The whole process was carried out in a closed hood equipped with nitrogen environment. FT-IR, XPS, TGA and UV-Vis spectroscopy analyses were utilized to confirm formation of GaAs compound. Transmission electron microscope (TEM) analysis has revealed that the synthesized GaAs compound is crystalline and does have nano-fibrous shape as a core inside PVA nanofibers. To precisely recommend the prepared GaAs nanofiber mats to be utilized in different applications, we have measured the electric conductivity and the band gap energies of the prepared nanofiber mats. Overall, the obtained results affirmed that the proposed strategy successfully remedied the drawbacks of the reported GaAs structures and did not affect the main physical properties of this important semiconductor.     

Direct manufacturing of flax fibers reinforced low melting point PET composites from nonwoven mats

There have been many interests in using natural fibers as substitutes for glass fibers to prepare fiber reinforced composites. Flax fibers, due to their specific strength, have been a hot issue in this field. The focus of this research work is to manufacture flax fiber reinforced low melting point PET composites directly from nonwoven mats. No consolidation methods are applied to the carded nonwoven mats before the hot-press molding. The effects of operating parameters like carding method, molding temperature, molding time, etc. on the mechanical properties of composites have been investigated. Results show it is a facile and cost-saving method to produce composites specifically in the application areas like automobile interior ornament and decoration materials, etc.     

Preparation and characterization of PVA/PU blend nanofiber mats by dual-jet electrospinning

A series of blend nanofiber mats comprising poly(vinyl alcohol) (PVA) and polyurethane (PU) were prepared by dual-jet electrospinning in various parameters. Orthogonal experimental design was used to investigate how those parameters affected on fiber diameters and fiber diameter distribution. Altogether three parameters having three levels each were chosen for this study. The chosen parameters were tip-to-collector distance (TCD), voltage and tip-to-tip distance (TTD). Fiber diameters, thermal properties, mechanical properties and hydrophilicity of the blend nanofiber mats were examined by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), tensile test, contact angle and water absorption test, respectively. The results showed that the optimum conditions for PVA/PU blend nanofiber mats fabricated by dual-jet electrospinning were TCD of 20 cm, voltage of 18 kV and TTD of 4 cm. Besides, the thermal stability of PVA/PU blend nanofiber mats had been improved compared with pure nanofibers. Furthermore, the elongation and tensile strength of the blend nanofiber mats were significantly increased compared with pure PVA and pure PU, respectively. And the blend nanofiber mats exhibited well hydrophilicity.     

Potential of using polyester reinforced coconut fiber composites derived from recycling polyethylene terephthalate (PET) waste

Unsaturated polyester resin synthesized from glycolyzed product of polyethylene terephthalate (PET) waste was used as a matrix to form coconut fiber/polyester composites. PET wastes were recycled through glycolysis and polyesterification reaction to produce a formulation for unsaturated polyester resin (UPR). FTIR spectra of glycolyzed product and prepared resin revealed that cross-links between unsaturated polyester chain and styrene monomer occurred at the saturated sites which resulted in the forming of cross linking network. To improve the adhesion between coconut fiber and polyester resin, various concentrations of alkali, silane and silane on alkalized fiber were applied and the optimum concentration of treatments was determined. The influence of water uptake on the sorption characteristics of composites was studied via immersion in distilled water at room temperature. Surface treatment of coconut fiber caused a significant increase in the tensile properties with the optimum treatment is 0.5 % silane on the 5 % alkalized coconut fiber/polyester composites. It was also observed that the treated fiber composites showed lower water absorption properties in comparison to those of untreated fiber composites. This observation was well supported by the SEM investigations of the fracture surfaces. From the study, it was concluded that polyester reinforced coconut fiber composites derived from recycling polyethylene terephthalate (PET) waste may have the potential application in the fields of construction and automotive interior substrates.     

Solution blowing of chitosan/PLA/PEG hydrogel nanofibers for wound dressing

In this study, a kind of hydrogel nanofibers were successfully fabricated via solution blowing of chitosan (CS) and polylactic acid (PLA) solutions mixed with various contents of polyethylene glycol (PEG) to offer hydration. The nanofibers with PEG content varying were average 341-376 nm in diameter with smooth surface and distributed randomly forming three-dimension (3D) mats. Glutaraldehyde (GA) vapor was then applied to impart stability, and the cross-linking reaction mainly occurred between GA and hydroxyl groups which was confirmed by XPS. The hydrogel nanofibers showed quick absorption behavior, high equilibrate water absorption and good air permeability which could help the mats absorbing excess exudates, creating a moist wound healing environment and oxygen exchanging in wound healing. The mats also exhibited good antibacterial activities against E. coil. The combination advantages of nanofibers mats and hydrogel will help it find promising application in wound healing.     

The non-uniform phase structure in blend fiber. I. Non-uniform deformation of the dispersed phase in melt spinning

By melt spinning of incompatible polymer blends, the deformation of the dispersed phase was investigated in the fiber spinning process, for polypropylene/polystyrene (PP/PS) blend fiber and low density polyethylene/polyamide 6 (LDPE/PA6) blend fiber, respectively. Two kinds of the take-up fiber all exhibit the matrix fibrillar morphology, but with the opposite morphology. For PP/PS take-up fiber, the dispersed PS fibrils were finer in the core than near the surface. On the contrary, the dispersed PA6 fibrils were finer near the surface than in the core for LDPE/PA6 take-up fiber. However, for the special fiber in which the extensional flow was absent, there was the uniform morphology in either PP/PS or LDPE/PA6. Thus, fibrils’ non-uniform deformation, occurred in the drawing process, was considered to be due to the radial non-uniform processing conditions across the spin-line cross-section. The distribution of fibrils’ diameter was also investigated on the whole cross section. Rheological properties of each component were measured by the capillary rheometer. The non-uniform phase structure in blend fiber is a new phenomenon in the extensional flow.