Dyeing behavior of polyacrylonitrile nanofibers: Physicochemical parameters of dyeing with basic dye in comparison with regular polyacrylonitrile fibers

Polyacrylonitrile nanofibers were produced using the electrospinning method and dyed with a basic dye alongside regular polyacrylonitrile fibers. In order to investigate the effect of high surface area to volume ratio of nanofibers on their adsorption behavior in comparison with regular fibers, the dyeing conditions for both types of fibers were kept just the same. Physiochemical parameters of dyeing such as adsorption isotherm, standard affinity, enthalpy change, rate of dyeing constant, diffusion coefficient, and activation energy of diffusion were investigated for both types of fibers. The results showed that the adsorption process can be well described with the Langmuir adsorption isotherm for both types of fibers whereas the standard affinity of dye to nanofibers was higher than regular fibers and the higher negative values of enthalpy changes were obtained for regular fibers. The nanofibers rate of dyeing was faster than regular fibers with higher amounts of diffusion coefficients and lower amounts of activation energy of diffusion. This study also revealed that in spite of the approximately same amount of dye exhaustion for both types of fibers, the color strength of regular fibers was noticeably higher than nanofibers.     

Spinnability in pre-gelled gel spinning of polyacrylonitrile precursor fibers

The spinnability in pre-gelled gel spinning of polyacrylonitrile (PAN) precursor fibers was investigated. The spinning solutions were aged at 25 °C for different times prior to fiber spinning. The pre-gelled spinning solution aged for 2.5 h was much more strain hardening than the ungelled one, which can increase the spinnability of the solution. The maximum take-up velocity of the first winding roller V _1m, which reflects the spinnability of the spinning solutions, was found to be largest when the aging time was 1.5 h. The spinnability increased with the increase of the air gap length and the lengthdiameter ratio L/D of the spinnerette. Once the L/D increased beyond 15, the spinnability hardly changed. The fibers spun from the spinning solution aged for 1.5 h had the best mechanical properties and favorable structure, showing that good spinnability favors the performance increase of resultant PAN precursor fibers.     

Effect of concentration on electrospun polyacrylonitrile (PAN) nanofibers

An allometrical scaling relationship between the diameter of electrospun nanofiber and solution concentration is established, the scaling exponent differs greatly between different polymers and the same polymer with different molecules or the same molecules with different properties. The diameter of electrospun polyacrylonitrile (PAN) nanofibers increases approximately linearly with solution concentration.     

Preparation of amidoxime-modified polyacrylonitrile nanofibers immobilized with laccase for dye degradation

A novel approach to preparing multifunctional composite nanofibrous membrane was developed. Polyacrylonitrile (PAN) nanofibrous membrane was fabricated by electrospinning and then the nitrile groups in PAN copolymer was chemically modified to obtain amidoxime modified PAN (AOPAN) nanofiber membrane which was further used as a functional support for laccase immobilization. During the process of reactive dye degradation catalyzed by the AOPAN nanofiber membrane immobilized with laccase, metal ion adsorption occurred at the same time. The chemical modification was confirmed by Fourier transform spectroscopy (FTIR). Scanning electron microscope (SEM) was employed to investigate the surface morphologies of the electrospun nanofibers before and after laccase immobilization. The effects of environmental factors on laccase activity were studied in detail. It was found that the optimum pH and temperature for the activity of immobilized laccase was 3.5 and 50 °C. The relative activity retention of the immobilized laccase decreased dramatically during the initial four repeated uses. After 20 days’ storage, the activity retention of immobilized laccase was still high above 60 %. It has also proved that laccase immobilized on AOPAN nanofiber membrane performed well in dye degradation and metal ion adsorption.     

Effects of ferric chloride on structure, surface morphology and combustion property of electrospun polyacrylonitrile composite nanofibers

In this work, the pure polyacrylonitrile (PAN) nanofibers and PAN/FeCl₃ composite nanofibers were prepared by an electrospinning process. Electrospinning solution properties including viscosity, surface tension and conductivity, had been measured and combined with the results of Scanning electron microscopy (SEM), Atomic force microscope (AFM) and Micro Combustion Calorimeter (MCC) to investigate the effects of FeCl₃ on the structure, surface morphology and combustion property of electrospun PAN nanofibers, respectively. It was found from SEM images that the diameters of composite nanofibers were decreased with the addition of FeCl₃, which was attributed predominantly to the increased conductivity of the polymer solutions compared to viscosity and surface tension. The AFM analyses revealed that the surface morphology of electrospun nanofibers changed from smooth and wrinkle-like structure (without FeCl₃) to rough and ridge-like structure (with FeCl₃). The results characterized by MCC showed that the loading of FeCl₃ decreased the heat release rate (HRR) and improved the combustion property of composite nanofibers.     

Examining the effects of balloon control ring on ring spinning

The ring spinning process has been used to produce fine and high quality staple fibre yarns. The stability of the rotating yarn loop (i.e. balloon) between the yarn-guide and the traveller-ring is crucial to the success and economics of this process. Balloon control rings are used to contain the yarn-loop, by reducing the yarn tension and decreasing the balloon flutter instability. Flutter instability here refers to the uncontrolled changes in a ballooning yarn under dynamic forces, including the air drag. Due to the significant variation in the length and radius of the balloon during the bobbin filling process, the optimal location for the balloon control ring is not easily determined. In order to address this difficulty, this study investigates the variation in the radius of a free balloon and examines the effect of balloon control rings of various diameters at different locations on yarn tension and balloon flutter stability. The results indicate that the maximum radius of a free balloon and its corresponding position depend not only on the yarn-length to balloon-height ratio, but also on yarn type and count. A control ring of suitable radius and position can significantly reduce yarn tension and decrease flutter instability of free single-loop balloons. While the balloon control rings are usually fixed to, and move in sinc with, the ring frame, results reported in this study suggest that theoretically, a balloon control ring that always remains approximately half way between the yarn-guide and the ring rail during spinning can lead to significant reduction in yarn tension.     

Comparison between artificial neural network and response surface methodology in the prediction of the production rate of polyacrylonitrile electrospun nanofibers

This paper focused on using response surface methodology (RSM) and artificial neural network (ANN) to analyze production rate of electrospun nanofibers. The three important electrospinning factors were studied including polymer concentration (wt %), applied voltage (kV) and the nozzle-collector distance (cm). The predicted production rates were in agreement with the experimental results in both ANN and RSM techniques. High regression coefficient between the variables and the response (R ²=0.975) indicates excellent evaluation of experimental data by second-order polynomial regression model. The regression coefficient was 0.988, which indicates that the ANN model was shows good fitting with experimental data. The obtained results indicate that the performance of ANN was better than RSM. It was concluded that applied voltage plays an important role (relative importance of 42.8 %) against production rate of electrospun nanofibers. The RSM model predicted the 2802.3 m/min value of the highest production rate at conditions of 15 wt % polymer concentration, 16 kV of the applied voltage, and 15 cm of nozzle-collector distance. The predicted value showed only 4.4 % difference with experimental results in which 2931.0 m/min at the same setting was observed.     

Mapping the influence of electrospinning parameters on the morphology transition of short and continuous nanofibers

A theoretical model for the morphology transition of short and continuous nanofibers by electrospinning has been proposed. The influences of polymer concentration, applied voltage, and flow rate on the fabrication of short and continuous nanofibers were mapped for use as a reference in the design and construction of the theoretical model. The morphology transition of short and continuous nanofibers occurred mainly due to changes in the flow rate and voltage. According to the concentration of the polymer in the solution, the map of the short nanofiber region was narrowed as the polymer concentration increased. The theoretical model derived from the conservation of kinetic energy and potential energy experienced by the polymer solution resulted in an equation that could be used to calculate the voltage and flow rates under certain boundary conditions when cutting nanofibers. The boundary conditions for voltage were 4.7-4.9 kV, and the boundary conditions for flow rate were 0.1-1.1 µl/min.     

Application of TOPSIS approach on parameters selection problem for rotor spinning machine

Classical statistical analysis has been generally used in obtaining optimum condition such as problems for rotor spinning machine. In these methods the preferences of the producer about yarn characteristics to achieve the desired end product properties have not been taken into consideration. However, machine parameters selection from possible alternatives with different performance levels about yarn quality is difficult task and is inherently a multi-criteria decision making problem. In the present study, valuable assistance in reaching acceptable solutions in order to select the appropriate doffing tube and its adjustment for 30 Ne rotor yarn spun to raise efficiency of weft knitting machine will be provided by technique for order preference by similarity ideal solution (TOPSIS) approach. In experimental part 30 Ne rotor yarn samples were spun by considering one quantitative variable, i.e., two different distances between the nozzle and rotor, and also two qualitative variables, i.e., nozzles in 4 different shapes and a draw-off tube with and without a torque stop. Then quality parameters of the yarns were analyzed with TOPSIS.     

The effects of some machine parameters on the spirality in single jersey fabrics

In this work, the effects of machine parameters on the fabric spirality, which is an important quality problem of single jersey knitted fabrics, are investigated. For this aim, two circular knitting machines with the same gauge, but one of them revolving in the reverse direction, are chosen. Single jersey fabric samples with the same weight per square meter and the same yarn count (Ne 20 Cotton) are knitted on the chosen machines at four different numbers of knitting systems. The effects of the number of the knitting systems and the rotation directions of the machines on the spirality angles are investigated.     

Facile fabrication of carbon nanotubes/polystyrene composite nanofibers for high-performance electromagnetic interference shielding

Polystyrene (PS) composites with nanofibrous structure consisting of multi-walled carbon nanotubes (MWCNTs) with 0-10 wt.% of nanofiller have been fabricated via electrospinning technique. The surface morphology and thermal properties of the composites were evaluated by scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA). The SEM analysis of the composite nanofibers samples revealed that the average diameter of the nanofibers increases with increasing MWCNTs content. The resultant MWCNTs/PS composite nanofibers diameters were in the range of 391±63 to 586±132 nm. The thermal stability of composites was increased after addition of MWCNTs to PS matrix. The electrical conductivity of the composites with different weight percentage of MWCNTs was investigated at room temperature. Electrical conductivity of MWCNTs/PS composite nanofiber followed percolation theory having a percolation threshold V _c= 0.45 vol% (~0.75 wt. %) and critical exponent q=1.21. The electrical conductivity and thermal properties confirmed the presence of good dispersion and alignment MWCNTs encapsulated within the electrospun nanofibers. The electromagnetic interference (EMI) shielding effectiveness of the MWCNTs/PS composites was examined in the measurement frequency range of 8.2-12.4 GHz (X-band). The total EMI shielding efficiency of MWCNTs/PS composite nanofibers increased up to 32 dB. The EMI shielding results for MWCNTs/PS composite nanofibers showed that absorption loss was the major shielding mechanism and reflection was the secondary mechanism. The present study has shown the possibility of utilizing MWCNTs/PS composite nanofibers as EMI shielding/absorption materials.     

Optimisation of spinning parameters for processing of 100% sunnhemp fibers

This study was an attempt to spin 100% sunnhemp fibers, grown in Akola district of Maharashtra, India, on Jute spinning system. The sunnhemp fibers were first sprayed with oil and then softened. These fibers were then processed through various machine sequence by varying the number of carding and drawing machines. The yarn was spun in each case and tested for Count Strength Product and Evenness. This yarn was then used as a weft yarn to weave a 3/1-drill fabric with a cotton warp and tested for tensile strength. It was concluded that the set III with three carding and three drawing sequence gave an even yarn. The optimum twist per inch in the yarn was found to be 6.0.     

The effects of altered ultrasound parameters on the recovery of sciatic nerve injury

Background: Initial studies have shown that low-energy ultrasound stimulates living tissue cells to reduce regeneration or speed up their recovery. The purpose of this study was to examine the effects of various ultrasound parameters on the speed of recovery in injured sciatic nerves NMRI.Methods: NMRI mice (n = 200) with injured left paw, caused by crushing their sciatic nerves, were randomly selected. The animals were exposed to ultrasound radiation with various frequencies, intensities, and exposure time. They were allocated into 20 groups (19 treatment and 1 control groups). Sciatic functional index (SFI) test was used to evaluate the difference between the groups with respect to functional efficiency of the sciatic nerve and its recovery. SFI ، (P=0.000).Results: The results of SFI test obtained from the 14^th day showed a significant difference among the groups (P<0.05). On the 14^th day after treatment, one of the groups (US11) recovered up to 90%..Conclusion: Altered ultrasound exposure parameters had more favorable outcomes compared with our previous work.Key Words: Sciatic nerve, Ultrasonic therapy, Regeneration     

The effect of spinning parameters on mechanical and physical properties of core-spun yarns produced by the three-strand modified method (TSMM)

The effect of spinning parameters on core-spun yarns properties manufactured using three-strand modified method (TSMM) was analyzed. Of the various spinning parameters, strand spacing, yarn linear density and yarn twist have a crucial effect on core-spun yarn properties. To achieve the objectives of this research, general physical properties of core-spun yarns together with existing standards were thoroughly studied. First of all, the strand spacing and yarn linear density were optimized. Afterwards, the effects of variation of yarn twist and sheath roving linear density on core-spun yarns properties were investigated. Finally, the physical and mechanical properties of TSMM yarns were compared with those of siro and conventional ring core-spun yarns counterparts. It was found that, the best strand spacing and yarn linear density to produce core-spun yarns are 8 mm and 45 tex, respectively. Results showed that, tenacity of TSMM yarns increases up to a certain twist level beyond which it reduces. The result confirmed that 45 tex yarns produced by three rovings of the same count are superior with regards to tenacity and hairiness. The optimized yarns produced by three-strand modified method enjoy superior physical and mechanical properties in comparison to the ring and siro core-spun yarns.     

The effect of salt on the roller electrospinning of polyurethane nanofibers

In this study, we investigated the effect of tetraethylammoniumbromide (TEAB) salt on the spinnability of polyurethane nanofibers via roller electrospinning method. At first, solution properties, spinnability and fiber properties were determined and then all the results were analyzed. According to the results, TEAB salt concentration has an important effect on the conductivity, viscosity, spinning performance, fiber diameter and morphology. It was found that all these parameters increased with salt concentration. Also it was indicated that viscosity decreased with shear rate. Polyurethane including 1.82 wt % TEAB gives the best spinning performance although 0.87 wt % TEAB is the optimum value related to fiber properties such as diameter, uniformity and morphology given the ideal polyurethane nano web structure.     

Investigation of inter fiber cohesion in yarns. I. Influence of certain spinning parameters on the cohesion in cotton yarns

This paper investigates the influence of raw material and process parameters in spinning that affect the inter fiber cohesion in yarns. An instrument has been developed for measuring the minimum twist of cohesion. With regard to the raw material parameters, the influence of different cotton fiber mixings for a given count of yarn is investigated. Also the effect of spinning to varying counts for a given cotton variety is studied. With regard to the process parameters, studies have been carried out to investigate the influence of noil extraction in comber, number of draw frame passages, draft pressure in ring frame and direction of twist. Cohesion improved with increase in the noil extraction percentage in the comber. Increase in the number of draw frame passages also improved the cohesion. Draft pressure in ring frame improved the fiber cohesion in yarn up to a pressure of 2.1 kg/cm². Direction of twist had no effect on the cohesion.     

Study on Spinning triangles in the common ring spinning and Super draft ring spinning systems

In the paper, one kind of super draft ring spinning frame with four drafting rollers and corresponding three drafting zones were introduced. The yarn qualities spun by the super draft ring spinning frame were analyzed by studying the shape of spinning triangles. Using the high speed camera system OLYMPUS i-speed3 and one kind of transparent front top roller, the spinning triangles were captured, and the geometry size of spinning triangle were measured. Then, according to the theoretical model of fiber tension in the spinning triangle, fiber tension distributions in the spinning triangles were presented by using Matlab software. Using the combed roving of 350 tex as raw material, three kinds of cotton yarns, 27.8 tex (21^S), 18.2 tex (32^S) and 14.6 tex (40^S), were spun in the common ring spinning frame with three different suitable spindle speeds, travelers and twist factors. Using the combed roving of 350 tex and 500 tex as raw material, 14.6 tex cotton yarns were spun in the super draft ring spinning frame with three different drafting ratios at back zone. It is shown that with the increasing of spindle speed, a more asymmetric shape of spinning triangle would be produced, and lead to worsen yarn evenness. With the decreasing of traveler weight, the height and horizontal deviation of the spinning triangle is decreased, and may lead to better yarn evenness and less long hairiness. By taking suitable large yarn twist factors, the comprehensive qualities can be improved. Comparing with the common ring spinning, the spinning triangle is larger in the super draft ring spinning. That is, in the super draft ring spinning, the fibers in the strand in the front roller nip are more dispersed, and not benefit for yarn qualities. Therefore, the compact device was introduced into the super draft ring spinning, and the cotton pure yarns and blend yarns were spun, and the yarn qualities were measured and analyzed.     

Evaluation of effective electrospinning parameters controlling gelatin nanofibers diameter via modelling artificial neural networks

The aim of this work was to evaluate the effective parameters for prediction of the electrospun gelatin nanofibers diameter using artificial neural network (ANN) technique. The various sets of electrospinning process including temperature, applied voltage and polymer and solvent concentrations were designed to produce pure gelatin nanofibers. The obtained results by analyzing Scanning Electron Microscopy (SEM) images indicated that the produced nanofibers diameter was in the range of 85 to 750 nm. Due to the volume of the data, k fold cross-validation method was used for data setting. Data were divided into the five categories and trained and tested using ANN technique. The results indicated that the network including 4 input variables, 3 hidden layers with 10, 18 and 9 nodes in each layers, respectively, and one output layer had the best performance in the testing sets. The mean squared error (MSE) and linear regression (R) between observed and predicted nanofibers diameter were 0.1531 and 0.9424, respectively. The obtained results demonstrated that the selected neural network model had acceptable performance for evaluating involved parameters and prediction of nanofibers diameter.     

Evaluating applicability of VIKOR method of multi-criteria decision making for parameters selection problem in rotor spinning

Optimum spinning machine parameters selection among available alternatives with different significances is a difficult task in textile industry. To overcome disadvantages associated with statistical methods that are used in such kind of problems, multi-criteria decision making approaches (MCDM) were employed by researchers. TOPSIS, AHP-TOPSIS and ELECTRE are three popular techniques in spinning problems. VIKOR, the Serbian name; Vlse Kriterijumska Optimizacija I Kompromisno Resenje, means multi-criteria optimization and compromise solution is a novel approach that has priority over other MCDM methods in terms of precision in final ranking. In this study, selecting the appropriate doffing tube components and its adjustment for 30Ne rotor spun yarn that is intended to be used for weft-knitted fabric will be provided by this approach. Yarn samples were spun considering three variables namely, the distance between the nozzle and rotor, the extractive nozzle and the draw-off tube. Feasible alternatives were ranked on the basis of the yarn quality parameters by the VIKOR and the best alternative for increasing weft-knitting machine efficiency was introduced. According to the final ranking, the spinning condition in which the sample was spun using a spiral nozzle, a doffing tube without a torque stop and a closer setting had the highest performance.     

The role of thermal stabilization on the structure and mechanical properties of polyacrylonitrile precursor fibers

The thermal stabilization stage of polyacrylonitrile (PAN) fibers is characterized by a steady and continuous reduction in fiber diameter and linear density values together with color changes from reddish brown to shiny black with increasing stabilization time. Thermally stabilized PAN fibers acquire infusible and nonburning characteristics prior to the carbonization stage. Structural characterization of thermally stabilized polyacrylonitrile fibers was carried out using an indepth analysis of equatorial X-ray diffraction traces. Curve fitting of X-ray diffraction traces provided accurate peak parameters which were subsequently used for the evaluation of apparent crystallinity, apparent crystallite size and X-ray stabilization index. The results showed the loss of crystallinity due to the amorphization processes together with a steady and continuous decrease in lateral crystallite size with increasing stabilization time. With the progress of thermal stabilization, a new amorphous phase with a crosslinked and aromatized structure is formed which is expected to withstand high carbonization temperatures. Mechanical properties of the thermally stabilized PAN precursor fibers were found to be adversely affected with the progress of stabilization time. Due to the influence of thermal degradation mechanisms heavily involving chain scission along the fiber axis direction, tensile strength and tensile modulus values were found to decrease by significant proportions with the prolonged stabilization times.