Studies on the electrospun Nylon 6 nanofibers from polyelectrolyte solutions: 1. Effects of solution concentration and temperature

Polyelectrolyte solutions of Nylon 6 in 99 vol% formic acid were electrospun, and the effect of polymer concentration was studied. Using a laser device to locally heat the needle spinneret, the solution temperature was feasibly elevated up to 66 °C, and its effect on electrospinning was investigated as well. The microstructure of the as-spun products was characterized by several analytical techniques, including electron diffraction, differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. Based on the solution rheology, the entanglement concentration (c_e) was determined to be 1 wt%. To prepare bead-free fibers, the minimum polymer concentration was 8 c_e, which was much higher than that (1.75-2.0 c_e) required for conventional neutral solutions. Increasing the polymer concentration and/or solution temperature led to a gradual change of electrospun products from round fibers with major γ form crystals to ribbon-like fibers in possession of exclusive α form ones. For intermediate concentrations, nanowebs made of nanofibrils with diameters of 20-40 nm were seen. Thin ribbon-like fibers (ca. 40 nm thick) with nanowebs became the dominant products obtained from the 15 wt% solutions at high temperatures. The dramatic variations in morphological features and crystal modification could be thoroughly explained on the basis of the interplay between solvent evaporation at the jet surface and solvent diffusion in the liquid jet. DSC heating traces on the ribbon-like fibers exhibited an unusually high melting temperature of ∼235 °C, which is higher than the equilibrium melting temperature of Nylon 6 crystals of 232 °C.     

Morphology and mechanical properties of Nylon 6/MWNT nanofibers

Aligned nanofibrous nanocomposites of Nylon 6 and surface-modified multiwalled carbon nanotubes (MWNTs) were successfully synthesized via electrospinning, using a rotating mandrel. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM) and dynamic mechanical analysis (DMA) were done to characterize the morphology and properties of the nanofibrous mats. DSC and XRD observations suggested the presence of MWNTs and the high speed take-up facilitated the transformation of Nylon 6 from γ phase crystals to a mixture of α and γ phase crystals. TEM and WAXD were used to characterize the nanotube and molecular orientations, respectively. The storage modulus of the fibers increased significantly although the concentration of MWNTs was relatively low (0.1 and 1.0 wt%). Thus the combination of carbon nanotubes and nanoscale processing results in structural and mechanical enhancements of Nylon 6.     

Fabrication of electronspun porous CeO2 nanofibers with large surface area for pollutants removal

The porous CeO₂ nanofibers with diameter of 100–140 nm were successfully synthesized by single-capillary electrospinning of a Ce(NO₃)₃·6H₂O/PVP precursor solution, followed by calcination. The preparation parameters, including solution parameters and process parameters, affecting the spinnability and the morphology of nanofibers were investigated and discussed systematically. And the effects of different calcination temperatures on the microstructure CeO₂ nanofibers were also studied. A plausible mechanism was proposed to explain the formation process of the CeO₂ nanofibers. The N₂ adsorption-desorption isotherm analysis showed that the specific surface area and average pore size of the nanofibers were 195.75 g/m² and 2.4 nm, respectively. Moreover, as absorbent, the porous CeO₂ nanofibers adsorbed the MO effectively. The adsorption experiment indicated that the adsorption process can be divided into two stages, including quick adsorption and gradual adsorption. And the adsorption capacities were not only determined by the specific surface area, but closely related to the pore size. Finally, the adsorption data were modeled by the pseudo-first-order and pseudo-second-order kinetics equations. The results showed that the pseudo-second order kinetics could best describe the adsorption of MO onto the porous CeO₂ nanofibers.     

Adsorption behavior of cationic dyes on citric acid esterifying wheat straw: kinetic and thermodynamic profile

The kinetic and thermodynamic behaviors of cationic dye adsorption onto citric acid esterifying wheat straw (EWS) from aqueous solution were investigated. Two cationic dyes, methylene blue (MB) and crystal violet (CV) were selected as adsorbates. The kinetic and thermodynamic parameters of dye adsorption were examined with a batch system by changing various experimental factors (e.g. initial pH, EWS dosage, dye concentration, contact time, temperature). The MB and CV removal ratios came up to the maximum value beyond pH 4. The 2.0 g/L or up of EWS could almost completely remove MB and CV from 250 mg/L of dye solution. The adsorption percentages of MB and CV kept above 95% over a range from 50 to 350 mg/L of dye concentration when 2.0 g/L of EWS was used. The isothermal data followed the Langmuir model. The adsorption processes could be described by the pseudosecond-order kinetic model. The dual linear plots of intraparticle diffusion indicated that two intraparticle diffusion steps occurred in the dye adsorption processes. The thermodynamic study indicated that the adsorptions of dyes were spontaneous and endothermic. High temperatures favored the adsorption processes.     

静电纺丝纳米纤维的工艺原理、现状及应用前景

本文从静电纺丝的基本原理出发，分析了其影响因素。并对静电纺丝的国内外研究状况、应用领域及发展趋势做了全面的介绍。     

Effect of solvent evaporation rate on the crystalline state of electrospun Nylon 6

The role of solvent evaporation on the crystalline state of electrospun Nylon 6 fibers was examined by electrospinning into a closed chamber filled with different concentrations of solvent vapor. It was found that the thermodynamically stable α form became increasingly dominant in Nylon 6 fibers electrospun out of both 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and formic acid as the vapor phase solvent concentration increased. It is believed that the formation of the metastable γ form is due in part to the fast solvent evaporation kinetics associated with the electrospinning process. By varying the vapor phase concentration and thus the rate of solvent evaporation during electrospinning, we were able to vary the resulting crystal structure of the electrospun Nylon 6, as shown by XRD, Raman and FTIR.     

Sawdust: A green and economical sorbent for thallium removal

Removal/preconcentration of thallium(I) ions from aqueous solution by sawdust; a waste material derived from the commercial processing of Cedrus Deodar wood for furniture production was investigated. A simple and low-cost modification results in increasing the sorption capacity of raw sawdust from 2.71 to 13.18 mg g⁻¹. Sorption was found to be rapid (98% within 8 min). The binding of metal ions was found to be pH dependent, optimal sorption accruing at around pH 6–9. Potentiometeric titrations of sawdust revealed two distinct pK_a values, the first having the value similar to carboxylic groups (3.3–4.8) and second comparable with that of amines (8.53–10.2) with the surface site densities of 1.99 × 10⁻⁴ and 7.94 × 10⁻⁵ mol g⁻¹, respectively. Retained Tl(I) ions were eluted with 5 ml 0.1 mol l⁻¹ HCl. Detection limit of 0.0125 μg ml⁻¹ was achieved with an enrichment factor of 160. Recovery was quantitative using sample volume of 800 ml. The Langmuir, Freundlich and D–R isotherm equations were used to describe partitioning behavior for the system at different temperatures. Kinetic and thermodynamic behavior of sawdust for Tl(I) ions removal was also studied.     

Preparation and characterization of electrospun ultrafine polyamide‐6 nanofibers

We report on the preparation and characterization of ultrafine polyamide‐6 nanofibers by the electrospinning technique. The effect of electrospinning on the formation of ultrafine polyamide‐6 nanofiber structure was examined. The morphological and structural characterizations and thermal properties of the ultrafine polyamide‐6 nanofibers were investigated in comparison with bulk polyamide‐6 pellets. In order to accurately characterize the ultrafine polyamide‐6 nanofiber structure by direct identification of mass resolved components, we performed matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) mass spectrometry. Field emission scanning electron microscopy images revealed the presence of ultrafine polyamide‐6 nanofibers bound between the main fibers. The diameter of the polyamide‐6 nanofibers was observed to be in the range 75–110 nm, whereas the ultrafine structures consisted of regularly distributed very fine nanofibers with diameters of about 9–28 nm. The MALDI‐TOF spectra showed the presence of protonated and sodiated ions that were assigned to polyamide‐6 chains. Copyright © 2011 Society of Chemical Industry     

Structural studies of electrospun nylon 6 fibers from solution and melt

Nylon 6 (N6) fibers have been fabricated via two different electrospinning schemes, from solution of N6 and formic acid at room temperature as well as from N6 melt at elevated temperature. The crystal structures of electrospun N6 fibers from solution and melt, and the annealing effect on the structures were studied by using various techniques. Combined analysis of the differential scanning calorimetry (DSC) at various heating rates, temperature-dependent X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy indicates that N6 fibers from melt predominantly exhibit the meta-stable γ-crystalline forms and low molecular orientation, while solution electrospun fibers from slowly evaporating solvent show both α- and γ-form crystals and higher degree of molecular orientation. At high annealing temperature, the meta-stable γ-crystals in melt electrospun fibers easily transform into thermodynamically stable α-form crystals, while crystals in solution electrospun fibers exhibit higher thermal stability. Nonisothermal modeling and in-situ measurements of jet temperature indicate that rapid quenching due to enhanced heat transfer by electrohydrodynamically driven air flow near the jet is responsible for the less stable γ-crystals and lower degree of molecular orientation in melt electrospun fibers.     

Kinetic and thermodynamic studies of adsorption of Cu2+ and Pb2+ onto amidoximated bacterial cellulose

Removal of Cu²⁺ and Pb²⁺ from aqueous solutions by adsorption onto amidoximated bacterial cellulose (Am-BC) was investigated. The effects of pH, initial concentration, contact time and temperature were studied in batch experiments. The pseudo-first and pseudo-second orders and intraparticle diffusion equation were used to evaluate the kinetic data and the constants were determined. The experimental data fits well to the pseudo-second order kinetic model, which indicates that the chemical adsorption is the rate-determining step, instead of mass transfer. The equilibrium adsorption data were described by the Langmuir, Freundlich, and Temkin isotherms. The Am-BC showed a better fit to the Langmuir isotherm. The separation factor (R _L ) revealed the favorable nature of the isotherm. The thermodynamic parameters (ΔH _ads⁰, ΔS _ads⁰, ΔG _ads⁰) for Cu²⁺ and Pb²⁺ adsorption onto Am-BC were also determined from the temperature dependence. The values of enthalpy and entropy indicated that this process was spontaneous and exothermic. The experimental studies indicate that Am-BC would be a potential effective adsorbent to remove the metal ions from wastewater.     

改性尼龙6纤维的制备与性能研究

采用MAH-g-PE与增塑剂邻苯二甲酸二辛酯(DOP)对尼龙6进行改性制得了改性尼龙6纤维(MPA),研究了MAH-g-PE和DOP用量对MPA流变性能、热性能、热延伸及比强力性能的影响.结果表明:MPA样品流动性随着DOP含量的增加而增强,说明增塑剂对于尼龙6的增塑效果比较明显.DSC分析表明,MAH-g-PE的加入...     

Fly ash as a sorbent for boron removal from aqueous solutions: Equilibrium and thermodynamic studies

ABSTRACT

This study presents the application of fly ash from brown coal and biomass burning power plant as a sorbent for the removal of boron ions from an aqueous solution. The adsorption process efficiency depended on the parameters, such as adsorbent dosage, pH, temperature, agitation time and initial boron concentration. The experimental data fitted well with the Freundlich isotherm model and the maximum capacity was found to be 16.14 mg g^?1. The adsorption kinetics followed the pseudo-second-order model. Also, the intra-particle diffusion model parameters were calculated. Thermodynamic parameters such as change in free energy (ΔG°), enthalpy (ΔH°), entropy (ΔS°) revealed on exothermic nature of boron adsorption onto the fly ash.     

A novel agricultural waste based adsorbent for the removal of Pb(II) from aqueous solution: Kinetics,equilibrium and thermodynamic studies

Fig sawdust was used as a precursor for the production of activated carbon by chemical activation with H₃PO₄. The developed Fig sawdust activated carbon (FSAC) was used as a biosorbent for the removal of Pb(II) from aqueous solution. Highest adsorption of Pb(II) (95.8%) was found at pH 4. Equilibrium data fitted very well with the Langmuir isotherm model. Maximum adsorption capacity was determined 80.645 mg g⁻¹ at pH 4. Kinetic studies demonstrated that the adsorption followed a pseudo second order kinetics model. The negative value of ΔG° confirmed the feasibility and spontaneity of FSAC for Pb(II) adsorption.     

Morphology of electrospun nylon‐6 nanofibers as a function of molecular weight and processing parameters

In the present study, the morphology and mechanical properties of nylon‐6 nanofibers were investigated as a function of molecular weight (30,000, 50,000, and 63,000 g/mol) and electrospinning process conditions (solution concentration, voltage, tip‐to‐collector distance, and flow rate). Scanning electron micrographs (SEM) of nylon‐6 nanofibers showed that the diameter of the electrospun fiber increased with increasing molecular weight and solution concentration. An increase in molecular weight increases the density of chain entanglements (in solution) at the same polymer concentration; hence, the minimum concentration to produce nanofibers was lower for the highest molecular weight nylon‐6. The morphology of electrospun fibers also depended on tip‐to‐collector distance and applied voltage concentration of polymer solution as observed from the SEM images. Trends in fiber diameter and diameter distribution are discussed for each processing variable. Mechanical properties of electrospun nonwoven mats showed an increase in tensile strength and modulus as a function of increasing molecular weight. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Non‐ionic surfactants for enhancing electrospinability and for the preparation of electrospun nanofibers

BACKGROUND: Electrospinning is widely used to produce nanofibers; however, not every polymer can be electrospun into nanofibers. To enhance electrospinability, much effort has been made in designing new apparatus, such as vibration‐electrospinning, magneto‐electrospinning and bubble‐electrospinning. RESULTS: A representative non‐ionic surfactant, TritonR X‐100, is used to enhance electrospinability. The surfactant is added to an electrospun poly(vinyl pyrrolidone) polymer solution, and a dramatic reduction in surface tension is observed. As a result, a moderate voltage is needed to produce fine nanofibers, which are commonly observed during the conventional electrospinning procedure only at elevated voltage. CONCLUSION: The novel strategy produces smaller nanofibers than those obtained without surfactants, and the minimum threshold voltage is much decreased. Copyright © 2008 Society of Chemical Industry     

Chitin as biosorbent for phenol removal from aqueous solution: Equilibrium,kinetic and thermodynamic studies

Phenol removal from aqueous solution was studied employing chitin as low cost biosorbent. Initial biosorption tests carried out in the pH range 2–10 pointed out an optimum pH of 2. Temperature and initial phenol concentration were then varied in the ranges 15 ≤ T ≤ 50 °C and 10.4 ≤ C₀ ≤ 90.8 mg L⁻¹, respectively. The good applicability of Langmuir, Freundlich and Temkin models (R² = 0.990–0.993) to describe equilibrium isotherms suggested an intermediate mono-/multilayer biosorption mechanism along with a semi-homogeneous architecture of biosorbent surface. Biosorption capacity progressively increased from 3.56 to 12.7 mg g⁻¹ when starting phenol concentration was raised from 10.4 to 90.8 mg L⁻¹, and the related sorption kinetics was investigated by pseudo first-order, pseudo second-order and intraparticle diffusion models. The pseudo second-order model, which showed the best fit of experimental data (R² = 0.999), allowed estimating a second-order rate constant of 0.151 g mg⁻¹ h⁻¹ and a theoretical sorption capacity of 7.63 mg g⁻¹. Phenol biosorption capacity increased with temperature up to a maximum value, beyond which it decreased, suggesting the occurrence of a thermoinactivation equilibrium. Finally, to identify the main functional groups involved in phenol biosorption, both raw and phenol-bound materials were explored by FT-IR spectroscopy.     

Analysis of equilibrium,kinetic, and thermodynamic parameters for biosorption of fluoride from water onto coconut (Cocos nucifera Linn.) root developed adsorbent

Drinking water with higher fluoride levels results in serious irremediable health problems that have attained a startle all over the world.Researches focused towards deflouridation through the application of biosorbents prepared from various plants are finding greater scope and significance.Present research is done on Cocos nucifera Linn.(coconut tree) one of the very commonly available plants throughout Kerala and around the globe.An adsorbent developed from the root portion of C.nucifera Linn.is used in the present study.Equilibrium study revealed that the fluoride uptake capacity is quite significant and linearly increases with initial adsorbate concentration.The adsorption data is analyzed for Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models at varying initial adsorbate concentrations(2–25 mg·L~(-1)).It is found that the adsorption of fluoride onto C.nucifera Linn.root adsorbent follows Langmuir isotherm.Langmuir isotherm constants "a" and "b" obtained are 2.037 mg·g~(-1) and 0.823 L·mg~(-1) at an adsorbent dose of 8 g·L~(-1) and temperature(26 ± 1) ℃.The mean free sorption energy, E obtained, is 9.13 kJ ·mol~(-1) which points out that the adsorption of fluoride onto C.nucifera Linn.root adsorbent is by chemisorption mechanism.The kinetic study also supports chemisorption with adsorption data fitting well with a pseudo-second-order kinetic model with an estimated rate constant K_2 of 0.2935 g·mg~(-1) min at an equilibrium contact time of 90 min.The thermodynamic study indicated the spontaneous and endothermic nature(ΔH =12.728 kJ·mol~(-1)) of fluoride adsorption onto the C.nucifera Linn.root adsorbent.Scanning Electron Microscopy(SEM), BET, FTIR, and EDX methods were used to analyze the surface morphology of adsorbent before and after fluoride adsorption process.Experiments on deflouridation using C.nucifera Linn.root adsorbent application on fluoride contaminated ground water samples from fields showed encouraging results.     

Assessment of the biosorption kinetic and thermodynamic for the removal of safranin dye from aqueous solutions using calcined mussel shells

Calcined mussel shells have been used as new low cost and eco-friendly biosorbent for the removal of safranin as cationic dye from aqueous solutions by biosorption technique. Batch mode experiments were conducted using various parameters such as pH, contact time, biosorbent amount and safranin concentration. Removal efficiency of safranin by the calcined mussel shells attained 87.56% using 200 mg of biosorbent and 150 mg/L as safranin concentration and for a pH above 9.2. Four kinetic models are used, pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion for the design and the optimization treatment. The kinetic analysis showed that the pseudo-second-order model had the best fit to the experimental data. Biosorption isotherms were also investigated using Langmuir, Freundlich and Temkin models. The experimental data fitted very well with both Langmuir and Freundlich isotherm models. Thermodynamic biosorption processes were found to be spontaneous, endothermic. The Gibbs energy ΔG° decreased from −1.956 kJ/mol to −2.456 kJ/mol with increase in temperature from 298 K to 313 K indicating a increase in feasibility of biosorption at higher temperature. Accordingly, calcined mussel shells were shown to be a very efficient, eco-friendly and low cost biosorbent and a promising alternative for removal dyes from aqueous solutions.     

Polyamide-baghouse dust nanocomposite for removal of methylene blue and metals: Characterization,kinetic, thermodynamic and regeneration

In this research, polyamide modified baghouse dust nanocomposite (PMBHD) was synthesized from steel industry waste using the interfacial polymerization technique. Adsorption capacities of the PMBHD were examined for the uptake of cadmium Cd (II), lead Pb (II), and methylene blue MB from simulated solutions. The effects of different operational factors of the adsorption, including contact time, pH, adsorbent dosage, initial concentration, and temperature, were investigated. The obtained results revealed that the equilibrium data of MB, Pb (II), and Cd (II) were best fitted to Dubinin-Radushkevich, Langmuir, and Freundlich isotherm. Maximum removal uptake was found to be 6.08, 119, and 234 mg·g^-1, whereas maximum removal efficiencies of 90%, 99.8%, and 98% were achieved for MB, Pb (II), and Cd (II). Adsorption kinetics of MB and metals well-fitted to the pseudo-second-order kinetic. The characterization results showed the presence of polymeric chain on the surface of the PMBHD. The thermodynamic study revealed that the values of the free energy ΔG for Pb (II) and Cd (II) were found to be negative, which indicates spontaneous, energetic, and favorable adsorption. While for MB removal, positive values of (ΔG) were noticed, which implies that the adsorption was unfavorable. The proposed mechanism for the adsorption of MB and metals on the PMBHD showed that the dominating mechanism is physisorption. The adsorption/desorption results verified the high reusability of the PMBHD for adsorption of MB and metals.     

锦纶6切片萃取后产生白点的原因及预防

在锦纶6切片生产过程中,有时会发现萃取后的切片在伍德灯下产生反射白点,这种白点切片的可纺性较差。通过相关的跟踪实验和统计分析,确定了白点是水溶性己内酰胺单体和低分子物,同时找到了产生这种白点切片的根本原因,给聚合装置提供了预防措施。