Color removal from dye wastewaters by adsorption using powdered activated carbon: Mass transfer studies

Color removal from synthetic dye wastewater which typically emanates from the Taiwan textile industry has been studied using powdered activated carbon (PAC) as an adsorbent. The CIE colorimetric system has been used in the measurement of color for the treatment of disperse-red-60 dye wastewater. The effect of contact time, dye concentrations and PAC dosage on color and color removal has been investigated. A film-pore double resistance diffusion model for mass transfer has also been used in this study to determine the effective diffusivity, D_eff, for the adsorption of disperse-red-60 dye wastewater to PAC.     

A significant approach to dye cotton in supercritical carbon dioxide with fluorotriazine reactive dyes

A series of fluorotriazine reactive dyes have been synthesized and applied to dye cotton in supercritical carbon dioxide (scCO₂) with good dyeing results. The pieces of cotton to be dyed were previously presoaked in a protic solvent and cosolvents were applied during dyeing. The colour strength of the dyeings was evaluated by K/S measurements. The K/S values achieved on cotton dyed were up to 35.8 ± 4.2. Even after the cotton was subjected to a Shoxlet extraction at 358 K for 1 h, a maximum K/S value of 20.2 ± 1.8 was measured. The percentage of dye molecules chemically fixed to the cotton was on average 85%. The excellent reactivity of fluorotriazines allowed a reduction of 3 h on the dyeing time. It is noticeable that a dye concentration of 10% on weight of the fibre (owf) can be applied to dye cotton with fluorotriazines, since no damage of the cotton fibres occurred, as observed for the chlorotriazines at this high dye concentration.Dyes with fluorotriazine as reactive group were found to be the most preferable dyes for dyeing cotton in scCO₂, as they were able to exceed the limitation of the reaction with the cotton.     

Influence of ultrasound on Avaram bark (Cassia auriculata) tannin extraction and tanning

Efficient processing methodologies such as ultrasounds which would achieve significant enhancements in processes thereby minimizing sectional stream wastes in one hand and bring about economic benefits on other are necessary. Hence, research studies on application of ultrasound in process industries such as leather, textiles and chemicals are gaining importance. In this regard, a case study has been presented in this paper for solid–liquid tanning extraction and tanning from a plant material. For this purpose, Avaram bark (Cassia auriculata) which contains ingredients such as polyphenolics, useful in stabilization of collagen, which is the main constituent of skins/hides. Avaram bark tannin come under the group of ‘condensed tannins’ useful in main tanning process of leather making. The influence of various process parameters such as ultrasonic power, time and agitation on extraction has been studied. The results show significant 1.6-fold improvement for total extract due to the use of ultrasound, 100 W as compared to magnetic stirring control process, suggesting better mass transfer enhancement in leaching of strongly bound tannins from avaram bark due to ultrasound. Efficacy of tannin extract (10% or 20% offer) has been analyzed through application in tanning process and found to be useful. There has been significant improvement in rate of tannin uptake for ultrasonic extract as compared to control extract by the bovine pelt, suggesting diffusion enhancement of tanning agent through the pelt matrix. Use of ultrasound in avaram extract tanning has also been studied and found to be useful. Therefore, the present study clearly indicates the use of ultrasound in Avaram bark tannin extraction and tanning as a viable option with added advantages even dispensing with external heating.     

Oxygen diffusion into polystyrene–bentonite films

A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene–clay composite films. The composite films were prepared from the mixture of surfactant-free pyrene (P)-labeled polystyrene latexes (PS) and modified bentonite (MNaLB) at various compositions at room temperature. These films were annealed at 200 °C above the glass transition (T_g) temperature of polystyrene for 10 min. Oxygen diffusion into the films was monitored with steady state fluorescence (SSF) measurements. Measurements were performed at room temperature for different film compositions (0, 5, 10, 20, 30, 50 and 60 mass% modified bentonite) films to evaluate the effect of MNaLB content on oxygen diffusion. The diffusion coefficient, D of oxygen was determined by the fluorescence quenching method by assuming Fickian transport and increased from 7.4 × 10^− 10 to 26.9 × 10^− 10 cm² s^− 1 with increasing MNaLB content. This increase in D value was explained by formation of microvoids in the film. These voids are large enough to contribute to the penetration of oxygen molecules through the films. The montmorillonite content did not affect the quenching rate constant, k_q and mutual diffusion coefficient, D_m values.     

Relationship between segmental dynamics and tracer diffusion of low mass compounds in polyacrylates

We studied the relationship between segmental dynamics of matrix polymers and tracer diffusion of low mass compounds by the use of forced Rayleigh scattering and dielectric spectroscopy. Specifically poly(methyl acrylate), poly(ethyl acrylate) and poly(n-butyl acrylate) were used as the polymer matrices and six azobenzene derivatives with various substituents as the diffusant. The temperature dependence of the tracer diffusion coefficient D was measured on methylyellow (MY)/polyacrylate blends at the MY concentration of 1 wt%. The results indicate that the temperature dependence of D is weaker than the dielectric loss maximum frequencies f_m for the α processes of the matrices. The effect of volume of the dye molecules on D was also investigated at 305 K. Comparison of the tracer diffusion coefficients among various dye/polymer systems indicates that log D in the same matrix decreases linearly with the molar volume of the dyes.     

Criteria for the affinity of dyes for fibres

An equation was obtained for evaluating the thermodynamic affinity of a disperse dye for a fibre. Quantities Δh _D and K _D , which are functions of the composition of the dye bath, temperature, and state of the fibre material, can characterize the change in the affinity of the dye for the fibre when the dyeing conditions are varied.     

High-temperature mechanical behavior of Al2O3/graphite composites

Uniaxial compressive creep behaviour of spark-plasma-sintered Al₂O₃/graphite particulate composites has been studied at temperature between 1250 and 1350 °C. Values of stress exponent, n, ranging from 1 to 1.4 and, activation energy, Q, of 600 ± 40 kJ/mol have been determined. With 10 vol% graphite in the composite, the creep deformation of the composite is controlled by the fine-grained Al₂O₃ matrix, where Coble creep has been identified as the dominant creep mechanism.     

Variations in diffusion coefficient of disperse dyes in single PET fibres: monitored and interpreted by confocal laser scanning microscopy

A novel method is proposed for determining the diffusion coefficient (D) of disperse dyes in PET fibres. Concentration-distance profiles are recorded on optical sections of single fibres by confocal laser scanning microscopy. This allows for an accurate value of the true diffusion coefficient in the fibres as well as for a founded insight in the dye diffusion process and its interrelation with the glass transition, which is not possible by the commonly used methods. At 130 °C, the common industrial dyeing temperature, the diffusion coefficient showed to be constant for the dyes tested, with D being about five times larger for the anthraquinone dye than for the benzodifuranone dye. At 100-110 °C, near to the start of the glass transition region of the fibres, D could no longer be regarded as a constant for the anthraquinone dye but was concentration dependent. This was explained by the plasticising effect of the anthraquinone dye.     

Diffusion of dyes in polyester fibers. II. Diffusion coefficients from the radial distribution curves

The computational method of a concentration-dependent diffusion coefficient D(C) of dyes in fibers has been presented. This method is based on concentration profiles determined with the microphotometric technique and the numerical solution of Fick's second law of diffusion for the cylindrical system. Exploiting the grid method and data of experimental concentration profiles, diffusion coefficients of disperse dye Synthene Scarlet P3GL in the anionically modified polyester fiber have been calculated. The results have been compared with those obtained by the Boltzmann–Matano method. It was stated that (1) in the investigated polymer–dye system the relation between D and C is of the form D(C) = D₀ exp(δC); (2) the allowance for the cylindrical symmetry of the fiber leads to the lower values D(C) in the total concentration range than those obtained by the Boltzmann–Matano method; and (3) values of D₀ calculated with both methods are coincident.     

Preparation and mechanical properties of exfoliated mica-polyamide 6 nanocomposites using sericite mica

A new mica/polyamide 6 (PA6) nanocomposite was formed by exfoliation of a mica, potassium sericite (K⁺-SE). The powder sample was separated through an air-classifier into D₅₀:6.0 μm (median particle diameter), D₁₀:3.5 μm, and D₉₀:9.5 μm. The K⁺-SE was modified with a dodecylammonium salt (DDA) by ion exchange at 70 °C for four days. The resulting organically modified SE was melt-kneaded with PA6 in a twin-screw kneader at 260 °C. In order to characterize the nanocomposite morphology, X-ray diffraction and transmission electron microscopy were used. Differential scanning calorimetry and mechanical property measurements were also carried out. The morphology of the nanocomposite revealed mica nanolayers with very high aspect ratios; that is, at levels about two times greater than that of conventional exfoliated clay-polymer nanocomposites. A small amount of organically modified SE with 2.1 mass% silicate was sufficient to improve the flexural properties and heat distortion temperature of the nanocomposite. However, overall mechanical properties were not completely improved, because the shearing stress induced during exfoliation of the silicate layers resulted in inhomogenous dispersion of silicate platelets in the matrix. The present study indicates that three factors, degree of exfoliation, aspect ratio and dispersion homogeneity of silicate platelets, play an important role for the development of high performance nanocomposites.     

Effect of structure of HEMA–DEGMA hydrogel matrix on diffusion coefficients of PEG tracers. Variation of hydrogel crosslink density by change of polymer concentration

Dependence of diffusion coefficients of spin-labeled poly(ethylene glycol)s (PEGs, M_w = 1500, 3000, and 6000) determined by One-Dimensional Electron Spin Resonance Imaging (1D ESRI) on the properties of hydrogel matrices prepared by photopolymerization of 2-hydroxyethyl methacrylate (HEMA) and 2-(2′-hydroxyethoxy)ethyl methacrylate (DEGMA) was studied. The hydrogels were characterized by degree of crosslinking, ν_gel, by hydrodynamic correlation length, ξ_gel, and by self-diffusion coefficient of water, D_H2O. The tracer diffusion coefficients were analyzed in the frame of scaling reptation and hydrodynamic models. Molecular weight dependence of the tracer diffusion coefficients follow expression D  M_w^x with exponent x = −1.2 ± 0.1 which excludes contribution of reptation to the diffusion. Steep decrease of the tracer diffusion coefficients with increasing polymer concentration was observed. Decrease of the tracer diffusion coefficients with increasing ratio of the hydrodynamic radius of the tracer to the hydrodynamic correlation length of the hydrogel matrix, R_H/ξ_gel, was well fitted with predicted stretched exponential expression. Dependence of the tracer diffusion coefficients on the degree of crosslinking ν_gel suggested as a new scaling variable was found to closely follow empiric stretched exponential dependence in the whole ν_gel range studied.     

The coloration of polypropylene fibres with acid dyes

Modified polypropylene fibre has been prepared by incorporating a polymeric additive into the polypropylene, followed by melt spinning. Fibres with various additive concentrations were dyed with acid dyes, and the amount of dye adsorbed by the fibre was compared with the concentration of dye sites supplied to the fibre by the additive. A diffusion mechanism of dye molecules through interconnected additive particles to the fibre matrix is proposed. Colour yield was assessed by reflectance spectroscopy and photoacoustic spectroscopy. The latter was shown to be particularly suitable for measuring very dark colours. Photoacoustics can also used to detect ring dyeing of fibres at lower additive concentration.     

Structure of nanoporous carbon produced from boron carbide

The structure of nanoporous carbon produced by chlorination of powdered boron carbide at 600, 800, 1000, 1300, 1500, and 1800 °C has been studied by scanning electron microscopy, X-ray diffraction analysis, helium pycnometry, and low-temperature adsorption of nitrogen. On the basis of the results obtained, suggestions are made concerning the type of organization of the nanoporous structure of these materials. The evolution of the structure of nanoporous carbon is analyzed in relation to the synthesis temperature of nanoporous carbon. It is shown that, as the chlorination temperature increases, the structure of nanoporous carbon becomes more perfect: it changes from paracrystalline to turbostratic. The specific surface area decreases from 2200 to 36 m²/g, the volume of micropores decreases from 0.93 to 0.01 cm³/g, and that of mesopores first increases from 0.15 cm³/g (600 °C) to 0.57 cm³/g (1000 °C) and then decreases to 0.19 cm³/g (1800 °C). The total pore volume decreases from 1.08 to 0.20 cm³/g.     

Effect of some aromatic hydroxy sulphonic acids on uptake of acid dyes by nylon 6

The major constituents of a synthetic tanning agent for leather, prepared from the condensation of a naphthol sulphonic acid with formaldehyde, have been separately synthesised and have been shown to be of low molecular weight. The effect of these ‘syntan components’ on the uptake of four acid dyes by nylon 6 has been studied as has the desorption of the agents during the uptake of dye. Although the components have only a minor effect on the rate at which dye is adsorbed by the fibre, they reduce the extent to which dye is taken up at equilibrium. The restraining effect observed is governed by the affinity of both dye and agent. It is concluded that unlike commercial syntans which are available for the aftertreatment of dyed nylon, the products studied diffuse readily into the polymer matrix and, after application to nylon, are not held firmly at the fibre surface.     

Surfactant-modified bentonite as adsorbent for the removal of humic acid from wastewaters

The effectiveness of surfactant-modified bentonite (SMB) in removing humic acid (HA) from wastewaters was evaluated. Hexadecyl trimethylammonium (HDTMA) chloride was used to modify the surface of the clay mineral. The SMB exhibits very high adsorption potential for HA and at pH 3.0 more than 99% removal was achieved from an initial concentration of 25 μmol/L. The experimental kinetic data were analyzed using the pseudo-first-order kinetic model. Adsorption occurs through film diffusion at low as well as at higher concentrations and temperatures. The adsorption of HA using SMB was an exothermic process. HA adsorption was found to decrease with increase of ionic strength due to the formation of outer-sphere surface complexes on SMB. The equilibrium isotherms were determined and data were analysed using the Langmuir isotherm model. The maximum adsorption capacity, Q° was 73.52 μmol/g with binding constant, b = 0.155 L/μmol at 30 °C and pH 3.0. The adsorbent was suitable for repeated use (more than 3 cycles) without any noticeable loss of capacity.     

Investigation of hygrothermal aging phenomena in model composites by Raman spectroscopy

Abstract

Raman spectroscopy combined with gravimetry has been used to investigate hygrothermal aging in model composites based on an epoxy resin containing a single filament of a reinforcing fibre. Three fibre types, namely PBO, M5 and Twaron, were investigated using two specimen configurations - the diffusion slab (DS) and the double fibre pullout (DFPO) geometry. Variables such as the fibre type, surface treatment in the case of Twaron fibres, and the penetrant type (water vapour and liquid phase), were screened by establishing development of the Raman strain profiles ?(x, t) and the water uptake M(t) with time. Experimental data were successfully modelled using relationships that describe Fickian diffusion into a solid parallelepiped. Relative water uptakes determined gravimetrically were reduced to time dependencies controlled by the specimen geometry, diffusion coefficient of the matrix D and the equilibrium uptake of water, M(∞). Using simple micromechanical models, the Raman strain profiles were rationalised in terms of the midfibre strain ?(x=0, t) and the dimensionless parameter n, which controls the stress transfer along the interface. The fibre strain energy G(t) was also obtained from the area under the Raman profile. At longer exposure times and for some fibres, debonding was observed and the time dependence of the propagation of the debond length L _d was quantified. Generic conclusions on composite behaviour were drawn by eliminating the exposure time. The swelling coefficient β was derived from the linear dependence of midfibre strain on the water uptake and a change in the fibre strain energy was related to the debond propagation.     

Microwave versus Conductive Heating Their Effect on the Solvent–assisted Dyeing of Polyester Fibre with Anthraquinonoid Disperse Dyes

The rates of dyeing of polyester fibre with amino– and hydroxy–substituted anthraquinones in aqueous N, N–dimethylformamide (DMF) using microwave and conductive heating have been compared. Structural changes, commonly associated with interactions between DMF and polyester fibre, were limited and minimal shrinkage occurred due to the low DMF to water ratio and short dyeing times. Tensile properties reflected this minimal shrinkage through increased elongation at break, and differential scanning calorimetry also indicated that structural changes were minimal. Microwave radiation increased dye diffusion, shrinkage, and elongation at break compared to conductive heating. It is believed that molecular oscillation within the microwave–irradiated dyebath increases the rate of migration of dye to the fibre interface and enhances the plasticization of the polymer by DMF, thereby increasing the rate of dye diffusion within the fibre. Localization of energy associated with the use of microwave radiation is believed to be the predominant cause of increase in the rate of dyeing.     

Kinetic studies on sorption of n-hexane in vanadium substituted MFI type zeolites of various crystal morphologies

The MFI type materials isomorphously substituted with vanadium form crystals of two morphology types. Investigations of sorption kinetics for n-hexane indicated for both morphologies a non-typical increase in the value of corrected transport diffusion coefficient with the crystals dimensions. An increase in the D₀ values with the vanadium content of the crystals has also been found, although it is not so well expressed as that with the dimensions. The increase in the D₀ values is from 1.1 × 10⁻¹¹ to 1.1 × 10⁻¹⁰ m²/s and may be a consequence of an additional system of larger pores, which is not reflected in the adsorption isotherms due to common occurrence of these pores in all crystals. It is also possible that vanadium causes a superior structure ordering and a decrease in/weakening of diffusion barriers.