A detailed study of sorption equilibria and kinetics of a model disperse dye in cellulose acetate

A detailed investigation of the sorption of 4-aminoazobenzene by cellulose acetate films from aqueous solution is reported. Sorption isotherms at 75 and 60°C were linear up to saturation, in agreement with previous findings that have led to the conclusion that cellulose acetate-disperse dye systems are thermodynamically ideal. Thermodynamic analysis of these data also gave results consistent with such previous findings. The isotherms for 45 and 25°C, on the other hand, exhibited increasing curvature, in line with similar recent findings for a variety of hydrophobic polymer-disperse dye systems, and consistent with the presence of some strong absorption sites. However, the situation appears to be more complex than envisaged by simple dual-mode sorption theory. Early time desorption kinetic data were found to be consistent with Fick's law, with no indication of any significant dependence of the diffusion coefficient D on concentration (in the medium- to high-concentration range) or on film thickness. On the other hand, D was affected significantly by the history of film formation, the method of introducing the dye or heat treatment of the film. The origin of these effects was traced by DSC to definite microstructural differences. Late time kinetic data deviated significantly from the theoretical predictions based on the corresponding early time data, indicating a progressive slowdown of the desorption process. The deviations in question were generally more marked at higher temperature or film thickness, or when dyeing had been effected from the vapor phase, and were attributed to slow release of strongly adsorbed dye molecules. © 1994 John Wiley & Sons, Inc.     

Theoretical investigation of azo dyes adsorbed on cellulose fibers: 1. Electronic and bonding structures

Structural, bonding and electronic characteristics of complexes of anthraquinone and 1-arylazo-2-naphtol dyes and cellulose I _β are studied using B3LYP density functional method with 6-31G** basis set based on the partially and fully optimized structures. Results reveal that for both partially and fully optimized complexes, there is a stabilizing attraction between dyes and cellulose surface. The hydrazone (Hy) tautomer in anionic state (Hy–SO₃ ^?) shows the strongest interaction with the cellulose surface. Natural bond orbital (NBO) and atoms-in-molecules (AIM) analyses have been carried out to study the nature of azo dyes-cellulose bonds in detail. According to NBO analysis, a remarkable charge transfer occurs between the –SO₃ ^? and –SO₃H functional groups of the dye and the cellulose surface which can be regarded as the main source of the large dye–cellulose interaction energy. AIM analysis confirms the existence of hydrogen and van der Waals bonds between the azo dyes and cellulose. Furthermore, a very good agreement is observed between the number of hydrogen bonding sites and dye–cellulose interaction energies.     

Anthraquinone and Azo Dyes in Dyeing Processes of PET Films and PET Knitted Fabrics Using Supercritical CO2 Medium

Summary: Dyeing processes using supercritical fluid present advantages over the conventional dyeing process using aqueous medium. Previous works from our group on polymeric fibers such as N,N-dimethylacrylamide (DMAAm) modified poly(ethylene terephthalate), PET, showed higher sorption of disperse dyes in supercritical medium. Furthermore, recent studies showed that the association of UV radiation and DMAAm treatment leads to a better incorporation of dyes in modified PET soaked in aqueous medium. In this work, modified and non-modified PET knitted fabrics (KF) were dyed in supercritical CO₂ medium. Azo and anthraquinone dyes were used in order to compare the extent of incorporated dye in PET films and PET KF in supercritical CO₂. The dyeing process variables were studied by factorial design and by a response surface methodology (RSM) technique. The anthraquinone dye presented a better incorporation in PET than the azo dye. The UV light exposure and the dyeing times inputs showed positive main effects in the incorporation of dyes in PET films and PET KF. From the RSM data, DMAAm and UV light modified PET KF presented 7.43 mg of incorporated azo dye by g of PET if the optimized dyeing conditions, time: 135 min and pressure: 212 bar would be used. In the respective optimized dyeing conditions for the anthraquinone dye, time 150 min and pressure 229 bar, the incorporated dye would be 22.9 mg of dye by g of PET.     

Sorption and transport of water in nylon-6 films

Sorption and transport properties of water through films of Nylon-6 were obtained at 5, 23, and 40°C. Commercially available films were used and a Cahn electrobalance was employed for measuring the water uptake by the polymer samples. Values of the water sorption isotherms are accurately described by the Langmuir/Flory-Huggins dual-mode sorption model. At water activity values below 0.15, the volume fraction of water described by the Langmuir portion of the model was greater than the Flory-Huggins population. Solubility and diffusion coefficients of water, as well as the diffusion activation energy and enthalpy of dissolution of water for Nylon-6, were determined from the sorption experiments. Values obtained support the hypothesis of a bimodal water sorption mode, and the formation of water clusters. © 1994 John Wiley & Sons, Inc.     

Sorption and partial molar volumes of gases in poly(ethylene-co-vinyl acetate)

Sorption and dilation properties of polymer-gas systems involving poly(ethylene-co-vinyl acetate) and N₂, CH₄, or CO₂, have been investigated at pressures up to 50 atm at temperatures of 10–40°C. Sorption isotherms for low-solubility gases (i.e., CH₄ and N₂) can be described by Henry's law, and those for high-solubility gas (i.e., CO₂) by Flory-Huggins dissolution equation. Dilation isotherms are similar in contour to the corresponding sorption isotherms. From the obtained sorption and dilation data, partial molar volumes of the gases in the polymer were determined as a function of temperature. Thermal expansivity of dissolved CO₂ molecules was estimated at ca. 2.4 × 10^?3°C^?1 from the temperature dependence of partial molar volume. The expansivity is smaller than that of liquid CO₂ and larger than those of the polymer and organic liquids. © 1994 John Wiley & Sons, Inc.     

Competitive permeation of gas and water vapour in high free volume polymeric membranes

Highly permeable glassy polymeric membranes based on poly (1‐trimethylsilyl‐1‐propyne) (PTMSP) and a polymer of intrinsic porosity (PIM‐1) were investigated for water sorption, water permeability and the separation of CO₂ from N₂ under humid mixed gas conditions. The water sorption isotherms for both materials followed behavior indicative of multilayer adsorption within the microvoids, with PIM‐1 registering a significant water uptake at very high water activities. Analysis of the sorption isotherms using a modified dual sorption model which accounts for such multilayer effects gave Langmuir affinity constants more consistent with lighter gases than the use of the standard dual mode approach. The water permeability through PTMSP and PIM‐1 was comparable over the water activities studied, and could be successfully model ed through a dual mode sorption model with a concentration dependent diffusivity. The water permeability through both membranes as a function of temperature was also measured, and found to be at a minimum at 80 ° C for PTMSP and 70 °C for PIM‐1. This temperature dependence is a function of reducing water solubility in both membranes with increasing temperature countered by increasing water diffusivity. The CO₂ ‐ N₂ mixed gas permeabilities through PTMSP and PIM‐1 were also measured and model ed through dual mode sorption theory. Introducing water vapour further reduced both the CO₂ and N₂ permeabilities. The plasticization potential of water in PTMSP was determined and indicated water swelled the membrane increasing CO₂ and N₂ diffusivity, while for PIM‐1 a negative potential implied that water filling of the microvoids hampered CO₂ and N₂ diffusion through the membrane. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 719–728     

Water sorption in poly(zwitterions) of the ammonioalkoxydicyanoethenolate type

Water sorption by amorphous (meth)acrylic poly(zwitterions)-bearing quaternary ammonioalkoxydicyanoethenolate side groups , dipole moment μ(D) = 25.9 and 30.8 for p = 2 and 3, respectively was studied at 23°C over a broad range of water activity a (0.14–0.98). Water diffusion is nearly Fickian (D_s = 5.9 10^?7 cm².s^?1 for a = 0.63) and the sorption isotherms may be quantitatively analyzed according to the Guggenheim-Anderson-De Boer equation for a multilayer process characterized by a number of site-bound water molecules per monomeric unit, n_m ? 0.7. The Flory χ interaction parameter is a strongly increasing function of the water content in the glassy hydrated systems and it always remains higher than 0.75. Clustering of water molecules (Zimm-Lundberg theory) is never observed. Differential scanning calorimetry allows to quantify nonfreezable bound water (type I) of strong plasticization efficiency, n(I) = 2.8 mol. of water per monomeric unit, and it points out the quasisimultaneous emergence of low amounts of freezable bound water (type II) crystallizing at ?40°C and melting at ?1°C and of bulkfree water (type III, n(II)/n(III) ? 0.1). All these typical features distinguish these rather hydrophobic poly(zwitterions) from their hydrophilic homologues of the quaternary ammoniopropanesulfonate type . © 1995 John Wiley & Sons, Inc.     

A Novel Kinetic Approach for Photocatalytic Degradation of Azo Dye with CdS and Ag/CdS Nanoparticles Fixed on a Cement Bed in a Continuous‐Flow Photoreactor

Azo dyes are one of the synthetic dyes that have been used in many textile industries. Azo dye and their intermediate products are toxic, carcinogenic, and mutagenic to aquatic life. Removal of azo dyes is one of the main challenges before releasing the wastes discharged by textile industries. Photocatalytic degradation of azo dyes by nanoparticles is one of the environment‐friendly methods used for the removal of dyes from textile effluents. Therefore, this study focused on degradation of azo dye, Direct Red 264. Photocatalytic degradation of DR 264 azo dye was investigated using CdS and Ag/CdS nanoparticles immobilized on a cement bed in a continuous‐flow photoreactor under UV‐C exposure. The effect of the parameters of type and mass of catalyst, temperature, flow rate, dye concentration, and light intensity were evaluated for azo dye removal. Under optimal conditions, photocatalytic degradation of DR 264 azo dye using Ag/CdS nanoparticles immobilized on a cement bed in a continuous‐flow photoreactor obtained an efficiency of 99.99%. A developed kinetic model was proposed based on the intrinsic elementary reactions. The proposed model is in a good agreement with the Langmuir–Hinshelwood (L–H) equation. The pseudo–steady‐state approximation has considered for the concentration of hydroxyl radicals associated with the L–H model under certain conditions and explains consistently the dependence of the apparent kinetic parameter, k_obs (the reaction rate constant), and K_R (the adsorption equilibrium constant) with the light intensity. Based on the model, k_obs for Ag/CdS was greater than the CdS nanoparticles.     

Polymer-Bromine Interactions. I. Interactions with Polyacrylonitrile

The present paper deals with the interactions of bromine with poly-acrylonitrile (PAN). Kinetics and equilibria of the sorption of Br₂ on PAN were studied at a concentration range of 0.01–0.1 mol/L and a temperature range of 25–40°C. Two kinds of sorption were found: a “reversible” sorption removable by water and an “irreversible” sorption removable by aqueous ammonia solutions. The irreversibly sorbed bromine is presumably linked by charge transfer to the nitrile groups of the PAN, as evidenced by UV spectra. The irreversible sorption follows the reversible sorption and is slower. Partition coefficients obtained from the linear Freundlich isotherms increased with temperature and, at 40°C, the values obtained were 97, 65, and 32 L/kg for the total, irreversible, and reversible sorptions, respectively. At 25°C the chemical potential, enthalpy, and change in entropy for the irreversible sorption were ?2.0 kcal/mol, 9.4 kcal/mol, and 38 cal·mol^?1·K^?1. Effects of a 6-day Br₂ treatment and ammonia rinse were: decrease in dry T _g from 74.5 to 61°C and in water from 38 to 35°C; no significant decrease in M _W ; decrease in tensile strength measured after the bromine stage, and improvement after ammonia stage; increased swollen dimensions from 57% in water to 75%; and stabilization of swollen dimensions upon drying. The results support the existence of two phases in the less ordered regions of PAN.     

Argon sorption and partial molar volume in poly(ethyl methacrylate) above and below the glass transition temperature

Sorption and dilation isotherms for argon in poly(ethyl methacrylate) (PEMA) are reported for pressures up to 50 atm over the temperature range 5–85°C. At temperatures below the glass transition (T_g=61°C), sorption isotherms are well described by the dual-mode sorption model; and isotherms above T_g follow Henry's law. However, isotherms for dilation due to sorption are linear in pressure at all temperatures over the range investigated. Partial molar volumes of Ar in PEMA are obtained from these isotherms. The volumes are approximately constant above T_g (about 40 cm³/mol), whereas the volumes below T_g are smaller and dependent on both temperature and concentration (19–26 cm³/mol). By analyzing the experimental data according to the dual-mode sorption and dilation model, the volume occupied by a dissolved Ar molecule and the mean size of microvoid in the glass are estimated to be 67 129 ų, respectively. The cohesive energy density of the polymer is also estimated as 61 cal/cm³ from the temperature dependence of the dual-mode parameters.     

Effects of type of adsorption isotherms on parallel diffusion of sulfonated dyes into porous cellulose membrane

Transport phenomenon of three sulfonated azo dyes, C.I. Acid Red 88, C.I. Direct Yellow 12, and C.I. Direct Blue 15 into water-swollen cellulose membranes has been analyzed on the basis of parallel transport theory by surface and pore diffusion. Langmuir equation was applied into the mass balance equation to estimate dye concentration in the pores. The results were compared with the results obtained by applying Freundlich equation in our previous papers. The surface diffusivity (D _s) and the pore diffusivity (D _p) for the parallel diffusion model obtained by applying Langmuir equation agreed with those obtained by applying Freudlich equation. The theoretical concentration profiles for parallel diffusion calculated usingD _s andD _p coincided accurately with the experimental data when we applied either Langmuir or Freundlich equations.     

Sorption of carbon dioxide in fluorinated poyimides

Sorption isotherms of CO₂ for ten fluorinated polyimides measured at 35°C and up to about 25 atm are analyzed according to the dual-mode sorption model. Sorption properties for these polyimides are compared with those for other glassy Polymers including unfluorinated polyimides. The glassy polymers with higher glass transition temperatures T_g tend to show greater CO₂ sorption. Introduction of a ? C (CF₃)₂? linkage into the repeat unit of the main chain increases the sorption by 20–80%. For glassy polymers, including the fluorinated and unfluorinated polyimides, the Langmuir affinity constant b and Henry's law solubility constant k_D are correlated with the content of functional (carbonyl or sulfonyl) groups [FG], and composite parameter reflecting the magnitude of both [FG] and free-space fraction V_F, respectively, with some exceptions. The Langmuir capacity constant C′_H is correlated with T_g, but there are two correlation lines; one for unfluorinated polyimides and a different one for other glassy polymers including fluorinated polyimides. The slope of the former group is smaller probably because of smaller differences in thermal probably because of smaller differences in thermal expansion coefficients in rubbery and glassy states. Most fluorinated polyimides show greater solubility of CO₂ than unfluorinated polyimides and other glassy polymers, because of their larger C′_H and k_D. © 1993 John Wiley & Sons, Inc.     

Water absorption in EVOH films and its influence on glass transition temperature

Moisture sorption kinetics of nonoriented ethylene vinyl alcohol copolymer (EVOH) film (EF‐E15) were studied at 25, 35, and 45°C. Anomalous diffusion was observed for the polymeric film at high relative humidities (RH) and higher temperatures. Diffusion and solubility coefficients of water were found to be concentration dependent. The moisture sorption isotherms of three types of EVOH films (EF‐E15, EF‐F15, and EF‐XL15) determined at 25, 35, and 45°C, were well described using the GAB equation. Glass transition temperatures (T_g) of the EVOH films, as influenced by RH, were measured using differential scanning calorimetry. T_g values decreased with increasing RH due to the plasticization effect of water, and were found to be dependent on ethylene content and orientation of the EVOH films. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 691–699, 1999     

Equilibrium sorption of C.I.Basic Red 18 by carboxymethyl cellulose membranes

The equilibrium sorption of a cationic dye, C.I.Basic Red 18, by a partially carboxymethylated cellulose membrane at pH 4.2 was investigated. The sorption isotherm was interpreted by considering a cooperative mode of binding of the dye by the polymer. The intrinsic binding constantK, the number of consecutive polymer residues occupied by a single dye moleculen, and the cooperativity parameter were determined. In the case of the polymer with high content of carboxylate groups an additional mode of dye binding was presumed.     

In silico enhancement of azo dye adsorption affinity for cellulose fibre through mechanistic interpretation under guidance of QSPR models using Monte Carlo method with index of ideality correlation

ABSTRACT

Azo dyes are a group of chemical moieties joined by azo (-N=N-) group with potential usefulness in different industrial applications. But these dyes are not devoid of hazardous consequence because of poor affinity for the fibre and discharge into the water stream. The chemical aspects of 72 azo dyes towards cellulose fibre in terms of their affinity by QSPR have been explored in the present work. We have employed two approaches, namely balance of correlation without IIC (TF₁) and balance of correlation with IIC (TF₂), to generate 16 QSAR models from 8 splits. The determination coefficient of calibration and validation set was found higher when the QSPR models were developed using the index of ideality correlation (IIC) parameter (TF₂). The model developed with TF₂ for split 3 was considered as a prominent model because the determination coefficient of the validation set was maximum (r ² = 0.9468). The applicability domain (AD) was also analysed based on ‘statistical defect’, d(A) for a SMILES attribute. The mechanistic interpretation was done by identifying the SMILES attributes responsible for the promoter of endpoint increase and promoter of endpoint decrease. These SMILES attributes were applied to design 15 new dyes with higher affinity for cellulose fibre.     

Key Factors Regarding Decolorization of Synthetic Anthraquinone and Azo Dyes

The factors affecting decolorization of anthraquinone dye represented by Reactive Blue 4 (RB4) and azo dye represented by Methyl Orange (MO) were studied in batch experiments under mesophilic (35 °C) and thermophilic (55 °C) anaerobic conditions. The results indicated differences in decolorization properties of the dyes with different chromophore structures. In abiotic conditions, MO could be decolorized by a physicochemical reaction when it was sterilized at 121 °C together with sludge cells or glucose. RB4 only showed absorption onto the cell mass. The presence of a redox mediator accelerated the decolorizing reaction when supplied together with glucose in the presence of sterilized sludge cells. In biotic conditions, the results indicated that the biological activity of microorganisms was an important factor in decolorization. The main factor involved in decolorization was the conversion of cosubstrate as electron donor, which reacted with dye as an electron acceptor in electron transfer. Redox mediators, anthraquinone-2-sulfonic acid, and anthraquinone could accelerate decolorization even if a small amount (0.2 mM) was applied. On the other hand, a high concentration of redox mediator (1.0 mM) had an inhibitory effect on decolorization especially under thermophilic conditions. In addition, the decolorization of dye was accelerated by increasing treatment temperature, as shown in biotic treatments. Based on these results, increasing the treatment temperature could be used to improve the decolorizing process of textile dye wastewater treatment, especially for recalcitrant dyes such as anthraquinone.     

Hydration mechanism of polysaccharides: A comparative study

Water sorption was studied at 20 °C on films composed of different natural polymers. Three polysaccharides were investigated: chitosan, cellulose, and alginate. The major differences between these polymers, from a structural point of view, lay in the substitution of an OH group by an NH₂ function for chitosan and by an ionic COO^?Na⁺ group for alginate. An analysis of the experimental water sorption isotherms, expressed as the number of water molecules sorbed per repeating unit in the amorphous phase, associated with an analysis of the enthalpy profile related to the water sorption allowed us to propose a water sorption mechanism in two steps for all the polymers: water sorption on polymer‐specific sites in the first step and water clustering around the first sorbed water molecules in the second step. It was determined that two water molecules interacted with the polymer chains for cellulose and chitosan, whereas four water molecules were bonded to alginate chains. The specific sorption sites were identified as OH groups for cellulose, OH and NH₂ groups for chitosan, and ionic and OH groups for alginate. A systematic reduction of the half‐sorption time was observed in the activity range corresponding to this first sorption step, and it was explained by a water plasticization effect. On the other hand, an increase in the half‐sorption time was observed in the second sorption step, at a high activity (>0.8), for chitosan and alginate. A modelization associating the Guggenheim–Anderson–de Boer model and the clustering theory, applied to our systems, allowed us to relate the occurrence of this last phenomenon to the formation of water clusters containing more than two water molecules. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 48–58, 2005     

Water sorption in poly(ammonium sulfopropylbetaines). II. Sorption isotherms

Water sorption by four amorphous acrylic and methacrylic poly(zwitterions) bearing ammonium sulfopropylbetaine side groups () was studied at a constant temperature of 23°C and over a broad range of water activity (0.14-0.90). Whatever the physical state of the hydrated polymer, glassy or viscoelastic, water diffusion is Fickian (average diffusion coefficient D?_s in the range 2-16 × 10^?8 cm² s^?1), and the sorption isotherms may be quantitatively analyzed according to the Guggenheim-Anderson-De Boer amended BET equation for multilayer sorption processes. The number of sitebound water molecules per monomeric unit is in the range 1.5–2.0, and apparently there is no great energy difference between direct site binding and indirect binding in the successive solvation layers. The polymer-water interaction parameter (?0.6 < χ Flory < 0.6) is an increasing function of the water content of the hydrated poly(zwitterions) over the whole composition range (water volume fraction < 0.5), without any clear transition from the glassy to the viscoelastic state. Clustering of water molecules (Zimm-Lundberg theory) is never observed, even at high water content. Because of the charged structure of their dipolar units, the poly(zwitterions) show a water sorption process similar to that of the corresponding poly(electrolytes) of the tetra-alkylammonium sulfonate type. © 1992 John Wiley & Sons, Inc.     

Sorption and diffusion of organic vapors in amorphous Teflon AF2400

Vapor sorption in amorphous Teflon AF2400 of various organic solutes was studied in a wide range of activity at 25 °C by means of the gravimetric technique. The sorption isotherms of hexane, toluene, and chloroform were shown to be concave to the pressure axis and are consistent with the dual mode sorption model (DMS). The parameters of the DMS model k_D and b reveal a linear correlation with squared critical temperature of solutes T. The third model parameter, the Langmuir sorption capacity C′_H decreases when the size of solutes (critical volume) increases. Sorption isotherms of methanol and ethanol were shown to be convex to the pressure axis and are consistent with cluster formation in this strongly hydrophobic polymer. Concentration‐dependent diffusion coefficients D were determined using a linear implicit difference scheme in analysis of sorption kinetics. It was shown that D values increase exponentially with concentration for all the solutes, except alcohols for which exponential reduction of D(C) was observed. The partitioning of the thermodynamic and mobility contributions in D indicated that the reduction of D values of alcohols is consistent with clustering phenomena in AF2400. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 832–844, 2006     

Sorption and transport of linear alkane hydrocarbons in biaxially oriented polyethylene terephthalate

Equilibrium sorption and uptake kinetics of n‐butane and n‐pentane in uniform, biaxially oriented, semicrystalline polyethylene terephthalate films were examined at 35 °C and for pressures ranging from 0 to approximately 76 cmHg. Sorption isotherms were well described by the dual‐mode sorption model. Sorption kinetics were described either by Fickian diffusion or a two‐stage model incorporating Fickian diffusion at short times and protracted polymer structural relaxation at long times. Diffusion coefficients increased with increasing penetrant concentration. n‐Butane solubility was lower than that of n‐pentane, consistent with the more condensable nature of n‐pentane. However, n‐butane diffusion coefficients were higher than those of n‐pentane. Infinite‐dilution, estimated amorphous phase diffusion and solubility coefficients were well correlated with penetrant critical volume and critical temperature, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1160–1172, 2001