A critical review of hazardous waste generation from textile industries and associated ecological impacts

Among many industries, the textile industry is the oldest industry of human civilization. Cloth is the second most important human need after food. Textile processing includes several steps in which wet processing is the most important. As wet processing involves an extensive amount of water and chemicals, an enormous volume of textile effluent generates during wet processing. Textile effluents is disposed of on bare land or on water bodies, which causes soil and water contamination. Improper disposal of textile effluents causes severe soil and water contamination. Textile effluents contain dyes, heavy metals, inorganic salts, surfactants, organic contaminants, oil, and grease. Textile effluents cause contamination in water bodies. The colour present in effluents hinders the photosynthesis of aquatic plants. Inorganic salts cause the degradation of water quality and soil excellence. Heavy metals enter the food chain and cause severe health impacts on human life. Various physical, chemical, bailogical and hybrid methods are used to treat textile effluents. Textile processing has been explained in brief in this study. The current research deals with different textile processing steps, various pollutants generated in textile processing and their ecotoxicity, various ecological crises associated with textile processing, and numerous treatment methods for the remediation of textile effluents.     

Solvent-based nanocomposite coatings I. Dispersion of organophilic montmorillonite in organic solvents

This study aims to determine the relevant parameters controlling the organophilic montmorillonite dispersion in various organic solvents which can be used as dispersion media for polymer coatings. These suspensions were studied at three scales: At nanometer scale by looking to interlayer distance: When the solvent surface energy is higher than the organophilic clay surface energy, i.e., gamma solvent > or = gamma montmorillonite, the intercalated organic chains of the quaternary ammonium modifier swell, leading to an increase of the interlayer distance. The balance between hydrophilic and hydrophobic character is the key to dispersion of nanoclays. At micrometer scale by studying the rheological behaviour of clay suspensions: Gels are formed by percolation of microgels, based on swollen 3-4 platelet tactoids. The viscoelastic properties and the flow behavior reveal the gel structuration by measuring the gel stiffness and the flowing stress. At macroscopic scale analyzed from the swelling of the nanoclay into solvents: The compatibility between solvent and organophilic clay governs the macroscopic swelling, i.e., interactions between organic chains borne by the intercalated ions and solvents govern the final suspension morphologies. The same methodology can be adopted for monomers or prepolymers selected for one in situ intercalation/exfoliation processing route.     

Partially exchanged organophilic bentonites

Phenol is a pollutant that has caused many problems even when present in low concentrations and still represents an environmental problem with difficult solution. This paper presents a study of phenol adsorption by organophilic clays, obtained from aVerde Claro bentonitic clay, from Bravo, Paraíba State, Brazil, at different partial cation exchange degrees with hexadecyltrimethylammonium (HDTMA) chloride, at increasing reacting ratios, from 20 to 120 mmol/100 g of clay, which were characterized in a previous paper. By using Freundlich isotherms obtained for each case, which presented the best correlation coefficients with experimental data, it can be seen that for equilibrium concentrations up to 0.53 mmol L⁻¹ of phenol, the adsorptive capacity decreases for organophilic bentonites obtained at cation exchange degrees higher than 80 mmol/100 g of clay. This indicates that in these cases, the higher is the exchange by organic cation, the higher is the difficulty for the phenol diffusion and sorption in the interlayer space of the organophilic clays. For higher equilibrium concentrations, the maximum adsorption occurs for the organophilic bentonite obtained at 100 mmol/100 g of bentonite exchange.     

Tannery waste solidification and stabilization

The stabilization/solidification of tannery waste containing chromium was studied as an option for its treatment and final disposal, by using a Portland cement type II and two different commercial bentonites (sodium and organophilic) as additives. Different compositions were evaluated by compressive strength analysis, porosity measurement, leaching tests and thermal analysis. The effect on the compressive strength is directly related to the resulting effect of the components present in the original paste on the hydration degree of the cement, which can be evaluated by thermogravimetric analysis from the dehydration steps of tobermorite and ettringite phases of the pastes. The results show that this process is suitable for the treatment of the tanning waste and that the best conditions of stabilization are obtained when both additives are used. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electrochemical treatment of slaughterhouse and dairy wastewater: Toward making a sustainable process

The industrial processing of meat and dairy production uses large amounts of fresh water, therefore, generates a significant volume of wastewaters. The treatment of these effluents has been performed using different technologies from biological to electrochemical advanced oxidation processes. Under the circular economy concept, the lack of available freshwater resources has increased the interest in reusing wastewater from slaughterhouses, and even in the recovering of by-products.This article reviews the application of electrochemical treatments to slaughterhouse and dairy wastewaters. In addition, an overview of added-value products and energy recovery from these industrial wastewaters is also presented with future perspectives.     

Effects of organophilic clay on the solvent‐maintaining capability,dimensional stability,and electrochemical properties of gel poly(vinylidene fluoride) nanocomposite electrolytes

Four quaternary alkyl ammonium salts were used in an organophilic procedure, performed on montmorillonite clay, and resulted in intercalation in dimethylformamide (DMF) or ethylene carbonate (EC)/propylene carbonate (PC) as a cosolvent between poly(vinylidene fluoride) (PVdF) and the organophilic clay. An examination using X‐ray diffraction revealed that PVdF entered galleries of montmorillonite clay, and it exhibited exfoliation and intercalation phenomena when it was analyzed with transmission electron microscopy. Gel PVdF nanocomposite electrolyte materials were successfully prepared by the addition of the appropriate percentages of DMF or PC/EC as a cosolvent, organophilic clay, and lithium perchlorate to PVdF. The maximum ionic conductivity was 1.03 × 10^?2 S/cm, and the materials exhibited better film formation, solvent‐maintaining capability, and dimensional stability than electrolyte films without added organophilic clays. The results of cyclic voltammetry testing showed that the addition of the organophilic clays significantly enhanced the electrochemical stability of the polymer electrolyte system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3873–3882, 2002     

Influence of four different types of organophilic clay on the morphology and thermal properties of polystyrene/clay nanocomposites prepared by using the γ-ray irradiation technique

Polystyrene (PS)/clay nanocomposites were successfully prepared by the γ-ray irradiation technique. Four different types of organophilic clays were used: three of the four contained a reactive group, while the other did not. Exfoliated PS/clay nanocomposites can be obtained by using reactive organophilic clay and intercalated PS/nanocomposites can be formed by using non-reactive ones, which was confirmed by X-ray diffraction (XRD) and by transmission electron microscopy (TEM). In the formation of exfoliated PS/nanocomposites, the effect of the double bond of the clay-intercalated agents is much more important than the alkyl chain length. The enhanced thermal properties of PS/nanocomposites were characterized by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). In particular, the enhancement of the thermal properties of PS/nanocomposites made using the reactive organophilic clay was much higher than that of the thermal properties of PS/nanocomposites incorporating non-reactive clay.     

Synthesis of Additives from Montmorillonite to Modify High Density Polyethylene Final Properties

Summary: This work brings about the modification of sodium montmorillonite clay (MNa) by the cationic exchange with hexadecyltrimethylammonium to turn it into organophilic clay (MC₁₆). Subsequently, MC₁₆ was treated with silanes. Three silanes with functional groups of different chemical nature were used. The objective was to determine if the clay could affect high density polyethylene (HDPE) final behavior after being modified with each silane. The following silanes were used: Cl₂Si(CH₃)₂, Cl₂Si(CH₃)(C₆H₅) and Cl₂Si(C₆H₅)₂. Finally, in situ hydrolysis was carried out to generate the respective siloxanes. These materials were characterized by XRD, FTIR and GPC analyses. Each one of these additives was mixed using melt compounding processing in a Haake torque rheometer Rheocord 9000 equipped with a mix chamber and roller rotors at 100 rpm and 190 °C. All hybrids were characterized by XRD, SEM and thermogravimetric analyses. Barrier properties to cyclohexane were also determined by pervaporation experiments. Results from all studies showed that the addition of approximately 3 wt% of clay has changed the macroscopic properties of the above-mentioned composites, as compared with pure HDPE. This can be explained considering the different polymer/filler interactions which take place in each system.     

Thermal stability and mechanical properties of sisal in cycle process

Differential thermal analysis (DTA) was the first thermal analysis technique used to qualitatively characterize natural clays and respective curves has been used since more than 60 years as their ‘fingerprint’. With the development of microprocessed equipments in the last decades, derivative thermogravimetric (DTG) curves also may be used for this purpose in some cases, which also may allow a quantitative characterization of clay components. TG and DTG curves are more indicated than DTA or DSC curves to identify and to better analyze the several decomposition steps of natural or synthetic organoclays. These questions are discussed in applications developed to characterize Brazilian kaolinitic clays, bentonites and organophilic clays.     

Thermal decomposition of various alkyl onium organoclays: Effect on polyethylene terephthalate nanocomposites' properties

The thermal stability of organically modified layered silicates is determinant for processing polymer nanocomposites and is believed to play a key role on their properties. In this work, alkyl phosphonium, alkyl pyridinium and dialkyl imidazolium surfactants were used as intercalating agents for the preparation of highly thermally stable organophilic montmorillonites. The thermal decomposition of the surfactants and of their organoclays was studied by combined thermogravimetric analysis (TGA) and mass spectroscopy (MS), which allowed the identification of specific volatile compounds issued from the degradation. In order to investigate the influence of the thermal decomposition of the intercalating agent during processing, the various organoclays were incorporated in a polyethylene terephthalate (PET) matrix. The color of the nanocomposites was significantly affected by the thermal decomposition of the intercalating agent. In the case of the alkyl pyridinium modified clay, the degradation of the intercalating agent during processing was found to alter the clay dispersion. Finally, the crystallization was analyzed by differential scanning calorimetric (DSC) analysis and polarized optical microscopy (POM): it was demonstrated that the kinetics of nucleation and growth is not only affected by the dispersion state of the clay, but also depends on the clay/polymer interface properties, and therefore on the nature of the intercalating agent.     

Rapid characterisation of agro-industrial effluents for environmental fate by UV–visible and infrared spectroscopy from fractions obtained by centrifugation

Agro-industrial systems (e.g. dairy farms, feed lot, pig breeding and food processing plants) provide large quantity of organic wastes that could be recycled within the productive systems. However, the basic chemical characterisation is not enough to predict the effect that they may generate on the environment. In this study, a centrifugation process was applied at various speeds between 3000 and 15,000 rpm and carried out separately on two different livestock effluents (dairy farm and pig anaerobic digestate), in order to obtain supernatants and precipitates, which were studied separately. The more water soluble fractions, with lighter components and/or simpler structures, remained as liquid supernatants, while the more complex fractions, with higher molecular weight and/or water insoluble fractions, constituted the solid precipitates. An increase in the centrifugation rate did not produce the differential precipitation of dissimilar functional groups. Hence, 5000 rpm was the most adequate velocity since it generated clear supernatants without denaturation of the organic matter. A basic cost-effective chemical analysis, complemented with ultraviolet–visible and Fourier transform infrared spectroscopy, enables a set of properties to be established qualitatively and quickly for the multiple components of the organic matter for its later use as fertilisers or amendments. This rapid and economical technique allows for a characterisation prior to the reuse of the effluents, which is necessary to optimise their application and avoid environmental problems.     

Organic-inorganic hybrids from renewable plant oils and clay

This study deals with the preparation and properties of a new class of organic-inorganic hybrids from renewable resources. The hybrids were synthesized by an acid-catalyzed curing of epoxidized triglycerides in the presence of an organophilic montmorillonite (a modified clay). The mechanical properties were improved by the incorporation of clay in the oil-based polymer matrix. The reinforcement effect due to the addition of clay was confirmed by dynamic viscoelasticity analysis. The hybrids showed relatively high thermal stability. The co-curing of epoxidized soybean and linseed oils in the presence of clay produced hybrids with controlled mechanical and coating properties. The barrier property of the hybrid towards water vapor was superior to that of the oil polymer. The development of the present hybrids consisting of inexpensive renewable resources, triglyceride and clay is expected to contribute to global sustainability.     

Phase behavior of modified montmorillonite– poly(ϵ‐caprolactone) nanocomposites

The thermal behavior and overall isothermal crystallization kinetics of a series of organophilic modified montmorillonite–poly(?‐caprolactone) nanocomposites were investigated. In general, the thermal behavior was influenced more by the type of dispersion than by the clay content. For nanocomposites in which silicate platelets were predominantly dispersed in the polymer matrix to give exfoliated structures, the thermal properties were improved with respect to those of neat poly(?‐caprolactone), whereas in those cases in which simply intercalated structures were attained, the thermal properties regularly decayed as the clay content increased. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1321–1332, 2004     

Solvent Effect on the Grafting of an Organophilic Silane Onto Smectite‐type Clay: Application as Electrode Modifiers for Pesticide Detection

The effect of a non‐swelling (toluene) and a swelling (ethylene glycol (EG)) solvent on the grafting of an organophilic silane (octyltriethoxisilane) onto a smectitic clay was investigated. XRD patterns of the resulting materials reveals that the grafting occurred exclusively on the edges of the clay particles without intercalation, as evidenced by the non‐variability of the d‐value before and after the grafting. FTIR and TGA characterizations show that higher amount of silane was grafted when toluene was used as solvent. With EG, the clay particles were well‐dispersed and the grafting well controlled. These functionalized materials were used as carbon paste electrode modifiers to evaluate their abilities for electrochemical detection of organophilic pollutants at trace level. Carbendazim (cbz), a widely used fungicide was used as model compound. The clay functionalized in EG was the most efficient modifier, due to the combined effect of the characteristics of the pristine clay and the grafted silane. The electroanalysis experimental parameters were carefully optimized (pH 6.8, 15 min of accumulation time and 10 % of the modifier in the carbon paste). By varying cbz concentration, a 0.03 μM detection limit was obtained. The sensor provide very reproducible response but strongly affected by some metal ions interferences. By varying cbz concentration in river water, used as environmental sample model, higher detection limit was obtained (0.2 μM), due to interfering species.     

Adsorption of fluorescent R6G dye into organophilic C12TMA laponite films

The absorption and fluorescence properties of rhodamine 6G (R6G) in organophilic laponite (Lap) clay films are studied. For this purpose, organo-Lap clays are synthesized by the incorporation of dodecyltrimethylammonium (C12TMA) as surfactant into the interlayer space of Lap clays. Two organo-Lap clays are prepared: one with moderate surfactant content (around 70% of the total cation-exchange capacity (CEC) of the clay) and a second with a high surfactant loading (about 130% CEC). Supported films are elaborated by the spin-coating technique and characterized by several techniques such as atomic force microscopy, elemental CHN analysis, X-ray diffraction, and thermogravimetry. IR spectroscopy reveals that the intercalation of R6G into organo-Lap films takes place at the detriment of the adsorbed C12TMA molecules. The photophysical properties of R6G monomers in the interlayer space of Lap films are improved by the presence of surfactant molecules. Moreover, organophilic environments can reduce the dye aggregation and favor the formation of fluorescent J-type aggregates, enhancing the fluorescence ability of dye/clay films with high dye contents. This improvement depends on the surfactant content.     

Partially exchanged organophilic bentonites

Using a sodium bentonite (VCNa) as substrate differently exchanged organophilic clays were obtained by reaction with hexadecyltrimethylammonium (HDTMA) chloride, at increasing reacting ratios (R) from 20 to 120 meq/100 g of clay (VC20–VC120). The sodium bentonite was previously synthesized from a Verde Claro policationic bentonite (VC) from Bravo, Paraiba State, Brazil. From the thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses of these clays on calcined mass basis and from TG and DTG curves data of VCNa clay, a method was developed to estimate the mass fraction of the exchanged cation present in each organophilic clay (M _org), as a function of R. When all sodium cations of VCNa are exchanged by HDTMA, the obtained organophilic clay presents a maximum value for M _org. From this value and TG and DTG curves data of VC and VCNa clays, the cation exchange capacity of the original VC bentonite can be estimated.     

Influence of the layered silicate type on the structure, morphology and properties of cellulose acetate nanocomposites

This paper deals with the effect of different montmorillonite source clays, including pristine and organophilic montmorillonites, on the structure, morphology and properties of cellulose acetate (CA)/clay nanocomposites. In this study, the nanocomposites were prepared by melt extrusion in the presence of the environmentally friendly triethyl citrate plasticizer. The structure and morphology of the materials were analysed by X-ray diffraction and scattering (SAXS), X-ray microtomography and energy filtered transmission electron microscopy (EFTEM). SAXS and EFTEM results indicated that the nanocomposite morphologies were made up of tactoids together with exfoliated clay platelets in different proportions depending on the clay type. It can be concluded that well distributed clay tactoids and platelets can be achieved in CA nanocomposites prepared by melt extrusion and consequently property improvements can be found by using pristine or organophilic clays. In this case, the addition of a plasticizer, able to intercalate in the clay gallery, seems to be sufficient to promote the clay delamination mechanism under shearing inside the cellulose acetate matrix.     

Influence of clay modification on the properties of aramid-layered silicate nanocomposites

Nanocomposites from organoclay and aromatic polyamide were prepared using solution intercalation method. Aramid chains were synthesised by reacting 4-aminophenylsulfone with isophthaloyl chloride in dimethylacetamide. Dodecylamine was used as a modifier to change the hydrophilic nature of montmorillonite into organophilic. Suitable quantities of organoclay were mixed in the aramid solution with high-speed stirring for homogeneous dispersion of the clay. Thin films cast from these materials after evaporating the solvent were characterised. The morphology of nanocomposites was determined by X-ray diffraction and TEM. Results revealed the formation of delaminated and disordered intercalated clay platelets in the aramid matrix. Mechanical data indicated improvement in the tensile strength and modulus with clay loading up to 6 wt.%. The glass transition temperature increased up to 20 wt.% organoclay, suggesting better cohesion between the two phases and thermal stability augmented with increasing clay loading. The water uptake reduced gradually as a function of organoclay showing decreased permeability.     

Poly(vinyl chloride)-paste/clay nanocomposites: Investigation of thermal and morphological characteristics

The paper concentrates on poly(vinyl chloride) - PVC - from the point of nanocomposite characterisation through thermal degradation of samples, evolution of the changes caused by elevating temperature using TGA, FTIR and Congo Red methods combined with morphological characterisation by XRD and TEM analyses. A novel method of PVC-paste/nanocomposite preparation while processing was used. During preparation, PVC plasticizer was mixed with clay, both natural and organophilic, and the suspension was then compounded with the other components. Two factors were followed: effect of shearing alone, and in combination with temperature. As is presented, the type of nano-filler and its chemical modifier have obvious influence on final properties either thermal or morphological. Presented contribution follows previous part of investigation and brings further information from PVC-paste/nanocomposite field.     

Photo‐stabilization of EPDM–clay nanocomposites: effect of antioxidant on the preparation and durability

The present study is to examine the photo‐stabilization effect of an antioxidant on the photo‐oxidation of ethylene‐propylene‐diene monomer (EPDM)–clay nanocomposites. During the preparation of EPDM–clay nanocomposites via melt processing antioxidants are usually incorporated along with clay, which allows phenolic antioxidant molecules to get adsorbed onto acidic clay platelets and their interaction with metallic impurities reduces the stabilizing efficiency of the antioxidant. The nanocomposites were obtained by solution dispersion followed by melt compounding of EPDM and organophilic montmorillonite (OMMT). The samples were characterized by conventional tools such as X‐ray diffraction (XRD), Fourier Transform Infra Red (FT‐IR) spectroscopy, and thermo‐gravimetric analysis (TGA). It was found, upon photo‐irradiation (λ > 290 nm) studies by following the changes in functional groups and surface morphology, that photo‐degradation was lowered by the antioxidant and the efficiency of the antioxidant could be improved by initial incorporation of antioxidant in the EPDM matrix. In EPDM–clay nanocomposites, a stabilizing activity of the antioxidant was observed above some threshold concentration of the antioxidant. The relationship between the nanoclay reinforcement and stabilizing efficiency in terms of photo‐oxidation and surface morphology for their applicability are discussed. The methodology adopted for this study is also justified through our observation. Copyright © 2007 John Wiley & Sons, Ltd.