Radiation preparation of PVA/CMC copolymers and their application in removal of dyes
Introduction
Dyes have been the subject of many interests in recent years because of increasingly stringent restrictions on the organic content of industrial effluents. The effluents of wastewater in some industries such as dyestuff, textiles, leather, paper, printing, plastic and food, etc. contain various types of synthetic dyestuffs. The treatment of textile wastewater comprising dyestuffs and other non-biodegradable organics and inorganic poses considerable problems in the wastewater treatment industry. However, the increased color intensity is the most serious problem of the wastewater provided by the textile industries because many of the commercial azo dyes can produce hazardous aromatic amines, as well as other highly toxic by-products through metabolic processes in plants and animals or directly after the disposal in lakes, rivers or sea [1], [2], [3], [4]. Concerning the reactive dyes which are mainly used for textile dying processes, it is known that 30% of the initial amount of the dye is released in the wastewater due to hydrolysis side reaction, resulting in limited degree of fixation [5]. Moreover, azo dyes which are synthetic products, show rather low biodegradability, firstly because of lack of natural biodegradation paths and secondly because of stereochemical interferences concerning the accession of the reductant or oxidant molecule to the azo-group [6]. As a result, traditional biological processes are not able to fully decolorize azo dye wastewater [7], [8], [9], [10], [11], [12]. Most studies have focused on the development of a technique and a method for the treatment of dye wastewater. In general, there are several methods of reducing color in textile effluent streams: coagulation–flocculation, biological treatment, oxidation–ozonation, adsorption and membrane processes. The advantages and disadvantages of each technique have been extensively reviewed. Of these methods, adsorption has been found to be an efficient and economic process to remove dyes, pigments and other colorants [13], [14], [15]. In recent years, polymeric adsorbents, due to their wide variations in porosity and surface chemistry, especially regenerability on site and reuse for continuous process, have been increasingly used to remove and recover organic pollutants from waste streams [16], [17]
Poly(vinyl alcohol)1 (PVA) has a wide commercial application due to its unique chemical and physical properties. It is a nontoxic, highly crystalline, and water-soluble polymer and has good film forming and high hydrophilic properties. However, PVA as a soluble polymer cannot be used in the treatment of wastewaters. Thus, it has to be converted to a completely insoluble material with high mechanical properties. The structure–property behavior and compatibility of PVA with other polymers have been investigated by many authors. Although extensive research work has been carried out on the synthesis and application of polymeric materials in the field of treatment of waste waters, few authors were concerned with PVA/poly(carboxymethyl cellulose) (CMC) polymer blends. It has been reported that the introduction of 6–16% of CMC Na salt to the PVA matrix leads to an increased sorption capacity with respect to water vapor [18].
The aim of this study is to focus a synthesized hydrophilic copolymer of poly(vinyl alcohol) (PVA)/carboxymethyl cellulose (CMC) on the retention of anionic dye pollutants such as acid green B, ismative violet 2R and direct pink 3B dyes
Section snippets
Materials
Commercial PVA with a molecular weight of about 17,000 was used. CMC of commercial grade was supplied by El Nasr Pharmaceutical Chemicals Co., Egypt. Three types of dyes were used as adsorbates. The dyes used in the experiments were acid (acid green B; λmax = 636 nm), reactive (ismative violet 2R; λmax = 550 nm) and direct (direct pink 3B λmax = 526 nm). The chemical structures of different dyes are depicted in Chart 1. All of dyes were commercial grade and were used without further purification. The
Gel fraction
CMC is one of the polysaccharides which were able to form hydrogel by radiation crosslinking in so-called “paste-like” status [20], considering the slow increment of gel fraction in the dose range of 5–20 kGy, we can conclude that chain scission took a significant role during gel formation procedure. In previous work, [21] the maximum gel fractions of pure CMC hydrogel in all the above mention cases were reported to be ca. 40–50% To improve the gel properties to meet the demands for many
Conclusions
PVA/CMC copolymer has been prepared by using electron beam irradiation technique. The prepared of PVA/CMC copolymer is confirmed qualitatively by FTIR. The gel fraction increases with increasing irradiation dose, while the swelling of PVA/CMC copolymer nearly tends to increase with increasing CMC content and reduced with enhanced irradiation doses. The thermal stability of PVA/CMC copolymer reduces with addition of CMC to PVA but of PVA/CMC with compositions; 70/30 wt% gave high thermal
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