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Synthesis and characterization of polymethylmethacrylate grafted barley for treatment of industrial and municipal wastewater
Journal of Water Process Engineering 18 (2017) 113–125
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Synthesis and characterization of polymethylmethacrylate grafted barley for treatment of industrial and municipal wastewater
MARK
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Kartick Prasad Dey, Sumit Mishra , Gautam Sen Department of Chemistry, Birla Institute of Technology-Mesra, Ranchi 835215, Jharkhand, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Barley Graft copolymer Radical polymerization Flocculation Wastewater treatment
In the present investigation, we have synthesized polymethylmethacrylate grafted barley (BAR-g-PMMA) using ceric ammonium nitrate as an initiator and methyl methacrylate as monomer in the presence of nitrogen atmosphere. The different grades of polymethylmethacrylate grafted barley were prepared by varying the concentration of initiator and monomer till the best grade was optimized. The synthesized grades have been confirmed by different analytical techniques like FTIR spectra, elemental analysis, TGA analysis, XRD analysis, intrinsic viscosity measurement, SEM morphology and number average molecular weight determination. The flocculation efficiency of the developed materials has been tested in coal fine, iron ore and kaolin suspensions. The best grade showed 86, 75 and 82% flocculation efficiency in coal fine, iron ore and kaolin suspension respectively and this was found to be 1.21, 1.25 and 1.24 times better than commercial flocculant Polyacrylamide. The settling rate was also determined during flocculation study. This material was further applied for treatment of municipal waste water. The acute oral toxicity of this material has been studied following Organization of Economic Co-operation and Development (OECD) guidelines showing its non toxic nature. Overall, on the basis of the above results, the developed non toxic graft copolymers can be safely used for treatment of the municipal as well as industrial waste water.
1. Introduction Fresh water is essential for human survival, agricultural and industrial activities. The shortage of fresh water is one of the major challenges worldwide [1,2]. This problem is aggravating day by day and creating endless demand of clean water due to increase in population, higher living standards, urbanisation etc. Around 0.35 billion people from 25 different countries (particularly from Middle east and Africa) are suffering from water shortage and this may shoot upto 3.9 billion in 52 countries by 2025 [3,4]. The major part of waste water comes from domestic and Industrial sources [5]. This type of waste water is contaminated by the toxic metals, micro and macroparticles, bacteria, other pathogens, toxic dyes, different types of inorganic and organic particles [6,7]. This is directly disposed off in rivers, seas or percolates ground water table which leads them to our food cycle. It enters human physiology which serves as an ideal host for various types of micro organisms [8,9]. Presently, numerous efforts are being taken towards sustainable water resource management. Flocculation is widely used for the treatment of different types of waste water such as palm oil mill effluent, textile waste water, pulp mill waste water, oily waste water, sanitary
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Corresponding author. E-mail address: [email protected] (S. Mishra).
http://dx.doi.org/10.1016/j.jwpe.2017.06.008 Received 14 February 2017; Received in revised form 2 June 2017; Accepted 6 June 2017 2214-7144/ © 2017 Elsevier Ltd. All rights reserved.
landfill leachates and many more [10,11]. Flocculation involves the addition of chemicals along with agitation which aids sedimentation or adsorption leading to removal of heavy metals, micro organism or other solids leading. The flocculation process destabilizes solid particles for the formation of larger aggregates. It also aggregates heavy metals and organic materials on the surface of the flocculants by the weak electrostatic interactions [12,13]. In waste water, the characteristics of the solid particles are influenced by the electro kinetic charges. The colloidal impurities in waste water contain negative charges developed due to the presence of polar groups such as carboxylic and amine groups [14]. The size of the colloidal particles range between 0.01–1 μm and the attractive forces among them are less compared to repulsive forces due to electrical charges [15]. As a result, the particles are suspended in water. In order to settle these suspended colloidal particles, the first step is to destabilize them followed by formation of larger aggregates. So, the weight of the aggregated particles increases and it settles down as a floc due to gravity [16]. Nowadays, polysaccharide based flocculants have received much attention for waste water treatment processes. The demand of these materials is increasing day by day due to several advantages over other
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Polyacrylamide was supplied by HIMEDIA, Mumbai, India. Coal fine and Iron ore were collected from Jharkhand state, India. All of the chemicals were used without further purification.
counterparts such as eco friendly, easy availability, low cost, biocompatibility and easy to modify for several applications [17,18]. Besides their several unique advantages, they have some disadvantages also like poor physical and mechanical properties which restrict their application. These restrictions can be overcome by their chemical modification with different types of acrylic and vinyl monomers [19–25]. Various techniques are used for the modification of these polysaccharides. Recently, the graft copolymerization has attained a unique status for modification of polysaccharides. Grafting can be achieved by conventional redox method, microwave initiated method, microwave assisted method, γ-ray irradiation, electron beams and photochemical methods [26–29]. Among these methods, the conventional redox method is the most widely accepted technique for the modification of the polysaccharides to achieve the desirable properties as per their potential use. Among the various types of polysaccharides, barley (Hordeum vulgare L) plays an important role since ancient times. It is an agricultural crop well known throughout the world. The main chemical component of barley is polysaccharide (i.e. 90–95%) and rest are protein and fats. Starch and dietary fibres are the main components of the barley polysaccharide [30]. Starch is a carbohydrate molecule made up of large number of glucose units joined through glycosidic bonds. Starch consists of about 25–30% amylase and rest amylopectin. Amylose is a linear carbohydrate made up by D-Glucose unit and bonded through α(1 → 4) glycosidic bonds. Amylopectin is a branched carbohydrate of glucose made up by glucose units bonded in a linear way by α(1 → 4) glycosidic bonds and branching with every 24–30 repeating glucose units. Dietary fibres are made by the D-Glucose monomer linked by βglycoside bond through 1, 3 & 1, 4 carbon atom of repeating glucose units respectively. Till now, barley is used for production of beer and other liquors like brandy, whisky and some medical purposes. The modification of barley is needed to suit various applications [31]. Among the various types of natural polysaccharides, the food grade polysaccharides play an important role as a flocculant due to their non toxic nature, economic viability and widespread cultivation [32,33]. Barley satisfies all these criteria in terms of abundant cultivation, low price and it is considered as safe and reliable material since ages. The municipal waste water treatment by adding chemicals is directly related with human metabolic system. So, we need safe material and flocculants must be non toxic in nature. The food vs chemical crisis does not arise here because it is used in a small quantity given the fact that it is the 4th most abundant crop worldwide. The polymethylmethacrylate polymer is biocompatible in nature and is already used in water treatment as well as in biomedical field successfully [34,35]. Bar-gPMMA has not been used for water treatment applications till now, so we have explored this material and found it to be an efficient flocculant. Hence, this project is novel and not reported so far anywhere. In this research article, we report the successful synthesis of novel BAR-g-PMMA graft copolymer by conventional redox grafting process. Ceric ammonium nitrate is used as radical initiator for polymerization reaction. The synthesis has been confirmed by the various analytical techniques. The flocculation efficiency of the developed materials is performed in various synthetic waste waters and assessed for its application in water treatment. The acute oral toxicity of the synthesized materials has been studied. On the basis of our experimental results, the BAR-g-PMMA and its derivatives can be safely used for municipal and industrial waste water effluents.
2.2. Synthesis of BAR-g-PMMA by radical polymerization The BAR-g-PMMA was synthesized following the radical polymerization pathway. In this procedure, 1gm of barley was taken in 250 ml round bottom flask and mixed with 40 ml of distilled water at 40–45 °C under 30 min of stirring. Then it was kept at room temperature under stirring till it cooled down. Methylmethacrylate was added in this reaction mixture in varying amounts and kept under stirring condition for 15 min to make a homogeneous mixture. Afterwards, nitrogen gas was purged in the reaction mixture followed by test amount of ceric ammonium nitrate in 0.1(N) HNO3 along with nitrogen purging. Then, the reaction mixture was left undisturbed for 24 h at room temperature [36,37]. The highly viscous reaction mixture was obtained in the reaction vessel after 24 h. A saturated solution of hydroquinone was added in the gel like mass for the completion of graft copolymerization reaction. It was poured in excess acetone. A white coloured gel like precipitate was obtained in the reaction vessel and it was kept in excess acetone. After that, gel like mass was poured in distilled water and kept for 1 h for washing the unreacted part. Again, the gel like mass was poured in acetone. Then, the precipitate was collected and dried in hot air oven till a constant weight was obtained. The concentration of methylmethacrylate as monomer and ceric ammonium nitrate as initiator were taken w. r. to fixed barley concentration i.e. 1 g. The optimized concentration of monomer and initiator were evaluated w. r. to percentage grafting, intrinsic viscosity and number average molecular weight for the synthesis of BAR-gPMMA. The synthesis details for all parameters of the graft copolymer have been tabulated in Table 1.
2.3. Purification of synthesized BAR-g-PMMA by solvent extraction The synthesized materials were kept in excess acetone for 72 h for removal of any homopolymer (polymethylmethacrylate). They were collected from excess acetone and again dried in hot air oven till a constant weight was obtained [38]. The percentage grafting was calculated on the basis of following formula.
Pg =
Wg−W W
× 100
(i)
Here, W is weight of barley, Wg is the weight of grafted product and Pg is the percentage of grafting. All the synthesis parameters are summarised in Table 1.
Table 1 Synthesis details of BAR-g-PMMA by “Conventional method”.
2. Experimental 2.1. Materials Barley was purchased from Reckitt Benckiser, Ltd. New Delhi, India. Acrylamide and Acetone was supplied by Rankem (AR grade), India and Ceric ammonium nitrate was supplied from E.Merck, Mumbai, India. Methylmethacrylate and kaolin was Acros Organics, India. 114
Polymer Grade
Wt. Of Barley (gm.)
Wt. Of methyl methyacrylate (gm.)
Wt. Of CAN (gm.)
% of grafting (% G)
Intrinsic viscosity (dl/g)
Number average molecular weight (k Da)
G-1 G-2 G-3 G-4 G-5 G-6 G-7 G-8 Barley
1 1 1 1 1 1 1 1 0
10 10 10 10 10 10 12.5 15 0
0.1 0.2 0.3 0.4 0.5 0.6 0.5 0.5 0.0
8.76 47.42 66.89 114.74 166.89 89.06 72.38 68.56 0.0
1.83 3.05 3.78 5.64 10.34 8.76 7.08 6.12 1.83
1234 2456 2987 3456 7435 5436 4325 3987 176.6
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2.4. Flocculation in different suspension media
2.7. Acute oral toxicity test of modified barley
The Flocculation study of barley and different grades of BAR-gPMMA has been carried out following Jar test method [22,38]. 0.25% kaolin, 1% coal fine & 1% iron ore colloidal suspension medium have been chosen for this study. The flocculation experiment has been compared with Polyacrylamide i.e. PAM. In this procedure, the measured amount of colloidal particles (0.25% kaolin, 1% coal fine & 1% iron ore) were taken in 400 ml distilled water in six identical 0.5L beakers to make homogeneous mixture for each suspension respectively. The measured amount of flocculant was added in suspension to achieve desire dosage. After adding the measured amount of flocculant (i.e. different grades of BAR-g-PMMA & PAM), each beaker was stirred well in the Jar test apparatus. At first, all the sets of beakers were stirred at 150 rpm for 1 min and 65 rpm for 15 min followed by 15 min of settling time. Afterwards, the supernatant solutions were collected from each beaker and turbidity was measured using a calibrated ELICO®, CL 52D Nephelometer, India. Distilled water was taken as reference for kaolin, coal fine & iron ore suspension. For coal fine suspension media optical density was measured by ELICO® Double Beam, SL 210 UV spectrophotometer, India. The resultant Turbidity or optical density vs concentration of flocculant are plotted in Fig. 5(a), Fig. 5(b) & Fig. 5(c) for barley, different grades of BAR-g-PMMA and PAM. The minima of each curve represent the optimal dosage of barley, different grades of BAR-g-PMMA and PAM. The flocculation efficiency for each flocculant has been measured and shown in Fig. 6.
The acute oral toxicity test of the modified barley was performed following the Organization of Economic Co-operation and Development (OECD) guidelines for the test of chemicals and materials 425 [42]. This protocol was adopted in Dec 17, 2001. According to this protocol, five four week old Albino mice were taken for the experiment. This experimental protocol was approved (Approval No. BIT/PH/IAEC/04/ 2014 dated 30/4/2014) by the animal ethics committee of Birla Institute of Technology, Mesra, Ranchi, India. All the mice were kept in the polycarbonate cage with the required amount of food and deionized reverse osmosis water, ad libitum at 20–25° C and 40–70% relative humidity in a 12 h light on/light off cycle. According to the OECD guidelines, a single dose of 2000 mg/kg was administered. The dose was administered in each mouse with the help of stomach tube to the first animal. Then, all the mice were kept under observation up to four hours. This observation was extended upto seven days. The mortality rate was evaluated after completion of visible observation and reported accordingly [43]. 3. Characterization 3.1. Evaluation of intrinsic viscosity The intrinsic viscosity of barley and different grades of BAR-gPMMA has been measured with the help of Ubbelohde viscometer (capillary diameter 0.46 mm) in distilled water (neutral pH) as a solvent. At first, the measured amount of barley and other synthesized grades were dissolved in distilled water for preparation of four different concentrations of polymeric solutions. The flow of time was measured using stopwatch. The flow time for distilled water (solvent) is denoted as t0. The relative viscosity of the different concentration solutions has been evaluated using mathematical relation ηrel = t/t0, similarly Specific viscosity as ηsp = ηrel-1, reduced viscosity as ηred = ηsp/C and inherent viscosity as ηinh = ln ηrel/C where C is the concentration of polymeric solution in g/dL. The reduced viscosity and inherent viscosity were simultaneously plotted against different polymeric solutions. The intersection point after the extrapolation of the two plots i.e. reduced viscosity and inherent viscosity to zero concentration i.e. intrinsic viscosity was determined. All the values of intrinsic viscosity have been tabulated in Table 1.
2.5. Settling test of the suspended particles The settling velocities of different suspended particles were measured following the standard protocol [22,39]. As per the protocol, measured amount of suspensions were taken in different 1L stoppered graduated cylinders. The cylinders were marked up to upper water level with a difference of 1 cm. The height of the upper level water in cylinder from the ground level was 25 cm. The optimal dose of barley, different grades of BAR-g-PMMA and PAM were added in the different suspension media. After that, all the cylinders were turned upside down 10 times to ensure proper mixing of flocculant in the colloidal suspension mediums. Then, the cylinders were kept undisturbed in upright position and interfacial height was measured w.r.to time among distinct layers. The interfacial height vs. settling time is plotted in Fig. 7(a), Fig. 7(b) & Fig. 7(c) for kaolin, iron ore and coal fine suspension medium. The rate of settling for kaolin, iron ore and coal fine suspension medium for different flocculant is shown in Fig. 8.
3.2. FTIR spectroscopy The FTIR spectra of barley and the best grades of modified barley were recorded with the help of FTIR spectrophotometer (Model IRPrestige 21, Shimadzu Corporation, Japan) between 400 and 4000 cm−1 at a resolution of 4 cm−1 followed by the KBr pellet method. The spectrum of barley and best grade of modified barley has been shown in Fig. 1.
2.6. Municipal waste water treatment by flocculation process The flocculation performance was assessed using Municipal waste water collected from BIT-Mesra hostel effluent discharge main pothole drain following the standard protocol [40,41]. The supernatant liquid of each beaker was collected in test tube and turbidity was measured using a calibrated ELICO®, CL 52D Nephelometer, India with distilled water as a reference solution. The Turbidity vs concentration of flocculant are plotted in Fig. 9 for barley, best grade (G-5) and PAM. The common water quality parameters like pH, TSS, TDS, Total iron, Total chromium & COD of the collected waste water were measured by chemical analysis on the basis of standard protocol before and after treatment of the waste water. The pH of the wastewater was measured using ORION 4 Star series, Singapore, pH meter. The TSS and TDS were determined by the gravimetric method. The total iron and total chromium was determined after acid digestion by ELICO® Double Beam, SL 210 UV spectrophotometer, India. The results have been tabulated in Table 4. The results of the common waste water parameters are important for the application of BAR-g-PMMA as a flocculant for treatment of wastewater.
3.3. Qualitative X-ray diffractometry The X-ray diffraction pattern of barley and its best grades were recorded with the help of Bruker axis diffractometer (D8-Advance) using CuKα radiation and scanned 10–80° 2θ. The recorded diffractogram is shown in Fig. 2. 3.4. Elemental analysis The elemental analysis of barley and its best grades were evaluated with the help of Elemental Analyzer (Make – M/s Elementar, Germany; Model – Vario EL III). From this analysis, the presence of carbon, hydrogen, nitrogen, and oxygen (by difference) is confirmed. The results have been summarized in Table 2. 115
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Fig. 1. FTIR spectrum of barley and BAR-g-PMMA (G-5).
3.5. Scanning electron microscopy
Table 2 Elemental analysis details of Barley and G-4 (best grade).
The surface morphology of barley and its best grades were evaluated by scanning electron microscopy (SEM) in powdered form (Model: JSM-6390LV, Jeol, Japan). The samples were prepared for the assessment of surface morphology by the platinum coating [JEOL Auto fine coater model: JFC-1600 auto fine coater, coating time is 120 s with 20 Ma]. The surface morphograms of the samples at various magnifications using SEM JEOL model: JSM-6390LV were recorded. The morphogram of barley and its best grade is shown in Fig. 3(a) & (b).
Polymer
%C
%H
%N
%O
Barley BAR-g-PMMA(G5)
40.28 54.53
6.119 8.399
1.314 0.0
51.89 37.071
shown in Fig. 4.
3.7. Number average molecular weight determination 3.6. TGA studies The Number average molecular weight of all the samples has been determined with the help of Osmometer (A+ Adv. Instruments, INC. Model 3320, Osmometer) with distilled water as a solvent.
The thermo gravimetric analysis of barley and its grades were determined with the help of TGA instrument (Model: DTG-60; Shimzadu, Japan). The analysis was carried out in an inert atmosphere (nitrogen) from 25 °C to 800 °C. A uniform heating rate i.e. 5 °C per minute was maintained throughout the analysis. The recorded results have been
Fig. 2. XRD of barley and BAR-g-PMMA (G-5).
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polysaccharide. CAN is added in water medium, then it forms a hexa hydrated complex, so the Ce4+ ion is bonded and no longer remains free. Thus, it is not suitable for generating free radical sites on the barley backbone. In HNO3 medium, the Ce4+ ion remains free and takes part in radical polymerization reaction. The inert atmosphere (N2 atmosphere) has been used during the reaction to stop the oxidation of Ce4+ ion to Ce3+ ion in presence of air. At first, Ce4+ ion forms the chelate complex with the barley polysaccharide and results in a five membered ring which is a stable intermediate. Then, the Ce4+ ion is converted to Ce3+ by single electron transfer processes generating free radical sites on the barley backbone [36,37]. The free radicals may be formed on the eOH group which is attached on the C-2 and C-3 carbon atom in glucose unit. This is called initiation step for the grafting reaction. In the initiation step, the single unit of methylmethacrylate monomer is added on the barley backbone. The new moiety (i.e BAR-gPMMA.) is formed which takes part in further polymerization reactions. In the propagation step, more methylmethyacrylate monomers are attached on the barley backbone through methylmethyacryl chains and length of the grafted chains increases. There is a probability of attachment of different number of polymethylmethyacryte chains on barley backbone. In the termination step, two different units are attached together and form the polymethylmethyacryte grafted barley. Another possibility is that hydroquinone abstracts one radical and gets converted to hydroquinone radical by which the polymerization reaction is terminated. On the basis of above discussion, the probable reaction mechanism has been shown in Scheme 1. The radical polymerization reaction of BAR-g-PMMA was optimized by varying the different amounts of CAN and methylmethacrylate. So, different grades were obtained with varying percentage grafting. Thus, the grafting reaction depends on the concentration of monomer and initiator. Fig. 3. (a) SEM morphology of barley (300X magnification). (b) SEM morphology of BARg-PMMA (G-5) (300× magnification).
4.1.1. Effect of initiator concentration From Table 1, it is clear that with the increase in the initiator concentration, the percentage grafting increases. After a certain concentration, the percentage grafting decreases. In this graft copolymerization reaction, the maximum percentage grafting was obtained, when initiator concentration was 0.5 g w.r.to. 10 g of monomer and 1 gm of barley. After that, the percentage grafting decreases when initiator concentration was 0.6 gm w.r.to 10 gm of monomer and 1 g of barley. It is proved that at low concentration of initiator, very less number of free radicals are generated on the barley backbone and low percentage grafting is obtained. When initiator concentration increases, sufficient
4. Results and discussion 4.1. Synthesis of BAR-g-PMMA by radical polymerization The BAR-g-PMMA graft copolymer has been synthesized following the radical polymerization pathway. The ceric ammonium nitrate in 0.1(N) HNO3 medium has been used as an initiator. HNO3 plays an important role in the graft copolymerization reaction for
Fig. 4. TGA of barley and BAR-g-PMMA (G-5).
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Fig. 5. (a) Flocculation profile in 0.25% kaolin suspension. (b) Flocculation profile in 1% coal fine suspension. (c) Flocculation profile in 1% iron ore suspension. Fig. 6. Comparative study of flocculation efficiency for kaolin, coal fine and iron ore suspension medium.
grafting decreases [22,30].
number of free radical sites are generated on the barley backbone and high percentage grafting is obtained. Till the optimized dosage of initiator 0.5 g, sufficient number of free radical sites are available for grafts to attach and even for further dangling of grafted chains. When the CAN concentration increases beyond the optimized dosage, sufficient sites are not available due to competition of space among the grafted chains on the parent backbone. As a result, the percentage
4.1.2. Effect of monomer concentration From Table 1, it is clear that the percentage grafting decreases with increase in the monomer concentration at fixed initiator concentration. Here, the percentage grafting decreases at 12.5 & 15 g concentration of monomer w.r.to. 0.5 g of initiator and 1 g of barley. This is due to 118
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Fig. 7. (a) Settling test in 0.25% kaolin suspension. (b) Settling test in 1% coal fine suspension. (c) Settling test in 1% iron ore suspension. Fig. 8. Comparative study of settling rate for kaolin, coal fine and iron ore suspension medium.
increase in monomer concentration to form a polymer which leads to formation of a homopolymer. So, few Polyacrylamide chains are grafted on the barley backbone and as result the percentage grafting decreases.
4.2. Characterization 4.2.1. Interpretation of intrinsic viscosity measurement The intrinsic viscosity of barley and different grades of BAR-gPMMA were measured and all results are summarized in Table 1. From Table 1, it is confirmed that the intrinsic viscosity of developed materials increases with increase in the percentage grafting. The 119
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Fig. 9. Flocculation study of municipal waste water by barley, PAM & BAR-g-PMMA (G-5).
which confirms that the polymethylmethacrylate chains are grafted on barley backbone through 10OH and 20 OH.
intrinsic viscosity of the graft copolymer depends upon the branching of the polymeric chains on the barley backbone. This is directly related to the hydrodynamic volume of the grafted copolymer. When the grafted materials are immersed in the suitable solvent (here distilled water), it occupies some volume in the solvent because the polymeric chains are relaxed in the solvent media. The relaxation of the grafted copolymer in the solvent increases with the number of polymeric chains grafted on the barley backbone. As a result, the molecular weight increases. The number average molecular weight of barley and different grades of BAR-g-PMMA are summarized in Table 1. A well known relationship exists between intrinsic viscosity and number average molecular weight as developed by Mark–Houwink–Sakurada i.e. η = KMα where K and α are constants, M is molecular weight and η is the intrinsic viscosity. Both parameters depend upon the grafted polymeric chains on the barley backbone.
4.2.3. Qualitative X-ray diffractometry In Fig. 2 barley shows five distinct peaks at 2θ of 15.360, 17.380, 18.280, 20.260 and 23.300 region. This observation indicates the partial crystalline nature due to intermolecular interaction of OeH group present in the barley polymeric materials. In Fig. 2 for BAR-g-PMMA(G5) a broad and low intense peak is observed in 2θ of 13.500 region. This observation indicates the amorphous nature of the grafted materials. Due to grafting, the partial crystalline nature has been lost and converted to amorphous nature. This confirms that polymethylmethacrylate chains are grafted on the barley backbone. 4.2.4. Elemental analysis The elemental analysis results for barley and its best grade (i.e. BARg-PMMA (G-5)) are summarized in Table 2. In barley, a small amount of nitrogen is present i.e. 1.314% due to protein in the barley molecule. The other elements i.e. carbon, hydrogen & oxygen are 40.28, 6.119 & 51.80% respectively in barley. The percentage of nitrogen in BAR-g-PMMA (G-5) is zero, which indicates that the polymethylmethyacryte chain are not grafted on the barley backbone and the remaining portion is removed after washing through the distilled water. The other elements i.e. carbon, hydrogen & oxygen are 54.53, 8.399 & 37.071% respectively present in BAR-g-PMMA (G-5). That indicates that percentage of carbon and nitrogen increases due to the polymethylmethacrylate chains grafted on the barley backbone. On the basis of the elementary results, the polymethylmethacrylate chains do not take part in grafting on barley protein, these polymethylmethacrylate chains are involved in the grafting on barley polysaccharide backbone.
4.2.2. FTIR spectroscopy In Fig. 1, broad peaks are observed at 3278 and 3529 cm−1 region respectively due to 10OH and 20 OH of polysaccharide moiety present in barley. An intermolecular attraction is observed in the OH group of the polysaccharide moiety, as a result, the peaks are broad and overlap each other. A sharp peak is observed at 2927 cm−1 due to CeH stretching and low intensity and overlapped peaks are observed at 1456–1335 cm−1 region due to the CeH bending. Another CeH bending (out of plane) peaks are observed at 927 and 856 cm−1 region. A sharp and low intensity peak at 1658 cm−1 is observed due to NeH bending of primary amine group but the stretching peak is not clear in this spectrum due to the overlap of OeH peaks. This indicates that the small amount of protein is present in barley materials [30]. In Fig. 1 peaks are observed at 2997 and 2951 cm−1 due to methylene (-CH2-) stretching vibration (Asymmetric) and low intensity peak at 2835 cm−1 due to methylene (-CH2-) stretching vibration (Symmetric). The CeH bending vibrations for methylene (-CH2-) are also observed at 1450 and 1381 cm−1. The CeH bending vibration (out of plane) peaks are also observed at 844 and 756 cm−1. It is clear that the sp2 carbon (]CH-) of methylmethacrylate monomer is converted to sp3 carbon atom (-CH2-) for polymethylmethacrylate chains which is formed in the polymerization reaction. A sharp and intense peak at 1732 cm−1 is observed due to carbonyl group present in polymethylmethacrylate chains. A sharp peak is observed at 987 cm−1 due to new CeOeC bond formed in the graft copolymerization reaction. OeH group peaks are not observed for BAR-g-PMMA (G-5) in Fig. 4
4.2.5. Scanning electron microscopy (SEM) analysis The Fig. 3(a) & (b) represents the morphograms of barley and BARg-PMMA (G-4) in 5KV and 200 magnifications. Distinct differences have been observed in morphograms of native polysaccharide and grafted polysaccharide. The granular morphology has been observed in native polysaccharide i.e. barley which is transformed to flaky morphology, as the grafted PMMA chains are agglomerated on the barley backbone. This observation indicates that the polymethylmethacrylate chains are grafted on the barley backbone. 120
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Scheme 1. Schematic representation of mechanism for synthesis of BAR-g-PMMA using conventional method.
This is due to protein and some glucose degradation at 400 °C. The complete degradation i.e. 100 percentage is observed in 400–800 °C. The TGA analysis of BAR-g-PMMA(G-5) (Fig. 4) shows two distinct weight loss zones. The 1st weight loss zone is observed in 30–250 °C region and the% weight loss is 8.284, due to small amount of moisture present in the grafted materials. The complete degradation is observed
4.2.6. Thermal gravimetric analysis (TGA) From the TGA analysis of barley (Fig. 4) three distinct weight loss zones are observed. The 1st weight loss is observed at 30–240 °C region and the percentage of weight loss is 3.303 percentage w.r.to initial weight, due to small amount of moisture. The 2nd weight loss zone is observed in 240–400 °C region and the percentage weight loss is 70.63. 121
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greater than the barley and PAM. On the basis of the experimental results, the flocculation efficiency increases with increase in the percentage grafting. The flocculation efficiency of different grades of BAR-g-PMMA is greater than the barley. Due to the grafting, the polymeric branches increase on the barley backbone. As a result the corresponding hydrodynamic volume of the synthesized BAR-g-PMMA also increases in the distilled water. This is also related to the intrinsic viscosity and number average molecular weight. When polymeric solution is added in the colloidal suspension medium, the polymeric branches come in contact with the colloidal particles and form flocs by the weak interaction of different groups present in the graft copolymer. The formation of flocs is graphically represented in Scheme 2. With increase in the hydrodynamic volume of BAR-g-PMMA, the probability of contact will be more, as a result, the floc size increases. As a result, flocs will settle more rapidly. So the flocculation efficiency increases. This phenomenon is observed at a particular concentration. This concentration is generally called the optimal dosage. Beyond this concentration, the flocculation efficiency decreases. At higher concentrations, the density of the polymeric branches increases in the colloidal suspension as intermolecular repulsion develops between the polymeric branches. The attractive force of the colloidal particles is less than the repulsion. As a result, the suspended particles are unable to come in contact with different groups of the polymeric branches. So, the flocculation efficiency decreases. This phenomenon is known deflocculation. In this study, we observe that the flocculation efficiency increases with flocculant dose i.e. 1 ppm to 4 ppm and the efficiency decreases at 5 ppm. The best grade i.e. G-5 shows better flocculation performance than PAM. This phenomenon is shown in Fig. 5(a)–(c).
Table 3 % of weight lost in various temperature differences of Barley and BAR-g-PMMA (G-5) from TGA analysis. Weight lost zone
1st 2nd 3rd 4th
Barley
BAR-g-PMMA(G-5)
Temperature different
% of weight lost
Temperature range
% of weight lost
30–240 °C 240–400 °C 400–800 °C 30–800 °C
3.30 67.33 25.11 100
30–250 °C 250–415 °C 415–800 °C 28–800 °C
8.28 91.71 0.0 100
at 250–415 °C region. The TGA analysis results of barley and BAR-gPMMA(G-5) have been summarized in Table 3. 4.2.7. Number-average molecular weight determination The number average molecular weight of barley and different grades of BAR-g-PMMA have been measured on the basis of osmometry. The distilled water is used as a solvent in this case. The number average molecular weight has been calculated on the basis of the following relation [30].
ρ Φ×n = × 103 Cdry Mn Where Mn is the number average molecular weight, Cdry is the concentration of the dry polymeric sample in aqueous solution, Φ is the osmotic coefficient, which suggests the non ideal behaviour of the solution (here, we assume that the solution behaves ideally), n is the number of components into which a molecule dissociates and ρ is the osmosis per kilogram solvent. The determined number average molecular weight of barley and different grades of BAR-g-PMMA has been tabulated in Table 1. The number average molecular weight increases with increase in the percentage grafting. As the number of polymeric branches increase, the solubility of the polymeric materials also increases. So, the number of molecules present per kilogram of the solvent increases. The osmomolarity of the grafted materials also increases. Consequently the number average molecular weight increases.
4.2.9. Settling test of the suspended particles The settling test of the suspended particles are performed for the confirmation of flocculation efficiency. The settling velocities of the suspended particles were measured at 4 ppm (optimized doses in flocculation experiments) by standard protocol. The settling time vs. Interfacial height is plotted in Fig. 7(a)–(c). The settling rates of all suspended media are calculated from the settling test results. The maximum settling rate is observed in coal fine suspension i.e. 0.49 cm/s compared to iron ore (0.40 cm/s) and kaolin (0.43 cm/s) for G-5 flocculant greater than PAM. So, the settling rate is iron ore < kaolin < coal fine for BAR-g-PMMA as shown in Fig. 8. On the basis of experimental results, it is shown that the settling rate increases with increase in the percentage grafting. The hydrodynamic volume of the graft copolymer increases with the percentage grafting, as the floc formation probability becomes more. So, more colloidal particles come in contact with the polymeric branches and form floc by weak intermolecular attraction of the particles. The weight of resultant floc will be more, due to the gravitational force and it settles faster. So, the settling rate increases. The settling rate is higher for G-5 flocculant for each case. The settling rate of coal fine suspension is higher due to the higher size of the coal particles (1106–2669 nm.) compared with iron ore (458–712 nm.) and kaolin (955–1484 nm) suspension. The comparative study of the settling rates in different suspension media for different flocculant is shown in Fig. 8. These results suggest the flocculation efficiency results. On the basis of the flocculation study, the BAR-g-PMMA(G-5) is proved as a better flocculant than PAM.
4.2.8. Flocculation study in different suspension media The flocculation efficiency of barley and different grades of BAR-gPMMA has been carried out in different suspension media like coal fine, iron ore and kaolin suspension media as per standard protocol. The Turbidity (iron ore & kaolin) and optical density (coal fine) vs. Flocculant doses have been plotted in Fig. 5(a)–(c). The physical characteristics (Particles size and zeta potential) of suspension media have been measured with the help of Dynamic light scattering. The particles size of coal fine, iron ore and kaolin suspension media are 1106–2669, 458–712 and 955–1484 nm respectively and Zeta potential of coal fine, iron ore and kaolin suspension medium are −25.6, −21.6 and −18.8 mV respectively. The optimized dose for each suspension medium for different flocculant is 4 ppm. The flocculation efficiency in coal fine suspension medium is greater than kaolin and iron ore for each case. The increasing order of flocculation efficiency for barley and different grades of BAR-g-PMMA is iron ore < kaolin < coal fine. This is shown in Fig. 6. The flocculation efficiency of best grade i.e. G-5 is Table 4 Comparative study of common parameter of municipal wastewater.
Waste water Barley PAM BAR-g-PMMA(G-5)
Flocculation efficiency (in%)
pH
Turbidity (ppm)
TDS (ppm)
TSS (ppm)
Total Iron (ppm)
Total chromium (ppm)
COD (ppm)
0.0 28.17 60.53 70.42
7.2 7.2 7.2 7.2
71 58 37 23
276 237 187 123
390 319 217 182
1.60 1.40 1.35 1.23
0.098 0.081 0.073 0.067
446 426 324 265
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Scheme 2. Schematic representation of floc formation between colloidal suspension and BAR-g-PMMA.
4.3. Municipal waste water treatment by flocculation
guidelines, for the test of chemicals 425 (adopted Dec 17, 2001, Annexure-4) if LD50 value is greater than 2000 mg/kg, then testing in animals should not proceed further. So it belongs to “category-5” and the toxicity is zero. So the acute oral toxicity of BAR-g-PMMA(G-5) is zero [42,43].
The municipal waste water was treated by the flocculation using barley and BAR-g-PMMA (G-5) following the standard protocol. The optimized doses of flocculant (barley, PAM & BAR-g-PMMA (G-5)) for this processes is 4 ppm. The flocculation efficiency of barley, PAM and BAR-g-PMMA (G-5) are 28.17, 60.53 and 70.42 percentage respectively on the basis of turbidity. The flocculation efficiency of BAR-g-PMMA (G-5) is greater than barley and PAM. This is shown in Fig. 9. The common waste water parameters like TSS, TDS, pH, total iron, total chromium and COD were assessed pre and post treatment by flocculant (barley, PAM & BAR-g-PMMA(G-5)). The resultant values have been summarized in Table 4. The TSS and TDS were removed after the treatment and the removal efficiency of BAR-g-PMMA(G-5) is greater than the barley. The polymeric branches i.e. polymethylmethacrylate is attached on the barley backbone. As a result, the working surface of BAR-g-PMMA(G-5) is greater than the barley. So, the interaction of the colloidal suspended particles towards BAR-g-PMMA(G-5) is more than barley. So, the settling of the colloidal particles will be more than barley. As a result, reduction efficiency will be more. The reduction of total iron and total chromium is also observed. The reduction of metal concentration after flocculation occurs due to the chelate formation in heteroatoms of polymethylmethacrylate chains with the metal ion [44]. The possibility of the interaction of BAR-g-PMMA(G-5) with the metal ion is shown in Scheme 3. The reduction of organic particulates is also observed after flocculation due to the interaction of heteroatoms of grafted materials with the organic particulates. The huge difference of TSS values in BARg-PMMA(G-5) than barley indicates that it is suitable for flocculation process for municipal waste water treatment.
5. Conclusion On the basis of present investigation results, the grafting of polymethylmethacrylate chains on the barley backbone has been successfully carried out by radical polymerization path way. The synthesized materials have been confirmed by various analytical techniques. The flocculation performance of BAR-g-PMMA particularly G-5 is higher than other grades and barley and PAM in coal fine, iron ore and kaolin suspension media which makes it a superior flocculant. This flocculant is very much efficient for the removal of solid particulates in municipal waste water and shows better performance than PAM. It is non toxic in nature. So, the developed materials can be safely used for municipal wastewater treatment purpose as well as industrial effluents.
Acknowledgments The authors deeply acknowledge the financial support received from Department of Science and Technology, New Delhi, India (Letter No: SR/FT/CS-113/2011 dated 29/06/2012) & All India Council for Technical Education (AICTE), New Delhi, India (Ref. No.: 8-207/RIFD/ RPS/POLICY-1/2014-15 dated 16th March 2015). We acknowledge the Central Instrumentation Facility, BIT Mesra for characterization studies, Department of Pharmaceutical Sciences and Technology, BIT-Mesra for Acute oral toxicity study and UGC- DAE CSR Kolkata centre for XRD analysis. One of the authors (Mr. Kartick Prasad Dey) is thankful to CSIR (File No.: 09/554(0040)/2016 EmR-I dated 30/03/2017) for his fellowship.
4.4. Acute oral toxicity test for modified barley No abnormal behaviour was observed in mice after the seven days of visible observation period for BAR-g-PMMA (G-5). It is confirmed that the LD50 is greater than the 2000 mg/kg. According to the OECD 123
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Scheme 3. Schematic representation of metal removal by BAR-g-PMMA flocculant. [22] S. Mishra, S. Sinha, K.P. Dey, G. Sen, Synthesis, characterization and applications of polymethylmethacrylate grafted psyllium as flocculant, Carbohydr. Polym. 99 (2014) 462–468. [23] S. Bharti, S. Mishra, K.P. Dey, Synthesis and characterization of novel OAT-g-PMMA matrices: its application in controlled and colonic drug delivery, Adv. Polym. Technol. (2015), http://dx.doi.org/10.1002/adv.21628. [24] G.U. Rani, K.P. Dey, S. Bharti, S. Mishra, Controlled drug release of 5-amino salicylic acid by poly (2-hydroxyethylmethacrylate) grafted agar, Front. Chem. Sci. Eng. 8 (2014) 465–470. [25] S. Mishra, G. Sen, K.P. Dey, G.U. Rani, Synthesis and Applications of Grafted Carboxymethyl Cellulose: A Review, In: Cellulose-Based Graft Copolymers: Structure and Chemistry, CRC Press, 2015, pp. 475–496. [26] K.P. Dey, S. Mishra, N. Chandra, Colon targeted drug release studies of 5-ASA using a novel pH sensitive polyacrylic acid grafted barley, Polym. Bull. (2017) 1–23. [27] V.K. Thakur, M.K. Thakur, R.K. Gupta, Graft copolymers from natural polymers using free radical polymerization, Int. J. Polym. Anal. Charact. 18 (2013) 495–503. [28] H. El-Mohdy, Radiation initiated synthesis of 2-acrylamidoglycolic acid grafted carboxymethyl cellulose as pH-sensitive hydrogel, Polym. Eng. Sci. 54 (2014) 2753–2761. [29] Y. Xing, X. Sun, B. Li, Poly (methacrylic acid)-modified chitosan for enhancement adsorption of water-soluble cationic dyes, Polym. Eng. Sci. 49 (2009) 272–280. [30] G. Sen, S. Mishra, K. Prasad Dey, S. Bharti, Synthesis, characterization and application of novel polyacrylamide‐grafted barley, J. Appl. Polym. Sci. 131 (2014). [31] G. Harris, The structural chemistry of barley and malt, Barley and malt, (1962) 431582. [32] A. Mishra, R. Srinivasan, M. Bajpai, R. Dubey, Use of polyacrylamide-grafted Plantago psyllium mucilage as a flocculant for treatment of textile wastewater, Colloid. Polym. Sci. 282 (2004) 722–727. [33] M. Agarwal, R. Srinivasan, A. Mishra, Synthesis of Plantago psyllium mucilage grafted polyacrylamide and its flocculation efficiency in tannery and domestic wastewater, J. Polym. Res. 9 (2002) 69–73. [34] M. Okamoto, S. Morita, Y. Kim, T. Kotaka, H. Tateyama, Dispersed structure change of smectic clay/poly (methyl methacrylate) nanocomposites by copolymerization with polar comonomers, Polymer 42 (2001) 1201–1206. [35] S.L. Tao, M.W. Lubeley, T.A. Desai, Bioadhesive poly (methyl methacrylate) microdevices for controlled drug delivery, J. Controlled Release 88 (2003) 215–228. [36] K. Gupta, S. Sahoo, K. Khandekar, Graft copolymerization of ethyl acrylate onto cellulose using ceric ammonium nitrate as initiator in aqueous medium, Biomacromolecules 3 (2002) 1087–1094. [37] K. Gupta, K. Khandekar, Temperature-responsive cellulose by ceric (IV) ion-initiated graft copolymerization of N-isopropylacrylamide, Biomacromolecules 4 (2003) 758–765. [38] P. Rani, S. Mishra, G. Sen, Microwave based synthesis of polymethyl methacrylate grafted sodium alginate: its application as flocculant, Carbohydr. Polym. 91 (2013) 686–692. [39] S. Pal, A.S. Patra, S. Ghorai, A.K. Sarkar, R. Das, S. Sarkar, Modified guar gum/SiO 2: development and application of a novel hybrid nanocomposite as a flocculant for the treatment of wastewater, Environ. Sci.: Water Res. Technol. 1 (2015) 84–95. [40] G.U. Rani, S. Mishra, G. Sen, U. Jha, Polyacrylamide grafted agar: synthesis and applications of conventional and microwave assisted technique, Carbohydr. Polym. 90 (2012) 784–791. [41] P. Rani, G. Sen, S. Mishra, U. Jha, Microwave assisted synthesis of polyacrylamide grafted gum ghatti and its application as flocculant, Carbohydr. Polym. 89 (2012) 275–281.
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Synthesis and characterization of polymethylmethacrylate grafted barley for treatment of industrial and municipal wastewater
MARK
⁎
Kartick Prasad Dey, Sumit Mishra , Gautam Sen Department of Chemistry, Birla Institute of Technology-Mesra, Ranchi 835215, Jharkhand, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Barley Graft copolymer Radical polymerization Flocculation Wastewater treatment
In the present investigation, we have synthesized polymethylmethacrylate grafted barley (BAR-g-PMMA) using ceric ammonium nitrate as an initiator and methyl methacrylate as monomer in the presence of nitrogen atmosphere. The different grades of polymethylmethacrylate grafted barley were prepared by varying the concentration of initiator and monomer till the best grade was optimized. The synthesized grades have been confirmed by different analytical techniques like FTIR spectra, elemental analysis, TGA analysis, XRD analysis, intrinsic viscosity measurement, SEM morphology and number average molecular weight determination. The flocculation efficiency of the developed materials has been tested in coal fine, iron ore and kaolin suspensions. The best grade showed 86, 75 and 82% flocculation efficiency in coal fine, iron ore and kaolin suspension respectively and this was found to be 1.21, 1.25 and 1.24 times better than commercial flocculant Polyacrylamide. The settling rate was also determined during flocculation study. This material was further applied for treatment of municipal waste water. The acute oral toxicity of this material has been studied following Organization of Economic Co-operation and Development (OECD) guidelines showing its non toxic nature. Overall, on the basis of the above results, the developed non toxic graft copolymers can be safely used for treatment of the municipal as well as industrial waste water.
1. Introduction Fresh water is essential for human survival, agricultural and industrial activities. The shortage of fresh water is one of the major challenges worldwide [1,2]. This problem is aggravating day by day and creating endless demand of clean water due to increase in population, higher living standards, urbanisation etc. Around 0.35 billion people from 25 different countries (particularly from Middle east and Africa) are suffering from water shortage and this may shoot upto 3.9 billion in 52 countries by 2025 [3,4]. The major part of waste water comes from domestic and Industrial sources [5]. This type of waste water is contaminated by the toxic metals, micro and macroparticles, bacteria, other pathogens, toxic dyes, different types of inorganic and organic particles [6,7]. This is directly disposed off in rivers, seas or percolates ground water table which leads them to our food cycle. It enters human physiology which serves as an ideal host for various types of micro organisms [8,9]. Presently, numerous efforts are being taken towards sustainable water resource management. Flocculation is widely used for the treatment of different types of waste water such as palm oil mill effluent, textile waste water, pulp mill waste water, oily waste water, sanitary
⁎
Corresponding author. E-mail address: [email protected] (S. Mishra).
http://dx.doi.org/10.1016/j.jwpe.2017.06.008 Received 14 February 2017; Received in revised form 2 June 2017; Accepted 6 June 2017 2214-7144/ © 2017 Elsevier Ltd. All rights reserved.
landfill leachates and many more [10,11]. Flocculation involves the addition of chemicals along with agitation which aids sedimentation or adsorption leading to removal of heavy metals, micro organism or other solids leading. The flocculation process destabilizes solid particles for the formation of larger aggregates. It also aggregates heavy metals and organic materials on the surface of the flocculants by the weak electrostatic interactions [12,13]. In waste water, the characteristics of the solid particles are influenced by the electro kinetic charges. The colloidal impurities in waste water contain negative charges developed due to the presence of polar groups such as carboxylic and amine groups [14]. The size of the colloidal particles range between 0.01–1 μm and the attractive forces among them are less compared to repulsive forces due to electrical charges [15]. As a result, the particles are suspended in water. In order to settle these suspended colloidal particles, the first step is to destabilize them followed by formation of larger aggregates. So, the weight of the aggregated particles increases and it settles down as a floc due to gravity [16]. Nowadays, polysaccharide based flocculants have received much attention for waste water treatment processes. The demand of these materials is increasing day by day due to several advantages over other
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Polyacrylamide was supplied by HIMEDIA, Mumbai, India. Coal fine and Iron ore were collected from Jharkhand state, India. All of the chemicals were used without further purification.
counterparts such as eco friendly, easy availability, low cost, biocompatibility and easy to modify for several applications [17,18]. Besides their several unique advantages, they have some disadvantages also like poor physical and mechanical properties which restrict their application. These restrictions can be overcome by their chemical modification with different types of acrylic and vinyl monomers [19–25]. Various techniques are used for the modification of these polysaccharides. Recently, the graft copolymerization has attained a unique status for modification of polysaccharides. Grafting can be achieved by conventional redox method, microwave initiated method, microwave assisted method, γ-ray irradiation, electron beams and photochemical methods [26–29]. Among these methods, the conventional redox method is the most widely accepted technique for the modification of the polysaccharides to achieve the desirable properties as per their potential use. Among the various types of polysaccharides, barley (Hordeum vulgare L) plays an important role since ancient times. It is an agricultural crop well known throughout the world. The main chemical component of barley is polysaccharide (i.e. 90–95%) and rest are protein and fats. Starch and dietary fibres are the main components of the barley polysaccharide [30]. Starch is a carbohydrate molecule made up of large number of glucose units joined through glycosidic bonds. Starch consists of about 25–30% amylase and rest amylopectin. Amylose is a linear carbohydrate made up by D-Glucose unit and bonded through α(1 → 4) glycosidic bonds. Amylopectin is a branched carbohydrate of glucose made up by glucose units bonded in a linear way by α(1 → 4) glycosidic bonds and branching with every 24–30 repeating glucose units. Dietary fibres are made by the D-Glucose monomer linked by βglycoside bond through 1, 3 & 1, 4 carbon atom of repeating glucose units respectively. Till now, barley is used for production of beer and other liquors like brandy, whisky and some medical purposes. The modification of barley is needed to suit various applications [31]. Among the various types of natural polysaccharides, the food grade polysaccharides play an important role as a flocculant due to their non toxic nature, economic viability and widespread cultivation [32,33]. Barley satisfies all these criteria in terms of abundant cultivation, low price and it is considered as safe and reliable material since ages. The municipal waste water treatment by adding chemicals is directly related with human metabolic system. So, we need safe material and flocculants must be non toxic in nature. The food vs chemical crisis does not arise here because it is used in a small quantity given the fact that it is the 4th most abundant crop worldwide. The polymethylmethacrylate polymer is biocompatible in nature and is already used in water treatment as well as in biomedical field successfully [34,35]. Bar-gPMMA has not been used for water treatment applications till now, so we have explored this material and found it to be an efficient flocculant. Hence, this project is novel and not reported so far anywhere. In this research article, we report the successful synthesis of novel BAR-g-PMMA graft copolymer by conventional redox grafting process. Ceric ammonium nitrate is used as radical initiator for polymerization reaction. The synthesis has been confirmed by the various analytical techniques. The flocculation efficiency of the developed materials is performed in various synthetic waste waters and assessed for its application in water treatment. The acute oral toxicity of the synthesized materials has been studied. On the basis of our experimental results, the BAR-g-PMMA and its derivatives can be safely used for municipal and industrial waste water effluents.
2.2. Synthesis of BAR-g-PMMA by radical polymerization The BAR-g-PMMA was synthesized following the radical polymerization pathway. In this procedure, 1gm of barley was taken in 250 ml round bottom flask and mixed with 40 ml of distilled water at 40–45 °C under 30 min of stirring. Then it was kept at room temperature under stirring till it cooled down. Methylmethacrylate was added in this reaction mixture in varying amounts and kept under stirring condition for 15 min to make a homogeneous mixture. Afterwards, nitrogen gas was purged in the reaction mixture followed by test amount of ceric ammonium nitrate in 0.1(N) HNO3 along with nitrogen purging. Then, the reaction mixture was left undisturbed for 24 h at room temperature [36,37]. The highly viscous reaction mixture was obtained in the reaction vessel after 24 h. A saturated solution of hydroquinone was added in the gel like mass for the completion of graft copolymerization reaction. It was poured in excess acetone. A white coloured gel like precipitate was obtained in the reaction vessel and it was kept in excess acetone. After that, gel like mass was poured in distilled water and kept for 1 h for washing the unreacted part. Again, the gel like mass was poured in acetone. Then, the precipitate was collected and dried in hot air oven till a constant weight was obtained. The concentration of methylmethacrylate as monomer and ceric ammonium nitrate as initiator were taken w. r. to fixed barley concentration i.e. 1 g. The optimized concentration of monomer and initiator were evaluated w. r. to percentage grafting, intrinsic viscosity and number average molecular weight for the synthesis of BAR-gPMMA. The synthesis details for all parameters of the graft copolymer have been tabulated in Table 1.
2.3. Purification of synthesized BAR-g-PMMA by solvent extraction The synthesized materials were kept in excess acetone for 72 h for removal of any homopolymer (polymethylmethacrylate). They were collected from excess acetone and again dried in hot air oven till a constant weight was obtained [38]. The percentage grafting was calculated on the basis of following formula.
Pg =
Wg−W W
× 100
(i)
Here, W is weight of barley, Wg is the weight of grafted product and Pg is the percentage of grafting. All the synthesis parameters are summarised in Table 1.
Table 1 Synthesis details of BAR-g-PMMA by “Conventional method”.
2. Experimental 2.1. Materials Barley was purchased from Reckitt Benckiser, Ltd. New Delhi, India. Acrylamide and Acetone was supplied by Rankem (AR grade), India and Ceric ammonium nitrate was supplied from E.Merck, Mumbai, India. Methylmethacrylate and kaolin was Acros Organics, India. 114
Polymer Grade
Wt. Of Barley (gm.)
Wt. Of methyl methyacrylate (gm.)
Wt. Of CAN (gm.)
% of grafting (% G)
Intrinsic viscosity (dl/g)
Number average molecular weight (k Da)
G-1 G-2 G-3 G-4 G-5 G-6 G-7 G-8 Barley
1 1 1 1 1 1 1 1 0
10 10 10 10 10 10 12.5 15 0
0.1 0.2 0.3 0.4 0.5 0.6 0.5 0.5 0.0
8.76 47.42 66.89 114.74 166.89 89.06 72.38 68.56 0.0
1.83 3.05 3.78 5.64 10.34 8.76 7.08 6.12 1.83
1234 2456 2987 3456 7435 5436 4325 3987 176.6
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2.4. Flocculation in different suspension media
2.7. Acute oral toxicity test of modified barley
The Flocculation study of barley and different grades of BAR-gPMMA has been carried out following Jar test method [22,38]. 0.25% kaolin, 1% coal fine & 1% iron ore colloidal suspension medium have been chosen for this study. The flocculation experiment has been compared with Polyacrylamide i.e. PAM. In this procedure, the measured amount of colloidal particles (0.25% kaolin, 1% coal fine & 1% iron ore) were taken in 400 ml distilled water in six identical 0.5L beakers to make homogeneous mixture for each suspension respectively. The measured amount of flocculant was added in suspension to achieve desire dosage. After adding the measured amount of flocculant (i.e. different grades of BAR-g-PMMA & PAM), each beaker was stirred well in the Jar test apparatus. At first, all the sets of beakers were stirred at 150 rpm for 1 min and 65 rpm for 15 min followed by 15 min of settling time. Afterwards, the supernatant solutions were collected from each beaker and turbidity was measured using a calibrated ELICO®, CL 52D Nephelometer, India. Distilled water was taken as reference for kaolin, coal fine & iron ore suspension. For coal fine suspension media optical density was measured by ELICO® Double Beam, SL 210 UV spectrophotometer, India. The resultant Turbidity or optical density vs concentration of flocculant are plotted in Fig. 5(a), Fig. 5(b) & Fig. 5(c) for barley, different grades of BAR-g-PMMA and PAM. The minima of each curve represent the optimal dosage of barley, different grades of BAR-g-PMMA and PAM. The flocculation efficiency for each flocculant has been measured and shown in Fig. 6.
The acute oral toxicity test of the modified barley was performed following the Organization of Economic Co-operation and Development (OECD) guidelines for the test of chemicals and materials 425 [42]. This protocol was adopted in Dec 17, 2001. According to this protocol, five four week old Albino mice were taken for the experiment. This experimental protocol was approved (Approval No. BIT/PH/IAEC/04/ 2014 dated 30/4/2014) by the animal ethics committee of Birla Institute of Technology, Mesra, Ranchi, India. All the mice were kept in the polycarbonate cage with the required amount of food and deionized reverse osmosis water, ad libitum at 20–25° C and 40–70% relative humidity in a 12 h light on/light off cycle. According to the OECD guidelines, a single dose of 2000 mg/kg was administered. The dose was administered in each mouse with the help of stomach tube to the first animal. Then, all the mice were kept under observation up to four hours. This observation was extended upto seven days. The mortality rate was evaluated after completion of visible observation and reported accordingly [43]. 3. Characterization 3.1. Evaluation of intrinsic viscosity The intrinsic viscosity of barley and different grades of BAR-gPMMA has been measured with the help of Ubbelohde viscometer (capillary diameter 0.46 mm) in distilled water (neutral pH) as a solvent. At first, the measured amount of barley and other synthesized grades were dissolved in distilled water for preparation of four different concentrations of polymeric solutions. The flow of time was measured using stopwatch. The flow time for distilled water (solvent) is denoted as t0. The relative viscosity of the different concentration solutions has been evaluated using mathematical relation ηrel = t/t0, similarly Specific viscosity as ηsp = ηrel-1, reduced viscosity as ηred = ηsp/C and inherent viscosity as ηinh = ln ηrel/C where C is the concentration of polymeric solution in g/dL. The reduced viscosity and inherent viscosity were simultaneously plotted against different polymeric solutions. The intersection point after the extrapolation of the two plots i.e. reduced viscosity and inherent viscosity to zero concentration i.e. intrinsic viscosity was determined. All the values of intrinsic viscosity have been tabulated in Table 1.
2.5. Settling test of the suspended particles The settling velocities of different suspended particles were measured following the standard protocol [22,39]. As per the protocol, measured amount of suspensions were taken in different 1L stoppered graduated cylinders. The cylinders were marked up to upper water level with a difference of 1 cm. The height of the upper level water in cylinder from the ground level was 25 cm. The optimal dose of barley, different grades of BAR-g-PMMA and PAM were added in the different suspension media. After that, all the cylinders were turned upside down 10 times to ensure proper mixing of flocculant in the colloidal suspension mediums. Then, the cylinders were kept undisturbed in upright position and interfacial height was measured w.r.to time among distinct layers. The interfacial height vs. settling time is plotted in Fig. 7(a), Fig. 7(b) & Fig. 7(c) for kaolin, iron ore and coal fine suspension medium. The rate of settling for kaolin, iron ore and coal fine suspension medium for different flocculant is shown in Fig. 8.
3.2. FTIR spectroscopy The FTIR spectra of barley and the best grades of modified barley were recorded with the help of FTIR spectrophotometer (Model IRPrestige 21, Shimadzu Corporation, Japan) between 400 and 4000 cm−1 at a resolution of 4 cm−1 followed by the KBr pellet method. The spectrum of barley and best grade of modified barley has been shown in Fig. 1.
2.6. Municipal waste water treatment by flocculation process The flocculation performance was assessed using Municipal waste water collected from BIT-Mesra hostel effluent discharge main pothole drain following the standard protocol [40,41]. The supernatant liquid of each beaker was collected in test tube and turbidity was measured using a calibrated ELICO®, CL 52D Nephelometer, India with distilled water as a reference solution. The Turbidity vs concentration of flocculant are plotted in Fig. 9 for barley, best grade (G-5) and PAM. The common water quality parameters like pH, TSS, TDS, Total iron, Total chromium & COD of the collected waste water were measured by chemical analysis on the basis of standard protocol before and after treatment of the waste water. The pH of the wastewater was measured using ORION 4 Star series, Singapore, pH meter. The TSS and TDS were determined by the gravimetric method. The total iron and total chromium was determined after acid digestion by ELICO® Double Beam, SL 210 UV spectrophotometer, India. The results have been tabulated in Table 4. The results of the common waste water parameters are important for the application of BAR-g-PMMA as a flocculant for treatment of wastewater.
3.3. Qualitative X-ray diffractometry The X-ray diffraction pattern of barley and its best grades were recorded with the help of Bruker axis diffractometer (D8-Advance) using CuKα radiation and scanned 10–80° 2θ. The recorded diffractogram is shown in Fig. 2. 3.4. Elemental analysis The elemental analysis of barley and its best grades were evaluated with the help of Elemental Analyzer (Make – M/s Elementar, Germany; Model – Vario EL III). From this analysis, the presence of carbon, hydrogen, nitrogen, and oxygen (by difference) is confirmed. The results have been summarized in Table 2. 115
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Fig. 1. FTIR spectrum of barley and BAR-g-PMMA (G-5).
3.5. Scanning electron microscopy
Table 2 Elemental analysis details of Barley and G-4 (best grade).
The surface morphology of barley and its best grades were evaluated by scanning electron microscopy (SEM) in powdered form (Model: JSM-6390LV, Jeol, Japan). The samples were prepared for the assessment of surface morphology by the platinum coating [JEOL Auto fine coater model: JFC-1600 auto fine coater, coating time is 120 s with 20 Ma]. The surface morphograms of the samples at various magnifications using SEM JEOL model: JSM-6390LV were recorded. The morphogram of barley and its best grade is shown in Fig. 3(a) & (b).
Polymer
%C
%H
%N
%O
Barley BAR-g-PMMA(G5)
40.28 54.53
6.119 8.399
1.314 0.0
51.89 37.071
shown in Fig. 4.
3.7. Number average molecular weight determination 3.6. TGA studies The Number average molecular weight of all the samples has been determined with the help of Osmometer (A+ Adv. Instruments, INC. Model 3320, Osmometer) with distilled water as a solvent.
The thermo gravimetric analysis of barley and its grades were determined with the help of TGA instrument (Model: DTG-60; Shimzadu, Japan). The analysis was carried out in an inert atmosphere (nitrogen) from 25 °C to 800 °C. A uniform heating rate i.e. 5 °C per minute was maintained throughout the analysis. The recorded results have been
Fig. 2. XRD of barley and BAR-g-PMMA (G-5).
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polysaccharide. CAN is added in water medium, then it forms a hexa hydrated complex, so the Ce4+ ion is bonded and no longer remains free. Thus, it is not suitable for generating free radical sites on the barley backbone. In HNO3 medium, the Ce4+ ion remains free and takes part in radical polymerization reaction. The inert atmosphere (N2 atmosphere) has been used during the reaction to stop the oxidation of Ce4+ ion to Ce3+ ion in presence of air. At first, Ce4+ ion forms the chelate complex with the barley polysaccharide and results in a five membered ring which is a stable intermediate. Then, the Ce4+ ion is converted to Ce3+ by single electron transfer processes generating free radical sites on the barley backbone [36,37]. The free radicals may be formed on the eOH group which is attached on the C-2 and C-3 carbon atom in glucose unit. This is called initiation step for the grafting reaction. In the initiation step, the single unit of methylmethacrylate monomer is added on the barley backbone. The new moiety (i.e BAR-gPMMA.) is formed which takes part in further polymerization reactions. In the propagation step, more methylmethyacrylate monomers are attached on the barley backbone through methylmethyacryl chains and length of the grafted chains increases. There is a probability of attachment of different number of polymethylmethyacryte chains on barley backbone. In the termination step, two different units are attached together and form the polymethylmethyacryte grafted barley. Another possibility is that hydroquinone abstracts one radical and gets converted to hydroquinone radical by which the polymerization reaction is terminated. On the basis of above discussion, the probable reaction mechanism has been shown in Scheme 1. The radical polymerization reaction of BAR-g-PMMA was optimized by varying the different amounts of CAN and methylmethacrylate. So, different grades were obtained with varying percentage grafting. Thus, the grafting reaction depends on the concentration of monomer and initiator. Fig. 3. (a) SEM morphology of barley (300X magnification). (b) SEM morphology of BARg-PMMA (G-5) (300× magnification).
4.1.1. Effect of initiator concentration From Table 1, it is clear that with the increase in the initiator concentration, the percentage grafting increases. After a certain concentration, the percentage grafting decreases. In this graft copolymerization reaction, the maximum percentage grafting was obtained, when initiator concentration was 0.5 g w.r.to. 10 g of monomer and 1 gm of barley. After that, the percentage grafting decreases when initiator concentration was 0.6 gm w.r.to 10 gm of monomer and 1 g of barley. It is proved that at low concentration of initiator, very less number of free radicals are generated on the barley backbone and low percentage grafting is obtained. When initiator concentration increases, sufficient
4. Results and discussion 4.1. Synthesis of BAR-g-PMMA by radical polymerization The BAR-g-PMMA graft copolymer has been synthesized following the radical polymerization pathway. The ceric ammonium nitrate in 0.1(N) HNO3 medium has been used as an initiator. HNO3 plays an important role in the graft copolymerization reaction for
Fig. 4. TGA of barley and BAR-g-PMMA (G-5).
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Fig. 5. (a) Flocculation profile in 0.25% kaolin suspension. (b) Flocculation profile in 1% coal fine suspension. (c) Flocculation profile in 1% iron ore suspension. Fig. 6. Comparative study of flocculation efficiency for kaolin, coal fine and iron ore suspension medium.
grafting decreases [22,30].
number of free radical sites are generated on the barley backbone and high percentage grafting is obtained. Till the optimized dosage of initiator 0.5 g, sufficient number of free radical sites are available for grafts to attach and even for further dangling of grafted chains. When the CAN concentration increases beyond the optimized dosage, sufficient sites are not available due to competition of space among the grafted chains on the parent backbone. As a result, the percentage
4.1.2. Effect of monomer concentration From Table 1, it is clear that the percentage grafting decreases with increase in the monomer concentration at fixed initiator concentration. Here, the percentage grafting decreases at 12.5 & 15 g concentration of monomer w.r.to. 0.5 g of initiator and 1 g of barley. This is due to 118
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Fig. 7. (a) Settling test in 0.25% kaolin suspension. (b) Settling test in 1% coal fine suspension. (c) Settling test in 1% iron ore suspension. Fig. 8. Comparative study of settling rate for kaolin, coal fine and iron ore suspension medium.
increase in monomer concentration to form a polymer which leads to formation of a homopolymer. So, few Polyacrylamide chains are grafted on the barley backbone and as result the percentage grafting decreases.
4.2. Characterization 4.2.1. Interpretation of intrinsic viscosity measurement The intrinsic viscosity of barley and different grades of BAR-gPMMA were measured and all results are summarized in Table 1. From Table 1, it is confirmed that the intrinsic viscosity of developed materials increases with increase in the percentage grafting. The 119
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Fig. 9. Flocculation study of municipal waste water by barley, PAM & BAR-g-PMMA (G-5).
which confirms that the polymethylmethacrylate chains are grafted on barley backbone through 10OH and 20 OH.
intrinsic viscosity of the graft copolymer depends upon the branching of the polymeric chains on the barley backbone. This is directly related to the hydrodynamic volume of the grafted copolymer. When the grafted materials are immersed in the suitable solvent (here distilled water), it occupies some volume in the solvent because the polymeric chains are relaxed in the solvent media. The relaxation of the grafted copolymer in the solvent increases with the number of polymeric chains grafted on the barley backbone. As a result, the molecular weight increases. The number average molecular weight of barley and different grades of BAR-g-PMMA are summarized in Table 1. A well known relationship exists between intrinsic viscosity and number average molecular weight as developed by Mark–Houwink–Sakurada i.e. η = KMα where K and α are constants, M is molecular weight and η is the intrinsic viscosity. Both parameters depend upon the grafted polymeric chains on the barley backbone.
4.2.3. Qualitative X-ray diffractometry In Fig. 2 barley shows five distinct peaks at 2θ of 15.360, 17.380, 18.280, 20.260 and 23.300 region. This observation indicates the partial crystalline nature due to intermolecular interaction of OeH group present in the barley polymeric materials. In Fig. 2 for BAR-g-PMMA(G5) a broad and low intense peak is observed in 2θ of 13.500 region. This observation indicates the amorphous nature of the grafted materials. Due to grafting, the partial crystalline nature has been lost and converted to amorphous nature. This confirms that polymethylmethacrylate chains are grafted on the barley backbone. 4.2.4. Elemental analysis The elemental analysis results for barley and its best grade (i.e. BARg-PMMA (G-5)) are summarized in Table 2. In barley, a small amount of nitrogen is present i.e. 1.314% due to protein in the barley molecule. The other elements i.e. carbon, hydrogen & oxygen are 40.28, 6.119 & 51.80% respectively in barley. The percentage of nitrogen in BAR-g-PMMA (G-5) is zero, which indicates that the polymethylmethyacryte chain are not grafted on the barley backbone and the remaining portion is removed after washing through the distilled water. The other elements i.e. carbon, hydrogen & oxygen are 54.53, 8.399 & 37.071% respectively present in BAR-g-PMMA (G-5). That indicates that percentage of carbon and nitrogen increases due to the polymethylmethacrylate chains grafted on the barley backbone. On the basis of the elementary results, the polymethylmethacrylate chains do not take part in grafting on barley protein, these polymethylmethacrylate chains are involved in the grafting on barley polysaccharide backbone.
4.2.2. FTIR spectroscopy In Fig. 1, broad peaks are observed at 3278 and 3529 cm−1 region respectively due to 10OH and 20 OH of polysaccharide moiety present in barley. An intermolecular attraction is observed in the OH group of the polysaccharide moiety, as a result, the peaks are broad and overlap each other. A sharp peak is observed at 2927 cm−1 due to CeH stretching and low intensity and overlapped peaks are observed at 1456–1335 cm−1 region due to the CeH bending. Another CeH bending (out of plane) peaks are observed at 927 and 856 cm−1 region. A sharp and low intensity peak at 1658 cm−1 is observed due to NeH bending of primary amine group but the stretching peak is not clear in this spectrum due to the overlap of OeH peaks. This indicates that the small amount of protein is present in barley materials [30]. In Fig. 1 peaks are observed at 2997 and 2951 cm−1 due to methylene (-CH2-) stretching vibration (Asymmetric) and low intensity peak at 2835 cm−1 due to methylene (-CH2-) stretching vibration (Symmetric). The CeH bending vibrations for methylene (-CH2-) are also observed at 1450 and 1381 cm−1. The CeH bending vibration (out of plane) peaks are also observed at 844 and 756 cm−1. It is clear that the sp2 carbon (]CH-) of methylmethacrylate monomer is converted to sp3 carbon atom (-CH2-) for polymethylmethacrylate chains which is formed in the polymerization reaction. A sharp and intense peak at 1732 cm−1 is observed due to carbonyl group present in polymethylmethacrylate chains. A sharp peak is observed at 987 cm−1 due to new CeOeC bond formed in the graft copolymerization reaction. OeH group peaks are not observed for BAR-g-PMMA (G-5) in Fig. 4
4.2.5. Scanning electron microscopy (SEM) analysis The Fig. 3(a) & (b) represents the morphograms of barley and BARg-PMMA (G-4) in 5KV and 200 magnifications. Distinct differences have been observed in morphograms of native polysaccharide and grafted polysaccharide. The granular morphology has been observed in native polysaccharide i.e. barley which is transformed to flaky morphology, as the grafted PMMA chains are agglomerated on the barley backbone. This observation indicates that the polymethylmethacrylate chains are grafted on the barley backbone. 120
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Scheme 1. Schematic representation of mechanism for synthesis of BAR-g-PMMA using conventional method.
This is due to protein and some glucose degradation at 400 °C. The complete degradation i.e. 100 percentage is observed in 400–800 °C. The TGA analysis of BAR-g-PMMA(G-5) (Fig. 4) shows two distinct weight loss zones. The 1st weight loss zone is observed in 30–250 °C region and the% weight loss is 8.284, due to small amount of moisture present in the grafted materials. The complete degradation is observed
4.2.6. Thermal gravimetric analysis (TGA) From the TGA analysis of barley (Fig. 4) three distinct weight loss zones are observed. The 1st weight loss is observed at 30–240 °C region and the percentage of weight loss is 3.303 percentage w.r.to initial weight, due to small amount of moisture. The 2nd weight loss zone is observed in 240–400 °C region and the percentage weight loss is 70.63. 121
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greater than the barley and PAM. On the basis of the experimental results, the flocculation efficiency increases with increase in the percentage grafting. The flocculation efficiency of different grades of BAR-g-PMMA is greater than the barley. Due to the grafting, the polymeric branches increase on the barley backbone. As a result the corresponding hydrodynamic volume of the synthesized BAR-g-PMMA also increases in the distilled water. This is also related to the intrinsic viscosity and number average molecular weight. When polymeric solution is added in the colloidal suspension medium, the polymeric branches come in contact with the colloidal particles and form flocs by the weak interaction of different groups present in the graft copolymer. The formation of flocs is graphically represented in Scheme 2. With increase in the hydrodynamic volume of BAR-g-PMMA, the probability of contact will be more, as a result, the floc size increases. As a result, flocs will settle more rapidly. So the flocculation efficiency increases. This phenomenon is observed at a particular concentration. This concentration is generally called the optimal dosage. Beyond this concentration, the flocculation efficiency decreases. At higher concentrations, the density of the polymeric branches increases in the colloidal suspension as intermolecular repulsion develops between the polymeric branches. The attractive force of the colloidal particles is less than the repulsion. As a result, the suspended particles are unable to come in contact with different groups of the polymeric branches. So, the flocculation efficiency decreases. This phenomenon is known deflocculation. In this study, we observe that the flocculation efficiency increases with flocculant dose i.e. 1 ppm to 4 ppm and the efficiency decreases at 5 ppm. The best grade i.e. G-5 shows better flocculation performance than PAM. This phenomenon is shown in Fig. 5(a)–(c).
Table 3 % of weight lost in various temperature differences of Barley and BAR-g-PMMA (G-5) from TGA analysis. Weight lost zone
1st 2nd 3rd 4th
Barley
BAR-g-PMMA(G-5)
Temperature different
% of weight lost
Temperature range
% of weight lost
30–240 °C 240–400 °C 400–800 °C 30–800 °C
3.30 67.33 25.11 100
30–250 °C 250–415 °C 415–800 °C 28–800 °C
8.28 91.71 0.0 100
at 250–415 °C region. The TGA analysis results of barley and BAR-gPMMA(G-5) have been summarized in Table 3. 4.2.7. Number-average molecular weight determination The number average molecular weight of barley and different grades of BAR-g-PMMA have been measured on the basis of osmometry. The distilled water is used as a solvent in this case. The number average molecular weight has been calculated on the basis of the following relation [30].
ρ Φ×n = × 103 Cdry Mn Where Mn is the number average molecular weight, Cdry is the concentration of the dry polymeric sample in aqueous solution, Φ is the osmotic coefficient, which suggests the non ideal behaviour of the solution (here, we assume that the solution behaves ideally), n is the number of components into which a molecule dissociates and ρ is the osmosis per kilogram solvent. The determined number average molecular weight of barley and different grades of BAR-g-PMMA has been tabulated in Table 1. The number average molecular weight increases with increase in the percentage grafting. As the number of polymeric branches increase, the solubility of the polymeric materials also increases. So, the number of molecules present per kilogram of the solvent increases. The osmomolarity of the grafted materials also increases. Consequently the number average molecular weight increases.
4.2.9. Settling test of the suspended particles The settling test of the suspended particles are performed for the confirmation of flocculation efficiency. The settling velocities of the suspended particles were measured at 4 ppm (optimized doses in flocculation experiments) by standard protocol. The settling time vs. Interfacial height is plotted in Fig. 7(a)–(c). The settling rates of all suspended media are calculated from the settling test results. The maximum settling rate is observed in coal fine suspension i.e. 0.49 cm/s compared to iron ore (0.40 cm/s) and kaolin (0.43 cm/s) for G-5 flocculant greater than PAM. So, the settling rate is iron ore < kaolin < coal fine for BAR-g-PMMA as shown in Fig. 8. On the basis of experimental results, it is shown that the settling rate increases with increase in the percentage grafting. The hydrodynamic volume of the graft copolymer increases with the percentage grafting, as the floc formation probability becomes more. So, more colloidal particles come in contact with the polymeric branches and form floc by weak intermolecular attraction of the particles. The weight of resultant floc will be more, due to the gravitational force and it settles faster. So, the settling rate increases. The settling rate is higher for G-5 flocculant for each case. The settling rate of coal fine suspension is higher due to the higher size of the coal particles (1106–2669 nm.) compared with iron ore (458–712 nm.) and kaolin (955–1484 nm) suspension. The comparative study of the settling rates in different suspension media for different flocculant is shown in Fig. 8. These results suggest the flocculation efficiency results. On the basis of the flocculation study, the BAR-g-PMMA(G-5) is proved as a better flocculant than PAM.
4.2.8. Flocculation study in different suspension media The flocculation efficiency of barley and different grades of BAR-gPMMA has been carried out in different suspension media like coal fine, iron ore and kaolin suspension media as per standard protocol. The Turbidity (iron ore & kaolin) and optical density (coal fine) vs. Flocculant doses have been plotted in Fig. 5(a)–(c). The physical characteristics (Particles size and zeta potential) of suspension media have been measured with the help of Dynamic light scattering. The particles size of coal fine, iron ore and kaolin suspension media are 1106–2669, 458–712 and 955–1484 nm respectively and Zeta potential of coal fine, iron ore and kaolin suspension medium are −25.6, −21.6 and −18.8 mV respectively. The optimized dose for each suspension medium for different flocculant is 4 ppm. The flocculation efficiency in coal fine suspension medium is greater than kaolin and iron ore for each case. The increasing order of flocculation efficiency for barley and different grades of BAR-g-PMMA is iron ore < kaolin < coal fine. This is shown in Fig. 6. The flocculation efficiency of best grade i.e. G-5 is Table 4 Comparative study of common parameter of municipal wastewater.
Waste water Barley PAM BAR-g-PMMA(G-5)
Flocculation efficiency (in%)
pH
Turbidity (ppm)
TDS (ppm)
TSS (ppm)
Total Iron (ppm)
Total chromium (ppm)
COD (ppm)
0.0 28.17 60.53 70.42
7.2 7.2 7.2 7.2
71 58 37 23
276 237 187 123
390 319 217 182
1.60 1.40 1.35 1.23
0.098 0.081 0.073 0.067
446 426 324 265
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Scheme 2. Schematic representation of floc formation between colloidal suspension and BAR-g-PMMA.
4.3. Municipal waste water treatment by flocculation
guidelines, for the test of chemicals 425 (adopted Dec 17, 2001, Annexure-4) if LD50 value is greater than 2000 mg/kg, then testing in animals should not proceed further. So it belongs to “category-5” and the toxicity is zero. So the acute oral toxicity of BAR-g-PMMA(G-5) is zero [42,43].
The municipal waste water was treated by the flocculation using barley and BAR-g-PMMA (G-5) following the standard protocol. The optimized doses of flocculant (barley, PAM & BAR-g-PMMA (G-5)) for this processes is 4 ppm. The flocculation efficiency of barley, PAM and BAR-g-PMMA (G-5) are 28.17, 60.53 and 70.42 percentage respectively on the basis of turbidity. The flocculation efficiency of BAR-g-PMMA (G-5) is greater than barley and PAM. This is shown in Fig. 9. The common waste water parameters like TSS, TDS, pH, total iron, total chromium and COD were assessed pre and post treatment by flocculant (barley, PAM & BAR-g-PMMA(G-5)). The resultant values have been summarized in Table 4. The TSS and TDS were removed after the treatment and the removal efficiency of BAR-g-PMMA(G-5) is greater than the barley. The polymeric branches i.e. polymethylmethacrylate is attached on the barley backbone. As a result, the working surface of BAR-g-PMMA(G-5) is greater than the barley. So, the interaction of the colloidal suspended particles towards BAR-g-PMMA(G-5) is more than barley. So, the settling of the colloidal particles will be more than barley. As a result, reduction efficiency will be more. The reduction of total iron and total chromium is also observed. The reduction of metal concentration after flocculation occurs due to the chelate formation in heteroatoms of polymethylmethacrylate chains with the metal ion [44]. The possibility of the interaction of BAR-g-PMMA(G-5) with the metal ion is shown in Scheme 3. The reduction of organic particulates is also observed after flocculation due to the interaction of heteroatoms of grafted materials with the organic particulates. The huge difference of TSS values in BARg-PMMA(G-5) than barley indicates that it is suitable for flocculation process for municipal waste water treatment.
5. Conclusion On the basis of present investigation results, the grafting of polymethylmethacrylate chains on the barley backbone has been successfully carried out by radical polymerization path way. The synthesized materials have been confirmed by various analytical techniques. The flocculation performance of BAR-g-PMMA particularly G-5 is higher than other grades and barley and PAM in coal fine, iron ore and kaolin suspension media which makes it a superior flocculant. This flocculant is very much efficient for the removal of solid particulates in municipal waste water and shows better performance than PAM. It is non toxic in nature. So, the developed materials can be safely used for municipal wastewater treatment purpose as well as industrial effluents.
Acknowledgments The authors deeply acknowledge the financial support received from Department of Science and Technology, New Delhi, India (Letter No: SR/FT/CS-113/2011 dated 29/06/2012) & All India Council for Technical Education (AICTE), New Delhi, India (Ref. No.: 8-207/RIFD/ RPS/POLICY-1/2014-15 dated 16th March 2015). We acknowledge the Central Instrumentation Facility, BIT Mesra for characterization studies, Department of Pharmaceutical Sciences and Technology, BIT-Mesra for Acute oral toxicity study and UGC- DAE CSR Kolkata centre for XRD analysis. One of the authors (Mr. Kartick Prasad Dey) is thankful to CSIR (File No.: 09/554(0040)/2016 EmR-I dated 30/03/2017) for his fellowship.
4.4. Acute oral toxicity test for modified barley No abnormal behaviour was observed in mice after the seven days of visible observation period for BAR-g-PMMA (G-5). It is confirmed that the LD50 is greater than the 2000 mg/kg. According to the OECD 123
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