Microwave Assisted Synthesis of Polyacrylamide Grafted Guar Gum and its Application as Flocculent for Waste Water Treatment

 

Hemant R. Badwaik¹*, Deepa Thakur¹, Kalyani Sakure², Tapan Kumar Giri¹, Kartik T. Nakhate¹, Dulal Krishna Tripathi¹

¹Rungta College of Pharmaceutical Sciences and Research, Kohaka-Kurud Road,

Bhilai, 490 024, Chhattisgarh India.

²Institute of Pharmaceutical Education and Research, Borgaon (Meghe), Wardha-442001 India.

 

 

ABSTRACT:

Industrial and municipal waste frequently contain metal ion, of which, industrial waste constitutes the major source of pollution in natural water. An abstraction of these colloidal metal particles from wastewaters becomes a serious challenge for the industries. Attention has been increasingly paid to natural polymer flocculants owing to their wide availability, biodegradability, and environment-friendliness. In the present investigation, polyacrylamide grafted guar gum (GG-g-PAAm) was synthesized using microwave assisted method in the presence of ceric ammonium nitrate (CAN) as an initiator. The synthesis was optimized for highest percentage grafting by varying the microwave irradiation time, power, initiator, and monomer concentration. Characterization of the grafted product was performed by the FTIR and TGA methods. The copolymer resulting from the graft copolymerization reaction was subsequently treated with gluteraldehyde (GA) to obtain crosslinked hydrogel. Further, flocculation efficacy of crosslinked hydrogel was studied by standard ‘Jar test’ procedure in 0.25% kaolin suspension, to assess its application as flocculating agent for wastewater treatment.

 

 

 

INTRODUCTION:

Water pollution due to heavy metals has attracted a wide attention because of their unfavorable effects on the environment and human health. Industrial and municipal waste frequently contain metal ion, of which, industrial waste constitutes the major source of pollution in natural water¹. The wastewaters originated from various industries contain very fine suspended particles (0.001–10 µm). Because of surface charge and very small size, it is challenging to bring these particles closer to make heavier mass for settling². Often these particles remain suspended for years. Hence, abstraction of these colloidal particles from wastewaters becomes a serious challenge for the industries³. Out of various wastewater treatment processes, flocculation is an economical and effective technique, plays a dominant role in a removal of suspended particles, dyes and heavy metals⁴.

 

Attention has been increasingly paid to natural polymer flocculants owing to their wide availability, biodegradability, and environment-friendliness⁵. The novel products with wide range of applications are obtained by grafting of synthetic polymers onto biopolymers. Such chemical modification yields new molecules with appropriate properties of both biopolymer and synthetic polymer^6-12.Polymers are usually synthesized by conventional grafting method^13-18, microwave irradiation^19-22, γ-ray irradiation^23-26, and using electron beam^27-28. Grafting with conventional procedures may lead to polysaccharide backbone degradation and are not responsive to block copolymer formation²⁹. As compared to conventional methods microwave-assisted synthesis has expanded the competence of synthetic chemist, since it enables faster and cleaner reactions and more pure products³⁰.

 

Guar gum (GG) is a natural non-ionic polysaccharide obtained from the two annual leguminous plants, Cyamopsistetragonalobus and psoraloides ³¹. India is the largest exporter of GG. The currently accepted structure of GG is a linear chain of β -1, 4-linked mannose residues to which galactose residues are α-1, 6-linked at every second mannose, forming short side-branches³².

 

The aim of the present work is to synthesize and evaluate ceric induced microwave assisted GG-g-PAAm hydrogel as flocculent for waste water treatment.

 

MATERIAL AND METHODS:

Materials

GG was supplied by Loba Chemie Pvt. Ltd., India. Acrylamide (AAm) was purchased from E. Merck (India). CAN was procured from SD Fine Chem, India.GA and Methanol were purchased from Loba Chemie Pvt. Ltd., India. All chemicals were used without further purification.

 

Methods

Microwave initiated synthesis of GG-g-PAAm

Briefly, 1 g of GG was dissolved in 40 ml distilled water. Desired amount of AAm was dissolved in 10 ml water and was added to GG solution. They were mixed well and were transferred to the reaction vessel. A catalytic amount of CAN was added. The solution so obtained was irradiated by microwave in domestic microwave oven for different times and different powers to prepare various batches of grafted gum. The microwave irradiation was paused periodically, just before boiling of the reaction mixture (∼65ºC) and was cooled by placing the reaction vessel in cold water. This was done to minimize the homopolymer formation and also to prevent formation of toxic/carcinogenic acrylamide vapors. After completion of microwave irradiation, the reaction vessel was cooled and kept undisturbed for 24 h, to complete the grafting reactions. The grafted GG was precipitated with excess of methanol and purified by solvent extraction method using a mixture of formamide and acetic acid (1:1; v/v) to remove the homopolymer. The resulting precipitate of graft copolymer was dried in hot air oven at 45ºC for 12 h. The grafted material was grinded until a homogenous powder was obtained. The mechanism of grafting is represented in fig. 1.

 

 

Fig. 1: Schematic representation for microwave assisted synthesis of GG-g-PAAm.

The % grafting (%G), % grafting efficiency (%GE), % conversion (%C) and % homopolymer (%H) was calculated using the following equations³³:

 

Where, W₁, W₀ and W₂ denote the weight of the grafted gum, the weight of original GG and the weight of the monomer used, respectively. The reaction parameters, i.e. effect of monomer concentration, effect of microwave power (MW) and exposure time were optimized in respect to %G, %GE, %C and %H. During optimization of one parameter, other parameters were kept constant.

 

Preparation of GG-g-PAAm crosslinked hydrogel

Crosslinked GG-g-PAAm was prepared by water-in-oil (w/o) emulsification method ³⁴. Briefly, 20 ml of 5.0% (w/v) GG-g-PAAm was prepared and acidified with 5 ml dilute sulphuric acid. 25% (w/v) and GA solution (7.5 ml) was added. This solution was then emulsified into 100 ml of light liquid paraffin with 2% (w/v) sodium laurelsulphate using mechanical stirrer at 600 rpm for 5 h at room temperature. Hardened hydrogel microspheres were filtered and washed repeatedly with hexane and water to remove liquid paraffin, unreacted GA and any adhered sodium laurel sulphate. The hydrogel microspheres were then dried overnight at 40 ºC. The crosslinking reaction is represented in fig. 2.

 

Fig. 2: Crosslinking of GG-g-PAAm with GA.

 

Characterization

FTIR spectroscopy

The FTIR spectrums of GG (Fig. 3a) and GG-g-PAAm (Fig. 3b) were recorded in solid state, by KBr pallet method using a FTIR spectrophotometer (Model IR-Prestige 21, Shimadzu Corporation, Japan) between 400 and 4000cm⁻¹.

 

Fig. 3: FTIR spectrum of (a) GG and (b) GG-g-PAAm.

TGA studies

The TGA of GG and GG-g-PAAm was carried out with TGA instrument (Model: DTG-60; Shimadzu, Japan). The study was performed in inert atmosphere nitrogen from 25- 600 ºC. The heating rate was uniform in all cases at 5 ºC/min. The concerned TGA curves (a and b) have been shown in fig. 4.

 

Fig. 4: TGA of (a) GG and (b) GG-g-PAAm.

 

Flocculation studies ³⁵

The flocculation efficiency of various polymer samples was carried out using standard Jar Test Method. All flocculation experiments were carried out in Jar test apparatus (Make: Simeco, Kolkata, India). A kaolin suspension 0.25 % (prepared by mixing 1 g in 400 mL of distilled water) was used for flocculation study. The suspensions were taken in a 1- Liter beakers and the flocculant was added in solution form. The following procedure was uniformly applied immediately after the addition of flocculant; the suspension was stirred at a constant speed of 75 rpm for 2 min, followed by low stirring at 25 rpm for 5 min. The flocs were then allowed to settle down for 15 min. afterwards, supernatant liquid was collected and turbidity measured in a calibrated nephelo turbidity meter (Digital Nephelo Turbidity Meter 132, Systronics, India). Distilled water served as reference. The relationship between polymer concentration and residual turbidity of the supernatant liquid was plotted.

 

RESULTS AND DISCUSSIONS:

Synthesis of GG-g-PAAm by microwave initiated method

GG-g-PAAm has been synthesized by CAN induced microwave assisted method. Various grades of the graft copolymer were synthesized by varying the CAN and AAm concentration. In each case, the microwave irradiation of the reaction mixture was continued until it sets into a viscous gel like mass. The grafting is optimized at AAm concentration of 10g and CAN concentration of 0.3 g in the reaction mixture (∼60 ml), when the MW is maintained at 800 W for 45 sec. The mechanism of microwave assisted grafting has been depicted in “Figure1”. CAN is electron deficient molecule. So it takes electrons from alcoholic oxygen in GG to form a new bond i.e. Ce-O. This bond being more polar (than O-H bond), breaks easily in the presence of microwave irradiation to form free radical site on the backbone of GG from where the graft chains grow.

 

Determination of the optimum grafting conditions

The grafting of AAm on GG backbone in the presence of catalyst (CAN) was occurred by free radical reaction mechanism. The scheme of free radical reaction is given in fig. 1. Reaction parameters like exposure time, monomer concentration and MW in respect to %G, %GE, %C were optimized keeping the total reaction volume fixed.

 

Effect of monomer concentration

The %G and %GE at different AAm concentrations were calculated for the copolymer samples synthesized at fixed concentration of the GG (1 g), CAN (0.3 g), keeping the power and exposure time fixed at 800 and 45 sec, respectively in the reaction mixture (60 ml). The concentration of the monomer was varied from 2.5 to 12.5 g. Initially on increasing the AAm concentration, %G increased due to availability of extra monomer for the copolymerization, however on increasing AAm concentration >10 g, %G decreased as more homopolymerization (Fig. 5) takes place due to increase in monomer to GG ratio.

 

Effect of CAN concentration

Increasing the concentration of CAN initially leads to an increase in the %G, %GE, and %C, but further increases in concentration have a negative effect (Fig. 6). The increase in the %G may be due to an increase in GG macroradicals in the propagation step (Fig. 1), since an increase in CAN concentration means that more CAN free radicals can attack the saccharide unit of GG. This would generate more GG macroradicals and more active sites to react with AAm. By further increasing the amount of CAN help to initiate the polymerization of AAm (homopolymer), thereby resulting in a decrease of the %G and %GE. The ceric concentration was varied from 0.1to 0.5 g, at  10 g AAm, keeping the total reaction volume, power and exposure time fixed at 60 ml, 800W and 45 sec respectively. %G and %GE increased with increase in CAN concentration and reached a maximum value at 0.3 g CAN.

 

Effect of microwave power

The effect of MW (MW) on grafting parameter was studied by varying power from 500 to 900 W (Fig. 7). %G, %GE increases with the increase of MW power in the beginning but when power was more than 800W the %G and %GE are lowered indicating that higher microwave radiation promotes homopolymerization more, than the graft co-polymerization and due to formation of more homopolymer the yield of grafted gum is lowered.

Effect of exposure time

It is obvious from fig. 8 that with increase in microwave irradiation time (up to 45 sec), %G and %GE increased. Higher the microwave irradiation time, greater was the number of free radical sites created on the GG backbone. This in turn resulted in higher extent of grafting of AAm. However, prolonged irradiation beyond 45 sec resulted in decrease in percentage grafting. This may be because prolonged exposure to microwave irradiation might have degraded the GG backbone, thereby decreasing the percentage grafting.

 

Fig. 5: %G, %GE, %C and %H at different monomer concentrations.

 

 

Fig. 6: %G, %GE, %C and %H at different CAN concentrations.

 

 

Fig. 7: %G, %GE, %C and %H at different microwave power.

 

 

Fig. 8: %G, %GE, %C and %H at different exposure time.

 

 

Characterization

FTIR spectroscopy

From the FTIR spectrum of GG (Fig. 3a), it has been observed that a broad peak at 3601.54 cm⁻¹ is due to the stretching vibrations of O–H, a smaller peak at 2900.48 cm⁻¹ is attributed to the C–H stretching vibrations. The bands at 1020.02 cm⁻¹ and 864.71 cm⁻¹ are assigned to C–O–C stretching vibrations. In the spectra of GG-g-PAAM (Figure 3b), a new shoulder peak at 3453.89 cm⁻¹and sharp peak at 1601.04 cm⁻¹ is attributed to N–H stretching. A small peak at 2912.41 cm⁻¹ is attributed to the C–H stretching vibration. The peak at 1682.15 cm⁻¹ is due to C=O stretching vibrations. Further there is one more additional band at 1457.27 cm⁻¹ corresponding to the C–N bending vibration also supports the grafting.

 

TGA studies

The TGA curves of GG (Fig. 4a) essentially involve three distinct zones of weight loss. The initial weight loss is at 40–120 ºC. This is because of the traces of moisture present. The second zone of weight loss (230–325 ºC) may be because of the degradation of polymer backbone (secondary alcohol –CHOH) and the third zone of weight loss (335–540 ºC) may be because of the degradation of polymer backbone (primary alcohol –CH₂OH).

In case of GG-g-PAAm (Fig. 4b), in addition to the above zones of weight loss, have an extra zone of weight loss (505–565 ºC). This extra zone of weight loss is because of amide group (–CONH₂) of the grafted polyacrylamide chain of the synthesized polymer. Hence, the presence of this extra zone is a clear recommendation that polyacrylamide has been grafted onto the backbone of GG.

 

Flocculation studies

The flocculation study in 0.25% kaolin suspension in ‘Jar test’ apparatus has been graphically represented in fig. 9 for both GG as well as the GG-g-PAAm hydrogel. It is obvious that GG-g-PAAm hydrogel shows better performance with low turbidity than GG itself. This phenomenon could be explained by considering bridging mechanism. It is concluded that GG-g-PAAm hydrogel is efficient flocculent, for the waste water treatment.

 

Fig. 9: Flocculation characteristics of GG and GG-g-PAAm hydrogel in 0.25% kaolin suspension.

CONCLUSION:

The results of the present study suggest that microwave assisted graft copolymerization is an efficient method for synthesis of GG-g-PAAm. Suitable improvements in the flocculation properties could further encourage the efforts for GG-g-PAAm hydrogel in water and wastewater treatment.

 

ACKNOWLEDGEMENTS:

The authors are thankful to Santosh Rungta Group of Institutions, Bhilai, India for providing necessary infrastructural facilities.

 

REFERENCES:

1.       Badruddoza AZ, Shawon ZB, Tay WJ, Hidajat K and Uddin MS. Fe₃O₄/cyclodextrin polymer nanocomposites for selective heavy metals removal from industrial wastewater. Carbohydrate Polymers. 9; 2013: 322-332.

2.       Bolto B and Gregory J. Organic polyelectrolytes in water treatment. Water Research. 41; 2007: 2301–2324.

3.       Divakaran R and Pillai VNS. Flocculation of kaolinite suspensions in water by Chitosan. Water Research. 35; 2001: 3904-3908.

4.       Crini G. Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment. Progress in Polymer Science. 30; 2005: 38–70.

5.       Renault F, Sancey B, Badot PM and Crini G. Chitosan for coagulation/flocculation processes - An eco-friendly approach. European Polymer Journal. 2009; 45: 1337-1348.

6.       Joshi JM and Sinha VK. Ceric ammonium nitrate induced grafting of polyacrylamide onto carboxymethyl chitosan. Carbohydrate Polymers. 2007; 67: 427-435.

7.       Meshram MW, Patil VV, Mhaske ST and Thorat BN. Graft copolymers of starch and its application in textiles. Carbohydrate Polymers. 2009; 75: 71–78.

8.       Badwaik HR, Giri TK, Nakhate KT, Kashyap P and Tripathi DK. Xanthan Gum and Its Derivatives as a Potential Bio-polymeric Carrier for  Drug Delivery System. Current Drug Delivery. 2013; 10: 587-600.

9.       Rui-He Y, Wang X, Wang Y, Yang K, Zeng J and Ding S. A study on grafting poly(1,4-dioxan-2-one) onto starch via 2,4-tolylene di isocyanate. Carbohydrate Polymers. 2006; 65: 28-34.

10.     Számel G, Domján A, Klébert S and Pukánszky B. Molecular structure and properties of cellulose acetate chemically modified with caprolactone. European Polymer Journal. 2008; 44: 357–365.

11.     Giri TK, Thakur D, Alexander A, Ajazuddin, Badwaik H and Tripathi DK. Alginate based Hydrogel as a Potential Biopolymeric Carrier for Drug   Delivery and Cell Delivery Systems: Present Status and Applications. Current Drug Delivery. 2012; 9: 539-555.

12.     Zhu J, Dong X, Wang X and Wang Y. Preparation and properties of a novel biodegradable ethyl cellulose grafting copolymer with poly (p-dioxanone) side chains. Carbohydrate Polymers. 2010; 80: 350-359.

13.     Behari K, Pandey PK, Kumar R and Taunk K. Graft copolymerization of acrylamide onto xanthan gum. Carbohydrate Polymers. 2001; 46: 185-189.

14.     da Silva DA, de Paula RCM and Feitosa JPA. Graft copolymerization of acrylamide onto cashew gum. European Polymer Journal. 2007; 43: 2620–2629.

15.     Hebeish A, Abd El-Thalouth I, El-Kashouti MA and Abdel-Fattah SH. Graft copolymerization of acrylonitrile onto starch using potassium permanganate as initiator. Angewandte Makromolekulare Chemie.1979; 78: 101–108.

16.     Kang HM, Cai YL and Liu PS. Synthesis, characterization and thermal sensitivity of chitosan-based graft copolymers. Carbohydrate Research. 2006; 11: 2851–2857.

17.     Singh V, Tiwari A and Sanghi R. Studies on K₂S₂O₈/ascorbic acid initiated synthesis of Ipomoea dasysperma seed gum-g-poly (acrylonitrile): A potential industrial gum. Journal of Applied Polymer Science. 2005; 98: 1652-1662.

18.     Giri TK, Thakur D, Alexander A,  Ajazuddin, Badwaik H, Tripathy M and Tripathi DK. Biodegradable IPN hydrogel beads of pectin and grafted alginate for controlled delivery of diclofenac sodium. Journal of Materials Science: Materials in Medicine. 2013; 24: 1179-1190.

19.     Kumar A, Singh K and Ahuja M. Xanthan-g-poly (acrylamide): Microwave-assisted synthesis, characterization and in vitro release behavior. Carbohydrate Polymers. 2009; 76: 261-267.

20.     Masuhiro T, Shafiul I, Takayuki A, Alessandra B and Giuliano F. Microwave irradiation technique to enhance protein fibre properties. Autex Research Journal. 2005; 5: 40-48.

21.     Mishra S and Sen G. Microwave initiated synthesis of polymethylmethacrylate grafted guar (GG-g-PMMA), characterizations and applications. International Journal of Biological Macromolecules. 2011; 48: 688-694.

22.     Singh V, Tiwari A, Pandey S and Singh SK. Peroxydisulfate initiated synthesis of potato starch-graft-poly (acrylonitrile) under microwave irradiation. eXPRESS Polymer Letters. 2007; 1: 51–58.

23.     Biswal J, Kumar V, Bhardwaj YK, Goel NK, Dubey KA, Chaudhari CV and Sabharwal S. Radiation-induced grafting of acrylamide onto guar gum in aqueous medium: Synthesis and characterization of grafted polymer guar-g-acrylamide. Radiation Physics and Chemistry. 2007; 76: 1624–1630.

24.     Geresh S, Gdalevsky GY, Gilboa I, Voorspoels J, Remon JP and Kost J.  Bioadhesive grafted starch copolymers as platforms for per oral drug delivery: A study of theophylline release. Journal of Controlled Release. 2004; 94: 391–399.

25.     Wang JP, Chen YZ, Zhang SJ and Yu. A chitosan-based flocculant prepared with gamma- irradiation-induced grafting. Bioresource Technology. 2008; 99: 3397–3402.

26.     Xu Z, Yang Y, Jiang Y, Sun Y, Shen Y and Pang J. Synthesis and characterization of Konjacglucomannan-graft-polyacrylamide via c-irradiation. Molecules. 2008; 13: 490-500.

27.     Jampala SN, Manolache S, Gunasekaran S and Denes FS. Plasma-enhanced modification of xanthan gum and its effect on rheological properties. Journal of Agricultural and Food Chemistry. 2005; 53: 3618-3625.

28.     Vahdat A, Bahrami H, Ansari N and Ziaie F. Radiation grafting of styrene onto polypropylene fibres by a 10MeV electron beam. Radiation Physics and Chemistry. 2007; 76; 787-793.

29.     Tizzotti M, Charlot A, Fleury E, Stenzel M and Bernard J. Modification of polysaccharides through controlled/living radical polymerization grafting towards the generation of high performance hybrids. Macromolecular Rapid Communications. 2010; 31: 1751–1772.

30.     Kappe CO. Controlled microwave heating in modern organic synthesis. Angewandte Chemie International Edition.  2004; 43: 6250-6284.

31.     Ma X and Pawlik M. Intrinsic viscosities and Huggins constants of guar gum in alkali metal chloride solutions. Carbohydrate Polymers. 2007; 70: 15–24.

32.     Ahmed ZF and Whistler RL. The Structure of Guaran. Journal of the American Chemical Society. 1950; 72:  2524–2525.

33.     Athawale VD and Lele V. Graft copolymerization onto starch. II. Grafting of acrylic acid and preparation of its hydrogels. Carbohydrate Polymers. 1998; 35: 21–27.

34.     Soppirnath KS and Aminabhavi TM. Water transport and drug release study from cross-linked polyacrylamide grafted guar gum hydrogel microspheres for the controlled release application. European Journal of Pharmaceutics and  Biopharmaceutics.  2002; 53: 87–98.

35.     Mishra S, Mukul A, Sen G and Jha U. Microwave assisted synthesis of polyacrylamide grafted starch (St-g-PAM) and its applicability as flocculant for water treatment. International Journal of Biological Macromolecules. 2011; 48: 106–111.

 

 

 

Received on 17.02.2014       Modified on 15.03.2014

Accepted on 19.03.2014      © RJPT All right reserved