GRAFTING ONTO GUAR GUM

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1 GRAFTING ONTO GUAR GUM Dr.Sandeep Rai GRPL Limited Panoli GIDC, Ankleshwar, India Dr.Purvi J naik Shroff S R Rotary Institute of Chemical Technology Vataria, Ankleshwar, India ABSTRACT Grafting is an innovative method to produce a new class of semi synthetic polymeric materials. By the way of grafting, original properties of polymer are retained, also additional and useful properties are incorporated. Natural polymers are available in large quantities on the earth since billions of years. Guar gum is a versatile polysaccharide and is used as food and medicinal plants. In this communication, we report graft copolymerization reaction of Acrylonitrile onto Guar gum. A probable mechanism of grafting was proposed and rate of grafting was calculated. Key Words: Grafting, Guar Gum, % Grafting, Natural polymers Introduction Guar gum is a non-ionic branched chain natural polymer. It consists of straight mannose units joined by β-d (1 4) linkage having β-d galactopyranose units to this linear chain by (1 6) linkages. Guar gum forms viscous, colloidal, dispersion when hydrated in cold water. It is mainly used as a viscosity builder and water binder in many industries i.e. mining, textiles, explosives, paper, petroleum, etc. Few of the applications of this natural polymer are defined in detail [1] as follows, 1 Food Guar Gum for Bakery: The major application of Guar Gum Powder is in the production of bread. Small quantities of Guar Gum powder can lead to increase in dough yield, impart greater resiliency, improve texture and extend shelf life. Guar Gum for Dairy: Guar Gum is a superb binder of water and a stabilizer. The large use of it can be seen in the production of cheese, liquid milk products, ice-creams, sherbets and others food products. It is also a famous gelling agent. Guar Gum for Meat: For different meat products, Guar is used as lubricants and excellent binder. It allows storage with less loss of weight and filling time for cans is also reduced. Guar Gum for Dressing and sauces: One of the important uses of Guar is as lubricant and it is also an excellent thickener used to improve the stability appearance of salad dressings, ketchups, relishes, barbecue sauces and others. It is fairly compatible with highly acidic emulsions. 1 Vol. 01 Issue 07 Oct. 2014

2 Guar Gum for Beverages: As a stabilizer for chocolate drinks, fruit nectars, and juices etc., there is a vast use of Guar gum is seen. Guar Gum for Miscellaneous food applications: There are various food applications of Guar Gum in Frozen food items, sweet dessert, and canned fish in sauce, Dry soups, and others. 2 Guar Gum for Pharmaceutical & cosmetics: Guar Gum is used as a disintegrator and binder in compressed tablets. Guar Gum is also used as a thickener for various cosmetics and pharmaceutical applications. A significant decrease in cholesterol levels was observed after administration of Guar Gum in human consumption in several studies [2]. The other major application of Guar Gum are in Water treatment, Mining, Oil-drilling, Textile printing, Tobacco Industry, Explosives and others. Although advantageous, this viscosity is very difficult to control. Moreover, aqueous solution of Guar Gum is readily attacked by microorganisms. To control the viscosity of solution by Grafting of vinyl monomers onto Guar Gum has been reported by several studies [3]. The most of the work is based on redox initiators. Highlights of the literature survey of the previous work is summarized below, Polymerization of water-soluble monomers: Number of water-soluble monomers produces water soluble polymers e.g poly acrylamides which widely used as flocculants in waste-disposal, sugar industries, paper, oil recovery, textile etc. Numerous workers have reported grafting of such monomers on to Guar Gum [4-7]. Bajpai et.al [8] developed processes in which acrylamides are polymerized by new redox initiating systems. In general, an oxidant-reductant containing system generates initially a free radical and that free radical initiates the polymerization of vinyl monomers. A wide variety of redox initiating systems has been developed but still there are opportunities to work on inorganic material containing redox systems. Redox systems are preferred over thermal polymerization because they create free radicals at low temperature; minimize side reactions which occur at higher temperature. As per the literature survey, the aqueous polymerization of vinyl monomers viz., acrylamide, methylacrylamide using a new redox initiating systems can be successfully carried out [9]. Drawbacks of guar gum can be minimized by grafting vinyl monomers on to it. Chemically initiated vinyl graft co-polymerization is easier than photochemical, thermal and other methods of initiation because it involves less costly equipments and can be adopted by industry easily. Rate of graft co-polymerization can be derived to get the optimum experimental conditions. In order to obtain this, different reaction parameters are varied and their effects in percentage grafting and grafting efficiency have been studied. The percentage grafting can be calculated by the following formula [8], % of grafting = w 1 w 0 w 0 X Vol. 01 Issue 07 Oct. 2014

3 w 1 = Weight of grafted Guar gum w 0 = Weight of Guar gum initially [Weight of grafted Guar gum = Weight of grafted guar gum + crucible- Weight of crucible] In this article, we report probable mechanism of grafting reaction of Acrylonitrile on to Guar Gum using Ferrous Sulphate/Reducing Agent (Ascorbic Acid) Redox system. Effects of different organic solvents, inorganic salts, surfactants have also been studied in detail to find out the optimum conditions for the polymerization reaction. Rate expression for the polymerization was also proposed. Experimental: Mechanism: In general free radicals are generated by the redox reaction between Reducing Agent and Oxidizing Agent [10].The mechanism of Ferrous Sulphate and a Reducing Agent may be represented as: Formation of free radicals: Radical Initiation: Mostly, free radical generating initiators are used in grafting onto guar gum, which are typically water soluble. Radical initiation is only considered to occur in the aqueous phase and modelled accordingly. The redox initiation is used for the grafting, where the reaction is carried out in the lower temperature range (from 5 o C to 35 o C). A general mathematical expression of Redox Polymerization is given as under [11], Kinetic of redox polymerization Kinetic scheme: Initiation Oxidant + Reductant k r R + Products k i R + M R - M Propagation R MM k p R - M - M R M M + M k p R M M M Termination M x + M y k tc M x+y M x + M k td y M x + M y Where R is the primary free radical and RM is the secondary free radical,k r and k i are the rate constants for the redox and initiation step. 3 Vol. 01 Issue 07 Oct. 2014

4 R - M - M and R M-M - M etc are the growing macroradicals, kp is the rate constant of the propagation step. K tc and k td are the rate constants for the termination by combination and disproportionation respectively. Making the useful assumptions, the following expressions can be derived for the rate (Rp) and degree of polymerization (p) Rp = d[m] = k p p = k r 2k tc +2k td 0.5 [oxidant] 0.5 [reductant] 0.5 [M] dt k p M x 1 2k r k tc +k 0.5 td oxident 0.5 reductant 0.5 A probable mechanism [9] of initiation and generation of primary free radicals involving Ferric salt and Reducing Agent is shown below, I + Fe 2+ R in + Fe 3+ + Y - (1) Fe 3+ + RA Fe 2+ + RA + (2) Similarly, mechanism for graft copolymerization on to Guar Gum has been depicted below: R + M (Monomer) R M (3) RM + n M R M n+1 (4) GOH + R M n GGO + R M n H (Homopolymer) (5) GOH + R GO + R H (6) GO + M GOM (7) (Guar gum radical) GO M + nm GOM n (8) 2 GOM n Graft copolymer (9) It is evident from the above reactions that R i radicals may initiate the graft copolymerization by H abstraction from the guar gum backbone. However, we proposed the generation of guar macro radical (GO ) by eq (6) as initiation of vinyl polymerization is relatively faster reaction than H abstraction by primary radicals. Based on the theoretical estimations, the rate of grafting (R g ) can be expressed as R g = K [GOM n ] [M] R g = K [Fe +3 ] 0.5 [RA] 0.5 [GOH] x It is therefore can be concluded that, Rate of grafting is proportional to the concentration of Ferrous Sulphate, reducing agent and Guar Gum. Effect of Ascorbic Acid The effect of ascorbic acid was studied in the range (10 x 10-3 to 42 x 10-3 M/L) at fixed concentration of acrylonitrile (10 x 10-2 M/L),ferrous sulphate (1x 10-3 M/L),and AgNO 3 (8 x 10-5 M/L) 4 Vol. 01 Issue 07 Oct. 2014

5 It was observed that percentage grafting increases with ascorbic acid concentration up to certain range. It can be explained by the fact that, in presence of ascorbic acid, AH Radical _. and SO 4 radicals are generated in the system. The number of initiating free radicals increases due to the increase in concentration of ascorbic acid. This fact may be responsible for the higher rate of grafting. Figure 1: Effect of Ascorbic acid on percentage grafting Time vs.% grafting curve for the grafting of acrylonitrile with varying concentration of ascorbic acid (10 x 10-3 to 42 x 10-3 M/L) at fixed concentration of 8 x 10-5 M/L (AgNO 3 ), 10 x 10-2 M/L (acrylonitrile), 22 x 10-3 M/L (FeSO 4 ), (guar gum) 0.1 gm, temperature 35 0 C Effect of molecular Oxygen Molecular oxygen plays an inhibitor role in system. In free radical polymerization oxygen plays an inhibiting role, and in this case also the molecular oxygen acts favourably, which was visible by very slow rate and negligible percentage grafting [12]. Ferrous sulphate Effect The change in percentage and efficiency of grafting at varying concentration of the Ferrous sulphate ( x 10-3 M/L) at fixed concentration of acrylonitrile (10 x 10-2 M/L), ascorbic acid (22x 10-3 M/L), guar gum (0.1 gm), AgNO 3 (8 x 10-5 M/L). The increase in percent and efficiency of grafting with Ferrous sulphate concentration is due to generation of more primary radicals: the numbers of propagating radicals thereby increase the number of grafted sites on the backbone of guar gum. The observed order with respect to ferrous sulphate concentration is 0.3 while the predicted order according to proposed mechanism is 0.5.Such a difference has been found in some other cases also and may be attributed to preliminary radical termination. 5 Vol. 01 Issue 07 Oct. 2014

6 Figure2: Effect of FeSo 4 on percentage grafting Time vs.% grafting curve for the grafting of acrylonitrile with varying concentration of ferrous sulphate (10-46 x 10-3 M/L) at fixed concentration of 8 x 10-5 M/L (AgNO 3 ), 10 x 10-2 M/L (acrylonitrile) 17 x 10-3 M/L (ascorbic acid ), ( guar gum).0.1 gm, temperature 35 0 C Monomer effect The initial rate of grafting was found to increase with an increase in initial concentration of monomer in the range (8-16 x 10-2 M/L), keeping other ingredients constant. The increase in rate of grafting with increase in acrylamide concentration may be due to the formation of more M n radicals, which in turn may generate more grafting sites on guar gum by abstraction of H atom. Figure 3: Effect of Monomer (AN) on percentage grafting Time vs.% grafting curve for the grafting of acrylonitrile with varying concentration of monomer(8-20 x 10-2 M/L) at fixed concentration of of 8 x 10-5 M/L (AgNO 3 ), 10 x 10-2 M/L 6 Vol. 01 Issue 07 Oct. 2014

7 (acrylonitrile),22 x 10-3 M/L (FeSO 4 ), 17 x10-3 M/L (ascorbic acid), (guar gum).0.1 gm, temperature 35 0 C Guar Gum Effect Effect of Guar Gum on grafting was studied in the range ( g) at fixed concentration of acrylonitrile (10 x 10-2 M/L),ascorbic acid (22x 10-3 M/L), guar gum (0.1 gm), AgNO 3 (8 x 10-5 M/L).and FeSO 4 (1 X 10-3 M/L) It has been found that both percent and efficiency of grafting increase with guar gum in a certain range ( g).increase in percent grafting and efficiency at a higher concentration may be due to availability of more guar gum back bone chains for grafting. It is also possible that at higher concentrations some of the guar gum molecules react with primary radicals to generate backbone macro radicals as shown below GOH + R GO + RH At higher quantity of guar gum (above 0.15 g ) a decrease in grafting in observed which may be due to the very high viscosity of the medium causing hindrance in normal graft copolymerization. Effect of guar gum concentration on percentage grafting Weight of guar gum(g) Grafting % 30 min 60 min 90 min 120 min Temperature Effect The rate of grafting and efficiency have been found to increase with increase in temperature from 25 to 50 0 C at constant concentration of other ingredients. The increase in grafting percentage and efficiency at higher temperature may be due to: 1. Increased number of collisions between the monomer and guar gum molecules due to decrease in the viscosity of the medium. 2. Formation and propagation of more active sites on backbone polymer due to higher rate of generation of primary radicals. 3. Enhancement in the activity of monomer with the increase in temperature. 7 Vol. 01 Issue 07 Oct. 2014

8 Figure 4: Effect of Temperature on percentage grafting Time vs.% grafting curve for the grafting of acrylonitrile with varying temperature (30 to 50 0 C) of the reaction at fixed concentration of 8 x 10-5 M/L (AgNO 3 ), 10 x 10-2 M/L (acrylonitrile), 22 x 10-3 M/L (Fe 2 SO 4 ), 17x 10-3 M/L (ascorbic acid),( guar gum)0.1 gm Effect of addition of Organic Solvents The effect of organic solvent such as MeOH, EtOH, BuOH, DMF and dioxane, on grafting was studied by addition of 5% v/v of the solvent to the reaction medium. The initial rate of grafting was found to decrease in presence of MeOH, EtOH, BuOH, dioxane and DMSO but limiting rate and percent grafting was found to enhance in case of alcohols. The initial decrease may be due to the fact that the addition of these organic solvents reduces the area of hydration layer and thus offers the macro radial end for premature termination. In the later course of reaction, the increase in grafting rate may be due to the oxidation of alcohols producing more sulphate ion radicals (SO 4 -. ) Figure 5: Effect of organic solvent on percentage grafting Time vs.% grafting curve for the grafting of acrylonitrile showing the effect of addition of solvent (by volume) at fixed concentration of of 8 x 10-5 M/L (AgNO 3 ), 17x 10-3 M/L (ascorbic acid )10 x 10-2 M/L (acrylonitrile),22 x 10-3 M/L (FeSO 4 ),( guar gum)0.1 gm temperature 35 0 C 8 Vol. 01 Issue 07 Oct. 2014

9 In case of DMF, the dielectric constant of the reaction medium is lowered, which leads to the formation of the sulphate radical ion (SO -. 4 ) and increase in the rate and percentage of grafting. In reaction of the proposed mechanism, as two oppositely charged ions are involved, the rate of this reaction will increase with decrease in dielectric of the medium. Effect of Salts In general, the addition of small amount of inorganic salts viz. LiCl, KCl and NaCl in the reaction medium have been found to accelerate grafting.this can be explained as: Addition of cations to the reaction medium brings about two opposing effects in aqueous medium. (i) The hydrated cations interact with SO -. 4 Ion and may produce more OH. Radicals which leads an increase in rate of grafting. (ii) Due to hydration of Cations, the availability of water molecules in the bulk of the solution decreases and the equilibrium of reaction AH 2 = AH - + H + shifts towards the right. This result into an increase in the rate of generation of AH. Radicals and an increase in rate of grafting was observed. The dielectric constant of reaction medium was lowered [13],which results in a greater electrostatic attraction between the hydrated cation and the SO -. 4 Ion which will bring an increase in grafting rate since Li+ ion is the largest hydrated ion reaction will be more effective with Li+,in comparison to Na + and K + ions,resulting in an increase in rate of grafting in the order Li + < Na + < K + On the other hand, the addition of anions, such as Cl - and Br - reduces the rate of grafting whereas that of I- ions increases the rate.the addition of Cl - and Br- increases the ionic strength of the medium, which may result in premature termination of the grafting radical chain. The increase in Figure 6:Effect of Salt on percentage grafting Time vs.% grafting curve for the grafting of acrylonitrile showing the effect of added natural salts and complexing agents (in equal amount) at fixed concentration of 8 x 10-5 M/L 9 Vol. 01 Issue 07 Oct. 2014

10 (AgNO 3 ), 10 x 10-2 M/L (acrylonitrile),22 x 10-3 M/L (FeSO 4 ),17x 10-3 M/L ( ascorbic acid), ( guar gum)0.1 gm, temperature 35 0 C grafting Rate by addition of I- ions is due to their oxidation in the system and therefore increases the rate References: 1.Ratna Sharma, Guar Gum Grafting and Its Application in Textile,Asian J. Exp. Sci., Vol. 19, No. 2, 77-81(2005) 2. Anek Pal Gupta and Devendra Kumar Verma, Guar gum and their derivatives: A research profile, ISSN International Journal of Advanced Research, Volume 2, Issue 1, , (2014) 3. G.S.Mishra and U.D.N.Bajpai,Prog.poly.Sci.,8, (1981) 4. Arti Srivastava, Vivek Mishra, Pooja Singh, Ambika Srivastava & Rajesh Kumar, Journal of Thermal Analysis and Calorimetry, 107: (2012) 5. Kunj Bihari,Jaya Benerjee,Artishrivastava,Dinesh kumar Mishra,Indian journal of chemical technology,vol 12,pp ,( 2005) 6. J. H. Trivedi, T.A. Bhatt, and H. C. Trivedi,Trends in Carbohydrate Research, 3(4), (2011) 7. Srivastava A. Behari K., Journal of Applied Polymer Science, 114(3), ,, Published by Wiley Interscience,(2009) 8. U.D.N.Bajpai and Sandeep Rai, J. Apply. Polym.Sci., 35, (1988) 9. U.D.N.Bajpai,Alka Jain and Sandeep Rai, J. Apply. Polym.Sci., 39, (1990) 10. W. Kern, Makromol.Chem. 1,209,249 (1948) 11.G.K.Mishra and C.V.Gupta, Makromol.Chem., (1973) 12. E.S. Roskin,Zh.Prikl. Khim., 30, 1030(1957); Chem. Abstr. 51, (1957) 13. K.J.Laidler, Chemical Kinetics,Tata McGraw Hill,New Delhi,p.213 (1973) 10 Vol. 01 Issue 07 Oct. 2014

Guar Gum Grafting and Its Application in Textile

Asian J. Exp. Sci., Vol. 19, No. 2, 2005, 77-81 Guar Gum Grafting and Its Application in Textile Ratna Sharma Textile and Clothing Sarojini Naidu Govt. Girls College Bhopal (M.P.) Abstract : It is a common