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Biodegradable Drag Reducing Agents and Flocculants Based on Polysaccharides: Materials and Applications [*].

Organic and inorganic flocculants are used in treatment of water and industrial effluents. Polymeric flocculants, synthetic as well as natural, because of their natural inertness to PH changes. low dosage, and easy handling, have become very popular in industrial effluent treatment. It has been established in the authors laboratory that by grafting polyacrylamide branches on rigid backbone of polysaccharides, the dangling grafted chains have easy approachability to contaminants in effluents. Thus grafted polysaccharides are very efficient, shear stable and biodegradable flocculants. They also exhibit turbulent drag reducing characteristics. Among grafted guar gum, xanthan gum, carboxymethyl cellulose, and starch grafted starch performs the best. Starch consists of amylose (a low molecular weight linear polymer) and amylopectin (a high molecular weight, branched polymer). The grafted amylopectin is found to be the best flocculant for various kinds of industrial effluents, providing credibility to the above-ci ted model. In the present paper, the details about grafted polysaccharides as turbulent drag reducers and flocculants are given, along with their applications.

INTRODUCTION

Flocculation is an essential phenomenon in domestic/industrial waste water treatment and mineral beneficiation [1-3]. It is caused by an addition of minute quantity of chemicals known as flocculants. The flocculants are of two types, i.e., inorganic and organic. Among inorganic flocculants, the salts of multivalent metals like aluminum and iron are used most [4]. The organic flocculants are essentially polymeric in nature. Both synthetic and natural water soluble polymers are used as flocculants. The synthetic polymers are mostly linear water soluble polymers such as polyacrylamide, polyacrylic acid, poly(diallyl) dimethyl ammonium chloride) (DADMAC) and poly(styrene sulphonic acid) etc. Among natural polymers, guar gum, starch and alginic acid are very often used as flocculants or retention aids. The synthetic flocculants are available in all the three forms, i.e., cationic, anionic and non-anionic. Some of the natural polymers also bear ionic groups. The extensive use of polymers as flocculant is due to the ir distinct characteristic attributes.

The polymers are convenient to use and do not affect the pH of the medium. They are used in minute quantities (1-5 ppm) and the flocs formed during flocculation are bigger and stronger. On the other hand, a large volume is required to obtain the same result using inorganic salt. Moreover, large tonnage use of inorganic compounds produces a lot of sludge which is hardly a problem in case of polymeric flocculants.

Among polymeric flocculants. the synthetic polymers can be tailor made by controlling molecular weight, molecular weight distribution, the structure of polymers and the nature and percentage of ionic groups. Thus the synthetic polymers are very efficient flocculants. Natural polymers, mainly polysaccharides, are biodegradable, cheap, fairly shear stable and easily available from reproducible agricultural resources. The biodegradability of natural polymers reduces their shelf-life and needs to be suitably controlled. It is thus evident that all polymers, whether natural or synthetic. have one or another disadvantage. Many attempts have been made to combine the best properties of both by grafting synthetic polymers onto the backbone of natural polymers [5]. One great advantage thus gained is the consequent reduced biodegradability because of the drastic change in the original regular structure of the natural polymer as well as the increased synthetic polymer content in the product, which is not food to bacteri a. It is also observed that grafting of shear degradable polymers onto the rigid polysaccharide backbone provides fairly shear stable systems [6].

It was envisaged in the authors' laboratory that by grafting flexible polyacrylamide chains on polysaccharides such as guar gum, xanthan gum, carboxy-methyl-cellulose and starch, it is possible to develop efficient, shear stable and biodegradable flocculants for treatment of industrial effluents and mineral processing. In these flocculants, the flexible chains of polyacrylarnide are grafted onto rigid backbone of polysaccharide, and hence, the approachability of polyacrylamide chains for metallic and non-metallic contaminants increases significantly [6] (Fig. 1). Thus they are endowed with highly efficient attributes.

A comprehensive program for development of graft copolymers based on polysaccharides and polyacrylamide was initiated at the Materials Science Centre in the late 1980s, mainly in pursuit of generating efficient and shear stable drag reducing agents [7]. As polymeric drag reducing agents and flocculants have the equivalent attributes, in the early 1990s, an endeavour to explore the potential of grafted polysaccharides as flocculants was systematically initiated.

In the authors' laboratory, many graft copolymers have been synthesized by grafting polyacrylamide chains onto guar gum [8], xanthan gum [9], carboxy methyl cellulose and starch [10]. Their shear stability and drag reduction efficiencies have been studied. Further, by variation in the number and length of grafted polyacrylamide chains onto the backbone, it has been found that the graft copolymers having fewer and longer chains are more efficient as drag reducing agents. Later on, the investigation on their flocculation characteristics yielded the same pattern, i.e., the graft copolymers having fewer and longer grafted chains were found to be more effective flocculants [6]. Among grafted guar gum, xanthan gum, carboxy methyl cellulose, sodium alginate and starch, it has been found that grafted starch is the most efficient flocculant [11-15].

Starch consists of linear amylose (molecular weight = 10,000-60,000) and branched amylopectin (mw = 50,000-[10.sup.6]). Hence, amylose and amylopectin were also grafted with polyacrylamide. Among all polysaccharides, grafted amylopectin [16] has the best flocculation efficiency, giving credence to the authors' proposed model [6].

This paper reviews the details of synthesis, characterization, and flocculation characteristics of grafted polysaccharides in treatment of synthetic as well as industrial effluents.

EXPERIMENTAL

Materials and Methods

The various polysaccharides, such as guar gum, xanthan gum, carboxymethyl cellulose, soluble potato starch, amylose and amylopectin, were obtained from commercial sources. Guar gum and xanthan gum were purified by soxlet extraction with 95% ethanol for five days. OMO was purified by washing with methanol containing dil. [HNO.sup.3] to remove inorganic impurities. Soluble potato starch, amylose and amylopectin were used as received. Analar acrylamide was recrystallised from acetone prior to use. Ceric ammonium nitrate and nitric acid of analar grade were used. Double distilled water was used during synthesis and solution preparation.

The various graft copolymers have been synthesized by ceric ion initiated solution polymerization technique [8-15]. Because in this technique, the free radicals are produced exclusively on the polysaccharide molecules. This technique thus minimizes the formation of homopolymers. Deshmukh [8, 9] has proved the absence of homopolymers by conducting blank experiments. Proof of grafting has also been obtained from rheological investigation [17]. Further proof of grafting and absence of homopolymerization is available from the studies of Owen and Shen [18]. They observed that a high concentration of acrylamide always resulted in homopolymerization, but acrylamide concentrations of less than 2.0 M and CAN concentrations of less than 0.1 M resulted in the absence of homopolymerization. Further proof of grafting is given by enzyme hydrolysis in cases of the graft copolymers of amylopectin-g-acrylamide [19]. The details will be discussed subsequently. The details of synthesis are described elsewhere [16]. Further det ails of the reaction parameters are given in Tables 1-4. GAm, XAm, CAm and SAm denote graft copolymers of guar gum, xanthan gum, CMC and starch. Similarly, SAM (St-g-PAM), AML AM (Am-g-PAM), AP-g-PAM, and SAG denote the graft copolymers of starch, amylose, amylopectin and sodium alginate respectively. The ratio of ceric ion to substrate determines the number of graft sites and thereby the number of grafts per backbone molecule. Similarly, at constant concentrations of ceric ion and substrate, the increase in acrylamide concentration gives rise to increase in length of the grafted chains keeping the number of grafted chains constant. Thus, large number of graft copolymers varying in number and length of grafted chains have been synthesized.

Characterization

The characterization of grafted and ungrafted polysaccharides by various techniques like thermal analysis, XRD, SEM, IR, NMR, viscometry and elemental analysis has been done [20]. Further proof of grafting by enzyme hydrolysis in a series of graft copolymers of amylopectin and acrylamide is given as follows [19]. All the graft copolymers were hydrolyzed with [alpha]-amylase. The 0.5 gm graft copolymer sample was dissolved at about 80-90[degrees]C in freshly prepared distilled water. The solution was cooled to room temperature. Ten cubic centimeters of [alpha]-amylase (0.1 gm/dL) was added to the polymer solution. It was slowly stirred for about 24 hours after which the solution was heated to 100[degrees]C to destroy the enzyme. It was cooled and made to 250 cc. The viscosity measurements before and after the treatment with [alpha]-amylase were carded out for all the polymers in 1 M [NaNO.sub.3] using Ubbelohde viscometer (CS/S: 0.00527) at 27 [plus or minus] 0.1[degrees]C. The time of flow was measured for s olutions at 5-7 dilutions. The intrinsic viscosity was obtained (from the point of intersection) after extrapolation of two plots i.e. [[eta].sub.SP]/C VS. C and ln ([eta].sub.rel])/C vs. C to zero concentration. Here C is the polymer concentration in g/dL and [[eta].sub.SP]/C = ([[eta].sub.rel]-1]/C, where [[eta].sub.rel] = [eta]/[[eta].sub.[omichron] = t/[t.sub.[omichron]], t being the time of flow of polymer solution (of viscosity [[eta].sub.[omichron] at the time of measurements. The details of the synthesis parameters of the graft copolymers, the flow times (of 0-0.06 g/dL solution) as well as the intrinsic viscosity of all the polymers before and after hydrolysis with [alpha]-amylase are presented in Table 5.

RESULTS AND DISCUSSION

The various graft copolymers have been synthesized by varying ceric ion and acrylamide concentrations to effect changes in the number and length of graft copolymers. This is well illustrated by the following example. Referring the Table 5, three distinct observations can be made.

In the case of the first four graft copolymers (sl. no. I-IV), a variation in the catalyst concentration was effected. keeping the moles of amylopectin and acrylamide constant. In the second series, four graft copolymers were synthesized at fixed catalyst concentration with variation in the moles of acrylamide. The mechanism of ceric ion reaction involves the formation of a chelate complex that decomposes to generate free radical sites on the polysaccharide backbone. These active free radical sites in presence of acrylic monomers generate graft copolymers. The number of free radicals sites so generated should be proportional to the concentration of ceric ions. In other words, the length of the grafted chains at a fixed monomer concentrations should be largest in case of lowest ceric ion concentration and vice versa. This trend is clearly observed in case of graft copolymers I-IV. The variation in length of grafted chains produces gradually decreasing intrinsic viscosity. The variation in the length of grafte d chains produces gradually decreasing intrinsic viscosity that can be explained in terms of increasing number and decreasing length of polyacrylamide chains. Similarly, there is decrease in the intrinsic viscosity between V and VI, which could be due to short branches because of lower acrylamide concentrations in the latter case. In cases VII and VIII, a deliberate attempt was made to use a very high molar concentration of acrylamide to observe the impact of the length of grafted chains on the intrinsic viscosity. The intrinsic viscosity values of VII and VIII are similar, which seems anomalous. This indicates that at a very high molar concentration of acrylic monomers, there may be a higher percentage conversion to homopolymer, and the resulting intrinsic viscosity might be the reflection of the mixture of homo- and graft copolymers. There could be some amount of homopolymerization formed at low acrylamide concentrations, but the percentage conversion to homopolymer is probably higher at higher monomer conc entrations in the reaction feed, according to the findings of Owen and Shen [18].

Another significant observation from Table 5 is the comparison of the time of flow of a 0.06 g/dL solution of each of the polymers both before and after treatment with [alpha]-amylase. There is not only a significant reduction in the flow times after hydrolysis, but also the difference in flow times ([t.sub.1]-[t.sub.2]) show a variation along the series (again indicating the occurrence of a series of graft copolymers with varying number and length of polyacrylamide chains). This may be due to complete hydrolysis of the amylopectin backbone, which releases the polyacrylamide chains and hence lowers the flow time. That the products are true graft copolymers and not simply physical mixtures of amylopectin and polyacrylamide is confirmed by subjecting a physical mixture of the two to treatment with [alpha]-amylase and measuring the flow time. As expected, the difference is negligibly small, which may well be within experimental error. In case of graft copolymers, the polyacrylamide chains are attached to the amy lopectin backbone, which is cleaved by enzyme. This gives the large difference in the [t.sub.1] and [t.sub.2] values of graft copolymers because of the difference in molecular weight and molecular structure (the graft copolymer is branched and of high molecular weight whereas the polyacrylamide fragments are linear and of low molecular weight) of polymer before and after hydrolysis with enzyme. In case of physical mixtures, the polyacrylamide and amylopectin are present as individual units and not as graft copolymers. Moreover, the polyacrylamide itself is not affected by enzyme, and whatever little difference is obtained may be because of the small amount of amylopectin, which is completely hydrolyzed by enzyme.

Finally, the intrinsic viscosities of graft copolymers on treatment with [alpha]-amylase are appreciably reduced. This again explains qualitatively that the products are actually graft copolymers. Interestingly, here also the difference between the intrinsic viscosities of VII and VIII after treatment with [alpha]-amylase is not too large. This supports the earlier observation that higher concentration of acrylic monomers enhances the formation of homopolymers.

Biodegradation of Grafted and Ungrafted Polysaccharides

The degradation of polymers refers to any chemical change in polymer structure. Degradation may be caused by physical, chemical, mechanical and biological means. Biodegradation involves living organisms (micro/macro) or their secretion and can be defined as a molecular phenomenon in which biological systems mediate at least one step of the overall transformation of the molecule into gaseous products and biomass [21]. Molecular degradation, which is promoted by enzymes, may occur under aerobic and anaerobic conditions, leading to complete or partial removal from the environment. For biodegradation to take place, the presence of microorganisms is essential, and the environment must provide the proper temperature, moisture level, oxygen (except for anaerobic bacteria) and nutrients. The biodegradation proceeds via hydrolysis and oxidation. Most biodegradable natural and biopolymers contain hydrolyzable groups along the main chain. The various factors affecting biodegradability are discussed by Albertsson and Ka rlsson [22].

In general, amorphicity, hydrophilicity and large surface volume ratio promote hydrolysis and microbial attack. Linear polymers are generally more biodegradable than branched polymers. The presence of oxygen in some form influences controlled biodegradation. Hydroxy. hydroperoxide and carboxyl groups formed during photodegradation may lead to increased hydrophobicity, which leads to biodegradation. Ester and anhydride group containing polymers are also prone to hydrolysis and biodegradation. All these features have been observed in biodegradation of grafted and ungrafted polysaccharides. The salient features are outlined below [23].

i) The industrial polysaccharides such as guar gum/xanthangum degrade faster, within twenty-four hours. The industrial guar and xanthan gums contain low molecular weight impurities, which can act as a nitrogen source for microorganisms. Thus its growth can be faster in industrial guar and xanthan gums than in the absence of a nitrogen source in purified guar and xanthan gums.

ii) Amylopectin, having a branched structure, does not biodegrade even in sixty days. Thus, linearity promotes biodegradation, as was outlined earlier.

iii) The graft copolymers are found less susceptible to biodegradation because grafting promotes alteration of structure of polysaccharide molecules and thus will make it less suitable as a substrate for enzymatic degradation. Moreover, the inert polyacrylamide content also increases with grafting in grafted polysaccharides, making it less prone to biological attack and more biodegradation resistant.

Biodegradation can be followed by monitoring absolute viscosities at certain intervals of time over the entire test. One-tenth of one-percent (0.1%) solutions of polysaccharides were prepared in distilled water, and viscosity was measured by the Ubbelohde viscometer. All viscosity measurements were carried out at 30[degrees]C or room temperature, where bacterial activity is at a maximum. The viscosity measurements of 1000 ppm solutions of xanthan gum were carried out on a co-axial cylinder rotary viscometer (MLW Germany) at a shear rate of 1312 [S.sup.-1] and at room temperature of 30[degrees]C. All features of biodegradation, as discussed above, are noticed in solutions of grafted and ungrafted polysaccharides. The details are given in ref. (23). The typical examples are illustrated in Figures 2 and 3.

Drag Reduction by Grafted Polysaceharides

Turbulent drag reduction is the phenomenon of drastic reduction of drag by factor of two or more below that for the solvent by addition of a small amount of some substances--mainly polymers, fibers, soaps, surfactants and their mixtures [24]. Even at the concentration of few parts per million by weight, these materials reduce turbulent intensity in flow and therefore allow liquids to flow at lesser resistance. Thus they increase the pumpability of the liquid, resulting in a net input energy saving [24, 25]. The reduction of drag during turbulent flows past solid boundaries, such as hydrofoils, ships, streamlined bodies, and flat plates, has been observed [25, 26]. Since the discovery of the phenomenon, successful applications have been made in saving energy in the trans-Alaska pipeline, storm sewers, district heating systems, irrigation, and other fields. The more exotic applications include drag reduction in blood flow; thereby less energy is needed to ensure blood circulation. As the phenomenon is of great potential benefit to several industrial processes and operations, the search for efficient and shear stable drag reducing agents is being continued. However, soluble polymers have the most potential as drag reducing agents mainly because drag reduction up to 80% can be obtained by the addition of a few tens of ppm polymer in a particular solvent. But drag reducing polymers suffer from mechanical degradation, and the drag reduction decreases with time [27, 28].

Recently there have been some attempts to improve the effectiveness of synthetic polymers to shear degradation by altering the chemical structure of polymers. Kowalik et al. [29] and Malik et al. [30] reported that intermolecular complexes formed by one polymer with anionic groups and another polymer with cationic groups increased polymer resistance. Singh et al. [6-9] tried to take advantage of the fact that natural polymers such as guar and xanthan gums are quite resistant to mechanical degradation. They grafted polyacrylamides onto polysaccharide backbones and found that the synthetic polymer becomes much more robust to shear degradation. The salient features of these grafted polysaceharides are as follows [6]:

* It has been observed that the purification of guar and xanthan gum enhances drag reduction efficiency of these polymers as removal of low molecular impurities like fats and proteins increases the effective concentration of high molecular weight polymers (Fig. 4).

* The drag reduction performance of graft copolymer depends on number and length of grafted chains. The graft copolymers with fewer and longer chains cause more drag reduction and have higher shear stability. Their molecular behavior is akin to that of flexible molecules. Their solutions in water are biodegradation resistant (Fig. 5).

* The drag reduction performance of graft copolymers is unaffected by salts present in sea water. The graft copolymers having higher solvation number have high shear stability.

* The maximum in drag reduction is obtained at concentrations of 50-100 ppm in the case of guar gum and xanthan gum. Drag reduction caused by grafted guar gum is much higher than drag reduction caused by crosslinked guar gum [31].

* The graft copolymers of starch and poly (vinyl alcohol) (Mw = 25,000) exhibit drag reduction effectiveness, even though backbone polymers are not drag reducing.

* The drag reducing characteristics of graft copolymers give credence to Brostow's polymer flow model [27, 28] (Fig. 6).

Attempts have been made to enhance the drag reduction characteristics of guar gum by crosslinking it with borax below the level of gelation [31]. The presence of intermolecular crosslinks leads to increased dimensions of the macromolecules, resulting in enhanced drag reduction though the flow induced degradation of the polymers is not apparently affected by the addition of crosslinking agent. The enhancement in drag reduction is up to 35% at concentrations above 500 ppm. On the other hand, grafting and purification enhance drag reduction up to 68% at concentrations below the 100 ppm achieved in the authors' laboratory [8].

Artificial irrigation is used in various countries to increase the production per unit area [32]. Drag reducing polymers do not have any negative effect on plant growth and soil. Hence, to increase the efficiency of centrifugal pumps for agriculture and sprinkler irrigation, the application of drag reducing polymers can be made. Singh et al. [32] demonstrated from their extensive studies that the application of drag reducing polymer reduces the energy requirement of sprinkler irrigation systems, and increases the area of coverage. In these studies, another advantage of drag reducing polymers in irrigation systems was found. The dilute polymer solutions percolate more slowly through the soil than pure water. This is due to solvation of drag reducing polymers and increased elongational viscosity of polymer solutions, which produces a higher resistance in the porous media flow in the soil.

Urea is the most prominent nitrogenous fertilizer. Singh et al. [32] developed a slow release urea by blending urea with drag reducing guar gum. Field trials of this urea have been done at IIT Kharagpur and the Indian Horticulture Institute, Ranchi [32]. These results indicate that there may be several benefits when using drag reducing polymers in irrigation systems in agriculture. Besides drag reduction, which leads to an increase in the irrigated area, the percolation loss of water in the soil can be reduced, which is important for all rain-deficient countries. The urea can be blended with drag reducing polymers, which cuts down the leaching of urea in the soil and enhances its utilization. Thus this technique is promising especially for paddy fields.

Drag reduction characteristics go hand in hand with flocculation characteristics [26]; hence it was envisaged that graft copolymers will be also effective flocculants for effluents containing metallic and non metallic contaminants. The following discussion demonstrates verification of this expectation.

Flocculation by Grafted Polysaccharides

It was pointed out in the Introduction that because of their molecular structural attributes, grafted polysaccharides are more efficient and more shear stable flocculants than polyacrylamide based flexible flocculants [6].

An extensive program was initiated in the authors' laboratory, with a materials science and engineering approach, to synthesize, characterize, and investigate structure-property relationships of grafted polysaccharide [6, 11-15, 16-20, 33-43]. Their performance in treatment of industrial effluents was also evaluated. The graft copolymers of guar and xanthan gum/carboxymethyl cellulose/starch/amylose, amylopectin/sodium alginate and polyacrylamide have been synthesized. Among them, mostly the graft copolymers--having fewer but longer branches, which gave the maximum drag reduction effectiveness and shear stability--were chosen for flocculation studies. In the guar gum, xanthan gum and starch based graft copolymers, the synthesis was scaled up in a 40 liter batch reactor. In the cases of guar gum and amylopectin, several graft copolymers were synthesized having varying number and length of grafted chains. First their effectiveness was evaluated in synthetic effluents. Later, industrial effluents were treated b y these graft copolymers [6, 15, 16, 33, 35, 38, 39, 41, 42, 43].

* The effect of molecular parameters of graft copolymers of guar gum and polyacrylamide was tested in the synthetic effluent of lead. The maximum efficiency was shown by [GA.sub.3], followed by [GAm.sub.4] and [GAm.sub.5] (41, 42). Among this series, [GM.sub.3] has fewer but longer grafted chains of polyacrylamide. It appears that the presence of lead ions in the effluent caused a straightening effect on the polymer chains. Because of this effect, the polymer chain did not assume globular form, thus making available all hydrogen bond forming sites to participate in the flocculation by bridging mechanism. [GAm.sub.5], with a larger number of shorter grafts, showed poor performance, but its flocculation efficiency was much higher than that of commercial polyacrylamide based flocculants [6, 12, 41, 42]. The synthesis of [GM.sub.3] was scaled up and tested for various synthetic and industrial effluents [41, 42].

It was observed that [GM.sub.3] performs better than guar gum and commercial flocculants based on polyacrylamide (Figure 7).

* [XM.sub.3] is the most effective drag reducing agent, having fewer but longer grafted polyacrylamide chains on a xantham gum backbone. Its synthesis was scaled up [44]. Its efficiency was tested in synthetic effluent containing lead and paper mill effluent. In the lead effluent, its performance is better than commercial and purified xanthan gum and polyacrylamide. However, the performance of [GM.sub.3] is better than [XM.sub.3]; the molecular basis of this observation has been discussed elsewhere [6, 12, 44]. In paper mill effluent treatment, the polymer acts as flocculant aids along with alum [12,44].

* Starch is used extensively for mineral treatment [37-40, 43]. Hence it was contemplated that grafted starch may perform better as a flocculant. As SAm has fewer and longer branches, it was chosen for scale-up and testing for synthetic as well as industrial effluents. A comparative study [6] was conducted for synthetic lead slurry. It has been found that it provides the best flocculating performance. At alkaline pH and higher shear rates, this flocculant perform better than the flocculant available commercially [43] (Fig. 8).

* Starch consists of linear amylose of low molecular weight (in range of 10,000-60,000) and branched amylopectin, which is major fraction of high molecular weight (in range of 50,000-[10.sup.6]). The grafted amylose performs inferiorly to grafted starch [16, 33, 36, 43].

* A large number of graft copolymers of amylopectin and polyacrylamide were synthesized (Ap-g-PAM1-Ap--g-PAM8) and their flocculation efficiency has been tested in Kaolin suspension, coal suspensions, and paper mill effluent (16, 33, 39). It has been found that Ap-g-PAM is the best flocculant (Fig. 9) compared with St-g-PAM and Am-g-PAM. The enhanced efficiency of Ap-g-PAM is because of its greater degree of branching and higher molecular weight. Among the various graft copolymers, the one with fewer but longer branch gives the best performance (Fig. 10). This also gives credence to the model proposed by Singh [6] as described in Figure 1.

* When the grafted branches were partially hydrolyzed in AP-g-PAM, its performance went on deteriorating with degree of hydrolysis. Hence it is concluded for efficient flocculation characteristics, the flexibility of grafted branches is necessary [15].

* A number of graft copolymers SAGI-SAGVI of sodium alginate and polyacrylamide have been synthesized. Their performance is inferior to that of AP-g-PAM. Similar is the performance of grafted CMC [15, 40].

Flocculation of Industrial Effluents

Several effluents from iron, copper, electroplating and paper industries have been treated by various grafted polysaccharides along with other commercial polymeric flocculants. The results of these investigations are summarized here.

* For the industrial effluents containing nickel, copper and lead ions, the performance of grafted guar gum is better than that of guar gum and Tulespar (a commercial flocculant) (41, 42).

* For industrial effluents from a copper industry (HCL, Ghatsila. India), the grafted starch (SAM-g-II) works better than Magnafloc-1011 (Allied Colloids, U.K.) at higher rpm of flocculator blades [43].

* For effluents from Steel Industry (TISCO, Jamshedpur, India) the efficiency grafted starch (SAM-g-II) is better than Magnafloc-l011 at lower concentrations of the flocculant [43].

* In flocculation of Hematite slimes, the grafted starch is found to be an efficient flocculant with small dose at with Magnafloc-1011 in the normal and acidic pH range. At alkaline pH grafted starch works even better than Magnafloc-1011 [43].

* For flocculation of iron ore slimes and Kiriburu slime pond overflows greater settling rate of particles was observed using Magnafloc-1011 when flocculant dose was 30 ppm and pulp density 10% than that using Ap-g-PAM, SAM-II and SAG-II. However, at 10 ppm flocculant dose, the performance of Ap-g-PAM and SAM-II was better than other commercial effluents [38].

* Settling and filtration experiment were also performed with commercial and laboratory synthesized biodegradable flocculants on iron ore slimes. It is observed at flocculant dose of 10 ppm the settling performance of Ap-g-PAM and SAM-II was better than Magnafloc-1011 (Fig. 11). In the filtration experiments, the performance of SAM-II is much better than SAG-II and Magnafloc-1011 at normal pH (Fig. 12) [38].

* The flocculation and settling characteristics of coking and non-coking coal suspensions were studied using biodegradable flocculants. The non-coking coals do not settle quickly and supernatant turbidity is quite high. Considering settling velocity and residual supernatant turbidity of the coal suspensions, the performance of Ap-g-PAM is the best followed by St-g-PAM both for coking and non-coking coals (Fig. 13) [39].

CONCLUSIONS

The following conclusions can be drawn from the investigation on synthesis, characterization, biodegradation, structure-property and performance of grafted polysaccharides by adopting materials science and engineering approach.

* Graft copolymers of polysaccharides can be synthesized by solution polymerization technique using ceric ion induced redox initiation. Though the technique is tedious, it can be scaled up, and homopolymerization is negligible.

* The proof of grafting can be furnished by enzyme hydrolysis of grafted polysaccharides.

* Graft copolymers are efficient and shear stable drag reducing and flocculating agents. By grafting polyacrylamide branches on guar gum, one can have a much more efficient and shear stable drag reducing agent, in comparison with the crosslinked guar gums recently reported [31]. The grafted polysaccharides having fewer and longer branches give the best performance as drag reducers.

* The application of grafted and ungrafted polysaccharides in sprinkler irrigation systems reduces energy requirements, increases area of coverage and its throughput, and the polymer added water percolates slowly through soil. Urea can also be made to release slowly by blending with polysaccharides. Thus its applications are manifold in irrigation water management and offers a viable technology to be adopted by water-deficient countries.

* Grafted polysaccharides are shear stable, efficient flocculating agents and settling aids for industrial effluent treatment and mineral processing. Of all the grafted polysaccharides, polyacrylamide grafted amylopectin, having fewer but longer branches, gives the best performance in a variety of synthetic and industrial effluents. Amylopectin, itself being a branched high molecular weight rigid polysaccharide, the grafted flexible polyacrylamide branches will have much more approachability in accordance with Singh's model [6] in comparison with other polysaccharides.

ACKNOWLEDGMENT

The authors acknowledge gratefully to CSIR, ICAR and AICTE, New Delhi. and IIT, Kharagpur, for financial support.

(*.) Based on the Invited talk by RPS at Polychar-6 (Jan. 1998) at the University of North Texas, Denton, Texas.

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(15.) R. P. Singh, R. P. Bhagat, S. R. Pandey and T. Tripathy, "Annual Progress Report, 70(0017)/95-EMR-II, Adsorption-Desorption of Polysaccharides-G-Acrylamide Copolymer on Iron Ore System and Their Correlation With Flocculation" (1997).

(16.) S. K. Rath and R. P. Singh, J. Appl. Polym. Sci., 66, 1721 (1997).

(17.) S. Ungeheur, H. W. Beversdorff and R. P. Singh, J. Appl. Polym. Sci., 37, 2933 (1989).

(18.) D. R. Owen and T. C. Shen, in Structure Solubility Relationship in Polymers, F. W. Harris and R. B. Seymour, eds., Academic Press, New York (1977).

(19.) S. K. Rath and R. P. Singh, "Enzyme Hydrolysis of Grafted Amylopectin," in Macromolecules New Frontiers, Vol. II, p. 680, K. S. V. Srinivasan, ed., Allied Publishers Limited, New Delhi (1998); J. Appl. Polym. Sci. 70, 2627 (1998).

(20.) S. K. Rath and R. P. Singh, J. Appl. Polym. Sci, 70, 1795 (1998).

(21.) Advances in Materials Technology Monitor, Advanced Polymers for Environment, Issue No. 34 (Dec. 1993).

(22.) A. C. Albertsson and S. Karlsson, "Controlled Degradation by Artificial and Biological Processes," in Macromolecular Design of Polymeric Materials, p. 793, K. Hatada, T. Kitayama and O. Vogel, eds., Marcel Dekker, New York (1997).

(23.) R. P. Singh, "Biodegradation and Enzyme Hydrolysis of Grafted and Ungrafted Polysaccharides," in Macromolecules New Frontiers, Vol. II, p. 1088, K. S. V. Srinivasan, ed., Allied Publishers, New Delhi (1998).

(24.) R. P. Singh, S. R. Deshmukh and S. K. Majumdar, "Studies on Turbulent Drag Reduction by Graft Copolymers," X International Congress on Rheology, Sydney, Vol. II, 2278, Plenum Press, New York (1988).

(25.) A. Gyr and H. W. Bewersdorff, Drag Reduction of Turbulent Flows by Additives. Kluger Academic Publishers, Dordrecht, The Netherlands (1995).

(26.) J. M. J. den Toonder, Drag Reduction by Additives. The State of Art Internal Report Lab. Aero and Hydrodynamics, Delft University of Technology (1992).

(27.) W. Brostow, Polymer, 24, 631 (1983).

(28.) W. Brostow, H. Ertepinar and R. P. Singh, Macromolecules, 231, 5109 (1990).

(29.) R. M. Kowalik, I. Duvdvani, D. G. Pffeifer, R. D. Lundeberg, K. Kitano and D. N. Scpultic, J. Non Newtonian Fluid Mechanics, 24, 1 (1987).

(30.) S. Malik, S. N. Shentre and R. A. Mashelkar, Macromolecules, 26, 55 (1993).

(31.) J. B. Bello, A. J. Muller and A. E. Salz, Polymer Bulletin, 36, 11 (1996).

(32.) R. P. Singh, J. Singh, S. B. Deshmukh, D. Kumar and A. Kumar, "Application of Drag Reducing Polymers in Agriculture," Current Science, 68, 631 (1995).

(33.) S. K. Rath and R. P. Singh, Colloids and Surfaces, A Physicochemical and Engineering Aspects, 139, 129 (1998).

(34.) G. P. Karmakar, T. Kumar and B. P. Singh, "Polysaccharide Based Water Soluble Graftcopolymers: Synthesis, Characterization and Their Applications in Oil Industries," accepted for presentation in Petrotech-99, 3rd International Petroleum Conference and Exhibition, New Delhi (Jan 9-12, 1999).

(35.) G. P. Karmakar and R. P. Singh, Synthesis and Application of Polymeric Flocculants for the Treatment of Paper Mill Effluents, Advances in Chemical Engineering, p. 201, Allied Publishers, New Delhi, (1996).

(36.) N. C. Karmakar, S. K. Rath, B. S. Sastry and R. P. Singh, J. Appl. Polym. Sci, 70, 2619 (1998).

(37.) R. P. Bhagat, G. P. Karmakar and R. P. Singh, On Filtration of Iron Ore Slime Using Synthesized Co-polymer, Recent Advances in Metallurgical Processes, Vol. 1, 89, New Age International (P) Limited Publishers, New Delhi (1997).

(38.) S. R. Pandey, T. Tripathy, B. P. Bhagat and R. P. Singh, "Behaviour of Iron Ore Slimes Using Various Polymeric Flocculants," in Macromolecules, New Frontiers, Vol. II, p. 275, K.S.V. Srinivasan, ed., Allied Publishers, New Delhi (1998).

(39.) N. C. Karmakar, B. S. Sastry and R. P. Singh, "Settling Characteristics of Coking and Non-Coking Coal Fines", Ibid, 114 (1998).

(40.) T. Tripathy, S. R. Pandey, R. P. Bhagat and R. P. Singh, Ibid, 267 (1998).

(41.) K. Kannan, M. Tech, thesis, Materials Science Centre, IIT, Kharagpur, India (1988).

(42.) S. K. Jain, M. Tech. thesis, Materials Science Centre, IIT, Kharagpur, India (1989).

(43.) G. P. Karmakar, PhD thesis, Materials Science Centre, IIT, Kharagpur, India (1994).

(44.) N. T. Lan, M. Tech. thesis, Materials Science Centre, IIT, Kharagpur, India (1990).
 Details of Synthesis of Grafted Polysaccharides.
Sample Moles in Yield (g) Intrinsic
 No. Reaction Viscosity
 Mixture [[eta]] (dL/g)
 Acrylamide Ce x [10.sup.3]
 GAm3 0.14 0.05 8.835 834
 GAm4 0.14 0.10 11.106 688
 GAm5 0.14 0.20 11.264 478
 GAm6 0.14 0.25 9.702 319
 GAm7 0.14 0.30 9.621 280
 GAm8 0.14 0.05 3.523 703
 GAm9 0.14 0.05 10.908 938
 XAm2 0.14 0.10 5.758 1884
 XAm3 0.14 0.20 9.65 1026
 XAm4 0.14 0.30 10.24 812
 XAm5 0.14 0.40 10.88 528
 CAm1 0.14 0.05 3.96 1150
 CAm2 0.14 0.10 9.17 734
 CAm3 0.14 0.20 9.18 605
 CAm4 0.14 0.30 10.0 541
 CAm5 0.21 0.10 13.83 850
 CAm6 0.28 0.10 15.48 900
 SAm1 0.14 0.03 8.51 512
 SAm2 0.14 0.03 9.23 397
 SAm3 0.14 0.10 10.04 305
 SAm6 0.21 0.05 12.21 410
 SAm7 0.28 0.05 16.45 509
 SAm8 0.35 0.05 16.94 546
 PAm1 0.14 0.063 6.45 476
 PAm2 0.14 0.125 8.9 400
 PAm3 0.14 0.25 9.1 310
 PAm4 0.14 0.375 10.9 220
 PAm5 0.14 0.438 10.7 100
Details of Synthesis and Characterization of PAM Grafted Poly (Vinyl
Alcohol).
 1 2 3 4 5 6 7 8 9
Grade Ia 0.008 0.14 0.0625 7.81 2.24 54.55 470
I Ib 0.008 0.14 0.125 15.63 1.12 79.09 400
 Ic 0.008 0.14 0.25 31.25 0.56 81.82 310
 Id 0.008 0.14 0.375 46.88 0.37 89.55 220
 Ie 0.008 0.14 0.438 54.75 0.32 87.27 100
 IIa 0.008 0.035 0.0625 7.81 0.56 61.79 115
 IIb 0.008 0.070 0.125 15.63 0.56 75.83 300
Grade IIc 0.008 0.14 0.25 31.25 0.56 81.82 310
II IId 0.008 0.21 0.375 46.88 0.56 95.94 330
 IIIa 0.008 0.035 0.25 31.25 0.14 87.5 90
 IIIb 0.008 0.07 0.25 31.25 0.28 81.67 140
Grade IIIc 0.008 0.14 0.25 31.25 0.56 81.82 310
III IIId 0.008 0.21 0.25 31.25 0.84 78.13 350


Column 2 - Polymer

Column 3 - Polyvinyl Alcohol (milimole)

Column 4 - Acrylamide (mole)

Column 5 - [Ce (IV)] in milimole

Column 6 - [Ce (IV)] [Poly (vinyl alcohol)]

Column 7 - [Acrylamide] / [Ce (IV) x [10.sup.3]]

Column 8 - Percent Yield

Column 9 - Intrinsic Viscosity [[eta]] (dL/g)
 Details of Synthesis and Characterization
 of Amylose Based Graft Copolymers. [1]
Acrylamide Samples Ce (IV) Yield Convers- [[eta]] [3] [M.sub.n] x
 X 10 [3] (%) ion (%) [2] (ml/g) 10 [-64]
 0.14 SAM I 0.03 85.7 84.26 660 1.10
 0.14 SAM II 0.03 89.71 88.69 820 1.52
 0.14 AML-AM-L3 0.03 58.93 54.8 700 1.20
 0.14 Aml-AM-L5 0.03 75.20 72.7 720 1.25
 0.14 AML-AM-L7 0.03 74.45 71.89 710 1.22
Acrylamide [M.sub.w] x
 10 [-64]
 0.14 1.88
 0.14 2.46
 0.14 2.02
 0.14 2.09
 0.14 2.06


SAM-L-I Starch-g-polyacrylamide

SAM-S-II Starch-g-Polyacrylamide (Scale up-II)

AML-AM-L3 Amylose-g-Polyacrylamide (Laboratory, 3 hrs)

AML-AM-L7 Amylose-g-Polyacrylamide (Laboratory, 5 hrs)

AML-AM-L7 Amylose-g-Polyacrylamide (Laboratory, 7 hrs)

(1.) The reactions were carried out in nitrogen atmosphere at 30 [plus or minus] 0.1[degrees]C Reaction time: SAM-L-1 and SAM-S-II - 24 hrs.; AML-AM-L - 3 hrs. AML-AM-L - 5 hrs. and AML-AM-L - 7 hrs.

(2.) Monomer Conversion = [[M.sub.o] - [M.sub.t])/[M.sub.0]/100 Where [M.sub.0] is the initial concentration of monomer and [M.sub.t] is the concentration of unreacted monomer

(3.) 30 [plus or minus] 0.1[degrees]C; Ubbelohde Viscometer (CS/S :0.01)

(4.) [[eta]] = 6.8 X [10.sup.-4] [[M.sub.n].sup.0.66]; [[eta]] = 6.31 X [10.sup.-5] [[[M.sub.w]].sup.0.80]

(C. L. McCormick and K. A. Lin, J. Macromol. Sci. -Chern A16(8), 1441, (1981))
 Synthesis Details of Sodium Alginate Based Graft Copolymers.
Polymer Ploysaccharide Acryamide CAN Conversion Intrin.
 (gms) (mole) (mole x [10.sup.4] (%) Visc.
 [[eta]]
 (dL/g) [**]
SAG I 2.5 0.12 1.003 83.76 6.75
SAG II 2.5 0.12 2.006 84.58 6.70
SAG III 2.5 0.12 3.009 85.88 6.63
SAG IV 2.5 0.12 5.15 92.35 6.15
SAG V 2.5 0.24 2.006 93.45 6.82
SAG VI 2.5 0.30 2.006 95.56 6.90
Percentage conversion is calculated from the relation: Percent
conversion = [{Wt. of graft copolymer - wt. of polysaccharide}/
{amount of acrylamide} X 100
(**.)Intrinsic viscosity was evaluated for Graft Copolymers in
aqueous 1M [NaNO.sub.3] solutions
Synthesis and Hydrolysis Details of the Amylopectin Based Graft Copolymers.
SI. Polymer AGU [a] Am. CAN Conversion [b]
No. (Mol.) (Mol.) (Mol. H [10.sup.4]) (%)
I Ap-g-PAM 5 0.0154 0.21 0.5016 70.8
II Ap-g-PAM 1 0.0154 0.21 1.003 87.6
III Ap-g-PAM 6 0.0154 0.21 1.5048 88.13
IV Ap-g-PAM 2 0.0154 0.21 2.006 90.95
V Ap-g-PAM 3 0.0154 0.28 1.003 77.8
VI Ap-g-PAM 4 0.0154 0.14 1.003 84.1
VII Ap-g-PAM 7 0.006 0.28 1.003 78.4
VIII Ap-g-PAM 8 0.006 0.35 1.003 81.6
IX Ap + PAM -- - -- --
SI. [[[eta].sub.1]] [c] [[[eta].sub.2]] [d] [t.sub.1] [e] [t.sub.2] [f]
No. dL/g dL/g Secs. Secs.
I 11.38 8.68 347.8 306.1
II 10.61 8.22 310.3 272.5
III 9.76 7.41 287.55 252.85
IV 6.95 5.45 250.7 230.1
V 9.93 8.37 332.35 293.05
VI 7.46 6.26 240.9 227.7
VII 11.68 10.77 367.6 348.1
VIII 11.67 10.97 371.2 354.0
IX -- -- 307.7 307.2
SI. [t.sub.1] - [t.sub.2] [t.sub.1] - [t.sub.2]/[t.sub.1] x 100
No. Secs.
I 41.7 11.98
II 37.8 12.18
III 34.70 12.08
IV 20.6 8.17
V 39.30 11.82
VI 13.2 5.80
VII 19.5 5.30
VIII 17.2 4.63
IX 0.5 0.16


(a.)Calculated on the basis of anhydroglucose units (one gram mole of AGU is equal to 162 grams).

(b.)Percent conversion is calculated from the relation: Conversion = [(Weight of graft copolymer -- weight of polysaccharide)/Amount of acrylamide] H 100

(c.)Intrinsic viscosity of the graft copolymer [Polymer solutions for intrinsic viscosity measurements were made in aqueous 1 M [NaNO.sup.3]]

(d.)Intrinsic viscosity of the graft copolymer after hydrolysis.

(e.)Time of flow of 0.06% solution of graft copolymer before hydrolysis.

(f.)Time of flow of a 0.06% solution of the graft copolymer after hydrolysis with [alpha]-Amylase.
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Author:SINGH, RAM PRAKASH; KARMAKAR, G. P.; RATH, S. K.; KARMAKAR, N. C.; PANDEY, S. R.; TRIPATHY, T.; PAND
Publication:Polymer Engineering and Science
Geographic Code:1USA
Date:Jan 1, 2000
Words:7397
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