Grafted amylopectin: applications in flocculation

Colloids and SurfacesA: Physicochemical and Engineering Aspects 139 (1998) 129–135

Grafted amylopectin: applications in flocculation

S.K. Rath, R.P. Singh *Materials Science Centre, Indian Institute of Technology, Kharagpur 721302, India

Received 29 May 1997; received in revised form 12 December 1997; accepted 22 December 1997

Abstract

Graft copolymers of amylopectin and polyacrylamide were synthesized using a ceric ion induced redox initiationtechnique. Flocculation characteristics of the graft copolymers were studied using two systems, one containing asynthetic effluent of kaolin clay (0.25% w/v) in distilled water, and the other containing a paper-mill white effluent. Theresults were compared with some of the commercially available flocculants. It was found that the performance of graftcopolymers is on a par with most of the commercial flocculants tested, although one of them performed better. Thesynthetic parameters affecting the variation in the number and length of polyacrylamide chains in the graft copolymersare found to affect the flocculation behaviour. Aquaset (AS 510) is found to be a better flocculant for the white paper-mill effluent in comparison with the graft copolymers. © 1998 Elsevier Science B.V. All rights reserved.

Keywords: Amylopectin; Graftcopolymer polyacrylamide; Flocculation effluent

1. Introduction anionic and nonionic. Some of the natural poly-mers also bear ionic groups. One requires largevolumes of inorganic salts to obtain similar resultsFlocculation [1,2] has played an important role

in domestic and industrial waste water treatment, to those obtained with a very small amount ofpolymeric flocculant. Also, the use of largemineral benificiation, etc. The flocculation is

caused by addition of a minute quantity of chemi- amounts of inorganic materials produces a lot ofsludge unlike polymeric flocculants. The inorganiccals termed as flocculants. The flocculants can be

inorganic or organic in nature. Among the inor- salts are effective over a particular pH. Therefore,there is frequent need for pH adjustment. This isganic flocculants the salts of multivalent metals

such as aluminium and iron are mostly used. The not a factor when using polymeric materials. Dueto the adaptivity of synthetic polymers, they areorganic flocculants may be synthetic or natural.

Synthetic flocculants are mostly water soluble [3,4] much more effective than natural polymers.However, natural polymers are biodegradable andlinear polymers like polyacrylamide, poly(acrylic

acid), poly(diallyl dimethyl ammonium chlo- non-toxic (the synthetic polymers themselves arenon-toxic but the associated unreacted monomersride)(poly DADMAC), poly(4-styrene sulfonic

acid) etc. Natural polymers [5] such as starch, may be). At the same time, the very advantage ofnatural polymers i.e. their biodegradability,cellulose, alginic acid, guar gum etc. are very oftenbecomes a major drawback since it reduces theirused as flocculants/retention aids. Synthetic floc-storage life and their efficiency due to the loweringculants are available in all three forms, i.e. cationic,of the molecular weight.

* Corresponding author. E-mail: [email protected] In the past, many attempts have been made to

0927-7757/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved.PII S0927-7757 ( 98 ) 00250-7

130 S.K. Rath, R.P. Singh / Colloids Surfaces A: Physicochem. Eng. Aspects 139 (1998) 129–135

combine the best properties of synthetic and natu- could be due to the larger fraction of the branchedand high molecular-weight amylopectin.ral polymers by grafting [6–12] the synthetic poly-

In our previous study [14], all the three poly-mers onto natural ones. The grafted products thussaccharides (i.e. amylose, amylopectin and starch)obtained have reduced biodegradability [7]were grafted with polyacrylamide and the floccu-because of the drastic change in the original struc-lation characteristics of the graft copolymers wereture of the natural polymer as well as the syntheticmeasured in kaolin suspension. It was found thatpolymeric content in the product that is not a foodthe graft copolymers of amylopectin and polyacryl-for the bacteria. It has also been observed thatamide performed better than the graft copolymersgrafting of shear degradable polymers such asof amylose and starch with polyacrylamide.polyacrylamide onto rigid polysaccharide back-Among a series of graft copolymers of amylopectinbones provides fairly shear stable systems withand polyacrylamide, the one with fewer but longerflexible grafted chains on rigid backbone. In thebranches performed better. However, in that study,authors laboratory many graft copolymers haveonly four graft copolymers were synthesized andbeen synthesized by grafting polyacrylamide ontoevaluated for their flocculation characteristics. Instarch [8], CMC [8], guar gum [9], xanthan gumthe present investigation, four more graft copoly-[7,10] etc., and their shear stability and biodegrad-mers have been synthesized in order to give aability as well as drag reduction efficiencies havebetter insight into the phenomenon. The compara-been studied. By varying the number and lengthtive evaluation of their flocculation characteristicsof the polyacrylamide chains grafted onto thein kaolin suspension as well as in the white effluentbackbone, it has been found that the graft copoly-from a paper mill is carried out. The flocculationmers with fewer but longer polyacrylamide chainscharacteristics of some commercial flocculantsare more efficient as drag reducing agents.were also studied for comparative evaluation. ThisThe same characteristics of the graft copolymerspaper reports the results of the above investigationare reflected in their flocculation behaviour i.e. thein detail.

graft copolymers with fewer but longer chains arefound to be more effective flocculants [11]. It waspostulated by one of the authors (R.P.S.) [11] that 2. Materialsgraft copolymers are more effective flocculantswhen compared with the linear polymers, because Amylopectin and amylose (both from corn) wereof the greater approachability of the dangling purchased from Sigma, USA. Soluble starch andflexible polyacrylamide chains to the particles in acrylamide were purchased from Merck, Germany.suspension. Among polyacrylamide grafted guar Ceric ammonium nitrate (CAN) was obtainedgum, xanthan gum and starch, it has been observed from Loba Chemie, Bombay, India. Acetone andthat grafted starch is the most efficient flocculant hydroquinone were supplied by S.D. Fine[11]. In another study [12], the flocculation behavi- Chemicals, Mumbai, India. Sodium nitrate wasour of starch-g-polyacrylamide and amylose-g- supplied by Merck (India), Bombay and kaolinpolyacrylamide was compared. The former showed by B.D. Pharmaceutical Works, Howrah, India.better results when compared with the latter. It is As for the commercial flocculants, only three ofwell known that starch consists of two polymers them, Aquaset (AS 510), Sufloc and Ap-273of anhydroglucose units, i.e. amylose, the linear (Separan) were used for comparison. Aquaset (AS[13] fraction and amylopectin, the branched [13] 510), which is a proprietary polyelectrolyte, wasfraction. Amylose, which is the minor fraction is obtained from Aquapharm Ltd., Pune, India.of low molecular weight (in the range of Sufloc was obtained from Suyog Chemicals Ltd.,10 000–60 000), whereas amylopectin which is the Nagpur, India. Ap-273 (Separan) was obtainedmajor fraction is of high molecular weight (in the from Dow, USA. It is a very high molecular-range of 50 000–106). It was thus anticipated that weight polyacrylamide. The commercial floccu-

lants used are of classified nature. The onlythe better efficiency of starch-g-polyacrylamide

131S.K. Rath, R.P. Singh / Colloids Surfaces A: Physicochem. Eng. Aspects 139 (1998) 129–135

information the authors could gather was that all from the relation gsp/C=(grel−1)/C, where grel=g/g0#t/t0. In this expression t is the time of flowof them are based on polyacrylamide. The chemi-

cals received were used as such without further of polymer solution and t0, the time of flow ofsolvent at the temperature of measurement.purification.( ln grel)/C is the inherent viscosity.

3.3. Flocculation3. Experimental

3.1. Synthesis The standard Jar test [18] was followed. Theflocculator used was supplied by M.B. Instruments,Bombay, India. The turbidity measurement wasThe graft copolymers of starch, amylose and

amylopectin were synthesized by a ceric ion carried out with the help of a Digital NepheloTurbidity meter 132, obtained from Systronics,induced redox initiation [15,16] method. The

experimental details are described elsewhere [14]. Ahmedabad, India. A 0.25% w/v suspension ofkaolin clay was used for flocculation study. 400 mlThe same method was used here with a variation

in the monomer and catalyst concentration to of suspension was taken in each of the five 1 lbeakers and the flocculant was added in solutionobtain a series of graft copolymers (Ap-g-PAM5

to Ap-g-PAM8) (Table 1). form. Dosage variation of flocculants was madefrom 0.025 to 1 ppm. The following procedure wasuniformly applied for all the flocculants.3.2. Viscosity measurementImmediately after the addition of the flocculants,the suspensions were stirred at an uniform speedViscosity measurements of all the graft copoly-

mers in solution were carried out with the help of 75 rpm for 2 min. This was followed by a slowstirring at 20–25 rpm for 5 min. Afterwards, aof a Ubbelohde capillary viscometer (constant:

0.00527) at 27±0.1°C. A stock solution of settling time of 10 min was allowed. At the end ofthe settling period, the turbidity of the supernatant0.5 g/250 ml was prepared which was further

diluted with NaNO3 solution and distilled water liquids was measured by the Digital NepheloTurbidity Meter. In all 10 dosage variations werein such proportions that the required concentration

of polymer was obtained in 1 M NaNO3. The time made (0.025–1.0 ppm).of flow for a fixed volume of solution was measuredat five different concentrations. The intrinsic vis-cosity was obtained (from the point of intersection) 4. Results and discussionafter extrapolation [17] of two plots i.e. gsp/Cversus C and ln(grel)/C versus C to zero concen- One of the advantages of using the ceric ion

induced redox method for the initiation of grafttration. Here C is the polymer concentration ing/dL and gsp/C is reduced viscosity, calculated copolymerization onto polysaccharide backbones

Table 1The synthesis details of the graft copolymers

S1 no. Graft copolymer AGU (mol )a AM (mol ) CAN (mol×104) % conversionb [g] (dl/g)

I AP-G-PAM 5 0.0154 0.21 0.5016 70.8 11.4II AP-G-PAM 6 0.0154 0.21 1.5048 88.13 9.775III AP-G-PAM 7 0.006 0.28 1.003 78.4 11.6IV AP-G-PAM 8 0.006 0.35 1.003 81.6 11.83

a Calculated on the basis of anhydroglucose units: 1 g/mol of anhydroglucose=162 g.b % conversion was calculated using the followingrelationship: % conversion=(wt. of graft copolymer−wt. of polyacrylamide)/wt. of acrylamide monomer.


is the minimized formation of homopolymers the same molecular weight. A branched polymerhas a lower hydrodynamic volume when compared[15,16 ]. The ceric ion forms chelate complexes

with the 1,2-diol groups on the anhydroglucose with a linear polymer which is reflected in its lowintrinsic viscosity. As shown in Table 1, the concen-units of the polysaccharide backbone, which

decompose to form free radical sites exclusively tration of monomer and polysaccharide was main-tained the same in both I and II, but the catalyston the backbone polymer. These free radical sites

in turn induce the polymerization of acrylic mon- concentration is three times in II. This was donewith the intention that a higher catalyst concen-omers to give rise to the grafted chains. It is

possible to obtain different numbers and lengths tration will induce a larger number of free radicalsites on amylopectin. This in turn will reduce theof polyacrylamide chains by changing the concen-

tration of monomer and catalyst. In our previous length of polyacrylamide chains in II compared toI. This has been observed in practice, in thestudy [14] we reported on the flocculation charac-

teristics of grafted and ungrafted starch, amylose difference between the intrinsic viscosity values.The fewer but longer polyacrylamide chains on II,and amylopectin. It was reported that grafted

amylopectin is a better flocculant when compared produce a higher hydrodynamic volume unlike thenumerous but shorter polyacrylamide chains on IIwith grafted amylose and starch. It was also

observed that that for grafted copolymers of amy- which give a lower hydrodynamic volume. In graftcopolymers III and IV, a deliberate attempt waslopectin and polyacrylamide, the one with fewer

and longer polyacrylamide branches performed made to produce the longest polyacrylamide chainspossible, by use of a low amount of amylopectinbetter than those with shorter but larger number

of branches. In that study, we reported the and high amount of acrylamide at fixed catalystconcentration. However, the values of intrinsiccomparative flocculation studies of only four graft

copolymers of amylopectin and polyacrylamide viscosities indicate that there has not been a dra-matic change compared with I and II, given the(synthesized with variation in the catalyst concen-

tration). Since variations in the concentration of much higher ratio in the concentration of acrylam-ide and amylopectin. This could be partly due toboth catalyst and monomer can effect a variation

in the number and length of grafted chains, it was a fraction of the acrylamide monomer gettingconverted to homopolymer at such a high mon-planned in this study to change these parameters

and see the impact on polymer properties. Table 1 omer concentration.The flocculation behaviour of graft copolymersshows the synthesis details of the present series of

graft polymers. The above series of graft copoly- with a synthetic effluent containing kaolin clay hasbeen compared in Fig. 1. The figure shows thatmers along with the previous series, has been

characterized for proof of grafting thermal analy- the efficiency of all the graft copolymers is moreor less similar at or beyond 0.75 ppm i.e. thesis, IR, NMR, XRD, SEM and elemental analysis

etc. The detailed results have been reported else- optimum dose of polymeric flocculants. The behav-iour of Ap-g-PAM 8 is better than Ap-g-PAM 7where (S.K. Rath, R.P. Singh, pers. comm.).

Further proof of grafting was obtained by the between 0.1–0.3 ppm, beyond which the trend isreversed. This may be because of the longer graftedcombined use of enzyme hydrolysis (by a-amylase)

and viscometry. It has been observed (S.K. Rath, branches of Ap-g-PAM 8 that are responsible forthe early onset of the phenomenon known asR.P. Singh, pers. comm.), that graft copolymers

are indeed formed in the above reaction. Only restabilization/deflocculation. The trend is similarbetween the copolymers Ap-g-PAM 5 and Ap-g-when the acrylamide concentration increases, is

homopolymer formed as noted above. PAM 6. It can be noted that amongst all the graftcopolymers Ap-g-PAM 8 is supposed to have theIt is known that the intrinsic viscosity of poly-

mers in solution is a measure of their hydrody- longest polyacrylamide branches. This is in factseen to be more efficient as a flocculant as evidentnamic volume, which in turn is dependent on the

molecular structure of polymers of approximately from the variation in supernatant turbidity with


Fig. 3. Flocculation characteristics of paper mill white effluent;Fig. 1. Flocculation characteristics of a kaolin suspensioncomparison among the graft copolymers.(0.25% w/v); comparison among the graft copolymers.

Fig. 4. Flocculation characteristics of paper mill white effluent;Fig. 2. Flocculation characteristics of a paper mill white effluent;comparison among commercial flocculants and Ap-g-PAM 7.comparison with some of the commercial flocculants.

polymer dosage. This corroborates the earlier pro- Orissa, are represented in Figs. 2–4. The constitu-ents of the white effluent are mostly suspendedposed model [11].

The results of the treatment of the white effluent cellulosic fibers, clay filler materials and otherchemical additives. In Fig. 2, a comparison hasfrom Konark Paper and Industries Ltd., Basta,


been made among some of the commercially avail- of the graft copolymers with kaolin suspensionshows that the graft copolymer with fewer butable flocculants. It was observed that the behaviour

of three flocculants, i.e. Separan (Ap273), longer polyacrylamide chains perform best amonggraft copolymers. This trend is not maintained inMagnafloc 1011 and Sufloc are almost similar to

each other, although Sufloc at its optimum dosage case of the flocculation study with the white papermill effluent. Among the commercial flocculantsof 1 ppm produces the lowest turbidity. On the

other hand, Aquaset (AS 510) has a very good aquaset (AS 510) shows the best performance.Comparison of the graft copolymer that performedperformance compared with the other three floc-

culants at all dosage levels (except, of course, best in case of kaolin suspension (Ap-g-PAM7)with the commercial flocculants shows that it isSufloc at 1 ppm). All the flocculants show an

optimum dosage where the supernatant turbidity similar to Sufloc but less effective than Aquaset(AS 510).is lowest. The turbidity shows an upward trend

afterwards which is probably due to the onset ofsteric stabilisation/deflocculation.

In Fig. 3 an attempt has been made to compareAcknowledgmentthe flocculation efficiency of the graft copolymers

with the white effluent. The characteristics of theFinancial assistance from IIT, Kharagpu, andcurves are similar to those observed with commer-

CSIR, New Delhi, for the above investigation iscial flocculants: the turbidity shows the usualearnestly acknowledged.upward trend after the optimum dosage. The

behaviour observed when using the syntheticeffluent containing kaolin clay is not observedhere. The copolymer Ap-g-PAM 7 seems to be

Referencesmore effective than Ap-g-PAM 8, the one withlongest polyacrylamide branches. This shows that

[1] J. Bratby, Coagulation and Flocculation, Uplands,not only the nature of polymeric flocculants, their London, 1980.structure and molecular weight but also the nature [2] F. Halverson, H.P. Panzer, Flocculating agents, in: H.F.

Mark, D.F. Othmer, C.G. Overberger, G.T. Seabergof colloidal particles and their surface properties(Eds.), Encyclopedia of Chemical Technology, 3rd edn.,etc. have a profound effect on the flocculationvol. 10, 1980, pp. 489–523.behaviour.

[3] B.A. Bolto, Prog. Polym. Sci. 20 (1995) 987.Lastly, Fig. 4 compares the flocculation behavi- [4] N.M. Bikales (Ed.), Water Soluble Polymers, Plenum, New

our of Ap-g-PAM 7 with the commercially avail- York, 1973.[5] R.L. Davidson, in: Handbook of Water-soluble Gums andable flocculants. It is apparent that the

Resins, McGraw-Hill, New York, 1980.performance of Ap-g-PAM 7 is similar to Sufloc.[6 ] G.F. Fanta, W.M. Doane, in: O.B. Wurzburg, (Ed.),However, Aquaset (AS 510) is by far the best

Modified Starches: Properties and Uses, CRC, Bocaflocculant maintaining a low turbidity over a wide Raton, FL, 1986, ch. 10, p. 149.range of polymer dosage. [7] S.R. Deshmukh, PhD Thesis, Indian Institute of

Technology, Kharagpur, 1986.[8] S.R. Deshmukh, K. Sudhakar, R.P. Singh, J. Appl. Polym.

Sci. 43 (1991) 1091.5. Conclusion[9] S.R. Deshmukh, R.P. Singh, J. Appl. Polym. Sci. 33

(1987) 1963.As a continuation of our earlier study [14], we [10] S.R. Deshmukh, R.P. Singh, J. Appl. Polym. Sci. 32

(1986) 6163.have prepared four more graft copolymers of[11] R.P. Singh, in: P.N. Prasad, J.E. Mark, T.J. Fai, (Eds.),amylopectin and polyacrylamide with variations

Polymers and Other Advanced Materials: Emergingin the monomer and catalyst concentration. TheTechnologies and Business Opportunities, Plenum, New

intrinsic viscosities of the graft copolymers do not York, 1995, pp. 227.show any sharp variation in the series although [12] G.P. Karmakar, PhD Thesis, Indian Institute of

Technology, Kharagpur, 1994.some variation is observed. The flocculation study


[13] R.L. Davidson, in: Handbook of Water-soluble Gums and [17] F.W. Billmeyer, Jr., Textbook of Polymer Science, Wiley,New York, 1971, p. 84.Resins, McGraw-Hill, New York, 1980, ch. 22.

[14] S.K. Rath, R.P. Singh, J.Appl. Polym. Sci. 66 (1997) 1721. [18] J. Bratby, Coagulation and Flocculation, Uplands,London, 1980, ch. 8.[15] G. Mino, S. Kaizerman, J. Polym. Sci. 31 (1958) 242.

[16 ] G.F. Fanta, in: R.J. Ceresa (Ed.), Block and GraftCopolymerization, vol. 1, Wiley, London, 1973, p. 1.

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Grafted amylopectin: applications in flocculation