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recent advances in modified starch as flocculant

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recent advances in modified starch as flocculant

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									13 The Proceedings of the 3rd International Conference on Functional Molecules

Recent Advances in Modified Starch as Flocculant
XING Guo-xiu, ZHANG Shu-fen*, JU Ben-zhi, YANG Jin-zong
State key laboratoroy of fine chemicals, Dalian University of Technology, Dalian, 116012, China Abstract Starch is one of the most abundant biomacromolecules on earth as renewable

resources and green resource. Starch itself may be used as flocculant, however, its flocculation efficiency is low. As a flocculant starch generally is modified in order to obtain products with good flocculation efficiency. Quaternary ammonium starch ethers was studied as flocculant because of its widely applicability, and quaternary starch additives and substrates are of an electrostatic nature and the fine flocculation was a charge patch mechanism. The mechanism starch-graft-copolymer as flocculant was known as bridging effect. In this article the research progress in ionized modified starch such as etherified starch, graft copolymers starch and amine-starch, and theirs application in waste water treatment were reviewed. The advanced prospect and research aspect of modified starch flocculant were predicted. Keywords Starch, Flocculant, Water treatment, Review

Introduction
Starch is a polysaccharide originated from plants as renewable resources. Native starch consists of two different types of glucose polymers, amylose and amylopectin. The main glucosidic linkage between glucose units in amylose is α-1,4 configuration, while in amylopectin additional α-1,6 glucosidic bonds make branch points in the macromolecule. Starch is stored as granules in the plant and the morphology and crystallinity of a starch granule are determined by the amylopectin fractionm, which constitutes about 70-80% of normal starch. With an increasing awareness of environmental problems in recent years, versatile application has been found for starch in many areas such as flocculant, adhesives, biodegradable plastics and drug-delivery systems. Starch itself may be used as flocculant[1], however, its flocculation efficiency is low. As a flocculant starch generally is modified in order to obtain products with good flocculation efficiency. The modification can be carried out by chemical methods by introducing small amounts of ionic or
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hydrophobic groups into the molecules which change flocculation performance, for example, cationic starch was prepared by introducing quaternary ammonium group into the starch molecules.

This review covers material published within the field of modified starch as flocculant in the last five years, from application of modified starch flocculant to study of flocculation mechanism.

Cationic starch as flocculants
Two main types of cationic starch are tertiary aminoalkyl starch ethers and quaternary ammonium starch ethers, the tertiary aminoalkyl starch ethers require an acidic pH to develop the full cationic charge, while the charge on quaternary ammonium starch ethers is independent of pH. The cationically modified starches are known to have good flocculation performance. Generally quaternary ammonium starch ethers was studied as flocculant because of its widely applicability. The flocculation of kaolin dispersion with

XING Guo-xiu et al.

14 Recent Advances in Modified Starch as Flocculant

modified cationic starch derivatives containing. quaternary ammonium groups (CMS) has been investigated [2]. Their flocculating efficiency has been compared with that of cationic polyacrylamide derivatives (CPAA). To achieve the same flocculation, much bigger amounts of CMS were necessary. The highest flocculation of kaolin occurred at the optimum amount of CMS. The higher degree of substitution (DS), the lower amount of CMS was required for flocculation. For the practical needs, it is advisable to use CMS with DS from 0.3 to 0.45. In the equitable conditions the amount of CMS adsorbed on kaolin particles depends on the charge density. in the macromolecules of CMS and is 2-3 times higher than for CPAA. A comparison of the flocculation and adsorption results shows that the absorbed amount of CMS is twice as high as the amount at which the maximum flocculating efficiency is reached. The difference in the flocculating efficiency of CMS and CPAA could be caused by different flocculation mechanisms.
Table 1 Flocculation efficiency of cationic starch
Untreated sample ρ(CODCr)/(mg/L) ρ(SS) /(mg/L) T/% 549.2 430 71.2 Treated sample 85.3 72 94.5 Efficiency 84.5 % 83.3 %

A highly substituted cationic starch prepared in a lab was used as flocculant to treat white water from paper mill [3]. The effects of the starch dosage, wastewater pH and the flocculation time on the flocculation effectiveness were studied. Flocculation efficiency of cationic starch was shown as table 1. The highest flocculation effectiveness was achieved at such optimal conditions as the cationic starch dosage of 200 mg/L, no pH adjustment requirement, and flocculating time of 24h. High substitution degree quaternary ammonium cationic cornstarch was applied in the treatment domestic waste water. The results showed: when c (PFS) = 200mg/L; c (HQCCS) = 10mg/L and pH = 7, the flocculation efficiency is best. The reduced percentage of
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CODCr reaches 80%. The color and turbidity removal rates are over 99%. Li, Houbin et al reported Interactions of cationized chitosan and cationized starch with components in a chemical pulp suspension[4]. N-(2-hydroxy-3-trimethylammonio)-Pr chitosan chloride (I), carboxymethyl chitosan (II), and cationic starch were tested as wet-end additives for peroxide bleached reed kraft pulp. The adsorption of these polysaccharide samples and their interactions with the main components of pulp suspensions (cellulosic fiber, fines, dissolved and colloidal carbohydrates) were investigated by spectrophotometric, microelectrophoresis, particle size and retention/drainage methods. The results showed that the adsorption and aggregation behaviors which occur in pulp suspension were not only affected by the surface physicochemical characteristics of the cellulosic substrates but were also strongly affected by the nature (charge density, charge type and molar mass) of the polysaccharide additives. That is, I additives were almost completely adsorbed onto the surfaces of the cellulosic fibers and aggregated the fines at low dosages, corresponding to those used in industrial operation. The optimum polymer concentration was increased with the reducing of the charge density of the quaternary chitosan additives. The adsorption of cationic starch onto the surfaces of cellulosic substrates was weaker than quaternary chitosan and showed higher optimum polymer concentration. The adsorption of II promoted the stabilization of the fines and colloidal carbohydrates rather than their aggregation. The polyelectrolyte complexes between hemicelluloses and the quaternary chitosans were formed in the adsorption processing, and these complexes then became adsorbed or deposited onto the cellulosic fibers, and this also correlates to the maximum fines retention and drainage. The experimental results also suggested that the dominant interaction between quaternary chitosan additives and cellulosic substrates are of an

15 The Proceedings of the 3rd International Conference on Functional Molecules

electrostatic nature and the fine flocculation was a charge patch mechanism. Mixtures of high molecule mass cationic starch and low molecule mass anionic Na polyacrylate were characterized (isothermal titration calorimetry, turbidity, polyelectrolyte titration, viscosity, and electrophoretic mobility) and used for controlled flocculation of semi-dilute Ca carbonate dispersions [5]. The polyelectrolytes were mixed at ratios ranging from pure Na polyacrylate to pure starch. For certain conditions strong correlation was found between the properties of the polyelectrolyte mixtures, foremo- st the amount of complexes
Table 2 Turbidity of mixtures and relative particle size of the flocculated CaCO3 dispersions
Electrolyte Salt free 0.01M NaCl 0.1M NaCl 0.033M CaCl2 0.01M CaCl2 τ (NTU) 15.3 109 15.0 p p dr 3.9 4.5 3.0 3.6 3.2

τ: turbidity, dr : relative particle size, p: precipitation.

formed, and the flocculation behavior of the Ca carbonate dispersions. The correlation was strong at low total amount of polyelectrolytes added, where the properties (or the amount) of the individual complexes determined the flocculation efficiency of the mixtures. At high amount of polyelectrolyte the Ca carbonate particles were likely, however, completely covered by complexes and the effects of the individual complexes were screened. From attempt to correlate the properties of the polyelectrolyte mixtures, used as flocculating agents, to the flocculation behavior of the Ca carbonate dispersions, further support was found for previously proposed mechanisms of the complex-induced flocculation observed in the Ca carbonate-starch-polyacrylate system. In particular, further support was found for the relation between the amount of complexes and

the degree of flocculation of the Ca carbonate dispersions. Turbidity of 5:5 NaPA: H02 (cationic starch of high molecular weight, DS=0.2) mixtures and relative particle size (height of peak) of the flocculated CaCO3 dispersions was shown as Table 2. Addition of NaCl and CaCl2 showed that both the ionic strength and the ion specificity are important tools when tuning the properties of the polyelectrolyte mixtures as well as the Ca carbonate dispersions. The interactions between highly cationic starch and likewise cationic calcite were investigated by determining the adsorption isotherms and the flocculation of the calcite dispersions at different concentrations of starch [6]. Starch of varying degree of substitution (DS), 0.2, 0.35, and 0.5, and molecule weight (MW), ~3800 and ~2*106 g /mol, were used. It was found that the interactions in most cases were of fairly low character. Consequently, the entropy and low solubility of the starch are expected to be the dominant driving forces for adsorption. The cationic character of both the untreated calcite and the starch generate an electrostatic repulsion that counteracts a possible adsorption.There is also repulsion between the cationic substituents in the starch, which among others factors controls the solubility of the starch in the aqueous phase. The repulsion can be affected by adding electrolytes. NaCl was used for this purpose in this investigation. As a result of the changes in the electrostatic repulsions the adsorbed amount of starch onto calcite did also change. The adsorption did increase with increasing NaCl concentrations, as did the degree of flocculation. The high MW starches did in all the conditions examined adsorb to a higher degree than did the low MW ones. Increasing the temperature from 25 to 45 causes changes in the adsorption and flocculation behavior of the dispersions, especially in systems where starch with DS of 0.2 is present. The starches of higher charge are less affected by the temperature due to stronger internal repulsion. The low MW starches did not
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XING Guo-xiu et al.

16 Recent Advances in Modified Starch as Flocculant

flocculate the calcite dispersions, while the starches of high MW initially flocculated the dispersions and restabilized them at higher concentrations. The high MW starch with DS 0.2 induced the strongest flocculation. Roger S. et al reported flocculation of semdilute calcite dispersions induced by Anionic sodium polyacrylate-cationic starch complexes [7,8,9] . The flocculation of calcite dispersions was induced by adding mixtures of high molecular weight cationic starch and low molecule weight anionic sodium polyacrylate (NaPA). The starch is industrially used as a fixative. As the starch forms complexes with anionic' substances in the wet end, the complexes strongly influence the flocculation of fibers and fillers. In order to reach further understanding of the complex-induced flocculation in general, the mode of addition of the polyelectrolytes was varied. The effect of changing the mode of addition was moderate. Especially at high ratios of NaPA to starch and high total amounts added, the flocculation behavior was completely determined by the deposition of the large amount of complexes formed in the aqeous phase. These mechanisms are strongly dependent on the ratio of NaPA to starch, and the total amount of polyelectrolytes added. However, interparticle bridging by the
Amounts of CaO+SGM (mg/L) 600+15 600+10 600+7.5 P amounts of untreated sample (mg/L) 55 55 55

polyelectrolyte complexes, and charge neutralization, induced by the deposition of the complexes, were found as the main reasons for the enhanced flocculation. Pretreating the bare calcite with anionic sodium polyacrylate changed the charge characteristics of the calcite from cationic to anionic.

Starch-graft-copolymer as flocculants
Flocculation studies of municipal wastewater with starch-graft-polyacrylamide were carried out[10]. Those results were compared with magnaflocLT-31, a component cationic polyacrylamide, and magnaflocLT-27, a component anionic polyacrylamide flocculant. Cationic polyelectrolyte like magnaflocLT-31 showed best performance compared to magnaflocLT-27 and starch-g-polyacrylamide and guar gum-g-polyacrylamide. The turbidity for magnaflocLT-31, magnaflocLT-27, and starch-g-polyacrylamide copolymer for municipal wastewater reduced from 225 to 12 NTU, 35 and 20 NTU respect. With optimum dosages respect. These flocculants could reduce colors of the effluents with FeCl3 coagulant. The optimum concentration for magnaflocLT-31, magnaflocLT-27, and starch-g-polyacrylamide were 100, 200, and 150ppm with pH 8 respectly.
P amounts of treated sample (mg/L) 0.90 0.85 1.05

Table 3 The flocculation result of flocculant treating yellow P wastewater

The flocculation of yellow P wastewater with starch-acrylamide graft copolymer (SGM) is described[11]. Its treatment effect was better than that of polyacrylamide (PAM). The results showed as table 3 that the flocculation effect was the best, when its branch molocule weight was 8*106, its hydrolytic degree was 27% and its graft degree was 60%. Graft copolymer had bigger specific surface area than homopolymer in spatial structure, which was propitious to bridging. That
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was why SGM could improve flocculation effect. Some flocculant agents were prepared by the copolymerization of acrylic acid (AC) and acrylamide (AA) and grafting of AC and AA onto unmodified and oxidized tapioca starch under different conditions[12]. The flocculability of these products has also been studied. Favorable conditions for the flocculation of Red River (Vietnam) water was at pH 6, with 0.5 mg polymer/L as flocculating agent in the presence of

17 The Proceedings of the 3rd International Conference on Functional Molecules

80 mg electrolyte/L. The flocculation efficiency of the AA-AC copolymer, as well as the oxidized grafted starch, was higher than that of the unmodified grafted one. Graft copolymers are being experimented on a labrary scale as flocculants[13]. All the four graft copolymers, starch-graft-polyacrylamide, amylopectin-graft-polyacrylamide, sodium alginate-graft-polyacylamide and sodium alginate-graft-polyacylamide performed well as flocculants on chromite ore fines suspension. Amylopectin-graft-polyacrylamide, in particular, performed the best from the point of view of settling velocity of flocculants, which is the most important aspect in solid-liquid separation.

Amphoteric starch-based natural polymer modified flocculants.
An amphoteric polymer flocculant with anionic and cationic moieties was synthesized from polyacrylamide-grafted starch by the Mannich reaction and hydrolysis. The optimum reaction conditions were: the molar ratio among graft polymer, formaldehyde, and dimethylamine was 1:1.1:1.5, the mass concentration of graft polymer was 2.5%, the temperature of the amine reaction was 50 the reaction time was 2.5 h, the cationic degree was 50%, the mass ratio of sodium carbonate to sodium hydroxide was 1.4:1, the molar ratio of hydrolytic agent to graft polymer was 1:1, the hydrolysis temperature was 65 , the hydrolytic time was 3 h, and the anionic degree was 23%. The turbidity and COD removal in the use of this product for dyeing factory and paper mill wastewater are better than those of hydrolyzed polyacrylamide (HPAM).

Amino-starch flocculants
A highly crosslinked starch was prepared by crosslinking with epichlorohydrin [14]. Further treatment with epichlorohydrin produced chlorohydroxypropyl ether groups on the starch chains. Under basic conditions, reaction with ethylenediamine produced a crosslinked amino-starch, which serves as a chelating agent for heavy metals. The capacity of the amino-starch for removing Cu from wastewater was 78.5 mg/g. An amine-starch is used not only as water treatment flocculant to absorb iron, lead aluminum, copper and zinc in waste water but also as separating or refining materials [15]. While conventional synthetic polymer flocculant aggregates 25-65% of heavy metal, the amine starch aggregates 74-96%. The production process includes: dissolving 10%(v) urea (to total vol. of ammonia water) in ammonia water of -33 and making temp. -35 ; mixing 30-35 wt%(to the solution.) corn starch with the solution. At -35 and swelling; drying the mixture at room temperature and drying again at 100 to evaporation ammonia; carrying out synthetic reaction at 135 by blowing in N2 gas for 4 h and separating and refining the product with size difference chromatogram.
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Conclusion
Modified starch flocculants had a series of virtues such as non-toxicity, abundance in resources, low price and biodegradability. In recent year people had paid high attention to develop and apply it in treating wastewater. But in practice complexes of polyacrylamide and Al2SO4 is mainly used in waste water flocculation in China because of its good flocculation performance and low dosage. Further efforts should be made to improved flocculation efficiency of starch derivatives as flocculant in order to take place of complexes of polyacrylamide and Al2SO4. By making full use of resources abundant in starch in our state, a great deal of highly effective, non-toxic and cheap modified starch will be studied to adapt to all kinds of wastewater. It showed that developing modified organic flocculants made by natural starch was very significant.

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18 Recent Advances in Modified Starch as Flocculant

Reference
[1] Ye, Aiqian; Hemar, Yacine; Singh, Harjinder. Flocculation oil-in-water and coalescence formed of droplets with in emulsions highly

2003 June 16-19: 17-21. [8] Nystroem, Roger S.; Rosenholm, Jarl B.; Nurmi, Kari Flocculation of Semidilute Calcite Dispersions Induced by Anionic Sodium Polyacrylate-Cationic Starch Complexes. [J]. Langmuir, 2003, 19(9): 3981-3986, [9] Nystrom, Roger; Backfolk, Kaj; Rosenholm, Jarl B.; Nurmi, Kari. The effect of pretreatment of calcite dispersions with anionic sodium polyacrylate on their flocculation behavior induced by cationic starch. [J]. Journal of Colloid and Interface Science, 2003, 262(1): 48-54. [10] Hossain, S. K. Masud; Anantharaman, N.; Das, Manas. Municipal wastewater treatment: Synthetic polyelectrolytes & graft polyelectrolyte onto starch. [J]. Chemical Engineering World, 2004, 39(5): 64-69. [11] Yang, Bo; Duan, Yunbiao; Zhao, Yulin., Flocculation of yellow phosphorus wastewater with starch-acrylamide graft copolymer [J]. Huagong Huanbao, 2002, 22(6): 367-370. [12] Nguyen, Van Khoi; Trinh, Duc Cong; Nguyen, Hong Anh; Preparation of some flocculant agents for water treatment from acrylic acid, acrylamide and tapioca starch. [J]. Tap Chi Hoa Hoc, 2003, 41(9): 29-34. [13] Karmakar, N. C.; Sastry, B. S.; Singh, R. P. Flocculation of chromite ore fines suspension using polysaccharide based graft copolymers. [J]. Bulletin of Materials Science, 2002,25(6): 477-478. [14] Xiang, Bo; Li, Yijiu; Ni, Yaming. Study on the preparation process for amino-starch flocculant. [J]. Huagong Huanbao, 2003, 23(5):300-303. [15] Han, Seung U.; Jung, Byeong Gon; Jung, Seung Hyeon; Jung, Yong Hyeon; Kim, Hak Ju. Amine bio-polymer and its preparation method. [P]. Republic Korean Kongkae Taeho Kongbo KR 2001081119A. 2001. of properties of cationic ,

hydrolysed whey proteins as influenced by starch. [J].Colloids and Surfaces, B: Biointerfaces, 2004, 38(1-2):1-9. [2] Klimaviciute, R.; Bendoraitiene, J.; Zemaitaitis, A.Flocculation 2002, (2): 40-44 . [3] Yang, Jianzhou; Lin, Li; Zhang, Rongli. A study of treatment of white water from paper mill using cationic starch with high degree of substitution. [J]. Gongye Yongshui Yu Feishui. 2003. 34(6):37-39. [4] Li, Houbin; Du, Yumin; Xu, Yongmei; Zhan, Huaiyu; Kennedy, John F. Interactions cationized chitosan with components in a chemical pulp suspension. [J]. Carbohydrate Polymers. 2004, 58(2): 205-214. [5] Nystrom, Roger; Hedstrom, Gun; Gustafsson, Jan; Rosenholm, Jarl B. Mixtures of cationic starch and anionic polyacrylate used for flocculation of calcium carbonate - influence of electrolytes. [J]. Colloids and Surfaces, A: Physicochemical and Engineering Aspects, 2004, 234(1-3):85-93. [6] Nystrom, Roger; Backfolk, Kaj; Rosenholm, Jarl B.; Nurmi, Kari, Flocculation of calcite dispersions induced by the adsorption of highly cationic starch. [J]. Colloids and Surfaces, A: Physicochemical and Engineering Aspects, 2003 ,219(1-3): 55-66.. [7] Nystrom, Roger; Rosenholm, Jarl B.; Gustafsson, Jan; Nurmi, Kari. The complex-induced flocculation of semi-dilute calcite dispersions influence of the mode of addition of the polyelectrolytes. [C]. Preprints International Paper and Coating Chemistry Symposium, 5th, Montreal, QC, Canada. polysaccharides. [J]. Chemine Technologija

To whom correspondence should be addressed E-mail addre ss: zhangshf@chem.dlut.edu.cn

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