改性淀粉的制备及其在水处理中的应用

淀粉是一种来源广泛的天然高分子,近几年,对改性淀粉絮凝剂的研究、生产和应用发展迅速,相对于无机高分子及有机高分子絮凝剂,改性的天然高分子絮凝剂具有无毒、环保、原材料丰富易得等优点,在工业废水及生活污水处理中得到广泛的应用,本文介绍了近几年国内外在利用淀粉改性制备各种新型的多功能絮凝剂的研究情况和应用现状。     

Shear and extensional investigations in solutions of grafted/ungrafted amylopectin and polyacrylamide

Various polysaccharides, such as starch and its constituent amylopectin, are used as flocculants in industrial effluent treatment. Grafting them with polyacrylamide branches enhances their flocculating and turbulent drag‐reducing characteristics drastically. Aqueous solutions of the graft copolymer of amylopectin with polyacrylamide show a shear thinning non‐Newtonian behavior. It is also expected that the solutions exhibit extensional effects. When the aqueous solution at 1000 ppm was subjected to a stretching device, the formation of a thread and reduction of the thread diameter with time were observed. The extensional relaxation time was thus estimated and compared with that of polyacrylamide. The measured relaxation time indicates that the performance of the rigid branched amylopectin, when grafted with fewer and longer polyacrylamide branches, is overwhelmed by the grafted polyacrylamide chains and the reduction of rigidity by the grafting process itself. This article reports the details of the investigations that led to these conclusions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2773–2782, 1999     

绿色试剂-天然高分子絮凝剂的研究与利用进展

介绍了国内外关于天然高分子改性絮凝剂———淀粉类、木质素类、甲壳素类以及植物胶类絮凝剂的研究及应用现状,并对天然高分子絮凝剂的开发趋势进行了分析和预测。     

Shear and extensional rheological investigations in solutions of grafted and ungrafted polysaccharides

Many polysaccharides with varying shear stability have been grafted with polyacrylamide branches to enhance their turbulent drag‐reducing and flocculating characteristics. Their aqueous solutions have been studied by shear and extensional rheometric techniques. All the solutions of grafted carboxymethyl cellulose, guar gum, starch, and sodium alginate exhibit shear‐thinning non‐Newtonian behavior. The viscosities are higher than those of ungrafted polysaccharides. The solutions of grafted carboxymethyl cellulose, guar gum and sodium alginate are spinnable. When subjected to uniaxial stretching in a stretching device, the formation of a thread and reduction of the thread diameter with time were observed. The stretching device was used to measure the relaxation time, which was found to be the largest (∼26 ms), on the order of flexible polyacrylamide, for the grafted carboxymethyl cellulose. Though a polyacrylamide solution degrades through nozzle flow and completely loses its extensional properties, a solution of grafted carboxymethyl cellulose retains about half its relaxation time because of the shear stability of polysaccharide chains and their structure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3200–3209, 2000     

Graft copolymers of starch with mineral acid salts of dimethylaminoethyl methacrylate. Preparation and testing as flocculating agents

Mineral acid salts of dimethylaminoethyl methacrylate (DMAEMA) have been graft polymerized onto starch with ferrous ammonium sulfate–hydrogen peroxide initiation. The nitric acid salt was used in most reactions, and graft polymerizations were run in both water and aqueous–organic solvent systems. Increased monomer concentration in water led to an increase in both the percentage of poly(DMAEMA · HNO₃) in the graft copolymer (percent add-on) and the molecular weight of grafted branches. Variations in initiator concentration altered the percent add-on only slightly but affected the molecular weight of grafted polymer significantly. When swollen starch, in contrast with unswollen starch was used in graft polymerization reactions run in water, the product had a higher per cent add-on and a larger number of grafted branches of lower molecular weight. The efficiency of starch–poly(DMAEMA · HNO₃) graft copolymers as flocculants for diatomaceous silica increased with per cent add-on; however, variations in grafting frequency and graft molecular weight had less effect on the behavior of these materials as flocculants.     

Characterization of drag reducing guar gum in a rotating disk flow

The turbulent drag reduction characteristics in a rotating disk apparatus were investigated by using polysaccharide guar gum in deionized water. The ultrasonic degradation method was adopted to obtain different molecular weight fractions of guar gum for this study. The stability of guar gum over time was observed to be better than the typical synthetic water‐soluble drag reducers [e.g., poly(ethylene oxide)]. A linear correlation between polymer concentration and the concentration/(drag reduction) for different molecular weights of guar gum was obtained, and the universal drag reduction curve for the guar gum/deionized water system was constructed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2938–2944, 2002; DOI 10.1002/app.10300     

天然高分子絮凝剂的研究和应用进展

天然高分子絮凝剂因具有其他合成聚合物不具备的优点，近年来得到国内外广泛重视。本文综述了以淀粉、壳聚糖、木质素和植物胶为原料改性而成的天然高分子絮凝剂的研究与应用概况，并提出开发研究方向。     

Degradation of drag reducing polymers in aqueous solutions

The performance of drag reducing polymers in turbulent flow is restricted by their mechanical degradation. This study examines how the working fluid can affect the degradation behavior of diluted drag reducing polymeric solutions. Solutions having different proportions of tap water and de-ionized water served as the working fluids. Three commercially available water soluble polymeric agents, namely, an anionic copolymer of polyacrylamide, xanthan gum, and polyethylene oxide, were then added to these solutions. All experiments had identical flow rates corresponding to turbulent conditions in a laboratory scale pipe line. Variation of pressure drop in the pipe line was then measured for 2 hours. It was found that polymer degradation is accelerated in tap water solutions compared to that in de-ionized water solutions. However, this is dependent on the specification of the polymer used, namely, the molecular weight of the polymer and the rigidity of its molecular backbone. Furthermore, a new mathematical relation has been developed to investigate degradation of the polymers over time.     

Comparative studies on the flocculation characteristics of polyacrylamide grafted guar gum and hydroxypropyl guar gum

The synthesis of two polysaccharide‐based graft copolymers with acrylamide, guar gum grafted polyacrylamide (GG‐g‐PAM) and hydroxypropyl guar gum grafted polyacrylamide (HPG‐g‐PAM) is described. The graft copolymers have been characterized by viscometry, infrared spectroscopy and thermal analysis. The flocculation characteristics of the graft copolymers have been studied in kaolin, iron ore, and silica suspensions. For the base polysaccharides guar gum (GG) and hydroxypropyl guar gum (HPG), it is observed that GG exhibits better performance than HPG in all three suspensions. For the graft copolymers, HPG‐g‐PAM shows better performance than GG‐g‐PAM. The flocculation characteristics of the best performing graft copolymer (HPG‐g‐PAM) are compared with various commercially available flocculants in the three suspensions mentioned above. © 2001 Society of Chemical Industry     

基于天然多糖的绿色表面活性剂

多糖是自然界中储量最大的天然高分子，其分子链通常具有结构上的两亲性，能够较好地吸附在相界面上并表现出改善固-液、液-液之间相容性的能力。 此外，多糖独特的理化结构使其在溶液中具有良好的流变学性质以及形成凝胶网络的能力，使多糖能够在较低表面活性下体现出较好的界面吸附能力，常被用于多相体系的乳化、分散、增稠和稳定。通过化学改性可对天然多糖进行亲水-疏水平衡，并赋予其一定的化学活性、表面电荷、流变性能等，能够获得性能更加优异的绿色大分子表面活性剂。基于此，该文主要介绍了多糖在表面活性剂中的应用，主要包括纤维素、淀粉、半纤维素、甲壳素、天然树胶等，并从多糖独特的理化性质、结构以及改性特点出发，剖析其对乳化、分散、破乳、增溶等表面活性作用的影响，阐述多糖及其衍生物在表面活性剂中的研究进展及应用潜力。 最后，对多糖表面活性功能增强改性的发展方向进行了展望。     

改性淀粉絮凝剂的开发与应用

淀粉来源广，价格低廉，产物可完全生物降解，因此淀粉改性絮凝剂的研究发展迅速。淀粉改性絮凝剂包括非离子型、阴离子型和阳离子型，文中综述了近十年来我国在这几方面的研究开发与应用方面的进展，并对今后进一步的研究提出了一些建议，建议今后加强实际工艺的研究，充分考虑到影响絮凝剂对废水处理效果的因素，开发出更加有效的絮凝剂。     

Characterization of cationic starch: An efficient flocculating agent

Starch is a known carbohydrate in which, regardless of its origin, two polysaccharides are found namely amylose and amylopectin. By insertion of a cationic moiety to the backbone of starch, a modified cationic starch can be developed which can be used as flocculant. Various grades of cationic starches were developed to optimize the best performing flocculant. The base polysaccharide, starch and the best performing cationic starch i.e., Cat St3 (which have been confirmed from flocculation characteristics and intrinsic viscosity measurement) have been characterized by various characterization techniques such as determination of molecular weight, elemental analysis, FTIR spectroscopy, intrinsic viscosity measurement, thermal analysis, etc. From the characterization, it could be concluded that there was a substantial incorporation of cationic moiety onto the backbone of starch. The flocculation efficacy of these cationized starches was compared with each other and with some of the commercial flocculants available in national and international market in manganese ore suspensions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Turbulent friction reduction by aqueous poly(ethylene oxide) polymer solutions as a function of salt concentration

Turbulent friction reduction by high molecular weight poly(ethylene oxide) polymers has been examined in a series of salt solutions ranging from pure water to nearly theta solvent conditions. The effects of polymer homology and solvent character have been successfully analyzed under these conditions and relationships are proposed for the observed effects. The reduction in turbulent friction (drag reduction) has been catalogued through evaluation of the polymer intrinsic concentration—an index of drag reduction effectiveness. Plots of the reciprocal of the polymer intrinsic concentration versus salt molarity are approximately linear and are similar to the plots of intrinsic viscosity versus molarity reported by other workers. An attempt is made to graphically and numerically combine these results. The suggestion is advanced that those solvent properties which bring about decided conformational changes in these polymer molecules (as indexed by intrinsic viscosity effects) also affect, in an apparently analogous fashion, the turbulent friction reduction efficiencies of these molecules. The decreases in turbulent friction reduction resulting from the increasingly collapsed state of the polymer coil suggest the possibility of correlating friction reduction with changes in the polymer expansion factor α. On the basis of the limited data available, the suggestion is also made that drag reduction studies might best be made under theta solvent conditions where different polymer families might be more meaningfully compared in the absence of solvent effects.     

水处理絮凝剂的研究与发展趋势

絮凝剂作为一类能使悬浮液中的细微颗粒凝聚,沉降的水处理药剂,被广泛应用。随着科学技术的发展,絮凝剂的种类也越来越多,功能也越来越完善,具体。综述了最近10几a来国内外对絮凝剂的研究与发展以及国内外在这个领域内所取得的进展及发展趋势。     

Flow-assisted degradation in dilute polystyrene solutions

The flow-assisted degradation behavior of polystyrene was studied as a function of solvent, polymer concentration, molecular weight, and molecular weight distribution. To obtain data at concentrations as low as 100 parts per million by weight, turbulent drag reduction measurements were used to augment the usual analytical techniques of viscosity and gel permeation chromatography. Turbulent flow measurements were found to be a valuable technique for evaluating the effects of degradation: the drag reduction onset point provides information about the largest molecules in the sample while the flow rate dependence is related to the shape of the top part of the molecular weight distribution. For the polymers and flow conditions studied, the degradation causes a shift in the distribution to lower molecular weights with little change in the shape. This suggests a complex mechanism where the probability of bond scission is not random but varies along the polymer backbone.     

Interaction mechanism of flocculants with coal waste slurry

Coal tailings are the inevitable by-product of coal mining and preparation plants, and often are problematic in terms of dewatering and solid-liquid separation. The interaction of multi-component fine coal tailings with various coagulants and flocculants are important in dewatering processes. Tunçbilek coal preparation plant wastes are composed of 81% inorganic solids with negative surface charges dominating at all pHs. The highest settling rate and turbidity values without flocculant are obtained at natural pH of 8.3 due to the presence of inorganic ions in the suspension particularly Mg²⁺and Ca²⁺that act as natural coagulants. Additon of medium and low charge density anionic flocculants with high molecular weight at natural pH produced higher settling rates at lower dosages than nonionic and cationic flocculants. It shown that the charge density of anionic flocculants has a significant effect on both settling rate and supernatant turbidity, also the settling rate increases with increasing the degree of anionicity. Anionic flocculants having high molecular weight and high anione charge density produced flocs at sufficient size necessary for settling conditions, yet anionic flocculants having low charge density were more effective in the clarification of suspensions containing clay minerals of high stability. The multivalent ions act as a bridge between negatively charged coal, quartz and clay minerals with anionic groups (-CH₂-(CH-CO)-COO groups) of the polymer. Non-ionic flocculants required higher dosages than other flocculants to achieve equivalent settling rates; though excellent turbidity values were obtained in most common pH values. Cationic flocculants of higher charge densities (%70) achieved good settling rates and low supernatant turbidities (9.9 NTU) at natural pH for a dosage of 119.7 g/t-solids flocculant. An interaction mechanism of each polymer type with different components of the tailings is proposed.     

SOME MOLECULAR EFFECTS IN DRAG REDUCTION: A SUMMARY†

Dilute solutions of high molecular weight polymers have drawn a great deal of interest in recent years because of their drag reducing characteristics. It is well-known now that a substantial reduction in turbulent frictional drag can be achieved with a very small amount of polymeric additives, usually only a few parts per million by weight (ppmw) in concentration. This unique phenomenon has offered a new dimension in the design development of new marine systems for higher speed, longer range, larger payload as well as possibly quieter machinery. Although the discovery of this turbulent drag reduction phenomenon may be traced back to Toms¹ and Mysels² in the 1940's, the U.S. Navy's exploration of the turbulent drag reduction effect did not begin until the pioneering effort of Hoyt and Fabula in the 1960's. ³ During a period of several years in the early 19707apos;s, an interdisciplinary group at the Naval Research Laboratory undertook an intensive basic research effort to study the effects of polymer molecular structure on turbulent drag reduction. Model compounds were synthesized in the laboratory, and their drag reducing properties characterized. Polymers including polyacrylamide and its derivatives, polyacrylic acid, poiyphosphate and association colloids have been investigated. In this report, an attempt is made to highlight some of the results from that program in a brief summary form.     

Water Soluble Polymer Flocculants: Synthesis,Characterization, and Performance Assessment

Water soluble polymer flocculants are important constituents of solid–liquid separation units for the treatment of a variety of process‐affected effluents. The systematic development of a flocculant relies on a good understanding of flocculation process, polymer synthesis, polymer characterization, and, not the least, flocculation performance assessment as desired for a particular treatment process, all of which are essential to establish meaningful relationships between flocculant microstructure and flocculation efficiency. The aim of this article is to communicate the bigger picture of this research area to the readers. The recent advances in the application of bio/natural, synthetic, and stimuli‐responsive flocculants are reviewed. Then, the basic polymer reaction engineering tools to control the microstructure of flocculants are provided and the techniques for the quantification of flocculant microstructure are concisely discussed. This is followed by a review of the methods used for the characterization of particle‐polymer force measurement, and flocculation/dewatering assessment with attention to the characterization of aggregate structures.     

阳离子高分子絮凝剂的研究概况

阳离子高分子絮凝剂在废水处理中有看广泛的应用.其产品受到人们的关注。综述了国内外阳离子高分子絮凝剂的研究开发和应用状况,内容涉及到阳离子聚丙烯酰胺、天然高分子改性阳离子絮凝剂、二甲基二烯丙基氯化铵(DMDAAC)的均聚物和共聚物。     

Diameter dependence of the cutoff molecular weights of drag-reducing polymers

Drag reduction data of poly(ethylene oxide) obtained in turbulent pipe flows were analyzed. A cutoff molecular weight for drag reduction was determined by correlating the drag reduction effectiveness with polymer molecular weight. Based on a time-correlation onset concept, this critical molecular weight was found to depend on the pipe diameter and Reynolds number. This effect is examined using available experimental data.