| Polysaccharides have been widely used in many industrial sectors including those of food, textiles, paper, adhesive, paint, pharmaceuticals, cosmetics, mineral processing and so on. They are condensation polymers of high molecular weight based on simple monosaccharide (sugar) units. They are natural organic polymers that are non-toxic and biodegradable. These properties make them ideal for industrial applications. Even though many different types of polysaccharides exist in nature, most of them have only been used by limited industrial systems because a general lack of understanding of the interaction mechanism between the polysaccharides and solid surfaces has hindered the wider application of these polymers and the development of novel synthetic polymers that can do even better job. In this work, multiprong approaches involving adsorption tests, electrophoretic mobility measurements, wettability and microflotation tests, fluorescence spectroscopy, FTIR, AFM and molecular modeling were performed to investigate the mechanistic aspect of polysaccharide adsorption and conformation at solid-liquid interfaces as a function of ionic strength, pH, solid composition and therefore the relationships between their surfaces and different polysaccharides. The behaviors of polysaccharides with different structures (guar, LBG, CMC, EHEC, HM-EHEC) at solid-liquid interfaces are systematically studied and the effort are made toward gaining a full understanding of mechanisms governing their adsorption and conformation at solid-liquid interfaces. In emphasis, this work not only focus on the experimental investigation but also attempt to theoretically analyze the data and propose a model that is able to explain the adsorption mechanism and predict the structure-performance relationship of polysaccharides with different structures in terms of various components of the system.;The results conducted with different polysaccharides showed their behavior to vary markedly from one type to another. It was found that adsorption of guar, LBG, EHEC and HM-EHEC on talc are not affected significantly by changes in solution conditions such as pH and ionic strength, while that of carboxymethyl cellulose (CMC) is affected dramatically by such solution property. Also on one hand, electrokinetic studies showed guar, LBG, EHEC and HM-EHEC to decrease the negative zeta potential of talc (without any shift of i.e.p.) even though did not reverse the charge; on the other hand, the adsorption of CMC on talc changed the i.e.p. of solid surface. Most interestingly, guar gum, LBG and CMC can adsorb on talc and alumina but not on silica. That is not the case for unmodified and hydrophobically modified ethyl hydroxyethyl cellulose (C 0-EHEC and C14-EHEC). C0-EHEC and C14-EHEC adsorb on talc and silica but not on alumina. Study with urea, a hydrogen bond breaker, showed the adsorption of polysaccharides on talc to be reduced significantly, which suggests hydrogen bonding to play an important role in adsorption. Also, fluorescence spectroscopic studies conducted to investigate the role of various forces showed the interface to become more hydrophilic as more polymer adsorbed on solid surface with no evidence of the formation of hydrophobic domains at talc-aqueous interface after polymer adsorption. From FTIR spectroscopic study, it was found that several strong bands appear on the spectrum in the region 1000-1050cm-1 after polymer adsorption, which may be due to the hydrogen bond formation between the primary alcoholic---CH 2OH and solid surface. In addition, Langmuir modeling of adsorption isotherm further suggests that hydrogen bonding is the dominant force for polysaccharide adsorption since the adsorption free energy of these polymers is close to that of hydrogen bond formation. "Cooperative sequential adsorption" (CSA) model proved a "two-stage" adsorption process of polysaccharides via Hill plot. The degree of cooperativity of polymer adsorption can be described quantitatively via Hill coefficient, which is relative to both polymer structures and solution conditions.;Conformational studies through AFM imaging and molecular modeling suggest flat conformation of these polymers adsorbed on solid surfaces.;To test the depressing efficiency of polysaccharides, microflotation and wettability tests were conducted. In talc microflotation tests, the depressing ability of anionic polysaccharide CMC was reduced by an increase of pH. Molecular weight of guar gum has a very minor effect on depression of talc. The adsorption of guar gum decreases talc recovery more effectively than LBG, which is in contrast to adsorption result. Nonionic and anionic polysaccharides (CMC, guar gum and LBG) are better depressants than hydrophobically modified and unmodified EHEC. Generally speaking, for the same type of polysaccharide, amount of polymer adsorbed determines the depressing ability. But for different polysaccharides, the hydrophilicity and the number of side chains along the main helix structure play a dominant role in controlling the surface hydrophobicity. |
