A novel strategy for faster and better flocculation in solid-liquid separation processes is reported: the use of the natural polyelectrolyte chitosan (CH2500) in combination with the biocompatible thermosensitive polymer poly(N-vinylcaprolactam) (PNVCL). Silica dispersions (Aerosil OX50) were used as model and evaluated by means of analytical centrifuge, laser diffraction, and turbidimetry studies. Results show that the sedimentation velocity is doubled by addition of PNVCL and that at 45°C the density of the sediment is 33% higher, as compared to the use of CH2500 only. This results from the temperature sensitive behavior of PNVCL that phase-separate expelling water at temperatures higher than its LCST (32–34°C) leading to compaction of the flocs. By using this strategy the sediment is more compact, contains less water, and contains a very small amount of biodegradable CH2500 and biocompatible PNVCL. 1. Introduction Solid-liquid separation through coagulation and flocculation is an important stage of many technological processes. Typical examples are waste water treatment, sludge dewatering, and pulp and paper production as well as the pharmaceutical, cosmetic, and metal working industry. The overwhelming majority of these processes use polyelectrolytes to regulate the stability and flocculation properties of dispersed systems. This resulted in a great variety of synthetic and natural flocculants, which are now commercially available to meet the specific demands of industrial fields, where an efficient solid-liquid separation is required [1, 2]. Application of polysaccharides like chitosan and starch as flocculants in solid/liquid and liquid/liquid separation is also an important field of high industrial relevance, as shown by numerous patents and publications [3–9]. Starch and chitin/chitosan are the most promising candidates to produce and apply natural flocculants on industrial scale [10, 11]. They are abundant and biodegradable polymers, which can be obtained from renewable natural resources at relatively low costs. High content of hydroxyl (starch and chitosan) and amino/acetamido (chitosan) groups allows advanced chemical modification through cationization, hydrolysis, oxidation, enzymatic grafting or degradation, and so forth to yield polysaccharide derivatives with specific properties to particular fields of application. In this work a novel strategy for a faster and better flocculation performance is reported: the use of natural polyelectrolytes like chitosan (CH2500) in combination with a biocompatible polymer that exhibit lower critical
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