Influence of montmorillonite on the rheological properties of water disperisons of carboxymethyl starch

Water dispersions are usually a colloidal system in which one of the phases is highly dispersed in a second of a continuous nature, called a dispersion medium (in this case it is water). Dispersal is also called the process of distraction and self- -disperse as such. Water dispersions of carboxymethyl starch are the basis for the preparation of many products that, due to their initial dispersion form, can be modified, e.g. by adding fillers such as biodegradable films that affect the rheological properties of the dispersion [1]. The carboxymethyl derivative of starch was synthesized for the first time in 1924. The carboxymethylation reaction has become one of the most important starch modifications used in the industry on a large scale. Carboxymethyl starch (CMS) is characterized by a good solubility in cold water and higher resistance to bacteria than unmodified starch [7–9]. The carboxymethyl starch is obtained by the reaction of carboxymethylation (etherification) of the alkaline starch consisting in the introduction of the substituents into the structure of the starch, by reaction with monochloroacetic acid sodium salt. This process is called Williamson’s synthesis and CMS with different degree of substitution can be obtained by means of the mentioned process [10, 11]. The degree of substitution of carboxymethyl starch has a significant influence on its rheological properties, water dispersion of CMS with DS = 0.87 showed five times higher viscosity than CMS with lower value of this parameter, i.e. 0.15. Water dispersions with an increase in the montmorillonite content showed a high viscosity increase (about twice the increase in viscosity with the addition of 3% by weight). In both cases, aqueous dispersions stored above one month may be subject to the environmental degradation. In addition, in cases of compositions containing MMT, a rapid drop in viscosity due to the montmorillonite sedimentation is observed [17]. Rheological research of water carboxymethyl starch dispersions has great importance for science and for the subsequent application possibilities of products obtained on their basis. The effect of fillers on viscosity, and thus on the possibility of mixing them with aqueous CMS dispersions, affects, for example, the production of biodegradable films based on CMS with MMT, where the film is obtained from an aqueous dispersion of CMS with MMT with the addition of glycerine and citric acid [22]. Moreover, water dispersion of carboxymethyl starch with the addition of montmorillonite can be used as an additive to drilling fluids, electro-reed liquids or foundry adhesives [17]