Wpływ montmorylonitu na właściwości reologiczne wodnych dyspersji karboksymetyloskrobi 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].
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