Celluloses and other polysaccharides such as xanthan belong to the group of polymeric, solid rheology additives that can be used in aqueous systems. In addition to their use as thickeners, they are used for a wide variety of purposes, such as binders and dispersing agents, water retention agents, protective colloids, stabilizers, and emulsifiers.
Celluloses can be obtained from natural cellulose which is chemically modified in various ways to form cellulose derivatives. This modification has an influence on parameters such as molecular weight, degree of substitution, quantity of OH groups and hydrophobic parts. The type of chemical modification of these cellulose derivatives is selected depending on the subsequent application. Typical examples of such derivatives are cellulose ethers such as methyl cellulose (MC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC) and carboxymethyl cellulose (CMC).
The powdered products are stirred into water. Depending on the temperature, the shear forces, the stirring conditions, and the pH value, the products can be homogenously dispersed at different rates, and complete dispersion can take up to several hours. To ensure homogenous, lump-free digestion, cellulose derivatives are also available in delayed-swelling grades.
The rheological properties of polysaccharides and their derivatives are strongly influenced by molecular weight and chemical modification. For example, the thickening effect (pseudoplastic flow behavior) increases significantly with increasing molecular weight, whereby other product properties (e.g. water retention capacity) are also changed in addition to the rheology. The rheological effectiveness of polysaccharides builds up via van der Waals interactions as well as via entanglements and hydrogen bonds. Due to their high content of hydroxyl groups, celluloses are characterized by a particularly good water retention capacity; on the other hand, water resistance is impaired. By incorporating non-polar groups, it is possible to produce hydrophobic types which, on the one hand, compensate for this disadvantage and, on the other hand, improve the application behavior, for example the coating resistance, through additional associative interactions. Another advantage of polysaccharides is their effectiveness over a wide pH range, which is why they are often used in combination with other rheology additives. A limitation of this product class is its susceptibility to microbial contamination, which is why preservation requires special attention.
