The development of rheological thickeners has been an important milestone in the history of materials science and engineering. Rheological thickeners are materials that can increase the viscosity and/or control the flow properties of liquids, suspensions, and emulsions.
The first rheological thickener was discovered accidentally in the 19th century, when a mixture of water and flour was left to stand for a period of time, resulting in a thick, gel-like substance. This mixture was later found to be a simple suspension of flour particles in water, which could be used as a thickener in various applications.
In the early 20th century, other materials were discovered to have thickening properties, such as starches, gums, and clays. These materials were used as rheological thickeners in a range of applications, from food and cosmetics to paints and drilling fluids.
However, these natural thickeners had limitations, such as variable performance, sensitivity to processing conditions, and potential microbiological contamination. This led to the development of synthetic rheological thickeners, such as cellulose ethers, acrylic polymers, and polyurethanes.
Cellulose ethers, such as sodium carboxymethyl cellulose (CMC), methyl cellulose (MC), and hydroxypropyl cellulose (HPC), have become one of the most widely used rheological thickeners in various applications, due to their unique properties, such as water solubility, pH stability, ionic strength sensitivity, and film-forming ability.
The development of synthetic rheological thickeners has enabled the formulation of products with consistent performance, improved stability, and enhanced functionality. With the growing demand for high-performance materials, the development of new rheological thickeners is expected to continue, driven by advances in materials science, chemistry, and engineering.