Relationship between viscosity decrease and cellulose ether during coating storage

After storage for a period of time, the coating shows a decrease in viscosity.

the reason

1. The molecular chain of the thickener is broken. Non-biologically stable cellulose thickeners are attack by enzymes.

The molecular chain is broken, reducing the thickening ability. The cause may be insufficient preservatives in the production formula, or contamination.

2. Changes in pH. In polyacid type thickening system. Using highly volatile ammonia to adjust the pH, the pH value will drift in the system after ammonia volatilizes.
. For example, when the pH value is low, it becomes insoluble, and the thickener molecules are roll up to reduce the thickening efficiency.

3. The presence of air bubbles in the coating results in a large initial apparent viscosity. After the coating in the tank is degass and defoam, excess air is eliminat, and the viscosity of the coating decreases. In this case, the coating properties have not changed.

prevention

For coatings containing cellulose ether, the amount of preservative additives should be adjust according to the season and cellulose content. In summer and rainy and humid seasons, increase the cleaning and disinfection of production equipment and increase the amount of preservatives.

For the viscosity drop due to pH drift, select low-volatile organic bases for prevention.

The effect of air bubbles should pay attention to the production process, and ensure that the air in the coating is exhaust before thickening. Otherwise, the bubbles become trapped in the coating after thickening to form an apparent viscosity.