HEMC (Hydroxyethyl Methyl Cellulose) and HPMC (Hydroxypropyl Methyl Cellulose) commonly used in the construction industry have excellent water solubility, but if directly added to water, they can cause clumping.

So for fine powdered methyl cellulose ethers (non surface treated), to avoid clumping in water, the appropriate dissolution method is:

First, disperse cellulose ether in hot water above gel temperature to form slurry, and then add cold water while stirring to cool it until it is completely dissolved. This method can avoid reunion.

Delayed solubility of cellulose ether

For some water-based coatings or daily chemical products, cellulose ether needs to be directly added to cold water for use. At this time, formaldehyde is often used to treat the surface of cellulose ether to improve its delayed solubility:

Acetaldehyde reacts with cellulose ether to form hemiacetals, resulting in moderate crosslinking of cellulose ether. This cross-linked product is insoluble in water, but has good dispersibility in water. During the hydration stage, which is the process of dispersion in water, there is only a small amount of swelling. At the same time, the hemiacetal structure begins to hydrolyze at a stable rate until the cross-linking bonds are broken, the molecular chains are unlinked, the cellulose ether dissolves rapidly, and the viscosity increases sharply.

When pH is between 4 and 5, the hemiacetal structure is most stable. The rate of hydrolysis increases with the deviation of temperature and pH from 4-5 degrees. In strong acids with pH values less than 2 and strong bases with pH values greater than 9, the delayed dissolution effect almost completely disappears.

Dialdehyde crosslinking is not only suitable for methyl cellulose, but also for other cellulose ethers or other polymers containing hydroxyl groups (such as starch, natural gum, etc.). The length of the delay time depends on the amount of formaldehyde used, pH value, reaction time, and temperature (the delay time here usually refers to the extended dissolution time at room temperature and pH values of 6-7). PH values that are too high or too low in temperature will cause irreversible crosslinking due to the conversion of hemiacetals into acetals, and cellulose ethers will become insoluble.