The cellulose ether products HPMC and HEMC have both hydrophobic and hydrophilic groups. The methoxy group is hydrophobic, and the hydroxypropoxy group is different according to the substitution position. Some are hydrophilic and some are hydrophobic. Hydroxyethoxy is hydrophilic. The so-called hydrophilicity means that it has the property of being close to water; the hydrophobicity means that it has the property of repelling water. Since the product is both hydrophilic and hydrophobic, the cellulose ether product has surface activity, which creates air bubbles. If only one of the two properties is hydrophilic or hydrophobic, no bubbles will be generated. However, HEC only has a hydrophilic group of hydroxyethoxy group and has no hydrophobic group, so it will not generate bubbles.
The bubble phenomenon is also directly related to the dissolution rate of the product. If the product dissolves at an inconsistent rate, bubbles will form. In general, the lower the viscosity, the faster the dissolution rate. The higher the viscosity, the slower the dissolution rate. Another reason is the granulation problem, the granulation is uneven (the particle size is not uniform, there are large and small). Causes the dissolution time to be different, produces the air bubble.
The advantages of air bubbles can increase the area of batch scraping, the construction property is also improved, the slurry is lighter, and the batch scraping is easier. The disadvantage is that the existence of bubbles will reduce the product’s bulk density, reduce the strength, and affect the weather resistance of the material.