1. HPMC Solubility in Water

 

HPMC is the same as hypromellose and is a water-soluble cellulose ether. HPMC dissolves in cold water and certain polar organic solvent, such as methanol, ethanol, isopropyl alcohol (IPA), and acetone. HPMC can also be dissolved in water-organic solvents and mixed solvents. But is not soluble in hot water.

 

 

2. Dissolving HPMC: Methods and Considerations

 

Various methods can be employed to dissolve Hydroxypropyl MethylCellulose (HPMC), including hot water solubility, the dry powder mixing method, and the organic solvent wetting method.

 

2.1 Solubility of HPMC in Hot Water

 

HPMC is not readily soluble in hot water; therefore, it is necessary to cool the HPMC hot solution to an appropriate temperature. Only under these conditions can HPMC dissolve and effectively enhance viscosity. There are three recommended approaches:

 

a. Pour the necessary amount of hot water into the container and heat it to approximately 70°C. Slowly stir the heated water and add HPMC to it. Initially, the HPMC powder may float on the water surface, gradually forming a slurry through continuous stirring. Continue stirring until the slurry cools to an appropriate temperature, at which point HPMC becomes water-soluble, and the solution gains viscosity.

 

b. Pour either 1/3 or 2/3 of the required hot water amount into the container and heat it to around 70°C. Add HPMC to the heated water, stirring slowly to ensure even dispersion and thorough wetting of the HPMC powder. Create a hot water slurry. Then, add the remaining amount of cold water to the hot slurry, cooling the mixture while maintaining continuous stirring.

 

2. Place either 1/3 or 2/3 of the needed hot water into the container and heat it to approximately 70°C. Slowly stir the heated water to disperse and wet the HPMC powder thoroughly. Create a hot water slurry. Add the remaining amount of cold water or ice water to the container. Introduce the HPMC hot water slurry to the cold water and stir continuously. Finally, allow the solution to cool down.

 

2.2 Dry Powder Mixing Method

 

The dry powder mixing method involves blending HPMC molecules with other dry powders in a mixer. The recommended ratio of dry powder to HPMC is typically 3:1 or 7:1. During stirring, water is gradually added, and the process continues until the mixture is fully hydrated.

 

At this stage, HPMC does not condense because its molecular powder is dispersed in every tiny corner, ensuring uniform distribution. As a result, this mixture readily dissolves upon contact with water.

 

Non-surfaced HPMC is commonly utilized in applications like wall putty and mortar, typically available in powder form. In the construction of dry mortar or wall putty, workers often prefer the dry powder mixing method over hot water methods.

 

2.3 Organic Solvent Wetting Method

 

Using an organic solvent to disperse or wet HPMC. Then add water. At this moment, HPMC is easy to dissolve.

 

3. HPMC Solubility in Cold Water

 

HPMC solubility in water has two types: surface-treated HPMC and non-surfaced treated HPMC.

 

3.1 Solubility of Surface-Treated HPMC in Cold Water

 

When surface-treated HPMC is added to cold water, it disperses into the water without exhibiting any viscosity. After stirring and waiting for approximately 2 minutes, the solution thickens and becomes viscous. This is attributed to the presence of a crosslinking agent on the surface of instant HPMC. Commonly, Glyoxal is employed as a crosslinking agent, aiding the dispersion in cold water initially. As a result, surface-treated HPMC tends to be more expensive than its non-surface-treated counterpart.

 

3.2 Solubility of Non-Surface-Treated HPMC in Cold Water

 

Hot melt products may condense upon contact with cold water due to the outer layer of non-surface-treated HPMC reacting with the cold water. This reaction leads to the solution becoming viscous and thickening. The HPMC powder becomes enveloped in a transparent gel, with only the outer layer dissolving. This process significantly slows down the dissolution rate of HPMC inside. Generally, non-surface-treated HPMC is dissolved more efficiently by dissolving in hot water.

 

4. Solubility of HPMC in Organic Solvents

 

Hydroxypropyl MethylCellulose (HPMC) can only be dissolved in organic solvents if they are polar and contain a higher percentage. This solubility is independent of whether the organic solvents have water. Compared to alternative substitutes, HPMC exhibits superior solubility in organic solvents. This section details the solubility of HPMC in specific organic solvents, such as IPA (isopropyl alcohol) or ethanol.

 

4.1 Solubility of HPMC in Ethanol or Isopropyl Alcohol

 

- Is HPMC soluble in IPA? Yes, it is.

- Is HPMC soluble in ethanol? Yes, it is, but insoluble in anhydrous ethanol. HPMC demonstrates good solubility in higher concentrations of ethanol or isopropyl alcohol.

 

Hand sanitizer gel typically comprises less than 40% water and more than 60% alcohol, which is used to prevent diseases and eliminate bacteria. HPMC is utilized in hand sanitizer formulations as a detergent thickener to increase viscosity.

 

Dissolution Method of Hydroxypropyl MethylCellulose in Water/Alcohol Mixture:

 

1. Place ethanol or isopropanol in a container. Slowly add HPMC powder or another detergent thickener while stirring with a mixer.

2. Continue stirring until a homogeneous suspension is achieved.

3. Slowly add cold water to facilitate dissolution.