HPMC water retention is affected by temperature and the following factors

1. PH: HPMC is most effective at retaining water in a neutral to slightly acidic environment. If the pH is too high or too low, the water retention properties of HPMC may be reduced.

2. Salt concentration: High salt concentrations can reduce the water retention capacity of HPMC. This is because the salt ions compete with the HPMC for water molecules.

3. Polymer concentration: The higher the concentration of HPMC in the solution, the greater its water retention capacity. However, at very high concentrations, the HPMC may become too viscous, and its ability to retain water may be reduced.

4. Molecular weight: Higher molecular weight HPMC polymers generally have better water retention properties than lower molecular weight ones.

5. Degree of substitution: The degree of substitution (DS) of HPMC refers to the number of hydroxyl groups on the cellulose backbone that have been replaced with methyl or hydroxypropyl groups. HPMC with a higher DS generally has better water retention properties.

6. Mixing time: The longer the HPMC is mixed with water, the better its water retention properties. This is because it allows the HPMC to fully hydrate and form a gel-like network that can trap water molecules.