Hydroxypropyl Methylcellulose (HPMC) is a commonly used water-soluble polymer cellulose derivative that is widely used in construction, pharmaceuticals, food, coatings and other fields. HPMC has good water retention, thickening, film-forming and stability properties, and its concentration in the solution has a significant impact on water retention.

1. Basic principles of HPMC water retention
HPMC forms a three-dimensional network structure through entanglement and physical cross-linking between molecular chains in aqueous solution, which can effectively capture and retain moisture. Its water retention is mainly reflected in the following aspects:

Physical adsorption: The hydroxyl groups on the HPMC molecular chain can form hydrogen bonds, interact with water molecules, and absorb and retain moisture.
Viscosity effect: HPMC increases the viscosity of the solution and reduces the fluidity of water, thereby slowing down the evaporation and penetration of water.
Film forming ability: HPMC can form a uniform protective film to block the evaporation of moisture.

2. Effect of concentration on water retention of HPMC
The water retention performance of HPMC is closely related to its concentration in the solution, and different water retention effects are shown at different concentrations.

2.1 Low concentration range
At lower concentrations (typically below 0.1%), HPMC molecules do not form an adequate three-dimensional network in water. Although there is a certain water absorption capacity and thickening effect, the water retention is limited due to weak intermolecular interactions. At this time, the water retention of the solution mainly depends on the physical adsorption capacity of the molecular chain itself.

2.2 Medium concentration range
When the concentration of HPMC increases to between 0.1% and 2%, the intermolecular interactions are enhanced and a more stable three-dimensional network structure is formed. At this time, the viscosity of the solution increases significantly, which enhances the water capture ability and water retention effect. HPMC molecules form a denser network through physical cross-linking, effectively reducing the flow and evaporation of water. Therefore, the water retention of HPMC is significantly improved in the medium concentration range.

2.3 High concentration range
At higher concentrations (usually greater than 2%), HPMC molecules form a very dense network structure, and the solution exhibits high viscosity and even approaches a gel state. In this state, HPMC is able to capture and retain moisture to the greatest extent possible. The high concentration of HPMC significantly increases the water retention capacity and reduces the evaporation rate of water, allowing it to exhibit excellent performance in applications requiring high water retention.

3. Practical application of HPMC concentration and water retention

3.1 Construction field
In construction mortar, HPMC improves construction performance by improving water retention, reducing water loss during construction, extending the opening time of mortar. HPMC is typically used in mortars at concentrations of 0.1% to 1.0%, a range that effectively balances water retention and application viscosity.

3.2 Pharmaceutical field
In pharmaceutical tablets, HPMC is used as a sustained-release material and tablet binder to achieve sustained-release effects of drugs by controlling the release rate of water. The concentration of HPMC in pharmaceuticals typically ranges from 1% to 5%, which provides appropriate water retention and cohesiveness to ensure structural integrity and drug release from the tablet.

3.3 Food field
In the food industry, HPMC is used as a thickener and stabilizer to improve the texture and water retention of products. For example, adding HPMC to bread can improve the water retention and softness of the dough, typically at concentrations between 0.2% and 1%.

4. Optimization of water retention by HPMC concentration
Optimizing the HPMC concentration for optimal water retention requires consideration of factors such as the specific requirements of the target application, interactions with other ingredients, etc. Usually, the optimal concentration is determined through experimental optimization, so as to ensure the water retention without affecting the processing performance and other properties of the solution.

The concentration of HPMC has a significant effect on the water retention of the solution. At low concentrations, water retention is limited; at medium concentrations, a stable network structure is formed to improve water retention; at high concentrations, the maximum water retention effect is achieved. Different application fields have different requirements for HPMC concentration, which should be reasonably adjusted according to actual needs to achieve a balance between the best water retention effect and processing performance.