Hydroxypropyl methylcellulose (HPMC) is a commonly used water-soluble polymer compound, widely used in many fields such as construction, coatings, pharmaceuticals and food. It is a product obtained by chemical modification (such as methylation and hydroxypropylation) of natural plant cellulose, and has good water solubility, viscosity, emulsification and film-forming properties. In gypsum mortar, HPMC mainly plays the role of thickening, water retention, and improving construction properties, which can significantly improve the working performance and final strength of the mortar.

1. Thickening effect
In gypsum mortar, HPMC, as a thickener, can increase the viscosity of the mortar. The fluidity of gypsum mortar is an important factor affecting the construction quality. Too low fluidity will make it difficult to apply the mortar evenly, while too high fluidity may cause the gypsum mortar to flow unevenly or unstable during the application process. The thickening effect of HPMC can effectively adjust the fluidity of the mortar, so that the mortar will not be too thin or too thick during the construction process, thereby ensuring the smooth progress of the construction.

2. Water retention effect
The water retention effect of HPMC in gypsum mortar is particularly important. Gypsum mortar contains a certain amount of water. The rapid evaporation of water will cause problems such as cracking and shrinkage on the surface of the mortar, thus affecting the construction quality and final effect. As a polymer compound, HPMC has strong hydrophilicity. It can firmly bind water in the mortar through intermolecular interactions, thereby delaying the evaporation of water and ensuring that the mortar maintains a proper wet state during the construction process. This water retention effect can not only effectively prevent the formation of cracks, but also promote the full hydration of gypsum, thereby increasing the hardening strength of the mortar.

3. Improve workability
The addition of HPMC can significantly improve the workability of gypsum mortar. Good workability means that the mortar is easy to apply and smooth during the construction process, and can maintain good operability for a long time. HPMC can effectively slow down the drying speed of the mortar through thickening and water retention, so that it can maintain good fluidity and workability for a long time, reducing problems such as insufficient viscosity and cracking during the construction process. In addition, HPMC can also improve the smoothness of mortar, making it smoother for construction workers to use mortar and reducing labor intensity.

4. Improve the bonding performance of mortar
HPMC can also effectively improve the bonding performance of gypsum mortar. During the construction process, gypsum mortar needs to form a good bond with the substrate surface to ensure its firm adhesion. HPMC can form a certain intermolecular force with other components in the mortar through the hydroxypropyl and methyl groups in its molecular structure, increase the adhesion of the mortar to the substrate, and thus enhance the bonding strength of the mortar. Especially on some special substrate materials (such as glass, ceramics, metals, etc.), HPMC can significantly improve the bonding performance of gypsum mortar and prevent it from falling off.

5. Improve crack resistance
The crack resistance of gypsum mortar is crucial during its use, especially in large-scale construction, the cracking problem of mortar may have a negative impact on its service life and appearance. The addition of HPMC can slow down the evaporation rate of water and reduce the shrinkage phenomenon in gypsum mortar through water retention and thickening, thereby reducing the risk of cracks caused by drying too fast. In addition, the HPMC molecule itself has certain elasticity and plasticity, which can relieve stress in the process of mortar hardening, thereby further improving the crack resistance of the mortar.

6. Improve the water resistance of gypsum mortar
In some humid or water-heavy environments, gypsum mortar needs to have good water resistance. The addition of HPMC can enhance the mortar’s ability to resist water immersion and reduce the damage of water to the mortar structure. HPMC has strong water retention and good hydrophobicity, which improves the water resistance of the mortar to a certain extent and reduces the expansion and shedding caused by water intrusion.

7. Enhance the final strength of the mortar
The final strength of gypsum mortar is usually closely related to the cement hydration reaction and the evaporation process of water. HPMC promotes the hydration reaction of gypsum by maintaining the appropriate moisture of the mortar, increasing the hardening speed and final strength of the mortar. At the same time, the molecular structure of HPMC can also strengthen the interaction between molecules inside the mortar, improve the structural stability of the mortar, and thus improve the mechanical strength of the mortar such as compression and bending.

8. Environmental protection and economy
Since HPMC is a natural plant cellulose derivative, its raw material source is abundant and renewable, which meets the requirements of modern environmental protection and sustainable development. In addition, as a functional additive, HPMC is usually used in small amounts, but it can significantly improve the performance of mortar. Therefore, adding HPMC to gypsum mortar is an economical and effective means to improve the performance of mortar.

The role of HPMC in gypsum mortar cannot be ignored. HPMC can significantly improve the comprehensive performance and use effect of gypsum mortar by thickening, retaining water, improving workability, improving bonding performance, crack resistance and water resistance. Especially in large-scale construction and special environments, the addition of HPMC has important practical significance. With the continuous improvement of the performance requirements of building materials, HPMC, as an important functional additive, will be more widely used in gypsum mortar.