Hydroxypropyl methylcellulose (HPMC) is a highly efficient organic polymer widely used in building materials, especially in the modification of cement-based products. Cement-based products such as mortar, putty and concrete are widely used in the construction industry. Its adhesion is a key factor affecting construction quality and long-term performance. Cement-based materials are often prone to insufficient adhesion, especially if the base surface is smooth or highly porous. Therefore, improving its adhesion has become an important technical issue. HPMC has shown remarkable results in enhancing the adhesion of cement-based materials due to its unique chemical structure and properties.

1. Chemical properties and mechanism of action of HPMC

HPMC is a water-soluble nonionic cellulose ether formed by chemical modification of natural cellulose. Its unique chemical structure gives it excellent water retention, thickening and film-forming properties. These properties play a key role in improving the performance of cement-based materials.

Improve water retention
One of the main functions of HPMC is to improve the water retention of cement-based products. During the construction process of cement-based materials, especially in dry or high-temperature environments, excessive water loss will lead to insufficient cement hydration reaction, thus affecting its adhesion and strength. HPMC has excellent water absorption and water retention capabilities, and can form a dense hydration film on the surface of the substrate to delay water evaporation and ensure that the cement is fully hydrated, thereby improving the bonding strength of the material.

Improve workability and lubricity
HPMC can increase the consistency and viscosity of cement-based products, thereby improving the workability of the material. In practical applications, good workability means that the material can spread evenly on the construction surface and adhere in place without being too fluid or too dry, resulting in reduced adhesion. By increasing the viscosity of the material, HPMC gives the material a certain degree of lubricity, making the construction smoother and avoiding the sag phenomenon of the slurry, thus improving the adhesion of cement-based materials on smooth or irregular surfaces.

Extend opening hours
The open time of cement-based materials, i.e. the time from completion of mixing to the time when adhesion is lost, is a critical construction parameter. Traditional cement-based materials evaporate too quickly and have a short opening time, which can easily lead to adhesion problems during construction. By delaying the evaporation of water, HPMC significantly extends the open time of cement-based products, giving workers more time to make adjustments and modifications to ensure the material fully adheres to the surface of the substrate.

Enhance slip resistance
For the construction of some facades or inclined surfaces, slip resistance is an important performance indicator of cement-based materials. HPMC can significantly improve the slip resistance of cement-based materials and prevent materials from slipping or falling during construction. This is achieved through the thickening effect and excellent surface adhesion of HPMC, which can effectively prevent the material from flowing on the facade, thereby improving the material’s stability and adhesion effect.

2. Effect of HPMC on the microstructure of cement-based materials

HPMC not only improves the adhesion of cement-based materials in terms of macroscopic properties, but also plays an important role in the microstructure of the material.

Form a dense hydration product structure
HPMC promotes the full hydration of components such as tricalcium silicate (C3S) and dicalcium silicate (C2S) in cement through water retention, generating more hydrated calcium silicate (C-S-H) gel. This gel is a key component in determining the strength and adhesion properties of cement. HPMC can help form a dense and continuous C-S-H gel network, significantly improving the cohesion and adhesion of the material.

Reduce the occurrence of cracks
During the curing process, cement-based materials often develop microcracks due to water loss and shrinkage. The water retention of HPMC helps slow down the loss of water, thereby reducing micro-cracks caused by shrinkage of cement-based materials in the early stages of curing. In addition, the film formed by HPMC has a certain degree of elasticity and can absorb part of the stress and prevent further crack expansion. The reduction in cracks directly contributes to improved bond strength and durability of the material.

3. Application examples of HPMC in different cement-based products

Tile adhesive
In tile adhesives, adhesion is one of the most critical properties. Through its thickening and water retention properties, HPMC enables the tile adhesive to firmly adhere to the wall and the tiles during the construction process, preventing the tiles from loosening and falling off. At the same time, it can also improve slip resistance to ensure that the tiles do not slip when pasted.

Exterior wall putty powder
The application of HPMC in exterior wall putty powder can effectively improve the water retention and adhesion of the putty, allowing it to adhere firmly to the surface of the exterior wall, preventing the putty from cracking or falling off due to too fast drying. In addition, HPMC can also improve the workability of putty, making it more evenly applied and enhancing adhesion to the base layer.

HPMC significantly improves the adhesion of cement-based products through its unique properties such as water retention, thickening, film-forming and extended open time. HPMC plays an important role in improving the workability of cement-based materials and enhancing the bonding strength of their microstructure. As the construction industry continues to improve its requirements for construction quality and durability, HPMC will be more widely used in cement-based materials, providing more effective solutions to the adhesion problems of cement-based products.