How to choose the right hydroxypropyl methylcellulose

Analysis of the relationship between the viscosity of hydroxypropyl methylcellulose (HPMC) and the water retention of cellulose in various applications. This information is crucial for understanding the properties and suitability of HPMC in different industries.

HPMC can be classified into fast-dissolving and hot-dissolving types. Fast-dissolving products readily disperse in cold water without true dissolution, resulting in a liquid with no viscosity. However, within approximately 2 minutes, the viscosity gradually increases, forming a transparent viscous colloid. In contrast, hot-melt type products quickly disperse in hot water and disappear, gradually developing viscosity until a transparent viscous colloid is formed. The hot-dissolved type is suitable for putty powder and mortar, whereas it may cause clumping and cannot be used in liquid glue and paint. On the other hand, instant type HPMC has a wide range of applications and can be used in putty powder, mortar, liquid glue, and paint.

Different viscosities of HPMC correspond to different properties. For instance, putty powder generally requires a viscosity of 100,000 to perform functions such as thickening, water retention, and aiding construction. Thickening ensures the suspension and uniformity of cellulose, resisting sagging. Water retention enables slower drying of putty powder while facilitating the reaction of auxiliary ash calcium. Construction is improved due to the lubricating effect of cellulose. HPMC solely plays a supporting role and does not partake in any chemical reactions. It is important to note that putty powder undergoes a chemical reaction when applied to walls, which prevents the reuse of removed putty powder due to the formation of new substances (calcium carbonate).

The viscosity of HPMC used in mortar should exceed 150,000 to fulfill higher requirements. Water retention remains the primary function of HPMC in mortar, with thickening being secondary.

For putty powder, a viscosity of 70,000 to 80,000 is suitable, as long as water retention is effective. However, higher viscosities also result in better water retention. Viscosity exceeding 100,000 has little effect on water retention but is useful for cement mortar.

In glue applications demanding instant-type products with high viscosity, HPMC is recommended.

Considering regions with significant temperature differences between summer and winter, it is advised to use lower viscosity HPMC in winter for better construction outcomes. This is because low temperatures cause an increase in cellulose viscosity, resulting in a heavy hand feel during scraping. A medium viscosity of 75,000 to 100,000 is commonly used for putty, ensuring good water retention. Similarly, high viscosity (150,000 to 200,000) is preferred in applications such as polystyrene granule insulation mortar rubber powder and vitrified microbead insulation mortar to prevent falling, sagging, and improve construction efficiency.

The water retention of hydroxypropyl methylcellulose depends on the hydroxypropyl content. Higher hydroxypropyl content enhances water retention, while reducing the methoxy group content is beneficial. A high methoxy group content increases the viscosity of HPMC. Therefore, when selecting a product, it is essential to choose the one that best suits your specific application requirements.