• • Blog
• March 31st 2026

Common Testing Methods for the Water Retention Performance of Hydroxypropyl Methylcellulose

The wide application of hydroxypropyl methylcellulose (HPMC) is primarily due to its excellent water retention. The quality of HPMC directly affects its overall quality. The water retention performance of hydroxypropyl methylcellulose ether under hot and high-temperature conditions is one of the indicators for judging the quality of cellulose ethers. Humidity, temperature, wind speed, and wind pressure all affect the rate of moisture evaporation in cement mortar and gypsum products. Therefore, the water retention effect will vary depending on the season when adding the same amount of HPMC. In practical applications, the water retention effect of the mortar can be adjusted by increasing or decreasing the amount of cellulose added. In hot weather, especially during thin-layer construction on sunny sides, HPMC is needed to improve the water retention of the slurry. High-quality cellulose has good water retention and uniformity. It can enhance the ability of oxygen atoms on the hydroxyl and ether bonds to associate with water to form hydrogen bonds, converting free water into bound water. This effectively controls moisture evaporation caused by high temperatures, achieving high water retention performance. So how do we test the water retention of hydroxypropyl methylcellulose (HPMC)?

I.A method for calculating water retention performance is also based on the specific drying time of its surface.

This method involves applying the mixed mortar to an asbestos cement board, controlling the thickness to 3mm. There are two testing methods: First, the finger-touch method: Use a clean finger to lightly touch the mortar surface at regular intervals. If the mortar feels slightly sticky but no mortar adheres to the finger, the surface is considered dry. The longer the interval, the better the water retention of the hydroxypropyl methylcellulose. Second, the cotton ball test: Gently place a cotton ball on the mortar surface. At regular intervals, lightly blow on the ball horizontally, keeping the mouth 10-15cm away. If the cotton fibers are blown away without leaving any on the mortar surface, the surface is considered dry. Again, the longer the interval, the better the water retention.

II. Filter Paper Testing Method

The filter paper testing method mainly assesses the water retention performance of hydroxypropyl methylcellulose by measuring its water absorption. The test consists of a metal ring mold of a certain height, a glass tray, and filter paper. Six layers of filter paper are located at the bottom of the mold. The first layer is a fast-acting filter paper, while the other five layers are slow-acting filters. A precision balance is used for weighing. First, the tray and the five layers of slow-acting filter paper are weighed. Then, the mixed mortar is poured into the mold, ensuring it is leveled. After 15 minutes, it is weighed again, this time again, this time weighing the tray and the five layers of slow-acting filter paper. There is a well-established formula:

M = (m1 – m2) / S

M – Water loss, g/mm2

m1 – Weight of tray + 5 layers of slow-speed filter paper (g);

m2 – Weight of tray + 5 layers of slow-speed filter paper after 15 minutes (g);

S – Area of ​​the test mold (mm2)

This allows for direct observation of the filter paper’s water absorption. Lower water absorption indicates better water retention. This test method is simple to operate, and most companies can meet the experimental conditions.

III. Vacuum Testing Method for Water Retention

Water content in the slurry before and after filtration

This testing method involves filling a Buchner funnel with mixed slurry and water, placing it on a filtration flask, and then starting a vacuum pump. Filtration is performed for 20 minutes at a negative pressure of (400±5) mmHg. The water retention rate is then calculated based on the water content of the slurry before and after filtration. The water retention rate (%) = (moisture content in the slurry after filtration / moisture content in the slurry before filtration) × 100

This vacuum method for measuring water retention rate is relatively accurate with minimal error. However, it has significant drawbacks, requiring specialized equipment and incurring substantial investment.

In summary, among the three methods mentioned above, the filter paper test and the surface drying time measurement method are the most commonly used and convenient. Users can use these methods to make a relative judgment on the water retention of hydroxypropyl methylcellulose. Currently, there are no specific testing methods for the water retention performance of hydroxypropyl methylcellulose ethers, and hydroxypropyl methylcellulose manufacturers generally do not provide detailed technical parameters. This causes considerable inconvenience for users requiring specific water retention performance. Based on other testing methods, the above methods for testing the water retention performance of cellulose ethers are summarized for user reference only.

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