How to measure water retention of Hydroxypropyl Methyl Cellulose?
As a more commonly used additive in dry powder mortar, hydroxypropyl methylcellulose plays an important role in it. Due to its own structural characteristics, it can also ensure that the water in the mortar will not be lost. This is its water retention. As one of the basic indicators of this additive, it is also important to do its detection work before using it. So what methods can help us?
(1) Vacuum method
This method refers to the industry standard JC / T517-2005 “Stucco Plaster”, and the test method is to refer to the original Japanese standard (JISA6904-1976). During the test, the mortar mixed with water was filled into the Buchner funnel, placed on a suction filter bottle, the vacuum pump was started, and the vacuum filtration was performed under a negative pressure of (400 ± 5) mm Hg for 20 min. Then based on the amount of water in the slurry before and after suction filtration, calculate the water retention rate as follows.
Water retention rate (%) = (Moisture in the slurry after suction filtration / Moisture in the slurry before suction filtration) × 100
The vacuum method is more accurate in measuring the water retention rate, and the error is small, but special instruments and equipment are required, and the investment is relatively large.
(2) Filter paper method
The filter paper method is based on the water absorption of filter paper to evaluate the water retention of hydroxypropyl methylcellulose. It consists of a certain height metal ring test mold, filter paper and glass tray. Below the test mold are 6 layers of filter paper, of which the first layer is fast filter paper and the remaining 5 layers are slow filter paper. Using a precision balance, first weigh the weight of the pallet and the 5 layers of slow-speed filter paper. After mixing, pour the mortar into the test mold and scrape it flat. After 15 minutes, weigh the pallet and the 5-layer of slow-speed filter paper weight. Calculated according to the following formula:
M = (m1-m2) / S
M — Water loss, g / mm2
M1 — weight of pallet + 5 layers of slow speed filter paper
M2–15min weight of rear pallet + 5 layers of slow filter paper
S — area of test mold mm2
You can also directly observe the degree of water absorption of the filter paper. The lower the water absorption of the filter paper, the better the water retention. The test method is easy to operate, and the average company can meet the experimental conditions.
(3) Surface drying time test method:
This method can refer to GB1728 “Determination Method of Drying Time of Paint Film and Putty Film”, and scrape the stirred mortar on asbestos cement board, and control the thickness to 3mm.
(4) Finger touch method
Lightly touch the surface of the mortar with a clean finger at regular intervals. If you feel some stickiness, but there is no mortar on the finger, the surface can be considered dry. The longer the time interval, the better the water retention of hydroxypropyl methylcellulose is considered.
(5) Cotton ball method
Gently prevent a skim cotton ball on the surface of the mortar, use a mouth 10 to 15㎝ away from the cotton ball at regular intervals, and gently blow the cotton ball in the horizontal direction. If it can be blown away and there is no cotton silk on the surface of the mortar, the surface is considered dry . The longer the time interval, the better the water retention is considered.
According to the experience of our manufacturers, according to the experience of our manufacturers, filter paper hair and finger touch methods are quicker, easier and more commonly used. People can choose a suitable method to measure the water retention of hydroxypropyl methylcellulose according to the actual situation.