Cellulose ether is the most commonly used additive in dry powder mortar. Cellulose ether plays an important role in dry powder mortar. After the cellulose ether in the mortar is dissolved in water, the effective effect of the cementitious material in the system is guaranteed due to the surface activity. As a protective colloid, cellulose ether “wraps” solid particles and forms a lubricating film on its outer surface, which makes the mortar system more stable and improves the fluidity and stability of the mortar during the mixing process. Smoothness of construction. Due to its own molecular structure, the cellulose ether solution makes the water in the mortar not easy to lose, and gradually releases it over a long period of time, endowing the mortar with good water retention and workability. The water retention of cellulose ether is the most important and basic indicator. The water retention refers to the amount of water retained by the freshly mixed mortar on the absorbent base after capillary action. The water retention test of cellulose ether currently has no relevant testing methods in the country, and manufacturers usually do not provide technical parameters, which brings inconvenience to users in use and evaluation. Referring to the test methods of other products, the following cellulose ethers are summarized The test method of water retention is for discussion.
1. Vacuum pumping method
Moisture in slurry after suction filtration
The method refers to the JC/T517-2005 “Plastering Gypsum” industry standard, and the test method refers to the original Japanese standard (JISA6904-1976). During the test, fill the Buchner funnel with the mortar mixed with water, put it on the suction filter bottle, start the vacuum pump, and filter for 20 minutes under the negative pressure of (400±5) mm Hg. Then, according to the amount of water in the slurry before and after suction filtration, calculate the water retention rate as follows.
Water retention (%)=moisture in slurry after suction filtration/moisture in slurry before suction filtration)KX)
The vacuum method is more accurate in measuring the water retention rate, and the error is small, but it requires special instruments and equipment, and the investment is relatively large.
2. Filter paper method
The filter paper method is to judge the water retention of cellulose ether by the water absorption of the filter paper. It is composed of a metal ring test mold with a certain height, filter paper and glass support plate. There are 6 layers of filter paper under the test mold, the first layer is fast filter paper, and the remaining 5 layers are slow filter paper. Use a precision balance to weigh the weight of the pallet and the 5 layers of slow filter paper first, pour the mortar into the test mold after mixing and scrape it flat, and let it stand for 15 minutes; then weigh the weight of the pallet and the 5 layers of slow filter paper weight. Calculated according to the following formula:
M=/S
M—water loss, g/nm?
weight of nu_pallet + 5 layers of slow filter paper; g
m2_ Weight of pallet + 5 layers of slow filter paper after 15 minutes; g
S_area dish for trial mold?
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 general enterprises can meet the experimental conditions.
3. Surface drying time test method:
This method can refer to GB1728 “Determination of Drying Time of Paint Film and Putty Film”, scrape the stirred mortar on the asbestos cement board, and control the thickness at 3mm
Method 1: cotton ball method
Gently put an absorbent cotton ball on the surface of the mortar, and at regular intervals, use your mouth to keep the cotton ball 10-15 inches away from the cotton ball, and gently blow the cotton ball along the horizontal direction. If it can be blown away and there is no cotton thread left on the mortar surface, the surface is considered dry , the longer the time interval, the better the water retention.
Method two, finger touch method
Gently touch the surface of the mortar with clean fingers at regular intervals. If it feels a little sticky, but there is no mortar on the finger, it can be considered that the surface is dry. The longer the time interval, the better the water retention.
The above methods, the filter paper method and the finger touch method are more commonly used and simpler; users can preliminarily judge the water retention effect of cellulose ether through the above methods.
Post time: Feb-14-2023