Hydroxypropyl Methyl Cellulose (HPMC), as the main additive in building dry mixed mortar products, plays a key role in the performance and cost of dry mixed mortar.
At present, the global cellulose ether products are mostly used in building materials. The important property of cellulose ether is its water retention in building materials.
If cellulose ether is not added, the thin layer of fresh mixed mortar will quickly dry out, making the cement unable to hydrate in normal way, resulting in mortar cannot harden and obtain a good bonding strength. At the same time, the adding of cellulose ether makes mortar have good plasticity and flexibility, improve bonding strength of mortar.
1. Particle size of HPMC
The fineness of cellulose ether affects its solubility. The finer cellulose ether is, the faster it dissolves in water, and water retention performance will also be improved. Therefore, particle size of cellulose ether should be included in one of its properties. Generally speaking, fineness of cellulose ether is 80 mesh all through.
2. Dry weight loss rate of HPMC
The drying weight loss rate, refers to the percentage lost weight in original sample weight, when drying in a certain temperature. Excessively high drying weight loss rate in of a certain quality cellulose ether will reduce the content of effective components in cellulose ether, affect the application effect of downstream enterprises, and also increase the purchasing cost. Usually drying weight loss rate of cellulose ether is not more than 5.0%.
3. Sulfate ash of HPMC
Excessive ash content in a certain quality of cellulose ether will reduce the content of effective components in cellulose ether and affect the application effect of downstream enterprises. Sulfate ash of cellulose ether is an important indicator of its own performance.
4. Viscosity of HPMC
The water retention and thickening effect of HPMC mainly depends on the viscosity and dosage of cellulose ether in cement-based Mortar.
5. pH Value of HPMC
HPMC at a higher temperature or storage after a long period of time, the viscosity gradually decreased, high viscosity product performance is particularly obvious, so it is necessary to limit pH value. Generally, pH range of cellulose ether should be controlled within 5 to 9.
6. Transmittance of HPMC
Transmittance of HPMC directly affects its application effect in building materials. The main factors that affect the light transmittance of cellulose ether are as follows:
(1) Quality of raw material;
(2) The effect of alkalinization;
(3) Technical proportion;
(4) Solvent ratio;
(5) Neutralization effect.
According to the use effect, the transmittance of cellulose ether should not be less than 80%.
7. Gel temperature of HPMC
HPMC in cement-based Mortar is mainly used as thickener, plasticizer, and water retaining agent, so viscosity and gel temperature are an important indicator of HPMC. Gel temperature is used to determine the type of cellulose ether, which is related to the degree of substitution of cellulose ether.
In addition, salt and impurities can also affect gel temperature. When the temperature of solution rises, cellulose polymer gradually loses water, the viscosity of solution decreases, and when reach the gel point, the polymer is completely dehydrated to form a gel. Therefore, the temperature of cement-based Mortar is usually controlled below the in initial gel temperature. Under this condition, the lower temperature, the higher viscosity, and the more obvious the viscosity and water retention effect is.