Influence of the indicators of HPMC on dry-mix mortar
As the main admixture in construction dry-mix mortar products, hydroxypropyl methyl cellulose plays a key role in the performance and cost of dry-mix mortars. Currently, the majority of cellulose ether products are used in construction materials worldwide. An important property of cellulose ethers is their water retention in construction materials. Without the addition of cellulose ethers, thin layers of freshly mixed mortar dry out very quickly. Then preventing the cement from hydrating in the normal way and resulting in the mortar not being able to harden and obtain a good bond. At the same time the addition of cellulose ethers gives the mortar good plasticity and flexibility and improves the bond strength of the mortar.
1. Fineness of hydroxypropyl methyl cellulose
The fineness of cellulose ether affects its solubility. The finer the cellulose ether, the faster it dissolves in water and the water retention performance will improve. So the fineness of cellulose ether should be included in one of its investigated properties. Generally speaking, the fineness of cellulose ether is 80 mesh all through.
2. Hydroxypropyl methyl cellulose dry weight loss rate
Drying weight loss rate, refers to a certain temperature drying cellulose ether, the loss of material mass of the original sample as a percentage of the mass. For a certain quality of cellulose ether in the dry weight loss rate is too high. It will reduce the cellulose ether in the active ingredient content, affect the downstream enterprise application effect, also increase the purchase cost. In general, the dry weight loss of cellulose ether is not more than 5.0%.
3. Sulphate ash of hydroxypropyl methyl cellulose
For a certain quality of cellulose ether in the ash content is too high, will reduce the cellulose ether in the content of the active ingredients, affect the effect of downstream enterprises applications. Cellulose ether sulfate ash is an important measure of its own performance indicators. Combined with the current production status of China’s existing cellulose ether manufacturers, usually the ash content of MC, HPMC, HEMC is not more than 5%.
4. Viscosity of hydroxypropyl methyl cellulose
The water retention and thickening effect of hydroxypropyl methyl cellulose mainly depends on the viscosity of the cellulose ether itself and the amount of admixture added to the cement slurry.
5. PH value of hydroxypropyl methyl cellulose
The viscosity of hydroxypropylmethylcellulose products gradually decreases at higher temperatures or after a longer storage period, especially for high-viscosity products. So the pH needs to be limited. The PH value of cellulose ethers is generally required to be controlled in the range of 5-9.
6. Light transmission of hydroxypropyl methyl cellulose
The light transmission of hydroxypropyl methyl cellulose directly affects its application in building materials. The main factors affecting the light transmission of cellulose ether are:
(1) The quality of the raw material.
(2) The effect of alkalinisation.
(3) The process ratio.
(4) The solvent ratio.
(5) the effect of neutralisation.
According to the effect of use, the light transmission of cellulose ether should be not less than 80%.
7. Gel temperature of hydroxypropyl methyl cellulose
Hydroxypropyl methyl cellulose is mainly used as a viscosity builder, plasticiser and water retention agent in cement products, therefore viscosity and gel temperature are important indicators of hydroxypropyl methyl cellulose. The gel temperature is used to determine the cellulose ether type and is related to the degree of substitution of the cellulose ether.
In addition, salt and impurities can also affect the gel temperature. As the solution temperature rises, the cellulose polymer gradually loses water and the solution viscosity decreases, reaching the gel point when the polymer is completely dehydrated, and a gel is formed.
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