Types of Methyl Cellulose Ether
A． Hydroxypropyl methylcellulose (HPMC) is mainly made of highly pure refined cotton as raw material, which is specially etherified under alkaline conditions.
B. Hydroxyethyl methyl cellulose (HEMC), a non-ionic cellulose ether, is a white powder, odorless and tasteless.
C． Hydroxyethylcellulose (HEC) is a non-ionic surfactant, white in appearance, odorless and tasteless and easy-flowing powder.
The above are non-ionic cellulose ethers, and ionic cellulose ethers (such as carboxymethyl cellulose (CMC)).
During the use of dry powder mortar, because ionic cellulose (CMC) is unstable in the presence of calcium ions, it is rarely used in inorganic gelling systems with cement and slaked lime as cementing materials. In some places in China, Some interior wall putties processed with modified starch as the main cementing material and Shuangfei powder as the filler use CMC as the thickener, but because this product is prone to mildew and is not water-resistant, it is gradually eliminated by the market .
At present, the most commonly used cellulose ethers in domestic dry-mixed mortar products are also called hydroxypropyl methylcellulose ether (HPMC) and hydroxyethyl methylcellulose ether (HEMC). For products with different uses, the dosage of cellulose ether is also different, as low as 0.02% such as wall mortar to 0.1%. Such as plastering mortar, the high one can be from 0.3% to 0.7% such as tile adhesive.
Properties of Cellulose Ether
❶ Cellulose ether has excellent water retention in mortar. Its water retention function can prevent the substrate from absorbing too much water too quickly and hinder the evaporation of water, so as to ensure sufficient water when the cement is hydrated. It can effectively prevent the mortar from drying and cracking due to rapid water loss, so that the mortar has a longer construction time.
Generally speaking, the water retention of cement slurry increases with the increase of the content of cellulose ether. The greater the viscosity of the added cellulose ether, the better the water retention.
❷ The thickening effect of cellulose ether can control the mortar to achieve the best consistency, improve the cohesion of the mortar, achieve anti-sag effect, improve operability, and greatly increase construction efficiency.
❸ Cellulose ether can significantly improve the wet viscosity of wet mortar, ensuring that the wet mortar has a good bonding effect on various substrates.
❹ Cellulose ether significantly improves the bond strength of the mortar, and can ensure sufficient water time to fully hydrate the cement even in a high temperature environment, thus ensuring better bondability of the mortar.
Application field of cellulose ether
Cement-based:
⑴, putty, ⑵, plastering mortar, ⑶, waterproof mortar, ⑷, caulking agent, ⑸, plastering mortar, ⑹, spray mortar, ⑺, decorative mortar, ⑻, tile adhesive, ⑼, cement self-leveling, ⑽ Underwater concrete, ⑾, masonry mortar, ⑿, repair mortar, ⒀, thermal insulation slurry, ⒁, EIFS thermal insulation bonding mortar, ⒂, non-shrinkage grouting material.
Other building materials:
⑴, waterproof mortar, ⑵, two-component mortar.
With the development of dry-mixed mortar, cellulose ether has become an important cement mortar admixture. However, there are many varieties and specifications of cellulose ether, and the quality between batches still fluctuates. When using it, you need to pay attention to:
1. The working characteristics of modified mortar are closely related to the viscosity development of cellulose ether. Although products with high nominal viscosity have relatively high final viscosity, due to slow dissolution, it takes a long time to obtain the final viscosity; in addition , The cellulose ether with coarser particles takes longer to obtain the final viscosity, so the product with higher viscosity does not necessarily have better working characteristics.
2. Due to the limitation of the degree of polymerization of cellulose ether raw materials, the maximum viscosity of cellulose ether is also limited.