Methyl hydroxyethyl cellulose ether (MHEC) and methyl hydroxypropyl cellulose ether (HPMC) are collectively referred to as methyl cellulose ether (Methyl Cellulose), referred to as MC. Methyl cellulose ether is one of the essential additives in dry-mixed mortar, which mainly plays the role of water retention and thickening.
Methyl cellulose ether is a powdery cellulose ether produced by the reaction of wood fiber or refined short cotton fiber as the primary raw material, after chemical treatment, through the reaction of micronizing agents such as ethylene chloride, propylene chloride, or ethylene oxide. The molecular structure of cellulose is composed of molecular bonds of anhydrous glucose units, each containing 3 hydroxyl groups. Under certain conditions, the hydroxyl groups are replaced by methyl, hydroxyethyl, and hydroxypropyl to produce various types of cellulose. Substituted by methyl is called methyl cellulose, substituted by hydroxyethyl is called hydroxyethyl cellulose, and substituted by hydroxypropyl is called hydroxypropyl cellulose. Since methyl cellulose is a mixed ether produced by etherification reaction, it mainly comprises methyl groups. However, it contains a small amount of hydroxyethyl or hydroxypropyl groups, called methyl hydroxyethyl cellulose ether or methyl Hydroxypropyl cellulose ether.
Due to different substituents (such as methyl, hydroxyethyl, and hydroxypropyl) and different degrees of substitution (the number of substances replaced by each active hydroxyl group on cellulose), there are various types of varieties and grades for cellulose ether. Different combinations can be widely used in other fields, such as construction engineering, food and pharmaceutical, daily chemical, and petroleum.
At present, there are four kinds of cellulose ethers with the most significant production volume in the world, and their main uses are as follows:
(1) Methyl hydroxyethyl cellulose ether (MHEC) accounts for 80% of chemical building materials and 20% of the coating industry. This type of cellulose ether is mainly used in dry-mixed mortar worldwide. Compared with other kinds, MHEC has better water retention and thickening properties and more stable quality.
(2) Methyl hydroxypropyl cellulose ether (HPMC) is mainly used in the pharmaceutical and daily chemical industries, and a considerable part of it is used in the chemical building materials industry. However, its water retention and thickening properties are slightly lower than those of Methyl Hydroxyethyl cellulose ether, especially at high temperatures with low water retention.
(3) Hydroxyethyl cellulose ether (HEC) is mainly used as a stabilizer in the coating industry and oil field drilling mud, but its dispersibility, thickening, and water retention are significantly lower than methyl cellulose ether (MC).
(4) Sodium carboxymethyl cellulose (CMC) is mainly used in daily chemical, food, papermaking, textile, and other industries, and a small amount is used in the coating industry.
2. Properties of methyl cellulose ether (MC)
Methyl cellulose ether is a necessary modified material for dry-mixed mortar such as plastering mortar, dry-mixed gypsum plaster, tile adhesive, putty, self-leveling material, spray mortar, wallpaper glue, and caulking material. In various dry-mixed mortars, methyl cellulose ether controls the mortar’s consistency, workability, bonding performance, and water retention.
The main characteristics of methyl cellulose ether are as follows:
(1) Excellent water retention
The water retention level is an important indicator to measure the quality of methyl cellulose ether, especially in the thin layer construction of cement mortar and stone-based products. Enhanced water retention can prevent strength loss and cracking caused by excessive drying and insufficient hydration. In addition, the excellent water retention of methyl cellulose ether under high-temperature conditions is one of the essential indicators to distinguish the performance of methyl cellulose ether. Under normal circumstances, most common methyl cellulose ethers decrease water retention as the temperature rises. When the temperature rises to 40T, the water retention of common methyl cellulose ethers reduces significantly. The thin-layer construction on the sunny side in summer will seriously impact. However, making up for the lack of water retention through high dosage will cause high viscosity of the material due to high dosage, which will cause inconvenience to construction.
High-quality methyl cellulose ether products are processed through a unique etherification process, which has excellent dispersion and water retention, which can effectively and evenly distribute cellulose in cement mortar and gypsum-based products and wrap all solid Particles and form a wetting film, making the whole system very stable. The moisture in the package is released gradually over a long period, and part of the moisture escapes from the pores due to drying and evaporation. Most remaining moisture continues to hydrate with cement, lime, or gypsum. Even in hot and high-temperature environments, there is sufficient moisture and time for hydration reactions, thereby ensuring the material’s bond strength and compressive strength. The water retention of methyl cellulose ether is also related to its viscosity, fineness, solubility, and additional amount. Generally, the higher the viscosity, the finer the fineness, and the more excellent the addition, the better the water retention.
(2) Strong adhesion and good sag resistance
Another essential characteristic of methyl cellulose ether is its excellent thickening effect. Adding methyl cellulose ether to dry-mixed mortar products can increase the viscosity thousands of times. Especially the use of high-quality methyl cellulose ether can obtain a much higher viscosity than ordinary methyl cellulose ether, making it have better sagging resistance and adhesion. In practical applications, methyl cellulose ether can precisely control the consistency of the product, which can be adjusted by the type and amount of methyl cellulose ether added.
The thickening effect of high-quality methyl cellulose ether is closely related to its unique rheology; its viscosity will significantly affect the bond strength, fluidity, structural stability, and workability of the material.
(3)Good solubility
Due to the special treatment of the surface particles of high-quality methyl cellulose ether, the solubility is excellent whether in cement mortar, gypsum, or paint system; it is not easy to agglomerate, and the dissolution speed is fast. It can promote rapid dissolution, especially in the mortar system with a high pH value. Usually, it can be completely dissolved in a few minutes; in the coating system, methyl ellulose ether can be formulated into a 2% ~ 3% thickened aqueous solution; as a thickener, water retaining agent, and emulsifier of paint, it has better solubility, workability and water retention than hydroxyethyl cellulose (HEC), and it is helpful for the leveling of paint and avoiding brush marks: uniform film formation, less splashing, better thixotropy.
