70000-80000cps

Water retention additives play an important role in modern building products, particularly in dry-mix mortars [1]. Their function is to prevent uncontrolled water loss into porous substrates such as brick, lime stone, and aerated concrete. In industrial products, cellulose ethers dominate this market because of their favorable cost effectiveness and their good environmental compatibility [2]. The first reports on the preparation of methyl cellulose and its derivates originate from Lilienfeld [3], Leuchs [4] and Dreyfus [5]. Based on their pioneering work in cellulose ether synthesis, production started in Germany in the 1920s and in the United States in 1938. Major current applications of cellulose ethers include wall renders and plasters, joint compounds for gypsum board paneling, cementitious tile adhesives (CTAs), floor screeds, self-leveling underlayments (SLUs) and water-proofing membranes [6]. In dry mortars, cellulose ethers serve to provide water retention and viscosity. Some types retard Portland cement hydration severely [7], [8]. The effect depends on the specific composition (e.g. degree and type of substitution) of the cellulose ether. Application dosages may range between 0.1 and 1.5% by weight of binder, depending on the desired properties. Among the most frequently used cellulose ethers are methyl hydroxyethyl cellulose (MHEC, also referred to as HEMC) and methyl hydroxypropyl cellulose (MHPC) [9], [10], [11]. MHEC is predominantly applied in self-leveling flooring compounds and cementitious tile adhesives (CTAs) while MHPC, because of its air-entraining effect stemming from the hydrophobic hydroxypropyl groups, is the product of choice for wall renders and plasters.

In general, the gel temperature of HPMC is around 60℃-75℃ depending on its group content and different production technique. Due to the characteristics of MHEC group, it has a higher gel temperature, usually > 80℃. Therefore its stability under high temperature is better that HPMC. In practical construction, in the hot construction environment in summer, the water holding capacity of MHEC with the same viscosity and dosage is better than that of HPMC. Especially in the Southeast Asian countries and India, mortar will sometimes be constructed at high temperature. Cellulose ether with low gel temperature will lose its thickening and water retention at high temperature, thereby accelerating the hardening of mortar, and affects the construction.