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.

2. Redispersible polymer powder
Redispersible rubber powder is made of special polymer lotion through spray drying. During the processing, protective colloid and anti hardening agent become indispensable additives. The dried rubber powder is some 80~100mm spherical particles gathered together. These particles can be soluble in water and form a stable dispersion slightly larger than the original lotion particles. This dispersion will form a film after dehydration and drying. This film is irreversible like the film formation of ordinary lotion, and will not disperse into a dispersion when encountering water.
Redispersible rubber powder can be divided into styrene butadiene copolymer, tertiary ethylene carbonate copolymer, ethylene acetic acid copolymer, etc., and on this basis, organic silicon and vinyl laurate can be grafted to improve the performance. Different modification measures make the redispersible rubber powder have different properties such as water resistance, alkali resistance, weather resistance and flexibility. It contains vinyl laurate and organic silicon, which can make the rubber powder have good hydrophobicity. Highly branched ethylene tertiary carbonate has low Tg value and good flexibility. The application of these powders in mortar has a retarding effect on the setting time of cement, but the retarding effect is smaller than that of the direct application of similar lotion. In contrast, the retarding effect of styrene butadiene is greater than that of ethylene vinyl acetate. If the dosage is too small, the improvement of mortar performance is not obvious.

Research Methodology