HPMC-Hydroxypropyl methyl cellulose introduction
November 21st 2024
The redispersible powder is a special water-based emulsion made by spray drying and a polymer binder prepared mainly based on the vinyl acetate-ethylene copolymer. After partial evaporation of water, polymer particles form a layer of polymer film by agglomeration and play the role of adhesive. When redispersible polymer powder is used together with inorganic cementitious minerals such as cement, it can have a modification effect on mortar. The main functions of redispersible polymer powder are as follows.
(1) Improve the bond strength, tensile strength and flexural strength.
Redispersible polymer powder can significantly improve the bond strength of mortar. The greater the amount is added, the more it will be improved. High bond strength can have a certain inhibitory effect on the contraction, while the stress generated by deformation is easily dispersed and released, so the bond strength is very important to improve the crack resistance. Studies have shown that the synergistic effect of cellulose ethers and polymer powders could help improve the bond strength of cement mortar.
(2) Reduce the elastic modulus of mortar, enabling the brittle cement mortar to have certain flexibility.
The elastic modulus of redispersible polymer powder is low, 0.001-10GPa; while that of cement mortar is high, 10-30GPa, so the elastic modulus of cement mortar will be reduced with the addition of polymer powder. But the type and dosage of polymer powders also have an effect on the elastic modulus. Usually, as the polymer-cement ratio increases, the elastic modulus decreases and the deformation capacity increase.
(3) Improve the water resistance, alkali resistance, abrasion resistance and impact resistance.
The network film structure formed by polymers closes the holes and cracks in cement mortar, and reduces the porosity of hardened body, thereby improving the impermeability, water resistance and frost resistance of cement mortar. This effect increases with the increase of the polymer-cement ratio. Improving the abrasion resistance is related to the type and polymer-cement ratio of polymer powder. In general, as the polymer-cement ratio increases, the abrasion resistance is improved.
(4) Improve the liquidity and workability of mortar.
(5) Improve the water retention of mortar and reduce water evaporation.
The polymer emulsion formed after the redispersible polymer powder dissolved in water is dispersed in mortar and forms a continuous organic film in mortar after solidification. This organic film can prevent the migration of water, thereby reducing the water loss of mortar and playing a role in water retention.
(6) Reduce the cracking phenomenon
The elongation and toughness of polymer modified cement mortar are much better than those of ordinary cement mortar. Fracture performance is more than twice that of ordinary cement mortar; and impact resistance toughness increases with the increase of polymer-cement ratio. With the increase in the amount of polymer powder added, the flexible buffering effect of polymer can inhibit or retard the development of cracks, and meanwhile with good stress dispersion.
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