Starch ether is a general term for a class of modified starches containing ether bonds in the molecule, also called etherified starch, which is widely used in medicine, food, textile, papermaking, daily chemical, petroleum and other industries. Today we mainly explain the role of starch ether in mortar.
Starch ether introduction
The more common and commonly used are potato starch, tapioca starch, corn starch, wheat starch and so on. Compared with cereal starches with higher fat and protein content, the starches ofroot crops such as potato and tapioca starch are more pure.
Starch is a polysaccharide polymer compound composed of glucose. It has two kinds of straight chain and branched molecules, called amylose (about 20%) and amylopectin (about 80%) respectively. In order to improve the use of starch in building materials, physical and chemical methods can be used to modify it, so that its properties more suitable for different purposes of building materials.
Etherified starch includes many types of products: Such as carboxymethyl starch ether (CMS), hydroxypropyl starch ether (HPS), hydroxyethyl starch ether (HES), cationic starch ether and so on. Commonly used hydroxypropyl starch ether (HPS).
The role of starch ether in mortar
（1） Thickening mortar, increasing anti-sagging, anti-sliding, and rheological properties of mortar.
For example, in the construction of tile adhesive, putty, plastering mortar, especially now mechanical spraying requirements of high fluidity, such as it is particularly important in gypsum based mortar (machine spraying gypsum requirements of high fluidity but will cause serious sagging, starch ether can make up for this defect)
Liquidity and sag resistance are often contradictory, and the improvements of liquidity will lead to the decline of sag resistance. The mortar with rheological properties can well solve the contradiction, that is, when the external force is applied, the viscosity decreases, which enhances the workability and pumpability, when the external force is withdrawn, the viscosity increases, improve the sagging resistance.
For the current trend of increasing tile area, adding starch ether can improve the slip resistance of tile adhesive.
For tile adhesive, it can meet requirements that extended opening time for the special tile adhesive. (E class, extended from 20min to 30min, reach 0.5MPa)
（3） Improvement of surface performance
Starch ether can make the surface of gypsum based and cement mortar smooth, easy to apply, and has a good decorative effect. It is of great significance for plaster mortars and thin-layer decorative mortars such as putty.
The mechanism of starch ether
When starch ether is dissolved in water, it will be uniformly dispersed in the cement mortar system. Because starch ether molecules have a network structure and are negatively charged, they will adsorb positively charged cement particles, which can be used as a transition bridge to connect cement, thus giving the larger yield value of the slurry, can improve the anti-sagging or anti-slip effect.
1. Starch ether can effectively improve the anti-sagging and anti-slip properties of the mortar
2. Thickening and viscosity
Generally, the viscosity of cellulose ether is in the tens of thousands, while the viscosity of starch ether is several hundred to several thousand, but this does not mean that starch ether is not as thick as cellulose ether in thickening mortar. The thickening mechanism of the two is different.
3. Anti-slip performance
5. Molecular structure of cellulose ether
Although both starch and cellulose are composed of glucose molecules, their composition is different. The orientation of all glucose molecules in starch is the same, while the orientation of cellulose is the opposite. The orientation of each adjacent glucose molecule is opposite. This structural difference also determines the difference in the properties of cellulose and starch.
Combining cellulose ether and starch ether can produce a good synergistic effect. Tests have proved that replacing 20%-30% of cellulose ether with starch ether used in mortar can not reduce the water retention capacity of the mortar system, and effectively improve the anti-sagging and anti-sliding capabilities.
Post time: Jan-05-2022