Do You Understand the Role of Starch Ether in Mortar Thoroughly ? 

Do You Understand the Role of Starch Ether in Mortar Thoroughly ? 

Introduction to Starch Ether

The more common and commonly used are potato starch, tapioca starch, corn starch, wheat starch, etc. Compared with cereal starches with higher fat and protein content, the starches of root crops such as potato and tapioca starch are purer.

Starch is a polysaccharide polymer compound composed of glucose. There are two kinds of molecules, linear and branched, called amylose (content about 20%) and amylopectin (content about 80%). To improve the starch properties used in building materials, physical and chemical methods can be used to modify it to make its properties more suitable for the needs of building materials for different purposes.

Etherified starch includes many types of products, such as carboxymethyl starch ether (CMS), hydroxypropyl starch ether (HPS), hydroxyethyl starch ether (HES), cationic starch ether, etc. The commonly used hydroxypropyl starch ether. 

  1. The Role of Starch Ether in the Mortar

    1. Thicken the mortar, increase the sag resistance, sag resistance, and rheology of the mortar

    For example, in the construction of tile adhesive, putty, and plastering mortar, especially now that mechanical spraying requires high fluidity, for example, it is imperative in a gypsum-based mortar (machine sprayed gypsum needs high fluidity but will cause severe sagging. Starch ether can make up for this defect).

    Liquidity and sag resistance are often contradictory, and the increase in fluidity will bring about a decline in sag resistance. The mortar with rheological properties can well solve the contradiction that when an external force is applied, the viscosity will decrease, and the workability and pumpability will be enhanced. When the external force is withdrawn, the viscosity will increase and improve the sag resistance.

    For the current trend of increasing tile area, adding starch ether can improve the tile adhesive slip resistance.

    1. Extend opentime

    It can meet the requirements of special tile adhesives for tile adhesives with extended opening hours (Class E, extend from 20min to 30min to reach 0.5MPa).

    1. Improved surface properties

    Starch ether can make the surface of gypsum-based and cement mortar smooth, easy to apply, and has an excellent decorative effect. It is significant for plastering mortars and thin-layer decorative mortars such as putty.

    The Mechanism of Action of Starch Ether

    When starch ether is dissolved in water, it will be evenly 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. As a transition bridge, the cement can be connected to give the slurry a more considerable yield value, improving the anti-sagging or anti-slip effect.

The Difference Between Starch Ether and Cellulose Ether

  1. Starch ether can effectively improve the anti-sagging and anti-slip properties of the mortar.However, cellulose ethers can generally only increase the viscosity and water retention of the system, but not the anti-sagging and anti-slip properties.
  1. Thickening and viscosity:generally, the viscosity of cellulose ether is about tens of thousands, while the viscosity of starch ether is several hundred to 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.
  1. Compared with cellulose ether, starch ether can significantly increase the initial yield value of tile adhesive, thereby improving its anti-slip performance
  1. Air-entraining: cellulose ether has strong air-entraining properties, while starch ether has no air-entraining properties.
  1. 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 cellulose is just the opposite, that is, the orientation of each adjacent glucose molecule is opposite. This structural difference also determines the difference in the properties of cellulose and starch. 

The combination of cellulose ether and starch ether can produce good synergy. Tests have proved that replacing 20%-30% of cellulose ether with starch ether used in mortar cannot reduce the water retention capacity of the mortar system and effectively improve the anti-sagging and anti-sliding capabilities.

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