Starch ether is a general term for a class of modified starches containing ether bonds in the molecule, also known as 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.
Introduction to Starch Ether
The more common and commonly used ones are potato starch, tapioca starch, corn starch, wheat starch, etc. Compared with cereal starch with higher fat and protein content, root crop starch such as potato and tapioca starch is more pure.
Starch is a polysaccharide macromolecular compound composed of glucose. There are two types of molecules, linear and branched, called amylose (about 20%) and amylopectin (about 80%). In order to improve the properties of starch used in building materials, physical and chemical methods can be used to modify it to make its properties more suitable for different purposes of building materials.
Etherified starch includes various types of products. Such as carboxymethyl starch ether (CMS), hydroxypropyl starch ether (HPS), hydroxyethyl starch ether (HES), cationic starch ether, etc. Commonly used hydroxypropyl starch ether.
The role of hydroxypropyl starch ether in mortar
1) Thicken the mortar, increase the anti-sagging, anti-sagging and rheological properties of the mortar
For example, in the construction of tile adhesive, putty, and plastering mortar, especially now that mechanical spraying requires high fluidity, such as in gypsum-based mortar, it is especially important (machine-sprayed gypsum requires high fluidity but will cause serious sagging, starch Ether can make up for this deficiency).
Fluidity and sag resistance are often contradictory, and increased fluidity will lead to a decrease in sag resistance. Mortar with rheological properties can well solve such a contradiction, that is, when an external force is applied, the viscosity decreases, enhancing the workability and pumpability, and when the external force is withdrawn, the viscosity increases and the sagging resistance is improved.
For the current trend of increasing tile area, adding starch ether can improve the slip resistance of tile adhesive.
2) Extended opening hours
For tile adhesives, it can meet the requirements of special tile adhesives (Class E, 20min extended to 30min to reach 0.5MPa) that extend the opening time.
Improved surface properties
Starch ether can make the surface of gypsum base and cement mortar smooth, easy to apply, and has good decorative effect. It is very meaningful for plastering mortar and thin layer decorative mortar such as putty.
Mechanism of action of hydroxypropyl starch ether
When starch ether dissolves in water, it will be uniformly dispersed in the cement mortar system. Since the starch ether molecule has a network structure and is negatively charged, it will absorb positively charged cement particles and serve as a transition bridge to connect cement, thus giving The larger yield value of the slurry can improve the anti-sag or anti-slip effect.
The difference between hydroxypropyl starch ether and cellulose ether
1. Starch ether can effectively improve the anti-sag and anti-slip properties of mortar
Cellulose ether usually can only improve the viscosity and water retention of the system but cannot improve the anti-sagging and anti-slip properties.
2. Thickening and viscosity
Generally, the viscosity of cellulose ether is about tens of thousands, while the viscosity of starch ether is several hundred to several thousand, but this does not mean that starch ether has strong air-entraining property, while starch ether has no air-entraining property.
5. Molecular structure of cellulose ether
Although both starch and cellulose are composed of glucose molecules, their composition methods are different. The orientation of all glucose molecules in starch is the same, while that of cellulose is just the opposite, and the orientation of each adjacent glucose molecule is opposite. This structural difference also determines the difference in the properties of cellulose and starch.