Although starch ether and cellulose ether are both composed of glucose molecules, they are composed in different ways. All glucose molecules in starch are arranged in the same orientation, while in cellulose, the orientation of each adjacent glucose molecule is opposite. This structural difference also determines the difference in the properties of cellulose and starch.
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Hydroxypropyl starch ether is a general term for a class of modified starches containing ether bonds in their molecules, also known as etherified starches, which are widely used in medicine, food, textile, papermaking, daily chemicals, petroleum and other industries. Today we mainly explain the role of starch ether in mortar.
The Introduction to starch ethers
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, starches from root crops such as potato and tapioca are more pure.
Starch is a polysaccharide polymer compound composed of glucose, which has two kinds of molecules: amylose (about 20%) and amylopectin (about 80%). In order to improve the use properties of starch 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. Commonly used hydroxypropyl starch ethers.
The role of starch ether in mortar
1) Thicken the mortar to increase the sag resistance, sag resistance and rheology of the mortar
For example, in the construction of tile glue, putty, and plastering mortar, especially now mechanical spraying requires high fluidity, such as in gypsum-based mortar, which is especially important (machine-spraying gypsum requires high fluidity but will bring serious sagging, starch ether can make up for this deficiency).
Mobility and sag resistance are often contradictory, with increased mobility leading to decreased sag resistance. The mortar with rheological properties can solve such a contradiction well, that is, when external force is applied, the viscosity decreases, which enhances the construction and pumpability, and when the external force is withdrawn, the viscosity increases and the sag resistance is improved.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 (E-grade, 20min extended to 30min to reach 0.5MPa) with extended opening time.
3) Improved surface properties
Semonova starch ether can make the surface of gypsum-based 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.
4) The mechanism of action of starch ethers
When the starch ether is dissolved in water, it will be evenly dispersed in the cement mortar system. Since the starch ether molecule is in a network structure and is negatively charged, it will adsorb positively charged cement particles. As a transition bridge, the cement can be connected, thereby giving The larger yield value of the slurry can improve 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 mortar
Cellulose ethers 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 around tens of thousands, while the viscosity of starch ether is in the range of hundreds to thousands, but this does not mean that starch ether is inferior to cellulose ether in thickening mortar, and the thickening mechanism of the two is different.
3. Anti-slip performance
Compared with cellulose ethers, starch ethers can increase the initial yield value of tile adhesives, thereby improving their anti-slip properties.
4. Air entrainment
Cellulose ethers have strong air-entraining properties, while starch ethers have no air-entraining properties.
5. Cellulose ether molecular structure
Although starch ether and cellulose ether are both composed of glucose molecules, they are composed in different ways. All glucose molecules in starch are arranged in the same orientation, while in cellulose, the orientation of each adjacent glucose molecule is opposite. This structural difference also determines the difference in the properties of cellulose and starch.
In conclusion
When cellulose ether and starch ether are used in combination, good synergy can occur. Tests have shown that replacing 20% to 30% of cellulose ether with starch ether can not reduce the water retention capacity of the mortar system, and effectively improve the anti-sagging and anti-slip capabilities.
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