Different effects of HPMC, starch ether and RDP on gypsum mortar
Hydroxypropyl methylcellulose (HPMC)
1. It is stable to acids and alkalis, and its aqueous solution is very stable in the range of pH=2~12. Caustic soda and lime water do not have much impact on its performance. But alkali can speed up its dissolution. And slightly improve the viscosity.
2. HPMC is a highly efficient water-retaining agent for dry mortar systems. Reduce mortar bleeding rate and delamination degree, and improve mortar cohesion. Effectively inhibit the formation of plastic cracks in mortar. Reduce the plastic cracking index of mortar.
3. It is a non-ionic and non-polymeric electrolyte. It is very stable in aqueous solutions with metal salts and organic electrolytes. Can be added to building materials for a long time. Ensure its durability is improved.
4. The working performance of mortar is significantly improved. The mortar appears to be “oily” in nature. It can make the wall joints full and the surface smooth. The mortar is firmly bonded to the base layer and the operation time can be extended.
The effect of HPMC on gypsum mortar
1. Water retention
Achieving internal maintenance is beneficial to improving long-term strength and inhibiting bleeding. Prevent mortar settlement and shrinkage to improve the crack resistance of mortar.
Prevent segregation, improve mortar uniformity, improve wet bonding strength, and improve sag resistance.
3. Entrain air
Improve the working performance of mortar As the viscosity of cellulose becomes higher and higher, the longer the molecular chain, the more obvious the air-entraining effect will be.
4. Slow setting
Synergizes with water retention to extend the opening time of mortar.
Hydroxypropyl starch ether
1. The higher hydroxypropyl content in starch ether gives the system stable hydrophilicity. Turning free water into bound water plays a good role in water retention.
2. Starch ethers with different hydroxypropyl contents have different abilities to assist cellulose in retaining water at the same dosage.
3. The substitution of hydroxypropyl group increases the swelling degree in water. Compresses the space for particle flow, thus achieving a viscosity and thickening effect.
Effect of hydroxypropyl starch ether on gypsum mortar
Starch ether quickly disperses in the mortar system, changing the rheology of the mortar and giving it thixotropy.
When external force is applied, the viscosity of the mortar decreases. Guaranteed good construction and pumpability. Gives a smooth feel.
When the external force is removed, the viscosity increases, giving the mortar good resistance to sagging and sagging. In putty powder, it has the advantages of improving the brightness of putty oil and polishing brightness.
2. The effect of assisting in water retention
Starch ether itself has hydrophilic properties due to the role of hydroxypropyl groups in the system. When combined with cellulose or added in a certain amount to the mortar, it can increase water retention to a certain extent and improve surface drying time.
3. Anti-sag and anti-slip
Excellent anti-sag effect and shaping effect
Redispersible polymer powder
1. Improve the workability of mortar
Rubber powder particles are dispersed in the system, giving the system good fluidity. Improve the workability and workability of mortar.
2. Improve the bonding strength and cohesion of mortar
After the rubber powder is dispersed and formed into a film, the inorganic and organic matter in the mortar system are blended together. Think of the cement and sand in the mortar as the bones. The latex powder forms the ligaments. The cohesion increases, the strength increases, and a flexible structure is gradually formed.
3. Improve the weather resistance and freeze-thaw resistance of mortar.
RDP is a thermoplastic resin with good flexibility. It enables the mortar to respond to external hot and cold changes. Effectively prevent mortar from cracking due to temperature changes.
4. Improve the flexural strength of mortar
Polymers and cement pastes have complementary advantages. When cracks are caused by external forces. Polymers can span cracks and inhibit crack expansion. As a result, the fracture toughness and deformability of the mortar are improved.