The influence of cellulose ether(HPMC) and starch ether(HPS) on the performance of mortar

HPMC (Hydroxypropyl Methyl Cellulose) and HPS (Hydroxypropyl Starch) are two main chemical additives -with strong thickening effect – used in the dry-mixed mortar industry.

How do they perform, and what are the differences in their effects?

Below is test data showing how these two additives influence mortar performance, including consistence, wet density, compressive strength, and adhesion strength.

The basic test formulation of mortar used is:
Cement 20%, Sand 80%, Water 16%

Observations from Table 1:

• As HPMC (Cellulose ether) dosage increases:
  • Consistence decreases, indicating a thicker and more viscous mortar due to the thickening effect of HPMC.
  • Density decreases, which suggests more voids due to the air-entraining property of HPMC.
  • Compressive strength decreases, likely due to reduced density.
  • Adhesion strength increases initially, peaking around 0.4% dosage, but then decreases. This shows that HPMC improves adhesion, but excessive dosage is not beneficial.

Observations from Table 2:

• As HPS (Starch) dosage increases:
  • Consistence decreases, due to the strong thickening effect of starch ether.
  • Density remains relatively unchanged, indicating that HPS does not have air-entraining effects like HPMC.
  • Compressive strength decreases, as starch ether can slow down the cement hydration reaction and significantly delay setting time.
  • Adhesion strength increases initially, peaking at around 0.05%, then declines, showing that the right amount of HPS enhances adhesion.

Conclusion:

From Tables 3, 4, and 5, we observe that the trends in performance are consistent across different levels of HPMC when varying the HPS dosage.

• The interaction between HPMC and HPS shows no adverse chemical reaction, indicating good compatibility.
• Both additives impact consistence and strength, but their influence varies depending on dosage.
• Optimal performance requires careful balance—more is not always better, especially regarding adhesion and strength.

The data in this article is cited from Guangdong Building Materials Journal, Issue 8, 2018.