4 Advice to Choose a Hpmc Makes Mortar High in Water Demand

In this paper, the effect of HPMC (hydroxypropyl methyl cellulose ether) on the cement mortar water retention (WR) and composition was studied. The relationship between the plastic viscosity and water retention of cement mortar was revealed. The results showed that HPMC formed a colloidal film with a 3D network structure in water, which changed the ability of water to migrate. The HPMC colloid adsorbed on the surface of cement and sand particles and played a bridging role due to the influence of the spatial network structure of the thin film. Fine particles formed a grid-like distribution, and the hydration products formed a unique fibrous tree-like structure. A positive correlation was observed between the plastic viscosity and the water holding capacity of cement mortar. Finally, the mechanism responsible for the improved water retention of cement mortar by HPMC was analyzed using the changing water migration capacity, migration channels, and mortar cohesion.

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1. Introduction

Cellulose ethers (CEs) are used to improve the workability of cement mortars while maintaining the water holding capacity and fluidity [1,2]. HPMC is the most widely-used CE [3]. High water retention improves the cement hydration and limits the absorption of the mixing water by a substrate and thus provides good mechanical and adhesive properties to the mortar [4,5]. Cellulose ethers thicken cement slurries, and their water retention is usually attributed to increased slurry viscosity. Desbrieres et al. [6] showed that polymers increase the water retention of cement-based pastes by increasing the viscosity, which reduces filtration loss. Anionic polymers can adsorb on the surface of cement particles, block cake pores, and act bridges between cement particles. Marlieres [7] et al. showed that the water-holding capacity of cellulose ethers affected many types of porous media, and could be polymerized in solution to render polymers hydrophobic. Water retention occurred because water migration between pores was blocked. Pourchez et al. [8,9] showed that cellulose ether had a retarding effect on the hydration of cement slurry, while also helping retain water. The degree of substitution (DS) and molar degree of substitution (MS) was the key parameter affecting the hydration of cement. Brumaud et al. [10,11] found that due to CE adsorption on the surface of cement particles, calcium silicate nucleation and the dissolution rate of tricalcium aluminate were slowed, thus inhibiting cement hydration. The results also showed that the adsorption capacity of CE on the surface of cement particles was related to the MS and DS. Weyer [12] showed that CEs with a lower degree of substitution had a greater retarding effect on cement hydration. Alexandre [4] et al. analyzed the concentration of cellulose ether of the interstitial fluid of cement paste and found that limited adsorption CE occurred on particle surfaces by the total organic carbon (TOC) analyzer. Water retention did not occur via adsorption on the surface of cement particles and was instead caused by blocking.

Water retention reflects the workability of cement mortars. In modern building products, CEs play an important role, particularly in dry-mix mortars such as wall renders and plasters based on mineral binders including lime and cement. Their main function is to prevent uncontrolled water loss into porous substrates [3]. Since the sand in different types of cement mortar accounts for 50–80% of the total mass, this research focuses on the effect of CEs and cement particles on the water retention mechanism of cement mortar, and the interactions of cellulose ether with sand and water are neglected. On the other hand, the physical interactions between cellulose ethers and cement paste, cement mortar, and concrete are still not well understood, and the use of cellulose ethers is often based on empiricism [1,10]. Therefore, it is important to study the effect of cellulose ethers on the water retention of cement mortar by studying the interactions between HPMC and cement, sand, and water.

In this paper, the HPMC distribution in water and the interactions between HPMC and fresh cement mortar were studied, and the effect of HPMC on the early hydration of cement paste was analyzed. The relationship between the plastic viscosity of cement mortar and the water-holding capacity was analyzed by studying the effect of HPMC on the plastic viscosity of cement mortar.

1. HPMC solubility in water

HPMC is the same as hypromellose and is a water-soluble cellulose ether. HPMC dissolves in cold water and certain polar organic solvent, such as methanol, ethanol, isopropyl alcohol (IPA), and acetone. HPMC can also be dissolved in water-organic solvents and mixed solvents. But is not soluble in hot water.

2. How do you dissolve HPMC?

HPMC solubility ways include hot water solubility, dry powder mixing method, and organic solvent wetting method.

2.1 HPMC solubility in hot water

Because HPMC is not soluble in hot water, we need to cool the HPMC hot solution to a proper temperature. Only in this way, HPMC can be soluble and play the function of increasing viscosity. There are 3 ways in the following.

1. Pour the required amount of hot water into the container. Heat it until about 70℃. Then stir it slowly. and add HPMC to it. In the beginning, HPMC powder floated on the water solution surface. Gradually forming a slurry through stirring. Stir until the slurry is cool. If the temperature is down to a proper degree, the HPMC becomes water solubility. The HPMC solution begins to have viscosity.

2. Pour 1/3 or 2/3 of the required amount of hot water into the container. Heat it until about 70℃. Then add HPMC. Then stir it slowly to make HPMC powder evenly disperse and thoroughly wet. hot water slurry is prepared. Then add the remaining amount of cold water to the hot slurry and cool the mixture while stirring. Then continue to stir.

3. Put 1/3 or 2/3 of the required amount of hot water into the container. Heat it to about. 70°C. Then stir it slowly to make HPMC powder evenly disperse and thoroughly wet. hydroxypropyl methylcellulose is dispersed. Hot water slurry is prepared. Then add the remaining amount of cold water or ice water to the container. Add HPMC hot water slurry to the cold water, and stir, At last cool down this solution.

2.2 Dry powder mixing method

There is a mixing process between HPMC molecular and other dry powders in a blender. The suggested ratio of dry powder to HPMC is 3:1 or 7:1. Then when stir, add water. Continue to stir until the mixture has completely hydrated.

At this moment, HPMC will not condense. Because HPMC powder molecular is dispersed in every tiny corner. Every corner has little. Therefore, this mixture can be dissolved immediately when meets water.

Non-surfaced HPMC often applies to wall putty and mortar. And this material usually is powder. So in the construction of dry mortar or wall putty, workers would like to use dry powder mixing method rather than use hot water methods.

2.3 Organic solvent wetting method

using an organic solvent to disperse or wet HPMC. Then add water. At this moment, HPMC is easy to dissolve.

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3. HPMC solubility in cold water

HPMC solubility in water has two types: surface-treated HPMC and non-surfaced treated HPMC.

3.1 surface treated HPMC solubility in cold water

When adding surface-treated HPMC into the water, HPMC will disperse into the cold water. But don’t have any viscosity. It is just dispersed. stir it and wait around 2 minutes, the solution becomes thick and viscous.

This is because instant HPMC’s surface has a kind of crosslinking agent. Most HPMC manufacturers like using Glyoxal as a crosslinking agent. This agent helps HPMC to disperse in cold water rather than dissolve at the beginning. So the price of surface treated HPMC is high than nor surface-treated HPMC.

3.2 Non-surface treated HPMC solubility in cold water

Hot melt products may condense when in contact with cold water. This is because the outer layer of non-surfaced treated HPMC reacted with cold water. This reaction makes the solution becomes viscous and thicken. The HPMC powder is wrapped in this transparent gel. Only the outer layer is dissolved. The dissolution rate of HPMC inside will be greatly slowed down.

Generally, it will be dissolved by dissolving in hot water.

4.HPMC solubility in organic solvents

Only in the case of polar organic solvents containing a higher percentage, HPMC can be dissolved in an organic solvent. This solubility doesn’t consider whether organic solvents have water. Compare to other substitutes, HPMC has a higher solubility in organic solvents. This is an HPMC solubility in organic solvents in detail. For example, HPMC solubility in IPA or ethanol.

4.1 HPMC solubility in ethanol or isopropyl alcohol

Is HPMC soluble in IPA?

Yes, it is

Is HPMC soluble in ethanol?

Yes, it is. But insoluble in anhydrous ethanol. HPMC exhibits good solubility in higher concentrations of ethanol or isopropyl alcohol.

Hand sanitizer gel generally consists of less than 40% water and more than 60% alcohol. Alcohol used to prevent diseases and eliminate bacteria. Hand sanitizer formulations use HPMC as a detergent thickener to increase viscosity.

Dissolution method of hydroxypropyl methylcellulose in water/alcohol mixture

1. Put ethanol or isopropanol in a container. Slowly add HPMC powder or another detergent thickener while stirring with a mixer

2. Continue stirring until a homogeneous suspension is observed

3. Slowly add cold water to dissolve