Water Retention Mechanism of HPMC in Cement Mortar

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.

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.

Overview of HPMC

1、What is HPMC?

（1）HPMC or Hydroxypropyl methylcellulose (INN name: Hypromellose), also simplified as hydroxypropyl methylcellulose (HPMC), is a kind of non-ionic cellulose mixed ether. It is a semi-synthetic, inactive, viscoelastic polymer. Hydroxypropyl methylcellulose is widely used in construction, food, medicine, and other industries.

HPMC CAS : No. 004-65-3

HPMC Structural：

Molecular weight: 86000.00000

（2）Physical property：

Appearance and Properties: White or quasi-white fibrous or granular powder

Density: 1.39 g/ cm³

Solubility: Almost insoluble in absolute ethanol, ether, and acetone; swelling in cold

water into a clear or slightly turbid colloidal solution

Stability: Solids are flammable and incompatible with strong oxidants.

（3）Chemical property：

Appearance: White or similar white powder.

Particle size; 100 mesh pass rate is more than 98.5%; 80 mesh pass rate is 100%. Particle sizes of special specifications ranged from 40 to 60 meshes.

Carbonization temperature: 280-300 ℃

Visual density: 0.25-0.70g/cm (usually about 0.5g/cm), specific gravity 1.26-1.31.

Discoloration temperature: 190-200 ℃

Surface tension: 2% aqueous solution is 42-56 dyn/cm.

Solubility: Soluble in water and some solvents, such as the appropriate proportion of ethanol/water, propanol/water, etc. The aqueous solution has surface activity. With high transparency and stable performance, the gel temperature of different specifications is different, the solubility changes with viscosity, the viscosity is lower and the solubility is greater. The performance of HPMC with different specifications has a certain difference. The dissolution of HPMC in water is not affected by the PH value.

2. HPMC produced by Celotech Chemicals

Celotech is producing and providing different types of HPMC for different fields of applications, generally Celopro HPMC series are consists of 3 types of standard products & several types of modified product.

Standard Types:

Celopro MK

Celopro MF

Celopro ME

Modified Types：

Celopro MT

Celopro MX

Celopro DK

Celopro CX

Celotech offers a wide range of Celopro® construction grades to ensure that for every conceivable situation the right product is available.

Applications

Products

Block Laying Adhesive

MK40M FP、MK70M FP、MT4016

Cement Tile Adhesive (CTA)

MK40M FP、MK70M FP、MT4016

Cement One Coat

MH25M FP、MK30M FP

Cement Skim Coat

MK30M FP、MT3025、MT3027

Tile Grouts

MT6001

Gypsum Hand Plaster

MK30M FP、MT4031、MT5503

Self levelling

MK400 FP、MT1004

3. What is HPMC used for?

(1) Construction industry: As a water-retaining agent and retarder of cement mortar, it makes the mortar pumpable. Use plaster, gypsum, putty powder or other building materials as adhesives to improve the applicability and prolong the operation time. It can be used to paste ceramic tile, marble, plastic decoration, paste reinforcing agent, and reduce the amount of cement. The water-retaining property of HPMC prevents the slurry from cracking due to drying too fast after smearing and enhances the strength.

(2) Ceramic manufacturing industry: widely used as adhesives in the manufacture of ceramic products.h after hardening.

(3) Coatings industry: As a thickener, dispersant and stabilizer in the coating industry, it has good solubility in water or organic solvents. As paint remover.

(4) Ink printing: As a thickener, dispersant and stabilizer in the ink industry, it has good solubility in water or organic solvents.

(5) Plastics: as forming release agent, softener, lubricant, etc.

(6) Polyvinyl chloride: As dispersant in the production of polyvinyl chloride, it is the main assistant in the preparation of PVC by suspension polymerization.

(7) Others: This product is also widely used in leather, paper products, fruit and vegetable preservation, and textile industry.

Construction Ceramic Tile Adhesive Mortar Used HPMC

Product Description

HPMC is the main additive of ceramic tile glue, ceramic tile glue with accurate ratio of HPMC additive by mixing mixing machine into the powder bonding material, has a certain flexibility, fundamentally solve the problems existing in the building decoration, such as cracking, empty drum, falling off and leakage.

Advantages

It can effectively improve the quality of building materials and increase work efficiency.

(1) Thickening: It can improve the adhesion and sag resistance, and prevent the slippage between the mortar and the substrate in construction projects.

(2) Water retention: It delays the absorption of water by porous materials, which is conducive to cement hydration and a longer open time, and promotes the cohesive force and strength of the mortar.

(3) Workability: It can act as a lubricant, improve the working performance of the cement base, and increase the plasticity of the mortar.

(4) Delayed swelling: After a certain delay, it will dissolve quickly without agglomeration, which can improve the coating efficiency of construction projects.