Effect of cellulose on tile adhesive

1 Introduction

Cement based tile adhesive is the largest application of special dry mortar. It is an organic or inorganic mixture based on cement.

It is the main cementing material, supplemented by graded aggregate, water retention agent, early strength agent and latex powder. Compared to ordinary cement mortar, it usually only needs to be mixed with water when used.

It can greatly improve the bond strength between the facing material and the substrate. And has good anti-slip properties. It has excellent water resistance, heat resistance and freeze-thaw resistance.

This is mainly used to paste decorative materials such as indoor and outdoor wall tiles and floor tiles. Widely used in indoor and outdoor walls, floors, bathrooms, kitchens and other decorative interiors. Therefore, it is the most widely used tile bonding material.

Usually we judge the performance of tile adhesives. In addition to pay attention to its operational performance and anti-slip ability. It also pays attention to its mechanical strength and opening time.

In addition to affecting the rheology of ceramic glues, there are also cellulose ethers in tile adhesives. Operations such as sliding performance, the state of the sticking knife, and the like also have a strong influence on the mechanical properties of the tile adhesive.

2 the impact of tile adhesive opening time

When the rubber powder and the cellulose ether coexist in the wet mortar. Some data models show rubber powder. Has a stronger kinetic energy attached to the cement hydration product.Lignite is more present in the tissue fluid, which more affects the viscosity and setting time of the mortar.

The surface tension of the cellulose ether is greater than the surface tension of the rubber powder. More cellulose ether is enrich at the mortar interface.It will be advantageous to form a hydrogen bond between the matrix and the cellulose ether.

In the wet mortar, the water in the mortar evaporates and the cellulose ether concentrates on the surface. A film is formed on the surface of the mortar within 5 minutes, which reduces the subsequent evaporation rate.

As more and more water migrates from the thicker portion of the mortar to the thinner portion of the mortar layer.The film opening portion of the initial stage is partially dissolve. And the migration of water results in more cellulose ether, which is concentrate on the surface of the mortar.Therefore, the formation of cellulose ether on the surface of the mortar has a great influence on the performance of the mortar.

1) The form film is too thin and will dissolve twice. Unable to limit water evaporation and reduce strength.

2) The form film is too thick, and the concentration of the cellulose ether in the mortar tissue liquid is high and the viscosity is large.

When the tile passes, it is not easy to break the film on the surface. From this, it is understood that the film form ability of the cellulose ether greatly affects the opening time.

The type of cellulose ether (HPMC, HEMC, MC, etc.) and the degree of etherification (degree of substitution) directly affect the film form ability of the cellulose ether. And the hardness and toughness of the film.

3 the impact on the pull strength

(1)

Cellulose ether imparts various beneficial properties to the above mortar. It also delays the hydration kinetics of the cement.This delay is primarily due to the adsorption of cellulose ether molecules on various mineral phases in hydrated cement systems.

However, it is generally believed that the cellulose ether molecules are mainly adsorbed on hydrated products such as C-S-H and calcium hydroxide. It is rarely adsorbe on the original mineral phase of the clinker.

In addition, the cellulose ether reduces ions (Ca2, SO42-, …) due to an increase in the viscosity of the pore solution. The activity in the well solution further delays the hydration process.

(2)

Viscosity is another important parameter indicative of the chemical nature of cellulose ethers. As mention above, viscosity primarily affects water retention capacity. It also has a major impact on the processability of the new mortar.

However, experimental studies have found that the viscosity of cellulose ether has little effect on the hydration kinetics of cement. Molecular weight has little effect on hydration.

The biggest difference between the different molecular weights is only 10 minutes. Therefore, molecular weight is not a key parameter for controlling cement hydration.

(3)

L. Schmitz, C-J. Hackers, tensor translation “cellulose ether in the application of cement-based dry mortar products” clearly pointed out.The delay of cellulose ether depends on its chemical structure. The trend summarized is MHEC. The higher the degree of methylation, the smaller the delay of the cellulose ether.

Furthermore, hydrophilic substitutions (eg, substitutions of HEC) are more inhibitory than hydrophobic substitutions (eg, substitutions of MH, MHEC, MHPC).The delay effect of cellulose ethers is primarily affect by two parameters of the type and amount of substituents.

(4)

Our system experiments have also found that the amount of substituents plays an important role in the mechanical strength of the tile adhesive. We evaluate the performance of HPMC with different degrees of substitution in tile adhesives.

The effects of different etherification conditions on cellulose ether and the effects of different groups on the mechanical properties of tile adhesives were test.

(5)

In the test we considered HPMC, which is a complex ether. Therefore, put these two numbers together. For HPMC, you need a certain level of supply.

In order to ensure its water solubility and light transmittance, we know that the content of the substituent also determines the gel temperature of HPMC.

It is also the environment that determines HPMC. The HPMC content of this general application is also in scope. We study how to combine methoxy and hydroxypropoxy groups in this range to get the best results.

Within a certain range, the methoxy group content increases, which leads to a downward trend in tensile strength. When the hydroxypropoxy group content is increase, the tensile strength tends to increase. For open hours, there are similar effects.

(6)

Cellulose ethers, especially modified HPMC. It is an essential additive in many dry mixing applications. The most important property of cellulose ethers is their water retention in mineral building materials.

If cellulose ether is add, the thin layer of fresh mortar will dry quickly. This prevents the cement from hydrating in the normal way.As a result, the mortar cannot be harden, and good adhesion to the base layer cannot be obtain.

There are many factors that affect the water retention of cellulose ethers. For example, the amount and viscosity and its inherent composition: the degree of substitution has a greater impact on the final properties of the mortar.For a long time, we have always believed that the viscosity of cellulose ether has a great influence on the setting time of cement-based materials.

(7)

Recent studies have found that viscosity changes have little effect on cement setting time. In contrast, the type and combination of substituents are the most important factors affecting the function of cellulose ethers.

When we look forward to high performance tile adhesive products, we must consider not only the rheological properties of cellulose ethers.In order to make the mortar easier to handle, it is also necessary to consider a cellulose ether product having an appropriate degree of substitution. Its mechanical contribution.