HPMC in Tile Adhesives

Tile adhesives a lot of people also known as ceramic tile adhesives, those who have contacted the use of ceramic tile adhesives to its anti-empty drum, sticky, construction, aging resistance and other advantages are absolutely recognized.

Cellulose ether HPMC as the most important additive in tile adhesives, tile adhesives pull strength and opening time have a strong impact, and these two items are also important indicators of high performance tile adhesives, through the experiment of cellulose ether effect on tile adhesives properties were summarized and reviewed.

1, the preface

Cement-based ceramic tile adhesives is currently the largest application of special dry mixing mortar, which is a kind of cement as the main cementing material and supplemented by gradation of aggregate, water retention agent, early strength agent, latex powder and other organic or inorganic admixtures. Usually used only with water mixing, compared with ordinary cement mortar, can greatly improve the bonding strength between the finishing material and the base material, has good anti-slip and has excellent water resistance, heat resistance and freezing-thawing cycle advantages, mainly used for pasting building interior and exterior wall tiles, floor tiles and other decorative materials, It is widely used in the decoration of walls, floors, bathrooms, kitchens and other buildings. It is the most widely used ceramic tile bonding material.

Usually when we judge the performance of a ceramic tile adhesives, in addition to paying attention to its operating performance, anti-sliding ability, but also pay attention to its mechanical strength and opening time. Cellulose ether in ceramic tile adhesives in addition to affect the rheological properties of porcelain glue, such as smooth operation performance, stick knife situation, but also on the mechanical properties of ceramic tile adhesives has a strong influence.

2, the influence of the opening time of ceramic tile adhesives

When rubber powder and cellulose ether co-exist in wet mortar, some data models show that rubber powder has stronger kinetic energy to adhere to cement hydration products, and cellulose ether exists more in the gap fluid, which affects the viscosity and setting time of mortar more. The surface tension of cellulose ether is larger than that of rubber powder, and the enrichment of more cellulose ether at mortar interface is beneficial to the formation of hydrogen bonds between the base plane and cellulose ether.

Moisture evaporation from in the wet mortar, mortar, cellulose ether in the surface enrichment, 5 minutes can form a membrane on the surface of the mortar, will reduce the evaporation rate of follow-up, with more water from the slurry thick part of the move to the mortar layer is thinner, open points partly dissolved when the initial formation of the membrane, the migration of water can bring more enrichment of cellulose ether in the mortar on the surface.

Thus, cellulose ether film formation on the surface of mortar has a great impact on the performance of mortar, 1) the film formed is too thin, will be dissolved twice, unable to limit the evaporation of water, reduce the strength. 2) the film formed is too thick, the concentration of cellulose ether in the slurry clearance liquid is high, and the viscosity is large. When the ceramic tile is pasted, it is not easy to break the film on the surface. It can be seen that the film forming performance of cellulose ether has a great influence on the opening time. The type of cellulose ether (HPMC, HEMC, MC, etc.) and degree of etherification (degree of substitution) directly affect the film forming performance of cellulose ether, to the hardness and toughness of the film.

3, the influence of drawing strength

Cellulose ether not only endows mortar with all the above beneficial properties, but also delays the hydration kinetics of cement. This retarded effect is mainly due to the adsorption of cellulose ether molecules on various mineral phases in the cement system being hydrated, but it is generally agreed that cellulose ether molecules are mainly adsorbed on hydration products such as C-S-H and calcium hydroxide, and rarely adsorbed on the original mineral phase of clinker. In addition, cellulose ether reduces ions (Ca2+, SO42-,…) due to increased viscosity of pore solution. Activity in pore solution, which further retards the hydration process.

Viscosity is another important parameter, which represents the chemical properties of cellulose ether. As mentioned above, viscosity mainly affects water retention capacity, and also has a significant impact on the workability of fresh mortar. However, the experimental study found that the viscosity of cellulose ether had almost no effect on the hydration kinetics of cement. Molecular weight has little influence on hydration, and the largest difference between different molecular weights is only 10min. Therefore, molecular weight is not the key parameter to control cement hydration.

The retardation of cellulose ether depends on its chemical structure. The general trend is that for MHEC, the higher the degree of methylation, the smaller the retarding effect of cellulose ether. In addition, hydrophilic substitution (such as substitution of HEC) has a stronger retarding effect than hydrophobic substitution (such as substitution of MH, MHEC and MHPC). The retarding effect of cellulose ether is mainly affected by the two parameters of the type and number of substituted groups.

Our systematic experiment also found that the content of substituents plays an important role in the mechanical strength of ceramic tile adhesive. We evaluated the performance of HPMC with different degrees of substitution in ceramic tile adhesive, and tested the influence of cellulose ether containing different groups under different curing conditions on the mechanical properties of ceramic tile adhesive.

The change trend of mechanical strength under the condition of opening time is consistent with the normal temperature condition, which is also consistent with the toughness of cellulose ether film we talked about in section 2. HPMC with high methoxy (DS) content and low hydroxypropoxy (MS) content has good toughness, but will affect the wettability of wet mortar for surface material.

4, summary

Cellulose ether, especially methyl cellulose ether such as HEMC and HPMC, is an essential additive in the application of many dry mortar products. The most important property of cellulose ether is its water retention in mineral building materials. If cellulose ether is not added, the thin layer of fresh mortar will dry out quickly, so that the cement cannot be hydrated in the normal way, resulting in the mortar cannot harden and cannot obtain good adhesion to the base. There are many factors affecting the water retention of cellulose ether, such as dosage and viscosity, and its inherent composition: Substitution degree for the ultimate performance of mortar has a greater impact, for a long time we have argued that the viscosity of cellulose ether for cement base material has a great impact on the coagulation time and so on, a recent study found that the change of viscosity of cement setting time effect is very small, but is instead of the kinds of group and cooperate with is the most important factor to affect the function of cellulose ether.

Now respectively to see the performance and role of tile adhesives main raw materials:

1, cement

We all know that cement is certainly non-toxic environmental protection, and has a strong aging resistance.

2, grading sand

Grading sand is actually river sand after washing after drying, and then sieving a certain size of grain size of sand, which is also non-toxic and environmental protection, its main role is to fill, in order to reduce the shrinkage of tile adhesives solidification.

Above is two kinds of everybody familiar with material, the polymer additive that the public is not familiar with in detail below, what thing in the end is?

3, HPMC (hydroxypropyl methyl cellulose ether)

HPMC added to the ceramic tile adhesives inside the main role is to keep water, thickening, the purpose is to improve the ceramic tile adhesives final solidification strength, prolong the opening time and improve the construction, its source is cotton after modification, that is to say, it comes from nature, is no harm to the human body, absolute environmental protection products;

4, Redispersible polymer powder RDP

Its main role in ceramic tile adhesives is to improve the bonding strength, it will not have any impact on the construction, that is to say, different brands of ceramic tile adhesives inside the addition of Redispersible polymer powder RDP we can not judge when the application, the only thing can reflect is the bonding strength of ceramic tile adhesives after the brick solidification, This performance is generally through the ceramic tile drawing instrument to check whether can meet the national standards, to Redispersible polymer powder RDP is not glue no glue ingredients, it is the emulsion at the edge of the drying tower by means of spray drying after the completion of the powder, can also describe it as emulsion powder, recover when it encounters water will dissolve again into the emulsion, That is to say, the adhesive of our ceramic tile adhesives is derived from emulsion rather than glue, and then Redispersible polymer powder RDP also belongs to environmental protection products, so there is no need to worry about ceramic tile adhesives containing glue such harmful substances;

5, wood fiber

The main function of ceramic tile adhesives is to resist cracking and reduce the cement skin of ceramic tile. It also comes from nature. It is broken to flocc by mechanical action of wood, and its essence is wood, so it is environmentally friendly.

6, starch ether

Its main role in ceramic tile adhesives is anti-flow, anti-slip and synergistic HPMC to improve construction, it is the product of natural plant starch modified by etherification, but also from the nature of environmental protection products.

Can see above 6 kinds of raw materials all are harmless, environmental protection material, so ceramic tile adhesives is not glue. And the component that comes from product, must use thin stick method, save time to save space already so. After the scientific research of experts, as well as the proof of time, it is worth to be promoted.