1 the introduction
Cellulose ether MHEC in the construction building materials industry has an extremely wide range of uses, a large amount, can be used as a retarder, water retention agent, thickener and adhesive. Cellulose ether MHEC plays an important role in ordinary dry mixed mortar, external wall insulation mortar, self-leveling mortar, ceramic tile binder, high-performance building putty, anti-crack internal and external wall putty, waterproof dry mixed mortar, plaster plaster, caulking agent and other materials. Cellulose ether MHEC has an important effect on the water retention, water demand, adhesion, retardation and construction of mortar system.
There are many different types and specifications of Cellulose ether MHEC, Cellulose ether commonly used in the field of building materials including HEC, MHEC, CMC, PAC, MHPC and so on, according to their respective role characteristics applied in different mortar systems. Some people have studied the influence of different kinds and different dosage of Cellulose ether MHEC on cement mortar system. In this paper, how to choose different varieties and specifications of Cellulose ether MHEC in different mortar products is discussed.
2 Cellulose ether MHEC in cement mortar function characteristics
As an important admixture in dry mortar, Cellulose ether MHEC has many functions in mortar. Cellulose ether MHEC in cement mortar is the most important role of water retention and thickening, in addition, because of its interaction with the cement system, will also play an auxiliary role of air induction, delay, improve tensile bonding strength.
The most important property of Cellulose ether MHEC in mortar is water retention. Cellulose ether MHEC as an important admixture in almost all mortar products, the main use of its water retention. Generally speaking, the water retention of Cellulose ether MHEC is related to its viscosity, dosage and particle size.
Cellulose ether MHEC as a thickener, its thickening effect is related to the degree of etherification of Cellulose ether MHEC, particle size, viscosity and degree of modification. In general, the higher the degree of etherification and viscosity of Cellulose ether MHEC, the smaller the particles, the more obvious the thickening effect. By adjusting the above characteristics of MHEC, mortar can achieve the appropriate anti-vertical flow performance and the best viscosity.
In Cellulose ether MHEC, the introduction of alkyl group reduces the surface energy of aqueous solution containing Cellulose ether MHEC, so that Cellulose ether MHEC has the effect of engassing cement mortar. Due to the ball effect of bubbles, the construction performance of mortar is improved, and the output rate of mortar is increased by the introduction of bubbles. Of course, the air intake needs to be controlled. Excessive air intake will have a negative impact on the strength of mortar, because harmful bubbles may be introduced.
2.1 Cellulose ether MHEC will delay the hydration process of cement, thus slowing down the setting and hardening process of cement, and correspondingly prolonging the opening time of mortar, but this effect is adverse to mortar in relatively cold areas. In the selection of Cellulose ether MHEC, should be based on the specific situation of the choice of appropriate products. The retarding effect of Cellulose ether MHEC is mainly prolonged with the improvement of its etherification degree, modification degree and viscosity.
In addition, Cellulose ether MHEC as a polymer long chain substance, after joining the cement system, under the premise of fully maintaining the slurry moisture, can improve the bond performance with the substrate.
2.2 The properties of Cellulose ether MHEC in mortar mainly include: water retention, thickening, prolonging setting time, gas permeability and improving tensile bonding strength, etc. The properties mentioned above are reflected in the characteristics of MHEC itself, namely, viscosity, stability, active component content (amount added), etherification substitution degree and its uniformity, modification degree and harmful substance content, etc. Therefore, in the selection of MHEC, Cellulose ether MHEC with its own characteristics can provide appropriate performance should be selected according to the specific requirements of specific mortar products for certain performance.
3. The characteristics of Cellulose ether MHEC
Generally speaking, the product instructions provided by Cellulose ether MHEC manufacturers will contain the following indicators: appearance, viscosity, group substitution degree, fineness, effective substance content (purity), moisture content, recommended field and dosage. These performance indicators can reflect part of the role of Cellulose ether MHEC, but in the comparison and selection of Cellulose ether MHEC, should also examine its chemical composition, degree of modification, degree of etherification, NaCl content, DS value and other aspects.
Take Kimacell MHEC‘s MH60M product specification for example. First,MH indicates that the composition is methyl hydroxyethyl Cellulose ether MHEC, the viscosity (Hoppler method determination) is 60000 Mpa. s, . In addition, in addition to the description of product appearance, viscosity, particle size, there are the following indicators: chemical composition for methyl hydroxyethyl Cellulose ether MHEC, after low degree modification; Moderate degree of etherification; The moisture content of 6% or less; NaCl content of 1.5% or less; Effective substance content >92.5%, loose density 300 g/L and so on.
3.1 Cellulose ether MHEC viscosity
The viscosity of Cellulose ether MHEC affects its water retention, thickening, retarding and other aspects, therefore, it is an important indicator of the examination and selection of Cellulose ether MHEC.
Before discussing the viscosity of Cellulose ether MHEC, it should be noted that there are four commonly used viscosity testing methods of Cellulose ether MHEC: Brookfield, Hakke, Hoppler and rotary viscometer method. The instruments, concentration of solution and testing environment used by the four methods are different, so the results of the same MHEC solution tested by the four methods are also varied. Even for the same solution, using the same method, under different environmental conditions, viscosity
The results also varied. Therefore, when explaining the viscosity of a Cellulose ether MHEC, it is necessary to indicate what kind of method to test, solution concentration, rotor, speed, temperature and humidity test and other environmental conditions at the same time, the viscosity value is valuable. Just say, “What’s the viscosity of a certain MHEC?”
It doesn’t make sense.
Take Kimacell MHEC product MH100M as an example. It is pointed out in the product manual that “the viscosity value determined by Hoppler method is 100000 Mpa.s”. As a corresponding, the specification also provides that “Brookfield RV, 20 RPM, 1.0 %,20℃,20°GH, the tested viscosity value is 4100~5500 Mpa. s”.
3.2 Product stability of Cellulose ether MHEC
Cellulose ether MHEC is known to be susceptible to erosion by cellulose mildew. Mold in the erosion of Cellulose ether MHEC, the first attack is not etherized Cellulose ether MHEC glucose unit, as a straight chain compound, once the glucose unit is destroyed, the whole molecular chain is disconnected, the viscosity of the product will drop sharply. After the glucose unit is etherified, the mold is not easy to erode the molecular chain, therefore, the higher the etherification substitution degree (DS value) of Cellulose ether MHEC, the higher its stability will be.
Taking Kimacell MHEC product MH100M as an example, the product specification clearly indicates that the DS value is 1.70(for water-soluble MHEC, the DS value is less than 2), which indicates that the product has high product stability.
3.3 Active component content of Cellulose ether MHEC
The higher the content of active components in Cellulose ether MHEC, the higher the cost performance of the product, so as to achieve better results under the same dosage. The effective component of Cellulose ether MHEC is Cellulose ether MHEC molecule, which is an organic substance, so when examining the effective substance content of Cellulose ether MHEC, it can be indirectly reflected by the ash value after calcination. In general, a higher ash value is associated with a lower effective substance. In the product description of Kimacell MHEC, the active ingredient of general products is above 92%.
3.4 content of NaCl in Cellulose ether MHEC
NaCl is an inevitable by-product in the production of Cellulose ether MHEC, which generally needs to be removed through multiple washing. The more washing times, the less NaCl residue. NaCl is known to be harmful to the corrosion of steel bars and wire mesh, etc. Therefore, although repeated washing of NaCl may increase the cost of sewage treatment, MHEC products with low NaCl content should be selected as far as possible. The NaCl content of Kimacell MHEC products is generally controlled below 1.5%, which is a product with low NaCl content.
4. The principle of selecting Cellulose ether MHEC for different mortar products
At the time of mortar products use Cellulose ether MHEC, first should be based on the description of the product manual, choose their own performance indicators, such as viscosity, etherification substitution degree, effective substance content, NaCl content etc) to compare optimal Cellulose ether MHEC according to concrete mortar products and performance requirements, integrated application of selected performance meets the requirements of high quality varieties of MHEC.
According to the corresponding requirements of different mortar products, the following introduces the corresponding principles of choosing suitable MHEC.
4.1 Thin plastering system
Take the thin plastering system of plastering mortar as an example, because the plastering mortar directly contact with the external environment, the surface water loss is faster, so it requires a high water retention rate. Especially in summer construction, mortar is required to be able to keep moisture at high temperature. MHEC with high water retention rate is required to be selected, which can be considered comprehensively from three aspects: viscosity, particle size and addition amount. Generally speaking, MHEC with high viscosity should be selected under the same conditions, and the viscosity should not be too high considering the requirements of construction. Therefore, the MHEC should be chosen with high water retention rate and low viscosity. Kimacell MHEC products,MH60M and others can be recommended for thin plaster bonding systems.
4.2 Cement based plastering mortar
Plastering mortar requires good uniformity of mortar, plastering is easier to evenly coated, and requires good vertical flow resistance, pumping capacity and fluidity and workability are relatively high. Therefore, MHEC with low viscosity and rapid dispersion and consistency development (smaller particles) in cement mortar is selected, such as Kimacell‘s MH60M and MH100M are recommended.
4.3 Tile adhesive
In the construction of ceramic tile adhesive, in order to ensure safety and efficiency, it is particularly required that the opening time of mortar is longer, the anti-slide performance is better, and there is a good bond between the base material and ceramic tile. Accordingly, ceramic tile glue is higher to MHEC requirement. And MHEC in ceramic tile glue generally have relatively high dosage. In the selection of MHEC, to meet the requirements of a long opening time, MHEC itself should have a high water retention rate, which requires appropriate viscosity, addition amount and particle size. In order to meet the good anti-sliding performance, MHEC‘s good thickening effect is required to make mortar’s vertical flow resistance strong. The thickening has certain requirements on viscosity, etherification degree and particle size. Therefore, MHEC that needs to be considered should meet the requirements of viscosity, etherification degree and particle size at the same time. It is recommended to use Kimacell MHEC‘s MH100M, MH60M and MH100MS, etc. (The water retention rate of vacuum extraction and filtration method has been measured to be above 95%).
To resist sliding tile glue, it requires MHEC with especially excellent anti-vertical flow performance to be thickened, so that highly modified MHEC can be selected. For example, MHEC MH100M of Kimacell can be recommended (this product is highly modified).
4.4 Self-leveling ground mortar
Self-leveling mortar has higher requirements on leveling performance, so it is suitable to choose Cellulose ether MHEC products with low viscosity. Because self-leveling requires evenly mixed mortar to be able to automatically level on the ground, it requires fluidity and pumping, so the water-material ratio is large. In order to prevent bleeding, MHEC is required to control the water retention of the surface and provide viscosity to prevent precipitation. H300P2 and H20P2 of Kimacell are recommended.
4.5 Laying mortar
Due to direct contact with masonry surface, masonry mortar is generally thick layer construction, requiring mortar to have high workability and water retention, but also to ensure the binding force with masonry, improve construction, improve efficiency. Therefore, the selection of MHEC should be able to help mortar improve the performance of the above, Cellulose ether MHEC viscosity is not too high, there is a certain amount of water retention, recommended to use MHEC MH100M, MH60M, MH6M, etc..
4.6 Thermal insulation slurry
Thermal insulation slurry is mainly applied by hand. Therefore, the MHEC selected is required to give the mortar good construction, good workability and excellent water retention, and the MHEC should have the characteristics of high viscosity and high air entraining. In view of the above characteristics, it is recommended to use Kimacell‘s MH100M, MH60M and other products with high water retention rate, high viscosity and good air entraining performance.
5 conclusion
Cellulose ether MHEC in cement mortar is the role of water retention, thickening, air induction, delay and improve the tensile bond strength.