Hydroxypropyl methylcellulose (HPMC) is made by special etherification of highly pure cotton cellulose under alkaline conditions. In recent years, HPMC, as a functional admixture, mainly plays a role in water retention and thickening in the construction industry and is widely used in tile adhesives. Tile adhesive is a new modern decoration material used for pasting decorative materials such as ceramic tiles, surface tiles, and floor tiles. It has the advantages of high adhesion, good flexibility, and so on. Tile adhesive is made up of cement, sand, calcium formate, and additives in a particular proportion. Tile adhesive contains a variety of additives. Generally, cellulose ethers that provide water retention and thickening effects are added to tile adhesives. The most used are HPMC and HEMC. In this article, I will take you through 7 things you need to know before buying HPMC, the most basic additive in tile adhesive.
1.1 According to the application field, HPMC is divided into construction-grade HPMC, daily chemical-grade HPMC, food-grade HPMC, and pharmaceutical-grade HPMC. The tile adhesive uses HPMC and belongs to the building material grade.
1.2 According to viscosity, viscosity is an essential indicator of HPMC. HPMC increases the viscosity of tile adhesive from the viscosity of HPMC solution. The viscosity of HPMC generally refers to a particular concentration (2%) of HPMC solution, at a specified temperature (20°C) and shear rate (or rotation rate, such as 20rpm), the viscosity value measured with a specified measuring instrument. Viscosity is an important parameter to evaluate the performance of HPMC. The higher the viscosity of the HPMC solution, the better the viscosity of the tile adhesive and the better the adhesion to the substrate. The stronger the anti-sagging and anti-dispersion ability, but if its viscosity is too strong, it will affect the fluidity and operability of the tile adhesive.
1.3 According to different viscosity, HPMC can be divided into three grades: low, medium, and high viscosity:
It should be noted that the results measured by different viscometers are quite different. Therefore, when testing samples, you must use a viscometer of the same brand and model as the supplier; otherwise, the measured viscosity is meaningless.
1.4 According to HPMC solubility in water, HPMC can be divided into delayed dissolution type HPMC, namely surface treatment type HPMC, and non-delay dissolution type HPMC, namely non-surface treatment type HPMC. In the construction industry, HPMC is often put into neutral water, and the HPMC product is dissolved separately to determine whether the HPMC has undergone surface treatment. After being placed in neutral water alone, the product that quickly clumps and does not disperse is a product without surface treatment; after being placed independently in neutral water, the product can disperse without clumping surface-treated.
Non-surface treatment HPMC:
Surface treatment HPMC:
For home decoration, we generally use ceramic tiles for unique places such as balcony walls ( wall tile adhesive ), bathrooms (shower wall adhesive), kitchens, stairs, etc., which look very beautiful and have the effect of waterproofing. Especially kitchens and bathrooms are usually prone to mold and bacteria, so it is recommended to use HPMC with high viscosity and water resistance. High-viscosity and waterproof HPMC will make the sealant and tile adhesive have good sealing properties, prevent various problems caused by moisture, extend the life of decoration, and reduce post-maintenance.
When designing outdoor spaces, such as swimming pools, outdoor balconies, etc., exterior tile adhesives, expecially pool tile adhesive, need to have water resistance, heat resistance, cold resistance, and abrasion resistance. Because outdoor spaces are generally exposed to long-term exposure to the sun, rain, pool water, and mud, strong adhesives must be used to solve these problems. Therefore, it is necessary to choose high-viscosity HPMC to make the ceramic tile adhesive meet these needs.
What is HPMC made from? Cellulose ether was first reported in 1905, made by Suida reacting alkali-swollen cellulose with dimethyl sulfate, but the cellulose ether could not be separated at that time. In 1912, a patent for the preparation of cellulose ethers appeared for the first time. In 1927, HPMC was successfully synthesized and separated. In 1938, the American DOW Chemical Company realized the industrial production of MC. Large-scale industrial production of HPMC was carried out in the United States in 1948, and the production process reached maturity in 1960~1970.
The production process of HPMC can be divided into two categories: gas-phase method and liquid-phase method.
Developed countries such as Europe, America, and Japan are more adopting the gas-phase process. Wood pulp is used as raw material (cotton pulp is used when producing high-viscosity products), alkalization and etherification are carried out in the same reaction equipment, the primary reaction is a horizontal reactor, and there is a central horizontal stirring shaft and a side-rotating flying knife specially designed to produce cellulose ether, which can obtain an excellent mixing effect. The reaction process adopts advanced automatic control means, which can accurately control the temperature and pressure. After the reaction is completed, the excess methyl chloride and the by-produced dimethyl ether enter the recovery system in gaseous form and are recycled and reused separately. The refining and purification treatment is carried out in a continuous rotary filter press. The crushing is carried out in a high-efficiency finished product crusher while drying to remove excess water. Auxiliary processes such as mixing and packaging are also completed under the automatic control system.
The gas-phase process has the following advantages
However, this process also has the following disadvantages:
At present, the production of HPMC from Chinese manufacturers is mainly based on the liquid-phase process. Generally, refined cotton is used as the raw material, and the combined pulverizer is used to pulverize, or the refined cotton is directly alkalized, and the etherification uses a binary mixed organic solvent. The reaction is carried out in a vertical reactor. The finished product is processed in batches, and the granulation is carried out at elevatemperaturesture (some manufacturers do not carry out granulation, and drying and crushing are carried out in conventional ways. Most special treatments are only to delay the hydration time (fast dissolution) of the product without anti-mildew, and compounding treatments and the packaging is manual.
The liquid-phase process has the following advantages:
However, this process also has the following disadvantages:
MIKEM has introduced an internationally leading flexible production line of large-scale HPMC reaction and purification equipment in its cooperative factory in China and imported equipment imported from Germany. The reactor is a 25m2 horizontal equipment. The alkalization and etherification reactions are carried out in the same equipment, and the DCS central control system is adopted. Through digestion and absorption of advanced international technology, the current HPMC product models and specifications are complete, and the production capacity has also been greatly improved. The distributed control system (DCS) is used to realize automatic control. Materials including liquid and solid materials can be accurately metered and added by the DCS system. The temperature and pressure control in the reaction process also all realize DCS automatic control and remote monitoring. The feasibility, reliability, stability, and safety of product production have been significantly improved than traditional production methods. It not only saves manpower, reduces labor intensity but also improves the on-site operating environment.
According to the survey, the price of HPMC for ceramic tile adhesive produced by Chinese manufacturers generally fluctuates around USD3000, and that in European and American countries typically exceeds USD4500.
The price of HPMC has a lot to do with its viscosity. From the current point of view, the viscosity is divided into two extremes: high viscosity, that is, the viscosity is above 20,000, and the extra-low viscosity, that is, the viscosity is below 100, and the price is relatively high. The price of medium viscosity is lower. The higher the purity, the higher the price. The price of 98%-99% high purity products is higher, and the price of products with purity below 96% is slightly lower. In general, the price difference of HPMC is closely related to the quality of the product. The price of high-quality products is correspondingly higher, while the price of low-end products is relatively lower.
The price changes are also closely related to the price changes of raw materials on the market. In early 2021, the increase in crude oil prices led to a collective price increase in the chemical industry. The price of HPMC’s raw materials has also been affected. In terms of refined cotton, international cotton prices have gradually increased. In the short term, cotton prices are expected to rise further, but they do not have the conditions for a substantial increase. The weather conditions in the later period need to be closely monitored. On the other hand, the prices of the produced reaction media ethanol, isopropanol, toluene, and propylene oxide have also increased relatively, leading to continued increases in the price of HPMC in the first quarter of 2021.
Price changes are inseparable from market demand. In 2020, due to the epidemic raging worldwide, many factories shut down, resulting in a decline in global demand, while production capacity is relatively stable, and there is an oversupplied market, so HPMC prices will also drop. At the beginning of 2021, due to the reduction of annual production capacity during the epidemic, when the epidemic was brought under control and demand resumed, HPMC prices rose again.
Price changes are affected by force majeure. Due to the global spread of the epidemic in 2020, factories all over the world have been closed collectively. Although the epidemic in some countries has been brought under control by mid-2020, the decline in global productivity has not yet fully recovered. In addition, in early 2021, affected by the polar cold current, parts of southern Texas in the United States began to experience extreme weather such as snowfall, icing, and freezing rain, resulting in road icing and road closures. There are many petroleum and chemical facilities both inside and outside the state. The power outage has “paralyzed” the production of many oil refineries and chemical plants in the state. The recovery of production capacity was once again interrupted, and the market appeared in short supply, which caused the price of HPMC to rise sharply again.
MIKEM is a professional manufacturer of cellulose ethers. We have established solid cooperative relations with many cellulose ether manufacturers and established our production base in China.
With China’s abundant and cheap raw material supply, our cellulose ether production capacity can reach 40,000 tons per year. Therefore, we have significant advantages in cost control and collection.
Although MIKEM’s cellulose ether MelaColl production base is located in China, the production process of Melacoll cellulose products is controlled by American ISO quality standards and technology to ensure the best quality and sustainability. Each product undergoes quality inspection before being delivered to the customer. We provide customers with high-performance, reliable quality products. Therefore, we also have a significant advantage in product quality.
6.1 Different production processes
The raw materials produced by HPMC can be refined cotton or wood pulp, which is part of the methyl group and part of the polyhydroxy propyl ether of cellulose. The cellulose is alkalized and then etherified with propylene oxide and methyl chloride—reaction system.
The production of HEMC is slightly different from HPMC. After cellulose is alkalized, it is made by replacing propylene oxide with ethylene oxide and substituting the hydroxyl group on the glucose ring group.
6.2 Different physical and chemical properties
The methoxy group on the HPMC methyl chloride replaces the hydroxyl group on the glucose ring group. The hydroxypropyl group replaces the hydroxyl group, and chain polymerization occurs. HPMC has thermal gel properties, and its solution has no ionic charge, does not interact with metal salts or ionic compounds, has strong mold resistance, and has good dispersion, emulsification, thickening, adhesion, water retention, and glue retention properties.
Compared with HPMC, the chemical structure of HEMC has more hydrophilic groups, so it is more stable at high temperatures and has good thermal stability. Compared with the common HPMC cellulose ether, it has a relatively high gel temperature, which is more advantageous in high-temperature use environments. Like HPMC, HEMC also has good mildew resistance, dispersion, emulsification, thickening, bonding, water, and glue retention properties. The specific indicators of the product, such as appearance, fineness, loss on drying, sulfate ash, solution PH value, and light transmittance, viscosity, etc. are related to the product model and function, and the level of different manufacturers is different, so we will not discuss it here.
6.3 Different cellulose ether group content
Under normal circumstances, the methoxy content of HPMC is 16%~30%, and the hydroxypropyl content can be 4%~32%; The methoxy content of HEMC is 22%~30%, and the hydroxy ethoxy content is 2%~14%.
How to identify and calculate the content of different groups:
Due to the different substituents of HPMC and HEMC, the cellulose ether sample can be heated and reacted in a closed reactor. Under the catalysis of adipic acid, the substituted alkoxy group is quantitatively cracked by hydroiodic acid to generate the corresponding iodoalkane. The reaction product is extracted with o-xylene, and the extract is injected into a gas chromatograph to separate the components. Through the separation time, hydroxypropyl and hydroxy ethoxy can be identified. Use the standard internal method to quantify and calculate the content of the component to be tested in the sample. It is not difficult to find that the separation time of the hydroxy ethoxy group is between the methoxy group and hydroxypropyl group, and the group type can be judged by comparing the separation time of the standard solution. The group type is judged by the peak time, and the peak-to-peak area calculates the group content.
6.4 Different gelation temperature
Gel temperature is an essential indicator of cellulose ether. The cellulose ether aqueous solution has thermal gel properties. As the temperature rises, the viscosity continues to decrease. When the temperature of the solution reaches a certain value, the cellulose ether solution is no longer uniform and transparent but forms a white gum and finally loses viscosity. Gel temperature test method: Prepare a cellulose ether sample with a concentration of 0.2% cellulose ether solution, and slowly heat it in a water bath until the solution appears white turbid or even white gel and completely loses viscosity. Currently, the temperature of the solution is the fiber Gel temperature of plain ether. The overall gel temperature of HEMC is slightly higher than that of HPMC. Generally, the gel temperature of HPMC is 60℃~75℃, and that of HEMC is 75℃~90℃.
The ratio of methoxy and hydroxypropyl content of HPMC negatively affects the water solubility, water retention capacity, surface activity, and gel temperature of the product. Generally, HPMC with high methoxy content and low hydroxypropyl content has good water solubility and surface activity, but low gel temperature; Appropriately increasing the hydroxypropyl content and reducing the methoxy content can increase the gel temperature, but if the hydroxypropyl content is too high, it will lower the gel temperature and deteriorate the water solubility and surface activity. The MIKEM experiment results show that when the methoxy content is 27-35, the all-around performance of HPMC reaches a relatively balanced state. Specifically, different ranges of HPMC can be selected according to different needs.
6.5 Different applications in tile adhesive
HPMC and HEMC can be used as a dispersant, water-retaining agent, thickener, and binder in tile adhesives and have water-retaining properties.
The gel temperature of cellulose ether determines its thermal stability in the application. The gel temperature of HPMC is usually between 60°C and 75°C, depending on the model, group content, and different production processes of other manufacturers. Due to the characteristics of the HEMC group, it has a higher gel temperature, usually above 80°C, so its stability under high-temperature conditions is better than that of HPMC. In practical applications, in a very hot construction environment, the water retention of HEMC with the same viscosity and content in tile adhesive has a more significant advantage than HPMC. Especially in tropical areas such as Southeast Asia, Africa, and South America, sometimes the construction is performed at high temperatures. HPMC with too low gel temperature will lose the original thickening and water retention properties of HPMC at high temperatures, which will affect the construction.
Since HEMC has more hydrophilic groups in its structure, it has better hydrophilicity. The water retention rate of HEMC in mortar is slightly higher than that of HPMC for products of the same viscosity at the exact dosage. In addition, the anti-sagging ability of HEMC is relatively better.
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