Viscosity Characteristics Of HPMC Aqueous Solution

The viscosity of aqueous solution of hydroxypropyl methyl cellulose is mainly affected by the degree of product polymerization, concentration of product in aqueous solution, shear rate and solution temperature. The viscosity of aqueous solution increases with the increase of product polymerization degree and concentration, and decreases with the increase of shear rate and solution temperature.Salt and safe insecticides can also be added to obtain better viscosity characteristics and application performance. Users should consider the actual situation and economy to choose hydroxypropyl methyl cellulose viscosity specifications and addition.

This product is industrial grade HPMC, mainly used as dispersant in polyvinyl chloride production, is the main auxiliary agent of PVC preparation by suspension polymerization. In addition in other petrochemical, building materials, paint remover, agricultural chemicals, printing ink, textile printing and dyeing, ceramics, paper, cosmetics and other products in the production of thickening agent, stabilizer, emulsifier, exciphers, water retention agent, film-forming agent.

Hydroxypropyl methyl cellulose HPMC in the application of synthetic resin, can make the product with particle neat, loose, appropriate specific gravity, good processing performance and other characteristics, which basically replaced gelatin and polyvinyl alcohol as dispersant.In addition, in the construction process of building industry, it is mainly used in the mechanized construction of wall, stucco and caulking. Special child decorates in construction, use as pasting ceramic tile, marble, plastic adornment, stickup intensity is high, still can reduce cement dosage.

Hydroxypropyl methyl cellulose HPMC in the coating industry for thickening agent, can make the coating bright and delicate, do not deduster, improve leveling performance. It can be used to paint gypsum, paste gypsum, caulking gypsum, water - resistant putty to improve its water retention and paste strength. Also can be used in functional ceramics, metallurgy, seed coating agent, water-based ink, cosmetics, electronics, printing and dyeing, paper and other fields.

The Difference In Physical And Chemical Properties of HPMC and HEMC(2)

Gel temperature is an important indicator of cellulose ether. The aqueous solution of cellulose ether has thermal gel properties. As the temperature increases, the viscosity continues to decrease. When the temperature of the solution reaches a certain value, the cellulose ether solution is no longer transparent, but forms a white colloid, and finally loses its viscosity. The gel temperature test means that the cellulose ether sample is slowly heated in a water bath from a 0.2% concentration of cellulose ether solution until the solution appears white or even white gel, and the viscosity is completely lost. The temperature of the solution is the gel temperature of the cellulose ether.

The ratio of methoxy, hydroxypropyl and HPMC has a certain effect on the water solubility, water holding capacity, surface activity and gel temperature of the product. Generally speaking, HPMC with high methoxy group content and low hydroxypropyl content has good water solubility and good surface activity, but the gel temperature is low: increasing the hydroxypropyl content and reducing the methoxy group content can increase the gel temperature. But excessive hydroxypropyl content will lower the gel temperature, reduce water solubility and surface activity. Therefore, cellulose ether manufacturers must strictly control the group content to ensure product quality and stability.

3. Application of construction industry

HPMC and HEMC have similar functions in building materials. It can be used as a dispersant, water-retaining agent, thickener, binder, etc. It is mainly used for the molding of cement mortar and gypsum products. Used in cement mortar to increase its cohesiveness and workability, reduce flocculation, increase viscosity and shrinkage, and have the functions of retaining water, reducing water loss on the concrete surface, increasing strength, preventing cracks and weathering of water-soluble salts. It is widely used in cement, plaster, mortar and other materials. It can be used as a film-forming agent, thickener, emulsifier and stabilizer for latex coatings and water-soluble resin coatings. It has good abrasion resistance, uniformity and adhesion, and improves surface tension, acid-base stability and compatibility with metallic pigments. Due to its good viscosity storage stability, it is especially suitable for emulsion coatings as a dispersant. All in all, although the system is small in volume, it has good effects and is widely used.

The gel temperature of cellulose ether determines its thermal stability in application. The gel temperature of HPMC is usually between 60°C and 75°C, depending on different types, group content and production processes of different manufacturers. Due to the characteristics of the HEMC group, it has a higher gel temperature, usually above 80°C, so its stability at high temperatures is due to HPMC. In practical applications, in the hot summer construction environment, the water holding capacity of HEMC with the same viscosity and dosage is better than HPMC. Especially in the south, mortar is sometimes applied at high temperatures. The cellulose ether of the low-temperature gel will lose its thickening and water-holding effects at high temperatures, thereby accelerating the hardening of the cement mortar and directly affecting the construction and crack resistance.

Because there are more hydrophilic groups in the structure of HEMC, it has better hydrophilicity. In addition, the vertical flow resistance of HEMC is relatively good. The application of HPMC for tile adhesive will be better.

The Difference In Physical And Chemical Properties of HPMC and HEMC(1)

Cellulose is the oldest and most abundant natural polymer on earth. It is the inexhaustible and inexhaustible human's most precious natural renewable resource. Cellulose has the characteristics of low price, abundant materials, biodegradability, low heat, non-toxicity, and good biocompatibility. The basic ring of cellulose macromolecule is anhydroglucose, the molecular formula is (c6h1005) n, which contains 44.44% carbon, 6.17% hydrogen, and 49.39% oxygen. Each glucose residue ring contains three alcoholic hydroxyl groups, of which two secondary alcoholic hydroxyl groups and one primary alcoholic hydroxyl group play a decisive role in the properties of cellulose. By chemically modifying cellulose, a series of cellulose derivatives can be obtained. Using natural cellulose as raw material, cellulose ether can be obtained through processes such as alkalization, etherification, neutralization, purification, and drying.

Cellulose ether is one of the important derivatives of cellulose. It has the characteristics of solubility, viscosity, stability, non-toxicity and biocompatibility. According to the different types of substituents, ionization and solubility of cellulose ethers, there are different classifications. The substituents on the cellulose ether have a great influence on its performance. According to the different substituents, cellulose ethers can be divided into MC, HEC, CMC, HPMC, HEMC, etc.

1. Structure

1.1 HPMC

Hydroxypropyl methyl cellulose (HPMC) can be produced from refined cotton, wood pulp, methyl and polyhydroxypropyl ether cellulose. It is made by etherification of cellulose with propylene oxide and chloroform. The methoxy group on the methyl chloride replaces the hydroxyl group on the glucose ring, and the hydroxyl group is replaced by a hydroxypropoxy group, and chain polymerization occurs. HPMC has the characteristics of thermal gel, its solution does not carry ionic charge, does not interact with metal salts or ionic compounds, has strong anti-mold properties, and has good dispersibility, emulsification, thickening, adhesion, water retention and retention Colloidal.

1.2 HEMC

The production and preparation of hydroxyethyl methyl cellulose (HEMC) is slightly different from HPMC. After the cellulose is alkalized, propylene oxide is replaced by ethylene oxide to replace the hydroxyl group on the glucose ring. 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 higher gel temperature and has advantages in high temperature. Like HPMC, HEMC has good mildew resistance, dispersibility, emulsification, thickening, adhesion, water retention and glue retention.

2. Physical and chemical properties

The physical and chemical properties of this standard include: appearance, fineness, dry weight loss, sulfate ash, pH value, solution transmittance, solution viscosity, gel temperature, group content (excluding mortar application test).

Appearance, fineness, loss on drying, sulfate ash, pH, solution transmittance, viscosity, etc. are all related to the model and function of the product. Different manufacturers have different levels, so I won’t discuss them here.

2.1 Cellulose ether base content

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 for component separation, which can distinguish between hydroxypropoxy and hydroxyethoxy. The internal standard method was used to quantitatively calculate the content of the components to be tested in the sample.

2.2 Gel temperature