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

May. 12, 2021

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.

Hydroxy Propyl Methyl Cellulose Ethers

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

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