What is HPMC

Hydroxypropyl methyl cellulose, HPMC is a kind of non-ionic cellulose mixed ether, unlike ionic methyl carboxymethyl cellulose mixed ether, it does not react with heavy metals. Due to the different ratio of methoxy content and hydroxypropyl content and different viscosity in hydroxypropyl methyl cellulose, it becomes several varieties with different performance. For example, the performance of high methoxy content and low hydroxypropyl content is close to that of methyl cellulose. And low methoxyl content and high hydroxypropyl content of the varieties, it is close to the performance of hydroxypropyl methyl cellulose production. But in each species, although only a small amount of hydroxypropyl or a small amount of methoxy, the dissolution performance in organic solvents or flocculation temperature in aqueous solution, there is a big difference.

Enzyme resistance of hydroxypropyl methyl cellulose

Theoretically, cellulose derivatives such as hydroxypropyl methyl cellulose are less susceptible to microbial attack if there is a firmly bound substituent group on each dehydrated glucose moiety, but in fact, the finished product is subject to enzymatic degradation when the substitution value exceeds 1, which means that the degree of substitution of each group on the cellulose chain is not uniform enough, and microorganisms can erode on the near unsubstituted dehydrated glucose moiety and form sugars as a result. This means that the degree of substitution of each group on the cellulose chain is not uniform enough for microorganisms to erode on the near unsubstituted dehydrated glucose groups and form sugars that are absorbed as nutrients for microorganisms. Therefore, if the degree of etherification substitution of cellulose increases, the resistance of cellulose ethers to enzymatic erosion is also enhanced. It is reported that the residual viscosity of hydroxypropyl methylcellulose (DS=1.9) is 13.2%, methyl cellulose (DS=1.83) is 7.3%, methyl cellulose (DS=1.66) is 3.8%, and hydroxyethyl cellulose is 1.7% as a result of hydrolysis by enzymes under controlled conditions, which shows that the enzyme resistance of hydroxypropyl methylcellulose is stronger.

Why HPMC is used in aqueous emulsion coatings？

As a result, the excellent enzyme resistance of hydroxypropyl methyl cellulose, combined with its good dispersibility, thickening and film-forming properties, is used in aqueous emulsion coatings and other applications, and generally does not require the addition of preservatives. However, for the long-term storage of the solution or the possible contamination of the outside world, preservatives can be added for precautionary purposes, and their selection can be decided according to the final requirements of the solution. Phenylmercury acetate and manganese fluosilicate are effective preservatives, but they are toxic and must be operated with care, and their dosage can generally be 1~5mg of phenylmercury acetate per liter of solution.

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