Hydroxypropyl methylcellulose solution can be mixed with a water-soluble polymer compound to become a uniform and transparent solution with higher viscosity. These polymer compounds include polyethylene glycol, polyvinyl acetate, polysiloxane, polymethyl vinyl siloxane, hydroxyethyl cellulose, and methylcellulose.
Natural polymer compounds such as gum arabic, locust bean gum, karaya gum, etc. also have good compatibility with its solution. Hydroxypropyl methylcellulose can also be mixed with mannitol or sorbitol esters of stearic acid or palmitic acid, as well as glycerol, sorbitol, and mannitol. These compounds can be used as hydroxypropyl methylcellulose.
In theory, cellulose derivatives, such as each anhydroglucose group if there is a firmly bonded substituent group, are not easily susceptible to infection by microorganisms, but in fact, when the substitution value of the finished product exceeds 1, it will also be affected by enzymes. Degradation, which means that the degree of substitution of each group on the cellulose chain is not uniform enough, and microorganisms can erode near unsubstituted anhydroglucose groups to form sugars, which are absorbed as nutrients for microorganisms.
Therefore, if the etherification substitution degree of cellulose increases, the resistance to enzymatic erosion of cellulose ether is also enhanced. Hydroxypropyl methylcellulose has excellent enzyme resistance, combined with its good dispersibility, thickening, and film-forming properties, and is generally used in water-emulsion coatings without adding preservatives. However, for the long-term storage of the solution or possible contamination from the outside world, a preservative can be added as a precaution.
Water-soluble cellulose ethers can be surface-crosslinked with aldehydes so that these water-soluble ethers are precipitated in the solution and become insoluble in water. The aldehydes that make hydroxypropyl methylcellulose insoluble include formaldehyde, glyoxal, succinic aldehyde, adipaldehyde, etc. The cross-linking reaction needs to be carried out under acidic conditions. Generally, the solution is first added with an inorganic strong acid or organic acid. Carboxylic acid to adjust the pH of the solution to about 2~6, preferably between 4~6, and then add aldehydes for cross-linking reaction. The acid and aldehyde can also be added simultaneously to allow the solution to crosslink in the desired pH range.
This reaction is often used in the final treatment process in the preparation process of cellulose ethers. After the cellulose ether is insolubilized, it is easy to use.20~25℃ water to wash and purify. When the product is in use, an alkaline substance can be added to the solution of the product to adjust the pH of the solution to be alkaline, and the product will dissolve in the solution quickly. This method is also applicable to the cellulose ether solution made into a film and then the film is processed to make it an insoluble film.
Hydroxypropyl methylcellulose has excellent film-forming properties, and its aqueous solution or organic solvent solution is coated on a glass plate, and after drying, it becomes a colorless, transparent and tough film. It has good moisture resistance and remains solid at high temperatures.
For example, adding a hygroscopic plasticizer can enhance its elongation and flexibility. To improve flexibility, plasticizers such as glycerin and sorbitol are the most suitable. If the content of plasticizer is too high, the shrinkage phenomenon of colloid dehydration will occur under high humidity. The tensile strength of the film with plasticizer added is much larger than that without the addition of plasticizer, and it increases with the increase of the added amount. As for the hygroscopicity of the film, it also increases with the increase of the plasticizer amount.
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