SU417154A1 - - Google Patents

Description

one

The invention can be applied to microencapsulation of water-immiscible liquids.

There are several methods for encapsulating liquids that are not miscible with water in gelatin, based on the preparation of a shell from a coacervate gelatin solution. For this, an emulsion that is not miscible with water in a solution of gelatin at 50-60 ° C is first obtained, then, adding substances that reduce the solubility of gelatin, gelatin is isolated as a new phase - drops of a concentrated gelatin solution (coacervate). When moving on the emulsion of the encapsulated substance on droplets, a liquid shell is formed from the droplets of the concentrated gelatin solution. Then the shell is cured by cooling and fixed with an aqueous formaldehyde solution.

The most crucial point in this encapsulation process is the process of separating the new gelatin phase in the form of microdroplets so that they form liquid shells around the droplets of the encapsulated substance. To do this, the following conditions must be carefully observed: the emulsification temperature, the concentration of the solutions, the pH of the medium, the speed of mixing and the rate of addition of the substance that reduces the solubility of gelatin in water. Change

One of these conditions leads to a new definition of the optimal amount of a substance that reduces the solubility of gelatin in water, since if there is a shortage or excess of it (under these conditions), the shell does not form, and therefore no encapsulation is possible. In addition, to form shells of the required thickness when preparing gelatin microcapsules from a coacervate solution

1-2 hours required At the same time, gelatin microcapsules fixed with formaldehyde tend to form aggregates during storage. The purpose of the invention is to develop such

the method of producing gelatin microcapsules, which will eliminate the coacervation process and reduce the time of shell formation, which is very important when encapsulating substances prone to reaction with water, as well as obtaining capsules with high resistance to aggregation.

According to the invention, the goal is achieved by forming a gelatin shell from a true concentrated gelatin solution. In addition, additional tanning of the gelatin shells is carried out with an aqueous solution of a mixture of chromium sulfate and p-naphtholsulfone. The proposed method for producing microcapsules from a true concentrated solution

gelatin is carried out as follows.

An emulsion is first produced, which is a drop of liquid that is capsulated, stabilized by structured layers of gelatin. The size of the emulsion droplets (the future size of the capsules) is determined by the surface tension at the interface of the aqueous solution of gelatin to the encapsulated liquid, as well as by the intensity of stripping during the formation of the emulsion. An emulsion is obtained by pouring the encapsulated substance in a thin stream with stirring into a concentrated solution of gelatin at 40-50 ° C.

The capsules are then separated from the aqueous solution of gelatin and the shells are cured on the encapsulated liquid by diluting the resulting emulsion with water while simultaneously drastically lowering the temperature.

The gelatinous microcapsule shells are dewatered, based on the gelatin's ability to change the solubility in water with a change in the pH of the medium. In order to achieve a pH value corresponding to the isoelectric point at which the solubility of gelatin in water is minimal, an aqueous electrolyte solution is added. To this end, after separating the capsules from water, process them at a temperature of 10 ° C with a 20% Na2SO4 solution for 30-60 minutes.

Then, tanning of the shells is carried out in two steps. For this, the capsules are first treated with an aqueous formaldehyde solution. The formation of additional bonds (bridges) between gelatin micromolecules by amine functional groups occurs. The capsules are then treated with an aqueous solution of a mixture of chromium sulfate and p-naphtholsulfone (synthetic tannin BNS) for 2-3 hours, resulting in gelatin macromolecules bound in peptide and carboxyl functional groups. This method of tanning allows to obtain easily dispersed gelatin microcapsules that are highly resistant to aggregation.

The obtained microcapsules are washed with water and dried in the open air at room temperature on a hygroscopic substrate.

Example 1. To 100 ml of a 10% aqueous solution of gelatin at 40 ° C and stirring 200 ml of carbon tetrachloride or freon are poured in a thin stream, emulsification is carried out for 15 minutes. The resulting emulsion with stirring, poured into 5-10-fold volume of cold water, followed by the fact that the temperature in the vessel does not rise above 10 ° C. Drain the excess water, the capsules are treated with 150 ml of a 20% aqueous solution of Na2SO4 at a lowered temperature for 30-60 minutes, and then 150 ml of a 38-40% aqueous solution of formaldehyde for 15 hours.

After that, 200 ml of a mixture of tanning agents consisting of a 3% aqueous solution of chromium sulfate and a 3% aqueous solution of p-naphtholsulfone is treated for 3 hours. After washing with water, the capsules are dried at room temperature on a hygroscopic substrate, for example on filter paper. Dried capsules are well dispersed, they can be easily dosed.

Example 2. To 100 ml of a 10% aqueous solution of gelatin at 40 ° C and stirring, pour in a thin stream of 100 ml of dibutyl phthalate. Emulsification is continued for 15 minutes. The finished emulsion with stirring, pour in an excess of cold water (10 ° C). After filtering off the excess water, the capsules are treated with 100 ml of a 20% aqueous solution of Na2SO4 for 60 minutes, and then with 100 ml of an aqueous solution of formaldehyde for 10-15 minutes. The subsequent processing of the capsules is the same as in Example 1.

Example 3. In 100 ml of a 10% gelatin solution at 40 ° C and stirring, 100 ml of tributyl phosphate are poured in a thin stream, emulsification is carried out for 5 minutes. Subsequent processing is the same as in example 2.

Subject invention

The method of producing microcapsules by dispersing the core material in the shell material and subsequent processing of the obtained shells with an aqueous solution of sodium sulfate and formaldehyde, characterized in that, in order to eliminate the coacervation process and reduce the curing time of the microcapsule shells, an aqueous solution of gelatin is used as the shell material, and shell obtained microcapsules additionally treated with a mixture of a solution of chromium sulfate with p-naphtholsulfone.