RU2458733C1 - Method of stabilising aqueous dispersion - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to stabilisation of dispersed aqueous systems which are used in pharmaceutics and cosmetology. Disclosed is a method of stabilising an aqueous dispersion with microencapsulated hydrophobisated nanosilica, involving addition of polyvinyl alcohol with concentration of not less than 5 wt % as a stabiliser into the aqueous dispersion.

EFFECT: low power consumption and costs when producing a stable aqueous dispersion which is resistant to freezing and thawing.

1 cl, 1 tbl

Description

The invention relates to the field of stabilization of dispersed aqueous systems, in particular aqueous solutions, microencapsulated with silica, which are used, for example, in pharmaceuticals and cosmetology.

A known method of obtaining resistant to freezing and thawing a stable aqueous dispersion of microencapsulated silica using an aqueous solution of a polysaccharide as a stabilizer [Carter B.O., Wang W.X., Bray C.L., Adams D.J., Cooper A.I. // Gas Storage in "Dry Water" and "Dry Gel" Clathrates, Langmuir. 2010. V.26. No. 5. P. 3186-3193].

To obtain an aqueous dispersion, a significant amount of polymer (20 wt.%) Is consumed and high energy costs are required to disperse a highly viscous polymer solution.

The challenge facing the invention is to reduce energy and economic costs in obtaining a stable aqueous dispersion that is resistant to freezing and thawing.

The problem is solved in that when stabilizing an aqueous dispersion microcapsulated with hydrophobized nanosilica, including the introduction of stabilizing additives (stabilizer), polyvinyl alcohol is introduced into the water as a stabilizer.

To obtain the dispersion, an aqueous solution of polyvinyl alcohol (GOST 10779-78) and hydrophobized nanosilica aerosil are used instead of water.

The method is as follows.

An aqueous solution of polyvinyl alcohol is prepared.

To prepare a solution of polyvinyl alcohol (PVA), grade 16/10 powder was used, manufactured in accordance with GOST 10779-78.

For the preparation of a five percent solution of polyvinyl alcohol, a weighed portion of 5 g of PVA is poured with 94 grams of hot water at a temperature of 70-90 ° C, while mixing until a homogeneous solution is obtained. Further, continuing stirring to enhance gelation during the preparation of the PVA solution, boric acid is added in small portions in an amount of 1 wt.%. All this is done in a steam bath. Stirring is continued until a liquid turbid solution is obtained, gel-like in consistency.

A solution of polyvinyl alcohol, weighing 95 g, with a given concentration and hydrophobized nanosilica, weighing 5 g, is placed in a blender container for whipping and mixed (shaft rotation speed 18750 rpm). As nanosilica, hydrophobized aerosil grade R 202 is used, the particle size of which is on the order of 10-14 nm and the density under normal compaction is about 50 g / l. The viscosity of the initial five percent hydrogels does not exceed 40 mm ² / s.

The result is an aqueous dispersion of PVA, the consistency of a paste. The use of an aqueous solution of polyvinyl alcohol while mixing it with hydrophobized aerosil at high speed promotes the formation of stable liquid droplets microencapsulated with nanosilica. The density of the resulting PVA dispersion (0.86 kg / l) approaches the density of a 5% PVA solution (0.98 g / l). This indicates that the volume of the dispersion is predominantly occupied by the PVA solution. The adsorption of PVA due to its high surface-active properties on the surface of aerosil particles prevents their association and the formation of an extended spatial network. This leads to a sharp increase in the concentration of droplets in the volume of the dispersion.

Studies have shown that using an aerosil concentration of less than 4 wt.% Does not provide the necessary disaggregation of crushed ice particles.

Table Detailed preparation of the system The concentration of the PVA solution, g / ml Preservation of the dispersed structure of the system after a freeze-thaw cycle Satisfactory viscosity (less than 50 mm ² / s) Conclusion one - + It is recommended to use a solution with a PVA concentration of approximately 5 wt.% Due to the fact that solutions with a concentration of less than 3 wt.% Do not ensure the dispersed structure of the system after freezing - thawing cycles, and with large ones have a high viscosity (more than 50 mm ² /from) 3 - + 5 + + 9 + - fourteen + -

It is recommended to use a solution with a PVA concentration of at least 5 wt.%, Since solutions with a lower concentration do not ensure the preservation of the dispersed structure of the system after freezing and thawing cycles.

Obtained by the proposed method, the dispersion retains a finely dispersed structure and when repeating cycles of freezing and thawing. The mechanism of the observed “cryostabilization” of the dispersion arises due to the formation of a cryogel polymer structure in them.

The proposed method allows to reduce energy and economic costs and to obtain a stable water dispersion that is resistant to freezing and thawing.

Claims (1)

A method of stabilizing an aqueous dispersion microencapsulated with hydrophobized nanosilica, comprising introducing stabilizing additives (stabilizer) into it, characterized in that polyvinyl alcohol with a concentration of at least 5 wt.% Is introduced into the water as a stabilizer.