CS216464B1 - A method for producing instant powder-alkali salts of high molecular weight polyacids - Google Patents

Abstract

The invention provides a method for producing instant powders of alkali salts of high molecular weight polyacids, the solutions of which are used mainly as antistatic and auxiliary textile preparations, additives to starch adhesives and hardeners. The essence of the invention is the addition of polyethylene glycol to a solution of a salt of a high molecular weight polyacid at a pH of 6.5 to 8.5 and subsequent drying of the solution in a spray dryer, whereby hollow spheres are formed, quickly and easily soluble in water.

Description

The invention relates to a method for producing instant powders of alkaline salts of high molecular weight polyacids, formed by copolymerization of ethylenic monomers and ethylenically unsaturated acids or anhydrides of these acids, used in particular as antistatic and auxiliary textile preparations, additives to starch adhesives and hardeners.

Aqueous solutions of alkali salts of high molecular weight polyfunctional acids are used in industry for the antistatic treatment of surfaces of plastics, films and fibres. Furthermore, these solutions have found application as surface-active preparations, and as sizing agents for the treatment of textile fibres. Their excellent adhesiveness has enabled their use as additives in starch adhesives.

The preparation of aqueous solutions of alkali salts of these copolymers is described and known in several variants. However, their difficult transportability still remains an indisputable disadvantage. Processable solutions of salts of these copolymers usually have a salt content of 25 to 30% by weight, because at higher concentrations the solutions lose their fluidity rapidly due to increasing thixotropy. This severely limits their direct pumping and transport in tanks, especially at reduced temperatures below freezing.

The optimal technical solution is to convert the product into a dry state and transport it as a powder. However, previous attempts to prepare a powder product have not yielded the desired result for several reasons. First of all, the basic requirement is to maintain the product in a state that allows it to be redissolved in water without residue and in a short time. Furthermore, it is necessary to stabilize the dried powder so that it forms defined particles - optimally hollow β spheres with a small dispersion of the average volume-surface diameter of the particles. Individual particles must not stick together at normal temperatures and humidity, they must retain their aypkoet during storage, transport and processing. Finally, a very important condition for processability is the direct solubility of the powdered salt of the copolymer in water without a swelling phase, in which individual swollen particles stick together, form solvated clusters, the dissolution of which is then very slow and disproportionately prolongs further processing operations.

Although the salts of the copolymers of the above type are relatively easy to dry, they do not achieve the desired properties, and therefore this technology is not practically used. Generally, an indirect process is used, in which a dry powdered copolymer is prepared as a polymeric polyacid, which is dissolved in an aqueous solution of an alkali hydroxide during further processing. Although the dissolution is slow and is characterized by a lengthy and slow swelling of the resulting salt, the storage and transportation of the powdered copolymer is almost problem-free. In addition, the necessity of using relatively concentrated solutions of alkali hydroxides is technically unacceptable for most processors in light industry, and generally, the preference is given to using the salts of these copolymers for the above purposes in the form of aqueous concentrated solutions.

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The above disadvantages are eliminated by the method of producing Instant Alkaline Salt Powders.

216,464 high molecular weight polyacids, formed by copolymerization of ethylenic monomers and pty 6Š -ethylenically unsaturated acids or anhydrides of these acids, for example styrene and maleic anhydride and neutralization of the resulting copolymer with alkali hydroxides according to the present invention, the essence of which consists in adding 0.1 to 10% by weight of polyethylene glycol a with a molecular weight in the range of 4,000 to 8,000 to an aqueous solution of the salt of the said copolymer, the pH of the solution ae is adjusted to the range of 6.5 to 8.5, (preferably 7.5 to 8) and the solution aa is dried in a stream of warm air in a spray dryer until dry hollow spheres are formed.

The actual technological process has two stages. In the first stage, polyethylene glycol with a molecular weight in the range of 4,000 to 8,000 is added to a warm solution of an alkaline salt of a polymeric polyacid, which suitably plasticizes the film-forming component of the solution, i.e. the alkaline polymeric salt, and advantageously adjusts the properties of the dry powder spheres so that at relative humidity of up to 85%, individual particles do not stick together, even during long-term exposure.

The second stage of treatment consists in adjusting the pH of the solution to the range of 6.5 to 8.5, with the maximum effect being achieved when the pH is set to 7.5 to 8.0. This treatment ensures, above all, the correct regulation of the mutual ratio of the swelling and dissolution rates of the powder in water, especially at elevated temperatures. At the same time, the effect of this treatment on the rheological properties of the solution sprayed during drying is also positive, especially in the narrow range of pH values of 7.5 to 8.0, when the thixotropic properties of the thickened solution are minimally manifested and the dispersed drops of the solution have a very uniform distribution.

The powder produced by this process consists of hollow spherical particles with a mean volume-surface diameter of 30 to 50 micrometers, stable during long-term exposure in conditions of normal and increased relative humidity and easily soluble in cold water even when heated and boiled.

To clarify the essence of the invention, examples of embodiments are given below.

Example 1

In the reactor, a copolymer of styrene and maleic anhydride is prepared by copolymerization in acetone at 58 °C. The resulting copolymer solution is gradually passed by gravity or forced under pressure into a second reactor, in which an aqueous solution of sodium hydroxide is prepared in a stoichiometric ratio, heated to a temperature higher than the boiling point of acetone. By gradually adding the copolymer solution, acetone is distilled off into the initial mixture and an aqueous solution of the sodium salt of the copolymer is formed in the reactor, the mass concentration of which is adjusted to 30%.

Polyethylene glycol 6000 is added to the prepared solution in an amount of 0.1% on dry matter and mixed. Then, by adding another amount of sodium hydroxide, the pH of the solution is adjusted to 6.2. This operation reduces the previous viscosity of the solution, which reached 6,000 to 10,000 mPa.s, to the range of 1,000 to 2,000 mPa.s/20 °C.

216,464

The solution thus prepared is dried in a pilot-scale spray dryer at a temperature of 80 °C (viscosity at this temperature 190 mPa.s) and with a dry matter content of approximately 30% by weight.

Drying mode: Sample Temperature air °C Moisture content in sample, % mass entry exit Chamber cyclone 1 165 72 5.8 1.9 2 200 87 6.2 2.0 3 250 lCfc 4.3 1.2

The dried substance forms hollow spheres with a bulk density of 450 to 480 kg/m^, which during processing dissolve in water at a temperature of 90 °C without the formation of swollen clusters in a very short time and without leaving a residue. The powder is packed for transport in polyethylene bags or metal drums. In this state it is capable of transport in various climatic zones without any noticeable deterioration in properties.

Example 2

In reactor 'a copolymer of 2-ethylhexyl acrylate and methacrylic acid in a molar ratio of 1:1.6 is prepared by copolymerization in methyl acetate in the presence of benzoyl peroxide as an initiator.

In the second reactor, a solution of potassium hydroxide in water is prepared in a stoichiometric ratio to the composition of the copolymers and heated to 85 °C. The copolymer solution is gradually pumped from the first reactor to the second by a gear pump at such a speed that methyl acetate is continuously evaporated and a copolymer salt is formed, which dissolves immediately.

The resulting solution of the potassium salt of the copolymer polyacid in water has a mass concentration of approximately 25% and a viscosity of 5,000 to 8,000 mPa.s/20 °C. 8% by weight of polyethylene glycol with an average molecular weight of 4,500 (based on the dry matter of the solution) is added to the solution while stirring at a temperature of 85 °C. After stirring, the pH of the solution is adjusted to 7.5 m, whereby its viscosity drops to 1,000 to 1,500 mFa.s/20 °C. The prepared solution is dried in a spray dryer.

Drying mode:

inlet air temperature outlet air temperature moisture content in the product

220°C 103°C

1.92% by weight

The dried substance forms hollow spheres, non-sticky, with a bulk density of 410 kg/m3. The processing properties of the product are identical to those of the product according to example 1.

Claims (1)

OBJECT OF THE INVENTION A process for producing instant powders of alkali salts of high molecular weight polyacids formed by copolymerization of ethylene monomers and 6-ethylenically unsaturated acids or enhydrides thereof, for example styrene and maleic anhydride, and neutralizing the resulting copolymer with alkali hydroxides such as sodium hydroxide, characterized in that 0.1 to 10% by weight of polyethylene glycol having a molecular weight of 4,000 to 8,000, the pH of the solution is adjusted to a range of 6.5 to 8.5 (preferably 7.5 to 8.0) and the solution is dried in a stream of warm of air on the sprayer to form dry hollow spheres.