JPH058744B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a process for the preparation of water-swellable substances, preferably in granular form, based on cross-linked polyacrylonitrile hydrolysates, which are suitable for the production of water-swellable substances in sandy soils and plant substrates. Particularly useful for improving retention. 1-20% by weight of polyacrylamide cross-linked with N,N-methylene-bis-acrylamide
It is already known from European patent application no. 0023347 that the water retention properties of sandy soils can be improved by adding This polymer is preferably added to the soil in granular form. There is a need to provide soil conditioners of this type with comparable or better properties and to produce them in a simple manner. This includes cross-linking agents made from aziridine and/or methylaziridine and at least difunctional esterification products of at least dihydric alcohols and acrylic acid and/or methacrylic acid, and hydrolyzed polyacrylonitrile. This is possible using the reagents of the present invention, which are obtained by reacting with a water-soluble polyelectrolyte based thereon. Accordingly, the present invention provides up to 100% of that, but preferably
60-95% ammonium and/or alkali and/or alkaline earth metal salts, e.g.
at least 30% by weight, preferably from 30 to 80% by weight, optionally present as Na, K, Mg salts;
The water-soluble hydrolysis product of a polyacrylonitrile polymer containing acrylic acid units is prepared in the form of a 5-65% by weight aqueous solution, preferably in the form of a 15-50% by weight aqueous solution, based on said polymer. 0.3-10% by weight,
Preferably from 1.5 to 5% by weight of a cross-linking agent, wherein the cross-linking agent is the esterification product of aziridine and/or methylaziridine from at least dihydric alcohol and acrylic acid and/or methacrylic acid. The polymer is produced by reacting the polymer with a cross-linking agent at a temperature within the range of 0 to 100°C, preferably 20°C.
The present invention relates to a method for producing a water-swellable substance of high molecular weight, characterized in that it is carried out at a temperature within the range of ~85°C and a pH value maintained in the range of PH3-8. The products prepared according to DE 30 29 027 can advantageously be used as hydrolysis products of polyacrylonitrile. In those cases, the hydrolysis preferably results in a hydrolysis product of 30-80% by weight.
acrylic acid units optionally present in salt form, 20 to 70% by weight of acrylamide units and 0
Continued to such an extent that it consists of ~10% by weight acrylonitrile units. Suitable cross-linking agents are, in particular, aziridine and/or methylaziridine combined with at least dihydric alcohols, such as glycols, glycerol,
trimethylolpropane, pentaerythritol,
Preferably trihydric alcohol, acrylic acid and/or
or products reacted with at least difunctional esterification products from methacrylic acid. Adducts of methylaziridine and trimethylolpropane triacrylate can be used with particular preference as crosslinking agents. To produce water-swellable substances, 5 to 65% by weight, preferably 15 to 50% by weight, of suitable polyelectrolytes in aqueous solution are added at temperatures of 0 to 100°C and a pH of 3 to 30% by weight.
In 8, from 0.3 to 20% by weight based on the polymer,
Crosslinking is preferably carried out using 1.5 to 5% by weight of at least difunctional acrylate and adduct with (methyl)aziridine. Since the cross-linking rate is temperature dependent, this not only makes it easily and economically applicable to the desired subsoil by known application techniques for liquids, but also allows free-flowing It also facilitates continuous manufacturing in the final product form. For example, 20% by weight of a polyelectrolyte consisting of 48% by weight polyacrylamide units and 52% by weight polyacrylic acid units of which up to 90% of its carboxyl groups have been neutralized by ammonium hydroxide.
The shelf life of a mixture consisting of an aqueous solution and 3% by weight of the above-mentioned preferred cross-linking agent is approximately
10000 seconds and approximately 30 seconds at 80°C.
Shelf life is defined as the time required for a dimensionally stable gel to form after mixing the ingredients. If the subsoil is to be coated with water-swellable materials prepared according to the invention, the aqueous polyelectrolyte solution is mixed with the crosslinking agent at a temperature below 20°C. When a mixture of two components is applied, cross-linking occurs during drying of the coated subsoil. The production of dry granules or free-flowing powders of water-swellable substances can be carried out continuously or in batches from the same mixture using heatable tubular screws, granulators and driers. Drying can also be carried out in air transfer dryers or fluidized bed dryers. The granules are preferably manufactured as shown in FIG. The polyelectrolyte and cross-linking components are added by metering pumps from separate storage vessels 1 and 2 via a static mixer 4 into a screw reactor 5, where they are heated at 60-100°C.
The reaction is preferably carried out at 80-90°C for 30 seconds to 5 minutes, and the reaction product is granulated in a granulator 6.
The granules are then dried in a fluid bed dryer 7. The soil conditioner according to the invention is preferably 1 to 8 kg/
m ³ , more preferably in an amount of 2 to 4 Kg/m ³ to give a water retention rate of up to 360 g/g of soil conditioner. Example 1 (a) Polyelectrolyte solution: Hydrolyzate of polyacrylonitrile with the following analytical data Solid content: 30% by weight PH value: 6.7 Viscosity (Hoppler, 20°C): 2000 mPa.s Relative viscosity η Relative: 1.8 Carboxyl group content, expressed as polymeric acrylic acid: 41% by weight on solids basis (b) Cross-linking agent: NeO Cryl CX100 (c) Production of water-swellable material: 1000 g of 30% by weight polyelectrolyte Solution (a) was weighed and added into a 1500 c.c. stainless steel container;
It was then heated to 85°C. Stir 45 g of a pre-prepared 20% emulsion of polyfunctional crosslinker (b) in water at 20°C into the heated solution using a laboratory stirrer rotating at 700 rpm. I added while doing so. Cross-linking occurred within 40 seconds resulting in a dimensionally stable, non-stick gel. The resulting gel was removed from the stainless steel container, cut into chunks with a knife, and granulated in a standard commercial mincer. The gel particles thus obtained were dried in a recirculating air oven at 140° C. for 1 hour and ground in a mortar to a particle size of 0.3 mm. The amount of water absorbed after swelling was determined as follows: 0.2 g of ground material was weighed and added into a 400 ml capacity glass beaker. After addition of 200 g of deionized water, the substance/water mixture was left at room temperature for 3 hours to obtain adequate swelling properties. The swollen material was then filtered through a 0.32 mm mesh polyethylene filter cloth. The weight of the swollen material was measured and divided by the amount of dry material used. The value obtained in this manner is defined as the water absorption rate. The water absorption value was 260 g/g subsoil. Example 2-4 Change in concentration of cross-linking agent. Starting products and reaction conditions are the same as in Example 1.

[Table] Example 5 The polyelectrolyte used in Example 1 was reacted with 7% KOH based on total solids, and the released ammonia was distilled off at 98°C until the pH value fell to 6.8. did. Next, use phosphoric acid to measure the PH value.
Adjusted to 5.5. The polyelectrolyte solution and the crosslinker emulsion were added via a static mixer into a continuous apparatus in such a way that a mixture of 97% polyelectrolyte and 3% crosslinker was obtained. The mixture was then heated to 85° C. in a screw reactor and allowed to react completely for 90 seconds to form a gel. The gelled granules were added into the fluidized bed dryer via a perforated disc placed at the top of the apparatus and dried to a residual moisture content of 3%. This product had a subsoil water uptake value of 160 g/g. Example 6 A polyelectrolyte was prepared as follows: In a stirrer-equipped autoclave of 300 liter capacity, designed for a pressure of 30 bar, 87.5
9.67Kg KOH in 88-90% wt solution in Kg water
of a 32.9% aqueous polyacrylonitrile copolymer suspension polymerized from 84 kg of a monomer mixture containing 95% by weight acrylonitrile and 5% by weight methacrylate (intrinsic viscosity of the copolymer [ η], 2.25 dl/g) and then heated to 185°C with stirring under nitrogen after closing the autoclave.
and hydrolyzed at that temperature for 5 hours. Upon completion of the reaction, autoclave heating was stopped and the reaction mixture was cooled to 100° C. by expansion. After further cooling to 30°C, the reaction mixture was taken out. The slightly colored product obtained had the following analytical data: Solids content: 35% by weight PH value: 7.0 Viscosity (Hoppler, 20°C): 24 400 mPa.s Relative viscosity η relative: 2.43 Carboxyl groups Content, (expressed as polymeric acrylic acid): 49% by weight Crosslinker: Trifunctional adduct of methylaziridine and trimethylolpropane triacrylate (NeO Cryl
CX100, polyvinyl hemi product). The polyelectrolyte solution and crosslinker emulsion were added via a static mixer into a continuous apparatus in such a way that a mixture of 98% polyelectrolyte and 2% crosslinker was produced. The mixture was then heated to 85° C. in a screw reactor and allowed to react completely for 90 seconds.
produced a gel. The gel-like granules are added into the fluidized bed dryer via a perforated disc located at the top of the apparatus, and
It was dried at 150°C to a residual moisture content of 2.3%. The product had a subsoil water uptake value of 630 g/g. By mixing this material with a standard commercial subsoil based on bark compost (Edaphon), the maximum water capacity was improved as follows: Maximum water retention Edaphon without added swelling products.
42% by volume H ₂ O Edaphon + 2 g/swelling product
55% by volume H ₂ O Edaphon + 4g/swellable product
Optimal levels for plant growth of 60% by volume H ₂ O and 50% by volume H ₂ O were thus reached with the addition of the products of the invention.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an apparatus for producing the product of the invention.

Claims (1)

[Claims] 1. Polyacrylonitrile polymers containing at least 30% by weight of acrylic acid units, up to 100% of which may be present as ammonium salts, alkali and/or alkaline earth metal salts. The water-soluble hydrolysis product is reacted in the form of a 5-65% by weight aqueous solution with 0.3-10% by weight, based on the polymer, of a crosslinker, wherein the crosslinker is aziridine and/or methyl It is obtained by reacting aziridine with an at least difunctional esterification product of at least dihydric alcohol and acrylic acid and/or methacrylic acid, and is obtained by reacting the polymer with a cross-linking agent. 0
A process for producing water-swellable substances of high molecular weight, characterized in that it is carried out at a temperature of ~100°C and a pH value of 3-8. 2. A process according to claim 1, wherein the hydrolyzed product is in the form of a 15-50% by weight aqueous solution. 3. The method of claim 1, wherein the hydrolyzed product is reacted with 1.5 to 5% by weight of the crosslinker, based on the hydrolyzed polymer. 4. The method according to claim 1, wherein the temperature range is from 20°C to 85°C. 5. The method according to claim 1, wherein aziridine and/or an adduct of methylaziridine and trimethylolpropane triacrylate is used as the cross-linking agent. 6. The claimed invention uses as hydrolysis product a polymer containing from 30 to 80% by weight of acrylic acid units, from 20 to 70% by weight of acrylamide units and from 0 to 10% by weight of acrylonitrile units. The method described in Scope No. 1.