Field of the invention Present invention relates to a polymeric water-soluble biodegradable material which arises through a mutual reaction of polyvinyl alcohol and/or partially saponified polyvinyl acetate with a natural oligomer by mixing them up in a solution or by thermoplastic processing them together in an extruder. Depending on the mutual ratio of polyvinyl alcohol and natural oligomer the new material is suitable to be used for the production of foils, fibres, formed products for various applications, as an additive serving as a carrier or encapsulant, mainly in agriculture and consumer chemistry, for the production of ecological adhesives and the like, all of the products showing improved ecological properties.

Background of the invention Several kinds of water-soluble film forming and fibre forming materials based on polyvinyl alcohol (PVA) are known which are used for various purposes in agriculture and for packing of various products in consumer chemistry designed to be dissolved in water.

Polyvinyl alcohol which is produced by several world-known producers (Hoechst, Kuraray, Wacker, Rhone Poulang) needs to be additionally modified by low molecular plasticizers, allowing it to be workable to a desired product.

Among the first methods of preparation of films and further products of PVA described in the patent literature was that described by Tagikawa et al. (US Patent 3607812) in 1971 already. Recently the research is orientated on the formation of compositions containing further polymeric components, while simultaneously using several kinds of plasticizers.

An interesting water-soluble polymeric mixture for film preparation has been presented by Wysang R. D. in the US Patent 4119604. The mixture consists of a low- molecular and medium-molecular PVA and a copolymer of vinyl alcohol and an ethylenic unsaturated ester. Polyethylene glycol is used as a plasticizer. The films are designed for packing of powder materials, so that they can be directly dissolved in water, and the problems with contact and precise weighing of the package content are eliminated.

In the US Patent 4692494, Sonnenstein G. G. describes water-soluble films based on PVA and polyacrylic acid. Films of a mixture of both of the polymers dissolve quickly in cold water, while showing high strength and transparency, they are tack-free and they are environment compatible. The improvement of properties has been achieved by adding a plasticizer, and an effective amount of a biocidic preparation has been used in the products.

US Patent 5349000 (Robertson L. M. et al.) describes extrudable PVA mixtures containing polyester-polyether block copolymers in an amount of 5 to 25 % by weight, for example a block copolymer of polyethylene terephthalate with polytetrahydrofurane.

Especially an improvement of tenacity has been achieved.

In the US Patent 5362778 Famili A. et al. describe an extrudable mixture of PVA with modified starches. A mixture with a thermally modified starch is characterized by lower sensitivity to water, an improved strength modulus and a lower deformability at a relatively high air moisture. The processing by extrusion is stressed which requires supplying a sufficient amount of energy into the composition to substantially eliminate crystallinity. At a sufficient speed, when no decomposition of PVA can occur yet, it is necessary to simultaneously eliminate energy.

The US Patent 5206278 relates to an extrudable mixture of PVA with thermoplastic polyethylene oxide having average molecular weight of 100 000 to 2 000 000, present in an amount of 5 to 95 % by weight. The thermoplastic polyethylene oxide may be added to PVA before homogenization.

"The above given extrudable mixtures based on PVA usually do not have sufficiently balanced properties, as are the quick solubility in cold water, high strength and a high biodegradability which is recently highly stressed from the point of view of ecology. The known and undoubtedly positive results are utilized and the problems are solved by a new material based on PVA and natural oligomer which quickly dissolves in cold water and is fully compatible with the bacterial flora of soil by which it is quickly biodegraded.

Description of the invention The solution according to the present invention is represented by a polymeric water- soluble biodegradable material which arises through a mutual reaction of polyvinyl alcohol or partially saponified polyvinyl acetate having a degree of hydrolysis of 70 to 99.5 % and a viscosity of 4% by weight aqueous solution at 20 °C of 3 to 80 mPas with a natural oligomer having average molecular weight of 3 000 to 30 000, containing from 2 to 16 % by weight of nitrogen, prepared by hydrolysis of proteins, for example of collagen, according to the method, described in the CZ Patent 280655. Material according to the present invention can be prepared by a reaction of both components in an aqueous solution without heating, or at an elevated temperature with a subsequent evaporation of water, where a polymer is resulting which can be mixed with the processing additives and fillers and subsequently processed by technologies which are commonly used for other polymers (injection moulding, extrusion, blow moulding, moulding and the like). Material according to the present invention may arise also in a melt during termochemical stressing a mechanical mixture of both components together with processing additives in an extruder having a screw with a compression ratio of 1: 2 to 1: 4 and the L/D ratio greater than 10. In the extruder there arises homogeneous melt of the new material which can be at the outlet of the extruder directly formed into a final product (for example by extruding to profiles, pipes, tubes, by blow moulding to foils, by injection moulding to various mouldings) or to be granulated, and the resulting granulate to be used in a further technological operation (for example moulding).

Material according to the present invention, containing from 1 to 99 % of the natural oligomer component in polyvinyl alcohol may be prepared by both methods, where materials which contain 1 to 50 % of the natural oligomer component are preferably prepared from dry mixtures in an extruder, and materials which contain from 50 to 99 % of the oligomer component are preferably prepared in an aqueous solution with subsequent evaporation of water.

An advantage of the material and of the methods of its preparation according to the present invention is the fact that the material has an excellent solubility in water in the whole composition range mentioned, also at reduced temperatures, and it is characterized by much better biodegradability in comparison with pure polyvinyl alcohol or its modifications according to the solutions known so far.

Materials, prepared from mixtures which contain from 1 to 40 % by weight, preferably from 3 to 30 % by weight, and most preferably from 5 to 25 % by weight of the natural oligomer are especially suitable for the production of ecological water-soluble biodegradable packing foils by blow moulding, where, in comparison with materials known Example % of hydrolysis viscosity of the content of content of oligomer Nr. of PVA 4 % PVA glycerol in in the mixture solution [rnPas] PVA [% by [% by weight] weight] Example 1 88 5 12 8 Example 2 88 8 15 l O Example 3 98 20 20 5 Example 4 88 5 1 15 25 Example 5 98 10 | 12 15 so far for the production of foils based on polyvinyl alcohol, the foils of the material according to the present invention have better mechanical properties, better solubility especially in cold water, and much better biodegradability. Moreover, these foils preserve their good mechanical properties also at a reduced air moisture. Considering the presence of organically bound nitrogen, these materials are especially suitable for agricultural applications (packing of fertilizers, of agents for plant protection, but especially for strip packing of seeds), where they act as donors of nitrogeneous fertilizer.

Materials, prepared from mixtures which contain natural oligomer in an amount over 50 % by weight, are particularly suitable for the production of ecological adhesives of different kinds, as additives for polymeric and rubber mixtures, cements, plasters, and as carriers of biologically active substances, for example in spray mixtures in agriculture and forestry and the like.

Examples of Embodiments Examples 1 to 5 Dry mixtures of polyvinyl alcohol (PVA) or partially saponified polyvinyl acetate, modified for thermoplastic processing by adding glycerol as a plasticizer, and natural oligomer having a molecular weight of 12 000, containing 11.8 % by weight of nitrogen, have been prepared by procedures as well as with physicochemical and chemical parameters which are presented in Table 1 a.

Table la From the mixtures of examples 1 to 5 foils have been prepared by blow moulding at conditions, given in Table lb.

Table lb Example Nr. L/D ratio Compression ratio foil thickness of the extruder [mm] Example 1 25 1: 2 0.020 Example1:30.03025 301:20.030Example3 281:40.040Example4 301:30.020Example5 The prepared foils had properties which are given in Table l c.

Table I c Example Time to dissolution in water Tension Ductility Biodegra- Nr. [s] strength [%] dability at 10 °C at 20 °C at 60 °C [MPa] z Example 1 100 60 38 250 16 Example 2 250 120-35 200 21 Example 3--60 40 150 10 Example 4 80 20 35 270 55 Example 5--35 37 200 32 PVA 1 230 170-37 150 3 PVA 2 300 180-35 150 5 PVA 3 60 38 100 2 PVA490411102- The foils PVA 1 to PVA 4 have been prepared of PVA without any addition of oligomer as reference samples to foils from the examples 1 to 5 as follows: PVA 1-to Examples 1 and 4, PVA 2-to Example 2, PVA 3-to Example 5 and PVA 4-to Example 3.

Biodegradability, expressed in %, has been determined by respirometrically using a test of simulated incubation in the soil: [(CO2)sample-(CO2)blank/ThCO2 sample] Examples 6 to 8 The procedure used was the same as in Example 1 except that 5 % of further natural polymeric component from among hydrophobized starch, hydroxyethyl cellulose and hydrolytic lignin were added to the composition. From the mixtures, foils were prepared by blow moulding at conditions which are given in Table 2a.

Table 2a Example Nr. Component L/D ratio compression foil thickness added ratio of the [mm] 5 % by weight extruder Example 6 Starch 25 1: 2 0.035 Example 7 Hydroxyethyl 25 1: 2 0.030 cellulose Example 8 Hydrolytic 25 l : 2 0.040 li The prepared foils had properties which are given in Table 2b.

Table 2b Example Time to dissolution in Tensile Ductility Biodegra- Nr. water [s] strength [%] dability at 10 °C at 20 °C [MPa] [%] Example 6 80 50 35 200 27 Example ? 75 50 35 210 22 Exarnple 8 80 55 30 180 19 Example 9 Dry mixture of polyvinyl alcohol having the degree of hydrolysis 88 % and viscosity of the 4 % by weight solution 10 mPas and partially saponified polyvinyl acetate having the degree of hydrolysis 72.5 %, polymerization degree 700 and viscosity of the 4 % by weight solution 6.7 mPas, or partially saponified polyvinyl alcohol with the weight ratio of both polymers 1: 1, modified for thermoplastic processing by adding 15 % by weight of ethylene glycol and 5 % by weight of polyethylene glycol having a molecular weight 400 as softening additives, with a natural oligomer having average molecular weight 12 000 and containing 11.8 % by weight of nitrogen, has been prepared according to the procedure, at which L/D = 25 and the compression ratio of the extruder screw is 1: 3, where a foil having the thickness of 0.30 mm has been prepared. The foil had similar mechanical properties as the foils which were prepared in Examples 1 to 5, the difference being in a lower solubility in water which was 650 s at a temperature of 10 °C and 500 s at a temperature of 20 °C. The change of biodegradability of the foils was insignificant.

Example 10 From the foil, prepared according to Example 1, a 16 mm strip was made onto which radish seeds were deposited, evenly spaced with 2 cm spacing from each other and having laboratory germinal power of 95 %. After having the strips planted the germinal power of the seeds remained at 95 %, but, in comparison with freely sown seeds, springing up of the seeds on the strips of the foil according to Example 1 was speeded up for 1 day, it was more uniform, the plants were in better physical condition and they were more uniformly developed. After 14 days of vegetation, the weight of the green parts of the plants from the seed strips was 14 % greater than that for the freely sown seeds.

Example 11 An aqueous solution of polyvinyl alcohol having the degree of hydrolysis of 88 % and a viscosity of the 4 % by weight solution 8 mPas has been prepared which was mixed with a solution of a natural oligomer having average molecular weight 20 000 and containing 13.5 % by weight of nitrogen, so that the content of the dry substance in the solution was 40 %, the ratio of polyvinyl alcohol to oligomer was 1: 3. The prepared solution was heated for 1 hour to a temperature of 80 °C under permanent stirring, subsequently it was cooled down and the resulting polymeric material from the solution was dried by spraying the solution through a nozzle into a stream of hot air. The prepared polymer had the form of fine powder. The prepared powder was subjected to a test on biodegradability which was 80 %.

Example 12 An aqueous solution of polyvinyl alcohol or partially saponified polyvinyl acetate having the degree of hydrolysis of 88 % and a viscosity of the 4 % by weight solution 5 mPas has been prepared which was mixed with a solution of a natural oligomer having a average molecular weight 10 000 and containing 11.5 % by weight of nitrogen, so that the content of the dry substance in the solution was 20 %, the ratio of polyvinyl alcohol to oligomer being 7: 3. The prepared solution was heated for 1 hour to a temperature of 80 °C under permanent stirring, subsequently it was cooled down. From the viscous solution a foil was made by casting. The foil had the following properties: tensile strength-42 MPa; ductility-190 %; solubility in water at 10 °C-95 s; solubility in water at 20 °C-95 s; biodegradability-52 %.

Example 13 Powdered PVA has been added to a 30 % solution of a natural oligomer in such an amount that the ratio of the components natural oligomer to PVA was set to 9: 1. After having dried the solution in a fluid drier powder material has been obtained which was homogeneously mixed with gypsum with a weight ratio of 5 parts of the powder material to 100 parts of gypsum. The resulting product was characterized by improved adhesion to bases, by uniform hardening and by prolonged hardening time.

Example 14 The procedure used was the same as in Example 9 except that the resulting ratio of basic components natural oligomer to PVA was 19: 1. The solution was further diluted with water in a ratio of 1: 10, and the fungicide Ridomil 48 WP was admixed to such a solution, so that its concentration was 0.25 %. This preparation was applied in the form of a spray on vine in June. In comparison with a spray which was prepared just with water, the above given preparation improved the adhesive properties of the spray manifested in the formation of a uniform film of the preparation on the leaves. Compared with a control (a spray applied just with water as the solvent) the protective effect lasted 7 days longer.

Example 15 The procedure used was the same as in Example 9 except that the resulting ratio of the components natural oligomer to PVA was 1: 1. The viscous solution was diluted with such an amount of water that the overall dry substance content was 10 %, and this solution was mixed with a solution of a starch glue designed for the process of seed coating in a ratio of 1: 1. This preparation was gradually applied by spraying on sugar beet seeds in a technological process of the seed coating at a temperature of 20 °C, while good quality of the seed coating was preserved. Subsequent vegetation tests have shown, in comparison with commonly coated seeds, quicker and more uniform germination of the plants which have sprouted from the seeds coated with the preparation used. After 28 days of vegetation, the weight of the green parts of the plants from the seeds which were coated with the preparation according to this invention was 12 % greater than that of plants from commonly coated seeds.

Industrial Applicabilitv A polymeric water-soluble biodegradable material which arises through a mutual reaction of polyvinyl alcohol with a natural oligomer with the content of up to 50 % by weight is especially suitable to be used for the production of ecological water-soluble biodegradable packaging foils by blow moulding, but also of fibres, formed products for various applications, or as an additive serving as a carrier or encapsulant. Materials, containing more than 50 % of a natural oligomer, are suitable especially for the production of ecological adhesives of various kinds, as additives to polymeric and rubber mixtures, cements, plasters, and as carriers of biologically active substances, for example in spray mixtures in agriculture and forestry and the like.