EP0631599A1

EP0631599A1 - Thermoplastic materials, moulded parts made thereof and process for producing the same

Info

Publication number: EP0631599A1
Application number: EP93906568A
Authority: EP
Inventors: Wolfgang Ritter; Michael Beck
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 1992-03-20
Filing date: 1993-03-19
Publication date: 1995-01-04
Also published as: WO1993019124A1; US5512617A; JPH07504933A; DE4209095A1

Abstract

Materials based on starch that has been thermomechanically disintegrated under high pressures and temperatures with admixture of water and/or low molecular plastifiers contain intimately mixed alkyd resins that can be cross-linked by oxidation. Preferably, these alkyd resins are composed at least for the most part of base materials based on renewable raw materials. The thus modified starch blends are suitable for producing moulded parts that are reactively cured by air exposure, so that their resistance, and in particular their resistance to water, is increased.

Description

Thermoplastic ^' processable starch-based materials, molded parts obtained from them and processes for their production

The invention relates to improvements in the production of materials and molded parts produced therefrom on the basis of modified starch, which is present in an intimate mixture with selected thermoplastic polymer compounds.

Numerous proposals from recent years have dealt with the attempt to open up high molecular polymer compounds of natural origin - and here in particular starch - to an expanded range of possible areas of application. This work is based in particular on the knowledge that native starch together with limited amounts of water and / or other auxiliaries can be converted into a thermoplastic material by thermo-mechanical digestion, the processing of which is possible in a conventional manner, for example by injection molding. The Thermomechanical digestion using elevated temperatures and pressures is possible in particular in conventional extruders that precede the shaping processing step. From the extensive literature, reference is made here to the publication RFT Stepto et al. Injection Molding of Natural Hydrophilic Polymers in the Presence of Water, CHIMIA 41 (1987) No. 3, 76 to 81, and the literature cited therein.

Extensive work deals with the improvement of the product properties in ther oplasticized starch by using selected organic auxiliary liquids in the starch digestion. PCT patent application WO 90/05 161 may be mentioned here as an example. Here it is proposed to add additives to the native starch, which lower the melting temperature of the starch and are additionally characterized by a certain solubility parameter. In particular, lower polyfunctional alcohols such as ethylene glycol, propylene glycol, glycerol, 1,3-butanediol, di-glyceride, corresponding ethers and other compounds are mentioned as additives.

Materials based on such thermoplasticized starch and the molded parts made from them are characterized by a very limited use value. This is particularly due to the extremely pronounced hydrophilicity of the material. Accordingly, the replacement of polymer compounds of synthetic origin with a biodegradable polymer material of natural origin, which is sought in many areas today, is accordingly not possible or is possible only to a very limited extent.

More recent proposals deal with the attempt to combine thermoplasticised starch with synthetically obtained waterproof polymer compounds in such a way that the hydrophilic polymer compound based on starch is more resistant to resistance has hydrophilic solvents, but substantial portions of the material or molded part are formed by the starch. From the relevant literature, reference is made to PCT patent application WO 90/01 043. What is described here is the coating of hydrophilic polymers, such as starch, with selected aliphatic polyesters, which in turn can be degraded in particular by bacteria or fungi. In particular, the coating of molded parts made of starch with polyesters from lower hydroxycarboxylic acids, such as glycolic acid, lactic acid, hydroxybutyric acid and hydroxyvaleric acid, is described. Since such layer combinations adhere poorly to one another, it is proposed to improve the adhesion by previously treating the starch surface and / or by adding a solvent or swelling agent for the starch to the coating solution.

EP-A2 327 505 describes another route - albeit with the same objective. Described here are polymer mixed materials which are obtained from a melt of water-containing destructurized starch and at least one essentially water-insoluble synthetic thermoplastic polymer compound. The individual procedure is as follows: First, starch is treated in untreated or pretreated form with the addition of auxiliaries such as hydrogenated fatty acid triglycerides, lecithin and in particular water by treatment in an extruder at elevated temperatures - for example 175 ° C. - and the resulting temperatures increased intrinsic pressure, ther oplasticized starch obtained and processed into granules. The water content in the granulate is set approximately to the range of the water content of natural starch (approx. 17% by weight). These starch granules are then mixed in a predetermined mixture ratio with synthetic polymer compounds in the dry state. Examples of such thermoplastic water-insoluble polymers of synthetic origin are polyethylene, polystyrene, polyacetals, ethylene / acrylic acid copolymers and Ethylene / vinyl acetate copolymers. The respective polymer mixtures are then processed in a conventional manner into molded parts on an injection molding device at material temperatures of 165 ° C.

Further suggestions from the field concerned here of thermoplastically processable polymer mixtures based on starch can be found in EP-AI 0400 531 and 0400532 and in PCT application WO 90/10671. The last-mentioned publication contains, in particular, extensive information on the mixing and the thermoplastic digestion of the polymer compounds used in the presence of water in suitable extruders, and on the at least partial removal of the water from the mixture, expediently within the process step in the extruder.

The older German patent application P 4038 732.1 relates to materials and / or molded parts based on thermomechanically digested starch mixed with synthetic thermoplastic polymer compounds. These polymer-modified materials are produced by mixing native starch with aqueous polymer dispersions of the synthetic thermoplastic polymer compounds and, if desired, further low-molecular plasticizers, the multicomponent mixture at elevated temperatures and pressures with simultaneous intensive mixing and / or kneading to the starch digestion subject to the formation of the thermoplastically processable starch and, if desired, the shaping of the homogenized polymer mixture. The water content introduced via the aqueous dispersions of the synthetic polymer compounds is an integral part of the process which is used and effective in the digestion process for starch digestion. Suitable at least largely water-insoluble thermoplastic synthetic polymer compounds are, according to this older proposal by the applicant, for example emulsion (co) polymers, such as polyvinyl esters, poly (meth) acrylates and / or corresponding copolymers. Also mentioned are polyesters, polyamides and / or polyurethane resins, preference being given to those thermoplastic polymer compounds which have polar groups or molecular constituents and, if appropriate, combine with molecular constituents of a pronounced oleophilic character.

Subject one another prior German patent application the An¬ melderin according to P 41 21 111 are to materials and / or moldings on the basis of a correspondingly thermomechanically digested starch be modified in such a way that in a blend with ^'of the thermo-plasticized starch as a synthetic thermoplastic Poly Corresponding polyesters and / or polyamides are present, which are at least partially composed of raw materials based on renewable raw materials.

The further development now described below takes up the applicant's proposals in her two older German patent applications mentioned here according to P 40 38 732 and P 41 21 111 and modifies their teaching in the manner described below. For the purpose of completeness of the disclosure, the disclosure content of the two older patent applications is hereby expressly made the subject of the disclosure of the present invention.

The teaching of the present invention is based on the following concept: The thermomechanically digested starch should be present in admixture with selected thermoplastically processable polymer compounds which show oxidative reactivity through selected functional groups. The polymer mixture is produced from thermoplasticized starch and the incorporated synthetic polymer compound in the manner described in the applicant's earlier applications, with the exclusion of oxygen or air to the extent that a oxidative reaction of the mixed-in oxygen-reactive polymer component does not occur or does not occur significantly. A thermoplastically processable polymer mixture based on starch is obtained, which can either be processed directly in a shape-shaping manner known per se or can be stored practically indefinitely with the exclusion of oxygen or air. The molded body made of this polymer mixture, which is brought into the desired spatial shape, is then exposed to the action of oxygen, and in particular simply to the action of air. The oxidatively reactive groups of the mixed-in polymer component are thus activated and lead to crosslinking or at least partial crosslinking of the synthetic polymer material homogeneously mixed with the thermoplastic starch. As the most important result of this reaction, the water resistance of the starch-based polymer material is positively influenced. The value in use of corresponding polymer mixtures is thus substantially increased. Further details can be found below.

Subject of the invention

Accordingly, the subject matter of the invention "in a first embodiment are thermoplastically deformable materials based on a starch which is thermomechanically digested at elevated pressures and temperatures and with the addition of water and / or low molecular weight plasticizers and which contains mixed thermoplastic synthetic polymer compounds in an at least largely homogeneous mixture The characteristic of the invention lies in the new embodiment that these materials contain oxidatively crosslinking or oxidatively reactive alkyd resins as synthetic polymer compounds, The oxidatively reactive alkyd resins are in particular designed as air-drying compositions and, in a preferred embodiment, predominantly from raw materials based on renewable Raw materials built up. In a further embodiment, the invention relates to molded parts with increased strength and, in particular, increased water resistance based on the materials or material mixtures described above, which are characterized in that they are produced by shaping these polymer mixtures based on thermoplasticized starch and the oxidatively reactive alkyd resins ¬ and by access of oxygen, especially air, which contain alkyd resin component in an oxidatively reacted form.

Finally, the invention relates to the process for the production of the oxidatively reactive thermoplastic material mixtures and the use of these valuable material mixtures for the production of molded parts with improved performance properties, in particular with increased resistance to the influence of water and / or moisture.

Details of the teaching according to the invention

The essential core of the teaching according to the invention lies in the selection of the thermoplastically processable synthetic mixed components based on oxidatively reactive or crosslinkable alkyd resins and their incorporation into the starch-based basic material. The invention not only intends to implement the approach, which the applicant has not previously described, of reactively strengthening starch-based materials as formed molded parts by using oxidatively reactive mixture components. By a plurality portrayed in the following and more preferably Zu¬ set of elements are in ^{'unterschiedlichster,} improvements are possible in the field in question.

First of all, it is essential to define the oxidatively reactive alkyd resins. The term alkyd resins, in particular thermoplastic alkyd resins, is known to encompass polyesters made from polycarboxylic acids, polyols and monofunctional alcohols and / or Carboxylic acids. Oxidatively reactive alkyd resins are fundamentally known products on the market, in this respect reference can be made to the general specialist knowledge. For example, they can be used as base materials for air-drying or self-drying lacquers. Known commercial products are in particular also in the form of aqueous dispersions which contain the self-drying alkyd resins as finely particulate dispersed resin in a closed aqueous liquid phase. Air-reactive aqueous alkyd resin dispersions of this type are particularly suitable materials for the purposes of the invention.

The oxidative reactivity of such alkyd resin derivatives is generally derived from a content of olefinically unsaturated substituents on the alkyd resin polyester. In a manner known per se, such olefinically unsaturated reactive elements can be introduced into the alkyd resin molecule by incorporating unsaturated alcohols and / or by incorporating unsaturated carboxylic acids. Of particular interest here - especially in connection with the teaching according to the invention - are those representatives of the alkyd resin types mentioned which are at least largely based on natural substance-based constituents. Thus, monocarboxylic acids and / or monofunctional alcohols of natural origin can be used to derivatize the alkyd resins. When dicarboxylic acids and at least 3-functional alcohols are used in combination with monofunctional carboxylic acids and optionally further diols, corresponding monocarboxylic acid-derivatized alkyd resins are available, for example, which can be made oxidatively reactive or oxidatively crosslinkable by at least the monocarboxylic acids used partially olefinically unsaturated and / or polyunsaturated. In a manner known per se, the functionalities can of course also be used to prepare an oxidatively reactive alkyd resin modified with olefinically unsaturated alcohols. Natural product-based alkyd resins of the type which are particularly preferred according to the invention are based on glycerol as a 3-functional polyol component and fatty acids of natural origin as an onofunctional carboxylic acid component. The monofunctional reactants are used on average in such amounts that the desired reaction with dicarboxylic acids - for example phthalic acid or phthalic anhydride - becomes possible. At least predominantly natural product-based modified alkyd resins of this type are characterized, for example, in that more than 50% by weight and preferably between 60 and 70% by weight of the alkyd resin is formed from these natural product-based components, in particular glycerol and monofunctional fatty acids, while the rest are dicarboxylic acids and optionally additional diol components are present in the polymer molecule. "

For the purposes of the invention, the selection of the monofunctional alkyd resin constituents and in particular the corresponding fatty acids can be of particular importance. First of all, the use of olefinically simple and / or polyunsaturated carboxylic acids ensures that the alkyd resin is sufficiently reactive when oxygen or air enters. In a preferred embodiment, however, the teaching of the invention also intends to make the following further improvement accessible via these monofunctional carboxylic acid residues: It is known that starch is capable of straight-chain hydrocarbon residues of a higher C number - for example the hydrocarbon residues of straight-chain fatty acids with 12 to 20 carbon atoms - in the form of inclusion compounds. The straight-chain hydrocarbon residue is stored in the interior of the starch molecule in chelical structure. The so-called cage inclusion compounds, also called "clathrates", are formed. Regarding the relevant literature, reference is made, for example, to J. Szejtli et al. "Determination of the dissociation constants for a ylose- Inclusion compounds ", STARCH / strength 30 (1978), 85-91, T. Davies et al." Inclusion Complexes of Free Fatty Acids with Amylose ", STARCH / strength 32 (1980), 149-158 and E. Krüger et al. "Starch inclusion compounds and their importance in mashing", monthly journal for brewing science, issue 12/1984, 505 - 511.

The teaching of the invention makes use of this knowledge in a preferred embodiment as follows: in addition to the olefinically unsaturated substituents, the oxidatively crosslinking alkyd resins are modified with straight-chain saturated hydrocarbon residues of sufficient length, in particular with corresponding straight-chain fatty acid residues with, for example, 12 to 20 carbon atoms . These straight chain saturated substituents on the alkyd resin molecule are then capable of inclusion with the helix formation of the starch. In the thermomechanical digestion process of starch to be described in detail below, which is carried out according to the invention in the presence of the substituted alkyd resin component (s), conditions are created which lead to an interaction between the starch helix and that with a straight-chain one saturated hydrocarbon residues lead substituted alkyd resin. In this way, an additional bond is created between the two types of polymer in the finished product, which is characterized by increased strength in the molded article ultimately sought.

Particularly suitable for use in the context of the invention are those oxidatively reactive alkyd resin types of the type described which on the one hand contain olefinically unsaturated and preferably sufficiently long-chain substituents, but on the other hand also straight-chain sufficiently long-chain hydrocarbon radicals as substituents. Accordingly, alkyd resins of the type described which are substituted with mixtures of olefinically unsaturated and saturated straight-chain monocarboxylic acids are particularly suitable. It It has been found that mixing ratios of about 20 to 60 mol% and in particular about 30 to 50 mol% of the unsaturated carboxylic acid residues in admixture with the straight-chain fatty acid residues are particularly suitable, the mol% details relating to the mixture being here are based on saturated and unsaturated substituents - in particular corresponding monocarboxylic acid residues.

Alkyd resins of the type described can have, for example, average molecular weights in the range from approximately 3,000 to 20,000 and preferably in the range from approximately 3,000 to 10,000.

If the alkyd resins are used in the form of their aqueous dispersions in the form preferred according to the invention, it may again be desirable in a preferred embodiment to use self-emitting alkyd resin types of the type described. In this context, however, those alkyd resin types are particularly suitable which are free from solvent-mediating salt groups and whose emulsifying power is due in particular to built-in free hydroxyl and / or ether groups. However, the invention is not restricted to such self-emulsifying alkyd resin types.

The oxidatively reactive or crosslinking alkyd resins shown here and now used for the first time together with starch in the sense of the teaching according to the invention are preferably incorporated into the starch in the manner described in the earlier application P 40-38732 and thereby included in the thermomechanical starch digestion. To complete the description of the invention, reference is briefly made to the corresponding information in the earlier application.

The selected starch feed is intimately mixed with the aqueous alkyd resin dispersion. If necessary, additional aids, in particular the low molecular weight ones, are required Plasticizer and / or further water are added, whereupon this multicomponent mixture is subjected to starch digestion at elevated temperatures and pressures with simultaneous intensive mixing and / or kneading to form the thermoplastically processable starch. In this form, the aqueous phase of the mixed-in alkyd resin dispersion acts as a reactant essential to the invention in the starch digestion.

The proportion of the oxidatively reactive alkyd resin in the solid mixture - based on the solid mixture of starch and alkyd resin free of water and / or low molecular weight plasticizers - can be comparatively very small and nevertheless have a substantial effect in terms of product optimization in the finished product. Thus, 0.5 to 1% by weight of alkyd resin and in particular at least about 1 to 2% by weight of alkyd resin in the starch / alkyd resin solid mixture are effective mixture components in the sense of the teaching according to the invention. The amount of alkyd resin can, however, also be chosen to be higher and can, for example, make up up to about 50% by weight of the solid phase, here and in the following% by weight, again based on the solid mixture free of water and low molecular weight plasticizers. Particularly suitable ranges for the amount of alkyd resin additive are up to about 30% by weight and preferably up to about 10 to 15% by weight.

In a manner known per se, the solid mixtures for thermomechanical processing contain water and / or low molecular weight plasticizers in amounts of at least about 10% by weight, preferably in amounts of at least about 15% by weight and in particular in amounts in the range of about 25 to 55% by weight. The mixing ratios of the components can be within the following range numbers, which as a guideline are the weight percentages based on the total amount used for thermoplasticization. describe the mixture of fabrics used:

Starch 20 to 50% by weight;

Alkyd resin 1 to 35% by weight;

Water 5 to 30% by weight; low molecular plasticizer, especially glycerin 10 to 50 wt .-%.

All components described in the prior art for this purpose can be used as low molecular weight plasticizers, particularly suitable compounds are lower polyfunctional alcohols and / or their ethers, the glycerol already mentioned being a particularly suitable representative. Glycerin will often be used in amounts of about 15 to 35% by weight, based on the total mixture.

The starch to be used in the process can be of any origin. Starch suppliers such as potatoes, corn, rice, the usual types of cereals and the like are to be mentioned here primarily. The starch is generally used in powder form. If desired, it can be subjected to pretreatments, such as partial drying, acid washing and / or further pretreatments, in particular to physically modify the starch. The water content of the, in particular, natural starch feedstock can vary within a wide range and, for example, make up about 5 to 40% by weight, based on the starch feedstock. Usually, the water content of the starch feed will be at least about 10% by weight and is often in the range of about 10 to 25% by weight, based on the starch feed again.

The mixing and starch digestion process is carried out in devices such as those used for the thermoplastic digestion of starch with water and / or lower organic auxiliary components described type are known per se. The mixture and starch digestion is accordingly carried out in closed kneaders or preferably in extruders. The residence time and the processing conditions are coordinated with one another in such a way that both the thermomechanical starch digestion and the most homogeneous possible mixing of the plasticized alkyd resin mixture components are ensured.

The individual mixture components can be fed to the working device used in each case, for example the extruder, separately in the feed area and preferably continuously in the amount required in each case. When the multicomponent mixture is transported in the extruder, the desired homogenization and mixing process in particular takes place in the front sections. This is followed by a processing line which is kept at product temperatures and pressures which lead to the desired thermomechanical starch exclusion. At least here the product temperatures are above 100 ° C. and preferably at or above 120 ° C., whereby working conditions in the range up to approximately 170 ° C. can be preferred at least in the final phases of the mixing and starch digestion process. The resulting working pressure usually corresponds to the intrinsic pressure of the water-containing mixture of substances at the specified working temperature. The residence times of the multicomponent mixture under the working conditions are generally not more than at most about 30 minutes, preferably at most about 20 minutes. It may be expedient to work with residence times of the multicomponent mixture at least in the range of the temperature and pressure conditions for starch digestion of about 0.5 to 10 minutes, preferably in the range of about 2 to 5 minutes.

The homogenized polymer blend can be obtained as an extrudate. Here is the oxidative reaction of the Note the mixture of substances. The investigations by the applicant have shown that a freshly produced extrudate can be processed without any problems under normal working conditions, that is to say in particular with the entry of air, if this processing step is quickly connected to the production of the polymer blend. However, it is also possible to temporarily store the reactive extrudate for a practically unlimited period of time. To do this, however, it is necessary to allow atmospheric oxygen to enter the primary material - ie the extrudate, which is generally converted into granulate form. to exclude. Accordingly! The invention here provides for the absorption and storage of the reactive mass in an inert gas atmosphere. In particular nitrogen and carbon dioxide come into consideration as inert gases. It may also be desirable to protect the intake area of the mixing extruder appropriately with inert gas from the ingress of air and oxygen.

If desired, at least a portion of the water added for the mixing and digestion process can be withdrawn from the polymer blend before it is shaped. This is already possible by evaporating a corresponding amount of water in the course of the mixing and digestion process after the desired implementations have been sufficiently achieved.

Core of the teaching of the invention form the described Stoff¬ mixtures of the thermomechanically digested starch on the one hand and the oxidatively reactive Alk ^'ydharzen other. In one embodiment, the invention also provides for the use of further thermoplastic polymer compounds in the sense of the teaching of the aforementioned older patent applications by the applicant. The idea of at least largely predominantly natural substance-based substance mixtures is best met if corresponding natural substance-based mixture components are incorporated as additional polymers, as described, for example, in the earlier application P 41 21 111 are described. If such third-party components are used in the context of the teaching according to the invention, then it may be expedient to increase their amount to at most about 50% by weight and preferably to amounts of at most about 30% by weight, based on the pure solid mixture. restrict.

B e i s p i e l e

The following general information applies to the devices and raw materials used in the examples below:

a) Devices

The production of TPS (thermoplastic starch) blends requires the following process steps:

Conveying the components present as a liquid, dispersion, granulate or powder into an extruder; - ^' Compacting the extrusion mass into a compact solid; Melting the extrusion mass; Homogenization of the melt; Pumping the melt through an extrusion tool (nozzle).

In principle, screw extruders in a wide variety of designs are suitable for this, such as single-screw extruders or co-rotating or counter-rotating twin-screw extruders. Due to advantages known from the literature (see also Handbuch der Kunststoff- extrusionstechnik, Volume 1, Hanser-Verlag, 1989) such as

Self-cleaning of the screws, narrow range of dwell times. uniform product stress

a co-rotating twin-screw extruder with the following characteristics was used for the examples described below

Type Continua C37, manufacturer Werner & Pfleiderer drive power 7.6 Kw Length of the screws 960 mm L / D ratio 24

Through a modular system of screws and housings, conveyor, plasticizing, homogenizing, pressure and degassing zones were realized in accordance with the task. In addition, the screw housing was divided into two heating zones of the same length and independently controllable. The components in liquid and solid form were supplied with gravimetrically controlled dosing units (Schenek). The following extrusion parameters were generally set:

Temperature 100 - 150 ° C screw speed 100 rpm total throughput 6 - 18 kg / h

b) raw materials

The following raw materials were used to produce TPS blends based on starch / alkyd resin polyester:

Potato starch (e.g. Süd Starch GmbH or E sland Starch) with a water content of 17-20% or wheat starch with a water content of 10-15%.

Air-drying alkyd resin polyesters in the form of aqueous dispersions, commercial products from Jäger with the product names. "JÄGALYD" WE 57, WE 102, WE 156.

As plasticizers. Polyols with a boiling point of 150 ° C, such as propylene glycol or preferably glycerol used. c) Examples of the production of TPS blends based on starch / alkyd resin polvester (commercial product JÄGALYD WE 57)

The following examples show the composition of the TPS blends and the resulting product properties. Depending on the equipment, the components can be metered individually and, as in the examples, in the form of recipe-dependent mixtures (in each case for the liquid and solid components). The compositions given below represent the initial composition in mass%. The products are degassed to a water content of <10% by weight during the extrusion.

example 1

At a screw speed of 100 rpm and a temperature of 120 ° C (body temperature) h starch 4.51 kg / Ab¬ and a mixture of water, glycerin, and alkyd resin (WE 57) in a ratio of 1.5: ^'6: 2 , 5 metered into the extruder at 1.49 kg / h. The extrudate has the composition:

If the extrusion parameters are otherwise constant, starch is added at 4.30 kg / h and a mixture of water, glycerol and alkyd resin dispersion (WE 57) in a ratio of 1: 5.3: 3.8 at 1.70 kg / h. The resulting blends have the following composition:

Under the conditions mentioned (see Example 1), starch is mixed at 4.08 kg / h and a mixture of water, glycerol and alkyd resin dispersion (WE 57) in a ratio of 0.5: 4.7: 4.8 at 1.92 kg / h metered. The resulting extrudates have the composition:

The product was stored in granular form under nitrogen immediately after production. After 14 days of storage under nitrogen, the product was below the above Manufacturing conditions again thermoplastic extrudable, i.e. networking had not occurred.

d) Material properties

TPS blends according to Examples 1 to 3 were stored in air for 14 days and then had the following material properties:

Example tensile strength N / mm ^

1 6.5

2 6.8

3 6.0 These extrudates can no longer be replastified and were very resistant to water (only swelling, no disintegration).

Claims

Patent claims

1. Thermoplastically deformable materials based on a starch which is thermo-mechanically digested at elevated pressures and temperatures and with the addition of water and / or low-molecular plasticizers and which contains mixed-in thermoplastic synthetic polymer compounds in an at least largely homogeneous mixture, characterized in that that they contain oxidatively crosslinking alkyd resins as synthetic thermoplastic polymer compounds.

2. Materials according to claim 1, characterized in that the oxidatively crosslinking alkyd resins are air-drying.

3. Materials according to claims 1 and 2, characterized in that the oxidative crosslinking alkyds least ^'anteilswe ise, preferably predominantly from raw materials based on renewable resources are set up.

4. Materials according to claims 1 to 3, characterized in that their content of oxidatively crosslinking alkyd resins is derived from corresponding polymer dispersions which contain the alkyd resins as a disperse polymer phase in an aqueous liquid phase and worked into the starch together with this aqueous phase have been.

5. Materials according to claims 1 to 4, characterized in that oxidatively crosslinking alkyd resins are present which contain residues of unsaturated monocarboxylic acids, preferably long-chain monocarboxylic acids having at least 12 C atoms, for example 12 to 20 C atoms, on a polyester base molecule .

6. Materials according to claims 1 to 5, characterized in that the polyester base molecules of the alkyd resin are substituted with mixtures of saturated and olefinically unsaturated monocarboxylic acids, in particular corresponding straight-chain and preferably long-chain monocarboxylic acids, which are preferably at least 12 C in the case of saturated monocarboxylic acids -Atoms, for example 12 to 20 carbon atoms, contained in the molecule.

7. Materials according to claims 1 to 6, characterized in that about 20 to 60 mol%, preferably about 30 to 50 mol%, of the unsaturated monocarboxylic acid residues are present in the mixture of the saturated and unsaturated monocarboxylic acids or monocarboxylic acid residues - mol % here based on the sum of the saturated and unsaturated monocarboxylic acid residues.

8. Materials according to claims 1 to 7, characterized in that self-emulsifying oxidatively crosslinking alkyd resins are incorporated into the polymer mixture.

9. Materials according to claims 1 to 8, characterized in that they contain the oxidatively crosslinking alkyd resins in amounts below about 40% by weight, preferably in the range from about 1 to 35% by weight and advantageously in the range from about 1 to 15% .-%, ent¬ - wt .-% based on the solid mixture free of water and low molecular weight plasticizers.

10. Materials ^' according to claims 1 to 9, characterized in that they contain water and / or low molecular weight plasticizers in amounts of at least about 10% by weight, preferably at least about 15% by weight and in particular in amounts of about 20 up to 40 wt .-% - based on the total mixture - contain.

11. Materials according to claims 1 to 10, characterized in that they contain, as low molecular weight plasticizers, lower polyfunctional alcohols, in particular glycerol, and / or their ethers, the proportion of which is preferably in the range from about 10 to 50% by weight, expediently can be in the range from about 15 to 35% by weight, based in each case on the total mixture.

12. Molded parts with increased strength and, in particular, increased water resistance based on a starch which is thermomechanically digested at elevated pressures and temperatures and with the addition of water and / or low-molecular plasticizing agents and which contains mixed synthetic polymer compounds in an at least largely homogeneous mixture, characterized in that that they are produced by shaping materials according to claims 1 to 11 and by the addition of oxygen, especially air, which contain alkyd resins in an oxidatively reacted form.

13. A method for producing the polymer-modified materials or molded parts obtained therefrom according to claims 1 to 12, characterized in that native starch with the aqueous. Dispersions of the oxidatively crosslinking alkyd resins and, if desired, the further low molecular weight plasticizers and / or water are mixed, the multicomponent mixture is subjected to starch digestion at elevated temperatures and pressures with simultaneous intensive mixing and / or kneading to form the thermoplastically processable starch and, if desired, this Homogenized polymer mixture processed immediately afterwards to shape or the polymer mixture is stored in the absence of air.

14. The method according to claim 13, characterized in that the mixing process and the starch digestion, preferably under Exclusion of air or oxygen, carried out in closed kneaders or preferably extruders, and the residence time and the processing conditions are coordinated in such a way that both thermomechanical starch digestion and homogeneous mixing of the alkyd resins are ensured.

15. The method according to claims 13 and 14, characterized in that with product temperatures above 100 ° C and preferably above 120 ° C, ^' in particular in the range of about 140 to 170 ° C, at least in the final phases of the mixing and starch digestion process is working.

16. The method according to claims 13 to 15, characterized in that with residence times of the multi-substance mixture under working conditions in the range up to about 30 minutes, preferably in the range of about 0.5 to 10 minutes and in particular m continuous process and under the autogenous pressure that arises at the process temperature in the system.

17. The method according to claims 13 to 16, characterized in that mixing and digestion of the polymer components is carried out in heated extruders to which the starch - preferably as a starch powder - and the aqueous alkyd resin dispersions, as well as any other low molecular weight plasticizers used in the feed section are expediently supplied separately are obtained while the homogenized and digested polymer mixture - if desired after a partial removal of excess water - as extrudate and is preferably collected and stored under inert gas.

18. Use of the polymer-modified materials according to claims 1 to 11, as a thermoplastic material for the production of Air access to molded articles to be solidified, for example packaging materials.