DE102013017024A1 - polymer composition - Google Patents

Abstract

Shown and described is a polymer composition containing, based on the total weight of the polymer composition, at least the following components: (a) 5 to 50 wt% destructurized starch and / or starch derivative, (b) 20 to 70 wt% aliphatic-aromatic Copolyester, (c) 10 to 50 wt .-% polyhydroxyalkanoate and (d) 5 to 25 wt .-% polylactic acid. Such polymer compositions are characterized by a high proportion of bio-based carbon and despite the presence of increased amounts of polyhydroxyalkanoate, even after storage, no significant embrittlement or deterioration of the mechanical property profile. Furthermore, production processes for the polymer composition according to the invention and their use for producing films, moldings or fibers are shown and described.

Description

The invention relates to a polymer composition and a process for its preparation. Furthermore, the invention relates to the use of the polymer composition for the production of films, moldings or fibers as well as such products containing the polymer composition according to the invention.

From the point of view of conservation of fossil resources, waste disposal and reduction of CO ₂ emissions, it is desirable to replace the widespread conventional plastics based on fossil raw material sources with plastics that can be obtained at least partially or completely from renewable raw materials. Polymers based at least partially or entirely on renewable resources are also called "bio-based" polymers.

Biodegradable plastics are not necessarily biobased at the same time. So there are some plastics from fossil, non-renewable resources that are biodegradable. The biodegradability is not bound to the raw material base, but depends solely on the chemical structure of the material and its ability to convert by biological activity in naturally occurring metabolic end products.

In practice, starch-based and aromatic-aliphatic copolyester polymer compositions have proven to be biodegradable polymer compositions having excellent mechanical properties.

Such a plasticizer-free thermoplastic polymer composition based on starch, which is particularly suitable for blown film extrusion, flat film extrusion and injection molding of completely biodegradable products, under the trade name "BIOPLASTIC ^® GF 106/02" by the firm BIOTEC GmbH & Co. KG in Emmerich (Germany ) commercially available.

The preparation and properties of plasticizer-free thermoplastic polymer blends based on starch and aromatic-aliphatic copolyesters are described, for example, in the publications EP 0 596 437 B1 and EP 02 203 511 B1 described.

The main applications of biodegradable polymer compositions are in the packaging and catering sector. In addition, there are applications in agriculture and horticulture as well as in the pharmaceutical and medical sector. Particularly relevant are biodegradable polymer compositions for the manufacture of garbage bags, carrier bags, disposable tableware (cups, cups, plates, cutlery), packaging films, bottles, fruit and vegetable trays, loose-fill chips, mulch films, Flowerpots and the like.

Although the highest possible content of renewable raw materials would be desirable for some fields of application (eg compostable garbage bags), the completely biodegradable polymer compositions hitherto available on the market and film products produced therefrom consist predominantly of polymeric materials of fossil origin, such as, for example, aliphatic-aromatic copolyesters , To ensure acceptable mechanical properties, the content of renewable raw materials (eg starch) in these polymer compositions is generally well below 50%.

Although a further increase of the starch content in existing starch-based polymer blends would be desirable for economic and ecological reasons, this is not readily possible, since an increase in the starch content is usually accompanied by a considerable deterioration in the mechanical properties of the polymer.

In addition to starch and starch derivatives, polyhydroxyalkanoates (PHA) are also promising bio-based replacement materials for polymers of fossil origin. PHAs are naturally occurring linear polyesters of hydroxy acids, which are formed by many bacteria as a reserve for carbon and energy and are deposited in the form of granules inside the cell. From the state of the art, industrial biotechnological PHA production using natural or genetically modified bacterial strains or plants is known. For an overview of the different PHAs and their production, see the chapter "Polyhydroxyalkanoates" in "Handbook of Biodegradable Polymers", pages 219 to 256, published by Rapra Technologies Limited, 2005 ,

A major disadvantage of PHAs, however, is that films produced therefrom are relatively brittle or fragile and the mechanical properties in this regard deteriorate further during the storage of the films. Thus, the use of larger amounts of completely bio-based PHA failed, such as. As PHB, PHBV and PHBH, in film formulations so far mainly on the uncontrolled, slow recrystallization of the PHA polymers following their processing into films. The resulting by the Nachkristallization Sphärolithe probably act as impurities in the film and thus seem to a significant loss of important mechanical film properties, such. As elongation at break and dielectric strength to lead.

The prior art discloses various approaches for improving the mechanical properties of PHA-containing polymer compositions, in particular in the area of injection molding applications nucleating agents, such as boron nitride (BN), talc (Mg ₃ [Si ₄ O ₁₀ (OH) ₂ ] ) and lime (CaCO ₃ ) particles, cyclodextrins, polyvinyl alcohol particles, terbium oxide, saccharin, thymine, uracil, orotic acid or cyanuric acid. The known methods have in common that the addition of such nucleating agent accelerates nucleation and crystal growth. This is to ensure that even during the cooling process after the processing of the PHA-containing polymer composition almost complete crystallization occurs rapidly and uncontrolled recrystallization is thereby prevented. Furthermore, the nucleating agents cause the crystallization to start at many points at the same time, so that no large spherulites but rather many small crystallites are formed. In contrast to spherulites, whose separating surfaces can form pronounced, macroscopically active structural weak points, a high crystallite density generally does not have a negative effect on the mechanical properties of the polymer compositions.

A disadvantage of the use of nucleating agents, however, is that they cause additional costs and labor. Moreover, the use of nucleating agents in PHA-containing polymer compositions has so far provided satisfactory results only in the field of injection molding applications. In the important application of film production, the addition of nucleating agents can hardly prevent the delayed postcrystallization and associated embrittlement and deterioration of the mechanical properties during the storage of the films. This is due to the very rapid cooling time of the melt in continuous film production compared to injection molding, which counteracts crystallization which is much faster at higher temperatures.

In the production of films from PHA-containing polymer compositions, the most promising route so far has been to minimize the amount of PHA and relatively large amounts (eg greater than 80% by weight, based on the amount of PHA formed) of a synthetic polymer component to combine excellent mechanical properties. It is also common in such films, to ensure satisfactory mechanical characteristics, the proportion of biobased polymers, such as starch, as small as possible, for example, a total of less than 30 wt .-% based on the total polymer composition to keep.

However, this approach is difficult to even impossible to achieve with the aim of keeping the proportion of bio-based carbon in polymer compositions as high as possible (eg greater than 50%). On the one hand, in the case of generic polymer compositions, it is precisely the biotechnologically produced PHA and the starch that contribute to the bio-based carbon. In addition, most synthetic polymers, especially those commonly used because of their biodegradability aliphatic-aromatic copolyester, so far produced exclusively from fossil raw materials. An increase in their share would therefore only lead to a deterioration of the bio-based carbon balance.

It is an object of the present invention to provide a starch-based biodegradable polymer composition which contains PHA levels relevant to the biocarbon balance of the composition and yet can be processed into films having only a slight delay Have subsequent crystallization. A further object of the invention was to provide a biodegradable polymer composition which has the highest possible proportion of bio-based polymers, such as starch and PHA, with simultaneously excellent mechanical properties.

This object is achieved by the polymer composition recited in claims 1 and 28, the method specified in claim 21, the use specified in claim 29 and the products mentioned in claim 30.

Advantageous embodiments of the invention are specified in the dependent claims and are explained below as the general inventive concept in detail.

• a) 5 bis 50 Gew.-% destrukturierte Stärke und/oder Stärkederivat,
• b) 20 bis 70 Gew.-% aliphatisch-aromatischer Copolyester,
• c) 10 bis 50 Gew.-% Polyhydroxyalkanoat,
• d) 5 bis 25 Gew.-% Polymilchsäure.

The polymer composition according to the invention contains at least the following components, based on the total weight of the polymer composition:

• a) from 5 to 50% by weight of destructurized starch and / or starch derivative,
• b) from 20 to 70% by weight of aliphatic-aromatic copolyester,
• c) 10 to 50% by weight of polyhydroxyalkanoate,
• d) 5 to 25 wt .-% polylactic acid.

An essential feature of the polymer composition according to the invention is the combination of relatively large amounts of the bio-based polymers starch or starch derivative (5 to 50 wt .-%) and PHA (10 to 50 wt .-%) with 5 to 25 wt .-% polylactic acid. Surprisingly, it has been found that the presence even small amounts of polylactic acid, such as 5 or 7.5 wt .-%, in the production of starch and PHA-containing polymeric composition to a significant improvement in the mechanical properties of the material, in particular its tensile strength, Elongation at break and / or dart drop measured after 24 hours of storage results. Usually, similar mixtures already after 24 hours have a significantly changed compared to the freshly manufactured state mechanical profile (curing, embrittlement), which is due to the described, uncontrolled Nachkristallisation.

Without wishing to be bound by any particular scientific theory, the addition of PLA appears to counteract the slow post-crystallization that would otherwise occur with PHA-containing polymer compositions. Polymer compositions according to the invention retain their good mechanical properties despite PHA contents of 10 to 50 wt .-% even after storage for example 24 h and show virtually no embrittlement. The effect of PLA addition is surprising since pure PLA, as a linear partially crystalline polymer itself, is relatively brittle and therefore was not expected to counteract embrittlement of the polymer composition.

The polymer composition according to the invention is distinguished by excellent mechanical properties. Thus, films made from the polymer composition preferably have a tensile strength according to DIN 53455 from 5 to 60 N / mm ² , in particular from 10 to 40 N / mm ² and / or an elongation at break according to DIN 53455 from 100 to 800%, especially from 200 to 600%.

In contrast to the polymer compositions known from the prior art with comparatively high proportions of PHA, the films produced from the polymer composition according to the invention retain these mechanical properties during storage as much as possible.

Thus, it is possible for the first time with the teaching according to the invention to produce starch-based polymer compositions having a PHA content of 10 to 50% by weight, films produced from the polymer composition having no, only slight or significantly delayed post-crystallization.

To measure this effect, the mechanical properties over the first 24 hours after film production are considered and reported below. This information relates to a comparison of film samples that were tested immediately after film production and those that were examined 24 hours after film production. In this case, film production means the completion of the film production process (time after coiler / rolling up of the film and cooling to room temperature). "Immediately after film production" means within the first 30 minutes after completion of the film production process.

The effect of only a slight recrystallization of the films according to the invention is directly detectable for the person skilled in the art if, after 24 hours of storage, he touches such a film with his hands and pulls or tears it apart. The film according to the invention still feels soft and elastic and shows no or only slight signs of embrittlement compared to the state of the film immediately after its production. In contrast, prior art comparative films containing equal amounts of PHA but no or less than 5 weight percent PLA feel hard and brittle after 24 hours of storage and crack rapidly.

The feature "no or only slight recrystallization" can be detected not only qualitatively but also quantitatively by means of DSC (Differential Scanning Calorimetry). If a polymer sample subjected to a defined heating / cooling program, so are phase transitions, which with a Energy conversion (glass transition, crystallization, melting, etc.), in the form of exothermic (eg crystallization) or endothermic (eg melting) peaks recorded. The precondition for the appearance of a peak in the DSC measurement is therefore that the phase transition takes place during the measurement, that is to say when the temperature program is run through. Thus, an amorphous sample which crystallizes during heating produces an exothermic peak. However, if the crystallization of the sample has already taken place before the measurement (for example during the storage of the sample), the energy conversion of the phase transition has already taken place before the beginning of the DSC measurement and generates the corresponding energy conversion and the associated peak during the measurement then no more.

Crystallization peaks can usually be detected on the first heating up of freshly processed, PHA-based materials in the DSC (the sample introduced into the measuring device is still largely amorphous and crystallizes during the measurement). In contrast, a stored over several hours / days (and recrystallized during storage) material of the same composition that peak no longer or only in attenuated form. The existence of crystallites in the material is detectable by the appearance of (endothermic) melting peaks after reaching the melting temperature during the DSC measurement. For the melting (destroying) of crystallites, the amount of energy previously released during crystallization is needed again and therefore appears as an endothermic melting peak in the DSC diagram. The size (area) of the crystallization or melting peaks can be determined and compared by means of common software for the evaluation of DSC diagrams.

According to one embodiment, films according to the invention show only a slight recrystallization within the first 24 hours after storage. This is characterized in that the size (area) of the crystallization peak measured 24 hours after storage has decreased by at most 60%, preferably at most 50%, more preferably at most 40% or 30%, as compared with the size (area) of the crystallization peak immediately after film production.

According to another embodiment, the polymer compositions according to the invention can also be characterized in that the degree of crystallinity of a film produced from the polymer composition increases in the first 24 hours after preparation by at most 20 percentage points, in particular at most 15 or at most 10 percentage points. For example, with a crystallinity level immediately after film formation of, for example, 40%, an increase of 20 percentage points means that the degree of crystallinity measured after 24 hours is 60%. The terms crystallinity, degree of crystallinity and crystallinity are used in the literature as synonyms and designate the crystalline portion of a semi-crystalline solid.

The degrees of crystallization specified above are by weight and not by volume and are determined calorimetrically by determination of the heat of fusion by fusion (cf., for example, US Pat Adolf Franck: Plastics Compendium, Vogel book publishing, 6th edition, chapter 3.2.4 on pages 92 and 93 or Menges et al .: Material Science Plastics, Hanser Verlag, 5th edition, chapter 8.2.4.2, page 263 to 265 ).

The remaining or only slight recrystallization can also be determined microscopically in the polymer compositions according to the invention. Experiments have shown that with polymer compositions according to the invention, in particular subsequent (ie during storage) spherulite formation is largely prevented or greatly delayed and reduced.

Sphärolites are radially symmetric crystal aggregates and are typical structural units for semi-crystalline thermoplastic materials. The size and number of spherulites in a polymer influences the mechanical properties of the plastic. A disadvantage of the PHA-containing polymer compositions described in the prior art is that spherulites form on their storage by subsequent crystallization. As a result, the mechanical properties of the films after storage and delivery to the customer often no longer correspond to the values originally measured directly after production. In particular, there is a significant deterioration in tensile strength, elongation at break and dart-drop values. This is probably due to the macroscopically effective impurities (interfaces or edges of the spherulites) in the film.

According to one embodiment of the invention, films containing polymer compositions according to the invention exhibit less than 5 spherulites on an area of 100 .mu.m.times.100 .mu.m (average of 10 evaluations of corresponding image excerpts) even after 24 hours of storage post-production, as viewed through a polarizing microscope. Since spherulites are crystalline regions and thus birefringent, they can be detected by polarization microscopy. The appearance is different and depending on the exact polymer composition. As a rule, spherulites are recognized as circular objects and / or on the basis of the typical pattern ("Maltese cross") whose dark bars are aligned parallel to the polarization direction of the polarizer and analyzer of the microscope.

The remaining, only slight or greatly delayed post-crystallization in the polymer compositions of the invention is also due to the fact that important mechanical characteristics do not or only insignificantly worsen during storage of the polymer composition and / or films produced therefrom.

Practical tests have shown that the tensile strength, a measure of the film hardness, measured after DIN EN ISO 527 a film made from the polymer composition according to the invention remains largely stable over the first 24 hours after film production. In this case, to a great extent stable means in particular that the tensile strength increases by at most 20%, preferably at most 15%, or at most 10% or 5%. Preferably, the tensile strength remains measured after DIN EN ISO 527 a film prepared from the polymer composition according to the invention also 14 days after film production largely stable.

Also the dart drop value, a measure of the dielectric strength, according to ASTM D-1709 a film produced from the polymer composition according to the invention remains largely stable over the first 24 hours after film production. To a great extent stable here means in particular that the dart drop value decreases by at most 20%, preferably at most 15%, or at most 10% or 5%. Preferably, the dart drop value remains measured after ASTM D-1709 a film prepared from the polymer composition according to the invention also 14 days after film production largely stable.

Furthermore, polymer composition according to the invention is characterized in that the elongation at break, a measure of the elasticity, according to DIN 53455 a film made from the polymer composition remains largely stable over the first 24 hours after film production. To a great extent stable here means in particular that the elongation at break decreases by at most 15%, preferably at most 10%, or at most 5%. Preferably, the elongation at break remains measured after DIN 53455 a film prepared from the polymer composition according to the invention also 14 days after film production largely stable.

Noteworthy with respect to the polymer compositions according to the invention are the good tear strength values in the direction of extrusion (MD, machine direction), which also do not deteriorate severely within 24 hours of storage after film production. In the case of polymer compositions with similarly high proportions of PHA which are known from the prior art, a short-term deterioration in the tear strength in the extrusion direction can be observed in particular. In the extrusion direction, the undesired post-crystallization is particularly noticeable, since linear polymers such as PHA align in the extrusion direction and also crystallize in this direction, whereby the tear strength in the extrusion direction compared to the transverse direction is significantly deteriorated.

According to a further embodiment, the polymer compositions according to the invention are characterized in that the tensile strength in the direction of extrusion (MD) according to DIN 53455 a film made from the polymer composition remains largely stable over the first 24 hours after film production. To a great extent stable here means in particular that the tensile strength in the direction of extrusion (MD) decreases by at most 20%, preferably at most 15%, or at most 10% or 5%.

According to a preferred embodiment of the invention, the polymer composition according to the invention is according to EN 13432 biological degradable, especially fully biodegradable.

According to a further preferred embodiment of the invention, the polymer composition according to the invention has thermoplastic properties. Preferably, the polymer composition is thermoplastically processable.

The starch or starch derivative used to prepare the polymer composition according to the invention is preferably obtained from potato, maize, tapioca or rice. Starch derivative as used herein means modified or functionalized starch. The starch derivative used is preferably starch whose free OH groups are at least partially substituted. In question comes, for example, with ether and / or ester groups modified starch. Further examples of suitable starch derivatives are hydrophobized or hydrophilized starch, in particular z. As hydroxypropyl starch or carboxymethyl starch.

Preferably, the destructurized starch contained in the polymer composition of the invention was formed in the preparation of the polymer composition from native potato starch, tapioca starch, rice starch and corn starch by mechanical and / or thermal destructuring.

According to the invention, the polymer composition contains from 10 to 50% by weight, based on the total weight of the polymer composition, of destructurized starch and / or starch derivative. According to a preferred embodiment of the invention, the polymer composition contains from 15 to 50% by weight, preferably from 20 to 50% by weight, more preferably from 25 to 45% by weight, most preferably from 25 to 40% by weight of destructurized starch and / or Starch derivative, in each case based on the total weight of the polymer composition. Whenever "starch and / or starch derivative" is mentioned here, it also includes mixtures of different starches and / or different starch derivatives.

In the polymer composition according to the invention, the starch or the starch derivative is in destructurized form. Destructured means that the granular, crystalline structure of native starch has been completely or at least largely destroyed. This can easily be determined, for example, when viewing cross-sections in the scanning electron microscope. Alternatively, the starch phase of the polymer composition can be isolated and examined under a polarizing microscope for the presence of crystalline constituents.

For the purposes of this invention, destructurized starch is to be distinguished from cases in which native starch is used merely as a filler and the granular structure of the starch is at least partially retained.

Destructured starch may conveniently be present in the form of (optionally prefabricated) plasticizer-containing thermoplastic starch (TPS) in the polymer composition according to the invention. However, the destructurized starch in the polymer composition according to the invention is preferably as free from plasticizer as possible.

In order to be able to obtain destructurized starch even without addition of carbon-containing plasticizers, native starch is preferably homogenized together with at least one hydrophobic polymer and at a sufficiently high water content under the action of high shear forces and temperatures. The water is preferably removed again by drying during or at the end of the homogenization. The preparation of such a plasticizer-free destructured starch in polymer blends with aromatic-aliphatic copolyesters is disclosed, for example, in the publications EP 0 596 437 B1 and EP 02 203 511 B1 described.

The polymer composition of the present invention, according to a preferred embodiment, contains less than 5% by weight, more preferably less than 2.5% by weight and most preferably less than 1% by weight or less than 0.5% by weight of carbon-containing plasticizers. In one embodiment, these carbon-containing plasticizers are glycerol and / or sorbitol. Further examples of carbon-containing plasticizers are arabinose, lycose, xylose, glucose, fructose, mannose, allose, altrose, galactose, gulose, iodosis, inositol, sorbose, talitol and monoethoxylate, monopropoxylate and monoacetate derivatives thereof, and ethylene, ethylene glycol , Propylene glycol, ethylene diglycol, propylene diglycol, ethylene triglycol, propylene triglycol, polyethylene glycol, polypropylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-, 1,3-, 1,4-butanediol, 1,5-pentanediol, 1 , 6-, 1,5-hexanediol, 1,2,6-, 1,3,5-hexanetriol, neopentyl glycol, trimethylolpropane, pentaerythritol, sorbitol and their acetate, ethoxylate and propoxylate derivatives.

The polymer composition of the invention further preferably contains less than about 10% by weight of low molecular weight substances and is thus substantially free from plasticizer. Low molecular weight substances in the context of the invention are understood to mean substances having a molecular weight of less than 500 g / mol, in particular less than 250 g / mol. Low molecular weight substances according to the invention are in particular water, glycerol, sorbitol and / or mixtures thereof.

According to a preferred embodiment of the invention, the polymer composition according to the invention contains less than 7% by weight, in particular less than 5% by weight, preferably less than 3% by weight or 1.5% by weight, based on the total composition, of low molecular weight substances.

The polymer composition according to the invention contains from 20 to 70% by weight, preferably from 20 to 65% by weight, more preferably from 20 to 60% by weight, particularly preferably from 30 to 58% by weight, more preferably from 30 to 55% by weight , most preferably 30 to 50 wt .-% aliphatic-aromatic copolyester, each based on the total weight of the polymer composition. If "aliphatic-aromatic copolyester" is mentioned here, it also includes mixtures of different aliphatic-aromatic copolyesters.

For the polymer composition according to the invention are in particular aliphatic-aromatic copolyesters in question, according to EN 13432 are biodegradable and / or have a glass transition temperature (Tg) less than 0 ° C, especially less than -4 ° C, more preferably less than -10 ° C, even more preferably less than -20 ° C and most preferably less than -30 ° C. Further, the aliphatic-aromatic copolyesters contained in the polymer composition of the present invention are preferably thermoplastic.

According to a particularly preferred embodiment of the invention is used as the aliphatic-aromatic copolyester, a random copolyester based on at least adipic acid and / or sebacic acid. More preferably, it is a copolyester or random copolyester based on 1,4-butanediol, adipic acid or sebacic acid and terephthalic acid or terephthalic acid derivative (for example dimethyl terephthalate DMT). This may in particular have a glass transition temperature (Tg) of -25 to -40 ° C, in particular -30 to -35 ° C, and / or a melting range of 100 to 120 ° C, in particular 105 to 115 ° C.

According to a further embodiment of the invention, the aliphatic-aromatic copolyester is essentially prepared from fossil raw materials and contains according to ASTM 6866 less than 5% bio-based carbon.

The polymer composition of the invention contains from 10 to 50% by weight of polyhydroxyalkanoate, based on the total weight of the polymer composition. According to a preferred embodiment, the polymer composition contains 15 to 45 wt .-%, in particular 15 to 40 wt .-%, more preferably 15 to 30 wt .-% polyhydroxyalkanoate, each based on the total weight of the polymer composition. Whenever "polyhydroxyalkanoate" is mentioned here, it also includes mixtures of different polyhydroxyalkanoates.

A particular aspect of the polymer composition according to the invention is that they contain polyhydroxyalkanoates in an amount of 10% by weight or more, in particular also 12.5% by weight or more, preferably 15, 18, 19 or 20% by weight or more can, without the products produced from the polymer composition, such as films, undergo considerable post-crystallization or embrittlement during storage.

The teaching according to the invention makes it possible for the first time to be able to introduce larger amounts of polyhydroxyalkanoate into a starch-based polymer composition without having to accept a serious deterioration of the mechanical characteristics. This makes it possible to increase the proportions of polyhydroxyalkanoate and destructured starch or starch derivative to the extent that the polymer composition according to the invention ASTM 6866 contains at least 50% bio-based carbon and still has satisfactory mechanical properties.

A convenient size for the bio-based carbon balance of the polymer composition of the invention is the ratio of polyhydroxyalkanoate (which is typically biobased) to the amount of aliphatic-aromatic copolyester present (usually of fossil origin) or the total amount thereof. According to a particularly preferred embodiment of the invention, the amount of components c) [polyhydroxyalkanoate] present in the polymer composition is at least 20% by weight, based on the total amount of components b) and c) contained in the polymer composition [total amount of aliphatic-aromatic copolyester and polyhydroxyalkanoate].

If polyhydroxyalkanoate is mentioned here, it means polyhydroxy fatty acids which contain monomers having a chain length of at least 4C atoms. Polylactic acid is thus z. For example, no polyhydroxyalkanoate according to the invention, poly-3-hydroxybutyrate (PHB) or poly-4-hydroxybutyrate (P4HB) already.

According to the invention, the polyhydroxyalkanoate used is preferably a polyhydroxyalkanoate which comprises repeating monomer units of the formula (1) [-O-CHR-CH ₂ -CO-] (1), wherein R is an alkyl group of the formula C _n H _{2n + 1} and n is a number from 1 to 15, preferably from 1 to 6.

Poly(3-hydroxybutyrat-co-3-hydroxyvalerat) (PHBV),

und Poly(3-hydroxybutyrat-co-3-hydroxyhexanoat) (PHBH)

und Mischungen daraus. Optimal results are obtained when the polyhydroxyalkanoate is selected from poly-3-hydroxybutyrate (PHB),

Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV),

and poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH)

and mixtures thereof.

Particularly good results are obtained when the ratio m: n in the above structural formulas is from 95: 5 to 85:15, particularly preferably from 90:10 to 88:12. According to a particularly preferred embodiment, the polyhydroxyalkanoate contains or consists of PHBH. Practical experiments have shown that a PHBH with a molar proportion of 3-hydroxyhexanoate of 5 to 15 mol%, particularly preferably 7 to 13 mol% or 10 to 13 mol%, in each case based on the total amount of PHBH, gives very good results.

According to a preferred embodiment, the polyhydroxyalkanoate is biobased and / or biotechnologically produced.

Polyhydroxyalkanoates for the purposes of this invention have, in particular, molecular weights _{M.sub.w of} from 100,000 to 1,000,000, preferably from 300,000 to 600,000, and / or melting points in the range from 100 to 190.degree.

The polymer composition according to the invention contains from 5 to 25% by weight of polylactic acid, based on the total weight of the polymer composition. According to a preferred embodiment, the polymer composition contains 5 to 20 wt .-%, in particular 5 to 15 wt .-%, more preferably 5 to 12 wt .-% polylactic acid, each based on the total weight of the polymer composition.

Particularly practical results are obtained according to the invention when the amount of polylactic acid is chosen such that the total amount of the components a) [starch and / or starch derivative] and d) [polylactic acid] contained in the polymer composition together is more than 30% by weight on the total weight of the polymer composition.

The polymer composition according to the invention may further comprise, as further constituent, an epoxide group-containing polymer, which is preferably an epoxide group-containing copolymer. Suitable polymers or copolymers containing epoxide groups are, in particular, those which have a molecular weight M _{w of} from 1,000 to 25,000, in particular from 3,000 to 10,000.

Preferably, the epoxy group-containing polymer is a glycidyl (meth) acrylate-containing polymer. A suitable glycidyl (meth) acrylate-containing polymer is, for example, a copolymer of (a) styrene and / or ethylene and / or methyl methacrylate and / or methyl acrylate and (b) glycidyl (meth) acrylate. Particularly suitable as the glycidyl (meth) acrylate-containing polymer is a copolymer selected from the group consisting of styrene-methyl methacrylate-glycidyl methacrylate, ethylene-methyl acrylate-glycidyl methacrylate and ethylene-glycidyl methacrylate. Therein, glycidyl (meth) acrylate is preferably in an amount of 1 to 60% by weight, more preferably 5 to 55% by weight, more preferably 45 to 52% by weight, based on the total composition of the glycidyl (meth) acrylate-containing polymer , contain.

As epoxide-containing polymers are also epoxy-containing copolymers based on styrene, ethylene, acrylic acid esters and / or methacrylic acid in question.

The mixture preferably contains 0.01 to 5 wt .-%, in particular 0.05 to 3 wt .-%, more preferably 0.1 to 2 wt .-% epoxy-containing polymer, based on the total composition.

For many applications, it is advantageous if the polymer composition according to ASTM 6866 contains at least 50% bio-based carbon.

The teaching of the invention allows for the first time the use of larger amounts of polyhydroxyalkanoate and starch or starch derivative in polymer compositions without adverse effects on the mechanical properties. According to the invention, therefore, a minimum content of 50% of bio-based carbon according to ASTM 6866 even if the aliphatic-aromatic copolyester also contained in the polymer composition is essentially made of fossil raw materials or according to ASTM 6866 contains less than 5%, in particular no bio-based carbon.

According to a preferred embodiment, at least 90% by weight, preferably at least 95% by weight or at least 98% by weight, of the polymer composition according to the invention are obtained according to the invention ASTM 6866 contained bio-based carbon from the components a) [starch or starch derivative] and / or c) [polyhydroxyalkanoate].

In addition to the main constituents starch or starch derivative, aliphatic-aromatic copolyesters, polyhydroxyalkanoate and polylactic acid, the polymer composition according to the invention may contain further constituents, in particular further polymers and / or customary additives, for example processing aids, plasticizers, stabilizers, anti-flaming agents and / or fillers.

With the teachings of the present invention, it is possible to dispense with the addition of nucleating agent provided in the prior art and still to prevent deterioration of important mechanical properties during storage in generic, PHA-containing polymer compositions. According to one embodiment of the invention, the polymer composition contains no or only minor amounts (eg less than 10% by weight or less than 3% by weight, based on the total composition) of nucleating agents, such as boron nitride (BN), talc (Mg ₃ [Si ₄ O ₁₀ (OH) ₂ ]) and lime (CaCO ₃ ) particles, cyclodextrins, polyvinyl alcohol particles, terbium oxide, saccharin, thymine, uracil, orotic acid and / or cyanuric acid. According to a further embodiment of the invention, the polymer composition contains less than 10% by weight of CaCO ₃ and / or less than 3% by weight of talc, in each case based on the total composition. Preferably, CaCO ₃ and / or talc in the polymer composition of the present invention are contained in total in an amount of less than 3% by weight, and most preferably less than 1% by weight, based on the total composition, or at most in traces.

The invention further provides methods by which it is possible to obtain the polymer compositions described above.

• (i) Herstellen eines Gemischs enthaltend, bezogen auf das Gesamtgewicht des Gemischs, wenigstens die folgenden Komponenten:
• a) 5 bis 50 Gew.-% destrukturierte Stärke und/oder Stärkederivat,
• b) 20 bis 70 Gew.-% aliphatisch-aromatischer Copolyester,
• c) 10 bis 50 Gew.-% Polyhydroxyalkanoat,
• d) 5 bis 25 Gew.-% Polymilchsäure.
• (ii) Homogenisieren des Gemischs unter Zuführen von thermischer und/oder mechanischer Energie;
• (iii) Einstellen des Wassergehalts des Gemischs, so dass das Endprodukt einen Wassergehalt von kleiner etwa 5 Gew.-%, bezogen auf die Gesamtzusammensetzung des Gemischs, aufweist.

In principle, the processes according to the invention comprise the following steps, wherein the individual steps can be carried out simultaneously or successively and in any order and frequency:

• (i) preparing a mixture containing, based on the total weight of the mixture, at least the following components:
• a) from 5 to 50% by weight of destructurized starch and / or starch derivative,
• b) from 20 to 70% by weight of aliphatic-aromatic copolyester,
• c) 10 to 50% by weight of polyhydroxyalkanoate,
• d) 5 to 25 wt .-% polylactic acid.
• (ii) homogenizing the mixture by applying thermal and / or mechanical energy;
• (iii) adjusting the water content of the mixture such that the final product has a water content of less than about 5% by weight, based on the total composition of the mixture.

The process steps are preferably carried out in the order indicated above.

• – ein Polymerblend A enthaltend die Komponenten a) [destrukturierte Stärke und/oder Stärkederivat] und b) [aliphatisch-aromatischer Copolyester] erhalten wird, dessen Wassergehalt kleiner etwa 5 Gew.-%, vorzugsweise kleiner etwa 1 Gew.-% bezogen auf das Gesamtgewicht des Polymerblends A, beträgt, und anschließend
• – unter Verwendung des Polymerblends A und Zumischung der Komponententen c) [Polyhydroxyalkanoat] und d) [Polymilchsäure] eine Polymerzusammensetzung wie oben beschrieben hergestellt wird.

The preparation of the mixture of the components of the composition according to the invention can be carried out in one or more stages. Particularly good results are obtained in practice if the preparation of the mixture in step (i) takes place in two stages, in such a way that initially

• A polymer blend A comprising the components a) [destructurized starch and / or starch derivative] and b) [aliphatic-aromatic copolyester], the water content of which is less than about 5% by weight, preferably less than about 1% by weight Total weight of the polymer blend A, is, and then
• Using polymer blend A and admixing the components c) [polyhydroxyalkanoate] and d) [polylactic acid], a polymer composition is prepared as described above.

Preferably, polymer blend A is prepared in an extruder and used as granules in the subsequent step. As A polymer blend may also be a ready-made, commercially available polymer blend, such as the & under the trade name "BIOPLASTIC ^® GF 106/02" by the company BIOTEC GmbH & Co. KG in Emmerich (Germany) available products are used.

According to the invention, it is preferable to keep the water content of the polymer composition as low as possible. Preferably, the water content of the mixture is adjusted to less than 3% by weight, more preferably less than 1.5% by weight, and most preferably less than 1% by weight, based on the total composition.

Water contents given here refer to the material leaving the extruder. To determine the water content, a sample of melted extrudate is collected at the nozzle exit on exit from the extruder in a closable vessel and this hermetically sealed. It is important to ensure that the vessel is filled as completely as possible with extrudate, so that the inclusion of air in the vessel is kept as low as possible. After cooling the closed vessel, this is opened, taken a sample and the water content determined by Karl Fischer titration.

Preferably, the water content is adjusted by drying during homogenization. The drying process can be carried out, for example, by degassing the mixture or the melt, expediently by removing steam during homogenization or extrusion.

The inventive method provides that the mixture is homogenized. Homogenization can be carried out by any measures known to those skilled in the art of plastics engineering. Preferably, the mixture is homogenized by dispersing, stirring, kneading and / or extruding. According to a preferred embodiment of the invention, shear forces act on the mixture during homogenization. Suitable preparation processes for starch-containing thermoplastic polymers, which can also be used analogously to the preparation of the polymeric material according to the invention, are described, for example, in the publications EP 0 596 437 B1 and EP 02 203 511 B1 described.

According to a preferred embodiment of the invention, the mixture is heated during the homogenization (for example in the extruder), preferably to a temperature of 90 to 250 ° C., in particular 130 to 220 ° C.

The polymer compositions of the invention are suitable for a variety of purposes. In particular, the compositions are suitable for the production of moldings, films or fibers. Due to the lack of or only slight recrystallization, the polymer compositions of the invention are particularly suitable for film production. The invention also relates to moldings, films and fibers produced from the polymer compositions according to the invention.

Inventive films may be blown, flat or cast films. Preferred film thicknesses for blown films according to the invention are from 12 to 100 .mu.m, for flat films of 150 to 500 .mu.m according to the invention and from 10 to 500 .mu.m for cast films according to the invention.

The principle of the invention will be explained in more detail below with reference to examples.

For the comparative and working examples, the following materials were used: polylactic acid, PLA (INGEO 2003D, NATUREWORKS); Poly (butylene adipate-co-terephthalate), PBAT (ECOFLEX F blend C 1201, BASF); Poly (hydroxybutyrate-co-hexanoate), PHBH (AONILEX X 151 A, KANEKA); Poly (hydroxybutyrate-co-valerate), PHBV (ENMAT Y 1000 P, TIANAN); native potato starch (EMSLANDSTÄRKE); epoxide group-containing copolymer, PMGMA (JONCRYL ADR 4370 S, BASF)

Example 1 (comparative example)

The following formulations A and B were compounded with a twin-screw extruder of the Werner & Pfleiderer type (COPERION) ZSK 40, screw diameter 40 mm, L / D = 42 (metered proportions in percentage by mass): Table 1: Formulations A B PBAT 41.5 41.5 PHBH 29.0 14.5 Strength 29.5 29.5 PHBV - 14.5

The following compounding parameters were observed: Tab. 2: Temperature profile ZSK 40 Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 Zone 8 jet 25 ° C 150 ° C 150 ° C 140 ° C 130 ° C 130 ° C 130 ° C 130 ° C 130 ° C Melting temperature at nozzle outlet: 127 ° C (A), 131 ° C (B) Rotation speed: 120 min ^-1 (A), 160 min ^-1 (B) throughput: 40 kg / h Degasing: active (vacuum, zone 7)

The granules A and B were melted with a single-screw extruder of the type COLLIN 30 (DR. COLLIN), screw diameter 30 mm, L / D = 33, and further processed to blown film.

The following processing parameters were set: Tab. 3: Temperature profile COLLIN 30 Zone 1 Zone 2 Zone 3 Zone 4 jet 165 ° C 170 ° C 170 ° C 170 ° C 170 ° C Rotation speed: 52 min ^-1 (A), 51 min ^-1 (B) ring die: ∅ = 80 mm Annular gap: 1.05 mm Melting temperature at nozzle outlet: 157 ° C (A), 152 ° C (B) blow: 2.5 Lying width film tube: 310 mm Film thickness: 22 μm

The mechanical properties of the films were determined after a storage time of 24 h at room temperature and ambient atmosphere as follows: Tab. 4: Mechanical properties of the films after 24 h foil Specific Dart Drop [g / μm] ASTM D 1709 Tensile strength [MPa] EN ISO 527 Elongation at break [%] EN ISO 527 Tear strength [N / mm] EN ISO 6383 Puncture resistance EN 14477 MD TD MD TD MD TD ε _B [mm] W _B [y / m] A 5.8 24.9 24.2 460 504 68 144 2.6 78.7 B 6.7 27.1 24.6 426 481 57 136 2.5 80.1

In the films A and B, significant Nachkristallisationseffekte occurred in the form of curing and embrittlement, as a comparison of the mechanical properties of the films showed directly after production and after 24 storage.

Particularly striking in the results from Example 1 (see Table 4) is the low breakdown strength (specific dart drop) and the low tear propagation resistance in the machine direction (MD) compared to the transverse direction (TD) for both formulations A and B. This result shows to a noticeable orientation of the linear PHBH polymer strands with resulting post-crystallization during film blowing. It had been suggested that (unintentional) postcrystallization, which is known to occur preferentially preferentially in chemically uniform polymer structures, in a polymer mixture (PHBV / PHBH, 50/50, formulation B), if not completely inhibited, could be noticeably slowed down. But this was not the case. The admixture of PHBV as a further polymer component could not effectively slow down the recrystallization and the resulting embrittlement and brittleness of the films.

Example 2:

The following recipe C was compounded with a twin-screw extruder of the Werner & Pfleiderer type (COPERION) ZSK 40, screw diameter 40 mm, L / D = 42 (metered proportions in percent by mass): Table 5: Formulations C PBAT 41.5 PHBH 21.5 Strength 29.5 PLA 7.5

The following compounding parameters were observed: Tab. 6: Temperature profile ZSK 40 Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 Zone 8 jet 25 ° C 150 ° C 150 ° C 140 ° C 130 ° C 130 ° C 130 ° C 130 ° C 130 ° C Melting temperature at nozzle outlet: 133 ° C Rotation speed: 140 min ^-1 throughput: 40 kg / h Degasing: active (vacuum, zone 7) Water content: > 1% by weight (measured after exiting the extruder)

As before granules A and B in Example 1, granules C was melted with a single-screw extruder of the type COLLIN 30 (DR. COLLIN), screw diameter 30 mm, L / D = 33, and further processed to blown film.

The following processing parameters were set: Tab. 7: Temperature profile COLLIN 30 Zone 1 Zone 2 Zone 3 Zone 4 jet 165 ° C 170 ° C 170 ° C 170 ° C 170 ° C Rotation speed: 53 min ^-1 ring die: ∅ = 80 mm Annular gap: 1.05 mm Melting temperature at nozzle outlet: 157 ° C blow: 2.5 Lying width film tube: 310 mm Film thickness: 22 μm

The mechanical properties of the film were determined after a storage time of 24 h at room temperature and ambient atmosphere as follows: Tab. 8: Mechanical properties of the film after 24 h foil Specific Dart Drop [g / μm] ASTM D 1709 Tensile strength [MPa] EN ISO 527 Elongation at break [%] EN ISO 527 Tear strength [N / mm] EN ISO 6383 Puncture resistance EN 14477 MD TD MD TD MD TD ε _B [mm] W _B [y / m] C 8.4 20.6 19.9 545 599 130 147 2.2 77.0

The results summarized in Table 8 illustrate the markedly increased values for the breakdown strength (specific dart drop) and tear propagation resistance in the extrusion direction (MD) compared with formulations A and B in Comparative Example 1. Obviously, the addition of even small amounts of PLA to a starch-based blend containing PHBH causes a marked increase in mechanical stability. This is surprising, since pure PLA is known as a relatively brittle and brittle material, with high tensile strength and relatively low puncture and tear propagation resistance. Obviously, even low levels of PLA are able to markedly retard the crystallization of PHA after processing.

Example 3 (two-step process):

The following polymer blend A was compounded with a twin-screw extruder of the Werner & Pfleiderer type (COPERION) ZSK 70, screw diameter 70 mm, L / D = 36 (metered proportions in percent by mass): Table 9: Formulations Polymer blend A PBAT 57.4 Strength 42.6

The following compounding parameters were observed: Tab. 10: Temperature profile ZSK 70 Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 Zone 8 Zone 9 Zone 10 Zone 11 jet 25 ° C 190 ° C 190 ° C 190 ° C 170 ° C 170 ° C 170 ° C 170 ° C 155 ° C 100 ° C 150 ° C 140 ° C Melting temperature at nozzle outlet: 163 ° C Rotation speed: 205 min ^-1 throughput: 400 kg / h Degasing: active (vacuum, zone 9) Water content: <1% by weight (measured after exiting the extruder)

With a twin-screw extruder of the Werner & Pfleiderer type (COPERION) ZSK 70, screw diameter 70 mm, L / D = 36, the following formulation D was subsequently compounded with the granules of polymer blend A (metered proportions in mass percent): Tab. 11: recipes D Polymer blend A 70.7 PHBH 21.8 PLA 6.6 PMGMA 0.9

The following compounding parameters were observed: Tab. 12: Temperature profile ZSK 70 Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 Zone 8 Zone 9 Zone 10 jet 25 ° C 160 ° C 160 ° C 130 ° C 130 ° C 120 ° C 140 ° C 170 ° C 140 ° C 140 ° C 150 ° C Melting temperature at nozzle outlet: 138 ° C Rotation speed: 180 min ^-1 throughput: 300 kg / h Degasing: active (vacuum, zone 8) Water content: <1% by weight (measured after exiting the extruder)

As before granules A, B and C in Examples 1 and 2, also granules D with a single-screw extruder of the type COLLIN 30 (DR. COLLIN), screw diameter 30 mm, L / D = 33, melted and further processed to blown film.

The following processing parameters were set: Tab. 13: Temperature profile COLLIN 30 Zone 1 Zone 2 Zone 3 Zone 4 jet 165 ° C 170 ° C 170 ° C 170 ° C 170 ° C Rotation speed: 53 min ^-1 ring die: ∅ = 80 mm Annular gap: 1.05 mm Melting temperature at nozzle outlet: 157 ° C blow: 2.5 Lying width film tube: 310 mm Film thickness: 22 μm

The mechanical properties of the film were determined after a storage time of 24 h at room temperature and ambient atmosphere as follows: Tab. 14: Mechanical properties of the film after 24 h foil Specific Dart Drop [g / μm] ASTM D 1709 Tensile strength [MPa] EN ISO 527 Elongation at break [%] EN ISO 527 Tear strength [N / mm] EN ISO 6383 Puncture resistance EN 14477 MD TD MD TD MD TD ε _B [mm] W _B [y / m] D 9.6 28.2 24.6 202 458 21.83 43.16 N / A N / A

The results summarized in Table 14 show, compared with Comparative Example 1, a significantly increased impact strength (specific dart drop) and a higher tensile strength in the extrusion direction (MD). Compared with Example 2, there is an increased dielectric strength (specific dart drop) and a significantly increased tensile strength, especially in the direction of extrusion (MD). At the same time, the values for elongation at break and tear propagation resistance are reduced. Obviously, certain mechanical properties can be modified by adding small amounts of an epoxide group-containing copolymer.

The invention has been described above with reference to exemplary embodiments. It is understood that the invention is not limited to the described embodiments. Rather, various modifications and modifications are possible for the person skilled in the art within the scope of the invention, and the scope of protection of the invention is defined in particular by the following patent claims.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0596437 B1 [0006, 0049, 0086]
• EP 02203511 B1 [0006, 0049, 0086]

Cited non-patent literature

• "Polyhydroxyalkanoates" in "Handbook of Biodegradable Polymers", pages 219 to 256, Publisher Rapra Technologies Limited, 2005 [0010]
• DIN 53455 [0022]
• DIN 53455 [0022]
• Adolf Franck: Plastics Compendium, Vogel book publishing, 6th edition, chapter 3.2.4 on page 92 and 93 or Menges et al.: Material Science Plastics, Hanser Verlag, 5th edition, chapter 8.2.4.2, pages 263 to 265 [0031 ]
• DIN EN ISO 527 [0036]
• DIN EN ISO 527 [0036]
• ASTM D-1709 [0037]
• ASTM D-1709 [0037]
• DIN 53455 [0038]
• DIN 53455 [0038]
• DIN 53455 [0040]
• EN 13432 biological [0041]
• EN 13432 [0054]
• ASTM 6866 [0056]
• ASTM 6866 [0059]
• ASTM 6866 [0073]
• ASTM 6866 [0074]
• ASTM 6866 [0074]
• ASTM 6866 [0075]
• ASTM D 1709 [0096]
• EN ISO 527 [0096]
• EN ISO 527 [0096]
• EN ISO 6383 [0096]
• EN 14477 [0096]
• ASTM D 1709 [0103]
• EN ISO 527 [0103]
• EN ISO 527 [0103]
• EN ISO 6383 [0103]
• EN 14477 [0103]
• ASTM D 1709 [0111]
• EN ISO 527 [0111]
• EN ISO 527 [0111]
• EN ISO 6383 [0111]
• EN 14477 [0111]

Claims (30)

Polymer composition comprising, based on the total weight of the polymer composition, at least the following components: a) from 5 to 50% by weight of destructurized starch and / or starch derivative, b) from 20 to 70% by weight of aliphatic-aromatic copolyester, c) 10 to 50% by weight of polyhydroxyalkanoate, d) 5 to 25 wt .-% polylactic acid. A polymer composition according to claim 1, characterized in that the polymer composition contains 10 to 50 wt .-%, 15 to 50 wt .-%, 20 to 50 wt .-%, 25 to 45 wt .-% or 25 to 40 wt .-% destructured starch and / or starch derivative, each based on the total weight of the polymer composition. Polymer composition according to claim 1 or 2, characterized in that the polymer composition contains 20 to 65 wt .-%, 20 to 60 wt .-%, 30 to 58 wt .-%, 30 to 55 wt .-% or 30 to 50 wt. -% aliphatic-aromatic copolyester, each based on the total weight of the polymer composition contains. Polymer composition according to one of the preceding claims, characterized in that the polymer composition contains 15 to 45 wt .-%, 15 to 40 wt .-% or 15 to 30 wt .-% polyhydroxyalkanoate, each based on the total weight of the polymer composition. Polymer composition according to one of the preceding claims, characterized in that the polymer composition contains 5 to 20 wt .-%, in particular 5 to 15 wt .-%, more preferably 5 to 12 wt .-% polylactic acid, each based on the total weight of the polymer composition , Polymer composition according to one of the preceding claims, characterized in that the amount of components c) present in the polymer composition is at least 20% by weight, based on the total amount of components b) and c) contained in the polymer composition. A polymer composition according to any one of the preceding claims, characterized in that the total amount of the components contained in the polymer composition a) starch and / or starch derivative and d) polylactic acid together more than 30 wt .-% based on the total weight of the polymer composition. Polymer composition according to any one of the preceding claims, characterized in that the polymer composition according to ASTM 6866 contains at least 50% of bio-based carbon. A polymer composition according to claim 8, characterized in that the aliphatic-aromatic copolyester is made substantially from fossil raw materials and contains less than 5% bio-based carbon according to ASTM 6866. Polymer composition according to one of the preceding claims, characterized in that the polymer composition according to EN 13432 is biodegradable, in particular completely biodegradable. A polymer composition according to any one of the preceding claims, characterized in that the polyhydroxyalkanoate comprises repeating monomer units of the formula (1) [-O-CHR-CH ₂ -CO-] (1), wherein R is an alkyl group of the formula C _n H _{2n + 1} and n is a number from 1 to 15 or from 1 to 6. A polymer composition according to claim 11, characterized in that the polyhydroxyalkanoate is selected from PHB, PHBV and PHBH or contains one or more of these polymers. Polymer composition according to one of the preceding claims, characterized in that the aliphatic-aromatic copolyester used is a random copolyester based on at least adipic or sebacic acid. Polymer composition according to one of the preceding claims, characterized in that the aliphatic-aromatic copolyester used is a random copolyester based on 1,4-butanediol, adipic acid and / or sebacic acid and terephthalic acid or terephthalic acid derivative, in particular dimethyl terephthalate DMT. Polymer composition according to one of the preceding claims, characterized in that a film produced from the polymer composition has no or only a slight recrystallization. Polymer composition according to one of the preceding claims, characterized in that the tensile strength of a film produced from the polymer composition remains largely stable over the first 24 hours after film production, ie in particular increases by at most 20%. Polymer composition according to one of the preceding claims, characterized in that the dart drop value according to ASTM D-1709 of a film produced from the polymer composition remains largely stable over the first 24 hours after film production, ie in particular decreases by at most 20%. Polymer composition according to one of the preceding claims, characterized in that the elongation at break according to DIN 53455 a produced from the polymer composition film remains largely stable over the first 24 hours after film production, ie in particular decreases by at most 15%. Polymer composition according to one of the preceding claims, characterized in that the tear strength in the extrusion direction according to DIN 53455 a produced from the polymer composition film remains largely stable over the first 24 hours after film production, ie in particular decreases by at most 20%. Polymer composition according to one of the preceding claims, characterized in that the polymer composition contains no or less than 5 wt .-% carbon-containing plasticizer, in particular glycerol or sorbitol. Process for the preparation of a polymer composition according to any one of Claims 1 to 20, characterized by: (i) preparing a mixture comprising, based on the total weight of the mixture, at least the following components: a) from 5 to 50% by weight of destructurized starch and / or starch derivative, b) from 20 to 70% by weight of aliphatic-aromatic copolyester, c) 10 to 50% by weight of polyhydroxyalkanoate, d) 5 to 25 wt .-% polylactic acid. (ii) homogenizing the mixture by applying thermal and / or mechanical energy; (iii) adjusting the water content of the mixture such that the final product has a water content of less than about 5% by weight, based on the total composition of the mixture. A method according to claim 21, characterized in that the homogenization of the mixture by dispersing, action of shear forces on the mixture, stirring, kneading and / or extrusion takes place. Method according to one of claims 21 or 22, characterized in that the mixture during homogenization or extrusion to a temperature of 90 to 250 ° C, in particular 130 to 220 ° C, is heated. Method according to one of claims 21 to 23, characterized in that the water content of the mixture to less than 3 wt .-%, more preferably less than 1.5 wt .-% and most preferably less than 1 wt .-%, based on the total composition, is set. Method according to one of claims 21 to 24, characterized in that the water content of the mixture is adjusted during the homogenization. Method according to one of claims 21 to 25, characterized in that the water content of the mixture by degassing of the mixture, in particular by degassing of the melt, is adjusted and / / or the water content of the mixture is adjusted by drying the mixture during homogenization or extrusion. Method according to one of claims 21 to 26, characterized in that the preparation of the mixture in step (i) takes place in two stages, in such a way that first in - a polymer blend A containing the components a) and b) is obtained, wherein the Water content is less than about 5 wt .-%, based on the total weight of the polymer blend A, and then - using the polymer blend A and admixture of components c) and d), a polymer composition according to any one of claims 1 to 20 is prepared. Polymer composition obtainable by the processes according to one of Claims 21 to 27. Use of a polymer composition according to any one of claims 1 to 20 or 28 for the production of moldings, films or fibers. Moldings, films or fibers containing a polymer composition according to any one of claims 1 to 20 or 28.