DE29619016U1 - Biodegradable plastic product - Google Patents

Description

Applicant:

Mr. Dr.-Ing. ₍ Mr. Dipl.-Biol.

Wolf-Rüdiger Müller ' Dietmar Schönberger Honigwiesenstr. 3 7 Lehenstraße 9a

70563 Stuttgart 70180 Stuttgart

2921 007 W/sch 31.10.1996-

WP96/4

Title: Biodegradable plastic product

DESCRIPTION

The invention relates to a biodegradable plastic product according to the preamble of claim

Biodegradable plastics and plastic products are available in large numbers today. The degradability of these substances is based on their respective structural and chemical composition. They are either of natural origin or are artificially or biotechnologically synthesized.

Naturally occurring polymers include polysaccharides such as cellulose and its chemically obtained derivatives, e.g. cellophane, cellulose nitrates, cellulose acetates and cellulose butyrates, as well as starch and its derivatives (Lit.: A. Pfeil: Biological

degradable plastics, Vol. 425, Renningen: Expert-Verlag 1994). Other important polysaccharides are xanthan, dextran and pullulan. Polyacids, on the other hand, can be of natural or artificial origin. Polyoxyacids, e.g. polyglycolic acid and polyhydroxy acids, have gained particular importance. The most important representatives include polyhydroxy fatty acids, in particular poly-(3-hydroxybutyric acid) PHB and its copolymer with hydroxyvaleric acid, poly-(3-hydroxybutyric acid co-)hydroxyvaleric acid PHB/HV. Also important are biodegradable waxes and oils, their derivatives and polymers based on lactic acid, so-called polylactides.

Synthetically produced biodegradable polymers include polyalcohols, polyethers, polyesters and polyurethanes. Important representatives of these groups of substances are poly-£-caprolactone (PCL; Union Carbide, USA), aliphatic polyesters made from glycols and carboxylic acids available under the trade name BIONOLLE (Showa Denko, Japan), copolyesters (press release K'95, 2102 from BASF AG), polyesteramides (press release ATI 968 d, e from Bayer AG) and copolymers thereof. Mixtures of two or more of these substances are also biodegradable, as filled and/or fiber-reinforced systems and in the form of homo- or heterophasic polymer blends, also in filled and reinforced modifiers. Examples of this are, on the one hand, with native or derivatized fibers (cellulose, flax,

Hemp, groundwood, ramie, jute, sisal, kenaf, etc.) reinforced and/or filled with granular, native or modified starch and biodegradable polymers. On the other hand, these are polymer blends made of destructured, thermoplastically processable starch (TPS) and a polymer component consisting of one or more biodegradable, synthetically or biotechnologically produced polymers. Well-known trade names for the latter group of materials include MATER BI and NOVON.

Biodegradable plastic products can of course also contain numerous additives such as stabilizers, lubricants, emulsifiers, hardeners, plasticizers, pigments, fillers, etc. Additives also include release agents, antistatic agents and flame retardants. Elias provides an overview: "Polymers: From monomers and macromolecules to materials/ an introduction", 1996. These additives are converted together with the polymer into a molding compound with homogeneous additive distribution through a dynamic melt mixing process using an extruder, rolling mill, mixer, kneader or another plasticizing, mixing and hot-nogenizing unit.

The biological degradation can take place under aerobic, anoxic or anaerobic conditions. The polymers serve as hydrogen and carbon donors for the

Microorganisms. For degradation under aerobic conditions, oxygen is required as a terminal hydrogen acceptor. The process can be summarised as follows if the polymer is completely degraded:

P ₁ + O ₂ + X ₀ => S _IP + X + CO ₂ + H ₂ O + Δ�EEgr;

P ₁ :' Polymer test start

X _Oi : Biomass test start

X : Biomass end of test

S _IP : Intermediary products

&Dgr;&EEgr; : volume-related heat of reaction

When degradation occurs under anoxia, the respiratory process known as nitrate respiration takes place, in which nitrate is used as a terminal hydrogen acceptor instead of oxygen. In summary, the equation for complete degradation of the polymer can be described as follows:

P ₁ + NO ₃ + X ₀ => SI _P + X + N ₂ + CO ₂ + OH + Δ�EEgr;

Under anaerobic conditions, the last electron acceptor is a reducible compound, but not atmospheric oxygen or nitrate. In general, anaerobic processes result in less biomass formation.

Anaerobic degradation can be divided into several steps (cf. Schlegel, Allgemeine Mikrobiologie, 7th edition 1992, Thieme-Verlagt, Stuttgart). In summary, this anaerobic degradation with complete degradation of the polymer can be described as follows:

P ₁ + X ₀ => S _IP + CO ₂ + CH ₄ + X + Δ�EEgr;

The biodegradability of polymers is determined under well-defined standardized test conditions. However, the degradation behavior in the environment depends largely on the conditions. These include the presence of active microorganisms, the quality and quantity of nutrients, pH value, temperature and the presence or absence of inhibitors. In addition, there are factors that result from the structure and processing of the plastics (see A. Pfeil, op. cit.). The actual degradation process in nature therefore does not correspond to the ideal conditions that are set in the degradation tests. Biological degradation often occurs more slowly than theoretically determined, sometimes not at all.

These considerations apply above all to the biodegradability of plastic waste. Another area of application for biodegradable polymers is the treatment of groundwater or surface water, especially into drinking water or aquarium water. This

The field of application is described in the German patents DE 34 10 412 C3 and DE 4 0 28 312 C2. For the denitrification of water, heterotrophic denitrifiers can be immobilized in a carrier matrix together with biodegradable plastics that serve as hydrogen and carbon donors, such as polyhydroxybutyric acid. The faster the plastic is broken down, the better the water can be denitrified.

The object of the invention is to provide a biodegradable plastic product of the above-mentioned type, the degradability of which is largely independent of the environmental conditions.

The solution is that it contains at least one additive that supports biodegradability.

The degradation of both conventional and inventive plastic products is carried out by enzymes, which are formed in the biofilm by the microorganisms. The degradation is thus coupled with the growth of the biomass (the microorganisms in the biofilm), which can be represented in a simplified manner by so-called "biomass equations". The biomass growth has so far been limited by the supply of nutrient salts, trace elements, etc., while carbon is present in excess in the plastic product. This supply has so far been dependent on the diffusion currents

on the biofilm, which in turn are determined by the individual concentrations in the surrounding environment. The degradation behavior was therefore only satisfactory when sufficient biomass was available, whereby the presence of microorganisms in itself is not limiting because they are ubiquitous, i.e. present everywhere.

The essentially limiting nutrients are now incorporated into the polymer matrix according to the invention. In this way, the diffusion flow limitation in a nutrient-poor environment is eliminated by appropriate nutrient supply. This significantly reduces the environment dependency of the degradation behavior. By choosing the concentrations, the degradation behavior of biodegradable polymers can be specifically adjusted under different environment conditions in aqueous systems, in compost and in the soil. Biodegradable polymers can thus be degraded faster and more easily in different environments, e.g. in the aquatic environment, on the compost, under aerobic, anoxic or anaerobic conditions. In addition, the performance of the microorganisms for denitrification is improved, i.e. larger nitrogen loads can be treated.

For example, degradation is possible in oligotrophic waters or on compost. In nutrient-poor ecosystems (for example

In the case of a surface (e.g. sea or lake bed), the degradation of these polymers is possible despite the lack of phosphate and other salts. Large quantities of such "plastic" waste that ends up in the sea or lakes can be degraded without limiting factors. It is conceivable, for example, that with suitable material that enables anaerobic degradation, lost fishing nets could be decomposed in the foreseeable future.

The biodegradable plastic product according to the invention can also be used, for example, as granules in drinking water containing nitrates in a denitrification reactor. In this case, the loss of additional nutrients and biomass can be minimized, since the biomass adheres to the granules as a film and the nutrients are gradually released from the polymer matrix as it degrades. By selecting the nutrient concentration in the plastic product according to the invention, the degradation behavior can be specifically adjusted depending on the nitrogen load.

In wastewater treatment, imbalances in nutrient loads (e.g. in one-sided industrial wastewater and dyeing wastewater) can be compensated by a suitable composition of the granules.

It is conceivable that the plastic product according to the invention could be used in reactors for nitrification and

Denitrification of aquarium water. It is important to note that nitrification and denitrification can take place simultaneously in one reactor if the granules have pores in which anoxic zones can form due to the diffusion conditions. By adding phosphate to increase bacterial growth and iron salts as co-factors for nitrate reductase and nitrogen monoxide reductase, denitrification in the polymer pores is increased. On a larger scale, the same system can be used in intensive fish farming in recirculation systems. This can significantly reduce fresh water consumption.

If there is an excess of plant nutrients in the matrix of plastic products according to the invention, these can be used as fertilizer when they are gradually released by the plants. In a similar way, instead of plant nutrients, plant protection agents and the like can also be incorporated into the matrix and slowly released during decomposition. One conceivable way of doing this is to reuse such polymer waste as decomposable plant pots or covering films, mulch films, seed tapes, active ingredient dispensers, etc. or in shredded form as a type of long-term fertilizer. In addition, by promoting the growth of microorganisms, the soil is sustainably revitalized, which leads to an improvement in its structure. For these applications, PCL, for example, is suitable due to its good

processing properties' (good formability and miscibility, low defined melting point).

There are numerous possibilities for producing the biodegradable plastic product according to the invention. Basically, the desired additives - depending on the application - are usually incorporated homogeneously into the existing plastic. This process step is preferably carried out in the melt state of the plastic, using an extruder, rolling mill, mixer, kneader or another plasticizing, mixing and homogenizing unit. The resulting plasticized product made of plastic and the homogeneously distributed additives can be granulated or processed directly into semi-finished products, profiles, films, tapes, hollow bodies, fibers and other consumer goods or industrial products.

To produce the plastic product according to the invention required for the embodiments described below, an extruder type ZSK 3 0 from Werner & Pfleiderer was used. This is a co-rotating, closely meshing twin-screw extruder. This type of extruder is often used for compounding (filling, reinforcing, mixing, destructuring, dividing and separating, homogenizing, blending, carrying out chemical reactions).

• «

■ ··

However, the relatively small amounts of additive to be incorporated compared to filling plastics also allow the use of single-screw extruders, as used in state-of-the-art extrusion systems (film, hollow body blow molding, sheet, profile and spinning systems).

In addition to the premix of plastic and additives, the additives can be introduced directly into the plastic melt, individually or separately, at various points in the extruder. This avoids the problems of segregation that occur during premixing, the additives are subjected to less stress and the resulting residence time, thermal stress and homogeneity can be influenced very flexibly. This also makes it possible to

> liquid additives using a pump and injection valve

to mix.

It is also conceivable to incorporate the additives without passing through the melt state of the plastic component, i.e. the production of granulate agglomerates. Starting from a homogeneous premix of the additives and the plastic in powder form, this only needs to be pressed and possibly sintered, provided that the granules can be used directly (e.g. for denitrification, etc.). Such granules can also be suitable as a precursor for injection molding or blow molding. Sensitive

· ·

In this approach, additives are exposed to the melting temperature of the plastic only once and not twice as in extruder compounding. This sintering process would also allow the production of a porous structure with increased surface area and enable rapid release of nutrients (if necessary).

Such a foam structure of the granules, with the advantages of the resulting surface enlargement and microcavity formation, can also be obtained in starch-containing plastic products using the water contained in the starch component or a biocompatible foaming agent (e.g. sodium bicarbonate + citric acid).

The above-mentioned premix of the additives and the plastic (powder or granulate) could also be processed directly into molded parts using an injection molding machine, provided that the plasticizing unit of this machine has a sufficient homogenizing effect.

In multiphase systems, the additives do not have to be evenly distributed (across the phases). Rather, the additives or even individual additive components can be concentrated in one phase, depending on the requirements in the

more or less easily degradable phase. This allows a targeted influence on the degradation kinetics to be achieved.

The additives can therefore basically be incorporated in the same way as the fillers described above and other known additives. Their concentration must be calculated by the specialist depending on the desired application. It is generally up to about 10% by weight and is therefore measured in such a way that the physical and chemical properties of the plastic are not permanently affected.

The nutrients are preferably added in the form of nutrient salts. These primarily include phosphorus, iron and nitrogen salts. Depending on the application, vitamins, enzymes, trace elements, minerals, etc. are also possible. In addition, other additives can be added that can at least partially break the bonds between the monomers, so that the biodegradable plastic becomes "easier to digest" for the microorganisms. Organic and inorganic acids or bases are generally suitable for this, since in most cases it is a hydrolytic split. This measure is particularly recommended when using polylactides. Stabilizing matrix components can also be used. For use as a biocatalyst, it can also be advantageous to also add alginates and

14

Carrageenans are used. These act as a permeable coating for finely ground polymer and microorganisms.

The invention is explained in more detail below using the attached figures. They show:

Figure 1 schematic representations of denitrification with a biocatalyst using conventional granulate or the plastic product according to the invention;

Figure 2 shows a process flow diagram of a fixed bed reactor in batch operation according to DIN 28004;

Figure 3 shows a representation of the nitrate reduction rates related to the granulate surface in a fixed bed reactor according to Figure 1 using a conventional plastic product or a plastic product according to the invention;

Figure 4 Scheme of nutrient supply during aerobic decomposition in aqueous environment and compost;

Figure 5a Scheme of nutrient supply during anoxic degradation in aqueous environment and compost;

·» * ·· • · • t · ·· ·· Kt

Figure 5b Scheme of nutrient supply in anoxic degradation during denitrification in an aqueous environment;

Figure 6 Scheme of nutrient supply during anaerobic degradation in aqueous environment and compost.

Figure 1 shows schematically a preferred possible use of the plastic product according to the invention, namely for biocatalysts for denitrification. The plastic product serves in granulate form as a carrier 1 for a biofilm 2 made of heterotrophic denitrifiers. During denitrification, nitrate is converted to nitrogen. Since the carrier 1 serves as a C and Ω source, it is gradually broken down. In addition, stabilizing carrier materials, in particular carrageenans and/or alginates, can be present in the carrier 1 (see left side). Particularly suitable are, for example, polyhydroxybutyric acid (PHB) and polycaprolactone (PCL) as well as copolymers of these substances. According to the invention, these carriers 1 now contain at least one additive 3 that supports biodegradability. These can be nutrient salts, trace elements, vitamins, enzymes, minerals, etc.

A variant of such a biocatalyst is obtained by the well-known process of co-immobilization. (Hartmeier, Immobilized Biocatalysts, Springer Verlag

Berlin 1988). At least one plastic product according to the invention in powder form, microorganisms and any other additives are pre-homogenized in a stabilizing matrix component, e.g. alginate or carrageenan, and added dropwise to a calcium chloride solution while stirring. Gel balls are formed in which the plastic product, the microorganisms and the other additives are evenly distributed. A preferred embodiment of such a biodegradable plastic product according to the invention contains polyhydroxybutyric acid (PHB) with a molar fraction of 6% of hydroxyvaleric acid (PHB/HV). Another preferred embodiment contains polycaprolactones (PCL).

The theoretically required amount of additives can be calculated under the different conditions of each individual case. The theoretically required amounts of nitrogen and phosphate result from the proportions of the elements C, N and ' P in the biomass (dry mass). According to Schlegel (loc. cit.) these are A ₀ = 0.5; A _n = 0.14/ A _p = 0.03. Another basic assumption for the calculation are the different yield coefficients for the respective biodegradable substances. The yield coefficient indicates the proportion of carbon that goes into the biomass. The yield is the difference between the initial and the maximum bacterial mass in grams of dry mass: X =

17

X _max - X ₀ .The ratio of the yield to the substrate consumption X/S (each in grams) is called the yield coefficient: Y = X/S). The yield coefficients with PHB as substrate can be estimated based on preliminary tests to be Y _aerobic = 0.5 for aerobic, Y _anoxic = 0.46 for anoxic and Y _anaerobic = 0.1 for anaerobic degradation. From this, the amounts of nitrogen and phosphorus as well as other nutrients for biomass build-up can be calculated.

As an example, rough calculations for nitrogen and phosphorus when using PHB as a substrate are shown:

The biomass X can be calculated from the substrate consumption:

X = Y * S

C-amount of biomass (g) C _bio = A ₀ * X

N-amount of biomass (g) N _bio = A _n * X

P-amount of biomass (g) P _bio = A _p * X

Aerobic degradation:

During aerobic degradation of 1000 g PHB, the following amount of carbon is transferred to the biomass:

18

C _bio = A ₀ * Y _aerobic * .S = 0.5 * 0.5 * 1000 g = 250 g C

Based on the biomass composition, the following N and P amounts result:

N _bi0 = A _n * Y _aerobic *S = 0.14* 0.5* 1000 g = 70 g N Pbio = Ap * Y _aerobic * S = 0.03 * 0.5 * 1000 g = 15 g P Anoxic degradation:

During the anoxic degradation of 1000 g PHB, the following amount of carbon is transferred to the biomass:

C _bio = A ₀ * Y _anoxic * S = 0.5 * 0.46 * 1000 g = 230 g C

Based on the biomass composition, the following N and P amounts result:

N _bio = A _n * Y _anoxic * S = 0.14 * 0.46 * 1000 g = 64 g N Pbio= Ap * Y _anoxic * S = 0.03 * 0.46 * 1000 g = 14 g P Anaerobic degradation:

During anaerobic degradation of 1000 g PHB, the following amount of carbon is transferred to the biomass:

19 *

* Y _anaerobic * S = 0.5 * 0.1 * 1000 g = 50 g C

Based on the biomass composition, the following N and P amounts result:

N _bi0 = A _n * Y _anaerobic * S = 0.14 * 0.1 * 1000 g = 14 g N Pbio= Ap * Y _anaerobic * S = 0.03 * 0.1 * 1000 g = 3 g P

The plastic product according to the invention can be in the form of plastic granules, for example. The nutrients, e.g. in the form of salts, such as calcium phosphate, potassium dihydrogen phosphate or ammonium chloride, are incorporated into the polymer matrices. To do this, the salts are incorporated in undissolved, finely powdered form into the polymer in melt form using an extruder. The resulting plasticized product, which contains the additives homogeneously distributed, is extruded and further processed into granules.

The granulate compositions described above are summarized again in the following table:

Tab. 1: Granule compositions

substance Aerobic Anoxic Anaerobic PHBHV in g 1000 1000 1000 N in g 70 14 N as NH ₄ Cl 267 53 P in g 15 14 3 P as Ca ₃ (PO ₄ J ₂
in g 75 70 15 P as KH ₂ PO ₄ in
G 66 62 13

The plastic product according to the invention can either be specifically inoculated with microorganisms. For example, numerous bacteria are known that accept PHB or PHB/HV as a substrate (Schlegel, ibid.). However, enrichment cultures can also be established on the plastic product according to the invention.

In a practical experiment, a granulate containing PCL, iron and phosphorus salts (PCL/EP granulate) as well as a "naked" PCL granulate without additives were tested in a denitrification reactor for its effectiveness as a carrier (Figure 1).

The calculation of the respective proportions for producing the PCL-EP granules was carried out analogously to the example for PHB shown above. In a further development of the invention, iron was incorporated into these granules, since iron plays a special role as a cofactor for enzymes in denitrification. The necessary theoretical P content was therefore introduced partly as iron phosphate and mostly as potassium dihydrogen phosphate. The following granule compositions result for denitrification with PCL, assuming a yield coefficient of Y _anoxic = 0.3, which was approximately determined from preliminary tests:

PCL in g: 1000

Pkg: 11,4

P as KH ₂ PO ₄ in g: 48.8

P as FePO ₄ in g: 2.0

Both experiments were inoculated with activated sludge from the Stuttgart-Büsnau teaching and research sewage treatment plant. The reactors were then run under test conditions for four weeks so that the corresponding microorganisms could accumulate. This can therefore be referred to as an enrichment culture.

The tests were carried out in batch mode at 20 ⁰ C and pH (Fig.2). The water to be denitrified is

It is pumped from a storage tank 10 through a line 14 over a fixed bed reactor 20 and is led via lines 24, 34 for biomass removal via a sand filter 30 and back into the storage tank 10. The storage tank 10 is mixed by means of circulation pumps. The sand filter 30 is backwashed as required via lines 44, 45.

A centrifugal pump 15, 25 is connected between the storage tank 10 and reactor 20 as well as between reactor 20 and sand filter 30. The flow in the lines 14, 24, 34, 44 and 45 is controlled by valves 16, 26, 36, 46, 47.

The fixed bed reactor 20 had a reactor bed 21 and a distributor bed 22. Acrylic glass tubes with an inner diameter of D ₁ = 72 mm and a height of H = 1100 mm served as reactors in the reactor bed 21. The filling height of the granules used was 300 mm in order to achieve a height to width ratio of at least 5:1, which is desired for process engineering purposes. Sampling nozzles were attached to the reactor bed 21 at intervals of 100 mm. A sampling point 12 was also provided on the storage container 10.

The distribution bed 22 consisted from bottom to top of a 100 mm thick layer of Berl saddles, glass balls with

• . . · · . ^e _tv i i'

Diameter d _kl . = 6 mm and glass balls with d _k2 = 1.5 mm. This achieved sufficient uniformity of the fluid flow over the entire reactor cross-section. The pressure drop in the distributor bed 22 was recorded using measuring devices (PL 1, PL 2) and was ~ 20%. The outlet at the reactor outlet was designed so that the largest possible surface was available in order to prevent rapid clogging due to any biomass formation.

The flow velocity was determined using variable area flow meters of accuracy class IV, which had been calibrated at a fluid temperature of 13 ⁰ C at the measuring point FL 1.

To control the dissolved amount of oxygen, an oxygen electrode was placed at the measuring point O ₂₁ , TL 1 at the reactor outlet, which also served to control the temperature. pH measurements were carried out continuously with a pH electrode (pH 1) inserted into the storage tank (30 to 120 L depending on the experiment).

The system had a temperature control; for this purpose, the respective storage container 10 was equipped with cooling coils 11 as heat exchangers. The temperature could be cooled down to 13 ⁰ C reactor temperature (depending on the experiment) using cryostats (TL 2). All hose lines were insulated against heat transfer. Control measurements

confirmed, it could be assumed that temperatures were approximately the same throughout the system.

To avoid oxygen entering the system, the system was operated in a closed state. To do this, the storage containers 10 were fitted with lids and were provided with the appropriate nozzles for the necessary drain and inlet hoses, cooling coils and sampling. It was also possible to gas these systems with nitrogen. A slight overpressure can be set in the storage container 10 using nitrogen, which makes it even more difficult for oxygen to enter the system. A high degree of gas tightness was achieved, which was confirmed by measuring the oxygen concentration.

A small proportion of bacteria growing on the granules are carried away with the volume flow. In order to prevent an accumulation of biomass in the storage container 10, the outlet was passed through a sand filter 30 after the reactor 20. This also made it possible to eliminate the dissolved organic carbon (DOC) by growing MO in order to remove the C source from the biomass that would otherwise accumulate in the system (hose walls). The sand used does not provide a C source, but only a large growth area that ensures rapid elimination of the C source. The sand used had a grain size of 1.6 - 2.0 mm; backwashing was carried out

* 4

with a flow rate of 5 m/min. Any nitrate reduction performance in the sand filter 30 in competition with the actual reactor 20 was determined in each test and taken into account when determining the reactor performance.

The systems were operated with tap water from the regional Lake Constance long-distance water supply. This water contains almost no iron and phosphate [Zweckverband Bodensee-Wasserversorgung 1993: Water quality parameters of drinking water from Lake Constance, annual average values]. For the control tests with conventional granulate, 5 mg/L phosphate, 0.1 mg/L iron and 10 mL/L trace element solution SL6 (according to DSM: German strain collection) were added to the water. Calcium chloride and magnesium sulfate were not added because calcium and magnesium are present in sufficient quantities in Lake Constance water.

These tests in a fixed bed reactor under denitrifying conditions have shown that in water without phosphate and iron contents, only the granules according to the invention show degradation. Figure 3 shows that when using pure polymer granules with external addition of phosphate and iron salts, an average denitrification performance of about 20 mg/(h * m ² ) can be measured. With the polymer granules according to the invention, an average denitrification performance of about 38 mg/(h * m ² ) can be achieved.

Although these experiments only concern denitrification in a fixed bed reactor, it can be concluded that the biodegradable plastic products according to the invention, regardless of their form, can be degraded in nutrient-poor ecosystems, under aerobic, anoxic or anaerobic conditions. These conditions are illustrated in the diagrams shown in Figures 4 to 6. Although primarily aerobic processes take place in compost, anoxic or anaerobic conditions can also occur. In anoxic degradation (Figures 5a, 5b), two cases must be distinguished: improvement of degradation under anoxic conditions (Fig. 5a) and use of the plastic product according to the invention as a solid substrate for biochemical nitrate elimination (Fig. 5b).

The extensive agreement of the schemes makes it clear how similar the basic conditions are with regard to the nutrient supply, although there are major differences with regard to the oxygen supply. It can therefore be seen that the application is not limited to carrier material for heterotrophic denitrifiers. Articles of daily use made from the biodegradable plastic product according to the invention, such as bags, bottles, films, foils, packaging moldings, but also fishing nets and the like, can be broken down much faster and better. The environment dependency of the

The internal supply of nutrients significantly reduces the biological degradation behavior. With the help of nutrient-enriched biodegradable polymers, a section of waste can be recycled in a new way. Furthermore, additional areas of application can be opened up, particularly in the area of drinking water treatment or aquaculture. The complex addition of liquid carbon sources, for example in denitrification in wastewater, can be replaced by this easy-to-use, self-regulating system. In nutrient-poor ecosystems, as in all other systems, degradation can be ensured, provided that uncontrollable conditions, such as temperature, for microbiological activity are present.

Claims (1)

19 016.0- 2921 Biodegradable plastic product 30.09.1997 PROTECTION CLAIMS 1. Biodegradable plastic product containing at least one biodegradable polymer from at least one of the groups of polyacids, ^: in particular polyhydroxy acids, polylactides, polyalcohols, polyethers, polyesters, polyurethanes, waxes, starch and starch derivatives, cellulose and cellulose derivatives, in particular cellulose acetate and cellulose diacetate, and/or at least one biodegradable copolymer, characterized in that it contains at least one additive which supports biodegradability and is selected from the group consisting of nutrient salts, trace elements and minerals, so that the biodegradation behavior of the resulting plastic product is independent of the environment. 2. Plastic product according to claim 1, characterized in that it is a consumer article or an industrial product, e.g. a bag, a foil, a film, a packaging molding, a fishing net and the like. 3. Plastic product according to one of the preceding claims, characterized in that the nutrient salts are selected from the group of phosphorus, iron and nitrogen salts. . Plastic product according to one of the preceding claims, characterized in that as a further additive one or more polymer-splitting, in particular hydrolytically acting additives are added. 5. Plastic product according to claim 4, characterized in that the polymer-splitting additive is selected from the group consisting of inorganic and organic acids and bases. 6. Plastic product according to one of the preceding claims, characterized in that it further comprises at least one stabilizing matrix component. 7. Plastic product according to one of the preceding claims, characterized in that it further comprises alginates and/or carrageenans. 8. Plastic product according to one of the preceding claims, characterized in that the biodegradable polymer is water-insoluble. 9. Plastic product according to one of the preceding claims, characterized in that it is in the form of granules. 10. Plastic product according to claim 9, characterized in that the granulate has pores. 11. Plastic product according to one of the preceding claims, characterized in that it contains PCL and/or PHB and/or copolymers thereof.