CA2295637A1 - Thermoplastic mixture with a starch base, for producing biodegradable moulded bodies - Google Patents

Abstract

The invention relates to a thermoplastic mixture with a starch base, for producing biodegradable moulded bodies with improved properties, preferably improved mechanical properties. The inventive thermoplastic mixture can be obtained by providing and mixing; A) 100 weight parts of any native, chemically modified, fermentative starch which is recombinant and/or produced by biotransformation and corrected to a water content of zero per cent by calculation, and/or derivatives of said starches, B) optionally up to 100 weight parts of a physiologically harmless, biodegradable, thermoplastically processable polymeric material which is different from A), C) 1 to 100 weight parts of water, D) at least one plasticiser in a quantity of between 10 weight parts to half of the sum of the weight parts of A) and B), E) at least one phosphate, preferably a phosphoric acid salt, in a quantity of between 0.01 weight parts and (A)+B))/10 weight parts, and F) optionally, up to (A)+B)) weight parts of other usual additives. At least the mixing of constituents A and A) is carried out with the introduction of heat and mechanical energy, preferably at a high temperature with shearing forces being applied to the thermoplastic mixture simultaneously.

Description

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THERMOPLASTIC MIXTURE BASED ON STARCH FOR PRODUCING
SHAPED BIODEGRADABLE ARTICLES
Thermoplastic mixture based on starch for producing shaped biodegradable articles with improved properties, preferably improved mechanical properties, and the preparation and use of the mixture.
The invention relates to thermoplastic mixtures based on starch, to the preparation of mixtures of this type, and also to the use of these mixtures for producing shaped biodegradable articles, preferably with improved mechanical properties, such as moldings or films.
Starch is a biocompatible material and, as such, has the great advantage of fundamentally good biodegradability. As a result of the increased use of what are called hydrophilic polymers as natural and also physiologically compatible and degradable plastics for a very wide variety of application sectors, considerable efforts are also being made to process starch by known plastics-processing techniques, e.g. injection molding or extrusion.
However, the products thus produced, such as moldings or films, frequently have inadequate mechanical properties, for example inadequate strength or insufficient dimensional stability.
Limited improvements can be made by chemically modifying the starch.
There are many and varied reactions used to modify starch. These include oxidative processes, polymer-analogous reactions with organic chemicals, crosslinking reactions, and also graft polymerizations in which, using starch as initiator, monomers are linked to the backbone.
In the further processing of starch mixtures using conventional polymer-processing technology, it is in most cases of interest to melt the polymer mixture (e.g. in injection molding, blow molding, extrusion and coextrusion).
This requires that the molding compositions based on starch exhibit thermoplastic behavior.
If attempts are made to improve the thermoplastic behavior of the starch by crosslinking, in which case an important role is frequently played by bifunctional molecules based on aldehydes, such as glyoxal, glutaric dialdehyde or dialdehyde starch, or else those based on diisocyanates, on epoxides, on epichlorohydrin, diesters, etc., and if the content of crosslinking agent is too high, the extent of the crosslinking reaction can hinder achievement of the desired effect, which is better plastification of the starch. In particular, relatively strong crosslinking results in an insoluble, though swellable, product.
For more detailed prior art the following publications are cited:
WO 90105161 (PCT/CH89/00185) = D1, DE-A 39 31 363 = D2, US 2,801,242 = D3, US 2,938,901 = D4, US 2,328,537 = D5, W O 94/21236 = D6, EP-A 0 143 643 = D7, DE-A 2 308 886 = D8, EP-A 0 391 853 = D9, , EP-A 0 298 920 = D10 and Solarek, D.B., in "Modified Starches: Properties and Uses," 1986, p. 97-112, Ed. Otto B. Publisher, Boca Raton, Florida = D11.
D1 describes the preparation of thermoplastically processable starch by admixing an additive with essentially native or natural starch and melting the mixture by introducing heat and mechanical energy. The additive is a substance which lowers the melting point of the starch, and the melting point of the starch together with this additive is therefore below the decomposition temperature of the starch. Specific examples of the additives are DMSO, 1,3-butanediol, glycerol, ethylene glycol, propylene glycol, butylene glycol, diglyceride, diglycol ether, formamide, N,N-dimethylformamide, N-methylformamide, N,N'-dimethylurea, dimethyl-acetamide and N-methylacetamide. D1 also proposes the addition of a crosslinking agent selected from the group consisting of the di- or polybasic carboxylic acids and/or anhydrides, the halides andlor amides of di- or polybasic carboxylic acids, the derivatives of di- or polybasic inorganic acids, epoxides, formaldehyde, the derivatives of urea, the divinyl sulfones, the isocyanates, mono- or polyfunctional oxo compounds, and also cyanamide.

D2 relates to a process for reducing the swellability of starch by modification, by adding the crosslinking reagent in a pure or in an encapsulated form and achieving the crosslinking reaction by subsequent annealing at elevated temperature. The crosslinking agents used are, inter alia, urea derivatives, urotropin, trioxane, di- or polyepoxides, di- or polychlorohydrins, di- or polyisocyanates, carbonic acid derivatives, diesters or else inorganic polyacids, such as phosphoric or boric acids. The mixtures described feature very high weight ratios of crosslinking agent (from 10 to 100% by weight) in order to achieve an appropriate increase in mechanical stability through the subsequent thermal treatment.
D3 discloses a process for preparing distarch phosphates with sodium phosphates. Here, two different starch chains are linked to a phosphate molecule and thus bridged. However, in this case the starch grains are retained and the starch is not plastified.
D4, similarly to D3, discloses a process in which the undissolved and unswollen starch grains are modified in suspension with phosphoric acid and its salts in order to prepare nondusting powders for application in the operative sector.
In D5, inorganic chlorides are used to modify starch grains in an aqueous suspension. Again, these starch mixtures are not thermoplastifled prior to or during processing with these chemicals.
D6 describes the use of crosslinking agents, in particular epichlorohydrin, for direct press-molding of a mixture of starch and crosslinking agent.
Starch mixtures of this type are claimed as binders in tablets.
The application of bifunctional carboxylic acids, in particular adipic acid, as crosslinking agents is also described, in more detail, in D7.
D8 describes a process in which a phosphate-containing solution is sprayed onto starch. Subsequent kneading gives a crumbly material which is then heated for periods of a number of hours at temperatures of at least 140°C. The product after cooling dissolves very readily in water. The good low-viscosity properties have to be set against the disadvantage of the heterogeneous reaction.

D9 discloses the use of starch with phosphate groups for preparing thermoplastic starches. For this, use is made of native vegetable starch.
The properties are modified by various additions, predominantly of bivalent cations.
D10 describes the preparation of native starch with phosphate groups. The starch is modified firstly by using a washing process with demineralized water to wash out the free electrolytes. After this, the acid protons of the phosphate ~roups are replaced by predominantly bivalent ions, such as Mg2+ or Ca +, and in this way the starch is modified.
D11 reflects the prior art in the modification of starch with phosphates, predominantly in suspension.
Bearing in mind the prior art described and discussed here, therefore, it was an object of the invention to provide a thermoplastic mixture based on starch which permits the production of shaped biodegradable articles with improved properties, for example with improved mechanical properties. , Another object of the invention was a process for preparing a thermoplastic mixture for extrudates or pellets, and also the use of the thermoplastic mixture.
These objects have been achieved by a mixture with the features of claim 1. Preferred embodiments are the subject matter of the dependent product claims. The subject matter of claim 8 solves the process-related problems existing prior to the invention. Advantageous modifications of the novel process are protected in the subclaims dependent on the independent process claim. Claim 12 gives a use according to the invention.
A thermoplastic mixture based on starch can be obtained by preparing and mixing 100 parts by weight, calculated after correction to zero percent water content, of any desired native, chemically modified, fermentative andlor recombinant starch and/or starch prepared by biotransformation and/or of derivatives of the starches mentioned; if desired up to 100 parts by weight of a physiologically nonhazardous, biodegradable, thermoplastically processable polymeric material other than A); from 1 to 100 parts by weight of water;
at least one plasticizer, in an amount within the range from 10 parts by weight to half the total of the parts by weight of A) and B);

5 at least one phosphate, in an amount within the range from 0.01 parts by weight to (A) + (B))/10 parts by weight;
if desired, up to (A) + (B)) parts by weight of other conventional additives;
where at least the mixing of component E) with component A) takes place with introduction of thermal and mechanical energy into the thermoplastic mixture, and it is therefore possible, in a manner which is not readily foreseeable, to produce thermoplastically processable starch-based mixtures which have excellent thermoplastic processability, can be processed to give moldings, have excellent mechanical properties and are nevertheless readily biodegradable, for example can rot or be composted.
In addition, the products, such as shaped articles or films, are substantially biocompatible and in some cases edible, opening up a route to edible packaging, i.e. in particular packaging for food or drink.
For the purposes of the present invention, packaging for food or drink here is either outer packaging for the food or drink, coming only into temporary contact therewith, or else packaging, such as tubes, casings, wrappings or coatings, the inner surface of which is in continuous contact with the food or drink. These packagings may therefore even be ingested with the food or drink. The packaging is therefore suitable for, inter alia, fruit, eggs, cheese, confectionery, cakes, biscuits or effervescent tablets, drinks, meat, sausage products or sausage-meat emulsion.
The use here of the shaped articles which can be obtained according to the invention from the thermoplastic molding compositions is not restricted to the use in combination with short-lived products, but can also extend to short-lived use for protecting consumer articles or commercial assets during shipping or storage. Particular consideration should be given here to protection from exposure to climatic conditions as occurs, for example, when automobiles are shipped overseas.
Surprisingly, it has now been found in particular that the use of particular defined additives, such as phosphates, preferably, for example, polyphosphates, metaphosphates andlor polymetaphosphates, under specific conditions, achieves effects which on the one hand modify the starch and on the other hand permit further processing of the starch using conventional thermoplastic plastics-processing techniques.
Under the conditions described according to the invention, the modification reaction can be carried out during processing, during which the additives according to the invention, even at low concentrations, have a positive effect on the properties and the processability of thermoplastic starch m ixtu res.
Component A) of the novel starch mixture Component A) is an essential component of the novel mixture.
Component A) is one or more starches, one or more derivatives of these, or mixtures of starch and starch derivatives.
An important group of starches comprises the starches obtained from vegetable raw materials. These include starches made from tubers, such as potatoes, cassava, maranta or sweet potato, from seeds, such as wheat, corn, rye, rice, barley, millet, oats or sorghum, from fruits, such as chestnuts, acorns, beans, peas and other pulses or bananas, or from plant pith, for example of the sagopalm.
The starches which can be used for the purposes of the invention are composed substantially of amylose and amylopectin in varying proportional quantities.
Particularly good results are achieved with, inter alia, starches made from potatoes (e.g. ~Toffena from Sudstarke) or corn (e.g. Com Starch from National Starch), or else from polyglucans, which feature a perfectly linear structure of the polymers.
The molecular weights of the starches which can be used according to the invention may vary over a wide range. The starches which can be used as a basis for the novel thermoplastic mixture are those which are composed substantially of a mixture of amylose and amylopectin, with molecular weights MW within the range from 5 x 104 to 1 x 107. Preference is given to relatively long-chain polymers with molecular weights MW of from 1 x 106 to 5 x 106.

Preference is also given to linear polysaccharides, preferably polyglucans, in particular 1,4-a-D-polyglucan, with molecular weights MW within the range from 5 x 102 to 1 x 105, preferably with molecular weights MW of from 1 x 103 to 5 x 104.
Besides molding compositions based on starches of native vegetable origin, the invention also includes thermoplastic mixtures or molding compositions with starches which have been chemically modified, have been obtained by fermentation, are of recombinant origin or have been prepared by biotransformation (or: biocatalysis).
For the purposes of the present invention, "chemically modified starches"
are starches whose properties have been altered from their natural state by chemical means. This is achieved substantially by polymer-analogous reactions in which starch is treated with mono-, bi- or polyfunctional reagents andlor oxidants. The hydroxyl groups of the polyglucans of the starch are preferably transformed here by etherification, esterification or selective oxidation, or the modification is based on a free-radical-initiated graft copolymerization of copolymerizable unsaturated monomers onto the starch backbone.
Particular chemically modified starches include starch esters, such as xanthogenates, acetates, phosphates, sulfates and nitrates, starch ethers, e.g. nonionic, anionic or cationic starch ethers, oxidized starches, such as dialdehyde starch, carboxy starch, persulfate-degraded starches and similar substances.
For the purposes of the present invention, "fermentative starches" are starches obtained by fermentative processes, or with the involvement or assistance of fermentative processes, using naturally occurring organisms, such as fungi, algae or bacteria. Examples of starches from fermentative processes are gum arabic and related polysaccharides (gellan gum, ghatti gum, karaya gum, gum tragacanth), xanthan, emulsan, rhamsan, wellan, schizophyllan, polygalacturonates, laminarin, amylose, amylopectin and pectins.
For the purposes of the present invention, "starches of recombinant origin"
or "recombinant starches" are specifically starches which can be obtained a by fermentative processes, or with the involvement or assistance of fermentative processes, using organisms which do not occur in nature, but with the aid of natural organisms modified by genetic engineering, for example fungi, algae or bacteria. Examples of starches from fermentative processes using genetically engineered modifications are amylose, amylopectin and other polyglucans.
For the purposes of the present invention "starches prepared by biotransfomnation° are starches, amylose, amylopectin or polyglucans prepared by a catalytic reaction of monomeric fundamental building blocks, generally of oligomeric saccharides, in particular of mono- or disaccharides, by using a biocatalyst (or: enzyme) under specific conditions. Examples of starches from biocatalytic processes are polyglucan and modified polyglucans, polyfructan and modified polyfructans.
Finally, advantageous thermoplastic mixtures may also be obtained using derivatives of the individual starches mentioned. For the purposes of the present invention, "derivatives of starches" and "starch derivatives" very generally are modified starches, i.e. starches whose properties have been altered by changing the natural amyloselamylopectin ratio or carrying out a pregelatinization, a partial hydrolytic degradation or a chemical derivatization.
Examples of particular derivatives of starches are oxidized starches, e.g.
dialdehyde starches or other oxidation products with carboxyl functions, and native ionic starches (e.g. with phosphate groups) and starches which have been further modified ionically, where this term covers both anionic and cationic modifications.
Particularly advantageous thermoplastic mixtures are obtained if the starches used have only a small proportion of other compounds which do not belong to the saccharides (e.g. proteins, fats, oils) (for example, and in particular, potato starch) or if ionic starches are used as base material or are admixed, andlor the starch bases used comprise polyglucans of exceptional homogeneity in terms of structure, molecular weight and purity, e.g. 1,4-a-D-polyglucan prepared by biotransformation.
In the novel thermoplastic mixture a calculation is made in relation to component A) or to a mixture made from component A) to correct the water content to zero percent. This means that the water content of component A) is determined and the appropriate quantity is subtracted in arriving at 100 parts by weight, but taken into account in arriving at the amount of component C).
Component B) of the novel thermoplastic mixture based on starch Component B) of the novel thermoplastically processable mixture is an optional component.
More specifically, this is a physiologically nonhazardous, substantially also biodegradable, thermoplastically processable polymeric material other than A), and may be present in the mixture in amounts of up to 100 parts by weight. Component B) may also be a mixture of two or more compounds of this type.
A group of materials which complies with these requirements is that~of the proteins. Components B) which can be used successfully for the purposes of the present invention include gelatins, vegetable proteins, such as sunflower protein, soya protein, cottonseed protein, groundnut protein, rape-seed protein, plasma proteins, egg white, egg yolk and the like.
Advantageous mixtures may also be obtained using additions of zein, gluten (com, potato), albumin, casein, creative, collagen, elastin, fibroin and/or whey protein.
Other materials of interest as component B) are polysaccharides other than the starches mentioned under A).
Use is preferably made of water-soluble polysaccharides, such as alginic acid and its salts, carrageenans, furcellaran, guar gum, agar-agar, gum arabic or related polysaccharides (ghatti gum, karaya gum, gum tragacanth), tamarind gum, xanthan gum, aralia gum, locust bean gum, arabinogalactan, pullulan, chitosan, dextrins or cellulose.
Additions of lentinan, laminarin, chitin, heparin, inulin, agarose, galactans, hyaluronic acid, dextrans, dextrins, poly-s-caprolactones and/or glycogen may also have beneficial effects.

Component C) of the novel starch mixture Component C) of the novel mixture is an essential component.
5 From 1 to 100 parts by weight of water are present in the novel mixture. If the amount of water is less than one part by weight, the destructuring and homogenization of the mixture is inadequate. If the water content is above 100 parts by weight, there is a risk that the viscosity of the mixture will be too low. Advantageous ranges are from about 10 to 75 parts by weight of 10 water. The range from 20 to 60 parts by weight is of particular interest.
If significant proportions of the optional component B) are present in the novel mixture, this may be taken into account separately in defining the amount of water. In this case the water content is preferably from one part by weight to half the total of the parts by weight of A) and B). If the water content is about half the total of the parts by weight of A) and B) the thermoplastification of the entire mixture is particularly good. Preferred water contents are also from about 5 to about (A)+(B))/2 parts by weight, and proportions of from 10 to (A)+(B))/3 parts by weight of water are particularly useful.
These preferred ranges give ideal plastification of the mixture, i.e. destructuring of the starch, homogenization of the mixture, and also thermoplastification of the same.
The amount of water C) comprises both water actually added and also water content which derives from other components and has to be taken into account in the calculation, in particular the amount of water present or bound within component A) and any water present or bound within the compounds E).
Other aspects of the nature of component C) are substantially noncritical.
Use may be made of demineralized water, deionized water, or equally well mains water or water from another source, as long as the content of salts or of other foreign substances in the water can be tolerated in the application intended.

Component D) of the novel starch mixture.
Component D) must be present in the novel mixture.
The amount of component D) is of particular significance, i.e. can be freely selected only within defined limits. One or more plasticizers is/are present in the novel composition in an amount within the range from 10 parts by weight to half of the total of the parts by weight of A) and B). If the content of plasticizing compounds is below 10 parts by weight, the plastiflcation is inadequate, even using relatively high amounts of mechanical and/or thermal energy. If the plasticizer content exceeds an amount of half the total of the parts by weight of A) and B), there is no significant improvement in the plastification of the mixture.
Advantageous amounts of plasticizer are within the range from 12.5 to (A)+(B))/2 parts by weight, and particularly useful plasticizer contents are within the range from 15 to (A)+(B))/4 parts by weight.
For the purposes of the present invention, the terms plasticizing agent, plastication agent, plasticating agent and eiasticating agent mean fundamentally the same as the term plasticizer.
Use may be made of any inert, preferably organic, substance which generally has a low vapor pressure and which interacts physically with components A) and, if present, B) and forms a homogeneous system with these without any chemical reaction, preferably via its solvent or swelling power, but also in the absence of these.
Component D) to be used according to the invention preferably lowers the freezing point of the mixture, increases its deformability, enhances its elastic properties, reduces its hardness and, if desired, raises its adhesion.
According to the invention, preferred plasticizers are odorless, colorless, resistant to light, cold and heat, not more than slightly hygroscopic, resistant to water, not hazardous to health, flame-retardant and as involatile as possible, of neutral reaction, and miscible with polymers and with auxiliaries, and have good gelling performance. In particular, they should have compatibility, gelling capability and plasticizing action with respect to components A) and, if used, B).

The components to be used according to the invention as component D) should also feature low migration, and this is particularly important for applications of the shaped articles according to the invention in the food and drink sector.
Examples of particularly preferred plasticizing components D) are dimethyl sulfoxide, 1,3-butanediol, glycerol, ethylene glycol, propylene glycol, diglyceride, diglycol ether, formamide, N,N-dimethylformamide, N
methylformamide, dimethylacetamide, N-methylacetamide and/or N,N' dimethylurea.
Other particularly useful materials are polyalkylene oxide, glycerol mono-, .
di- or triacetate, sorbitol and other sugar alcohols, such as erythritol, sugar acids, such as gluconic acid, polyhydroxycarboxylic acids, saccharides, such as glucose, fructose or sucrose, and also citric acid and its derivatives.
Component E) of the novel thermoplastic mixture based on starch Component E) is essential to the novel mixture.
The amount of component E) present in the novel mixture is particularly significant. The novel mixture comprises amounts of from 0.01 parts by weight to (A)+B))/10 parts by weight of component E). Useful amounts are at least 0.1 part by weight, preferably from 0.1 to (A)+B))/20 parts by weight.
If the amount of component E) is too small, the mechanical properties of the shaped articles which can be obtained from the novel mixture become poor. If the amount exceeds (A)+B))/10 parts by weight, the plastification of the molding composition is impaired.
According to the invention, phosphates are component E). For the purposes of the present invention, these are salts or esters of the various phosphoric acids, but the salts of the various phosphoric acids are by far preferable for the invention. According to the invention, the component E) used may comprise one or more salts and/or esters of the various phosphoric acids, and therefore one or more phosphates may form component E).

Compounds which may be used successfully as component E) are, inter alia, orthophosphates of the formulae M H2P04 (e.g. NaH2P04) and Mll(H2PO4)21 [e.g. Ca(H2P04)2J, secondary orthophosphates of the general formulae M 2HP04 or M HP04 (e.g. K2HP04, CaHP04) or tertiary orthophosphates of the general formulae M~3P04 or M~~3(P04)2 [e.g. Na3P04, Ca3(P04)~J, where M~ is a monovalent ration, such as NRR'R"R"', where R, R', R" and R"', independently of one another, are identical or different and are hydrogen, (C~-Cg~alkyl, linear or branched, (C4-Cg)-aryl, preferably phenyl, an alkali metal ion, preferably Na+ or K+, and Ml~ is a bivalent ration, preferably an alkaline earth metal ion, particularly preferably Ca2+.
Also of particular interest as component E) is the group of condensed phosphates deriving from the acid salts of orthophosphoric acid and produced on heating, with evolution of water. These can be subdivided in tum into metaphosphates (systematic terminology: cyclopolyphosphates) and polyphosphates (systematic terminology: catenapolyphosphates).
Preferred examples include Graham's salt, Kurrol's salt and Maddrell's salt, and also f~rsed or calcined phosphates.
Particularly useful modifiers E) are, inter alia, metaphosphates of the general formula Min[Pn03n1, where M~ is a monovalent ration, preferably a metal ion, usefully an alkali metal ion, preferably Na+ or K+, or +NRR'R"R"', where R, R', R" and R"', independently of one another, are identical or different and are hydrogen, (C~-Cg)-alkyl, linear or branched, or (C4-Cg)-aryl, preferably phenyl, and n is a positive integer, preferably within the range from 3 to 10. Among these, preference is in tum given to metaphosphates in which n is 3, 4 or 5 and M~ is sodium or potassium.
Most preference is given to sodium trimetaphosphate, sodium tetrametaphosphate and sodium pentametaphosphate.
Advantageous mixtures are also obtained with polyphosphates of the general formula Min+2[Pn03n+1] or Min[H2nPnO3n+1l~ where M~ is a monovalent ration, preferably a metal ion, usefully an alkali metal ion, preferably Na+ or K+, or +NRR'R"R"', where R, R', R" and R"', independently of one another, are identical or different and are hydrogen, (C~-Cg)-alkyl, linear or branched, or (C4-Cg)-aryl, preferably phenyl, and n is a positive integer greater than 2. Among these, preference is given to sodium polyphosphates and potassium polyphosphates in which n > 10.
Mixtures with advantageous properties may also be obtained by using, as component E), polyphosphates of the general formula Mln+2[P~03n+11~
where MI is a monovalent ration, preferably a metal ion, usefully an alkali metal ion, preferably Na+ or K+, or +NRR'R"R"', where R, R', R" and R"', independently of one another, are identical or different and are hydrogen, (C~-Cg)-alkyl, linear or branched, or (C4-Cg~aryl, preferably phenyl, and n is a positive integer from 3 to 10. Among these preference is given, inter alia, to pentasodium tripolyphosphate.
In a particular embodiment, the novel thermoplastic mixture has the further feature that component E) is an alkali metal metaphosphate or alkali metal polyphosphate.
Another advantageous modification of the novel thermoplastic mixture is obtained if component E) is sodium trimetaphosphate, sodium metaphosphate, sodium polyphosphate and/or sodium hexametaphosphate, preferably sodium polyphosphate.
The phosphates mentioned may have different degrees of hydration. The proportions of component E) in the thermoplastic mixture are relatively low, and their water content is therefore generally insignificant when determining the parts by weight of E) and is not detrimental, since component C) is always present.
Component F) of the novel starch mixture Component F) of the novel starch mixture is optional, i.e. it does not have to be present in the novel mixture.
This may be one or more materials, which may be used together as component F) in amounts of up to 200 parts by weight, preferably not more than 100 parts by weight.
Conventional additives include fillers, lubricants other than the plasticizers mentioned under D), flexibilizing agents, pigments, dyes and mold-release agents.

Examples of suitable fillers are synthetic polymers which are virtually soluble in the mixture, for example lactic-acid-based polymers, such as ~Lacea from Mitsui, ~Resomer from Boehringer Ingelheim, and also other 5 lactic-acid-based polymers and similar lactic-acid polymers, from Wako Pure Chemical Industries Ltd., Medisorb Co., Birmingham Polymers Inc., Polysciences Inc., Purac Biochem BV, Ethicon, Cargill or Chronopo. This list clearly cannot be absolutely comprehensive.
10 It is also possible to use other polyesters made from preferably physiologically nonhazardous hydroxycarboxylic acids, such as polyhydroxybutyric-co-valeric acids, in particular polyesters with the trademark ~Biopol, inter alia.
15 The addition of at least one inorganic filler, such as magnesium oxide, aluminum oxide, Si02, Ti02, etc., is also proposed.
For pigmenting the mixture, organic or inorganic pigments are particularly suitable, as are, in particular, so-called pearl-luster pigments which are biocompatible, i.e. can be classified as nonhazardous to living organisms.
These are based on silicate structures and can therefore in principle be classified as edible, and are used in amounts of from 0.001 to 10 parts by weight.
Materials particularly suitable for improving flow properties are animal or vegetable fats andlor lecithins, preferably used in hydrogenated form.
These fats and other fatty acid derivatives preferably have a melting point above 50°C.
In order to reduce the hydrophilic character and thus the sensitivity of the thermoplastically processable mixture to water during and after processing, a subordinate amount of a crosslinking agent may be added to the mixture in order to modify the starch chemically. To this end, use is preferably made of amounts up to 5 parts by weight of alkylsiloxanes.
Suitable crosslinking agents are, inter alia, di- or polybasic carboxylic acids, and also anhydrides of these, acid halides of di- or polybasic carboxylic acids, amides of di- or polybasic carboxylic acids, derivatives of di- or polybasic inorganic acids other than component E), epoxides, formaldehyde and/or urea derivatives, divinyl sulfones, isocyanates, oxo compounds and/or cyanamide. These compounds are also particularly suitable for chemical modification after thermoplastic processing and can therefore contribute to further improvement of in particular the mechanical properties.
Components A) to F) of the novel mixture are mixed with one another in such a way that at least the mixing of component E) with component A) takes place with introduction of thermal and mechanical energy into the thermoplastic mixture.
The mechanical and the thermal energy are preferably introduced simultaneously, e.g. by working at an elevated temperature and simultaneously exerting shear forces on the thermoplastic mixture which is to be plastified and is based on starch.
Better homogeneity of the mixtures is generally obtained at relatively high temperatures. However, to avoid unnecessary discoloration or decomposition of the molding compositions, the temperatures should not be too high. In this context, mixing at temperatures within the range from > 60°C to 200°C is the preferred form of thermoplastic mixing according to the invention.
Fundamentally, the homogenization of the mixture increases with the work introduced. This means that as the work introduced into the mixing assembly increases, the homogenization of the thermoplastic starch mixture improves. A further modification of the invention therefore provides a mixture obtainable by mixing with strongly shearing mixing assemblies.
The energy introduced into the mixture may be derived in particular from the work done by the processing machinery used. For example, an apparatus whose plastificating element has a torque within the range from 5 to 300 Nm (1 newton meter) is particularly suitable for the process. A
torque within the range from 10 to 100 Nm has proven advantageous for the process. Preference is given to carrying out the process with a torque within the range from 20 to 40 Nm.
Particularly advantageous take-up of thermal and/or mechanical energy by the mixture is achieved if the constituents of the novel mixture are mixed and homogenized in a plastics-processing machine, such as an extruder, kneader or a similar assembly. The process may preferably be carried out in single- or twin-screw extruders, these preferably being assembled from individual barrels which have temperature-controlled jackets. There is no restriction on the design of the screws. There may be conveying elements (with or without thrust edges), kneading elements and/or mixing elements.
It is, furthermore, possible and frequently advantageous to have elements which are in some parts, i.e. in some sections, flow-restricting or reverse-conveying in the extruder, to adjust and control the residence time and the properties of the mixture.
The sequence of mixing the ingredients A) to F) may also have particular significance.
The invention therefore also provides a process for preparing a thermoplastic mixture based on starch by preparing, and mixing with one another, A) 100 parts by weight, calculated after correction to zero percent water content, of any desired native, chemically modified, fermentative and/or recombinant starch and/or starch prepared by biotransformation and/or of derivatives of the starches mentioned;
B) if desired up to 100 parts by weight of a physiologically nonhazardous, biodegradable, thermoplastically processable polymeric material other than A);
C) from 1 to 100 parts by weight of water;
D) at least one plasticizer, in an amount within the range from 10 parts by weight to half the total of the parts by weight of A) and B);
E) at least one phosphate, in an amount within the range from 0.01 parts by weight to (A) + (B))/10 parts by weight;
F) if desired, up to (A) + (B)) parts by weight of other conventional additives;
by adding component E) to components A) to D), and also, if desired, F), where at least the mixing of component E) with the remaining components takes place with introduction of thermal and mechanical energy into, and preferably with the action of elevated temperature and simultaneous exertion of shear forces onto, the thermoplastic mixture.

The nature and effect of this procedure differs markedly from the known prior art.
Previously, when phosphoric acids or their salts or esters were used as modifiers in preparing thermoplastic mixtures based on starch, it was exclusively the starch grains which were always directly modified, or else a large addition in terms of parts by weight of the phosphate, followed by heat treatment, was used to bring about crosslinking, which gives molding compositions that can no longer be processed thermoplastically.
In contrast to this, the novel procedure ensures that what is modified is not merely the surface of the starch grains but the entirety of the starch molecules, preferably at the starch backbone. This gives products of a different type, the improved properties of which were not readily foreseeable.
Adding component E) during the processing in the homogenizing or mixing assembly, for example in the kneader or extruder, and under alkaline to acid conditions, causes the reaction with starch, or with starch derivatives, or else with admixed proteins, to have only little of the nature of a crosslinking, i.e. the prime factor is the modification of the polymer back bone.
This difference from known starch phosphates from the prior art may also, for example, be reflected in the degree of substitution.
The number of hydroxyl groups replaced by another functional group (phosphate) per glucose unit of the starch is termed the degree of substitution DS.
Three free hydroxyl groups are present per glucose unit. The degree of substitution can therefore vary from 0.0 to 3Ø
The degree of substitution DS is therefore a purely statistical variable. A
degree of substitution DS of 1.0 means merely that on each glucose unit on average one hydroxyl group has been replaced by a substituent. A DS
1.0 does not therefore necessarily mean that on every glucose unit there is precisely one substituent together with two remaining unsubstituted hydroxyl groups.

It is known, for example, that native starch per se may contain phosphate groups. The degree of substitution here is in the region of about 0.001.
Purely from a statistical point of view, therefore, a phosphate group occurs in the polymer after about every 300 glucose units.
In the known processes, therefore, which modify the starch as grains, and therefore very substantially only on the surface, degrees of substitution DS
within the range from about 0.001 to 0.01 can be assumed.
According to the invention, however, the modification with phosphates (component E)) achieves a markedly higher DS during the plastification.
This is approximately from > 0.01 to 1Ø The DS for component A) modified according to the invention is preferably approximately within the range from 0.05 to 0.5, and particularly expediently from 0.1 to 0.3.
Addition of plasticizers which per se have a high ratio of hydroxyl groups, or of other groups which develop hydrogen bridges, to carbon atoms can moreover, with suitable conduct of the reaction, through the reaction of the phosphate, also achieve linking of the plasticizer to the starch back bone, and the result of this - particularly during processing - is a reduction in the migration of the plasticizer out of the mixture. However, this does not remove the plastifying effect of the plasticizer which is necessary in the first place for destructuring the starch, i.e. opening up the starch grains. This possible interpretation of the reactions occurring and leading to the surprising results found does not, however, exclude other possible interpretations.
The novel thermoplastic molding composition may be processed by known processing methods to give products. For example, in a first step it may be pelletized.
The invention therefore also provides pellets which can be obtained from the thermoplastic mixture according to the invention by extrusion and pelletization.
It is also possible, either directly or by further thermoplastic processing of thermoplastic pellets, to obtain moldings or films with good biodegradability and improved properties, preferably improved mechanical properties.

Finally, the invention also includes the use of the thermoplastic mixtures for producing moldings or films.
The thermoplastic molding compositions here, and also the shaped articles 5 and films obtained by further processing, achieve both increased heat resistance and also improved flame retardancy as a result of admixing the essential component E).
The novel products therefore cover a wide variety of possible applications.
10 These include, specifically, adhesives for paper and corrugated board, shaped articles produced by injection molding, especially rods, tubes, bottles, capsules, pellets, additives for food or drink, foils, in the form of coatings or free-standing foils, also in the form of laminates, especially films, packaging materials, bags, and release-slowing materials for 15 controlled release of active substances in general, in particular drugs, pesticides or other active substances used in agriculture, fertilizers, flavorings, etc. The release of the active substance here may take place from foils, films, tablets, particles, microparticles, rods or other extrudates or other shaped articles.
More preferred applications include packaging for food or drink, in particular sausage casings or cheese wrappings, absorbers, powders and the like.
In a particular embodiment, the novel thermoplastic mixtures are used to produce shaped articles for the controlled release of active substances, for example tablets or dragees.
Another expedient and particularly advantageous use of the novel thermoplastic mixture relates to the production of shaped articles which are suitable for producing solid shaped articles, hollow articles or combinations of these.
Another excellent use of the novel thermoplastic mixture is for producing films for use in agriculture.
Another particular variant of the invention is the use of the thermoplastic mixture for producing films for use in food or drink applications.

Another specific use of the thermoplastic mixture is for producing films for use as an outer package for surrounding food or drink.
One more highly advantageous use of the novel thermoplastic mixture is in producing films for use as packaging for food or drink where there is full surface contact between the packaging and the food or drink.
A final particularly advantageous use of the novel thermoplastic mixture is in producing flat or tubular films for use as food casings or wrappings for sausages or cheese.
For the purposes of the present invention preference is also given to the use of the thermoplastic mixture as temporary protective films for technical consumer articles.
The examples below illustrate the subject matter of the invention.
Example 1 Preparation of a thermoplastically processable blend made from potato starch with sodium polyphosphate, gum arabic and glycerol:
The compounds are prepared in a commercially available kneading assembly (Brabender kneader). The kneading assembly is heated to 100°C. 30 g of potato starch (~Toffena from Sudstarke) are charged to the kneading assembly in its operating condition. 0.9 g of NaC03 is dissolved in 10 g of water and added to the potato starch which is in the kneader.
The mixture is homogenized. The procedure takes about 3 minutes. 9 g of gum arabic are then added all at once. The mixture is again homogenized.
9 g of glycerol are then added in portions (about 3 equal-sized portions with in each case a 2 minute kneading interval between the additions).
1.2 g of sodium polyphosphate (Riedel de Haen) dissolved in 5 ml of water are added after a further 2 minutes. The entire mixture is kneaded again for a further 2 minutes. The composition is removed while the apparatus is still in its heated condition. The product is a homogeneous composition with a slightly yellowish color and is nontransparent. The thermoplastic composition may be further processed after cooling.

The foils obtained by thermoplastic processing of the product are transparent and have good mechanical strength.
Comparative Example 2 Preparation of a thermoplastically processable blend made from potato starch with sodium polyphosphate and gum arabic:
The mixture is prepared in the manner described in Example 1. The sole difference in the mixing specification is the non-use of glycerol as plasticizer.
After homogenization has ended, the composition is removed while the apparatus is still in its heated condition. The product is a homogeneous composition with a slight brownish color, is non-transparent and tends toward brittleness. Further processing, in particular to give films or foils, can be achieved only after prior addition of water to the molding composition.
Example 3 Preparation of a thermoplastically processable blend made from casein and potato starch with sodium polyphosphate:
The compounds are prepared in a commercially available kneading assembly (Brabender kneader). The kneading assembly is heated to 100°C. 20 g of casein and 10 g of potato starch (Toffena from Siidstarke) are charged to the kneading assembly in its operating condition. 1.2 g of sodium polyphosphate (Riedel de Haen) dissolved in 5 ml of water are immediately added. The mixture is homogenized for 3 minutes. 6 g of glycerol are then added in portions (about 3 equal-sized portions with in each case a 2 minute kneading interval between the additions). The mixture is homogenized for a further 2 minutes. The product is a slightly yellowish thermoplastically deformable composition which may be further processed directly after removal from the kneading assembly still in its heated condition, or after cooling.

The foils obtained from thermoplastic processing are transparent and have good mechanical properties in terms of elongation at break and tear resistance.
Example 4 Preparation of a thermoplastically processable blend made from potato starch with sodium polyphosphate:
The method is as described in Example 1. The kneading assembly (Brabender) is heated to 100°C. 30 g of potato starch (Toffena from Siidstarke) are charged to the kneading assembly in its operating condition. 0.9 g of Na2C03 dissolved in 10 ml of water is immediately added. The mixture is homogenized for 3 minutes. 15 g of glycerol are then added in portions (about 3 equal-sized portions with in each case a 2 minute kneading interval between the additions). The mixture is homogenized for a further 2 minutes and then 0.15 g of sodium polyphosphate (Riedel de Haen) in 5 ml of water is added. After a further homogenization phase the experiment ends. The product is a slightly yellowish, thermoplastically deformable composition which can be further processed after cooling.
The foils obtained from thermoplastic processing are transparent and have very high mechanical strength. The film thicknesses are within the range from 100 to 150 Vim. The flexibility of the films permits further processing, for example filling with foods.
Example 5 Preparation of a thermoplastically processable blend made from potato starch and casein with sodium polyphosphate:
The method is as described in Example 1. The kneading assembly is heated to 120°C. 21 g of potato starch (Toffena from Sudstarke) and 9 g of casein are charged to the kneading assembly (Brabender) in its operating condition. 0.9 g of NaC03 is dissolved in 10 g of water and added to the mixture of casein and potato starch which is in the kneader. The mixture is homogenized. The procedure takes about 3 minutes. 1.5 g of Pluronic F 68 in 10 ml of water, and also 6 g of glycerol, are then added one after the other. The mixture is homogenized again. After about 2 minutes, 1.2 g of sodium polyphosphate (Riedel de Haen) dissolved in 5 ml of water are added. The entire mixture is again kneaded for a further 2 minutes. The composition is removed while the apparatus is still in its heated condition.
The product is a very white homogeneous composition. The thermoplastic composition can be further processed after cooling.
The films obtained from thermoplastic processing are opaque. The film thickness is from about 160 to 200 pm. The mechanical strength, together with the film thickness achieved by compression molding, gives a degree of brittleness. Addition of water is therefore needed for further processing in relation to applications in the food or drink sector.
Example 6 Preparation of a thermoplastically processable blend made from casein and com starch with sodium polyphosphate:
The method is as described in Example 1. The kneading assembly (Brabender) is heated to 100°C. 24 g of casein and 6 g of corn starch are charged to the kneading assembly in its operating condition. After a short time, 10 ml of water, and also 4 g of glycerol, are added. After a further short homogenization phase, 0.8 g of sodium polyphosphate (Riedel de Haen) in 2 ml of water is added. After a further homogenization phase the experiment ends. The product is a slightly yellowish, thermoplastically deformable composition which can be further processed after cooling.
The foils obtained from thermoplastic processing (compression molding technique) are slightly opaque and have high mechanical strength. The film thicknesses are within the range from 170 to 190 Vim. The flexibility of the films permits further processing, for example filling with foods.
Example 7 Preparation of a thermoplastically processable blend made from casein and potato starch with sodium polyphosphate:

The method is as described in Example 1. The kneading assembly (Brabender) is heated to 100°C. 15 g of casein and 15 g of potato starch (e.g. Toffena from Sudst~rke) are charged to the kneading assembly in its 5 operating condition. After a short time, 1.5 g of citric acid in 10 ml of water, and also 6 g of glycerol, are added. After a further short homogenization phase, 1.2 g of sodium polyphosphate (Riedel de Haen) in 5 ml of water are added. After a further homogenization the experiment ends. The product is a yellowish, homogeneous solid composition which can be 10 further processed after cooling.
The foils obtained from thermoplastic processing (compression molding technique) are yellowish, and transparent to slightly opaque. The films are very thin, within the range from 80 to 100 Vim.
Example 8 Production of films using a compression molding technique from the thermoplastic molding compositions prepared in Examples 1 to 7:
The following procedure is used to process a thermoplastic molding composition as described. A commercially available Schwabenthan (Polystat 300 S) press is used. The press is preheated to 100°C. The preparation of the specimens uses a "sandwich technique" between two fabric-reinforced polytetrafluoroethylene (PTFE, ~Teflon) sheets held apart by a metal frame of about 100 ~m thickness. During the preparation about 2 g of the composition prepared in the kneader are placed in the middle of the lower sheet. The specimen is held for 5 minutes at a temperature of 100°C and a pressure of 1 t. The specimen is then compression molded at 100°C for 5 minutes, at a pressure of 10 t. This corresponds to a pressure of 200 bar. The pressure is released and the specimen is transferred to another press for cooling. This is a water-cooled press from Robert Fuchs Hydraulische Maschinen and Werkzeuge. A pressure of 50 bar is applied during the cooling procedure for a period of 2 minutes. The specimen can then be removed for use in further tests. It should be noted that, depending on the hydrophilicity of the materials used, storage in air gives rise to aging phenomena attributable to variations in water content.

Example 9 Preparation of a thermoplastically processable blend made from com starch with a high sodium polyphosphate content:
The compounds are prepared in a commercially available kneading assembly (IICA Duplex kneader). The kneading assembly is heated to 100°C. 150 g of com starch (from National Starch) and 45 g of glycerol are charged to the kneading assembly in its operating condition. 5.0 g of NaC03 are dissolved in 50 g of water and added to the com starch which is in the kneader. The mixture is homogenized. The procedure takes from about 5 to 10 minutes, during which it becomes glassy. 15 g of sodium triphosphate (Riedel de Haen) are then dissolved in 25 ml of water and added. The entire mixture is again kneaded for a further 5 minutes. The composition is removed while the apparatus is still in its heated condition.
Comparative Example 10 Preparation of a thermoplastically processable blend made from com starch without sodium polyphosphate:
The compounds are prepared in a commercially available kneading assembly (IKA Duplex kneader). The kneading assembly is heated to 100°C. 150 g of com starch (from National Starch) and 45 g of glycerol are added to the kneading assembly in its operating condition. 5.0 g of NaC03 are dissolved in 50 g of water and added to the corn starch which is in the kneader. The mixture is homogenized. The procedure takes from about 5 to 10 minutes, during which the mixture becomes glassy. The entire mixture is kneaded again for a further 5 minutes. The composition is removed while the apparatus is still in its heated condition.
Example 11 Preparation of films using a compression molding technique from thermoplastic materials based on starch.

The thermoplastic molding compositions are further processed to give films using the compression molding technique described here. For this, use is made of a commercially available Schwabenthan (Polystat 300 S) press.
The press is preheated to 100°C. The preparation of the specimens uses a "sandwich technique" between two fabric-reinforced Teflon sheets held apart by a metal frame of about 100 wm thickness. During the preparation about 2 g of the composition prepared in the kneader are placed in the middle of the lower sheet. The specimen is held for 5 minutes at a temperature of 100°C and a pressure of 1 t. The specimen is then compression molded at 100°C for 5 minutes, at a pressure of 10 t. This corresponds to a pressure of 200 bar. The pressure is released and the specimen is transferred to another press for cooling. This is a water cooled press from Robert Fuchs Hydraulische Maschinen and Werkzeuge. A
pressure of 50 bar is applied during the cooling procedure for a period of 2 minutes.
Example 12 Tests on the heat resistance of films produced as in Example 11 from the thermoplastic molding compositions from Example 9 and Comparative Example 10:
A film of dimensions 5 cm by 5 cm is placed upon a ring with an internal diameter of 3 cm, and held by metal clamps so as to be unaffected by any slight air movements. The ring is held horizontally by means of a holding rod attached to the ring, so that the film is arranged at a height of 20 cm above the laboratory bench. Underneath the ring is arranged an open flame which supplies an identical amount of energy per unit of time for all of the tests and has a height of from 1 to 2 cm. The upper boundary of the open flame here is 5 cm +/- 0.5 cm distant from the film. A stopwatch is used to measure the times required to achieve coking of the film over more than 50% of the surface of the ring covered by the thermoplastic film. In each case the average of ten measurements is calculated.
Film from Example 9 with sodium triphosphate: 25 +/- 3 sec.

Film from Comparative Example 10 without sodium triphosphate:
16 +I- 3 sec.
Other advantages and embodiments of the invention are given in the patent claims below.

Claims (19)

claims:

1. A thermoplastic mixture based on starch for producing shaped biodegradable articles with improved mechanical properties, obtainable by preparing and mixing A) 100 parts by weight, calculated after correction to zero percent water content, of any desired native, chemically modified, fermentative and/or recombinant starch and/or starch prepared by biotransformation and/or of derivatives of the starches mentioned;
B) if desired up to 100 parts by weight of a physiologically nonhazardous, biodegradable, thermoplastically processable polymeric material other than A);
C) from 1 to 100 parts by weight of water;
D) at least one plasticizer, in an amount within the range from 10 parts by weight to half the total of the parts by weight of A) and B);
E) at least one phosphate, in an amount within the range from 0.01 parts by weight to (A) + (B))/10 parts by weight;
F) if desired, up to (A) + (B)) parts by weight of other conventional additives;
where at least the mixing of component E) with component A) takes place with introduction of thermal and mechanical energy into the thermoplastic mixture.

2. A thermoplastic mixture as claimed in claim 1, wherein the amount of component E) present is at least 0.1 parts by weight.

3. A thermoplastic mixture as claimed in claim 1 or 2, wherein the amount of component E) present is up to (A) + (B))/20 parts by weight.

4. A thermoplastic mixture as claimed in one or more of the preceding claims, wherein component E) is an alkali metal metaphosphate or alkali metal polyphosphate.

5. A thermoplastic mixture as claimed in claim 4, wherein component E) is sodium trimetaphosphate, sodium metaphosphate, sodium polyphosphate and/or sodium hexametaphosphate, preferably sodium polyphosphate.

6. A thermoplastic mixture as claimed in one or more of the preceding claims, which can be obtained by mixing at temperatures within the range from > 60°C to 200°C.

7. A thermoplastic mixture as claimed in one or more of the preceding claims, which can be obtained by mixing using mixing assemblies having high-shear plasticating elements, where the plasticating elements can achieve torques within the range from 10 to 100 Nm, preferably from 20 to 40 Nm.

8. A process for preparing a thermoplastic mixture based on starch, by preparing, and mixing with one another, A) 100 parts by weight, calculated after correction to zero percent water content, of any desired native, chemically modified, fermentative and/or recombinant starch and/or starch prepared by biotransformation and/or of derivatives of the starches mentioned;
B) if desired up to 100 parts by weight of a physiologically nonhazardous, biodegradable, thermoplastically processable polymeric material other than A);
C) from 1 to 100 parts by weight of water;
D) at least one plasticizer, in an amount within the range from 10 parts by weight to half the total of the parts by weight of A) and B);
E) at least one phosphate, in an amount within the range from 0.01 parts by weight to (A) + (B))/10 parts by weight;
F) if desired, up to (A) + (B)) parts by weight of other conventional additives;
which comprises adding component E) to components A) to D), and also, if desired, F), where at least the mixing of component E) with the remaining components takes place with introduction of thermal and mechanical energy into, and preferably with the action of elevated temperature and simultaneous exertion of shear forces onto, the thermoplastic mixture.

9. Pellets which can be obtained from the thermoplastic mixture as claimed in any of claims 1 to 7 by extrusion and pelletization.

10. A biodegradable molding or film with improved mechanical properties, comprising the thermoplastic mixture as claimed in any of claims 1 to 7.

11. The use of the thermoplastic mixture as claimed in any of claims 1 to 7 for producing moldings or films.

12. The use of the thermoplastic mixture as claimed in any of claims 1 to 7 for producing shaped articles for the controlled release of active substances.

13. The use of the thermoplastic mixture as claimed in any of claims 1 to 7 for producing shaped articles for producing solid shaped articles, hollow articles or combinations of these.

14. The use of the thermoplastic mixture as claimed in any of claims 1 to 7 for producing films for use in agriculture.

15. The use of the thermoplastic mixture as claimed in any of claims 1 to 7 for producing films for use in food or drink applications.

16. The use of the thermoplastic mixture as claimed in any of claims 1 to 7 for producing films for use as an outer package for food or drink.

17. The use of the thermoplastic mixture as claimed in any of claims 1 to 7 for producing films for use as packaging for food or drink where there is full surface contact between the packaging and the food or drink.

18. The use of the thermoplastic mixture as claimed in any of claims 1 to 7 for producing flat or tubular films for use as food casings or wrappings, for sausages or cheese.

19. The use of the thermoplastic mixture as claimed in any of claims 1 to 7 for use as temporary protective films for technical consumable items.