EP1000119A1

EP1000119A1 - Thermoplastic mixture with a starch base, for producing biodegradable moulded bodies

Info

Publication number: EP1000119A1
Application number: EP98939538A
Authority: EP
Inventors: Holger Bengs; Arnold Schneller; Gitte Böhm; Silke Schuth
Original assignee: Aventis Research and Technologies GmbH and Co KG
Current assignee: Celanese Ventures GmbH
Priority date: 1997-07-09
Filing date: 1998-06-26
Publication date: 2000-05-17
Also published as: HUP0003025A2; CA2295637A1; PL338049A1; DE19729272A1; JP2001509525A; DE19729272C2; WO1999002595A1

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

THERMOPLASTIC MIXTURE BASED ON THE STRENGTH FOR THE PRODUCTION OF BIODEGRADABLE MOLDED BODIES

Thermoplastic mixture based on starch for the production of biodegradable moldings with improved properties, preferably improved mechanical properties, production of the mixture and use

The invention relates to thermoplastic mixtures based on starch, the production of such mixtures and the use of these mixtures for the production of biodegradable moldings, preferably with improved mechanical properties, such as moldings or films.

Starch as a biocompatible material has the great advantage of generally good biodegradability. In the course of the increased use of so-called hydrophilic polymers as natural and thus physiologically compatible and degradable plastics for a wide variety of applications, considerable efforts are also being made to process starch by means of the known plastics processing techniques, i.e. H. for example by means of injection molding and extrusion. However, products made from them, such as molded parts or foils, often lack sufficient mechanical properties, such as sufficient strength or sufficient dimensional stability.

This can be remedied by chemical modification of the starch. Reactions used to modify starch are legion. These include oxidative processes, polymer-analogous reactions with organic chemicals, cross-linking reactions or graft polymerizations in which monomers are coupled to the backbone based on starch as an initiator.

When processing starch mixtures by means of conventional polymer process technology, in most cases it is of interest to melt the polymer mixture (eg injection molding, blow molding, extrusion, coextrusion). This requires a thermoplastic behavior of the starch-based molding compositions.

Attempts are made to improve the thermoplastic behavior of the starch by crosslinking, bifunctional molecules based on aldehydes often playing an important role, such as glyoxal, glutardialdehyde, dialdehyde starch, but also based on diisocyanates, epoxides, epichlorohydrin, diesters , etc., if the crosslinker content is too high, the extent of the crosslinking reaction can counteract the desired effect, which consists in better plasticization of the starch. In particular, stronger networking results in an insoluble but swellable product.

The publications become closer state of the art

WO 90/05161 (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,

WO 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. called.

D1 describes the production of thermoplastically processable starch by adding an additive to essentially native or natural starch and melting the mixture by adding heat and mechanical

Energy. The aggregate is a substance that The temperature of the starch is reduced, so that the melting temperature of the starch together with this additive is below the decomposition temperature of the starch. Specifically, it is in the aggregate, for example, DMSO, 1, mamid 3-butanediol, glycerol, ethylene glycol, propylene glycol, butylene glycol, diglyceride, diglycol ether, research, N, N-dimethylformamide, N-methylformamide ,, N, N ^{'-Dimethylhamstoff,} Dimethylacetamide, N-methylacetamide. D1 also proposes the addition of a crosslinking agent from the group of di- or polyvalent carboxylic acids and / or anhydrides, the halides and / or acid amides of di- or polyvalent carboxylic acids, the derivatives of di- or polyvalent inorganic acids, the epoxides, Formaldehyde, the urea derivatives, the divinyl sulfones, the isocyanates, the mono- or polyvalent oxo compounds and cyanamide.

D2 relates to a process for reducing the swellability of starch by modification, in such a way that the crosslinking reagent is added neat or in encapsulated form, and the crosslinking reaction is achieved by subsequent tempering at elevated temperature. The crosslinking agents used are u. a. Urea derivatives, urotropin, trioxane, di- or polyepoxides, di- or polychlorohydrins, di- or polyisocyanates, carbonic acid derivatives, di-esters or also inorganic polyacids, such as phosphoric acids or boric acids. The mixtures described are distinguished by the fact that very high weight ratios of crosslinking agent are used (between 10 and 100% by weight) in order to achieve a corresponding increase in mechanical stability through the subsequent thermal treatment.

A method for the production of distarch phosphates with sodium phosphates is known from D3. Two different starch chains are attached to a phosphate molecule and bridged in this way. However, the starch is not plasticized, rather the starch grain is retained.

Similar to the D3, the D4 discloses a process in which the undissolved and non-swollen starch grain in suspension with phosphoric acids and their salts is modified. is used to manufacture non-dusting powders for use in the surgical sector.

According to D5, inorganic chlorides are used to modify starch granules in aqueous suspension. These starch mixtures are not thermoplasticised with these chemicals either before or during processing.

D6 describes the use of crosslinking agents, in particular epichlorohydrin, in such a way that a mixture of starch and crosslinking agent is pressed directly. Starch mixtures of this type are claimed as binders in tablets.

The use of difunctional carboxylic acids, especially adipic acid as a crosslinking agent, is also discussed in more detail in D7.

D8 describes a process in which a phosphate-containing solution is sprayed onto starch. The subsequent kneading gives a crumbly mass which is subsequently heated at temperatures of at least 140 ° C. over a period of several hours. After cooling, the product can be easily dissolved in water. The good low-viscosity properties are offset by the disadvantage of the heterogeneous implementation.

D9 shows the use of starch with phosphate groups for the production of thermoplastic starches. For this, native vegetable starch is used. The properties are modified by different additions of predominantly divalent cations.

D10 describes the provision of native starch with phosphate groups, which is modified in that the free electrolytes are first washed out by a washing process with demineralized water. Subsequently, the acidic protons of the phosphate groups are replaced by predominantly bivalent ions, such as Mg ²⁺ or Ca ²⁺ , and the starch is modified in this way. The D11 reflects the state of the art of modifying starch with phosphates, mostly in suspension.

In view of the prior art specified and discussed herein, it was therefore an object of the invention to provide a thermoplastic mixture based on starch, which allows the production of biodegradable moldings with improved properties, for example improved mechanical properties.

The object of the invention was also a method for producing a thermoplastic mixture for extrudates or granules and the use of the thermoplastic mixture.

These tasks are solved by a mixture with the features of claim 1. Preferred embodiments are the subject of the dependent product claims. In procedural terms, the subject matter of claim 8 solves the problems existing up to the invention. Advantageous modifications of the method according to the invention are protected in the subclaims which refer back to the independent method claim. Claim 12 specifies a use according to the invention.

The fact that a thermoplastic mixture based on starch is available by providing and mixing

100 parts by weight of any native, chemically modified, fermentative, recombinant and / or biotransformation-corrected starch and / or derivatives of the starch mentioned, arithmetically corrected for a water content of zero percent; optionally up to 100 parts by weight of a physiologically acceptable, biodegradable, thermoplastically processable polymer material different from A); 1 to 100 parts by weight; at least one plasticizer in an amount in the range from 10 parts by weight to half the sum of parts by weight A) and B); at least one phosphate in an amount ranging from 0.01 part by weight to (A) + B)) / 10 parts by weight; optionally up to (A) + B)) parts by weight of other customary additives;

wherein at least the mixing of component E) with component A) takes place with the introduction of thermal and mechanical energy into the thermoplastic mixture, it is not readily possible to create thermoplastically processable starch-based mixtures which have excellent thermoplastic processability which can be processed into molded parts which have excellent mechanical properties and which are nonetheless easily biodegradable, for example rot or compostable.

In addition, the products, such as moldings or films, are essentially biocompatible and, if appropriate, edible, which paves the way for edible packaging, in particular food packaging.

Food packaging is understood to mean both outer packaging that has only temporary contact with the food as well as packaging, such as hoses, casings or coatings, that are in constant contact with the food on their inner surface and are therefore also taken with them when the food is ingested can. The packaging is therefore suitable, among others, for fruit, eggs, cheese, candy, cakes, cookies or effervescent tablets, drinks, meat, sausages or meat.

The use of the molded articles obtainable from the thermoplastic molding compositions according to the invention is not limited to the use in combination with temporary products, but can also be used for the temporary use to protect commodities and capital goods during transport or storage. In particular, here is the protection against climatic To think of influences such as those that occur when transporting automobiles overseas.

In particular, it has now surprisingly been found that when using special, defined additives, such as phosphates, preferably polyphosphates, metaphosphates and / or polymetaphosphates, effects are achieved under special conditions which, on the one hand, modify the starch, but on the other hand further process the starch with conventional thermoplastic processing techniques.

Under the special conditions according to the invention, the modification reaction can be carried out during processing. The additives according to the invention have a positive influence on the properties and the processability of thermoplastic starch mixtures even in low concentrations.

Component A) of the starch mixture according to the invention Component A) is an essential component in the mixture according to the invention.

Component A) is one or more starches, one or more of their derivatives or mixtures of starch and starch derivatives.

An important group of starches comprises the starches obtained from vegetable raw materials. These include starches from tubers, such as potatoes, cassava, maranta, batata, from seeds such as wheat, corn, rye, rice, barley, millet, oats, sorghum, from fruits such as chestnuts, acorns, beans, peas, and the like. a. Legumes, bananas, and from vegetable pulp, e.g. B. the sago palm.

The starches which can be used in the context of the invention essentially consist of amylose and amylopectin, in varying proportions. Particularly good results are obtained, among other things, with starches made from potatoes (e.g. ^® Toffena from SüdStar) and corn (e.g. Maize Starch from National Starch) or polyglucans, which are characterized by a perfectly linear structure of the Mark up polymers.

The molecular weights of the starches useful according to the invention can vary over a wide range. Starches which essentially consist of a mixture of amylose and amylopectin and have molecular weights M _w in the range between 5 × 10 ⁴ and 1 × 10 ⁷ can be used as the basis of the thermoplastic mixture according to the invention. Longer-chain polymers with molecular weights M _{w of} between 1 × 10 ⁶ and 5 × 10 ⁶ are preferred.

Linear polysaccharides, preferably polyglucans, in particular 1,4-aD polyglucan, with molecular weights M _w in the range between 5 × 10 ² and 1 × 10 ⁵ , preferably with molecular weights M _w between 1 × 10 ³ , are also preferred and 5 x 10 ⁴ .

In addition to molding compositions based on starches of native vegetable origin, the invention also includes those thermoplastic mixtures or molding compositions with starches that are chemically modified, obtained by fermentation, are recombinant in origin or were produced by biotransformation (also: biocatalysis).

The invention understands "chemically modified starches" to mean starches in which the properties have been changed chemically compared to the natural properties. This is essentially achieved by polymer-analogous reactions in which starch is treated with mono-, bi- or polyfunctional reagents or oxidizing agents. The hydroxyl groups of the starch polyglucans are preferably converted by etherification, esterification or selective oxidation, or the modification is based on a radical method initiated graft copolymerization of copolymerizable unsaturated monomers onto the starch backbone.

Special chemically modified starches include starch esters such as xanthates, acetates, phosphates, sulfates, nitrates, starch ethers, such as. B. nonionic, anionic or cationic starch ethers, oxidized starches such as dialdehyde starch, carboxy starch, persulfate-degraded starches and similar substances.

"Fermentative starches" in the parlance of the invention are starches which can be obtained by fermentative processes using organisms which occur in nature, such as fungi, algae or bacteria, or which can be obtained by means of fermentation processes. Examples of starches from fermentative processes include, among others, gum arabic and related polysaccharides (Gellan Gum, Gum Ghatti, Gum Karaya, Gum Tragaeauth), xanthan, Emulsan, Rhamsan, Wellan, Schizophyllan, Polygalacturonate, Laminarin, Amylose, Amylopectin and Pectins.

"Starches of recombinant origin" or "recombinant starches" means in particular starches which are obtained by fermentative processes using organisms which do not occur in nature, but modified with the aid of genetic engineering methods, such as natural organisms such as fungi, algae or bacteria Switching on and with the help of fermentative processes. Examples of starches from fermentative, genetically modified processes include amylose, amylopectin and other polyglucans.

"Starches produced by biotransformation" means in the context of the invention that starches, amylose, amylopectin or polyglucans are produced by a catalytic reaction of monomeric building blocks, generally oligomeric saccharides, in particular mono- and disaccharides, using a biocatalyst (also: enzyme) is used under special conditions. Examples of starches from biocatalytic processes include polyglucan and modified polyglucans, polyfructan and modified polyfructans.

Finally, advantageous thermoplastic mixtures can also be obtained using derivatives of the individual starches mentioned. The terms "derivatives of starches" or "starch derivatives" generally mean modified starches, i. H. starches in which the natural amylose / amylopectin ratio has been changed in order to change their properties, a pre-gelatinization has been carried out, which have undergone partial hydrolytic degradation or which have been chemically derivatized.

Special derivatives of starches include oxidized starches, e.g. B. dialdehyde starch or other oxidation products with carboxyl functions, or native ionic starches (z. B. with phosphate groups) or ionically further modified starches, both anionic and cationic modifications come under this term.

Particularly favorable thermoplastic mixtures are obtained if starches are used which have only a small proportion of other compounds which are not attributable to the saccharides (e.g. proteins, fats, oils) (for example and in particular potato starch), or ionic starches as Base material or as an admixture and / or by their uniformity in terms of structure, molecular weight and purity outstanding polyglucans, z. B. 1,4-a-D-polyglucan produced by biotransformation can be used as a starch base.

The thermoplastic mixture according to the invention is arithmetically corrected with respect to component A) or a mixture of components A) to a water content of zero percent. That is, the water content of component A) is determined and deducted accordingly when dimensioning 100 parts by weight, but is taken into account when dimensioning component C). Component B) of the thermoplastic mixture according to the invention _. Starch base

Component B) of the thermoplastically processable mixture according to the invention is an optional component.

It is more precisely a physiologically harmless, essentially also biodegradable, thermoplastically processable polymer material different from A), which can be contained in the mixture in amounts of up to 100 parts by weight. Mixtures of two or more such compounds are also suitable as component B).

A group of materials that meet these requirements is the group of proteins. Components B) which can be used successfully in the context of the invention include, inter alia, gelatin, vegetable proteins such as sunflower protein, soy protein, cotton seed protein, peanut protein, rapeseed protein, plasma proteins, protein, egg yolk and the like.

Favorable mixtures also result in additions of zein, gluten (corn, potatoes), albumin, casein, creatine, collagen, elastin, fibroin and / or whey protein.

Also of interest as component B) are polysacetarides which differ from the starches mentioned under A).

Water-soluble polysaccharides such as alginic acid and its salts, carrageenans, furcellaran, guar gum, agar-agar, gum arabic and related polysaccharides (gum ghatti, gum karaya, gum tragaeauth), tamarind gum, xanthane gum, aralia gum, carob bread are preferred ( ^' locust bean gum ^' ), arabinogalactan, pullulan, chitosan, dextrins, cellulose. Additions of lentinan, laminarin, chitin, heparin, inulin, agarose, galactans, hyaloronic acid, dextrans, dextrins and / or glycogen can also have a favorable effect.

Component C) of the starch mixture according to the invention

Component C) of the mixture according to the invention is an essential component.

Water is contained in the mixture of the invention in an amount of 1 part by weight to 100 parts by weight. If the amount of water is below one part by weight, the destructuring and homogenization of the mixture is insufficient. If the water content is greater than 100 parts by weight, there is a risk that the viscosity of the mixture is too low. Favorable ranges are between about 10 and 75 parts by weight of water. The range between 20 and 60 parts by weight is of particular interest.

If significant proportions of the optional component B) are present in the mixture of the invention, this can be taken into account separately when defining the amount of water. In this case, the water content is preferably between one and to). If the water content is approximately half the sum of the parts by weight A) and B), the thermoplasticization of the entire mixture is particularly good. Preferred water contents are also between about 5 and (A) + B)) / 2 parts by weight, water parts between 10 and (A) + B)) / 3 parts by weight are particularly useful.

Optimal plasticization of the mixture, ie destructuring of the starch, homogenization of the mixture and its thermoplasticization take place in these preferred areas. In addition to the water actually added, the amount of water C) also includes the water contents of other components to be taken into account, in particular the amount of water bound or contained in component A) or, if appropriate, water bound or contained in compounds E).

The nature of component C) is essentially not critical. You can use demineralized water, deionized water or tap water or water of other origin just as well, provided that the water content of salts or other foreign substances is tolerable with regard to the intended use.

Component D) of the starch mixture according to the invention

Component D) is essentially contained in the mixture according to the invention.

The amount of component D) is of particular importance, i. H. freely selectable only within defined limits. One or more plasticizers are contained in the composition of the invention in an amount in the range from 10 parts by weight to half the sum of parts by weight A) and B). If the content of plasticizing compounds is below 10 parts by weight, the plasticization is not sufficient, even with higher mechanical and / or thermal energies. If the plasticizer content exceeds an amount which corresponds to half the sum of parts by weight A) and B), no appreciably better plasticization of the mixture is observed.

Plasticizer amounts in the range from 12.5 to (A) + B)) / 2 parts by weight are favorable; contents of plasticizers in the range from 15 to (A) + B)) / 4 parts by weight are particularly expedient. In the context of the invention, the terms plasticizing,

Plasticizers, plasticizers, or elasticizers synonymous with plasticizers.

All indifferent, preferably organic, substances with generally low vapor pressure can be used, which, without chemical reaction, preferably through their dissolving and swelling capacity, but also without such, interact physically with components A) and optionally B) and form a homogeneous system with them.

Component D) to be used according to the invention preferably gives the mixture a lower freezing temperature, increased shape-changing capacity, increased elastic properties, reduced hardness and, if appropriate, increased adhesion.

Preferred plasticizers according to the invention are odorless, colorless, light, cold and heat resistant, low hygroscopic, water resistant, not harmful to health, hardly flammable and as little volatile, neutral reaction, miscible with polymers and auxiliaries and have good gelling behavior. In particular, they should have compatibility, gelling power and plasticizing activity with respect to components A) and optionally B).

Furthermore, the compounds to be used according to the invention as component D) should have low migration, which is particularly important for applications of the shaped bodies according to the invention in the food sector.

Particularly preferred plasticizing components D) include, among others, dimethyl sulfoxide, 1, 3-butanediol, glycerin, ethylene glycol, propylene glycol, diglyceride, diglycol ether, formamide, N, N-dimethylformamide, N-methylformamide, dimethylacetamide, N-methylacetamide and / or N, N ^' -dimethylurea.

Polyalkylene oxide, glycerol mono-, di- or triacetate, sorbitol, or other sugar alcohols, such as erythritol, sugar acids, such as gluconium, are also particularly useful. acid, polyhydroxycarboxylic acids, saccharides such as glucose, fructose or sucrose, as well as citric acid and its derivatives.

Component E) of the starch-based thermoplastic mixture according to the invention

Component E) is essential for the mixture according to the invention.

The amount with which component E) is contained in the mixture according to the invention is of particular importance. Component E) is contained in the mixture according to the invention in amounts between 0.01 parts by weight and (A) + B)) / 10 parts by weight. At least 0.1 part by weight is preferred, preferably 0.1 - (A) + B)) / 20 parts by weight.

If the amount of component E) is too small, the mechanical properties of the moldings obtainable from the mixture according to the invention are neglected. If the amount exceeds the value of (A) + B)) / 10 parts by weight, the plasticization of the molding composition is impaired.

According to the invention, component E) is phosphates. In the context of the invention, this includes salts and esters of the various

Understand phosphoric acids. However, the salts of the various phosphoric acids are far preferred for the invention. According to the invention, one or more salts and / or esters of the various phosphoric acids, and therefore one or more phosphates, can form component E) as component E).

As component E), ortho-phosphates of the general formulas M'H ₂ PO ₄ (for example NaH ₂ PO ₄ ) and M "(H ₂ PO ₄ ) ₂ [for example Ca ( H ₂ PO ₄ ) ₂ ], secondary orthophosphates of the general formulas M ' ₂ HPO ₄ or M "HPO ₄ (eg K ₂ HPO ₄ , CaHPO ₄ ) or tertiary orthophosphates of the general formulas M' ₃ PO ₄ or M " ₃ (PO ₄ ) ₂ [e.g. Na ₃ PO ₄ , Ca ₃ (PO ₄ ) ₂ ], where M 'for a monovalent cation such as ⁺ NRR ^' R ^" R ^'" , where R, R ^' , R ^" and R ^{'" are} independently the same or differently represent hydrogen, (C _r C ₈ ) -alkyl, linear or branched, (C ₄ -C ₈ ) -aryl, preferably phenyl, alkali metal ion, preferably Na ⁺ or K ⁺ , M "for a divalent cation, preferably alkaline earth metal ion , particularly preferably Ca ^2+, is used.

Of particular interest as component E) is also the group of the condensed phosphates, which are derived from the acid salts of orthophosphoric acid and form as a result of heating, which in turn can be divided into metaphosphates (systematic name: cyclopolyphosphates) and polyphosphates (systematic name: catena -Polyphosphate).

Preferred representatives include, among others, Graham's salt, Kurrol's salt and Maddrell's salt as well as melting or glow phosphates.

Particularly useful modifiers E) include metaphosphates of the general formula M ' _n [P _n O _3n ], in which M ^{1 is} a monovalent cation, preferably metal ion, advantageously alkali metal ion, preferably Na ⁺ or K ⁺ , or ⁺ NRR ^' R ^" R ^'" , in which R, R ^' , R ^" and R ^'", independently of one another, are the same or different for hydrogen, (C _r C ₈ ) -alkyl, linear or branched, (C ₄ -C ₈ ) -aryl, preferably phenyl, is and n is a whole natural positive number, preferably in the range between 3 and 10. Of these turn, those metaphosphates are preferred in which n is 3, 4 or 5 and M 'is sodium or potassium. Most preferred are sodium trimetaphosphate, sodium tetrametaphosphate and sodium pentametaphosphate.

Advantageous mixtures also result with polyphosphates of the general formula M '^ P _n O ^] or M' _n [H _2n P _n O _{3n + 1} ], in which M 'is a monovalent cation, preferably metal ion, suitably alkali metal ion, preferably Na ⁺ or K ⁺ , or ⁺ NRR ^' R ^" R ^'" , in which R, R ^' , R ^" and R ^'", independently of one another, are the same or different for hydrogen, (C _r C ₈ ) -alkyl, linear or branched, (C ₄ - C ₈ ) aryl, preferably phenyl, and n is a whole natural positive number greater than 2. Of these, sodium and potassium polyphosphates in which n> 10 are preferred. Mixtures with favorable properties can also be obtained if, as component E), polyphosphates of the general formula M ' _{n + 2} [P _π O _{3n + 1} ] are used, in which M' is a monovalent cation, preferably metal ion, advantageously alkali metal ion, preferably Na ⁺ or K ⁺ , or ⁺ NRR ^' R ^" R ^" \ where R, R ^' , R "and R '" are, independently of one another, the same or different for hydrogen, (C _r C ₈ ) -alkyl, linear or branched, (C ₄ -C ₈ ) aryl, preferably phenyl, and n is a whole natural positive number in the range between 3 and 10 ,. Among others, pentasodium tripolyphosphate is preferred.

Furthermore, the thermoplastic mixture according to the invention is distinguished in a particular embodiment in that component E) is an alkali metal salt of a metaphosphate or polyphosphate.

A further advantageous modification of the thermoplastic mixture according to the invention results from the fact that component E) is sodium trimetaphosphate, sodium metaphosphate, sodium polyphosphate and / or sodium hexametaphosphate, preferably sodium polyphosphate.

The phosphates mentioned can have a different degree of hydration. Due to the relatively small proportions of component E) in the thermoplastic mixture, this water content is generally irrelevant when determining the parts by weight of E) and is not harmful because of the essential component C).

Component F) of the starch mixture according to the invention

Component F) of the mixture according to the invention is optional, ie it does not have to be present in the mixture according to the invention. It can be one or more substances which can be used in total as component F) in amounts of up to 200 parts by weight, preferably not more than 100 parts by weight.

Common additives or additives include fillers, lubricants that differ from the plasticizers mentioned under D), flexibilizing agents, pigmenting agents, dyes, mold release agents and others.

Suitable fillers are, for example, synthetic polymers which are virtually soluble in the mixture, such as polymers based on lactic acid, such as ^® Lacea from Mitsui, ^® Resomer from Boehringer Ingelheim, and other polymers based on lactic acid and related polymers of lactic acid, from Wako Pure Chemical Industries Ltd., Medisorb Co., Birmingham Polymers, Inc., Polysciences Inc., Purac Biochem BV, Ethicon, Cargill or Chronopo, it being clear that this list cannot correspond to an absolute completeness.

Furthermore, it is also possible to use other polyesters made of preferably physiologically harmless hydroxycarboxylic acids, for example polyhydroxybutter co-valeric acids, in particular polyester from the ^®Biopol brand, etc.

It is also proposed to add at least one inorganic filler, such as magnesium oxide, aluminum oxide, SiO ₂ , TiO ₂ , etc.

Organic or inorganic pigments are particularly suitable for coloring the mixture, especially also biocompatible, i.e. so-called pearlescent pigments to be classified as harmless to living organisms, based on silicate structures, which in principle can therefore be classified as edible and are used in amounts between 0.001 and 10 parts by weight. Animal or vegetable fats and / or lecithins, which are preferably used in hydrogenated form, are particularly suitable for improving the flow properties, these fats and other fatty acid derivatives preferably having a melting point of greater than 50.degree.

In order to reduce the hydrophilicity and thus the water resistance of the thermoplastically processable mixture during and after processing, a crosslinking agent can be added to the mixture in minor amounts in order to chemically modify the starch. Alkyl siloxanes are preferably used in amounts of up to 5 parts by weight.

Also suitable as crosslinking agents are, inter alia, di- or polyvalent carboxylic acids and their anhydrides, acid halides of di- or polyvalent carboxylic acids, acid amides of di- or polyvalent carboxylic acids, derivatives of di- or polyvalent inorganic acids which are different from component E) , Epoxides, formaldehyde and / or urea derivatives, divinyl sulfones, isocyanates, oxo compounds and / cyanamide, these compounds also being particularly suitable for chemical modification subsequent to thermoplastic processing and can thus contribute to further improvement, in particular of the mechanical properties.

Components A) to F) of the mixture according to the invention are mixed with one another in such a way that at least the mixing of component E) with component A) takes place with the introduction of thermal and mechanical energy into the thermoplastic mixture.

Preferably, the mechanical and thermal energy are introduced simultaneously, e.g. B. by working under elevated temperature and simultaneously applying shear forces to the thermoplastic mixture to be plasticized on a starch basis. In general, the mixtures are more homogeneous at higher temperatures. However, the temperatures should not be too high to avoid unnecessary discoloration or decomposition of the molding compounds. In this connection, the thermoplastic mixture of the invention can be obtained in a preferred modification by mixing at temperatures in the range from> 60 ° C. to 200 ° C.

Basically, the homogenization of the mixture increases with the performance. I.e. the higher the power introduced into the mixing unit, the better the homogenization of the thermoplastic starch mixture.

A further modification of the invention therefore provides a thermoplastic mixture which can be obtained by mixing under the action of high-shear mixing units, the energy introduced into the mixture being able to be derived in particular from the performance of the processing machines used. Processing is possible, above all, with apparatuses whose plasticizing elements are equipped with torques in the range from 5 to 300 Nm (1 Newton meter). Processing with a torque in the range from 10 to 100 Nm has proven to be advantageous. Processing in a torque range of 20 to 40 Nm is preferred.

A particularly favorable absorption of thermal and / or mechanical energy by the mixture is achieved if the components of the mixture according to the invention are mixed and homogenized in a plastic processing machine, such as an extruder, kneader or similar units. The process can preferably be carried out on single or twin screw extruders. These are preferably composed of individual housings which have temperature-controlled jackets. The design of the screws is not subject to any restrictions; conveying elements (with or without shear edges), kneading elements and / or mixing elements can be present. In addition, it is possible and often advantageous in some cases, that is to say sections that are stagnating or returning in sections. Use elements in the extruder to influence and control residence time and mixing properties.

The order in which ingredients A) to F) are mixed can also be particularly important.

The invention thus also relates to a process for producing a thermoplastic mixture based on starch, in which

A) 100 parts by weight of any native, chemically modified, fermentative, recombinant and / or biotransformation-corrected starch and / or derivatives of the starches mentioned, arithmetically corrected for a water content of zero percent;

B) optionally up to 100 parts by weight of a physiologically acceptable, biodegradable, thermoplastically processable, polymeric material different from A);

C) 1 to 100 parts by weight of water;

D) at least one plasticizer in an amount in the range from 10 parts by weight to half the sum of parts by weight A) and B); E) at least one phosphate, preferably phosphoric acid salt, in an amount in the range from 0.01 part by weight to (A) + B)) / 10 parts by weight; F) optionally up to (A) + B)) parts by weight of other customary additives; prepared and mixed together,

wherein component E) is added to components A) to D) and optionally F), at least mixing component E) with the remaining components with the introduction of thermal and mechanical energy, preferably under the action of elevated temperature and simultaneous exercise of Shear forces, the thermoplastic mixture takes place. This procedure differs significantly in terms of type and effect from the known prior art.

Until now, phosphoric acids or their salts or esters have been used as modifiers in the production of thermoplastic mixtures based on starch, the starch grain was exclusively and always directly modified, or crosslinking was brought about by a high addition of parts by weight of the phosphate and subsequent thermal treatment Molding compounds that are no longer accessible to thermoplastic processing.

In contrast to this, the procedure according to the invention ensures that not only the surface of the starch grain, but also the starch in the entirety of its molecules is preferably modified on the starch backbone. This leads to different types of products, the improved properties of which were not easily predictable.

Addition of component E) during processing in the homogenization or mixing unit, such as in a kneader or extruder, under alkaline to acidic conditions means that the reaction with starch, starch derivatives or admixed proteins is only to a minor extent equivalent to crosslinking. That the focus is on the modification of the polymer backbone.

This difference to known starch phosphates from the prior art can also be reflected, for example, in the degree of substitution.

The number of hydroxyl groups per glucose unit of starch, which is replaced by another functional group (phosphates), is referred to as the degree of substitution DS (“degree of substitution”).

There are three free hydroxyl groups per glucose unit. Thus the degree of substitution can vary from 0.0 to 3.0. The degree of substitution DS is therefore a purely statistical variable. A degree of substitution DS of 1.0 only means that, on average, one hydroxyl group on each grucose unit is replaced by one substituent. That is, a DS of 1.0 does not necessarily mean that there is a substituent next to two unsubstituted hydroxyl groups on each glucose unit.

For example, it is known that native starch per se can contain phosphate groups. The degree of substitution is in the range of about 0.001. This means that, purely statistically, a phosphate group is present in the polymer approximately every 300 glucose units.

Now it is the case with the known methods which modify the starch as a grain and thus largely only on the surface in such a way that degrees of substitution DS in the range from about 0.001 to 0.01 can be assumed.

According to the invention, however, a significantly higher DS is achieved by the modification with phosphates (component E)) during the plasticization. This is between> 0.01 and 1.0. The DS for component A) modified according to the invention is preferably in the range from 0.05 to 0.5. The DS is particularly useful from 0.1 to 0.3.

In addition, by adding plasticizers which per se have a high ratio of hydroxyl groups or other hydrogen-bonding groups to carbon atoms, the reaction of the phosphate can also couple the plasticizer to the starch backbone with suitable reaction control, which ultimately - especially during processing - leads to a reduction in the migration of the plasticizer from the mixture. At the same time, however, the plasticizing effect of the plasticizer is not close, which enables the destructuring of the starch in the sense of an opening of the starch grain. However, this possibility of interpreting the reactions that lead to the surprisingly found results does not exclude other possibilities of interpretation.

The thermoplastic molding composition according to the invention can be processed into products by the known processing methods. So it can e.g. B. granulated or pelletized in a first step.

The invention thus also relates to granules which can be obtained by extrusion and pelletization from the thermoplastic mixture according to the invention.

In addition, biodegradable moldings or films with improved properties, preferably improved mechanical properties, can be obtained either directly or by renewed thermoplastic processing of a thermoplastic granulate.

Finally, the invention also includes the use of the thermoplastic mixtures for the production of molded parts or films.

The thermoplastic molding compositions and the shaped articles and films obtained by further processing are distinguished in that the admixture of the essential component E) achieves both increased temperature resistance and an improvement in flame resistance.

Overall, the products according to the invention thus cover a large number of possible uses. These include, in particular, adhesive adhesives for paper and corrugated cardboard, moldings which are produced by injection molding, in particular rods, tubes, bottles, capsules, granules, food additives, films, as coatings or free-standing films, also as laminates, especially Films, packaging materials, pouches, controlled release release materials of active substances in general, in particular pharmaceuticals, pesticides or other active substances, fertilizers, flavorings etc. used in agro-culture, etc. The active substance can be released from films, foils, compacts, particles, microparticles, rods or other extrudates or other shaped articles.

Further preferred applications include food packaging, in particular sausage or cheese casings, absorbers, powder and the like.

In a particular embodiment, the thermoplastic mixtures according to the invention are used for the production of moldings for the controlled release of active substances, such as tablets or coated tablets.

Another expedient and particularly advantageous use of the thermoplastic mixture according to the invention relates to the production of moldings which are suitable for the production of solid moldings, hollow bodies or combinations thereof.

Another outstanding use of the thermoplastic mixture according to the invention is in the production of films for use in agriculture.

In a further particular modification, the invention provides for the use of the thermoplastic mixture for the production of films for use in food applications.

Another special use according to the invention of the thermoplastic mixture lies in the production of films for use as food packaging.

Another extremely favorable use of the thermoplastic mixture according to the invention results in the production of films for use as food packaging with full surface contact with the food.

Finally, it is also particularly advantageous to use the thermoplastic mixture according to the invention, in which flat or tubular films are produced for use as food casings for sausage and cheese.

Also preferred in the context of the invention is the use of the thermoplastic as temporary protective films for technical articles of daily use.

The following examples illustrate the subject matter of the invention.

example 1

Production of a thermoplastic processable blend of potato starch with sodium polyphosphate, gum arabic and glycerin:

The compounds are provided in a commercially available kneading unit (Brabender kneader). The kneading unit is heated to 100 ° C. 30 g of potato starch ( ^® Toffena from SüdStar) are added while the kneading unit is in the operating state. 0.9 g of NaCO ₃ are dissolved in 10 g of water and added to the potato starch in the kneader. The mixture is homogenized. The process takes about 3 minutes. Then 9 g of gum arabic are added at once. It is homogenized again. Then 9 g of glycerin are added in portions (about 3 portions of equal size, each with a 2-minute kneading interval between the additions). After a further 2 minutes, 1.2 g of sodium polyphosphate (Riedel de Haen) dissolved in 5 ml of water are added. The entire mixture is kneaded for a further 2 minutes. The mass is removed while the device is still heated. The product is a homogeneous Mass that is slightly yellow in color. It is a non-transparent product. After cooling, the thermoplastic mass can be processed further.

The films obtained from thermoplastic processing of the product are transparent and show good mechanical strength.

Comparative Example 2

Production of a thermoplastic blend mixture from potato starch with sodium polyphosphate and gum arabic:

The preparation of this mixture is identical to the description in Example 1. The only difference in the recipe is that glycerol is not used as a plasticizer.

After homogenization has been completed, the mass is removed while the device is still heated. The product is a homogeneous mass that is light brown in color. It is a non-transparent product that tends to become brittle. Further processing, in particular into foils or films, can only be achieved after the molding compound has been washed beforehand.

Example 3

Production of a thermoplastically processable blend of casein and potato starch with sodium polyphosphate:

The connections are made in a commercially available kneading unit (working kneader). The kneading unit is heated to 100 ° C. 20 g of casein and 10 g of potato starch (Toffena from SüdStar) are added in the operating state of the kneading unit. 1.2 g of sodium polyphosphate (Riedel de Ha- en) added dissolved in 5 ml of water. It is homogenized for 3 minutes. 6 g of glycerin are then added in portions (about 3 portions of equal size, each with a 2-minute kneading interval between the additions). It is homogenized for a further 2 minutes. The product is a slightly yellowish, thermoplastically deformable mass that can be further processed immediately after being removed from the kneading unit while it is still heated or after it has cooled.

The films obtained from thermoplastic processing are transparent and show good mechanical properties in terms of elongation at break and tensile strength. Example 4

Production of a thermoplastically processable blend of potato starch with sodium polyphosphate:

The procedure is analogous to that described in Example 1. The kneading unit (Brabender) is heated to 100 ° C. 30 g of potato starch (Toffena from SüdStar) are added while the kneading unit is in operation. 0.9 g of Na ₂ CO ₃ dissolved in 10 ml of water are immediately added. It is homogenized for 3 minutes. 15 g of glycerin are then added in portions (about 3 portions of equal size, each with a 2-minute kneading interval between the additions). It is homogenized for a further 2 minutes and then 0.15 g of sodium polyphosphate (Riedel de Haen) in 5 ml is added. The experiment is ended after a further homogenization phase. The product is a slightly yellowish, thermoplastic material that can be processed after cooling.

The films obtained from thermoplastic processing are transparent and show very high mechanical strengths. The film thicknesses range from 100 to 150 mm. The flexibility of the foils permits further processing, for example filling with food. Example 5

Production of a thermoplastic processable blend of potato starch and casein with sodium polyphosphate:

The procedure is analogous to that described in Example 1. The kneading unit is heated to 120 ° C. 21 g of potato starch (Toffena from SüdStar) and 9 g of casein are added in the operating state of the kneading unit (Brabender). 0.9 g of NaCO ₃ are dissolved in 10 g of water and added to the mixture of casein and potato starch in the kneader. The mixture is homogenized. The process takes about 3 minutes. Then 1.5 g of Pluronic F 68 in 10 ml of water and 6 g of glycerol are added in succession. It 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 kneaded again for a further 2 minutes. The mass is removed while the device is still heated. The product is a very white, homogeneous mass. After cooling, the thermoplastic mass can be processed further.

The films obtained from thermoplastic processing are opaque. The film thickness is approximately 160 to 200 mm. The mechanical strength together with the film thickness, which is achieved by processing by pressing, results in a certain brittleness. For further processing with regard to an application in the food sector, watering is therefore necessary.

Example e

Production of a thermoplastically processable blend of casein and corn starch with sodium polyphosphate:

The procedure is analogous to that described in Example 1. The kneading unit (Brabender) is heated to 100 ° C. 24 g casein and 6 g corn starch are in the Operating state of the kneading unit added. After a short time, 10 ml of water and 4 g of glycerin are added. After a further brief homogenization phase, 0.8 g of sodium polyphosphate (Riedel de Haen) in 2 ml of water are added. The experiment is ended after a further homogenization phase. The product is a slightly yellowish, thermoplastically deformable mass that can be processed after cooling.

The films obtained from thermoplastic processing (pressing technique) are slightly opaque and show high mechanical strength. The film thicknesses range from 170 to 190 mm. The flexibility of the foils permits further processing, for example filling with food.

Example 7

The procedure is analogous to that described in Example 1. The kneading unit (Brabender) is heated to 100 ° C. 15 g of casein and 15 g of potato starch (e.g. Toffena from SüdStar) are added when the kneading unit is in the operating state. After a short time, 1.5 g of citric acid in 10 ml of water and 6 g of glycerin are added. After a further brief homogenization phase, 1.2 g of sodium polyphosphate (Riedel de Haen) in 5 ml of water are added. The experiment is ended after further homogenization. The product is a yellowish, homogeneous, solid mass that can be processed after cooling.

The films obtained from thermoplastic processing (press technology) are yellowish and transparent to slightly opaque. The foils are very thin and range from 80 to 100 mm.

Example e Production of foils by means of pressing technology from the thermoplastic molding compositions produced in Examples 1 to 7:

The procedure for processing a thermoplastic molding composition as described is as follows. A commercially available press from Schwabenthan (Polystat 300 S) is used for this. The press is preheated to 100 ° C. The sample preparation is carried out in a "sandwich technique" between two tissue-reinforced polytetrafluoroethylene (PTFE, ^® Teflon), which are kept at a distance with an approximately 100 mm thick metallic frame. About 2 g of the mass produced in the kneader are mixed in during the preparation The sample is heated for 5 minutes at 100 ° C. and a pressure of 1 t, and then the sample is pressed at 100 ° C. for 5 minutes and a pressure of 10 t, which corresponds to a pressure of 200 bar. The press is relieved and the sample is transferred to another press for cooling, which is a water-cooled press from Robert Fuchs Hydraulische Maschinen und Werkzeuge. During the cooling process over a period of 2 minutes, a pressure of 50 The sample can then be taken to be used for further investigations, and it should be noted that storage in air depends on the hydrophi iie the materials used shows signs of aging due to fluctuating water content.

Example 9

Production of a thermoplastically processable blend mixture from corn starch with a high content of sodium polyphosphate:

The connections are made in a commercially available kneading unit (IKA duplex kneader). The kneading unit is heated to 100 ° C. 150 g of potato starch (maize starch from National Starch) and 45 g of glycerin are added in the operating state of the kneading unit. 5.0 g of NaCO ₃ are dissolved in 50 g of water and added to the corn starch in the kneader. The mixture is homogenized siert. The process takes about 5 to 10 minutes, during which time the mixture becomes glassy. 15 g of sodium triphosphate (Riedel de Haen) are then dissolved in 25 ml and added. The entire mixture is kneaded for a further 5 minutes. The mass is removed while the device is still heated.

Comparative Example 10

Production of a thermoplastically processable blend mixture from corn starch without sodium polyphosphate:

The connections are made in a commercially available kneading unit (IKA duplex kneader). The kneading unit is heated to 100 ° C. 150 g of potato starch (maize starch from National Starch) and 45 g of glycerin are added in the operating state of the kneading unit. 5.0 g of NaCO ₃ are dissolved in 50 g of water and added to the corn starch in the kneader. The mixture is homogenized. The process takes about 5 to 10 minutes, during which time the mixture becomes glassy. The entire mixture is kneaded for a further 5 minutes. The mass is removed while the device is still heated.

Example 11

Production of foils using press technology from thermoplastic materials based on starch

The thermoplastic molding compositions are further processed into films using the pressing technique described here. A commercially available press from Schwabenthan (Polystat 300 S) is used for this. The press is preheated to 100 ° C. The sample preparation takes place in a "sandwich technique" between two tissue-reinforced Teflon foils, which are kept at a distance with an approximately 100 mm thick metallic frame. About 2 g of the mass produced in the kneader are placed in the middle of the bottom slide during preparation. The sample is tempered for 5 minutes at 100 ° C and a pressure of 1 t. The sample is then pressed at 100 ° C. for 5 minutes and a pressure of 10 liters. This corresponds to a pressure of 200 bar. The press is relieved and the sample is transferred to another press for cooling. This is a water-cooled press from Robert Fuchs Hydraulische Maschinen und Werkzeuge. A pressure of 50 bar is applied during the cooling process over a period of 2 minutes.

Example 12

Investigation of the temperature stability of films produced according to Example 11 from the thermoplastic molding compositions from Example 9 and Comparative Example 10:

A film measuring 5 cm by 5 cm is placed on a ring with an inner diameter of 3 cm. Fixation is achieved with metal clips so that slight air movements on the fixation of the foils do not change anything. The ring is fixed in a horizontal arrangement via a holding rod attached to the ring in such a way that the film is in a parallel arrangement at a height of 20 cm above the laboratory bench. An open flame is arranged below the ring, which provides identical energies per time for all examinations and has a height of 1-2 cm. The upper limit of the open flame is 5 cm +/- 0.5 cm from the film. The times are measured with a stopwatch which are necessary to achieve a charring of the film which comprises more than 50% of the ring area covered by the thermoplastic film. Averages of ten measurements each are formed.

Film from Example 9 with sodium triphosphate: 25 sec. +/- 3 sec.

Film from comparative example 10 without sodium triphosphate: 16 sec. +/- 3 sec. Further advantages and embodiments of the invention result from the following patent claims.

Claims

claims

1. Thermoplastic mixture based on starch for the production of biodegradable moldings with improved mechanical properties, obtainable by providing and mixing

B) optionally up to 100 parts by weight of a physiologically acceptable, biodegradable, thermoplastically processable polymer material different from A);

C) 1 to 100 parts by weight of water;

D) at least one plasticizer in an amount in the range from 10 parts by weight to half the sum of parts by weight A) and B);

E) at least one phosphate in an amount in the range of 0.01 parts by weight to (A) + B)) / 10 parts by weight;

F) optionally up to (A) + B)) parts by weight of other customary additives;

wherein at least the mixing of component E) with component A) takes place with the introduction of thermal and mechanical energy into the thermoplastic mixture.

2. Thermoplastic mixture according to claim 1, characterized in that component E) is contained in an amount of at least 0.1 part by weight.

3. Thermoplastic mixture according to claim 1 or 2, characterized in that component E) is contained in an amount up to (A) + B)) / 20 parts by weight.

4. Thermoplastic mixture according to one or more of the preceding claims, characterized in that component E) is an alkali metal salt of a metaphosphate or polyphosphate.

5. Thermoplastic mixture according to claim 4, characterized in that component E) is sodium trimetaphosphate, sodium metaphosphate, sodium polyphosphate and / or sodium hexametaphosphate, preferably sodium polyphosphate.

6. Thermoplastic mixture according to one or more of the preceding claims, characterized in that it is obtainable by mixing at temperatures in the range from> 60 C to 200 ° C.

7. Thermoplastic mixture according to one or more of the preceding claims, characterized in that it is obtainable by mixing under the action of high-shear plasticizing elements having mixing units, with the plasticizing elements torques in the range from 10 to 100 Nm, preferably 20 to 40 Nm, achievable are.

8. A process for the preparation of a thermoplastic starch-based mixture, in which

A) 100 parts by weight of any native, chemically modified, fermentative, recombinant and / or biotransformation-corrected arithmetically corrected to a water content of zero percent and / or derivatives of the named starches;

B) optionally up to 100 parts by weight of a physiologically acceptable, biodegradable, thermoplastically processable, polymeric material different from A); C) 1 to 100 parts by weight of water; D) at least one plasticizer in an amount in the range from 10 parts by weight to half the sum of parts by weight A) and B);

E) at least one phosphate, preferably phosphoric acid salt, in an amount in the range from 0.01 part by weight to (A) + B)) / 10 parts by weight; F) optionally up to (A) + B)) parts by weight of other customary additives;

provides and mixed with one another, characterized in that component E) is added to components A) to D) and optionally F), at least mixing component E) with the remaining components while introducing thermal and mechanical energy into , preferably under the influence of elevated temperature and simultaneous exertion of shear forces, the thermoplastic mixture takes place.

9. Granules obtainable from the thermoplastic mixture according to claims 1 to 7 by extrusion and pelletization.

10. Biodegradable molding or film with improved mechanical properties having the thermoplastic mixture according to the

Claims 1 to 7.

11. Use of the thermoplastic mixture according to claims 1 to 7 for the production of moldings or films.

12. Use of the thermoplastic mixture according to claims 1 to 7 for the production of moldings for the controlled release of active ingredients.

13. Use of the thermoplastic mixture according to claims 1 to 7 for the production of moldings for the production of solid moldings,

Hollow bodies or combinations thereof.

14. Use of the thermoplastic mixture according to claims 1 to 7 for the production of films for use in agriculture.

15. Use of the thermoplastic mixture according to claims 1 to 7 for the production of films for use in food applications.

16. Use of the thermoplastic mixture according to claims 1 to 7 for the production of films for use as food packaging.

17. Use of the thermoplastic mixture according to claims 1 to 7 for the production of films for use as food packaging with full surface contact with the food.

18. Use of the thermoplastic mixture according to claims 1 to 7 for the production of flat or tubular films for use as food casings for sausage and cheese.

19. Use of the thermoplastic mixture according to claims 1 to 7 for use as temporary protective films for technical commodities.