EP0799245A1

EP0799245A1 - Biodegradable thermoplastic starches

Info

Publication number: EP0799245A1
Application number: EP95943167A
Authority: EP
Inventors: Volker Warzelhan; Ursula Seeliger; Ivan Tomka
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1994-12-23
Filing date: 1995-12-19
Publication date: 1997-10-08
Also published as: JPH10511419A; WO1996020220A1

Abstract

Biodegradable thermoplastic starches contain side chains bound by ester groups. The percentage by weight of the side chains equals at least 10 in relation to the molecular weight (numeric mean value Mn) of the biodegradable thermoplastic starches. Global migration is lower than 200 mg/dm2 when determined in the conditions set by guideline 90/128/EEC.

Description

Biodegradable and thermoplastically processable starch

description

The present invention relates to biodegradable and thermoplastically processable starch which contains side chains bonded via ester groups, the proportion by weight of the side chains being at least 10% by weight, based on the biodegradable and thermoplastically processable starch, and the global migration being less than 50 mg / dm ² , determined in accordance with the conditions laid down in Directive 90/128 / EEC.

In addition, the present invention relates to methods for producing this starch and to the use thereof. Preferred embodiments can be found in the subclaims and in the description.

In order to melt starches and thus process them thermoplastically, their crystal structure stabilized by hydrogen bonding must be disturbed. For this purpose, so-called native starch, which is produced by drying raw starch obtained from plants and has a water content of about 10 to 20% by weight, based on the starch, with mechanical work and optionally with the addition of further water and under Pressure to be heated. However, this physically modified fusible starch has the disadvantage that it can only be processed under special conditions. Fusible starches have therefore been developed which are homogeneous mixtures of native starch and an additive and which are referred to as thermoplastically processable starch (TPS) (WO 90/05161).

From US-A-5 095 054 it was known that starch can be plasticized with polyvinyl alcohol. However, polyvinyl alcohol breaks down very slowly when mixed with starch.

Certain ethers and esters of starch, such as starch acetate or starch acetate butyrate, are known which can be processed thermoplastic - essentially without the addition of plasticizers or plasticizers. However, these known derivatives of starch are not biodegradable or only very slowly.

From EP-A-542 155 and DE-A-42 37 535 it was known that TPS can be partially esterified with polyhydroxyalkanoates or with the lactones of hydroxyalkanoates. DE-A-42 37 535 discloses the starches which, for example, are converted into TPS with hydroxy acids such as lactic acid as an additive. For the Dried native starches, ie native starches with a water content of less than 10%, are preferably used to produce the TPS. The TPS is then reacted with polymers which contain groups reactive towards the starch. According to the description, suitable reactive groups are epoxy, anhydride or ester groups which are built into the polymer chain and become reactive with the starch at elevated temperature. The starches obtainable in this way have a low degree of grafting and contain homogeneously mixed aggregate.

DE-A-42 37 535 e.g. the implementation of certain TPS with polycaprolactone described. For this purpose, the TPS is degassed with polycaprolactone before the reaction in order to be able to use a TPS with the lowest possible water content. Compositions produced in this way are biodegradable. However, they can only be processed thermoplastically as long as the aggregate is contained in the composition. However, they have the disadvantage that the aggregate mixed homogeneously with the starch emerges from the composition during processing and also later in the course of time or can be eluted. This is particularly disadvantageous if packaging materials for the food sector are to be produced from the compositions or their blends with other polymers.

It was therefore an object of the present invention to provide starch-based compositions which can be processed well thermoplastically using the customary processes, are biodegradable at the same time and, moreover, have the lowest possible content of constituents which can be eluted.

This task is fulfilled by the compositions defined at the beginning. Preferred embodiments can be found in the subclaims and the description.

According to the invention, such a wide variety of origins or compositions can be used as starch. The expression starch includes, for example, polysaccharides of natural, vegetable origin, which are mainly composed of amylose and / or amylopectin. Starch can be obtained from various plants, for example potatoes, rice, tapioca, corn, peas or cereals such as wheat, oats or rye. Starches made from potatoes, corn, wheat or rice are preferred. Mixtures of starches of different origins can also be used. In general, native starches, which are produced by drying raw starch obtained from plants and have a water content of about 10 to 20% by weight, based on the starch, are assumed. However, physically modified starches can also be used. These can also be starches which have been modified by adding acids.

Starches can also be used in which the ions contained in the starch have been partially or completely replaced by other ions. Native starches are preferred. Particular preference is given to native starches with a reduced water content, for example a water content of less than 6% by weight, in particular less than 1% by weight, very particularly preferably 0.001 to 0.2% by weight, based on the starch .

The starches according to the invention are biodegradable. In general, this means that the strengths disintegrate under environmental influences in a reasonable and verifiable period of time. The degradation takes place, for example, hydrolytically and / or oxidatively, for the most part through the action of microorganisms such as bacteria, yeast, fungi and algae. Biodegradability can be determined, for example, by mixing samples with compost and storing them for a certain period of time. For example, compost ripened according to ASTM D 5338 is flowed through with CO-free air during co-posting and subjected to a defined temperature program. The ratio of the net C0 release of the sample (after deduction of the C0 ₂ release by the compost without sample) to the maximum C0 ₂ release of the sample (calculated from the carbon content of the sample) is defined as biodegradability. Films made from the starches according to the invention generally show clear signs of degradation, such as fungal growth, cracking and pitting, after only a few days of storage in the compost.

According to the invention, the starches can be processed thermoplastically, i.e. they can be processed at elevated temperatures, for example in the range from 100 to 230 ° C., preferably in the range from 120 to 160 ° C., using conventional methods such as extrusion or injection molding to give extrusion films, blow-molded (tubular) films or molded parts.

According to the invention, the biodegradable and thermoplastic processable starch chains contain side chains which are bonded to the starch molecules via ester groups. To a lesser extent, the starches according to the invention can also contain side groups which are bonded to the starch molecules via ether or acetal groups or a mixture of these groups. The side chains can be derived from monomeric, oligomeric or polymeric compounds which can be esterified, etherified or acetalized with the hydroxyl groups or aldehyde groups contained in the starch. Side chains of different chain lengths can also be bound to the starch molecules. A wide variety of side chains are possible, but preference is given to those which are derived from compounds which are themselves biodegradable. Particular preference is given to those which, during biodegradation, do not give rise to any additional compounds which are harmful to the environment, such as nitrogen compounds which can lead to overfertilization.

Examples of suitable side chains are those derived from hydroxyalkenylcarboxylic acids, their oligomers or polymers, esters of alkane carboxylic acids with diols, their oligomers or polymers or mixtures of the compounds mentioned. Lactic acid, dilactide, polylactide, glycolic acid, glycolide are included , Polyglycolide, caprolactone, polycaprolactone, C to C esters of adipic acid, succinic acid, subacid, glutaric acid, oligomers or polymers of C to C ₄ esters of adipic acid, succinic acid, subacid or glutaric acid. It is also possible to use copolyesters of the compounds mentioned.

Side chains of the following structures are particularly preferred:

wherein R ¹ , R ² , R ^{3 are the} same or different and, independently of one another, can mean a C 1 to C ₅ alkenyl radical. This can be both linear and branched. Preferred alkenyl radicals are methylene, ethylene, propylene, i-propylene, n-butylene, i-butylene and t-butylene. The variables n and m can independently be an integer from 1 to 10.

The biodegradable and thermoplastically processable starch particularly preferably contains side chains which are derived from a mixture of lactic acid and polycaprolactone. The molecular weights (M _π , number average) of the oligo- Polymeric or polymeric side chains are generally in the range from 500 to 100,000, preferably 1000 to 80,000 g / mol.

As a rule, 20 to 80% by weight of all side chains are derived from monomeric compounds and 20 to 80% by weight of all side chains from oligomeric or polymeric compounds.

The degree of substitution of the starch is essential to the invention, since it can only be processed thermoplastically with a sufficiently high degree of substitution, for example at least 0.5 (based on the anhydroglucose units of the starch).

The proportion by weight of the side chains is therefore at least 10% by weight, based on the biodegradable and thermoplastically processable starch according to the invention. It can be, for example, up to 40% by weight, but is also higher. It is preferably at least 15, in particular at least 20% by weight, based on the starch according to the invention. The proportion is particularly preferably at least 30% by weight.

According to the invention, the biodegradable and thermoplastic processable starches have a global migration of less than 50 mg / dm ² , determined in accordance with the conditions specified in Directive 90/128 / EEC. Alternatively, they have a global migration of less than 300 mg / kg of food. Preferred biodegradable and thermoplastically processable starches according to the invention have global migrations of less than 40 mg / dm ² or 240 mg / kg of food, in particular less than 20 mg / dm ² or 120 mg / kg of food. Biodegradable and thermoplastically processable starches according to the invention which have global migrations of less than 10 mg / dm ² or 60 mg / kg of foodstuffs are very particularly preferred. This means that they do not contain any components which, in accordance with the standardized tests listed in the aforementioned directive, leak in an amount that exceeds these limits. Global migration values are determined according to the directive by exposing plastics to various solvents at certain temperatures and for a prescribed period of time. The amount of the components washed out of the plastic is then determined and given in mg / dm ³ . Alternatively, the global migration can be measured by bringing certain foods into contact with the plastic to be examined under standardized conditions. The foreign substances ingested in the food are determined. The global migration figure is expressed as mg / kg of food. The biodegradable and thermoplastically processable starches according to the invention can be prepared by melting native starches or preferably dried native starches with esterifiable additives in a first step. These additives capable of esterification are preferably volatile above 120 ° C. at normal pressure. Both an esterifiable additive and a mixture of different esterifiable additives can be used. Lactic acid is one of the preferred additives capable of esterification. In general, the native starch is melted with the additive capable of esterification at temperatures from 180 to 200 ° C. in closed apparatus such as extruders, cocneters or other mixing units. In a subsequent process step, the flowable mixture of native starch and esterifiable additives thus prepared is reacted in the presence of catalysts with other compounds in the melt or in the presence of at least one solvent which can form ester groups with the hydroxyl groups of the starch (hereinafter called reactive connection). Suitable catalysts are, for example, alkoxylates of titanium (IV) acid or the amino derivatives of these compounds. In addition, carbodiimides such as dicyclohexylcarbodiimide or salts which have "soft", voluminous cations can be used as catalysts. These cations include tetrabutylammonium and tris (dimethylamino) sulfonium. Phosphazene bases, for example P4-phosphazene bases, such as t-octylimino-tris (dimethylamino) phosphorane, l-ethyl-2,4,4,4-pentakis (dimethylamino) -2λ ⁵ , 4λ ⁵ -catenadi (phosphazene, according to -Butyl-4,, 4-tris (dimethylamino) -2,2-bis [tris (dimethylamino) -p osphoranyliden- a ino] -2λ ⁵ , 4λ ⁵ -catenadi (phosphazene), lt-octyl-4, 4,4-tris (diethy-laminol-2,2-bis [tris (dimethylamino) phosphoranylide- na ino] -2λ ⁵ , 4λ ⁵ -catenadiphosphazen, KF / crown ether, LiBr / amidine bases such as LiBr / 1, 8- Diazabicyclo [5.4.0.] Undec-7-ene (LiBr / DBU) and distannoxane are further suitable catalysts. The preferred catalysts include triethoxydiisopropylaminotitanate and P4-phosphazene bases. Mixtures of different catalysts can of course also be used.

Alternatively, the starches according to the invention can also be prepared by dissolving native starches, preferably dried native starches, with the reactive compounds in a solvent without addition of additives and then reacting them in the presence of one of the catalysts mentioned. The reaction can take place in the presence of a dipolar aprotic solvent. Examples of suitable solvents are dimethyl sulfoxide, N, N-dimethylformamide or N, N-dimethylacetamide. However, the reaction can also be carried out in dispersion. 5

The reaction is preferably carried out under the action of shear forces, for example in a kneader or an extruder.

The temperatures are generally in the range from 100 to 10 230 ° C. The temperatures are preferably in the range from 120 to 160.

Unreacted additive that can be esterified can be removed by degassing before or during workup, it being necessary to work at elevated temperatures.

The reaction product can, for example, be washed with suitable solvents and then e.g. dried by degassing and granulated. 0

The biodegradable and thermoplastically processable starch according to the invention can be used alone or as a blend with other biodegradable polymers such as starch or biodegradable polyesters for the production of moldings, films or fibers. It is particularly well suited for the manufacture of packaging materials of all kinds, in particular films for the food sector.

The process according to the invention can also be used for the production of polyesters from mono- and / or oligo- and / or polyesters of different compositions by transesterification and / or esterification and the presence of starch can be dispensed with. The monomers here can be diglycols with dicarboxylic acids, where the dicarboxylic acids can be aliphatic and / or aromatic or can be selected from the range of the hydroxyalkanoates or their lactones.

0

5 Examples

The starch used in all the examples was homogenized from native potato starch with 0.2% by weight of water at 105 ° C. in a kneader.

example 1

Starch and polycaprolactone (PCI), characterized by a Mo lekulargewicht (weight average M _") of 250 000 was dried in Va¬ uum over phosphorus pentoxide. Then 1 g of starch (dried native potato starch with a water content of 0.2% by weight) and 3 g of polycaprolactone were dissolved in 100 ml of dimethyl sulfoxide (DMSO) dried over calcium hydride. The solution was heated to 160 ° C. at 12 mPA and traces of water were expelled.

4.1 g of triethoxy-diisopropylaminotitanate (TEAT) were added to the solution in portions dissolved in DMSO. The reaction temperature was 160 ° C. After the reaction had ended, water was added to the reaction mixture, dialyzed against water, the reaction product was filtered off and washed with water. After drying, the reaction product was washed with 1,2-dichloroethane, dried and examined by spectroscopy.

Examples 2 to 8

Example 1 was repeated, but the catalysts and starch / polycaprolactone ratios given in the table were used.

The following catalysts were used:

A: 1,8-diazabicyclo [5.4.0] -undec-7-ene (1.55)

B: Mixture of N, N-dicyclohexylcarbodiimide (bi) and 4-pyrrolidone-pyridine (b), the following mixing ratios being used.

[% By weight] bi [% by weight] b

BI 70 30

B2 74 26

B3 80 20

B4 96 4

B5 99 1

Phosphazene base P4t-Bu, e.g. available from Fluka.

In Example 2, the catalyst concentration was 15% by weight, based on the starch, and that in Example 8 was 25% by weight, based on the starch. In Examples 3 to 7 so much catalyst mixture was used that the ratio of bi to starch was equimolar.

table

product

Example cat. Weight ratio Reaction% by weight% by weight Sales No. Starch / PCI time PCI starch [%]

[H]

2 A 1.0: 0.7 1.3 31 69 18.9

3 BI 1.62: 1.14 42 47.9 52.1 4.1

4 B2 1.62: 1.14 18.5 12.7 87.3 36.6

5 B3 1.62: 1.14 42 30.3 69.7 6.6

6 B4 1.62: 1.14 18.5 12.7 87.3 9.9

7 B5 1.62: 1.14 20 10.2 89.8 41.0

8 C 1.0: 2.0 2 17.8 82.2 38.8 Biodegradability

The biodegradability of the samples produced was examined in accordance with ASTM D 5 338. For this purpose, approximately 120 g each of the products according to the invention were mixed with 1200 g compost, which came from the organic fraction of urban clear sludge matured for four months, and stored for 45 days. During the composting, the recipient was flowed through by C0 -free air and subjected to a defined temperature program. The CO ₂ gas released during composting was measured continuously. The net C0 release obtained after deduction of the blank value (C0 ₂ release by the compost without sample) was compared with the maximum C0 release (calculated from the carbon content of the sample). This resulted in the biodegradability in% B = [C0 _2net to / C0 _m aχ] • 100.

The starches according to the invention had a biodegradability of 99.7% (standard deviation: 0.5; 95% confidence interval ± 1.4).

Claims

claims

1. Biodegradable and thermoplastically processable starch, containing side chains bonded via ester groups, the weight fraction of the side chains being at least 10% by weight, based on the biodegradable and thermoplastic processable starch, and the global migration being less than 50 mg / dm ² , determined in accordance with the conditions laid down in the Riehlinie 90/128 / EWG.

2. Biodegradable and thermoplastically processable starch according to claim 1, in which the side chains are derived from hydroxyalkenylcarboxylic acids, their oligomers or polymers, esters of alkane carboxylic acids with diols, their oligomers or polymers or mixtures of the compounds mentioned.

3. Biodegradable and thermoplastically processable starch according to claim 1 or 2, in which the side chains are derived from a mixture of lactic acid and polycaprolactone.

4. Biodegradable and thermoplastically processable starch according to one of claims 1 to 3, in which the weight fraction of the side chains is at least 20% by weight, based on the biodegradable and thermoplastically processable starch.

5. A process for the preparation of biodegradable and thermoplastically processable starch, containing side chains bonded via ester groups, characterized in that native starch is reacted in the presence of a catalyst with compounds which can form ester groups with the hydroxyl groups of the starch.

6. A process for the preparation of biodegradable and thermoplastic plastically starch, containing side chains bonded via ester groups, characterized in that native starch is melted in a first step with additives capable of esterification and in a second step in the presence of catalysts with further compounds, which can form ester groups with the hydroxyl groups of the starch, in the melt or in the presence of at least one solvent.

7. The method according to claim 5 or 6, characterized in that triethoxy-diisopropylaminotitanate, dicyclohexylcarbodiimide, 4-pyrrolidone pyridine, lithium bromide or 1,8-diazabi- cyclo [5.4.0. ] undec-7-en or their mixtures used as a catalyst.

8. The method according to claim 5 or 6, characterized in that P4-phosphazene bases are used as the catalyst.

9. Use of biodegradable and thermoplastically processable starch according to one of claims 1 to 4 for the production of moldings, films or fibers.

10. Use of biodegradable and thermoplastically processable starch according to claim 9 for the production of films in the food sector.

Biodegradable and thermoplastically processable starch

Summary

Biodegradable and thermoplastically processable starch, containing side chains bonded via ester groups, the weight fraction of the side chains being at least 10% by weight, based on the molecular weight (number average M _n ) of the biodegradable and thermoplastically processable starch and the global migration being less than 200 mg / dm ² , determined in accordance with the conditions laid down in Directive 90/128 / EEC.