DE19633476A1 - Biodegradable thermoplastically deformable materials for food packaging - Google Patents

Abstract

According to the invention the materials consist of blends of starch esters and aliphatic straight-chained or branched polycarbonates in a ratio of 5:95 to 95:5. Instead of usual softeners for starch esters so-called secondary softeners, which act at the same time as compatibility mediators, are used. The manufactured blends are distinguished by good migration values.

Description

The invention relates to molding compositions for the production of biodegradable ren or compostable thermoplastically deformable materials that are in the special for use in food packaging, fast food etc. suitable and made of biodegradable or compostable blends, esp from starch esters and polyesters and other biocompatible additives consist of sentences.

Resource shortages and growing mountains of garbage reduce demand biodegradable materials or materials based on the Raw materials in areas that were previously conventional thermoplastic Plastics were reserved, grow steadily.

The previously known biodegradable materials show that the use of such Materials in many areas is possible. But it is still difficult the broad property spectra known for conventional plastics cover with new, environmentally friendly materials. Often there are still Excessive costs that hinder their widespread use so far.

A solution that meets both requirements, biodegradability and low production costs, has been in the recent past in the Use of starch and starch derivatives seen.

Blends of starch or starch derivatives and synthetic polymers are all Commonly known (inter alia DE 42 37 535).

If starch derivatives are described, the corresponding An relate gave low substituted products with a DS (Degree of Substitution) <1.

As copolymers u. a. used: EVOH, poly-ε-caprolactone, Po lyhydroxybutyric acid, ethylcellulose, special polyamides or polyesteramides.  

Since starch or low-substituted starch derivatives in these blends usually the Main component, resulting for the products made therefrom one Set of application problems:

• The plasticizers used are usually hydrophilic and migrate in the aqueous Medium very fast. This in turn prohibits applications in the food industry rich.
• - The immiscibility of the components requires that it is not clear transparent masses acts.
• - The achieved heat resistance often enough for the desired Application areas are not enough.

For higher substituted and thus water-insensitive esters of starch (DS <1.8) is described in DE 41 14 185 a coester with longer-chain fatty acids by means of plasticizers, such as ethyl citric acid, glycerol acetate and lactic acid ester is processed.

In EP 0638609 is a blend of starch acetate (DS 1.8-2.6) and Polyethy lenglycol (MW 200-2000) using various adjuvants beat.

Both variants show a significant improvement in water stability, the Problem of migration of water-soluble constituents is not yet sufficient solved. The heat distortion resistance is too many applications low.

DE 44 43 539 discloses blends of starch esters and polyalkylene carbonates beaten. The solution proposed there with plasticizer mixtures of Polyalkylene glycols as primary softeners for starch acetate and a second, secondary plasticizer component for compatibilization between the two polymer components brings significant benefits in terms of me chanical properties and the water resistance of the products.  

Not yet satisfactory are these variants in terms of plasticizer migration and heat resistance.

Thus, many interesting for the desired product group application not be taken into account.

The invention is therefore based on the object with economically justifiable To provide effort to materials that are biodegradable and thermoplastic are processable and due to lower migration values for applications in the Food sector or due to their improved weathering stability and increased heat resistance for outdoor applications and / or applications are suitable in the earth.

The blends according to the invention consist of starch esters which are based on starches ba which have an amylopectin content of 20-80%, preferably starch Ceacetate with a degree of substitution of 1.5-2.6, preferably 1.8-2 and aliphati polycarbonates with or without the addition of oxydicarboxylic acids and / or Oxytricarboxylic acids with 2-10 C atoms in the ratio 100: 2 to 1000: 1 to polyfunctional carboxylic acid using plasticizers and usual additives.

Instead of the usual plasticizers for starch acetate so-called Secondary softeners for starch acetate are used, which at the same time the radio tion of a compatibilizer.

As such, secondary plasticizers are preferably biocompatible Compounds considered.

Very suitable are esters of polyols with aliphatic monocarboxylic acids or Esters of polyfunctional carboxylic acids with short-chain alkanols. The Ge weight ratio of the carboxylate groups to the CH, CH₂ and CH₃ groups can between 1: 0.5 to 1: 4, preferably between 1: 1 to 1: 2. These include, for example, citric acid trialkyl (-ethyl or -butyl) esters, Gly cerincarboxylate (tributyrate), adipic acid esters with C₁ to C₅ alcohols, Triethylengylkoltriacetat.  

The aliphatic polycarbonates are carbonic acid ester group-containing Po lymere whose chemical structure of the formula

corresponds, wherein R₁ and R₂ is hydrogen and straight or branched C₁- to C₄-alkylene groups are the same or different or with one another and n = 250-10,000, preferably 350-3000.

Particularly favorable is the use of polyethylene, polypropylene and poly butylene carbonate.

For the sake of better biodegradability should be given priority Polyethy lencarbonat (PEC) are used.

The use of polypropylene carbonate (PPC) and polybutylene carbonate (PBC) bie u. a. in the case of shaped bodies which are used over relatively long periods (2-8 years) have certain mechanical properties, but then at For example, in the soil of rotting can be left.

The mixtures according to the invention may also contain customary fillers and pigments such as Talc, chalk, titanium dioxide, cellulose powder or starch in sizes order 0-30% based on the total mass.

The ratio of starch ester to aliphatic polycarbonates may be 5:95 to 95: 5 be. The proportion of additives and plasticizers should be 0 to 15% by mass, before preferably 3 to 12% by mass.

In order to produce the molding compositions described, it is appropriate that the fe submitted components in a high-speed mixer and during the intensive  mixing the liquid components by spraying. Subsequently, these mixtures can be extruded and granulated. Likewise, a direct metering of the plasticizer component in the Extrusi onsprozeß or a separate addition of all components possible. Granules produced in this way can be heated at temperatures of 130 ° C to 180 ° C processed on conventional injection molding machines. The result products are largely insensitive to water, although they still have one Water absorption of 5-10%.

In experiments could be demonstrated that the essential mechani properties of the blends according to the invention over one for many relevant period of 1 year, when used from PPC over 2-3 years.

The migration values in different test foods are invented by a According to the design of the blends far below the legally permissible limit values lowered.

Depending on the design of the blends, for example, transparent ones can also be used Shape objects. The amounts used are polyalkylene carbonates in other areas, the other mentioned blend components in low rem dimensions variable.

A high heat resistance is achieved by the plasticizer components be kept low. An advantage of the approach proposed here is that the mixtures described even then process very well and also show good mechanical characteristics.

To illustrate the mixtures according to the invention were injection molding body made. The composition of the individual samples is given in Table 1 remove.  

Table 2 contains some of the essential characteristics of the examples given. The characteristic values were transferred to the o. G. Test specimens determined as follows:

Melt index (150 ° C, 2.16 kp, MFI DIN ISO 1133 Impact resistance DIN 53 488 flexural strength DIN 53 452 Flexural modulus DIN 53 457 tensile strenght DIN 53 455 tear strength DIN 53 455 elongation at break DIN 53 455 Ball indentation hardness DIN ISO 2039 HDTA (1.82) DIN 53 461

The migration was in accordance with EC Directive 9318, EEC (implementation according to ASU B 80.30-1-3 EG) for 1 h at 70 ° C in water and in oil. From the examples it can be clearly seen that according to the proposed In particular, better patterns of migration can be found in the patterns produced sen.

But also the impact resistance and the elongation at break are partly clear improved.

Claims (4)

1. Biodegradable, thermoplastically deformable materials for food packaging, characterized in that it consists of blends of starch esters based on starches having an amylopectin content of 20 to 80% and their degree of substitution between 1.5 and 2.6, and alipha polycarbonates of the formula where R₁ and R₂ are hydrogen and straight-chain or branched C₁-C₄ alkyl groups, may be the same as or different from each other, and n = 250-10,000 is preferably 350-3,000, be and that the ratio of starch esters to polyalkylene carbonate 5: 95 to 95: 5 and these ingredients are compounded with a starch ester secondary biocompatible plasticizer which is also a mediator between the two polymer phases. 2. Molding compositions according to claim 1, characterized in that the used secondary plasticizer esters of polyols with aliphatic Monocarboxylic acids or esters of polyfunctional carboxylic acids are, wherein the mass ratio of carboxylate groups to the CH, CH₂ and CH₃ Grup pen of 1: 0.85 to 1: 4, preferably from 1: 1 to 1: 2. 3. Molding compositions according to claim 1 to 2, characterized in that they have a Addition of saturated dicarboxylic acids and / or oxydicarboxylic acids with 2 to 10 C atoms in the ratio of starch ester to polyfunctional carboxylic acid such 100: 2 to 1000: 1 included.   4. Molding compositions according to claim 1 to 3, characterized in that they are for Plastics usual fillers in the order of 0-30% based on the Total mass included.