Biologically degradable polymer mixture

Details Biologically degradable polymer mixture Biologically degradable polymer mixture

1997-12-15

2000-08-01

Merriam, Andrew E. C.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

524386, 524539, 524605, 525 5424, 523128, 5283086, C08L 302, C08L 6700

Patent

active

060968095

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a biologically degradable polymer mixture, to a process for its preparation and to a method of processing the polymer mixture according to the invention.
Proposals for the preparation of biologically degradable polymer mixtures are known from a large number of patent documents and articles. The great problem in the case of polymer mixtures lies, as a rule, in that those mixtures which have an excellent, biological degradability have only limited possibilities for use in the area of engineering plastics, thereby explaining the relatively modest success to date. Polymer mixtures having improved properties are either biologically inadequate or degradable with increased effort, or else are too expensive.
From EP-535 994 a polymer mixture is known essentially consisting of starch and an aliphatic polyester, for example polycaprolactone, where the starch is preferably destructured with water.
Aliphatic polyesters are, per se, suitable mixing components for the preparation of biologically degradable polymer mixtures, since they have a good biological degradability. However, aliphatic polyesters have only moderate material properties, for example with regard to melting point, tensile strength, etc., which is why even corresponding mixtures using a polymer prepared on the basis of renewable raw materials, for example thermoplastic starch, have only moderate properties, thereby again placing in question the possibility for use in the field of engineering plastics.
It is therefore an object of the present invention to propose a biologically degradable polymer mixture which both is flawlessly degradable biologically and in addition has good mechanical and thermal properties, so that use as an engineering plastic or as a polymer material is appropriate. A further prerequisite for suitability as a polymer material also lies in the price for the polymer mixture proposed having an acceptable magnitude.
The multitude of biopolymers or biologically degradable polymer mixtures proposed in the prior art are to a great extent in accordance with object having an acceptable magnitude.
In accordance with the invention the object proposed above is achieved by means of a biologically degradable polymer mixture in accordance with the wording of claim 1.
The multitude of biopolymers or biologically degradable polymer mixtures proposed in the prior art are to a great extent constructed on the basis of starch or use starch, although native starch is hardly suitable as a technically usable polymer. Starch is proposed because it is readily degradable biologically, has a favorable price and is independent of petroleum products because it is based on a renewable raw material. Because of the poor suitability of native starch as an "engineering plastic" it is proposed according to the invention to use so-called thermoplastic starch, as is proposed, for example, in PCT/WO90/05161. This thermoplastic starch is obtained by processing native starch in the melt, by means of a plasticizing or swelling agent, to a homogeneous mass, where the proportion of swelling or plasticizing agent can as a rule amount to between 10 and about 40%, based on the overall weight of the mixture. [As set out in claim 4,] Suitable swelling or plasticizing agents are, inter alia, for example, glycerol or sorbitol.
Particularly suitable materials for improving the rather moderate material properties of thermoplastic starch include:
The aliphatic polyesters proposed in the prior art, which although having good biological degradability are not particularly suitable because of their likewise moderate material properties with regard to melting point and drawability, themselves contribute to an improvement in the material properties of the thermoplastic starch. In contrast, aromatic polyesters exhibit excellent material properties but their biological degradability is rather moderate. On the other hand, inter alia, polyester copolymers based on aromatic and aliphatic dicarboxylic acids, polyesteramides and also polyesterurethanes have both ou

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International Preliminary Exam Report (IPER), PCT/IB96/00275, published Aug. 26, 1996.
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