Degradation of biologically degradable polymers using enzymes

Details Degradation of biologically degradable polymers using enzymes Degradation of biologically degradable polymers using enzymes

1999-08-10

2001-07-03

Truong, Duc (Department: 1711)

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

Synthetic resins

Treating polymer containing material or treating a solid...

C435S018000, C435S019000, C435S029000, C435S252100, C435S254100, C435S255100, C435S262000

Reexamination Certificate

active

06255451

ABSTRACT:

This invention relates to the complete degradation by enzymes of mouldings, sheet-like products, coatings, adhesives or foams made of biodegradable polymers. The invention relates in particular to the enzymatic degradation of polyester amides, and of polyester urethanes which contain urea groups.
Materials which are completely biodegradable and compostable are becoming increasingly important. In recent years, a multiplicity of polymers of this type has been developed with the aim of providing a plastics material which can be utilised by composting. At the same time, various regulations and standards have been issued which regulate the use of materials of this type for composting (LAGA leaflet M 10) or which are capable of detecting that materials can be composted harmlessly (DIN 54900). In this connection, the expression “biological degradation” is always understood to mean that, in the presence of microorganisms, materials which are thus described are completely metabolised by the latter to form CO
2
and biomass.
It is known that the degradability of some plastics can be detected not only by the growth of microorganisms on the polymer, but can also be detected with the aid of enzymes. In the latter procedure, the test material is incubated with suitable enzymes and the products of degradation are analysed (Jap. Pat. 56022324, Jap. Pat. 06322263, Polymer Degradation and Stability, 1992, pages 241-248). In the context of basic research, other authors have made use of enzymatic degradability in order to detect a capacity for biodegradation in principle (Y. Tokiwa et al. in: J. E. Glass (Editor) ACS Symposium Series 433, 1990, pages 136-148). In this cited article it is expressly mentioned that the complete degradation of the polymer was not investigated. What is supposedly the complete degradation of a polymer has been reported (FR 93-6070). However, for the polypropylene fumarate which was used in the latter document it was only the cleavage of the ester bonds which was achieved. Polypropylene, which is not biodegradable, as is known, remained behind. In all the cases which were known hitherto, enzymatic polymer degradation has proceeded either to a very slight extent only, or very slowly. There is no mention of a targeted selection of enzymes which degrade the polymers investigated particularly efficiently and rapidly. Likewise, there is no mention of any applications, which can possibly be modified for commercial use, of the complete degradation of polymers by means of enzymes.
It is generally known that polyester amides can undergo biodegradation (J. Appl. Polym. Sci., 1979, pages 1701-1711, U.S. Pat. No. 4,343,931, U.S. Pat. No. 4,529,792, Jap. Pat. 79119593, Jap. Pat. 79119594, EP-A 641817).
It is also known that polyester urethanes which contain urea groups can be completely biodegradable. The rate and extent of degradation depend on the monomer composition (DE-A 195 17 185). Enzymatic attack by a proteolytic enzyme on individual bonds in polymers such as these has been described (G. T. Howard, R. C. Blake, ASM General Meeting 1996, Abstracts page 430). The complete degradation of a film or sheet, or of a moulding, is not described.
It has been found that mouldings of biodegradable polymers can be completely degraded by means of defined enzymes or mixtures of these defined enzymes, optionally with other enzymes. It has also been found that selected enzymes are capable of completely degrading polymers of this type within timescales which can be employed commercially. In the course of this degradation procedure, the molecular weight of the polymer is reduced to such an extent that products formed therefrom are rapidly degraded to form monomers and are completely decomposed. This applies in particular to films, sheet-like products, coatings, adhesives, injection-molded parts and granular materials made of biodegradable polymers.
The periods of time which are necessary for the complete decomposition of the polymer are extraordinarily short. Rapid, complete degradation is only achieved, however, if a special combination of polymer and enzyme is selected. The effect which has been discovered here thus differs significantly from the work on the enzymatic degradation of biodegradable polymers which was known hitherto.
The present invention relates to a method for the enzymatic degradation of biodegradable polymers, particularly of polyester amides and of polyester urethanes which contain urea groups, wherein the biodegradable polymers are treated with an aqueous solution which can be buffered and which contains one or more lipases or cutinases selected from the group comprising the lipase from
Candida antarctica
, particularly component B, the lipase from
Mucor Miehei
(e.g. Lipozyme 20,000 L), the lipase from
Aspergillus niger
and the cutinase from Humicola insolens or one or more of said lipases and cutinases in combination with other enzymes.
Suitable biodegradable and compostable polymers include aliphatic or partially aromatic polyesters, thermoplastic aliphatic or partially aromatic polyester urethanes which may also contain urea groups, aliphatic-aromatic polyester carbonates and aliphatic or partially aromatic polyester amides. Polyester amides, and polyester urethanes which contain urea groups, are preferred.
The following polymers are suitable:
Aliphatic or partially aromatic polyesters formed from
A) linear bifunctional alcohols, preferably C
2
-C
12
alkyl diols, such as ethanediol, butanediol or hexanediol for example, preferably butanediol, and/or optionally from cycloaliphatic bifunctional alcohols such cyclohexanedimethanol for example, and/or optionally from small amounts of branched bifunctional alcohols, preferably C
3
-C
12
alkyl diols such as neopentyl glycol, and optionally from small amounts of alcohols of higher functionality in addition, preferably C
3
-C
12
alkyl polyols, such as 1,2,3-propanetriol or trimethylolpropane for example, and from aliphatic bifunctional acids, preferably C
2
-C
12
alkyl dicarboxylic acids, such as, for example and preferably, succinic acid or adipic acid, and/or optionally from aromatic bifunctional acids such as terephthalic acid or isophthalic acid or naphthalene dicarboxylic acid and optionally from small amounts of acids of higher functionality in addition, such as trimellitic acid for example, or
B) those formed from acid- and alcohol-functionalised components, preferably components containing 2 to 12 C atoms in their alkyl chain, for example hydroxybutyric acid or hydroxyvaleric acid or lactic acid, or derivatives thereof, for example &egr;-caprolactone or dilactide,
or a mixture or a copolymer of A and B,
wherein the content of aromatic acids is not more than 50% by weight with respect to all the acids.
The acids may also be used in the form of derivatives, such as acid chlorides or esters for example;
aliphatic or partially aromatic polyester urethanes, which may also contain urea groups, and which comprise
C) an ester constituent formed from bifunctional alcohols, preferably C
2
-C
12
alkyl diols such as ethanediol, butanediol or hexanediol for example, preferably butanediol, and/or from cycloaliphatic bifunctional or polycyclic aliphatic alcohols, such as cyclohexanedimethanol for example, and/or optionally from smaller amounts of branched bifunctional alcohols, preferably C
3
-C
12
alkyl diols, such as neopentyl glycol for example, and optionally from small amounts of alcohols of higher functionality in addition, preferably C
3
-C
12
alkyl polyols, such as 1,2,3-propanetriol or trimethylolpropane for example, and from aliphatic bifunctional acids, preferably C
2
-C
12
alkyldicarboxylic acids, such as, for example and preferably, succinic acid or adipic acid, and/or optionally from aromatic bifunctional acids such as terephthalic acid or isophthalic acid or naphthalene dicarboxylic acid and optionally from small amounts of acids of higher functionality in addition, such as trimellitic acid for example, or
D) those formed from acid- and alcohol-functionalised components, preferably components containing 2

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