Bioabbaubare Kunststoffe - Entwicklung eines Labortestsystems zur Messung der biologischen Abbaubarkeit in der Kompostierung

At the Fraunhofer-Institut ILV a laboratory test system was developed for measuring the degree and rate of degradation of biodegradable plastics in a compost environment. Compost is a very heterogeneous environment which does not allow to prove total biodegradation of a plastic because of limited possibilities to analyze metabolites in compost. Therefore, the microbial degradation of a plastic is measured under standardized conditions in an aerated, synthetic aqueous medium where the plastic is the sole source of carbon for micro-organism. The synthetic mineral medium is inoculated with a mixed microbial population from the aqueous eluate of mature compost. The biodegradation process is monitored by measuring the carbon dioxide production resulting from the microbial metabolism. Completeness of biodegradation is assessed by conducting a carbon balance, i.e. only if 100 % of the plastic's carbon is transformed by microbial action to carbon dioxide or is built into new biomass the plasti c is called biodegradable. The rate of biodegradation in the synthetic aqueous medium, however, is different from the compost environment. Therefore, on a second test level biodegradation is measured in a compost simulation test by adding the plastic to a fixed bed made from mature compost. The rate of biodegradation is assessed by measuring the difference in carbon dioxide formation of a compost reactor with the addition of polymer to a compost reactor without polymer. The aqueous tests as well as the composting tests are conducted with a time dependent temperature profile comparable to the natural self heating process during composting. Completeness of biodegradation, however, can only be proved in the aqueous test, because the build up of new biomass and the formation of soluble metabolites can only be measured therein. Results of the aqueous biodegradation test for a starch based biodegradable plastic were compared to a compost simulation test. After a period of 45 days identical c arbon dioxide formation resulting from the biodegradation process was measured in both test systems. The rate of biodegradation, however, was significantly higher in the aqueous system. It could be shown that magnesium in cocoa products can be very well determined by means of flamme AAS after chemical digestion in a microwave. The result of both ashing techniques (pressure and microwave) were in good agreement. The specific advantage of this microwave digestion method is represented