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Synthetic, biodegradable aliphatic polyesters often do not provide optimal properties of application (e.g. melting point of polycaprolactone: 60°C). Material properties of such polyesters can be improved by introducing aromatic compounds into polymers. It could be shown that random aliphatic/aromatic copolyesters consisting of components like 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, adipic acid, sebacic acid and terephthalic acid (35-55 mol-% with regard to the diacid components) exhibit melting points of up to 145°C. These copolyesters are still biodegradable making this material of great commercial interest. Significant weight losses of polyester films could be observed in three months soil burial experiments(up to 40 mol-% terephthalic acid) and in compost simulation tests at 60°C (up to 50 mol-% terephthalic acid). From degradation experiments with aromatic model oligoesters from terephthalic acid and 1,2-ethanediol (1,3-propanediol, 1,4-butanediol, respectively) it could be concluded that, aromatic intermediates (oligomers) will be assimilated very fast by microorganisms, if the degree of polymerization is one or two. It seems that longer oligomers are not accessable for an enzymatic attack, but will probably be hydrolyzed chemically at elevated temperatures (60°C), too. Using especially screened thermophilic microorganisms (55°C) on agar plates and analysis of residual material by size exclusion chromatography, the above mentioned finding could be confirmed. Some of the components of polyesters, described here can be obtained from renewable resources. For instance, 1,3-propanediol can by produced by a fermentation process from glycerol and a number of aliphatic dicarboxylic acids are available from natural oils. This option can make biodegradable high-tech polyesters with a defined structure part of natural cycles. |
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