BIOLOGICAL DEGRADABLE POLYESTER COPOLYMER S FROM PETROCHEMICAL AND RENEWABLE RAW-MATERIAL

Synthetic, biodegradable aliphatic polyesters often do not provide opt imal properties of application (e.g. melting point of polycaprolactone : 60 degrees C). Material properties of such polyesters can be improve d by introducing aromatic compounds into polymers. It could be shown t hat random aliphatic/aromatic copolyesters consisting of components li ke 1,2-ethanediol, 1,3-propanediol 1,4-butanediol adipic acid, sebacic acid and terephthalic acid (35-55 mol-% with regard to the diacid com ponents) exhibit melting points of up to 145 degrees C. These copolyes ters are still biodegradable making this material of great commercial interest. Significant weight losses of polyester films could be observ ed in three months soil burial experiments(up to 40 mol-96 terephthali c acid) and in compost simulation tests at 60 degrees C (up to 50 mol- % terephthalic acid). From degradation experiments with aromatic model oligoesters from terephthalic acid and 1,2-ethanediol (1,3-propanedio l, 1,4-butanediol, respectively) it could be concluded that, aromatic intermediates (oligomers) will be assimilated very fast by microorgani sms, if the degree of polymerization is one or two. It seems that long er oligomers are not accessable for an enzymatic attack, but will prob ably be hydrolyzed chemically at elevated temperatures (60 degrees C), too. Using especially screened thermophilic microorganisms (55 degree s C) on agar plates and analysis of residual material by size exclusio n 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 dicarbo xylic acids are available from natural oils. This option can make biod egradable high-tech polyesters with a defined structure part of natura l cycles.