| Research Abstract |
A variety of microorganisms produce and accumulate a polyester in their cells as an energy source. The microbial polyester is a thermoplastic with biodegradable and biocompatible properties. Under optimal fermentation conditions, a microorganism produces a large amount of polyester at a high efficiency from alkanoic acids and alcohols. The content of polyester in dried cells increases up to 80 wt%.
Recently, we have found that a new copolyester of 3-hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB) is produced by Alcaligenes eutrophus from various carbon sources of 4-hydroxybutyric acid, 1,4-butanediol, and butyrolactone. The composition of copolyesters varies from 0 to 60 mol-% 4HB units, depending on both fermentation conditions and carbon sources supplied. The physical and mechanical properties of P (3HB-co-4HB) are strongly dependent upon the copolymer compositions. The crystallinity of copolyester decreases with the 4HB fraction, and the strain of copolyester film increases from 5 to 444% at 16mol% 4HB. The copolyesters of over 40 mol% 4HB exhibit the mechanical properties of an elastic rubber. These copolyesters behave as thermoplastics with a melting point of 140-180^ﾟC and can be processed into transparent film and strong fiber by conventional extrusion and moulding equipment.
The products of P (3HB-co-4HB) copolyesters are biodegradable in soil and activated sludge. The copolyester films were degraded after 6 weeks at 20-25^ﾟC in soil. Some microorganisms excrete extracellular depolymerases to degrade environmental polyesters into non-toxic monomers and utilize the decomposed compounds as nutrients. These microbial copolyesters have attracted much attention as environmentally degradable bioplastics for a wide range of agricultural, marine, and medical applications.
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