THERMAL-DEGRADATION OF MICROBIAL COPOLYESTERS - POLY(3-HYDROXYBUTYRATE-CO-3-HYDROXYVALERATE) AND POLY(3-HYDROXYBUTYRATE-CO-4-HYDROXYBUTYRATE)

Thermal degradation processes of microbial copolyesters were studied in the temperature range 100-200 °C by monitoring the time-dependent changes in molecular weights of melt samples. Two types of copolyesters, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV); 3HV = 0-71 mol %) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB); 4HB = 0-82 mol %), were used in this study. All copolyester samples used were thermally unstable at temperatures above 170 °C, and their molecular weights decreased rapidly with time. The time-dependent changes in molecular weights during the thermal degradation followed the kinetic model of random chain scission at ester groups. The rates of random chain scission were independent of the compositions of the copolyesters but dependent strongly on temperature. These copolyester samples were thermally stable at temperatures below 160 °C. It has been suggested that the microbial copolyesters with melting temperatures below 160 °C are applicable to conventional plastics processing methods. © 1990, American Chemical Society. All rights reserved.