THE INFLUENCE OF THERMAL HISTORY ON THE PROPERTIES OF 3-HYDROXYBUTYRATE-CO-12-PERCENT-3-HYDROXYVALERATE)

The influence of thermal history on the properties of commercial P(3HB -co-12%-3HV) was studied. Thermogravimetric analysis and differential scanning calorimetry revealed that the plasticizer evaporated at 140 d egrees C or higher. The loss of plasticizer during thermal treatment a t, 170 and 180 degrees C resulted in a slight increase of the melting temperature of the polymer. The processing time and temperature, as we ll as the cooling procedure influenced the thermal behaviour of the ma terial. A decrease in molecular weight with time was found at the temp eratures investigated and this significantly affected the mechanical p roperties of the polymer prepared at 180 and 200 degrees C. The rate c onstant k(d) of thermal degradation was slightly higher for samples du ring a shape-forming process in a Minimax apparatus than during a quie scent heating process (DSC) and its value increased with temperature. Limiting the processing at 170 degrees C to 2 min gave a material with useful properties but in creasing the residence time resulted in a de crease in strength, elongation at break, molecular weight and viscosit y although it did not significantly influence the modulus of elasticit y. Materials prepared at 180 or 200 degrees C were more brittle and lo nger residence times resulted in a deterioration of the mechanical pro perties. (C) 1996 John Wiley & Sons, Inc.