INFLUENCE OF PROCESSING PARAMETERS ON THE MASS CRYSTALLINITY OF POLY(3-HYDROXYBUTYRATE-CO-3-HYDROXYVALERATE)

It is proposed that melt-extrusion of poly(3-hydroxybutyrate-co-3-hydr oxyvalerate) at varying processing temperatures and screw speeds cause s changes in the atomic positioning of the oxygen atoms in the helix s tructure due to torsion of the main chain bonds. By wide angle X-ray s cattering it was observed that an increase of the processing temperatu re has a pronounced effect on the intensity of the two sharp Bragg ref lections (020) and (110). The unit cell dimensions remain, however, un changed. The observed repositioning did not change during conditioning for two weeks at 60 degrees C, although the degree of crystallinity i ncreased by approximately 10%. The degree of crystallinity is largely unaffected by the processing conditions. Model differential scanning c alorimetry experiments indicate that the observed shoulders or double melting peaks with different relative size are due to recrystallizatio n phenomena governed by morphology changes induced by the processing. This study has served as a test case for a flexible dialogue computer program, designed to be used as a routine tool for determination of th e degree of mass crystallinity of polymers from X-ray diffraction data . The change in atomic position of oxygen, as indicated in this work, may be one explanation for the varying enzymatic degradability of the polymers from renewable resources.