RAPID EVOLUTION OF HIGHLY-ORIENTED CRYSTALLINE LAMELLAE AND SLOW TRANSFORMATION OF METASTABLE LAMELLAE INTO CLOSELY-PACKING LAMELLAE INHERENT IN THE SURFACE REGION OF BIODEGRADABLE POLYHYDROXYBUTYRATE

摘要

Polyhydroxybutyrate (PHB) and Polyhydroxyalkanoates (PHAs) are widely-known semicrystalline biodegradable polyesters. As a substitute for petrochemical materials, any research on these biodegradable polymers has attracted considerable attention. Our recent study revealed that a melting behavior of a new random copolymer, Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(HB-co-HHx)) showed a sharp contrast with that of PHB. A novel inter- and intra-molecular interaction proposed in these studies successfully explained the X-ray diffraction data and FT-IR data on bulk samples. As a next step, we have performed X-ray reflectivity (XR) and grazing incidence X-ray diffraction (GIXD) measurements for thin films of PHB and P(HB-co-HHx) ranging from 20 nm to 120 nm thick at various temperatures. The aim of the present study is to clarify the relationship among surface morphology, crystallinity and crystal structure in the surface region, since there is a possibility that a slight difference in molecular structure between PHB and P(HB-co-HHx) can be a clue for understanding about the physical properties inherent in the surface region of these materials.