Berlin 2005 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 17: Physics of polymers I

CPP 17.3: Talk

Tuesday, March 8, 2005, 10:15–10:30, TU C130

Ageing of biosynthetic PHB — •Antje Bergmann and Anthony J. Owen — Fakultät für Physik, Universität Regensburg

The semicrystalline polymer polyhydroxybutyrate (PHB) is a bacterially processed polyester and therefore biocompatible and completely biodegradable. Its properties are similar to those of some conventional plastics such as polyethylene (PE). However, its mechanical characteristics show detrimental changes with time - an ageing process occurs. It is not yet satisfactorily understood why samples crystallised at room temperature embrittle increasingly with time, whereas annealing treatments may restore the excellent mechanical properties of freshly moulded material. Using wide-angle x-ray diffraction we analysed the crystal structure of samples annealed at various temperatures after several storage times. Differential scanning calorimetry experiments were carried out to observe melting and crystallisation processes. The results of our research seem to be interpretable in a remarkably simple way: We found that only a specific structural state is thermodynamically stable enough not to be prone to further crystallisation and ageing. This state is characterised by certain elementary cell dimensions, degree of crystallinity and crystal size.