CRYSTAL MODULUS OF POLY(HYDROXYBUTYRATE)

The crystal modulus of poly(hydroxybutyrate) (PHB) has been measured u sing changes in the X-ray diffraction pattern of oriented samples unde r stress. Results obtained below the beta transition temperature give a value of 9 GPa. Two molecular modelling packages, BIOSYM and CERIU(2 ), have been used to predict the full matrix of stiffness coefficients for PHB and hence via the aggregate model, the properties of a uniaxi al fibre. The modulus along the chain direction compares well with the experimental value. Both packages predict a high transverse modulus a nd this is shown to be consistent with the measured modulus of the iso tropic polymer on the basis of the aggregate model.