Crystal modulus of poly(hydroxybutyrate)

Abstract

The crystal modulus of poly(hydroxybutyrate)(PHB) has been measured using changes in the X-ray diffraction pattern of oriented samples under stress. Results obtained below the β transition temperature give a value of 9 GPa.

Two molecular modelling packages, BIOSYM and CERIUS², have been used to predict the full matrix of stiffness coefficients for PHB and hence via the aggregate model, the properties of a uniaxial fibre. The modulus along the chain direction compares well with the experimental value. Both packages predict a high transverse modulus and this is shown to be consistent with the measured modulus of the isotropic polymer on the basis of the aggregate model.