The influence of semicrystalline morphology on the dielectric relaxation properties of poly(3-hydroxybutyrate)

The dielectric relaxation characteristics of poly(3-hydroxybutyrate) (PHB) in the glass–rubber (α) relaxation region has been investigated. A series of cold-crystallized samples were examined, with emphasis on the influence of semicrystalline morphology on relaxation properties. The presence of crystallinity had a marked impact on the α-relaxation characteristics of the various cold-crystallized specimens as compared to the wholly amorphous material. The constraining influence of the crystallites produced a progressive relaxation broadening and a positive offset in relaxation temperature. With regard to the dielectric relaxation strength, Δε, we found that the amorphous phase relaxation in the semicrystalline sample had a completely different temperature dependence compared to the wholly amorphous sample, leading to an increase in relaxation strength as the temperature increases above the glass transition temperature (Tg). This was explained by the existence of a rigid amorphous phase interface which relaxes gradually above the Tg of the mobile amorphous material. We suggest that the mobile material is essentially located in the amorphous gaps between lamellar stacks.