MISCIBILITY, CRYSTALLIZATION AND MELTING OF POLY(3-HYDROXYBUTYRATE) POLY(L-LACTIDE) BLENDS/

The spherulitic structure, growth rates and melting behaviour of blend s of bacterially produced poly(D(-)-3-hydroxybutyrate) (PHB) and poly( L-lactide) (PLLA) were investigated using polarized light microscopy. Results indicated that low-molecular-weight PLLA (M(n) = 1759) was mis cible in the melt over the whole composition range, whereas a blend of high-molecular-weight PLLA (M(n) = 159 400) with PHB showed biphasic separation, in accordance with calculations based on Flory-Huggins the ory. Two types of spherulite were formed on cooling, relating to the c rystallization of PHB and PLLA respectively. In some blends, spherulit es of opposite type interpenetrated when the growth fronts met. It is proposed that lamellae belonging to one type of spherulite continued t o grow in the interlamellar regions of the other type of spherulite.