Poly(3-hydroxybutyrate)-based copolymers and blends: Influence of a secondcomponent on crystallization and thermal behavior

Isotactic poly (3-hydroxybutyrate) (P3HB) is an aliphatic polyester obtaine d by bacterial fermentation. This truly biodegradable polymer has been wide ly investigated, mainly with the aim to replace conventional plastics, whic h cause environmental pollution. To improve its properties, extensive studi es have been conducted to modify it properly by copolymerization or blendin g with other polymers. Macroscopic properties of polymers, particularly of polymer blends, are strongly affected by their microstructure, especially b y the allocation of different phases and their level of dispersion and adhe sion. In nonreactive blends, the adhesion level is mainly determined by the similarity between the chemical structure of the components, and the arran gement of the phases is remarkably controlled by the crystallization condit ions. The superstructure of the crystalline phases accounts for the mechani cal resistance of the blend, but the composition and the distribution of th e amorphous phases also play an important role, especially with respect to toughness properties. This article reviews data on thermal properties and t he crystallization process of P3HB and its copolymers, both alone and in th e presence of other polymers. In particular, copolymers of 3-hydroxybutyrat e with 3-hydroxyvalerate and with 4-hydroxybutyrate and blends of P3HB and the copolymers with atactic poly(3-hydroxybutyrate), poly(vinyl acetate), p oly(vinyl alcohol), poly(ethylene oxide), poly(methylene oxide), poly(epich lorohydrin), and poly(methyl methacrylate) are considered. Major attention is directed toward the influence of miscibility and composition on solidifi cation kinetics and crystal structure with the objective to provide an over view of the current state of the art.