TABLE OF CONTENTS In the following section some case studies on the design criteria for the preparation of biodegradable blends and composites are reported, together with their characterisation and analysis of the most relevant properties.
The first microbial polyester that has attracted interest from a technological point of view was PHB and its copolymers with valerate (PHBV). PHB was introduced in the early 1980s by ICI as an innovative thermoplastic material obtained through a biotechnological approach [83, 84]. It is produced by the fermentation of sugars by bacteria such as Wautersia eutropha [85]. High yields and high purity are obtained.
It has been found that PHB is thermoplastic with a high degree of crystallinity and a well-defined melting point (T m) (around 180 C). At relatively low undercooling (temperature between melting and crystallisation), PHB crystallises from the melt, giving rise to the formation of large spherulites (see Figure 2.4). The nucleation behaviour, the crystallisation and the morphology of PHB have been studied by Barham and co-workers [86] . Unlike other thermoplastic polymers, such as PP and PE, PHB is truly biodegradable and highly biocompatible.
Films of PHB show gas barrier properties comparable to polyvinyl chloride and PET. The combination of all these properties indicates that PHB may compete with commodity polymers in the packaging industry, especially in areas where non-biodegradable plastic items, due to environmental pollution, are not allowed. PHB...
