7.1 Introduction

Polyhydroxyalkanoates (PHA) are a family of biodegradable aliphatic co-polyesters produced by bacterial fermentation. These polymers are synthesised in the bodies of bacteria fed with glucose (e.g., from sugar cane) in a fermentation plant. PHA was first discovered in prokaryotes as a high molecular weight storage molecule in cytoplasmic granules. Since then over one hundred PHA compositions have been reported, some made by genetically engineered bacterial strains. PHAs are extremely versatile polymers as their crystallinity can be manipulated to provide a broad range of mechanical and barrier properties, in some cases matching the performance of engineered thermoplastics.

Polyhydroxybutyrate (PHB) is the most common type of PHA. In recent years there has been growing interest in the use of PHB and PHB copolymers in the biodegradable plastics industry. The biodegradable and non-toxic effect of PHBs also make them a strong possibility for many medical applications, including drug release, bone regeneration, and nerve guidance.

PHA biodegradable polymers are still largely at the development stage of market development, although there a few commercial applications available. The main candidates for commercialisation are Biopol PHBV, being developed by Metabolix, and Nodax PHBH, marketed by Procter & Gamble.

Metabolix is the leading producer of PHA biodegradable material. The company produces PHA through aerobic fermentation, which involves converting natural sugars or oils into PHA polymers directly inside aerated fermentation tanks. Each fermentation consists of a growth phase, during which empty cells (bio-factories) are grown to target concentrations, followed by a production phase, during which the...