Definitions and Types of Microbial Biopolyesters and Derived Biomaterials

Currently, humankind is confronted with emerging threats like growing piles of recalcitrant plastic waste, depletion of fossil resources, the microplastic debate, and, most of all, the omnipresent topic climate change, which, inter alia , is driven by steadily increasing greenhouse gas emissions caused by burning fossil feedstocks and their follow-up products like plastics. As a strategy to overcome these problems, we currently witness ambitious activities all over the world in intensifying not only the use of biogenic fuels, but also the development of biobased and biodegradable polymers with properties emulating those of established plastics from petrochemistry or even outperforming them. However, many of the materials nowadays commercialized as "green plastics" or "bioplastics" do not display the characteristics justifying such categorization. Some of them are biobased, but highly recalcitrant toward biodegradation and composting, while others are environmentally degradable, but stem from fossil resources. Moreover, a third group of "bioplastics" exist, which are based on renewable resources and, at the same time, undergo biodegradation and composting, but still need chemical processes for polymerization. Therefore, this chapter presents different types of "bioplastics" and compares them based on the criteria "biobased," "biosynthesized," "biodegradable," "compostable," and "biocompatible." Major focus is directed to microbial polyhydroxyalkanoate (PHA) biopolyesters, which constitute the main class of "bioplastics" in the strict sense with an increasing number of companies launching their commercialization these days. Key aspects of PHA biosynthesis from renewable resources, their intracellular organization, factors impacting their molecular mass, types of PHA with highly diverse properties, and selected fields of application are discussed.