Production, Characterization, and Applications of Biodegradable Polymer: Polyhydroxyalkanoates

Abstract

The usage of petroleum-based polymers by the human beings has enhanced the quality and comfort of life in the recent decades. These polymers are extremely persistent in the environment, and none of the conventional techniques can effectively degrade such polymers. A remedy to this issue is the application of biodegradable polymers from different organic sources. Biodegradable polymers are comprised of monomers that are linked with one another through various functional groups with unstable links in the backbone. During degradation, these polymers are broken down into molecules that are degradable by conventional biological techniques. Biodegradable polymers have been synthesized from four different sources: agro-resources, microorganisms, biotechnological renewable sources, and classical chemical synthesis. Polyhydroxyalkanoates (PHAs) are one of the prime substitutes for conventional plastics because they are derived from renewable feedstock by fermentation and are completely biodegradable upon disposal. The fermentation route for the synthesis of PHAs is one of the best substitutes for petroleum-derived polymers. PHAs have excellent physical characteristics, such as low toxicity and high molecular weight, and they can be naturally produced from several carbon sources using numerous microorganisms. Moreover, they possess mechanical and physical properties similar to synthetic plastics such as polyethylene and polypropylene like tensile strength and melting point, etc. More than 300 different types of bacteria, including both gram-positive and gram-negative strains, produce PHAs. In order to reduce the production cost of PHAs, several inexpensive substrates, such as whey, malt, soy and starch waste, palm oil, beet, and cane molasses, are being used. In the recent past, several invasive weed biomasses have been used in the microbial fermentation process for the production of PHAs. This invasive alien species (IAS) is non-native to an ecosystem and when introduced outside its natural habitats, affects the native biodiversity in almost every ecosystem. Hence, the production of Poly(3-hydroxybutyrate) (PHB) using these invasive weeds is a brand new technology for the production of biodegradable polymers. Various blends like copolymers have been developed to improve the cost, performance, and physical properties of PHAs. Several PHA nanocomposites have been developed to enhance mechanical properties. PHAs degrade into carbon dioxide and water under aerobic conditions and to methane under anaerobic conditions without any harmful products. These biopolymers can also be degraded either by thermal mode or by enzymatic hydrolysis. The last two decades have seen a shift from bio-stable materials to biodegradable (i.e., hydrolytically and enzymatically) materials for medical and related applications. Initially, PHAs were used in the packaging industry, but their importance was later shifted to the medical industry, pharmacological, and agricultural sectors. This chapter addresses the synthesis and benefits of PHAs over petroleum-derived polymers, their biodegradable characteristics, and applications in several sectors.