1.1 Introduction
The prefix “bio” in the term “biopolymer” signifies that these polymers are of biological origin, i.e. inherently produced in living organisms. Biopolymers, bio-based polymers, biodegradable polymers, and bioplastics are used synonymously in specific contexts, but each term has a different meaning. Bio-based polymers are materials produced from natural resources such as plants, animals, and microorganisms that can be biodegradable (e.g. starch, polylactic acid [PLA]) or non-degradable (e.g. biopolyethylene) [1]. Biodegradable polymers are materials that completely degrade when exposed to soil, air, water, and microorganisms over a specific time period. Biodegradable polymers may be natural (e.g. starch, cellulose, proteins, lipids) or synthetically produced (e.g. polycaprolactone and polybutylene succinate). A bioplastic is a plastic polymer manufactured from a natural or renewable source, and it is biodegradable [2]. Biopolymers are primarily composed of repeating units of monomers made of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) and are found in living organisms such as plants, animals, and microorganisms. Based on this definition, biopolymers include bio-based polymers and natural polymers, including biodegradable polymers such as polysaccharides, proteins, lipids, and polynucleotides (DNA and RNA). However, biopolymers such as DNA and RNA have complex molecular structure, in which monosaccharide, protein/amino acids, and functional groups such as phosphate groups are joined together by complex intramolecular interactions like hydrogen bonding, disulfide bridges, and hydrophobic interactions to create three-dimensional (3D) structure and termed as bio-based heteropolymers or biomacromolecules [3].
The physicochemical properties of biopolymers such as stiffness, elasticity, conductivity of electricity and heat, resistance to corrosion, appearance such as transparency, and color depend on the type(s) of monomer, degree of polymerization, and type(s) of intramolecular bonds. Compared to synthetic polymers obtained from fossil fuels, biopolymers offer the obvious advantage of eco-friendly degradation, which leads to effective waste management and a healthy environment. The biopolymers are excellent candidates for various applications such as food, pharmaceuticals, and cosmetics and in several industries including packaging, agriculture, textiles, and water treatment due to their biocompatibility, non-toxicity, and biodegradability [4–6]. However, impact strength, tensile strength, permeability, and thermal stability of biopolymers are relatively inferior compared to synthetic (i.e. petroleum-based) polymers. Reinforcement of fillers or additives in biopolymers significantly improves the mechanical properties, such as tensile and impact strengths of the resulting composites, and thermal and optical properties [7–9]. Cellulose, chitosan, starch, polyvinyl alcohol (PVA), polylactic acid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL), polyhydroxybutyrate (PHB), polybutylene succinate (PBS), etc. have gained substantial attention as biopolymers in food packaging applications [5, 6, 8].
Synthetic polymers like polyethylene (PE), polypropylene (PP), nylon, polyester (PS), polytetrafluoro-ethylene (PTFE), and epoxy are commonly known as plastic and are derived from petroleum hydrocarbons [10]. These materials are still an integral part of our human life, and they have found their way into our daily routine. The demand for petroleum-based polymers in our commercial world is increasing because of their versatility, high mechanical strength, flexibility, resistivity, transparency, chemical inertness, low mass, and low cost [11]. Moreover, these plastic do not readily react with the product with which they are in contact, and they have excellent resistance to water, gases, temperature, and chemical degradation. Synthetic plastics are made from petroleum hydrocarbon, which is a non-renewable resource, and they emit large quantities of greenhouse gases during production [11]. In addition, burning of plastics can emit toxic chemicals such as dioxins [12]. Plastics that are used for short time periods and single-use plastics should not be made of synthetic plastics due to their low density and slow decomposition....
