Abstract
The global polymer economy now produces more than 400 million tonnes of plastics annually, making material substitution a scale as well as a chemistry challenge. This chapter evaluates bio-based, biodegradable, recyclable, and functionally advanced polymers through their chemistry, performance, life-cycle evidence, environmental fate, and deployment constraints. Polylactic acid (PLA), polyhydroxyalkanoates (PHA), thermoplastic starch, cellulose-derived materials, drop-in bio-polyethylene and bio-PET routes, polyethylene furanoate (PEF), dynamic covalent networks, and nanocomposites are assessed without treating bio-based origin or biodegradability as automatic evidence of sustainability. Industrial examples include current PLA scale-up, partially bio-based PET, renewable polyethylene, emerging FDCA/PEF production, and recyclable thermoset-composite pathways. The chapter emphasizes condition-specific biodegradation, transparent life-cycle boundaries, safe-by-design additives, circularity metrics, and alignment between material design, regulation, collection, and end-of-life infrastructure as prerequisites for credible sustainability claims.