Advances in Poly(Lactic Acid) Chain Extenders: Mechanisms, Performance, and Sustainability

ABSTRACT Poly(lactic acid) (PLA) is a biodegradable polymer from renewable sources whose limited thermal stability, brittleness, and processing hinder broader use. Chain‐extension techniques overcome these issues by raising molecular weight, introducing branching or cross‐linking, and adjusting viscoelasticity. This review surveys advances from 2015 to 2024 in PLA chain extension, covering reaction mechanisms, characterization methods, extender types, and effects on performance and sustainability. Chain‐extension mechanisms include esterification (epoxide‐based), polycondensation (isocyanate‐ and anhydride‐based), and free‐radical coupling (peroxide‐based). Processing parameters—temperature, extender concentration, and reaction time—influence molecular architecture. Structural analyses, thermal analyses, and mechanical tests quantify increases in molecular weight, crystallinity changes, and property improvements. Chain extension also alters degradation. Higher molecular weight and modified crystallinity slow hydrolytic and enzymatic breakdown, though additives such as diatom frustules or plant fibers can accelerate biodegradation when desired. Thermal and photo‐oxidative stability generally improve, while catalyst systems and processing history affect degradation kinetics. Mechanical loading in tissue engineering illustrates the importance of mechanoresponsive degradation. Socio‐economic and sustainability aspects highlight the need to balance cost, scalability, and environmental impact. High‐performance extenders often raise costs and may hinder end‐of‐life degradability, whereas bio‐based and recyclable extenders remain in development. Future work should target multifunctional, biodegradable extenders, optimize dispersion processes, and integrate chain extension with other modifications to create intelligent, responsive PLA materials.