Strength and Flexibility of Eco‐Friendly Poly Lactic Acid–Lignin Composites Made With Treated Natural Fibers for Sustainable Packaging

ABSTRACT Due to increasing environmental concerns from nonbiodegradable packaging waste, a poly lactic acid (PLA) based bio‐composite is developed using nano‐chitosan‐treated pineapple leaf fiber (PALF) and coir fiber, with lignin as a bio‐filler. The aim is to create biodegradable packaging materials with improved chemical and environmental stability properties as a sustainable alternative to conventional plastics. Five formulations are produced with a fixed PLA content of 65 wt% while varying lignin content from 0 to 20 wt%. Nano‐chitosan treatment enhanced fiber matrix adhesion and introduced antibacterial functionality. The composite containing 10 wt% lignin (NC‐2) showed the highest performance, with a tensile strength of 22.3 MPa, flexural strength of 38.4 MPa, improved impact resistance, faster degradation and higher surface hardness. This superior performance is attributed to uniform dispersion, effective adhesion, and strong interfacial bonding between fibers and the PLA matrix. Thermogravimetric and dynamic mechanical analyses confirmed improved thermal stability and damping properties, Fourier transform infrared spectroscopy validated the chemical interactions. SEM images revealed more uniform morphology with fewer voids. The composite also exhibited appreciable degradability (47.3% weight loss in 6 months) and antioxidant activity above 40%. This multifunctional green bio‐composite combines strength, stability, and biodegradability properties, offering a sustainable solution for packaging applications.