Fully green and scalable solvent-free functionalization of banana waste fibers for high-performance biodegradable thermoplastic starch/DES composites

Sustainable packaging requires starch-based biocomposites that combine low-impact processing with effective lignocellulosic reinforcement. Here, banana pseudostem fibers (PBF) were upgraded through a solvent-minimized sequence and used to reinforce deep-eutectic-plasticized thermoplastic starch (TPS). A one-step peracetic acid (PAA) treatment reduced lignin and hemicellulose and improved fiber structure, increasing cellulose content from 23% to 64%, crystallinity from 51% to 67%, and thermal onset from 110 to 260°C. The bleached fibers were then functionalized via solvent-free citric esterification, providing the highest carboxyl density among the routes examined (–COOH ~3.28 mmol g−1) and exceeding TEMPO oxidation and maleic-anhydride modification under the conditions studied. When compounded at 15 wt% into choline chloride:glycerol (ChCl:Gly) deep eutectic solvent plasticized TPS (TPS–DES), citric-modified fibers increased tensile strength to 7.4 MPa (vs. 4.4 MPa for bleached-fiber composites) and Young’s modulus to 122 MPa (vs. 1.6 MPa for neat TPS–DES), with reduced elongation (~12%). DMA, supported by second-heating DSC, indicated an upward shift in glass transition and distinct damping behavior consistent with interphase-controlled chain confinement. SEM fractography confirmed improved interfacial cohesion with reduced pull-out, and surface moisture resistance increased (water contact angle ~61°). Overall, this scalable route enables biodegradable starch composites suitable for packaging films/sheets, thermoformed trays, and short-lifetime molded components from agricultural residues.