Modification of thermoplastic starch (TPS) with PLA and PCL via ring-opening polymerization (ROP): Comparative study of water solution and solvent-free approaches

The chemical modification of thermoplastic starch (TPS) via ROP of lactic acid and ε-caprolactone to grafting of poly(lactic acid) (PLA) and polycaprolactone (PCL) onto starch was investigated, utilizing starch hydroxyl groups as initiation sites. Both bulk and aqueous polymerization conditions were employed, using tin(II) 2-ethylhexanoate (Sn(Oct) 2 ) serving as the catalyst. The influence of the reaction medium and starch-to-monomer ratios on grafting efficiency and copolymer properties was assessed. Fourier transform infrared (FTIR) spectroscopy confirmed successful grafting by the appearance of characteristic carbonyl signals at ∼1730 cm⁻¹ for PLA and ∼1720 cm⁻¹ for PCL. Nuclear magnetic resonance (NMR) analyses verified the formation of polyester chains on the starch backbone, with PCL exhibiting higher grafting density and chain length compared to PLA. Dynamic light scattering (DLS) demonstrated that PCL grafting produced larger copolymer particles with a narrower size distribution in bulk polymerization. Aqueous polymerization resulted in a broader particle size distribution due to increased starch solubility and chain separation. These findings highlight the potential of ROP grafting to improve starch’s compatibility with hydrophobic polymers, offering a biodegradable alternative in certain thermoplastic applications. • Synthesis of starch-g-PLA and starch-g-PCL via ring-opening polymerization. • Comparative study of aqueous and bulk polymerization conditions. • Characterization of grafting efficiency using FTIR NMR, and DLS. • Higher grafting density and chain length observed for PCL compared to PLA.