Transparent, flexible, and glycerol-free TEMPO-oxidized starch/montmorillonite nanocomposites with high mechanical strength and high anti-UV properties

Abstract

The transparent, flexible, and glycerol-free 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized starch (OS) films were first successfully prepared using the TEMPO/NaClO/NaClO₂ system. The OS05 film (degree of oxidation 5 %, ∼33 μm in thickness) exhibited high transparency (89–91 % light transmittance at 400–700 nm), superior mechanical properties (Young's modulus of 1.6 GPa, tensile strength of 42.4 MPa), anti-UV property (light transmittance <26 % at 200–275 nm), and low water vapor permeability (1.81 × 10^–10 g m^–1 s^–1 Pa^–1). After incorporating 2.5 % montmorillonite (MMT) to form the OS05M2.5 composite film, transparency was maintained, and all other properties improved, particularly Young's modulus (1.8 GPa) and anti-UV property (<16 %). XRD results show the d-spacing of MMT nanoplatelets increased from ∼1 to ∼1.9 nm after combining with OS, indicating successful intercalation of OS molecules into MMT interlayers, consistent even with 10 % MMT content. The effective modulus of MMT nanoplatelets in the OS matrix was determined to be 18.5 GPa. Based on the experimental evidence, the biodegradable OS05 and OS05M2.5 films are promising candidates for transparent packaging materials.