Improvement of UV stability of thermoplastic starch matrix by addition of selected lignin fraction- Photooxidative degradation

This paper examines the additivation of thermoplastic starch (TPS) matrix by selected fractions of kraft lignin (KL) and correlates its structure-performance when exposed to photooxidative degradation. KL from Eucalyptus urograndis wood was refined by a sequential fractionation process in ethyl acetate (EtOAc). Films were prepared by mixing lignin fractions as additive in TPS matrix by casting and pressing. The lignin employed were KL, fraction of KL insoluble in EtOAc (INS) and fraction of KL soluble in EtOAc (SOL). The samples were exposed to accelerated aging with Ultraviolet-C light (UV-C) for 432 h. Structural changes were measured by FTIR (Fourier -Transform Infrared) spectra. Thermal properties, such as melting enthalpy, glass transition temperature and thermal decomposition, were evaluated by DSC (Differential Scanning Calorimetry) and TG (Thermogravimetry). Morphology of the films was obtained by SEM (Scanning Electron Microscopy). Surface property of wettability was measured by contact angle. Mechanical properties were explored before and after exposure to UV-C light. It was observed that the least photodegraded films were those resulting from the addition of the lignin fraction with higher phenolic hydroxyl group content. According to structural and morphological observations, the soluble fraction (TSOL) presented the highest photoprotection and stabilizing effect as an UV-C light blocker additive on TPS matrix.

Automated summary

This study investigates the effect of different fractions of kraft lignin on the structure and performance of thermoplastic starch (TPS) matrix during photooxidative degradation. Kraft lignin from Eucalyptus urograndis wood was fractionated in ethyl acetate (EtOAc), and the fractions were added to TPS matrix films. The samples were exposed to UV-C light for accelerated aging, and their structural, thermal, morphological, and mechanical properties were analyzed. It was found that the fraction of lignin with higher phenolic hydroxyl group content provided the best photoprotection and stabilizing effect on TPS matrix.