Effect of lignin extracted by different methods on the properties and structure of lignin/starch fiber membranes

Starch is widely used in food packaging materials, but polymers or chemical additives are added to improve the performance of the fiber membranes. In this study, we used electrospinning technology and incorporated lignin with multifunctional groups to enhance the performance of starch (ST) fiber membranes. Mill wood lignin (MWL), kraft lignin (KL), and organosolv lignin (OL) were obtained from pine wood using ball milling, sulfate pulping, and organic solvent method. Subsequently, ST and lignin/starch (L/ST) electrospun fiber membranes were prepared. Nuclear Magnetic Resonance (NMR) results showed that KL had more hydroxyl groups and H structure units compared to OL and MWL, which resulted in better UV resistance of the kraft lignin/starch (KL/ST) fiber membranes. In the preparation of KL, higher alkali concentrations and temperatures resulted in loosening of lignin structure, reducing condensation, and releasing more hydroxyl groups. These hydroxyl groups enable the formation of stronger hydrogen bonds with starch which improves the crystallinity, thermal stability, barrier properties, and hydrophobicity of the fiber membranes. Higher concentrations of phenolic hydroxyl groups were present in both KL and OL. These groups could donate hydrogen protons to bind [DPPH-] radicals, thus demonstrating enhanced DPPH radical scavenging activity. In summary, this study compared the structure of lignin obtained by different extraction methods and analyzed the effect of its structure on the performance of fiber membranes, especially in terms of antioxidant performance, mechanical strength, and gas barrier performance, paving the way for future applications in packaging materials. • The properties of milled wood, kraft, and organosolv lignin were systematically analyzed. • Kraft Lignin/starch electrospun membrane had better strength, stability, antioxidant, and hydrophobicity. • High -OH content of lignin gave excellent stability, gas barrier and hydrophobicity to membrane. • Lignin with higher Ph-OH, -COOH and H-unit content afforded better UV resistance of membrane.