Valorization of Multifunctional Lignin for Green and Facile Synthesis of Bio-inspired PLA/lignin Composites and a Light-colored Lignin Nanoparticle Sunscreen

Abstract

This study encompasses two areas of lignin utilization i.e. fabrication of lignin/PLA composites for biomedical purposes and synthesis of Lignin nanoparticles for sunscreen applications. Firstly, acetylated and non-acetylated soda lignin were utilized to fabricate anti-oxidant PLA/lignin composites for biomedical applications. After acetylation of lignin a good compatibility between PLA and lignin was observed in SEM images. The tensile properties of all the PLA/ASL composites were higher than PLA/SL composites. PLA/ASL5 displayed highest tensile strength and elongation at break of around 56 MPa and 10% respectively. PLA/SL15 and PLA/SL20 demonstrated superior UV-blocking potential with UV-transmittance less than 10%. Anti-oxidant test by DPPH assay showed that PLA/SL composites rendered excellent radical scavenging activity with PLA/SL20 displaying RSA value of around 80%. Furthermore, In vitro antioxidant activity was evaluated by H2O2 exposure and was confirmed by live/dead assay. The results demonstrated that PLA/SL composites could protect both type of cell lines from oxidative stress. In addition, all the PLA/SL and PLA/ASL composites promoted cell proliferation compared to neat PLA. PLA/SL5 and PLA/SL10 displayed the highest cell proliferation amongst all the composites. Lastly, all the PLA/SL and PLA/ASL composites had haemoglobin release below 2%. Secondly, Kraft lignin was fractionated and acetylated to obtain fractions with different molecular weights (Mw 2,175 – 8,150) and phenolic hydroxyl group content (total 3.05 – 3.2 mmolg-1). Subsequently, the lignins fractions were synthesised into Lignin nanoparticles (LNPs) by nanoprecipitation. Spherical LNPs of size between 219nm – 912nm were obtained. Fractions with high molecular weight generated particles of small diameter. The biocompatibility test with Human skin cell lines demonstrated good biocompatibility at low concentration of LNPs. Moreover, follow up analysis will be performed in order to develop a light-coloured, high SPF and antioxidant sunscreen from lignin nanoparticles. The results of the first study indicate that lignin/PLA composites could be a sustainable option to develop green, antioxidant, bioactive and hemo-compatible biomaterials for biomedical applications