Size reduction of lignin leads to PLA-based composites with superior properties Zoi Terzopoulou 1 , Eleftheria Xanthopoulou 1 , Sofia Makri 1,2 , Alexandros Zoikis- Karathanasis 2 , Savvas Koltsakidis 3 , Dimitrios Tzetzis 3 , Miguel Angel Valera 4 , Dimitrios Bikiaris 1 1 Laboratory of Polymer and Colors Chemistry and Technology, Department of Chemistry, 3 Digital Manufacturing and Materials Characterization Laboratory, School of Science and Technology, International Hellenic University, 14 km Thessaloniki, 57001 N. Moudania, Greece 4 AIMPLAS, Asociación de Investigación de Materiales Plásticos Y Conexas, Carrer de Gustave Eiffel, 4, 46980 Paterna, Valencia, Spain Poly(lactic acid) (PLA) composites with 0.5 wt% lignin or nanolignin were prepared with in-situ ring opening polymerization (ROP) with reactive extrusion (REX). The ROP was followed by monitoring the torque. The composites were rapidly synthesized with REX in under 20 min, and when the amount of catalyst was doubled, the reaction time was reduced to under 15 min. The dispersion, thermal transitions, mechanical properties, antioxidant activity and optical properties of the resulting PLA-based composites were evaluated with SEM, DSC, nanoidentation, DPPH assay and UV-Vis spectroscopy. All composites were characterized by means of SEM, GPC, ATR and NMR, to assess their molecular weight, chemical structure and free lactide content. Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece 2 Creative Nano PC, 43 Tatoiou, Metamorfosi, 14451 Athens, Greece The addition of both lignin and nanolignin reduced the UV transmittance and improved the antioxidant activity of PLA. Comparing the characteristics of the resulting composites showed that the dispersion, crystallization, mechanical, and optical properties were improved. These improvements were attributed to the better dispersion of L and NL via REX, which was facilitated by the formation of interfacial covalent bonds. Lignins are polyols with high functionality and acted as macroinitiators in the ROP of lactide, yielding the grafting of PLA chains on lignin particles. The bigger catalyst amount successfully decreased polymerization time while retaining the achieved intrinsic viscosity and molecular weight. The reduction in lignin size toward nanolignin had a significant beneficial effect on the cold crystallisation and nanomechanical properties of PLA, with a maximum Young’s modulus of ~6000 MPa, demonstrating the importance of the size of the lignin in the properties of the synthesized composites. Funding: This work was funded from the European Union’s Horizon 2020 Research and Innovation Program under Grant Agreement No. 952941 (BIOMAC Project).
P293-L
© The Author(s), 2023
Made with FlippingBook Learn more on our blog