Transformation of lignin and lignocellulose into nanoparticles: Structure-property relationship and applications

Abstract

Lignin, a heterogenous and complex aromatic polymer, is known as a recalcitrant product from pulp & paper industry with limited applicability but recent advances showed that it can be valorized via its transformation into water dispersible particles.

The objective of the doctoral thesis work was to produce colloidal lignin particles (CLPs) from various lignin sources, including two technical lignins and a residue from bioethanol production, and to explore new potential applications for these particles. Spherical CLPs were produced following the nanoprecipitation method in which lignin, dissolved in an organic sol-vent, is poured into water, acting as a non-solvent. In order to study the effect of the molecular weight on the particle size of CLPs, oxidative polymerization of kraft lignin with laccases and solvent fractionation of soda lignin were performed. Two solvents (tetrahydrofuran and acetone) were utilized to produce the CLPs and resulted in different particle sizes. The surface properties of CLPs were modified by adsorption of proteins or polymers for broadened and more efficient use in applications. CLPs coated with proteins were utilized for adhesives of soft materials with biomedical purposes in mind. Cationic CLPs were prepared by adsorption of cationic lignin and utilized to agglomerate cowpea chlorotic mottle viruses for facilitation of water purification processes. Ecotoxicity evaluation of CLPs from soda and hydrolysis lignins, indicated that they display lower toxicity than metallic nanoparticles that are used for similar applications.

Controlled combination of different lignin materials within cellulose nanofibrils (CNFs) or cellulose nanocrystals (CNCs) was studied to produce potential materials for bioactive packaging with improved mechanical properties, and with good anti-UV and antioxidant properties. The addition of crude lignin or CLPs within CNFs or CNCs films increased the under-standing about the impact of the lignin molecular and supramolecular structures on the antioxidant activities of the composite films. Lignocellulose nanofibrils (LCNFs) were obtained after a solvent fractionation of a recalcitrant hydrolysis lignin from biorefinery. The films produced by partial substitution of CNFs by LCNFs displayed competitive oxygen barrier properties than other plastics. The results presented in this thesis will contribute to increase the understanding about colloidal lignin and help the further developments of lignin-based materials for medical or environmental applications.