Composites and active materials: lignocellulosic fibres for bio-based products

This doctoral thesis is based on a research work carried out over a period of more than 20 years and was written in order to obtain a PhD diploma by Validation of Acquired Experience (VAE). My research work is in total adequacy with the current societal and environmental expectations since it deals with the study and use of lignocellulosic fibers for two major fields of application: biocomposites and active materials for packaging and biomedical. In the case of biocomposites, the studies presented in this work mainly address the issue of compatibility between lignocellulosic reinforcements and polymeric matrices.

Indeed, lignocellulosic fibers or their derivatives are polar while matrices are generally apolar. In order to obtain good properties, it is therefore necessary to improve the reinforcements/matrix interactions. For this purpose, we were mainly interested in the modification of these lignocellulosic reinforcements.
Three strategies have been used.

The first one deals with cellulose nanocrystals (CNC) used as reinforcement. They have been chemically modified by aromatic acids, using a green process, to make them less polar.

The second strategy is based on the adsorption of biobased molecules, xyloglucan (XG), and CNC on flax woven fabrics, with the same objective of improving interactions.

The last strategy is based on the use of a simple soda extraction process of bamboo fibers. This process allows maintaining high yields and increasing the surface roughness of the fibers to improve mechanical anchoring of the matrix. For the active material application, we have taken advantage of the properties of nanocellulose and in particular of nanofibrils (CNF). CNFs are of interest as a modification “platform” for obtaining active properties. The presented work is based on the use of oxidized or non-oxidized CNFs and modified by grafting or adsorption. The antimicrobial activity of the obtained materials has been analyzed and their interest in the field of packaging and biomedical applications, more particularly as external dressing, has been evaluated.

Thesis available on: https://cnrs.hal.science/LGP2/tel-04226047v1