Doctoral Thesis in the Paper Engineering CELBIOTECH group: “IONIC LIQUID-ASSISTED THE PREPARATION OF TRANSPARENT CELLULOSIC BIOCOMPOSITE FILMS”

On December 14, 2023, Elahe Amini defended her doctoral thesis at the Escola Superior d’Enginyeries Industrial, Aeroespacial i Audiovisual de Terrassa (ESEIAAT) of the Universitat Politècnica de Catalunya_BarcelonaTech. This thesis has been directed by the phD M. Blanca Roncero and Cristina Valls within the framework of the Doctoral Program in Textile and Paper Engineering. The work reflected in the thesis was carried out in the laboratories of the Paper Engineering research group (CELBIOTECH) of the Department of Graphic Engineering and Design, and has been financed thanks to different research projects of the Ministry of Science, Innovation and Universities.

Elahe Amini's work has focused on addressing a new approach to developing cellulose films with high barrier properties. The starting material has been a paper made from cotton linters that has been dissolved with an ionic liquid. The ionic liquid acts as a smart nanowelding agent to assemble nanosized cellulose structures. Different types of bionanocomposites have been obtained by combining regenerated cellulose with polylactide acid, polycaprolactone and zinc oxide nanoparticles, or with lignin nanoparticles as reinforcing agents.

The thesis begins with an extensive review of the different ionic liquids and their enormous potential in different applications, including the dissolution of lignocellulosic biomass. Next, the ionic liquid 1-ethyl-3-methylimidazole acetate ([Emim]OAc) is applied with the hydrophobic polymers PCL (polycaprolactone) and PLA (polylactic acid) through the presence of zinc oxide nanoparticles. [Emim]OAc and zinc oxide nanoparticles are used to catalyze the ring-opening polymerization of L-lactide and ε-caprolactone in the cellulose matrix under mild conditions. The role of each component on the obtained films is evaluated in order to optimize their barrier properties (to water and oxygen), their mechanical resistance and their UV ray blocking capacity. In addition, both the antioxidant activity and the optical properties of the films are improved.

In the last part of the thesis, the ionic liquid [Emim]OAc is used to synthesize lignin nanoparticles (LNP) in situ using a sonication method, which allows a uniform distribution without the need for additional reducing agents or stabilizers. These bionanocomposites are produced using a partial cellulose dissolution process that traps the synthesized LNPs. The effect of the amount of LNP on the mechanical resistance, antioxidant and antimicrobial activities, as well as the barrier properties to water vapor, oxygen and UV rays of the films obtained is investigated.

Interest in new cellulose-based biomaterials has increased enormously in recent years. These biomaterials can be found in various forms and have potential applications in different sectors thanks to the abundance and versatility of cellulose as a biopolymer. In addition, they have the advantage of being biodegradable, which makes them environmentally friendly.