Aplicació de nous sistemes enzimàtics per al refinatge i la modificiació de fibres celulòsiques

Resumen

This thesis is focused on the analysis of raw materials and the functionalization of cellulose fibres via enzyme treatments. The research carried out is framed by one of the lines of research of the Textile and Paper Engineering Department from the UPC: Application of biotechnology in pulp and papermaking processes, which aims to use new enzymes and to develop new bioprocesses based on their application to obtain cellulose products. This work comprises different studies that correspond to each of the chapters in Part II, dealing with the application of various enzyme treatments of cellulose fibres, from wood (Eucalyptus globulus) and nonwood (Linum usitatissimum) plants, for the improvement of the refining stage and the modification of the fibres to obtain paper products with new and better properties. Firstly, the characterization of the raw material was performed by studying in deep the methodologies for the measurement of the electrokinetic properties of cellulose fibres (zeta potential and cationic demand). The conditions and variables that affect these assays were defined and established. The potential of the new cellulase Cel9B for the modification of cellulose flax fibres was for the first time assessed in this work. Cellulase treatments were found to enhance the development of properties during the refining of fibres, thus improving the physicomechanical properties of paper. New applications of the enzymatic system laccase-HBT were assessed with the following purposes: to modify bleached flax fibres (ECF and TCF), and to improve the physicomechanical properties of paper. The enzyme treatments were found to increase the density of papers, followed by the reduction of the air permeance. Therefore, refining time and energy could be saved to obtain a certain level of density and air permeance in papers by treating cellulose fibres with laccase and HBT. Lipids from TCF bleached flax fibres were removed by the laccase-HBT treatments. Although these chemical changes did not account for the modification of mechanical properties of paper, pitch problems could be avoided during the manufacture of paper by the application of the laccase-HBT system. Finally, laccase was also used in combination with hydrophobic compounds with the aim of conferring new properties on cellulose fibres. These enzyme treatments were studied in detail with different types of cellulose fibre, from wood (Eucalyptus globulus) and nonwood (Linum usitatissimum) plants, and with novel cellulose materials as well, including microfibrillated cellulose and cellulose nanocrystals. The results obtained demonstrated that the enzymatic system consisting of lacasa and a hydrophobic compound is effective towards the hydrophobization of cellulose fibres. The chemical and water absorption properties of paper were assessed. Moreover, various novel techniques such as ATR-FTIR and QCM-D were employed to elucidate the mechanisms of the hydrophobization of cellulose fibres and paper. These studies resulted with the development of a new bioprocess for the internal sizing of paper via the enzyme treatments of cellulose fibres with laccase in combination with a hydrophobic compound. The success achieved in reducing the water absorption led to the patent of this new and innovative method for the internal sizing of paper via enzyme treatments.