Lignocellulosic fibers: Source of Materials and Fermentable Sugars

Abstract

This project aims at valuing lignocellulosic fibers by using them to produce fermentable sugars (which may generate ethanol) as well as bio-based materials. Sisal and coconut fibers were initially selected. The motivation of this choice was due to the fact that both of them are widely available in the country and present a different composition and morphology. Sisal has high cellulose content and low lignin content, while the coconut has higher lignin content when compared with sisal. The cellulose has a great potential for the production of ethanol, since it can be generated from sugar produced from the hydrolysis of cellulose. An important aspect related to the production of ethanol from lignocellulosic materials refers to the elimination or not of lignin and hemicelluloses which are present before hydrolysis. The present project is intended to subject the biomass to pre-treatments in order to remove the lignin and hemicelluloses from lignocellulosic fibers, for example by using an alkaline solution (NaOH, mercerization). Optimum conditions will be sought in these pre-treatments to obtain fibers which will lead to better results for both the preparation of materials and to obtain fermentable sugars. An alternative to pre-treatments that remove lignin before the enzymatic hydrolysis is the use of surfactants compatible with lignin, whose presence usually interferes with the performance of hydrolysis reactions. In this project, the use of a biosurfactant will be considered. In all enzymatic hydrolysis reactions, aliquots will be removed from the medium during the reaction. The liquor containing fermentable sugars will be separated from the solid, i.e. non-hydrolyzed biomass, and both will be characterized. The liquor will be assessed via high-performance liquid chromatography (HPLC), and the non-hydrolyzed fibers via crystallinity (X ray diffraction), surface morphology (Scanning Electron Microscopy), size (thickness length, using MorFi). It is important to emphasize that this study of the non-hydrolized fibers during the hydrolysis process besides adding information to the study of hydrolysis, generate information for obtaining cellulose nanocrystals from lignocellulosic fibers. Considering the desirable process integration in biorefineries producing cellulosic ethanol, the lignocellulosic fibers will be also used in the preparation of materials. This project has as one objective to use the lignocellulosic fibers in the preparation of filmogenic materials, without significantly interfering with the structures of the principal components of these fibers, i.e. cellulose, hemicelluloses and lignin. It is intended to obtain membranes (mats) based on ultrathin fibers and nanofibers from electrospinning using the lignocellulosic fibers (treated or not) as the starting material. Additionally, films will be obtained from starting solutions (via conventional process) of lignocellulosic fibers disrupted by using appropriate solvent systems, such as lithium chloride / dimethylacetamide (LiCl / DMAc). Taking into account the approach linked to the lignocellulosic biorefinery of this project, the use of glycerol as a solvent will be also explored. Glycerol can potentially be obtained as a byproduct of the platform chemicals in a biorefinery. After the identification of optimal conditions for the preparation of films, they will be prepared with the addition of nanocrystalline cellulose (CNC), which is already available, in order to evaluate the influence of its presence on film properties, such as mechanical and barrier properties. Therefore, the valuation of lignocellulosic fibers abundant in the country will take place in two parts: the first consisting of pre-treatment studies and subsequent enzymatic hydrolysis, and the second part consisting of generation of materials.