Isolation and characterization of lignins from Wheat straw and cardoon biomasses

Abstract

The progressive reduction in the availability of oil resources, the unstoppable increase in their costs and the growing need for efficient environmental protection, imply an urgent development of new technologies for the exploitation of renewable energy with low environmental impact. From this point of view, lignocellulosic materials represent one of the largest reservoirs of solar energy stored in the chemical bonds of the most abundant forest biopolymers on Earth: cellulose and lignin. These resources are continuously renewed and have great potential for obtaining combustible substances and for the preparation of raw materials and intermediate molecules for the fine chemistry for industrial applications. From an environmental point of view there would be a considerable advantage to use a renewable source of raw material such as biomass, avoiding the use of fossil fuels and helping to decrease the concentration of greenhouse gases in the atmosphere. The design and development of new plant biomass materials and processes requires the identification and development of new analytical techniques for the structural characterization of biopolymers and the monitoring of the extent of biopolymer degradation of lignocellulosic materials. The research project is aimed at the use of waste lignocellulosic raw materials not competing with the food supply chain to produce products or materials to be re-inserted into the production cycle as a replacement (partial) of the current products of origin fossil. All this is consistent with the industry 4.0 model, which envisages rebuilding a constructive and balanced relationship between industry and all other components of the economy through the development of a circular economy. Economic and environmentally efficient pathways for production and utilization of lignocellulose for chemical products and energy are needed to expand the bioeconomy. The use of residual biomasses to obtain bioenergy and green chemicals is a real possibility to contribute to sustainable development. These materials are composed mainly of polycarbohydrates (cellulose, hemicellulose) and phenolic polymers (lignin) and have great potential for use. One of the most interesting topics of the so-called "green chemistry" is the valorisation of lignin, a natural substance that can be isolated from biomass. Lignin is one of the three main components of plant cells along with cellulose and hemicelluloses (Fig.1). The development of the cellulose and hemicellulose transformation chain in biorefinery ambitions has already achieved industrial

objectives, while the study of lignin for these applications is still in a pioneering phase of experiments that hopefully will help resolve some negative aspects related to the use of fossil-based products. The particular chemical composition of lignin is potentially suitable to replace fossil sources in the production of basic chemicals and some polymers. For many years, this macromolecule has been used almost exclusively, after isolation, for energy purposes in the pulp and paper industries. Today, lignin is considered a potential renewable precursor in the development of high-value applications such as controlled release devices, novel composites, nanoparticle applications, application devices in electronics, carbon fiber manufacturing, and absorbing and dispersing agents. Furthermore, among the various applications, lignin is currently being studied to be used in the future as a starting point for the preparation of adhesives for the production of green building panels, polyurethanes and coating surfaces. The aim of the thesis project was to isolate the lignins derived from wheat straw and cardoon residues by different extraction techniques and to characterize them to highlight the structural properties and therefore the potential applications. [edited by Author]