Synthesis and optimization of novel polyols from renewable lignin waste

The objective of this dissertation is the production of flexible polyurethane foams through the synthesis of new polyols derived from the liquefaction of lignin, a waste of the paper industry. Lignin was depolymerized using microwave heating, employing polyols from renewable sources as liquefaction solvents. The operational conditions, such as time, temperature, type of solvent and amount of catalyst were studied to obtain polyols with optimal characteristics for the production of flexible polyurethane foams. In particular, a design of experiment (DoE) has been used to assess the most significant processing parameters on the final quality of the lignin polyol. By using the optimized polyol, several polyurethane flexible foams were produced. The physical-mechanical characterization of the foams was carried out through measurements of density, thermal conductivity, and compression strength, while the foam morphology was analyzed using scanning electron microscopy. This was followed by thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and fire behavior characterization (limiting oxygen index and cone calorimeter test). The properties of the foams obtained using lignin-based polyols were compared with those of foams made with commercial polyol, obtained from fossil source. The results show that, by optimizing both the operational conditions of the liquefaction process and the formulation of the foams, it is possible to obtain foams with comparable properties to those of foams made from fossil-based polyols, using up to 30% of lignin based polyol. This, therefore, offers the possibility of reusing lignin, paving the way for the introduction of polyols synthesized from renewable sources into the market for the production of foams with good performance.