Recycling liquid glass modified waste-lignin into bio-based polyurethane foam composites for building materials industry

Abstract

Local governments around the world are pursuing pretentious zero waste policies with the aim to reduce methane and CO2 emissions, release of solid particles to the atmosphere and minimize the waste which are landfilled. Lignin, as a secondary raw material for the wood industry, is obtained by hydrolysis of polysaccharides (cellulose) from shredded wood. It landfilled in Lithuania as a precursor for further use in the production of biofuel, as a binding material for straw briquettes and wood pellets and as a substrate for plants as it improves the soil structure. Furthermore, lignin is characterized by favorable properties such as low water permeation and mechanical support and can have even wider application areas such as building materials industry. Theoretically, lignin particles can be immobilized in polymer matrices such as bio-based rigid polyurethane (PUR) foams. However, existing hydroxyl groups in lignin cause expansion and dimensional instabilities. Consequently, the present study investigates the possibility of “locking“ the hydroxyl groups on the surface of lignin particles by using liquid glass and vacuum infusion technique. The obtained PUR foam composites with 2.5-10% unmodified lignin particles had by ~15% lower tensile strength, by ~60% reduced compressive strength and unfavorable dimensional changes at 7.5% and 10% lignin particles while liquid glass infusion technique led to significant improvements of the mentioned properties and enabled the incorporation of higher amounts of particles. Moreover, thermal conductivity value of PUR foam composites with liquid glass modified lignin particles was in the range of (0.026÷0.028) W/(m·K) while water absorption was not affected indicating effective thermal insulation and moisture barrier behavior.