Lipase-catalyzed glycerolysis of technical lignin towards high-density polyurethane foams

Abstract

The lignin can be applied in the synthesis of several products, including polymers. Nevertheless, its direct application can affect negatively the mechanical properties of the material, since it presents a highly cross-linked and complex structure. In this scenario, some chemical methods have been explored to increase the reactivity of lignin to produce of polyurethane. Although the literature reports methods intended the modification and incorporation of the lignin in the monomers production, to the best of our knowledge, there are no reports on the use of lipases in transesterification using this biomass. Thus, in this study, biopolyols were synthetized by enzyme-catalyzed transesterification using an ester (castor oil) and an alcohol (glycerol) in the presence of low-sulfur alkaline lignin as substrates, to produces a monomer. Then, high-density rigid foams were obtained via bulk polymerization. An increase in the apparent density and mechanical strength was observed with increasing lignin content. By Scanning Electron Microscopy (SEM) it was possible to observe more elongated and denser mixed cells, associated with the incorporation of lignin. Moreover, the compressive strength reached values of 0.14–0.52 MPa and polymer insoluble fraction were higher than 80 % for all the foams. Then, through this study, it was possible to obtain rigid and high density lignopolyurethane for industrial applications derived from enzymatic glycerolysis and renewable resources.