Oxypropylation of Lignins and Preparation of Rigid Polyurethane Foams from the Ensuing Polyols

Summary: Different lignins were converted into polyols by a chain extension reaction with propylene oxide (PO). Thus, soda lignin from Alfa (Stipa tenacissima) (SL), organosolv lignin from hardwoods (OL), kraft lignin (KL) from softwood and oxidized organosolv lignin (OOL) were oxypropylated in a batch reactor at 180 °C in the presence of KOH as catalyst. The ensuing polyols were characterized by FTIR and 1H NMR spectroscopy, which showed that they had incorporated poly(propylene oxide) grafts into their structure. Their viscosity varied from 5 mPa · s to infinity, depending on the Lignin/PO ratio and their hydroxy index was in the range of 100–200, which made them suitable for rigid polyurethane foam (RPU) formulations. The RPUs thus obtained had a Tg of ca. 60 °C and a thermal conductivity of ≈20 mW/m · K before ageing and ≈25 mW/m · K after accelerated ageing for 10 d at 70 °C. The analyses of the gases inside the cells showed that these were mostly closed, since the partial pressure did not decrease significantly with ageing. Photograph of polyurethane foam made from OLOP. magnified image Photograph of polyurethane foam made from OLOP.