Title
Oxypropylation of soda lignin: characterization and application in polyurethane foams production
Authors
BESMA BERRIMA GERARD MORTHA SAMI BOUFI ELIMAM EL ALOUI and MOHAMED NACEUR BELGACEM

Received April 11, 2015
Published Volume 50 Issue 9-10 October-December
Keywords lignin, polyol, oxypropylation, rigid polyurethane foam

Abstract
Soda lignin precipitated from black liquor of Stipa tenacissima L. cooking was converted into polyols by a chain extension reaction with propylene oxide (PO). It was oxypropylated in a batch reactor in the presence of potassium hydroxide (KOH) as a catalyst. The reaction conditions were optimized by modifying the lignin/propylene oxide ratio [L/PO (w/v)], the temperature and the catalyst content. L/PO ratios of 20/80, 30/70 and 40/60 and catalyst contents from 3% to 5% were used. The temperature of the reaction was varied from 120 to 140 °C. The ensuing polyols were characterized by FTIR, 1H-NMR spectroscopy and size exclusion chromatography. Also, their viscosity and hydroxyl index were determined. A decrease in the molecular weight was observed after the oxypropylation reaction, which was explained by lignin depolymerisation. The viscosity and the hydroxyl index of the polyols ranged from 0.48 to 4.2 Pa.s and 150 to 375, depending on the lignin/PO ratio. Rigid polyurethane foam (RPU) was prepared from the PO extended lignin polyols, and its compressive strength and cell morphology were analysed.