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Effect of different catalysts on the oxyalkylation of eucalyptus Lignoboost® kraft lignin

Authors
  • Vieira, Fernanda R.1
  • Barros-Timmons, Ana1
  • Evtuguin, Dmitry V.1
  • Pinto, Paula C. R.2
  • 1 University of Aveiro, 3810-193 , (Portugal)
  • 2 Forest and Paper Research Institute, Quinta de S. Francisco, 3801-501 , (Portugal)
Type
Published Article
Journal
Holzforschung
Publisher
De Gruyter
Publication Date
Jun 02, 2020
Volume
74
Issue
6
Pages
567–576
Identifiers
DOI: 10.1515/hf-2019-0274
Source
De Gruyter
Keywords
License
Yellow

Abstract

Lignin obtained by Lignoboost® procedure from black liquor after kraft pulping of Eucalyptus globulus wood was characterized and converted into liquid polyols via an innovative and safe procedure using base catalyzed oxyalkylation with propylene carbonate (PC). The effect of four catalysts, Potassium carbonate (K2CO3), 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU), dicyanodiamide (DICY), and 1,4-diazabicyclo [2.2.2] octane (DABCO) was evaluated in terms of lignin polyol yield and weight gain. The ensuing polyols were also characterized by fourier transform infrared (FTIR), 1H NMR, 13C NMR, and size exclusion chromatography (SEC) to determine the degree of the substitution (DS), degree of polymerization (DP), and the molecular weight, respectively. Only a minor proportion of PC (ca. 3–15%) was converted to propylene glycol/homooligomers as revealed by high performance liquid chromatography (HPLC). All catalysts promoted preferential derivatization of lignin phenolic OH groups by oxypropyl moieties. The maximum average DP of propylene oxide chains in oxyalkylated Lignoboost® kraft lignin (oKL) was 1.85 per one phenylpropane unit (PPU) using DBU. Conversely, the DP of oKL using DICY was very low (0.27/PPU). DICY’s catalytic activity seems to be jeopardized due to the formation of unreactive adducts with lignin. The oKL obtained using DBU, DABCO, and K2CO3 have potential to be used as polyols in the production of polyurethanes as the corresponding hydroxyl number (IOH) is in the range of 198–410 mg KOH g−1.

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