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

Abstract

<jats:title>Abstract</jats:title><jats:p>Lignin obtained by Lignoboost® procedure from black liquor after kraft pulping of <jats:italic>Eucalyptus globulus</jats:italic> 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 (K<jats:sub>2</jats:sub>CO<jats:sub>3</jats:sub>), 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), <jats:sup>1</jats:sup>H NMR, <jats:sup>13</jats:sup>C 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 (<jats:italic>ca.</jats:italic> 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 K<jats:sub>2</jats:sub>CO<jats:sub>3</jats:sub> have potential to be used as polyols in the production of polyurethanes as the corresponding hydroxyl number (I<jats:sub>OH</jats:sub>) is in the range of 198–410 mg KOH g<jats:sup>−1</jats:sup>.</jats:p>

Nanocomposite Polymeric Materials Based on Eucalyptus Lignoboost® Kraft Lignin for Liquid Sensing Applications

“…Considering that sensors based on the polyurethanes, synthesized using kraft lignin isolated using conventional procedure, did not display sensitivity to Cu(II) [16], response of the sensor developed in this work can be attributed to the capability of phenolic hydroxyl groups to complex transition metals with higher specificity towards copper and mercury. This proposition is further corroborated by the reported higher chelating capacity of tannins with vicinal phenolic groups towards Cu(II) when compared to other bivalent transition ions, such This behavior can be explained by the differences in the composition of eucalyptus LignoBoost ® kraft lignin and other technical lignins [30][31][32], most noticeably, lower content of redox quinone type moieties and significantly higher content of polyphenolic groups with vicinal hydroxyls originating from concomitant tannins in the former [18]. In particular, the LignoBoost ® kraft lignin has a higher total content of total hydroxyl groups and higher relative content of phenolic hydroxyl groups compared to the technical kraft lignin obtained from the cooking of the same wood species, but isolated by the conventional procedure [32].…”

“…Incompletely dissolved highly swollen aggregated lignin was previously detected in PU obtained by copolymerization of conventional acid-precipitated eucalyptus kraft lignin and PPGDI [14]. In addition, conjugated aromatic rings of flat ellagic acid structure could positively contribute to the conductivity of the final PU more than kraft lignin, whose structural units are predominantly linked by alkyl-alkyl, alkyl-aryl, and aryl-ether bonds, i.e., having less conjugated aromatic structures [18].…”

“…A similar approach was adopted in this work to increase the conductivity of the eucalyptus LignoBoost ® kraft lignin and ellagic acid-based polyurethanes. Ellagic acid was used in this study as the main eucalyptus kraft lignin contaminant of polyphenolic origin [18]. This tannin contributes substantially to the phenolic functionalities of the isolated lignin.…”

“…The critical exponent reflects the dimensionality of the system and usually takes values between 1.3 and 1.9, corresponding to two-and three-dimensional percolating systems, respectively [21,22]. The LignoBoost ® kraft lignin possesses higher molecular weight than the conventional kraft lignin and higher content of phenolic groups [18], two factors favoring the association of lignin molecules in solution with copolymer (PPGDI). This negatively affects the dispersion of lignin in the polymeric matrix and, therefore, the dispersion of associated nanotubes in bulk.…”

“…Contrary to these findings, LignoBoost ® kraft lignin-based sensor did not display redox sensitivity, showing a very low response to Cr(VI) and redox pair, but instead it showed a selective response to Cu(II). This behavior can be explained by the differences in the composition of eucalyptus LignoBoost ® kraft lignin and other technical lignins [30][31][32], most noticeably, lower content of redox quinone type moieties and significantly higher content of polyphenolic groups with vicinal hydroxyls originating from concomitant tannins in the former [18]. In particular, the LignoBoost ® kraft lignin has a higher total content of total hydroxyl groups and higher relative content of phenolic hydroxyl groups compared to the technical kraft lignin obtained from the cooking of the same wood species, but isolated by the conventional procedure [32].…”