Enhanced Thermal Stability of Esterified Lignin in Different Solvent Mediums

Abstract

In this study, soda alkali lignin from oil palm empty fruit bunch (EFB-AL) and kenaf core (KC-AL) are esterified with maleic anhydride under two different conditions, namely i) pyridine at temperature of 120°C for 3h and ii) aqueous alkaline solution at room temperature for 4h. As a result, the weight percentage gain (WPG) of the esterified EFB-AL (EFB-EL) and esterified KC-AL (KC-EL) in pyridine demonstrated a higher compared to aqueous alkaline solution. The FT-IR results of EFB-EL and KC-EL in both solvents exhibited some changes at the carbonyl and hydroxyl groups. Furthermore, the esterification process induced the carboxylic peak to appear in both alkali lignin samples. The outcome is confirmed by conducting H-NMR analysis, which demonstrated ester and carboxylic acid peaks within the spectral analysis. Finally, the TGA results showed both EFB-EL and KC-EL that are exposed to aqueous alkaline actually possessed better thermal stability and higher activation energy (Ea) compared to the esterified samples in pyridine.

Formulation of Multifunctional Materials Based on the Reaction of Glyoxalated Lignins and a Nanoclay/Nanosilicate

“…This is in accordance with the S/G ratios previously discussed in Section . Between 8 and 9 ppm, protons derived from phenolic hydroxyl groups are normally reported. , To confirm the presence of the mentioned groups, the lignin samples were added to trifluoroacetic acid (TFA) prior to the 1 H NMR analysis. TFA is known to react with alcohols through the hydroxyl groups, leading to the esterification of the polymer .…”

Understanding the Effects of Alkali Pretreatment and Acid Treatment of Oil Palm Trunk Fibres

“…30 The C=O stretching peak can be seen at 1750 cm -1 , which is assigned to uronic and ester groups in the hemicellulose or ester groups found in p-coumaric acid of lignin. 31,32 This peak reduced after the alkali and acid treatments, suggesting that the interruption of the lignin-carbohydrate linkages has occurred. Subsequently, this phenomenon has improved the cellulose digestibility.…”

“…33 The peak at 1640 cm -1 was assigned to the carboxylate groups, while the peak at 1505 cm -1 was attributed to the polymer structure of the aromatic lignin group (C=C). 32 The functional group of C-O-C corresponds to the ether groups in lignin, which are present at 1250 cm -1 and 1050 cm -1 . 34 The reduction of this peak after the alkali and acid treatments was correlated with the partial removal of lignin in the OPTF, as the ether groups between lignin and cellulose were broken.…”