Fast Curing Bio-Based Phenolic Resins via Lignin Demethylated under Mild Reaction Condition

Abstract

Abstract:Demethylation technique has been used to enhance lignin reactivity for preparation of phenolic resins. However, the demethylation efficiency and the demethylated lignin (DL) reactivity were still unsatisfactory. To improve the demethylation efficiency, alkali lignin was demethylated under different mild conditions using sodium sulfite as a catalyst. Lignin and DL were characterized by 1 H-NMR (nuclear magnetic resonance) and Fourier transform infrared (FT-IR) spectroscopy to determine the demethylation mechanism. With the demethylation of lignin, the methoxyl group content decreased from 1.93 m mol/g to 1.09 m mol/g, and the phenolic hydroxyl group content increased from 0.56 m mol/g to 0.82 m mol/g. These results revealed that methoxyl groups were attacked by SO 3 2− , and some methoxyl groups were converted to phenolic hydroxyl groups by a nucleophilic substitution reaction, generating DL with high reactivity. The chemical properties of lignin-based phenolic resins were studied by 13 C-NMR and FT-IR spectroscopy, and their physical properties were also investigated. The results indicated that lignin-based phenolic resins exhibited faster curing rate and shorter gel time. In addition, the bonding strength increased from 0.92 MPa to 1.07 MPa, and the formaldehyde emission decreased from 0.58 mg/L to 0.22 mg/L after lignin demethylated at the optimum condition.

Curing properties of high‐Ortho phenol‐formaldehyde resins with co‐catalysis

“…The peaks at 2920–2870 cm −1 were associated with the CH stretching vibration of methylene groups, and bands at 1669 cm −1 were assigned to the unconjugated carbonyl groups . The presence of aromatic rings in all the resin samples could be observed at 1606, 1457, and 1446 cm −1 . The absorption band at 1244 cm −1 was assigned to the CO stretching vibration of the phenolic hydroxyl groups.…”

Valorization of Technical Lignin for the Production of Desirable Resins with High Substitution Rate and Controllable Viscosity

“…The chemical structures of the LRs correlate with the curing temperature. The main reactive sites for the methylolation reaction were the para and ortho C atoms . The peak intensities of the unsubstituted ortho ( δ =114.6–114.7 ppm) and para ( δ =118.7–118.8) C atoms of LR 2 are markedly lower than those of LR 1 (Figure ).…”

Silane‐functionalized graphene oxide/epoxy resin nanocomposites: Dielectric and thermal studies

“…However, the same trend can be observed for modified CE with different GO hybrids and CE modified with GONSi exhibited even higher thermal stability with the degradation step started at 321 °C. Moreover, graphene is known for its high heat capacity and thermal conductivity; therefore, it absorbs heat energy and leads to decomposition of CE at a higher temperature. The modified resins revealed also higher final decomposition temperature compared to pure CE sample.…”