Kraft Lignin Periodate Oxidation for Biobased Wood Panel Resins

Abstract

The development of biobased resins with high-bonding performance has gained considerable attention in the wood industry. In this study, we developed biobased novolacs phenol-formaldehyde (BNPF) resins by partially replacing petroleum-based phenol and formaldehyde with lignin derived from kraft biorefinery and modified kraft biorefinery-derived lignin, respectively. We first performed a mild and efficient chemical modification of the lignin through the periodate oxidation process. Sodium periodate was used to oxidize the hydroxyl functional groups present in the interunit linkages (β-O-4 bond) in the lignin structure and convert lignin partly to quinones. This was assessed by Fourier-transform infrared spectroscopy, elemental analysis, solid-state 1H–13C 2D HETCOR NMR, and aldehyde content analysis. We synthesized a series of BNPF resins by replacing phenol with lignin, then by replacing formaldehyde with oxidized lignin, and finally by replacing both phenol and formaldehyde with lignin and oxidized lignin. The structural characterization results of the NPF resins revealed the formation of methylene linkages in the phenolic rings. Before application as wood adhesives, we studied the curing behavior of the formulated adhesive via differential scanning calorimetry. The adhesion strength of the adhesive was determined using the tensile shear strength analysis. The bonding performance tests indicated that BNPF resin adhesives have high adhesion strengths (>0.7 MPa). The outcome of this research provides a promising perspective to utilize natural polymers such as lignin for the synthesis of biobased wood adhesives.

Soybean Meal–Oxidized Lignin as Bio-Hybridized Wood Panel Adhesives with Increased Water Resistance

“…Figure 2 displays the FTIR spectra of the prepared adhesive. Initially, L presented a characteristic peak such as the one near 3434 cm −1 , which represents the stretching vibration of the -OH group; the peak near 2933 cm −1 reveals the methyl and methylene groups in the C-H bonds; the peak near 1612 cm −1 indicates the corresponding absorption peak of the aromatic rings; and the peak near 1267 cm −1 indicates the stretching vibration of the methoxy groups [42,43].…”

“…peak of the aromatic rings; and the peak near 1267 cm −1 indicates the stretc of the methoxy groups [42,43].…”

“…As the HP dosage continues to increase, L undergoes over-oxidation, which causes the severe degradation of lignin chains, weakening the intermolecular hydrogen bonds. At the same time, lignin undergoes a ring-opening reaction to form muconic functional groups [42]. This over-oxidation reaction is unfavorable for crosslinking and results in a decrease in the bond strength.…”

Lignin Modification for Enhanced Performance of Polymer Composites

“…Since lignin’s structure contains OH (aliphatic and phenolic) units, it is a potential for oxidation processes. The quantity of phenolic groups presents, pH, and oxygen concentration can all affect how quickly an material oxidizes at a particular temperature. − Vanillin are created by the most frequent oxidants, which also preserve the aromatic rings in lignin. Nitrobenzene, several metallic oxides, air, and oxygen are examples of substances whose production is dependent on the oxidant like H 2 O 2 , KMnO 4 , with copper (ΙΙ) and cobalt (ΙΙ) or without catalysts .…”