Phenol‐enriched hydroxy depolymerized lignin by microwave alkali catalysis to prepare high‐adhesive biomass composites

Abstract

Lignin, a by‐product produced during pulping and papermaking, is a phenol‐rich compound with excellent prospect to be used as a substitute for phenol in phenolic resin adhesive. Phenol‐enriched hydroxy depolymerized lignin by microwave alkali catalysis is an effective method to prepare high‐adhesive biomass composite. This study investigated the microwave digestion of lignin under different conditions of the alkali catalysis (sodium hydroxide) concentration, power, reaction time, and reaction temperature. The results show that on the condition of sodium hydroxide concentration of 0.3 mol/L, temperature of 170 °C, and time of 20 min, the highest phenolic hydroxy content obtained by depolymerization of lignin is 21.68%. SEM shows that the depolymerized lignin has no original basic constituent units and lignin‐based phenolic resin has dense uniform pine needle units. Therefore, it has a high bonding strength of 1.934 MPa. The bonding strength and phenol content obtained by the microwave depolymerization method are much higher than those of other modification methods.

Revealing the Structural Influence on Lignin Phenolation and Its Nanoparticle Fabrication with Tunable Sizes

“…The main reason for the increment of Ph-OH contents after phenolation was that phenols were grafted onto the lignin molecules . Meanwhile, L/P ratios strongly affected lignin degradation in the phenolation process, which was indicated by the weight-average molecular weight ( M w ) in Table . The M w of phenolated KL decreased significantly after phenolation with the decrease of the L/P ratio.…”

“…51 Meanwhile, L/P ratios strongly affected lignin degradation in the phenolation process, which was indicated by the weight-average molecular weight (M w ) in Table 1. 20 The M w of phenolated KL decreased significantly after phenolation with the decrease of the L/P ratio. For instance, when the L/P ratios were 1/1, 1/2, 1/3, and 1/4, the M w values of phenolated KLs were 4103, 2976, 2613, and 2325 g/mol, respectively.…”

“…Lignin modifications, including methylation, demethylation, , hydrolytic depolymerization, , and phenolation, , are extensively applied in lignin research studies. As one of the most efficient ways to improve the reactivity of lignin, phenolation efficiently increases lignin’s phenolic hydroxyl group (Ph-OH) contents and active sites, which facilitates the utilization of technical lignins. , Lignin phenolation under acidic conditions is the most commonly used method. − Under strongly acidic conditions, phenols could be grafted on lignin by the electrophilic substitution between phenol and the α or γ-carbocation at a low pH value after dehydration, and then because of the cleavage of β–O–4, Cα–Cβ, and Cβ–Cγ bonds, new reactive sites are generated by releasing formaldehyde (Figure ).…”

Valorization of sawdust biomass for biopolymer extraction via green method: Comparison with conventional process

“…91,92 Furthermore, the high-intensity bands of C-C-, aromatic rings, in lignin at 1600 and 1506 cm À1 seen in SW T1-H spectra, disappear after bleaching treatment. Small signals of lignin are observed at 1415 93 and 1260 cm À1,75 indicating that they were not completely eliminated during the process. Similar trend of the reduction of signals from hemicellulose and lignin was observed in SW T2-C samples.…”

Lignin and Lignin-Derived Compounds for Wood Applications—A Review

“…An LPF resin with 0–100% phenol substitution with wheat straw lignin depolymerized by alkali-catalyzed microwave digestion was prepared. The bonding strength of a plywood was higher with 40% substitution than for reference PF resin, and it was similar even at 80% substitution [ 84 ].…”