Modification with carboxymethylation-activated alkali lignin/glutaraldehyde hybrid modifier to improve physical and mechanical properties of fast-growing wood

A novel, environmentally friendly, biomass-based modification technique utilizing carboxymethylation-activated alkali lignin (CAAL) and glutaraldehyde (GA) is proposed to enhance the physical and mechanical properties of poplar and fir wood. Water-soluble CAAL was prepared by modifying alkali lignin (AL) with sodium chloroacetate following low-temperature activation under a NaOH/urea system. AL is a biomass-based material from industrial by-products. As such, it does not rely on fossil resources nor emit volatile compounds that might limit its range of application. The successful preparation of CAAL was demonstrated by Fourier transform infrared spectroscopy (FTIR), H-1 nuclear magnetic resonance spectroscopy (NMR), and C-13 NMR, and the changes in structure were analyzed by 2D-heteronuclear singular quantum correlation (2D-HSQC), P-31 NMR, and gel permeation chromatography (GPC). The following characteristics of the modified wood samples were investigated in detail: weight percent gain (WPG), bulking, anti-swelling efficiency (ASE), water absorption rate (WAR), leachability of the modifier, microstructure, and mechanical properties. Water immersion results demonstrated that the CAAL/GA hybrid modifier enhanced ASE to 41.3% and 31.5% for fir and poplar, respectively, at a concentration of 15 wt.%. Furthermore, the WAR of fir was reduced by nearly three times to 30.7%, compared to that of a control sample treated solely with GA. GA-treated samples showed high brittleness, whereas both poplar and fir showed enhanced modulus of rupture and elasticity following treatment with the CAAL/GA hybrid modifier.

Automated summary

This study proposes a novel, environmentally friendly biomass-based modification technique using carboxymethylation-activated alkali lignin (CAAL) and glutaraldehyde (GA) to enhance the physical and mechanical properties of poplar and fir wood. The water-soluble CAAL was prepared through modification of alkali lignin with sodium chloroacetate. The successful preparation of CAAL was demonstrated by various techniques, and the structural changes were analyzed. The modified wood samples were investigated for various characteristics, and it was found that the CAAL/GA hybrid modifier significantly enhanced the properties of the wood.