Modified Lignin Nanoparticles as Potential Conservation Materials for Waterlogged Archaeological Wood

Lignin is the most abundant component in archaeological waterlogged wood, making it a potential consolidant with high compatibility for historical wood conservation. However, its consolidation effect is limited by its low penetration into the wood. In this study, modified lignin nanoparticles (LNPs) were proposed for the first time as conservation materials for waterlogged archaeological wood. Two modified LNPs were prepared with low molecular weight, small size, and high solubility in ethylene glycol (EG) for consolidating waterlogged wood samples. These nanoparticles, hydrophilic aminated LNPs (ALNPs) and hydrophobic esterified LNPs (MALNPs), greatly improved the consolidation effect of waterlogged wood samples compared to LNPs. This was demonstrated by measuring their physical properties, dimensional stability, and mechanical properties. The surface color change was almost within the acceptable range for the human eye. We also discussed two different reinforcement mechanisms of ALNPs and MALNPs. ALNPs can form hydrogen bonds with hemicellulose/cellulose in the wood to strengthen the fragile wood cell wall, while MALNPs can fill the wood cell lumen to support the cell wall and prevent deformation during drying. Our work provides an approach of using biomaterials as consolidants for archaeological waterlogged wood and expands the use of lignin in this field.