Nondestructive moisturization of artificially aged bamboo using glycerol microemulsions

Bamboo and wooden artifacts unearthed in archaeological excavations often shrink, warp or crack due to rapid moisture loss. Conventional moisturizing methods, such as physical wrapping or pure glycerol solutions, are cumbersome, show limited moisture retention, or risk structural damage. Here, a glycerol-based microemulsion is developed for aged bamboo artifacts, composed of Tween 80/Span 80 (4:1), liquid paraffin and a 50% glycerol aqueous solution. Five surfactant-to-oil ratios (9:1–5:5) are evaluated on artificially aged bamboo strips produced by 120 dry-wet cycles. Moisturizing ability increases with oil fraction, and the S7-P3 formulation (7:3) shows the best performance: it reduces hourly moisture loss by ∼ 70%, maintains >70% water after 24 h at 60 °C, and decreases the water contact angle to 23.4°. This behavior results from a synergistic mechanism in which surfactants promote uniform spreading, glycerol slows evaporation via hydrogen bonding, and liquid paraffin acts as a bulking agent to provide structural support. The treatment does not alter cellulose, hemicellulose or lignin, while color change (ΔE* = 4.7), dimensional change (<1%) and bending strength remain within the minimum-intervention range. The proposed microemulsion provides a practical strategy to prevent cracking in bamboo artifacts during excavation.