Mechanism of Ink and Pigment Detachment from Palm Leaf Manuscripts Driven by Hygroexpansion

Abstract

Palm-leaf manuscripts use palm leaves as their medium. The inherent poor dimensional stability of this biological material is the main reason for ink and pigment detachment. As a valuable cultural heritage, the detachment of ink or pigment on the surface of palm leaf manuscripts under humid-dry cycling poses a critical challenge in the field of conservation. This study simulated traditional palm leaf manuscript preparation and employed accelerated humid-dry cycling to elucidate ink/pigment detachment mechanisms. The substrate—composed of cellulose, lignin, hemicellulose, waxes, and pectin—exhibits anisotropic deformation during cycling: thickness/tangential expansion significantly exceeds longitudinal direction. Chromatic analysis showed minor ΔE* increases in substrate, ink, and pigment, confirming stable chemistry. Color changes primarily resulted from interfacial microcracks and light scattering due to physical deformation. Detachment area escalated with cycles, driven by substrate-ink/pigment expansion mismatch. This induces interfacial tensile-compressive stress cycling, causing mechanical fatigue, adhesion loss, and eventual powdering/flaking. Key conservation strategies include stabilizing environmental humidity and developing flexible protective coatings to buffer interfacial stress. This provides theoretical foundations for scientific preservation of palm leaf manuscripts and conservation material design.