Freeze-Drying (Vacuum Lyophilisation)
Definition
A drying technique in which water is first frozen and then sublimed under reduced pressure (below 611 Pa), bypassing the liquid phase. Used for sodden bound volumes because it removes moisture without the capillary action and surface tension that cause adhesion, cockling, and dimensional distortion during conventional drying.
- Also called
- Vacuum lyophilisation
- Process
- Freeze water, then sublime it under reduced pressure
- Pressure threshold
- Below 611 Pa (water's triple point)
- Application
- Sodden bound volumes and water-damaged documents
Common questions
Why does freeze-drying avoid the damage conventional air-drying causes to wet books?+
Conventional drying passes water through a liquid phase, and as it evaporates, capillary action and surface tension pull adjacent pages together, causing cockling, blocking, and warping. Freeze-drying sublimes ice directly to vapour, so the liquid phase and its surface-tension forces never occur.
Why must the pressure stay below the triple point of water for this to work?+
Above roughly 611 Pa, ice melts to liquid water before it can vaporise, which reintroduces the very capillary damage the technique is meant to prevent. Vacuum conditions keep the material in the solid-to-vapour sublimation path throughout the drying cycle.
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