In today’s environment preserving documents for business and historical purposes is not only a need, it is often the law. Retention of records is required in many cases for decades. Additionally, some documents may have historical value to an organization and they want to preserve these permanently. Often, these materials are highly secure and confidential. Documents and books that have become wet, moldy or have debris such as soot can be recovered while in a secure environment.
What is Freeze drying via sublimation?
Freeze drying via sublimation is the process that allows us to dry documents so they are never wet again. Simple, isn’t it? When paper gets wet from something as devastating as a hurricane or as simple as a pipe breaking, it needs to be stabilized, dried and cleaned. Let’s talk about stabilizing the documents. When a document gets, wet we need to stop the deterioration of the paper. We do this by freezing the box, or boxes, of documents. Documents are inventoried, palletized and placed into a refrigerator truck.
The truck will be able to get the boxes to a temperature that will freeze the boxes and will stop the deterioration of the paper. We then ship the boxes to our facility for freeze-drying. When the boxes arrive at our facility, the next step is to verify the inventory and place the frozen boxes into the freeze drying chamber.
When the documents are placed into the chamber, probes are inserted into the frozen boxes to track the progress of documents. At this point, the chamber is closed causing a vacuum to be created and the process of sublimation begins. The moisture is pulled out of the documents as a gas so the documents are not damaged any further. This is the part I’ve been telling you about! The documents are NEVER wet again. The moisture actually left the document as a gas. With freeze-drying, your documents are returned in the same condition as we received them. Once removed from the freeze drying chamber, the documents are then cleaned and returned, back to business as usual! This process results in a document that is in good condition and safe to handle.
Why Should You Choose Freeze Drying?
Documents exposed to water will continue to experience further damage as the water equalizes or wicks into the paper. The Library of Congress and the National Archives & Records Administration both recommend vacuum freeze drying by sublimation as the preferred method for removing water from paper.
Modern large-scale freeze-drying chambers actually cost less than desiccant or air drying papers/books. During the freeze-drying process, the quality of paper is maintained. By comparison, papers dried by air or dehumidification will swell up to 25%, wrinkle (cockle) and lose tensile strength.
Water exists in three phases: liquid, solid and gas. It is the liquid phase of water that is most damaging to paper and any media printed on it. The cross-scission and cross-fusion of paper are gradually destroyed by water, and the tiny fibers of the paper separate, and in turn, these fibers no longer serve as an adhesive. Most writing pen inks are water soluble and begin to run or dissolve. And finally, mold now has an optimal environment for growth. Because of this, simply air drying water soaked paper is not practical.
By allowing paper and books to start drying instead of freezing, additional damage is occurring to the documents. The escaping water molecules separate and break the paper fibers while rendering the lignin useless. Paper generally swells about 25% greater in volume and 30% or greater in reduced strength, causing it to tear easily.
When wet books start to air dry, the same issues mentioned above occur, but to a greater degree. The spines of the books are generally stitched. This stitching will minimize the dimensional change of the spine but all the energy of moisture evaporation into the air will cause massive swelling on the fore-edge of the book. For this reason, it is important to remove all books prior to any attempts in dehumidifying the area. If necessary, a plastic vapor barrier can be constructed to section off the area. In order to minimize damage, freezing books in a timely manner are very important to remember.
Drying frozen, water-soaked paper via sublimation (or freeze drying) is slower than evaporation directly from the liquid phase. However, sublimation causes the least amount of damage to the paper and content. The drying rate using sublimation can be controlled by manipulating process parameters, minimally impacting the time difference. Due to the damage produced by air drying and desiccant drying wet paper and books, it is clear that drying via sublimation is the best solution.
How Do You Know If Documents are Wet?
If paper items, such as books and manuscripts, have been exposed to excessive humidity, are near a water intrusion, under a sprinkler discharge or partially submerged in water, they should be inspected for moisture content with a moisture meter. The moisture meter will determine the amount of moisture present in the material. Simply visually inspecting the items or touching them will not tell the whole story. Moisture can be deceiving, you cannot always feel or see it. An archivist’s electronic moisture measurement meter will give you the full picture.
The meter will read from 4.3% to 18% (saturation) moisture range on paper. It is important to check the owner’s manual for instructions on how to calibrate the device prior to use and calibrate before each use.
Moisture Content is considered within the acceptable range when the measurement is < 7% MC (Moisture Content). Many offices may have documents that are in the 5% to 7% MC range. Moisture Content is considered higher than desired when the range is >7% MC but < 11% MC. Document moisture content is then considered “humid-damp”.
It is recommended that action reduces the moisture content to less than 7% be taken within 48-72 hours. During this time frame, it is acceptable to try moisture removal on site with blocking or air movement when dealing with small batches of documents. If you are unable to remove moisture within 72 hours, schedule documents for freeze drying.
Moisture Content is considered “unacceptable” when the moisture content is greater than 11% MC. At this point, the documents are considered “wet” and should be freeze dried via sublimation immediately. Your first step is to freeze the documents to mitigate any further damage until the documents can be shipped to the freeze drying chambers.
Benefits of Freezing and Freeze Drying via Sublimation
Freezing Documents Halts Mold: Mold requires three things to thrive: moisture, food, and temperature. By freezing documents, the temperature required for mold to thrive is lowered to a point where it cannot survive. While mold spores are not destroyed by freezing, they remain dormant until a more favorable environment is available. Freezing will stop the infection of mold thus harmful damage to the documents ceases.
Freezing Stabilizes Soluble Inks and Dyes: Freezing has the additional advantage of stabilizing inks, dyes, dyestuffs and colorants used for manuscripts, maps, sketches and drawings that are soluble in water. Later, when freeze-drying takes place, migration or feathering of inks or dyes can be restrained since the liquid stage is by-passed.
Freezing Prevents Adhesion of Pages: Books and periodicals are generally printed on stock that uses a coating pigment with a binder of casein and starch, both of which are highly water-soluble. If coated stock is permitted to dry, it will turn the book into a clay-like brick at which point restoration is impossible. The only practical method to salvage these items, especially when large quantities are involved, is freezing while wet then freeze drying.
Freezing Gives You Time To Assess: By freezing water-damaged documents, they are stabilized as long as they remain frozen. Disasters can be stressful and confusing. When stabilizing documents through freezing, there is time to assess the damage. Decision makers can determine which documents can be discarded, replaced or copied. It allows time to determine what repairs or restoration is required and how much time it will take to recover damaged storage areas.
Freeze Drying Uses Fewer Chemicals & Produces Fewer Odors: The process uses fewer chemicals, thus producing limited odors. The vacuum chambers cause VOC’s (Volatile Organic Compounds) to “flash off”, boil or vaporize because the pressure in the chamber is lower than the boiling point of the VOC’s. Additionally, many chemical contaminants escape with the gasses released during the process. As a result, the documents will smell better and have very few (if any) remaining contaminants. If any contaminants do remain, they can be removed during the cleaning process.
Following a plane crash in the Hudson River, many paper documents were submerged in water overtaken by pungent jet fuel. Our freeze drying chambers were able to remove most of the odor from the jet fuel.
Freeze Drying is Safe for Documents and Books: “In studies conducted by the Research and Testing Office of the Library of Congress, there was NO evidence found that freeze-drying causes damage of cellulosic and proteinaceous materials (5).” Source: Vacuum freeze-drying, a method used to salvage water-damaged archival and library materials. A UNESCO (United Nations Educational, Scientific, and Cultural Organization); Study 1987.
Freeze Drying Produces a Cleaner Document: The gasses released during the sublimation process deposit loose matter to the surface of the papers. This facilitates a better cleaning to the papers by removing silt, loose mold spores, and other contaminants.
Freeze Drying Is a Safe and Secure Way To Dry Documents: According to the National Archives (NARA), “Records can dry in their original containers reducing the risk for disruption of original order.” This allows us to have a secure process, keeping clients documents segregated from other client’s documents.
According to the National Archives (NARA), “Records must be removed from their containers, spread on shelves to dry in warm dehumidified air, and periodically rotated to expose wet paper surfaces.” As you can imagine, a great deal of space must be used to spread the paper out individually. The risk of this process is that documents can be knocked off of shelves and intermixed with other client’s documents. Because paper is spread throughout a facility, there is a greater risk of retrieving the wrong file or intermixing files.