Drying frozen books

Removing Water from Frozen Books by Solvent Extraction. Solvent Extraction/Air Dry. Frozen books are submerged in a precooled anhydrous solvent in a sealed container and stored in a freezer. As the ice dissolves the water/solvent mixture is replaced periodically until all water is removed. Books saturated with solvent are then interleaved with absorbent paper and air dried (5). 

Subsequent to freeze stabilization, wet books can be thawed and air dried with or without interleaving or they can be vacuum dried in heated chambers (5). The moisture in frozen books can be sublimed by freeze drying (10) or removed by a vacuum/thaw/outgassing process (8), with microwave energy (6, 14), with dielectric energy (6), or by solvent extraction with or without vacuum assistance (5). 

Assess whether it is possible to devise mechanical methods (pressing) to return distorted frozen books to their original condition during mass drying operations. 

Vacuum Dry (1A, IB). The frozen books were placed horizontally on the floor of the chamber. The heated walls melted the ice. A vacuum pump was applied to evaporate the water from the books. Pumping was continued until the books returned to their original weight. The process produced for drying IB was exactly the same as 1A however, the samples were dried in separate independent experiments. The book dried in the 1A experiment was frozen, while the book dried in the IB experiment was placed in the drying oven immediately after the standard drainage period. 

Vacuum Dry—Air Cycle. The frozen books were set on their bottom edge in a chamber the air in the chamber was removed. Dry heated air (0% relative humidity) was allowed to enter and to circulate around the books until atmospheric pressure was attained. When the moisture content of this circulated air became high, it was removed by evacuation. This cycle was repeated until the books were dry. A Ts and A TL designate smallest and largest acceptable temperature differences between the heated input air and that in the ambient room. 

Freeze-Thaw, Vacuum Drying (1A, IB). The frozen books were laid with the spine vertical on metal shelves inside a large chamber. A controlled amount of heat was applied to the shelves to thaw the ice and to allow the water to evaporate. A vacuum was established to remove the water from the books. Progress in removing water from the books was checked by noting the return of the book s weight to its original value. 

Freeze-Thaw, Vacuum Drying (2). The frozen books were arranged separately in a horizontal position on the shelves of a small freezer dryer. The temperature of the shelf was set above freezing and held constant to supply energy for thawing the ice and evaporating the water. A vacuum to remove the water vapor was applied until the book became dry. 

Drained-Air Dried (1A, IB). Individual frozen books were laid on their side, not stacked, while room temperature air was gently circulated around them. Gradually the ice thawed, and the water drained from the books and evaporated. By weighing the books periodically, one could determine when all of the flood water was removed. Both samples A and B were treated by the same technique however, it was used at two different times. 

These preliminary tests indicated an erratic response by the frozen book to the radiation. Equivalent drying did not occur with similar damaged materials. Whether the irregularities were caused by the material or the equipments performance was not evident. After the initial experiments with both dielectric and microwave heaters, the dielectric apparatus was chosen for additional experiments. This decision was based primarily upon this equipment s having the higher power capability. 

A replica of the previous flooded, drained, and frozen uncoated-paper research book was dried by again applying the sandwich technique in another 27-MHz heater. The frozen weight of the book was 449.0 g the dry weight was 290.0 g. Only 14 30-sec bursts, contrasted to the earlier 27-MHz heaters 20 bursts, were required to thaw and to dry this book. The appearance of the dried cover and text was equivalent to that observed previously. The sandwich technique was applied successfully. 

Air Drying Books. Frozen (or unfrozen but wet) books are (A) placed flat on open shelves as room air temperature thaws the ice, the surplus water drains from the book and evaporates (5). (B) Frozen (or unfrozen but wet) books are stood on end on a table in a current of room temperature air. As frozen (or wet) pages open naturally, they are interleaved with absorbent paper (changed frequently) until books are dry (5). 

Vacuum Drying Books. (A) Frozen (or wet) books are placed in a chamber and heated by warm air. Vacuum is applied to remove water vapor as the ice thaws (5, 7). This is sometimes called the purged air system. (B) Frozen (or wet) books are placed in an unheated chamber. Moist air is evacuated and replaced with dry heated air (0% r.h.). When the replacement air becomes saturated with moisture, it is evacuated and the process repeated until the books are dry (4, 5). (C) Thawing books are put in a chamber. Vacuum is applied and then controlled at a pressure of about 5 torr. Heat is then applied to books through shelves to replace latent heat of vaporization. As moisture is released from books in vapor form (outgassing), it is collected by pumps and reverted to ice on cooled condensers in the chamber. After most of the water leaves the books, the book temperature is increased gradually from 32 °F to 80°-85°F the chamber is opened after 48 hr, the books are removed from the shelves, and the condensers are defrosted (4,5,10). 

M) Better results can be obtained when drying with interleaving wet books if they are frozen first (4). This does not apply to vacuum drying. 

Determine whether it is possible before mass drying to wash mud-damaged frozen or wet books. 

Freeze-thaw vacuum, inter leave-air, and solvent extraction processes offer the greatest potential in drying these types of coated- and uncoated-paper books after they have been wetted and frozen. The drained-air, vacuum-air cycle, vacuum, microwave, and dielectric drying processes work well on uncoated paper, but they fail to dry books containing this type of coated paper. Small and large units for freeze-thaw, vacuum drying have been used successfully to remove water from these frozen coated and uncoated books. 

The successful application of either microwave or dielectric energy for drying requires that water, as it is evaporated, be removed from the paper and book. Air with low relative humidity is forced through the chamber to facilitate water vapor removal from the object. Since interaction of the water molecules at different locations in the chamber may not be uniform, each frozen flood-damaged item was inverted and partially rotated between each burst of energy. Radiation leakage from both types of equipment is possible therefore, special precautions for com-... 

Exploratory experiments in thawing and drying randomly selected materials from the museums collection were conducted. Frozen flood-damaged books and file materials that the librarians knew could be discarded or replaced were chosen for the initial experiments. The dielectric grid current was kept constant as the plate current or electrode separation space was varied according to the size of the frozen library materials and an estimate of the water they contained. 

Some of the problems that arose while operating the dielectric and microwave equipment are listed in Table II. Books with leather covers, bindings applied with some synthetic adhesives, or excessive amounts of frozen mud on the spine or back edge could not be dried by either the... 

The text of the frozen coated-paper book was put in the oven and dried. After each burst, the text was turned and rotated. Its inside temperature and incremental water loss were noted. A total of 48 bursts was applied to this frozen 682-g text to remove water until its dry weight of 321.0 g was reached. An inspection showed that all the coated-paper pages in the text were stuck, a condition similar to that which resulted when the 27-MHz heater was used to dry the same type of book (1). 

The text of the frozen uncoated-paper research book was dried in the next experimental run with this oven. Eight 45-sec bursts of energy were required to remove the water from this lightly wetted 244.5-g text. The amount of water absorbed by this text during the simulated flood was small since it was in the tightly packed position (1). Its dry weight... 

Special Research Books. The sandwich technique, placing the wetted book between two inert plastic trays, was used to dry the flooded, drained, and frozen coated- and uncoated-paper research books (1) in an improved 27-MHz heater. The covers of these books were not removed in applying this drying procedure. 

One frozen uncoated-paper research book weighing 480.5 g was dried by applying 20 30-sec bursts. The final weight of the dried book was 287.5 g. The sandwich technique used for this book, cover intact, gave excellent results. 

The critical need for equipment which would quickly thaw frozen materials was satisfied by use of these dielectric heaters. The librarians and conservator could identify the extent of damage to each item and effectively plan the restoration required. The economical application of dielectric and microwave drying to coated-paper books needs a major breakthrough to bring about success. 

In the field of frozen food, the book by Tressler and Evers, The Freezing Preservation of Foods, and for dehydrated foods, Von Loesecke s Drying and Dehydration of Foods are valuable references. 

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