Following wetting, molding, and subsequent vacuum freeze drying, books were sterilized by licensed practitioners using either ethylene oxide (EtO) or gamma radiation. It should be noted that both sterilization methods required books to be free of liquid water before treatment as any
moisture not chemically bound to the cellulose will otherwise react with the sterilizing agent.
In the Czech National Archives in the Prague (Czech Republic), vacuum freeze dried moldy books were placed in a 6.4 m3 vacuum sterilization chamber (Matachana, type 3.100 LGE-2). The chamber was preheated to 30 C/86°F, air was evacuated to 0.069 bar and a calculated amount of water injected. The water was evaporated at 0.09 bar and the air evacuated a second time to reach 0.054 bar. At 1,125 torr (150 kilopascals) the temperature was held at 30 C/86°F and 80% relative humidity. Books were exposed to a 10% ethylene oxide/90% carbon dioxide mixture (trade name, Etoxen) for 6 hours at 1.5-2.5 bar. The chamber was then aerated, exhausted, and refilled thirty times with the EtO gas incinerated in a plasma flame. At the end of the process books were transferred to a ventilation tunnel where they offgassed for six days.
At Sterigenics, a licensed, commercial gamma irradiation facility in Fort Worth, Texas (USA), vacuum freeze dried moldy books were passed through an irradiation chamber were they received a calculated dosage in the range 12.6-18.8 kilogray (kG). No pretreatment dehydration
or post-treatment equilibration was required.
To evaluate treatment-associated loss of mechanical integrity, 24 leaves were removed at equal intervals from each dried or sterilized book and sent to one of two analytical labs. Each leaf was subjected to four internationally standardized mechanical tests: tensile strength, stretch-to-break,
tearing resistance; and MIT fold endurance.10