An improvement in nonaqueous processes for deacidification and preservation of cellulosic materials is disclosed, comprising reacting the deacidified cellulosic material with alkylene oxide such as ethylene oxide. Particularly effective is contacting cellulosic material, such as books, which are deacidified by a nonaqueous deacidification process, with ethylene oxide for 15 minutes or less at ambient temperature and atmospheric pressure, and equivalent reaction conditions at other pressures and temperatures. -- AATA