A method for the aqueous deacidification of oxidized paper

Concentrated aqueous solutions of pH-neutral salts were evaluated for their effectiveness at deacidifying photo-oxidized filter paper. Short immersions in these solutions successfully neutralized acidic paper sheets. However, subsequent rinses to remove excess salt were necessary to prevent yellowing upon thermal aging. Sheets treated with concentrated solutions of calcium chloride showed no significant chemical damage from the treatment and deteriorated more slowly during thermal aging compared with untreated sheets. Sample papers that were given a dilute alkaline rinse after the concentrated salt treatment degraded less upon thermal aging than papers treated with either solution alone. This method of neutral deacidification was also evaluated for use prior to chemical reduction of oxidized paper with sodium borohydride. A treatment procedure involving steps of deacidification, chemical reduction, and alkalization was found to greatly stabilize photo-oxidized papers against thermal aging, as well as to produce a bleaching effect.