The Treatment Process

The millions of books produced since the beginning of the 19th century are not expected to last 50 years unless they are treated and carefully looked after. Over the years a large number of deacidification techniques and processes have been tried and developed to overcome the problems of ‘acidic paper’. The deacidification processes have been the most beneficial as they neutralize the acids that are harmful to the cellulose, leaving an alkaline reserve to buffer against future acid attack. The following deacidification treatments are some of the methods used to treat books affected by acid hydrolysis:

DEZ mass treatment - involves placing the books in trays inside a vacuum chamber. After removal of air the books are dried (at 20 torr) to remove their moisture content from ambient. Diethyl zinc (DEZ) gas is then pumped into the vacuum chamber at pressure (20 torr) and after 12 hours of exposure the unreacted DEZ is removed and the chamber is flushed with nitrogen (to ensure complete hydrolysis and rehydration of the paper). The method forms a uniform distribution of zinc oxide, which buffers and therfore protects the paper from future attack. The following reactions are involved in the removal of the acid:

Equation (1) neutralizes the paper, and then the extra moisture reacts with the additional DEZ to form zinc oxide (equation 2) in the fibers, which provides the alkaline reserve.

Nanotechnologies - nanotechnology can be used to disperse nano- and micron-sized calcium hydroxide particles onto the paper cellulose fibers. The calcium hydroxide deacidifies the fibers and reacts with carbon dioxide (in the air) to form a calcium carbonate reservoir on the paper.
Another very simple method involves placing the acidic sheets of paper in close contact with an alkaline sheet of paper containing calcium carbonate. With time, ions migrate between the sheets resulting in the neutralization of the hydrogen ions by ions from the calcium carbonate sheet. This method requires the humidity to be maintained at a relatively high value.

All methods have their advantages and disadvantages and there are many other possible methods, which are being used/tested, of which some claim to deacidify and strengthen the paper at the same time.

Although the deacidification treatments allow libraries to maintain books and manuscripts for several centuries instead of only a few decades, preventative measures against the external factors that accelerate the aging of paper also have to be made to ensure that the life expectancy of the books is not minimized. Millions of books have been saved by various deacidification processes but it is the production of exclusively alkaline sized paper that will inhibit the degradation of future books and manuscripts.