3 DISCUSSION AND CONCLUSIONS

AS EXPECTED, deacidification of the rag and newsprint papers resulted in a significant decrease in their rates of yellowing and embrittlement during accelerated aging, as shown by the data in Table II. Results of this kind have often been reported in the technical literature, and the beneficial effect of reducing the acidity of paper is generally accepted. However, the assumption that the beneficial effect of deacidification is simply a result of a decrease in the rate of acid-catalyzed hydrolysis appears to be an oversimplification. Atmospheric oxidation, as well as the oxygen-independent component of deterioration, was retarded by deacidification, as shown by the data in Table III.

The division of the deterioration process into an atmospheric-oxidation fraction and an oxygen-independent fraction is experimentally convenient but somewhat arbitrary. It is possible, and perhaps probable, that each of these fractions of the deterioration process is a result of more than one chemical sub-process. Although acid-catalyzed hydrolysis may be a sub-process that makes up part of the oxygen-independent fraction of deterioration, it would seem likely that other sub-processes are also involved. The two different values of Yd/Yu obtained for the rag paper by following the change in reflectance and the change in tensile strength, for example, suggest that the oxygen-independent processes leading to yellowing and embrittlement are somewhat different.

In conclusion, the influence of acidity on the thermally induced deterioration of paper appears to be more complex than has previously been assumed, and the way in which deacidification treatments may alter the various deterioration processes is, as yet, not thoroughly understood.

Many questions remain to be answered before the maximum benefit of deacidification is likely to be realized. What are the optimum pH values for regarding the various processes that contribute to deterioration? How does acidity influence the light-induced deterioration of paper? What are the possible roles of the common metal ions associated with the various deacidification techniques? Answers to questions such as these must be sought if optimum conditions for deacidification of the many types of paper found in museums and libraries are to be developed.