The bleaching of paper by reduction with the borane tert-butylamine complex

Acids, strong alkalies and many oxidizing agents cause degradation of cellulose, leading to the loss of paper resistance. The normal deacidification treatments with calcium compounds are able to transform the acid carboxyl groups into stable insoluble salts, but they do not react with the other carbonyl groups. The presence of these functions in the cellulose polymer makes the acid and alkaline hydrolysis easier and it is in part responsible for the yellowing of the paper. Much work has been undertaken to discover a compound with selective reducing power for these groups. The borane tert-butylamine complex gave particularly good results in reducing aldehydes and ketones and it is also able to produce an optical bleaching of paper. The aim of this experiment was to test its application on several kinds of printed paper with different graphic media and colours, as well as to optimise the time of application. The effectiveness of the borane tert-butylamine complex was demonstrated not only on artificially oxidized paper but also on original prints. The visual effect of all the prints was good. Concerning optimisation of the application time, we can conclude that ancient paper needs a long treatment time. We chose a time of 5 hours as a compromise between the needs of the paper and the stability of the inks. This time could be increased in the case of very oxidized paper, taking into account the stability and insolubility of the inks.