Development of conservation methods for the restoration of paper materials

Paper, one of the most common materials of Cultural Heritage, undergoes serious deterioration caused by physical, chemical and biological factors. One of the main causes of deterioration is the acidic and/or oxidative environment. The studies of deterioration and conservation of paper have been increasing and require further development of methods and treatments that can stabilize and strengthen the paper. Various conservation treatments are being applied to model and to historical paper by using different chemicals methods. Their effectiveness for conservation and restoration are under study. Internal and external factors degrade the paper by promoting various reaction pathways. The two most important classes of reactions are acid hydrolysis that shortens the cellulose polymeric chains thus weakening the mechanical properties of the paper, and oxidation with subsequent development of chromophores that cause discoloration of the remaining substratum and other byproducts. The effort of researchers as well as that of restorers has been mainly focused to the problem of paper acidity. For stabilizing and preventing acidic paper degradation, alkaline compounds are used in order to neutralize the acidic agents and to form deposit of alkaline reserve. Nanolime dispersions for the deacidification of ancient paper constitute a valid alternative to the lime traditional ones. Its efficacy depends on particles size, polydispersity and agglomeration that can be controlled depending on the preparation method. Different researches showed that nanolime particles dispersed in aqueous and alcoholic media can be applicable to paper conservation giving rise to good results. Up to now the problem of oxidation is neglected. Only a limited number of reducing agent can be used on degraded paper without damaging the fibers structure and the inks. Several researchers from different areas showed the efficiency of tert-butyl amine borane complex (TBAB) as a reducing agent for paper conservation. TBAB has been experimented by researchers from “Istituto Centrale per la Patologia del Libro” (ICPL) of Rome and its use is accepted by restaurateurs as reducing agent for the carbonyl groups. During the PhD research activity, with the aim to study conservative problems of paper, a new method for nanolime preparation by insolubilisation-precipitation has been devised. Nanoparticles dispersed in a water/2-propanol mixture were obtained without any manipulation of the dispersion. The stability of the dispersion together with particle size and morphology were found to be dependent on water to 2-propanol molar ratio and on the synthesis temperature. One of the prepared dispersion was applied on two manuscripts to assess its efficiency. Further, an innovative treatment based on nanolime and TBAB for the simultaneous deacidification and reduction of ancient paper was set and applied on model and ancient papers. Physical chemical characterization showed that the samples subjected to the proposed treatment improve their mechanical and optical properties as a consequence of their state of oxidation, acidity and degree of polymerization. The thesis is divided into two parts. In the first part, an overview of the causes and the mechanisms of paper degradation and of the characterization methodologies is presented. The second part is structured in three chapters: in the first the deacidification of paper is treated. The new synthesis methodology of calcium hydroxide nanoparticles is presented and the evaluation of its efficiency is discussed. In the second chapter the innovative treatment for the simultaneous deacidification and reduction is presented. Its efficacy on specimens of cellulose paper, unwritten and written with iron gall ink, and of lignin paper is discussed. In the third chapter the above systems are applied on three case studies. The appendix reports the characterization methods utilized during the research activity