Advanced Technology For Deacidification And Conservation Of Paper Relics

Paper relics are important part of cultural heritage. As a medium for written information, paper relics are greatly important for transmitting and preserving knowledge and cultural history, containing considerable precious cultural historical materials and records. However, with aging, more and more precious paper relics have become yellowed and brittle due to the acidification. Deterioration and changes to the chemical, physicomechanical and optical properties of historic paper documents, paintings and calligraphies are responsible for an enormous loss of cultural heritage. Therefore, removal of acidity and protection of fragile paper are the most significant problems to be addressed in paper reinforcement and conservation. Currently several methods for paper deacidification and protection have been presented in paper conservation and restoration. However, these solutions have several unavoidable drawbacks such as complex implementation, unfriendly reagents, instability effects and so on. Thus, an efficient, convenient, harmless and long-term stable method for paper deacidification and protection is in urgent need.In this paper, a cold plasma system has been used with a deacidification reagent consisting of saturated Ca(OH)2solution to impregnate alkaline groups into the paper fibers and to modify the fiber surfaces. Besides, an electrospinning technology has been used for paper conservation with PVDF solution as the spinning feedstock for the membranes for further protection. For a clear statement, the primary achievements of this work are summarized as follows.(1) The cold plasma technology is first used in deacidification for paper relics. Parameters like flow rate of the deacidification reagent, energy density of plasma and treatment times are controlled to ensure the optimal condition for deacidification. Moreover, this technology is applied on different types of paper samples. The results prove that plasma treatment can efficiently decrease the acidity even after artificial aging, and prevent the degradation of the cellulose over long periods of time without damaging the structure of the fibers or changing the appearance of the paper. SEM and EDS show that plasma technology could strengthen the paper since part of shallow surface fibers might be activated and split into tiny fibers to form more hydrogen bonds with neighboring fibers, while the original appearance of paper could be preserved due to the short plasma processing period that avoids the degradation of cellulose.(2) PVDF fiber membranes are prepared directly onto paper surfaces using electrospinning for the conservation of paper relics. Parameters like concentration solvent ratio and spinning time are controlled to ensure the optimal condition for electrospinning protection. The results show that the ultrathin, hydrophobic membranes can effectively protect paper from damage by external water, dust, insects and mould, while allowing necessary gas molecules to pass through nano-pores in PVDF fibers to maintain the initial conservation condition of the paper. In addition, the fiber membrane covering can lead to a10%increase in tensile strength and over50%increase in elongation of the underlying paper, while maintaining stability after artificial hydrothermal and ultraviolet aging, meaning that it shares part of the strain resulting from an external stress, thereby reducing damage to the paper. Furthermore, acrylic pigments are added in the PVDF solution to make the fiber membrane show a similar color as paper relics to reduce the color changes after protection.(3) Both of the plasma deacidification technology and electrospinning coating technology are used on the protection of different kinds of papers in Ming, Qing Dynasty and the republic period and achieve good results. The pH of all the paper increased a lot without influencing their appearance and texture. Paper protected by PVDF membrane could prevent the damage from dust and moisture effectively and the color of the fiber membrane could be well controlled to make paper relics remain the same as they were.