Paper has played a vital role in the cultural and economic progress of mankind. Handwritten and meticulously illustrated books and early printed works are like precious treasures. But deterioration is threatening much of this cultural heritage in libraries and archives. The bearers of human knowledge, in some cases centuries old, are damaged by acidification, oxidation and microorganisms. For this reason a special group of research workers has formed at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB: Microbiologists and plasma chemists are collaborating with book restorers on the development of processes to arrest the deterioration of precious books and to remedy existing damage.

The team intends in particular to develop plasma technology for this purpose. In industry this technology is applied as a standard process e.g. for cleaning surfaces, preparing materials for painting or applying protective coatings. The researchers are now investigating to what extent plasma treatment can restore precious books. “Paper is a very sensitive material and deteriorates very easily,” explains Dr. Iris Trick of the IGB. “We therefore treat it in an after-glow operation, i.e. the page of a book is not exposed directly to the plasma, we guide the extremely reactive gas molecules and atoms on the paper surface in a separate chamber.” Tests on various papers and with different types of plasma show that after treatment pages which were stuck together or discolored are restored to legibility, and dark stains largely disappear. The work is mainly concentrated on increasing the strength of the paper and removing harmful microorganisms. The scientists have proved that plasma is effective against resistant and widespread types of bacteria and mould. “It would be possible using plasma technology to apply thin protective coatings to single brittle pages enabling the book to be leafed through again. The research work in this direction is still in its infancy however,” reports IGB scientist Dr. Uwe Vohrer.

In the food processing and pharmaceutical industrie plasma techno-logy offers an alternative to the sterilisation processes used hitherto. Depending on the item being sterilised, the process parameters have to be adapted. The great advantage is that the surface can at the same time be given a functional coating, such as a barrier layer.