MIICS2008. The degradation of manuscripts and old books, sterilization, consolidation and preservation of paper by plasma process

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1 MIICS2008 The degradation of manuscripts and old books, sterilization, consolidation and preservation of paper by plasma process Raffaele Scopa Italian Vacuum Association

2 INTRODUCTION Causes of deterioration may be internal (endogenous) or external (exogenous). In the first case, if the component elements of a paper are relatively pure, it base good durability and quite long life expectancy. This is a case of most of the papers made up until 19 century. Unfortunately, the appearance of wood pulp in the 19 century led to a reduction of quality. Chemicals deterioration of industrially-produced paper results largely from the production process used. There are two main types of deterioration: hydrolysis and oxidation. External factors may also be added to the internal causes of deterioration such as air pollution, unfavorable climate, lighting conditions and biological agents. The microbial degradation of documents is one of the must serious and unappreciated sources of damage to library and archived materials. For this reason, it is desirable to focus research activities on conservation and protection techniques to develop appropriate treatments against the growth of microorganisms. A new technology in the field of conservation could be plasma treatment, which is a wellestablished technique in a number of other process, such a plasma cleaning, etching and coating. With regard to paper, the main advantages of plasma treatment are the dry nature of the process and the possibility of combining different effects, such as the biological agent eradication and the strendghtening of deteriorated materials through the deposition of superficial layers.

3 Reduction of microbial contamination brevetto Trattamento al plasma per il restauro e la conservazione di libri e documenti antichi N Mi2004A del 21/01/2004 Paper samples Microbial contamination 19 th century paper Aspergillus niger whatman paper circles Penicillium funiculosum Plasma parameters mixture power treatment time pressure Ar/H2 or O2/H W s 0.4 mbar The microbial reduction was measured before and after the plasma treatment using the standard plate count method.

4 % reduction O2/H2 Ar/H2 After plasma treatment After plasma treatment Treatment example : Power(W) Ar/H2, 200 W, 300 s, 0.4 mbar Colonization untreated paper (control) ~ 105 cfu/cm2 treated paper ~ 10 cfu/cm2 Before plasma treatment

5 Effect on the spores of the plasma sterilization After plasma treatment Only vacuum treatment

6 Plasma sterilization: Mechanism Charged particles Radicals UV-Radiation Wall Membrane DNA Proteins Chemical etching O H 2 O, CO 2, CO + O 2 Physical etching UV photodesorption H 2, CHx, CO UV inactivation of DNA

7 Results These results show that the plasma is able to destroy the microorganism. The following processes are involved in plasma sterilization: Direct destruction of the genetic material of microorganism by UV radiation Erosion of microorganism, atom by atom, by intrinsic photodesorption. UV photons break the chemical bonds in the microorganism material, leading to the formation of volatile compounds (small molecules, e.g. CO and CH x ) from atoms intrinsic to the microorganism. Erosion of microorganism (macromolecules formed mainly made up of carbon, hydrogen, oxygen and nitrogen), atom by atom by etching

8 Surface modification of the ancient paper after plasma treatments XPS analysis on the ancient paper surface has detected the presence of Sulphur and Calcium species. Inorganic Silicon is also present and Carbon presence evidenced the contamination of carbonaceous materials. A detailed analysis of the chemistry that takes place during theprocess is complicated by the fact that some contamination is present on the surface of the paper. Consequently, the plasma can lead to the chemical reactions with both cellulose chains and the contaminants. The plasma treatments with O 2 /H 2 caused a variation of the superficial chemical composition. From the sample untreated to the plasma treated sample, the C-H composition decreases while C=O and C-O weakly increase. This suggests that active species in O 2 H 2 plasma at the beginning react with the superficial contamination of the sample and later attack the cellulose, modifying the chains ends. After the Ar/H 2 treatment the C-H concentration decreases with respect to other components, as a function of the discharge power. This variation probably is due to the removal of the aliphatic contamination carbonaceous by sputtering effect. Argon in plasma phase is not capable of reacting with atoms of the cellulose. Its only action is to remove material of the surface of the paper by physical impact.

9 Is there a surface modification of the paper? % composition C-H C-O C=O O-C=O 2 untreated 30W 40W Relative contributions to the C(1s) XPS peak (in %) for untreated paper and plasma treated paper 84 with Ar/H 2 gas mixture at different power for 2 minutes of treatment time. 98, %T paper untreated , ,00 O-H C-H C=O 1723,33 C-O of carbonyl groups plasma treatment with O2/H2 Mixture plasma treatment with Ar/H2 Mixture 1426, , , C-O of alcohol groups 1029,20 73,4 4000, ,0 cm-1 ATR spectra for untreated paper and plasma treated paper with Ar/H 2 gas mixture at different power for 2 minutes of treatment time.

10 Plasma deposition of silicon-like Electric power Si C Plasma H CO O 2 +Organosilicon H 2 O CH OH SiO CO SiO x C y SiC x H y C x H y CO 2

11 Enhancement of mechanical properties of the ancient paper after plasma treatments After plasma treatments the mechanical properties of an ancient and Whatman paper were determined by tensile strength measurements. Whatman paper was utilized as a reference substrate. The comparison between the ancient and Whatman papers clearly indicate that the tensile strength increases after plasma treatment for both the samples

12 Paper consolidation 20 ancient paper whatman paper 18 Tensile strength (Mpa) untreated Ar/H2 mixture O2/H2 mixture With SiOx film

13 Paper consolidation 20 ancient paper whatman paper 18 Tensile strength (Mpa) untreated Ar/H2 mixture O2/H2 mixture With SiOx film the tensile strength of the paper depends on the molecular properties of the cellulose, it increases when the degree of polymerisation increases too, evidently the plasma treatment induces an increase of the degree of polymerisation due to formation of inter and intra-molecular ether bonds

14 Paper consolidation and conservation 20 ancient paper whatman paper 18 Tensile strength (Mpa) untreated Ar/H2 mixture O2/H2 mixture With SiOx film plasma SiOx thin films deposition

15 1x1 µm2 before deposition 1x1 µm2 after deposition

16 Contact angle measurements Three interfacial free energies have to be assumed, if a liquid is in contact with a solid surface ad indicated in figure : σ l the surface tension of the liquid σ sl the interfacial free energy between the liquid and the solid σ s the surface free energy of the solid. The angle, which is enclosed by the baseline and a tangent to the drop contour at the three phase point, is called the contact or wetting angle. + Θ = 0 Perfect Wettability Θ <90 High Wettability Θ > 90 Low wettability

17 CONCLUSIONS Reduction of microbial contamination of the paper could be achioeved by using plasma treatments. An increase in paper stability is possible by using O 2 /H 2 mixture. Surface analysis chemistry has shown that even a brief exposure to the glow discharge results in a weak chemical change in a surface composition. These results permit to asses that plasma treatment could be a new and innovative technique for paper restoration and consolidation.