Microgels are soft, adaptive and penetrable objects characterized by a gel-like internal structure swollen by the dispersing solvent.
Their viscoelastic properties, controlled and predictable, and their responsiveness to external stimuli like temperature, pressure, pH and ionic strength make them favorite model systems for fundamental science as well as for a broad range of applications from industrial to artistic fields.
In particular, in recent years they are employed in paper artworks restoration, a delicate procedure that must take into account degradation and deterioration phenomena over time.
Hydrogels, thanks to their retentive properties can ensure a more controlled cleaning with respect to the traditional method, e.g. washing for immersion, since they are able to confine the solvent into gel matrix and release it in a controlled way.
In this project gellan gum microgels, composed of a natural gelling system, will be studied as novel agents for cleaning modern and ancient papers since they could offer several advantages when compared to hydrogels.
The micrometric dimension of microgel particles allows in fact to penetrate more easily the porous structure of paper and to adapt to inhomogeneities removing the impurities of cellulose.
In this context the preparation and the physical- chemical characterization of gellan gum microgels are fundamental for a successful application in cleaning paper.
Hence in this work we will perform an experimental preliminary study on the behaviour of microgel and on the overall effect of the cleaning treatment of paper samples.
To gain this knowledge a variety of experimental techniques will be employed such as Rheology, Dynamical Light Scattering (DLS), scanning electron microscopy (SEM), fluorescence optical microscopy, high performance liquid chromatography (HPLC), Fourier Transform Infrared (FTIR) and optical reflectance spectroscopy.
In the last few years microgels have been widely used not only in computer simulations and theoretical physics [1-5] but also in applications ranging from biomedical and pharmaceutical to technological fields [6-12]. Nevertheless, despite their many possibilities, they are not broadly used in cultural conservation.
Preserving culture and ensuring its transmission and accessibility are duties for our society as well as a great economic resource for the whole country. Degradation processes, caused by environmental and atmospheric conditions, often contribute irremediably to the wrecking of artworks. The best way to avoid losing this cultural heritage is to develop increasingly efficient and less invasive conservation and restoration methods.
The idea of employing microgels in wet paper cleaning has started to be implemented just a year ago within Gelarte, a regional research project in collaboration with ISC (Institute of Complex Systems of CNR). For this purpose gellan gum, a wide spread material already used as hydrogel for paper cleaning [13-14], has been prepared as microgel and applied on ancient and modern paper samples.
Gellan gum microgels were prepared by me and my research team under shear cooling following the procedure described by Caggioni et al. in 2007 [15] and preliminary measurements were performed, leading to very interesting initial results [16].
The employment of particles of micron size could offer many advantages with respect to the macroscopic counterpart of gellan gum hydrogels. The porous structure of the paper contains dirt and dust which could be better reached by micrometric particles in even shorter times. They are also more adaptable to irregular surfaces thanks to their softness that can be opportunely tuned. Indeed, during gellan gum microgels preparation, the addition of a monovalent salt is fundamental and its content allows to regulate rheological properties. Many experimental parameters can be modified during preparation, such as gellan gum weight concentration, molarity and type of salt, stirring speed, pH, cooling rate etc. On the other hand, various paper samples formed by different materials (e.g. rags or treated lignin free wood pulp) and with diverse chronological age could be tested. A deeper understanding of viscoelastic and phase behavior of microgels, would lead to an advancement of knowledge, useful to the application field of paper conservation and restoration.
Furthermore, experimental paper cleaning tests and comparisons both with previous method (e.g. hydrogels) and also between differently prepared microgel samples are fundamental. For these reasons, further research is needed.
The idea to apply microgels in paper cleaning is very recent and never implemented. In the near future the use of microgels could also be extended to other materials with delicate surfaces. This project will investigate the idea that microgels and other soft materials would have a great, still not fully employed potentiality in cultural heritage field of restoration and conservation as suggested in recent years [17].
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