Gellan Gum Microgels as Effective Agents for a Rapid Cleaning of Paper

Abstract

Microgel particles have emerged in the past few years as a favorite model system for fundamental science and for innovative applications ranging from the industrial to biomedical fields. Despite their potentialities, no works so far have focused on the application of microgels for cultural heritage preservation. Here we show their first use for this purpose, focusing on wet paper cleaning. Exploiting their retentive properties, microgels are able to clean paper, ensuring more controlled water release from the gel matrix, in analogy to their macroscopic counterpart, i.e., hydrogels. However, differently from these, the reduced size of microgels makes them suitable to efficiently penetrate in the porous structure of the paper and to easily adapt to the irregular surfaces of the artifacts. To test their cleaning abilities, we prepare microgels made of Gellan gum, a natural and widespread material already used as a hydrogel for paper cleaning, and apply them to modern and ancient paper samples. Combining several diagnostic methods, we show that microgels performances in the removal of cellulose degradation byproducts for ancient samples are superior to commonly employed hydrogels and water bath treatments. This is due to the composition and morphology of ancient paper, which facilitates microgels penetration. For modern paper cleaning, performances are at least comparable to the other methods. In all cases, the application of microgels takes place on a time scale of a few minutes, opening the way for widespread use as a rapid and efficient cleaning protocol.

Glass and Jamming Rheology in Soft Particles Made of PNIPAM and Polyacrylic Acid

“…Among these, microgels, spherical particles made of crosslinked polymer networks, have emerged as intriguing systems combining the peculiarities of polymers and colloids with distinctive viscoelastic properties and a rich phase behaviour [ 11 , 16 , 40 , 41 ]. They can be responsive to external stimuli such as temperature, pH or light [ 11 ] and this makes microgels widespread in practical applications [ 16 , 42 , 43 , 44 , 45 , 46 ]. In the case of microgels made of the thermoresponsive polymer poly( N -isopropylacrylamide) (PNIPAM), particles undergo the so-called Volume Phase Transition (VPT) at T ∼305 changing their mutual interactions and their size from a swollen state at low temperature to a compact and shrunken one at high temperature.…”

Chemical-Physical Behaviour of Microgels Made of Interpenetrating Polymer Networks of PNIPAM and Poly(acrylic Acid)

“…Finally, microgels have been recently investigated for applications in cultural heritage conservation [ 35 ] taking advantage of the long tradition of macroscopic hydrogels for the cleaning of several kinds of artworks [ 36 ]. Exploiting their retentive properties, microgels are able to clean paper, ensuring a highly controlled water release from the gel matrix.…”

Detection and Identification of Possible Gel Residues on the Surface of Paintings after Cleaning Treatments

“…In particular, the physical properties of gels are important for confining the cleaning to a specific area of the artwork and to prevent the penetration of the liquid phase into the deep layers. The range of physical properties spans from the rigid (e.g., agar or gellan) to the paste-like (e.g., Carbopol), passing through the viscoelastic systems [4][5][6][7][8][9][10]. These last systems are…”