BR102019017415A2 - process of obtaining polymeric hydrogels cross-linked by ionizing radiation to clean surfaces of works of art - Google Patents

Abstract

process of obtaining polymeric hydrogels cross-linked by ionizing radiation to clean surfaces of works of art. the present invention corresponds to a synthetic and biodegradable polymer hydrogel synthesis process for cleaning cultural collections, including delicate papers, graphic materials, paintings, etc. In this process, ionizing radiation from cobalt-60 or electron beam is used to simultaneously crosslink the polymers and sterilize. this process has a big difference in relation to the hydrogels used for cleaning works of art described in the literature, as these are obtained by chemical cross-linking or physical freezing and thawing processes, having restricted applications, short shelf life, and an unviable cost of export to the routine use in the restoration of cellulosic materials such as paper. in view of the complexity and variety of the work of art compositions, this patent seeks to improve these hydrogels, aiming to increase cleaning efficiency without damaging the integrity of the works.

Description

PROCESS OF OBTAINING POLYMERIC HYDROGELS LINED BY IONIZING RADIATION TO CLEAN SURFACES OF WORKS OF ART Field of invention

[001] The present invention belongs to the sector of nanotechnology and ionizing radiation. More particularly, it refers to the development of a new product made of polymeric hydrogels cross-linked by ionizing radiation from a cobalt-60 source or electron beam, for cleaning works of art in cultural collections, including delicate papers. The main feature of the present invention is to develop polymer hydrogels based on gellan gum and other polymers. As an example, the combination of gellan gum and Poly (N-2-vinyl pyrrolidone (PVP) is used, with the same 1/1 ratio between the components being used. Gellan gum forms gel in low concentrations and PVP prevents the degradation of the gum gelanine during the crosslinking process by ionizing radiation.The compound forms a malleable, elastic, transparent hydrogel and allows the incorporation of biocides such as silver (AgNP), zinc (Zn), copper (Cu). (sequestrant), such as EDTA, calcium acetate, etc. In view of the complexity and variety of the work of art compositions, these hydrogels are efficient in cleaning without damaging the integrity of the constituent materials of various works.

Background of the invention

[002] The use of modified synthetic and natural polymers has stimulated the application of nanotechnology in polymeric systems formed by new structures [Peppas, 2006]. There are several techniques for the modification of polymers, among them the physical process by freezing and thawing cycles, chemical cross-linking (esterification) and ionizing gamma or electron beam radiation, which has demonstrated great efficiency in these modifications over the years. It has also been recognized as a very viable tool because there is no need to add additives to promote crosslinking, in addition to promoting simultaneous sterilization [Jagur-Grodzinski, 2010]. Among the development of polymeric nanotechnology, there are hydrogels as actuators: in the release of drugs and silver nanoparticles for the health area [Ulansk, 2004; Rosiak, 2004; Vitaliy, 2007]; in agriculture, performing the function of maintaining soil moisture [Abanto-Rodriguez, 2017]; and in the area of artistic heritage, being a controlled release tool for cleaning agents in the treatment of delicate surfaces in art restoration [Bonelli, 2013; Ferrari, 2017].

[003] Processing by radiation, or simply ionizing irradiation, is a technology that has been well accepted with traditional applications that include sterilization of healthcare products, crosslinking (curing) of polymers, irradiation of food and ultimately the disinfection of works of art. However, new applications have emerged as a reaction to global trends and needs. In recent years, the irradiation of human tissues for transplantation has also been researched and today it is applied routinely [Al Assaf, 2016].

[004] The Cobalt-60 Multi-Purpose Radiator from the Energy and Nuclear Research Institute has developed its activities basically along two lines, that of providing services and that of supporting research. In the service provision area, routine activities have been carried out processing various materials that need disinfection, disinfestation and sterilization. In the research support area, several materials have been treated, in order to find correlations between the applied dose and some property of the material that can be modified with gamma radiation [Santos and Vásquez, 2015].

[005] Surfaces are the most important regions of works of art, not only from an artistic point of view, but also for the role they play related to aging and degradation. Dirt deposits, stains due to the handling and attack of fungi, and aged protective layers can in many cases limit the enjoyment or, at worst, catalyze the degradation process leading to irreversible damage to works of art. For these reasons, the removal of materials from an artistic surface is of paramount importance to preserve the cultural message, allowing its transfer to future generations. In conservation, cleaning is considered one of the most challenging tasks during the process of restoring an artistic surface, due to the variety of materials (such as composition, structure, surface and roughness) of the artifacts, the environmental conditions and the forms of unwanted coatings that must be removed [IEIA 2018].

[006] The need for an innovative, low-risk surface cleaning technique is particularly growing when considering the restoration field of modern and contemporary art. In fact, the physical and chemical properties of many of the new materials used by modern and contemporary artists challenge and in some cases, even exclude the use of methodologies, consolidated among conservatives. As an example, some newer oil paints show sensitivity to water, making cleaning methods no longer optional. In addition, a particularly challenging task is the removal of old coatings and the use of modern acrylic paint protectors [Beglioni, 2013]. The similar solubility of the two surfaces, the one to be preserved and the other to be removed, makes the process of varnish removal potentially invasive, destructive or unviable, imposing the use of increasingly controllable and selective cleaning systems.

[007] In patent PI0705575-7 (Teodorico de Castro Ramalho, Hudson Wallace Pereira de Carvalho, Ana Paula de Lima Batista, Gustavo H. Pereira da Luz) the authors describe the invention of the hydrogel composition, which has several applications. These water-absorbent composites can be applied to various products, including disposable diapers, towels and intimate absorbents. Hydrogels, on the other hand, present a series of other industrial applications, among which we can mention: constituent in the formulation of cosmetics, vehicle for skin medications, soil conditioner due to its high water retention capacity and resistance to dehydration. Another important application of the composite is its ability to remove metals in aqueous solution, which enables its use as a filtering element for the treatment of natural or industrial effluents contaminated with metals.

[008] Patent WO2014094085 A1 (Foglio, Mary Ann; Servat, Lella; Reyes-Ortega, Felisa, González Gómez, Álvaro; San Román, Julio, Oliveira Souza, Ilza María; Pedroza Jorge, Michelle; Carvalho, João Ernesto de) deals with a process of obtaining products based on chitosan and enriched with extract of Arrabidaea chica. As final products, nanoparticles, films, hydrogels and sponges are obtained, which are applied in the healing of skin ulcers, mucosal ulcers caused by chemical and / or physical agents, in addition to ulcers of the gastrointestinal tract.

[009] The patent US9603934B2, (John Borja, Stephanie Sharon Hayano, Anhydrous hydrogel composition and delivery system) refers to anhydrous hydrogels that function as mucoadhesives (oral compositions) or as topical agents and can be used to administer an active agent, such as pharmaceutical agents (API's), coagulants, fragrances, flavorings and other active ingredients and excipients.

[010] It is evident that there are many hydrogel products obtained by chemical cross-linking, physical process, ionizing radiation, among other cross-linking processes. This can be noticed by the large number of patents with different applications. However, unlike all existing products, the present invention has the purpose of using, in an unprecedented way, hydrogels cross-linked by ionizing radiation for cleaning works of art in cultural collections. The purpose of the present invention is to use ionizing radiation to crosslink polymeric hydrogels according to the sensitivity of each type of artwork and each need for cleaning application, without damaging the integrity, such as texture and color of the various works.

[011] The preliminary results of the prototype type 1: gellan gum / PVP, showed that hydrogels cross-linked by ionizing radiation, are viable for cleaning delicate papers as they do not leave residues and do not damage their integrity.

Detailed description of the invention

[012] The product of the present invention refers to polymeric hydrogels for cleaning works of art, according to the need for cleaning in the restoration of cultural heritage, including documents on delicate papers, without damaging the integrity of the surface to be applied.

[013] These hydrogels are matrices that have aroused interest, as they are formed by three-dimensional networks of cross-linked polymers, with swelling capacity in aqueous media. The simulation of the structure of the polymeric network is shown in Figure 1: the polymeric solution (1) is subjected to ionizing radiation (2), giving rise to the cross-linked polymer (3). The polymeric mesh prevents the structural integrity of the hydrogel from being undone, thus keeping the work of art intact after cleaning, as each proposed hydrogel variation has the ability to control humidity according to the type and need for protection of the material that it will be clean.

[014] Ions or nanoparticles for biocidal use, such as silver (AgNP), or zinc (Zn), or copper (Cu) can be added to the hydrogels proposed in this invention. These ions have biocidal effects for fungi and bacteria, present in most works of art, with no evidence of ionic migration to the surrounding environment. Likewise, complexing agents can be added to hydrogels to retain dirt from pollution and microorganisms without damaging the work of art. EDTA, for example, combines with metal ions in a 1: 1 ratio regardless of the cation charge, as shown in the following generic reaction: [015] The main feature of the present invention is to develop polymeric hydrogels based on gellan gum and others synthetic or biodegradable polymers, which have malleable, elastic, transparent characteristics and allow the incorporation of biocides such as silver (AgNP), zinc (Zn), copper (Cu), in concentrations of 20 to 1,000 ppm, in addition to complexing (sequestering) , such as EDTA, calcium acetate, etc. It should be noted that the metal and polymer are chosen according to the surface of the work of art to be cleaned.

[015] The main feature of the present invention is to develop polymeric hydrogels based on gellan gum and other synthetic or biodegradable polymers, which have malleable, elastic, transparent characteristics and allow the incorporation of biocides such as silver (AgNP), zinc (Zn) , copper (Cu), in concentrations of 20 to 1,000 ppm, in addition to complexing agents (scavenger), such as EDTA, calcium acetate, etc. It should be noted that the metal and polymer are chosen according to the surface of the work of art to be cleaned.

[016] One of the products developed in the present invention is the gellan gum hydrogel with poly (N-2-vinyl pyrrolidone) (PVP) and calcium acetate. Solubilization in water (milli-q or reverse osmosis) of 04 g / l of calcium acetate was carried out, in the concentration between 2% to 5%, and the resulting solution was separated into two parts (one part solubilized the PVP from 2% to 10% and the other part solubilized the gellan gum from 2% to 10%). The mixture of gelan gum and PVP, in the proportion of 1/1, were solubilized separately. These formulations were left to stand at room temperature for 16h to 20h, for solubilization of PVP and pre-solubilization of gellan gum. Then, both solubilizations were mixed with a manual stirrer. After mixing the formulation, it was heated in a water bath to 90 ° C in an autoclave for total solubilization of the gelan gum. After removing the formulation from the autoclave, it was homogenized immediately with a manual stirrer and placed, still hot, in the packages. Finally, after cooling to room temperature, they were sealed and subjected to ionizing radiation, where simultaneous cross-linking and sterilization occurs, leaving the product ready for use.

[017] For the other formulations mentioned above, they must follow the same procedure as the hydrogel made in the preliminary test, except for the poly (vinyl alcohol) polymer that does not solubilize at room temperature. The PVAl, must be solubilized under mechanical agitation with a magnetic stirrer, with controlled temperature between 85 ° C to 90 ° C, so that polymeric degradation does not occur, for a period of 4 hours.

[018] The relevance of this work is the need to develop effective hydrogels for cleaning cultural collections, including delicate papers, without causing damage to the work of art.

[019] The following are examples of products and preliminary tests done with hydrogels only on delicate paper.

Example 1

[020] Hydrogels obtained with gellan gum / PVP and calcium acetate were subjected to ionizing radiation at doses of 5, 10.15, 20 and 25 kGy. Hydrogels in doses of 5 kGy and 10 kGy were easy to be removed from the packaging. Figure 2 shows the hydrogels, in doses of 6 and 10 kGy, which have: (a) flexibility; (b) softness; and (c) resistance to handling. While the hydrogels obtained in doses of 15, 20 and 25 kGy, showed fragility and rupture when removed from the packaging. This fragility can be associated with gellan gum, as it is sensitive to high doses of ionizing radiation, considering that it is a long-chain polysaccharide. This result was confirmed by the gel and swelling fraction shown in Table 1. The gel fraction is the representation of how much the polymer has been cross-linked by ionizing radiation. While swelling is associated with crosslinking, a factor that determines the space between polymer chains. The process is inversely proportional: the greater the crosslinking, the less swelling. As polymer chains break down, it is possible to observe an increase in swelling, as shown in Table 1.
Table 1 - Gel fraction and swelling of hydrogels

Example 2

[021] In the first analysis, an original work was not used, but an acid paper support that was in contact with the original work and, due to the acidity, the image was transferred to this wood pulp paper with weight 60. The paper served as a support for an engraving for a long time, with an image transfer of the engraving to this support. The result of applying the hydrogel for cleaning was satisfactory because it did not damage the image of the print transferred from this paper, as shown in Figure 3: (a) photo before cleaning; (b) and (c) during cleaning; (d) after cleaning.

[022] For the second analysis, a work of art was selected from a particular map, made of thick paper and with a surface treatment, that is, little impermeable. It was photographed before the analysis to record the effect after undergoing cleaning. The gelan gum / PVP hydrogel, calcium acetate and 5 kGy dose were used. The hydrogel was applied to a small oily spot. Figure 4 shows the artwork during the cleaning of the oil stain. The hydrogel remained for a short time on the stain, about an hour, and there was a softening of the color, maintaining the integrity of the surface where it was applied. The hydrogel used for cleaning in this work had already been used to clean the previous test. Another advantage of the hydrogel is the fact that it can be cut to the required size.

[023] The results presented are preliminary tests and have not yet been tested in a wide range of works of art. The first test was not performed on original paper as previously described. In the second test, the work was original and it was a simple test: the hydrogel remained for an hour on the stain showing its clarification. These hydrogels can have applications in a variety of papers that are delicate with respect to color, type of paint and grammatology. Also included are works of art in fabric and wood. During the cleaning process, the restorer must select the type of hydrogel to be used, depending on the sensitivity of the artwork. The hydrogel may have higher or lower humidity and this control is done by the concentration of polymer and radiation dose. For this reason, it is not possible to limit the radiation dose. In this case, the range of 5 to 30 kGy is used for the development of these hydrogels.

Claims (3)

PROCESS OF OBTAINING POLYMERIC HYDROGELS RETICULATED BY IONIZING RADIATION FOR CLEANING SURFACES OF ART WORKS, characterized by being based on the combination of gellan gum and other biodegradable synthetic polymers, such as poly (N-2-pyrrolidone vinyl) (PVP), in addition to allow the incorporation of complexants, such as EDTA and calcium acetate, comprising the following steps:

• (a) Solubilization in milli-q water or reverse osmosis of calcium acetate at a concentration between 0.2% to 5%;
• (b) Division of the solution resulting from (a) in two parts, solubilizing the PVP in one of the parts, in the concentration between 2% to 10%, leaving it to rest between 16h and 20h, at room temperature, and, in the second part, gellan gum in a concentration between 2% to 10%, at room temperature, between 16h to 20h;
• (c) Addition of the solubilized PVP to the gellan gum solution, mixing with a manual stirrer, then placing the mixture in a glass beaker covered with polyethylene plastic film;
• (d) Introduction of the beaker in the autoclave with water heated to 100 ° C, leaving for about 6 minutes until the volume of the formulation reaches 90 ° C;
• (e) After removing the formulation from the autoclave, it must be homogenized immediately with a manual stirrer and placed, still hot, in the packages;
• (f) Cooling the formulation to room temperature and packaging it with polypropylene film;
• (g) Submission of ionizing irradiation from cobalt-60 and electron beam, in doses from 6kGy to 25 kGy, containing silver ion solution, or silver nanoparticles (AgNP), or copper (Cu), or zinc (Zn ) (20 to 1,000 ppm) to crosslink and sterilize, simultaneously.

PROCESS OF OBTAINING POLYMERIC HYDROGELS LINED BY IONIZING RADIATION TO CLEAN SURFACES OF ART WORKS, according to claim 1, characterized by being based on the combination of gellan gum and other polymers, including poly (vinyl alcohol) (PVAl ), which, because it does not solubilize at room temperature, is solubilized under mechanical stirring with a magnetic stirrer, with a controlled temperature between 85 ° C to 90 ° C, for a period of 4 hours. POLYMERIC Nano-STRUCTURED HYDROGENS, crosslinked by ionizing radiation, products manufactured according to claim 1, characterized by having a gel fraction between 52.5 and 59.5% and swelling between 109.2 and 96.1%, when subjected to ionizing radiation from cobalt-60 and electron beam, in doses of 5 kGy and 10 kGy, respectively, and have formulations with hybrid three-dimensional mesh, be synthetic or biodegradable, with application for cleaning cultural collections, including delicate papers, fabric and wood, without damage the integrity of texture and color of the building materials.

Images