RO128766A2 - Composition for paper deacidification, process for obtaining and process for applying the same - Google Patents

Abstract

The invention relates to a composition for the neutralization of the deteriorated paper acidity for preservation and restoration purposes and to a process for obtaining and applying the same. According to the invention, the composition consists of hydroxyapatite and carboxymethyl cellulose in a 50 : 50 ratio, expressed in mass percentage, as a solution in 100 ml of isopropyl alcohol. As claimed by the invention, the process consists in preparing a suspension of 0.2 g of carboxymethyl cellulose in 100 ml of isopropyl alcohol, there being obtained hydroxyapatite nanoparticles and there being added 0.2 g of nanoparticles to the previous suspension, while vigourously stirring. The said composition is applied by spraying onto the paper surface, which was dedusted, straightened and cleaned, having as an effect the pH modification from 4.5 to 7.2, after which the paper is let to dry for 24 h at the room temperature.

Description

The present invention relates to a novel chemical composition based on a suspension of hydroxyapatite (HA) nanoparticles in carboxymethyl cellulose (CMC), in alcoholic solution (isopropanol), used for deacidification of the paper, by annihilating the acidity from 4.5 to 7. ,2. The preparation of the composition, the process of obtaining it, the process of applying this composition are presented.

The state of knowledge

The degradation of the paper due to the excessive acidity (due to the action of the chemical or biological agents), is reflected by the appearance of yellow tones accompanied by the increase of the fragility because the paper is transformed into a very fragile substance that is destroyed at the slightest touch. Acid hydrolysis of cellulose that occurs during aging represents about 95% of the deterioration process, and is considered to be the most significant cause of cellulose material deterioration. The acid attack causes the random attack on the hemiacetal connections between different constituents of the cellulose molecules. This reaction shortens the molecules, and weakens them at the same time, leading to the fragility of cellulose material.

The most common types of paper damage are:

• Increased acidity (due to either the polluting agents or the inks used in printing) with the decrease of the mechanical resistance until the perforations appear. This is accompanied by the erosion and brittleness, thinning and transparency of the paper.

• Spotting by the appearance of brown, yellow, green, pink, purple, orange pigments, accompanied by deeper unsensitive degradation with the naked eye, due to the fungi and especially the diffusible pigments produced by them;

0 1 1 - 0 1 4 0 5 - '5 - »- 2011 •„ foxing: or the appearance of reddish-brown spots of 0.5-5 mm diameter, due also to the fungi, and especially the cessation of their action. These foxing spots can also be produced by molds, which generally live unobserved in paper, and become visible through the sharp smell and marked brown color that appear when the paper is permeabilized.

Processes to eliminate paper acidity are also known as paper deacidification. Despite the research done so far, the problem of paper deacidification is far from being fully resolved. Some mass deacidification methods have been developed and improved, but it cannot be said that any of them fully meet the quality criteria recommended in the field, such as the pre-selection of the material to be restored, the pre-drying, the duration of the treatment, the effect of the inks, the color, the covers, the neutralization of the acidity of the paper, the final pH, the alkaline reserve, the risks to which the restaurador and the reader are subject, the impact on the environment, the costs of the equipment and the cost of the treatment.

The discoveries in the field existing so far are:

> German patent DE19921616 (A1), which presents a method of neutralizing the acidity of historical paper using a dispersion of calcium carbonate or magnesium carbonate (1.2% by weight) with organic acid stabilizer in cyclohexane. But this method uses organic solvent (cyclohexane, with a high degree of flammability and toxicity), with the danger of ignition of the material (book) being treated. In addition, the treated material dries hard and may have browning aspects on certain portions.

> Patents AU2003215817 and WQ03082742 entitled: Process for the preparation of nano- and micro-particles of oxides and hydroxides of transition metals and of the group III, nano- and micro-particles thus obtained and their use in the ceramic, textile and paper industries, in which only the synthesis methods of these ¢ - 2 0 1 1 - 0 1 4 0 5 -1 5 -12- _Zfl1î nanoparticles are mentioned, mentioning their potential application in the above-mentioned fields;

> Patent US2005042380 (A1), entitled: Basic suspension, preparation and deacidification process of paper, in which basic suspensions of type Li ₂ 0, Na ₂ 0, K ₂ O, MgO, CaO, SnO, SnO ₂ , PbO are addressed. , Pb ₂ O, Pb ₂ O ₃ , BiO, Bi ₂ 0 ₃ , Sb ₂ 0 ₃ or mixtures thereof, as well as their hydroxides having dimensions between 10 nm and 500 nm and the de-acidification procedures of the paper by immersing the paper materials in baths with suspensions of the above-mentioned oxides and bases. This method has the secondary effect of cellulose depolymerization, due to the strong alkaline conditions.

> In the work "Conservation and restoration of documents and books", authors: Carmen Crespo and Vicente Vinas, several methods of restoration of damaged paper are addressed, including the use of calcium hydroxide and magnesium hydroxide, but bubbled in solution of dioxide carbon so that on the surface of the paper a carbonate layer of the two metals mentioned above is formed. The method has disadvantages: the formation of carbonates, in the form of a solid layer distributed unevenly and easily exfoliated from the surface of the paper, the use of carbon dioxide which can lead to the formation of carbonic acid, which would increase the acidity of the paper treated with destructive effects. emphasized on the paper subjected to the treatment, and the carbonates formed can cover the pigments used in figures or drawings on the respective paper, producing their discoloration and making it difficult to reinvigorate their color.

> The paper: Nanoparticles of Mq (QH) ?: Synthesis and applications in paper conservation, authors: Giorgi, R., Bozzi, C., Dei, L., Gabbiani, C., Ninham, BW, Baglioni, P. Langmuir 21 , 8495-8501 (2005), presents alternative methods for the preparation of Mg (OH) ₂ and the influence of the reactants on the quality of this hydroxide, as well as its use in cj- 2 Ο 1 1 - 0 1 4 0 5 -1 5-12. ζοπ deacidification of some paper samples by transforming it to the surface of the treated paper into the corresponding carbonate.

> The paper "A new method of deacidification of paper based on calcium hydroxide dispersed in non-aqueous media", authors: Giorgi, R., Dei, L., Schettino, C., Baglioni, P, published in Preprint of the IIC Baltimore Congress 2002, Work of Art on Paper, Books, Documents and Photographs: Techniques and Conservation, 69, Baltimore (2002) presents the use of calcium hydroxide in alcohol suspensions. Unfortunately, calcium, magnesium and barium hydroxides in intensely aqueous solutions used in the last decades, induce undesirable side effects, due to the strong alkaline conditions that cause the cellulose depolymerization after the treatment application. In addition, for paper samples with alkaline tank that have undergone the process of deacidification, atmospheric CO ₂ as a weak acid, causes the pH of the solutions used for deacidification to be lowered by more than 1.5 pH units. This also contributes to the easy dissolution of the carbonates of the alkaline earth metals present in the system.

> In the book Technologies of book preservation ”. The US Congress, Office of Technology Promotion, Washington, D.C., presents some issues and solutions to these problems. An additional reliable process, from Preservation Technologies, Inc., uses MgO with particles between 0.2 and 0.9 microns, a surfactant and perfluoroheptane as a solvent.

> Wei T'o method, leads to good de-acidification results, but does not have good results regarding the homogeneity of the alkaline reserve; due to the poor solubility of the reagents in methanol, they produce side effects on the inks. The alkaline reserve created in the paper following the process is relatively weak, so after a short time it is necessary to repeat the de-acidification.

> Patents U8 5091111 and US 5208072, have a composition for deacidifying paper containing 0.1 - 20% methyl carbonate

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magnesium in an organic solvent that does not attack the paper, but requires special use measures due to its toxicity.

> US Patent 5770148 relates to an improved method of deacidifying books, printed paper and other printed materials containing cellulose by treating them with basic metal oxides, hydroxides or salts dispersed in hydrofluoreter, alone or in combination with perfluorinated carriers, in the presence of surfactants. The results are also difficult to obtain and with special precautions due to the dispersing media.

> US patent 6676856 shows improvements in the composition and method of preservation of cellulose materials by using multi-valent organic metal carbonate solutions, C1-C4 alcohols with a humidity degree of less than 100 ppm, and 86-99% solvent with a degree of humidity less than 100 ppm.

> Patent RO126570 (A2) entitled: Composition and method of treatment, chemical restoration and biological disinfection of the surface of historical paper with hydroxyapatite (HA) nanoparticles, presents the preparation and application of a suspension of 0.8% HA in isopropanol for chemical restoration and disinfection biological (for Aspergillus and Penicillium fungi) of damaged paper surface.

Detailed description of the invention

For this invention, hydroxyapatite (HA) was used in the form of nanoparticles, prepared by soaking in a vibrator of a hydroxyapatite powder, until it reached dimensions of about 30 nm.

In order to avoid lowering the alkaline reserve of the paper subject to deacidification, HA in the form of nanometric powder was mixed with a solution of carboxymethyl cellulose (CMC) in isopropyl alcohol at 50%: 50% (mass percentage), and the suspension obtained is applied to the surface of the paper damaged by the acid attack.

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The use of carboxymethyl cellulose (CMC) aims to over-activate the hydroxyapatite (HA) surface by increasing hydrogen bonds and electrostatic links between the two components, and smoothing the paper surfaces on which the suspension of the two components is applied. On the other hand, the functional groups contain positively charged pairs of calcium ions and clusters of six negatively charged oxygen atoms associated with phosphate crystal triplets, generating hexagonal column crystals with an ideal ratio Ca: P = 1.67. Ca, P ions and hydroxyl groups are positioned on the surface of HA. Upon contact with CMC, there is also an electrostatic interaction between the Ca ²⁺ ions of HA with the carboxyl anions of the CMC structure, which is not a classical ion exchange interaction, being much accentuated in acidic environment [Bernardi, G. Chromatography of proteins on hydroxyapatite, Methods Enzymol 22, 32-339 (1971)]. This means that in the acidic environment of the degraded paper, the two components will form a compact powder both with each other and with the paper support (the paper).

In our invention, the two components of the HA mixture: CMC at the primary contact, interact only through weak hydrogen bonds, this interaction being visible in the FTIR spectrum by widening the bands of the OH group in the domain (3000-3500 cm ' ¹ ).

Deposition on high acidity paper (pH 4.5) also favors electrostatic bonding of the two components, since in the range of acid pH values, the Ca ²⁺ ions ^pre- positioned on the HA surface come in contact with the COO ² ions on the CMC surface. The electrostatic bond formed stabilizes the two components and thus neutralizes the pH of the paper to be sprayed (also visible through the 1460 cm ' ¹ band in the FTIR spectrum, attributed to the COO ² ' Ca ²⁺ ion pair). For this reason, atmospheric CO ₂ no longer has the capacity to react with either component, the risk of transforming the pH of the paper from the basic domain into acid being practically zero.

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The novelty and advantages offered by the invention consist of:

> use of suspensions of Ca ₁₀ (PO ₄ ) 6 (OH) 2 hydroxyapatite nanoparticles suspended in carboxymethyl cellulose (CMC) alcoholic solution (isopropyl alcohol), 50%: 50% (weight percent), the solution being sprayed onto the surface acid paper;

> Deposition on paper involves hydrogen bonds between the H atoms and the OH groups present in the structures of the two components, but also the electrostatic bonding of the two components, favored by the acidic environment of the paper (pH 4.5), since in the field of acid pH values , the Ca ²⁺ ions ^pre- positioned on the HA surface come into contact with the COO ^2- ions from the CMC surface, forming ion pairs - COO ² 'Ca ²⁺ . For this reason, atmospheric CO ₂ no longer has the capacity to react with either component, the risk of transforming the pH of the paper from the basic domain into acid being practically zero.

> Isopropyl alcohol has low toxicity, is volatile, has low surface tension and is environmentally friendly.

> In comparison with the methods available up to now and used in many books and libraries, the hydroxyapatite composition: carboxymethyl cellulose prepared by us, has the following advantages:

o (1) HA and CMC nanoparticles are non-toxic, being recognized as biocompatible materials;

o (2) has minor disadvantages in terms of the solvent used (isopropanol) compared to CFC used in the Wei t'O method;

o (3) the nanoparticles treatment of the paper is not followed by the carbonation of the applied reagents, and there is no risk of disappearing the alkaline deposit of the paper with the reappearance of the acidity of the paper.

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The invention is further described in relation to Figures 1-5 which represent: Figure 1 shows the FTIR spectra of HA, CMC and HA-CMC samples (50%: 50%) with hydrogen bonding (a) and COO bonding ² 'Ca ²⁺ (b) Figure 2 shows the micrograms obtained by scanning electron microscopy (SEM) and atomic force microscopy (AFM) of the untreated paper samples (left quadrants a, b) as well as the paper samples sprayed with HA: 50% - 50% CMC (in isopropanol) (right quadrants a, b);

Figure 3 shows the AFM topology of the untreated paper;

Figure 4 shows the AFM topology of the paper after HA treatment: CMC = 50%: 50% in isopropanol;

Figure 5 shows the visual appearance of an acid paper sample before (left) and after HA treatment: CMC = 50%: 50% in isopropanol (right).

An example of the invention is given below.

Example 1

The operations performed to treat the yellowed, discolored and fragile portions of the paper:

1. Mechanical dusting, operation performed with a soft brush, in a niche with poor ventilation;

2. mechanically straightening the sheets subjected to treatment with a soft brush and a bone splint;

3. Dry mechanical cleaning: with gum powder and eraser;

4. removal of wax deposits with the scalpel;

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5. 0.2 grams of HA in the form of nanometric powder were mixed with 100 ml of isopropyl alcohol containing 0.2 grams of carboxymethyl cellulose (CMC) 50%: 50% (percentage by mass), and the suspension obtained was spray-applied. the surface of the damaged paper. HA.CMC suspension spraying by rotating movements, in successive circles from left to right and from top to bottom;

6. The respective paper is allowed to dry in the atmosphere at room temperature, so as to make connections between the pulverized nanoparticles and the fibers degraded by cellulose in the paper's constitution, and the paper to gain consistency and strength. Drying the respective sheets 24 hours on the rack, at room temperature.

7. Following the application of the uniform jet of HA-CMC in isopropyl alcohol and drying, the paper was subjected to physico-chemical analyzes such as: FTIR, scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was observed, on the one hand, the topology of hydroxyapatite nanoparticles suspended in CMC, their size, but also the homogeneity of the hydroxyapatite layer: carboxymethyl cellulose sprayed on the paper sample.

8. The efficiency of the composition presented in this invention is determined by pH measurements. For pH measurement, 0.5 grams of unprinted paper were weighed, defibrillated by ultrasonication (for 15-20 minutes) with an ultrasonicator, in special sealed test tubes. After defibrillation, the pH value was continuously measured to a constant value. The measurements were performed in triplicate. To determine the pH, a pH meter with a metrologized glass electrode was used. If at the primary contact between the sprayed composition and the paper, the pH was 4.5, after treating the paper, its pH became 7.2. It was stable for several months, without any visual modification of the treated papers.

Claims (3)

1. The composition according to the invention characterized in that it consists of: hydroxyapatite and carboxymethyl cellulose (50% - 50%) (percentage by mass) in 100 ml isopropyl alcohol solution; 2. The process for obtaining the composition according to claim 1, characterized in that it consists of the following steps: production of a suspension of carboxymethyl cellulose in isopropyl alcohol, production of hydroxyapatite nanoparticles, combination of the components obtained in the following proportions: 0.2 grams HA , 0.2 grams CMC, 100 ml isopropyl alcohol by energetic stirring. 3. Method of applying the composition according to claim 1, characterized in that it consists of the following steps: mechanical dusting, mechanical means straightening of the sheets subjected to the treatment, dry mechanical cleaning and removal of wax deposits, and application of this composition by spraying on the surface. damaged paper, for deacidification of the paper with the acidity of the paper from 4.5 to 7.2, followed by drying for 24 hours at room temperature.