Alkaline Nanoparticles for the Deacidification and pH Control of Books and Manuscripts

  • Piero Baglioni
  • David Chelazzi
  • Rodorico Giorgi
  • Huiping Xing
  • Giovanna Poggi


Manuscripts and books are susceptible to fast degradation owing to the presence of detrimental components used in the papermaking techniques, and to the action of environmental pollutants. As a result, the acidity of documents increases, promoting the acid-catalyzed depolymerization of cellulose. The latter process strongly reduces the mechanical properties of paper, reducing its long-term resistance to natural aging. The presence of inks concurs to degradation, making the conservation of manuscripts particularly demanding. In this chapter, the use of dispersions of alkaline earth metal hydroxide nanoparticles will be discussed as a method for counteracting the degradation of paper. These systems have proven efficient for the deacidification of cellulose-based artifacts, providing a mild alkaline buffer and maintaining a stable neutral environment. The palette of formulations nowadays available to conservators includes systems designed for the treatment of manuscripts featuring metal gall inks and modern industrial inks.


Cellulose Chain Magnesium Hydroxide Aqueous Treatment Hydroxide Nanoparticles Titanium Ethoxide 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

1 Introduction

This chapter provides an overview on the use of nanomaterials, in particular dispersions of alkaline nanoparticles in non aqueous media, for the preservation of cellulose-based artifacts, such as those commonly found in archives, libraries, museums and private collections. First, a brief introduction will be given on cellulose chemistry and on degradation mechanisms both in acidic and in alkaline environments. We will focus on factors that influence the aging of books and manuscripts, in particular the presence of iron gall inks and their detrimental action on paper. Then the traditional conservation treatments will be discussed before describing the advantages of the methodologies developed in the framework of Colloids and Nanosciences. The syntheses, stabilization, and characterization of alkaline nanoparticles dispersions will be outlined, and applicative aspects will be illustrated in the Case Studies Sect. (5.4).

2 Chemistry and Degradation of Cellulose-Based Material

Cellulose based-materials are largely present in the cultural patrimony of all civilizations. Paper, canvas, and wood objects constitute a significant amount of the documentary, historical, and artistic heritage that needs to be preserved and transferred to future generations. Authors belonging to different countries worldwide have brought this issue to the attention of the scientific and conservation communities (Dobrodskaya et al. 2004; Strlič and Kolar 2005; Wouters 2008; Yanjuan et al. 2013; Afsharpour and Hadadi 2014). Before discussing the use of nanomaterials for the conservation of cellulose-based artifacts, a brief introduction on the properties and degradation pathways of cellulose will be given.

2.1 Cellulose Chemistry

Cellulose is a linear polymer naturally found in the walls of plants cells and plays a fundamental role in determining the mechanical properties of vegetal tissues. Cellobiose, which is the repeating unit of cellulose, consists of two molecules of D-glucose, linked through a β-1,4-glycosidic bond formed upon condensation. One of the most important parameters in evaluating the conservation status of cellulose-based artifacts is the degree of polymerization (DP), which is defined as the average number of monomer units for cellulose chain. The degree of polymerization of native cellulose depends upon the vegetal species, ranging between 9000 and 15,000 (Fengel and Wegener 1984). Typically, the manufacturing process of cellulose, i.e. its extraction from wood, significantly reduces the original DP. It is worth noting that the mechanical properties of the polymer are related to the average chain length; for instance, if DP decreases down to 300, which is a possible value for aged cellulose in historical objects, the resistance is dramatically reduced resulting in mechanical failure (crumbling, rupture).

The supramolecular structure of cellulose is due to hydrogen bonds formed between hydroxyl groups either of the same chain (intramolecular bonds) or of different chains (intermolecular bonds). Hydroxyl groups can also give hydrogen bonds to water molecules, accounting for the hygroscopicity of cellulose, whose average water content is 6–7 % (w/w) at standard conditions. Hydrophobic interactions also contribute to the network of bonds and their importance in determining the solubility of cellulose has been recently discussed (Medronho et al. 2012; Glasser et al. 2012). Overall, the polymer chains are organized into a hierarchical structure. The chain network exhibits both amorphous and crystalline regions (Nisizawa 1973). Elementary fibrils are formed by a succession of highly crystalline sites (crystallites) and amorphous zones. The elementary fibrils are in turn bound to form microfibrils (see Fig. 1). The latter are arranged into fibrils and fibers, to create the cellulose network of paper, canvas and wood.
Fig. 1

a Structure of a single cellulose chain. Gray arrows indicate the hydrogen bonds b a cellulose Iβ microfibril, composed by single cellulose chains. (Reprinted from Altaner et al. (2014)

Degradation via hydrolysis and oxidation is known to affect amorphous regions first, as the crystallites are less accessible to degradation agents. As a matter of fact, the acid-catalyzed hydrolysis of β-1,4-glycosidic bonds can proceed up to complete depolymerization of the amorphous zones, leaving the crystallites to set a lower DP limit, known as Levelling-off Degree of Polymerization (LODP) (Calvini 2005), which can be seen as a watershed between amorphous and crystalline regions of cellulose (Calvini 2014).

The crystalline structure of cellulose has been widely studied starting from the second half of the 20th century (Wilkie 1961). The structure established by von Nägeli in 1858 was confirmed by Meyer and Misch through X-ray crystallography (Meyer and Misch 1937). Four different crystalline allomorphs have been identified (Cellulose I–IV), cellulose I being the most abundant in nature. It is well known (Atalla and Vanderhart 1984) that the crystalline structure of cellulose I is composed of celluloses Iα (triclinic) and Iβ (monoclinic), whose relative amount depends on the original source. Cellulose crystallites are usually about 5 nm in width. The relative amount of crystalline portions is defined by the crystallinity index (CI), and typically ranges from 50 to 90 %, depending on the cellulose source and on the measurement method (Park et al. 2010).

2.2 Reactions in Acidic Medium

The main reaction that takes place in acidic media is the acid-catalyzed hydrolysis of β-1,4-glycosidic bonds, leading to the depolymerization of cellulose and, macroscopically, to the loss of mechanical properties of the polymer. Beside the concentration of hydrogen ions, several factors concur to speed up the reaction, including temperature, and relative humidity. It is worth noting that the scission of glycosidic bonds occurs even at room temperature, posing a threat to the conservation of any cellulose-based artworks. The acid-catalyzed hydrolysis (see Fig. 2) can be described as a three-step process where (i) a hydrogen ion interacts with a glycosidic oxygen, forming a conjugate acid; (ii) the glycosidic bond is cleaved (a water molecule is required) and a cyclic carbocation is formed; (iii) the electron couple of the water molecule flips to the carbocation and a new hydrogen ion is available for further reaction (Harris 1975; Banait and Jencks 1991; Zhang et al. 1994; Lundgaard et al. 2004).
Fig. 2

Acid-catalyzed hydrolysis of β(1-4)-glycosidic bonds in cellulose. (Reproduced from Sequeira et al. (2006). Copyright © 2006 Elsevier Masson SAS. All rights reserved)

Degradation in acidic environments is also due to oxidation, which is interconnected to acid-catalyzed hydrolysis. Oxidized groups on cellulose chains are unstable in acidic conditions, favoring scission of bonds even at room temperature (Calvini et al. 2008). Oxidation of cellulose chains can also result in the production of acids, including glucuronic, glucaric, uronic and aldaric acids that promote hydrolysis in the so-called spiraling effect (Shanani and Harrison 2002). Conjugated carbonyl and carboxyl compounds formed during degradation are chromophores responsible for browning of aged paper (Bronzato et al. 2013).

Volatile acids are developed during the aging of cellulose-based material and, if not removed, result in an autocatalytic degradation process (Calvini et al. 2008). This can be the case in sealed environments, for instance when books are tightly packed in shelves (Carter et al. 2000). Instead, the removal of volatile acids leads to an auto retardant degradation process (Calvini et al. 2008).

2.3 Reactions in Alkaline Medium

Polysaccharides are affected by concentrated alkaline solutions at high temperature, the main steps being: (i) dissolution of polysaccharides; (ii) peeling of end-groups; (iii) alkaline hydrolysis of acetyl groups and glycosidic bonds; (iv) degradation of dissolved polysaccharides and peeled monosaccharides (Rydholm 1965; Sjostrom 1977).

Through the well-known β-alkoxy elimination mechanism, an alkali attacks a hydrogen atom in position α to carbonyl groups and, as a result, the group in position β is eliminated, leading to the peeling of the cellulose chain (Strlič et al. 1998; Santucci and Zappalà 2001). On undegraded cellulose, only carbonyls at the end of each chain are affected by this mechanism, with no dramatic consequences in terms of DP decrease. On the other hand, oxidized cellulose is very sensitive to alkaline solutions even at room temperature (Calvini et al. 1988), and the β-alkoxy elimination causes the random cleavage of polymeric chains (see Fig. 3).
Fig. 3

Fragmentation of oxidized cellulose due to β-alkoxy elimination. (Reprinted with kind permission from Springer Science + Business Media. Calvini and Gorassini (2012), Fig. 1)

3 Factors Affecting Books and Manuscripts Degradation

The degradation of archival material is due to several factors that are either internal, i.e. related to the presence of detrimental compounds from making processes, original components or even past conservation treatments, or external, i.e. environmental factors.

3.1 External Factors

There are many environmental factors that can affect paper stability. Merely day light, in combination with temperature and oxygen, plays a fundamental role in the degradation of cellulose (McKellar and Allen 1979; Feller 1994; Zervos 2010). In particular, the interaction between light and cellulose leads to the oxidation of functional groups and to the formation of oxidized compounds, as described above. At the macroscopic scale, these phenomena result in the typical browning of paper. Air pollutants such as sulfur and nitrogen oxides hydrate in moisture within cellulose fibers and form acids that promote hydrolysis (Carter 1989). The migration of degrading compounds from packing materials, cardboard as well as furniture, cabinet, and cases, in particular if treated with poly vinyl acetate based coatings, is another factor to be taken into account (Tétreault and Stamatopoulou 1997; Carter et al. 2000; Tétreault 2003). In fact, it has been shown that detrimental organic compounds can also be found inside microclimate frames (Lopez-Aparicio et al. 2010; Grøntoft et al. 2010). Environmental factors also include the attack of cellulose by fungi and bacteria, both aerobic and anaerobic, for instance through the use of hydrolytic enzymes (Coughlan 1991).

3.2 Internal Factors

The internal factors affecting paper stability include the quality of raw materials, as well as the presence of compounds introduced during the manufacturing processes. For instance, the purity and crystallinity of cellulose are important parameters in determining its resistance to degradation, as mentioned above. Up to 19th century, papers were obtained from cotton and linen rags, which are mainly composed of cellulose. On the other hand, the onset of the large-scale production of paper gradually imposed the use of wood as a raw material. This involves several conservation issues: (i) both lignin oxidation products and residual chemicals from the pulping and bleaching processes can increase the intrinsic acidity of paper; (ii) paper sheets made from chemical and mechanical pulp, containing considerable amount of lignin, tend to absorb more SO2 from polluted atmosphere than lignin-free paper (Bégin et al. 1998; Tse et al. 2002).

Regarding the manufacturing processes, it must be considered that, from the beginning of the 19th century until the mid 20th, papermaking used alum and rosin for the sizing of paper sheets. Both materials are major sources of acidity, and Chamberlain (2007) showed that the reactivity of aluminum salts in catalyzing the degradation of cellulose can be predicted with reference to the aqueous chemistry of aluminum ions. In fact, it is interesting to note that gelatin, historically used in combination with alum, has anionic groups capable of interacting with aluminum cations, and this could hinder the degrading action of alum on paper (Dupont 2002).

3.2.1 Iron Gall Ink

Iron gall inks have been widely used since the 5th century up to the 20th, when organic dyes and pigments replaced them. Throughout the centuries, a number of recipes have been used to prepare these inks, the main components being: (i) gall nuts, from which tannic acid was extracted; (ii) iron or copper sulfate; (iii) vinegar or wine; (iv) water; (v) arabic gum as a binder (Lucarelli and Mandò 1996; Neevel et al. 1999). Metal gall inks, which include formulations with iron and copper, contain several compounds that are detrimental to cellulose. Gallic acid, coming from hydrolization of tannic acid, reacts with iron(II) sulfate to form sulfuric acid and iron(III) pyrogallate complex that provides color to the ink (Neevel et al. 1999). Sulfuric acid catalyzes the hydrolysis of cellulose and causes its oxidation. Iron sulfate was used in excess in traditional recipes, and the iron ions that are not involved in the formation of the coloring complex promote the formation of hydrogen peroxide in acidic environment:
$$ \begin{array}{*{20}l} {{\text{Fe}}^{2 + } + {\text{O}}_{2} + {\text{H}}^{ + } \to {\text{Fe}}^{3 + } + {\text{HOO}}^{ \cdot } } \hfill \\ {{\text{Fe}}^{2 + } + {\text{HOO}}^{ \cdot } + {\text{H}}^{ + } \to {\text{Fe}}^{3 + } + {\text{H}}_{2} {\text{O}}_{2} } \hfill \\ \end{array} \begin{array}{*{20}l} {{\text{Formation}}\;{\text{of}}\;{\text{peroxides}}\;{\text{in}}\;{\text{acidic}}\;{\text{environment}}} \hfill \\ \end{array} $$
Moreover, free iron ions are also involved in the formation of hydroxyl radicals through a mechanism known as Fenton reaction, which requires the presence of hydrogen peroxide:
$$ \begin{array}{*{20}l} {{\text{Fe}}^{2 + } + {\text{H}}_{2} {\text{O}}_{2} \to {\text{Fe}}^{3 + } + {\text{OH}}^{ - } + {\text{OH}}^{ \cdot } } \hfill & {{\text{Fenton}}\;{\text{reaction}}} \hfill \\ \end{array} $$
Both hydroxyl radicals and hydrogen peroxide oxidize cellulose. A similar reaction, called Fenton-like, describe the production of hydroxyl radicals in the presence of copper ions:
$$ \begin{array}{*{20}l} {{\text{Cu}}^{ + } + {\text{H}}_{2} {\text{O}}_{2} \to {\text{Cu}}^{2 + } + {\text{OH}}^{ - } + {\text{OH}}^{ \cdot } } \hfill & {{\text{Fenton-like}}\;{\text{reaction}}} \hfill \\ \end{array} $$
Iron and copper ions are transition metal that can easily change their oxidation state by reacting, for instance, with cellulose reducing groups, creating a cyclic process. It is worth noting that Šelih et al. (2007) showed that copper ions are far more active than other transition metals in the oxidative degradation of cellulose. Not surprisingly, documents featuring metal gall inks typically show severe degradation in the form of cellulose corrosion, and paper perforation, in particular in correspondence to the inked areas (see Fig. 4).
Fig. 4

18th century manuscript featuring iron gall ink. Corrosion of paper due to the writing fluid is evident. (Reprinted with permission from Poggi et al. (2010). Copyright © (2010) American Chemical Society)

4 State-of-the-Art Methods for the Conservation of Cellulose-Based Artworks

Besides preventive measurements, such as the choice of appropriate display materials and storage conditions, several conservation strategies have been developed for counteracting cellulose oxidation and hydrolysis. These include deacidification treatments and antioxidants, even if there is a strong interest in finding a single method capable of hindering both degradation mechanisms in one step.

4.1 Deacidification Treatments

There is a long tradition on deacidification in the conservation practice, and conservation scientists have developed and proposed many methodologies throughout the last decades (Baty et al. 2010). Neutralization of acidity needs to be achieved because in neutral conditions both the random cleavage of cellulose chains catalyzed by acids and the oxidation reactions favored by an acidic environment proceed at a much slower pace. Hydroxides, applied directly or formed in situ, are used to neutralize acidity on the substrates. Sometimes, carbonates or bicarbonates are directly used as milder neutralizing agents. Deacidification methods should use solvents that are neither toxic to the operator nor dangerous for the environment. Moreover, the deacidification treatment must be physically and chemically compatible with the substrate and its components, i.e. sizing, fillers, inks etc., which means that the treatment must not produce any undesired alteration of the substrate’s original characteristics. To this end, it is important to carry out preliminary tests to evaluate the compatibility between the neutralizing system and the object to be treated. The cost of a deacidification treatment is a crucial factor in most conservation scenarios. For instance, when entire library or archival collections need to be neutralized, interventions on single paper sheets are simply not feasible. Therefore mass deacidification methodologies were developed in order to keep the costs low and increase the number of books deacidified with a single intervention. Mass deacidification methods are typically based on non-aqueous solvents that produce fewer undesired effects than water. In the next sections we will briefly introduce the most important and common deacidification methods in conservation practice.

4.1.1 Aqueous Treatments

During aqueous deacidification treatments, paper sheets (separated from the binding) are either immersed into the neutralizing solution or sprayed with it (Barrow and Sproull 1959); aqueous solutions of calcium (or magnesium) bicarbonate and calcium hydroxide are commonly used. Neutralization of cellulose-based material by aqueous alkaline treatments is very effective because of the high mobility of the hydroxide ions.

Moreover, aqueous treatments can improve the visual aspect of samples owing to direct washing of hydro-soluble dirt and of sizing compounds usually involved in the browning of paper (Sequeira et al. 2006); in fact, a resizing bath is usually needed after aqueous treatments (Giorgi et al. 2005).

On the other hand, aqueous treatments also show severe drawbacks.

Any excess of free hydroxide ions will readily interact with cellulose, which might be depolymerized and degraded in highly alkaline aqueous environments as described in the previous sections. Besides, both the aqueous medium and the alkaline environment can lead to the removal of original material (inks, sizing), and in some cases to ink discoloration due to the decomposition of the ink complex (Kolar 1997; Neevel 2000; Malesič et al. 2002; Sequeira et al. 2006; Stefanis and Panayiotou 2007).

4.1.2 Non Aqueous Treatments

Non-aqueous wet treatments are based on neutralizing agents dispersed or dissolved in solvents that are less polar than water, in order to limit or completely avoid ink bleeding or solubilization of sizing and other hydrophilic paper components (Sequeira et al. 2006). The most inert solvents are usually employed in mass deacidification methods.

The Bookkeeper

The Bookkeeper (Preservation Technologies, L.P.) is a commercial dispersion of micron-sized particles of MgO (concentration of about 4 g/L) in a blend of perfluoroalkanes. Fluorinated solvents are completely inert to paper components, including modern inks. However, the stabilization of magnesium oxide microparticles in the dispersing media requires several additives, including surfactants, probably either a perfluorinated Mg-soap, a perfluoropolyether derivative or a non-ionic fluorinated acyl ester (Zumbühl and Wuelfert 2001).

After the application, magnesium oxide is converted into hydroxide in contact with moisture; the hydroxide neutralizes acidity and, if in excess, forms a carbonate buffer against recurring acidity.

The Bookkeeper is available for single sheet deacidification, i.e. spray products, or for mass deacidification. The latter has been used in the National Congress Library of Washington, D.C., since its development in 1992.

Although it presents several advantages over conventional deacidification methods, Bookkeeper also shows some drawbacks: for instance, its application is discouraged on low porosity material, on highly calendered paper, and on black and dark colored substrates due to the fact that the micro-particles do not penetrate easily through the fiber network, resulting in light whitening of the documents surface (Pauk 1996; Boone et al. 1998), see for instance Fig. 5.
Fig. 5

a Bookkeeper application on a 16th century manuscripts. A white haze is visible where MgO microparticles were sprayed. b The same sample treated with Ca(OH)2 nanoparticles, showing no white haze. [Printed with the kind permission of SELIDO (at IPCE, Instituto del Patrimonio Cultural de España, Madrid)]

The influence of surfactants on the neutralization process has been studied by Zumbühl and Wuelfert (2001) that showed how the presence of a hydrophobic coating hampers the reactivity of magnesium oxide. Slow conversion of magnesium hydroxide into carbonate might create a too alkaline environment that could be risky for the cellulose fibers. Despite these drawbacks, Bookkeeper is widely used and it is one of the best non-aqueous mass deacidification treatments available.

The Battelle or Papersave Process

The National German Library, back in 1987, asked the Battelle Ingenieurtechnik GmbH to investigate different deacidification methods and to develop an innovative system. In 1994, the Battelle process was tested and approved by the Library; the treatment was based on a combination of magnesium ethoxide and titanium alkoxides in hexadimethyl disiloxane (HMDO), a colorless organic silicon compound. The complex formulation is referred to as METE (Magnesium Ethoxide Titanium Ethoxide). Some authors also reported that a surfactant is added to the system to improve paper impregnation (Dufour and Havermans 2001). Magnesium ethoxide reacts with moisture to form magnesium hydroxide that neutralizes cellulose acidity and, if present in excess, is transformed into carbonate by reaction with carbon dioxide. Titanium ethoxide, on the other hand, hydrates to form titanium oxide and water, thus not contributing to the deacidification process (Blüher and Grossenbacher 2006). In fact, the role of titanium alcoholate is to increase the solubility of magnesium ethoxide in HMDO. This method is also known as Papersave and is currently being developed by the German company ZFB. Finally, the Ink save process targets ink corrosion through the use of neutralizing agents (calcium and magnesium alkoxides) in conjunction with quaternary ammonium halides as antioxidants (Baty et al. 2010).

4.2 Anti-oxidants

In the field of conservation science, only a limited number of reducing agents, namely mild agents, can be applied on paper in order to preserve the status of the fibers. In this regard, borane amine complexes, where the high boron reactivity is reduced by complexation with nitrogen, are thought to reduce oxidized groups. In particular, the borane tert-butylamine complex in a non-aqueous solvent, has been widely used in the ICRCPAL Laboratories of Rome (previously known as ICPL) as a reducing agent for carbonyl functionalities (Bicchieri and Brusa 1997; Bicchieri et al. 1999, 2000). More recently, its capability of neutralizing carboxyl groups has been evaluated (Sanna et al. 2009) with the aim of developing a single treatment for inhibiting acid-catalyzed hydrolysis and oxidation of paper. Further data are needed to confirm these interesting preliminary results (Sanna et al. 2009).

Alternatively, J. Neevel proposed the usage of phytates as metal deactivators capable of inhibiting metal gall ink corrosion, back in 1995 (Neevel 1995). Phytate is the commonly used term to indicate myo-inositol hexaphosphate that is the salt of myo-inositol hexaphosphoric acid, a substance present in various food of plant origin. Being a metal deactivator, phytate reduces the oxidizing potential of iron(II) ions, inhibiting its oxidation to iron(III), hence hampering the Fenton reaction.

The method has become popular among conservators and many scientific papers have been published on the subject (Neevel 2000; Botti et al. 2005; Kolar et al. 2005; Zappalà and Stefani 2005; Henniges et al. 2008; Potthast et al. 2008). More recently, J. Kolar proposed the usage of magnesium phytate (Kolar et al. 2007), which can be completely dissolved at standard working conditions, avoiding the risk of forming surface deposits.

According to Kolar et al. (2003), the chelating action of phytate is specific to iron ions, which could hinder the effectiveness of the method in the presence of metal gall inks containing substantial amount of copper ions. However, some authors reported that phytate copper ions complexes are very stable between pH 5 and 7 (Persson et al. 1998). In fact, the phytate treatment increased the resistance to aging of paper featuring metal gall inks with both copper and iron ions (Henniges et al. 2008). Treatment with phytate does not hamper acid-catalyzed hydrolysis of cellulose, therefore, a subsequent deacidification treatment is carried out commonly using calcium hydrogen carbonate aqueous solutions.

In recent years, Kolar et al. proposed the application of quaternary ammonium halides that are specifically designed for the inhibition of cellulose oxidation induced by metal gall inks. Halides are known to act as antioxidants, as they are catalytic peroxide decomposers; therefore they can limit the degradation of paper that contains metal gall inks, regardless of the transition metal ions contained in the inks. The first new antioxidant proposed was tetrabutylammonium bromide (TBABr) (Kolar et al. 2003). In 2005, experimental data acquired on several quaternary ammonium halides showed that the efficiency of the treatment is related to the size of the associated cation. In particular, halides with large counter ions were demonstrated to be more efficient in hampering cellulose degradation; among the tested quaternary ammonium halides, TBABr and TBACl (tetrabutylammonium chloride), in water and dichloromethane, resulted the best systems for the preservation of inked paper (Malešič et al. 2005a, b). More recently, the usage of alkylimidazolium halides and alkaline compounds (i.e. magnesium and calcium ethoxide in ethanol) has been proposed (Kolar et al. 2008). This method is interesting as it combines deacidification with antioxidants in a low-polar system.

5 Alkaline Nanoparticles for pH Control

As highlighted in the previous sections, the ideal deacidification treatment must fulfill several requirements in terms of effectiveness, physico-chemical compatibility with the artifacts, feasibility, and low impact both on the operator and the environment. In this sense, a significant contribution to the development of advanced solutions has come from colloids and nanoscience. The first works date back to the early 2000s, and introduced the use of nanoparticles of alkaline earth metal hydroxides as neutralizing agents for paper and canvas (Giorgi et al. 2002a, b, 2005).

In fact, using these hydroxides as nanoparticles dispersed in carrier solvents (e.g. short chain alcohols or less polar solvents) avoids the limitations typically involved in the state-of-the-art deacidification methods. First, the possibility of dispersing solid particles stably in a solvent allows for overcoming the solubility limit of hydroxides and carbonates commonly applied for neutralizing acidity in aqueous treatments. Moreover, hydroxide ions are released more gradually and have less mobility in nanoparticles dispersions as opposed to aqueous solutions, where free and highly mobile OH ions in excess are immediately disposable for interaction with alkali-sensitive cellulose (Calvini et al. 1988). The size of the particles plays a fundamental role: for instance, the surface area of a spherical microparticle (diameter of 1 µm) can be increased by a factor 10 dividing the same mass into spherical nanoparticles (diameter of 100 nm). A higher surface area grants higher reactivity to acids and carbon dioxide. The latter transforms the excess of hydroxides in carbonates, which are milder deacidifying agents that remain as a buffer against reoccurring acidity. Reducing the size of particles also allows obtaining stable dispersions in several solvents without using stabilizers (e.g. surfactants). Finally the reduced size favors penetration of the particles and limits the formation of surface deposit, such as white veils. The particles distribute homogeneously and adhere to cellulose fibers (see Fig. 6), possibly favored by the interaction between the positively charged surface of the particles and hydroxyl groups on cellulose (Giorgi et al. 2002a).
Fig. 6

SEM image of calcium hydroxide nanoparticles adhering to cellulose fibers; the panel in the right upper corner is an enlargement (2-fold). (Adapted with permission from Baglioni et al. (2013). Copyright © (2013) American Chemical Society)

For what concerns the solvents, short chain alcohols were initially selected (and are still used) as dispersing media because they exhibit several advantages: (i) they exhibit good wetting properties; (ii) they favor the dispersion of nanoparticles, probably due to the presence of a hydrophobic layer on the surface of the particles; this layer is formed upon physisorption of the alcohol hydroxyl group on the surface of particles (Ambrosi et al. 2001), resulting in inhibition of the particles face-to-face sticking (Fratini et al. 2007).

In the next sections, we will illustrate the main synthetic routes of nanoparticles dispersions, as well as the characterization of these systems and their application to deacidification of works of art throughout the last 15 years.

5.1 Synthesis of Alkaline Nanoparticles Dispersions

Several different strategies can be used to prepare inorganic particles. Synthetic methods are usually divided into top-down and bottom-up, based respectively on breaking particles down to the nanoscale, or on building up nanoparticles atom by atom (or molecule by molecule). A detailed description of the methods for the preparation of inorganic nanoparticles is beyond the scope of this chapter. Therefore, in this section, we will focus on the synthetic routes of alkaline nanoparticles for the pH control of cellulose-based artworks.

A bottom-up synthesis of calcium hydroxide nanoparticles from aqueous homogenous phase was the first method used for the preparation of an alkaline system to be used on paper and canvas artifacts (Giorgi et al. 2002a). Particles were obtained by adding an aqueous solution of sodium hydroxide to an aqueous solution of calcium chloride, both kept at 90 °C. The supersaturation degree (S) of the resulting solution was kept high, S being defined as:
$$ S = \frac{{\left[ {{\text{Ca}}^{2 + } } \right]}}{{\left[ {{\text{Ca}}^{2 + } } \right]_{sat} }} $$
where [Ca2+]sat is the concentration of Ca2+ ions in the Ca(OH)2 saturated solution. High values of S promote the nucleation of particles rather than their growth, leading to the formation of nanoparticles. After sedimentation, the particles are separated from the supernatant, and washed with lime water to remove sodium chloride, a byproduct of the reaction. The usage of lime water is necessary to avoid the growth of particles due to Ostwald ripening (Sugimoto 1978; Marqusee and Ross 1983). Calcium hydroxide nanoparticles obtained from these synthetic procedures show an average diameter of about 260 nm. Dispersions were prepared by mixing 10 g of particles with 1 L of 2-propanol, and used to control the pH of paper dating from the 14th, 17th, 19th and 20th century, which is representative of documents usually found in archives.

A completely different synthetic strategy for the preparation of calcium hydroxide nanoparticles was recently proposed (Poggi et al. 2014), based on a solvothermal reaction. The main advantage of this process relies in the possible future up-scale of the method, with great benefits in terms of costs. The use of dispersions obtained by the solvothermal process to hinder the degradation of cellulose-based materials will be discussed in Sect. 5.4.

As previously discussed, several state-of-the-art deacidification methods (e.g., Bookkeeper and PaperSave) are based on the usage of magnesium compounds as precursors for magnesium hydroxide, which then acts as the neutralizing agent. Alternatively, a coprecipitation reaction in aqueous solutions was achieved in 2005 (Giorgi et al. 2005) with the aim of synthesizing Mg(OH)2 nanoparticles to be dispersed in alcohols and directly applied on cellulose-based materials. Aqueous solutions of sodium hydroxide were added to solutions of different magnesium salts, such as sulfate, chloride, nitrate and perchlorate. The size of the obtained Mg(OH)2 particles range from ca. 50 to 200 nm, and was shown to be dependent on the counterions, following the Hofmeister anion series. Magnesium hydroxide nanoparticles were then dispersed in 2-propanol and applied by brushing on paper samples. The resistance of paper to photo-oxidative and hydrothermal aging was evaluated in terms of percentage of broken bonds in cellulose and tensile strength, showing that the nanoparticles dispersion is more efficient than the other state-of-the-art methods in preventing degradation.

A modified procedure to synthesize magnesium hydroxide nanoparticles has been recently proposed, where the removal of residual water (by drying) from particles before dispersion in propanol was demonstrated a key factor in further reducing the particles’ size. Particles obtained with this method were used to control the pH of paper containing metal-gall inks (see Sect. 5.4; Poggi et al. 2010).

5.2 Stabilization of Alkaline Nanoparticles Dispersions

To be applied for deacidification purposes, nanoparticles are typically dispersed in solvents. As previously indicated, solvents should be neither toxic to the operator nor dangerous for the environment; in addition to that, their compatibility with the original materials found in artifacts should be checked prior to application. The preparation of stable dispersions of solid particles in liquids can be achieved in several ways, commonly including the usage of stabilizers, mechanical stirring and sonication by ultrasound. It is worth noting that in the framework of works of art conservation, the usage of electrolytes and additives should be avoided, as it might result in the presence of salt efflorescence or residues on the treated artifacts. Therefore, ultrahomogenizer and ultrasonic treatments are preferred to improve the stability of particles in organic solvents. In some cases, for instance in solvothermal synthetic routes, the synthesis directly yields dispersed particles that exhibit good stability, e.g. several weeks. For what concerns nanoparticles obtained from a co-precipitation reaction (see previous section), it has been shown that the stability of dispersions depends on the presence of residual water from the synthesis, which interacts with hydroxide particles through hydrogen bonds, leading to particles’ aggregation (Fratini et al. 2007). Vacuum-drying of particles prior to their dispersion decreases crystal size (Poggi et al. 2010), thus enhancing the stability of dispersions. Besides particles’ size, stability is governed by different kinds of interactions, such as Van der Waals interactions, Coulombic interactions, steric interactions, hydrophobic forces and solvation forces (Luckham 2004). Coulombic interactions play a fundamental role in particular when nanoparticles of ionic solids (e.g. hydroxides) are considered, as these typically exhibit surface charges already after their preparation. When particles are dispersed in polar media, the particles surface charge influences the distribution of nearby ions. Some counterions are located close to the particles surface, defining the Stern layer, and the remainder is broadly distributed in the diffuse layer (see Fig. 7). The potential difference between the Stern plane and the diffuse layer is called the zeta-potential (Hunter 1981). Both the zeta potential and the thickness of the diffuse layer should not be too small, in order to favor repulsion between particles and increase the stability of the dispersions. When the concentration of ions in the solvent is high, both the thickness and the potential decrease, the repulsion between the particles is reduced, and stability is lowered.
Fig. 7

Negatively charged particles in a polar solvent. The Stern and diffuse double layer are indicated

Depending on the synthetic routes, the stability of the dispersions commonly used for deacidification purposes may range from several hours to months. It is worth noting that the stability of dispersions should be at least on the same timescale as the application onto artifacts, which normally requires from some minutes up to few hours. Another important factor is the reversibility of particles sedimentation. In many cases, after settling calcium and magnesium hydroxide nanoparticles can be easily re-dispersed again by gently shaking the container. After long storage time, sonication of dispersions might be used to favor the re-dispersion of settled nanoparticles in the organic solvent.

5.3 Characterization of Alkaline Nanoparticles Dispersions

Size, shape, polydispersity, specific area, superficial charge, composition and crystallinity, all are fundamental properties of the nanoparticles, which have to be characterized before application for conservation purposes. For what concerns solid particles, the crystallinity grade is usually assessed by XRD (X-Ray Diffractometry), while chemical composition and purity grade are commonly checked by Fourier-Transform InfraRed Spectroscopy (FTIR). Gas-porosimetry and Z-potential are used to measure the specific area of particles and their superficial charge distribution, respectively.

Microscopy techniques, such as Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) are widely used for the morphological investigation of particles. Besides information about morphology, surface texture, and roughness, SEM and TEM analysis can also be used for compositional analysis (SEM-EDS) and crystal structure determination (HR-TEM). It is worth noting that TEM provides a unique tool that allows direct visualization of particles (see Fig. 8) and can be used for obtaining size distribution and polydispersity of nanoparticles, even if the method requires careful considerations about the statistical significance of the obtained results (Pyrz and Buttrey 2008). In this respect, Dynamic Light Scattering (DLS) is to be considered the most important tool for the analysis of colloidal systems. In fact, this technique provides accurate particles size distribution and polydispersity, in a wide range of size, in a fast and simple way (Gabrowsky and Morrison 1983; Hassan et al. 2015).
Fig. 8

a TEM image of calcium hydroxide nanoparticles obtained from a solvothermal reaction in ethanol. (Reprinted with kind permission from Springer Science + Business Media. Poggi et al. (2010). Figure 1) b Calcium hydroxide nanoparticles obtained from a solvothermal reaction, dispersed in ethanol at 10 g/L

5.4 Application of Alkaline Nanoparticles Dispersions

Brushing or spraying dispersions of alkaline nanoparticles onto the surface of the cellulose-based artifacts are two methods commonly used to carry out a deacidification intervention (see Fig. 9).
Fig. 9

a Application (spraying) of calcium hydroxide nanoparticles dispersed in ethanol on a 16th century manuscript. b Optical microscope picture (magnification = 10×) of an inked area, before treatment with nanoparticles. c Optical microscope picture (magnification = 10×) of an inked area of the same manuscript, after treatment with calcium hydroxide nanoparticles dispersed in ethanol. [Printed with the kind permission of SELIDO (at IPCE, Instituto del Patrimonio Cultural de España, Madrid)]

When manuscripts and documents are treated, both sides of the paper sheets (recto and verso) should be treated if possible. Artworks can also be immersed in the dispersion. The choice of the most appropriate application procedure is usually made by conservators. As previously indicated, before any deacidification treatment, compatibility tests should be carried out, to check solvent interactions with the original components of artworks.

For the deacidification of cellulose-based artifacts, a concentration of 2.5 g/L usually grants the neutralization of present acidity and, at the same time, avoids the formation of white veils on the surface. The use of less concentrated nanoparticles dispersions is advisable when low porosity substrates, e.g. calendered paper, need to be treated.

Before applying the nanoparticles, pH measurements should be carried out on the artifacts. Several methods are commonly used to measure pH, including standardized procedures such as cold extraction (ASTM D788-97 2002; TAPPI T 509 Om-02 2002) and surface determination (TAPPI T 529 Om-04 2004). If pH is below 5.5, a deacidification intervention is advisable.

As previously indicated, hydroxide nanoparticles react with artworks acidity and, if in excess, turn into carbonate, which acts as a mild alkaline buffer against reoccurring acidity. The amount of particles applied can be tuned so to obtain a final pH of 7.0–8.0 after carbonation, as checked with pH measurements. This value is optimal for counteracting acidity and avoiding excessive alkalinity on cellulose fibers. More detailed information has been recently provided by Baglioni et al. (2015) regarding application procedures and examples of quantities typically applied in paper deacidification.

Finally, it must be noticed that the carbonation of hydroxide nanoparticles depends upon several factors including temperature, relative humidity and carbon dioxide concentration. In standard conditions (room temperature, RH = 60 %), full carbonation requires approximately two weeks.

5.5 Case Studies

In this section we will discuss some recent case studies on the use of nanomaterials for the pH control of cellulose-based artifacts.

As previously stated, the corrosion of documents featuring metal gall inks is due to the concomitant action of sulfuric acid and free metal ions, which pose a threat to the preservation of manuscripts and archival material. In 2010, Poggi et al. proposed the synthesis and use of magnesium hydroxide nanoparticles dispersed in 2-propanol for the inhibition of both mechanisms involved in cellulose corrosion due to iron gall inks (Poggi et al. 2010). The rationale for the treatment is the following: alkaline nanoparticles readily react with sulfuric acid and, if in excess, turn into carbonate that is milder to alkali-sensitive cellulose fibers. In fact, the quantity of applied nanoparticles can be feasibly tuned to obtain a final pH of 7–8, which hinders acid-catalyzed hydrolysis of cellulose. A pH value around neutrality is also fundamental in hindering the oxidation of cellulose induced by iron and copper ions, whose catalytic activity is minimal when pH is around 7–7.5 (Strlič et al. 2003). Mg(OH)2 nanoparticles in alcohol were applied on Whatman filter paper samples that had been brushed with metal and iron gall inks. Both deacidified and untreated inked samples were aged under severe hydrothermal conditions (RH = 75 % and T = 90 °C) for up to 48 h. When inked paper is not protected with the nanoparticles, this aging protocol causes a degradation of cellulose in terms of scissored glycosidic bonds that is representative of that found in historical samples (final DP lower than 300). On the other hand, the number of scissored glycosidic bonds over time was drastically reduced when the neutralizing dispersions are applied prior to aging of the samples (Fig. 10).
Fig. 10

a, b Whatman filter paper featuring metal gall ink after 48 h of artificial aging. While the untreated sample is fragile and cannot be manipulated (a), paper deacidified prior to aging using magnesium hydroxide nanoparticles retains the original mechanical resistance (b). Degradation curves showing the percentage of glycosidic bonds scissored (S) upon aging on untreated sample (c) and deacidified sample (d). The visual aspect reflects the difference in degradation curves. (Adapted with permission from Poggi et al. (2010). Copyright © (2010) American Chemical Society)

Macroscopically, at the end of the aging the deacidified samples retained their original mechanical resistance, while untreated samples showed dramatic discoloration and severe mechanical failure. Overall this showed that an enduring stabilization of pH around neutrality is effective in preventing cellulose fibers degradation in manuscripts that feature metal and iron gall inks.

One of the recent upgrades of this methodology is the investigation of hybrid systems where the nanoparticles dispersions are mixed to gelatin and applied onto paper that already exhibits reduced mechanical properties. In fact, hydroalcoholic solutions of gelatin are commonly used in paper conservation for the lamination of manuscripts fragments, carried out by gluing Japanese paper tissue to the degraded paper sheets. The mechanical resistance of degraded manuscript is thus increased. In order to prevent the degradation of the laminated manuscript, nanoparticles can be easily added to the hydroalcoholic solutions of gelatin, creating a combined treatment that allows mechanical strengthening and hampering of cellulose degradation. Preliminary test conducted on mockups samples and on 16th and 18th century manuscripts showed that the combined method may improve on the traditional conservation method, prolonging the useful life of historical manuscripts and granting, at the same time, their manipulation (Poggi et al. 2015).

As mentioned in the previous section, dispersions of calcium hydroxide nanoparticles have been recently obtained using a two-step solvothermal process (Poggi et al. 2014). The first step of the reaction consists in the oxidation of calcium metal by short chain alcohol, such as ethanol and 1-propanol, resulting in the formation of the corresponding alkoxide. Addition of water to the reaction bulk induces the precipitation of colloidal calcium hydroxide, meaning that these nanoparticles can be synthesized as dispersed in alcohol and directly applied without any further processing. Another interesting feature of this synthetic route is the possibility of obtaining highly concentrated dispersions (about 35 g/L), which in turn is essential for the upscale of the production, with great benefits in terms of cost. Nanoparticles obtained via solvothermal reaction consisted of highly crystalline platelets of Portandite, having an average diameter below 300 nm for the system dispersed in 1-propanol and 80 nm for the system in ethanol, and a thickness of about 20–30 nm (Fig. 11).
Fig. 11

a Size distribution of calcium hydroxide nanoparticles dispersed in 1-propanol obtained by DLS. b XRPD of calcium hydroxide nanoparticles synthesized in ethanol (black line) and in 1-propanol (grey line). Stars correspond to the peaks of Portlandite, used as a reference. (Reprinted with kind permission from Springer Science + Business Media. Poggi et al. (2014), Figs. 3 and 4)

These calcium hydroxide nanoparticles were applied on artificially acidified Whatman paper samples, which were then subjected to severe hydrothermal conditions. In acidic samples, the increase of bonds scissions in cellulose chains during aging has an initial linear shape that is followed by a deceleration toward a horizontal asymptote, corresponding to the reaching of the LODP (see Sect. 2.1). This pattern is typically showed by autocatalytic degradation mechanisms (Calvini et al. 2007, 2008). Instead, the degradation plots over time obtained for deacidified paper samples, highlight that the treatment with Ca(OH)2 nanoparticles increases the resistance of samples to aging (see Fig. 12). Paper samples were also analyzed using Differential Thermo Gravimetry (DTG), which allows determining the pyrolysis temperature of cellulose (Tp), used as an indicator of the paper’s conservation status (Soares et al. 1995; Franceschi et al. 2001; Sandu et al. 2003).
Fig. 12

a Degradation curves showing the scissions per initial cellulose chain (S*) occurred upon aging of acidified paper sample (P_Ac), and of acidified paper neutralized with calcium hydroxide nanoparticles in ethanol and in 1-propanol (respectively, P_E and P_1P). The lines show the trends for each system. b Thermal analyses on paper samples: comparison after 48 h of aging between acidified paper (P_Ac) and acidified paper neutralized with calcium hydroxide nanoparticles in ethanol and in 1-propanol (P_E and P_1P). (Reprinted with kind permission from Springer Science + Business Media. Poggi et al. (2014), Figs. 6 and 7)

Acidification of Whatman paper lowered cellulose Tp of about 35 °C as compared to pristine samples. As can be seen in Fig. 12, treatment of acidic paper with nanoparticles (either dispersed in ethanol or propanol) kept cellulose Tp 20 °C higher than that of non-protected acidic samples throughout 48 h of aging. As a matter of fact, neutralization of acidity inhibits the dehydration of cellulose, which is the first step of the thermal degradation process (Fengel and Wegener 1984). In addition to that, it has been hypothesized that bivalent calcium ions are capable of interacting with cellulose carboxylate groups (formed upon neutralization of carboxylic groups). These interactions could create a network between the deacidified cellulose chains, increasing both paper resistance to thermal degradation (Bukovský 2000; Baglioni et al. 2012) and to folding, which has been observed during tests on treated paper samples.

As previously discussed, manuscripts featuring iron and metal gall inks exhibit good compatibility with alcohols, and can be successfully treated using formulations of calcium and magnesium nanoparticles both in ethanol and in 2-propanol. On the contrary, only few available treatments can be safely used on contemporary drawings or contemporary artworks on paper. As a matter of fact, during the 20th century, the notion of drawing underwent great changes. The use of paper changed from a simple support for studies or sketches to form the basis for autonomous work, at times torn, burnt, folded, perforated, twisted or scraped. At the same time a large number of new media, such as acrylic and vinyl resins, pressure sensitive adhesives, ballpoint and felt-tip pens and markers, entered the world of art. All of these media are rarely compatible with traditional restoration procedures. This makes the conservation and restoration of of contemporary drawings a widely unexplored field.

Calcium hydroxide nanoparticles obtained by the solvothermal process exhibit another interesting feature, i.e. their dispersibility in apolar solvents such as alkanes. A good candidate is cyclohexane, which is a colorless, volatile, nonpolar liquid. Due to its high volatility, the spraying of the solvent guarantees a fast and simple application. Moreover, owing to its nonpolar character, cyclohexane does not affect cellulose fibers and does not cause solubilization of several modern inks (see, for instance, Fig. 13).
Fig. 13

Application of calcium hydroxide nanoparticles dispersed in cyclohexane on paper inked with a red felt-tip pen. The use of cyclohexane prevents bleeding or leaching of the ink; moreover, no white veil is observed after the evaporation of the solvent

Therefore, even in the case of creased or folded paper, such as Simon Schubert, Kiki Smith or Stefano Arienti artworks, the treatment will not cause any changes in the original visual aspect of the object. Promising results obtained on preliminary laboratory tests led to the application of this innovative formulation on contemporary drawings from a private collection, potentially paving the way for the treatment of a significant portion of contemporary artworks.

To conclude, dispersions of nanoparticles in non aqueous solvents have proven in the last fifteen years as feasible and effective tools for the preservation of cellulose-based artifacts. As a matter of fact, these systems are able to counteract the main degradation mechanisms affecting cellulose (acid-catalyzed hydrolysis and oxidation), and represent valid alternatives to traditional conservation treatments. Moreover, the potential applications of nanomaterials in this field have been recently expanded, with new perspectives opened by the preparation of nanoparticles-polymer hybrid systems and by the dispersion of nanoparticles in inert solvents.



This work was partly funded by NANOFORART – Nano-materials for the conservation and preservation of movable and immovable artworks, FP7-NMP European project, (; and by NANORESTART, NANO materials for the REStoration of works of ART, H2020-NMP-2014 project (


  1. Afsharpour M, Hadadi M (2014) Titanium dioxide thin film: environmental control for preservation of paper-art-works. J Cult Herit 15:569–574. doi: 10.1016/j.culher.2013.10.008 CrossRefGoogle Scholar
  2. Altaner CM, Thomas LH, Fernandes AN, Jarvis MC (2014) How cellulose stretches: synergism between covalent and hydrogen bonding. Biomacromolecules 15:791–798.
  3. Ambrosi M, Dei L, Giorgi R, Neto C, Baglioni P (2001) Stable dispersions of Ca(OH)2 in aliphatic alcohols: properties and application in cultural heritage conservation. In: Koutsoukos PG (ed) Trends in colloid and interface science XV. Springer, Berlin, pp 68–72CrossRefGoogle Scholar
  4. ASTM D788-97 (2002) Standard test methods for hydrogen ion concentration (pH) of paper extracts (hot-extraction and cold-extraction procedures)Google Scholar
  5. Atalla RH, Vanderhart DL (1984) Native cellulose: a composite of two distinct crystalline forms. Science 223:283–285. doi: 10.1126/science.223.4633.283 CrossRefGoogle Scholar
  6. Baglioni P, Chelazzi D, Giorgi R, Poggi G (2012) Nanoparticles for the conservation of cultural heritage: paper and wood. In: Somasundaran P (ed) Encyclopedia of surface and colloid science, 2nd edn. Taylor & Francis, New York, pp 1–16Google Scholar
  7. Baglioni P, Chelazzi D, Giorgi R, Poggi G (2013) Colloid and materials science for the conservation of cultural heritage: cleaning, consolidation, and deacidification. Langmuir 29:5110–5122Google Scholar
  8. Baglioni P, Chelazzi D, Giorgi R (2015) Nanotechnologies in the conservation of cultural heritage—a compendium of materials and techniquesGoogle Scholar
  9. Banait NS, Jencks WP (1991) Reactions of anionic nucleophiles with alpha-D-glucopyranosyl fluoride in aqueous solution through a concerted, ANDN (SN2) mechanism. J Am Chem Soc 113:7951–7958. doi: 10.1021/ja00021a021 CrossRefGoogle Scholar
  10. Barrow WJ, Sproull RC (1959) Permanence in book papers: investigation of deterioration in modern papers suggests a practical basis for remedy. Science 80–129:1075–1084. doi: 10.1126/science.129.3356.1075
  11. Baty JW, Maitland CL, Minter W, Hubbe MA, Jordan-Mowery SK (2010) Deacidification for the conservation and preservation of paper-based works: a review. BioResources 5:1955–2023Google Scholar
  12. Bégin P, Deschâtelets S, Grattan D, Gurnagul N, Iraci J, Kaminska E, Woods D, Zou X (1998) The impact of Lignin on paper permanence. A comprehensive study of the ageing behaviour of handsheets and commercial paper samples. Restaurator 19:135–154. doi: 10.1515/rest.1998.19.3.135 Google Scholar
  13. Bicchieri M, Brusa P (1997) The bleaching of paper by reduction with the borane tert-butylamine complex. Restaurator 18:1–11. doi: 10.1515/rest.1997.18.1.1 Google Scholar
  14. Bicchieri M, Bella M, Semetilli F (1999) A quantitative measure of borane tert-butylamine complex effectiveness in carbonyl reduction of aged papers. Restaurator 20:22–29. doi: 10.1515/rest.1999.20.1.22 Google Scholar
  15. Bicchieri M, Sementilli FM, Sodo A (2000) Application of seven borane complexes in paper conservation. Restaurator 21:213–228. doi: 10.1515/REST.2000.213 Google Scholar
  16. Blüher A, Grossenbacher G (eds) (2006) Save paper! mass deacidification, today’s experiences, tomorrow’s perspectives: paper given at the international conference, 15–17 Feb 2006. Swiss National Library, BernGoogle Scholar
  17. Boone T, Kidder L, Russick S (1998) Bookkeeper® for spray use in single item treatments, 17Google Scholar
  18. Botti L, Mantovani O, Ruggiero D (2005) Calcium Phytate in the Treatment of Corrosion Caused by Iron Gall Inks: Effects on Paper. Restaurator 26:44–62. doi:  10.1515/REST.2005.44
  19. Bronzato M, Calvini P, Federici C, Bogialli S, Favaro G, Meneghetti M, Mba M, Brustolon M, Zoleo A (2013) Degradation products from naturally aged paper leaves of a 16th-century-printed book: a spectrochemical study. Chemistry 19:9569–9577. doi: 10.1002/chem.201300756 CrossRefGoogle Scholar
  20. Bukovský V (2000) The influence of light on ageing of newsprint paper. Restaurator 21:55–76. doi: 10.1515/REST.2000.55 Google Scholar
  21. Calvini P (2005) The influence of levelling-off degree of polymerisation on the kinetics of cellulose degradation. Cellulose 12:445–447. doi: 10.1007/s10570-005-2206-z CrossRefGoogle Scholar
  22. Calvini P (2014) On the meaning of the Emsley, Ding & Wang and Calvini equations applied to the degradation of cellulose. Cellulose 21:1127–1134. doi: 10.1007/s10570-014-0224-4 CrossRefGoogle Scholar
  23. Calvini P, Gorassini G (2012) Surface and bulk reactions of cellulose oxidation by periodate. A simple kinetic model. Cellulose 19:1107–1114Google Scholar
  24. Calvini P, Grosso V, Hey M, Rossi L, Santucci L (1988) Deacidification of paper—a More fundamental approach. Pap Conserv 12:35–39. doi: 10.1080/03094227.1988.9638560 CrossRefGoogle Scholar
  25. Calvini P, Gorassini A, Merlani AL (2007) Autocatalytic degradation of cellulose paper in sealed vessels. Restaurator 28:47–54Google Scholar
  26. Calvini P, Gorassini A, Merlani AL (2008) On the kinetics of cellulose degradation: looking beyond the pseudo zero order rate equation. Cellulose 15:193–203. doi: 10.1007/s10570-007-9162-8 CrossRefGoogle Scholar
  27. Carter HA (1989) Chemistry in the comics: part 3. The acidity of paper. J Chem Educ 66:883. doi: 10.1021/ed066p883 CrossRefGoogle Scholar
  28. Carter H, Bégin P, Grattan D (2000) Migration of volatile compounds through stacked sheets of paper during accelerated ageing—part 1: acid migration at 90°. C Restaurator. doi: 10.1515/REST.2000.77 Google Scholar
  29. Chamberlain D (2007) Anion mediation of aluminium-catalysed degradation of paper. Polym Degrad Stab 92:1417–1420. doi: 10.1016/j.polymdegradstab.2007.04.006 CrossRefGoogle Scholar
  30. Coughlan MP (1991) Mechanisms of cellulose degradation by fungi and bacteria. Anim Feed Sci Technol 32:77–100. doi: 10.1016/0377-8401(91)90012-H CrossRefGoogle Scholar
  31. Dobrodskaya TV, Egoyants PA, Ikonnikov VK, Romashenkova ND, Sirotin SA, Dobrusina SA, Podgornaya NI (2004) Treatment of paper with basic agents in alcohols and supercritical carbon dioxide to neutralize acid and prolong storage time. Russ J Appl Chem 77:2017–2021. doi: 10.1007/s11167-005-0211-5 CrossRefGoogle Scholar
  32. Dufour J, Havermans JBGA (2001) Study of the photo-oxidation of mass-deacidified papers. Restaurator. doi: 10.1515/REST.2001.20 Google Scholar
  33. Dupont (2002) The role of gelatine/alum sizing in the degradation of paper: a study by size exclusion chromatography in lithium chloride/N,N-dimethylacetamide using multiangle light scattering detection. In: Daniels V, Donnithorne A, Smith P (eds) Preprint of IIC Baltimore congress 2002, works of art on paper, books, documents and photographs: techniques and conservation. International Institute for Conservation, Baltimore, pp 59–64Google Scholar
  34. Feller (1994) Accelerated ageing in conservation science. Getty Conservation Institute, Los AngelesGoogle Scholar
  35. Fengel D, Wegener G (1984) Wood: chemistry, ultrastructure, reactions. Walter De Gruyter, BerlinGoogle Scholar
  36. Franceschi E, Palazzi D, Pedemonte E (2001) Thermoanalytical contribution to the study on paper degradation. characterisation of oxidised paper. J Therm Anal Calorim 66:349–358CrossRefGoogle Scholar
  37. Fratini E, Page MG, Giorgi R, Cölfen H, Baglioni P, Demé B, Zemb T (2007) Competitive surface adsorption of solvent molecules and compactness of agglomeration in calcium hydroxide nanoparticles. Langmuir 23:2330–2338. doi: 10.1021/la062023i CrossRefGoogle Scholar
  38. Gabrowsky E, Morrison I (1983) Particle size distributions from analysis of quasi-elastic light scattering data. In: Dahneke BE (ed) Wiley-Interscience, New YorkGoogle Scholar
  39. Giorgi R, Dei L, Ceccato M, Schettino C, Baglioni P (2002a) Nanotechnologies for conservation of cultural heritage: paper and canvas deacidification. Langmuir 18:8198–8203. doi: 10.1021/la025964d CrossRefGoogle Scholar
  40. Giorgi R, Dei L, Schettino C, Baglioni P (2002b) A new method for paper deacidification based on calcium hydroxide dispersed in nonaqueous media. In: Daniels V, Donnithorne A, Smith P (eds) Preprint of IIC Baltimore congress 2002, works of art on paper, books, documents and photographs: techniques and conservation. International Institute for Conservation, Baltimore, pp 69–73Google Scholar
  41. Giorgi R, Bozzi C, Dei L, Gabbiani C, Ninham BW, Baglioni P (2005) Nanoparticles of Mg(OH)2: synthesis and application to paper conservation. Langmuir 21:8495–8501. doi: 10.1021/la050564m CrossRefGoogle Scholar
  42. Glasser WG, Atalla RH, Blackwell J, Malcolm Brown R, Burchard W, French AD, Klemm DO, Nishiyama Y (2012) About the structure of cellulose: debating the Lindman hypothesis. Cellulose 19:589–598. doi: 10.1007/s10570-012-9691-7 CrossRefGoogle Scholar
  43. Grøntoft T, Odlyha M, Mottner P, Dahlin E, Lopez-Aparicio S, Jakiela S, Scharff M, Andrade G, Obarzanowski M, Ryhl-Svendsen M, Thickett D, Hackney S, Wadum J (2010) Pollution monitoring by dosimetry and passive diffusion sampling for evaluation of environmental conditions for paintings in microclimate frames. J Cult Herit 11:411–419. doi: 10.1016/j.culher.2010.02.004 CrossRefGoogle Scholar
  44. Harris JF (1975) Acid hydrolysis and dehydration reactions for utilizing plant carbohydrates. Appl Polym Symp 28:131Google Scholar
  45. Hassan PA, Rana S, Verma G (2015) Making sense of brownian motion: colloid characterization by dynamic light scattering. Langmuir 31:3–12. doi: 10.1021/la501789z CrossRefGoogle Scholar
  46. Henniges U, Reibke R, Banik G, Huhsmann E, Hähner U, Prohaska T, Potthast A (2008) Iron gall ink-induced corrosion of cellulose: aging, degradation and stabilization. Part 2: application on historic sample material. Cellulose 15:861–870. doi: 10.1007/s10570-008-9238-0 CrossRefGoogle Scholar
  47. Hunter RJ (1981) Zeta Potential in Colloid Science. Elsevier, LondonGoogle Scholar
  48. Kolar J (1997) Mechanism of autoxidative degradation of cellulose. Restaurator 18:163–176. doi: 10.1515/rest.1997.18.4.163 Google Scholar
  49. Kolar J, Strlič M, Budnar M, Malesič J, Šelih VS, Simčič J (2003) Stabilisation of corrosive iron gall inks. Acta Chim Slov 50:763–770Google Scholar
  50. Kolar J, Šala M, Strlič M, Šelih VS (2005) Stabilisation of Paper Containing Iron-Gall Ink with Current Aqueous Processes. Restaurator 26:181–189. doi:  10.1515/rest.2005.26.3.181
  51. Kolar J, Možir A, Strlič M, de Bruin G, Pihlar B, Steemers T (2007) Stabilisation of iron gall ink: aqueous treatment with magnesium phytate. e-Preservation Sci 4:19–24Google Scholar
  52. Kolar J, Možir A, Balažic A, Strlič M, Ceres G, Conte V, Mirruzzo V, Steemers T, de Bruin G (2008) New antioxidants for treatment of transition metal containing inks and pigments. Restaurator 29:184–198. doi: 10.1515/rest.2008.013 Google Scholar
  53. Lopez-Aparicio S, Grøntoft T, Odlyha M, Dahlin E, Mottner P, Thickett D, Ryhl-Svendsen M, Schmidbauer N, Scharff M (2010) Measurement of organic and inorganic pollutants in microclimate frames for paintings. e-Preservation Sci 7:59–70Google Scholar
  54. Lucarelli F, Mandò PA (1996) Recent applications to the study of ancient inks with the Florence external-PIXE facility. Nucl Instruments Methods Phys Res Sect B Beam Interact with Mater Atoms 109–110:644–652. doi: 10.1016/0168-583X(95)00985-X CrossRefGoogle Scholar
  55. Luckham PF (2004) Manipulating forces between surfaces: applications in colloid science and biophysics. Adv Colloid Interface Sci 111:29–47. doi: 10.1016/j.cis.2004.07.008 CrossRefGoogle Scholar
  56. Lundgaard LE, Hansen W, Linhjell D, Painter TJ (2004) Aging of oil-impregnated paper in power transformers. Power Deliv IEEE Trans 19:230–239CrossRefGoogle Scholar
  57. Malesič J, Kolar J, Strlič M (2002) Effect of pH and carbonyls on the degradation of alkaline paper factors affecting ageing of alkaline paper. Restaurator 23:145–153. doi: 10.1515/REST.2002.145 Google Scholar
  58. Malešič J, Strlič M, Kolar J, Polanc S (2005a) The influence of halide and pseudo-halide antioxidants in Fenton-like reaction systems containing copper(II) ions. J Mol Catal A: Chem 241:126–132. doi: 10.1016/j.molcata.2005.06.047 CrossRefGoogle Scholar
  59. Malešič J, Kolar J, Strlič M, Polanc S (2005b) The use of halides for stabilisation of iron gall ink containing paper—the pronounced effect of cation. e-Preservation Sci 2:13–18Google Scholar
  60. Marqusee JA, Ross J (1983) Kinetics of phase transitions: theory of Ostwald ripening. J Chem Phys 79:373–378. doi: 10.1063/1.445532 CrossRefGoogle Scholar
  61. McKellar JF, Allen NS (1979) Photochemistry of man-made polymers. Elsevier, LondonGoogle Scholar
  62. Medronho B, Romano A, Miguel MG, Stigsson L, Lindman B (2012) Rationalizing cellulose (in)solubility: reviewing basic physicochemical aspects and role of hydrophobic interactions. Cellulose 19:581–587. doi: 10.1007/s10570-011-9644-6 CrossRefGoogle Scholar
  63. Meyer KH, Misch L (1937) Positions des atomes dans le nouveau modele spatial de la cellulose. Helv Chim Acta 20:232–244. doi: 10.1002/hlca.19370200134 CrossRefGoogle Scholar
  64. Neevel JG (1995) Phytate: a potential conservation agent for the treatment of ink corrosion caused by Irongall Inks. Restaurator 16:143–160. doi: 10.1515/rest.1995.16.3.143 Google Scholar
  65. Neevel JG (2000) (Im)possibilities of the phytate treatment. In: Brown JE (ed) Newcastle upon Tyne. The University of Northumbria, pp 127–134Google Scholar
  66. Neevel JG, Mensch CTJ, Cornelis TJ (1999) The behaviour of iron and sulphuric acid during iron gall ink corrosion. In: Bridgland J (ed) ICOM committee for conservation triennial meeting. James and James, London, pp 528–533Google Scholar
  67. Nisizawa K (1973) Mode of action of cellulases. J Ferment Technol 51:267–304Google Scholar
  68. Park S, Baker JO, Himmel ME, Parilla PA, Johnson DK (2010) Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance. Biotechnol Biofuels 3:10. doi: 10.1186/1754-6834-3-10 CrossRefGoogle Scholar
  69. Pauk S (1996) Bookkeeper mass deacidification process—some effects on 20th-century library material. Abbey Newsl 20:50–53Google Scholar
  70. Persson H, Türk M, Nyman M, Sandberg A-S (1998) Binding of Cu2+, Zn2+, and Cd2+ to Inositol Tri-, Tetra-, Penta-, and Hexaphosphates. J Agric Food Chem 46:3194–3200. doi:  10.1021/jf971055w
  71. Poggi G, Giorgi R, Toccafondi N, Katzur V, Baglioni P (2010) Hydroxide nanoparticles for deacidification and concomitant inhibition of iron-gall ink corrosion of paper. Langmuir 26:19084–19090. doi: 10.1021/la1030944 CrossRefGoogle Scholar
  72. Poggi G, Toccafondi N, Melita LN, Knowles JC, Bozec L, Giorgi R, Baglioni P (2014) Calcium hydroxide nanoparticles for the conservation of cultural heritage: new formulations for the deacidification of cellulose-based artifacts. Appl Phys A 114:685–693. doi: 10.1007/s00339-013-8172-7 CrossRefGoogle Scholar
  73. Poggi G, Sistach MC, Marin E, Garcia JF, Giorgi R, Baglioni P (2015) The GEOLNAN, a combined deacidification and reinforcement treatment for metal gall ink manuscriptsGoogle Scholar
  74. Potthast A, Henniges U, Banik G (2008) Iron gall ink-induced corrosion of cellulose: aging, degradation and stabilization. Part 1: model paper studies. Cellulose 15:849–859. doi:  10.1007/s10570-008-9237-1
  75. Pyrz WD, Buttrey DJ (2008) Particle size determination using TEM: a discussion of image acquisition and analysis for the novice microscopist. Langmuir 24:11350–11360. doi: 10.1021/la801367j CrossRefGoogle Scholar
  76. Rydholm S (1965) Pulping processes. Interscience Publisher, New YorkGoogle Scholar
  77. Sandu ICA, Brebu M, Luca C, Sandu I, Vasile C (2003) Thermogravimetric study on the ageing of lime wood supports of old paintings. Polym Degrad Stab 80:83–91. doi: 10.1016/S0141-3910(02)00386-5 CrossRefGoogle Scholar
  78. Sanna C, Sodo A, Laguzzi G, Mancini G, Bicchieri M (2009) Tert-butyl amine borane complex: an unusual application of a reducing agent on model molecules of cellulose based materials. J Cult Herit 10:356–361. doi: 10.1016/j.culher.2008.10.008 CrossRefGoogle Scholar
  79. Santucci L, Zappalà MP (2001) Cellulose viscometric oxidometry. Restaurator 22:51–65. doi: 10.1515/REST.2001.51 Google Scholar
  80. Šelih VS, Strlič M, Kolar J, Pihlar B (2007) The role of transition metals in oxidative degradation of cellulose. Polym Degrad Stab 92:1476–1481. doi: 10.1016/j.polymdegradstab.2007.05.006 CrossRefGoogle Scholar
  81. Sequeira S, Casanova C, Cabrita EJ (2006) Deacidification of paper using dispersions of Ca(OH)2 nanoparticles in isopropanol. Study of efficiency. J Cult Herit 7:264–272. doi: 10.1016/j.culher.2006.04.004 CrossRefGoogle Scholar
  82. Shanani CJ, Harrison G (2002) Spontaneous formation of acids in the natural aging of paper. In: Daniels V, Donnithorne A, Smith P (eds) Works of art on paper: books, documents and photographs. International Institute for Conservation of Historic and Artistic Works, London, pp 189–192Google Scholar
  83. Sjostrom E (1977) TAPPI J 60:151Google Scholar
  84. Soares S, Camino G, Levchik S (1995) Comparative study of the thermal decomposition of pure cellulose and pulp paper. Polym Degrad Stab 49:275–283. doi: 10.1016/0141-3910(95)87009-1 CrossRefGoogle Scholar
  85. Stefanis E, Panayiotou C (2007) Protection of lignocellulosic and cellulosic paper by deacidification with dispersions of micro- and nano-particles of Ca(OH)2 and Mg(OH)2 in alcohols. Restaurator 28:185–200. doi: 10.1515/REST.2007.185 Google Scholar
  86. Strlič M, Kolar J (eds) (2005) Ageing and stabilization of paper. National and University Library, LjubljanaGoogle Scholar
  87. Strlič M, Kolar J, Žigon M, Pihlar B (1998) Evaluation of size-exclusion chromatography and viscometry for the determination of molecular masses of oxidised cellulose. J Chromatogr A 805:93–99. doi: 10.1016/S0021-9673(98)00008-9 CrossRefGoogle Scholar
  88. Strlič M, Kolar J, Šelih VS, Kocar D, Pihlar B (2003) A comparative study of several transition metals in Fenton-like reaction system at circumneutral. Acta Chim Slov 50:619–632Google Scholar
  89. Sugimoto T (1978) General kinetics of Ostwald ripening of precipitates. J Colloid Interface Sci 63:16–26. doi: 10.1016/0021-9797(78)90030-9 CrossRefGoogle Scholar
  90. TAPPI T 509 Om-02 (2002) Hydrogen ion concentration (pH) of paper extracts (cold extraction method)Google Scholar
  91. TAPPI T 529 Om-04 (2004) Surface pH measurement of paperGoogle Scholar
  92. Tétreault J (2003) Airborne pollutants in museums, galleries and archives: risk assessment, control strategies and preservation management. Canadian Conservation Institute, OttawaGoogle Scholar
  93. Tétreault J, Stamatopoulou E (1997) Determination of concentrations of acetic acid emitted from wood coatings in enclosures. Stud Conserv 42:141–156. doi: 10.2307/1506710 Google Scholar
  94. Tse S, Bégin P, Kaminska E (2002) Highlights of paper research at the Canadian Conservation Institute. International Institution for Conservation of Historic and Artistic Works, London, pp 193–198Google Scholar
  95. Wilkie JS (1961) Carl Nägeli and the fine structure of living matter. Nature 190:1145–1150. doi: 10.1038/1901145a0 CrossRefGoogle Scholar
  96. Wouters J (2008) Coming soon to a library near you? Science 80–322:1196–1198. doi: 10.1126/science.1164991
  97. Yanjuan W, Yanxiong F, Wei T, Chunying L (2013) Preservation of aged paper using borax in alcohols and the supercritical carbon dioxide system. J Cult Herit 14:16–22. doi: 10.1016/j.culher.2012.02.010 CrossRefGoogle Scholar
  98. Zappalà A, Stefani C De (2005) Evaluation of the Effectiveness of Stabilization Methods. Treatments by Deacidification, Trehalose, Phytates on Iron Gall Inks. Restaurator 26:36–43. doi:  10.1515/REST.2005.36
  99. Zervos S (2010) Natural and accelerated ageing of cellulose and paper: a literature review. In: Lejeune A, Deprez T (eds) Cellulose: structure and properties, derivatives and industrial uses. Nova Science Publishers Inc, New YorkGoogle Scholar
  100. Zhang Y, Bommuswamy J, Sinnott ML (1994) Kinetic isotope effect study of transition states for the hydrolyses of alpha- and beta-glucopyranosyl fluorides. J Am Chem Soc 116:7557–7563. doi: 10.1021/ja00096a012 CrossRefGoogle Scholar
  101. Zumbühl S, Wuelfert S (2001) Chemical aspects of the bookkeeper deacidification of cellulosic materials: the influence of surfactants. Stud Conserv 46:169–180. doi: 10.2307/1506808 Google Scholar

Copyright information

© Atlantis Press and the author(s) 2016

Authors and Affiliations

  • Piero Baglioni
    • 1
  • David Chelazzi
    • 1
  • Rodorico Giorgi
    • 1
  • Huiping Xing
    • 1
  • Giovanna Poggi
    • 1
  1. 1.Department of Chemistry and CSGIUniversity of FlorenceFlorenceItaly

Personalised recommendations