Stabilization of copper- and iron-containing papers in mildly alkaline environment

Multi-Analytical Study of Copper-Based Historic Pigments and their Alteration Products

Copper-containing materials such as verdigris are commonly found in historic and artistic works of art, often at advanced states of decay. Applied on paper as inks and watercolors, many of which needed a binder such as gum arabic, the intrinsic instability of this pigment was known since the medieval period. The decay of verdigris (a mixture of copper acetates) as a pigment, as watercolor, and as a dye, was studied using a combination of vibrational (Fourier transform infrared) and X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) instrumental techniques. Changes in the copper oxidative states and the formation of copper oxide were monitored during accelerated degradation as powdered solids and applied on mockup samples (with and without binder). Accelerated aging of both commercially available and synthesized verdigris pigments showed the presence of an intermediate species, Cu(CH₃COO)₂•3Cu(OH)₂•2H₂O, which points to the beginning of the decay processes, that culminates in the formation of Cu(II) oxide. However, the presence of gum arabic seems to delay deterioration, by temporarily reducing Cu(II) to Cu(I), even when the final product includes Cu(II). This novel application of XPS and supporting techniques has significant implications in art conservation, as the identified behavior helps explain the better preservation state of some works of art.

Microscopic characterization of acidic paper manuscripts

Purpose

This paper aims to investigate the effect of acidity on the morphology of archeological paper, especially in the presence of colors and whether natural pigments play a role in the process of degradation.

Design/methodology/approach

The morphological changes in the cellulosic fibers of the manuscripts because of acidity were investigated using environmental scanning electron microscope (ESEM). Ten historical samples were collected from different manuscripts suffering from acidity. X-ray diffraction was used to identify the inks and pigments that were used in some samples. Additionally, Fourier transform infrared microscopy was used to identify the binding medium.

Findings

The results confirmed that carbon ink, ultramarine, cinnabar and gold pigments were applied to some manuscripts with Arabic gum. As for ESEM investigation, the results proved that acidity badly affected the integrity of the cellulosic fibers resulting in their embrittlement. The micrographs showed differences in fiber degradation according to pH value. The presence of inks and pigments increased the degradation extent resulting from acidity.

Originality/value

This paper addresses a specific need to study the behavior of degradation in paper manuscripts, thus helping the conservators find solutions to the phenomenon.

Evaluation of Alkaline Compounds Used for Deacidification and Simultaneous Lining of Extremely Degraded Manuscripts

Iron gall ink’s natural acidity promotes the degradation of manuscripts. This process mostly affects the areas containing ink, causing fragility of the paper carrier that limits its manipulation. The cellulosic material is modified by two chemical reactions, acidic hydrolysis and oxidation, both depending on the pH of the paper. This article explores the distribution of acidity in manuscripts and its link to iron gall ink corrosion and cellulose degradation. Subsequently, different treatment methods of deacidification, specifically designed for extremely degraded paper documents and sheets bound in volumes were tested. Documents were deacidified and at the same time mechanically supported, using an alkaline compound for deacidification that increases the pH to a range at which iron ion oxidation is decreased. Three alkaline compounds at different concentrations were evaluated: (1) calcium carbonate microparticles, (2) calcium hydroxide nanoparticles and (3) calcium propionate solution. The immediate and long-term effects after ten months of storage of these compounds on the increase of the pH of manuscripts are described in this study. All tested compounds were able to increase the pH and maintain it in the course of the observed period. Moreover, a lining with thin tissue and a mixture of 3 % gelatine dissolved in 60 % water and 40 % alcohol provides the consolidation required for manipulation of the manuscripts.

How copper corrosion can be retarded--New ways investigating a chronic problem for cellulose in paper

To better assess the stabilization effects of chemical treatments on Cu(II)-catalyzed cellulose degradation, we developed Cu(II)-containing model rag paper with typical copper corrosion characteristics using e-beam radiation. The paper can be prepared homogeneously and quickly compared to tedious pre-aging methods. Using the Cu(II)-containing model rag paper, the stabilization effects of various chemicals on Cu(II)-catalyzed degradation of cellulose were tested. Benzotriazol was highly effective in retarding the degradation of the Cu(II)-containing model rag paper under hot and humid aging condition, as well as under photo-oxidative stress. Tetrabutylammonium bromide reduced Cu(II)-catalyzed degradation of cellulose, but its efficacy was dependent on the accelerated aging conditions. The results with the alkaline treatments and gelatin treatment suggested that their roles in the degradation mechanisms of cellulose in the presence of Cu(II) differ from those of benzotriazol and tetrabutylammonium bromide.

Evaluation of Treatments for Stabilization of Verdigris and Malachite Containing Paper Documents

Copper ions and acids lead to enhanced degradation of the paper carrier. Stabilization treatment of documents with pigments such as verdigris and malachite should therefore include addition of alkalis to combat acid hydrolysis of cellulose and antioxidants to retard oxidative degradation catalysed by copper ions. The paper reviews present approaches for stabilisation of green copper pigments. Furthermore, two recently proposed treatments containing tetraalkylammonium bromide antioxidants and alkali are evaluated. The first treatment is based on interleaving of paper samples containing malachite or verdigris pigments with papers, impregnated with alkaline buffer and antioxidant at elevated relative humidity and applied pressure. The second one is based on the use of non-aqueous suspensions of nano calcium carbonate and/or magnesium oxide particles and tetrabutylammonium or tetrapropylammonium bromide. Size exclusion chromatography is used to monitor the extent of degradation of samples during accelerated ageing, while colour changes of pigments are determined using colourimetry. Results demonstrate that effective stabilization of paper samples can be achieved with tetrabutylammonium bromide and calcium carbonate containing interleaves at 90% RH. When non-aqueous immersion treatment is applied, tetrabutylammonium bromide at a concentration 0.09 M in combination with calcium carbonate nano particles had the most beneficial effect on the paper as well as on the colour of the copper based pigments.

Strong and moldable cellulose magnets with high ferrite nanoparticle content

A major limitation in the development of highly functional hybrid nanocomposites is brittleness and low tensile strength at high inorganic nanoparticle content. Herein, cellulose nanofibers were extracted from wood and individually decorated with cobalt-ferrite nanoparticles and then for the first time molded at low temperature (<120 °C) into magnetic nanocomposites with up to 93 wt % inorganic content. The material structure was characterized by TEM and FE-SEM and mechanically tested as compression molded samples. The obtained porous magnetic sheets were further impregnated with a thermosetting epoxy resin, which improved the load-bearing functions of ferrite and cellulose material. A nanocomposite with 70 wt % ferrite, 20 wt % cellulose nanofibers, and 10 wt % epoxy showed a modulus of 12.6 GPa, a tensile strength of 97 MPa, and a strain at failure of ca. 4%. Magnetic characterization was performed in a vibrating sample magnetometer, which showed that the coercivity was unaffected and that the saturation magnetization was in proportion with the ferrite content. The used ferrite, CoFe2O4, is a magnetically hard material, demonstrated by that the composite material behaved as a traditional permanent magnet. The presented processing route is easily adaptable to prepare millimeter-thick and moldable magnetic objects. This suggests that the processing method has the potential to be scaled-up for industrial use for the preparation of a new subcategory of magnetic, low-cost, and moldable objects based on cellulose nanofibers.

Novel optically active poly(amide-thioester-imide)s containing l-α-amino acids and thiadiazol anticorrosion group

Here, for the first time, we report the synthesis of a new class of optically active polymers, poly(amide-thioester-imide)s (PATEI)s, containing flexible and anticorrosion linkages. Step growth polymerization of a novel diamine with diacids containing amino acid and trimellitylimide groups in tetrabutylammonium bromide, in the molten state, which acts as a molten ionic salt medium, was carried out. The obtained polymeric materials were of the nanoscale size and were assembled by filamentary particles as shown by field-emission scanning electron microscopy micrographs, which were distributed uniformly and randomly, with an average nanosize diameter of about 40 nm. The polymeric samples were readily soluble in a variety of common organic solvents and formed low-colored and flexible thin films via solution casting. The values of absorption edge wavelength ( λ0) were determined by ultraviolet–visible spectroscopy, and all of the resulting PATEI films exhibited high-optical transparency. According to x-ray diffraction patterns, all the PATEIs were amorphous. The structure of PATEIs were also characterized by Fourier-transform infrared spectroscopy, Proton-nuclear magnetic resonance, elemental, and thermogravimetric analysis techniques. The effect of ultrasound on the morphology of polymers was also investigated. This study confirmed that the size of polymer particles decreased and there was a change in their morphology.