Abstract
Borax-agar gel has been used recently in the deacidification and other conservation processes for paper manuscripts. However, the residues of borax-agar can be damaging to the cellulose fibers. Conservators are trying to solve this problem, especially with the great success achieved by the borax / agar based gel in the acidity neutralization and improve the mechanical properties of the paper manuscripts. The current study considers whether the use of paper barriers such as Japanese gampi, linen, and rayon can reduce harmful borax-agar residues. Historical paper specimens were treated with 3% and 6% of agar poultice with different barriers such as rayon, pure linen, and Japanese gampi paper. After drying, the treated paper samples were exposed to hot-moist ageing at 80 °C and 65% relative humidity for 72 h. The role of different barriers used in the reduction of residues from agar poultice and the effect of these residues on cellulose fibers were studied via some analytical techniques, such as digital optical microscopy, scanning electron microscopy, pH, color change, and Fourier-transform infrared spectroscopy (FTIR), were used. The results showed that 3% of the agar poultice-borax with a linen barrier gave the best results with no residue left after treatment.
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Reduction of Borax / Agar-based Gel Residues Used to Neutralize Acidity of a Historical Manuscript with use of Different Paper Barriers: Artificial Ageing Results
Eman Salim,a Mostafa Abdel-Hamied,a Sehame Salim,a Sheeren Gamal,a Shimaa Mohamed,a Fatma El-Zahraa Galal,a Fatma Tarek,a Rushdya Rabee Ali Hassan,a Hayssam M. Ali,b,c and Mohamed Z. M. Salem d,*
Borax-agar gel has been used recently in the deacidification and other conservation processes for paper manuscripts. However, the residues of borax-agar can be damaging to the cellulose fibers. Conservators are trying to solve this problem, especially with the great success achieved by the borax / agar based gel in the acidity neutralization and improve the mechanical properties of the paper manuscripts. The current study considers whether the use of paper barriers such as Japanese gampi, linen, and rayon can reduce harmful borax-agar residues. Historical paper specimens were treated with 3% and 6% of agar poultice with different barriers such as rayon, pure linen, and Japanese gampi paper. After drying, the treated paper samples were exposed to hot-moist ageing at 80 °C and 65% relative humidity for 72 h. The role of different barriers used in the reduction of residues from agar poultice and the effect of these residues on cellulose fibers were studied via some analytical techniques, such as digital optical microscopy, scanning electron microscopy, pH, color change, and Fourier-transform infrared spectroscopy (FTIR), were used. The results showed that 3% of the agar poultice-borax with a linen barrier gave the best results with no residue left after treatment.
Keywords: Agar gel residues; Optical microscope; SEM; pH; Color change; FTIR
Contact information: a: Conservation Department, Faculty of Archaeology, Cairo University, Giza 12613, Egypt; b: Botany and Microbiology Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia; c: Timber Trees Research Department, Sabahia Horticulture Research Station, Horticulture Research Institute, Agriculture Research Center, Alexandria 21526, Egypt; d: Forestry and Wood Technology Department, Faculty of Agriculture (EL-Shatby), Alexandria University, Alexandria 21545, Egypt; *Corresponding author: zidan_forest@yahoo.com
INTRODUCTION
Many libraries, museums, and stores contain paper manuscripts that are suffering from deterioration aspects, such as acidity and dirt, and such problems call for deacidification and cleaning (Zou et al. 1996; Warda et al. 2007; Baglioni et al. 2009; Domingues et al. 2013; El-Feky et al. 2014). The acidity plays an important role in degradation of ancient manuscripts (Kolar et al. 1997, 2003, 2006). In principle, paper is formed with a network structure involving cellulose and non-cellulose (hemicelluloses and lignin) components. These materials are held together with hydrogen bonds; therefore, the mechanical properties of different paper samples are substantially influenced by the individual characteristics of cellulose fibers, by the nature, concentration and chemical properties of fillers and additives, as well as by the network structure of the paper (Hinterstoisser and Salmén 2000).
When cellulosic materials are exposed to elevated temperatures, changes can occur in their chemical structures that affect its performance. The changes in chemical structure may be manifested only as reduced strength, and water content and of course change of pH (Hassan 2016).
Furthermore, the acidity may be due to the use of iron ink in writing. Such ink which contains mainly sulfur compounds (sulfate ferric) with tannic and gallic acids, and sulfuric acid (H2SO4) is formed in the presence of moisture and dust. This leads to formations of burns beneath it in some cases. The acidity plays an important role in the damage and degradation of historical paper and its holdings (Badea et al. 2012; Elamin et al. 2018a,b). With the passage of time, the paper gradually becomes more and more brittle which leads finally to a complete disintegration after several hundred years of storage. Two processes have explained the degradation of paper; metal-catalyzed oxidation and acid-catalyzed hydrolysis of cellulose. Both phenomena can occur simultaneously or independently from each other; the final stage of these reactions is the high acidity and decomposition of the paper (Baty et al. 2010; Hubbe et al. 2017).
A recent study showed that impregnated interleaving papers with the ethanolic extracts produced from Lemna gibba and Eichhornia crassipes effectively neutralized the acidity of decayed paper after 7 d from the treatment with evidently chelated transition metals (Mohamed et al. 2019). Furthermore, the daylight and the artificial light interior, especially the more energy-rich component – near ultraviolet radiation (UVA) cause gradual degradation of paper, fabrics and other organic based materials (Olabi 2017; Brunetti et al. 2019). Many authors associate the yellowing of bleached pulp and paper with oxidation of cellulose and subsequent increasing of carbonyl group content. This is a result of acid hydrolysis – the degradation of macromolecules of cellulose, hemicelluloses, and lignin, with the creation of increased share of low molecular fractions with high presence of carbonyl and carboxyl groups, which may be the cause of increased paper acidity (Feller 1994; Fan et al. 2011). Several processes have been introduced to effectively neutrals the acidity in paper and arrest its deterioration action (Agrawal and Barkeshli 1997).
Some researchers have studied the effects of various type of deacidification on stability of cellulose, where none of the methods gave homogeneous distribution of active compounds in the paper. For example, a natural dye (in dyed paper) like turmeric is not stable and will change color during the deacidification process, and it was found that the chemical composition of the paper components is affected by organic solvents commonly used in deacidification of archaeological paper; this is especially the case for toluene and ethyl alcohol, which accelerated oxidation and hydrolysis of paper samples (Wahba et al. 2020).
The sol-gel process is one of the most important approaches used in the conservation of historical paper manuscripts, where it has some advantages, such as easy and securely controlled, which makes it useful in applications of paper preservation. Additionally, the gel has a multi-function structure. Most associated studies within the last 15 years have tended to use gel in the treatment of paper manuscripts in cleaning, to extract salt from some materials (Ellis and Ellis 1997; Campbell et al. 2011; Hassan 2015; Hassan and Mohamed 2017, 2018; Hamed and Hassan 2019).
Recently, agar gel has been used in deacidification and other conservation processes of paper manuscripts (Hughes and Sullivan 2016). The material is regarded by some today as one of the most innovative for use in conservation. Agar, a polysaccharide complex derived from marine seaweeds, is indeed the oldest known gelling agent, used over the centuries in numerous fields, mainly as a food additive (Jönsson et al. 2020). Agar is composed of two different polymers, both made from the simple sugar galactose: agarose, a linear-chain, neutral and high-molecular weight polymer; and agaropectin, the same basic structure containing methyl, sulphate, and pyruvate substituent groups. Perhaps one of the most important adverse effects of agar on paper is to increase the rate of bacterial activity (Ishida et al. 2003; Bae et al. 2004).
Polymeric gel systems can be prepared by means of reversible chemical crosslinks between borate ions (from borax salt [Na2B4O7 • 10H2O]) and partially hydrolyzed agar to obtain agar-borate gels with a highly viscous liquids that can conform to multi-dimensional and complex surfaces, and as elastic solids (Angelova et al. 2015; Riedo et al. 2015). Responsive agar – borax gels offer several advantages over nonresponsive physical solvent gels for conservation applications. These gels are both effective as cleaning tools and are easily removable from the painted surface once they have carried out their function because they are converted rapidly to free-flowing liquids. Thus, by modulating the chemical and/or conformational properties of the gelator, it is possible to apply a gel and, after the activation of a chemical or physical switch, induce a physical gel/sol transition (Sacco et al. 2018).
Removing the sol from the surface of a work of art minimizes mechanical action over the surface of the work of art and diminishes the possibility of surface damage (Khandekar 2000; Alam et al. 2012). Furthermore, such cleaning generally requires no aqueous clearance procedure. In some instances, the soiling material dislodged from the surface is drawn into the gel particles, or simply on to the surface of the gel membrane. In other instances, particularly when a film-forming material gives the soil coherence and some character of an actual film, application of the rigid Agar gel simply swells the soil layer, which can then be removed by the gentle action of a dry cotton swab. Within this working strategy, the use of a grated rigid agar gel leads to further improvements: more gentle and uniform action, without any problems due to adhesiveness (Cremonesi 2016). Nevertheless, the researchers did not pay attention to the borax-agar residues that could cause damage to the paper structure, so the present study is unique in terms of its study to reduce the borax material residues in the gel agar systems through the usage of various barriers. A further goal was to assess the extent of the efficiency of borax/agar based gel in deacidification and the amount of borax harmful residues after application. Several studies have tried to improve the use of gel in cleaning processes with different methods, either mechanical or chemical cleaning, which left uncontrolled residues. Some previous studies revealed that the use of agar poultice is better than the use of chemicals in the treatment processes, and the remains of which are lower compared with the remains of solutions on cellulose fibers. The ageing is one of the important steps that has an active role in the evaluation of treatment after its ageing for long-term (Devanathan 2012).
This study aims to evaluate the use of different barriers as a means to reduce the residues of borax-agar on historical manuscripts and the effect of those residues on cellulose fibers under artificial ageing. Therefore, this work is complementary to the actual evaluation of the efficacy of the agar and borax material in the deacidification of paper manuscripts. The study was undertaken on historical samples from special groups, which gives more accurate and realistic results for the nature of manuscripts. In addition, it provides a number of solutions for the residues within the paper structure.
EXPERIMENTAL
Historical Paper Samples
A historical paper manuscript sheet (Fig. 1) was used in the experimental aspect in the current study. It dates back to 1887 AD, and the manuscript was obtained from special collections, Cairo, Egypt. The authors used a microscopic examination to identify the type of paper. The scanning electronic microscope (FEI Quanta 200 ESEM FEG; FEI Company, Seto, Japan) examination showed that the manuscript paper was probably made from flax (Fig. 2).
Fig. 1. The historical paper manuscript with leather bookbinding
Fig. 2. The SEM image of historical paper before treatment with agar gel
The fiber was inherently characterized as flax based of its strength and durability with a low percentage of lignin, ranging from 2 to 5%, as well as the cylindrical compartmentalized partitions with walls incidental thick canal central narrowness.
Preparation of Agarose Poultice
Two concentrations (3% and 6%) of agarose were prepared (Granan et al. 1987; Kelly 1987; Zarubica et al. 2015). Briefly, water was boiled at 100 ℃, and then agar with borax (Kraemer Company, Bremen, Germany) were added gradually under stirring. After completely solving the agar (Fig. 3a), the beaker was put inside an oven for 1 min. Then, the prepared material was poured into a glass mold with 1 cm thickness. The poured material was left for 1.5 h to reach the jelly state (texture) (Fig. 3b).
Fig. 3. Preparation steps of agar poultice: (a) Agarose after completely solving; (b) Agarose poured inside glass mold
Application of Agarose with Different Barriers
After reaching to the jelly state, the agarose was cut into small samples. Then, different barriers were put onto historical paper samples before treatment processes, such as pure linen, rayon, and Japanese gampi paper (Fig. 4). These were used to evaluate how well these barriers will succeed in reducing poultices gel residue. Agarose was put on the paper samples with different barriers and left for 1.5 h. After the 1.5 h, the agarose with different barriers were removed from the samples and left to completely dry at room temperature.
Accelerated Moist-heat Ageing
The treated and untreated historical samples were exposed to a moist-heat treatment at 80 ℃ and 65% relative humidity for 72 h, as per ISO 5630-4 (1986). The oven used in this ageing process was from the National Institute for Standards, Giza, Egypt.
Analytical Techniques
Digital microscope
A portable USB digital microscope (model PZ01; Shenzhen Super Eyes Co., Ltd., Guangdong, China) was used to investigate the surface of the experimental samples.