Organosilicons of different molecular size and chemical structure as consolidants for waterlogged archaeological wood - a new reversible and retreatable method

A multi-technique and multiscale comparative study on the efficiency of conservation methods for the stabilisation of waterlogged archaeological pine

Archaeological wood can be preserved in waterlogged conditions. Due to their degradation in the ground, these archaeological remains are endangered after their discovery, since they decay irretrievably during drying. Conservation measures are used to preserve waterlogged archaeological objects, maintaining their shape and character as much as possible. However, different methods have been developed leading to varying results. This study compares their effectiveness in order to clarify their mode of action. The methods including alcohol-ether resin, lactitol/trehalose, melamine formaldehyde, polyethylene glycol impregnation prior to freeze-drying, saccharose and silicone oil were assessed by analysing mass changes and volume stability using structured-light 3D scanning. The state of the conserved wood samples including the spatial distribution of the conservation agent was examined using synchrotron micro-computed tomography. Raman spectroscopy was used to observe the agent´s spatial distribution within the cells. The findings demonstrated that melamine formaldehyde stabilises the degraded cell walls. The lumens are void, as in the case with alcohol-ether resin, while polyethylene glycol, silicone oil, saccharose and lactitol/trehalose also occupy the lumens. It is assumed that the drying method has an effect on the distribution of the solidifying agent. The knowledge gained affords insights into the mechanism of conservation methods, which in turn accounts for the varied outcomes. It also allows conclusions to be drawn about the condition and stability of conserved museum objects and serves as a starting point for the further development of conservation methods.

Optimization and characterization of silver nanoparticle-modified luffa for the adsorption of ketoprofen and reactive yellow 15 from aqueous solutions

In the current work, luffa was modified with silver nanoparticles to prepare LF/AgNPs adsorbent for the elimination of ketoprofen and reactive yellow 15 (RY15) from aqueous media. Various characterization techniques, including FT-IR, XRD, BET, and SEM-EDS analysis, were employed to confirm the successful modification of LF/AgNPs. Several key parameters such as contact time, adsorbent dosage, concentration, pH, and agitation technique were fine-tuned to optimize the adsorption process. Ketoprofen removal was found to be most effective in weakly acidic conditions (pH = 5), while reactive yellow 15 adsorption was enhanced in an acidic environment (pH = 2). At 298 K, the highest adsorption capacities reached 56.88 mg/g for ketoprofen and 97.76 mg/g for reactive yellow 15. In both scenarios involving the elimination of ketoprofen and RY15, the Temkin isotherm exhibits higher R2 values, specifically 0.997 for ketoprofen and 0.963 for RY15, demonstrating a strong correlation with the observed adsorption data. Additionally, the kinetics of ketoprofen adsorption were best described by the Pseudo-first order model (R2 = 0.989), whereas the Pseudo-second order model provided the most accurate fit for reactive yellow 15 adsorption (R2 = 0.997). Importantly, the LF/AgNPs adsorbent displayed consistent performance over five consecutive reuse cycles, affirming its stability and efficacy in removing both contaminants. These findings underscore the exceptional potential of LF/AgNPs as a reliable adsorbent for the removal of reactive yellow 15 and ketoprofen from aqueous solutions.

Thermal and Mechanical Characterization of Yarn Samples from Flemish Tapestry of the Sixteenth Century

We propose a physico-chemical approach for theharacterization of the conservation condition of yarns from a Flemish tapestry of the sixteenth century. The aging effect on the yarns' performance was evaluated by comparison with commercial materials. Water uptake experiments highlighted the aptitude of yarns toward water sorption and their increased hydrophilicity upon aging. Thermogravimetric analysis can be considered a fast approach for the fiber identification and assessment on the material life-time. The dynamic mechanical analysis provided direct evidence on the yarns, conservation state and their performance under different mechanical stresses. The proposed characterization path can be relevant for stating the condition of the tapestry and for designing a conservation protocol for the preservation of the artwork.

Reactivity of Waterlogged Archeological Elm Wood with Organosilicon Compounds Applied as Wood Consolidants: 2D 1H-13C Solution-State NMR Studies

Some organosilicon compounds, including alkoxysilanes and siloxanes, proved effective in stabilizing the dimensions of waterlogged archaeological wood during drying, which is essential in the conservation process of ancient artifacts. However, it was difficult to determine a strong correlation between the wood stabilizing effect and the properties of organosilicon compounds, such as molecular weight and size, weight percent gain, and the presence of other potentially reactive groups. Therefore, to better understand the mechanism behind the stabilization effectiveness, the reactivity of organosilicons with wood polymers was studied using a 2D ¹H–¹³C solution-state NMR technique. The results showed an extensive modification of lignin through its demethoxylation and decarbonylation and also the absence of the native cellulose anomeric peak in siloxane-treated wood. The most substantial reactivity between wood polymers and organosilicon was observed with the (3-mercaptopropyl)trimethoxysilane treatment, showing complete removal of lignin side chains, the lowest syringyl/guaiacyl ratio, depolymerization of cellulose and xylan, and reactivity with the C6 primary hydroxyls in cellulose. This may explain the outstanding stabilizing effectiveness of this silane and supports the conclusion that extensive chemical interactions are essential in this process. It also indicates the vital role of a mercapto group in wood stabilization by organosilicons. This 2D NMR technique sheds new light on the chemical mechanisms involved in organosilicon consolidation of wood and reveals what chemical characteristics are essential in developing future conservation treatments.

Stabilisation of waterlogged archaeological wood: the application of structured-light 3D scanning and micro computed tomography for analysing dimensional changes

Cultural heritage objects made of wood can be preserved under waterlogged conditions for many years, where decay is slowed down and the wood structure is more or less completely filled with water. Depending on the degree of degradation, finds may collapse and shrink when they are allowed to dry in an uncontrolled manner after excavation, leading to total loss of the object and its information. Conservation measures are taken to prevent damage of objects and dimensional stability is an important criterion. In this study, structured-light 3D scanning and micro-computed tomography were used to analyse the dimensional stability of wood after conservation, as well as its long-term stability. 83 samples from a reference collection established between 2008 and 2011 allowed this comparative study of the most common conservation methods at that time. The effects of conservation methods using alcohol-ether resin, melamine-formaldehyde (Kauramin 800^®), lactitol/trehalose, saccharose, and silicone oil on dimensional stability were investigated. In addition, different polyethylene glycol (PEG) treatments with subsequent freeze-drying were also investigated: one-stage with PEG 2000, two-stage with PEG 400 and PEG 4000 and three-stage with PEG 400, PEG 1500 and PEG 4000. The data received from analyses of both volume and surface gave detailed information about the success of each conservation method. Attempts were made to quantify the damage patterns, specifically shrinkage, collapse, and cracks. While PEG and freeze-drying, alcohol-ether-resin, as well as the Kauramin 800^® method gave the best results, analysis also highlighted the failures of each method.

Sustainability in Heritage Wood Conservation: Challenges and Directions for Future Research

Conserving the world’s cultural and natural heritage is considered a key contributor to achieving the targets set out in the United Nation’s Sustainable Development Goals, yet how much attention do we pay to the methods we use to conserve and protect this heritage? With a specific focus on wooden objects of cultural heritage, this review discusses the current state-of-the-art in heritage conservation in terms of sustainability, sustainable alternatives to currently used consolidants, and new research directions that could lead to more sustainable consolidants in the future. Within each stage a thorough discussion of the synthesis mechanisms and/or extraction protocols, particularly for bio-based resources is provided, evaluating resource usage and environmental impact. This is intended to give the reader a better understanding of the overall sustainability of each different approach and better evaluate consolidant choices for a more sustainable approach. The challenges facing the development of sustainable consolidants and recent research that is likely to lead to highly sustainable new consolidant strategies in the future are also discussed. This review aims to contribute to the ongoing discussion of sustainable conservation and highlight the role that consolidants play in truly sustainable heritage conservation.

The Viscoelastic Behaviour of Waterlogged Archaeological Wood Treated with Methyltrimethoxysilane

Waterlogged wood treatment with methyltrimethoxysilane (MTMS) proved effective in stabilising wood dimensions upon drying (anti-shrink efficiency of 76-93%). Before the method can be proposed as a reliable conservation treatment, further research is required that includes the evaluation of the mechanical properties of treated wood. The aim of the study was to characterise the effect of the treatment on the viscoelastic behaviour of archaeological waterlogged elm and oak wood differing in the degree of degradation. Dynamic mechanical analysis in the temperature range from -150 to +150 °C was used for the study. To better understand the viscoelastic behaviour of the treated wood, pore structure and moisture properties were also investigated using Scanning Electron Microscopy, nitrogen sorption, and Dynamic Vapour Sorption. The results clearly show that methyltrimethoxysilane not only prevents collapse and distortions of the degraded cell walls and decreases wood hygroscopicity (by more than half for highly degraded wood), but also reinforces the mechanical strength by increasing stiffness and resistance to deformation for heavily degraded wood (with an increase in storage modulus). However, the MTMS also has a plasticising effect on treated wood, as observed in the increased value of loss modulus and introduction of a new tan δ peak). On the one hand, methyltrimethoxysilane reduces wood hygroscopicity that reflects in lower wood moisture content, thus limiting the plasticising effect of water on wood polymers, but on the other hand, as a polymer itself, it contributes to the viscous behaviour of the treated wood. Interestingly, the effect of silane differs with both the wood species and the degree of wood degradation.

Conservation of Waterlogged Wood—Past, Present and Future Perspectives

This paper reviews the degradation, preservation and conservation of waterlogged archaeological wood. Degradation due to bacteria in anoxic and soft-rot fungi and bacteria in oxic waterlogged conditions is discussed with consideration of the effect on the chemical composition of wood, as well as the deposition of sulphur and iron within the structure. The effects on physical properties are also considered. The paper then discusses the role of consolidants in preserving waterlogged archaeological wood after it is excavated as well as issues to be considered when reburial is used as a means of preservation. The use of alum and polyethylene glycol (PEG) as consolidants is presented along with various case studies with particular emphasis on marine artefacts. The properties of consolidated wood are examined, especially with respect to the degradation of the wood post-conservation. Different consolidants are reviewed along with their use and properties. The merits and risks of reburial and in situ preservation are considered as an alternative to conservation.

Drying Stress and Strain of Wood: A Review

Wood drying stress causes various drying defects, which result from the wood microstructure and the transfer of heat and mass during the drying. It is the fundamental way to solve the problem of defects to clarify the law and mechanism of wood stress and strain development during drying. In this paper, based on the defects of wood drying, the theory and experimental testing methods of drying stress and strain were summarized. Meanwhile, artificial neural networks (ANN) and their application in the wood drying field were also investigated. The traditional prong and slicing methods were used practically in the research and industry of wood drying, but the stress changes in-process cannot be trapped. The technologies of image analysis and near-infrared spectroscopy provide a new opportunity for the detection of drying stress and strain. Hence, future interest should be attached to the combination of the theory of heat and mass transfer and their coupling during drying with the theory of microscopic cell wall mechanics and macroscopic drying. A more complete image acquisition and analysis system should be developed to realize the real-time monitoring of drying strain and cracking, practically. A more feasible and reasonable prediction model of wood drying stress and strain should be established to achieve the accuracy of the prediction.

Gap-Fillers for Wooden Artefacts Exposed Outdoors—A Review

Conservation of wooden artefacts that are exposed outdoors, mainly in open-air museums, is a very complex and difficult issue that aims to preserve both the integrity and aesthetics of valuable objects. Unceasingly subjected to several factors, such as alternating weather conditions and the activities of microorganisms, algae, and insects, they undergo continuous changes and inevitable deterioration. Their biological and physical degradation often results in the formation of gaps and cracks in the wooden tissue, which creates a need not only for wood consolidation, but also for using specialist materials to fill the holes and prevent further degradation of an object. To ensure effective protection for a wooden artefact, a filling material must both protect the wood against further degradation and adapt to changes in wood dimensions in response to humidity variations. A variety of substances, both organic and inorganic, have been used for conservation and gap filling in historic wooden objects over the years. The filling compounds typically consist of two components, of which one is a filler, and the second a binder. In the case of inorganic fillers, plaster has been traditionally used, while the most popular organic fillers were wood powder, wood shavings, and powdered cork. As with binders, mainly natural substances have been used, such as animal glues or waxes. Nowadays, however, due to the lower biodegradability and better physicochemical properties, synthetic materials are gaining popularity. This article discusses the types of filling compounds currently used for gap filling in wooden artefacts exposed outdoors, outlining their advantages and drawbacks, as well as future perspective compounds. It appears that particularly composite materials based on natural polymers deserve attention as promising filling materials due to their high elasticity, as well as similarity and good adhesion to the wooden surface. Their main shortcomings, such as susceptibility to biodegradation, could be eliminated by using some modern, bio-friendly preservatives, providing effective protection for historic wooden artefacts.

Restoration of a XVII Century’s predella reliquary: From Physico-Chemical Characterization to the Conservation Process

We report on the restoration of a XVII century’s predella reliquary, which is a part of a larger setup that includes a wall reliquary and a wooden crucified Christ, both belonging to the church of “Madre Maria SS. Assunta”, in Polizzi Generosa, Sicily, Italy. The historical/artistic and paleographic research was flanked successfully by the scientific objective characterization of the materials. The scientific approach was relevant in the definition of the steps for the restoration of the artefact. The optical microscopy was used for the identification of the wood species. Electron microscopy and elemental mapping by energy-dispersive X-ray (EDX) was successful in the identification of the layered structure for the gilded surface. The hyperspectral imaging method was successfully employed for an objective chemical mapping of the surface composition. We proved that the scientific approach is necessary for a critical and objective evaluation of the conservation state and it is a necessary step toward awareness of the historical, liturgical, spiritual and artistic value. In the second part of this work, we briefly describe the conservation protocol and the use of a weak nanocomposite glue. In particular, a sustainable approach was considered and therefore mixtures of a biopolymer from natural resources, such as funori from algae, and naturally occurring halloysite nanotubes were considered. Tensile tests provided the best composition for this green nanocomposite glue.

Interactions between Different Organosilicons and Archaeological Waterlogged Wood Evaluated by Infrared Spectroscopy

The goal of the study was to characterise chemical interactions between waterlogged archaeological wood and organosilicon compounds applied for its conservation to shed lights on the mechanism of wood dimensional stabilisation by the chemicals. Two alkoxysilanes (methyltrimethoxysilane and (3-mercaptopropyl) trimethoxysilane) and a siloxane (1,3-bis(diethylamino)-3-propoxypropanol)-1,1,3,3-tetramethyldisiloxane) were selected for the research since they already have been proven to effectively stabilise waterlogged wood upon drying. Fourier transform infrared spectroscopy was used for structural characterisation of the degraded wood and evaluation of reactivity of the applied chemicals with polymers in the wooden cell wall. The results obtained clearly show much stronger interactions in the case of alkoxysilanes than the siloxane, suggesting a different mechanism of wood stabilisation by these compounds. The results of this study together with other data obtained in our previous research on stabilisation of waterlogged archaeological wood with organosilicon compounds allow the conclusion that the mechanism of waterlogged wood stabilisation by the used alkoxysilanes is based on bulking the cell wall by silane molecules and wood chemical modification, while in the case of the applied siloxane, it builds upon filling the cell lumina.

Pickering Emulsions Based on Wax and Halloysite Nanotubes: An Ecofriendly Protocol for the Treatment of Archeological Woods

A novel green protocol for the consolidation and protection of waterlogged archeological woods with wax microparticles has been designed. First, we focused on the development of halloysite nanotubes (HNTs) based Pickering emulsions using wax as the inner phase of the oil-in-water droplets. The optimization of the preparation strategy was supported by both optical microscopy and scanning electron microscopy, which allowed us to show the morphological features of the prepared hybrid systems and their structural properties, i.e., the distribution of the clay at the interface. Also, the dependence of the overall dimensions of the prepared systems on the halloysite content was demonstrated. Microdifferential scanning calorimetry (μ-DSC) was conducted in order to assess whether the thermal properties of the wax are affected after its interaction with HNTs. Then, the Pickering emulsions were employed for the treatment of waterlogged wooden samples. Compared to the archeological woods treated with pure wax, the addition of nanotubes induced a remarkable improvement in the mechanical performance in terms of stiffness and flexural strength. The proposed protocol is environmentally friendly since water is the only solvent used throughout the entire procedure, even if wax is vehiculated into the pores at room temperature. As a consequence, the design of wax/halloysite Pickering emulsions represents a promising strategy for the preservation of wooden artworks, and it has a great potential to be scaled up, thus becoming also exploitable for the treatments of shipwrecks of large size.

Halloysite Nanotubes: Interfacial Properties and Applications in Cultural Heritage

The peculiar surfaces of halloysite nanotubes and their biocompatibility are attracting the interest of researchers based on the wide range of attainable applications. The large aspect ratio of this nanotubular material ensures promising properties as a reinforcing agent in polymeric matrixes, such as cellulose and its derivatives, that entail strengthening due to, for instance, aging-induced degradation. The halloysite cavity has a suitable size for hosting a large variety of active species such as deacidifying (calcium hydroxide) and flame retardant agents (fluorinated surfactants) for a controlled and sustained release relevant to the conservation of cultural heritage. Additionally, anionic surfactants can be selectively adsorbed at the inner surface generating inorganic micelles able to solubilize hydrophobic species in a controlled cleaning protocol. We briefly discuss how the natural halloysite nanotubes can be supportive in various conservation processes of cultural heritage and present an outlook for future perspectives.