PL235395B1 - Preparation for preservation of archaeological wood and method for preservation of wood - Google Patents

Description

Description of the invention

The present invention relates to a preparation for the preservation of wet archaeological and historic wood, in particular wooden artifacts extracted from a high humidity environment, in particular from water, soil or peat. The invention also relates to a method of preserving wet archaeological and historic wood with the preparation according to the invention. The preservation of wood with the preparation according to the invention is aimed at preventing deformations resulting from its slow or accelerated drying.

The main purpose of the conservation of wet archaeological wood is to prevent its deformation resulting from the collapse of cell walls during the drying process. It is also important to maintain the original appearance of a wooden monument. The maintenance procedure must not weaken the mechanical properties of the object. It is even desirable to strengthen the mechanical strength of the wood.

As a result of physical, chemical and biological corrosion, historic wooden buildings lose both their physical properties and aesthetic and artistic values. If these processes are not consciously stopped by the application of appropriate conservation measures, with time they begin to threaten the existence of historical monuments. The wealth of material evidence of history related to human activity is extremely diverse, therefore there are no universal methods of its conservation.

Conservation of wooden historic buildings is an extremely difficult and complex issue on the border of science, aesthetics and art. Objects of this type are usually extremely fragile and unstable due to the advanced degree of destruction, caused mainly by the action of biotic factors, i.e. primarily by the activity of fungi decomposing the wood tissue, the development of bacteria and insects feeding therein. Accordingly, as disclosed, for example, in the article by Tuduce-Traistaru et al. 2010, in the conservation of wooden monuments, their absolute priority is their consolidation, i.e. preserving the physical integrity of the wood, while maintaining the authenticity of the objects.

Archaeological monuments are both those freshly acquired from archaeological sites, as well as exhibited in museums and preserved many years earlier with the use of various means and methods. Objects freshly harvested from water or soil, for effective reinforcement and maintaining dimensional stability, require the possibility of introducing preservatives into wet wood. On the other hand, previously preserved monuments often require restoration or even removal of previously used substances in order to protect the wood tissue from further decomposition or to obtain more satisfactory aesthetic effects. Archaeological objects, which were first excavated as a result of research, and then filled up again after completion of the earthworks, pose another problem. It has been shown that this type of practice negatively affects the condition of historical wood, because as a result of disturbing anaerobic conditions and natural moisture balance, the secondary development of fungi and bacteria occurs, which leads to the destruction of wood tissue.

The most frequently used methods of archaeological wood preservation include: alcohol-ether drying, freeze drying, i.e. freezing and sublimation, slow drying with oil preservation, alum method, polyethylene glycol (PEG) preservation method, synthetic resin impregnation method ( resole, urea-formaldehyde) in mixtures of solvents (alcohol, glycol, water). Preventing deformation of archaeological wood resulting from the collapse of cell walls during the drying process is also possible thanks to other methods described in patents.

For example, PL 130 387 discloses a chemical impregnation with the use of the products of the extrification of glycerin or glycols in a mixture with boric acid.

In turn, US 5789087 and US 6432553 disclose a method of preservation using polyethylene glycol as a preservative and a method of preventing the negative effects of glycol on the preserved material.

At present, the most popular preservative of wet archaeological wood is polyethylene glycol (PEG), perfectly soluble in both water and alcohols (ethanol, methanol or isopropanol). PEG, replacing water molecules, has the ability to penetrate deep into degraded wood tissue, strengthening its structure and improving dimensional stability [Jensen and Schnell 2005]. Unfortunately, in conditions of high air humidity (above 80%) it is hygro

PL 235 395 Β1 the ability of PEG increases rapidly, as a result of which the impregnated wood absorbs water very intensively. This leads to its strong swelling and cracking [Olek et al. 2016], Under the influence of liquid water, water-soluble PEG is washed out. Wood deprived of a consolidating substance cracks irreversibly, shrinks and deforms [Smith 2003]. It has also been shown that PEG can react with other chemical compounds, including iron and sulfur compounds, often present in archaeological wood. As a result of the oxidation reaction, low molecular weight organic acids (formic, glycolic, oxalic acid) are formed, causing both the depolymerization of polyethylene glycol itself and the progressive degradation of the object preserved with it, as described in the article by Almkvist 2013, Almkvist and Persson 2007, Sandstróm et al. 2005],

The most important disadvantages of the archaeological wood preservation methods used so far are: excessive volumetric and linear shrinkage of wood as a result of drying, leading to deformation of the original shape of the object, significant color change in relation to the natural one, insufficient protection against biological and chemical corrosion, excessive hygroscopicity leading to volume changes and as a result cracking with changing ambient humidity, excessive plasticization of wood, undesirable increase in weight of impregnated wood, duration of maintenance (tedious and long-lasting treatments related to the conservation process itself, as well as finishing processes, i.e. drying).

It has surprisingly been found that certain organosilicon compounds, including alkoxysilanes, are potential alternatives to PEG. Until now, they have been used mainly to increase the durability of contemporary wood, limiting its hydrophilicity, and thus also biodegradability [Donath et al. 2006, Donath et al. 2007, Hill et al. 2004, Mazela et al. 2014, Mai et al. 2004, Panov et al. 2009, Tshabalala et al. 2003, Xie et al. 2010], Due to the presence of reactive groups, these compounds can form permanent Si-OC and Si-O-Si bonds with the wood surface, reducing its hydrophilicity, and thus eliminating undesirable features of this material, such as susceptibility to biological corrosion [Cappelletto et al. 2013], Wood saturated with alkoxysilane solution shows resistance to brown decomposition fungi. The positive effect of organosilicon compounds on the dimensional stabilization of the wood modified with them has also been confirmed [Smith 2002, Tejedor 2010]. Alkoxysilanes usually hydrolyze and condense in an aqueous environment, therefore, in combination with a hydrophobic and fungistatic effect, they potentially constitute an effective solution in the conservation of wet archaeological wood, being an alternative for traditionally used agents such as polyethylene glycols. The water content of the wood ensures the hydrolysis of the alkoxysilanes and their binding in the wood tissue, thus preventing the collapsing of the cell walls, and thus the cracking and deformation of the wood. Chemical bonding of silanes with wood, in contrast to the solutions used so far, prevents their rinsing, thanks to which the protection of archaeological wood against drying and biological decomposition is durable and effective. Due to their unique properties, including the possibility of functionalisation, alkoxysilanes, as well as other organofunctional silanes and organofunctional siloxanes, turn out to be effective compounds for dimensional stabilization and thus conservation of wet archaeological wood.

The effect of wood strengthening depends on the distribution of the preparation in the morphological elements and the mechanism of bonding to the wood. There are two known possibilities of distributing the preparation in the wood structure. In the former case, the large molecule polymer only penetrates inside the cells, while in the latter case the small molecule polymer or monomer is deposited inside the cells and in the cell wall. The first case concerns high-molecular polymers which fill the free spaces in the wood and thus prevent the phenomenon of collapsing degraded wood cells. The second case, although it gives the expected preservation of the original shape of the object, causes a significant increase in the mass of the wood.

The aim of the invention was to develop a preparation for the conservation of archaeological and historic wood, free from the disadvantages of preparations previously used. The aim was also to preserve the principle of inviolability of aesthetic values related to form, structure, color and, to a certain extent, the principle of reversibility of the conservation process.

The preparation for the conservation of wet archaeological and historic wood according to the invention contains an organofunctional silane of the general formula 1 (RO) sSi (CH2) 3Z (general formula 1) where R is CH3 or C2H5, and Z is SH or SCN or S4 (CH2) 3Si ( OR) 3, dissolved in an organic solvent, preferably selected from alcohols, ketones and hydrocarbons

Are aliphatic or aromatic, preferably selected from methanol, ethanol, propanol, isopropanol, acetone, pentane, hexane, toluene and benzene.

The method of conservation of wet archaeological and historic wood with a preparation for the conservation of wet archaeological and historic wood according to the invention consists in introducing into the wood an organofunctional silane solution of the general formula 1 (RO) 3Si (CH2) 3Z, where R is CH3 or C2H5, and Z is SH, or SCN or S4 (CH2) 3Si (OR) 3 and drying the wood sample. The organofunctional silane solution of general formula I is introduced into wet archaeological and historic wood by any known method, preferably by a pressure swing method and / or by soaking and / or by lubrication. Preferably, the pressure swing method comprises at least 4 cycles of alternating pressure, each cycle being from -0.05 to -0.1 MPa for 10 to 60 min, then 0.6 to 1.2 MPa for 1 to 10 hours. Preferably, the pressure swing method comprises 6 cycles of alternating pressure, each cycle of -0.1 MPa for 30 min, then 1 MPa for 6 h. Preferably, after saturation, the wood is dried at room temperature for 1 week. Preferably, the wood is dehydrated, preferably in 96% ethyl alcohol, prior to the introduction of the organofunctional silane solution of general formula I. Preserved wood can be re-deposited at the site of extraction or another humid environment.

The silane in the form of an alcoholic solution is introduced into the preserved wood, thanks to which the hydrolysis and condensation process takes place only after the solution penetrates deep into the preserved material. As a result of the impregnation of archaeological wood directly with an organofunctional siloxane derivative generated in situ from an organofunctional silane of the general formula I, the cell walls themselves, which determine the mechanical strength of the wood, are strengthened. The solvent that fills the free spaces in the wood then evaporates. Such a mechanism of strengthening degraded wood tissue is significantly different from the mode of operation of solutions used so far (i.e. primarily PEG). The preparation for the conservation of wet archaeological and historic wood according to the invention has in its structure groups that enable binding with cellulose fibers and functional groups that give specific properties (e.g. hydrophobicity or increased resistance to biodegradation) or enable cross-linking and thus improve dimensional stabilization.

The advantages of the preparation for wood preservation and the method of preserving archaeological and historic wood according to the invention are ensuring the dimensional stability of a wooden object, limiting the hygroscopicity of wood, increasing its resistance to biodegradation, keeping the wood low and maintaining its mechanical properties. The method can be used for the preservation of wood previously preserved with polyethylene glycol or other methods.

The invention is illustrated in detail in the following examples.

P r z k ł a d I

The preparation for wood preservation was obtained by diluting 3-mercaptopropyltrimethoxysilane in methyl alcohol to a concentration of 50%.

Archaeological wood was used for conservation, cut from the crescent part of an elm beam extracted from Lake Lednickie, dating from the 10th-11th century. The results of the chemical analysis confirmed the high degree of degradation of the tested wood. The cellulose content in wet archaeological wood was 5.1% in the outer layers and about 7% in the core layer. It proved a high degree of destruction of the wood tissue. For comparison, contemporary elm wood contains about 50% of this component [Unger et al. 2001]. The H / L ratio (ratio of holocellulose to lignin), considered to be a particularly useful indicator of the degree of decomposition of wood [Pizzo et al. 2010], was respectively 0.12 for the outer layers and 0.16 for the root layer of wet archaeological wood. For modern elm wood, this value is 3.31 [Unger et al. 2001]. The low H / L value indicates a significant degradation of the tested wood, confirming the results of the analysis of physical parameters. The archaeological wood samples used for impregnation had dimensions of 20 x 20 x 10 mm and had been previously dehydrated in 96% ethanol.

A 50% solution of 3-mercaptopropyltrimethoxysilane in methyl alcohol was used to impregnate wet archaeological wood. The impregnation solution was introduced into the archaeological wood using the alternating pressure method. The pressure impregnation consisted of 6 cycles of variable pressure (-0.1 MPa for 30 minutes, then 1 MPa for 6 hours), during which the samples were immersed in the impregnation solution all the time. After saturation, the samples were dried at temperature

Room temperature for 1 week. All samples were dimensioned in three anatomical directions before and after impregnation and after drying. In this way, the linear shrinkage and the dimensional stability factor (ASE - anti-shrink efficiency) were calculated. ASE = 100% means that the wood was not deformed. Values above 100% indicate swelling, while values below 100% indicate shrinkage of the wood. The control sample was non-impregnated archaeological wood. The reference material was archaeological wood saturated with polyethylene glycol, traditionally used in the conservation of this type of wood, for which the ASE values range from 90-100%. The ASE for wood samples impregnated with 50% methanolic solution of 3-mercaptopropyltrimethoxysilane ranged from 97.4% (ASE for cross-section) to 98.6% (ASE by volume).

P r z x l a d II

The preparation for wood preservation was obtained by diluting bis [3- (triethoxysilyl) propyl] tetrasulfide in ethyl alcohol to a concentration of 60%. The archaeological wood described in Example 1 was used for conservation.

A 60% solution of bis [3- (triethoxysilyl) propyl] tetrasulfide in ethyl alcohol was used to impregnate wet archaeological wood. The impregnation solution was introduced into the archaeological wood using the alternating pressure method. The pressure impregnation consisted of 6 cycles of variable pressure (-0.1 MPa for 30 minutes, then 1 MPa for 6 hours), during which the samples were immersed in the impregnation solution all the time. After saturation, the samples were dried at room temperature for 1 week. The samples obtained were dimensioned as in Example 1. The ASE for wood samples impregnated with 60% ethanolic bis [3- (triethoxysilyl) propyl] tetrasulfide solution ranged from 70.6% (ASE for the cross-section) to 74.3% (ASE by volume).

P r x l a d III

The preparation for wood preservation was obtained by diluting 3-thiocyanatopropyltrimethoxysilane in methyl alcohol to a concentration of 40%. The archaeological wood described in Example 1 was used for conservation.

A 40% solution of 3-thiocyanatopropyltrimethoxysilane in methyl alcohol was used to impregnate wet archaeological wood. The impregnation solution was introduced into the archaeological wood using the alternating pressure method. The pressure impregnation consisted of 6 cycles of variable pressure (-0.1 MPa for 30 minutes, then 1 MPa for 6 hours), during which the samples were immersed in the impregnation solution all the time. After saturation, the samples were dried at room temperature for 1 week. The samples obtained were dimensioned as in Example I. The ASE for the wood samples impregnated with 40% methanolic 3-thiocyanatopropyltrimethoxysilane ranged from 71.1% (ASE for the cross-section) to 62.7% (ASE by volume).

List of non-patent literature

Almkvist G. (2013). Iron removal from waterlogged wood, Uppsala: Swedish University of Agricultural Sciences. SLU Repro, Uppsala.

Babinski L. (2012). Research on dimensional stability in waterlogged archaeological wood dried in a non-cooled vacuum chamber connected to a laboratory freeze-dryer. Wood. Pr. Science. Reports. Communication, 55 (187), 5-19.

Catsambis A., Ford B., Hamilton D.L. (2011). The Oxford Handbook of Maritime Archeology, 297.

Donath S., Militz H., Mai C. (2006). Creating water-repellent effects on wood by treatment with silanes. Holzforschung, 60 (1), 40-46.

Donath S., Militz H., Mai C. (2007). Weathering of silane treated wood. Holz a. Roh. u. Werkst., (65), 35-42.

E. Cappelletto E., Maggini S., Girardi F., Bochicchio G., Tessadri B., Di Maggio R. (2013). Wood surface protection with different alkoxysilanes: a hydrophobic barrier. Cellulose, 20 (6), 3131-3141.

Hill CAS, Farahani MMR, Hale MDC (2004). The use of organo-alkoxysilane coupling agents for wood preservation. Holzforschung 58 (3), 316-325.

Jensen P., Schnell U. (2004). The implications of using low molecular weight PEG for impregnation of waterlogged archaeological wood prior to freeze drying. In: Proceedings of the 9th ICOM group on wet organic archaeological materials conference, pp 279-308.

PL 235 395 Β1

Mai C., Militz H. (2004). Modification of wood with Silicon compounds. Treatment Systems based on body Silicon compounds - a review. Wood Science and Technology, 37 (6), 453-461.

Mazela B., Kowalczuk J., Ratajczak I., Szentner K. (2014). Moisture content (MC) and multinuclear magnetic resonance imaging (MRI) study of water absorption effect on wood treated with aminofunctional silane. European Journal of Wood and Wood Products, 72 (2), 243-248.

Olek W., Majka J., Stempiń A., Sikora M., Zborowska M. (2015). Hygroscopic properties of PEG treated archaeological wood from the rampart of the 10th century stronghold as exposed in the Archaeological Reserve Genius loci in Poznań (Poland). Journal of Cultural Heritage.

Panov D., Terziev N. (2009). Study on some alkoxysilanes used for hydrophobation and protection of wood against decay. International Biodeterioration & Biodegradation, 63 (4), 456-461.

Persson I., Almkvist G. (2007). Degradation of polyethylene glycol and hemicellulose in the Vasa. DOI: https: //doi.orq/10.1515/HF.2008.009

Sandstrom M., Jalilehvand F., Damian E., Fors Y., Gelius U., Jones M., Salome M. (2005). Sulfur accumulation in the timbers of King Henry Vlll's warship Mary Rosa: A pathway in the sulfur cycle of conservation concern. DOI: 10.1073 / pnas.0504490102

Smith W. (2002). A review of archaeological wood analyzes in Southern Englang. Center for Archeology Report 75/2002.

Tejedor C.C. (2010). Re-conservation of wood from the seventeenth-century Swedish warship the vasa with alkoxysilanes: A Re-treatment Study Applying Thermosetting Elastomers.

Tshabalala, M.A., Kingshott, P., VanLandingham, M.R., and Plackett, D. (2003). Surface Chemistry and Moisture Sorption Properties of Wood Coated With Multifunctional Alkoxysilanes by Sol-Gel Process, J. Appl. Polym. Sci., 88 (12): 2828-2841.

Tuduce-Traistaru A.A., Campean M., Timar M.C. (2010). Compatibility indicators in developing consolidation materials with nanoparticle insertions for old wooden objeets. International journal of conservation science, 219-226.

Xie Y, Hill C.A.S., Xiao Z., Militz H., Maia C. (2010). Silane coupling agents used for natural fiber / polymer composites: A review. Composites Part A: Applied Science and Manufacturing, 41 (7), 806-819.

Claims (11)

Patent claims 1. Preparation for the preservation of wet archaeological wood, characterized in that it contains an organofunctional silane of the general formula 1 (RO) 3Si (CH2) sZ (general formula 1) where R is CH3 or C2H5 and Z is SH or SCN or S4 (CH2 ) 3Si (OR) 3 dissolved in an aqueous solution of an organic solvent. 2. A formulation according to claim 1 The process of claim 1, wherein the organofunctional silane is 3-mercaptopropyl trimethoxysilane. 3. The formulation according to claim 1 The process of claim 1, wherein the organofunctional silane is bis- [3- (triethoxysilyl) propyl] tetrasulfide. 4. A formulation according to claim 1 The process of claim 1, wherein the organofunctional silane is 3-thiocyanatopropyltrimethoxysilane. 5. The formulation according to claim 1 The process of claim 1, wherein the organic solvent is selected from alcohols, ketones and aliphatic or aromatic hydrocarbons. 6. A formulation according to claim 1 A process as claimed in any one of the preceding claims, characterized in that the organic solvent is selected from methanol, ethanol, propanol, isopropanol, acetone, pentane, hexane, toluene and benzene. 7. A method of conserving wet archaeological or historic wood with the preparation disclosed in claim A formulation according to any one of claims 1 to 6, characterized in that the formulation according to any of the preceding claims 1 or 2, or 3, or 4, or 5, or 6 is introduced into the wet archaeological wood, preferably under After prior dehydration in 96% ethanol, the wood is then dried. 8. The method according to p. 7, characterized in that the formulation according to claim 7 1 or 2, or 3, or 4, or 5, or 6 are introduced into wet archaeological wood by a pressure swing method and / or by soaking and / or by lubrication. 9. The method according to p. The method of claim 8, characterized in that the pressure swing method comprises at least 4 cycles of alternating pressure, each cycle comprising from -0.05 to -0.1 MPa for 10 to 60 min and then 0.6 to 1.2 MPa for 1 up to 10 hours. 10. The method according to p. The method of claim 9, characterized in that the pressure swing method comprises 6 cycles of alternating pressure, each cycle comprising -0.1 MPa for 30 min, and then 1 MPa for 6 h. 11. The method according to p. 7. Method according to claim 7, 8 or 9 or 10, characterized in that after impregnation, the wood is dried at room temperature for at least 1 week.