Annals of Warsaw University of Life Sciences SGGW Forestry and Wood Technology 93, 2016: 99-104 (Ann. WULS - SGGW, For. and Wood Technol. 93, 2016) Determination of the wettability of European lime wood (Tilia cordata Mill.) as sculptures and painting supports material AGNIESZKA KUROWSKA, PAWEŁ KOZAKIEWICZ Department of Wood Science and Wood Preservation, Faculty of Wood Technology, Warsaw University of Life Sciences - SGGW, 159 Nowoursynowska St., 02-776 Warsaw Abstract: Determination of the wettability of European lime wood (Tilia cordata Mill.) as sculptures and painting supports material. European lime wood, which is the subject of the research, is used in Europe principally for making sculptures, frames and painting supports. In this paper, the wettability of European lime wood has been determined by measuring the contact angle of wood wetted with water and diiodomethane, using the sessile drop method. Surface tension, wetting energy and work of adhesion for the wood - water and wood - diiodomethane structures have been marked. Surface free energy of the tested wood species was determined in accordance with the Owens - Wendt method. The course of wetting the wood with polar liquid, i.e. water, showed considerable dynamics. After 60 s from placing a water drop on the lime wood surface the contact angle decreased by 70%. When the wood was wetted with diiodomethane, however, the contact angle decreased by 30%. The dominant component, which was also more variable in time, was the energy which originated from the polar liquid (water). Key words: European lime, wettability, contact angle, surface free energy, wetting energy, work of adhesion, surface tension INTRODUCTION Lime (Tilia cordata Mill.) is a common tree species in Poland; it grows in the entire plain and in sub - mountainous areas. It is a relatively slow - growing species, but it does not have high habitat requirements (Gałczyński 1928, Strojny 1981). It is also a longeval tree. An 18th century author, Fr Krzysztof Kluk, wrote (1778) "it stands unspoilt for more than a thousand years". Moreover, it grows to considerable size, reaching ca. 40 m in height and ca. 800 cm in trunk circumference (Strojny 1981). Lime wood belongs to diffuse - porous wood species without heartwood. Because of its low density, 350-600 kg/m 3 in air drying condition (Kollmann and Cöte 1968, Krzysik 1978), and straight fibre composition, lime wood is an easy material for planing, turning and sculpting (Warywoda 1957, Galewski and Korzeniowski 1958). Many valuable historic objects (sculptures and painting supports) made of lime wood are found at the present time in museum collections and churches. These objects are in different states of preservation (e.g. Popescu et al. 2005, Trochimowicz and Swaczyna 2005, Trochimowicz 2010, Wiłkojć 2012), as this type of wood has low natural durability (only class 5 according to EN 350-2:1994) and is often attacked by insects and microorganisms (Galewski and Korzeniowski 1958, Strzelczyk 2004, Kozakiewicz et al. 2011). In preserving and restoring objects made of lime wood it is often necessary to insert plug patches made of modern wood. Glued patches are covered and saturated with various substances. The crucial role in such treatment is played by the characteristics of wettability as well as the physicochemical properties of lime wood surface, such as the contact angle, surface tension, wetting energy, work of adhesion, and surface free energy. Quantification of the above has been the purpose of this paper. 99
MATERIAL AND METHODS European lime wood (Tilia cordata Mill.) was used for the tests. Samples of 135 135 15 mm were cut in accordance with the principal anatomical section lines of the wood in such a manner as to obtain tangential section (dominant in lime wood products) on the broad surfaces (planes). The surfaces of wood samples were planed. The samples having been brought to air drying condition, wood moisture content was determined in accordance with ISO 13061-1:2014, and wood density in accordance with the requirements of ISO 13061-2:2014. Table 1. Data of surface tension and components of the test liquids Liquid Property Surface tension Dispersion Polar Acid Base [mn/m] [mj/m 2 ] [mj/m 2 ] [mj/m 2 ] [mj/m 2 ] water (H2O) 72.80 21.90 51.00 25.50 25.50 diiodomethane (CH2I2) 50.80 50.80 0.00 0.00 0.00 The contact angles in wetting the wood with reference liquids were measured according to the sessile drop method in Phoenix 300 goniometer manufactured by Surface Electro Optics. The reference liquids were polar, i.e. water, and nonpolar, i.e. diiodomethane (tab.1). Surface tension, wetting energy and work of adhesion were determined for the wood - water and wood - diiodomethane structure. Surface free energy of the wood was determined on the basis of tests using the Owens - Wendt method (Owens and Wendt 1969). The parameters characterizing wood wettability were measured after 1, 2, 3, 10, 20, 30, 40, 50 and 60 seconds from placing the liquid drop on the wood surface. Trend lines illustrating the changes in time in individual parameters were drawn, parameters of curve equation (yd) were stated, as well as determination coefficients R 2. The statistical study of the tests results was carried out at a significance level of 0.050. RESULTS AND DISCUSSION Lime wood was characterized by 497 kg/m 3 density (±11 kg/m 3 ) and 6.41% (±0.6%) moisture content. The density was typical for this wood species (Galewski and Korzeniowski 1958, Wagenführ 2007), as well as its variation. For example, according to the tests of Sekhar and Negi (1960) involving 250 logs of 50 different wood species, the variation coefficient within a single wood species in air drying condition amounts on the average to ca. 6%. The results of the wettability measurements are presented in figures 1 and 2. a). b). Figure 1. Contact angle (a) and surface tension (b) of the structure lime wood - water (y W), lime wood - diiodomethane (y D) 100
Lime wood parameters changed significantly within the analysed time span, i.e. 60 seconds. The changes had exponential function character; they were most rapid in the first seconds of the tests. The process of wetting the wood with polar liquid, i.e. water, showed greater dynamics than with nonpolar liquid, i.e. diiodomethane; this is significant dependence for gluing lime wood and finishing its surface. After 60 s from placing the water drop on the lime wood surface the contact angle changed from 56 o to 16 o (i.e. by 71%). In the case of nonpolar liquid, i.e. diiodomethane, the decrease in contact angle was from 23 o to 16 o (by 30%) (fig. 1a). Other effects of wood wetting included changes in liquid surface tension; they were largest in the drop of water (fig. 1b). The surface tension doubled in 60 s from placing the water drop on the surface of lime wood. In the case of diiodomethane, however, the increase in surface tension observed 60 s after placing the drop on wood surface was by 20%. a). b). Figure 2. Wetting energy (a) and work of adhesion (b) of the structure lime wood - water (y W), lime wood - diiodomethane (y D) Moreover, significant changes in wetting energy (fig. 2a) and the work of adhesion (fig. 2) were observed in the lime wood water structure. After 60 seconds from placing the water drop on the tangential surface of lime wood the wetting energy increased by ca. 70%. In the case of the lime wood diiodomethane structure, however, 5% increase in wetting energy was observed 60 s after depositing the drop on the surface of wood. Furthermore, in the case of wetting the wood with water, an increase in the work of adhesion by ca. 26% was observed after 60 seconds from placing the drop on the surface of wood. For the structure lime wood diiodomethane, however, the increase in the work of adhesion was at the level of 2%, i.e. statistically insignificant. Figure 3. Surface free energy (SFE), dispersion and polar components 101
Figure 3 presents the curves which illustrate the changes in time in surface energy and its components (polar and dispersive). Obtained results indicate that the dominant component, which is also more variable in time, is the energy which originates from the polar liquid (water). The results are typical for species without heartwood with open wood structure and low extractives content, e.g. beech or poplar wood (Santoni and Pizzo 2011). CONCLUSIONS The research into the surface wettability of lime wood (Tilia cordata Mill.) enabled the following conclusions to be drawn: 1. The course of the wetting process, in particular with polar liquid (water), shows considerable dynamics. After 60 s from placing a water drop on lime wood surface the contact angle decreased by 70%. However, when the wood was wetted with diiodomethane, the contact angle decreased by 30%. 2. When the wood was wetted with water, 60 seconds after the drop was deposited on wood surface the wetting energy was observed to increase by ca. 70%. In the case of lime wood diiodomethane structure, the increase in wetting energy was at the level of 5%. 3. The dominant component, which was also more variable in time, was the energy which originated from the polar liquid (water). REFERENCES 1. EN 350-2:1994 Durability of wood and wood - based products. Natural durability of solid wood. Part 2: Guide to natural durability and treatability of selected wood species of importance in Europe. 2. GALEWSKI W., KORZENIOWSKI A., 1958: Atlas najważniejszych gatunków drewna. Państwowe Wydawnictwo Rolnicze i Leśne, Warszawa. 3. GAŁCZYŃSKI B., 1928: Drzewa liściaste leśne i alejowe. Nakładem Autora. Piaseczno pod Warszawą. 4. ISO 13061-1:2014 Physical and mechanical properties of wood Test methods for small clear wood specimens Part 1: Determination of moisture content for physical and mechanical tests. 5. ISO 13061-2:2014 Physical and mechanical properties of wood Test methods for small clear wood specimens Part 2: Determination of density for physical and mechanical tests. 6. KLUK K., 1778: Roślin potrzebnych, pożytecznych osobliwie krajowych, albo które w kraju użyteczne być mogą utrzymanie, rozmnożenie, zażycie. Warszawa. 7. KOLLMANN F., CÖTE W.A., 1968: Principles of wood science and wood technology. Solid wood part I. Berlin-Heidelberg-N.York. 8. KOZAKIEWICZ P., MAŃKOWSKI P., WIŁKOJĆ E., 2011: Evaluation of Paraloid B- 72 lime wood reinforcement efficiency. Annals of Warsaw University of Life Sciences SGGW, Forestry and Wood Technology 74: 216-220. 9. KRZYSIK F., 1978: Nauka o drewnie, Państwowe Wydawnictwo Naukowe, Warszawa. 102
10. OWENS D.K., WENDT R.C., 1969: Estimation of the surface free energy of polymers. Journal of Applied Polymer Science 13 (8): 1741-1747. 11. POPESCU C.M., SAKATA Y., POPESCU M.C., OSAKA A., VASILE C., 2005: Degradation of lime wood painting supports. e-preservationscience 2: 19-29. 12. SANTONI I., PIZZO B., 2011: Effect of surface conditions related to machining and air exposure on wettability of different Mediterranean wood species. International Journal of Adhesion & Adhesives 31: 743-753. 13. SEKHAR A.C., NEGI G.S. 1960: Über die Variationskoeffizienten der mechanischen Eigenschaften des Holzes. Holz als Roh- und Werkstoff 18 (10): 367-369. 14. STROJNY W., 1981: Nasze drzewa. PWRiL. Wydanie I. Warszawa. 15. STRZELCZYK A.B., 2004: Observations on aesthetic and structural changes induced in Polish historic objects by microorganisms. International Biodeterioration & Biodegradation 53 (3): 151-156. 16. TROCHIMOWICZ A., 2010: Conservation of wooden sculpture of saint Anne. Annals of Warsaw University of Life Sciences SGGW. Forestry and Wood Technology 72: 382-385. 17. TROCHIMOWICZ A., SWACZYNA I., 2005: Species of wood used in cradle structures. Annals of Warsaw University of Life Sciences SGGW. Forestry and Wood Technology 72: 386-389. 18. WARYWODA A., 1957: Encyklopedia techniczna tom I. Drzewa użytkowe w architekturze przestrzennej i przemyśle. A-Z ważniejsze gatunki iglaste i liściaste produkujące drewno i inne surowce znane na międzynarodowych rynkach handlowych. Krakowski Zespół Pracowników Naukowych. Kraków. 19. WAGENFÜHR R., 2007: Holzatlas.6., neu bearbeitete und erweitere Auflage. Mit zahlreichen Abbildungen. Fachbuchverlag Leipzig im Carl Hanser Verlag, München. 20. WIŁKOJĆ E., 2012: Christ Blessing The Children by Lucas Cranach the Elder in the Collection of the Wawel Royal Castle, study and conservation. Publishing by Wawel Royal Castle, Cracow. 103
Streszczenie: Oznaczenie zwilżalności drewna lipy drobnolistnej (Tilia cordata Mill.) jako materiału używanego w rzeźbiarstwie i na podobrazia drewniane. Drewno lipy stosowane jest w krajach europejskich głównie do wytwarzania rzeźb, ram i podobrazi. Przy konserwacji i restauracji obiektów z drewna lipowego często istnieje potrzeba stosowania uzupełnień ze współczesnego drewna. Wklejane wstawki są pokrywane i przesycane różnymi substancjami. Przy tego typu zabiegach decydujące znaczenie mają właściwości charakteryzujące zwilżalność i fizykochemiczne właściwości powierzchni. W pracy określono zwilżalność drewna lipy metodą osadzonej kropli dla układu drewno - woda oraz drewno - dijodometan. Przebieg procesu zwilżania, w szczególności cieczą polarną (wodą), wykazuje znaczną dynamikę. W przypadku zwilżania drewna wodą stwierdzono wzrost wartości energii zwilżania o ok. 70% po 60 sekundach od naniesienia kropli na powierzchnię drewna. Natomiast dla układu drewno lipy - dijodometan wzrost wartości energii zwilżania był na poziomie 5%. Dominującą składową swobodnej energii powierzchniowej drewna lipy jest energia pochodząca od cieczy polarnej (wody). Corresponding authors: Agnieszka Kurowska Department of Wood Sciences and Wood Preservation Faculty of Wood Technology Warsaw University of Life Sciences SGGW 159 Nowoursynowska St. 02-776 Warsaw, Poland email: agnieszka_kurowska@sggw.pl phone: +48 22 59 38 661 Paweł Kozakiewicz Department of Wood Sciences and Wood Preservation Faculty of Wood Technology Warsaw University of Life Sciences SGGW 159 Nowoursynowska St. 02-776 Warsaw, Poland email: pawel_kozkiewicz@sggw.pl http://pawel_kozakiewicz.users.sggw.pl phone: +48 22 59 38 647 104