The maximum moisture content of lime wood ... - Paweł Kozakiewicz [PDF]

Abstract: The maximum moisture content of lime wood impregnated with Paraloid B-72 solution in butyl acetate. Lime wood

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Annals of Warsaw University of Life Sciences - SGGW Forestry and Wood Technology № 95, 2016: 236-241 (Ann. WULS - SGGW, For. and Wood Technol. 95, 2016)

The maximum moisture content of lime wood impregnated with Paraloid B-72 solution in butyl acetate PIOTR MAŃKOWSKI, PAWEŁ KOZAKIEWICZ, SŁAWOMIR KRZOSEK Department of Wood Science and Wood Preservation Faculty of Wood Technology, Warsaw University of Life Sciences - SGGW, 159 Nowoursynowska St., 02-776 Warsaw Abstract: The maximum moisture content of lime wood impregnated with Paraloid B-72 solution in butyl acetate. Lime wood because of its particularly favorable machining characteristics was used, among other things, in artistic products. Currently, it is a material found in many monumental works of art in various states of preservation. In the present study changes in the maximum moisture content of lime wood were examined after it was impregnated with Paraloid B-72. The presence of polymer in the wood causes a decrease in the maximum moisture content but the dependence of the properties of the wood density remains unchanged. Keywords: lime wood, maximum moisture content, wood density, Paraloid B-72

INTRODUCTION Lime wood with low natural durability [EN 350-2:1994] is often attacked by fungi and insects. One way of consolidating the damaged lime wood in antique works of art is to saturate it with Paraloid B-72 [Schniewind 1990, Kozakiewicz et al 2011,Wiłkojć 2012]. Paraloid solution in butylacetate with a low concentration penetrates the wood well, but results in rather a low retention of the polymer, making it necessary to repeat the impregnation. Unfortunately, a higher concentration of polymer with one single impregnation usually results in uneven deposition of the wood [TuduceTraitaruet al.2011]. The effectiveness of the protection of the wood usually is expressed by measuring the retention of the said polymer [Mańkowski, Kozakiewicz, Krzosek 2015]. It appears that a similar indicator may also be the maximum moisture content, which also contains information about the degree of hydrophobization of wood saturated with paraloid. The aim of the study was, among other things, to verify whether the maximum moisture content is a feature which depends on the degree of saturation of lime wood with polymer B-72 and what is its connection with the density of the wood. MATERIAL AND METHODS For the research a total of 60 rectangular samples of lime wood were prepared, their dimensions are 20Rx20Tx30L mm. These samples were dried at 60oC until their weight became constant (moisture content less than one percent)determining the initial density (before saturation) and after saturation according ISO 13061-2:2014. The samples were divided into three groups: control (LW), saturated once (W1) and saturated twice (W2).The wood samples were vacuum impregnated in a 10% solution of Paraloid B-72 in butyl acetate. This process was carried out for 30 minutes under the vacuum mmHg. The saturated samples were submerged in the impregnating solution for a week, then removed from the solution and dried under an extraction hood. . In the group of samples (W2) the two previous steps were each performed twice [Mańkowski, Kozakiewicz, Krzosek 2015]. The Impregnated samples were again dried at 60oC to a constant weight (a higher temperature could cause degradation of the polymer).

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To determine the effect of saturation with Paraloid B-72 on maximum moisture content of lime wood all samples (groups LW, W1, W2) were poured hot water and placed in a vacuum oven. They were kept in the vacuum for 1hour then submerged in water for 30 days. Finally, the samples were weighed and measured to determine their density [ISO 130612:2014], retention of the polymer and maximum moisture content. The retention of the polymer was calculated from the formula [Mańkowski, Kozakiewicz,, Krzosek 2015]: m − mo [1] R= n Vo where: R- retention of polymer [kg·m-3] mn – wood mass after polymer saturation [kg], mo – mass of dry wood [kg], Vo – volume of dry wood [m3]. The maximum moisture content was estimated from the weight of water absorbed by the samples [on the basis on ISO 1306-1: 2014], from the following relationship: m w max − mo m H 2O max [2] = mo mo gdzie mwmax – maximum mass of wet wood ( after the process of soaking water) [kg] mo – mass of absolutely dry wood [kg] mH2Omax – the maximum mass of water contained in the wood [kg]. WmaxE =

Isochronally to this theoretical maximum moisture content was calculated of the following general dependence [Kozakiewicz 2012]: W max T = W pnw + ρ H 2 0 ⋅

ρ sd − ρ o 1,5 ⋅ ρ o

WmaxT = 0,35 +

1500 − ρ o 1,5 ρ o

[3]

were: Wmax T - maximum moisture content [%] Wpnw - moisture content fiber saturation point of lime wood – Wpnw =35 % [Tredelenburg and Mayer-Wegelin, 1955] ρsd – density of wood substance [1500 kg·m-3] ρo – density of absolutely dry wood kg·m-3] RESULTS AND DISCUSSION The results of the research, relating to the maximum moisture content, is shown in Table 1. The average density of the tested lime wood (moisture content of less than1%) in each group of samples is similar and is in the range of 510 to 530 kg·m-3. It is a high density as lime wood, but it is the typical density range of the species [Galewski, Korzeniowski 1958, Wagenführ 2007]. The maximum moisture content determined experimentally for the control sample (unmodified lime wood) amounts to 160% .The maximum moisture of lime wood after a single impregnation with Paraloid B-72 is lower and amounts to an average of 143% (10% decrease), while the double impregnation 131% (18% decrease compared to natural wood). Theoretically calculated the maximum moisture content based on the accepted constant value of the fiber saturation point of lime wood equals to 35% [Tredelenburg and Mayer-Wegelin, 1955] and the accepted density of absolutely dry wood is identical to the findings obtained on the basis of experience only in the case of not impregnated wood.

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After the saturation of the wood with Paraloid B-72 its density changes from 512 kg·m-3 to 597 kg·m-3 (an increase of 65 kg·m-3 more than 12%) after a single saturation, and from 521 kg·m-3 to 641 kg·m-3 ( an increase of 120 kg·m-3, can be more than 23%) after double saturation. A significant increase in the density of the treated wood resulting from the deposition of polymer in its structure is not fully reflected in the intensity of blocking the access of water in the process of soaking. The actual, experimentally determined maximum moisture content of impregnated wood is higher than that resulting from theoretical estimates. Table 1. Comparison of the results obtained in the above research including the maximum moisture content determined experimentally and theoretically calculated in accordance with the formula of general and details. Investigated property of lime wood Symbol Study group samples [unit] - an average value (standard deviation) LW W1 W2 Density of absolutely dry wood before g1 529 (71) 512 (77) 521 (86) impregnation [kg·m-3] Retention of polymer R 102 (6) 148 (11) [kg·m-3] Density of absolutely dry wood after g2 597 (72) 641 (75) impregnation [kg·m-3] Maximum moisture content WmaxE 160 (31) 143 (23) 131 (24) [%] experimentally determined 160 (28) 137 (21) 126 (19) maximum moisture content theoretically Wmax1 [%] calculated according formula no 3

a)

b)

c)

d)

Figure 1. The relationship between the maximum moisture content and density of absolutely dry lime wood before impregnation: a) control group (WL), b) after a single saturation – group W1, c) after double saturation – group W2, d) summary of all groups

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Percentage Increase of density of lime wood after single and double impregnation. Paraloid B-72 is comparable with the percentage decrease of its maximum moisture content. In this respect, both qualities are just as useful in assessing the effectiveness of the treatment involving the saturation of lime wood. In the study was also examined the relationship between experimentally determined: between the density of the wood and maximum moisture for each batch of wood: control (WL), after a single saturation (W1), and after double saturation with Paraloid B-72. The obtained results are shown in Figure 1. With increase in wood density exponentially decreases maximum moisture content of lime wood. Single and double saturation did not result in significant alterations in the relationship between the final density (after drying) and moisture content compared to the maximum course in the relationship of control samples (WL). The rates of approximation equations are similar to each other. Maximum moisture content of the wood is indirect evidence of its affinity for water. According to a study Burmester (1970) the age of lime wood has no significant impact on its hygroscopic properties, so this factor should not affect the resulting dependence. The obtained results and insights on contemporary lime wood probably also apply to antique wood. CONCLUSIONS On the basis of the research and calculations following conclusions were formulated: 1. Increasing saturation of lime wood with Paraloid B-72 solution in butyl acetate significantly reduces the empirically determined maximum moisture of the wood. With the retention of polymer approx 150 kg·m-3 average maximum moisture content is reduced by approx. 18% compared to untreated lime wood. 2. The increase in the density of treated lime wood resulting from the deposition of polymer in its structure does not translate fully to the intensity of blocking water absorption in the process. The actual, determined maximum moisture content of treated wood is higher thantheoretical estimates claim. 3. Changes in the density of the wood and moisture contentcan serve as an indicator of the effectiveness of the impregnation of lime wood with Paraloid B-72. 4. The nature of the change in the maximum moisture content (decrease in accordance with the exponential curve with an increase in density) is the same in natural lime wood, and after the single and double impregnation of Paraloid B-72. REFERENCES 1. BURMESTER A., 1970 : Veranderung des Sorptions - und Quelingsvermogens verschiedener Holzarten durch Alterung. Materialprufung 12 / 4 str. 132 -134. 2. EN 350-2:1994 Durability of Wood and Wood-based Products – Natural Durability of Solid Wood: Guide to natural durability and treatability of selected wood species of importance in Europe. 3. GALEWSKI W., KORZENIOWSKI A., 1958: Atlas najważniejszych gatunków drewna. Państwowe Wydawnictwo Rolnicze i Leśne. 4. GONET B., 1956: Analiza wzorów na nasiąkliwość drewna. Sylwan – Seria A, 3: 52– 59. 5. 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.

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6. 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. 7. KOZAKIEWICZ P., 2012: Fizyka drewna w teorii i zadaniach. Wydanie IV zmienione. Wydawnictwo SGGW. Warszawa. 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 No 74, s. 216-220. 9. MAŃKOWSKI P., KOZAKIEWICZ P., KRZOSEK S., 2015: Retention of polymer in lime wood impregnated with Paraloid B-72 solution in butyl acetate. Annals of Warsaw University of Life Sciences – SGGW, Forestry and Wood Technology No 92, 2015: 263-267. 10. SCHNIEWIND A.P., 1990: Solvent and moisture effect in deteriorated wood consolidated with soluble resin, Holz and Roh- und Werkstoff 48, 1990, pp.11-14. 11. TREDELENBURG R., MAYER-WEGELIN H., 1955: Das Holz als Rohstoff. Carl Hanser Verlag. München. 12. TUDUCE TRAISTARU A.A., TIMAR M.C., CAMPEAN M.,2011: Studies upon penetration of Paraloid B72 into poplar wood by cold immersion treatments. Bulletin of the Transilvania University of Brasov Series II: Forestry Wood Industry Agricultural Food Engineering Vol. 4 (53) No. 1 – 2011, Brasow 2011. 13. WAGENFÜHR R., 2007: Holzatlas.6., neu bearbeitete und erweitere Auflage. Mit zahlreichen Abbildungen. Fachbuchverlag Leipzig im Carl Hanser Verlag. 14. 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.

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Streszczenie: Wilgotność maksymalna drewna lipowego nasyconego roztworem paraloidu B72 w octanie butylu. Drewno lipy ze względu na szczególnie korzystne cechy obróbcze znalazło zastosowanie między innymi w wyrobach artystycznych. Obecnie stanowi ono tworzywo wielu zabytkowych dzieł sztuki, w różnym stanie zachowania. Obiekty te są zabezpieczane między innymi poprzez przesycenie drewna różnymi polimerami. W ramach niniejszej pracy przeanalizowano zmiany wilgotności maksymalnej drewna lipowego po jego przesyceniu paraloidem B-72. Wzrost gęstości impregnowanego drewna lipowego wynikający z osadzania się polimeru w jego strukturze nie przekłada się w pełni na intensywność blokowania dostępu dla wody. Rzeczywista, oznaczona doświadczalnie wilgotność maksymalna drewna impregnowanego jest wyższa niż wynikająca z oszacowań teoretycznych. Charakter zmian wilgotności maksymalnej (spadek zgodnie z krzywą wykładniczą wraz ze wzrostem gęstości) jest taki sam w naturalnym drewnie lipowym jak i po jego jedno oraz dwukrotnej impregnacji paraloidem B-72. Zmiany gęstości drewna i wilgotności maksymalnej mogą służyć jako wskaźniki skuteczności impregnacji drewna lipowego paraloidem B-72.

Corresponding authors: Piotr Mańkowski Department of Wood Sciences and Wood Protection Faculty of Wood Technology Warsaw University of Life Sciences – SGGW 159 Nowoursynowska St. 02-776 Warsaw, Poland email: [email protected] http://piotr_mankwski.users.sggw.pl phone: +48 22 59 286 38 Paweł Kozakiewicz Department of Wood Sciences and Wood Protection Faculty of Wood Technology Warsaw University of Life Sciences – SGGW 159 Nowoursynowska St. 02-776 Warsaw, Poland email: [email protected] http://pawel_kozakiewicz.users.sggw.pl phone: +48 22 59 38 647 fax: +48 22 59 386 59 Sławomir Krzosek Department of Wood Sciences and Wood Protection Faculty of Wood Technology Warsaw University of Life Sciences – SGGW 159 Nowoursynowska St. 02-776 Warsaw, Poland email: [email protected] phone: +48 22 59 386 33

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