Wood wetting with various liquids

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1 Annals of Warsaw University of Life Sciences - SGGW Forestry an Woo Technology 83, 013: (Ann. WULS - SGGW, For. an Woo Technol. 83, 013) Woo wetting with various liquis JOZEF KÚDELA, FRANTIŠEK WESSERLE Faculty of Woo Sciences an Technology, Technical University in Zvolen, Slovak Reublic Abstract: Woo wetting with various liquis. Woo wetting with stanar liquis is a comlex rocess controlle by chemical comosition of the liquis use, roerties of the substrate, interactions among unsaturate force fiels across the hase bounary between woo an liqui as well as by seconary effects of a range of factors imlie by secific roerties of the woo an the liquis use. The results suggest that both iserse an olar comonents of the woo surface free energy are necessary to quantify searately. The γ SV values have been foun roerly etermine at the hase bounary between woo with α-bromonahtalene an between woo an iioomethane; the γ SV values at the hase bounary between woo an aolar-olar liquis with the olar comonent bigger than the olar comonent of woo. In our case, such liqui was water. Thus, the woo surface free energy values SV reresenting the sum of the iserse an olar comonent γ SV an γ SV, resectively, etermine as escribe in this aragrah are higher than the woo surface free energy values etermine with one liqui only. Keywors: wetting, aolar liquis, aolar-olar liquis, contact angle, surface free energy, beech woo INTRODUCTION Wetting of woo surface with liquis has the ecisive role for ahesion of liqui an soli materials to the woo. This is imortant for gluing, surface treatment an moification of woo. The caacity of a liqui to wet the surface of a soli is assesse through the size of the contact angle between the two materials. The values of contact angle measure at the hase bounary with a liqui stanar rovie the base for etermining the thermoynamic characteristics of the woo surface surface free energy an its comonents. As liqui stanars erform liquis constraine in woo surface wetting, that means aolar an aolar-olar liquis showing aitive roerties for surface free energy. The ifferences in the chemical comosition of these liquis affect the origin an character of their hase bounary with woo. These ifferences are manifeste through ifferent values of surface free energy an its comonents. The main subject of the aers ublishe in the recent 15 years has been the measurement of surface free energy of woo SV, its comonents iserse an olar: SV an SV, Lifshitz van er Waals comonent SV LW an Lewis aci-base comonent SV AB. These methos also use exerimentally measure values of the contact angle at the hase bounary between woo an liqui stanars. In general, there are use arallel three liquis iffering in their surface free energy. The contact angle is measure at the beginning of wetting rocess. The time interval for all the simultaneously use liquis is always the same, not consiering ifferences in their chemical an hysical roerties. The most frequently use liqui stanars are α-brom-nahtalene, iioomethane, formamie, ethylene glycol, glycerine an water (GARDNER 1996, ZHANG et al , GINDL et al. 001, GINDL an TSCHEGG 00, BLANCHARD et al. 009, PIAO et al. 010 an other). These liquis are aolar or aolar-olar, with aitive toerties of surface free energy. The woo wetting with these liquis is constraine. LIPTÁKOVÁ an KÚDELA (1994) calculate surface free energy base on the contact angle w associate with an ieally smooth surface. The values of this contact angle are generally smaller than the values of the contact angle 0 occurring at the beginning of the wetting rocess. 156

2 This results in higher values of surface free energy an its olar share for w. We roose this angle as more fitting for calculation of thermoynamic characteristics exressing interactions at the hase bounary between woo an liqui or soli substances. However, neither this metho has been accete without oubts (SUNGUO an JOHANSSON 1996, PIAO et al. 010). Summarising the results, there were foun ifferences in contact angle values an free energy values for the same material between the authors. There shoul be, however, no ifferences in surface free energy values. The aim of our work was to analyse the wetting rocess in selecte woo secies, with using liquis of iverse olarity currently use for etermining surface free energy of woo an the comonents of this energy. MATERIAL AND METHODS The exerimental works were erforme with beech woo secimens, mm in size. The wetting of secimens was stuie on their raial an tangential surfaces treate with microtome. The woo surfaces obtaine in this way only een on the woo anatomical structure (KÚDELA an LIPTÁKOVÁ 006). Fig. 1 Parameters of a sessile ro The secimens re-treate in this way were lace into a conitioning box, an then acclimate to a 1% moisture content. The moisture content in the secimens was measure gravimetrically before the wetting rocess itself. For the calculation of contact angle were use the results aate from ŠTRBOVÁ et al. (013): arameters (iameter an height) of a sessile ro alie onto woo surface Fig. 1. The woo wetting rocess was stuie with using an analyser DSA30 Stanar with the attache rogramme ackage. The woo wetting liquis were five (Table 1). Tab.. 1 Parameters of liqui stanars use in stuy. Testing liqui [mjm ] [mjm ] [mjm ] + [mjm ] -- [mjm ] [Pas] Water Ethylene glycol Formamie Bromonahtalene Diioomethane The equilibrium state in the wetting rocess was ientifie accoring to LIPTÁKOVÁ an KÚDELA (1994) who assign it to the moment when the liqui stos sreaing onto the surface an starts receing. This moment can be etermine through the ro iameter. We consiere the contact angle etermine in this way as the equilibrium one an the basic one for further calculations. For alying the liqui onto the secimen surface we use a osing alicator (injection syringe). The amounts alie were ml each. The varying ro shae was observe in the fibre irection, onto the tangential an raial surface, from the moment of alication to the comlete soaking into the substrate. The ro image was scanne with a camera an transmitte onto a monitor. The measuring results were automatically assemble in a comuter. The values of contact angle w etermine form the woo wetting with one liqui were use for calculation of surface free energy accoring to the moifie equation roose by NEUMANN et al. (1974) (0,0137 S,00) S L L cos. (1) (0,015 1) L S 157 L

3 The iserse an olar comonent S (1974), by solving the equations an S were calculate accoring to KLOUBEK 1 cos 1 cos ( ) S ( ) S L L () L 1 cos 1 cos ( ) S ( ) S L L.. (3) L RESULTS AND DISCUSSION During the wetting of beech woo surface with aolar an aolar-olar liquis, the contact angle was always subjecte to ermanent changes with time. For all the testing liquis use, the stuy of ro iameter confirme to earlier observations that the ro iameter augments until a certain moment an then iminishes graually. This means that the avancing contact angle switche to the receing in all cases. In the receing text (see.3) we efine this moment as the equilibrium state. There occurre ifferences in the time t u, necessary to reach the equilibrium state as well as ifferences in the values of contact angles 0, u, w. The values of equilibrium time (t u ) were ifferent for ifferent liquis (Table ). It is evient that the time t u eens on the liqui s olarity. In aolar liquis, the time t u was shorter in - bromonahtalene. Tab. Basic statistical characteristics of time t u values for various liquis Raial surface Tangential surface Liqui Basic stat. characteristic t u x[s] s[s] v[%] x[s] s[s] v[%] Water Ethylene glycol Formamie Bromonahtalene Diioomethane In liquis islaying aolar-olar roerties (water, ethylene glycol, formamie), the time t u increase with increasing olar comonent of surface free energy of the liquis. On the other han, the results obtaine with ethylene glycol show also an imact of viscosity substantially higher in this liqui than in the other teste ones. We euce that the ifferences in erformance among the liquis reflect the ifferences in their surface free energy an viscosity. Our metho for etermining the equilibrium contact angle u, however, can ensure elimination of viscosity influence in liquis. The variability of t u values in frame of the same liqui was the result of the comosition unevenness of woo surface an the ranom location of the ro onto the surface. This is true equally for raial an tangential surfaces. This high variability cause that there was no significant ifference in t u values between the raial an the tangential surfaces. The ifferent erformance of liquis at their hase bounary with woo was also reflecte in the values of contact angles θ 0, θ u an θ w (Table 3). The highest contact angle 0 values at the moment of the ro alication were measure in case of reistille water, the lowest ones in the case of -Bromonahtalene. There were not big ifferences among the other liquis. At the moment of the ro alication onto the surface, there are two ifferent hases (woo substance an air) with ifferent surface energies beneath the ro. In this case, the values of 0 were the results of interactions at the hase bounary between woo an water, the morhological an chemical roerties of woo surface; while θ w values only een on the chemical roerties of the substrate (LIPTÁKOVÁ et al. 1998, 000). 158

4 Further we etermine the surface free energy an its comonents. Table 4 islays average values of these items. The surface free energy values varie in quantity an quality, accoring to the liqui the value was etermine with. The results assemble in Table 4 show that the surface free energy values of woo o not only een on the woo surface roerties but also on the chemical structure of the liqui stanar use. The ifferences are rather big, being in contraiction with the surface free energy concetion as a material constant of substances. Tab. 3 Average values of contact angles Θ 0, Θ u an Θ w at the hase bounary woo liqui Liqui Raial surface Tangential surface Θ 0 Θ u Θ w Θ 0 Θ u Θ w [ ] Water Ethylene glycol Formamie Bromonahtalene Diioomethane Tab. 4 Average values of surface free energy values an its comonents in beech woo Raial surface Tangential surface Liqui s s s s s [mjm-] Water Ethylene glycol Formamie Bromonahtalene Diioomethane The surface free energy etermine with using aolar liquis (-Bromonahtalene an Diioomethane), was the lowest, ractically the same as their iserse comonent, with the olar comonent nearly zero. Aolar liquis with iserse comonent bigger than the iserse comonent of woo are suitable for etermining only the iserse share of the surface free energy of woo. To etermine the olar share of surface free energy of woo, there are neee liquis whose surface free energy shows aitive roerties. The ifferences between the values γ LV (Table 1) an the etermine values γ SV (Table 4) allow us to conclue that crucial values for etermining the olar share of surface free energy of woo are the values obtaine with water. The results also imly that the surface free energy of woo cannot be etermine comletely with using one single liqui from the ones iscusse in this aer. The iserse an the olar share of the surface free energy of woo are ossible to etermine searately with using aroriate an aolar an an aolar-olar stanars. The surface free energy of materials reresents the sum of its iserse an olar shares, consequently, the surface free energy of the stuie surfaces is higher that the energy obtaine with using one liqui only. The surface free energy values SV an the values of its iserse an olar comonents γ SV an γ SV obtaine in this way are higher than the values reorte in the literature. This is ue to the liqui use as well as ue to the methos use for etermining the equilibrium contact angle. Our results show that the values of surface free energy of woo SV as well as the values of its iserse an olar comonents γ SV an γ SV are in general higher than it has been suose until now in the case when the iserse comonent of woo is etermine with using aolar liquis with their iserse comonent higher than the iserse comonent of woo an the olar comonent of woo is etermine with using aolar-olar liquis with their olar comonent higher than the olar share of woo execte. Consequently, there also s 159

5 will occur stronger cohesion in woo an stronger ahesion at the hase bounary between the woo an liqui or soli materials. This fact, however, will not have a ecisive influence on the relations between woo an these materials, incluing coating materials an glues escribe in (LIPTÁKOVÁ et al. 000, LIPTÁKOVÁ an KÚDELA 00, PROSZYK et al. 1997, KÚDELA an LIPTÁKOVÁ 006, PECINA an PAPRZYCKI 1995 an others). CONCLUSION Our results have confirme that the woo wetting with stanar liquis eens on the chemical structure of the liquis use, on the roerties of the substrate, on the interactions of unsaturate force fiels at the hase bounary between woo an liquis an also on seconary effects of a large number of factors imlie by the secific roerties of woo an of the liquis use. The currently use liqui stanars for assessment of woo surface roerties erform in a ifferent way at the hase bounary with woo. The interactions of surface forces uring woo wetting with aolar liquis are controlle by isersion forces, that means by forces with aolar character. The equilibrium occurs at the beginning of the wetting rocess. Aart from isersion forces, at the hase bounary between woo an aolar-olar liquis, olar forces act too. Also in this case, the interaction among aolar forces occurs at the beginning of the wetting rocess, the olar forces, however, come into effects graually. The equilibrium occurs at the time t u, which is the time of the equilibrium contact angle u. The contact angle u an the erive value of the contact angle corresoning to the ieally smooth woo surface w grow roortionally with growing olar share of the surface free energy LV. These results suggest that it is necessary to etermine the iserse an the olar comonents of surface free energy of woo searately. For etermining the values of γ SV were foun suitable the results obtaine at the hase bounary between woo an - Bromonahtalene an Diioomethane; for etermining γ SV, the results obtaine at the hase bounary between woo an aolar-olar liquis with olar comonent bigger than the olar comonent of woo. In our case, such liqui was water. Thus, the surface free energy of woo SV is the sum of the etermine iserse an olar shares γ SV an γ SV. LITERATURE 1. BLANCHARD V., BLANCHET P., RIEDL B. 009: Surface energy moification by raiofrequency inuctive an caacitive lasmas at low ressures on sugar male: an exloratory stuy. Woo Fiber Sci. 41(3): GARDNER D. J. 1996: Alication of the Lifshitz van er Waals aci base aroach to etermine woo surface tension comonents. Woo Fiber Sci., 8(4): GINDL M., SINN G., GINDL W., REITERER A., TSCHEGG S. 001: A comarison of ifferent methos to calculate the surface free energy of woo using contact angle measurements. Collois an Surfaces. A: Physicochemical an Engineering Asects, 181: GINDL M., TSCHEGG S. 00: Significance of the aciity of woo to the surface free energy comonents of ifferent woo secies. Langmuir 18: KLOUBEK J. 1974: Calculation of surface free energy comonents of ice accoring to its wettability by water, chlorbenzene an carbon isulfie. J. Colloi Interface Sci., 46: KÚDELA J., LIPTÁKOVÁ E: 006. Ahesion of coating materials to woo. J. Ahesion Sci. Technol., 0(8):

6 7. LIPTÁKOVÁ E., KÚDELA J., BASTL Z., SPIROVOVÁ I. 1995: Influence of mechanical surface treatment of woo the wetting rocess. Holzforschung, 49(4): LIPTÁKOVÁ E., KÚDELA J. 1994: Analysis of the woo wetting rocess. Holzforschung, 1994, 48(): LIPTÁKOVÁ E., KÚDELA J. 00: Stuy of the system woo coating material. Part. Woo soli coating material. Holzforschung, 56: LIPTÁKOVÁ E., KÚDELA J., SARVAŠ J. 1998: Problems concerning equilibrium state on the hase bounary woo liqui material. In: Woo structure an roerties 98 (Es. S. Kurjatko an J. Kúela). Zvolen: Arbora Publishers, LIPTÁKOVÁ E., KÚDELA J., SARVAŠ J. 000: Stuy of the system woo - coating material I. Woo liqui coating material. Holzforschung, 54(): NEUMANN A. W. et al. 1974: An equation of state aroach to etermine surface tensions of low- energy solis from contact angles. Colloi Interface Sci., 49(): PECINA H., PAPRZYCKI O. 1995: Lack auf Holz. Hannover: Vinzentz Verlag, PIAO C., WINANDY J. E., SHUPE T. F. 010: From hyrohilicity to hyrohobicity: a critical review: Part I. Wettability an surface behavior. Woo Fiber. Sci., 4(4): PROSZYK S., KRYSTOFIAK T., WINNIK A. 1997: Stuies on ahesion to the woo of two comonent PVAC ahesives harene with aluminium chlorie. Folia Forestalia Polonica, Seria B. 8: SUNGUO W., JOHANSSON I. 1996: Evaluation of a olar an aci base roerties of woosurfaces by contact angle measurements. In: Moern ahesion theory alie on coating an gluing of woo. Stockholm: Forskarskolan Träoch Träfiber, ŠTRBOVÁ M., WESSERLE F., KÚDELA J. 013: Contact Angle Measurement on Woo by Dro Shae Analysis. In: Science for Sustainability. Györ Soron: University of West Hungary, ZHANG H. J., GARDNER D. J., WANG J. Z., SHI Q. 1997: Surface tension, ahesive wettability an bonability of artificially weathere CCA treate southern ine. Forest Pro. J., 47(10): Streszczenie: Zwilżalność rewna róznymi cieczami. Zwilżanie rewna cieczami jest złożonym rocesem związanym ze skłaem chemicznym cieczy, własnościami substratu, interakcjami omięzy ukłaami sił na granicy faz oraz wieloma czynnikami związanymi z własnościami cieczy oraz ołoża. Praca rzestawia rozważania oraz wyniki ekserymentów zwilżalności rewna za omocą róznych cieczy. ACKNOWLEDGEMENT: We highly acknowlege the suort from the Scientific Gran Agency of the Ministry of Eucation SR an the Slovak Acaemy of Sciences (Grant No. 1/0893/13 Surface roerties an hase interface interactions of the woo liqui system ). Corresoning author: Jozef Kúela,.František Wesserle Deartment of Woo Science, Faculty of Woo Sciences an Technology, Technical University in Zvolen, T. G. Masaryka 4, Zvolen, Slovak Reublic kuela@tuzvo.sk 161