Mechanical properties of wood from Pinus sylvestris L. treated with Light Organic Solvent Preservative and with waterbone Copper Azole

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1 Instituto Ncionl de Investigción y Tecnologí Agrri y Alimentri (INIA) Forest Systems (3): Avilble online t ISSN: eissn: Mechnicl properties of wood from Pinus sylvestris L. treted with Light Orgnic Solvent Preservtive nd with wterbone Copper Azole A. Villsnte 1 *, R. Lin 2, J. A. M. Rojs 3, I. M. Rojs 2 nd S. Vignote 2 1 Deprtmento de Ingenierí Agroforestl. ETSEA. Universidd de Lleid. Avd. Rovir Roure, Lleid, Spin 2 Deprtment of Forest Economy nd Mngement. ETSI de Montes. Universidd Politécnic de Mdrid. Ciudd Universitri, s/n Mdrid, Spin 3 Deprtment of Signl Theory nd Communictions. Escuel Politécnic Superior. Universidd de Alclá. Ctr. de Mdrid-Brcelon, km Alclá de Henres (Mdrid), Spin Abstrct Aim of study: To determine the effect on wood from Pinus sylvestris of tretment with preservtives on mechnicl properties nd to estblish the reltion between the penetrtion nd compression strenght. Are of study: Spin. Mteril nd methods: 40 smples of defect-free wood from Pinus sylvestris L. were treted with Light Orgnic Solvent Preservtive (Vcsol Azure WR 2601) nd 50 with wterborne Copper Azole (Tnlith E 3492). 40 control smples were not treted (wter or preservtive). Mechnicl resistnce to sttic bending, modulus of elsticity nd compression strength prllel to the grin were compred with untreted wood. Regression nlysis between the penetrtion nd compression strength prllel ws done with the smples treted with wterborne preservtive. Min results: The results indicte tht the treted wood (with either product) presents sttisticlly significnt increse in mechnicl resistnce in ll three mechnicl chrcteristics. The results obtined differ from erlier studies crried out by other uthors. There ws no correltion between prllel compression strength nd the degree of impregntion of the wood with wterborne Copper Azole. The most probble explntion for these results concerns chnges in pressure during tretment. The use of untreted control smples insted of smples treted only with wter is more likely to produce significnt results in the mechnicl resistnce studies. Reserch highlights: Treted wood presents sttisticlly significnt increse in MOE, modulus of rupture to sttic bending nd prllel compression strength. There ws no correltion between prllel compression strength nd the degree of impregntion with wterborne preservtive. Key words: Light Orgnic Solvent Preservtive; MOE; prllel compression; sttic bending; wterborne Copper Azole; wood technology. Introduction Currently the most widely used method of protection for wood ginst biodegrdtion consists of pplying chemicl substnces. When using treted wood in structures, it is essentil to be wre of the ltertions tht its mechnicl chrcteristics cn undergo s result of this tretment. In most of the studies published, the influence of the tretment on mechnicl strength ws not significnt. * Corresponding uthor: villsnte@egrof.udl.ct Received: Accepted: Abbrevitions: C m (prllel compression to the grin t moisture m); C 12 (prllel compression to the grin t 12% moisture); C-A (wterborne Copper Azole); LOSP (Light Orgnic Solvent Preservtive); MOR (modulus of rupture to sttic bending t test moisture); MOR 12 (modulus of rupture to sttic bending t 12% moisture).

2 Mechnicl properties of wood treted with LOSP nd wter borne preservtive C-A 417 Tretments included lkline copper qut (Brnes et l., 1993), wterborne copper nphthente (Brnes et l., 2005), micronized copper qut nd copper zole (Brnes et l., 2008) nd copper xyligen in the study of MOR (Brnes et l., 2009). Winndy (1995) indictes tht the mechnicl strength of wood treted with oil-type preservtives is not ltered. A significnt reltion is found in very few studies, nd most point to losses in strength in the treted wood, s in the cse of Winndy (1995) with wterborne preservtives. Brnes nd Lindsey (2009) hve studied the effects of tretment on the bending properties of southern pine using product composed of propiconzole, tebuconzole nd imidcloprid (PTI). They observe improvements in mechnicl behvior compred to the control smples. Losses in mechnicl strength re lso reported in Brnes et l. (2009), who detected slight reductions in the MOE in wood treted with copper xyligen; nd in Yildiz et l. (2004), who used different wterborne preservtives on wood from Pinus sylvestris. Furthermore, Simsek et l. (2010) lso tested reduction in mechnicl resistnce for wood impregnted with environmentlly-friendly bortes. Forest Products Lbortory (2010) indictes tht wter-bsed protectors my yield losses in mechnicl strength in treted wood, n effect which is not observed in wood treted with orgnic-bsed products due to the fct tht they do not rect with the cell wll. It lso reports tht both the MOE nd the prllel compression of treted wood re not ffected, or else present only slight increses, unlike bending strength, which decreses between 0% nd 20%. Another interesting spect reported here is tht wood of higher qulity yields greter losses in mechnicl strength. The reltion between mechnicl strength nd protection of wood is reported in the recent Europen regultion EN 15228:2009, whose nnex A contins list of protective substnces used in Europe which do not produce modifictions in the strength or rigidity of structurl wood. Most studies on the effect of chemicl products on the mechnicl strength of wood hve estblished comprisons using smples treted only with wter. In the present study we hve opted to use smples of rtificilly dried wood which were not treted with wter (Brnes nd Lindsey, 2009), s commonly occurs in the usul commercil process for untreted wood. The objectives of this study were: 1) to determine the effect on wood from Pinus sylvestris of tretment with Light Orgnic Solvent Preservtive (Vcsol Azure WR 2601) nd wterborne Copper Azole (Tnlith E 3492) on sttic bending, modulus of elsticity nd compression strength prllel to the grin; nd 2) to estblish the reltion between the penetrtion of the product into the wood nd compression strength prllel to the grin. Mterils nd methods The smples were obtined in Segovi (Spin), from pure stnds of Pinus sylvestris L. (one of the most commonly used species in Europe for construction). The logs were swn into bords nd dried t mximum tempertures of 65 C. They were subsequently plned nd thinned until dimensions of 20 mm 20 mm 370 mm (rdil, tngentil nd longitudinl mesurements respectively). Smples which showed evidence of knots, crcks or processing defects were lso eliminted. Additionlly, smples whose trnsversl surfce showed ngles of over 15 between the trnsversl edges nd the rings were eliminted (ccording to Nichols et l., 2009). Before of tretment, ll the smples were cut to length of 280 mm to obtin the smples for subsequent bending tests. The remining length of ech smple ws used to obtin compressive strength prllel to the grin smples (with section of 20 mm 20 mm nd length of 60 mm). The 280 mm nd 60 mm smples were treted simultneously in the impregntion phse. The Light Orgnic Solvent Preservtive (LOSP) used ws Vcsol Azure WR 2601, composed of the ctive substnces tolylflunid (1.55%), tebuconzole (0.776%), propiconzole (0.776%) nd permethrin (0.776%). The remining components re light nphth nd excipients. The wterborne Copper Azole (C-A) used ws Tnlith E 3492, composed of copper crbonte (20.5%), 2- minoethnol (18.5%), boric cid (4.5%), propiconzole (0.56%) nd tebuconzole (0.42%). The remining components re solvents nd excipients. The product ws pplied fter dissolving in wter t proportion of 6% s recommended by the mnufcturer. Three groups of smples were selected t rndom from the defect-free smples: 40 smples to be impregnted with LOSP. 50 smples to be impregnted with C-A. 40 control smples, which were not impregnted. The 40 smples treted with LOSP were impregnted by mens of n initil vcuum of 20 kp for 10

3 418 A. Villsnte et l. / Forest Systems (2013) 22(3): minutes, fter which time the protective product ws dded nd mintined under tmospheric pressure for 10 minutes. The process ws concluded with finl vcuum of 87 kp for 25 minutes. The 50 smples in the C-A btch were treted by mens of n initil vcuum of 20 kp for ten minutes, fter which time the protective product ws dded nd mintined t tmospheric pressure for 15 minutes. The process ws concluded with finl vcuum of 87 kp for 25 minutes. A representtive group of the specimens treted (12 smples per tretment) ws weighed individully before nd fter impregntion in order to monitor the mount of product bsorbed. The weight retention per volume of the smples ws obtined from these vlues nd from the impregnted volumes. The following prmeters were mesured in ech smple: Length (precision ±0.5 mm). Rdil dimension (precision ±0.01 mm). Tngentil dimension (precision ±0.01 mm). Number of growth rings t the squred end. Percentge of hertwood, in surfce % (precision ±5%). Percentge of devition of the grin from the xis of the smple (precision ±1%). Weight t the time of the mechnicl tests (precision ±0.01 g). Density t the time of the mechnicl tests (precision ±0.001 g cm 3 ). The smples for the bending test were ir-dried for two months nd subsequently exmined to determine the modulus of rupture to sttic bending t the test moisture (MOR m ), nd the modulus of elsticity (MOE), following the protocol estblished by Stndrd UNE 56537:1979. The estimted vlue of the MOR ws clculted t 12% moisture (MOR 12 ) bsed on the informtion contined in Forest Products Lbortory (2010) ccording to the following formul [1]: MOR 12 = MOR m [ (%moisture 12)] [1] The smples for the compression prllel tests were ir-dried for five months. The subsequent process ws the sme s for the bend tests. The smples were tested following the protocol estblished in Stndrd UNE 56535:1977 to obtin the prllel compressive strength t the test moisture (C m ), nd using the formul included in the forementioned Stndrd [2] to correct prllel compressive strength to 12% moisture content (C 12 ). C 12 = C m [ (%moisture 12)] [2] Moisture content ws clculted by oven-drying the smples t 103 C immeditely fter the test. The penetrtion of the tretment ws clculted by pplying regents nd evluting the percentge of cross section re treted (with n pproximtion of 1%). The regent used to detect the penetrtion of the LOSP ws solution of niline t 15% in glcil cetic cid. In the cse of the C-A, 0.05 g of chromzurol S nd 0.5 g of sodium cette were dissolved in 99 ml of distilled wter. The impregntion ws complete in woods treted with LOSP. In woods treted with C-A, the cross section res were digitlized with scnner with resolution of 600 points per inch, nd the proportion of green in the imge ws enhnced in order to highlight the presence of copper. The res were clculted using the Geogrphicl Informtion System Softwre gvsig 1.10 (GVSIG Assocition, 2011). In the first stge, vrious chrcteristics of the smples (devition of the grin, number of rings, percentge of hertwood, rdil dimension nd tngentil dimension) were nlyzed in order to verify tht there ws no bis in the tretments (s indicted by Brnes nd Lindsey, 2009 for specific grvity). The tests selected were the Anlysis of vrince nd the nonprmetric Kruskl-Wllis test. This lst test ws pplied in the cse of smples which did not meet the requirements of normlity (Shpiro-Wilk test) nd homoscedsticity (Brtlett test). In the cse of significnt p-vlues in the Anlysis of vrince, the mens were seprted using Tukey s comprison. The level of significnce ws set t 5%. In the second stge, the sme sttisticl tests were pplied to determine whether the fctor resulting from the tretment bore reltion to the results obtined for mechnicl properties. Finlly, given the significnt increse in mechnicl properties of the treted woods compred to the control specimens, it ws decided to exmine the reltion between this increse nd the mount of protector pplied to ech smple by mens of Regression nlysis. This ws only done for the smples tested for compression strength, due to the fct tht in the bend test the strin is complex combintion of tensile nd compressive strengths on impregnted irregulr-serrted cross section. Results Tble 1 shows the results of the sttisticl nlysis for the detection of bis in the rndomiztion of the

4 Mechnicl properties of wood treted with LOSP nd wter borne preservtive C-A 419 Tble 1. Results of the sttisticl nlysis for the detection of bis in the rndom selection of smples Shpiro- Brtlett Anlysis Kruskl- Wilk test test of vrince Wllis test (p-vlue) (p-vlue) (p-vlue) (p-vlue) Block vrible b Grin slope (1) (2) (3) Number (1) of rings (2) (3) % hertwood (1) (2) (3) Rdil (1) dimension (2) (3) Tngentil (1) dimension (2) (3) (1) LOSP, n = 40. (2) C-A, n = 50. (3) Control smples, n = 40. n = number of specimens. Grin slope, number of rings, % hertwood nd rdil dimension were nlyzed with the Kruskl-Wllis test due to the heteroscedsticity detected in the Brtlett test. vribles in the block. It cn be seen tht in no cse re there ny significnt differences in the Anlysis of vrince or in the nonprmetric Kruskl-Wllis test. It cn therefore be ssumed tht the smples were correctly chosen. The verge retentions obtined in the smples were 15 kg m 3 in the cse of C-A nd 106 kg m 3 for LOSP. Sttic bending strength ws nlyzed by mens of the Kruskl-Wllis test due to the presence of the mrked heteroscedsticity in the distribution (the p- vlues of Brtlett s test of the MOR m nd the MOR 12 were nd respectively). Although this test is more conservtive thn the Anlysis of vrince, the p-vlues obtined from Kruskl-Wllis clerly indicte the influence of the tretment on bend strength, nd re below 0.01 ( in the cse of MOR m nd in MOR 12 ). The box grph corresponding to the MOR 12 is shown in Fig. 1. The bsic vlues of the distribution re shown in Tble 2. The grph nd the distribution of the MOR m re very similr, due to the negligible differences in moisture content between the pieces fter the conditioning period (95% confidence intervl is between 12.18% to 12.80%).Both Fig. 1 nd Tble 2 show the increse in the MOR 12 in the treted woods (both with LOPS nd with C-A) MOR12 (N mm 2 ) LOSP C-A Control Figure 1. Box Plot grph of estimted bending strength with 12% moisture, MOR12, for ech type of tretment. Tretments without common letter (, b) re significntly different t p = compred to the control specimens. The increse in the vlues of the mens nd the medins is greter thn 13%. This increse compred to the control specimens is prcticlly the sme for both tretments. In the cse of the modulus of elsticity to sttic bending (MOE), the Anlysis of vrince ws pplied due to the fct tht the smple correctly meets the conditions of normlity nd homoscedsticity. The p-vlue ws highly significnt. Fig. 2 nd Tble 2 show the results obtined for the MOE depending on the tretment pplied. Tukey s comprison indictes there re three differentited non-overlpping groups, the group of smples of C-A bove the rest, the group of LOSP in n intermedite sitution, nd the control group below the others (Fig. 2). Tble 2 shows tht the woods treted with LOSP hve men MOE which is 14.3% greter thn tht of the control specimens; nd in the cse of woods treted with C-A, this figure is 24.8% greter. Compression strength prllel to the grin ws nlyzed using the Anlysis of vrince, s the dt exceeded the Shpiro-Wilk normlity test nd Brtlett s vrince test. In both the cse of the vlue t the test moisture (C m ) nd t the estimted 12% moisture vlue (C 12 ), the p-vlues were highly significnt: in C m nd in C 12. We cn confirm tht there is cler reltionship between the tretment nd compression strength prllel to the grin. The type of

5 420 A. Villsnte et l. / Forest Systems (2013) 22(3): Tble 2. Results of the sttisticl nlysis of the MOR 12, MOE nd C 12 for ech type of tretment Mechnicl Averge SD Trtment property (N mm 2 ) (N mm 2 ) Shpiro- Brtlett Kruskl-Wllis n Wilk test test test or ANOVA (p-vlue) (p-vlue) (p-vlue) MOR 12 LOSP (kw) C-A Control MOE LOSP 7,647 1, (n) C-A 8,345 1, Control 6,688 1, C 12 LOSP (n) C-A Control SD: stndrd devition. n = number of specimens. kw: Kruskl-Wllis test. n: ANOVA. influence is shown in Fig. 2 nd Tble 2. This figure shows three different non-overlpping situtions. On the one hnd, the treted woods re more resistnt thn the control specimens, nd on the other hnd, the woods impregnted with C-A present significntly higher results thn those treted with LOSP. Tble 2 shows 19.2% increse in the verge vlues of C 12 compred to the control smples in the cse of LOSP, nd 30.4% increse in the cse of C-A. The Regression nlysis between the penetrtion nd C 12 ws done only with the smples treted with C-A, given tht the smples treted with LOSP hd totl impregntion. The result showed tht the reltion is prcticlly negligible, s cn be seen in Fig. 3. The pttern of dots does not llow n cceptble fit with ny type of curve or stright line. The low vlue of R 2 (0.015 in the liner cse, similr to other non-liner regressions tested), indictes tht the percentge of trnsversl surfce re impregnted is not relted to the increse in prllel compression strength. Only MOE (N mm 2 ) 12,000 10,000 8,000 MOE C 12 b MOE 6, LOSP C-A Control Figure 2. Confidence intervls to 95% for the MOE nd C 12. Tretments without common letter (, b, c) re significntly different t p = b C 12 c c MOE C C 12 (N mm 2 ) 1.5% of the behvior of C 12 could be explined by mens of the penetrtion of the product. Fig. 3 lso includes the corresponding Chi-plot, which clerly shows tht most cses re locted in the centrl bnd, demonstrting the independence of the two vribles. Therefore, if the greter compression strength of the treted woods does not depend on the degree of impregntion, the incresed strength could be due to the chnges in pressure experienced during tretment, which do ffect the whole of the test btch. Discussion Results gree with the findings of Brnes nd Lindsy (2009), nd coincide in tht the vlues of the modulus of rupture in wood treted with orgnic products PTI nd with CA-B re greter, lthough sttisticlly significnt results were not chieved. The uthor himself invited further discussion s to whether these differences were merely sttisticl or the result of the tretments. The results obtined for bending (MOR nd MOE in Pinus sylvestris) differ from Yildiz et l. (2004), who did not observe ny significnt differences between the control smples nd the woods treted with C-A Tnlith E The most likely explntion is tht the greter number of smples per vrible mkes it esier to observe the differences (40, s opposed to 10 in the works of Yildiz et l., 2004). Similrly, these results do not concur with the findings of Simsek et l. (2010) for Pinus sylvestris. The vrition in the results could be explined by the different chemicl substnce environmentlly-friendly bortes used for tretment. Indeed, these uthors found

6 Mechnicl properties of wood treted with LOSP nd wter borne preservtive C-A C 12 = 49.8 Penetrtion C 12 (N mm 2 ) Chi Penetrtion (%) ,5 Lmbd Figure 3. Sctter plot nd Chi-plot showing the reltion between the mount of protector (percentge of trnsversl surfce impregnted compred to totl trnsversl surfce) nd estimted prllel compression strength with 12% moisture (C 12 ). greter vrition in mechnicl properties s the concentrtion incresed. It should lso be noted tht some of the results do not concur with the findings reported in Forest Products Lbortory 2010, s insted of detecting similr vlues for MOE nd prllel compression in conjunction with the decreses in bending strength, ll cses point to significnt nd considerble increses. Similrly, the vlues of the wter-bsed protector re higher thn those obtined in the orgnic-bsed product, contrsting with the indictions of the Forest Products Lbortory, It is essentil to tke into ccount tht the studies on the mechnicl properties of treted woods use two different types of control smples s reference: untreted wood nd wood treted with wter. The use of wood treted only with wter is widespred, nd the results it offers re often not significnt (Brnes et l., 2005; Brnes et l., 2008; Brnes et l., 2009). In contrst, the studies by Brnes nd Lindsy (2009) using untreted control smples s reference did detect significnt increses in the MOR nd MOE, coinciding with the results obtined in the present study. The decrese in mechnicl resistnce in wood treted with wterborne preservtives is commonly ttributed to the chemicl rections between the wood nd the protective products (Forest Products Lbortory, 2010; Winndy, 1995; Yildiz et l., 2004; Simsek et l., 2010). The results obtined in the present work contrdict this explntion. No reltionship ws detected between the penetrtion of the product nd the resistnce to prllel compression. The ltertion in the wood explined by the chnges in pressure nd vcuum during the tretment is more convincing explntion. The significnt decrese in mechnicl resistnce (MOE studied in Brnes et l., 2009) my be prtly due to the ppliction of vcuum nd pressure tretments. The use of VAC-VAC tretment (without pressure) in the present study could be the reson for the significnt increse in mechnicl resistnce. Conclusions VAC-VAC tretment of wood with Light Orgnic Solvent Preservtive or with wterborne Copper Azole significntly increses its resistnce to sttic bending, its MOE nd its compression strength prllel to the grin. The negligible reltionship between wterborne preservtive penetrtion nd prllel compression strength (R 2 = 0.015) indictes tht this is not due to the presence of protective products to the cell wll, but could be explined by chnges in vcuum pressure during tretment. The significnt decrese in mechnicl properties observed in previous studies my be prtly cused by the use of pressure tretments.

7 422 A. Villsnte et l. / Forest Systems (2013) 22(3): It is lso importnt to tke into ccount the type of control smple. The use of wood treted only with wter nd submitted to process of vcuum nd pressure identicl to the treted smples is more likely to produce non-significnt results. Acknowledgements The uthors wish to cknowledge the Vcuum Process tretment provided by Mr. Eugenio Alonso Herbis of the Deprtmento de Selvicultur, Universidd Politecnic de Mdrid (Spin). References Brnes HM, Lyon DE, Zhor A, Muisu F, Strength properties of ACQ-treted southern pine lumber. Proceedings of the Americn Wood-Preservers Assocition 89. pp: Brnes HM, Mupin M, Lindsey GB, Bending properties of southern pine treted with wterborne copper nphthente. Proceedings of the Americn Wood-Preservers Assocition 101. pp: Brnes HM, Lindsey GB, Hill JM, Pompeo M, Hodge R, Bending properties of southern pine treted with micronized preservtive systems. Interntionl Reserch Group on Wood Protection. IRG/WP Brnes HM, Lindsey GB, Bending properties of wood treted with new orgnic wood preservtive system. Bioresour Technol 100: Brnes HM, Lindsey GB, Hill JM, Effect of copper xyligen tretment on bending properties of wood. Holzforschung 63: EN 15228, Structurl timber Structurl timber preservtive treted ginst biologicl ttck. Europen Committee for Stndrdiztion, Brussels, Belgium. Forest Products Lbortory, Wood hndbook: wood s n engineering mteril. Generl Technicl Report FPL-GTR-190 ed. US Deprtment of Agriculture, Forest Service, Forest Products Lbortory, Wshington, USA. GVSIG Assocition, gvsig, ver GVSIG Assocition. [online]. Avilble in web/. [7 September 2011]. Nichols DD, Shi J, Schultz TP, Evlution of vribles tht influence dynmic MOE in wood decy studies. Interntionl Reserch Group on Wood Protection. IRG/WP pp. Simsek H, Bysl E, Peker H, Some mechnicl properties nd decy resistnce of wood impregnted with environmentlly-friendly bortes. Construction nd Building Mterils 24: UNE 56535, Crcterístics físico-mecánics de l mder. Determinción de l resistenci l compresión xil [Mechnicl properties of Wood. Stndrs for mesuring. Compressive strength prllel to grin]. Asocición Espñol de Normlizción y Certificción, Mdrid, Spin. UNE 56537, Crcterístics físico-mecánics de l mder. Determinción de l resistenci l flexión estátic [Mechnicl properties of Wood. Stndrs for mesuring. Sttic bending resistnce]. Asocición Espñol de Normlizción y Certificción, Mdrid, Spin. Winndy JE, Effects of wterborne preservtive trement on mechnicl properties: review. Proceedings of the Americn Wood-Preservers Assocition 91. pp: Yildiz UC, Temiz A, Gezer ED, Yildiz S, Effects of the wood preservtives on mechnicl properties of yellow pine (Pinus sylvestris L.) wood. Building nd Environment 39: