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【溫馨提示】壓縮包內(nèi)含CAD圖有下方大圖片預(yù)覽，下拉即可直觀呈現(xiàn)眼前查看、盡收眼底縱觀。打包內(nèi)容里dwg后綴的文件為CAD圖，可編輯，無水印，高清圖，壓縮包內(nèi)文檔可直接點開預(yù)覽，需要原稿請自助充值下載，所見才能所得，請見壓縮包內(nèi)的文件及下方預(yù)覽，請細(xì)心查看有疑問可以咨詢QQ：11970985或197216396 Wood Sci Technol (2004) 38: 93107DOI 10.1007/s00226-003-0207-3ORIGINALG. J. Goroyias M. D. HaleThe mechanical and physical properties of strand boards treatedwith preservatives at different stages of manufactureReceived: 5 May 2001 / Published online: 25 March 2004 Springer-Verlag 2004Abstract The physical and mechanical properties of boards treated with apreservative at dierent points during the manufacture process were evaluatedto determine the best stage for the application of preservative. A copper borontebuconazole amine water-based preservative was used in 3% PF-bondedstrand boards to achieve ve dierent retentions. Preservative addition wasexamined at dierent stages of the manufacture cycle, namely, green stranddiusion, dry strand vacuum treatment, glue-line spray addition, heat and coldquench of manufactured board, and by post-manufacture vacuum treatment.The treatment methods had marked eects on the mechanical properties ofsome of the boards when the boards with the highest preservative retentionwere compared with their respective untreated controls. The best results wereachieved where the preservative was applied by vacuum treatment of drystrands or by diusion of green strands before board manufacture. Increasingpreservative retention had minimal eects on board properties with these twomethods but signicant deterioration was noted when the preservative wasapplied by spraying dry strands or by post-board-manufacture heat and coldquench. An increase of pressing temperature resulted in signicant improve-ments to the mechanical properties of the spray-treated boards. Post-manu-facture vacuum treatment of boards caused excessively high losses in internalbond strength.IntroductionOriented strand board (OSB) is a structural board widely used in buildingconstruction and other applications mainly for interior use or for short-termexterior out-of-ground contact exposure. The use of OSB in exterior conditionsis restricted due to its low durability against decay fungi (Chung et al. 1999;Goroyias and Hale 2000a), swelling under high moisture conditions, and theresultant reduction in internal bond strength (Goroyias and Hale 2000a).Preservative treatment is readily applied to solid wood and may also beapplied to improve the properties of panel products. In this context it is appliedG. J. Goroyias M. D. Hale (&)School of Agricultural and Forest Sciences,University of Wales, LL57 2UW Bangor, U.K.E-mail: m.d.halebangor.ac.uk 94for commercial use to plywood after manufacture. A product of this type,treated with a suitable preservative, shows sucient decay resistance for groundcontact use (AWPA C9 1999). However, the lower cost of production of OSBcompared to plywood and solid wood gives a cost-competitive incentive todevelop a system to improve decay resistance and the dimensional stability ofOSB. Fluid preservative treatment of OSB after manufacture results in highswelling so alternative application stages in the manufacture cycle need to beinvestigated. For this, a series of factors, including time of treatment, stage ofpreservative addition, physical and mechanical properties of the treated board,resistance of the preservative to leaching, and decay resistance (with andwithout leaching) need to be considered. The combination of preservative andadhesive type and the stage of addition play an important role in the successfulproduction of a preservative-treated board.Goroyias and Hale (1999, 2000a, 2000b) have recently reviewed the literaturerelated to the eect of point of preservative application on board properties.Preservative addition to wood-based panel products has been shown to result insignicant losses to the mechanical and physical properties (Boggio and Ger-tjejansen 1982; Laks et al. 1988; Vick 1990; Vick et al. 1990; van Acker andStevens 1993; Jeihooni et al. 1994; Barnes et al. 1996).Many preservatives were applied by several researchers to prevent wood-based panel products from decay. These include pentachlorophenol, didecyldimethyl ammonium chloride (DDAC), DDAC with copper, DDAC withcarbamate, sodium uoride, ammonium hydrogen biuoride, ammoniacalcopper zinc arsenate (ACZA), borate preservatives, copper naphthenate (CuN),copper octoate, chlorpyrifos, zinc naphthenate. However, various problemsmay occur: substantial vapour losses of toxic preservatives may occur duringpressing, preservatives may interfere with the adhesive, and the resultant sig-nicant loss of board mechanical properties result in restricted widespreadcommercial application (Huber 1958; Vintila et al. 1967; Deppe and Petrowitz1969; Becker 1972; Laks et al. 1988; Vick 1990; Vick et al. 1990; Fushiki et al.1993; Jeihooni et al. 1994). However, non-acidic preservatives (e.g. DDAC-based) and emulsied CuN have shown fewer negative eects on boardmechanical properties (Vick et al. 1990; Schmidt 1991). Azaconazole, applied asa powder to aspen wafers after the application of resin, had no signicant eecton the board properties tested (Schmidt and Gertjejansen 1988).Composite boards can be preserved at a variety of points during and aftermanufacture. Diusion treatment using several preservative formulations i.e.ammoniacal copper arsenate (ACA), copper-chromium-arsenic (CCA) beforeblending has been shown to produce a panel with good properties, abovestandard specications (Hall et al. 1982), but with poorer properties whencompared to the untreated board (Boggio and Gertjejansen 1982; Jeihooni et al.1994).Surface addition of preservative as a liquid (i.e. ACA, CCA) by spray or as apowder during, before, or after resin blending has been shown to result in asignicant decrease of board properties (Hall and Gertjejansen 1979; Jeihooniet al. 1994; Schmidt and Gertjejansen 1988). The extent of inuence dependson the degree of compatibility of the preservative with the adhesive. It has beenshown that several preservative formulations (chlorpyrifos-CP, dichlorophen-thion-ECP, silauofen-HOE, propetanphos-PP, IF-IF-100, IPBC) do notinterfere with UF resins. However, UF is not suitable for exterior specication 95boards as UF-bonded boards fail dramatically when wetted (Becker and Deppe1969; Deppe 1987; Subiyanto et al. 1994). Several types of powder preservativeformulations have been applied with the resin before board manufacture(Schmidt and Gertjejansen 1988). This method gives good mechanicalproperties only when the preservative is heat-stable and compatible with theadhesive.Liquids may be applied post-manufacture by dipping, spraying, brushing, orvacuum or vacuum-pressure, but due to drying, conditioning, and mechanicalstrength limitations of such methods (Deppe 1967; van Acker and Stevens 1993;Barnes et al. 1996), approaches with vapour treatments (Turner et al. 1990) andsupercritical uids (Acda et al. 1997) have been investigated. These novelapproaches have given some promising results with no changes in boardmechanical or physical properties. Brushing, dipping, and spraying frequentlyyields unsatisfactory depths of penetration and products treated with thesemethods are only suitable for out-of-ground use, because preservative pene-tration is limited only to the surface regions of the board.It can be concluded from the literature that a variety of isolated studies havelooked at the preservation of dierent types of panel products. These studiesinvolve various preservatives, various formulation types (e.g. powder, oil, orwaterborne), application of preservatives at dierent stages in the manufactureprocess, and dierent wood species, resins, and pressing conditions. Thesestudies cannot be directly compared with each other to determine the bestmethod for the application of preservation because they involve too manyunrelated variables. However, they do give indications that some ground-con-tact preservatives are not suitable. This paper is a comprehensive study onnumerous physical and mechanical properties of strand boards, preserved witha new generation ground-contact wood preservative formulation (Tanalith3485) at dierent stages of the manufacture process. Where dierent pressingconditions have been used to achieve successful board production comparablecontrols have been included. The leach and decay resistance of these boards willbe reported in a later publication.ExperimentalPF-bonded Scots pine unoriented strand boards treated with Tanalith 3485(copper azole borate) were made under laboratory conditions to achieve ve)3dierent preservative retentions (0, 1.5, 3, 6, and 12 kg m ). The internal bondstrength (IB), modulus of elasticity (MOE), modulus of rupture (MOR),thickness swelling (TSw), water absorption (Wabs), shear strength, and densityof the boards were then evaluated.Board treatmentFive dierent treatment methods were evaluated: diusion treatment ofgreen strands, vacuum treatment of dried strands, spray treatment of driedstrands in the resin blender, heat and cold quench (HCQ) of manufacturedboards, and post-manufacture vacuum treatment of boards. Goroyias and Hale(1999, 2000a, 2000b) have described in detail the methods of preservativeaddition used in this study. 96Board manufactureBoards were produced to a target thickness of 15 mm and a target density of)3650 kg m , using commercial Scots pine OSB strands with an average density)3of 400 kg m . Board manufacture variables are presented in Table 1. Fourdierent types of control (untreated) boards were made (Table 1).Board testingSampling and cutting of the large-sized boards (Table 1) was based onstandard EN 3261:1993. When this was not possible, due to the smaller sizeof the boards, the sampling and cutting was based on a specic pattern whichwas determined from the results of an analysis of variance (one way ANOVAand Tukeys pairwise comparisons) of properties (IB, MOR, MOE, TSw,Wabs) between replicate boards. For this purpose small untreated(400400 mm) boards were produced and tested. The sample variance of eachproperty tested was then analysed using ANOVA (p=0.05) and Tukeyspairwise comparisons between replicate boards. The results showed that therewas no signicant dierence in properties tested between the replicate small-sized boards.Samples were then tested for various mechanical and physical properties andthe variances for each property between the boards were analysed (ANOVA,p=0.05, Tukeys pairwise comparisons).The density prole of the boards was measured by using an ATR densityprole machine (software v2.09) and average densities were calculated. MOE,MOR, IB, TSw, and Wabs were tested according to EN 310:1993, EN319:1993, EN 317:1993. In addition, a modied, non-standard shear strengthtest was performed on blocks with 502515-mm thickness (Fig. 1). Loadwas applied parallel to the strand direction along the sample length inspecially designed steel jigs. The load versus displacement curves are shownin Fig. 2.3Table 1 Process variables for the manufacture of the test boardsTreatment methodResincontent content timeWaxBlending Temp. Press SizebNumberof boardscyclea(s) (m)(%)(%)(min)(C)Diusion333333333,4,6,101.2303030303030303030210210210210210210230210210360360360115523285222 4Heat and cold quench (HCQ)Control (diusion and HCQ)Vacuum-pressureControl (vacuum-pressure)Spray 1Spray 2Spray ControlPost-manufacture vacuum1.21.21.21.21.21.21.21.21111360 0.40.4360 0.40.4660540 0.40.466011360 0.2 0.2113caPressing cycle includes 90 s press close time and 30 s decompressionBoard untrimmed size is displayedFor post-manufacture vacuum treatment the controls used were the same boards but wereuntreated. The replicates in this case were two boards for each resin content.bc 97Fig. 1 Block shear testFig. 2 Load versusdisplacement curves for eightspecimens using the blockshear testThe assessment of results was based on comparisons of the properties of the)3highest retention preservative-treated boards (12 kg m ) with their appropri-ate untreated controls (ANOVA, p=0.05, Tukeys pairwise comparisons usingMinitab version 11). Fifteen replicates were tested for each property, except forthe boards produced with vacuum-pressure-treated strands where 30 replicateswere tested.To examine for the eect of increasing preservative retention on boardproperties, a correlation test (Pearson correlation, Minitab version 11) betweenpreservative retention and each property was performed. The MOR and MOE)3tests for the boards treated to the intermediate retentions (1.5, 3, 6 kg m )included four replicates from the core, and the density prole, IB, shear, TSw,and Wabs tests included six core replicates. 98ResultsResults for the eect of resin concentration on IB and TSw of the post-man-ufacture vacuum-treated boards are presented in Table 2. Results for the dif-ferent treatment methods on the physical and mechanical properties at eachpreservative level and their correlations are shown in Table 3.Discussion)3The null hypothesis that the 12 kg m -treated boards do not dier signicantlyfrom their respective controls was tested using ANOVA and Tukeys pairwisecomparisons. When no signicant dierence is shown, preservative addition didnot result in a change of board properties, but where there is a signicantdierence, an improvement or a reduction of board properties occurred.Post-manufacture vacuum treatmentPost-manufacture treatment was not a successful treatment method in aboard containing only 3% resin as high IB loss (42%) and TSw (34%) oc-curred and sub-standard boards resulted. Higher resin content boards (410%) were made and tested for IB and TSw after treatment. Increasing theresin content from 3 to 4% resulted in boards of sucient IB (Table 2) to)2pass standards (EN 300, 0.30 N mm ) but even these had high IB losses (5056% as compared to their control values, Table 2) and showed noimprovement in TSw after treatment. Further increases in resin content above4% did not result in proportionately higher IB values after treatment. Irre-versible TSw was observed even at high resin contents (Table 2). This dete-rioration is in accordance with work by Hall et al. (1982) who examinedaspen waferboards treated under vacuum.Table 2 Mean IB (mean of 4 samples) before and after post-manufacture vacuum treatment,IB loss (%), and percentage thickness swelling (TSw) immediately after post-manufacturevacuum treatment and after the drying (102C) of boards made with dierent resin contents.Standard deviations are shown in bracketsResin content(%)IB (EN 319)TSwUntreated)2Preservative-treated)2Loss(%)Wet(%)Dry(%)(N mm)(N mm)30.38(0.0)0.57(0.01)0.72(0.02)0.69(0.04)0.16(0.04)0.32(0.02)0.36(0.03)0.38(0.01)4256505534.225.19(9.70)28.45(5.5)27.76(1.85)31.90(2.32)(8.48)35.79(4.50)39.85(0.07)33.97(5.25)4610 99 100 101Green strand diusionGreen strand diusion proved to be a successful method for board manufac-ture, producing a board with good properties, although slightly inferior toboards made from vacuum-treated strands. There were no signicant dier-3ences between the control and the 12 kg m -treated boards for the IB, MOE,Wabs (2 h), TSw (2 h and 24 h), and shear, but the intermediate preservativeloading boards were marginally worse (Table 3) for the MOR and Wabs (24 h).)3However the 3 kg m loading appears to have reduced the Wabs (2 h) (Ta-)3ble 3). The lower MOR value with the 12 kg m loading board is an edge eectof the test samples.Similar works (Hall and Gertjejansen 1979; Boggio and Gertjejansen 1982)using diusion into wet strands with dierent kinds of copper-based preser-vatives showed pronounced negative eects on a variety of mechanical andphysical properties of the boards. This is in contrast with the results of ourstudy in terms of severity. No correlations were found between preservativeretention and board properties (Table 3). The lack of correlation shows that thepreservative addition did not aect the board properties and poor results (e.g.)312 kg m ,MOR) can be explained by other factors, e.g. edge eects.Vacuum pressure treatment of dry wood strandsVacuum-pressure-treated strands produced boards with better properties thanall of the other treatment methods. The mechanical and physical testing resultsare no dierent from their respective controls although signicantly less Wabs(2 h) and consequently less TSw (2 h) occurred (Table 3). However, with pro-longed soaking (24 h) these dierences were no longer signicant. No othercorrelations were found between preservative retention and board propertieswith this treatment method (Table 3). This shows that this method of pre-servative application does not have any signicantly negative eects on boardproperties.Vick et al. (1990) found that vacuum preservative treatment of boards withACA and CuN did not interfere with PF resin bonding as assessed by a lapshear test. Similar results are seen here as both IB and shear test data show noeect of preservative. The vacuum treatment method gives a good distributionof preservative within the wood strands and the preservative is encouraged tox with the wood, which may reduce preservative interference.Spray applicationBoards produced by spraying the preservative at the glue-line stage showedpoor properties when compared to their respective controls; these were signif-icant for every property tested except MOE and MOR (Table 3). Boardstreated to intermediate levels showed better values for MOE.High correlations between preservative retention and board properties arenoted for spray treatment (Table 3). However, the correlations for the MOEand MOR are much lower than those for the other properties, especially IB andshear. This shows that in strand board the MOE and MOR are not directlyrelated to the quality of woodresin bond. The orientation and the large size ofstrands proved a key factor for the board bending strength. 102Table 4 Mechanical and physical properties of spray-treated (12 kg m)3) boards pressed at230C. Standard deviations are shown in bracketsPropertySpray(230C)IB (N mm)2)0.50 (0.08)9575 (991)2MOE (N mmMOR (N mm)246.62 (7.37)24.42 (3.69)29.66 (4.07)60.55 (13.59)74.23 (12.61)2.51 (0.24)aTSw (2 h) %aTSw (24 h) %bWabs (2 h) %bWabs (24 h) %)2Shear (N mm)aThickness swelling after 2- and 24-h immersion.Water absorption after 2- and 24-h immersion.bAs the spray-treated boards pressed at 210C were so inferior, another seriesof boards were pressed at 230C. Preserved boards pressed at 230C (Table 4)had very good mechanical properties but these boards initially absorbed faster(Wabs, 2 h) than the 210C untreated controls and also showed increased initialswelling (TSw, 2 h). Rapid uid uptake during the immersion test and rapidsubsequent swelling may have been caused by cell wall damage, i.e. crack for-mation, although other possibilities, such as increased resinwood bond sti-ness (low exibility resin unable to accommodate swelling), cannot be ruled out.Preservative addition by spraying resulted in an increase in mattress moisturecontent from 5 to 9%. This alone had a signicant negative eect on boardprop