North American composites, including laminated veneer lumber, oriented strandboard, and medium density fiberboard, were treated by vapor boron technology and subsequently tested in static bending. Tensile properties were also determined for the two composite board products. The study was designed as a 2 x 3 factorial with two mill locations and three treatment levels for each composite type. In general, mill location significantly affected most property values, while treatment level caused only significant reductions at the highest treatment level. The significance of mill location was attributed mainly to species differences since species varied between locations for each composite type

Barnes, H. Michael

Murphy, Richard J.

English

Wood and Fiber Science (E-Journal)

BENDING AND TENSILE PROPERTIES OF VAPORBORON-TREATED COMPOSITESH. Michael Barnes†ProfessorForest Products LaboratoryForest & Wildlife Research CenterMississippi State UniversityBox 9820Mississippi State, MS 39762-9820andRichard J. MurphySenior LecturerDepartment of Biological SciencesSir Alexander Fleming BuildingImperial College of Science, Technology, & MedicineSouth Kensington CampusImperial College RoadLondon, England SW7 2AZUK(Received August 2004)ABSTRACTNorth American composites, including laminated veneer lumber, oriented strandboard, and mediumdensity fiberboard, were treated by vapor boron technology and subsequently tested in static bending.Tensile properties were also determined for the two composite board products. The study was designedas a 2 x 3 factorial with two mill locations and three treatment levels for each composite type. In general,mill location significantly affected most property values, while treatment level caused only significantreductions at the highest treatment level. The significance of mill location was attributed mainly to speciesdifferences since species varied between locations for each composite type.Keywords: OSB, MDF, LVL, vapor boron, tensile strength, bending properties.INTRODUCTIONThe past decade has seen a substantial in-crease in the production and utilization of treatedproducts. The application of innovative technol-ogy to problems of wood treatment is a requisitefor improved utilization of wood in areas wherehazards from agents of biotic deterioration arepresent. Of particular importance has been theinability to successfully treat new generationcomposite materials with biocides without sig-nificant loss in properties. The importance ofprotecting wood-based composites from a vari-ety of causal agents (decay, insects, fire) was thetheme of a recent international conference (Pres-ton 1993). One conclusion of this conferencewas that failure to protect composite materials,especially in exterior applications, could lead tothe loss of markets to competitive materials suchas masonry, vinyl, and aluminum.Research in the United Kingdom and in NewZealand has led to the development of a vapor† Member of SWST.This project was funded in part by USDA CSREES Spe-cial Research Grant Program No. 98-34158-5869. Ap-proved for publication as Journal Article No. FP-319 of theForest & Wildlife Research Center, Mississippi State Uni-versity.Wood and Fiber Science, 37(3), 2005, pp. 379 – 383© 2005 by the Society of Wood Science and Technologyboron treatment (VBT) which could have a tre-mendous impact in North America (Bergervoetet al. 1992; Burton et al. 1990; Dickinson andMurphy 1989; Murphy and Turner 1989; Turnerand Murphy 1987). Vapor-phase treatments of-fer several advantages to conventional liquidtreatments (Schuerch 1968). There is no liquidwater to excessively swell the material, a factorimportant in treating wood-based composites.Impregnation problems arising from liquid ten-sion and other interfacial considerations areeliminated. Since treatment comes after matconsolidation, potential bonding properties aris-ing from chemical treatment are eliminated.Hashim et al. (1992, 1994) found little negativeeffect of treatment on UK-produced boards. An-cillary board properties and tool wear for VBT-treated medium density fiberboard (MDF) andoriented strandboard (OSB) have been reported(Barnes et al. 2004; Jones et al. 2001). This re-search documents the mechanical properties ofvapor boron-treated North American compositematerials.MATERIALS AND METHODSMaterialsOriented strandboard (OSB) manufacturedfrom mixed southern pine and southern hard-wood furnish (designated MS) and from mixednortheastern conifer and hardwood furnish (des-ignated ME), and laminated veneer lumber(LVL) were acquired from commercial produc-ers. The MS-OSB was bonded with liquid phe-nol-formaldehyde resin and the ME-OSB wasbonded with a powdered phenol-formaldehyderesin. Commercial medium density fiberboard(MDF) intended for the siding market and manu-factured from southern hardwood furnish (SO)or mid-Atlantic hardwood (MA) furnish wereincluded in the study. The SO-MDF was a wetprocess board and the MA-MDF was a dry pro-cess board. Both were bonded with a phenol-formaldehyde resin. Nominal OSB and MDFboard thickness was 12.5 mm. The LVL wasproduced from two species (southern pine,Douglas-fir). Nominal thickness was 44 mm forDouglas-fir and 38 mm for southern pine.TreatmentThe composites were shipped to the ImperialCollege of Science, Technology and Medicine inLondon, England where they were vapor phase-treated with trimethyl borate as has been de-scribed elsewhere (Hashim, et al. 1992, 1994).Each type of composite was treated to differentretention levels [nominally 1% (LOW) or 5%(HIGH) BAE (w/w)] in a 0.8-m3 treatment ves-sel. Samples were separated by 3-mm stickersand loaded into the vessel. The vessel wasevacuated to 5 mbar and a metered amount oftrimethyl borate sufficient to achieve the targetretentions was admitted. Gas contact time was 8h for the high retention and 40 min for the lowretention level. Comparison was with untreatedcontrols.Testing methodsStandard ASTM (1997) D1037 testing proce-dures were followed for testing MDF and OSBin bending and tension. ASTM D143 procedureswere used for testing LVL in static bending.Thirty replicates for each combination of treat-ment level (TL) and mill location (MILL) weretested for each composite type. Data were ana-lyzed using analysis of variance and mean sepa-ration techniques. The study was designed as a2 × 3 (MILL × TL) factorial arrangement oftreatments within a completely random designfor each composite type.RESULTS AND DISCUSSIONMedium density fiberboardSpecific gravity (G) and moisture content(MC) were treated as covariants in all analyses.Additionally, MOE was considered as a covari-ant for the MOR analysis. For all bending prop-erties, specific gravity was found to be a signifi-cant covariant (Table 1). For MOE, mill loca-tion, treatment level, and their interaction werefound to be significant variables (Table 1). Thesignificance of mill location was taken to meanthat furnish species and/or processing differ-ences significantly reduced these property val-WOOD AND FIBER SCIENCE, JULY 2005, V. 37(3)380ues with values being higher for the southernmill. Recall that board from the MA mill was adry process board while the SO mill produced awet-process board. In analyzing the interaction,no significant differences were found acrosstreatment levels for the SO board, so no delete-rious effect of treatment on MOE is noted. In thecase of the MA, treatment at the high level re-sulted in a significant lowering of 11% whencompared to the control value for MOEIn addition to specific gravity, MOE was asignificant covariant in the MOR analysis. TheMILL × TL interaction was significant for MORso no conclusions could be drawn from the maineffects, even though mill and treatment levelwere significant (Table 1). Analysis of the databy mill indicated a slight effect of treatment onthe SO board as compared to the control. Whilestatistically significant, the actual change inMOR due to treatment level is 11%. The data forthe MA board showed no significant differenceamong retentions. In either case, the practicalsignificance would seem to indicate little effectof treatment level.For fiber stress and work values, both mill andtreatment levels were significant but not theirinteraction (Table 1). Specific gravity was a sig-nificant covariant in both analyses. For bothproperties, a reduction was shown for the high-est treatment level only. Across all property val-ues in static bending, it can be concluded thateffect of treatment was of practical significanceonly at the highest retentions. Other than theeffect of process or furnish species, the mechani-cal properties from static bending testing wereunaffected at the lower retentions required forcontrol of decay or insect attack. A similar resultis shown in Table 2 for tensile strength whereonly mill location was found to be significant.Oriented strandboardSpecific gravity was a significant covariant inthe analyses of MOE, fiber stress, and work forOSB (Table 3). Once adjusted for specific grav-ity, then neither mill, treatment level nor theirinteraction was significant in the analyses of fi-TABLE 1. Comparison of static bending least square meansfor medum density fiberboard.1Modulus of elasticity (MPa) [mill, treatment level, M × TL] (G)Mill × treatment levelSO Low 3,379 S MA Low 3,312 ASO Control 3,374 A MA Control 3,125 ASO High 3,192 A MA High 2,790 BModulus of rupture (kPa) [mill, treatment level, M × TL] (MOE, G)Mill × treatment levelSO Control 34,101 A MA Control 18,761 ASO Low 31,695 B MA High 18,216 ASO High 30,378 B MA Low 17,988 AFiber stress (kPa) [mill, treatment level] (G)Mill Treatment levelSO 18,113 A Control 16,341 AMA 13,203 B Low 16,113 AHigh 14,520 BWork-to-proportional limit (kJ/m3) [mill, treatment level] (G)Mill Treatment levelSO 5.52 A Control 4.63 AMA 3.19 B Low 4.46 AHigh 3.98 B1 Means not followed by a common letter are significantly different onefrom another at p  0.05 or higher; significant sources of variation areshown in brackets; significant covariants are in parentheses.TABLE 2. Comparison of static bending least square meansfor oriented strandboard.1Modulus of elasticity (MPa) [mill] (G)MillMS 4,178 AME 5,168 BModulus of rupture (kPa) [mill, M × TL] (E, MC)Mill × treatment levelMS High 28,496 A ME High 27,248 AMS Low 27,841 A ME Control 21,394 BMS Control 26,979 A ME Low 20,760 BFiber stress (kPa) [no effects] (G)MS Control 16,954 A ME Control 17,140 AMS Low 16,589 A ME Low 17,133 AMS High 14,913 A ME High 17,644 AWork-to-proportional limit (kJ/m3) [no effects] (G)MS Control 3.39 A ME Control 2.97 AMS Low 3.87 A ME Low 3.02 AMS High 3.59 A ME High 3.82 A1 Means not followed by a common letter are significantly different onefrom another at p  0.05 or higher; significant sources of variation areshown in brackets; significant covariants are in parentheses.Barnes and Murphy—PROPERTIES OF VAPOR BORON-TREATED COMPOSITES 381ber stress and work. For MOE, only mill loca-tion was significant with board from the MElocation being 19% stiffer than MS mill board.Treatment had no impact.For MOR, both MOE and MC were signifi-cant covariants for OSB (Table 3). Analysis ofthese data showed both mill and the mill-treatment level interaction to be significantsources of variation. No impact of treatmentlevel was noted for the MS mill. While there wasa significant impact of treatment level for theME board, the data indicated no deleterious ef-fect since the MOR for ME board treated to thehighest level was significantly greater than thatfor controls or low level treatment. As withMDF, only mill location was significant in theanalysis of tensile strength (Table 2).Treatment seems to have even a lesser effecton OSB compared to MDF. Differences can beattributed to the different furnish types in thetwo OSBs.Laminated veneer lumberStatic bending property values are shown inTable 4 for LVL. Specific gravity was a signifi-cant covariant in the analysis of MOE and fiberstress. MOE was a significant covariant in theanalysis of MOR, while the analysis of workvalues showed no significant covariants.Species differences in LVL are evident in theanalyses of both MOE and MOR where milllocation was the only significant source of varia-tion (Table 4). Similar to the results for MDFand OSB, the mill effect can be attributed to thespecies difference (Douglas-fir vs. southernpine). Treatment appeared to have no effectwhatsoever. In the case of fiber stress, treatmentlevel was significant but not deleterious sinceboth treatments yielded fiber stress valuesgreater than the controls. For work, both treat-ment level and the mill-treatment level interac-tion were significant. For the southern pineLVL, no differences among treatments werenoted (Table 4). Differences among treatmentsdid exist for the Douglas-fir LVL, but both treat-ments yielded higher work values than the con-trols. As with the other composite types, no realdeleterious effect of treatment was shown withmost differences being due to species.SUMMARY AND CONCLUSIONSData are presented as the effects of VBT-treatment on the bending properties of MDF,OSB, and LVL made from North American fur-nish. For most composite types, differences inproperty values can be attributed to differencesin furnish, species, or processing. Deleteriouseffects due to treating, when found, were onlyfor the highest treatment level. Treatments forprotection in terrestrial applications (∼1% BAE)had no negative effects on composite bendingand tensile properties.TABLE 3. Comparison of static bending least square meansfor laminated veneer lumber.1Modulus of elasticity (MPa) [mill] (G) Modulus of rupture (kPa) [mill] (E)Mill MillSO 11,236 A SP 69,989 AD-F 11,953 B D-F 57,102 BFiber stress (kPa) [treatment level] (G)Treatment levelLow 41,203 AHigh 40,141 ABControl 38,314 BWork-to-proportional limit (kJ/m3) [treatment level, M × TL] (none)Mill × treatment levelSP High 8.20 A D-F Low 8.27 ASP Low 8.04 A D-F High 7.03 ABSP Control 7.98 A D-F Control 6.47 B1 Means not followed by a common letter are significantly different onefrom another at p  0.05 or higher; significant sources of variation areshown in brackets; significant covariants are in parentheses.TABLE 4. Comparison of tensile strength least squaremeans for medium density fiberboard and oriented strand-board.1Medium density fiberboard Oriented strandboardTensile strength (kPa) [mill] (none) Tensile strength (kPa) [mill] (none)Mill MillSO 19,567 A MS 12,011 AMA 10,914 B ME 10,549 B1 Means not followed by a common letter are significantly different onefrom another at p  0.05 or higher; significant sources of variation areshown in brackets; significant covariants are in parentheses.WOOD AND FIBER SCIENCE, JULY 2005, V. 37(3)382REFERENCESAMERICAN SOCIETY FOR TESTING AND MATERIALS. 1997.D143-94 Standard Test Methods for Small Clear Speci-mens of Timber; D1037-96a Standard Test Methods forEvaluating Properties of Wood-base Fiber and ParticlePanel Materials. In: Annual Book of ASTM Standards, Sec-tion 4 Construction, Volume 04.10 Wood. American So-ciety for Testing and Materials, West Conshohocken, PA.BARNES, H. M., H. A. STEWART, AND R. J. MURPHY. 2004.Vapor boron treatment of composites reduces tool wear.Forest Prod. J. 54(10):69–73.BERGERVOET, A., R. BURTON, K. NASHERI, D. PAGE, AND P.VINDEN. 1992. Gaseous boron treatments of wood andwood products. International Research Group on WoodPreservation, Doc. No. IRG/WP/3691-92, 6 pp.BURTON, R., A. BERGERVOET, K. NASHERI, P. VINDEN, AND D.PAGE. 1990. Gaseous preservative treatment of wood. In-ternational Research Group on Wood Preservation, Doc.No. IRG/WP/3631, 7 pp.DICKINSON, D. J., AND R. J. MURPHY. 1989. Development ofboron based wood preservatives. Record, BWPA AnnualConvention, pp. 35–44.HASHIM, R., R. J. MURPHY, D. J. DICKINSON, AND J. M. DIN-WOODIE. 1992. Effect of vapour boron on mechanicalproperties of wood based board materials. InternationalResearch Group on Wood Preservation, Doc. No. IRG/WP/3727-92. 17 pp.———, ———, ———, and ———. 1994. The mechani-cal properties of boards treated with vapor boron. ForestProd. J. 44(10):73–79.JONES, W. A., H. M. BARNES, AND R. J. MURPHY 2001. An-cillary properties of vapor boron-treated composites. In-ternational Research Group on Wood Preservation, Doc.No. IRG/WP 01-40210, 6 pp.MURPHY, R. J., AND P. TURNER. 1989. A vapour boron pre-servative treatment of manufactured wood based boardmaterials. Wood Sci. Techol. 23(3):273–279.PRESTON, A. (ed). 1993. Proc., IUFRO Symposium on theProtection of Wood-based Composites, May 15, 1993,Forest Products Society, Madison, WI [ISBN 0-935018-61-1].SCHUERCH, C. 1968. Treatment of wood with gaseous re-agents. Forest Prod. J. 18(3):47–53.TURNER, P, AND R. J. MURPHY. 1987. A novel process for thetreatment of manufactured wood based board materials.Pages 283–284 in Proc., IUFRO Wood Protection Sub-ject Group S.5.03, Ontario, Canada.Barnes and Murphy—PROPERTIES OF VAPOR BORON-TREATED COMPOSITES 383

Bending and Tensile Properties of Vapor Boron-Treated Composites

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Bending and Tensile Properties of Vapor Boron-Treated Composites

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