Progress 12/01/01 to 11/30/06
Outputs
This study was conducted to investigate the influence of borate modification of wood flakes on structural and biological performance of oriented strandboard (OSB). The research consisted of several components, including studies on the effects of powder zinc and calcium borate on resin gel time, creep/strength, swelling, leaching, termite, decay, and mold resistance properties of OSB; effect of polymetric methylene diisocynante (pMDI) resin on mechanical, physical and leaching properties of borate-treated OSB; and the effect of borate and wood on the curing of phenol-formaldehyde resins used for OSB manufacturing. The results of structural performance analysis showed that the predicted creep deflection of 10-year loading duration under both 15% and 40% stress levels of all borate-modified OSB panels met the long-term deflection requirement of the National Design Specification for Wood Construction. Significant effect of borate modification on the fractional deflection
was observed under cyclic relative humidity environments. Four-element burger body creep model was found to be appropriate in predicting the creep response of borate modified OSB under constant RH condition. Separation of the observed creep strain into three components was made to identify the true mechano-sorptive (MS) creep strain. The proposed model provided reasonably accurate prediction of MS creep strain. Biological analysis showed that borate loading at Boric Acid Equivalent (BAE) levels above 1 percent is effective in protecting panels from decay, mold and termites. The negative influence of the borates on the OSB's physical and mechanical properties was not significant when the borate content was under 4.5 percent. Increasing the content of pMDI resin could significantly improve the properties of OSB. Studies of the effect of zinc borate on the cure kinetics of commercial phenol-formaldehyde (PF) face and core resins for OSB showed that cure reactions of the face resin were
comprehensively retarded by the addition of ZB. The reaction order and the activation energy of the face resin were both increased. ZB also lowered the onset cure temperature of the core resin, and caused the addition reaction to happen at much lower temperatures. The addition reactions happened at temperatures lower than 60C, while the condensation reactions began slowly at temperatures higher than 85C. Compared with the pure core resin, the addition reactions of the core resin/ZB mixture also followed the nth-order cure kinetics with the lower reaction orders, but the mechanism of the condensations was changed to follow an nth-order cure mechanism with the reaction order being 1.04. Experimental data fitted well the models erected for the resin/ZB mixtures, and the relationships among curing degree, cure temperature, and cure time were predicted. A comprehensive review was also done to contrast chemical treatment process, to discuss long-term performance of treated composites, and
to outline future research directions for treated structural wood composites. The results of the study were published in 14 technical papers and abstracts, one Ph.D. dissertation and one MS thesis.
Impacts
Results of this project can be used to help better understand the treatment process for structural wood composites and field performance of the treated products. This will allow the composite manufacturers producing durable composites with sound mechanical performance to meet increased market demand.
Publications
- Lei, Y., and Q. Wu. 2006. Cure Kinetics of Aqueous Phenol-Formaldehyde Resins Used for Oriented Strandboard Manufacturing: Effect of Zinc Borate. Journal of Applied Polymer Science 101:3886-3894.
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Progress 01/01/05 to 12/31/05
Outputs
A comprehensive review was done to contrast chemical treatment processes, to discuss long-term performance of treated composites, and to outline future research directions for structural wood composites. The results show that current treatment options include pre-treatment of wood furnish, in-line or integral treatment, and post treatment of finished products. Treated products include glulam timbers, softwood plywood, LVL, PSL, LSL, OSB, I-joist/I-beam, particleboard, and fiberboard products. It is concluded that treated structural engineered composite products have a strong future. As the type of timber available for use in forest products continues to grow, there will be an increasing need for fungal and insect-resistant structural composites. Successful commercialization of treated structural composite depends on the development of a cost-effective manufacturing process and a solid market base.
Impacts
Results of this work can help to better understand the treatment process for structural wood composites and field performance of the treated products. This will help the composite manufacturers to produce durable composites to meet increased market demand.
Publications
- Smith, W.R., and Q. Wu. 2005. Durability improvement for structural wood composites- Current state of the art. Forest Products Journal 52(2):8-17.
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Progress 01/01/04 to 12/31/04
Outputs
Work is being done to study effect of borate and wood on curing of phenol-formaldehyde resins used for oriented strandboard manufacturing. This is a continuation of previous work on developing borate-treated structure composite with improved durability and strength properties. The cure kinetics of both neat face and core resins was studied using both isothermal and dynamic differential scanning calorimetry (DSC). The cure reaction of the face resin under heat completely followed an nth-order cure kinetic mechanism. The reaction order was nearly 1, with the activation energy of 79.29KJ/mol. While the core resin showed more complicated reaction, including an nth-order reaction and an autocatalytic one, and a new model was developed. The nth-order part with reaction order of 2.38 began at lower temperatures, but the reaction rate of the autocatalytic part increased much faster with temperatures. The total reaction order for the autocatalytic part was 5.30. The comparison
between theoretical and experimental data showed that the experimental data well fitted the new model for the core resin at certain temperatures. The isothermal DSC was much more reliable than the dynamic DSC in studying the cure kinetics. Furthermore, the relationships among reaction reversion (curing degree), cure temperature, and cure time were predicted. The curing tests with borate and wood as resin additives are currently being conducted and the kinetics models are being further developed to account for the effect of borate and wood.
Impacts
Treated structural wood composites such as oriented strandboard (OSB) have a strong future. As the type of timber available for use in forest products continues to change and the demand for exterior-use products continues to grow, there will be a growing need for fungal- and insect-resistant structural composites. The processing conditions developed for producing decay and insect-resistant OSB from major southern wood species allow process modification and species selection to produce durable structural panels with desired biological performance.
Publications
- Lee, S., Q. Wu, and W. R. Smith. 2004. Formosan subterranean termite resistance of borate-modified strandboard manufactured from southern wood species: a laboratory trial. Wood Fiber Sci. 36(1):107-118.
- Wu, Q. 2004. Borate-treated strandboard from southern wood species. In Proc. the 58th Forest Products Society Annual Meeting in Grand Rapids, MI. June 30, 2004. (Abstract)
- Wu, Q. 2004. Borate treated structural wood composites for durable home constructions. In Proc. NSF and HUD Housing Research Workshop, Orlando, FL. February 12, 2004. (Abstract)
- Zhou, Y. 2004. Properties of borate-treated strandboard bonded with pMDI resin. MS thesis. Louisiana State Univ., Baton Rouge, LA 105 pp.
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Progress 01/01/03 to 12/31/03
Outputs
Borate-treated strandboard bonded with polymetric methylene diisocynante (pMDI) resin was produced and tested for mechanical, physical, and leaching properties. The effect of borate type (zinc versus calcium), resin content (2.5% versus 5% of the dry wood weight), borate loading level (0, 1.5, 3.0 and 4.5% of the dry wood weight), and wood species group (southern pine versus mixed hardwoods) on various properties was studied. It was shown that the use of pMDI resin can significantly reduce leaching of the chemical from the test panel, while maintaining desired mechanical and swelling properties for the treated strandboard. The leaching rate was further reduced at the higher resin loading level. The effect of borate type was also insignificant on various properties with the resin system. Further testing of the pMDI bonded boards under long-term cyclic conditions is still on-going.
Impacts
Treated structural wood composites such as oriented strandboard (OSB) have a strong future. As the type of timber available for use in forest products continues to change and the demand for exterior-use products continues to grow, there will be a growing need for fungal- and insect-resistant structural composites. The processing conditions developed for producing decay and insect-resistant OSB from major southern wood species allow process modification and species selection to produce durable structural panels with desired biological performance.
Publications
- Wu, Q., S. Lee, and J. P. Jones. 2003. Decay and mold resistance of borate modified oriented strandboard. CD-ROM: IRG/WP03-40260. In Proc. 34th Annual Conference for the International Research Group on Wood Preservation, Brisbane, Australia. May 12-17, 2003.
- Lee, S. 2003. Fundamental Properties Of Borate-Modified Oriented Strandboard From Southern Wood Species. School of Renewable Natural Resources, Louisiana State University. Ph.D. Dissertation. 158 pp.
- Wu, Q. 2003. Preservative-treated structural wood composites for durable home construction. In Proc. NSF Housing Research Agenda Workshop. Orlando, FL. February 12-14, 2004. 9 p.
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Progress 01/01/02 to 12/31/02
Outputs
This study was conducted to examine the effects of powder zinc borate (ZB) and calcium borate (CB) on resin gel time, strength, swelling, leaching, termite, decay, and mold resistance properties of oriented strandboard (OSB). It was found that gel time of phenol formaldehyde (PF) resin decreased with increased amount of ZB, indicating interaction between the borate and the resin. The reduced gel time was partially recovered by using polyethylene glycol (PEG) in combination with ZB. Although panel stiffness was not affected by borate up to a 3.5 percent boric acid equivalent (BAE) level, ZB and CB showed a negative effect on the bending and internal bond (IB) strength. Thickness swelling (TS) of treated panels after 24-hour water soaking increased with borate level. ZB-treated OSB displayed less TS than CB-treated OSB at an equivalent BAE level. CB with a larger particle size caused significant TS. However, the chemical with a smaller particle size helped bring TS to a
stable and acceptable level. A certain portion of borate leached out from OSB samples under the water-soaking conditions. The leaching rate varied with wood species, borate types, and amount. The use of borate with a smaller particle size helped reduce the leaching rate. The relationship between assayed BAE and leaching time followed a decaying exponential function for ZB and a decaying power function for CB. Laboratory termite tests showed that wood weight loss decreased and termite mortality increased with the increased BAE level. At the 1 percent BAE or above, there was little damage on wood samples. There were significant correlations among termite mortality, weight loss, and visual damage ratings. Both borate chemicals provided an excellent decay and mold resistance for OSB. The information on various properties of borate-modified OSB is of significant value for developing durable structural panels from southern wood species. Further development of the products with other resin
and chemical systems is currently on-going.
Impacts
The research provides comparative properties between zinc and calcium borate modified OSB and thus identifies alternative treating methods for structural OSB (i.e., calcium borate). This will allow the OSB manufacturers, which are not included in the license agreement for using zinc borate, to manufacture chemically modified OSB.
Publications
- Wu, Q., S. Lee, and J. N. Lee. 2002. Mechanical, physical, and biological properties of borate-modified oriented strandboard. Pages 137-144 in Advances in Building Technology edited by M. Anson, J.M. Ko, and E.S.S. Lam (ISBN: 0-08-044100-9). Elsevier Science Ltd., Oxford, UK. 1762 p.
- Wu, Q., and J. N. Lee. 2002. Long-term creep response of borate-modified oriented strandboard. Pages 129-136 In Advances in Building Technology edited by M. Anson, J.M. Ko, and E.S.S. Lam (ISBN: 0-08-044100-9). Elsevier Science Ltd. Oxford, UK. 1762 p.
- Wu, Q., J. N. Lee, Sunyoung Lee, W. Ramsay Smith, and B. Strickland. 2002. Developing Termite-Resistant Structural Wood-based Panels From Southern Wood Species. Louisiana Agriculture. Summer. 45(2):20-21
- Lee, Sunyoung. 2002. Fundamental Properties of Borate-Modified Oriented Strandboard From Southern Wood Species. Ph.D. Dissertation. School of Renewable Natural Resources, Louisiana State University. 158 p.
- Wu, Q., and S. Lee. 2002. Leachability of borate-modified oriented strandboard: a comparison of zinc and calcium borate. CD-ROM: IRG/WP02-40232. In Proc. 33rd Annual Conference for the International Research Group on Wood Preservation, Cardiff, England. May 12-17, 2002.
- Smith, W.R., D. Ring, T. Shupe, G. Henderson, Q. Wu, and M. Voitier. 2002. Louisiana and the Formosan Subterranean Termite: An Update. Abstract in Biographies & Abstracts, Forest Products Society 56th Annual Meeting, Madison, WI. June 23-26, 2002. (Abstract)
- Lee, S, J. N. Lee, and Q. Wu. 2002. Leachability of borate-modified OSB:a comparison of zinc and calcium borate. In Proc. 56th Forest Products Society Annual Meeting, Madison, WI. June 23-26, 2002. (Abstract)
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