(Received 17 December 2001; accepted 18 September 2002)
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The objective of this work was to evaluate (a) the effects of a new boron-nitrogen, phosphate-free fire-retardant (FR) formulation on the initial strength of Douglas-fir AB-grade plywood and (b) the potential of this FR treatment to experience subsequent thermal degradation inservice when exposed to elevated temperatures. Test Method ASTM D 5516 was generally followed. The results of our analysis indicated that treatment and post-treatment redrying with the new boron-nitrogen, phosphate-free FR had a significant negative effect of about 7% on bending strength and a significant negative effect of 26% on energy-related properties, such as work to maximum load. The properties of modulus of elasticity and maximum moment canying capacity were not significantly reduced. Our results indicate that the likelihood of FR-treated plywood to experience in-service reduction in mechanical properties when exposed to elevated temperatures is no different than that of matched untreated plywood. As a result of our analysis, we recommend a revision to the cutting procedure specified by D 5516-96. We recommend that users first cut the specimens, then inspect and cull specimens with defects, and finally allocate specimens to experimental groups prior to FR treatment and redrying. We also recommend the substitution of commercially available grades of higher quality plywood, such as AA or AB, for the custom-made N-grade plywood currently recommended by D 5516-96.
Supervisory Wood Scientist, USDA Forest Service, Forest Products Laboratory, Madison, WI
Manager, Griffin Development Center, Research Division, Osmose Inc., Griffin, GA
Stock #: JTE12410J