Effect of fire-retardant treatment on plywood pH and the relationship of pH to strength properties |
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Authors: | S T Lebow J E Winandy |
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Institution: | (1) USDA Forest Service, Forest Products Laboratory, Madison, Wisconsin 53705-2398, USA, US |
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Abstract: | Summary This paper investigates the relationship between wood pH and the strength properties of fire-retardant-treated (FRT) plywood,
as it is affected by fire-retardant (FR) formulations, processing variables, and extended high temperature exposure conditions.
The objectives of this study were to (1) identify the effect of post-treatment kiln-drying temperature, followed by high temperature
exposure, on wood pH; (2) identify the effect of various mixtures of FR components, followed by high temperature exposure,
on wood pH; (3) determine if treatment effects on strength and pH are affected by plywood thickness; and (4) quantify the
relationship between changes in wood pH and strength loss and whether pH can be used as a predictor of strength loss. Results
indicate that the differences in pH resulting from the initial redry temperature became insignificant after extended periods
of high temperature exposure. All FR treatments studied caused large, rapid decreases in pH, with the most rapid decreases
occurring with formulations containing phosphoric acid. Additions of borate compounds, especially disodium octaborate tetrahydrate
(Timbor), produced a measurable buffering effect that slowed or lessened the decreases in pH. No differences in the effect
of FRT on the wood pH-strength relationship were noted between the two plywood thicknesses evaluated. A strong relationship
was noted between changes in pH of the plywood and reductions in strength and energy-related properties. These findings suggest
that the pH of FRT plywood is a good indicator of its current condition and may have potential as a predictor of future strength
loss as the plywood is subjected to elevated in-service temperatures.
Received 8 January 1997 |
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