Jerrold E. Winandy

Chemical mechanism of fire retardance of boric acid on wood

It is commonly accepted that the fire retardant mechanism of boric acid is a physical mechanism achieved by the formation of a coating or protective layer on the wood surface at high temperature. Although a char-forming catalytic mechanism has been proposed by some researchers, little direct experimental support has been provided for such a chemical mechanism. In this paper, new experimental results using thermal analysis, cone calorimetry (CONE), and gas chromatography–Fourier transform infrared spectroscopy (GC–FTIR) analysis are presented and the fire retardant mechanism of boric acid on wood is discussed. Basswood was treated with boric acid, guanylurea phosphate (GUP), and GUP–boric acid. Treated wood was then analyzed by thermogravimetry (TG/DTG), differential thermal analysis (DTA), CONE, and GC–FTIR analysis. Thermogravimetry showed that the weight loss of basswood treated with boric acid was about three times that of untreated or GUP-treated wood at 165°C, a temperature at which GUP is stable. The DTA curve showed that boric acid treated basswood has an exothermal peak at 420°C, indicating the exothermal polymerization reaction of charring. CONE results showed that boric acid and GUP had a considerable synergistic fire retardant effect on wood. The GC–FTIR spectra indicated that compounds generated by boric acid treated wood are different than those generated by untreated wood. We conclude that boric acid catalyzes the dehydration and other oxygen-eliminating reactions of wood at a relatively low temperature (approximately 100–300°C) and may catalyze the isomerization of the newly formed polymeric materials by forming aromatic structures. This contributes partly to the effects of boric acid on promoting the charring and fire retardation of wood. The mechanism of the strong fire retardant synergism between boric acid and GUP is due to the different fire retardant mechanisms of boric acid and GUP and the different activation temperatures of these two chemicals.

Effects of Post Heat-Treatment on Surface Characteristics and Adhesive Bonding Performance of Medium Density Fiberboard

A series of commercially manufactured medium density fiberboard (MDF) panels were exposed to a post-manufacture heat-treatment at various temperatures and durations using a hot press and just enough pressure to ensure firm contact between the panel and the press platens. Post-manufacture heat-treatment improved surface roughness of the exterior MDF panels. Panels treated at 225°C for 30 min had the smoothest surface while the roughest surface was found for the control panels. Wettability and the adhesive bonding strength between veneer sheet and panel surface were decreased as post-treatment press temperature increased. A significant relationship (R 2 = 0.92) existed between contact angles and adhesive bond strength.

Experimental method to quantify progressive stages of decay of wood by basidiomycete fungi

A biological exposure method was developed that allows wood samples to be progressively removed for monitoring colonization and decay by basidiomycete fungi. Monitoring involves strength tests, determination of weight loss, and chemical analysis. To optimize the procedure, several variations of the method were tested using two species of brown-rot fungi (Gloeophyllum trabeum and Oligoporus placentus (Postia placenta)) and one white-rot species (Trametes versicolor) against southern pine sapwood. The variations involved type of culture medium and exposure method. All variations enabled substantial and rapid decay. Specimens exposed to brown-rot fungi lost 80-100% strength and 25-40% weight after 12 weeks; the white-rot fungus was less effective, but nevertheless caused 20-40% loss in strength. For both brown- and white-rot fungi, strength loss exceeded weight loss. For brown-rot fungi, there was a direct relationship between strength loss and weight loss, suggesting a quantitative relationship between strength loss and chemical composition (hemicellulose sugars) during incipient decay of southern pine by these fungi.

Spectroscopic analysis of southern pine treated with chromated copper arsenate. II. Diffuse reflectance Fourier transform infrared spectroscopy (DRIFT)

Abstract Although chromated copper arsenate (CCA) is one of the most important treatment methods for the prevention of decay in wood, the nature of wood/CCA reactions are not clear. The current study was undertaken to elucidate the nature of chemical reactions occurring between the components of the treating solution and the constituents of wood. Small, clear Southern pine samples were treated with six different preservative solutions (Cr; Cr/Cu; Cr/As; CCA-A; CCA-B; CCA-C), at 6.4 and 40 Kg/m3 (0.4 and 2.5 pcf) retentions, and compared to water treated and untreated controls. Samples were dried following treatment and analyzed by diffuse reflectance Fourier transform infrared spectroscopy (DRIFT). Evaluation of DRIFT data indicated that the preservative components reacted with the aromatic and carbonyl groups in wood.

Spectroscopic Analysis of Southern Pine Treated with Chromater Copper Arsenate. I. X-Ray Photoelectron Spectroscopy (XPS)-17

Abstract The amount of southern pine lumber treated with chromated copper arsenate annually is considerable, yet the association of this preservative with the wood structure is not clear. The current study was undertaken to elucidate the nature of chemical reactions occurring between the components of the treating solution and the constituents of wood. Small, clear Southern pine samples were treated with six different preservative solutions (Cr; Cr/Cu; Cr/As; CCA-A; CCA-B; CCA-C), at 6.4 and 40 Kg/m3 (0.4 and 2.5 pcf) retentions, and compared to water treated and untreated controls. Samples were dried following treatment and analyzed by X-ray photoelectron spectroscopy (XPS). Evaluation of XPS data indicated that the preservative components reacted with wood, through aromatic and possibly alkene substitution, while oxidation of hydroxyl groups was not detected. The proposed wood/CCA bonding also offers an explanation for differences in hardwood and softwood durability following treatment.

Effect of fire-retardant treatment on plywood pH and the relationship of pH to strength properties

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.

Chicken feather fiber as an additive in MDF composites

Abstract Medium density fiberboard (MDF) panels were made with aspen fiber and 0-95% chicken feather fiber (CFF) in 2.5%, 5%, or 25% increments, using 5% phenol formaldehyde resin as the adhesive. Panels were tested for mechanical and physical properties as well as decay. The addition of CFF decreased strength and stiffness of MDF-CFF composites compared with that of all-wood control panels. However, MDF-CFF panels showed a marked improvement in resistance to water-soak absorption, which provided limited protection against decay fungi. This benefit was probably related to the hydrophobic keratin in the CFF. Further research is focused on the thresholds of CFF required to decrease thickness swelling and increase water resistance.

How variability in OSB mechanical properties affects biological durability testing

Summary Loss in bending strength of wood has been shown to be a more sensitive measure of decay than is weight loss. Using modulus of rupture as the decay criterion is problematic for oriented strandboard (OSB) because of variation in mechanical properties due to particle orientation and size. Moreover, the small specimen size required for such tests increases the variance in mechanical properties. This study compared the variance in bending strength of ASTM D1037 standard-sized specimens and small specimens from two samples of commercial OSB. The small specimens were found to have a significantly higher level of variance in bending strength than the standard-sized specimens. A simple method of sorting the specimens based on strand orientation on the tensile surface significantly reduced the level of variance measured. The effects of differing levels of variance on the size, design and limitations of the experimental study are presented.