Meticulous chemical analysis of decaying xylem and linking it to corresponding anatomical modification at the cellular level can improve our understanding of the decay process. The aim of this study was to monitor the histological, chemical, photochemical, and progression of wood degradation by two white-rot fungi at different intervals. Oriental beech wood (Fagus orientalis) blocks were exposed to Pleurotus ostreatus and Trametes versicolor to investigate the degradation capabilities of these two fungi. Light microscopy was used to study the decay patterns in wood. Decayed wood samples were also analyzed to determine lignin, cellulose and sugar contents and also evaluated at two week intervals by FT-IR spectroscopy to study chemical alterations. According to chemical analyses lignin is the most degraded polymer followed by cellulose and hemicelluloses for both white rot fungi. However, both test fungi tended to consume lignin more than cellulose. FT-IR spectra changes for lignin and carbohydrates in beech wood supported chemical alteration and indicated that both fungi decay wood in a simultaneous pattern.

Improved methods are needed for detecting and quantifying the effect of decay fungi on wood products. The focus of the present paper is a soil block decay test with exposure to the brown rot fungus Gloeophyllum trabeum, where the changes in elasticity and strength were compared in both the radial and tangential directions as a function of the decay degree. The stress-strain analysis was employed by a transverse compression (transC) testing technique in which a load was applied over the specimen’s tangential or radial surface. It was found that early effects of decay were detected in either direction of loading, but the overall reduction in elasticity and compression strength after 7 days of exposure to the fungus was approximately two times greater in the radial direction. This difference is interpreted that decay occurs mainly in the earlywood (EW). Significant strength loss at 5% compression was detected after 2 days of exposure to the fungus. However, 3 days of exposure was required before significant strength loss was evident as a result of the reduction in modulus of elasticity (MOE) or mass loss (ML). In comparison to ML, the compression strength loss was found to be a more sensitive measure of wood decay.

Oilborne pentachlorophenol (penta) is one of the three major wood preservatives employed for treating industrial forest products in the United States (U.S.). However, due to toxicity concerns penta has been listed as a restricted use pesticide in the U.S. for three decades and is no longer permitted in many other countries. A relatively benign substituted isothiazolone, 4,5 dichloro-N-octylisothiazolin-3-one (DCOI), has good wood preservative properties. This study examined the long-term ground contact performance of samples treated with DCOI versus penta, both formulated using the same oilborne carrier so that the efficacies of the two biocides can be directly compared, at two field test sites with high or severe deterioration in Mississippi. After 25 years of ground contact exposure the decay and termite deterioration ratings indicated that DCOI had equal or slightly more efficacy at about half the retention as samples treated to a penta retention specified for many commercial products.

Soy flour was evaluated as a partial substitute for resin in the manufacture of oriented strand board (OSB), a wood-based composite that often replaces solid lumber and plywood in structural applications in the construction industry. Since the presence of soy could alter OSB biodegradation properties, termite resistance of OSB panels made with 0, 10, and 20 percent of polymeric methylene diphenyl diisocyanate (pMDI) resin substituted with soy flour (OSB0, OSB10, and OSB20, respectively) was investigated. Single choice tests between three types of OSB and southern yellow pine (SYP) solid wood and an OSB choice test (OSB0 vs. OSB10) were evaluated. Results indicated that termites always showed a preference for SYP, with the OSB becoming less palatable when soy flour was present. Percentage weight losses for OSB0, OSB10, and OSB20 were 5.7×, 8.4×, and 8.6× less, respectively, compared with SYP. In the absence of SYP, termites did not differentiate OSB0 from OSB10, with OSB10 showing 1.5× less weight loss compared with OSB0. Visual rating data supported weight loss data, except significantly less damage was only found when the choice paired SYP with OSB made with soy (OSB10 or OSB20). Termite consumption preference for SYP was explained by differences in water absorption kinetics. SYP reached saturation (105% moisture content) within 1 week on moist sand, while moisture content of OSB composites slowly climbed to 79 percent over 4 weeks, never reaching a plateau. Lower moisture content was due to the presence of water-repellent resin and wax in the OSB.

A need exists to develop new organic, environmentally benign wood preservatives for industrial applications to replace the older creosote and pentachlorophenol systems. In this study the performance of creosote at three retentions was compared to a new wood preservative candidate formulated with Polymeric Xylenol Tetrasulfide (PXTS) in an E7 AWPA field study using two sets of southern pine and yellow poplar field stakes treated with three creosote retentions or five retentions of PXTS. The stakes were installed at two test sites and evaluated after 3,5 years, 6 years, and 14 years exposure. After six years of exposure at both sites, which is double the minimum recommended exposure period of three years’ field data for AWPA submission of a proposed new preservative system, the average decay ratings data for southern pine stakes after three years exposure was not sufficient to definitively determine which system provides superior protection against decay and termite attack (Creosote at the AWPA UC4B pole retentions versus pine stakes treated with much lower PXTS levels). However, after a longer exposure time of 14 years the data conclusively shows that pine stakes treated to the utility pole AWPA UC4B creosote retention performed poorer at both sites against decay and termite degradation than pine stakes treated with 26 Kg/m³ PXTS. Similar results were obtained with the yellow poplar stakes. We conclude that: 1) much longer E7 exposure times are necessary then the minimum recommended three years in the AWPA GDA Standard for submission of new systems to definitively determine the efficacy of a proposed oil borne system compared to the efficacy of a traditional organic preservative for commercial applications, and 2) long term field PXTS performance against decay and termite deterioration is equal or greater than that obtained with creosote at about four times the PXTS retention.