Decay unsterile soil tests

Tjeerdsma etal. (1998a) subjected thermally modified wood to soft rot decay in unsterile soil tests. Although decay resistance was enhanced by thermal treatment, it was not possible to prevent attack entirely. Treatments giving the best performance in terms of decay resistance also exhibited the highest strength losses. Viitanen etal. (1994) have also reported on some preliminary experiments on heat-treated wood in unsterile soil. 

Four different methods (vapour-phase acetylation using acetic anhydride, acetylation using ketene gas, liquid phase acetylation using acetic anhydride/xylene, or neat acetic anhydride) were used to acetylate pine wood chips to a variety of WPGs for the production of MUF-bonded particleboards (Nilsson etal., 1988). Composite boards were exposed to unsterile soil in fungal cellar tests. Boards made from ketene acetylated chips were not found to be resistant to decay at the maximum WPG level achieved (17 %) with a liquid acetic anhydride modification, no decay was recorded at a WPG level of c. 18 % after 12 months exposure, whereas with a vapour-phase treatment at the same WPG, evidence for decay was found. 

Sugar maple was reacted with propylene and butylene oxide (Rowell etal., 1982). The modulus of elasticity (MOE) and modulus of rupture (MOR), fibre stress at proportional limit, and maximum crushing strength all exhibited a reduction, compared to unmodified samples. Nilsson and Rowell (1983) reacted ponderosa pine with butylene oxide and exposed the wood in an unsterile soil decay test. At low WPGs, severe surface decay due to soft rot and tunnelling bacteria was observed. Such attack was reduced at 15 % WPG,... 

Hill et al. [31] manufactured EFB/polyester composites after various chemical treatments. The composites were then tested by exposure to decay fungi in unsterile soil for up to 1 year. It was found that such exposure resulted in deterioration of mechanical properties. The chemical treatments, however, significantly protected the composites from severe deterioration. 

Testing of decay resistance can be performed in a laboratory environment or in outdoor field trials, and there are many standards defined for these tests. The first objective of a laboratory-based test is to provide a methodology for the rapid screening of a candidate wood preservative, treatment or modification in order to assess which ones exhibit decay resistance. Broadly speaking, laboratory-based tests can be divided into sterile (pure culture) tests and unsterile tests (such as fungal cellar, soil burial etc.). 

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