Using fungicides or combinations of fungicides to provide mold and decay fungal protection to OSB
Creators: name: Choi, Baek Yong
Publisher: name: University of British Columbia
Year: 2008

description: The use of wood-based composites has increased dramatically over the last two decades due to a number of factors. One reason is that Oriented Strand Board (OSB) is being increasingly utilized in residential applications in place of plywood. However, the use of OSB in residential construction is often limited because of its susceptibility to attack by biological pathogens such as mold and decay fungi. The environmental conditions that exist in certain use categories can be so adverse that the performance of these composites is negatively affected. This study was divided into two parts. The first phase examined the effectiveness of fungicides or combinations of fungicides (including some metal-containing preservatives) for enhancing the mold resistance of strandboard. During the second part of the study, preliminaryexperiments investigated the effectiveness of fungicides or combinations of fungicides using anagar-block test to estimate the preservative toxic threshold retention. The compatibility of the fungicide on the resin curing was studied by measuring change in the resin gelation and viscosity. After these screening experiments were completed, large size boards were prepared and mechanical and decay resistance properties were examined. It was found that mold and decay resistance properties of strandboard directly were related with the biocide type and its concentration. Greater protection of the strandboard was achieved with an increase in preservative retention levels. However, due to the relatively high cost of non-metallic (organic) preservatives, it is important to find the minimum amount of preservative that can protect the OSB against mold and decay fungi. One method of reducing the cost and increasing efficacy is to combine different fungicides to determine whether synergism exists. Even if synergism does not occur, it may reduce the overall cost by combining a less expensive biocide with a smaller amount of a more expensive biocide wheretheir biocidal efficacy complements each other. In addition, it is important to understand that high retention of preservative may also cause negative effects on the mechanical properties of strandboard. This maybe noticeable of the high retention level of the biocide when a greater negative effect on the internal bonding (IB) strength may be recorded. Lower IB strength for treated strandboard may be attributed to the formulation of chemical residue in the wood surface, which may interfere with the reaction between wood and phenol formaldehyde (PF) resin. Surface-active agents in the preservative may also cause the PF resin to over-penetrate into wood decreasing bond strength. Increasing moisture content of strands by the introduction of an emulsified aqueous biocide solution, may cause dilution of the resin, and reduced bonding. It should also be noted that high retention of preservative which cause a change in the viscosity and gelation time of PF resins would be problematic for the operation of an OSB plant. For viscosity change, it could significantly affect the flow properties of the resin on the wood furnish and its atomization as it is spraying onto the wood furnish. In addition, it may require further modification to the equipment that supplies the resin to the spray nozzle. For changes in the gelation time, this may require changes to the press time at the OSB plant.