A Look At Degradation in Particleboards for Exterior Use

This discussion is divided into three parts: 1) A discussion of the properties that exterior particleboard must have for various uses, based on the supposition that the uses are divided into two classes: Class 1, where the exterior particleboard must have at least one smooth surface, and Class 2, where the particleboard will be used unfinished and surface characteristics are of minor importance; 2) An evaluation of currently available board materials, indicating the areas where improvements ought to be made to meet the severe requirements of exterior exposure; and 3) A review of current research aimed at improving exterior board properties. Of all the combinations of factors and environmental conditions known to have a degrading effect on particleboard in exterior exposures, severe cycling changes in moisture content deserve the most attention. Similarly, degradation, in the form of excessive thickness and linear changes accompanied by nonuniform thickness swelling, particle popping, and surface roughening, all associated with severe moisture changes, head the list of degradation characteristics. Reduction in strength, color changes and warping are all secondary to excessive dimensional changes. Most anticipated exterior uses of particleboard are essentially nonstructural, thus minimizing, somewhat, the importance of loss of strength. Particleboards typical of the current state-of-the-art exhibit have somewhat questionable properties due to excessive thickness and linear movement with severe moisture changes. The dimensional changes are decidedly greater than in exterior Douglas-fir plywood, but are equal or possibly somewhat better than in conventional high-density hardboard. Current research on post treatments, combined with wise choice of particle geometry and species, gives much promise of producing particleboard that will more closely approach the dimensional performance of plywood and the surface characteristics of hardboards.

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