An optical technique for determination of layer thickness swell of MDF and OSB

A nondestructive optical technique was developed to determine thickness swell of discrete layers within intact samples of wood composites. Layer thickness swell of commercial medium density fiberboard (MDF) and oriented strandboard (OSB) are presented. Layer swell within the sample is important in understanding the swell phenomena of wood composites. Results from standard specimens show edge layer thickness swell after 2-, 8-, and 24-hour water soak and include measures of precision and variation for this technique. The relative difference for overall thickness swelling compared between the optical technique and the traditional method decreased as water exposure time increased and was less than 3.44 percent after 24-hour water exposure. The contributions of high-density surface layers to overall MDF thickness swell were 95.76, 75.50, and 61.77 percent after 2-, 8-, and 24-hour water exposure, respectively. The contributions of high density surface layers to overall OSB thickness swell were 74.36, 64.39, and 57.30 percent after 2-, 8-, and 24-hour water exposure, respectively. Thickness swell for both products was dominated by the high density surface layers throughout the 24-hour soak cycle. However, dense surface layers contributed more to the overall swell measurement during the early period of the soak cycle compared to the swell measurement at the completion of the 24-hour soak cycle. The relative contribution of the core layers to overall thickness swell increased with length of exposure period. This optical technique is recommended for the measurement and study of in-situ layer swell properties for all wood composite panel materials.

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