Shavings stored outdoors may be susceptible to attack by fungi, which in turn could influence the quality of shavings, the resulting fiber quality, and the final medium density board (MDF) performance. Three piles of shavings were constructed as hemispheres (11 feet in height and 11 feet in diameter), which contained roughly 250 ft3 (7 m3) or 1,480 lb (675 kg) of shavings obtained from a local MDF plant. The shavings in Pile 1 and Pile 2 were protected with a biological agent and by a shelter, respectively; Pile 3 was built without protection during storage.
It was observed that outdoor storage of shavings influenced the fiber physical and chemical properties. In most cases, stored shavings resulted in a high percentage of longer fibers being retained on a 14-mesh screen (1.190 mm) compared to fresh shavings (control). Storage also resulted in less acidic fibers, as indicated by higher pH values and acid buffer capacity. The hot water solubility of the fibers was higher for the shelter-protected shavings and lower in both the biologically protected and unprotected shavings, compared to the control. In addition, the refining process made the wood more acidic. Converting the shavings to fibers decreased the pH in the control by 19% and by 17 to 27% in the stored shavings. The conversion also reduced the buffer capacity by 44% in the control and by 25 to 50% in the stored shavings.
The outdoor storage of shavings also affected the mechanical and physical properties of the resulting MDF board. In general, the shelter-protected shavings fibers yielded the strongest board, followed by the biologically protected and unprotected shavings fibers, while the least strong board was made from fresh shavings fibers. With regard to location of the shavings in the piles, in most cases, fibers made from exterior shavings resulted in stronger boards than fibers made from interior shavings. These results imply that outdoor storage of shavings for a selected time period (4 months) did not seem to negatively influence board performance, but instead seemed to significantly improve bond quality.
An apparent correlation existed between board performance and fiber chemical property. Fibers prepared from shelter-protected shavings not only showed higher hot water solubility, but also yielded overall stronger board, compared with other stored shavings fibers and the control fibers. This study also indicated that the physical or mechanical and chemical properties of the fibers were important to board quality. Therefore, the best quality fibers for high quality MDF could be obtained from a given wood raw material by optimizing the fiber refining process.