The effect of storage time and moisture content on grindability of loblolly pine (Pinus taeda L.)

Specific grinding energy and particle size distribution of grinds are usually used to assess the efficiency of grinding equipment and material grindability. The objective of this study was to quantify the effects of moisture content and storage time on the specific grinding energy of loblolly pine woodchips and the physical properties of the resulting grinds. Samples were ground in a hammer mill fitted with 3.18 and 6.35 mm screen sizes. The specific grinding energy, moisture loss during grinding, particle size distribution, and bulk density of the grinds were measured. Moisture loss during grinding increased with increase in moisture content of woodchips and decreased with increase in hammer mill screen size. Bulk density of grinds reduced from 273.64 to 106.03 kg/m³ and from 251.14 to 131.40 kg/m³ (for 3.18 mm and 6.35 mm hammer mill screen size, respectively), when the moisture content of woodchips was increased from 13.6 to 100.0 % (dry basis). Results also showed that storage time did not significantly affect (p < 0.05) the specific grinding energy. However, specific grinding energy was significantly affected (p < 0.05) by the moisture content of woodchips and hammer mill screen size. The specific grinding energy of woodchips ground through 3.18 mm hammer mill screen size increased with increase in moisture content of woodchips. However when loblolly pine woodchips were ground through 6.35 mm hammer mill screen size, the specific grinding energy initially increased as moisture of woodchips increased from 13.6 to 42.9 % (dry basis), then decreased with further increase in moisture content of woodchips from 42.9 to 100.0 % (dry basis).