Morphological Properties and Breakage Behavior of Three Ground Biofeedstocks by Hammermilling
Size reduction is one of the most important first steps during processing of biofeedstocks for food, feed, fuel, or fiber production. Size reduction improves conversion processes because of the creation of larger reactive surface areas, and it is also used to improve material handling in the process. This study investigated the particle size, particle size distribution, and morphological changes of three biofeedstocks (switchgrass, corn kernels, and soybean seeds) ground by hammermilling through three screen sizes (6.4 mm, 3.2 mm, and 1.6 mm). Feedstock particle size was analyzed based on both screen size and feedstock type. Significant differences were found among screen sizes; however, particle size differences among feedstock types were only significant for material passing through 6.4 mm and 3.2 mm screens. Of the three feedstocks, ground corn exhibited the smallest particle size as expressed by its geometric mean diameter (dwg), while soybean seeds exhibited the largest dwg. The morphological features of all the feedstocks, expressed as circularity, roundness, and aspect ratio, did not change significantly, as was initially hypothesized. While ground switchgrass had very high aspect ratios (10 to 12) and low circularity (0.20) and roundness (0.10), the opposite was seen for ground corn and soybean, which exhibited more spherical particles. It was concluded that the breakage behavior of biofeedstocks is an inherent material property that changes very little with size reduction by hammermilling.