Fineness of Hemp (Cannabis Sativ L.) Fiber Bundle after Post-Decortication Processing Using a Planetary Ball Mill

Hemp (Cannabis Sativ L.) fiber can be used for biocomposites, textile, and many other applications. However, hemp fibers directly from decortication process are often too coarse for most applications. In this study, post decortication processing of hemp coarse fibers was investigated to mainly improve the fiber fineness. A lab-scale planetary ball mill was used to refine coarse hemp fibers collected from decortication plans. The coarse fibers were ground using the planetary ball mill under different grinding speeds (100, 200, 300, 400, 500, and 600 rpm) and grinding durations (2, 5, and 8 min). The refined fibers (longer than 20 mm or 0.79 in.) were characterized by the mass fraction, length, and fineness. The shorter fibers were disposed as chaff after grinding. The results showed that grinding resulted in fiber fraction in the range of 0.69 to 0.96, (i.e. the chaff fraction range being 0.31 to 0.04). Grinding slightly shortened the fiber length, but significantly improved the fiber fineness. In general, higher grinding speed and longer grinding duration produced less, shorter, and finer fiber. To evaluate the performance of the planetary ball mill, reduction of fiber fineness relative to the original fineness was determined from the fiber fineness data before and after grinding, and grinding index was also defined as the ratio of the mass fraction of refined fiber to its fineness. The results of these two parameters indicated that the grinding process was more effective in dealing with a coarser feedstock fiber. The grinding speed of 300 to 600 rpm appeared to be the suitable operational speeds of the mill for post-decortication processing of hemp fiber.