Engineering perspectives of the hemp plant, harvesting and processing: A review

The special characteristics of the hemp (Cannabis sativa L.) plant make it one of the most challenging crops to handle. Several studies, both in the laboratory and the field, have been conducted at the University of Manitoba, Canada, on the engineering perspectives of hemp production, including the physical and mechanical properties of the hemp plant, hemp harvesting and processing. Physical properties of the hemp plant, such as plant height, seed-head length, stem diameter and stem specific mass, vary highly within a field and across fields. The force and energy required for cutting a hemp stem are much greater than those required for cutting maize stalk and forage crops. The two-windrow harvesting concept has been demonstrated to be feasible and can be implemented into a commercial windrower for harvesting dual-purpose hemp. Conditioned hemp dries significantly faster than unconditioned hemp. However, conditioning hemp requires more power than conditioning a forage crop. The basic machine functions required for hemp fibre processing are separating the fibre from the core and cleaning the fibre. A field-going processing unit can be formed by combining a modified forage harvester and a straw walker from a grain combine. However, the effectiveness of such a unit is limited, and the design of new separating and cleaning devices may be required for higher fibre yield and purity.