Bast Fiber Decortication for Biocomposites by a Mastication Process

This paper discusses a new method for decorticating bast fiber stalks, particularly hemp and flax, through a mastication process without damaging the fiber for use in biocomposites. Conventional automated decortication methods provide high stalk processing throughput, but they significantly damage the bast fibers and adversely affect their performance in biocomposite applications. Initial experiments with industrial hemp using a matched set of tools indicate that indexing the stalk by, at most, half a tooling period for each mastication cycle maximizes both the crushed stalk flexing action and dehurding efficiency. Further process insight was gained through simple stalk-crushing experiments (force vs. deflection) between matching teeth with no indexing, where force spikes correspond to initial collapse of the stalk cross section and initial hurd bending fracture along the stalk length. A more extensive experimental design with stiffer tooling reveals that hurding efficiency is maximized by adding spaces in the bottom die for hurd to fall through, using the smallest practical indexing distance of less than half a tooling period, and using as many teeth as possible. However, shorter indexing and more teeth also decrease the throughput rate and complicate stalk handling. Future work for optimizing and commercializing the process is suggested.