Transverse thermal properties of commingled hemp and flax thermoplastic tows for biocomposite processing applications

There is growing industrial and academic interest in manufacturing of biocomposite parts comprised of natural fibers in a thermoplastic matrix that begin as a commingled, unconsolidated preform. Unfortunately, little thermal property data exists in the literature for simulation/analysis of processes used to make parts (e.g., pultrusion, Automated Fiber Placement (AFP), and compression molding). In this paper, the authors explain how specific heat capacity and thermal conductivity values of both constituent materials and the biocomposite preform are measured in a direction transverse to the fiber length, and how the effect of entrained air is included. Thermal property values for hemp and flax fibers along with polypropylene and polyethylene filaments, measured both individually and combined into apparent values for the preforms, are compared with experimental values. Finally, determination of thermal properties for use in pultrusion simulation is explained as a case study.