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Reduction of biomass resilience by torrefaction: apparent stiffness during failure (ASF) and specific failure energy (SFE) assessed by a custom impact device

Abstract The present work focusses on the loss of resilience of torrefied wood as an indicator of its grindability. An impact device was developed to evaluate the mechanical behaviour of wood at high compression rates with a particular emphasis on the surface area of the particles produced. It allows the energy determination needed to produce particles without a traditional grinding test. Pine (Pinus pinaster) and oak (Quercus robur) were tested in radial (R) and tangential (T) directions and for various torrefaction intensities. With increasing heat intensity, the material becomes more fragile and finally loses its fibrous character, which increases the number of peak events on the stress/strain curve and significantly reduces the deformation energy. Two indices were derived from the experimental results: the apparent stiffness during failure (ASF) and the specific failure energy (SFE). These criteria allow the quantification of the loss of mechanical strength due to torrefaction, as well as the surface area increment of particles for a given grinding energy.