Single particle mechanical characterization of ground switchgrass in air dry and wet states using a microextensometer

To understand the mechanical process of pelletization, it is critical to study the particle level interactions that cause particles to bind together and form a pellet. A micromechanical extensometer device, inspired by the MEMS technology, was developed and used to perform tensile experiments to deduce the stress-strain response of single particles of ground biomass. The effect of moisture, which has a significant role in forming pellets, was examined based on the micromechanical characterization of moisture conditioned and unconditioned (control; air dried) switchgrass particles. Conditioned particles exhibited three phases sigmoidal shaped stress-strain response. The three phases include the first linear elastic zone, where the particle behaved linearly up to approximately 1.6% strain, the second linear elastic zone (strain ranging from 1.6 to 2.1%) with significantly increased elastic modulus (168.9-223.7%), and the third zone (strain beyond 2.1%), where elastic modulus declined sharply (down to 90.9% of the second zone). The modulus of elasticity up to 1.5% strain for unconditioned and conditioned switchgrass particles were 1.60 +/- 0.33 GPa and 6.99 +/- 1.66 GPa, respectively (p = 0.00). The nominal fracture strength of unconditioned (6.2%, w.b.) and conditioned (17.5%, w.b.) switchgrass particles were determined as 35.77 +/- 14.99 MPa and 130.42 +/- 87.56 MPa, respectively (p = 0.08). The nominal fracture strain of unconditioned and conditioned switchgrass particles were determined as 2.43 +/- 0.70% and 1.51 +/- 0.66%, respectively (p = 0.06). Increase in the stiffness of switchgrass particles is contributed to the bundling of fibers promoted by the activation of binders due to increased moisture content. (C) 2016 Elsevier B.V. All rights reserved.