Rheology and extrusion of high-solids biomass

Economical biorefining of lignocellulosic biomass (LCB) requires processing high-solids particulate streams. We have developed new techniques and testing protocols to measure the rheological properties of high-solids LCB using a modified torque rheometer (TR). The flow field in the TR is similar to that of a twin-screw extruder and for modeling purposes can be adequately represented as a dual-Couette viscometer. Our experiments show that LCB exhibits Bingham plastic behavior with very large yield stresses. We observe that in the initial stages of mixing, torque values are extremely large and erratic. During this period, considerable particle-size reduction takes place with correspondingly large energy consumption. We show that the addition of a rheological modifier (e.g., carboxymethyl cellulose) reduces biomass apparent viscosity and mixing energy requirements. We take advantage of this effect to further investigate the viability of continuous processing by extrusion.