Mechanical properties of microcrystalline cellulose - Part I. Experimental results

This paper describes a set of laboratory diagnostic tests performed in order to reveal the main mechanical properties exhibited by several cohesive powders. The laboratory tests were carried bout on several powders, however only the results for microcrystalline cellulose, PH-105, mean particle size 20 pm will be mainly presented here. A few results of other materials will be incorporated as examples to explain the development of these diagnostic tests, as well as the development of improved methodologies. First, the powder was tested to see if it exhibits "instantaneous" response. For this purpose we have used a "quasi-static" procedure described later to determine the elastic parameters. All the elastic parameters were obtained experimentally by using an enhanced triaxial tester (Development of a New Technique for Measuring Volume Change of Dry Particulate Systems under Very Low Confining Pressures. IMECE: Recent Trends in Constitutive Modeling of Advanced Materials AMD-Vol. 239 (2000) 65). The tests were carried out at low to moderate confining pressures which are typical in storage and handling facilities such as bins and hoppers and mechanical feeders. Afterwards, we tried to see if the powder exhibits irreversible deformation and if this deformation is time dependent. We have found that the volume is either compressible or dilatant, and that irreversible volumetric deformation is taking place by creep. Compressibility is a transient phenomenon. Microcrystalline cellulose does not exhibit much dilatancy, but a rate effect was also recorded and this phenomena is of great importance for many industrial applications. Shortly, the diagnostic tests reveal that only elastic/viscoplastic non-associated constitutive equations are able to describe the mechanical properties discussed above. The paper describes all the data needed to determine such constitutive equations. (C) 2002 Elsevier Science Ltd. All rights reserved.