The aim of the project is to establish a relationship between the product properties and feed material and the mill functions for milling of organic solids. The specific objectives are:
a) To characterise the physical, mechanical, and thermal properties of organic feed materials (material function) at the single particle level, and to examine the effects of temperature and humidity on these properties,
b) To investigate the breakage behaviour of single organic particles at quasi-static and dynamic conditions under the influence of temperature and humidity,
c) To investigate the bulk milling behaviour of model organic solids and mill hydrodynamics (mill function),
d) To characterise the properties of milled product, and to correlate the product properties to material and mill functions.
Model materials planned and approved for use in the project by the TC of IFPRI include aspirin, á -lactose monohydrate, sucrose or sorbitol, starch, and microcrystalline cellulose. These materials cover a fairly wide range of physical, mechanical and thermal properties, hence ensuring generality of the results to be achieved. This report summarises the work done over the second year of the project. The work includes the single particle breakage studies using the impact tester under both ambient and sub-ambient conditions, surface characterisation of the product particles using the Dynamic Vapour Sortion (DVS) device, measurements of Young’s modulus and hardness of single aspirin crystals using the nano-indentation method, analysis of the bulk milling behaviour of aspirin under both ambient and sub-ambient conditions, analysis of the mill dynamics, the use of a flow aid Aerosil to prevent re-agglomeration of milled products during the bulk milling, and population balance modeling of the milling of aspirin in collaboration with Du Pont. An attempt has also been made to relate the characteristics of the milled products in terms of particle size to the properties of feed material - the primary aim of the research. The single particle impact tests at the ambient conditions show that data on the breakage extent fit well to the model developed by Ghadiri and Zhang (2002) for semi-brittle materials. The aspirin particles used in this work are non-spherical but very close to the cubic shape. High speed digital video recording suggests that aspirin particles impact on the target from edges/corners of the particles. SEM analysis of particles after the impact testing shows that the failed surfaces under the ambient conditions are fairly smooth, suggesting possibility of particle failure at the cleavage planes. A reduction in temperature has a marked effect on the single particle breakage behaviour of aspirin. The new surfaces at the sub-ambient conditions are rougher than that in the ambient conditions, suggesting that the particle failure may be not at the cleavage planes under the sub-ambient conditions.