The overall aim of the project is to elucidate the effect of feed material properties, mill dynamics and prevailing environment on milling of organic materials. This requires the use of a multi-scale approach covering molecualr scale, to single particle scale and the bulk scale.
The recently concluded IFPRI programme (IFPRI FRR 52-03) addressed the effect of material properties on single particle breakage and bulk milling, which enabled etsablishment of a relationship between the single particle properties and the bulk milling. The main aims of this follow-up programme are to understand single particle breakage behaviour from the molecualr scale, and to bridge the gap between the properties and behaviour at the single particle scale and those at the molecular scale. The principle methodology used in the follow-up programme is to investigate the single particle breakage behaviour as a function of temperature, huimidity and strain rate. The work over the past 12 months has led to the following results:
• Effect of temperature was investigated at a relative humidity of ~30%. The results show that the extent of impact breakage of aspirin particles increases with increasing temperature, whereas little effect of temperature is seen for sucrose.
• Effect of humidity was studied at the ambient temperature (20oC). The results show no clear influence of the relative humidity for sucrose and aspirin particles on their single particle breakage behaviour.
• Effect of repeated impacts on single particle breakage (fatigue tests) was investigated using sucrose at the ambient temperature and ~30% relative humidity. The results show that the extent of breakage increases first with increasing number of impacts, reaches a maximum after a certain number of impact, and then followed by a slow decrease with a further increase in the number of impacts. The impact velocity has a great effect on the maximum value of the cumulative extent of breakage; a higher impact velocity gives a higher peak breakage extent; however, the number of impacts needed to reach the peak breakage extent also increases with increasing impact velocity.