Milling of organic solids has a profound influence on the characteristics of the products to the extent that the pharmaceutical and agrochemical industries are extremely cautious about loss of crystallinity and formation of amorphous content and polymorphs as a result of milling. Humidity, temperature and strain rate all affect milling operations as well as the physical and chemical properties of the products and for soft and sticky or rubbery particles the procedure of specifying size reduction is still by trial and error. We are developing a methodology for predicting the milling characteristics of organic solids based on the fundamentals of materials science by characterising the feed material properties, mill dynamics and operating conditions.

Single particle impact and quasi-static indentation fracture testing methods are used to quantify the mechanical properties that influence the breakage. The breakage rate and product size distribution are quantified for a simple laboratory ball mill and are analysed by population balance modelling to provide a generic tool for relating the breakage function to single particle material properties. On going work on the characterisation of milling behaviour of sucrose will be presented.