Milling of agglomerates in an impact mill

Milling of agglomerates is one of the common unit operations during preparation of oral dosage forms like capsules and tablets. In literature the breakage of granules is mostly determined after single impact at an ideally formed granule or of single particles. In this paper the breakage behavior of agglomerates after milling with multiple impacts has been studied. It investigates the effects of the formulation and the influences of the mill settings. With respect to the formulation it has been found that both the size of the particles before granulation and the amount of binder used determine the breakage behavior. Both parameters have an influence on the strength of the granule to be milled, where initial particle size has the largest effect. A relation has been found between the strength of granules and the degree of size reduction. Regarding the mill settings, there are no mill parameters which influence the formation of fines independently. Formation of fines is always the result of the total degree of size reduction. It is not possible to achieve a large degree of size reduction without intensive fines formation. The results indicate that it is possible to achieve every desired average particle size. However, when formation of dust has to be reduced, multiple milling steps with separation of in-size particles is necessary.