Nucleation, growth and breakage phenomena in agitated wet granulation processes: a review

Wet agglomeration processes have traditionally been considered an empirical art, with great difficulties in predicting and explaining observed behavio ur. Industry has faced a range of problems including large recycle ratios, poor product quality control, surging and even the total failure of scale u p from laboratory to full scale production. However, in recent years there has been a rapid advancement in our understanding of the fundamental proces ses that control granulation behaviour and product properties. This review critically evaluates the current understanding of the three key areas of we t granulation processes: wetting and nucleation, consolidation and growth, and breakage and attrition. Particular emphasis is placed on the fact that there now exist theoretical models which predict or explain the majority of experimentally observed behaviour. Provided that the correct material prop erties and operating parameters are known, it is now possible to make usefu l predictions about how a material will granulate. The challenge that now f aces us is to transfer these theoretical developments into industrial pract ice. Standard, reliable methods need to be developed to measure the formula tion properties that control granulation behaviour, such as contact angle a nd dynamic yield strength. There also needs to be a better understanding of the flow patterns, mixing behaviour and impact velocities in different typ es of granulation equipment. (C) 2001 Elsevier Science B.V. All rights rese rved.