Attrition strength of different coated agglomerates

The goal of this paper is to test the strength against attrition of coated particles. What is the influence of different coating materials on different particles? To answer this question, two different core materials are coated with four different water-soluble polymers. The core materials are micro-crystalline cellulose (MCC) and sodium benzoate granules in the size range between 850 and 1000μm. The coated granules are attrition tested in the repeated impact tester (RIT). During attrition testing the uncoated MCC granules do not show any attrition. When the MCC granules are coated, all the attrition observed is due to the failure of the coating. When the sodium benzoate (Purox-S) granules are attrition tested, significant attrition is observed. Coating the sodium benzoate granules with the polymers increases the strength against attrition. During attrition three typical failure modes are distinguished viz. the peeling mechanism, the erosion mechanism and the layer fatigue mechanism. For the four different coatings different attrition mechanisms are observed indicating that the polymer mechanical properties play an important role. For example, a higher molecular mass for poly(ethylene glycol) increases the mechanical stability of the granules. It is now important to study the mechanical polymer properties in more detail, to explain further the observed failure modes. With the RIT it is possible to select the optimal settings in the coating process, to optimize the coating material or composition and finally to optimize the coating thickness.