A review of existing mixing indices in solid-based continuous blending operations

Abstract Blend uniformity is a critical quality attribute in continuous pharmaceutical manufacturing. However, its measurement is challenging due to the difficulty and inaccessibility of sampling locations in a continuous blender. Though computational approaches like Discrete Element Method (DEM) can address this, one of the underlying challenges is the appropriate selection of mixing index for measurement of blend uniformity. Given the wide plethora of literature implementing different indices, it becomes cumbersome to identify suitable index for specific blending application. The proposed article aims to address this concern using a detailed review, classification and comparison of existing mixing indices. These indices are used to evaluate mixing in a periodic section of blender using DEM. The effects of process parameters, like blade speed, on mixing are further investigated. This review article, thus, contributes towards devising a systematic strategy for selection of appropriate mixing index based on the powder system and its application.