Including flow additives in a blend in order to tailor flowability, is common practice in many powder processing industries. Often powders developed to meet certain product performance targets are not conducive with consistent and predictable flow, creating a demand for additives that can enhance flow properties.
Within food processing for example, flow additives are routinely employed to reduce or eliminate powder caking, a phenomenon that compromises product value, while in pharmaceutical blends additives help to support the efficient die filling needed for successful tableting. Although typically incorporated to improve process efficiency, the use of additives can also have a substantial influence on final product quality. In the powder coatings industry, for example, additives are used to produce blends that flow and level easily, to create a high-quality surface finish.
When optimising the use of flow additives, it is important to recognise that their impact on behaviour may extend beyond a simple improvement in flowability. Choosing the most appropriate grade of flow additive for a particular blend and incorporating it at an optimal level for the application is also crucial. Many powders have poor basic flow properties: They block in hoppers and die feed frames, exhibit inconsistent or pulsatile discharge rates, adhere to surfaces of equipment or don’t mix readily with other materials.
In such cases, it is possible to reduce particle-particle friction and change the powder’s bulk resistance to movement by the addition of a lubricant powder. Magnesium Stearate (MgSt), highlighted in the study below, is used extensively as a lubricant in the manufacture of pharmaceutical oral solid dosage forms. It is commonly added to formulations in low concentrations (typically <1% w/w) immediately prior to tableting.
Over a range of processes, however, the relationship between flow additive and substrate is less well-understood. Due to the differing demands placed on powders by different processes, the relative influence of a given additive on a given substrate may not be consistent under all circumstances.
Click here to read ‘The Influence of Flow Additives on Powder Behaviour’ which presents case study data.