(225d) Comparison of Magnetically Assisted Impaction Coating (MAIC) with Traditional Mixing Techniques for the Addition of a Silica Flow Aid

Many powders have poor basic flow properties, they block in hoppers and die feed frames, exhibit inconsistent or pulsatile discharge rates, adhere to equipment surfaces or donâ??t mix readily with other materials. Additionally, many powders tend to cake on storage or during transport due to changes in environmental conditions and/or consolidation. As such, flow aids are frequently added to a blend to enhance flow properties and/or inhibit caking.

In order to optimise the influence of a flow aid, it must be dispersed in a fine, uniform layer on the surface of the substrate particles. However, most flow aids, for example Fumed Silica or Magnesium Stearate, consist of very fine particles that have a tendency to form agglomerates. The mixing/coating process employed can therefore have a major influence on how efficiently the flow aid is distributed. The process must be intense enough to disperse the agglomerated flow aid without damaging the particles of the substrate or the flow aid itself. This is particularly true for many food and pharmaceutical ingredients which are often relatively friable and easily deformed by extreme mechanical forces[1].

Magnetically Assisted Impaction Coating (MAIC) has been demonstrated as a technique for coating soft host particles without causing major changes to particle shape and size[1]. This system relies on a pounding process in which an oscillating magnetic field is used to accelerate and spin large magnetic particles, which are mixed with host and guest particles (flow aid), causing the magnetic particles to fluidise. The agitated magnetic particles impart energy to the host and guest particles and coating is then achieved by means of impaction or peening of the guest particles onto the host particles as collisions occur between particles and between particles and the vessel wall[1].

This study compared MAIC with V-blending through comparison of the flow properties of the substrate after the addition of silica. In addition, this study also investigated the effect of silica concentration on samples blended via MAIC.

For the first part of this study citric acid was blended with 0.5% w/w and 2.0% w/w silica. Blending was undertaken using MAIC and a V-blender. The resultant four blends were tested using an FT4 Powder Rheometer® to evaluate their dynamic, bulk and shear properties[2].

The results indicated that at both concentrations of silica, the MAIC blends exhibited improved dynamic flow properties as well as the ability to pack more efficiently when subjected to an external force.

In the second part of the study, citric acid was combined with 0.05%, 0.5% and 2.0 % w/w silica using MAIC. The resulting blends, and the unlubricated substrate, were evaluated using the powder rheometer. The results indicated that as the concentration of silica increased the flow properties improved, however, change was not proportional to the concentration of silica with the greatest improvement in flowability observed at the lower concentration, and only slight improvements exhibited with 0.5% and 2% silica.

Overall, the results showed that MAIC resulted in improved flowability when compared with V-blending, suggesting that this method provides better dispersion of the flow aid onto the surface of the host particles. The results also indicate that only a small quantity of silica is required to achieve significant improvement in flow properties when the MAIC process is employed.

References

 ADDIN EN.REFLIST [1] Ramlakhan, M., Wu, C.Y., Watano, S., et al., Dry particle coating using magnetically assisted impaction coating: Modification of surface properties and optimization of system and operating parameters. 2000:112:137-148.

[2] Brockbank, K., Armstrong, B., Chandorkar, Y., et al., Understanding powder caking as a consequence of a range of mechanisms by means of powder rheometry. 2015:33:102-108.