The core idea to improve the flowability of powder particles is to weaken the interaction forces between particles. Traditional methods for enhancing powder flowability in various industries mainly fall into two categories: increasing particle size and modifying particle surfaces.
(1) Flow Additives
Flow additives can significantly improve powder flowability and effectively prevent powder caking and hardening. Their core mechanism is to reduce the adhesion force between particles. Additives increase the inter-particle gap and weaken the van der Waals force between particles. Common flow additives include nano-particles, surface-active additives (surfactants), and polymers.
Nano-particles have long been used as flow additives. During application, nano-particles need to be fully dispersed to uniformly coat the surface of powder particles. Featuring strong affinity with base powder, nano-particles can tightly attach to particle surfaces. At the initial stage of mixing, nano-particles adhere to powder surfaces in the form of agglomerates. Due to weak internal forces within agglomerates, these agglomerates gradually disintegrate and redistribute on powder particles during mixing to achieve more uniform dispersion. The nano-agglomerates attached to particle surfaces reduce inter-particle contact interactions, ultimately improving powder flowability.
(2) Increasing Particle Size
Increasing particle size is the most classic improvement method. Larger particles possess greater gravitational force, which helps overcome friction and other inter-particle forces and improves flowability. The term agglomeration (food industry) and granulation (pharmaceutical industry) share the same principle: numerous fine individual particles are assembled into large particles while retaining the inherent physicochemical properties of primary particles. The resulting large particles have a much bigger size than the original fine powder, delivering markedly enhanced flowability.
Taking dairy powder as an example, agglomeration can take place inside the spray drying chamber or in an external fluidized bed after spray drying. Inside the spray drying chamber, primary agglomeration occurs from collisions between wet particles, and secondary agglomeration arises from collisions between wet and dry particles. Lecithin, a natural phospholipid-rich surfactant, is commonly used as a binder in this process to bind particles together and form large cluster structures.
(3) Optimization of Crystallization Process
For crystalline powders, apart from particle size enlargement, crystallization can be adopted to adjust crystal morphology and particle size so as to optimize powder flowability. This process integrates crystallization and granulation in one single step with simple operation. In addition, it has many advantages: the whole process can be operated under sterile conditions, no extra excipients are required, and it is compatible with GMP production.
Studies show that optimizing crystallization processes (solvent selection, raw material selection, supersaturation control) can regulate the morphology and particle size of crystals. Particle size directly affects powder bulk density, flowability and other volumetric properties. In Anneke’s research, re-designing the crystallization process produced larger crystals with uniform particle size distribution and improved bulk density and other flowability-related indicators. Methods to adjust crystal morphology include solvent screening, crystal structure analysis, compound screening, and additive-controlled crystallization.
This article is reproduced from Powder Network for study and reference only, and does not constitute any professional advice or commercial basis.
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