Powder mixture
A powder is an assembly of dry particles dispersed in air. If two different powders are mixed perfectly, theoretically, three types of powder mixtures can be obtained: the random mixture, the ordered mixture or the interactive mixture.
Different powder types
A
Random mixture
A random mixture can be obtained if two different free-flowing powders of approximately the same particle size, density and shape are mixed (see figure A).[3] Only primary particles are present in this type of mixture, i.e., the particles are not cohesive and do not cling to one another. The mixing time will determine the quality of the random mixture. However, if powders with particles of different size, density or shape are mixed, segregation can occur.[4] Segregation will cause separation of the powders as, for example, lighter particles will be prone to travel to the top of the mixture whereas heavier particles are kept at the bottom.
Ordered mixture
The term ordered mixture was first introduced to describe a completely
Interactive mixture
If a free-flowing powder is mixed with a cohesive powder an interactive mixture can be obtained. The cohesive particles adhere to the free-flowing particles (now called carrier particles) to form interactive units as shown in figure B.[3] An interactive mixture may not contain free aggregates of the cohesive powder, which means that all small particles must be adhered to the larger ones. The difference from an ordered mixture is instead that all carrier particles do not need to be of the same size and a different number of small particles attached to each one. A narrow size range of the carrier particles is preferred to avoid segregation of the interactive units.[6] In practice a combination of a random mixture and an interactive mixture may be obtained which consists of carrier particles, aggregates of the small particles and interactive units.[7]
Formation
The formation of interactive mixtures cannot automatically be assumed, especially if smaller carrier particles [8] or a greater proportion of fine particles [9][10] are used. If an interactive mixture is to be formed, it is necessary that enough force is exerted by the carrier particles during dry mixing to break up the aggregates formed by the fine particles. Adhesion can then be achieved if the adhesive forces exceed the gravitational forces that otherwise lead to separation of the constituents.[3]
Applications
Interactive mixtures for example can be used in the manufacturing of tablets
The
The schematic formation of a random mixture (A) and an interactive mixture (B) by dry mixing two powder materials.
References
- .
- ^ N.A. Orr & E. Shotton (1973). "The mixing of cohesive powders". Chemical Engineer. 269: 12–18.
- ^ a b c d "AVHANDLINGAR.SE: Studies on a Novel Powder Formulation for Nasal Drug Delivery".
- ISSN 0032-5910.
- .
- .
- ^ J.N. Staniforth (1981). "Total mixing". Int J Pharm Tech & Prod MFR. 2: 7–12.
- .
- S2CID 6880102.
- PMID 12084498.
- ^ Bredenberg, Susanne New Concepts in Administration of Drugs in Tablet Form : Formulation and Evaluation of a Sublingual Tablet for Rapid Absorption, and Presentation of an Individualised Dose Administration System. Doctoral thesis (2003). Uppsala University, Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmacy
- S2CID 23665573.
- .
- ISSN 0032-5910.
External links
- Improving Powder Flow During Pharmaceutical Operations, an Rx Times article