Powder mixing homogeneity

At the other extreme, solid solutions are difficult to prepare. To form a solid solution, individual atoms or molecules must mix homogeneously within the solid network. Given that the atoms or molecules in a solid cannot move freely about, such mixing is difficult to achieve. Even if we grind two solids to fine powders and then mix them thoroughly, the resulting mixture will not be a solution, because the mixture will remain heterogeneous at the... 

To achieve the goal of required performance, durability, and cost of plate materials, one approach is improvement of the control of the composition and microstructure of materials, particularly the composite, in the material designing and manufacturing process. For example, in the direction of development of thermoplastics-based composite plate, CEA (Le Ripault Center) and Atofina (Total Group) have jointly worked on an irmovative "microcomposite" material [33]. The small powders of the graphite platelet filler and the PVDF matrix were mixed homogeneously by the dispersion method. The filler and matrix had a certain ratio at the microlevel in the powder according to the optimized properties requirements. The microcomposite powders were thermocompressed into the composite plate. 

A.S. El-Hagrasy, F.D Amico and J.K. Drennen III, A process analytical technology approach to near-infrared process control of pharmaceutical powder blending. Part III Quantitative near-infrared calibration for prediction of blend homogeneity and characterization of powder mixing kinetics, J. Pharm. Sci, 95(2), 422-434 (2006). 

This guidance describes methods of sampling that might be used to demonstrate active ingredient homogeneity. These methods are put forward as suggestions and are not intended to be the only methods for meeting FDA requirements for demonstration of the adequacy of a powder mix. 

From the representative bulk sample, a smaller, homogeneous laboratory sample is formed that must have the same composition as the bulk sample. For example, we might obtain a laboratory sample by grinding an entire solid bulk sample to a fine powder, mixing thoroughly, and keeping one bottle of powder for testing. Small portions (called aliquots) of the laboratory sample are used for individual analyses. Sample preparation is the series of steps needed to convert a representative bulk sample into a form suitable for chemical analysis. 

Traditional powder blend sampling and testing is first used to demonstrate the adequacy of the powder mix. A series of studies are performed on the blending process and homogeneous testing procedure as follows ... 

The mixing homogeneity of an interactive mixture is not better compared with a random one, but it leads to an interaction between a fine component and a coarse carrier and then to a higher stability of the system. Pharmaceutical powder mixtures are quite often between a random and an interactive mixture, and... 

NIRS has been shown by several researchers to be useful for evaluating the powder-mixing process. Wargo and Drennen demonstrated the use of a NIR method to determine homogeneity of powder blends. 

Because almost all materials used in the pharmaceutical industry have NIR spectra, the use of NIR for assuring blend homogeneity may prove to be a valuable application. Ciurczak [24,25] reported some of the first work on this subject. His work involved the use of a fiber probe to collect spectra from various locations in the mixer. Spectral matching and principal component analysis (PCA) were used to measure how similar the powder mix in a particular portion of the blender was to a predetermined good, or complete, mix. The match index or PCA scores were plotted versus time to assess the optimal blending time. 

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