Powder stability tests, described

Silvered Vessel test. The so-called Silvered Vessel test is a stability test that consists in determining the period of heating necessary to cause exothermic decomposition of the substance. It is usually limited to determining the stability of smokeless powder and is described in Vol. III. 

Mr A.P. Sy ( Jour. Amer. Chem. Soc., 1903) describes a new stability test for nitro-cellulose which he terms "The Elastic Limit of Powder Resistance to Heat." The test consists in heating the powder on a watch glass in an oven to a temperature of 115° C., after eight hours the watch glass and powder are weighed and the process repeated daily for six days or less. He claims that the powder is tested in its natural state, all the products of decomposition are taken into account, whilst in the old tests only the acid products are shown, and in the Will test only nitrogen, that it affords an indication of the effect of small quantities of added substances or foreign matters on the stability and that it is simple, and not subject to the variations of the old tests. 

In contrast to the common practice of studying the interaction between a drug substance and excipients as described in the previous section, a proposal had been made that the preparation of initial formulations for stability screening of dosage forms is more meaningful and economical than the test for excipient compatibility in powder mixtures. ... 

A small-scale fluidized-catalyst test unit has been described by McReynolds (25). A standard gas-oil is vaporized and passed through a fluidized catalyst bed (400 g. of powdered catalyst) at 920°F. and at a rate of 925 ml. (800 g.) of liquid per hour for thirty minutes. The product is condensed, stabilized, and fractionated to 400°F. end-point gasoline. The activity of the catalyst is reported in terms of total conversion and per cent D + L."... 

For other powder properties, such as bulk density, particle attrition, or dustiness, some standardized methods [160] exist that may serve as a guide to establishing a test method but may not be applicable in every case. For example, the dustiness of a material is a matter of definition, depending on the initial particle size of the tested product. If the determination of dustiness is combined with testing the attrition stability of the particles, the stress mechanism also has to be considered. Consequently, the methods for determining dustiness and particle attrition are mostly very specific to the product and the stress mechanism that is to be simulated [161]. In many other cases (e.g., solubility, moisture, and temperature sensitivity), no general standardized tests are available, and different approaches are nsed to describe the powder properties (see examples in Refs 110 and 162). 

Some studies with filled and unfilled rigid PVC were made in our laboratory to describe the effect of chalk as additional stabilizer. A suspension PVC (K-value 70) with an organotin stabilizer (2 phr) and lubricants (1.8 phr) was used as the experimental material. A part of this compound was filled with a stearic acid coated calcium carbonate (10 phr) as an additional component. The PVC powder and the additives were mixed at a high speed in an intensive mixer. The received dry blends were pelletized by extrusion to get a better dispersion of the additives in the polymer material. Finally, the granulates were processed by injection molding to test specimens for measurements of mechanical properties. 

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