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unconfined yield strength

Unconfined Yield Strength of Moderately Compressed Powders

Unconfined Yield Strength is a measurement of the force required to cause unsupported material to shear. It is a very useful metric to evaluate powders’ flow behaviors and thus assist companies in understanding the propensities of powders to experience caking, arching, rat-holes, erratic flow, uneven distribution of active ingredients, etc. It is important to know the UYS of powders to understand how they need to be stored, transported and metered throughout any production process. Many common powder problems can be addressed if the unconfined yield strength of the material is known. The yield stress of lightly consolidated powders can be measured with equipment such as SMS’ Powder Flow Analyzer or shear cell tests. The yield stress of highly consolidated powders can be measured with tablet hardness tests, such as SMS’ TA.XTPlus Texture Analyzer or many other tablet hardness testing tools. No convenient existing techniques address measuring the UYS of moderately consolidated powders, which is a consolidation state that many powders routinely experience. This application study describes a method to quantify the unconfined yield strength of moderately consolidated powders using Stable Micro System’s TA.XTPlus. This method was presented by Polizzi, Yuan and Hancock in their poster Direct Measurement of the Unconfined Yield Strength of Moderately Compressed Pharmaceutical Powders at the AAPS Annual Meeting in 2011. The method uses the TA-403 TTC Unconfined Yield Strength Fixture on eight moderately compressed powders.