Compression characteristics of binary mixtures

Abstract

Most powder compression data are treated by the Heckel equation −ln(ϵ)= − kP + u where ϵ is porosity, P is pressure, and k and u are constants. This equation, however, is only applicable at pressures above the yield strength. It is felt that most pharmaceutical compression data may be at pressures below the ones corresponding to φ, and that, therefore, such plots are curved. An equation (different from the Cooper—Eaton equation) is developed for this curved region in such a fashion that it can be extended to more than a one-component system. The basis for the equation is that the void volume decreases exponentially with pressure, and that (in the pharmaceutical pressure range) tends toward a value different from zero. This is tantamount to saying that the final compressed solid always possesses some porosity. The equation is of the form ln( 1 1 - ϵ −J) = − aP + ln( V A D) where D is the true (non-porous) density (g/cm 3) and J is V s D, where V s is the actual specific solids volume toward which the solid tends during the low pressure region of compression.