Freeze drying is known to be a time consuming process with primary drying phases ranging from several hours up to weeks, depending on the product. During primary drying the product temperature at the ice sublimation interface (T p ) must not exceed the critical formulation temperature (collapse or eutectic temperature, respectively) to prevent impairment of final product quality by collapse or meltback. T p is determined by several factors like chamber pressure, shelf temperature, vial heat transfer coefficient and resistance of the dried layer.
Product resistance (R p ) has been recently suggested as a critical product parameter (CPtP) in freeze drying because it instantaneously draws a picture of the (already dried) inner cake morphology at the point of measurement. From a physical point of view, Rp of the dried product layer impacts the resistance to water vapor flow and thus…
Tags: primary drying, resistance