The relationship between finished granule properties and the outputs of granule endpoint monitoring devices and the rheological properties of the wet masses

Abstract

Endpoint monitoring is critical in high shear granulation. The objective of this research was to study the relationship between the outputs of selected granulation endpoint monitoring devices (capacitive sensor, wattmeter and torque transducer) and the finished granule properties, and to study the rheological properties of the wet granules in an attempt to correlate the outputs of granulation monitoring devices with the properties of the forming granules. Two granulation systems were studied in a Littleford high shear mixer: lactose, representing soluble materials and dicalcium phosphate (DCP), representing insoluble materials. Polyvinylpyrrolidone was the binder and water was the binder liquid. A face centered central composite design was used. The amplitude channel of the capacitive sensor monitored resistive properties of the material and the frequency channel monitored capacitive changes. Analysis showed that the capacitive sensor outputs were dependent on the impeller speed, particle size distribution of the granules, the quantity of fines and the moisture content. The effects of these variables on torque and power consumption differed with lactose and DCP granulations. For both granulations, impeller speed had greater effect on the power consumption than any other variable studied. The capacitive sensor was more sensitive in differentiating the particle size of the raw materials than torque or power consumption. An Instron dynamic testing system was used to perform creep analysis on the wet masses. Total compliance and the torque and power consumption values were linearly related. Compliance values increased with impeller speed, moisture content, particle size of the raw material, binder concentration, and were found to be intrinsic to each material. When a mixture MCC and lactose was studied, the rheological properties could be related to the each material in the mixture. The capacitive sensor monitored the material properties directly and could be recommended as the endpoint monitoring device of choice because of its ability to relate its output to the particle size distribution of the finished granules.