The development of a radiotelemetric data acquisition system to measure punch force and displacement on a high-speed rotary tablet press and an investigation of the rate-sensitive behavior of pharmaceutical materials

Abstract

The first phase of this project was the design, construction, and implementation of a system to acquire punch force and displacement data from a high speed rotary tablet. The system was unobtrusive and allowed for the manufacture of tablets under normal production conditions, in batches, with a feedframe. The instrumentation was shown to be accurate, sensitive, reliable, and robust. The data was collected via a radiotelemetry link. This system allowed for the full characterization of the compaction process on a high-speed rotary tablet press. A number of parameters were shown to deviate significantly from the theoretical values, including: punch displacement, total punch speed, and contact time. Also, the relationship between the area under the force-time curve and the net work of compaction was shown to be essentially non-linear and material dependent. Increased tableting rate caused a decrease in tablet tensile strength for plastically deforming materials. A number of compaction parameters were studied to explain the changes in tablet hardness that included: net work, power, and elastic recovery. No parameter alone appeared to explain the changes in tensile strength. A study performed on a compaction simulator illustrated that the loss of hardness as a result of increased rate of output was caused by the effects of a number of parameters. It was concluded that one parameter can't be used to explain rate-sensitive tensile strength behavior. Force-displacement and Heckel behavior was shown to be confounded by the total punch speed of the compression event. It was concluded that the area under the force-displacement curve did not relate well to tablet tensile strength at different rates of output and Heckel Analysis should be performed using "saw-toothed" displacement-time waveforms. Two methods to decrease the loss of tensile strength as a result of increased rate of output were studied. The use of precompression was shown to deliver a compression event which supplied greater net work and greater tensile strength with a slight increase in punch speed when compared to main compression at the same contact time. Activation of the overload spring was shown to increase the net work and tensile strength when compared to a normal compression event. It was concluded that both methods appear to make harder tablets for some formulations as a result of compaction dynamics and not due to increased contact time.