Monitoring the acoustic activity of a pharmaceutical powder during roller compaction

Acoustic relaxation emissions (ARE) from microcrystalline cellulose (MC) and maize starch (MS) were detected during roller compaction using a microphone with flat frequency response up to 20 kHz and a tunable high pass filter the limiting frequency of which was set at 15 kHz. The noise from the compactor itself was found to appear mainly below 15 kHz. The ARE intensity of MC was observed to increase as a function of applied compressive force up to 45 kN, while the ARE intensity-force curve of MS had a maximum at 50 kN. A Gaussian-shaped function fitted reasonably to the data in both cases. (C) 1997 Elsevier Science B.V.