ACOUSTIC CHARACTERIZATION OF A MICROCRYSTALLINE CELLULOSE POWDER DURING AND AFTER ITS COMPRESSION

Acoustic emissions were detected, both during the roller compaction of the microcrystalline cellulose powder and from single tablets after compaction by a single-punch tablet machine, via air using a microphone with a flat frequency response up to 20 kHz. Both of the compaction units were instrumented for the measurement of applied compressive force. The microcrystalline cellulose roller compacted using compressive forces below 30 kN showed a quite normal compaction behaviour but the product compacted at this force split into two and turned to yellow by its edges. This ''capping'' phenomenon was indicated by an enhancement of acoustic emission in the region of about 17-23 kHz. Acoustic emissions from single tablets after compaction by a single-punch tablet machine seemed to appear as wave packets consisting in very many frequency components that may, in addition, be time-varying. However, some small peaks were found probably being characteristic of these transient sounds.