Acoustic deinking of paper: Pulse effectiveness in particle detachment

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Deinking remains an important step in environmentally conscious manufacturing of paper. Removing xerographic ink from a print sample using acoustic microcavitation provides an easy method to observe context for studying cavitation-induced erosion at surfaces. Experiments indicate that microcavitation evolves microimplosions which are effective in causing deinking preferentially at ink sites. Acoustic microcavitation is brought about by low megahertz acoustic fields giving rise to micron-size bubbles that live a few microseconds. In exposing a surface to continuous waves for a defined duration, one could obtain cavitation effects in an average, overall sense; the details of nucleation, evolution of inertial events, and the precise interplay of field parameters in effecting cavitation, however, get glossed over. Studying pulsed cavitation using tone bursts at low duty cycles, instead of CW insonification, reveals interesting details of the initiation and evolution of acoustic microcavitation. Specifically, it is found that short-pulse deinking is more effective than long-pulse deinking. This fact seems to raise an anomalous question of how the sample knows it is being visited by a short pulse or a long pulse. Recent experiments operationally demonstrate why short-pulse deinking is more effective. [Work supported by NSF.]