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A New Approach for Study of pH- Solubility Profile of Bleached Shellac Film by Drop Shape Analysis

The aim of this study was to apply contact angle method for the determination of the pH solubility profile of bleached shellac film. Various pH of buffer solution was dropped on the bleached shellac film and drop shape analysis was investigated. The changes in the contact angle and contact line were recorded during 10-min measurement. The graphs of change in slope –obtained from plot between contact angle and time-and % change in contact line were plotted against various pH. The results illustrated the slight change in slope and % change in contact line at low pH while the significant change was reported at high pH. The results were in agreement with % dissolved film at various pH. The bleached shellac film started to dissolve at pH 7. The higher % dissolved film was obtained at pH 8 and 9 and at pH 10 was completely dissolved. Therefore, the contact angle method by the drop shape analysis, a simple method and less solvent used, can be an indicator for determination of pH solubility profile of bleached shellac. The result obtained could then be applied to the other substances.