Mechanical properties of melamine-formaldehyde microcapsules

The mechanical properties of melamine-formaldehyde (M-F) microcapsules were studied using a micromanipulation technique. Single microcapsules with dia meters of 1-12 mum were compressed and held between two parallel planes, co mpressed and released, and compressed to burst at different speeds, whilst the force being imposed on the microcapsules and their deformation were mea sured simultaneously. This force increased as single microcapsules were com pressed and then relaxed slightly as they were held. When the microcapsules were repeatedly compressed and released, a pseudo yield point was found fo r each microcapsule. Before the microcapsules were compressed to this point , the deformed microcapsules recovered to their original shape once the for ce was removed. However, when the deformation was beyond the 'yield point' there was profound hysteresis and the microcapsules showed plastic behaviou r. As the microcapsules were compressed to burst at different speeds, rangi ng from 0.5-6.0 mum/s, it was found that their mean bursting forces did not change significantly. The deformations at the pseudo yield point and at bu rsting were also independent of the compression speed. On average, these me lamine-formaldehyde microcapsules reached their 'yield point' at a deformat ion of about 19 +/-1%, and burst at a deformation of 70 +/-1%.