AbstractOcclusions of some of the continuous phase within polymer beads produced by suspension polymerisation is well-known, although little understood by the polymer industry. Occluded aqueous phase of levels approaching 30'/o (w/w) can give rise to major difficulties in handling the finished product, particularly at the drying stage. This investigation is an attempt to understand the mechanisms by which the phenomenon occurs and to correlate the variables which influence it.
This study has shown the process of occlusion to be dependent on the same mechanism that dictates the particle size of polymer beads; that is, the process of drop break-up and coalescence. Therefore, the eventual volume of the continuous phase occluded within the beads (assuming constant agitation throughout the reaction) is determined during the initial stages of monomer dispersion.
Further, a relationship was derived between the occluded moisture content of polymer beads and the principle reaction variables such as dispersed phase volume fraction, interfacial tension, density of the system, stirrer speed and stirrer width. The equation used to correlate the data is of the form:
The dependence of those properties of the polymerisation system, such as interfacial tension, viscosity and phase density on suspending agent and salt concentration as well as temperature were quantified.
It is also shown that during the latter part of the polymerisation, after the onset of high exotherm, a pore network is formed linking the reservoirs of occluded moisture to the bead surface. The radii of these pores were measured and found to be generally less than 0.05 micrometers and frequently smaller than 93 A. Due to the high bead temperatures associated with this stage of the reaction it is thought that the occluded moisture is vapourised and hence pressurised out of the bead into the surrounding continuous phase.
It is on cooling that the aqueous phase refills the voids in the bead giving the occluded moisture detected in the polymeric product.
|Date of Award||Oct 1981|