Aspects of Suspension & Emulsion Polymerisation
Suspension polymerisation involves a dynamic equilibrium between monomer break up and coalescence. A water soluble polymer (the suspending agent) is added to the aqueous phase to stabilise the monomer drop form during its conversion to a solid reaction product. Depending on the type and molecular weight of the suspending agent the aqueous phase can behave in a Newtonian or non Newtonian manner. In a Newtonian system the final particle size is a function of the Weber and Reynold s number. This dissertation is concerned with the properties of the suspension system and, in particular, those factors which influence the equilibrium drop size under non Newtonian conditions. The process variables (stirrer size and. speed, volume fraction of mono-Tier and interfacial tension) are studied using a laboratory scale suspension system. The results obtained are incorporated into an experimental model involving monomer polarity, interfacial tension and Reynold s number. The equations used to correlate the data are of the form: It was found possible to relate the observed particle size directly with the polymer polarity. In section 2, factors which cause sub micron/polystyrene particle to agglomerate or disperse in a water/polyvinyl alcohol system are investigated. It was shown that both monomer and monomer soluble initiator pass into the aqueous phase from the monomer phase by mass transfer where homogeneous particle nucleation of the monomer occurs. Particle destabilisation then occurs which is followed by the coalescence and agglomeration of the polymer particles. The size of the spherical agglomerates produced is shown to be 5. function of the protective colloid concentration. The bonding energy between the particles in the agglomerate is independent of the protective colloid concentration and is of the order 0.30 x 10~10 dynes per particle pair. It was shown that under high shear conditions the agglomeration process is reversible. In the presence of difunctional monomers, fibrous agglomerates are produced. The bonding energy between these particles is lower than that found in spherical agglomerates and is of the order 0.20 x 10~12 dynes per particle pair. The agglomeration process in the presence of the protective colloid is explained in terms of particle stabilisation theory.
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