Study Of The Agglomerate Dispersion In Polymer Under Shear

The dispersion process of additive agglomerates into the polymer matrix determines the material processibility and product quality. Mixing and dispersion of powder solids in viscous media is the result of the competition of stress exerted by the external flow and the agglomerate strength, so it is influenced by the flow type, flow strain distribution and the agglomerate structure etc. The transmission of stress in agglomerates, and hence the stress required for breakup of the agglomerate, is strongly dependent on the agglomerate structure. So the influence of agglomerate structure on the dispersion process through the use the computer simulation is one of our purposes.Four types of typical fractal agglomerates, i.e. DLA, RLA, LTA, Eden agglomerate, were simulated based on the simple cubic lattice by Monte Carlo method and their fractal dimensions were 2.50, 2.63, 2.96, and 3.00 respectively. The structure of these fractal agglomerates range from tenuous, i.e. DLA agglomerate, to dense, i.e. Eden agglomerate. By comparison of regressed fractal dimension values with the literature values, it is showed that the structure isotropy caused by lattice is not obvious.We simulated the stress required to break up the fractal agglomerates according to two different models in simple shear flow. When the fractal agglomerate break up along a planar plane, it is showed that the critical dimensionless stress increased as the fracture plane approaches inward and predicted that the rupture would occur in the outer fringe of agglomerate. The fractal agglomerates were supposed to fracture along an irregular plane in the second model and stress concentration at the roots of branches in the agglomerates was accounted in this model. The irregular fracture model predicted that the critical dimensionless stress decreased as the fracture plane approaches inward, so larger fragment will be produced according to this model. The irregular fracture model also predicted a stronger dependent of dimensionless critical stress on agglomerates size and the critical stress is lower comparing to planar fracture model. The planar fracture model represent erosion model observed experimentally while the irregular plane fracture model represent the rupture dispersion model.The influence of two kinds of powdered additive, i.e. calcium carbonate and Talc, on the Theological properties of polydimethyl siloxane and effect of surface modification of coupling agent were also experimentally studied. The originally Newtonian PDMS become pseudoplastic in low shear rate region because of the addition of powdered additives and the pseudoplasticity increased and the flow activation energy of the compounding system was lowered as the increasing of amount of additives. The compatibility can be enhanced by the surface modification by means of coupling agent. The silane-coupling agent can better improve the compatibility between PDMS and Talc but almost has no effect on calcium carbonate while the titanate coupling agent bas obvious effect on calcium carbonate. The optimum amount of both kinds of couple agents is weight fraction 2% of powdered additives.