Fillers redistribution

N. Dontula, N. S. Ramesh, G. A. Campbell, J. D. Small and A. L. Fricke, An experimental study of polymer-filler redistribution in injection molded parts. Journal of Reinforced Plastics and Composites, 13, 98-100 (1994). 

The work [40] deals with the redistribution of filler particles in the process of injection molding. In this case nonuniform distribution may occur both in the cross-section of a sample and along its length. Both kinds of nonuniformity are linked together if particle moves away from the mold walls it enters the zone of high velocity flow, therefore, a deficit of particles near the walls should be accompanied with a surplus of them far from the inlet. It should be noted that all the works mentioned consider spherical particles there are no theoretical or experimental studies of the redistribution of particles of other shapes, say, fibers or bars. 

The Emerman quantitative model [40] makes it possible, with sufficient accuracy, to predict the redistribution of filler particles depending on the parameters of processing and to explain the existing (still not extensive) experimental data. Good agreement should be noted between the experimental data and those calculated according to the Emerman model [40],... 

A possible interpretation for the stress-softening in silicon rubbers could be due to changes in the positions of filler particles relative to the direction of stretching at the first deformation. Since the filler particles provide numerous topological hindrances for elastomer chains (see Section 1.4 and Fig. 11) [13, 14], the deformation energy for the second deformation could be lowered by redistribution of these topological hindrances caused by rearrangements of filler particles at the first deformation. 

Loss of backside electrical contact on transistors and other semiconductor devices due to redistribution of filler at the interface or to oxidation/corrosion of the metallization. 

It follows that for polymer interaction with the filler surface as a result of adsorption and orientation effects, caused by interphase boundaries, redistribution of the segments and small portions of macromolecular chains caused by conformation changes occurs in the polymer siuface layers. At the same time, a boundary layer is formed, which might conditionally be termed rigidly elastic. Formation of this layer determines the maximum strength of the filled polymer-solid substrate adhesive bond. 

Spreading and redistribution of sizing agent over fibre and filler surfaces... 

The mechanism proposed by F. Bueche comprises the following fundamental steps 1) the splitting of the chain fragments located between two particles of filler 2) recovering to a statistical distribution of tensions, after 3) tensions relaxation and 4) stress redistribution on the network chains. 

A further form of composite is one where the second component acts as a filler. Carbon black in vehicle tyres is an example of a filler needed to provide the required properties. Each carbon particle provides an anchorage for many rubber molecules, and so assists in the redistribution of stress and the carbon is also essential to obtain the desired hysteresis behaviour and abrasion resistance. A much simpler application of a filler is the use of sawdust or other cheap powder in mouldings made from a thermosetting plastic. Although the mechanical properties of the base material are degraded (except possibly for impact resistance), they are still adequate for the proposed application, and the product cost is reduced. We shall not consider fillers in the discussion that follows. 

When compared to conventional foams, reentrant foams display superior resiliency and toughness. This structure has applications where the redistribution of stresses is desired in air filters, flexible fasteners, gaskets, sound-absorbing layers, fillers for highway joints, ankle wraps, wheelchair cushions, and many more. An air filter made of reentrant foam would, for example, address the problem of a pressure rise behind a clogged conventional filter. The pore space in the reentrant foam would open rather than close as the pressure increased, to prevent clogging. And if it were used in a flexible fastener, it would expand when the pull-out tension was applied. 

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