Primary particle properties agglomeration

The most challenging part of rubber mixing is the dispersion of the filler The filler agglomerates have to be broken into smaller particles, the aggregates, but not completely to the level of primary particles. An optimal particle size distribution has to be achieved in order to obtain the best properties of the final rubber product [14]. 

Catalytic activity and electrochemical performance generally increase as the NiO and YSZ particle sizes are reduced. However, ultrafine powders are prone to agglomeration during the milling and mixing process the distributions of the phases (and hence the percolation threshold and many other important properties) are determined by the agglomeration size, not by the primary particle size. 

Tensile properties of PVC filled with precipitated calcium carbonate particles having two different mean sizes were studied. The particles were porous agglomerates of spherical primary particles. 10-50 parts of the particles were mixed with 100 parts PVC and 3 parts lead stearate using a mixing roll. Tensile tests were carried out using dumbbell test specimens. 20 refs. 

Improve the instant properties. Food powders often need to be easily dispersed or dissolved in water (instant soups, sauces etc). By agglomeration, the primary particles are bound to one another, forming pores between them, which enhance the wettability by the capillary forces when put into contact with water. After they are wetted, they will easily fall apart and disperse or dissolve. 

The macroscopic properties of liquid suspensions of fumed powders of silica, alumina etc. are not only affected by the size and structure of primary particles and aggregates, which are determined by the particle synthesis, but as well by the size and structure of agglomerates or mesoscopic clusters, which are determined by the particle-particle interactions, hence by a variety of product- and process-specific factors like the suspending medium, solutes, the solid concentration, or the employed mechanical stress. However, it is still unclear how these secondary and tertiary particle structures can be adequately characterized, and we are a long way from calculating product properties from them [1,2]. 

It is necessary to exercise strict control over primary particle formation and agglomerate growth to obtain a product with constant properties. 

Polyvinyl alcohols (PVAl) are manufactured by saponification of vinyl acetate polymers (PVAc). Properties of PVC using PVAl as a protective colloid are influenced by the solution viscosity of the PVAl, i.e. the degree of polymerization of the PVAc and the degree of saponification. Polyvinyl alcohols of 75-90% hydrolysis are primary suspension agents for S-PVC, whereas polyvinyl alcohols of 25-40% hydrolysis are secondary suspension agents, which control the agglomeration of the primary particles. Partially hydrolyzed PVAc can be block or random polymers. 

---