MICRONIZED POWDERS IN PLASTIC AND RUBBER
A good powder dispersion in a polymer, even in small quantities, is known to be always fundamental to obtain excellent physical and mechanical properties of the vulcanized product or of the compound made of plastic materials. In the working process of low or low-medium viscosity polymers, no matter how long the mixing/working process takes place, the dispersion is often not good if you use standard products. In this case, since the shear stress of the compound are not sufficiently high to allow the breaking of agglomerates, some fundamental physical and mechanical properties of the vulcanized product are compromised, such as: the resistance to repeated flexure and generally to any periodically repeated stress (vibration, tension etc.), the resistance to cracking and in general to aging because coarse agglomerates (greater than 45-50 µ) enhance the attack of external oxidant agents along the polymeric surface in contact with the agglomerate. In this case the micronization of powders is necessary to avoid such phenomena.
Thanks to the use of a sieving or of a screening system of any kind, it is possible to eliminate only those agglomerates superior to 200 µ which are obviously insufficient to obtain an optimal dispersion of powders. On the contrary, in the case in which a polymer has a high or a medium-high viscosity and the mixing/working time is sufficiently long, the cutting efforts in the compound are sufficient to obtain a good dispersion, even with standard products. Also in this case, the use of a micronized product can bring to a reduction of the working time and/or a reduction of the quantity of active products necessary for the
working process; such aspects can significantly affect the cost/benefit relation.
With all these assumptions, we can suggest micronized products to all the compound producers requiring a high and homogeneous dispersion of powders during the polymeric phase; non-micronized products could cause dispersion problems and/or not reach the requested performance levels
COMPARISON BETWEEN STANDARD POWDERS AND MICRONIZED POWDERS
The main physical properties characterizing the advantages of a micronized powder compared to a
standard powder are the following:
-Lower particle size
-Larger specific surface
These features assure an optimal dispersion of the powder in the compound and reduce the percentage of wastes deriving from a bad dispersion.
The larger specific surface brings to a further advantage: the possibility to reduce the quantity of active product used inside the compound. In fact, in etherophasic systems only the superficial side of particles reacts and therefore the quantity of active product effectively reacting in the compound is the same if using a standard product or a lower quantity of micronised product but with a significantly larger specific surface.