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It is well known that PP manufacturers
modify flow of Polypropylene by making adjustments of molecular
weight using peroxides to breakdown molecular chains. This process,
known as "vis" breaking helps PP producers to rationalize
polymerisation operation.
Most of these peroxides are liquid and extremely
hazardous. The producers of PP have excellent safety setups capable
of handling these peroxides. However, the converters, such as producers
of PP non-wovens using melt blown process or manufacturers of large
moulded products like bumpers, etc. would find it very difficult
to handle peroxides directly on the processing equipments. These
peroxides can be developed in the diluted solid form using one of
the following methods.
Absorption in fillers:
Peroxides can be absorbed to almost
50% level by mineral fillers like CaCO3, chalk or sillica.
Since the amounts of peroxide required is quite small
(250-1000 ppm), the total usage of the peroxide concentrate
in fillers is quite small, making usage feasible. The
dispersion of filler in the main product would be difficult
and can cause some quality problems (for instance, in
melt blown fibers).
Absorption in Porous PP
polymer:
Spheripol process has the ability
to produce porous PP powder. Peroxides could be absorbed
in this porous PP polymer almost to the extent of 20%.
This option is more expensive than fillers, but offers
better dispersion. There are some ultraporous PE/PP/EVA
powders that can absorb more than 50% of peroxides. However
these ultra porous polymers are very expensive.
Peroxide Masterbatches:
Peroxides have a very high flow characteristic,
can be incorporated into a polymer carrier upto 10%, hence
can be extruded/compounded at very low temperatures to
avoid decomposition. There are very few suppliers of Peroxide
Masterbatches due to a difficult manufacturing process,
causing the cost of the peroxide masterbatches to be quite
high.
However, the masterbatch offers significant advantages
in terms of :
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Accurate dosing |
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Excellent Homogenization |
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Absence of fine powder |
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Absence of special legislation required for storage, etc. {Since
below 10% peroxide is not considered dangerous}
The converters can select one of the three products depending upon
requirements. However, the masterbatches possibilty offers the best
option. |
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