Thermoplastic compounds with mineral
fillers have a special position in many applications
including automotive, consumer products and
myriad of other applications. The mineral fillers
used in thermoplastic compounds are:
Calcium carbonate is the least
expensive and the largest mineral filler used
in thermoplastic as well as thermoset compounds.
PP and other polyolefin compounds and SMC/BMC
compounds are the largest users of calcium carbonate.
Besides providing economy, it reduces shrinkage
and offers good surface finish. Calcium carbonate
can be incorporated at a very high level of
more than 70%. While SMC/BMC compounds use plain
calcium carbonate, polyolefin compounds require
surface modified calcium carbonate. While the
surface treatment of coating has a limited role
in polyolefin compounds- mainly due to non-polar
polymeric nature, the functionalized polymer
such as malice anhydride polymer acting as coupling
agent is more efficient.
Dolomite is quite similar to calcium carbonate with the exception of the fact that it contains more of magnesium carbonate. It can be used for all the application as a replacement of calcium carbonate.
Talc or hydrous magnesium silicate has a platy structure compared to crystal structure of calcium carbonate. It helps in enhancing the stiffness of thermoplastic compounds and raises the heat deflection temperature significantly. Talc also provides better dimensional stability. PP uses talc significantly among all thermoplastics. The particle size of talc determines the impact strength, as the finer particle size enhances or maintains impact, and increases stiffness at the same time. Talc also reduces coefficient of linear shrinkage of the plastic product.
Barium sulfate being the densest mineral finds use in a few end products such as sound barrier or dampening applications. It also finds use in eraser.
Wollastonite, a calcium silicate, is basically
quite similar to calcium carbonate but has a
different structure. It is comparatively more
difficult to disperse in a polymer matrix compared
to calcium carbonate. It is used alone or in
combination with glass fiber mainly to balance
the cost of glass reinforcement. Additionally,
it helps to improve the surface finish of glass
fiber reinforced thermoplastic products. Wollastonite
requires surface treatment for easy dispersion.
Finer particle size is essential better dispersion.
Polyamide is the major thermoplastic polymer
that uses wollastonite.
Kaolin or clay or natural alumnisilicate provides good impact modification. It competes well with talc. Polyamide is one of the major thermoplastic that uses kaolin particularly for automotive applications. Clay also helps in providing cost economy. Clay also requires surface treatment for ease of dispersion. Clay also improves dimensional stability like talc. Clay provides better sound dampening effect compared to wollastonite and talc but not as well as barium sulfate.
All these minerals grow along with thermoplastic compound growth. Typically thermoplastic compounds grow slightly higher level (5-6%) compared to polymer growth of about 4-5%. In fact, the usage of mineral for plastic modification grows at higher level compared to its other usages. The main drivers of mineral fillers for plastic modification are:
