Talc Filled PP
Talc, chemically is hydrated magnesium silicate and can be represented at 3 MgO.4SiO2-H2O. Naturally occuring talc can exist in various forms like fibrou,s lamellar, needle, modular etc.
A typical composition of talc is as under:
SiO2 :40-62%
Al2O3 :0.2-11%
Fe2O3 :0.1-0.5%
FeO :0.1-6.0%
CaO :0.3-1.0%
MgO :30-33%
H2O :16-17%

Typical Mineral properties are
Density :2.90 g/cc
Oil absorption :28-51 g/100 g. powder
Moh's Hardness :1

Talc is generally selected to achieve higher stiffness than is possible with CaCO3, although at the cost of reduced impact strength and greater sensitivity to moisture. It helps to decrease shrinkage and warpage and increases thermal conductivity of the PP compound. Additional effects are higher HDT's and higher tensile strength as compared to CaCO3 formulations.
Table (2) summarizes typical physical properties of talc filled PP.

Table 2 : Typical product properties of talc filled - PP

In addition to structural and thermal property improvements, talc contributes to better dimensional stability, enhanced thermoforming opacity and depending on talc grade, white colour. The purity of talc is particularly important to the thermal properties. The presence of metal ions can catalyze the degradation of PP, which will decrease the long-term thermal stability of the composite. Small amounts of stabilizer packages are often used in combination with talc, as in under- the hood applications. Surface treated talc do not affect the thermal properties of PP adversely.

Talc-filled masterbatches are available at loading upto 75%. Dark talc is often used for exterior and interior automotive engineering applications where colour is not so critical Although the reinforcement properties of dark talc are lower than those of white-talc grades, the dark talc provides acceptable performance and costs less.. Often compounds for such applications contain both talc and CaCO3. White talc are used in PP garden furniture and domestic appliances such as washers, dryers etc. PP is the largest volume plastic usage for talc. Talc provides the structural strength (stiffness) and high temperature resistance needed for automotive and appliances.

Mica Filled PP
Mica as a filler is not quite as popular as CaCO3 or talc, but it does offer some unique characteristics.
Mica occurs as complex structures of potassium and/or aluminium sillicates namely, Typical mineral properties are:
Density : 2.80 g/cc
Moh's hardness: 4
Oil absorption :48-500 g/100 g powder