Ultrasonically delaminated and coarse mica particles as reinforcements for polypropylene

The effect of the size of mica platelets used, at 30% by mass, to reinforce polypropylene was studied by comparing ultrasonically delaminated mica (diameter 5μ aspect ratio about 40) with a coarser mica (150–420μ) with and without the coupling agent 3‐(triethoxysilyl)‐1‐propanamine (Union Carbide A‐1100). Reducing the particle size of the mica (treated with coupling agent) significantly increased the tensile modulus and strength but did not affect elongation at break; it gave a small improvement in Izod impact strength; the heat distortion temperature was lower and the melt flow index was increased. Dynamic mechanical evaluation (Rheovibron) was done with a series of coarse micas (>44μ, 45–150μ, 150–250μ, and one with a broad distribution around 100μ), and an ultrasonically delaminated mica made in a continuous process (>20μ), all treated with N ‐(4‐vinylphenyl) methyl‐ N ′‐(3‐trimethoxysilylpropyl)ethylenediamine (Dow Corning Z‐6032), at 20% by mass in polypropylene. Except for the disappearance of a peak at 0°C in the loss tangent due to the glass transition, the composite with delaminated mica did not differ from pure polypropylene, melting at 175°C. Use of the coarser micas raised the melting temperature to 200°C, increased the storage modulus, and lowered the loss tangent in the case of the three fractionated samples. The results were concordant with theories of reinforcement and microheology. The hoped‐for improvement in some properties on changing to the finer mica may not have been realized because of incomplete dispersion.