| Summary: | The microstructure, small and large strain mechanical properties and modes of microstructural failure in one novel and a range of conventional particulate CaCO(,3) polyethylene (PE) composites were investigated by electron microscopy, Instron testing, dilatometry and differential scanning calorimetry. The novel PE-CaCO(,3) composite (63.5 weight % CaCO(,3); M(,w)(' )of PE = 1.5 x 10('6)) used was prepared elsewhere by polymerizing ethylene on catalyst coated filler surface. The conventional PE-CaCO(,3) composites were prepared with a range of PEs (M(,w)(' )=(' )59,000, 200,000 and 2 x 10('6)) and filler content (0, 2, 4, 8 and 19 volume %). Particulate CaCO(,3) (D(,w)(' )=(' )2.5 (mu)m) both with and without titanate coupling agent were utilized. Electron microscopy showed that long range organization of polymer microstructure is not present at levels of filler studied. Radially oriented lamellar growth up to 500 - 1000 nm away is observed at the interface. Dynamic mechanical spectra of unfilled and filled PEs obtained at 11 Hz over the temperature spectrum 100K to 400K revealed that the storage modulus expectedly increases upon introduction of filler. Filler presence decreased tan(delta) in the vicinity of the (gamma)-transition of PE while increasing it at higher temperatures. Complex moduli of model viscoelastic composites were determined using the correspondence principle to explain these observations. Tensile tests showed that yield stress and elongation at break both decreased in presence of filler. Volume dilatation studies revealed that beyond the yield point the presence of filler increased dilatation. Titanate treatment of filler suppressed the dilatation observed. Scanning electron microscopy studies of specimens undergoing deformation revealed formation of void-fibril microfailure zones which resemble crazes. Another area of investigation was the diffraction contrast imaging of thin PE films in the electron microscope. Image contrast is shown to arise from differential diffraction efficiency of differently oriented lamellae. Development of new scanning transmission electron microscopy imaging techniques permitted observation of multiple bend contours arising from curvature of lamellae and consequently estimation of lamellar dimensions.
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