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The effect of molecular weight on polypropylene (PP) extrusion foaming was investigated and the process to make soft touch, largely expanded, high cell density non-crosslinked PP foam using environmental friendly CO2 is presented. In previous research, when the cell density was high, cell opening was dominant and large expansion could not be achieved even in HMS PP materials. The effects of processing and material parameters on the foam morphologies of PP materials with three different melt flow rate (MFR) were studied using single-screw tandem foam extrusion system. By selecting proper material and die, and by tailoring the processing conditions, large expansion (25 fold) and high cell density (>109 cells/cm3) was successfully achieved in the high MFR PP without any additives. The mechanism of locally induced crystallization was found to be significantly affecting the foaming behavior of PP and was successfully verified using SEM, DSC, HPDSC, shear viscosity and solubility measurements.

The effect of molecular weight on polypropylene (PP) extrusion foaming was investigated and the process to make soft touch, largely expanded, high cell density non-crosslinked PP foam using environmental friendly CO2 is presented. In previous research, when the cell density was high, cell opening was dominant and large expansion could not be achieved even in HMS PP materials. The effects of processing and material parameters on the foam morphologies of PP materials with three different melt flow rate (MFR) were studied using single-screw tandem foam extrusion system. By selecting proper material and die, and by tailoring the processing conditions, large expansion (25 fold) and high cell density (>109 cells/cm3) was successfully achieved in the high MFR PP without any additives. The mechanism of locally induced crystallization was found to be significantly affecting the foaming behavior of PP and was successfully verified using SEM, DSC, HPDSC, shear viscosity and solubility measurements.

Polypropylene (PP) composites includ a mineral filler, though they can be enhanced by blending with an elastomer. Blending rigid fillers with PP increased strength while decreasing toughness. Blending soft elastomers with PP decreased strength while increasing toughness. PP-elastomer-filler ternary composites offer synergism because the increase of strength due to filler may compensate the loss of strength due to the elastomer. Two morphologies were identified, separated elastomer and filler particles in PP, and filler particles encapsulated by elastomer in PP. Interaction between filler and PP matrix are proposed to increase with the addition of polar elastomers when encapsulated morphology is formed, leading to enhanced mechanical properties. PP-elastomer-filler blended tapes were prepared via single-screw extrusion. Annealing was performed after cooling the tapes, and this combination proved to increase the modulus. Characterization of the composites was carri ed out using thermogravimetry, dynamic-force thermomechanometry, modulated-force thermomechanometry, and Fourier transform infrared imaging. Incorporation of polysiloxane elastomer increased the mobility of PP during extrusion. Elongation at break increased with increasing polysiloxane content, while the tensile modulus was slightly decreased. The silica core within the polysiloxane particles provided an additional strength enhancement. Polar elastomers aided binding between PP and fillers, while enhancing strength and toughness. Glass transition temperature and segmental motion activation energy was shifted to higher temperature with addition of elastomer and filler, including kaolin and talc.

Thesis (Ph.D.) -- McMaster University, 2003. / Includes bibliographical references (p. 154-172). Also available via World Wide Web.

Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references (leaves 175-177). Also available via World Wide Web.