No abstract

in inducing crazing and/or shear yield of the isotactic poly(propylene) (iPP) matrix. However, if the dimension of the rubbery domain in the iPP matrix is smaller than the size of the fracture ligament curvature then the rubbery domain is not able to stop the crack propagation. Thus, Jang et al. suggested that the optimal size of EPR domain is 0.5 μm. [ 2 ] The regular hiPP powder morphology (i.e., regular particle shape, narrow particle size distribution, homogeneous distribution of EPR phase in iPP matrix) contributes to the high reactor throughput and good hiPP powder processability. Many works focus on the morphology of the fi nal hiPP material in the molded or extruded form [3][4][5][6][7] but the characteristic application properties of hiPP are strongly infl uenced directly in the polymerization process. Although a number of papers dealing with the particle morphology after the fi rst (homopolymerization) stage [8][9][10][11] and after the second (copolymerization) stage [11][12][13][14][15][16][17] were published, important questions related to hiPP particle multiphase morphology and its evolution are still open. This paper reconstructs the principle of rubber incorporation in high impact poly(propylene) (hiPP) particles. The detailed information about the pores and rubber distribution inside and on the surface of hiPP particles is obtained by micro-computed tomography and atomic force microscopy. The strong effect of homopolymer origin on hiPP particle morphology and rubber distribution is demonstrated. To obtain the most homogeneous rubber distribution, the low homopolymer porosity is required. The initial particle porosity has a negligible effect on the thickness of the rubber layer on the particle surface at the medium rubber content. The rubber forms not only along the iPP primary particles and directly or close to the pores but also on or close to the particle surface rather than it fl ows there. The evidence for these claims is based on the systematic investigation in dependence on EPR content, homopolymer particle porosity (prepared by different catalysts) and antistatic agent deactivating catalyst close to particle surface.

No abstract

The influence of molecular structure and microstructure on the fracture of high density polyethylene materials has been studied. By changing the chromium-based catalyst composition and optimising polymerisation conditions, polymers having differing levels of branching, comonomer unit placement and breadth of molecular weight (MW) distribution have been prepared. Structural analyses obtained by gel permeation chromatography (GPC), thermal analysis and elution fractionation were correlated with mechanical characteristics obtained from S4 tests, notch pipe tests and modified plane strain impact Charpy tests. The structural factors underlying this correlation are discussed. Specifically, the ability to place short chain branches into high MW fractions appears to provide good resistance to slow crack growth, whereas the degree of crystallinity and lamellar thickness play a decisive role in the rapid crack propagation process. Polymer grades with improved resistance to both rapid crack propagation and slow crack growth have been successfully produced.