A comparative evaluation of manufacturing technologies and their effect on morphology and mechanical properties of poly-(propylene-ethylene) copolymers
This project is a technological benchmark exercise for Sasol Polymers where different poly (propylene-ethylene) copolymer grades from five foremost licensed manufacturing PP technologies are evaluated. These copolymer grades were manufactured using the following processes: Novolen PP technology (Sasol grades), Innovene PP technology (BP grades), Spheripol PP technology (Basell grades), Univation PP technology (DOW grades) and Borstar PP technology (Borealis grades). Form this investigation, thirty different grades where evaluated to determine their structural morphology in relation to their physical and mechanical properties. For the ease of analysis, the grades are grouped into three ethylene content ranges; low ethylene contents (below 8%), medium ethylene contents (between 8 -10%) and high ethylene contents (above 10%). Within each of these ethylene content ranges, there is a melt flow index (MFI) range, which increases from low to high. The differences in the MFI added further complications, especially when trying to determine optimum mechanical properties of the copolymer grades. The impact test results show that the toughness is at a maximum at low MFI, and then drops drastically as the MFI increases. Since an addition of ethylene improves the toughness of the copolymer, it was observed that by considering MFI's below 35 g/10 min, the toughness could be enhanced by increasing ethylene content. Grades with MFI's below 35 g/10 min show a drastic increase in impact strength at ethylene content around 8.5%. SEM results show that particle size and spacing are independent of ethylene contents for the grades examined. However, for the BP and DOW grades, the ratio between interparticle distance and particle size decrease steadily with increasing ethylene content. The Basell and BP grades showed a narrow rubber particle size distribution followed by Sasol grades. The DOW grades showed a broad particle size distribution. TEM results show that the internal morphology of the rubber particles differ from grade to grade, with the Sasol and BP grades showing several numbers PE inclusions within the rubber particles, whilst Basell grades having only few PE inclusions. It was observed that those grades with several PE inclusions have a better impact performance compared with those with fewer inclusions.
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