Plastic products are prepared by various technological processes, such as injection moulding, extrusion, thermoforming and blowing. Final properties of the semi-crystalline polymer product largely depend on the internal structure formed during the manufacturing process. The formation of the internal crystalline structure depends on various parameters. One of the most important ones is the cooling rate.
In the experimental part of the master's thesis, the research was focused on the effect of cooling rate on the rheological, thermal and morphological properties of low-density polyethylene (LDPE) and high-density polyethylene (HDPE). Differential scanning calorimetry (DSC) was used to determine the influence of different cooling rates on phase transitions temperatures. Moreover, for each cooling rate, the percentage of the crystal structure – degree of crystallinity was calculated. Rheological measurements were performed at the same temperature conditions and the results were used to understand the impact of the rate of temperature changes on rheological properties. Finally, the changes in morphology were followed by using an optical polarizing microscope.
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