Prediction of the Crystallinity of Polyethylene after Heating

Thermoforming of semicrystalline polymers, such as polyethylene (PE) and polypropylene (PP), typically occurs around the peak melting temperature. This leads to a very narrow processing window, as small temperature variations... [ view full abstract ]

Thermoforming of semicrystalline polymers, such as polyethylene (PE) and polypropylene (PP), typically occurs around the peak melting temperature. This leads to a very narrow processing window, as small temperature variations can have a significant impact on the polymer in this temperature range. If the polymer is too stiff it will not fill the mould, alternatively if it is too soft the material distribution will not be constant. The current study outlines the potential of using a combined computation and experimental procedure to determine the optimal processing parameters for the thermoforming of PE, where the degree of crystallinity is used to optimise both the heating and forming processes. This methodology revolves around the determination of the degree of crystallinity experimentally and then inputting this crystallinity into a process simulation to determine the final wall thickness of the thermoformed part, through the incorporation of a constitutive material model. The preliminary work outlined in this study described relevant material models for polyethylene along with using Differential Scanning Calorimetry (DSC) and Raman Spectroscopy to determine the degree of crystallinity, post-heating, pre-forming.