Constant temperature embossing of supercooled polymer films
Kuduva Raman Thanumoorthy, Ramasubramani
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In this dissertation work, a constant temperature embossing process was developed and investigated. By softening and crystallizing a supercooled polymer at the same temperature, the embossing and solidification stages can be carried out isothermally without thermal cycling. The new process was demonstrated for replicating rectangular trenches with different aspect ratio for two different polymers PET and PEEK. The raw materials were characterized for their thermal and rheological properties to determine the processing parameters. The polymers were also characterized by a modified tensile testing apparatus to determine the tensile properties of the film during embossing. The processing parameters including embossing temperature, embossing pressure and embossing time were varied based on the material properties and optimized. A semi-empirical model was established to correlate the crystallizing kinetics of the materials to the change in rheological properties during embossing. The model was used as a tool to predict the rheological properties of the polymer at conditions where experimental determination is difficult. Finally, embossing simulations with the semi-empirical rheological model were conducted to study the unique process dynamics of constant-temperature embossing and verify some experimental findings. Different cases of constant-temperature embossing involving low to high rates of crystallization were simulated and compared with the conventional embossing process. Based on the experimental and simulation results, processing strategies for constant-temperature embossing were devised.