Discussion
Thermoforming operation of semi-crystalline polymers with glass transition temperature, \(T_g\), and melting temperature, \(T_m\), is carried out at a temperature \(T\), in the range of
Answer: A
Thermoforming is carried out at \(T_g \lt T \lt T_m\).
In thermoforming a sheet is heated until it is soft and rubbery, then drawn over a mould by vacuum, pressure or a plug. For a semi-crystalline polymer this rubbery window lies above the glass transition, where the amorphous regions are mobile, and below the melting point, where the crystallites still hold the sheet together so it does not sag or flow.
Below \(T_g\) the sheet is too stiff to form, and above \(T_m\) it is a melt that cannot support itself. The other options mix up these limits or are not valid ranges.
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