Author Question: What are the differences between adiabatic heating and thermal heating as applied to extruders and ... (Read 78 times)

ap345 · **on:** Aug 19, 2018

What are the differences between adiabatic heating and thermal heating as applied to extruders and why are both important?

What will be an ideal response?

Question 2

(a) Explain why stretching an elastomer causes an unstable state and, therefore, when the stretching force is removed, why the elastomer recovers. (b) Explain why stretching of some polyethylene molecules results in blushing a situation not eliminated when the stretching force is removed.

What will be an ideal response?

CourtneyCNorton · **Reply #1 on:** Aug 19, 2018

Answer to Question 1

Adiabatic heating is caused by the mechanical action of the screw on the resin inside the extruder. Thermal heating is caused by the heaters that surround the extruder barrel. Both are important because they combine to give the internal energy needed for melting. Some especially thermal-sensitive polymers cannot tolerate much thermal heating

Answer to Question 2

(a)The entropy of the system decreases when the polymer is stretched because the stretching causes the molecules to become aligned and, therefore, more ordered. Increases in order cause decreases in entropy which causes a net increase in free energy and, therefore, the state is unstable. When the stretching force is removed, the entropy can increase and thus the energy will decrease, causing a return to the original state.