Question

Exercise 6. By looking at this graph respond to the following questions and justify your answer Temperature (°F) 250 300 350 150 200 400 450 106 Relaxation modulus, E,(10) (MPa) Relaxation modulus (psi) 100 200 150 Temperature (°C) a) Among polymer A, B, and C, which one does not display a melting temperature? How is this type of polymer generally called, and what is the process that prevents them from melting? (2 points) b) Among A, B, and C, which polymers display a glass transition? What happens during a glass transition? (2 points) c) Which polymer is highly crystalline? Why? (2 points)

Answer 1

Solution:

1. Among polymer A, B and C, polymer B does not display the melting temperature because it begin with polymer C and becomes steady at certain temperature and stops without any intersection. This type of polymer is generally called as an amorphous polymers. A reason prevents it to be as a totally amorphous polymer will have no melting point since this thermal transition is associated with crystalline or ordered phase. When this solid polymer is heated, it will soften (if it is a thermoplastic) until it becomes a viscous liquid but a technique will not record a melting point.

2. Polymer A is showing glass transition. In this the crystalline state of polymer is observed just temperature below of melting temperature. In transition state physical properties of polymers changes to crystalline state.

3. Polymer A is highly crystalline. Because at very low temperatures, E (Young's Modulus) is very high owing to the rigidity of crystalline and amorphous molecules. With temperature rise E slightly decreases until to Tg ( Transition Temperature). At this point, there is a sudden drop in E with activation of molecular movement of the amorphous chain segments.