Based on the graph and the information known about Tg and Tm, why is the second

Question

Based on the graph and the information known about Tg and Tm, why is the second answer the best option? Explain what is happening in each part of the graph.

A high density polyethylene (HDPE) sample has been cooled slowly from 200 C to -150 C. The cold sample is subjected to differential scanning calorimetry heating at 10°C/min. The result is shown in the Figure below 10 ?6 What characterizes the events labelled A and B? A: at-110 C crystallization changes the PE from a fully amorphous glass to a partially crystalline glass. B: at 140 ° C the partially crystalline glass becomes a partially crystalline material where the amorphous domain are above Tg 2 A: at-110 C PE changes from a partially crystalline glass to partially crystalline material where the amorphous domain are above Tg. B: at 140 C the crystals in the partially crystalline material where the amorphous domain are above Tg changes to a fully amorphous polymer melt. A: at-110 C PE changes from fully amorphous glass to a fully amorphous polymer melt. B: at 140 C the amorphous polymer melt partially crystalizes and changes into a partially crystalline material where the amorphous domain are above Tg A: at-110 C melting of the crystals changes the material from at partially crystalline glass into to a fully amorphous glass. B: at 140° C the material passes the glass transition and becomes a fully amorphous polymer melt.

Explanation / Answer

at point A glass transition(Tg) event takes place where the rigidity of the material gets reduced and mobility increases significantly and as a result the heat flow rate slightly increases. This transition is not a discrete one i.e it does not have a distinct peak but is distributed over a certain temperature range. From the graph we can see that this range is lying somewhere in between -1100C to 1200C.

At 1400C ( point B) we can observe a sharp peak. this is the melting point( Tm) of the polymer where the polymer becomes fully amorphous.

so second is the correct option

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