3. Problem 5 in Chapter 7 in Painter & Coleman (p. 256-257). Question 5 Poly(eth

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3. Problem 5 in Chapter 7 in Painter & Coleman (p. 256-257). Question 5 Poly(ethylene terephthalate) (PET), which has glass transition (Tg) and crystalline melting temperatures of 69 and 267°C, respectively, can exist in a number of different states depending upon temperature and thermal history. Thus it is possible to prepare materials that are semi-crystalline with amorphous regions that are either glassy or rubbery and amorphous materials that are glassy, rubbery or melts. Consider a sample of PET cooled rapidly from 300°C (state I) to room temperature. The resulting material is rigid and perfectly transparent (state II). The sample is then heated to 100°C and maintained at this temperature, during which time it gradually becomes translucent (state III). It is then cooled to room temperature, where it is again observed to be translucent (state IV) (a) Identify each of the states. (b) In state IV PET has a higher modulus and is less flexible than in state III. Why is this ? (c) Why is the PET transparent in state II, yet translucent in state IV ? plus add d) what is the typical application for PÉT?

Explanation / Answer

SOLUTION:-

A)

B) PET in state 4has a higher modulus and is less flexible than in State 3 because Here, only one crystalline family was encountered with smaller values of lc, L and in respect to the other states. In this stateP, lc remained constant as a function of time indicating that there is no crystal thickening during the process. The increase in molecular weight has produced low crystalline degrees and relatively small lc, both associated with diffusion problems of long molecules.

C) PET is Transparent in state 2 because Here, the highest crystallinity was obtained and the morphology was composed of thick primary structures coexisting with thin and small secondary structures. The crystal perfection was higher than that determined . But it is translucent in state 4 due to amorphous zones are formed.

D) APPLICATIONS :-

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