Question

5. Anyone who has ever owned a car will recognize the following situations. Suggest what might be occurring in the structure of the material in each case. a. The insides of the windows develop a haze that resembles smoke, but it is not smoke. b. Vinyl seats crack after a period of time. Those areas exposed to sunlight are especially susceptible.

7 Draw a log modulus-temperature plot for a typical amorphous polymer. Indicate the
regions exhibited by the polymer (eg., glass, rubbery, viscous, leathery)?
a. To which regions do the following polymers belong at room temperature: chewing
gum, a hydrogel used as a styling gel; PVC notebook covers; rubber bands,
PlexiglassTM ?
b. Draw another similar graph and sketch comparative curves for the following
polymers: i. Amorphous ii. Crystalline iii. Crosslinked iv. High molecular weight
v. Low molecular weight

Answer 1

5. a) This phenomenon would generally be observed during winters, or whenever the ambient temperature is moderately cold. When the passengers inside the closed car breathe, they release water vapor along with the breathed out air into the car. This water vapor then comes in contact with the glass windows which are cold due to contact with the colder air outside. As a result the water vapor condenses on to the windows from inside and forms a hazy layer which feels as if there is some smoke inside the car. This haze goes off if the inner temperature of the car is also reduced to a value comparable with the outside temperature, or when the outer surface of the glass window is increased, say by sunlight.

b) Car seats and interior are made of up of Polyvinyl Chloride (PVC), often called simply as vinyl, which contain "plasticizers" to keep the material from becoming brittle. Plasticizers introduce a certain flexibility to the PVC material (or in general to any plastics to which they are added). These plasticizers are quite volatile, and evaporate quickly when exposed directly to ambient atmosphere. Over time, the plasticizer content of the vinyl seats evaporates, leaving the seats material devoid of the required amount of plasticizer to keep them non-brittle. As a result, the seats start cracking up with time. Moreover, if a particular part is frequently exposed to sunlight, the process of loss of plasticizer gets accelerated and hence the observation made gets explained.