Actactic polystyrene (Tg ~ 100 degree C) quenched (i.e.. cooled very quickly) fr

Question

Actactic polystyrene (Tg ~ 100 degree C) quenched (i.e.. cooled very quickly) from 120 degree C to room temperature. a. Is a rubbery1 material b. Crystallizes c. Is a glassy material High density polyethylene cooled slowly from 160 degree C to room temperature a. Is still amorphous b. Crystallizes c. Is a glass d. Is a mixture where some regions are rubbery and some regions are glassy Polyethylene and polypropylene (in the melt) will a. Form hydrogen bonds with one another b. Interact strongly due to polar forces c. Only interact weakly through dispersion forces Discuss briefly the effect of increasing the degree of crystallinity on the following properties: a. Density b. Modulus (stiffness) c. Transparency Polyethylene terephthalate, (PET), can exist in a number of different states (semi crystalline with the amorphous regions glassy or rubbery, amorphous glass, amorphous rubbery, amorphous melt). Consider a sample of PET cooled rapidly from 300 degree C (state 1) to room temperature. The resulting material is rigid and perfectly transparent (state 2). The sample is then heated to 100 degree C and maintained at that temperature, during which time it gradually becomes translucent (state 3). It is then cooled down to room temperature and is again found to be rigid, and still this polymer. T_m = 267 degree C. and T the stages (in parentheses above). from the "solid" to the liquid below on a plot of specific volume

Explanation / Answer

2) HDPE when cooled from 160oC to room temperature it crystallizes

3) Polyethylene and Polypropylene will only interact through weak dispersion forces as their are no polar groups present in both of them.

1) Atactic polystyrene when cooled from 1200C to room temperature very fast turns into an amorphous material.

4) stiffness- increasing crystalinity increases the stifness as their is order in molecular packing.

tranparency- incresing crystallinity decreases transparency as light can be reflected on incidence on a crystal lattice.

density- increase in crystallinity increases density as crystalline areas are more densely packed than amorphous areas.

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