The World of Polymers and Plastics

Question 1

Acetone is a weak acid that most polymers are able to dissolve in. Styrofoam packaging is held in a rigid shape due to its bonds between the section of the chains, holding the polymer in its rigid shape. This rigid shape does not efficiently pack the long-chain polymer, thus having many air-pockets. When the styrofoam is dissolved in acetone, the bonds holding the long-chain polymer in its rigid structure is broken, while the covalent bonds holding atoms in the long-chain polymer is still intact. The rigid stucture of the polymer collapse, condensing into an efficiently packed solid, eliminating the air pockets. Hence, the final solid styrofoam is much denser than before.

Question 2

a) LDPE cannot be used because it does not have the strength needed.

b) Molecules of HDPE must line up so that they provide the strength required. HDPE is flexible enough to be successful in this application.

Question 3

No. When a piece of plastic is stretched, the weak but extensive forces allows the molecules to slip pass one another allowing the plastic to stretch and ‘neck’.The molecule will rearranged itself parallel to the direction of force applied. This is plastic deformation. The deformation caused by the force on the plastic is irreversible. Further deformation will cause the structure to fracture. Paper is made of cellulose.  It has crystalline regions  as it is made up of a linear chain of glucose monomers. Therefore, the structure is more compact and it is not as flexible as a plastic bag. It does not have the characteristic of being able to deform plastically. Thus, it will fracture when the same puling force is applied to it.

Question 4

(a) Non-toxic, Insoluble in bodily fluids, Not too rigid, Non-reactive in the body

(b) Hard lenses: Polymethyl methacrylate (PMMA)

Soft lenses: Silicon polymers e.g. Polymacon (38% water)

Properties: non-toxic, allows oxygen to pass through to reach eyes, not too thick to provide comfort, shape of lenses needs to be similar enough to fit the eye contour

(c) Hard contact lenses are usually made of PMMA, a non-gas permeable and rigid plastic.

Soft contact lenses are usually made of silicon, which has breathable properties to allow oxygen to pass through and reach the eyes. Soft lenses generally makes the eyes more at ease as it is more flexible than the hard lenses.