CM8001

Styrofoam is a kind of polystyrene. During the production of polystyrene, foaming agent is used to form bubbles and expand the foam. When acetone dissolves the polymer, it allows the gas of the foaming agent to escape. The polymer collapses on itself and is more dense because the gas has been removed.

a. LDPE does not have the required strength as it is weak.

b. HDPE has a linear structure which is weak but extensive dispersion forces that allows molecules to slip pass one another and gives the stretch properties. In order to meet the required strength, the molecules of HDPE are arranged in the linear orientation. In order to improve the flexibility, a thin HDPE is used for surgical gloves.

When a piece of plastic is stretched, the molecules slip pass one another and the strip necks down. It arranges the molecules parallel to each other in the direction of the pull force.
The change of molecular structure is irreversible and plastic breaks when more force is applied. Paper is composed of cellulose molecules. When force is applied to paper, the paper tears. It is because the cellulose molecules in paper are more rigid and cannot be rearranged in direction of pull force.

a. non-toxic, low cost, not reactive to body fluids, not soluble in body fluids

b. PMMA is used for hard contact lenses. Desirable properties are nontoxic, permeable to oxygen, comfortable to wear, and inexpensive.

c. Hard contact lenses are typically made of PMMA which is not permeable to oxygen. Soft contact lenses are made of silicone. It allows oxygen to reach the eye. Thus, the soft lenses are more comfortable.