Acetone dissolves the polymer, allowing 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 cannot be used in this application because it does not have the required strength.

b) The molecules of the HDPE must line up in a way that produces the required strength. Using a thin liner of HDPE allows sufficient flexibility.

When the piece of paper is stretched, the strip narrows and “necks down” as the molecules become align parallel to each other and in the same direction of the pull. This alteration of the 3 dimensional structure is not reversible, and if the pulling continues, the plastic breaks.

When the same pulling force is applied to a piece of paper, the paper tears rather than stretching to any significant extent. The cellulose molecules in the paper are held more rigidly in place and are not free to become aligned

a) – non toxic
-low cost
-stable overtime of intended use
-lack of solubility in body fluids

b) Contact lenses are made from polymethyl methacrylate and/or polycrylamide, which are non toxic and comfortable to wear

c) Soft contact lenses are made of pliable hydrophilic plastics called hydrogel, which absorbs significant amount of water to keep the lens soft while hard contact lenses are made from polymethyl methacrylate which are harder and requires more blinking of the eyes to produce tears that act like lubricant. Soft contact lenses, containing hydrogel having the ability to absorb water would be softer and thus would be easier to wear as compared to hard contact lenses.