CM8001

Acetone dissolves the polymer which allows gas of the foaming agent to escape. The polymer collapses on itself and thus it becomes denser as the gas is being removed.

a. It cannot be used as it does not have the required strength to withstand its resistance.

b. The molecules of HDPE must be lined up in a way that produces the required strength. Hence, the use of the liner of HDPE allows sufficient flexibility.

Plastic is a series of long chain polymers. These chains stretch when they are all aligned and facing the same direction. Other plastics have polymer chains facing in cross directions. These plastics are stiff and often brittle. Paper is similar to cross linked polymers and does not stretch.

a. The benefits for polymers intended for use should far outweigh any risks. The 2 main properties are 1) stable over time of intended use and 2) non toxic. Other factors include low cost, lack of solubility in body fluids, lack of reactivity in body fluids in the case of implantation.

b. Several types of contact lenses are on the market and each uses a different type of polymer. Polymathy methacrylate (PMMA) is one of the earliest polymers used for rigid gas permeable lenses, is structurally similar to Lucite and Plexiglas. Silicone-acrylate materials are more commonly used. Desirable properties include being non-toxic, permeable to oxygen, comfortable to wear and inexpensive. Contact lenses should conform to eyeshape and also be easily cleaned or disposed.

c. Hard contact lenses are made of PMMA, a rigid non-gas permeable plastic. Soft lenses are made of silicone, which is flexible and allows oxygen to reach the eye. Thus, soft lenses are more comfortable and easier to wear.