CM8001

Acetone dissolves the polymer, allowing the gas of the forming agent to escape. The polymer collapses on itself & is more dense because the gas has been removed.

a)LDPE cannot be used as it does not have the required strength.

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

When we stretch a piece of plastic bag, the length of the piece of plastic bag being pulled increases dramatically and the thickness decreases as the plastic has weak but extensive dispersion forces. This force allow the molecules to slip pass one and another allowing the plastic to stretch and neck. On the other hand, when the same pulling force is applied to paper, it tears rather than stretch. This is because the cellulose molecules in paper are held far more rigidly in place and are not free to become aligned.

a. 1. Stable over time of intended use
2. Non-toxic
3. Lack of solubility in body fluids
4. Lack reactivity with body fluids

b. Contact lenses are made from polymethyl methaacrylate (PMMA), silicone-acrylate materials such as Kolfocon. It also consists of fluoro-silicone-acrylate polymers, fluoro-silicones, polymacon and methacrylates which include hioxifilcon, methafilcon or lidofilcon. Their desired properties are non toxic, permeable to oxygen, comfortable to wear and inexpensive.

c. Hard contact lenses are made from PMMA, a rigid non-gas permeable plastic while soft contact lenses are made from silicon which is flexible and allows oxygen to reach the eyes. Hence, soft lenses are more comfortable.