Week 10 Application Exercise

1) Acetone dissolves the polymer causing some of the gas of the foaming agent to escape. As a result, the polymer collapses on itself and becomes denser due to the removal of the gas.

2a) LDPE cannot be used as it does not meet the minimum strength required.

2b) The molecules of HDPE must be arranged in a particular way in order for it to produce the required strength. By using a thin liner of HDPE, it will allow sufficient flexibility for its application in surgical gloves.

3) When a piece of plastic bag is stretches, the plastic becomes thinner and narrower at the center. The molecules align parallel to each other, in the direction of the pull. This action is irreversible as it alters the three-dimensional structure of the molecule and further stretching will tear the plastic. On the other hand, when paper is stretched with the same amount of pulling force, it will tear instead. This is due to the cellulose molecules in paper being more rigidly held in place, thus the molecules are not free to become aligned and will break apart.

 

 

4a) The properties of polymer that would be desirable for use in the human body are (1) stability over time of intended use and (2) non-toxic. (3) wide range of physical and chemical properties to meet the needs of its function by varying the monomer units (4)  Responsiveness to physical stimuli like mechanical stress

4b) There are many types of contact lenses on the market and each consist of a different polymer. One of the earliest polymers used for rigid gas permeable lenses, Polymethyl methacrylate (PMMA), is structurally similar to Lucite and Plexiglas. Silicone-acrylate materials are now more commonly used under trade names such as Kolfocon. Newer rigid gas permeable (RGP) polymers contain fluorine-silicone-acrylate polymers and fluoro-silicones. Polymacon (38% water) is typical of the polymers used for soft lenses and is a polymer of 2-hydroxyethyl methacrylate (HEMA). Other methacrylates include hioxifilcon (48% water) and methafilcon (55% water) or even lidofilcon (70% water). It’s important to find out more before buying a product and manufacturers’ websites are often good sources of information. Some properties that are desirable in contact lenses include being non-toxic, permeable to oxygen, comfortable to wear and inexpensive. The ability to conform to the shape of the eye and ease of cleaning or whether it’s disposable are also qualities that are desirable and need to be considered when manufacturing contact lenses.

 

4c) As mentioned above, PMMA and rigid non-gas permeable plastic are typically used to make hard contact lenses. Soft contact lenses, which were developed to replace hard contact lenses, are made of silicone, which is flexible and allows oxygen to reach the eye. Due to these properties, soft contact lenses tend to be more comfortable.