CM8001

Acetone dissolve 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) Branched LDPE is not very strng and would be easily cut as compared to HDPE, hence cannot be used in this application.
b) HDPE is able to privide the required strength for this application. By using linear HDPE, it is able to get a balance between strength and flexibility.

When the piece of plastic is stretched, the strip narrows and “necking” occurs. The molecules become aligned parallel to each other and in the direction of the pull. This alteration of the 3D structure is not reversible and if the pulling continues the plastic would break. When the same pulling force is applied to paper, the paper tears because the cellulose molecules in paper are held more rigidly in place and are not free to become aligned. “Necking” does not occur on paper.

a) 1- Stable over a long period of time
2- Non-toxic
3-Does not dissolve in body fluids
4-Does not react in body fluids

b) Polymethyl methacrylate (PMMA) or silicone-acrylate.
These materials have a low coefficient of friction and are highly transparent

c) Hard Contact lenses are usually made of PMMA and is rigid non-gas permeable plastic. Users would always feel that the hard contact lenses are present and are typically not as comfortable. Soft contact lenses are made of silicone which is flexible and allows oxygen to reach the eye. They are usually comfortable.