Acetone dissolves the polymer, allowing gas of foaming agent to escape. This polymer collapses on itself and is more dense because the gas has been removed

a. A LDPE does not have the required strength.
b. HDPE molecules must line up in a way that produces the required strength. Using this film of HDPE allows sufficient flexibility.

The plastic molecules become aligned parallel to each other and in the direction of the pull. This alteration of the 3-D structure is not reversible. The paper will tear if pulled because the molecules are held more rigidly in place, and are not free to be aligned,which implies that the molecular interactions in paper is stronger.

a. They are – Stable over time, Non – toxic , lack of reactivity with body fluids and have appropriate permeability and process-ability for designed application.

b. PMMA(plexiglas) hard lenses.
Rigid gas permeable.
Hydrogel-polymacon.
Silicone hydrogel.

c. Hard contact lens :
PMMA, excellent optical qualties, durability and biocompatibility but no oxygen permeability.

Soft lens:
hydrogel, water – retaining and permeability of oxygen.