Q1) When Styrofoam packing peanuts are immersed in acetone (the primary component in some nail-polish removers), they dissolve. If the acetone is allowed to evaporate, a solid remains. This solid still consists of Styrofoam, but now it is solid and much denser. Explain. (Hint: Remember that Styrofoam is made with foaming agents)
Answer:
Acetone dissolves the polymer (Styrofoam), allowing the foaming agent to escape. Once the acetone has evaporated, the polymer remains and is now solid and more dense than before as it has collapsed due to the lack of foaming agent.
Q2) Consider Spectra, Allied-Signal Corporation’s HDPE fibre, used as liners for surgical gloves. Although the Spectra liner has a very high resistance to being cut, the polymer allows a surgeon to maintain a very delicate sense of touch. The interesting thing is that Spectra is linear HDPE, which is usually associated with being rigid and not very flexible.
A) Suggest a reason why branched LDPE cannot be used in this application.
Answer:
LDPE does not have the required strength to resist being accidentally cut during surgery.
B) Offer a molecular-level reason for why linear HDPE is successful in this application.
Answer:
As the arrangement of molecules affects the material’s flexibility, the arrangement of molecules in a linear fashion offers the material sufficient flexibility.
Q4) When you try to stretch a plastic bag, the length of the piece of plastic being pulled increases dramatically and the thickness decreases. Does the same thing happen when you pull on a piece of paper? Why or why not? Explain on a molecular level.
Answer:
When the plastic bag is stretched, it necks and narrows down. Molecules become aligned parallel to each other and in the direction of the pull. When stretching paper in the same way, however, it does not stretch but breaks instead. This is due to the molecules in the cellulose in paper being arranged in a more rigid way that does not permit the molecules to be re-aligned like in the case of the plastic bag.
Q5) Some polymers are biocompatible and now used to repair human body parts.
A) List 4 properties that would be desirable for polymers used within the human body.
Answers:
The materials should be non-toxic, should not degrade over time, easy to transplant into the body, and does not react with body tissues and fluids.
B) Other polymers may be used outside the body, but in close contact with it. For example, a surgeon is not needed to use contact lenses- they can be removed, stored, and cleaned yourself. From which polymers are contact lenses made? What properties are desirable in these materials? Either a call to an optometrist or a search on the Web may provide some answers.
Answers:
Polymethyl methacrylate (PMMA), polyacrylamide, and rigid gas permeable (RGP) polymers. Properties desirable in these materials include: does not react with substances on the eye surface, permeable to oxygen so as to allow oxygen to reach the eyeball, easy to manufacture, comfortable to wear, and easily deformable so as conform to the shape of the eyeball. Ease of cleaning is also important for reusable contact lenses.
C) What is the difference in the material used in “hard” and “soft” contact lenses? How do the differences in properties affect the ease of wearing contact lenses?
Answers:
“Hard” lenses are usually made of PMMA, which was more rigid and non gas-permeable. “Soft” lenses are made of silicone, PMMA and fluoruopolymers, which is more flexible and allowed oxygen to permeate through it to reach the eyeball. The soft lenses may be more comfortable due to these properties.
References
- Polymers in everyday things- contact lenses [PDF]. (n.d.). RSC. http://www.rsc.org/Education/Teachers/Resources/Inspirational/resources/3.1.1.pdf