This week, we covered Polymers and Plastics.
Here are our answers to AE 7
Question 1
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. The solid still consist of Styrofoam, but now it is solid and much denser. Explain. Hint: Remember that Styrofoam is made with foaming agents.
Acetone dissolves the polymer, allowing the gas of the foaming agent to escape.The volume of the polymer decreases and the polymer is more dense because the gas has been removed.
Question 2
Consider Spectra, Allied-Signal Corporation’s HDPE fiver, 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 delicate sense of touch, The interesting thing is that Spectra is linear HDPE, which is usually associated with being rigid and not very flexible.
- suggest a reason why branched LDPE cannot be used in this application
- Offer a molecular level reason for why linear HDPE is successful in this application.
LDPE cannot be used because it is weaker than HDPE. This is because LDPE has more branches in the chemical structure, leading to there being multiple points of weakness.
HDPE has molecules that are packed closely in a linear fashion, giving it strength. The thin sheets allow room for flexibility.
Question 3
When you try to stretch a piece of plastic, 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
No, it does not.
For plastic bags, the polymer chains interact with each other using Van der Waal’s force, which is weaker. The molecules become aligned parallel to each other and in the direction of the pull.
Cellulose is composed of covalent bonds between glucose branches, causing it to be very strong.
Question 4
A Teflon ear bone, fallopian tube or heart valve? A Gore-Tex implant for the face or to repair a hernia? Some polymers are biocompatible and now used to replace or repair body parts.
- List four properties that would be desirable for polymers and used within the human body
- Other polymers may be used outside your body, but in close contact with it. For example, no surgeon is needed for you to use your contact lenses — you insert, remove, clean and store them 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.
- What is the different in the material used in “hard “ and “soft” contact lenses? How do the differences in properties affect the ease of wearing contact lenses?
It is stable over time of intended use, non-toxic, low-cost, and lacks solubility in body fluids
Polymethyl methacrylate (PMMA). It is non-toxic, permeable to oxygen, easy to wear, inexpensive, able to conform to the shape of the eye, and easily cleaned if not disposable
Hard lenses are made of PMMA. Soft lenses are made of silicon which. This leads to soft lenses being more comfortable.