Qualities of a "Good" Plastic?

Question

For a science class, we're asked to make a project regarding plastics. We're supposed to be able to make a plastic using a specific procedure.

Are there any specific parameters that dictate whether or not a plastic is of good/high quality? How can you say that the plastic we made was good or not?

If there are any parameters or guidelines, how will we be able to measure them? Are there any specific criteria that the plastic should meet? (we were thinking along the lines of water resistance, flexibility, and texture)

Thanks in advance. =]

Answer 1

For this project, it sounds like you need to think in terms of materials engineering as much as materials science.  Your best answer depends largely upon the desired properties of your product.  What may be a great material in one application may be horrible in another.

After that, in many cases the stability of the material properties can be a major concern.  With some plastics in some applications, what first may appear to have the best properties may be a poor choice, because the properties may not be sufficiently retained over time (rapid loss of plasticizers, etc.).

And sometimes you have to think outside the box.  I know of a specific application where PTFE is used because of its relative chemical inertness at ambient conditions, but yet it provides gaseous fluoride ions during a thermal processing operation.  In this case, PTFE is used in lieu of an alternative process involving HF gas.

Answer 2

try putting also in your criteria biodegradability and toxic content (ozone depleting compounds). It's in the top list of plastic research.

Answer 3

The desirable properties depend on the specific application. Health, safety and environment (HSE) are also among the most important concerns in engineering practice.

Some properties to consider are:

- Chemical compatibility with grease, oil, food stuff (application dependent)

- Dimensional accuracy

- Low coefficient of thermal expansion (plastics may be affected a lot by weather changes)

- Resistance to UV (sunlight) exposure (should be chemically inert and not lose mechanical strength)

- Low water absorption

- Strength and flexibility

- Hardness (think of the difference between plastic combs, lawnchairs, toothbrushes. they all have different hardness of plastics)

- High softening temperature and melting point

- Density may be a factor in some applications. For example, is the plastic heavier than water?

- Thermoplast or thermoset (thermoplasts may be recycled)

I hope this helps.