Science Buddies: "Ask an Expert"

i have to present a project in january 2006 on plastics...if anyone knows anything about the laboratory preparation of any sort of a plastic or any other experiment or some intersting matter PLEASE TELL ME!!!!....i am in the need of very intersting facts about plastics which the people would be INTERESTED in !!!!

thanxxx

oh..i forgot to mention...just don't worry about the duration of a particular experiment...just give me the idea...

Hi Ammara,

I did a google search on neat plastic properties and found a website that gives a lot of information about plastics and their properties. http://www.manufacturingcenter.com/dfx/ ... 00plst.asp

I don't know much about plastics but you could probably do an experiment testing how different types of plastics act under heat or pressure.

Good luck and please let us know how your project is coming



Philip

There are some interesting differences among the various types of plastics. Some, like polyethylene, soften as the temperature increases and melt at a temperature close to the boiling point of water. Other plastics retain good properties up to high temperatures. You probably have several kinds of plastics in your recycling bin. Look at the different numbers in the triangles that identify the type of plastic. I thinks if you search on recycling + plastics, you can find out what each synbol stands for. Then you can look up the properties of each type. You might make a nice display board of recyclable plastics with some notes on the properties of each type. For example, some types of plastic are approved for contact with food and others are not.

The state of the art may have changed a bit since I was in grad school 18 years ago, but from what I remember, creating plastics was largely a matter of deciding how long the polymer chains were that you wanted and making sure your process generated them. Keep in mind that most of this is from memory, and the memory is pretty old. Still it may spark some research ideas for you.

"Plastic" is a rather generic term for a material that is made up of long chains of carbon and hydrogen atoms, that are just kind of tangled together, rather than in a fixed crystal structure such as iron or in a loose liquid state, like glass.

If the carbon chains are really short, you get wax. It deforms in your hands, melts in very low heat, etc...it isn't much of a solid because the structural integrity is tied to the molecules tangling, and there isn't much "tangle" in wax.

If they're really long, you get a pretty strong structural material. All the different kinds of plastics you see in consumer products are mostly differentiated by how long their carbon chains are. This used to be a big recycling problem....if you mixed multiple types of plastic into a vat and melted it, you couldn't then pour the slush into molds an make new plastic goods unless everything you melted had roughly the same length of molecule. In theory though, you could take advantage of the basic properties to distill out the different categories of plastics (shorter chained molecules melt sooner). Nowadays, most recyclers take all kinds of plastic in the same bins, but they may still be sorting them by hand.

Sunlight often degrades plastic because the rays break up the carbon chains. Shorter chains = more brittle, even if not all the chains have been damaged.

New plastic manufacture is about controlling the length of the chains, using the minimum heat (heat is expensive) and making sure it has the right properties to get into molds correctly. Quite often chemical solvents are used to manipulate the plastic rather than heat. This is cheaper, and in theory most of the organic solvents used will evaporate away from the plastic as it hardens, so it won't interfere with the final product.

There are also other considerations:

Color: Basic polyethelene gets you white or clear. Other colors are the results of little dye particles that reside between the carbon chains. If you introduce color, you introduce variables into the production process.

Impurities: These can weaken the material, or change its color, or make the final product toxic to the consumer (very important in food packaging apps). Most plastics can't hurt you because the large molecules are very unlikely to separate into the food, and even if they do, your body won't react to them. The solvents that they use to manufacture the plastics though, sometimes stick around and do leach into the food, and anything that degrades the plastic (example - sunlight, or storing a solvent such as alchohol in a plastic container not designed to hold it) can also cause the plastic itself to leak into the product. This may not be toxic, but it'll taste horrible.