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Re: Forensics C
Posted: September 9th, 2015, 6:37 pm
by iwonder
daydreamer0023 wrote:Does anyone have any tips for identifying the different polymers? What do the supervisors provide you with to help with identification? I really have no clue what is going on in this area of the event. All help will be greatly appreciated!
Most of them can be done based on density, so I'd get really good at density tests. Use a lot of solutions since you don't know what you're gonna have at any given contest. Then, figure out how to differentiate between plastics with similar densities by burn test or maybe usage. Probably a few other that I've forget or didn't have to use...
Re: Forensics C
Posted: September 9th, 2015, 7:44 pm
by AlphaTauri
iwonder wrote:daydreamer0023 wrote:Does anyone have any tips for identifying the different polymers? What do the supervisors provide you with to help with identification? I really have no clue what is going on in this area of the event. All help will be greatly appreciated!
Most of them can be done based on density, so I'd get really good at density tests. Use a lot of solutions since you don't know what you're gonna have at any given contest. Then, figure out how to differentiate between plastics with similar densities by burn test or maybe usage. Probably a few other that I've forget or didn't have to use...
Just fyi, you're not allowed to do burn tests yourself on plastics, but it's good to have them noted down somewhere in case the event supervisor gives you the theoretical results. But yeah, density is the most common differentiator. Sometimes you can get a clue of what it might be based just on appearance, but that's not a definitive test.
Re: Forensics C
Posted: September 10th, 2015, 6:30 pm
by Catie314
daydreamer0023 wrote:Does anyone have any tips for identifying the different polymers? What do the supervisors provide you with to help with identification? I really have no clue what is going on in this area of the event. All help will be greatly appreciated!
For the plastics, you should definitely know some basic uses for each of them. Also, try to have an idea of what they can look like as samples. But, if nothing else, learn how to do a density test on the plastics.
In any tests that I have done, the plastics have been provided with supplies to do a density test. However, that was only in one state. Good Luck!
Re: Forensics C
Posted: September 12th, 2015, 8:08 am
by daydreamer0023
Thank you for the help! Also, how would you differentiate between a "floating" plastic and a "sinking" plastic in a solution if it seems somewhere in between?
Re: Forensics C
Posted: September 12th, 2015, 8:38 am
by iwonder
daydreamer0023 wrote:Thank you for the help! Also, how would you differentiate between a "floating" plastic and a "sinking" plastic in a solution if it seems somewhere in between?
I usually poke it with something so surface tension doesn't effect it, and watch how it rises or falls. You can also do two types side by side if they're close enough to the density of the solution to see which one's more or less dense. If I can move it to different depths in the solution and it stays then I say it's the same density.
Re: Forensics C
Posted: September 12th, 2015, 10:52 am
by samlan16
iwonder wrote:daydreamer0023 wrote:Thank you for the help! Also, how would you differentiate between a "floating" plastic and a "sinking" plastic in a solution if it seems somewhere in between?
I usually poke it with something so surface tension doesn't effect it, and watch how it rises or falls. You can also do two types side by side if they're close enough to the density of the solution to see which one's more or less dense. If I can move it to different depths in the solution and it stays then I say it's the same density.
Alternatively, if you are testing the plastic in salt water, you could change the concentration to determine the effects. This may be advantageous if you know for a fact that you have NaCl as a sample at competition and distilled water and alcohol are inconclusive. For example, if you have a plastic that sinks slowly half the time and floats the rest of the time (i.e. PS), you could take several samples believed to be at different densities on the spectrum (PS has a decently large range- 9 kg/m^3 to 45 kg/m^3) and test them in concentrations of salt water ranging from 0% NaCl to 20% and beyond.
Re: Forensics C conductivity tests
Posted: September 22nd, 2015, 9:00 pm
by nmsciencemom
Is there any of the powders this year in which doing a conductivity test would be the best identifier of that powder? My students do not think doing that test is really very helpful compared to other tests.
Re: Forensics C
Posted: September 23rd, 2015, 7:22 pm
by pikachu4919
nmsciencemom wrote:Is there any of the powders this year in which doing a conductivity test would be the best identifier of that powder? My students do not think doing that test is really very helpful compared to other tests.
It mostly helps identify ionic compounds since those dissociate completely into ions that can conduct electricity when dissolved in water. I guess in a way, you could use it more along the lines of confirming a powder instead of using it as a primary eliminator.
Re: Forensics C
Posted: September 23rd, 2015, 7:31 pm
by pikachu4919
pikachu4919 wrote:nmsciencemom wrote:Is there any of the powders this year in which doing a conductivity test would be the best identifier of that powder? My students do not think doing that test is really very helpful compared to other tests.
It mostly helps identify ionic compounds since those dissociate completely into ions that can conduct electricity when dissolved in water. I guess in a way, you could use it more along the lines of confirming a powder instead of using it as a primary eliminator.
Re: Forensics C
Posted: October 8th, 2015, 12:48 pm
by justgreene
Can anyone refer me to a website to buy good quality plastics to test for density? I have beads but they seem to be inconsistent. For example some of the beads of HDPE float in 48% isopropyl alcohol, whereas others sink.