Forensics C

[daydreamer0023]

Anyone have a good way to distinguish nylon vs polyester?

[markuswso17]

Anyone have a good way to distinguish nylon vs polyester?

Under a microscope, Nylon looks like small clear rods. Polyester is the same thing but it isn't clear.
During burn test, Nylon curls when a few inches away form the flame while Polyester does not.

[pikachu4919]

Anyone have a good way to distinguish nylon vs polyester?

Under a microscope, Nylon looks like small clear rods. Polyester is the same thing but it isn't clear.
During burn test, Nylon curls when a few inches away form the flame while Polyester does not.

You might also want to read up on the chemical makeups of each fiber, they can also tell you about chemical properties that the fibers might have (such as scent in the burn test, behavior during the burn test, etc.)

I think I know who both of you are and that you'll both be in this event at nationals, so here's a tip from me: The microscopes at nats aren't top-notch quality (believe me, I know) - sometimes, they might not really give you a good view of whatever you're looking at, and/or it is hard to quickly adjust the microscope to a good, focused view. That plus the fact that time flies so quickly at nats due to the sheer amount of stuff that the supervisor makes you do means that you possibly won't have that much time to do a microscope analysis if you're really really pressed - for me when I took this supervisor's exams, that's why I actually relied more on burn tests and my gut feelings/instinct for fiber and hair ID.

[KSSOISLIT]

For the Nationals test, does the Woz set up slides with hair on microscopes, or do we have to prepare slides with hair they give us?

[KSSOISLIT]

Another question, what would be the best way to distinguish between PP and LDPE as they behave similarly in most density tests and have similar appearances?

[pikachu4919]

*caution - try not to double post

anyways....

For the Nationals test, does the Woz set up slides with hair on microscopes, or do we have to prepare slides with hair they give us?

It's DIY. You'd be really lucky to get a supervisor that would be willing to do such a thing for you.

Another question, what would be the best way to distinguish between PP and LDPE as they behave similarly in most density tests and have similar appearances?

Corn oil, which has a density of 0.91 g/cm^3, should work since PP's density is 0.90 g/cm^3 and LDPE's is 0.92 g/cm^3. It's really subtle but yeah. They additionally have different chemical monomers that might translate to differences in their overall properties but idk if they'd be the kind that you could easily see (then again the only plastic burn test result that's really relevant that I suspect is the only one that the supervisor at nats might mention at all if applicable to the test is PVC, which is green).

[markuswso17]

It's been a while since we took our nationals tests and it's been pretty quiet on the Forensics forum, so what was your favorite/least favorite part about Forensics this year?

[daydreamer0023]

It wasn't a bad test - my partner and I were just really bad at time management. However, the plastics solution containers were somehow contaminated with oil from the people before (we were in the 5th block) so we abandoned plastics. Apparently, the other team at our table said the hot water bath was filled up too high so they couldn't put their test tubes in proper - I'm not sure because I didn't do Benedict's test.

[markuswso17]

It wasn't a bad test - my partner and were just really bad at time management. However, the plastics solution containers were somehow contaminated with oil from the people before (we were in the 5th block) so we abandoned plastics. Apparently, the other team at our table said the hot water bath was filled up too high so they couldn't put their test tubes in proper - I'm not sure because I didn't do Benedict's test.

I had issues with the water bath as well. What I ended up doing was just balancing it with a test tube holder, but then when I came back, the solution had spilled inside because it came unbalanced somehow. We also didn't use a microscope because the microscope at our table (back-right) had a huge scratch on the lens so it was nearly impossible to figure out what we were looking at.

[alleycat03]

This was my second test with the Woz, and I was definitely more prepared this time. I think the test was well written and very difficult, which is to be expected. My only complaint is that the microscope that my team had was really crappy. It was super difficult to focus and the lens was super dirty. It took too long to ID the hairs with the crappy microscope so I basically had to make educated guesses on about 1/2 of the hairs. Otherwise, the test was well-written, the Woz was strict but a good proctor, and I enjoyed taking the test.