Lexan Bottles

Metal conducts heat well and it’s thin.. therefor the exterior surface of the material is effectively equal to the interior surface (aka High Heat Flux at very low delta Ts)

Lexan, on the other hand does not move heat well and most lexan bottle are significantly thicker… what this means is that in order to get the heat conducted into the water you have to have an relatively high delta T from the outside to the inside of the material… in order to get the interior to 212 degrees you likely need to get the exterior to well over 400 degrees… possibly higher… what this means is that the outside surface is likely to melt before the water boils… notice that a microwave works differently as there is an energy (radiation – not thermal radiation) that passes straight through the lexan and causes the water to heat up withought having to heat up the lexan first…

Lexan is plaaaaaaaaaaaastic!!!

Lexan is amorphous, so it doesn’t actually have a melting point…however, it will start to soften at ~150C. Even below that temperature you will likely start to get migration of compounds (e.g., bisphenol A, which has been identified as a endocrine disruptor or artificial hormone). I doubt that anyone has even tested this container to see what migrates out at those conditions.

You can argue the true effect of that stuff on humans (and they do), but I think that most people (manufacturer included) would agree that it’s a bad idea to expose these bottles to a direct flame.

Thomas,

thanks for the info. how would like to educate me a bit?

>>”amorphous”
are you saying that Lexan is not a solid (i.e., not in the solid phase), but rather is a highly viscous fluid similar to asphalt tar and glass? this is the way i interpreted your statements of “amorphous” and “it doesn’t actually have a melting point”. was i correct? is this what you meant?

thanks in advance for taking the time to reply and educate me. i appreciate it. take care.

Paul,
You’re right…PC doesn’t have a significant amount of crystallinity, so it could be considered a glass (although that term can be confusing the the layperson). Some other amorphous polymers include PMMA (Plexiglass) and polystyrene. Polyethylene and PET are crystalline polymers. Although the crystallinity affects properties, the polymer chemistry and structure also play a big role. You can often make amorphous polymers crystalline and the other way around by tweaking the chemistry and/or processing.

However, the fact that it’s amorphous isn’t the main reason I would recomend against cooking with it.

If you have other questions along this line, I’d be glad to further discuss it off-line since this could stray off topic. My graduate degree was in Materials Science and I have been doing lots of permeability work (O2, CO2, and water vapor transmission) in the plastic industry, so I have enjoyed the level of detail that is included in the BPL articles and forum discussions.

Tom

Tom,

thanks for the “off-line” offer. no further questions. already had some rudimentary understanding of these matters from many chemistry courses – a very long time ago. have never considered cooking in it. thanks for weighing in here in this Thread with your invaluable info. i’m sure it helped someone (probably many). take care, pj

As a minor note, glass isn’t a liquid, but it’s a pretty common urban myth that it is one because of the way some old stain glass windows were made :)

i know some PhD Chemists who would disagree with you. best i can recall is that it can get pretty involved – even the type of glass has some bearing here and to some extent the rate at which it cools. this is actually a pretty debatable (and relatively unimportant) point involving first and second order phase transitions. glass is often referred to as a supercooled liquid, a highly viscous fluid (perhaps more so back in my school days – eons ago), and sometimes as an amorphous solid. a fluid??? why? because no first order phase transition occurs as it cools. in a first order phase change a sudden discontinuous change in density takes place when the phase change occurs. in glass such a discontinuous change of density does not occur and there is no latent heat of fusion. the structure of glass actually possesses properties of both solids and fluids: viz. there is no crystalline lattice as the molecules are not ordered (fluidic property), but rigidly bound (un-fluidic property). i don’t recall much more (hope i’m even recalling this correctly), but if you check out Gear Swap (Thread = Waypoint1 for sale) for my email address & email me. i’ll explain whatever else i remember (not much) to you off-line (perhaps even the “Chaff” section is not appropriate for such a Thread).

perhaps leaving it at amorphous is best.

acutally, the best bet is for Tom Clark to get involved here. he undoubtedly knows much more about this than i learned in a bunch of undergraduate chem courses.

Well above it’s Tg (glass transition temperature) I would not consider glass to be a liquid…but that’s a Material Scientist’s view based on its physical/mechanical properties. Maybe a chemist has a different view.

after my last post, since i don’t trust my memory, i checked with several PhD’s and Metallurgists/Material Science guys (nearly all with advanced degrees) here at work as well as one of our Chief Scientists.

As I queried them, a pattern of responses was immediately obvious. queried ~15 individuals.

Glass = amorphous sold = without exception this was the first answer of everyone educated in the USA who was under ~40yrs olds.

Glass = a highly viscous fluid = without exception this was the first answer of everyone educated in foreign countries (Russia and Korea), and guys over 50 yrs old educated in the USA.

not sure how typical these results would be elsewhere. just found it rather interesting.

Hi Paul,

Be it naturally occuring as obsidian (volcanic glass- generally appears black or red) or a fulgarite (as in lightning strike in and fusing sand), or man made, glass is amorphous because it is quenched too quickly to form any true micro crystaline or crystaline structure. I believe that glass is an unusual solid that has the tendancy to flow (though very slowly) like a very viscous liquid.

Rich

If I may interject: I can’t think of any liquids that posess covalent bonds between their molecules. Glass is silicon dioxide, and in another of its forms it is crystalline (quartz). As pointed out earlier, the molecular structure depends on how fast it is cooled. So maybe this doesn’t completely resolve the issue, but it would seem difficult for me to classify glass as a liquid since its molecules are covalently bonded to one another and thus highly restricted in their motion. Thanks for the stimulating thread.

appreciate the input as i always like to learn something (or be reminded of things long since forgotten – an increasing reality as my “old-timers” progresses). at this point, i’m bowing out so i can get back to UL Backpacking – really need to learn more about this as i’m only in my “Sophmore Season” since i’ve “seen the Light” (to paraphrase GVP’s website).

Tonight on Unsolved Mysteries

Part I:

For centuries, great minds throughout the world have been plagued by one burning question: is glass a solid or a liquid? To this day, material science experts at backpackinglight.com are bitterly divided over this conundrum. Will we have to hand it down to the next generation unanswered? Find out at 8 pm tonight.

Part II:

Peanuts: peas or nuts?

legumes

[Stephan, very humorous post. still chuckling. thanks for weighing in here.]

If it doesn’t splash when I throw a rock in it, it’s a solid.
There problem solved!

David, he say: “If it doesn’t splash when I throw a rock in it, it’s a solid.
“

How big is the rock and how fast is it going? Inquiring dinosaurs want to know. Liqufied Yucatan anyone?