PTFE max temp on a routine basis  

RE: PTFE max temp on a routine basis

260c ... and that is pretty much the limit for the hot end. Thermistors also become prone to fail above that temp.

http://www.rjchase.com/ptfe_handbook.pdf

That said, the PTFE is never subjected to print temps, so it's maximum limit is not an issue.

RE: PTFE max temp on a routine basis

Super, tks Tim.

This explain why we may print ABS on our MK3S.

Phil

RE: PTFE max temp on a routine basis

Concerns about PTFE temps are relevant for printers that do not use all-metal hotends, unlike the Prusas. These are particularly common in the low-end (cheap) machines. In these designs, PTFE is directly butted up against the heated nozzle. The the "all metal" design produced by E3D, there is PTFE but only up in the cold end that never gets hot.

While most of the manufacturers claim these designs can be used "up to 250C", they're only concerned about the temperature at which the tubing begins to physically degrade. If you do a bit of research, you quickly find that PTFE (teflon) begins to emit harmful emissions (neurotoxins) at 200C to the point of killing nearby birds. It really bothers me when I see hobbyists using those low-end machines trying to print PETG and other higher temps without any discussion of safety.

RE: PTFE max temp on a routine basis

Bob, can you point to a source for the safety issues?

Not that I trust everything I read, Dupont makes this claim: 

Decomposition at Elevated Temperatures
Rate of decomposition of a part of Teflon® PTFE depends on the particular resin, temperature, heatexposure time, and, to a lesser extent, pressure and nature of the environment. In designs where the rate of outgassing is important, as in high-vacuum work or for safety considerations, initial rates of decomposition in Table 12 may be used. For most applications these decomposition rates are small enough below the maximum service temperature (260°C [500°F] for Teflon® PTFE resins), and no special precautions are necessary.

RE: PTFE max temp on a routine basis

I actually wrote about PTFE failing at 200C and below in the CR-10 Facebook groups because we had users that cooked through it in as little as two weeks. I posted the bird article in my original post. It's from experiments with Teflon done by a health group. 

https://www.ewg.org/research/canaries-kitchen/teflon-kills-birds

I recommended upgrading to Capricorn XS as a replacement for stock PTFE on hot ends that have PTFE that ends at or before the heater block area as it takes longer to degrade.If you want to see what failing PTFE looks like just search google images.

RE: PTFE max temp on a routine basis

Yeah - not defending Teflon - but that article was related to cooking with temps exceeding 260c (500f).  While commoners are believing they aren't exceeding a certain temp, in most cases they are, and simply don't know it. Most users of these goods are not engineers and technicians, nor generally good observers.  And, they tend to be irrational when pets die.  Like the cases of ovens set to 400f: they actually get much hotter on surfaces irradiated by the heating elements; and electric cook top burners easily exceed 600f with pans in contact - and if an element is glowing its already near 1000f.

That said, am I comfortable with measurable weight reduction of 400f PTFE in only one hour?  Heck no.  Now I am worried about my non-stick cooking pans - they say they are titanium coated, but they are slick like Teflon (and I didn't do a deep dive into the non-stick surfaces).   I often heat oil too hot and to the smoking point; and canola gets to 400f before smoking - well in the inferred PTFE isn't good range.  And a new appliance I had to put out in the garage due to stink - is set to 400f - an air fryer. Ugh. 

RE: PTFE max temp on a routine basis

@tim-m30

The info about PTFE degrading was known way back in 1955 as crazy as it sounds. So Dupont was aware it broke down at 200C for quite a long time. Their white papers leave out alot of info.

Abstract: Teflon (9002-84-0), a physically inert tetrafluoroethylene (116-14-3) resin, is discussed in a paper presented at the American Industrial Hygiene Association Annual Meeting in Cincinnati, Ohio on April 26, 1955, and it is noted that its pyrolytic products are toxic, and exposure to various mixtures of them will induce polymer fume fever in humans. The latter influenza like syndrome has not been reproduced in animals. Sufficiently intense exposure of animals to Teflon's thermal products, however, is generally lethal. The associated evidence of pulmonary edema, together with other early test results, originally suggested that hydrogen fluoride (7664-39-3) (HF) was the responsible toxic agent. The pyrolysis of Teflon starts at 200 degrees-C and proceeds slowly up to 420 degrees-C; at 500 to 550 degrees-C, the degradational weight loss reaches 10% to 5% per hour, respectively, depending on conditions. In the temperature range 300 to 360 degrees-C, hexafluoroethane (C2F6) and octafluorocyclobutane (C4F8) were identified as decomposition products. In the range 380 to 400 degrees-C, octafluoroisobutylene (also C4F8) could be detected and, at 500 to 550 degrees-C, the chief pyrolysis products other than tetrafluoroethylene (116-14-3) (C2F4) were hexafluoropropylene (116154), (C3F6) octafluorocyclobutane, and octafluoroisobutylene plus a complex residue of perfluoroolefins. Inhalation toxicity tests indicated that the octafluoroisobutylene gas, the most potent product, was approximately ten times as toxic as phosgene (75-44-5). The rat mortality factor seemed to be proportional to the product of exposure time and Teflon surface area as a function of pyrolysis temperature. Teflon 6, a lower molecular weight polymer than Teflon 1, produced more toxic pyrolysis products. Other kinds of industrial polymers were observed to produce lethal atmospheres under less drastic conditions than either form of Teflon.
Ref: Toxicity of Pyrolysis Products of "Teflon" Tetrafluoroethylene Resin by Zapp JA Jr, Limperos G, Brinker KC. Proceedings of the American Industrial Hygiene Association Annual Meeting, Cincinnati, Ohio, April 26, 1955.

Abstract: The toxic properties of the tetrafluoroethylene (9002-84-0) monomer and of products of the thermal treatment of the tetrafluoroethylene polymer in acute experiments on cats, rabbits, albino rats and albino mice are reported. In rats and rabbits the inhalation of monomer induced hyperemia of organs, especially the brain, hemorrhage in the spleen and lungs, and dystrophic changes in the kidneys. Emphysema and atelectasis was observed in the lungs, desquamation of the epithelium in the bronchi also was observed. The threshold mortality for the monomer was 2.5 volume percent for albino rats and 4.0 volume percent for rabbits. The pyrolytic decomposition of tetrafluoroethylene polymer was lethal to cats, rabbits, mice, and rats. Death was caused by acute pulmonary edema, sometimes accompanied by pneumonia. Renal dystrophy was observed in the cats. There was acute irritation of the upper respiratory tract mucosa in all test animals. It is concluded that the pathology observed upon inhalation of the products of thermal decomposition of the polymer is apparently explained by the presence in the pyrolyses gas of difluorophosgene, perfluoroisobutylene (382-21-8), and other highly toxic hydrocarbons. (Russian: English translation available)
Ref: Toxicity of Tetrafluoroethylene by Zhemerdi A. Trudy Leningradskogo Sanitarno-gigienicheskogo Meditsinskogo Instituta, Vol. 44, pages 164-176, 1958. Document Number: NIOSH/00080478.

Abstract. Toxic effects following inhalation exposure to polytetrafluoroethylene (9002-84-0) (PTFE) pyrolysis products were determined in rats. Greenacres-Flora-rats were exposed to PTFE pyrolysis products containing hydrolyzable fluoride equal to 50 parts per million of carbonyl fluoride (353-50-4) for 1 hour daily for 5 days. On day 1 and 5 of the exposure period, and 3, 7, and 18 days post exposure urine samples were collected and examined for fluoride excretion and glucose, protein, and ketones. On each of those days, a test animal was killed, and kidney and lung tissues were tested for succinic-dehydrogenase activity. Weight changes and mortality during the course of the experiment were also noted. During the 5 exposure days and shortly afterwards, mortality reached 22 percent, although the total exposure dose was less than half the median lethal dose for one exposure. Daily urinary fluoride excretion jumped to 14 times normal on the first exposure day and remained at 4 times normal by the eighteenth postexposure day. By the fifth exposure day, body weights dropped 30 percent, urine glucose, protein, and ketones were abnormal, and succinic-dehydrogenase activity dropped to near zero in the kidney and had more than doubled in the lung; by the eighteenth post exposure day, these values had returned to normal. The authors conclude that carbonyl fluoride generated during the pyrolysis of PTFE hydrolyzes in body fluids and produces fluoride toxicity. The cumulative effect of repeated exposures is much more toxic than a single equivalent exposure. If death does not result, the metabolic inhibition due to fluoride poisoning is completely reversible.
Ref: Biochemical Changes Associated with Toxic Exposures to Polytetrafluoroethylene Pyrolysis Products by Scheel LD, McMillan L, Phipps FC. American Industrial Hygiene Association Journal, Vol. 29, No. 1, pages 49-53, 1968.

Abstract: The pathologic effects of exposure to combustion products of polytetrafluoroethylene (9002-84-0) (PTFE) were studied in rats. Fischer-344-rats received single 30 minute exposures to concentrations from 0.005 to 5.025 milligrams per liter aerosol products of PTFE heated to 595 degrees-C. The median lethal concentration (LC50) was determined. Necropsies were performed at 0, 2, 12, 24, and 36 hours post exposure or between 2 and 17 days. The LC50 for thermal degradation products of PTFE was 0.045 milligrams per liter. Conjunctival erythema and serous occular and nasal discharge were seen in survivors immediately after exposure. Lesions were found in lungs of 84 percent of exposed rats. Focal hemorrhages, edema, and fibrin deposition in the lungs were found. Focal interstitial thickenings developed and increased. Alveolar macrophages became more severe up to 96 hours. Thrombosis or embolism of pulmonary capillaries and veins were found in 38 percent of exposed rats. The degree of pathologic change increased as the dose increased up to the LC50, but fluctuated above that. Disseminated intravascular coagulation occurred in 53 percent of exposed rats and was positively related to the amount of lung damage. Renal infarcts due to disseminated intravascular coagulation were found but no other kidney lesions were seen. The authors conclude that disseminated intravascular coagulation appears to be a consequence of exposure to PTFE combustion products.
Ref: Pathologic Findings In Rats Following Inhalation Of Combustion Products Of Polytetrafluoroethylene (PTFE) by Zook BC, Malek DE, Kenney RA. Toxicology, Vol. 26, No. 1, pages 25-36, 1983.

CDC Decomposition of Products Report 1977:
https://stacks.cdc.gov/view/cdc/19394/cdc_19394_DS1.pdf

Besides there site with the pet owners there was a recent lawsuit against Dupont for Teflon contamination. 

https://www.theguardian.com/us-news/2019/sep/11/pfas-toxic-forever-chemicals-hearing-3m-dupont-chemours

https://ohiovalleyresource.org/2017/02/13/dupont-offers-670m-settlement-teflon-chemical-contamination-water/

https://qz.com/1630348/dupont-and-3m-face-a-growing-list-of-water-contamination-lawsuits/

https://en.wikipedia.org/wiki/Perfluorooctanoic_acid

RE: PTFE max temp on a routine basis

There's a good discussion on StackExchange on the topic. I took a look at some of the older 1950-1960s publications, and they noted that there was a change in DuPont's formulation that reduced toxicity at lower temps. This summary wraps it up nicely:

However, the chemicals (species) listed above are for controlled lab experiments. What happens in real life cooking scenario is not (or cannot) be anticipated. But, it can be readily said that the above species can react with other chemicals in food to give fluorinated compounds that will be harmful for humans. As a precaution, one should not cook above 200 C on PTFE coated utensils to be completely safe.

More discussion here relevant to birds deaths at temps below 200C here.

So as long as your cheap PTFE mass-produced in locations with very low quality and safety control is using DuPont's formulation, the toxicity is probably less of an issue. If they aren't adhering to standards for quality and safety, you're trusting the manufacturer's word for it.

RE: PTFE max temp on a routine basis

One test concentration was "0.005 to 5.025 milligrams per liter" and I presume that was liter of air.  1L of moist air at 1.2 gram results in tests starting at 4 ppm, ending at 4000 ppm.  50% death rate in rats at at 37 ppm.  Hmm.  

I might be looking for new aluminum oxide cookware (last set I bought was horribly expensive, but stuff didn't stick to it as much as cast iron or stainless).  I don't fry much, but it is really hard to judge how hot a pan gets - especially the side you aren't cooking on that is in contact with that 1000 degree burner.  And now you guys have me concerned -- thank you not so very much.

RE: PTFE max temp on a routine basis

Posted by: @tim-m30

[...]  And now you guys have me concerned -- thank you not so very much.

At least cookware has gotten some attention. I spend a lot of time lurking in the various 3D printing reddits and it's alarming to see how many kids have 3D printers in their bedrooms, especially when they start trying to figure out how to print PETG and higher-temp materials using inexpensive hotends that clearly haven't been manufactured to particularly high standards. I suspect the PTFE tubing butting up against those hot nozzles in the not all-metal designs is putting off bad stuff at 250C than Capricorn or DuPont manufactured teflon/PTFE. You'll often see an obviously quite young kid asking about safety of family and pets, only to be told it's not a big deal.

Maybe I was wrong about the kids not having the experience of dangerous toys such as the Vac-U-Form. Unfortunately, the hazards they face are a lot more insidious and long-lasting than burnt fingers!

RE: PTFE max temp on a routine basis

PTFE doesnt melt until over 300 degrees and doesnt Pyrolyse until over 400°C so there is not really any issue for normal 3d printing use and this is also why all metal hot ends exist for higher temperature materials.

RE: PTFE max temp on a routine basis

Posted by: @pixel

PTFE doesnt melt until over 300 degrees and doesnt Pyrolyse until over 400°C so there is not really any issue for normal 3d printing use and this is also why all metal hot ends exist for higher temperature materials.

Did you read the referenced articles? Lower grade stuff starts putting out sufficiently nasty stuff to kill birds at below 200C, and certainly well below PTFE melting temps, while the offshore low-end hotends are "rated" at up to 250C. I mean, by all means, huff all the stuff you want, but I'm not going to run one of the cheap printers anywhere near those temps without replacing the PTFE-against-nozzle hotend. Not an issue for a Prusa, and certainly one argument in favor of one!

RE: PTFE max temp on a routine basis

This is somewhat like the neighbor who had his 1940's truck sandblasted in his driveway.  Ignorance is bliss. A couple days later when he was outside with his two young kids (about 7 yo) sweeping up the dust I was going to say something, but figured it was too late, damage was already done - they'd been sweeping all morning.  

And yes, most every car produced before 1970 has lead primer and lead additives in the paint.  Even worse are the red yellow and brown cadmium based paints, which also have lead. Yee-Haw. 

RE: PTFE max temp on a routine basis

Posted by: @tim-m30

[...] And yes, most every car produced before 1970 has lead primer and lead additives in the paint.  Even worse are the red yellow and brown cadmium based paints, which also have lead. Yee-Haw. 

I was watching a show where an old car enthusiast was lamenting all of his buddies that were always working on cars in the 1950s & 60s that passed away from asbestos-related exposure. Apparently working on brakes on old cars was bad news.

RE: PTFE max temp on a routine basis

@bobstro

You never know when you could be exposed to something crazy. People worry about PTFE exposure but Radon exposure is worse than that. https://www.radon.com/radon_facts/

There's all kinds of exposure from material outgassing in homes and offices that is not common knowledge. We had all kinds of issues with Chinese Drywall off gassing.  https://www.popularmechanics.com/home/how-to/a4884/4336471/

There are Natural Asbestos Superfund sites in California where people are exposed to asbestos in the wind for years and never knew it. https://archive.epa.gov/region9/toxic/web/html/basic.html

My grandfather worked for US Steel and he got exposed to asbestos while building office buildings in downtown Houston, TX. My grandmother and her sister died from acid exposure due to a spill in the late 80s. https://www.upi.com/Archives/1987/11/03/Marathon-OSHA-investigating-acid-leak/1409562914000/

I lived in Texas City, TX from 1990-2000 and I heard all kinds of crazy chemical exposure stories. The plants there make acids, gasoline, plastics,  solvents, Listerine(which is harmful in vapor form), they also grow oil eating bacteria there. A good friend of mine named Big John was an engineer at the chemical plants there and he said workers used to wash their hands and arms in Benzene. They would use it to wash their tools off. They would smoke around it. Stuff that would be crazy OSHA violations now was happening all the time back in the day.

My dad worked at the original VA Hospital in Houston and they tore the building down because it had become infected with bacteria from lab testing and overly radioactive in some parts of the hospital. So much so that they had to abandon using some of the x-ray rooms. They were like trading off usage for some rooms as well. When they tore the old hospital down to build the current hospital the entire building was burned and buried somewhere because it was an EPA hazard. That was also when I found out that some buildings have been found to be radioactive that weren't even hospitals.

So you never know how much stuff is going to kill you without anyone actually knowing it was a happening.