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Harmless
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Non-friable high temp fabric options?
I'm looking for a high temperature [>350C] non-conductive fabric for apparatus insulation. Fiberglass works well, but its friable nature means that
it is not very resistant to regular manipulation. It irritates the skin and lungs and disperses fine particulate glass throughout the workspace.
Polybenzimidazole fiber seems to be an excellent candidate, with a wide range of chemical resistance and decomposition point over 700C. However, it
seems to be very difficult to acquire. Only one company produces the fabric.
Kevlar, para-aramid, is the next best thing that I can think of. It degrades at around 500C, and is used in textiles. It is friable, and causes lung
irritation akin to silica, but is significantly more resilient than glass fiber. I would assume it doesn't irritate the skin significantly, as it is
used in airplane seat covers as well as clothing.
Would kevlar be a reasonable insulation replacement for glass fiber at modest (200-400C) temperatures? Being able to tightly wrap and unwrap the
material without impacting the durability is my primary goal. Cases such as maintaining a set temperature in a column through wrapped heating tape.
Kevlar is significantly more resistant to fatigue than glass fiber.
I don't know whether kevlar is able to withstand high temps for long periods of time. It loses strength when exposed to high heat, but I am unsure as
to whether this is a permanent change, or merely a weakness while at that specific temperature. DuPont provides charts indicating "aging time" varying with temperature, but only for the metrics of dielectric strength, and tensile strength under load.
That's in contrast to glass, which to my understanding can be heated and cooled as much as you want to, and subsequently lacks a "useful life"
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Heptylene
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Carbon fiber maybe?
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SWIM
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How about Nomex?
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Herr Haber
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Second criteria: non conductive
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horribilis
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Would ceramic fiber be less friable than conventional fiberglass?
[Edited on 7-6-2019 by horribilis]
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DavidJR
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Would MICC (mineral-insulated copper-clad) cable be suitable?
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Sulaiman
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I bought some very fine (0.03mm) fibre woven fibreglass cloth via eBay, being made of fine continuous threads makes the cloth very soft and not
friable.
https://www.ebay.co.uk/itm/1M-0-03mm-Ultra-Thin-Fiber-Glass-...
The fibreglass cloth feels like satin.
[Edited on 7-6-2019 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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The polymer [kevlar, para-aramid] cannot be melted, but degrades chemically at around 500°C.
https://www.sciencedirect.com/science/article/pii/B008043152...
It [kevlar] loses half of its strength at about 400°C, and reaches zero strength at 455°C. [Figures 11 and 12]
https://www.sciencedirect.com/science/article/pii/B008042993...
from DuPont: "Kevlar 29"
"Decomposition Temperature in Air = (427–482) °C"
"Recommended Maximum Temperature Range for Long-Term Use in Air = (149–177) °C"
However, this maximum temperature range appears to be the maximum for stress situations. Effectively, the "if you go above this temperature
we can't guarantee it's going to stop bullets or whatever."
"Increasing temperatures reduce the modulus, tensile strength and break elongation of Kevlar® yarns and other organic fibers. This should be
taken into consideration when using Kevlar® at or above 300°F to 350°F (149°C to 177°C) for extended periods of time."
"Kevlar® does not shrink like other organic fibers when exposed to hot air or hot water. Most other fibers suffer significant, irreversible
shrinkage"
http://www.dupont.com/content/dam/dupont/products-and-servic...
Nomex [meta-aramid] RTI (celcius): 220
https://iq.ul.com/ul/cert.aspx?ULID=230941
[Nomex] "Fabric scorching or charring can occur in as little as 30 seconds at 662°F (350°C) in air."
"After exposing fibers of NOMEX® to dry air at 500°F (260°C) for 1,000 hours and then returning them to room temperature, the breaking strength
and toughness of NOMEX® is approximately 65% of that exhibited before exposure."
This indicates a permanence of heat-induced weakening.
"fabrics of NOMEX® III and NOMEX® IIIA [93% Nomex, 5% Kevlar, 2% antistatic] are not recommended for protection from high-temperature metal
splash, such as aluminum or steel, where the molten metal may have a temperature in excess of 1,000°F (538°C). Fabrics of a 50/50 blend of
NOMEX®/KEVLAR®, 100% KEVLAR®, or FR rayon blends with KEVLAR® are commercially available for welding and molten metal splash protection."
This indicates that Nomex is less resistant to high temperatures than Kevlar.
http://www.nakedwhiz.com/gasketsafety/nomextechnicalguide.pd...
******I was operating with the understanding that meta-aramid (Nomex) would be less resistant chemically and thermally than para-aramid
(kevlar). My logic being that the para form is a more stable conformation, and therefore a more stable polymer. I would assume that nomex would be
used in kevlar blends to offer a more comfortable textile, as nomex is more elastic. However, this report contradicts this, listing Nomex as having a
HIGHER continuous operating temperature (400F) than Kevlar (375F). This runs counter to my intuition, and has effectively dumbfounded me. I was
prepared to pull the trigger on a sheet of kevlar, but now I am doubting my comprehension as to why kevlar would be superior, or inferior, to
nomex.
http://www.intexa.com/downloads/hightemp.pdf
Again, the concept of nomex being superior to kevlar is illustrated here, but with contradictory information compared to DuPont.
"Nomex fibre retains useful properties at temperatures as high as 370C... . It has a weight loss at 450C (Fig. 2) and a use temperature of 370C."
"The continuous operating temperature of PPTA [kevlar] in air is up to 190C. PPTA degrades in air above 400C"
Continuous operating temperature: Kevlar = 190C, Nomex = 200C
In addition, the copolymer (meta and para) [Technora] has even better thermal resistance, somehow?
"Technora has a decomposition temperature of 500C. It can be used at 200C for long periods of time and, even at 250C, it maintains more than half
of its tensile strength measured at room temperature."
The experimental data from this same paper indicates a two-step decomposition of Kevlar, initializing at 200C, and entering a main stage at
500C. This is contradictory to the DuPont whitepaper. However, I have seen reference to evolution of residual DMAc from kevlar fabric when heated.
This isn't a decomposition, but a loss of trapped solvent from manufacture. Since the kevlar in the experiment is from DuPont, and NMP is the solvent
they use in manufacture (bp: 202C), this COULD explain the mass loss reported. In such a case, the 500C degradation temperature is in line with
DuPont's reported.
https://www.egr.msu.edu/kodur/Fire%20Research%20PhD/2002%20H...
Conlusion (tl;dr):
After an afternoon of research, I am totally unsure as to whether or not Kevlar (or nomex) would be best suited to this application. I am unsure which
material is more thermally stable. I am unsure as to the reason to choose Kevlar over Nomex (or a blend of both). There is a ton of contradictory
information, and vague descriptions of methodologies. I am left with more questions than I started with.
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andy1988
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Quote: Originally posted by advanced warning  | | I'm looking for a high temperature [>350C] non-conductive fabric for apparatus insulation. Fiberglass works well, but its friable nature means that
it is not very resistant to regular manipulation. It irritates the skin and lungs and disperses fine particulate glass throughout the workspace.
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Well, I'm pleased to share this with you then. I'm not a fan of fiberglass either.
Morgan Thermal Ceramics Superwool. "Low biopersistent fibres". Other ceramic blankets are not good for lungs, this one different.
Superwool Resources
Thermal Conductivity
Can be "rigidized" with a rigidizer product (sodium silicate blend brushed on or whatever).
I'd read that inhaled fibers break down in the lungs... unlike other ceramic blankets. "No special requirements for dust control". I'm not even sure a
dust mask is required, I've not ordered some yet so I don't know.
This vender has a decent selection on ebay. I was probably going to order from this distributor because it's near me. Pottery stores carry it too.
Consider ceramic paper as well. Or wrap it in aluminum foil or something to maximize the insulative effect (trap air preventing convection of the air
within to outside the volume).
[Edited on 8-6-2019 by andy1988]
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