High Temp Plastic for Firefighting

[RescueMe]

I am a firefighter developing a product for personal protective equipment. The piece I am creating is a knee pad with a plastic impact shell and foam padding. I have very little knowledge on the vast variety of plastics available. There are limitations to what I can use. The plastic needs to be fire resistive with a melting point of 500 deg F. It will need to have good impact qualities and not be brittle. The plastic shell will be about 0.1875 thick. I will need to be able to use an industrial machine to stitch the padding to it. Does anyone have suggestions on what type of plastic would be best for this application? We will most likely be injection molding this but a thermoform is possible too.

 

[IRstuff]

Why not the same plastic used for your helmets?

http://www.bullard.com/V3/products/fire_service/choosing_a_helmet.php

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[KENAT]

RescueMe, where does the 500°F requirement come from, and what is the context?

Is the plastic really going to be in the 500°F environment long enough for it to reach that temperature? I know you guys are tough but if exposed for long won't you cook too?

Or is it more a case of having to kneel on a hot surface for short period or similar? If so how much damage to the knee pad is permissible?

Is having an over mold of high temp silicone (e.g. some oven gloves, baking sheets etc.) to serve as a thermal barrier an option?

In fact, perhaps a 'stiff' shell completely overmolded with suitable silicone may be an option - on the outside surface the silicone is insulating the 'stiff' core, while on inside it is the padding to the users knee - with the benefit of giving even more thermal insulation.

http://info.craftechind.com/blog/dont-sweat-it-these-4-high-temp-plastics-can-take-the-heat

You could look into the plastics used in oven cookware though most are for stove top not oven use.

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[RescueMe]

Thank you both for your input.

The NFPA has standards for firefighting equipment. Although accessories like the knee pads are not explicitly covered in the standards many firefighters will be weary of anything that is less than the standard for the rest of their gear.

NFPA 1971: STANDARD ON PROTECTIVE ENSEMBLES FOR STRUCTURAL FIRE FIGHTING AND PROXIMITY FIRE FIGHTING
NFPA 1975: STANDARD ON STATION/WORK UNIFORMS FOR EMERGENCY SERVICES.

The standard states that in testing the plastic cannot melt to the point of dripping at temps up to 500 deg. You are correct that at that temp inside of our gear we have bigger problems but that is the standard.

I will be using a closed cell silicone foam for the padding that will be attached to the plastic. Looking at cookware plastics is a good idea.

 

[John2025]

CPET ?

 

[1gibson]

Hard shell - whatever a plastic spatula is made of (I would guess glass filled nylon, but temp range seems too low?) then a layer of silicone all over.

If the plastic is completely encased in silicone, it's not going to be dripping, is it?

 

[KENAT]

OK, so the plastic can't melt to dripping - is there any time limit?

Like wise does the test apply to the raw material or assembled items?

http://www.siliconeproductdevelopment.com/

gives some ideas on the over molding I mentioned.

You might want to check if Bakelite would work for you, fear it may be little fragile/brittle but maybe. Some Bakelite is cloth reinforced, not sure if you could use Nomex cloth or something as the cloth.

http://www.stug.com.au/materials/engineering-plastics-properties/min-max-operating-temperatures.php

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[btrueblood]

Polyimides (Kapton is one brand name)
Polyetherimides (Ultem)
PTFE (Teflon)
PEEK, and some of its related compounds PEKK, PEK, see

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

Some Polyamide-imides (Torlon is one brand)

All of the above are quite expensive as plastics go. Technically, neither polyimide or ptfe are true thermoplastics, but they can be molded into simple, open shapes/shells using compression molding.

Like Kenat said, a lot of fire suits and flexible clothing articles use Nomex, or more technically, meta-aramid fabrics (I think Twaron is a competitor); the related and more well known Kevlar is also fire resistant, but is susceptible to degradation by hydrolysis, i.e. water and steam can break it down over time, which is why bullet proof vests using it can only be laundered a certain number of times before being retired, and why you should never buy a used vest.

Some types of epoxy and phenolics (Bakelite) can withstand those temperatures but with some charring occurring, they are probably the thermosets used for fiberglass composite helmets, as they need some reinforcement in order to give them some strength and impact resistance.

 

[Pud]

For low cost tooling (relatively), inherently flame retardant, non-melting and lowish cost, I would suggest a mineral filled thermoset phenolic or urea as above (aka "Bakelite", which is a trade name).

Cheers
H



www.tynevalleyplastics.co.uk

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[Pud]

Forgot: you won't be able to stitch it but holes can be moulded in to fix stuff to it.

h

www.tynevalleyplastics.co.uk

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