Low specific gravity Flame retardent compound

[SometimesStumped]

I am new to this forum and look forward to learning and sharing knowledge with everyone.

I am currently working on a project where the lower specific gravity of the compound the better. This job is a rubber coated fabric (both sides) and has a fire retardancy callout. The fabric is a nylon/Kevlar that is RFL treated (currently for neoprene but if needed that can be changed). The compound I am currently using is a neoprene containing Hydral 710, antimony oxide and a chlorinated paraffin oil and has a gravity of 1.40. My problem is, this job has a very low overall weight callout and the compound along with the fabric limits me to a very small amount of compound on each side of the fabric (calendared on). This small amount is barely enough to cover the fabric and does not give me much leeway at the calendar. I would like to create a compound that has a lower specific gravity (cannot change the fabric other than the type of RFL coating). The fire retardency callout is 8 sec max to extinguish with 2 sec max afterglow. I will be trying an RFL treatment that is supposed to be fire retardant but unsure what it will do to my adhesion and how much weight it will add to the fabric (which would affect the amount of compound I can put on if it goes higher).

Type of rubber used is open. Cost is not a limiting factor (at least not at this point). The lower the gravity the better. Fire retardant type is also open, there are no restrictions as far as toxicity, etc. at this point.

Thank you for your help.

 

[GrahamBennett]

Aluminium trihydrate (ATH) has an SG of ~2.4 compared with 5.5 for antimony trioxide. This means you can add much more ATH to your formulation and still have a much lower compounded specific gravity.

 

[SometimesStumped]

Our initial formulation is using the 3:1 ratio (12 pph:3pph) of ATH to antimony oxide. Although the compound extinguishes it fails the callout and has a Specific Gravity higher than what I would like. Even taking out the antimony altogether I am still high on gravity and failing retardancy. That is why I am looking for another type of fire retardancy additive other than ATH. I am only familiar with ATH systems since that is all we use (and very limited). Are there any other types of fire retardancy additives available that have a lower gravity?

 

[Compositepro]

Boric acid is 1.4 sg and releases water at a lower temp. You can get it really cheap at many stores as a roach killer.

 

[tom1953]

Can you change the polymer? EPDM has a SG of ~0.86 vs. 1.23 for neoprene, SBR is ~0.93. Of course, with the chlorine in the neoprene, it's inherently better for flame retardancy.

Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[SometimesStumped]

Yes I can change the polymer and I have thought about EPDM. SO far the issue I have found with the EPDM is adhesion to the fabric. Not sure if there is a RFL treatment specifically for EPDM. I have found some EPDMs will adhere to a neoprene RFL but it does not work in this case, I already tried it. I have a 16 lb min. adhesion to meet with approx. .011" compound.
I have also thought about an SBR but looking for an alternative to ATH due to its high gravity and need for a heavy loading. My other thought, if I went with SBR and ATH fire retardant, would be to add PVC for the chlorine content. But I still feel I would end up with a high gravity.

 

[GrahamBennett]

If you can change the polymer, how about using chlorobutyl? This will adhere well to textile substrates.