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Topic: Help with Composition Percentage by Weight of Buna N Rubber  (Read 429 times)

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Offline zkober

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Help with Composition Percentage by Weight of Buna N Rubber
« on: September 22, 2020, 05:09:40 PM »
Hi All,

I am a physicists working on creating a Monte Carlo simulation of a proton beam irradiation experimental setup. I am using TOPAS MC to create this simulation. For our experiment we used a target holder with some some rubber seals made of Buna N (Nitrile) rubber. In order to implement this material into the simulation I need to know the composition by weight as well as the density. For example, a typical breakdown of 303 Stainless Steel that I found is: 17-19% Cr, 8-10% Ni, 0.15% C, 2% Mn, 0.75% Si, 0.045% Ph, 0.03% S and 0.1% N with a density of 8.06 g/cm^3. I tried to find this information online but am struggling to find what I am looking for as there seems to be a lot of variance in how synthetic rubber is made. As per the spec sheet from the supplier I am hoping to get this information for BUNA N NITRILE 70 DURO SHORE A, BLACK.

Please let me know if anyone can help.
« Last Edit: September 22, 2020, 05:45:14 PM by zkober »

Offline Enthalpy

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Re: Help with Composition Percentage by Weight of Buna N Rubber
« Reply #1 on: September 23, 2020, 04:29:44 PM »
True: polymers are extremely variable. You would have decent chances with a simple one like PETP. Though, many polymers, and more so for elastomers, are blends or copolymers. The proportion of monomers changes the atomic composition of your elastomer.

That one seems to be nitrile rubber (is it?)
https://en.wikipedia.org/wiki/Nitrile_rubber
See the picture on top right at Wiki? Depending on m/n, the proportion of nitrogen will change. also, elastomers can be loaded with many things like carbon black.

But if your aim is to evaluate a penetration depth for the protons (not a damage amount!) then you could live with an approximate composition. If some nitrogen replaces carbon, it will change the penetration depth little. So you could just count the C, N and H atoms from both the acrylonitrile and the butadiene on Wiki's page and deduce a mass proportion. With a little bit of luck, (C+N)/H is about the same for both monomers, and then m/n has little effect on proton stopping.

For more accurate values, you could let analyse a sample and get an atomic composition.

==========

I doubt about your C and N amounts in 303 steel.

Offline zkober

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Re: Help with Composition Percentage by Weight of Buna N Rubber
« Reply #2 on: September 23, 2020, 04:54:32 PM »
Hi,

Thank you for the response. I believe that wiki link is correct. I appreciate your input and I will try to implement following your suggestion. I will be sure to validate my sources for the 303 steel as well.


Offline Corribus

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Re: Help with Composition Percentage by Weight of Buna N Rubber
« Reply #3 on: October 01, 2020, 11:09:46 AM »
For properties of commercial polymers, you either need to (1) contact the manufacturer or (2) make measurements yourself (or pay someone to do it). Manufacturers may not be forthcoming with information they see as proprietary, but basic information may be available as part of spec sheets, e.g. density. Keep in mind that spec sheets are usually based on a tolerance range and may not reflect exact properties of specific lots or batches. I suggest you either collaborate with a polymer scientist to measure these values for you or pay a contract lab (e.g. Evans Analytical) if you need precise and accurate information for your polymer sample.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

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