Sciencemadness Discussion Board

hows this calculated ? nitration of htpb question

DubaiAmateurRocketry - 22-8-2017 at 07:44

http://onlinelibrary.wiley.com/doi/10.1002/prep.201300031/ab...


in this paper, they said after nitration, avg molecular weight of the HTPB polymer became 2500 >> 3100.

they also said 15% of its double bonds are nitrated, however if you try to compute the weight of the polymer but on 15% of its double bonds adding a nitro groups, the avg mol weight does not seems to be as high as 3100?

am i doing it wrong or can someone help me confirm? thanks :D



[Edited on 22-8-2017 by DubaiAmateurRocketry]

Bert - 30-8-2017 at 06:14

I would like to read that paper... And find what physical difference nitration may cause to bonding, strength and elasticity of the cured material.

PBX with an active binder?

hissingnoise - 30-8-2017 at 11:32

Introducing nitro groups adversely affects the elasticity of htpb, with higher nitration destroying it completely.

PHILOU Zrealone - 30-8-2017 at 14:38

Quote: Originally posted by DubaiAmateurRocketry  
http://onlinelibrary.wiley.com/doi/10.1002/prep.201300031/ab...


in this paper, they said after nitration, avg molecular weight of the HTPB polymer became 2500 >> 3100.

they also said 15% of its double bonds are nitrated, however if you try to compute the weight of the polymer but on 15% of its double bonds adding a nitro groups, the avg mol weight does not seems to be as high as 3100?

am i doing it wrong or can someone help me confirm? thanks :D


I have a big interest into I2/NaNO2 nitrating media... so I can share a bit of my knowledge about it...
==>@DAR, I would also like to read the paper if you don't mind?

(I have already typed this 3 times the last days but my calculation and post were lost while posting... so this time I copy my reply prior to posting and I haven't put the full calculations)...

You are right assuming15% of the bonds are nitrated, then the Molecular weight comes closer to 2780 if the amount of n units remains the same (I found it to be 46-47) and if the polymer is wel n-PNB/PB (linear poly-nitro-butadiene-polybutadiene copolymer).

The molecular weight comes closer to 3700 if the amount of n units remains the same but that we talk about n-PINB/PB (linear poly-iodo-nitro-butane-polybutadiene copolymer).

So there are only a few possibilities:
1°) They have made a wrong calculation.

2°) Their determination of the molecular weight is false.

3°) They have more than 15% nitro introduced.

4°) They have a mix of nitroalkene (when HI is lost) and uncomplete dehydroiodination from starting addition product (thus iodo-nitro-butane moeity)...
The addition step of I2 + NaNO2 passes via transcending I-NO2...
So -CH=CH- + I-NO2 --> -CHI-CH(NO2)-
and
-CHI-CH(NO2)- <--==> -CH=C(NO2)- + HI
Of course remaining I atoms will increase the MW markedly

5°)The number of units changes and becomes > n = 46-47
This may occure during the addition of I-NO2 via I2/NaNO2
Since I-NO2 may add to double links via two pathways:
-via ionic splitting I-NO2 <==> I(+) + NO2(-)
-via radical splitting I-NO2 <==> I° + °NO2
Both may induce further polymerisation of the 85% remaining freely accessible alkenic double links and of the <15% remaining nitroalkenic ones...

Voilà I hope this helped.


[Edited on 31-8-2017 by PHILOU Zrealone]

Bert - 30-8-2017 at 19:10

Quote: Originally posted by hissingnoise  
Introducing nitro groups adversely affects the elasticity of htpb, with higher nitration destroying it completely.



After curing, does nitrated HTPB adhere adequately to such things as crystals of oxidizers, spheroidal aluminum and/or molecular explosives such as RDX? How is DENSITY of the cured rubber affected...

Is the loss of elasticity beyond remediation by additional plasticizers? I do recall mention of energetic plasticizer here in the past as well.

Considering the relatively small % by weight of binder to metalic fuels & oxidizer in composite rocket fuels, there are only small gains in propellant performance available from such methods?

hissingnoise - 31-8-2017 at 06:22

Quote: Originally posted by Bert  
Quote: Originally posted by hissingnoise  
Introducing nitro groups adversely affects the elasticity of htpb, with higher nitration destroying it completely.
After curing, does nitrated HTPB adhere adequately to such things as crystals of oxidizers, spheroidal aluminum and/or molecular explosives such as RDX? How is DENSITY of the cured rubber affected...

I don't have the original ref., but even a single nitro-group affects viscosity.

More here.


DubaiAmateurRocketry - 31-8-2017 at 21:04

I thought this paper is easily accessible with libgen or sci-hub, anyways here is the paper.

NHTPB does allow it to be miscible with many other plasticizers to allow for better viscousity, also better OB means more binder can be added in the place of the oxidizer, so i would not be worried from the viscousity changes.

Maybe synthesizing NHTPB from a lower starting mol weight can also help with that. the paper used htpb of 2500+ mol weight, maybe 2000 would produce better results.

Attachment: paper.pdf (703kB)
This file has been downloaded 514 times

PHILOU Zrealone - 13-9-2017 at 01:32

@DubaiAmateurRocketry,
Thank you for the document ;)