ShotBored
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Binders for NC-Based Energetic Compositions
Hopefully I'm in the right place here.
I've got some pretty sweet NC-based compositions containing anywhere from 40-85% Nitrocellulose...as far as the binding is concerned, I've been using
2-5% ethocel with either IPA or EtOH (I seem to get better results with EtOH) and either 1-5% of Red Gum or Vinsol Resin. For small stars/tablets,
this seems to work fine. However when I try to press larger tablets in the 20 mm range, the stars are significantly weaker.
I'm trying to find a good binding system for NC that is solvent based, as I just don't have the patience to wait 72 hours for water to come off. I
also have to place the constraint that I use alcohols for binding, as most other solvents seem to have a pretty good chance of colloiding the NC which
is definitely something I don't want. Finally, I know the idea of using hexamine as a copolymer to phenolic resin (1:9 ratio) is fairly popular with
some, but I worry about hexamine's tendency to destabilize NC.
Some binding systems I've attempted (to no avail):
Polyvinyl Alcohol (2-5% range)
Polyvinyl Pyrrolidone (2.5-10% range)
PSO 810001 methyl hydroxyethyl- and methyl hydroxypropyl cellulose
Polyethylene Glycol (MW = 80,000)
Polyethylene Glycol - Polyvinyl Alcohol Co-Polymer
Epon 813/Versamid 140
Epon 813/Epikure 3140
Has anyone bound any Nitrocellulose formulas and successfully pressed them into tablets without post-press expansion? I'd be curious to see what
people have learned. I've also been looking into the possibility of crosslinking NC with IPDI and PEG as a bridging compound. Here is a paper
detailing this "Step-ladder" Nitrocellulose:
https://drive.google.com/file/d/1-f9w_dgI1eLmJ_yqvPxAVMvY_WX...
Any ideas for binders to be used with energetic, fibrous compositions would be appreciated.
[Edited on 5-7-2018 by ShotBored]
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Herr Haber
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What's preventing you from using NC as a binder itself ?
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ShotBored
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NC is my primary fuel in the composition, and in my experience binding with your primary fuel is bad practice, as it takes away from reactivity and
gives me unwanted burn characteristics.
That being said, I have looked into using a solvent gradient of various ketones (namely acetone or MEK) in small percentages to the ethanol(usually
1:99) and results have been better in terms of binding but I still see a good deal of post-pressing expansion in the tablets and loss of favorable
burn characteristics.
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DubaiAmateurRocketry
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I made a post regarding energetic binders few years back here:
http://www.sciencemadness.org/talk/viewthread.php?tid=27095
"For small stars/tablets, this seems to work fine. However when I try to press larger tablets in the 20 mm range, the stars are significantly weaker.
"
Do you want something that cures with it ?
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ShotBored
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Yeah, I took a look at your post before posting this and definitely got some good info from some of the articles. HTPB is a likely route of approach
next.
| Quote: |
Do you want something that cures with it ?
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To be honest, I'd be ok with anything that gives me:
1. good granules for ease of use when pressing into tablets or tubes
2. doesn't affect the burn characteristics of the formula, or if it does, the characteristics can be fixed with minimal reformulation
I am a little hesitant to mess with GAP (a peer of mine has a horror story or two about it), but I'd be perfectly content with either a binder/solvent
system or a cured binder system.
I did have some problems when working with the Epon/Versamid and Epon/Epikure epoxy/curing agent mixtures, in that the fibrous nature of the NC seemed
to impede the curing significantly. I attempted to suspend both the epoxy and the curing agents in solvents and ended up with a huge mess and some
ruined pans haha.
On the other hand, my testing with polyvinylpyrrolidone (PVP) led to granules that were fairly weak and would likely generate lots of fine
particulates over months of handling and jarring, yet seem to contribute a lot more "binding effect" in the dry compression stage of my process. I
think that something I want to look into is adding 1-3% PVP before wet granulating with HTPB.
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ShotBored
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A slight update to my inquiry, I've done some testing with a two-component binder system and have had a little bit better results. The compositions
contain ~58-80% Nitrocellulose. I added 2% dry ethocel to the composition as well as 2% polyvinylpyrrolidone before granulating with 50 mL of 1% (w/w)
ethocel in ethanol solution. The composition was thoroughly mixed and small additions of ethanol (10-20 mL) were used to get it to a consistency I
liked. Granules formed well on their own for the most part with simple hand-mixing, and a dry granulation was done with a -16 mesh screen to delump
and break apart any larger granules. About 10-20% of the mass of the composition was particulate/fine matter that fell through a 60-mesh screen.
I got good dry compression on a pneumatic press. We will see if there is any repress during priming and I'll let you all know how it turns out.
EDIT: Also @DubaiAmateurRocketry, I don't know if you've seen it, but a great article on nitrating HTPB was just released in Journal of Propellants,
Explosives, and Pyrotechnics. Their synthesis pathway and best physical/chemical results for the Nitro-HTPB was at a 5.8% nitration. More
interestingly, the used a synthesis pathway I wasn't really familiar with: Sodium Nitrite and Iodine.
Here's the link: https://onlinelibrary.wiley.com/doi/pdf/10.1002/prep.2017003...
[Edited on 9-7-2018 by ShotBored]
[Edited on 9-7-2018 by ShotBored]
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DubaiAmateurRocketry
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Yes, the iodine and sodium nitrite mechanism greatly reduce the cost of nitro-HTPB, it's a one-pot synthesis and the original inventor Pant et al in
2013.
https://onlinelibrary.wiley.com/doi/abs/10.1002/prep.2013000...
Based on the mol weight of ~2550 they gave (your paper), the HTPB is about OH-(C4H6)n-OH where n is ~46-47. And their end product had a molecular
weight of ~2750, that means 4-5 NO2 groups is added per molecule of HTPB.
Although not a great increase, it will make HTPB way more miscible with other energetics, and also greatly enhance the burn rate as compared to HTPB
alone.
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