Sciencemadness Discussion Board

Is it necessary to fractionate PETN for plasticizing?

DennyDevHE77 - 9-8-2023 at 23:18

As far as I know, industrial plastic explosives with a high fill factor are made from powerful high explosives (PETN / RDX / HMX) of two fractions, the first is about 200-300 µm and the second is about 50 µm.

In my case, only PETN is available to me. Recrystallized from boiling acetone by a quick pour into water, it precipitates in the form of small long polyhedral needles (0.2-0.5 mm long and 0.05-0.1 mm thick). Such PETN has poor flowability, sticks to surfaces and is extremely low-density. Is it suitable for plasticization (a mixture of polyisobutylene and polybutylene with a crosslinker 10/80/10) into formulations of at least 86/14??

If not, can PETN be ground? As far as I know, already at 60% water content, PETN does not detonate from the detonator cap No. 8 and a bullet hit. Maybe it can be filled with water and simply ground in a coffee grinder at low speed (bullet speed 670 m/s, coffee grinder blade speed 20 m/s)? But how then to control factions? All the same, a coffee grinder is not a burr mill with adjustable grinding.

I also thought to draw a boiling PETN acetone solution into a large syringe (50 ml) and squeeze it sharply into ice water. But I believe that PETN will still fall out in the form of needles.

I will be very grateful to you forum users for your advice and suggestions.


[Edited on 10-8-2023 by DennyDevHE77]

Etanol - 10-8-2023 at 07:52

Quote: Originally posted by DennyDevHE77  
Recrystallized from boiling acetone by a quick pour into water,


You should do the opposite: water should be added drop by drop to the acetone very slowly with rapid stirring. When most of the needles stand out, you should break them with a mechanical stirrer in water-acetone liquid, and then continue diluting.

Microtek - 10-8-2023 at 09:06

Bimodal powders are necessary for the highest density because spheres (free flowing powder is roughly spherical) of uniform size cannot be packed to a volume fraction of more than about 74%. The rest of the volume must then be occupied by the binder/plasticizer matrix. In bimodal powders, spheres of a smaller diameter can fit into the voids and thus increase the volume fraction. In principle, higher modalities could approach 100% volume fraction (but then there would be nowhere for the binder matrix to go).
You can fraction a distribubtion of particle sizes using a number of sieves with a suitable incrementing mesh sizes.
In the context of plastique, you can mix the energetic filler with the binder and plasticizer solution, and then grind the mix while evaporating the solvent. This achieves much the same thing.

DennyDevHE77 - 10-8-2023 at 20:33

Quote: Originally posted by Microtek  
Bimodal powders are necessary for the highest density because spheres (free flowing powder is roughly spherical) of uniform size cannot be packed to a volume fraction of more than about 74%. The rest of the volume must then be occupied by the binder/plasticizer matrix. In bimodal powders, spheres of a smaller diameter can fit into the voids and thus increase the volume fraction. In principle, higher modalities could approach 100% volume fraction (but then there would be nowhere for the binder matrix to go).
You can fraction a distribubtion of particle sizes using a number of sieves with a suitable incrementing mesh sizes.
In the context of plastique, you can mix the energetic filler with the binder and plasticizer solution, and then grind the mix while evaporating the solvent. This achieves much the same thing.


What should be the solvent? As far as I know, pure gasoline is used for the plasticizer, but does PETH seem to be insoluble in it? That is, I do not understand how PETN will be crushed in it.

Thanks for the idea with sieves, it seems to be banal, but somehow I didn’t think of it.

Actually, that's why I asked the question, because I found many compositions with PETH with a filling of up to 88%. But the factions were not listed there. Many of the first plastic explosives contained ~75% of explosives, as you correctly write, otherwise their plasticity disappeared.

I decided that there are those on the forum who played with PETN plasticization and have experience in obtaining a density of at least 1.5

Microtek - 10-8-2023 at 22:38

PETN is not soluble in gasoline. The crushing is done mechanically, such as with a motar and pestle.

Laboratory of Liptakov - 10-8-2023 at 23:44

Microtek suggests the best way. Make a thick paste from PETN + binder + gasoline and grind this mixture mechanically. During this mechanical process (which usually takes 10 minutes to 1 hour) the gasoline will gradually evaporate. The paste will get thicker and the PETN grain will get finer. After all the gasoline evaporates, a high-density plastic is formed.....:cool:

Etanol - 11-8-2023 at 01:24

Quote: Originally posted by Microtek  
Bimodal powders are necessary for the highest density because spheres

It is very interesting how to create spherical PETN.

DennyDevHE77 - 11-8-2023 at 01:40

Quote: Originally posted by Laboratory of Liptakov  
Microtek suggests the best way. Make a thick paste from PETN + binder + gasoline and grind this mixture mechanically. During this mechanical process (which usually takes 10 minutes to 1 hour) the gasoline will gradually evaporate. The paste will get thicker and the PETN grain will get finer. After all the gasoline evaporates, a high-density plastic is formed.....:cool:


if it is grinded during plasticization, then how to control the fractions?

Is it possible to prepare two fractions of PETN in advance, mix them together, add gasoline + polybutylene, and mix them, then take out the "dough", roll it into thin pancakes, and leave it to dry on the windowsill for a week so that the gasoline evaporates?

Microtek - 12-8-2023 at 04:54

1)
You don't need to control the fractions, a distribution of grain sizes will naturally form during the grinding.

2)
Yes, of course. That is how it is done commercially, since it is easier at the larger scale.