Water trapped inside the star priming with phenolic resin?

[MinamotoKobayashi]

I rolled a 1,5 KG batch of Winokur 39J using only water and a very little bit of bioethanol 95 (some drops just to break the water surface

tension), then I primed it with Monocapa. I know, It was not necessary a so strong prime, but I eliminated every kind of prime from my lab except Monocapa because it ignite every kind of stars, especially if I replace magnalium with german dark, as Jopete suggest.

My fear is that I have created an issue: Winokur 39J need only water to be pumped (or rolled), but Monocapa need 70% water and 30% alcohol to activate correctly both dextrin and phenolic resin. The result of both activations is a prime hard like a rock. Well, the phenolic resin seems to have created a sort of waterproof diving suit around the water-based star and trapped inside the water.

I made a shit, or is it possible that the prime has maintained a minimum of porosity to allow the stars to dry, although more slowly, and with the risk that the aluminum will oxidize in the time ruining the final effect?

Edited July 9, 2020 by MinamotoKobayashi

[mabuse00]

I've got phenolic resin in my stock for years now but I never had the opportunity to try it out, so I can't provide practical experience with that in particular.

 

There are different types of phenolic resin out there, but I assume you use the alcohol soluble variant without crosslinking agent allready included.

 

 

Well, the phenolic resin seems to have created a sort of waterproof diving suit around the water-based star and trapped inside the water.

I agree on that, that's likely what happened.

 

 

I made a shit, or is it possible that the prime has maintained a minimum of porosity to allow the stars to dry, although more slowly, and with the risk that the aluminum will oxidize in the time ruining the final effect?

Only one way to find out...

It's your only chance anyway. Test the stars in a stargun before you waste a good shell/rocket for them.

Maybe the water is able to permeate through the plastic layer.

 

 

My feeling in general is that your idea of a universal prime is not ideal.

Using monocapa is OK, but in a classic waterbound glitter application it should be used with only the dextrine activated. The redgum/phenolic stuff is usually not activated, it's particles are just bound together with the rest. Using water and verly little - 5% or so - alcohol should be the way.

 

That way the moisture can easily pass through.

 

When using the monocapa for phenolic/alcohol bound stars, I would leave the dextrine out and fill the fuel value up with an according amount of more phenolic (I dont have the numbers in front of me now...).

 

If you want only one container of universal prime in your production, maybe just leave the binder out and add it later for every application...?

 

 

PS:

just curious, do you prime the monocapa itself?

Or is it really just one layer?

 

 

[Mumbles]

Dextrin and phenolic resin don't really work like that. You can't add a mixture of both water and alcohol and expect to fully activate both. They're inhibitory toward one another. Alcohol to some degree inhibits activation of dextrin, and 30% will likely partially deactivate it. Along the same lines, water inhibits the activation of phenolic resin. I would guess the phenolic is not the main binder in your prime, and it's mostly the dextrin.

 

What it really sounds like is that the prime dried faster than the star due to the addition of alcohol and sealed it in. You can create a barrier like this even with all water and without hydrophobic components. It's really best practice to fully dry your stars before adding prime.

 

The stars may still dry, but it will probably be slow going. You may want to monitor the mass of the stars periodically to check on them and monitor the progress. Some people will recommend rewetting the exterior of the star to re-dampen it (preferably with pure water), and then allowing the stars to re-dry naturally hopefully allowing normal evaporation and drying phase

 

You will also want to be on the look out for cracking or rattling. Cracking would be a sign of a reaction happening inside the star and it heating up and swelling. Rattling happens when the outside core dries faster than the inside, and the inner star shrinks slightly and pulls away from the prime. It sometimes makes for an interesting jetting effect.

[robbo]

When I have stars which may or may not be completely dry, I like to put some of them in a sealed container with indicating silica gel (or indicating "Drierite or equivalent) and wait a day or a week or more. Unless the moisture is permanently driven/sealed in, the moisture indicator will tell you if the water's diffusing out slowly.

Or just do what Mumbles says: wait and weigh.

I just love my indicator silica gel. It also tells me if my "sealed" containers are airtight...

[Arthur]

I've seen examples of prime only partially covering the surface. SO with a simple star, dip one side/end in prime then the rest can dry from one side.

 

It's rare to ever find a "fits all" approach that doesn't come with caveats, that's why there are so many formulations.

[justvisiting]

I don't have a whole lot of experience rolling stars, or using phenolic resin. From my limited experience, I've made an observation that may or may not be helpful. I rolled some purple stars with phenolic resin and used straight alcohol as the solvent. The stars stayed soft for weeks! Putting them in a hot van or in front of a fan did nothing to harden them up. Eventually, and I forget how long it took, they finally hardened up.

 

I did a little experiment after that. I took straight isopropyl alcohol and dissolved the phenolic resin to form a syrup. That was many months ago, maybe a year. I've poured it on parchment paper, exposed it to heat, and eventually put the 'pancake' of resin on a warm air register. After all this, it is STILL soft! I'm talking about a 'pancake' of resin a sixteenth of an inch thick.

 

I realize that my experiences are not the typical ways that phenolic resin is used in pyro, but I think it's helpful to understand the physical properties of the chemicals we use. Then later if we have a problem, it might be easier to solve. My very limited experience with phenolic resin indicates that it should be used with a minimum of solvent, so it it doesn't form an impermeable skin that prevents drying.

[Carbon796]

How long have they been drying ?

 

Have you checked them in a sealed ziploc bag in the sun ?

[MinamotoKobayashi]

x Mabuse00: Tonight I made a little mortar and I will test the star.

It is really a good idea to make Monocapa without any kind of binder and add them later, choosing between dextrin or phenolic resin!

Following the Jopete's directive, I can use only 1 layer made of Monocapa of about 1mm thickness, but only at condition that I replace Magnalium with German Dark.

 

x Mumbles: ... and now I'm really confused!

For about 2 years, following the Jopete's hints, I used both phenolic and dextrin wetting the mix with 30 alcohol and 70 water.

The Jopete's stars need this mix.

A day I asked him if I can omit the alcohol or the dextrin. He replied that I could but the stars would have been weaker.

This admission is the exactly opposite of the Your one.

The only disvantage using some kind of phenolic resins is that the mix burn fastest, so he advises me to use red gum for the stars and phenolic resin only for the Monocapa.

Also, water and alcohol form an aziotrope, and for this reason part of water can be trapped inside the star (thanks to NeighborJ for the hint).

And this confuses me even more ...

 

About to completely dry the stars before to prime them is another cause of confusion.

Some schools insist to prime the stars while they are wet to avoid the detachment of the star prime during the drying process or during the shell break.

Effectively I suffered partial prime detachment in some stars if applied over a completely dried ones!

 

I weight the stars every 24 hours. A 1,5KG batch of Winokur 39J stars lose some grams every day.

I suppose this means that the prime is not waterproof and the drying process is still in progress.

The stars are now heavy like a stone. I risked to put one of them in my electric dehydratator at 70* for one hour.

and I have made a single shot launch: the star was not ruined.

Here You can found the launch video:

 

https://www.amateurpyro.com/forums/topic/13627-winokur-39j-single-shot-and-5-shell-sugar-rocket-powered/

Edited July 10, 2020 by MinamotoKobayashi

[Mumbles]

I would wet a small sample of each binder with your solvent mix and see how they behave. You may want to do dextrin and pure water and phenolic and pure alcohol as a control. Maybe I'm mistaken or have been mislead all these years. I'd bet the dextrin will still be sticky, while the phenolic might not do a whole lot with the mixed solvent.

 

I've never had stars detach from the prime, even when using totally different/incompatible binders and solvent systems. I do tend to get the outside of the star a little wetter when I'm first going at it though. This can dissolve or soften the very exterior and make a sort of mini-step prime. If I'm not doing that, I use slurry priming which sticks to everything.

 

Depending on which alcohol you use, the azeotrope is fairly alcohol heavy. 95.5% Ethanol/4.5% water or 91% Isopropyl Alcohol/9% water. The star mix should get more water heavy as it dries.

 

Glad to hear they're still drying. They'll get there.

[kingkama]

In my experience, the stars must to be bone hard, perfectly dried, then well wetted with solvent then primed, i also use a personal super prime with boot dextrine and phenolic, this mix is birth by error but i find perfect, porosity of prime depends from charcoal mesh, may be that you works the stars in roller for too much time, aspect is not perfection, stars rough outside catch fire well than stars perfectly smooth. I also use a alcool water mix, sometime when no magnesium is in composition i add a bit of aceton to speed up the drying time, because, i use pasta as core and pasta tends to expand if there is too much moisture or drying time is too long. Edited July 10, 2020 by kingkama

[MinamotoKobayashi]

Hi friends.

I will try to make the Jopete's stars in a new way: only alchol for the coloured mix and alcohol plus water for the Monocapa.

The main concern is drying completely the stars. Using only alcohol permit me to dry faster the stars without the water trapping issue and avoiding a possibile aluminum oxydation.

Besides this, I can dry the stars directly in my electric dehydratator at 70* without the risk to ruin the effect.

So, when the stars will be hardened and totally dried, I will follow Mumbles' suggestion overwetting the dried stars with a mix 70/30 to firmly apply the Monocapa layer.

Surely in that way I cannot risk to trap water inside the star, and I will still get very hard stars thanks to the fully activated Monocapa.

 

Now I have an important question for You: since dextrin will not be activated in the star due to the absence of the water, can I omit it,

or in some way dextrin act like an added fuel in star composition? My fear is that the absence of dextrin will unbalance the original formula.

My idea is to leave the dextrin in the mix anyway. Since bio ethanol still contain 5% of water (for the aziotrope law), part of the dextrin should be activated.

I think so because when I mill BP in my ballmill soaked in bioethanol and let the slurry compound dry over a wax sheet for an entire night, I will find an hard-to-break

BP plate! This surely means that the 5% of the water present in bioethanol is sufficient to partially activate dextrin.

So why eliminate it? It is an added value

Edited July 10, 2020 by MinamotoKobayashi

[Carbon796]

Divide the dex amount in half, and then use PR in its place. That will be a very close approximation for fuel value. And, probably a better binding prime, since its kinda lacking in PR for ideal binding strength.

 

Then just use straight denatured alcohol, for binding. This will give you fully activated PR, and a stronger bond.

 

Same goes for Dex, if you want its full strength for binding. Use straight distilled water and no alcohol.

Edited July 10, 2020 by Carbon796

[MinamotoKobayashi]

Hi Carbon796.

So, for example, this is the original Jopete's RED2 formula:

 

0.24 Potassium perchlorate

0.24 Strontium nitrate

0.11 Strontium carbonate

0.10 Red gum

0.12 Parlon

0.15 Magnalium, 230-mesh

0.04 Dextrin

1.00 Total

If I replace red gum with phenolic resin I will obtain a too fast burning star, so I will keep the original formula.

I assume that red gum and phenolic resin can be switched maintaining the same percentage.

So I can omit the dextrin and add +0,02 of red gum, for a total of 0.12 ... right?

Edited July 11, 2020 by MinamotoKobayashi

[Carbon796]

Phenolic Resin has a slightly higher fuel value than Red Gum. Some people replace it 1 to 1. But technically it's .83 PR to 1 RG.

 

PR is a "better" more energetic fuel than RG, so color and KP based comps will sometimes be slightly faster.

 

Yes that is correct. if you omit the dex. Because, Dex has about half the fuel value of RG.

Edited July 11, 2020 by Carbon796

[kingkama]

In perchlorate e chlorate stars dextrine works also as fire retardant, stars burns slower, that is useful to avoid swimming stars

[Mumbles]

Dextrin has some fuel value. It's usually added in such a small amount to be fairly negligible. It's essentially a polymeric sugar. Some people like to ignore it. I don't have a good answer for you, but when I just leave out dextrin it tends to burn a slightly different tinge to me. I may be going to deep, but most star comps are balanced to burn slightly to somewhat fuel rich relatively to CO2. This produces a reducing flame. This promotes the colorant species we want versus things like BaOH and SrOH for instance that emit colors not quite what we want. Dropping the dextrin totally may shift it in an undesirable direction. I'm sure theres a conversion to phenolic or red gum, I just don't know it off hand. It's probably minor, but it's something I care about and notice.

[MinamotoKobayashi]

Hi Mumbles.

What happen if I keep the dextrin in the original formula but I do not activate it with water? The formula will rest balanced anyway?

Considering also that the small percentage of the water present in the ethanol will activate a little bit some dextrin.

Edited July 11, 2020 by MinamotoKobayashi

[mabuse00]

The dextrine's fuel value is independent from wether it's activated or not.

Edited July 16, 2020 by mabuse00