Phenolic Resin Stars Don't Dry?

[LiamPyro]

I searched around a bit regarding this issue, but couldn't find any definitive solutions, so here we are. I made up a batch of Pirotex's purple (see formula) and, after many failed attempts at rolling microstars starting from riced granules and wetting with 99% isopropyl alcohol, I gave up and just wet the batch with more alcohol and pressed it through 1/8" hardware cloth to make "mouse turds". Phenolic resin was from Fireworks Cookbook. I know alcohol/resin stars can have a tendency to skin over and become driven-in, so I gently dried the stars at room temperature (~68 deg F) for a few days before gradually incorporating heat (up to 120 deg F). However, the stars never dried! They remain almost as gummy and soft as when I first cut them, and this was almost two weeks before the 4th of July. Granted, I haven't been force-drying them the whole time, they've just sat on a screen at room temp since the end of June. What can be done? And what should be done to prevent this problem next time? I thought about using a different alcohol like methanol for it's higher vapor pressure /faster evaporation, although this might intensify the skinning over phenomenon. Maybe adding some dextrin and wetting with water is the best option. How do folks successfully bind stars with phenolic resin?

 

Pirotex Purple:

KClO4 - 44%

CuO - 20%

MgAl - 12%

PVC - 8%

SrCO3 - 6%

Phenolic Resin - 10%

[Almostparadise]

I had some do almost this exact thing. They eventually ended up drying after multiple weeks. I haven't rolled w it since. I put them in my dehydrator, a few sessions worth. They'd come out soft from being heated but each time they cooled down they were a little bit harder. 

[Zumber]

2 hours ago, LiamPyro said:

I searched around a bit regarding this issue, but couldn't find any definitive solutions, so here we are. I made up a batch of Pirotex's purple (see formula) and, after many failed attempts at rolling microstars starting from riced granules and wetting with 99% isopropyl alcohol, I gave up and just wet the batch with more alcohol and pressed it through 1/8" hardware cloth to make "mouse turds". Phenolic resin was from Fireworks Cookbook. I know alcohol/resin stars can have a tendency to skin over and become driven-in, so I gently dried the stars at room temperature (~68 deg F) for a few days before gradually incorporating heat (up to 120 deg F). However, the stars never dried! They remain almost as gummy and soft as when I first cut them, and this was almost two weeks before the 4th of July. Granted, I haven't been force-drying them the whole time, they've just sat on a screen at room temp since the end of June. What can be done? And what should be done to prevent this problem next time? I thought about using a different alcohol like methanol for it's higher vapor pressure /faster evaporation, although this might intensify the skinning over phenomenon. Maybe adding some dextrin and wetting with water is the best option. How do folks successfully bind stars with phenolic resin?

 

Pirotex Purple:

KClO4 - 44%

CuO - 20%

MgAl - 12%

PVC - 8%

SrCO3 - 6%

Phenolic Resin - 10%

I have made red stars before many times which contains phenolic resin (fine powder 200 mesh) but I often bind them with 4 percent dextrin and water as a solvent. It drys up in 4 to 5 days depending on weather.

Edited July 9 by Zumber
Spelling correction

[PyroGnome]

I've used a 50/50 iso/acetone solvent when rolling phenolic stars and had no issues drying them that way.   The thickest layers got stuck drying during a week of heavy rainstorms and 100% humidity but were dry in a couple of days anyway.  Acetone evaporates off so quickly that the previous layer of comp is substantially dry by the time you're spritzing them and rolling on more comp so there isn't very much chance for anything to be driven in.  Both solvents have roughly the same explosive ranges in air and are equally flammable so it's not like you're changing much.  Isopropanol can even form explosive peroxides on the shelf over time just like acetone, so even that awful aspect isn't improved any.  Isopropanol was 99.9%.

One difference though:  I didn't use anywhere close to 10% phenolic resin for these stars.  I'd have to look at the formulas but the phenolic bound dragon egg cores were rolled on mustard seeds and only contained 2% phenolic with no other binder.  For the "dragon flower" layer I stuck with the red gum from the original formula since I wanted the slaggier burning to help the center core ignite and 50/50 solvent again. I split out the ones where multiple cores had stuck together early on that had an interesting mini-shell-core effect and rolled a hybrid formula I came up with by balancing some things between a Pihko blue and Naud blue over them.  Those were especially heavy thanks to big clusters of bismuth-based microstars at the center.  I was going to do 50/50 again but there was parlon in the mix and I wanted to avoid that gummy mess so I just used alcohol.  That mix also only had 2% phenolic in it.  I rolled them up to a range of 0.75-1" in a single go and they were dry in a couple of days.  I test primed stars by hammering them out of fairly tight fitting tubes with too much benzolift for their size...  none of them broke up.  I couple had a chunk of the star comp layer break off while rolling them but they mostly held up to that too. 

The other stars got a layer of a slightly modified version of the chinese / stanbridge microstar blue formula (swapped out the HCB for PVC) with the 2.5% dextrin replaced with phenolic, I set half aside like that, and finally went immediately to rolling a barium sulfate green which I wasn't too impressed by directly on top of the blue.  I think I swapped 4g of red gum it wanted for 3.5g of phenolic resin but I'd have to check my notes, I may have left it high on that one since it was such a dense composition and I was rolling over another fairly thick layer of comp that wasn't dry yet. I lost maybe 8 stars to having the roller speed too high and both outer layers shearing off from a high fall but that was better than I thought given the weight of the stars at that point.   Both of those layers were also 50/50 iso / acetone. 

The acetone somewhat mitigates the issue isopropanol has as a single-solvent system...  acetone can absorb water from the atmosphere but doesn't have any particular affinity for doing so...  isopropanol forms a 91% azeotrope with water so it guzzles it until things are equalized.  I keep my bottles  open long enough to splash what I think i'll need into a 250mL beaker and then close them up again.  Breaking azeotropes is non-trivial and with something like isopropanol it's cheaper just to order more if it gets wet and use the wet stuff as the 25% alcohol in dextrin-bound stars. If your iso was less than 99.9% in the first place or was just old and had absorbed water due to a poorly fitting lid (the bottles they sell iso in are usually horrible, I try to remember to put teflon tape on the threads right after I open them to keep water out longer) you might have had trapped water.  The 91% stuff will probably still dissolve phenolic but the water will still be there lowering the evaporation rate and probably making it harder for the azeotrope to escape from the hardened plastic binder.

Anyway my point with all that is I think you'll have far less problems with phenolic being driven in if you cut the amount down to about 1/2-1/3 of what you're using (even for cut stars 10% of any binder is probably overkill (I've only used that much when it was parlon that was already there as the chlorine donor and I didn't feel like pre-treating magnesium) or just use a 50/50 iso / acetone mix.  Red gum bound stars could get away with having higher percentages like that and still be bound by alcohol because it's a much dirtier binder and doesn't form the same level of solid layer when it dries as the plastics.  The methanol thing would probably work but I wouldn't work with enough methanol to make cut stars unless I had plenty of the antidote for methanol poisoning on hand and preferably in my system in advance (hint:  It's large doses of ethanol).  Always keep in mind that the organic gas cartridges on your 3M mask only provide a multiplier on the exposure level numbers of ~10x.  I think the tests with comets on the connecticut pyro site indicated that ethanol and methanol were kinda bad at binding phenolic too, but they tested with standard wetting and pressing methods.  The patents that use phenolic as a binder almost always pre-dissolve it in ethanol at 50% by weight then dump that into a paddle mixer with the rest of the comp and finish getting the consistency right with more alcohol from there.  I think you'd need to do something similar with methanol or enough of the stuff won't dissolve before it evaporates and you'll get a weakly bound star.  I do the 50/50 thing with acetone because acetone is nearly as good a solvent for phenolic so I can get an evap rate closer to a lighter alcohol without having to jump through extra hoops. 

 

[Carbon796]

I've always used Denatured rather than Iso. I've also only used phenolic from Jim W/ctpyro. No idea if the cookbook stuff is any good.

If your trying to heat cure them. You need to add hexamine and get the temp a lot hotter.

Phenolic doesn't always play well with carbonates. Which was discussed somewhat recently.

[LiamPyro]

Interesting, thanks for all the replies. The 10% resin content is “high” in the sense of its role as a binder, but it’s also serving as an organic fuel, so I can’t just cut the percentage down arbitrarily. I thought about using an acetone/isopropanol blend but was worried about it dissolving the PVC creating an even stickier mess. I think my best option may be to add some dextrin and bind with water. Carbon, what’s this about phenolic resin and carbonates? 

[Carbon796]

 

[pyrokid]

Earlier this spring I hand rolled a number of colors to 5/16" from the Jopetes document. I followed the substitutions from APC member braddsn: 1:1 substitution of phenolic resin (ctpyro sourced) for red gum. Rolled with 91% isopropyl alcohol. The red and orange were carbonate based. I added additional 2.5% PVB based on prior experience. I had concerns during drying because I was able to crush the stars like Skittles candy, not shattering but staying in one piece like some sort of putty; basically some unfounded apprehension that the phenolic was retarding the solvent evaporation. In the end, all the stars dried within 4 days and performed well. PVB is an excellent binder for rolled color stars in my opinion.

[Mumbles]

I've heard about the carbonate thing before as well, but don't have enough experience with phenolic stars to really speak from much experience. I won't pretend to understand how it works, but it may be worth noting that the material we use in pyro is a novolac type phenolic resin. These are phenol rich formulas, acid catalyzed, solid resins, and can be thermally cross-linked. Being acid catalyzed, maybe fairly alkaline reagents can start causing weird effects.

The other type of phenolic resin is called resole. It's base catalyzed and typically a liquid.

[Carbon796]

PVB when added to a phenolic binding system. Adds toughness/durability to a heat cured/crosslinked, bound comp. In extreme pressure/velocity ( Probably also mass ) situations.  Phenolic binding alone can be too brittle. Such as Jim W's/CYPyro's  36", 48" and Guinness W/R shells.

https://youtu.be/ZyjKbx36k90?feature=shared

PVB can also be used as the sole binder in a comp. Without out any phenolic present.

If the issue is the carbonate in the comp. They will eventually harden up. But it may take months, or more. They will also turn much darker. ( If this is solely a air dry comp and not heat cured / crosslinked )

Edited July 19 by Carbon796

[snapper]

only use alcohol if lightly dampening to pump, use acetone for wetting for cutting or grating.
On a hot day dried in the shade with a breeze they will harden fully dry in hours using these methods unless water is introduced
The worst mess I ever created was over wetted stars with redgum/shellac binder using alcohol and I tried to press it in a star plate. I was scrubbing those star plate holes and pins for over 2 hours. Learned a lesson that day, plan way ahead and to be patient in that not ever mistake is a failure if you take a step back.

[braddsn]

FWIW, I have rolled hundreds of pounds of stars using a 1:1 substitution of phenolic for redgum, wet with 91% isopropyl. They always were rock hard, I then primed with Jopetes Monocapa. Before I started using phenolic, I had previously only used dex for a binder, and with these stars the Monocapa sometimes had problems igniting fast-moving stars (stars from flash boosted shells). For me, the phenolic solved 2 issues... 1. The stars dried 10x faster, and way more consistently, and 2. Lowered ignition temperature, allowing a single layer prime (Monocapa) as opposed to 2 layer prime that was required with dex bound stars. Dex is fine as a binder but I was building hundreds of shells, and the efficiency and consistency of phenolic was a game-changer for me! 

[snapper]

A small fraction of hexamine may be required to harden a higher % of phenolic for proper hardening, I would try the 50/50 iso/acetone first or just straight acetone if cutting or rolling. Hydraulic pumping will push excess liquid out so they rapidly harden.

[Carbon796]

A " small fraction " of hexamine. Isn't going to help it harden any quicker. If it isn't heat cured. 

If you are " pushing excess liquid out " while hydraulicly pressing stars or comets. You are NOT doing something correctly.

Edited September 4 by Carbon796