Stars Not Hardening

[Almostparadise]

Ive had some issues lately. I rolled some red and orange stars for which the formulas i came across on a skylighter web page. Originally from Jopetes they had been reformulated to work with phenolic resin. I rolled them w 99% iso to about 5/16" to use as cores. It's been 5 days and I can still more or less split one in half w a fingernail. The air temp and humidity are normal. I tried the oven at 150° for 45 minutes hoping in vain they would harden upon cooling. The phenolic resin is from fireworks cookbook and I'm sure is quality stuff. Its a fine orange powder. I have hexamine but didn't think cross-linking was necessary. Is there anything I can do to salvage these stars and get them to harden up?

[Zumber]

Is there any chance they absorbed a moisture if you have used strontium nitrate?

Drying stars in oven is not a good is idea it's totally unsafe.

[cmjlab]

Agree that an oven is not a good idea.  A cheap and quick drying box can be made with a $10.00 ceramic heater and a cardboard box.  Put your stars on a screen for drying, cover with a cardboard box, and make a hole to accommodate the ceramic heaters hot air flow into the box on one end, and a small vent hole on the other end of the box.  Voila - cheap and easy drying box you can let your stars dry for hours in.  

If you used at least 6% phenolic resin, and put them in a drying box for 10 to 12 hours, it will drive off the water, soften the phenolic resin and once cooled off will give you rockhard stars (even without using hexamine). 

However like Zumber mentioned above, stars with strontium nitrate will easily reabsorb moisture from the air and soften back up most of the time.

Edited November 7 by cmjlab

[Almostparadise]

No strontium nitrate in these. Yes the oven was terrible idea. It's not something I do normally. I am working on a drying box as we speak. 

[Almostparadise]

So you all think the stars picked up some moisture along the way. The phenolic is slowing down the evaporation and the heated drying box will soften it enough to allow the moisture to escape? That would be great news.

Edited November 7 by Almostparadise

[Almostparadise]

Another question. Could a solution of 1 part 99% iso and 3 parts water have enough alcohol to stop dextrin from fully activating? Does too much alcohol hurt the dextrin or just keep it from activating? 

Edited November 7 by Almostparadise

[cmjlab]

Strontium and Sodium Nitrates are the worst offenders for absorbing moisture from the air.  If you didn't use Strontium or Sodium Nitrate then I'm nit sure why they won't dry unless they skinned over and locked in moisture, but since you used 99% ISO that shouldn't really be an issue either.  

Are they damp to the touch?  Or just soft?  Are you sure you used at least 6% Phenolic Resin (the guy that really introduced PR to hobbyist wrote a paper sharing that you needed at least 6% PR of the total comp in his observations to get a solid / hard star).  

To be comoletely honest, and without knowing your exact formula, I'm not sure why your stars would be soft still unless there is a possible human error factor in there of maybe you forgot to include an ingredient?  It happens to the best of us.  

All the phenolic resin stars I've made did NOT include hexamine, as I don't have a drying box to achieve the necessary temps to cross link, and they came out of the drying box a bit soft, and hardened up as they cooled off.  Then went into ziplocks and out into the sun to make sure no moisture remained locked inside.  

If your positive there is no error, then just let them continue to dry.  Could be a slow drying star comp. Besides, you have nothing to lose if they are a complete loss otherwise, may as well let them sit till you know they are dry.

I'm sure someone more knowledgeable than I may weigh in here and give you some suggestions.  I'm still a newbie by all measurable standards!  

Edited November 7 by cmjlab

[cmjlab]

32 minutes ago, Almostparadise said:

Another question. Could a solution of 1 part 99% iso and 3 parts water have enough alcohol to stop dextrin from fully activating? Does too much alcohol hurt the dextrin or just keep it from activating? 

Not sure here either.  I've always just used water for dextrin bound stars.  I've read some differing opinions about this that say you shouldn't exceed 30% alcohol, and others that say not to exceed 10%, but I don't have any practical experience with it. 

I think Mumbles had provided some input on the subject several times as well that made a lot of sense at the time, something about chemicals competing for the water, where some have a higher affinity to water and would take away from the amount that activated the dextrin.....  (I could be way off base here too).

[Almostparadise]

Strontium carbonate, sorry. Thank you! That is all very helpful input. 

Edited November 7 by Almostparadise

[Zumber]

Why don't you mention full ingredients alongwith percentage?

It will be useful for further discussion.

Have you tried drying stars in sun?

I think oven have no vent hole like drying box have. So evaporated water has to go through another vent hole.

As we have two types of Phenolic resin available here one is water soluble and other is alcohol soluble that could be another reason for binder from being inactivated.

It is just my thinking I am also eager to know more expertise reply.

Edited November 7 by Zumber

[Arthur]

I heard of one person who put racks of stars out, put a (refrigeration) dehumidifier next to them and covered both with a huge cardboard box (fridge-freezer sized). This made a small air volume that was ultra dry and recirculated round the stars. Many stars dry in an hour or two.

Some binders harden with water, some with alcohol some with other solvents. Part of the art of compounding stars is to make a mix the colour and effect that you want that hardens well in a reasonable time. A Binder that needs alcohol will not hardent the mix if you use water.

There are enough books (Lancaster, Shimizu, Hardt and others) available new, second hand or digitally that you need never try to design a star formula -enough are already tried and tested.

[Almostparadise]

5 hours ago, Zumber said:

Why don't you mention full ingredients alongwith percentage?

It will be useful for further discussion.

Have you tried drying stars in sun?

I think oven have no vent hole like drying box have. So evaporated water has to go through another vent hole.

As we have two types of Phenolic resin available here one is water soluble and other is alcohol soluble that could be another reason for binder from being inactivated.

It is just my thinking I am also eager to know more expertise reply.

Red

Potassium perchlorate 49.5

Strontium carbonate 17.6

MgAl 11.3

Parlon 10.3

Phenolic resin 11.3

 

And yes of course I tried drying stars in the Sun and I do when it's appropriate. I had the oven door open. There hasn't been much sun lately. I now feel confident that they will harden now that I know cross-linking is not necessary.

Edited November 7 by Almostparadise

[DavidF]

I rolled some purple star cores with phenolic resin a while back, using 99% isopropyl alcohol to moisten.. They refused to harden. I tried heat as well, and sunshine. They took MONTHS to harden, but they finally did. I also tried cutting stars with phenolic/alcohol and got a crumbly mess. I made up a syrup of phenolic resin/alcohol and left it in an open container to see what would happen. It took several months to eventually harden. I concluded that phenolic resin seems to be best suited to pumped stars, where very little solvent is used. I felt that my star cores had formed an almost impermeable skin, and that the isopropyl alcohol was 'driven in', as can happen with water-damped stars. I'm sure I overused the alcohol too. I'm not a very good star roller, tbh.

[Carbon796]

Usually it's best to choose Water or solvent binding. Most people will run into far less issues this way. Choose which binder you want to use. Then only use the appropriate " activator " for it. There's no second guessing it, because it was done correctly the first time.

The generally accepted rule of thumb. That I've always heard ( and trusted ) is 10% or less of alcohol when binding with dex. Still though, I preferred water only binding. The more alcohol you use, the weaker the binding strength will be.

Both strontium/sodium nitrate based stars can be water bound. With strontium, it's the impurities that make it take on water. Usually this is only an issue with Chinese manufactured strontium nitrate. I've Water bound 10's of pounds ( or more ) of strontium nitrate based stars. With out any issues. But, I would only buy/use Japanese or dupont manufactured strontium nitrate.

With sodium nitrate it can also be water bound. But, the relative humidity needs to be below 66% for them to dry. If the RH is above 66% they will take on water. The lower the RH the faster they will dry. I've also made 10'S of pounds ( or more ) of water bound sodium nitrate based stars, with no issuses.

Phenolic Resin, doesn't play well, with high carbonate based stars some times. Iirc, if the quality of the carbonate is overly alkaline. It will affect the drying/curing of a phenolic bound star. I've had this happen to me before. When I first stared using phenolic resin. Back when Jim W was selling it as big crushed "rocks" and you had to process yourself.

You can probably get around this, with your current materials. If you Water bind the formula. Using No Acohol. That way the phenolic is just along for the ride as a fuel.

Edited November 7 by Carbon796

[Almostparadise]

1 hour ago, DavidF said:

I rolled some purple star cores with phenolic resin a while back, using 99% isopropyl alcohol to moisten.. They refused to harden. I tried heat as well, and sunshine. They took MONTHS to harden, but they finally did. I also tried cutting stars with phenolic/alcohol and got a crumbly mess. I made up a syrup of phenolic resin/alcohol and left it in an open container to see what would happen. It took several months to eventually harden. I concluded that phenolic resin seems to be best suited to pumped stars, where very little solvent is used. I felt that my star cores had formed an almost impermeable skin, and that the isopropyl alcohol was 'driven in', as can happen with water-damped stars. I'm sure I overused the alcohol too. I'm not a very good star roller, tbh.

 I was thinking the same thing that I was sure using alot of alcohol trying to roll these particular cores and likely over doing it. I was not thinking that the alcohol could get driven in. 🤔 I'm sure your onto something here.

[Almostparadise]

1 hour ago, Carbon796 said:

Usually it's best to choose Water or solvent binding. Most people will run into far less issues this way. Choose which binder you want to use. Then only use the appropriate " activator " for it. There's no second guessing it, because it was done correctly the first time.

The generally accepted rule of thumb. That I've always heard ( and trusted ) is 10% or less of alcohol when binding with dex. Still though, I preferred water only binding. The more alcohol you use, the weaker the binding strength will be.

Both strontium/sodium nitrate based stars can be water bound. With strontium, it's the impurities that make it take on water. Usually this is only an issue with Chinese manufactured strontium nitrate. I've Water bound 10's of pounds ( or more ) of strontium nitrate based stars. With out any issues. But, I would only buy/use Japanese or dupont manufactured strontium nitrate.

With sodium nitrate it can also be water bound. But, the relative humidity needs to be below 66% for them to dry. If the RH is above 66% they will take on water. The lower the RH the faster they will dry. I've also made 10'S of pounds ( or more ) of water bound sodium nitrate based stars, with no issuses.

Phenolic Resin, doesn't play well, with high carbonate based stars some times. Iirc, if the quality of the carbonate is overly alkaline. It will affect the drying/curing of a phenolic bound star. I've had this happen to me before. When I first stared using phenolic resin. Back when Jim W was selling it as big crushed "rocks" and you had to process yourself.

You can probably get around this, with your current materials. If you Water bind the formula. Using No Acohol. That way the phenolic is just along for the ride as a fuel.

I was tempted to add dextrin to the remainder of the comp I had already mixed and try again w water. I wasn't sure if it would change the way it burned though.

I am going to stop using any alcohol in water bound compositions moving forward that way I don't need to second guess. Do you suppose new dextrin would need to be added to a charcoal comp that failed to harden due to too much alcohol? I've dried it out and milled it back down for round two to make cut stars out of. 

Edited November 8 by Almostparadise

[FrankRizzo]

Instead of alcohol, try acetone. It'll also partially dissolve the parlon. The formula you're working with intially specified red gum, not phenolic.

[Almostparadise]

Someone from Skylighter (marketing maniacs) re worked some of Jopetes colored star formulas to drop the red gum in place of phenolic. I came across that web page and decided to try a few. Yes, cutting with acetone for cores of this comp instead of rolling them w alcohol would have been better in many ways! 

[robbo]

I had the same experience as DavidF.  10% phenolic stars rolled beautifully with alcohol and I thought I'd discovered a shortcut.  Several weeks later they were still soft inside.  It's been a couple of months and they're hard on the outside, but still a bit soft deep inside.  Reminds me of the behavior of shellac.  But worse.

[Almostparadise]

28 minutes ago, robbo said:

I had the same experience as DavidF.  10% phenolic stars rolled beautifully with alcohol and I thought I'd discovered a shortcut.  Several weeks later they were still soft inside.  It's been a couple of months and they're hard on the outside, but still a bit soft deep inside.  Reminds me of the behavior of shellac.  But worse.

Oh boy, at this stage will they burn at all?

[Crazy Swede]

Using only phenolic resin does not create a strong binding effect!

Adding hexamine for cross linking improves it but makes a brittle binder and is still not perfect. 

Phenolic resin should be combined with PVB for a really strong binding effect!

If NC is also added, then acetone or butyl acetate must be used as solvent, the binding effect is further improved. 
 

EDIT

Just to be clear, by combining phenolic resin and hexamine with PVB, you can use less and the problem connected to driven in solvent will be less pronounced. 

Edited November 8 by Crazy Swede

[Carbon796]

7 hours ago, Almostparadise said:

I was tempted to add dextrin to the remainder of the comp I had already mixed and try again w water. I wasn't sure if it would change the way it burned though.

I am going to stop using any alcohol in water bound compositions moving forward that way I don't need to second guess. Do you suppose new dextrin would need to be added to a charcoal comp that failed to harden due to too much alcohol? I've dried it out and milled it back down for round two to make cut stars out of. 

If you added dex to bind the remaining portion of comp. My guess is that it would have a minor/negligible effect. It might be slightly slower. With slightly more smoke production. You'd probably hardly be able to tell, unless you shot them side by side. 

With the failed one, my guess would be. That it would not need additional dex. Since the alcohol has been driven off and the comp dried/milled. But, I really don't know. Maybe try reconstituting a decent sample of it. And let's us know how it turns out. 

The original intent, with the higher quoted alcohol percentages. Is usually in reference to rolling small star cores. Where you want to decrease the tact and adhesive strength. So the small cores don't stick to themselves, and become a mess. As the cores become bigger and gain mass. The alcohol is reduced/eliminated.

Edited November 8 by Carbon796

[Almostparadise]

2 hours ago, Crazy Swede said:

Using only phenolic resin does not create a strong binding effect!

Adding hexamine for cross linking improves it but makes a brittle binder and is still not perfect. 

Phenolic resin should be combined with PVB for a really strong binding effect!

If NC is also added, then acetone or butyl acetate must be used as solvent, the binding effect is further improved. 
 

EDIT

Just to be clear, by combining phenolic resin and hexamine with PVB, you can use less and the problem connected to driven in solvent will be less pronounced. 

Ive not been able to find a source for PVB.

[Carbon796]

Jim W / CT Pyro has it. I personally didn't really care for it.  Using it, had no real advantages for me. But, I wasn't building Guinness World Record shells like Jim either . . .

[Almostparadise]

1 hour ago, Carbon796 said:

Jim W / CT Pyro has it. I personally didn't really care for it.  Using it, had no real advantages for me. But, I wasn't building Guinness World Record shells like Jim either . . .

I just came across CT Pyro a minute ago. Thank you.

Update, the red stars have finally begun to firm up in the open air going on 6 days now. I'm just glad it won't be a waste. 

I re-wet the charcoal comp with 2g of dextrin dissolved in the water and nothing more added to the composition. I was too nervous to just add nothing. It's only been a few hours and I can already tell the dextrin is doing it's job! I have to assume I would have been fine w out the dextrin liquor and the alcohol didn't ruin the dextrin and just rendered it inoperable until it evaporated.

Edited November 8 by Almostparadise