Replacing Red Gum with Shellac in Brilliant Rubber Stars

[Bju90]

I want to replace red gum with shellac in the following formulas. Red gum is not readily available here in small quantities so it's super expensive @ $70/100g compared to shellac at less than $14/100g. Unless someone also in Australia has excess red gum and want to sell me some, pm me :). 

Component	Red	Green	Yellow	Peach/Lavender
Strontium nitrate	0.53		0.13
Barium nitrate		0.53	0.40
Potassium nitrate				0.53
Magnalium	0.19	0.19	0.19	0.19
Parlon	0.17	0.17	0.17	0.17
Red gum	0.11	0.11	0.11	0.11

From reading various posts it should work but there are mixed experiences with shellac vs red gum in various comps. Everything I could find was to do with perchlorate vs chlorate comps. 

I'll start experementing to see but it would be helpful if anyone else has had any experience with these particular comps as a starting point. 

According to ChatGpt shellac has a higher oxygen demand by aabout 22% so will have to account for that. 

Resin	Oxygen Demand (g O₂/g)	Relative Difference
Red Gum	1.78 g O₂/g	Lower
Shellac	2.17 g O₂/g	Higher

My other concern is drying. From previous threads users reported shellac being more difficult to dry if there was too much solvent used. I will be using acetone, much cheaper than denatured alcohol here. 

[Carbon796]

Phenolic resin would be a better substitute. If you have access to it.

If your not stuck on solvent binding. You can just add a water based binder. That will also eliminate any solvent entrapment issues.

[Bju90]

I looked for that but cant find anything unless I purchase commercial quantities.

Can I clarify if you are referring to the binder as the Red Gum or the Parlon? I thought in this application the Parlon is acting as the Binder/Chlorine donor and the Red Gum is primarily there as a fuel, in which case the Parlon won't activate with the water?

I have a decent amount of Parlon so i'd prefer to use that.

This might be a dumb question but can a water soluble binder/fuel be used in place of the red gum and press the stars rather than making rubber cut stars?

 

[Bju90]

Something like this with water or water/alcohol to make a pumped star. 

Component	Red

Strontium nitrate

0.53

 

Magnalium (Mg/Al)

0.19

Parlon

0.17

Sulfur

0.07

Dextrin

0.04

Edited March 13 by Bju90
Error.

[Carbon796]

If you used alcohol, it would dissolve the RG or shellac. But not the parlon. 

If you used acetone it would dissolve the RG or shellac and soften the parlon.

Subbing for sulfur and adding dex. Activating with water should work well.

[Bju90]

Tried a small amount with the Sulfur and dextrin as above. Hand pressed some of the comp dry in to an 8mm paper tube to test it. 
 

Don’t have anything to compare it to but it’s lit up easy, burnt red and bright. 
 

I will make a few pumped stars over the weekend and see how they go.

[Bju90]

Using sulfur and binding with dextrin burnt fine on the ground. Had big trouble getting it to burn in the air. Launch 6mm stars in a mine/comet they would either blow blind or only start to burn once they slowed at the apogee.

Have some Shellac in the ball mill now. Will try this as a fuel with dex to bind it.

 

 

Edited May 9 by Bju90

[Carbon796]

Were they primed with a KP based hot prime. And, finished with scratch mixed  prime ?

[Bju90]

I did step prime them but I don’t have access to perchlorates/chlorates. I can’t seem to find the formula I used, it was from a post on the forum somewhere. Iirc it was something like bp + mgal but lower nitrate to slow it down a bit, i think.

I wasn’t sure if the Sulfur would also effect the colour? 

Figured I’ll try the shellac formula with Dex binder and see how it compares then deal with sorting out a reliable hot prime if I can’t get it to ignite. Without perchlorates, the reccomendation seems to be adding silicone?

 

 

Edited May 10 by Bju90

[Carbon796]

I would concentrate on your prime comp & technique first. Then color tuning. Priming is basically, one the foundational processes. You need to have sorted, and absolute. In order to build reliable devices. Otherwise you are literally just throwing away your time and materials.

My scratch mixed prime was 

75/15/10 +3%Mg/AL +3% silicone +3%SGRS.

I would want something better than that for an initial prime. For those stars.

Their claim to " fame " is that they are expedient to make. Using the screen sliced method.

Ease of ignition and critical wind velocity, were not. The fact that you don't have access to KP. Kind of compounds that.

I would be using silicon even with KP. As seen above, in my scratch mixed prime. My kp based hot prime, also contained 3%.

Doubtful the sulfur affected the color much. But, kno3 migration can. 

Iirc, fence post or pinball prime may have been kno3 based. You may want to research one of those. There are definitely advocates for both of them. 

Was your step priming something like  ?

Star comp / prime

75 /25              Initial 

50 / 50

25 / 75

00 / 100 %       final 

If it wasn't stepped out at least that much. That's likely part of the issue. 

Edited May 10 by Carbon796

[Bju90]

Thanks, that makes sense. I’m looking for a source of Silicon now and will have to do a bit more searching for a hot initial prime or use multiple steps as you suggested and see how that goes.

[Carbon796]

Look into the two primes above. I believe one of them uses diatomaceous earth. Which is supposed to work similarly. And may be easier for you to find.