Discussion on SugPro stirred curiousity about what pectin could provide to sugar propellants.
(Check the SugPro archives for Nov. 2007 for more)
In one post I made three guesses: At the end of this page the accuracy, or lack thereof, for those guesses is discussed.

Hypothesis:
My main hope/guess was that pectin might be able to give melt method sugar propellants a desirable rubbery texture.

Experiment:
Purchased some MCP Pectin powder which lists ingredients as: Dextrose, Pectin, and Citric acid.
Made the following formulas into strands for 1 atm burn tests:

Formula #
KNO3/Sorbitol/MCP-Pectin
A:
65/35/0
B:
65/31.5/3.5
C:
65/28/7
D:
65/24.5/10.5
E:
65/17/5/17.5
F:
65/0/35
Used fine powder KNO3 from FireFox.
Dry ingredients/no water.
Formula #A is standard 65/35 KN03/Sorbitol as a control.
Formula #F has no sorbitol; only MCP as fuel.

Five gram amounts of each formula were melted from dry powder form in a double boiler using wax as the heating buffer. This was rolled into 2.5 inch strands and allowed to cool.

RESULTS:
Observations noted:

MELTING:
As the pectin amount increases the mix becomes harder to melt. Formula F never did melt completely but tapping and kneading it did finally make a solid strand.

LINER/CASE BONDING:
Formula E and F would not stick to paper while melted so probably would have problems binding to liners or cases.

DENSITY:
Formula F was noticeably less dense.

CURED FLEXIBILITY:
Cooled strands for 1 hour and found none that had the desired rubbery consistency.
Formula A was somewhat pliable (like KN/sorbitol always is before it has time to fully cure.)
Strands of formulas B through F became less and less pliable as the pectin amount increased.
I'm guessing that this was due to the dextrose in the MCP-pectin speeding up the cure rate
Similar to what was seen in the sorbitol dextrose alloy experiments:
http://www.science-guy.com/rocketry/PDT-5c.html

Bottom line is that no desired rubbery effect was seen :-(
so it was time to do 1 atmosphere burn rates. :-)

Formula #
KNO3/Sorbitol/MCP-Pectin
1 Atm Burn Rate
A:
65/35/0
9-10 seconds/inch
B:
65/31.5/3.5
9 seconds/inch
C:
65/28/7
8 seconds/inch
D:
65/24.5/10.5
8 seconds/inch
E:
65/17/5/17.5
flame front jumped **
F:
65/0/35
flame front jumped **

** Didn't get accurate burn rate because flame front jumped due to what looked like porosity in the strand?
For formula E the burn was still very vigorous (similar to A through D)
For formula F the burn appeared less vigourous than the other formulas but still burned reasonably well.

It is interesting that pectin did not inhibit burn rates with sorbitol. Others on SugPro had results showing burn rate inhibition. However their tests had used different sugars and also water in the propellant production.

I had made some guesses early in the SugPro discussions about how Pectin might affect sugar propellants by the melt method. Let's see how I did:
1. It might make the molten propellant thicker and harder to pour. Disadvantage
RESULT: True
2. Once cooled/hardened that it could make the grains less brittle. Advantage
RESULT: False
3. It could make the propellant grains less dense. Disadvantage
RESULT: True

Conclusion:
So both theorized disadvantages panned out. And the one theorized advantage did not.

A better way to test the effect of pectin alone might be to do this experiment with KN/dextrose. This would avoid the effect of the sorbitol and the dextrose in the MCP causing an alloyed sugar situation.

Perhaps I'll try ;-) Perhaps not %-P






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