I have been doing a bit of experimenting with what type of glue to use for the envelopes. I purchased a glue that is suppose to be flexible once set and also can handle extreme temperatures. This sounded really good at the time so I picked some up to give a try. This is a picture of what I bought.
I fear that I jumped the gun a little with this one. It did not occur to me at the time to think about how this stuff sets. So after the 12 hours that the packaging says to wait for before the glue sets on non-porous materials, the glue still wasn’t dry. I got carried away with life for the next few days and when I came back, most of it still wasn’t dry and the parts that were dry just pealed away.
I did a little bit more research at this point and found that the water in the air is actually the substance that causes super glues to set. Since space blankets are water proof, there was no way that the moisture in the atmosphere was ever going to get inside properly to create a strong join. I also found a reference, lost that one sorry, that said that PE needs to be surface treated before it will take a proper bond when gluing it together. For the next experiment I am going to test some plastic glue I have laying around that comes with a marker that you prime the surface with before applying it. If this fails to work then I am going to try and find a two part epoxy kind of glue that is flexible enough for a balloon envelope but also does not rely on molecules in the atmosphere to set.
For now though, I will go through the process I used to test the glue;
The first thing to do is find out which side of the blanket is the aluminium and which side is the PE. To do this, it is a simple matter of using a sharp knife to scratch a either side of the blanket. The side that the metal scrapes off of is obviously the aluminium side. I then labelled each side for future reference.
Next, I cut off two small pieces and labelled both sides of each piece so that I knew which side was the metallised side. It is important to glue the two PE sides together and not the metallised sides, or one of each. Otherwise, the join will just peal away due to the weak bond between the PE and the metallised layers.
I then ran a small bead of glue down one side of a PE side of a piece of the blanket and laid the PE side of the other piece on top of that.
After the two pieces were glued together, I sandwiched them between a bunch of books to promote a strong join. After the 12 hour period, when I found out that it hadn’t set, I removed the books and let it sit out for another few days.