Microtek
March 21st, 2004, 02:09 PM
Most types of ordinary household film are simply sheets of low density polyethylene ( LDPE ). LDPE is basically chains of (CH2)n with some degree of branching in the chains, whereas HDPE has no branching but is otherwise similar. Both LDPE and HDPE are thermoplasts, meaning that they soften when heated but LDPE, which the rest of this post will deal with, does not melt completely at sufficiently low temperatures. Instead, it softens at about 110 C much like hot-glue. This viscousity makes mixing it with crystalline HE inconvenient though doable, but the HE can be sprinkled onto a sheet of LDPE which is then folded, more HE is added, the sheet is folded again, and so on. At the end of this procedure a wafer consisting of alternating layers of LDPE and HE is obtained. This is then placed on a hotplate or in the oven and heated to a temp in the 110-180 C range ( assuming RDX or other high melting HE ). This causes the LDPE to soften and flow together like hot glass. Then the mix must be worked with a spoon or other utensil to form a homogenous mix of LDPE and HE. This is effectively done by flattening the mass, and then folding it onto itself, then flattening again and so on. About 10-20 times usually does it.
The soft mass can now be cut up and packed into whatever shape is desired while maintaing a temperature of 110-180 C. Applying a little pressure makes the flakes merge seamlessly and on cooling, the product will be quite strong and well suited for machining.
In this manner I easily produced a PBX consisting of 90.5 % RDX and 9.5 % LDPE. It had a density of about 1.5 g/cc and was very strong.
Another useful property of polyethylene is the very high heat of combustion; ca 42 KJ is released when one gram of PE is burned in excess oxygen.
This makes it a suitable binder/fuel for rocket propellants as it gives a very robust grain with high chemical stability in addition to the high energy content.
Thus, a mix of 30 g LDPE and 200 g KClO4 makes for a slightly fuel rich mix which has an energy content of about 5000 J/g; better than many other non-metallized propellants.
Finally, LDPE is a useful material in the lab due to its chemical resistance ( as evidenced by its successful use in HNO3 destillation ) so many different types of labware can be made with a little creative thinking.
The soft mass can now be cut up and packed into whatever shape is desired while maintaing a temperature of 110-180 C. Applying a little pressure makes the flakes merge seamlessly and on cooling, the product will be quite strong and well suited for machining.
In this manner I easily produced a PBX consisting of 90.5 % RDX and 9.5 % LDPE. It had a density of about 1.5 g/cc and was very strong.
Another useful property of polyethylene is the very high heat of combustion; ca 42 KJ is released when one gram of PE is burned in excess oxygen.
This makes it a suitable binder/fuel for rocket propellants as it gives a very robust grain with high chemical stability in addition to the high energy content.
Thus, a mix of 30 g LDPE and 200 g KClO4 makes for a slightly fuel rich mix which has an energy content of about 5000 J/g; better than many other non-metallized propellants.
Finally, LDPE is a useful material in the lab due to its chemical resistance ( as evidenced by its successful use in HNO3 destillation ) so many different types of labware can be made with a little creative thinking.