Monday, September 20, 2010

Polymers in Space - Part 1

Long time readers know how much I hate PR blurb and the coverage of science by the popular press. Add this one to the pile. What is so appalling in this case is the actual science report is pretty interesting [*], while what is reported in the popular press is gut rot.

Here's the science: Researchers from the University of Sydney sent some uncured epoxy up into the stratosphere (40 km up) for three days using balloons. Being uncured and exposed to all the radiation that the atmosphere normally protects us from, the epoxy did what you would it expect to do: it started reacting. The samples reached a solid state, but still needed additional curing to be fully reacted. I suspect that the low temperatures at night (-40 oC) are a reason for incomplete cure. Radiation initiation of a radical polymerization is usually independent of temperature; it’s the remaining steps (chain growth, crosslinking and termination) that are temperature sensitive.

The authors make a suggestion of how this could be applied. A prepreg for a structure could be made here on earth and rolled, folded or otherwise assembled in a smaller size than the final product. It can then be shipped to space uncured, assembled into the final shape and size and then the space radiation will do the curing.

So all that is fine and good. Here’s how the popular press reported it: “Space Makes Polymers Hard” Wow! Isn’t that amazing! While being accurate, it certainly misleads you into thinking that this is newly discovered behavior.

And this line in the blurb is worse “But the University of Sydney group was the first to investigate the effects of the electrons, ions, X-rays and gamma-rays that constantly bombard — and usually damage — structures in space.” Hardly. Pull open the Polymer Handbook and look at Chapter II, Radiation Chemical Yields. You’ll find a summary of published literature of how effective radiation is at changing polymer chemistry.

Since you have the Handbook open, let me point out one other item in that chapter is largely overlooked. The columns of the data show two key values – the amount of scissioning that occurs and the amount of crosslinking that occurs. In many polymers, BOTH occur, although one phenomenon tends to dominate. Looking at chemistry textbooks, you only ever see one option discussed for a given polymer.

[*] It is an amusing report to read in that they included details of the many trials and tribulations associated with launching and recovering the balloons, stuff that is normally left out of the whitewashed reports published in journals.

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