=construction =polymers =materials
Modern buildings have a lot of
windows. If you look at a recent skyscraper, its facade is likely to be
mostly glass. Why use glass for that? Why not use a sheet of plastic
instead? Glass sheets are heavy and brittle; plastic film would be much
lighter and cheaper.
The main problem with plastic film is UV
degradation. Most plastic degrades over time when exposed to sunlight and
air. Is it possible to make clear plastic with good resistance to UV and
water? Could that be used instead of glass for buildings? Yes, and people
have done that.
When ethylene and tetrafluoroethylene are polymerized
together, they naturally tend to alternate, producing
ETFE. Each carbon is either
fluorinated or next to a fluorinated carbon, which increases UV resistance.
That wikipedia page lists some
buildings using it, notably including the
Eden Project
and the "water
cube". It also notes:
ETFE's first large-scale use architecturally came in 2001 at the Eden Project where ETFE was selected as it can be printed and layered to control solar conditions and because it was found to have a low friction coefficient, which saves on maintenance as dust and dirt do not stick.
Current ETFE building facades typically have 3 layers clamped at the edges with aluminum frame, with some air pumped between the layers. So, current designs typically use some electricity. The frames are more expensive than the ETFE film, and my understanding is that they result in ETFE being slightly more expensive than glass. Cost reduction of such frames seems possible.
ETFE has some notable advantages over glass:
- As thermal
insulation, ETFE is slightly better than the same number of glass layers: 3
layers are slightly better than triple-glazed windows. That's good.
- The
frames are heavier than the ETFE film, but the overall system is still
typically <0.5x the weight of windows. That's good. (That lower weight is
advantageous when
moving building sections on wheels.)
- ETFE is slippery. Water will
run off it at small slopes. Dust adheres poorly to it, so cleaning isn't
usually needed. That's good.
- Windows with irregular shapes are easier with ETFE than glass. That's good as long as you trust architects to use this capability wisely.
There are also some ways in which ETFE is different from glass but not exactly better or worse:
- ETFE film
is much lighter and less rigid than glass, so it transmits sound much more
and reflects sound less.
- ETFE film is mostly transparent to UV down to
200nm. Soda-lime glass blocks UV below ~320nm but mostly transmits UV-A,
which means you can get a suntan through a window but are less likely to get
a sunburn and won't get much Vitamin D. (Despite what you may have heard from Feynman, watching a nuclear
explosion through a car windshield is not safe for your eyes.) The extra UV
transmitted through ETFE also causes slightly more heating inside buildings,
might have some disinfectant effects, and might cause more degradation of
plastic objects.
- ETFE film generally transmits slightly more visible
light than glass, but it's usually curved, which can cause some slight
visual distortion.
Overall, I expect ETFE usage for buildings to increase significantly.