Re: [Paddlewise] fiberglass [edging toward off topic]

Hank Hays wrote:
> 
> >Dave Williams wrote:
> >> What does "isophthalics" mean?
> >>
> >> What does "orthophthalics" mean?
> 
> [snip} ... isophthalic polyester is stronger (and more
> expensive) than orthophthalic resin.  I think there is more crosslinking
> between the molecules in iso than with ortho.  Could be some other
> characteristics are better also, but Dave K would be the guy to quiz about
> that <grin>.  Vinylester is even better yet (and more expensive still) and
> some epoxies are the best (and often *lots* more expensive.  Iso is a bit
> newer than ortho and vinylester is newer still.  Epoxy has been around for
> quite a while, too, but  many of the newer ones are better than the old
> originals.

To round out Hank's summary, here is a little more information.  Extracted
from this commercial boat-building site, which also touches on other resin
issues:  http://www.duroplastic.com/art_bbfg.html  

Actually, Hank has a lot of this same information on his business's Web
site, IIRC (http://www.paddles.com/index.html).

--BEGIN:		RESIN TYPES   

  There is a choice of resins too, on a rising scale of cost and
performance, orthophthalic polyester being the cheapest and
  easiest to use. (Incidentally, it is not the resin that gives a freshly
moulded boat its characteristic smell, but the styrene
  solvent.) Next comes isophthalic polyester, 50% more expensive, but more
resilient and with better resistance to water (see
  under "Blistering". Then there's vinylester, stronger and more water
resistant still, but more than double the price of
  ortho-polyester. All three behave in the same way chemically, and begin
to cure following the addition of a tiny amount
  (1-2%) of a catalyst to start the polymerisation process. And finally
there's epoxy, five times the price of ortho-polyester but
  far superior in every other respect, notably in its resistance to water
degradation as well as in its adhesive strength. Instead
  of a catalyst, epoxy requires a large proportion of hardener to start the
reaction (from 20% to as much as 50%, depending
  on the particular product) and this hardener forms part of the final
polymer. The use of epoxy allows composites to be
  produced with very high fibre-to-resin ratios making them much stronger
and lighter than is possible with the other resins,
  but it is still too costly to be considered as a universal replacement
for them. 
--END

-- 
Dave Kruger
Astoria, OR

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