I am trying to create a .5" thick composite specimen for photoelastic
analyisis.  I have selected e-glass for the reinforcement material,
and am still searching for a better epoxy.  There are several
requirements needed for epoxy.  First it needs to be fairly
transparent.    In addition, it is equally important that the index of
refraction of the matrix must be as close as possible to that of
E-glass(1.548).  Furthermore, as I have found that the epoxy must
interact favorably, or bond well with glass; otherwise interface
separation could cause the whitening in the sample. Also, the matrix
needs to be not very viscous, and be able to cure slowly.  The matrix
must have a low viscosity so that it may encapsulate all the fibers of
the reinforcement and
completely gas out.  Lastly, the material must cure slowly so the
composite
will have minimal residual stress.  Also, the epoxy needs to be
somewhat
stiff.  Any idea what epoxy i could try?

Hello there.  Sounds like you're looking for what's known as "optical
grade epoxy".  By searching on this term, I found one that seems to
meet your needs at:

http://www.epoxies.com/tech/20-3238.htm


It has a low viscosity, high adhesion to glass, slow curing and an
Index of refraction of 1.5403 (pretty close!).  I'm not sure just how
one measures the "stiffness" aspect -- take a look at the
specifications and see if it meets your needs.

If this doesn't suit, let me know, and I'll look at some others.

Good luck with your project.

Dave

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Request for Answer Clarification by dibeaux-ga on 26 Jun 2002 12:14 PDT

The following epoxies have been evaluated, but have come out too
opaque:

Epoxies, Etc... 20-3238 Optical Grade Epoxy
Epoxies, Etc... 20-3302 Optically Transparent Epoxy
Epoxy Set EB-106 Optical Grade Epoxy
Epoxy Set EB-107 Optical Grade Epoxy
Epoxy Technology 301-2 Optical Grade Epoxy
Epoxy Technology 302-3M Optical Grade Epoxy
Norland Products NOA65 Optical Adhesive
Bicron BC-600 Optical Cement
Nitto Denko NT-8005S Clear Molding Compound
Measurments Group PLM-9 Resin 
Shell EPON Resin 828
Sartomer CN151 Epoxy Methacrylate
Derakane 441-400 Epoxy Vinyl Ester
Derakane 470-300 Epoxy Vinyl Ester
TRA-BOND 2115 Epoxy 
His Glassworks, Inc. XTR-311 Epoxy Adhesive
Star Technology UVA4000 Epoxy

Some of the optical grade epoxies come out reasonably well, but they
are not clear enough.   Even the UVA 4000 which has a index of
refraction of 1.547 did not come out very well.  I think that the
epoxies are bonding well enough with the glass.

i have already found this epoxy, and it did not work out too well

You should evaluate Contact Lens grade HEMA prepolymer solution from
Benz, Sarasota, FLA.