-----Original Message-----
From: Rob Housman <ROB-HOUSMAN@worldnet.att.net>
Date: Monday, October 01, 2001 8:32 PM
Subject: Re: Use of White Pigment with Ampreg 20
>Optical plastics, e. g., CR-39 and polycarbonate that are used in plastic
>eyeglass lenses, have UV absorbers in the mix but I doubt that the windows
>in the Europa have an absorber, and your experience confirms this
suspicion.
>
>
That begs the question of why NOT include a blocking agent in the epoxy.
Uvasorb is a commonly used "blocker" in a variety of products from plastics
to lipsticks and acts to filter-out UV.
I raised this with SP Resins a few years ago. They said that Uvasorb made
the hardener/epoxy turn bright yellow, which was an indication that the
hardener was "b*gg*r*d". So they didn't pursue the matter further.
In normal circumstances, yellowing of the hardener means that its past its
best. But Uvasorb also tints yellow most things that it is added to, so SP's
conclusion may have been misguided.
Not daunted by that I tried a few trial mixes (NOT incorporated into the
aircraft!!). Indeed, this turned the epoxy a quite bright yellow, but a
subjective evaluation of the cured mix by means of ad hoc flexural strength
and hardness (scratch resistance) did not suggest there had been any marked
degradation of mechanical property.
I've finished mixing resin, so perhaps someone else (SP Resins?) may like to
do some controlled experimentation.
Duncan McFadyean
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