Rudy, you can even use "free radical initiation"! There must be some
formulations folks out there who can divulge a bit more about the reactions
without giving away formulation secrets! Dr. Roos, you out there???
Thanks for the info Rudy,
Jana Carraway
MSEI
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Rudy Sedlak
Sent: Thursday, April 11, 2002 12:11 PM
To: [log in to unmask]
Subject: Re: [TN] Chemistry of discoloration?
Jana:
You have asked a BIG question.
There really is no known absolute answer.
Organics tend to discolor, if they have any sort of reactivity left in them,
and often, under the right circumstances even if they do not have any
reactivity left in them.
The general rule is they turn dark(er). The reactions are many, and clearly
going to be dependent on the base material. Discoloration is driven by
heat,
and often exposure to sunlight.
Not to get too technical, but polymers (laminate, and soldermask, for
example) only rarely really react fully, and there is almost always some
unreacted polymer (called monomer when it is totally unreacted, and oligomer
when it is partially reacted) lurking in the matrix. When this contacts
air,
water, and heat and UV, all sorts of unexpected things happen. In fact,
these very polymers often have added "preservatives" to prevent these
post-polymerization reactions from occurring.
The bottom line is (as if this really has ANY significanse in our industry)
that this discoloration rarely affects the physical properties of the
polymer. I think a great English playwright described this situation
centuries ago..."Much ado about nothing"?
Rudy Sedlak
RD Chemical Company
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