CORROSION GUIDE 181108_new table content format ... - Reichhold

Laminate Construction
Post-Curing
Post-Curing at elevated temperatures can enhance
the performance of a composite product in most
environments. Post-Curing of composites provides
two benefi ts. The curing reaction is driven to completion
which maximizes the cross-link density of
the resin system, thus eliminating unreacted crosslinking
sites in the resin. This improves both chemical
resistance and physical properties. Thorough and even
Post-Curing for an extended period of time can also
relieve stresses formed in the laminate during cure,
thus reducing the likelihood of warping during normal
thermal cycling/ operation.
In general, one can relate the recommended Post-
Curing temperatures to the chemistry of the matrix resin
used in the construction - this mostly relates to the HDT
of the resin.
It is recommended that the construction is kept for 16-
24 hours at room temperature (>18° C) before Post-
Curing at elevated temperature starts. Increasing and
decreasing temperature should be done stepwise to
avoid possible thermal shock, and consequent possible
built-in stresses.
Post-Curing
Temp °C
Post-Curing, hours
HDT of the resin, °C
65 85 100 130
40 24 48 96 120
50 12 24 48 92
60 6 12 18 24
70 3 6 9 12
80 1.5 3 4 6
Table shows typical recommended Post-Curing
temperatures and times for different resins, related
to their HDT.
Secondary Bonding
One of the most common locations of composite
failure is at a secondary bond. To develop a successful
secondary bond, the composite substrate must either
have a tacky, air-inhibited surface or it must be specially
prepared.
Composites with a fully-cured surface may be prepared
for secondary bonding by grinding the laminate down
to exposed glass prior to applying a new laminate.
Secondary bond strength can be greatly enhanced
by using the Atprime ® 2 primer system. Atprime ® 2
is specially designed to provide a direct, chemical
bond between fully-cured composites and secondary
laminates. Atprime ® 2 can also improve the bond
of FRP composites to concrete, metals, and some
thermoplastics.
Resin Top Coating
Top coats are often used to protect the exterior of
composite products from weathering and from the
effects of occasional exposure to corrosive agents. A
topcoat may be prepared by modifying the resin used to
manufacture the product with thixotrope, a UV absorber
and a small amount of wax. Blending 3% fumed silica,
suitable UV inhibitor along with 5% of a 10% wax
solution (in styrene) to a resin is a typical approach to
top coat formulation.
Dual Laminate Systems
When vinyl ester or bisphenol fumarate corrosion
barriers are unsuitable for a particular environment,
it may still be possible to design equipment that takes
advantage of the benefi ts of composite materials by
employing a thermoplastic corrosion barrier. This
technology involves creating the desired structure by
shaping the thermo plastic, then rigidizing it with a
composite outer skin. Thermoplastics such as polyvinyl
chloride, chlorinated polyvinyl chloride, polypropylene,
and a wide variety of high performance fl uoropolymers
are commonly used. Dual laminates may be used
and can provide cost-effective performance in
conditions where composites are otherwise inappropriate.
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