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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 benefits. The curing reaction is driven to com- pletion which maximizes the cross-link density of the resin system, thus eliminating unreacted cross- linking 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, hours Post -Curing HDT of the resin, °C 65 85 100 130 Temp °C 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 benefits 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 fluoropolymers are commonly used. Dual laminates may be used and can provide cost-effective performance in conditions where composites are otherwise inap- propriate.