In some cases, the effects of corrosion may be especially critical, even for a high-strength FRP laminate. In these cases, the solution is to protect the laminate by the addition a material with higher chemical resistance. This generates a dual system, consisting of a liner in contact with the corrosive medium, reinforced by an FRP laminate. The purpose of such a construction is to obtain a composite material whose properties are better than the FRP and liner separately, having the resistance to corrosion of the liner and the strength and stiffness of FRP. The liner materials used are thermoplastics, which will be of various types, depending on the nature of the application, as reflected in the following table:
In the case of a dual system, the typical composition of this type of construction is shown in the figure below:
- Liner – thermoplastic material with high resistance to corrosion
- Structural wall – layer high in fibre, responsible for mechanical strength and stiffness
- Termination – layer of high resin content responsible for the integrity of the whole laminate against the weather
The use of a dual system has a number of advantages over the use of an unreinforced thermoplastic material:
- The possibility of operating at higher pressures / temperatures
- The whole is less brittle at low temperatures
- The distance between supports is considerably greater (in the case of pipes)
- The thermoplastic liner is protected from the environment and U.V. radiation
There are also advantages over the use of FRP without a liner:
- Increased resistance to corrosion and abrasion
- The material that provides the mechanical strength (FRP) is isolated from the corrosive environment by the liner
