Chemical resistance

The following should be considered if the composite is to be used in a chemical application:

Fibre reinforced plastic has been used for many years as a cost-effective material for chemical containers. However, all organic resins are permeable to water, and a number of other liquids to a certain extent. The absorption varies significantly but whereas thermoplastics can be completely dissolved, thermoset materials will just swell.

The material selection depends on the severity of the environment. For weak acids a chlorinated or long chain iso-polyester would be suitable, whereas more aggressive environments such as caustics and most solvents require vinyl ester resins. Vinyl esters are commonly used, as they are more resistant to chemicals than polyesters yet cheaper and easier to manufacture than epoxies. Although epoxies have a greater solvent and thermal resistance than vinyl esters they are more difficult to process and more expensive.

Alkaline solutions can attack composites by accelerating the degradation of the bonds between resin and fibre and also the bonds in the resin itself. However, there is a lack of knowledge regarding the exact mechanisms of degradation and there are currently no standard test methodologies available for evaluating the effects of alkaline solutions on fibre reinforced polymers. Since the resin acts to protect the fibre and slow the diffusion of alkaline solution into the material, epoxies and vinyl esters are preferred over polyesters.