Aramid fibers provide the highest tensile strength-to-weight ratio among reinforcing fibers. They provide good impact strength. Like carbon fibers, they provide a negative coefficient of thermal expansion. The disadvantage of aramid fibers is that they are difficult to cut and machine. Aramid fibers are produced by extruding an acidic solution (a proprietary polycondensa-tion product of terephthaloyol chloride and p-phenylenediamine) through a spinneret.
The filaments are drawn through several orifices. During the drawing operation, aramid molecules beome highly oriented in the longitudinal direction.
As discussed, composites are made of reinforcing fibers and matrix materials. Matrix surrounds the fibers and thus protects those fibers against chemical and environmental attack. For fibers to carry maximum load, the matrix must have a lower modulus and greater elongation than the reinforcement.