Pultrusion Process Development of a Graphite Reinforced Polyetherimide Thermoplastic Composite

Developing a pultrusion process for fabricating composites using a graphite reinforced high-performance thermoplastic presents a technological challenge to the pultruder. Unlike conventional pultrusion of thermosets containing monomeric reactants and solvents which react in the pultrusion die causing polymerization, high-performance thermoplastic polymers either do not contain solvents or contain solvents which must be removed before polymerizing. In either case, consolidation is performed with rigid or boardy prepreg. In pultruding with conventional thermosetting polymers, fiber wetting and consolidation are performed at very low resin viscosities, which range from 500 to 1000 centipoises. In pultruding with high-performance thermoplastics, the die system must perform consolidation with polymers having viscosities as high as 1,000,000 centi poises or higher. Die temperatures in thermosetting pultrusion range from 149 to 204°C (300 to 400°F), whereas in thermoplastic pultrusion the die system may approach 427°C (800°F). Engineering is critical in any attempt to design a system capable of pultruding high-temperature, high-performance thermoplastics. This paper presents a methodical approach in developing a pultrusion process for polyetherimide which can also be adapted to other high-performance thermoplastics. Resin characterization and methods of testing thermoplastic pultrusions are discussed. The effective use of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), ultrasonic C-scanning, scanning electron microscopy (SEM), conventional press molding, and material properties evaluation tests in thermoplastic pultrusion development is described.