Investigation of carbon fiber-reinforced thermoplastic polymers using thermogravimetric analysis

The high chemical resistance of the advanced thermoplastic polymers, such as polyether ether ketone (PEEK), polystyrene (PS), or polyamide (PA), makes methods of the composites' composition evaluation based on chemical etching difficult and tedious. Wider application of the composites with thermoplastic matrix creates a need to find more capable, faster, and easier method of fiber and void content determination. Thermogravimetric analysis (TGA) is known to be one of the most promising candidates. Numerous reports have shown that TGA could be successfully applied for glass-reinforced composites. In this study, carbon fiber/PEEK composite was investigated. Initial tests showed that a simple method based on total burn-up of the matrix cannot be used for such advanced composites due to the high thermal resistance of PEEK. Tests carried with various parameters and microscopic investigation of the degradation process allowed to propose an analysis method that can give a satisfactory outcome. Results obtained with carbon fiber/PEEK composite using TGA-based method matched those obtained by chemical etching. Supplementary investigation of PA-based and epoxy resin composites showed the applicability of the method to a wider group of both thermoplastics- and thermoset-based carbon fiber-reinforced composites.