Measurement of Percent Crystallinity of Polyaryletherketone Composites using Fourier Transform Infrared Spectroscopy

The drive for lightweight, high-performance, and cost-effective aircraft in the aerospace industry has brought thermoplastic polymer composites to the forefront. These materials offer significant advantages over traditional thermosetting composites, including rapid consolidation, reformability, and excellent fracture toughness. As their material properties are intimately linked to crystallinity, understanding and controlling the crystalline structure of these polymers is crucial for advanced manufacturing processes. The National Aeronautics and Space Administration (NASA) Hi-Rate Composite Aircraft Manufacturing (HiCAM) project is actively developing new technologies for the rapid production of composite aircraft, with a strong focus on these advanced thermoplastic systems. The material properties of semi-crystalline polymers are influenced by the crystallinity of polymer molecules. The processing conditions, including tool temperature, placement speed, and material heating/cooling rate, can change the polymer crystallinity and homogeneity of the composite matrix. A homogeneous distribution of crystallinity is desired in consolidated composites. Fourier transform infrared spectroscopy (FTIR) has been used to characterize the crystalline phase of polyaryletherketone (PAEK). This technique enables identification of crystalline regions on the surface. Differential scanning calorimetry (DSC) is widely used for characterizing polymer crystallinity. In this work, the results from DSC were compared to those from FTIR. The crystalline phase quantities of PAEK materials including polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and low-melt PAEK were investigated from the FTIR spectra using the peak ratio of the peaks at 1305 cm⁻¹ and 1280 cm⁻¹. The DSC and FTIR results were correlated to results generated from X-ray diffraction (XRD) data.