Cross‐referenceable microscopic and micro‐spectroscopic analysis of fiber reinforced thermoplastics

Abstract This study aims at the assessment of damage on crystallinity of fiber reinforced thermoplastic (FRTP) composites resulting from mechanical polishing to demonstrate a novel methodology enabling comprehensive crystalline structural characterization. Investigating the crystalline structure is relevant for understanding the relationship with the mechanical properties. In a previous study, FRTPs have successfully been processed to the thickness of 5 μm or below via an innovative polishing strategy, which for the first time visualized the crystalline morphologies by polarized optical microscopy. Analyzing these sections via micro‐Raman and micro‐infrared spectroscopies facilitate the quantification of these structure. However, no study reports on the correct interpretation of FRTP data appropriately considering the damage resulting from mechanical polishing to date. Herein, we report fundamental knowledge on this aspect via detailed Raman micro‐spectroscopic investigations to demonstrate our novel strategy. Four types of FRTPs with major matrix resins (GF/PBT, CF/PA6, CF/PEEK and GF/PP) were analyzed and the damage on both polished cross‐sections, prepared by traditional process, and the thin sections was confirmed to be approx. 1%–2% crystallinity, which solidified the credibility of the obtained analytical data. Then, the newly established methodology of ‘cross‐referenceable microscopic and micro‐spectroscopic analyses for FRTPs’ was applied for comprehensive crystalline structural characterization. Highlights Cross‐sectioning and thin‐sectioning of FRTPs. Evidencing of damage on the crystallinity resulting from mechanical polishing. Equations to convert Raman spectral data into crystallinity. Strategy for considering the anisotropy of Raman measurements. Practical application of novel microscopic and micro‐spectroscopic strategies.