Quantitative characterization of crystallinity in semi-crystalline fluoropolymer through 19F LF-NMR relaxometry

Crystallinity is important to the properties of a semi-crystalline fluoropolymer, such as solubility, mechanical property, bonding strength, etc. This study extended the use of 19F Low-Field Nuclear Magnetic Resonance (19F LF-NMR) to the measurement of crystallinity in the semi-crystalline fluoropolymer F2314, which is the copolymer of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE) with a molar ratio of 1:4 and commonly used as binder in polymer-bonded explosives (PBXs). Based on the difference between spin-spin relaxometry of the 19F in crystalline region and in amorphous region, the crystallinity of F2314 can be qualitatively characterized. The obtained crystallinity exhibited a positive correlation to the time duration of thermal treatment, which is in consistent to the result of Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD). Moreover, 19F LF-NMR detected the slight decrease in segmental motion of crystalline region with the increase of crystallinity, and on-line monitored the evolution of segmental motion during heating. This study not only demonstrates the practicality and reliability of 19F LF-NMR in quantification of crystallinity, but also laid the foundation for in-situ characterization of fluoropolymers in PBXs in future work. •The use of 19F LF-NMR technology was originally extended to the quantitative characterization of crystallinity.•The increase of crystallinity in F2314 was accompanied with the decrease in segmental motion of crystalline region.•In-situ 19F LF-NMR technology realized online detection of the segmental motion during melting.