Factor analysis of time domain NMR data: Crystallinity of poly(tetrafluoroethene)

Factor analysis was applied to the F-19 NMR time domain data of a set of 38 PTFE samples of varying crystallinity. The largest eigenvalue corresponding to 99.62% of the variance between the NMR data sets is associated with the correlation of monotonically decaying signals. Factor I associated with this eigenvalue was poorly correlated with the PTFE crystallinity. On the other hand excellent correlations were found between X-ray diffraction, differential scanning calorimetry, density, FT-IR and Raman indicators of crystallinity and factors 2 and 3 derived from the NMR data. The repeatability of the NMR data was excellent; the variation in factor 2 implying a %RSD of only 0.2% in the resulting crystallinity. On the other hand the reproducibility was poorer with a %RSD of 2.8% when no special precautions are taken to ensure equivalent acquisition conditions.