Determination of Crystallinity in Polyethylene From
نویسنده
چکیده
Hansen and coworkers (Zhang, L; Hansen, E. W.; Helland, I; Hinrichsen, E.; Larsen, Aa.; Roots, J. Macromolecules, 2009, 42 (14), 5189-5195) recently reported on the room temperature crystallinity of a series of ethene-1-hexene copolymers using solid-state 1 H-NMR FID analysis. However, due to the required 10 s blanking time of the receiver vital information in the initial part of the FID was lost resulting in an underestimation of the sample crystallinity. To compensate for this information loss we made use of the significant increase in T2 at or above the melting point which enabled the intensity of the FID at time t = 0 to be reliably estimated. Hence, by applying the Curie law the room temperature intensity of the FID was re-evaluated and resulted in an improved crystallinity value. However, it was still too small compared to the crystallinity obtained by solid-state 13 C-NMR. However, by multiplying the proton FID intensity (determined at the melting point) by a factor of 1.25 before applying the Curie law, the room temperature crystallinity derived from the two different NMR techniques became – within experimental error – consistent. In this work we present experimental evidence that the empirical multiplication factor of 1.25 strictly originates from a non-Curie temperature behaviour of the NMR signal intensity.
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