Poly(3-hydroxybutyrate) (PHB) is a semicrystalline biodegradable polymer with chains consisting of methyl (CH3), methylene (CH2), methine (CH) and carbonyl (CO) groups. The 1 H-13 C cross polarization NMR measurements were performed on an as-supplied powder PHB sample at a magic-angle spinning rate of 10 kHz. The measured cross polarization build-up curves and their analysis provided information on the dynamics of 1 H-13 C NMR cross polarization in functional groups with directly bonded hydrogens. The measurements required setting up the Hartmann-Hahn condition, which was inferred from the Hartmann-Hahn matching profiles measured for each functional group. The cross polarization build-up curves displayed an oscillatory course, which indicates the presence of rigid 1 H-13 C spin pairs isolated from the lattice. The frequency of the observed oscillations is directly proportional to the 1 H-13 C dipolar coupling constant, which is related to the C-H distance and its value also reflects the mobility of particular functional groups. The values of dipolar coupling constants were derived from splittings in the Fourier transforms of cross polarization build-up curves. The mobility of particular groups was assessed with the order parameter S calculated using experimental and rigid lattice values of dipolar coupling constants.
In present work structural properties and aging of thermoplastic starches prepared by plasticization of cornstarch with urea, glycerol and their mixtures are studied using solid‐state 1H NMR and 13C NMR spectroscopy and WAXS measurements. Broad line 1H NMR spectra reveal phase separation of plasticizers during aging of the samples with the same or higher relative amount of glycerol than the amount of urea. Glycerol in the TPS samples induces motion of starch chain segments, the mobility of which depends on the relative amount of glycerol. At the scale of nm, formation of B‐type crystallites in the samples containing glycerol and also of single‐helical crystallinity in all samples is observed during one‐year aging through cross‐polarization magic angle spinning 13C NMR spectra. Urea, when used as the sole plasticizer, prevents the ordering of starch chains in B‐type crystallites. WAXS diffractograms show that regular crystals do not form in any of the samples.
Single-pulse 13 C NMR spectra and spin-lattice relaxation times T 1 ( 1 H), detected indirectly via 13 C carbons, and T 1 ( 13 C) were measured at 31°C for virgin pelletized and annealed polylactic acid (PLA) samples using the magic-angle spinning technique. The structural relaxation resulting in more regular crystals with narrower conformation distribution and increase in the lamellae thickness and crystallinity brought about by annealing at 100°C was deduced from the narrowing of the 13 C NMR lines and proton spin-lattice relaxation times T 1 ( 1 H). The spin-lattice relaxation times T 1 ( 13 C) related to the respective carbons of the -polymorph of PLA are also discussed in the study.
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