โ Scribed by Roger H. Newman
No coin nor oath required. For personal study only.
Differences in proton rotating-frame spin relaxation rates were exploited to edit the 13 C NMR spectra of solid lignocellulosics, separating signals assigned to cellulose crystallites from signals assigned to amorphous material. Clusters of signals at 89 and 85 ppm were assigned to C-4 in the interiors and on the surfaces of cellulose crystallites, respectively. Relative signal areas were used to estimate the weight-averaged lateral dimensions of crystallites, using a model in which crystallites have approximately square cross sections. The same 10 samples were also characterized by wide-angle X-ray ลฝ . ลฝ 2 . scattering WAXS . There was a strong correlation r s 0.988 between the two sets of lateral dimensions, but those estimated by WAXS were typically 10% lower than those estimated by NMR. The deviations were attributed to differences in molecular conformations between interior and surface chains, causing broadening of the WAXS peaks. In the case of an eleventh sample containing well-ordered xylan, the NMR and WAXS methods were in good agreement only after exclusion of a xylan signal at 82.6 ppm from the NMR data.
๐ SIMILAR VOLUMES
~'opolymers of ethyl acrylate (Mt) and n-butyl methacrylate (M2) were prepared by benzoyl peroxide initiation in solution at 60 and copolymer compositions estimated b~ [tsC]-NMR spectroscopy. The kinetic behaviour is approximately ideal with r t = 1/r 2 = 0.47. Relaxation times Tz were determined fo