Dipolare Spin‐Gitter‐Relaxation in Polyethylen niederer Dichte

Ludwigs, K.; Geschke, D.

doi:10.1002/andp.19814930416

Cited by 2 publications

(1 citation statement)

References 10 publications

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“…for the amorphous and crystalline regions of several other polymer systems. [19][20][21][22] There is considerable evidence from X-ray diffraction,23'24 electron microscopy,26 and computer modeling studies18 that natural cellulose exists in the form of elementary fibrils with cross-sectional dimensions of 35 Á X 35 Á. These elementary fibrils aggregate in a regular manner to form larger crystalline microfibrils with sizes which depend upon the biological source of the cellulose.…”

Section: Discussionmentioning

confidence: 99%

Proton nuclear magnetic resonance moment and relaxation study of cellulose morphology

MacKay¹,

Tepfer²,

Taylor³

et al. 1985

Macromolecules

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Proton magnetic resonance pH NMR) has been used to determine the second moment (M2) of the line shape, solid echo decay, and dipolar (Tld), rotating frame (Tlp) and spin-lattice (Tt) relaxation times of unaltered, crystallite-enriched, and gelled-reprecipitated samples of cotton and filter paper cellulose.For all samples, the measured M2 was within 30% of that for the rigid lattice, indicating that cellulose microfibrils are almost rigid on the NMR time scale of 10"5 s. Measurements of 7\ as a function of frequency indicated the presence of a low amplitude but important motion occurring in cellulose at about 10-15 MHz which may be methylol group reorientation. Measurements of Tld, Tlp, and the solid echo decay revealed the presence of two types of domains which we assign to crystalline and paracrystalline cellulose. Crystallite-enriched cellulose contained material of only one domain type. Cellulose of reduced crystallinity (gelled-reprecipitated) contained a corresponding increase in the domain we assigned to paracrystalline cellulose. Our results are in agreement with a model in which the crystalline cellulose domains consist of rigid crystalline microfibrils with cross-sectional widths of 100-400 Á and the paracrystalline cellulose domains consist of smaller elementary fibrils with lower packing density.

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Section: Discussionmentioning

confidence: 99%