Structural differences between non-wood plant celluloses: evidence from solid state NMR, vibrational spectroscopy and X-ray diffractometry

Cellulose from flax, hemp, kenaf and sorghum was investigated by solid state NMR and vibrational spectroscopy, and the structural differences found were validated by X-ray diffractometry. All three techniques indicate a notable region of order in the cellulose of both flax and hemp, but the absolute crystallinity values are not directly comparable. CP-MAS 13C-NMR and FTIR spectroscopy revealed the presence of Ia and Ib forms in all the samples. On passing from flax and hemp to kenaf and sorghum the progressive loss in the crystalline phase is evidenced by 13C-CPMAS T1 measurements; 1H-CPMAS T1r measurement revealed an analogous loss in phase dimension for the ordered phase, but similar dimension values for the paracrystalline and amorphous phases. The FTIR and FTRaman spectra of all the cellulose samples reveal the same chain conformation but a different hydrogen bond pattern, and this accounts for the NMR and X-ray results.