C-13 NMR-STUDY OF SOLID-STATE REACTION OF CELLULOSE WITH LIGNIN MONOMERS

Interactions between cellulose and lignin during thermal treatment of lignocellulosic materials have been investigated by C-13 NMR spectrosc opy of the products obtained by solid-phase reaction of cellulose with lignin model compounds. High resolution NMR spectra of the product of reaction between vanillyl alcohol and cellulose, dissolved in a syste m of dimethyl sulfoxide - N,N-dimethyl morpholine oxide at 90 degrees C, indicated that the linkage between lignins and polysaccharides coul d be formed. Since the product obtained from the reaction of veratryl alcohol was not soluble in this solvent, the formation of the carbohyd rate-lignin bond has also been investigated by C-13 CP-MAS NMR spectro scopy. The spectra were found to be comparable with those recorded for lignin-saccharide complexes in native lignocellulosic materials. Prot on relaxation times were measured during a spin-diffusion experiment f rom the point of view of each phase. This made it possible to study th e magnetisation of C-13 nuclei under high resolution conditions. The l ignin monomers and the amorphous phase of cellulose showed the same re laxation times indicating that spin diffusion between the lignin model compounds and cellulose is complete and homogeneous due to spacial pr oximity of spins. This result is consistent with the existence of lign in-carbohydrate linkages formed during the thermal treatment of wood.