Investigating structural changes of cellulose using NMR spectroscopy

Licentiatavhandling, 2013

In this thesis solid-state NMR and NMR cryoporometry were used to gain information of the structure of cellulose. Measurements were conducted on both native and regenerated cellulose, exposed to a range of different treatments. The impact of co-crystallization for hornification was investigated using nanocrystalline cellulose (NCC) as a model system of the crystalline parts of the pulp fiber. Signs of hornification, in form of an irreversible pore collapse and decreased amount of surface area were seen both for native and regenerated cellulose when exposing the samples to drying treatment and it was concluded that co-crystallization could contribute to hornification. In addition, it was proposed that elements of higher hydrophobicity in native cellulose fibrils have an increased preference for aggregation. Both the dissolution and coagulation steps were found to be of importance during regeneration of cellulose. By altering the coagulation media it was possible to form regenerated cellulose ranging from a mainly crystalline sample using water as coagulation medium to an almost non-crystalline sample using an alcohol. It was concluded that water present in the solvent during dissolution could affect the properties of the regenerated cellulose. However, with a small addition of water an apparent maximum conversion to crystalline cellulose II was found which implies that the cellulose has been dissolved to a higher extent in the dissolution step. At high concentration of water the conversion to cellulose II was completely inhibited. The initial cellulose concentration was also concluded to be of importance. At high cellulose concentration the conversion was largely restricted to a semi-crystalline/non-crystalline material.