The production of Micro-Fibrillated Cellulose (MFC) requires high energetic cost, and the reduction of the energy consumption is still a target of extensive studies. During the intensive mechanical treatment, the residual hemicelluloses that are strongly interacting with cellulose in the starting pulp appeared to have a positive correlation with MFC quality as judged by their reinforcement capacities of handsheets. We analysed the structure of these residual hemicelluloses and their adsorption features on cellulose. Various chemical pulps, differing by the wood species (softwood/hardwood) and pulping process (sulfite/Kraft) with or without drying, were selected as raw materials for MFC production. The hemicelluloses/cellulose compositions of the pulps and the resulting MFC were determined with sugar component analysis. Aggregation of microfibrils in MFC suspensions was characterized using UV visible spectroscopy and insights on molecular conformation and crystallinity were obtained using CP-MAS NMR spectroscopy in humid and dry conditions.<br/>More than 60% of residual hemicelluloses were extracted from birch Kraft MFC using aprotic polar solvents. The extracted fraction corresponded to a homopolymer of β-1,4 linked xylan of high purity. In the dry state, the NMR spectra of MFC before extraction were a linear combination of cellulose and hemicelluloses fractions. In the wet state on the other hand, isolated xylan shows spectra typical of three-fold helix with a signal of C4 at 75 ppm whereas that in the MFC before extraction has a supplementary component at 82 ppm in agreement with the putative conformational change of xylan when adsorbed on the cellulose surfaces. Similar results were obtained on reconstructed models. The amount of residual xylan together with the accessible cellulose surface estimated from nitrogen adsorption of solvent exchange-lyophilized aerogel suggest that a monolayer of xylan is adsorbed on the microfibril aggregate surfaces. The residual xylan seems to prevent the tight aggregation of cellulose microfibrils by poisoning the interaction between the surfaces of cellulose.

Residual xylan desorption and re-adsorption on the cellulose microfibril

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.