Localisation and quantification of chemical functional groups on pulp fibres

[摘要] ENGLISH ABSTRACT: The distribution of different free chemical functional groups on wood and pulpfibres was determined by means of atomic force microscopy (AFM) withchemically modified tips. Because these functional groups show a higheraffinity to similar groups on the substrate surface during scanning, AFMimages were recorded using an additional digital pulsed-force mode (DPFM)controller. This allowed the distribution of the chemical components to beimaged and to a degree, also to be quantified. The investigated tip coatingsshowed different sensitivities towards the major chemical components presentin wood fibres. These components were determined on spin-coated films aswell as wood fibres. It was possible to make a clear distinction betweencellulose and lignin in both cases. This technique could therefore be used todifferentiate between cellulose and lignin present on pulp fibre surfaces and toconfirm the successful removal of lignin by pulping.The chemical composition of wood fibres and fibre surfaces of several acaciaand eucalyptus species, and hybrids originating from various growth sites inSouth Africa, are compared. The objective was to determine the differences inchemical surface composition due to genetics or site. The motivation for thiswas to eventually facilitate a tailor-made supply of wood for pulping whichresults in an optimal blend of fibres that can be pulped together with similaryields. This, however, first requires a sound knowledge of the fibre properties.The surface functionality on the single fibre level is a key property because itdetermines how good inter-fibre bonding will be when paper is formed, whichin turn depends to a large degree on the amount of free hydroxyl groups thatare available and therefore on the cellulose content on the fibre surface.The cellulose and lignin contents on the fibre surface were determined withchemical force microscopy (CFM), a variation of AFM. CFM involves the useof chemically modified tip using selected functional groups. Since, the generalbulk composition of the fibre and the surface composition differ, bothparameters were determined. Significant differences in the cellulose and lignincontent on fibre surfaces were found, with regard to genotype and site, respectively. In some, but not all, cases the surface composition of woodfibres followed the bulk composition and differences were generally morepronounced. Differences due to genotype were significant, especially withregards to the surface lignin content - but variation due to site was alsodistinctly recognisable.This variation in surface functionality could be the reason why some pulpwoodblends result in a lower pulp yield and different quality.

[发布机构] Stellenbosch University