Bulk and surface characterization of unbleached and bleached softwood kraft pulp fibres

The main difficulties in wood and pulp fibre characterization arise from the numerous components of the different chemical structures. The processing of wood determines some structural modifications in its components, depending on the wood type and on the applied procedure. In-bulk and Surface methods (ATR-FT-IR, XPS, SEM, XRD, DSC, TG) have been applied to analyze unbleached and bleached softwood kraft pulp fibres, and the differences between the samples have been established. The hands corresponding to the allomorph phases I alpha and I beta in cellulose were identified in softwood kraft pulp fibres. The crystallinity degree was determined from the absorbance FT-IR ratio (1280/1200) and XRD data. The increase in the apparent crystal size (ACS) and crystallinity index of the cellulosic fibres, determined after bleaching by XRD, evidenced a lower number of small crystallites, which improved fibre crystallinity, a reaction which was also due to the removal of amorphous hemicelluloses and lignin during bleaching.The differences between unbleached and bleached softwood kraft Pulp fibres referred to characteristic temperatures and mass losses during various thermogravimetric steps, lower overall activation energies being recorded in the first step and higher, respectively, in the other two steps of the bleached softwood kraft pulp fibres, comparatively with the values registered In unbleached pulps.The ATR-FT-IR and XPS results supported the idea that the amount of oxygen atoms was higher on the surface of the bleached kraft pulp fibres than on that Of the unbleached kraft pulp ones. The decrease in the O/C ratio and the increase in the C(ox)/C(unox) Suggest the removal of the carbon-containing compounds from the pulp fibre surfaces after bleaching.The unbleached material was quite heterogeneous, with intact individual fibres, while, after bleaching, the surface of the individual fibres changed, becoming smooth. It was also observed that cellulose aggregates were running in fibre direction and that, after bleaching, the diameter of the cellulose fibres was smaller.