CHEMISTRY AND SURFACE CHEMISTRY OF VESSELS IN EUCALYPTUS KRAFT PULPS

Vessel picking is a problem that paper professionals are coping with and struggling to find a solution for. The behaviour of vessel elements in pulp and papermaking processes needs to be understood and their chemistry and morphology has to be clarified. This study focused on the vessel chemistry and surface chemistry, morphology and nanostructure of vessel elements. Our efforts have been put in to clarify the effects of cooking and bleaching on the vessel chemistry and ultrastructure. XPS was applied to the surface measurements, and the ultrastructure was investigated by FE-SEM and AFM. Vessel chemical composition was also investigated by Py-GC/MS. The main findings can be summarized as following: 1) Vessel elements of pulps had a similar chemical composition with fibres. The most significant differentiation could be found in the content of cellulose and lignin, i.e. vessel elements were richer in cellulose compared to fibres, and lignin could be found in the vessels even after bleaching stages. 2) FE-SEM images suggested that the cell wall structure of vessel elements was layered and complex, and the different layers were removed layer by layer during the pulping and bleaching processes. The layered wall structure strengths the vessel elements and due to this unique construction the vessel elements may pass through the whole fibre line, including refining and recycling, undamaged.

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