Ultrastructural Characterization fo Stone Groundwood (SGW) Fibre Development Provides Insights on Derived Pulp Properties, 2007 International Mechanical Pulping Conference

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Fundamental knowledge on fibre development at the cell wall ultrastructural level is still very limited for mechanical pulps, particularly for groundwood pulps. Therefore, a pilot scale stone groundwood (SGW) pulping study was performed on selected juvenile and mature Norway spruce wood with emphasis on ultrastructural aspects of fibre development and cell wall modification using scanning electron microscopy (SEM). SGW pulps and handsheets from juvenile wood (JW) exhibited improved physical properties such as light scattering, tensile- and tear strength and higher sheet density compared to mature wood (MW). SEM investigation indicated that an explanation for the differences is most likely related to the manner of fibre processing and development at the ultrastructural level. Results showed MW fibres to contain reduced long-fibre fractions and, more open fibres as a consequence of longitudinal fibre breakage and enhanced S1 fibrillation. In contrast, juvenile fibres showed a 14% increased long-fibre fraction and typical S2 fibrillation. JW fibre fibrillation showed features similar to that reported for thermomechanical pulp fibres where the native morphological fibre micro- and nanostructure regulate the manner of fibre fibrillation. Studies suggest that raw materials rich in juvenile wood (e.g. top logs) may be advantageous for the SGW process.