Effect of cellulose structure on reactivity of eucalyptus acid sulphite dissolving pulp

Three industrial Eucalyptus globulus acid sulphite dissolving pulps of different intrinsic viscosity (ca. 490–570 cm3/g) with similar xylan content (2.4–3.0%) were partially (ca. 60%) converted to cellulose II by treatment with 12% NaOH and hornified by drying for 8 h at 105 °C to induce changes in physical structure. All three initial and modified pulps were analysed on their Fock reactivity method and Chinese filterability. These dissolving pulps were also examined for the crystallinity degree and the crystallite dimensions assessed by wide-angle X-ray scattering and the fibril aggregation assessed by solid-state 13C nuclear magnetic resonance. The results showed that the reactivity of the dissolving pulp was negatively correlated with the degree of cellulose crystallinity and depended almost linearly on the lateral dimension of the fibril and the dimensions of the fibril aggregates. In hornified pulps, the effect of cellulose physical structure on reactivity was even more pronounced than the intrinsic viscosity of the dissolving pulp. In addition, no unambiguous dependence between the reactivity and the filterability of dissolving pulps was found. Filterability did not correlate clearly with lateral dimension of fibril or fibril aggregates, but depended only on pulp viscosity.