Pulp and fiber characteristics of wheat straw and eucalyptus pulps -: A comparison

The response to refining of wheat straw and eucalyptus pulps as well as the relationships between refining, fiber properties and paper properties are described in this paper. Pulps were bleached applying different bleaching sequences and thereafter refined to varying degrees. Pulp and fiber properties were investigated and set into relation to the final sheet properties. The results show that wheat straw pulps respond to refining more easily than eucalyptus pulps and that the differences are due mainly to morphological and ultrastructural differences as well as fines content and xylan content. The development of strength properties of the different pulps was found to be strongly correlated to the number of dislocations, i.e. weak points in the fiber wall, as well as to the morphological appearance of the pulp fibers after refining. A higher initial number and a faster development of dislocations together with the creation of large amounts of fines explain the slower and lower development of strength properties of wheat straw pulps than of eucalyptus pulps. Removal of fines from wheat straw pulps improved not only the drainability of the pulp suspension but also the mechanical and optical sheet properties. This indicates that the fines in the wheat straw pulps act mainly as filler with low bonding properties. Wheat straw pulps are of interest as an alternative for eucalyptus pulps, especially at Shopper- Riegler values lower than 400SR, where good mechanical sheet properties are achieved with wheat straw pulps with no or only minor refining requirement.