The influence of structural changes caused by dry-defibration of the pulp on the mechanical properties of dry-formed cellulosic networks has been investigated. The effects of fibre length, fibre curl and content of fine material on these properties are discussed. The fluff pulps used were one CTMP-grade and two kraft pulps. The primary parameters used to describe the networks were the storage modulus, G'(o) (measured at low strain amplitudes), and the critical strain, gamma(c) (at which the network yields), obtained from dynamic-mechanical measurements, and the maximum force, F-max, sustained by the network and the maximum strain, gamma(max) (at F-max), measured with a specially constructed shear tester. It was noted that the storage shear modulus, G'(o), and maximum force, F-max, were affected in the same manner by the defibration conditions. To improve the deformability of the cellulosic network before rupturing, the ideal dry-defibration process should provide a greater number of free fibres per unit volume without producing fine material, at the same time as the curl index of the fibres should increase. Long and curled fibres are thus to be preferred. (C) 1998 Chapman & Hall.
