Rheological characterization of dry-formed networks of rayon fibres

The viscoelastic properties of low-density dry-formed fibre networks have been evaluated by dynamic mechanical measurements in shear. The fibres used were rayon fibres of different diameters (13, 30 and 60 lm) and lengths (2, 4 and 6 mm). The effects of network density and grammage on the viscoelastic properties of the network were demonstrated. An important objective of this study was to assess relations between mechanical properties and fibre or network characteristics. The primary mechanical parameters used to describe the networks were the storage modulus G(0)' measured at very low imposed strain amplitudes (in the linear region) and the critical strain gamma(C) at which the network yields significantly. It was noted that if the network is to be able to withstand high deformations it should exhibit a high value of gamma(C), which in turn, is promoted by a short free segment length between fibre crossings and a large number of contact points per fibre in the network. Long and thin fibres provide an advantage in this context. The modulus G(0)' appeared to be related to the ratio of the free segment length to the fibre diameter. A lower value of this ratio corresponds to a higher G(0)' value and an improved load transfer through the network structure. The networks studied here should in general be regarded as weak compared with other types of networks, e. g. paper. (C) 1998 Chapman & Hall.