The dynamic viscoelastic properties of pulp suspensions having consistencies, cm3 ranging from 2-13% were measured using a Weissenberg Rheogoniometer. A special reservoir-type parallel plate fixture was designed to minimize oozing and compression during sample loading. Data for the complex modulus, G*, were obtained for a chemical thermal mechanical pulp and a pine sulfate pulp as functions of strain and frequency. Results for the elastic part of the modulus, G', show a relative insensitivity to frequency over the range l0 -* to 5 s-'. The applied strain has a significant effect, in some cases reducing the modulus by half. This effect was most pronounced at the lower consistencies where it is postulated that the suspension consists of small flocs loosely connected by individual fibres. At small strains, the linkages are disturbed elastically, whereas, as the strain increases, the connections are broken and must reform. At higher consistencies there is a continuous network of fibres, and this breakage-reformation mechanism is not active. This view is supported by nonlinear effects observed in the suspensions (harmonic stresses produced in response to a single frequency strain) which are largest at the low consistencies. The measured yield stress values, as determined from the storage modulus data, are shown to agree with earlier studies.
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Damani et al. (1993) studied this question.
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