The effect of industrial beating on tensile strength properties has been compared with laboratory beating and the differences observed have been explained in terms of fibre properties.
Tensile strength development is less pronounced for industrial beating than for laboratory PFI-mill beating. Beating in the laboratory Escher-Wyss conical refiner was found to develop strength to an level intermediate between those of the other two.
The fibre characteristic causing these differences was found to be the ability of the fibres to transmit load in thesheet. Fibre deformations introduced during pulping and bleaching are to a large degree removed by PFI-mill beating. Industrial beating shows very little effect in this respect.Tensile strength development could be explained wholly by changes in fibre swelling (water retention value) and in the ability of the fibres to transmit load. The latter property was evaluated by zero-span measurements on rewetted sheets.