Determination of Weibull Parameters by Single Fibre Fragmentation for use in Modelling of Paper Tensile Properties

Abstract: The thesis presents a method for characterization of pulp fibre tensile strength. Single Fibre Fragmentation (SFF) and Weibull statistics were used. Methods for specimen preparation, sampling and analysis of fragmentation data from digital images were developed. The influences of fibre morphology, observable fibre damage and PFI beating on the strain to failure were studied. The increased flexibility of PFI beaten fibres leads to shorter distances between fibre bonds and a higher expected strain at failure. This is suggested as a main contribution to the increase in paper strength by PFI beating.



The Weibull parameters for the studied spruce fibres were also used in a model of a laboratory handsheet. From the model, the influence of fibre tensile and bond properties on the paper tensile behavior was analyzed. Also, the localization of the fracture process zone was modeled. By tuning the prediction to fit an experimental stress-strain curve for handsheets of the corresponding pulps, average values for fibre bond strength were estimated.



Experiment on single fibres and the modeling using the experimental data, clearly suggest that the tensile strength of paper is clearly influenced by the tensile properties of the fibres, rather than the magnitude of the fibre bond strengths alone. SFF combined with the paper model are suggested as a tool for characterizing fibre and bond properties for a pulp. Such knowledge can be used to predict functional properties of paper