Abstract
Tensile tests of individual bleached kraft pulp fibers and paper sheets of industrial origin were conducted in order to investigate the effect of refining and small-scale fiber deformations on the extensibility of fibers and paper. The shape of the tensile curves of most of the fibers was concave upward (i.e., increasing slope) and consisted of two or three phases suggesting that the fibrillar structure and disordered regions in the fiber wall were straightened out during straining. Only a few of the individual BSKP fiber tensile curves were apparently linear. Elongation of the individual kraft fibers varied from 8 to 32% and the average elongation was not increased by high consistency refining. Tensile test results of laboratory sheets made of the same BSKP pulp suggested that the fiber bonding not only governs paper strength, but also is highly relevant for the elongation of fiber networks. The key conclusion related to this investigation and freely dried sheets was that the increased network elongation and strength after refining is mainly due to increased inter-fiber bonding and a higher shrinkage tendency of the fiber network and not due to the increased elongation or strength of individual fibers.Graphical abstract
Highlights
Properties of individual pulp fibers play a pivotal role in the development of the mechanical properties of fiber networks and structures
The elongation potential of fiber networks is governed by the behavior of single fibers, inter-fiber bonding (Seth 2005) and the network properties (Vishtal and Retulainen 2014)
The effect of mechanical treatments on the load-elongation behavior of commercial bleached softwood kraft pulp (BSKP) fibers and the corresponding papers was studied in order to improve the extensibility of this type of materials
Summary
Properties of individual pulp fibers play a pivotal role in the development of the mechanical properties of fiber networks and structures. From the images (presented in electronic supplementary material), it was possible to divide the tested untreated BSKP fibers into thick-walled and thin-walled fibers using the microtome photographs and a cross-sectional area of 190 lm2 as a limit. Breaking length was reported in order to improve comparability with classical articles related to individual pulp fibers bDue to the low number of BSKP fiber repeats and missing identification images of the tested individual viscose fibers, the value is a ratio of the average breaking force and the average cross-section area.
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