Cellulose (2019) 26:1995–2012
2003
Fig. 3 Untreated bleached softwood kraft fiber (#14): a visible dislocations and microcompressions, b collapsed cross-section of this thick-walled BSKP fiber. Width 33.4 l m, thickness 9.35 l m, cross-section area 276 l m 2 , breaking force 300 mN
Fig. 4 HC treated bleached softwood kraft fiber (#6): a external fibrils and a possible longitudinal dislocation, b collapsed cross- section of this relatively thin-walled BSKP fiber. Width 30.3 l m, thickness 4.7 l m, cross-section area 140 l m 2 , breaking force 87 mN
Width 33.2 l m, thickness 9.3 l m, cross-section area 294 l m 2 , breaking force 121 mN
Fig. 5 HC ? LC treated bleached softwood kraft fiber (#3): a external fibrils and longitudinal dislocations and microcom- pressions, b collapsed cross-section of thick-walled BSKP fiber.
Characteristic dimensions of the individual fibers
(b) present cross-section images of the fibers. The microscope images of the fiber cross-sections showed that the lumen of all studied BSKP fibers was completely collapsed, whereas the viscose fibers did not have a lumen. The images of the other tested fibers are presented in the electronic supplementary materi- als S1-S4. A major finding from the individual fiber images was that the untreated BSKP fibers already had a significant number of dislocations.
Characterization of fiber cross-sectional properties (thickness, cross-section area and collapse) is gener- ally difficult using only the fiber width. However, inspecting cross-section area and fiber thickness reveals that a cross-section area of 190 l m 2 approx- imately divides the fibers into thin- and thick-wall classes (see Figures in supplementary material S1). Accordingly, fibers with a cross-sectional area greater
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