2002
Cellulose (2019) 26:1995–2012
Table 3 Fiber cleavage of BSK pulps and a viscose fiber suspension
Untreated
HC treated
HC ? LC treated
Viscose
LW fiber length of pulp (mm)
1.83
1.87
1.80
5.54
AR fiber length of pulp (mm)
0.63
0.64
0.58
2.07
AR fiber length of HCl-treated (mm)
0.32
0.24
0.26
0.72
Cleavage (per fiber)
1.01
1.57
1.21
1.95
Cleavage index (arithmetic) (mm - 1 )
1.58
2.50
2.08
0.94
LW length weighted, AR arithmetic mean
Fig. 2 Schematic image of the fiber bond tester with the laser displacement detection system
et al. (2016). The sample holder was placed under a light microscope, which was equipped with a digital camera (Fischer et al. 2012) and a computer monitor. The tensile test was recorded with the imaging system, which enabled rejection of the tests in which gluing failed. The fibers were strained until break at 1 l m/s elongation speed (0.2%/s strain rate). The initial part of the force-strain curve was not recorded due to pre- tensioning of the fiber before the test. The initial strain that corresponded to the initial force was calculated using the initial slope (initial tangential modulus) of the force–elongation curve. All tests were performed in a climate room at 23 C temperature and 50% relative humidity. The primary data obtained from the single fiber tensile test were load and displacement data. Tensile strength( r f ) in MPa units (Eq. 1) corresponding to the break load (F break ) was calculated using the measured fiber cross-sectional area (A cross ) of each fiber. r f ¼ 1 Þ As the fibers exhibit non-linear stress–strain behav- ior, the tangential stiffness and tangential modulus values were chosen to present the maximum slope of the tensile curve of the individual fiber. Tangential F break A cross ð
stiffness and modulus were calculated as the maxi- mum slope of the load-strain curve of a single fiber divided by the width or the cross-directional area (A cross ), respectively. Tangential slopes, covering all stress–strain data until breaking, were calculated by applying a moving average slope over a constant strain range of 0.6%. The resulting tangential slope was an average at the region of the highest slope. The maximum of the slope on the load-strain curve of a single fiber was defined as force tangent modulus and here denoted simply by M f . In this investigation, the tangential modulus (E f ) (Eq. 2) of a single fiber was obtained by dividing the M f by the fiber cross- sectional area (A cross ). E f ¼ M f A cross ð 2 Þ
Results
Characteristic images of the studied fibers
Figures 3, 4, 5 and 6 present photograph examples of the tested fibers: sub-figures denoted (a) present length–width direction and sub-figures denoted
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