GÜLSOY and KILIÇ PEKGÖZLÜ / Turk J Agric For
Also, increased screen mesh resulted in lower fiber aspect ratio. The weight percentage of long fiber fractions was 83% and 68.7% for European black pine and European aspen, respectively. Fiber fraction had a statistically significantly effect on tensile index (P < 0.05). Also, effect of fiber fraction depended on the wood species (Figure 1). Tensile indexes of R16, R30, R50, and R100 fractions in European black pine kraft pulp were determined as 39.71 Nm/g, 45.30 Nm/g, 43.96 Nm/g, and 34.86 Nm/g, respectively (P < 0.05). These results can be explained by long and stiff fibers of lower screen numbered fractions, which have poor bonding characteristics (Huang et al., 2012). Tensile index depends on bonding ability of fibers (Rydholm, 1967; Levlin, 1999, Dutt et al., 2009; Jahan and Rawshan, 2009). Flexible fibers produce large contact areas for fiber-
to-fiber bonding. In European aspen samples, tensile indexes of R30, R50, R100, and R200 fractions were found as 33.22 Nm/g, 38.47 Nm/g, 42.20 Nm/g, and 46.85 Nm/g, respectively. This result can be attributed to increasing vessel element numbers in high screen mesh fractions. Thin-walled vessel elements collapse during papermaking, and their wide surface increases the interfiber bonding. On the other hand, it can be ascribed to the high apparent density of handsheets of high screen mesh numbered fractions. Higher density indicates better interfiber bonding in the sheet. A positive correlation between screen mesh number and tensile index has also been reported in previous studies (Reyier, 2008; Hafrén et al., 2014). The relationships between the fiber fraction and tear index of handsheets are presented in Figure 2. As can be seen in Figure 2, the tear index of handsheets
55
d
50
d
c
c
45
b
b
40
a
a
35
30
25
20
15
10
5
0
R50 R100 European aspen
R16
R30 R50 European black pine
R100
R30
R200
Figure 1. Effect of fiber fractionation on the tensile index of handsheets.
a
12
b
10
c
8
6
d
4
a
b
c
d
2
0
R16
R30 R50 European black pine
R100
R30
R200
R50 R100 European aspen
Figure 2. Effect of fiber fractionation on the tear index of handsheets.
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