Cellulose
Table 5 Selected properties of papers with added bran
Paper type
Breaking length* (km)
Extensibility* (%)
Tearing resistance* (mN)
Burst test* (kPa)
Air permeability* (s)
Absorbency* (g/m 2 )
2.9 a
0.97 b 0.87 a 0.93 b 0.97 b
980 b 879 a 880 a 960 b
567 a 678 b 689 b 683 b
4.5 a
166 b 184 c 190 c 123 a
WP
WP3W 3.4 b WP5W 3.4 b WP3R 3.8 c WP5R 3.9 c
4.8 ab 5.0 ab
6.1 c 5.1 b
1.05 c 182 c *Differences significant at p \ 0.05, letters in superscript correspond to the statistically similar groups determined with Tukey post hoc test 870 a 689 b
The influence of bran additives on selected paper properties is summarized in Table 5. The breaking length of papers with bran additives is about 25% higher than control samples. It can be explained by a positive effect of the filler increasing the number of connections between paper fibres and therefore the degree of bonding (Retulainen and Ebeling 1993). In this case the bran particles take part in the hydrogen bonds promoting consolidation of the paper structure. It was also noticed that the effect of mixing fibres with bran additions was not following the linear rule of mixture (Karlsson 2007). The breaking length increase was not significantly higher in 5% bran content compare to 3%. The breaking length was highest for paper products with rye bran. The addition of bran seems to have rather casual influence on the paper extensibility, even if increased share of bran slightly augmented extensibility value. Conversely, tearing resistance diminished with increase of the bran content. It was expected as tearing is usually inversely correlated with the tensile strength and breaking length (Caufield and Gunderson 1988). The reduction of tearing can be explained by the fact that addition of bran particles affects fibre–fibre
bonding promoting pulling up of fibres out the network (Yu 2001). The burst resistance index, frequently used to determine the quality of paper, does not depend on the kind, but rather on the amount of filler introduced. It is lowest for the paper without additives, and slightly increases with the added bran content. The trend corresponds to that expected as the burst resistance is as well correlated to the tensile strength (Caufield and Gunderson 1988). Air permeability and absorbance increased in papers with additives. Both properties might be desirable when increased barrier properties against water are required. In the case of waste paper, adding bran leads to early disassembly of the structure of the paper while exposed to degradation; consequently, affecting the air permeability. This peculiarity has a beneficial effect for paper pots, where high air permeability improves the natural ventilation of the root system and stimulates plant growth (Nambuthiri et al. 2015; Akelah 2013). The results of mechanical tests for the compression strength of paper pots before degradation are pre- sented in Table 6. The lowest crushing strength was
Table 6 Results of the crushing strength of paper pots (kPa)
Pot type
Crushing strength* (kPa) SD (kPa) The crushing strength after 3 compression cycles* (kPa) SD (kPa)
414 e 359 d 339 c 330 b 357 d
388 d 320 c 300 a 299 a 315 b
WP
12
11
WP3W
15
6
WP5W
5
7
WP3R
8
6
WP5R
14
6
Commercial pots 291 a
9
0**
–
*Differences significant at p \ 0.05, letters in superscript correspond to the statistically similar groups determined with Tukey post hoc test **Experimental samples were damaged already after first compression cycle
123
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