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Xhmka PACTHTE^BHOTO CBIPBA. 2009. №2. C. 43-46.
UDK 676.022.6
IMPACT OF XYLANASE PRETREATMENT ON PEROXIDE BLEACHING STAGE OF HEMP PULP
© I. Cil1, H. Bermek2, C. Atik1*
Istanbul University, Faculty of Forestry, Bahcekoy Istanbul, 34473 (Turkey)
E-mail: [email protected]
2Istanbul Technical University, Istanbul (Turkey)
Pretreatment of hemp pulp with xylanase was investigated. Unbleached hemp pulp was treated with commercial xylanase, and then bleached with hydrogen peroxide. Control pulp bleached with out xylanase was compared with xylanase bleached pulp. Application of xylanase was found to have a positive effect on followed peroxide stage in terms of low kappa number and high brightness of pulp.
Keywords: hemp, xylanase, peroxide, bleaching.
This work was supported by the Research Fund of the Istanbul University. Project Number T-269/18062003. Introduction
The process following the cooking and causing the great deal of environmental pollution in pulp production is bleaching, especially conventional chlorine bleaching. Therefore researchers try to develop bleaching methods, which will reduce chlorine consumption or totally omit the chlorine from the process. Part of these studies is focus-sed on biological processes in pulp bleaching. Due to the difficulties on the controls of fungal growth, the usage of fungi for bleaching purposes does not find a wide utilization. On the other hand, after initial reports that xylanase enhances bleaching of pulp and saves up to 25 % chlorine containing chemicals [1], research was focused on xylanase and other fungal enzymes. Xylanases provide the possibility of selectively removing up to 20% of xylan from kraft pulp [2]. Nowadays prebleaching of pulps with xylanase is being applied in many plants. Meanwhile, Totally Chlorine Free bleached pulp production is estimated as more than 15% of total pulp production [3].
One potential source of fiber source is agricultural crops, either in the form of residues of food crops or plants grown especially for fiber. One species that have generated interest as a fiber source is industrial hemp (Canabis sativa L.). Hemp has a number of properties (long and strong fiber, low lignin content) that favor its use as a paper-making raw material [4].
The objective of the present study was to evaluate the benefit of the treatment of hemp pulp with enzyme in terms of pulp yield, bleachability and quality of the pulp.
Materials and methods
Unbleached hemp was supplied by the Mopak Taskopru Mill Turkey. Commercial xylanase Pulpzyme HC from NovoNordisk were used.
The enzyme activities were determined by dinitrosalicylic acid (DNS) method [5]. 200 ^l of diluted enzyme solution was incubated with 1.8 ml of %1 (w/v) birch wood xylan (Sigma) solution (100 mM/l acetate buffer with 0,4% Tween 20 pH 5) at 50 °C for 10 min. One unit (U) of xylanase activity was defined as the amount of enzyme that catalyses the release of one micromole of xylose equivalent per minute of reaction.
* Autor to correspondence.
Chemical bleaching of pulps. The bleaching of pulps was carried out using oxygen (O), chelating (Q), enzyme (X) and hydrogen peroxide (P) treatments in sequence OQXP. All bleaching stages except oxygen were performed in plastic ziplock bags in a water bath with intermittent kneading. The oxygen stage was carried out in a 450 cm3 stainless steel pressurized vessel immersed into a water bath. Oxygen stage conditions were 40 g pulp (o.d.), 10% consistency, 70 °C temperature, one hour duration, 1,5% NaOH, 0.2% MgSO4 and pressurized with oxygen (1 MPa). The EDTA treatment was carried out at % 3 consistency using 0,2% EDTA for 60 minutes at 60 °C. The pulps (10% consistency and without buffer) were treated with 600 mU/g and 900 mU/g dry pulp Xylanase AN for one hour at 60 °C, pH 5. The multiple variations of peroxide bleaching stages were performed, and consistency 10%, NaON - 1,5%, MgSO4 - 0,2% conditions was equal for all of them. The peroxide concentration, temperature and duration conditions were consequently 2% H2O2 and 3% H2O2, 70 and 80 °C, 2 and 3 hours
The control samples were bleached with omitting the xylanase treatment under the equal other conditions. At the end of the bleaching stage, spent liquor was removed from pulp by centrifuging to 35% dry matter content and the pulp was washed. Prior to use and after each bleaching step pulp was thoroughly washed with one liter of distilled water, and finally with 0,5% H2SO4.
Analyses of pulps. Handsheets were prepared in buhner funnel, while distilled water was used for stock preparation and sheet formation. Chemical properties of pulp were determined according to TAPPI test methods. Optical properties were determined with Elrepho 3300 spectrophotometer (Datacolor) according to ISO test methods.
Results and discussion
Figure 1 shows that during the O and Q bleaching stages kappa number values decrease steadily. Kappa number of xylanase stage with 600 mU/g xylanase remains approximately the same decreasing trend of previous bleaching stages. Increasing of enzyme concentration from 600 to 900 mU/g also corresponds to decrease of kappa number with about 0,4 points (in other words increasing of enzyme concentration with 50% corresponds to 3,9 times more effective lignin removing).
Lignin removing ratio in peroxide stages was also straight proportional to peroxide concentration and temperature conditions of the particular case. Increase of peroxide concentration from 2 to 3% and temperature from 70 to 80 °C cause 7,4% increase of lignin removing. While difference in kappa number between control and low xylanase treated samples are 0,31 points for low temperature and peroxide concentration, the differences for high enzyme were at least 1,05 point and higher. After prolongation of peroxide stages form 2 to 3 hours, the decrease ratios in kappa number for all cases do not change at all.
Alkaline solubility data (Figure 2) shows decrease of hemicellulose ratio after O stage and increase during the following Q stage. As it is expected the hemicellulose ration decrease after xylanase treatment and decreasing depend on concentration of enzyme. Enzymatic pretreatment of pulps contribute to alpha cellulose degradation. After peroxide stage of enzyme treated hemp the Si8 solubility increase with about 1,0 point.
Si0 solubility of bleached pulp decreases after O stage. In other words the ratio of hemicellulose and low molecular weight cellulose decrease. During the stage oxygen and alkaline cause peeling reaction [6], therefore removed hemicellulose and low molecular weight fraction in pulp decrease. During the following bleaching stages the degradation occur faster than removing therefore S10 solubility values increase. After O stage the ISO brightness development of hemp pulps was approximately 6 points. The brightness development can be increased with further increase of temperature, but the cellulose degradation (mass lost) increase to and drain ability decrease dramatically.
During the chelating was not observed significant changes on pulp brightness properties, while decrease was observed after enzymatic treatments. In spite of this decrease (3,4-2,8%) during the enzyme stage the ISO brightness values after peroxide stage increase rapidly (23%) to the level (11%) higher than the control. The highest brightness value was reached at 80 °C temperature and 3% peroxide conditions.
Impact Of Xylanase Pretreatment On Peroxide Bleaching
45
-o edta —o-p-2% / 70 °c
.............□...............p-3% / 70 °c —a—p-2% / 80 °c —0-p-3% / 80 °c
.......x-600 -x-900 .. .o... p-2%/70 °c (x-600)
....... p-3%/70 °c (x-600) —•-p-2%/70 c (x-900) —■-p-3%/70 °c (x-900)
p-2%/80 °c (x-600) p-3%/80 c (x-600) —*-p-2%/80 °c (x-900)
-*-p-3%/80 °c (x-900)
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.............o...............p-3% / 70 °c
.......x-600
p-3%/70 °c (x-600) p-2%/80 °c(x-600) —*-p-3%/80 °c (x-900)
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x-900
— p-2%/70 °c (x-900)
- p-3%/80 °c (x-600)
-o-p-2% / 70 °c
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■-©■■■ p-2%/70 °c (x-600)
-■-p-3%/70 °c (x-900)
-a-p-2%/80 °c (x-900)
Figure 1. Changes of Kappa number during the bleaching Figure 2. Changes of S18 solubility during the bleaching stages stages of pulp of pulp
-o
......p-3% / 70 °c
■ x-600
■ p-3%/70 °c (x-600)
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-p-2% / 80 °c x-900
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p-2%/80 °c (x-600) —o- - - p-3%/80 °c (x-600) -«-p-3%/80 °c (x-900)
—o-p-2% / 70 °c
—o-p-3% / 80 °c
■ -0— p-2%/70 °c (x-600)
—■-p-3%/70 °c (x-900)
—a-p-2%/80 °c (x-900)
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.............q...............p-3% / 70 °c —6—p-2% / 80 °c
.......x-600 -x-900
....... p-3%/70 °c (x-600) —•-p-2%/70 °c (x-900)
■ p-2%/80 °c (x-600) —o- - - p-3%/80 °c (x-600)
—♦-p-3%/80 °c (x-900)
—o-p-2% / 70 °c
—o-p-3% / 80 °c
- -o- ■ ■ p-2%/70 °c (x-600)
-■-p-3%/70 °c (x-900)
—a-p-2%/80 °c (x-900)
Figure 3. Changes of S10 solubility during the bleaching stages of pulp
Figure 4. Changes of ISO brightness during the bleaching stages of pulp
Conclusion
Treatment of hemp pulp with xylanase has a positive effect on hydrogen peroxide bleaching stage. There was observed decrease of kappa number value with one point while the increase of ISO brightness was more significant. After xylanase treatment the effectiveness of peroxide bleaching stage nearly doubled
Reaching the same brightness level of hemp pulp without the xylanase treatment will be possible with prolongation of treatment, increasing of temperature or increasing of peroxide concentration. But, in all these cases the degradation of cellulose will be higher as it was seen in pulp solubility data.
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Bibliography
1. Viikari L., Rauna M., Kantelinen A., Linko M., Sundquist J. Bleaching with enzymes. Biotechnology in the Pulp and Paper Industry // 3rd International Conference Stockholm, Proceedings 1986. P. 67-69
2. Kantelinen A., Hortling B., Sundquist J., Linko M., Viikari L. Proposes Mechanism of the enzymatic bleaching of kraft pulp with xylanases // Holzforshung. 1993. V. 47. P. 318-324.
3. Young R.A., Akhtar M. Environmentally friendly technologies for the pulp and paper industry. Jon Wiley & Sons, Inc. 1998.
4. Bowyer J.L. Industrial hemp (Canabis sativa L.) as a papermaking raw material in Minesota: Technical, economic and environmental considerations. 2001.
5. Bailey, M.J., A note on the use of dinitrosalicylic acid for determining the products of enzymatic reactions // Applied Microbiology and Biotechnology, 1988. V. 29. P. 494-496.
6. Sousa I.J., Bouchard J., Methot M., Berry R., Argyropoulos D.S. Carbonhydrates in Oxygen delignification. Part I: Changes in Cellulose crystallinity // Journal of pulp and paper sciance 2002. V. 28. P. 167-170.
Поступило в редакцию 1 сентября 2008 г.
После переработки 3 ноября 2008 г.
