The Papermaking Potential of Canola Residues; Viable Raw Material

The Papermaking Potential of Canola Residues; Viable Raw Material Reza Hosseinpour Department of Wood and Paper Science, Science and Research Branch, Islamic Azad University, Tehran, Iran. hosseinpourreza@gmail.com Ahmad Jahan Latibari Department of Wood and Paper Science, Karaj Branch, Islamic Azad University. Karaj, Iran. latibari_24@yahoo.com Abstract Non-wood pulping is gaining momentum not only in fiber deficient regions, but also new interest is shown in North America and Scandinavia. Among non-woods fiber sources, chemical pulping of wheat straw and bagasse has been practiced for a long period and reached its mature stage, but uncommon non-wood fibers are being studied. Among such uncommon fiber sources, canola residue is unique. Its woody stem grows to the height of almost 1.5 meter and its diameter reaches 10 mm. Such woody stem exhibits pulping potential which has not been explored. This is on the contrary to the availability of its vast quantities after harvesting. Wheat straw and even bagasse is used as cattle feed in some countries, but canola residue is not suitable for such application. This also indicates the need for pulping study. The objective of present study was to analyze the potential application of canola residue in pulping. At first, the fiber characteristics and chemical composition were assessed and compare with other non-wood fibers. Then different pulping were conducted applying different chemical treatments, and the corresponding pulp properties were characterized. Generally, the result demonstrated the unique behavior of canola lignin toward chemical treatment. After mild chemical treatment applying a mixture of sodium sulfite and sodium hydroxide, pulp brightness reached almost 44% and strength of pulp were comparable with those from bagasse and wheat straw. Such unique behavior confirms its potential as supplementary pulp for paper production. Keywords: Canola, CMP, Brightness, Tensile, Tear. Paper PS-16 1 of 8

Introduction Many developing countries have shown interest in establishing domestic paper production capacities and to fulfill their growing demand for paper commodities and to become selfsufficient. In order to satisfy this requirement, paper production facilities have been forced to utilize uncommon raw materials, especially non-wood fibers. In addition, shortage of wood fiber, the cost-effectiveness and abundance of this fiber sources make non-woods reasonable candidates for pulp and paper production (Fatehi et al., 2009). By far, cereal straws have been the major source of non-woods for the paper production (Sun et al., 2001). However, the results on chemical pulping and papermaking properties of several other non-woods are also available in the literature (Ghatak, 2002; Tutus and Eroglu, 2003). Among agricultural crops, canola has been cultivated to produce seeds for edible oil production, and the interest in its cultivation is increasing around the globe. The canola woody stem has a diameter of one cm and an average height of 1.5 m. After harvesting, the volume of woody stem remaining in the fields is approximately 7 tons/ha. In contrast to cereal straw, the canola stem cannot be used as cattle feed. It is available at a very low cost and apparently suitable for pulping (Sefidgaran et al. 2005). So far the chemical pulping of non woods has been practice successfully and the unbleached chemical pulps of non-woods has been used in the production of corrugated-medium grades, and the bleached ones can be used in the production of printing and writing papers (Fatehi et al., 2009). However, recent reports and finding have shown that, the chemimechanical pulping (CMP) process provides the advantages of a mild chemical treatment and of high pulping yield compared with the chemical pulping process. Due to the importance of emerging CMP pulping, the CMP pulping of woody materials has also been investigated and promising results have been reported (Janson and Mannstrom, 1981; Law and Daud, 2000; Guerra et al., 2005), but the CMP of non-woods and their corresponding paper properties have received much less attention. Recently, the potential application of canola straw on medium density fiberboard (MDF) has shown promising results (Yousefi, 2009). The objective of the report is to provide the information on the papermaking potential of canola residues and to provide data on different pulping of this raw material. Fiber Morphology and Chemical Characteristics Canola fiber length, fiber width, and lumen width are listed in Table 1. The average fiber length of canola (1.32mm) is longer than that of corn, wheat straw, bangkot, and sunflower, but is shorter than that of bamboo (3.49 mm) and of kenaf (2.32 mm). Canola fiber width (31 μm), lumen width (19.5 μm), and cell wall thickness are higher than that of other non-woods in Table1 (Hosseinpour et al. 2010). Species Fiber length (mm) Fiber width ( μm) Cell wall thickness (μm) Lumen width (μm) References Canola 1.32+-0.5 31+-7.4 3.75 19.5+-6.5 Our data Paper PS-16 2 of 8

Corn 0.903 18.45 3.69 11.07 Latibari et al. 2009 Wheat straw 0.74 13.2 4.6 4 Deniz et al 2004 Bamboo 3.49 17.7 5 7.7 Lwin et al 2001 Bongkot 0.82 27 - - Loutfi & Hurter 2004 Kenaf (bark) 2.32 21.9 4.2 11.9 Ververis et at 2004 Sunflower 1.28 22.1 3.3 15.6 Eroglu et al 1992 Table 1- Properties of depithed Canola fibers and other non-wood fibers The chemical composition of canola straw is listed in Table 2 ( Hosseinpor et al. 2010). Species α-cellulose Lignin Holocellulose Pentosans Ash Alcohol-Acetone extractives Hot water solubility Cold water solubility Canola 48.5 20 77.5 17 6.6 6.6 5 13.8 50.3 Our data Corn 33.6 17.4 64.8-7.5 9.5 14.8-47.1 Usta et al, 1990 Wheat straw 38.2 15.3 74.5-4.7 7.8 14 10.7 40.6 Deniz et al. 2004 Rice straw 48.19 17.3 70.85 24.5 16.6 3.52 16.24 10.65 49.1 5 Tutus et al. 2004 Bongkot 42.7 17.2 70 27.2 0.7 0.9 2.8-17.2 Loutfi &Hurter 2001 Sunflower 37.5 18.2 74.9-8.2 7 16.5 15.5 29.8 Eroglu et al. 1992 1% NaOH solubility Reference Table 2- Chemical composition of depithed canola fibers and other non-wood fibers Evidently, the holocellulose content of canola is somewhat higher than that of wheat straw, but similar to that of hardwood or bagasse, while the α-cellulose content of canola straw is lower than that of others. As is well known, the total hemicelluloses and cellulose contents of lignocellulosic materials is expressed as holocellulose content. Thus, these results indicate that the hemicellulose content in canola straw is higher than in other raw materials listed in Table 2. Also, the lignin content of all samples is comparable. CMP Pulping CMP pulping of canola residues were performed applying mild chemical condition in a rotary digester. The liquor-to-fiber ratio was 7:1, while the ph was approximately 13. The CMP process was conducted in three different stages. Firstly, the pretreatment of canola straw was carried out using the chemicals. In this stage, the temperature of the digester was raised to 125 o C in 23 min, and kept at this temperature for 15 min. Secondly, the pretreated canola straw was refined three times using a single disk refiner under an atmospheric pressure. After refining, the pulp samples were washed thoroughly with water, and the total yield of pulps was determined. Then, the fibers were screened using a 14-mesh screen to determine the Paper PS-16 3 of 8

amount of rejects. Thirdly, to further improve the property, a post-refining was performed on the canola straw CMP, using a PFI refiner according to TAPPI T 248. The characteristics of canola canola straw CMP were evaluated in accordance with TAPPI test methods. The tensile, tear and burst strengths were measured according to TAPPI T 494, T 414 and T403, respectively. The thickness of paper-sheets was measured according to Tappi T 411 and then the apparent density was determined considering the actual basis-weight and thickness of the paper-sheets. Sample/Refer ence NaOH Na2SO3 Total yield Reject Cellulose Holocellulose Lignin Ash Non-wood species 1 4 8 68.9 5.9 23.7 48.8 14.5 2.06 Canola Starw 2 4 10 67.3 5.5 23.2 49.2 13.4 2.01 3 8 8 63.3 6.8 22.4 44.7 13.6 1.89 4 8 10 63.1 5.0 22.1 45.0 13.7 1.88 5 12 8 61.4 4.4 20.9 44.0 14.3 1.84 6 12 10 60.7 3.9 20.7 43.6 12.7 1.82 7 12 12 60.0 3.3 20.0 43.8 12.3 1.80 Peng 5.8-72 - - - 17.6 - Bagasse &Simonso n,1992 Mirskokrae 4 8 - - - - 17.8 - Bagasse i et al. 2005 Petit-Conil et al. 2001 5.2-71 2.1 - - - - Wheat Straw Table 3- Pulping condition and chemical composition of Canola straw CMP The effect of the chemical charges on the CMP pulping and the properties of canola straw CMP are summarized in Table 3. By increasing the charge of the chemicals, the total yield and the amount of rejects were reduced. The relatively low yield of canola straw CMP pulps is attributed to the great loss of lignin, α-cellulose, and holocellulose, which were 20%, 48.5%, 72.5% (Tables 2). Additionally, a lower charge of the chemicals applied in the pretreatment of bagasse CMP and of wheat straw CMP in the literature than that applied in the pretreatment of canola straw CMP in the present work (Table 3). However, a similar yield, but at higher lignin content, was obtained for bagasse CMP and for wheat straw CMP than for canola straw CMP (Table 3). Sample ID NaOH Na 2 SO 3 Total Yield Apparent Density (g/cm 3) Tensile Index (N.m/g) Burst index (kpa.m 2 /g) Tear index (mn.m 2 /g) 1 4 8 68.9 0.46 15.94 1.6 3.50 2 4 10 67.3 0.48 16.02 1.2 3.52 3 8 8 63.3 0.50 15.31 1.4 3.35 4 8 10 63.1 0.50 15.25 1.5 4.21 Paper PS-16 4 of 8

5 12 8 61.4 0.59 15.47 2 4.20 6 12 10 60.7 0.50 18.61 1.7 4.64 7 12 12 60.0 0.52 17.79 1.8 3.93 Table 4- Properties of canola straw post refined CMP pulp The tensile index at a given apparent density for canola straw CMP is similar to that for bagasse CMP reported by Peng and Simonson (1992). The tensile index and apparent density of the paper-sheets increased by 15 24% and 18 20%, respectively, by the post-refining treatment Table 4). It is shown that a modest post-refining treatment of canola straw CMP can improve the tensile strength significantly. As described earlier, the post-refining improved the fiber straightening, as evidenced by the decreases in curl and kink index. In this case, the increase in the amount of fines as well as in the fiber straightening can account for the pronounced tensile improvement. The increase in the apparent density is attributed to the improvement in the fiber bonding. By increasing the dosage of the chemicals, the burst and tear indices increased somewhat. Peng and Simonson (1992) reported a much lower tear index (1.5 2 Nm 2 /kg) for the bagasse CMP. In another study, similar burst and tear indices were reported for an industrially produced wheat straw CMP (Sig-oillot et al., 1997). These results imply that the wheat straw CMP and the canola straw CMP had similar strength properties. It is also evident, by postrefining of canola straw CMP, the burst index increased by 20 43%, while the tear index increased by 3 6%. The significant improvement in the burst index from the post-refining treatment is attributed to the straightening of fibers that improves the fiber bonding, as addressed earlier. Neutral Sulfite Pulping Ahmadi et al (2010) investigated the performance of canola straw in neutral sulfite semichemical (NSSC) pulping. Different dosages of active alkali and pulping times at sodium sulfite to sodium carbonate ratio of 3:1 and pulping temperature of 170 o C were applied. Both digester and defibration yields were measured and then the strength of the selected pulps was evaluated. The results of the measurements on the selected pulps are summarized in Table 5. Active alkali Pulping time (min) Total yield Kappa No. Tear index (mn.m 2 /g) Tensile index (N.m/g) Breaking length (km) 8 20 72 66 6 35.6 3.63 1.7 10 20 71.5 65 6.2 38.2 3.89 1.75 12 20 69 64.5 6.4 39.2 3.99 1.87 14 20 68.5 63.5 6.6 42 4.28 2.03 16 20 67 56.5 6.9 44 4.48 2.04 12 40 63.5 50 7.4 57.8 5.89 2.46 12 60 58.7 45 7.5 66.5 6.78 2.57 Table 5- The properties of selected NSSC pulps from canola residues Burst index (kpa.m 2 /g) Paper PS-16 5 of 8

It has been expressed that the performance of canola residues in NSSC pulping varies considerably and the pulping yield is usually low. It is possible to reach defibration yield between 54.5-72% (digester yield between 58.5-87%), but reaching higher yield is difficult using this material. However, with careful refining and back water circulation, defibration yield can be improved. Changing the alkali charge between 8% and 16%, increased the tear strength index from 6 to 6.9 mn.m 2 /g, breaking length from 3.63 km to 4.48 km, burst strength index from 1.7 to 2.04 kpa.m 2 /g and tensile strength index from 35.6 to 44 Nm/g. It can be concluded that canola residues can be considered suitable for unbleached NSSC pulp production to be used as substitute pulp in the production of corrugating medium paper. Soda Pulping Enayati et al. (2010) hace examined the application of soda pulping on canola residues applying active alkali (% NaOH) between 15-22% based on the dry weight of the straw, liquor to straw ratio of 8:1 at 170 o C pulping temperature and different pulping times. The results of pulping yield and kappa number is shown in Table 6. NaOH Pulping time ( min.) Screen yield Reject Kappa No. Degree of polymerization 15 60 35.2 14.5 101.2-15 80 36.9 12.7 97.3-15 100 37.0 11.0 94.6-18 60 43.3 4.6 89.8-18 80 42.6 3.5 83.5-18 100 42.2 3.1 82-20 60 40.5 1.5 70.7 1435 20 80 39.1 1.4 54 1511 20 100 38.5 0.9 36.0 1553 22 60 37.3 0.6 40.0 1579 22 80 37.2 0.4 25.9 1448 22 100 36.6 0.3 24.2 1408 Table 6- The results of soda pulping of canola residues (Enayati et al. 2010) The pulping results indicated that at higher chemical charge, the pulping yield is scarified and the reject is unexpectedly high even after 100 minutes pulping time. However, increasing the alkali charge improved the performance of the soda pulping of this material but the total yield was reduced significantly producing uniform pulp. The kappa number of the pulps varied between 70.1 and 36. Therefore, even 20% active alkali charge did not produce bleachable pulp to be able to produce bleachable pulp. Therefore, the active alkali charge should be increased to 22%. Pulp produced applying 22% active alkali, and 100 minutes time at 170 o C was selected for Elemental Chlorine Free (ECF) bleaching under D 0 EpD1 with 2.8 kg/ton charge of chlorine dioxide and 1.2% NaOH and 0.3% hydrogen peroxide. The brightness of the bleached pulp was raised from the unbleached value of 36.5% ISO to the final value of 78.4% ISO. Paper PS-16 6 of 8

Bleaching partially reduced the strength properties of the canola soda pulp and the tensile index was reduce from 24 Nm/g to 23.1 Nm/g, tear index from 5.07 mn.m 2 / to 4.76 mn.m 2 /g and burst Index was improved from 1.22 kpa.m 2 /g to 1.39 kpa.m 2 /g. The overall results showed the promising potential of canola soda pulp to be used in combination with wood pulps in paper making. References Ahmadi, M., Jahan Latibari, A., Faezipour, M., Hedjazi, S. 2010. Neutarl sulfite pulping of canola residues. Turk. J. Agric. For. 34(2010):11-16. Enayati, A.A., Hamzeh, Y., Mirshokraei,S.A., Molaei,M. 2010. Paper making potential od Canola stalks. Bioresources 4(1): 245-256. Eroglu, H., Usta, M., Kirci, H., 1992. A review of oxygen pulping of some non-wood plants growing in Turkey. Tappi Conference, Boston, USA: 215 222. Fatehi, P., Tutus, A., Xiao, H., 2009. Cationic PVA as a dry strength additive for rice straw pulp. Bioresour. Technol. 100 (2), 749 758. Ghatak, H.R., 2002. Papermaking potential of congress grass: pulpability and fiber characteristics. Tappi J. 1 (1), 24 27. Guerra, A., Mendonça, R., Ferraz, A., 2005. Bio-chemimechanical pulps from Eucalyptus grandis: Strength properties, bleaching, and brightness stability. J. Wood Chem. Technol. 25 (4), 203 216. Hosseinpour, R., Jahan Latibari, A., Farnood, R., Fatehi, P., Sepiddehdam, S.j., 2010. Fiber morphlogy and chemical composition of canola (Brassica napus) stems. IaWA Joiunal 31(4):457-464. Jahan Latibari, A., Golbabaei, F. Ziadzaheh, A. Farzi, M. Vazzirian, A., 2009. Investigation on size distribution and fiber dimensions of corn stalks. Iranian J. Wood Paper Res. 1: 1 14. Loutfi, H., Hurter, R.W., 1997. Bongkot-A potential source of nonwood fiber for paper making. Proceedings of Tappi Pulping Conference, San Francisco, California 2: 817 819. Lwin, M. K., Han,Y.Y., Maung, K.W., Moe, A.Z., Than, S.M., 2001. An investigation on morphology, Anatomy and chemical properties of some Myanmar Bamboos. Proceedings of the Annual Research Conference, Yangon, Myanmar: 267 288. Janson, J., Mannstrom, B., 1981. Principles of chemical pretreatment in the manufacture of CMP and CTMP from hardwood. Pulp Paper Can. 82 (4), 51 63. Law, K.N., Daud, W.R.W., 2000. CMP and CTMP of a fast-growing tropical wood:acacia mangium. Tappi J. 83 (7), 61 68. Paper PS-16 7 of 8

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