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Pulpwood Quality of the Second Generation Acacia auriculiformis

  • The physical, chemical and fibre characteristics of the 6, 8 and 10 years old akashmoni (Acacia auriculiformis) wood from the second generation seed and their suitability for pulping were assessed and compared with the wood of 10 years old from the first generation seed. The A. auriculiformis of 8 years old had the highest α-cellulose and lower lignin than those of 6 and 10 years old, which are similar to the first generation wood. This study also evaluated the effect of cooking time, temperature and active alkali on kraft pulping. The most important influence factors for pulp yield and kappa number were active alkali charge and time. The highest screened rejects were observed for young tree. Delignification degree of the 1st generation was faster than that of the 2nd generation A. auriculiformis.
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    Griffin A R, Twayi H, Braunstein R, et al., 2014. A comparison of fibre and pulp properties of diploid and tetraploid Acacia mangium grown in Vietnam. Appita Journal, 67(1):43. DOI:10.1007/s10570-013-0129-7.
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    Jahan M S, Chowdhury N, Ni Y H, 2010. Effect of different locations on the morphological, chemical, pulping and papermaking properties of Trema orientalis (Nalita). Bioresource Technology, 101(6):1892-1898. DOI:10.1016/j.biortech.2009.10.024.
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    Jahan M S, Sabina R, Rubaiyat A, 2008. Alkaline pulping and bleaching of Acacia auriculiformis grown in Bangladesh. Turkish Journal of Agriculture and Forestry, 32(4):339-347. DOI:10.1590/S0103-90162008000600016.
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    Jusoh I, Abu Zaharin F, Adam N S, 2013. Wood quality of Acacia hybrid and second-generation Acacia mangium. BioResources, 9(1):150-160. DOI:10.15376/biores.9.1.150- 160.
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    Lourenço A, Baptista I, Gominho J, et al., 2008. The influence of heartwood on the pulping properties of Acacia melanoxylon wood. Journal of Wood Science, 54(6):464-469. DOI:10.1007/s10086-008-0972-6.
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    Oluwafemi O A, 2007. Wood properties and selection for rotation length in Caribbean pine (Pinus caribaea Morelet) grown in Afaka, Nigeria. American-Eurasian Journal of Agricultural and Environmental Science, 2007, 2(4):359-363.
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    Ribeiro R A, Colodette J L, Vaz Júnior S, 2018. Effect of residual effective alkali on eucalyptus kraft pulp yield and chemistry. Cerne, 24(4):408-419. DOI:10.1590/010477602018-24042593.
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    Rosli W D W, Mazlan I, Law K N, 2009. Effects of kraft pulping variables on pulp and paper properties of Acacia mangium kraft pulp. Cellulose Chemistry and Technology, 2009, 43(1):9-15. DOI:10.1007/s00226-008-0200-y.
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    Santos A, Anjos O, Amaral M E, et al., 2012. Influence on pulping yield and pulp properties of wood density of Acacia melanoxylon. Journal of Wood Science, 58(6):479-486. DOI:10.1007/s10086-012-1286-2.
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Pulpwood Quality of the Second Generation Acacia auriculiformis

    Corresponding author: M Sarwar JAHAN, sarwar2065@hotmail.com
  • 1. Pulp and Paper Research Division, Bangladesh Council of Scientific & Industrial Research Laboratories, Dhaka 1205, Bangladesh
  • 2. Department of Applied Chemistry and Chemical Engineering, University of Dhaka, Dhaka 1205, Bangladesh

Abstract: The physical, chemical and fibre characteristics of the 6, 8 and 10 years old akashmoni (Acacia auriculiformis) wood from the second generation seed and their suitability for pulping were assessed and compared with the wood of 10 years old from the first generation seed. The A. auriculiformis of 8 years old had the highest α-cellulose and lower lignin than those of 6 and 10 years old, which are similar to the first generation wood. This study also evaluated the effect of cooking time, temperature and active alkali on kraft pulping. The most important influence factors for pulp yield and kappa number were active alkali charge and time. The highest screened rejects were observed for young tree. Delignification degree of the 1st generation was faster than that of the 2nd generation A. auriculiformis.

1.   Introduction
  • Akashmoni (Acacia auriculiformis), an exotic fast growing tree species, was introduced to Bangladesh in 1960s as the shade tree in tea estates. In 1983, the trial plantations of the Acacia were established and people found that the A. auriculiformis and A. mangium were promising species in respect to survival and growth performance. The participatory plantations were raised by exotics fast growing species such as Acacias, Eucalyptus. In the social forestry programs, these exotics species provided return shortly. The A. auriculiformis are able to create vegetation cover in degraded forest areas easily. The Acacia also planted in agro-forestry. Bangladesh Forest Department has 44 000 hm2 forestland for social forestry program. Produced wood can be utilized in pulp mill as Bangladesh facing acute shortage of raw material.

    A lot of studies have been carried out on the pulping of Acacia species. Pulpwood samples from 8-year old A. mearnsii and Eucalyptus grandis plantations grown in Zimbabwe were evaluated for kraft pulping, bleaching and papermaking properties by Muneri (1997). At about the same kappa number, the A. mearnsii pulp had lower strength properties but higher opacity. Xue et al. (2001) studied on three species of plantation fast-growing Acacia woods of different ages, which were subjected to kraft cooking and bleaching by the use of CEH sequence. These three Acacias were easily pulped using the conventional kraft process with acceptable pulp yields, i.e., 50% total yield with kappa number of 20. The pulp could be bleached using conventional CEH bleaching sequence giving brightness higher than 75%. Miyanishi and Watanabe (2004) studied on A. mangium, which was used for the first time afforestation in 1991 at provinces of South Sumatra, Indonesia. Prior to the construction of a new pulp mill, kraft pulping characteristics of plantation-grown A. mangium was investigated in laboratory. It was found that the pulp yield was very high and comparable to E. globules. Khristova et al. (2004) studied on two A. seyal varieties (fistula and seyal) grown in Sudan for pulping and papermaking with different alkaline methods. The alkaline sulfite anthraquinone and methanol (ASAM) pulping gave the best results in yield, degree of delignification and strength properties. In our previous study, A. auriculiformis from the first generation seed was investigated and obtained pulp yield of 43%– 44% and kappa number of 22–24 at the conditions of 20% alkali and 2.5 h of cooking in soda, 16% alkali and 2.5 h of cooking in soda-AQ, and 18% alkali in 2 h of cooking in kraft process (Jahan et al., 2008). Rosli et al. (2009) studied on the influence of the pulping variables (active alkali charge, sulfidity, temperature and pulping time) on the pulp yield, kappa number and strength properties of A. mangium kraft pulp. When beaten to a freeness of 500 mL and 50% yield, the kraft pulp from A. mangium evidenced excellent physical properties. Santos et al. (2012) investigated A. melanoxylon and its natural variability. Under the same experimental conditions of kraft pulping, screened pulp yield ranged from 47.0% to 58.2%, kappa number of 10.9–18.4 with the variation of wood density from 449 kg/m3 to 649 kg/m3 were obtained. Pulping properties and fibre characteristics of the clones of A. mangium grown in Vietnamwere reported by Griffin et al. (2014). Kraft pulp yield at kappa 20 was similar for that of the diploid and tetraploids clones, compared with the diploid clones (683 μm and 15.6 μm), tetraploid clones produced pulp with significantly longer (883 μm) and wider (20.0 μm) fibres. A lot of variations among different studies were found.

    The pulping wood quality of A. melanoxylon was evaluated by Lourenço et al. (2008) in relation to the presence of heartwood. Pulping heartwood differed from sapwood in chemical and optical terms: lower values of pulp yield (53% VS. 56%, respectively), higher kappa number (11 VS. 7), and lower brightness (28% VS. 49%). Khider et al. (2012) investigated A. mellifera stem for its suitability for pulping and paper production. The Soda- AQ, AS-AQ, ASAM and soda processes were evaluated, and results found that the ASAM pulping shown the excellent results in yield, degree of delignification, mechanical and optical properties. Xiong et al., (2016) carried out the kraft cooking of acacia wood as well as the beating and paper-making experiments of the resultant pulp. The results showed that the acacia wood kraft pulp with yield 52.25%, kappa number 17.9, viscosity 987.3 mL/g, breaking length 9.32 km, tensile index 93.6 N·m/g, tearing index 10.0 mN·m2/g and bursting index 5.34 kPa·m2/g was obtained at the conditions of 15% alkali charge, 30% sulfidity, 1:4 liquor to wood ratio and 2 h cooking at the 165℃. Liew and Chong (2016) studied the organosolv pulping of acacia hybrid. Wood chips were digested at 185℃ for 3 h and pressure of 1.1–1.2 MPa. It was observed that increasing of ethanol concentration led to increment in pulp yield and delignification degree. At 90% ethanol concentration, pulp yield of 44.19% with 5.24% reject and 15.32 kappa number was screened. From the above results on acacia pulping, there are a lot of variations of the pulp yield and delignification degree.

    The A. auriculiformis is one of the most common exotic trees in Bangladesh and millions of scattered trees are planted around farms, homesteads, roads and villages. A tree improvement program for Acacias was started in 1981 by the Bangladesh Forest Department with the aim of improving the growth and stem of the species. Apparently, the growth of Acacias from the second generation seed was hindered.

    This work dealed with the optimization of the kraft pulping of A. auriculiformis grown from the second generation seed in social forestry plantation program in Bangladesh at the age of 6, 8 and 10 years and compared with 10 years old A. auriculiformis grown from first generation seed. The chemical and morphological characteristics were also assessed. The effects of alkali concentration, duration and temperature on both pulp yield and kappa number were assessed by means of an incomplete, centered, factorial design. The best operational conditions were chosen to evaluate the effects on pulp yield and kappa number.

2.   Materials and Methods
  • The A. auriculiformis was collected from the Gazipur Forest Station at the age of 6, 8 and 10 years old from the second generation seed and the 10 years old A. auriculiformis was from the first generation seed. The 8 years old A. auriculiformis was not available in the same plantation site. It was collected near another plantation site. Three trees were selected for this experiment. Left from top and bottom and branches of these trees was discarded and the remained portion was debarked and chipped into 0.5 cm×0.5 cm×2.0 cm size. The chips were ground in a Wiley mill and the 40–60 mesh size was used for chemical analysis.

  • The basic wood density of A. auriculiformis was determined according to Pulp and Paper Technical Association of Canada (PAPTAC) Standard A. 8P. For the measurements of fiber length, sample was macerated in a solution containing HNO3 and KClO3 (1:1). A drop of macerated sample was taken in a slide. The fiber diameter and length was measured by image analyzer Euromex- Oxion using Image Focus Alpha software.

    The extractive (T204 om88), 1% alkali solubility (T212 om98), water solubility (T207 cm99), Klason lignin (T211 om83) and ash content (T211 os76) were determined in accordance with Tappi Test Methods. Holocellulose was determined by treating extractive free wood meal with NaClO2 solution. The pH of the solution was maintained at 4 by adding CH3COOH-CH3COONa buffer and α-cellulose was determined by treating holocellulose with 17.5% NaOH.

  • Pulping was carried out in a thermostatically controlled electrically oil bath contained four bomb digesters. The capacity of the digester was 1.5 L. The normal charge was 100 g of oven dried A. auriculiformis. Pulping conditions of kraft are as follows: Active alkali was 14%, 16%, 18% and 20% on oven-dry raw material as Na2O. Cooking time was 1.5 h, 2.0 h and 2.5 h at maximum temperature, and cooking temperature was 160℃, 165℃ and 170℃. Ratio of liquor to material was 4. Sulphidity 30% for kraft process.

    After digestion, pulp was washed till free of residual chemicals, and screened by flat vibratory screener (Yasuda, Japan). The screened pulp yield, total pulp yield and screened reject were determined gravimetrically as percentage of oven dried raw material. The kappa number (T236 om99) of the resulting pulp was determined in accordance with Tappi Test Methods. Three replicates of all experiments were done and the average reading was taken.

3.   Results and Discussion
  • The average chemical composition, morphological and physical properties of A. auriculiformis obtained from the first and second generation seeds are shown in Table 1. It is seen that extractives soluble in acetone were higher than that of the other hardwood species (Jahan et al., 2010). Extractives in A. auriculiformis from the first generation seed were 4.06%, while the same from the second generation seed was above 7% except 8 years old. In another study on A. melanoxylon, extractives ranged from 5.3% to 7.8% (Miyanishi and Watanabe, 2004). Acetone soluble extractives were much higher than the Eucalyptus species (1.3–2.2) (Ribeiro et al., 2018). Cold and hot water solubilities decreased with tree age. Holocellulose and α-cellulose are the most important components of pulpwood, which affect pulp and papermaking properties. The highest holocellulose and α-cellulose value were determined as 66.6% and 43.4%, respectively, for 8 years old A. auriculiformis from second generation seed, which were similar to A. auriculiformis from the first generation seed. The A. auriculiformis from 8 years old was collected from plantation site of Gazipur district. Nutritive value of the soil may affect the properties of wood. The α-cellulose content in A. auriculiformis was found to be 44.1% in our previous study (Jahan et al., 2008) and 35% studied by Yamada et al. (1991). The α-cellulose content in A. auriculiformis in this study was much lower than that of Eucalyptus species (Ribeiro et al., 2018). Pentosan is the main hemicelluloses component in hardwood species, and it contributes fiber bonding in paper sheet and also increases pulp yield. As shown in Table 1, pentosan content increased with the tree age. The pentosan content in A. auriculiformis at 10 years old was 15.2%, which was 1.7% lower than that of the first generation seed. The pentosan content in A. auriculiformis was found as 15.8% in other study (Yamada et al., 1991). The pentose sugars content in Eucalyptus species was very close to the pentosan content in A. auriculiformis (Ribeiro et al., 2018).

    Parameter 2nd generation 1st generation
    Age (a)
    6 8 10 10
    Extractive (%) 7.8 2.6 7.0 4.06
    1% Alkali (NaOH) solubility (%) 14.09 11.39 13.23 15.49
    Cold water solubility (%) 4.29 2.22 2.20 3.24
    Hot water solubility (%) 8.61 6.45 4.60 5.20
    Holocellulose (%) 60.1 66.8 60.9 65.0
    α-cellulose (%) 41.2 43.4 42.3 43.0
    Pentosan (%) 12.8 13.2 15.2 16.9
    Klason lignin (%) 30.4 25.2 29.8 33.2
    Ash content (%) 0.395 0.410 1.32 0.65
    Density (g/mL) 0.3126 0.3808 0.4231 0.5110
    Fiber length (mm) 0.85 0.76 0.78 0.89
    Fiber width (μm) 14.24 15.69 17.89 16.13

    Table 1.  Chemical, morphological and physical properties of 1st and 2nd generation A. auriculiformis

    Lignin is the undesirable part pulpwood, which is removed during pulping process. It requires the high amount of energy and chemicals. Lower lignin content of pulpwood makes them suitable for delignification to reach a desirable kappa number at milder pulping conditions (lower temperatures and chemical charges). Unfortunately, the lignin content in A. auriculiformis was higher than that of the other hardwoods in Bangladesh (Jahan et al., 2011; Mun et al., 2011), which was similar to the lignin content obtained by Yamada et al. (1991) and higher than our previous study (Yamada et al., 1991).

    As seen in Table 1, wood density increased from 0.3126 g/cm3 at the age of 6 years old to 0.4231 g/cm3 at the age of 10 years old. The A. auriculiformis wood was denser from the first generation seed than the second generation (0.5110 g/cm3 VS. 0.4321 g/cm3). Similarly, Jusoh et al. (2013) found significantly lower wood density for the second generation A. mangium. As shown in Fig. 1 of cross section, growth of the second generation of A. auriculiformis was slower than that of the first generation. According to Zobel and Buijtenen's study (1989), faster growth did not affect wood density.

    Figure 1.  Cross section 1st and 2nd generation A. auriculiformis

    The average fiber length of A. auriculiformis from different ages and the first and second generation were in the range of tropical hardwoods (0.7–1.5 mm) considered as short (Hale, 1959). No relation was found in the fibre length and tree age of A. auriculiformis. The average fibre length of A. auriculiformis from the second generation was 0.80 mm, which was lower than the fibre length of A. auriculiformis from the second generation (0.89 mm). Similarly, Jusoh et al. (2013) found slightly lower fibre length of the second generation A. mangium. The fiber width was medium-narrow and in the hardwood range (l0–35 μm).

  • Experimental results of the kraft pulping of A. auriculiformis of 6, 8 and 10 years old wood chips are shown in Table 1. Effects of each independent experimental varying in time, temperature and active alkali charge on the total pulp yield and kappa number were analyzed using MATLAB software. Apparently, it is seen that pulp yield from 8 years old A. auriculiformis was higher compared with the 6 and 10 years old counterpart. The mean screened pulp yield of 8 years old A. auriculiformis was 44% ranging from 41% to 46% with kappa number of 17–25, while those were 41% ranging from 36% to 45% with kappa number of 17–24 and 42% ranging from 39% to 45% with kappa number of 17–32 for 6 and 10 years old A. auriculiformis, respectively. Oluwafemi (2007) demonstrated that the oldest age class tree had the highest screen pulp yield. The uncooked material (rejects) for 8 years old A. auriculiformis was very low (0.67%) when only cooking with 14% active alkali charge for 2 h cooking at 170℃ and it was zero in all other conditions. But the reject was 12.1% for 6 years old A. auriculiformis at the conditions of 16% active alkali for 1.5 h cooking at 160℃. Similarly, results from Oluwafemi (2007) also showed that the rejects in the older tree was lower compared with the young tree. Screened reject decreased from 12.1% to 0.2% with increasing temperature from 160℃ to 170℃ (Table 24). The screen pulp yield range in this study was close to the screen pulp yield from A. mangium studied by Rosli et al. (2009) but much lower than eight-year-old clones of A. mangium grown in Vietnam (Griffin et al., 2014). Another study showed that 6 years old A. auriculiformis produced pulp yield of about 50% with kappa number of about 20 at the conditions of 60 min cooking at 170℃ (Xue et al., 2001). This variation can be explained by variation of location.

    Temperature (℃) Time (h) Active alkali (%) Pulp yield (%) Kappa number
    Screened Reject Total
    160 1.5 16 36.80 12.09 48.89 24.60
    165 1.5 16 44.20 2.1 46.30 22.40
    170 1.5 16 44.99 0.2 45.19 20.63
    160 2.0 16 43.34 0.8 44.14 22.02
    165 2.0 16 41.60 0 41.60 21.22
    170 2.0 16 40.85 0 40.85 20.06
    160 2.5 16 41.68 0 41.68 21.91
    165 2.5 16 41.00 0 41.00 21.20
    170 2.5 16 39.51 0 39.51 20.40
    160 1.5 18 43.24 0.4 43.64 19.92
    165 1.5 18 42.30 0.1 42.40 18.97
    170 1.5 18 42.00 0.1 42.10 18.05
    160 2.0 18 42.88 0.2 43.08 18.35
    165 2.0 18 41.20 0 41.20 18.00
    170 2.0 18 40.80 0 40.80 17.81
    160 2.5 18 40.95 0 40.95 18.00
    165 2.5 18 40.10 0 40.10 17.51
    170 2.5 18 39.69 0 39.69 17.24
    160 1.5 20 41.86 0.2 42.06 19.32
    165 1.5 20 41.27 0 41.27 18.24
    170 1.5 20 39.43 0 39.43 17.37
    160 2.0 20 41.04 0 41.04 18.47
    165 2.0 20 40.14 0 40.14 17.35
    170 2.0 20 39.02 0 39.02 17.02
    160 2.5 20 39.05 0 39.05 17.92
    165 2.5 20 39.00 0 39.00 17.80
    170 2.5 20 38.40 0 38.40 17.40

    Table 2.  Effect of active alkali, cooking time and temperature on pulping of 6 years A. auriculiformis

    Temperature (℃) Time (h) Active alkali (%) Pulp yield (%) Kappa number
    Screened Reject Total
    8 years
    170 2.0 14 46.13 0.67 46.8 24.65
    170 2.0 16 44.34 0 44.34 19.48
    170 2.0 18 44.16 0 44.16 17.25
    170 2.0 20 44.00 0 44.00 16.38
    170 1.5 16 44.64 0 44.64 20.94
    170 2.0 16 44.34 0 44.34 19.48
    170 2.5 14 45.21 0.20 45.41 23.22
    170 2.5 16 43.32 0 43.32 18.18

    Table 3.  Effect of active alkali, cooking time and temperature on pulping of 8 years A. auriculiformis

    Temperature (℃) Time (h) Active alkali (%) Pulp yield (%) Kappa number
    Screened Reject Total
    170 2.5 16 42.86 0 42.86 18.15
    170 3.0 16 40.94 0 40.94 17.17
    160 1.5 16 44.91 0 44.91 32.12
    165 1.5 16 44.24 0 44.24 27.65
    170 1.5 16 43.34 0 43.34 24.89
    160 2.0 16 43.94 0 43.94 23.67
    165 2.0 16 42.68 0 42.68 23.09
    170 2.0 16 42.43 0 42.43 22.05
    160 2.5 16 43.12 0 43.12 23.56
    165 2.5 16 42.23 0 42.23 23.07
    170 2.5 16 41.11 0 41.11 21.70
    160 1.5 18 42.52 0 42.52 21.65
    165 1.5 18 41.62 0 41.62 20.13
    170 1.5 18 41.30 0 41.30 18.53
    160 2.0 18 42.43 0 42.43 19.44
    165 2.0 18 41.05 0 41.05 19.24
    170 2.0 18 40.16 0 40.16 19.05
    160 2.5 18 41.43 0 41.43 19.13
    165 2.5 18 39.79 0 39.79 18.90
    170 2.5 18 39.10 0 39.10 18.23
    160 1.5 20 41.24 0 41.24 19.06
    165 1.5 20 40.34 0 40.34 18.79
    170 1.5 20 40.07 0 40.07 18.6
    160 2.0 20 41.10 0 41.10 18.52
    165 2.0 20 41.06 0 41.06 18.11
    170 2.0 20 40.48 0 40.48 18.24
    160 2.5 20 40.12 0 40.12 18.31
    165 2.5 20 39.38 0 39.38 18.40
    170 2.5 20 39.22 0 39.22 17.20

    Table 4.  Effect of active alkali, cooking time and temperature on pulping of 10 years A. auriculiformis

    Effect of cooking time, temperature (temp) and active alkali (AA) charge on total pulp yield as well as their statistical significance on the basis of F-test number are presented in regression equations (1)–(3). As shown in equations, cooking time at the maximum temperature had a pronounced effect on pulp yield followed by active alkali charge. Effect of temperature on pulp yield was less in employed cooking conditions.

    The most influential factor were active alkali charge and cooking time and pulp yield, which showed an almost linear dependence on both operational variables.

    For total pulp yield:

    Total pulp yield (10 years) = 82.05–0.151 temp–

    Total pulp yield (8 years) =55.482–2.993×time–

    Total pulp yield (6 years) =99.36–0.217×temp–

    Similarly, the most influential factors for kappa numbers were active alkali charge and cooking time, which also showed an almost linear dependence on both operational variables (equations (4)–(6)).

    For kappa number:

    Kappa number (10 years) = 85.28–0.189×temp–

    Kappa number (8 years) =46.051–2.936×time–

    Kappa number (6 years) =64.899–0.162×temp–

    In order to optimize the pulping conditions, three- dimensional (3D) response surface plots were created by plotting the response (total pulp yield and kappa number) on the Z-axis versus the most influential two independent variables time and alkali charge as shown in Fig. 2 and Fig. 3. Pulp yield decreased linearly as cooking time and alkali charge increased. Pulp yield of 8 years old A. auriculiformis was 44.34% at the conditions of 16% AA and 2 h of cooking, while the same for 6 years old was 40.85% and 42.43% for 10 years old. Under the same conditions, kappa numbers were 20.1, 19.5 and 22.1 for 6, 8 and 10 years old A. auriculiformis, respectively.

    Figure 2.  Effect of active alkali and cooking time on pulp yield

    Figure 3.  Effect of active alkali and cooking time on kappa number

  • From the above discussion, it is clearly seen that 8 years old A. auriculiformis from the second generation seed show better pulp yield and delignification. Therefore, the pulp yield-kappa relationship of 8 years old A. auriculiformis was compared with 10 years old A. auriculiformis from the first generation. As shown in Fig. 4, the delignification degree of the first generation A. auriculiformis was faster than that of the second generation. Pulp yield of 44% was achieved for the 1st generation A. auriculiformis with kappa number of only 12, while to obtain the same pulp yield, the kappa number reached 20 for the 2nd generation. Although the lignin content in the 1st generation A. auriculiformis was higher, easier delignification can be explained by higher syringyl to guaiacyl ratio of lignin (Fengel and Wegener, 1989).

    Figure 4.  Pulpability of 1st and 2nd generation A. auriculiformis

4.   Conclusions
  • The basic wood density and fiber length of A. auriculiformis from the second generation seed was lower than that of the first generation seed. Water and alkali solibilities decreased and pentosan content increased with the tree age. The highest α-cellulose content was found at the 8 years old A. auriculiformis. Kraft pulping was optimized by varying cooking time, temperature and active alkali. The most important influencing factors for pulp yield and kappa number were cooking time followed by active alkali. The A. auriculiformis from the first generation seed showed easier delignification than that of the second generation seed. The A. auriculiformis from the 2nd generation seed planted in social forestry program can be used in pulp mill.

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