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Effect of pulping variables on the characteristics of oil-palm frond-fiber
Bioresource Technology 93 (2004) 233–240
Effect of pulping variables on the characteristics of oil-palm frond-fiber W.D. Wan Rosli b
a,*
, K.N. Law b, Z. Zainuddin a, R. Asro
a
a Universiti Sains Malaysia, 11800 Penang, Malaysia Pulp and Paper Research Center, University of Quebec in Trois-Rivieres, Box 500, Trois-Rivieres, Que., Canada G9A 5H7
Received 15 April 2002; received in revised form 27 October 2003; accepted 3 November 2003
Abstract Caustic pulping of oil-palm frond-fiber strands was conducted following a central composite design using a two-level factorial plan involving three pulping variables (temperature: 160–180 °C, time: 1–2 h, alkali charge: 20–30% NaOH). Responses of pulp properties to the process variables were analyzed using a statistical software (DESIGN-EXPERTâ ). The results indicated that frond-fiber strands could be pulped with ease to about 35–45% yield. Statistically, the reaction time was not a significant factor while the influences of the treatment temperature and caustic charge were in general significantly relative to the properties of the resultant pulps. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Caustic pulping; Oil-palm fiber; Fronds; Central composite design (CCD)
1. Introduction In the past decade the global consumption of paper and board augmented from 237.11 million tonnes in 1990 (Anon., 1991) to 323.38 million tonnes in 2000 (Anon., 2001), an increase of 86.27 million tonnes. This figure is expected to rise further with the increasing world population, and improved literacy and quality of life worldwide. The continued high growth in paper consumption will lead to increased demand for fiber, creating additional pressure on the world’s diminishing forest resources. Meanwhile, the paper industry is also constantly facing mounting resistance from the conservationists and environmental groups. To maintain the paper industry growth, governments as well as industry executives have to establish and implement policies and plans to ensure a sustainable fiber supply, including reforestation program, plantation management, recycling, and development of nonwood fibers. The ever-increasing manufacturing costs and uncertainty in wood supply in some regions due to restrictions on logging and inadequate forest resources have caused increasing concerns over future fiber supplies. Many
*
Corresponding author. Fax: +60-4-657-3678. E-mail address: [email protected] (W.D. Wan Rosli).
0960-8524/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2003.11.016
North American and European papermakers are searching for alternative fiber sources such as nonwood plant fibers. Within the mixed portfolio of nonwood fibers, oil palm (Elaeis guineensis) is one that shows great potential as a papermaking raw material, particularly for Indonesia and Malaysia (Fuad et al., 1999). Oil palm is vastly cultivated as a source of oil in West and Central Africa, where it originated, and in Malaysia, Indonesia and Thailand. In Malaysia, oil palm is one of the most important commercial crops. The explosive expansion of oil-palm plantation in these countries has generated enormous amounts of vegetable waste, creating problems in replanting operations, and tremendous environmental concerns. It is reported that Malaysia alone produced during the recent past years about 30 million tonnes annually of oil-palm biomass, including trunks, fronds, and empty fruit bunches (Anon., 1997). An estimation (Lim, 1998) based on a planted area of 2.57 million ha, and a production rate of dry oil-palm biomass of 20,336 kg/ha/yr, shows that Malaysian palm oil industry produced approximately 52.3 million tonnes of lignocellulosic biomass in 1996. This figure is expected to increase substantially when the total planted hectarage of oil palm in Malaysia could reach 3.151 million ha in 2000 (Chan, 1999), whilst in Indonesia the projected availability of oil-palm solid wastes for 2000 was about 24.5 million tonnes (Lubis et al., 1994). Malaysia, in
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2000, produced an estimated 56.9 million tonnes of oilpalm biomass (Chan, 1999). Taking into account the proportion of useful fibrous elements that can be extracted from various oil-palm components, an overall recovery rate of 75% and a pulp yield of 45%, the net useful pulp would amount to about 14.8 million tonnes. The chemical and physical properties, and the pulping characteristics of oil-palm fibers have been recently reviewed in detail by Law and Wan Rosli (2001). Among various fibrous components of the oil-palm tree (i.e. trunk, frond, fruit bunch, mesocarp) frond fiber is the longest with an average length of 1.59 mm which is longer than that of most hardwood fibers. Based on the hectarage of 3.151 million ha mentioned earlier (Chan, 1999) and the dry weight of fronds available from annual pruning of 11 t/ha (Husin et al., 1986), the availability of oil-palm fronds in Malaysia, in 2000, would be about 34.661 million tonnes (dry weight basis). In addition, 16.0 t/ha of dry fronds (Husin et al., 1986) is also available at time of felling for replantation at about 25-year rotation. Owing to this important availability of fronds and the particularly high performance in tensile and tear strengths of these fibers (Mohd Yusoff, 1997), a further investigation of the pulping characteristics of oilpalm fronds, using a central composite design (CCD) to examine the responses of pulp properties in caustic cooking was completed and the results presented herein.
2. Methods 2.1. Materials Processed oil-palm frond-fiber strands used in this study were obtained from a local palm oil mill in Perak, Malaysia. Before pulping, the raw material was washed, cleaned, sorted and air-dried. The chemical composition of the strands was determined as follows: 14.81% lignin, 86.53% holocellulose, 62.34% a-cellulose, and 1.8% extractives, on an oven-dry weight basis. The variations of these means were <10%. The holocellulose and acellulose were determined using the method described in Wise et al. (1946) and the Japanese Standard Method JIS 8101, respectively. The contents of lignin and extractives were, respectively, determined following the Tappi methods as T 222 om-98 and T 204 cm-97.
ð1; þ1Þ superimposed on a star design or 2k axial points and several repetitions at the design centre points. Three pulping variables, which are most likely to affect the pulp and paper properties produced from soda pulping, were identified and investigated by the CCD. These variables were: (1) temperature (T ), (2) time (t) and (3) alkali charge (AC), expressed as percentage NaOH. The experimental design matrix with both the coded and real variables are shown in Table 1, where the former is calculated by Eqs. (1)–(3) below: Tcode ¼ ðT 170 °CÞ=10 °C
ð1Þ
tcode ¼ ðt 1 hÞ=0:5 h
ð2Þ
Acode ¼ ðAC 25%Þ=5%
ð3Þ
The values of responses obtained allow the calculation of mathematical estimation models for each response, which were subsequently used to characterize the nature of the response surface. All statistical analyses were carried out using the statistical software, DESIGNEXPERTâ of Stat-Ease, Inc., USA. 2.3. Pulping All pulping trials were carried out in a 4-l stationary stainless steel digester (NAC Autoclave Co. Ltd., Japan) fitted with a computer-controlled thermocouple in accordance with the design matrix given in Table 1. The ratios of liquor-to-material and time to maximum temperature were maintained at a constant of 6:1 and 90 min respectively throughout the experiment. After cooking, the pulps were mechanically disintegrated in a three-bladed mixer for 1 min at 2% consistency and screened on a flat-plate screen with 0.15 mm slits (a 6-cut slot screen). Rejects and screened yield were determined on an oven-dry weight basis. The screened pulps were characterized without being further refined. The freeness of the unbeaten pulps was 670 ± 25 ml. 2.4. Pulp characterization Kappa number of the screened pulps was determined using Tappi method T 236 cm-85 while the freeness was measured following the method T 227 om-94. Handsheets of 60 g/m2 were formed and their properties were evaluated in accordance with the Tappi standard methods. The handsheets were conditioned at 23 °C and 50% RH for at least 24 h before testing.
2.2. Experimental design Response surface methodology was utilized to optimize the soda pulping process and a CCD was adopted. It involves outlining the composition of the experimental process conditions subsequently used to develop the regression models. The basic CCD for k variables consists of a 2k factorial design with each factor at two levels
3. Results and discussion 3.1. Response surface analysis of soda pulping The results for soda pulping of oil-palm fronds are summarized in Table 1. By employing DESIGN
No.
Pulping variables
Response
Coded
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Values
T
AC
t
T (°C)
AC (%)
t (h)
)1 1 )1 1 )1 1 )1 1 )1.68 1.68 0 0 0 0 0 0 0
)1 )1 1 1 )1 )1 1 1 0 0 )1.68 1.68 0 0 0 0 0
)1 )1 )1 )1 1 1 1 1 0 0 0 0 )1.68 1.68 0 0 0
160.0 180.0 160.0 180.0 160.0 180.0 160.0 180.0 153.2 186.8 170.0 170.0 170.0 170.0 170.0 170.0 170.0
20.00 20.00 30.00 30.00 20.00 20.00 30.00 30.00 25.00 25.00 16.59 33.41 25.00 25.00 25.00 25.00 25.00
1.00 1.00 1.00 1.00 2.00 2.00 2.00 2.00 1.50 1.50 1.50 1.50 0.66 2.34 1.50 1.50 1.50
Reject (%)
Screened yield (%)
Kappa no.
Burst index (kPa m2 /g)
Tear index (mN m2 /g)
Tensile index (N m/g)
ISO brightness (%)
2.8 0.8 0.9 0 1.6 0.6 0.3 0 2.3 0.38 8.4 0.1 0.5 0.2 0.4 0.4 0.3
42.25 38.19 39.61 35.57 43.93 39.79 39.09 32.31 40.81 34.59 39.67 33.76 41.26 39.31 39.68 38.82 36.81
63.39 36.31 40.46 12.11 63.24 37.76 26 9.64 50.58 17.1 87.5 21.19 30.06 22.49 21.53 24.49 23.5
2.9 3.4 2.75 3.64 3.54 3.67 3.31 3.46 2.13 4.04 1.92 3.51 4.72 4.14 4.15 4 4.06
9.21 9.84 9.33 9.86 9.11 8.99 9.15 8.85 8.71 9.25 9.11 9.87 11.09 9.96 10.02 10.1 10.06
46.31 45.11 42.38 48.88 46.17 49.4 45.95 50.84 36.37 58.38 29.9 47.5 58.78 53.37 50.96 51.09 54.56
20.93 21.29 22.61 29.79 20.93 15.82 25.68 31.08 21.11 28.86 12.58 30.48 25.26 26.86 26.28 25.71 26.19
W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240
Table 1 A three-variables CCD as composed by DESIGN EXPERTâ and the corresponding response for soda pulping of EFB
Note: T ––cooking temperature (°C); t––time-at-temperature (h); AC––NaOH level (w/w based on oven dried fiber).
235
0.0006 0.30 0.8312 0.0039 0.44 0.7569
0.0113 0.1763 0.8485 0.0091 0.0014
<0.0001 4.70 0.9654 <0.0001 1.10 0.9121 Prob > F Root MSE R-squared
Note: (1) All the coefficients are in terms of the coded factors since the size of coefficients in a coded model relates directly to the observed change in the response and the coefficients in actual model cannot be compared to one another due to their dependence on unit of measure. (2) CE refers to coefficient estimates.
1.23
2.17
0.1668 0.2614 0.0040 0.0001 0.0045
0.0089 4.94 0.6509
0.0048 )4.72
)1.58
<0.0001 1.65 0.9329
0.0620
0.0041
0.0062
0.0066 <0.0001 0.8012 0.0172 0.1188 0.9751
25.48 1.53 4.41 0.12
Prob > jtj CE
51.79 3.69 2.24 0.043
Prob > jtj Prob > jtj CE Prob > jtj
10.19 0.12 0.097 )0.30 )0.48 )0.30
0.0441
Rejects of pulp may indicate the uniformity of raw material or the efficiency of chemical treatment. The quantity of rejects on a 6-cut screen (0.15 mm slots) ranged from traces to about 2.8%, except for Run 11 which had 8.4% (Table 1). The particularly high rejects of Run 1 is probably attributable to experimental error. In most cases (13 runs), the rejects were inferior to 1%, indicating that the cooking of frond fibers with sodium hydroxide was relatively efficient and uniform. Since the rejected fibers did not constitute part of the pulps evaluated, the rejects content will not be subjected to statistical analyses.
)0.88
3.2. Rejects
0.0111
In Table 2 are summarized some of the statistical analysis of Eqs. (4)–(9) and the results confirm the adequacy of the fitted models, where all models with the exception for burst and tensile index are significant at a level of 0.001 or less. Also shown are the coefficient estimates for each term in the selected models for every dependent variable.
0.93
Brightness ¼ 25:48 þ 1:53T þ 4:41AC þ 0:12t 1:58AC2 þ 2:17T AC þ 1:23AC t ð9Þ
<0.0001 <0.0001 0.1305 0.0471 <0.0001
ð8Þ
<0.0001 <0.0001 0.3716
0:48T 2 0:30 AC2
4.22 0.36 0.17 0.0236 )0.39 )0.52
Tear index ¼ 10:19 þ 0:12T þ 0:097 AC 0:30t
CE
ð7Þ
Prob > jtj
0:39T 2 0:52 AC2
23.93 )11.25 )16.40 )2.08 2.99 10.24
Burst index ¼ 4:22 þ 0:36T þ 0:17 AC þ 0:0236t
CE
ð6Þ
Prob > jtj
4:72 AC2
37.81 )2.16 )2.02 )0.28
Tensile index ¼ 51:79 þ 3:69T þ 2:24 AC þ 0:043t
Burst index (kPa m2 /g)
ð5Þ
Kappa no.
þ 2:99T 2 þ 10:24 AC2
Table 2 Statistical analysis of reduced models and coefficient of screened yield, Kappa no., viscosity, a-cellulose and ash content
Kappa no: ¼ 23:93 11:25T 16:40 AC 2:08t
Tear index (mN m2 /g)
ð4Þ
Screened yield (%)
þ 0:93t2 0:88 AC t
CE
Screened yield ¼ 37:81 2:16T 2:02 AC 0:28t
Intercept T AC t T2 AC2 t2 T AC Tt AC t
Tensile index (N m/g)
Brightness ISO
EXPERTâ , a computer-aided response surface analyzer, the most compatible model among mean, linear, quadratic and cubic expressions are fitted to each response based on all statistical analysis results available. After obtaining the said model, the terms in the model were scrutinized with the Student’s t test (Ott, 1988) so as to reduce the number of terms in the model that could enable creation of a simple and practical model with a minimum of equation terms. A significance level of 0.05, which is based on a null hypothesis test (Ott, 1988) that the term equals zero, is arbitrarily set as the guideline for each term in the model. To survive in the final model, all terms should be significant at a confidence level of 95% or higher; consequently, the insignificant terms at a level of 0.05 were eliminated. The following Eqs. (4)–(9) are reduced models for each response:
CE
W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240
Factor
236
W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240
237
3.3. Screened yield Within the limit of the study the screened yield ranged from about 32% to 44% (Table 1), which is typical for chemical pulping of nonwood materials. It is evident from Eq. (4) that temperature and alkali charge were the most important factors affecting the pulp yield. Statistical analyses (Table 2) indicated that the treatment time had no significant influence on screened yield, indicating the possibility of reducing the treatment time to 1 h to achieve similar screened yield. It also means that the dissolution of lignin, hemicellulose and extractives from the frond fiber in a caustic milieu could be achieved with ease, requiring a relatively short period of reaction time within the range of temperature and alkali charge used. A response surface graph showing the interaction effects (at 1.5 h) is presented in Fig. 1.
Fig. 2. Three-dimensional graph showing the response of Kappa number at 1.5 h.
3.4. Kappa number The principal effects of temperature, alkali charge and treatment time on Kappa number are shown in Table 2 and Eq. (5). It should be noted that the alkali charges had the most influence on reducing the residual lignin in the pulp, followed by the cooking temperature. Statistically, the treatment time showed no significant influence, again indicating that the chemical treatment might be effectively conducted for times no longer than 1 h. The responses of Kappa number to temperature and alkali charge at a cooking time of 1.5 h are illustrated in Fig. 2.
Of the three factors affecting tensile index, the most influential is temperature, with alkali charge a smaller role and treatment time the least (Table 2 and Eq. (6)). It
is interesting to observe that cooking temperature is the main driving force for the alkali reaction that improves the bonding potential of frond fibers. Statistically, the treatment time had insignificant effect upon the interfiber bonding. The influence of temperature and alkali charge at a constant cooking time of 1.5 h is presented in Fig. 3. In the region of low temperature (160 °C), the increase in alkali charge from 20% to 30% had no significant effect. However, at 180 °C the tensile index is significantly improved by the increase in alkali charge. It should also be noted that at low (20%) alkali charge, the tensile index is not significantly affected by the increase in temperature from 160 to 180 °C. This implies that the maximum tensile index occurred when the temperature and alkali charge were at high levels, corresponding to the lowest point of screened yield (tensile-yield relationship is shown in Fig. 8).
Fig. 1. Three-dimensional graph showing the response of screened yield at 1.5 h.
Fig. 3. Three-dimensional graph showing the response of tensile index at 1.5 h.
3.5. Tensile index
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W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240
3.6. Burst index It is obvious from Eq. (7) and Table 2 that temperature was the most significant followed by alkali charge while the treatment time was the least. The cooking temperature is the main driving force for the alkali reaction that improves the burst index of paper made from fibers. In the low temperature region of 160 °C, the increase in alkali charge from 20% to 30% had no significant effect on burst index. In the high temperature region of 180 °C the burst index was marginally improved by the increase in alkali charge. The interaction of alkali and temperature is shown in Fig. 4. 3.7. Tear index In terms of the main effects on tear index, it is surprising that treatment time has the greatest, followed by temperature and alkali charge to a lesser extent (Table 2 and Eq. (8)). It has however been established that tear strength is a function of both fiber strength and fiber bonding (Page and MacLeod, 1992; Seth and Page, 1988). The dependency on time is most probably related to these parameters. At short cooking times, the degree of delignification is relatively small; hence a considerable amount of lignin is still left in the pulp, resulting in lower bonding and consequently reduced tear strength. At the other end of longer cooking times, the degree of delignification is much higher, and some degree of fiber damage is to be expected, leading to a reduction in tear strength. The interaction effects (at 1.5 h) in form of a response surface graph is shown in Fig. 5.
Fig. 5. Three-dimensional graph showing the response of tear index at 1.5 h.
alkali charge was the most influential factor in relation to the brightness of frond pulp, followed by the temperature, in order of importance. The effect of cooking time was comparatively small. Statistical analyses of the interaction effects of the pulping variables show that the cooking time had no significant effect on pulp brightness at all levels of temperature and caustic usage. Conversely, the increase in caustic charge significantly augmented the brightness at both levels of temperature. However, at a low alkali charge (20%), temperature had no significant influence when the cooking time was 1.5 h or lower. A response surface graph showing the interaction effects on brightness (at 1.5 h) is presented in Fig. 6.
3.8. Brightness 3.9. Discussion The main effects of temperature, alkali charge and treatment time on brightness (measured as ISO) are shown in Table 2 and Eq. (9). It is apparent that the
The study on the responses of pulp properties to the process variables provides a useful means for optimizing
Fig. 4. Three-dimensional graph showing the response of burst index at 1.5 h.
Fig. 6. Three-dimensional graph showing the response of brightness at 1.5 h.
W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240
seen that over the broad range of pulp yield from about 32% to 44%, the variation in tear index (9–10 mN m2 /g) was rather small when compared with those of tensile and burst indices. As shown in Fig. 11, burst index is strongly correlated with tensile index (R2 ¼ 0:7593) while the tear index shows a much smaller significant relationship with the tensile index (R2 ¼ 0:3422).
ISO Brightness
40 30 20
2
R = 0.7567
10 0 0
20
40
60
80
100
Kappa Number
Tensile Index, Nm/g
Fig. 7. Brightness versus Kappa number.
60 50 40 30 20 30
32.5
35
37.5
40
42.5
45
Screened Yield, %
Burst Index, kPa m2/g
Fig. 8. Tensile index as function of screened yield.
5 4 3 2 1 30
32.5
35
37.5 40 Screened Yield, %
42.5
45
Fig. 9. Burst index as a function of screened yield.
12
Tear Index, Nm2/g
the pulping conditions. It gives, however, little insight into the chemical and physical changes that the raw material has undergone during the process. In this investigation, the chemical agent (NaOH) used is the only variable that has direct impact on the physical and chemical nature of the resulting pulp. The treatment temperature may be considered as a catalyzer that accelerates the alkali reaction in dissolving the lignin and carbohydrates from the raw material; it exerts no direct influence on the nature of the pulp produced. The latter is in fact affected by the alkali action that causes delignificaton, hydrolysis of carbohydrates and swelling of the fiber matrix. Even at low temperature sodium hydroxide could significantly modify the nature of the material. Similarly, the treatment time maintains the chemical reaction and has no direct influence in determining the characteristics of the resulting pulp. As noted earlier, the cooking time has practically no significant effect upon almost all properties discussed, within the scope of the study. Besides, the development of each pulp property in chemical pulping has its own limitation, which is dictated by both the chemical and morphological characteristics of the constituent elements of the raw material, that is the individual fibers. For example, the range of strength properties such as tensile, burst and tear indices is finite for each particular type of fiber. The increase in one property is not necessarily always in parallel with the changes in other properties of the same pulp. For instance, the tensile strength is principally associated with the effective number of bonding sites (hydrogen bonds) available on the fiber surface while the tear index depends mainly on fiber length. The average length of fibers of a particular raw material would remain unchanged during the course of chemical pulping while the degree of hydrogen bonding, which is finite in nature, may depend, to a certain extent, on the severity of chemical treatment or the extent of dissolution of fiber constituents. These relationships may also be complicated by the degree of depolymerization of the cellulosic material or the inherent mechanical strength of fibers. It is of interest to notice that the increase in alkali charge improved the brightness, which is associated with the amount of chromophoric groups remaining in the pulped frond fiber. Fig. 7 clearly reveals the close relationship of brightness and Kappa number (R2 ¼ 0:7567). Pulp yield is one of the key factors determining the physical characteristics of pulp fibers. The inter-relationships of tensile, burst and tear indices with screened yield are shown in Figs. 8–10, respectively. As seen in Figs. 8 and 9, the fiber-bonding dependent properties such as tensile and burst indices tend to increase with decreasing screened yield while the fiber-length dependent tear index seems to have a maximum value in the neighbourhood 37–38% yield (Fig. 10). It could also be
239
11 10 9 8 7 30
32.5
35
37.5 40 Screened Yield, %
42.5
Fig. 10. Tear index as a function of screened yield.
45
240
W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240
12 10
2
Acknowledgements
2
Financial support from Universiti Sains Malaysia in the form of IRPA short-term grant 304/PTEKIND/ 633074 and IRPA EA grant 305/PTEKIND/612602 is gratefully acknowledged.
R = 0.3422
Tear Index, Nm2/g
8
R = 0.7593
6
Burst Index, kPa m2/g
4 2 0 30
35
40
45
50
55
60
Tensile Index, Nm/g Fig. 11. Tear and burst indices versus tensile index.
Evidently, it is the desired properties of the final product that dictate the optimum pulping conditions for a particular raw material. It is noteworthy that the pulp characteristics presented in the study were obtained using unbeaten pulps, that is they had not been mechanically treated or refined. The freeness was high (670 ± 25 ml CSF). A mechanical treatment would certainly improve the tensile and burst indices and it might change the tear index either positively or negatively due to the expected fiber fibrillation and shortening effect caused by beating or refining. For this reason, the effects of the pulping variables as well as the relationships between the paper properties discussed earlier might differ somewhat depending on how the pulps would respond to the mechanical treatment.
4. Conclusion Caustic pulping of oil-palm frond fiber requires a relatively short reaction time (about 60 min) within the limits of treatment temperature (160–180 °C) and of alkali charge (20–30% NaOH) used. The delignification of frond fiber can be achieved with ease using sodium hydroxide as the sole cooking agent. The caustic reaction is greatly enhanced by the increases in temperature. Each property studied varies somewhat differently with the pulp yield. As such, it would be the desired properties of the final product that will dictate the optimized pulping conditions.
References Anon., 1991. Annual Report, Pulp and Paper International 33 (7), 26– 27. Anon., 1997. Industrial News––Malaysia studies making paper from palm waste. Appita 50 (2), 88. Anon., 2001. Annual Report, Pulp and Paper International 43 (7), 8–9. Chan, K.W., 1999. Biomass production in the oil palm industry. In: Singh, G. et al. (Eds.), Oil Palm and the Environment: A Malaysian Perspective. Malaysian Oil Palm Growers’ Council, Kuala Lumpur, pp. 41–53. Fuad, M.A., Rohana, A.R., Chua, B.G., 1999. Socio-economic considerations in the development of jungle to oil palm. In: Singh, G. et al. (Eds.), Oil Palm and the Environment: A Malaysian Perspective. Malaysian Oil Palm Growers’ Council, Kuala Lumpur, pp. 1–7. Husin, M., Hassan, A.M., Tarmizi, A.M., 1986. Availability and potential utilisation of oil palm trunks and fronds up to year 2000. Palm Oil Research Institute Malaysia Occasional Paper No. 20, pp. 1–17. Law, K.N., Wan Rosli, W.D., 2001. Nonwood materials (with special reference to oil palm fibers) as papermaking materials: potentials and challenges in the new millennium. In: Proceedings of USMJIRCAS Joint International Symposium on Lignocellulosic Materials, Penang, Malaysia, pp. 1–13. Lim, K.O., 1998. Oil palm plantations––a plausible renewable source of energy. RERIC Int. Energy J. 20 (2), 107–116. Lubis, A.U., Guritno, P., Darnoko, A., 1994. Prospects of oil palm solid wastes based industries in Indonesia. In: Proceedings of the 3rd National Seminar on Utilisation of Oil Palm Tree and other Palms, Kuala Lumpur, Malaysia, FRIM, pp. 62–69. Mohd Yusoff, M.N., 1997. High yield pulping of oil palm frond fibers in Malaysia. In: Proceedings of the Nanjing International Symposium on High Yield Pulping, Nanjing, China, Chinese Academy of Forestry, pp. 201–210. Ott, L., 1988. An Introduction to Statistical Methods and Data Analysis, third ed. PWS, Kent, Boston. Page, D.H., MacLeod, J.M., 1992. Fiber strength and its impact on tear strength. Tappi 75 (1), 172–174. Seth, R.S., Page, D.H., 1988. Fiber properties and tearing resistance. Tappi 71 (2), 103–107. Wise, L.E., Murphy, M., D’Addieco, A.A., 1946. Chlorite holocellulose––its fractionation and bearing on summative wood analysis and on studies on the hemicelluloses. Paper Trade J. 122 (2), 35–43.
Effect of pulping variables on the characteristics of oil-palm frond-fiber W.D. Wan Rosli b
a,*
, K.N. Law b, Z. Zainuddin a, R. Asro
a
a Universiti Sains Malaysia, 11800 Penang, Malaysia Pulp and Paper Research Center, University of Quebec in Trois-Rivieres, Box 500, Trois-Rivieres, Que., Canada G9A 5H7
Received 15 April 2002; received in revised form 27 October 2003; accepted 3 November 2003
Abstract Caustic pulping of oil-palm frond-fiber strands was conducted following a central composite design using a two-level factorial plan involving three pulping variables (temperature: 160–180 °C, time: 1–2 h, alkali charge: 20–30% NaOH). Responses of pulp properties to the process variables were analyzed using a statistical software (DESIGN-EXPERTâ ). The results indicated that frond-fiber strands could be pulped with ease to about 35–45% yield. Statistically, the reaction time was not a significant factor while the influences of the treatment temperature and caustic charge were in general significantly relative to the properties of the resultant pulps. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Caustic pulping; Oil-palm fiber; Fronds; Central composite design (CCD)
1. Introduction In the past decade the global consumption of paper and board augmented from 237.11 million tonnes in 1990 (Anon., 1991) to 323.38 million tonnes in 2000 (Anon., 2001), an increase of 86.27 million tonnes. This figure is expected to rise further with the increasing world population, and improved literacy and quality of life worldwide. The continued high growth in paper consumption will lead to increased demand for fiber, creating additional pressure on the world’s diminishing forest resources. Meanwhile, the paper industry is also constantly facing mounting resistance from the conservationists and environmental groups. To maintain the paper industry growth, governments as well as industry executives have to establish and implement policies and plans to ensure a sustainable fiber supply, including reforestation program, plantation management, recycling, and development of nonwood fibers. The ever-increasing manufacturing costs and uncertainty in wood supply in some regions due to restrictions on logging and inadequate forest resources have caused increasing concerns over future fiber supplies. Many
*
Corresponding author. Fax: +60-4-657-3678. E-mail address: [email protected] (W.D. Wan Rosli).
0960-8524/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2003.11.016
North American and European papermakers are searching for alternative fiber sources such as nonwood plant fibers. Within the mixed portfolio of nonwood fibers, oil palm (Elaeis guineensis) is one that shows great potential as a papermaking raw material, particularly for Indonesia and Malaysia (Fuad et al., 1999). Oil palm is vastly cultivated as a source of oil in West and Central Africa, where it originated, and in Malaysia, Indonesia and Thailand. In Malaysia, oil palm is one of the most important commercial crops. The explosive expansion of oil-palm plantation in these countries has generated enormous amounts of vegetable waste, creating problems in replanting operations, and tremendous environmental concerns. It is reported that Malaysia alone produced during the recent past years about 30 million tonnes annually of oil-palm biomass, including trunks, fronds, and empty fruit bunches (Anon., 1997). An estimation (Lim, 1998) based on a planted area of 2.57 million ha, and a production rate of dry oil-palm biomass of 20,336 kg/ha/yr, shows that Malaysian palm oil industry produced approximately 52.3 million tonnes of lignocellulosic biomass in 1996. This figure is expected to increase substantially when the total planted hectarage of oil palm in Malaysia could reach 3.151 million ha in 2000 (Chan, 1999), whilst in Indonesia the projected availability of oil-palm solid wastes for 2000 was about 24.5 million tonnes (Lubis et al., 1994). Malaysia, in
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2000, produced an estimated 56.9 million tonnes of oilpalm biomass (Chan, 1999). Taking into account the proportion of useful fibrous elements that can be extracted from various oil-palm components, an overall recovery rate of 75% and a pulp yield of 45%, the net useful pulp would amount to about 14.8 million tonnes. The chemical and physical properties, and the pulping characteristics of oil-palm fibers have been recently reviewed in detail by Law and Wan Rosli (2001). Among various fibrous components of the oil-palm tree (i.e. trunk, frond, fruit bunch, mesocarp) frond fiber is the longest with an average length of 1.59 mm which is longer than that of most hardwood fibers. Based on the hectarage of 3.151 million ha mentioned earlier (Chan, 1999) and the dry weight of fronds available from annual pruning of 11 t/ha (Husin et al., 1986), the availability of oil-palm fronds in Malaysia, in 2000, would be about 34.661 million tonnes (dry weight basis). In addition, 16.0 t/ha of dry fronds (Husin et al., 1986) is also available at time of felling for replantation at about 25-year rotation. Owing to this important availability of fronds and the particularly high performance in tensile and tear strengths of these fibers (Mohd Yusoff, 1997), a further investigation of the pulping characteristics of oilpalm fronds, using a central composite design (CCD) to examine the responses of pulp properties in caustic cooking was completed and the results presented herein.
2. Methods 2.1. Materials Processed oil-palm frond-fiber strands used in this study were obtained from a local palm oil mill in Perak, Malaysia. Before pulping, the raw material was washed, cleaned, sorted and air-dried. The chemical composition of the strands was determined as follows: 14.81% lignin, 86.53% holocellulose, 62.34% a-cellulose, and 1.8% extractives, on an oven-dry weight basis. The variations of these means were <10%. The holocellulose and acellulose were determined using the method described in Wise et al. (1946) and the Japanese Standard Method JIS 8101, respectively. The contents of lignin and extractives were, respectively, determined following the Tappi methods as T 222 om-98 and T 204 cm-97.
ð1; þ1Þ superimposed on a star design or 2k axial points and several repetitions at the design centre points. Three pulping variables, which are most likely to affect the pulp and paper properties produced from soda pulping, were identified and investigated by the CCD. These variables were: (1) temperature (T ), (2) time (t) and (3) alkali charge (AC), expressed as percentage NaOH. The experimental design matrix with both the coded and real variables are shown in Table 1, where the former is calculated by Eqs. (1)–(3) below: Tcode ¼ ðT 170 °CÞ=10 °C
ð1Þ
tcode ¼ ðt 1 hÞ=0:5 h
ð2Þ
Acode ¼ ðAC 25%Þ=5%
ð3Þ
The values of responses obtained allow the calculation of mathematical estimation models for each response, which were subsequently used to characterize the nature of the response surface. All statistical analyses were carried out using the statistical software, DESIGNEXPERTâ of Stat-Ease, Inc., USA. 2.3. Pulping All pulping trials were carried out in a 4-l stationary stainless steel digester (NAC Autoclave Co. Ltd., Japan) fitted with a computer-controlled thermocouple in accordance with the design matrix given in Table 1. The ratios of liquor-to-material and time to maximum temperature were maintained at a constant of 6:1 and 90 min respectively throughout the experiment. After cooking, the pulps were mechanically disintegrated in a three-bladed mixer for 1 min at 2% consistency and screened on a flat-plate screen with 0.15 mm slits (a 6-cut slot screen). Rejects and screened yield were determined on an oven-dry weight basis. The screened pulps were characterized without being further refined. The freeness of the unbeaten pulps was 670 ± 25 ml. 2.4. Pulp characterization Kappa number of the screened pulps was determined using Tappi method T 236 cm-85 while the freeness was measured following the method T 227 om-94. Handsheets of 60 g/m2 were formed and their properties were evaluated in accordance with the Tappi standard methods. The handsheets were conditioned at 23 °C and 50% RH for at least 24 h before testing.
2.2. Experimental design Response surface methodology was utilized to optimize the soda pulping process and a CCD was adopted. It involves outlining the composition of the experimental process conditions subsequently used to develop the regression models. The basic CCD for k variables consists of a 2k factorial design with each factor at two levels
3. Results and discussion 3.1. Response surface analysis of soda pulping The results for soda pulping of oil-palm fronds are summarized in Table 1. By employing DESIGN
No.
Pulping variables
Response
Coded
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Values
T
AC
t
T (°C)
AC (%)
t (h)
)1 1 )1 1 )1 1 )1 1 )1.68 1.68 0 0 0 0 0 0 0
)1 )1 1 1 )1 )1 1 1 0 0 )1.68 1.68 0 0 0 0 0
)1 )1 )1 )1 1 1 1 1 0 0 0 0 )1.68 1.68 0 0 0
160.0 180.0 160.0 180.0 160.0 180.0 160.0 180.0 153.2 186.8 170.0 170.0 170.0 170.0 170.0 170.0 170.0
20.00 20.00 30.00 30.00 20.00 20.00 30.00 30.00 25.00 25.00 16.59 33.41 25.00 25.00 25.00 25.00 25.00
1.00 1.00 1.00 1.00 2.00 2.00 2.00 2.00 1.50 1.50 1.50 1.50 0.66 2.34 1.50 1.50 1.50
Reject (%)
Screened yield (%)
Kappa no.
Burst index (kPa m2 /g)
Tear index (mN m2 /g)
Tensile index (N m/g)
ISO brightness (%)
2.8 0.8 0.9 0 1.6 0.6 0.3 0 2.3 0.38 8.4 0.1 0.5 0.2 0.4 0.4 0.3
42.25 38.19 39.61 35.57 43.93 39.79 39.09 32.31 40.81 34.59 39.67 33.76 41.26 39.31 39.68 38.82 36.81
63.39 36.31 40.46 12.11 63.24 37.76 26 9.64 50.58 17.1 87.5 21.19 30.06 22.49 21.53 24.49 23.5
2.9 3.4 2.75 3.64 3.54 3.67 3.31 3.46 2.13 4.04 1.92 3.51 4.72 4.14 4.15 4 4.06
9.21 9.84 9.33 9.86 9.11 8.99 9.15 8.85 8.71 9.25 9.11 9.87 11.09 9.96 10.02 10.1 10.06
46.31 45.11 42.38 48.88 46.17 49.4 45.95 50.84 36.37 58.38 29.9 47.5 58.78 53.37 50.96 51.09 54.56
20.93 21.29 22.61 29.79 20.93 15.82 25.68 31.08 21.11 28.86 12.58 30.48 25.26 26.86 26.28 25.71 26.19
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Table 1 A three-variables CCD as composed by DESIGN EXPERTâ and the corresponding response for soda pulping of EFB
Note: T ––cooking temperature (°C); t––time-at-temperature (h); AC––NaOH level (w/w based on oven dried fiber).
235
0.0006 0.30 0.8312 0.0039 0.44 0.7569
0.0113 0.1763 0.8485 0.0091 0.0014
<0.0001 4.70 0.9654 <0.0001 1.10 0.9121 Prob > F Root MSE R-squared
Note: (1) All the coefficients are in terms of the coded factors since the size of coefficients in a coded model relates directly to the observed change in the response and the coefficients in actual model cannot be compared to one another due to their dependence on unit of measure. (2) CE refers to coefficient estimates.
1.23
2.17
0.1668 0.2614 0.0040 0.0001 0.0045
0.0089 4.94 0.6509
0.0048 )4.72
)1.58
<0.0001 1.65 0.9329
0.0620
0.0041
0.0062
0.0066 <0.0001 0.8012 0.0172 0.1188 0.9751
25.48 1.53 4.41 0.12
Prob > jtj CE
51.79 3.69 2.24 0.043
Prob > jtj Prob > jtj CE Prob > jtj
10.19 0.12 0.097 )0.30 )0.48 )0.30
0.0441
Rejects of pulp may indicate the uniformity of raw material or the efficiency of chemical treatment. The quantity of rejects on a 6-cut screen (0.15 mm slots) ranged from traces to about 2.8%, except for Run 11 which had 8.4% (Table 1). The particularly high rejects of Run 1 is probably attributable to experimental error. In most cases (13 runs), the rejects were inferior to 1%, indicating that the cooking of frond fibers with sodium hydroxide was relatively efficient and uniform. Since the rejected fibers did not constitute part of the pulps evaluated, the rejects content will not be subjected to statistical analyses.
)0.88
3.2. Rejects
0.0111
In Table 2 are summarized some of the statistical analysis of Eqs. (4)–(9) and the results confirm the adequacy of the fitted models, where all models with the exception for burst and tensile index are significant at a level of 0.001 or less. Also shown are the coefficient estimates for each term in the selected models for every dependent variable.
0.93
Brightness ¼ 25:48 þ 1:53T þ 4:41AC þ 0:12t 1:58AC2 þ 2:17T AC þ 1:23AC t ð9Þ
<0.0001 <0.0001 0.1305 0.0471 <0.0001
ð8Þ
<0.0001 <0.0001 0.3716
0:48T 2 0:30 AC2
4.22 0.36 0.17 0.0236 )0.39 )0.52
Tear index ¼ 10:19 þ 0:12T þ 0:097 AC 0:30t
CE
ð7Þ
Prob > jtj
0:39T 2 0:52 AC2
23.93 )11.25 )16.40 )2.08 2.99 10.24
Burst index ¼ 4:22 þ 0:36T þ 0:17 AC þ 0:0236t
CE
ð6Þ
Prob > jtj
4:72 AC2
37.81 )2.16 )2.02 )0.28
Tensile index ¼ 51:79 þ 3:69T þ 2:24 AC þ 0:043t
Burst index (kPa m2 /g)
ð5Þ
Kappa no.
þ 2:99T 2 þ 10:24 AC2
Table 2 Statistical analysis of reduced models and coefficient of screened yield, Kappa no., viscosity, a-cellulose and ash content
Kappa no: ¼ 23:93 11:25T 16:40 AC 2:08t
Tear index (mN m2 /g)
ð4Þ
Screened yield (%)
þ 0:93t2 0:88 AC t
CE
Screened yield ¼ 37:81 2:16T 2:02 AC 0:28t
Intercept T AC t T2 AC2 t2 T AC Tt AC t
Tensile index (N m/g)
Brightness ISO
EXPERTâ , a computer-aided response surface analyzer, the most compatible model among mean, linear, quadratic and cubic expressions are fitted to each response based on all statistical analysis results available. After obtaining the said model, the terms in the model were scrutinized with the Student’s t test (Ott, 1988) so as to reduce the number of terms in the model that could enable creation of a simple and practical model with a minimum of equation terms. A significance level of 0.05, which is based on a null hypothesis test (Ott, 1988) that the term equals zero, is arbitrarily set as the guideline for each term in the model. To survive in the final model, all terms should be significant at a confidence level of 95% or higher; consequently, the insignificant terms at a level of 0.05 were eliminated. The following Eqs. (4)–(9) are reduced models for each response:
CE
W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240
Factor
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W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240
237
3.3. Screened yield Within the limit of the study the screened yield ranged from about 32% to 44% (Table 1), which is typical for chemical pulping of nonwood materials. It is evident from Eq. (4) that temperature and alkali charge were the most important factors affecting the pulp yield. Statistical analyses (Table 2) indicated that the treatment time had no significant influence on screened yield, indicating the possibility of reducing the treatment time to 1 h to achieve similar screened yield. It also means that the dissolution of lignin, hemicellulose and extractives from the frond fiber in a caustic milieu could be achieved with ease, requiring a relatively short period of reaction time within the range of temperature and alkali charge used. A response surface graph showing the interaction effects (at 1.5 h) is presented in Fig. 1.
Fig. 2. Three-dimensional graph showing the response of Kappa number at 1.5 h.
3.4. Kappa number The principal effects of temperature, alkali charge and treatment time on Kappa number are shown in Table 2 and Eq. (5). It should be noted that the alkali charges had the most influence on reducing the residual lignin in the pulp, followed by the cooking temperature. Statistically, the treatment time showed no significant influence, again indicating that the chemical treatment might be effectively conducted for times no longer than 1 h. The responses of Kappa number to temperature and alkali charge at a cooking time of 1.5 h are illustrated in Fig. 2.
Of the three factors affecting tensile index, the most influential is temperature, with alkali charge a smaller role and treatment time the least (Table 2 and Eq. (6)). It
is interesting to observe that cooking temperature is the main driving force for the alkali reaction that improves the bonding potential of frond fibers. Statistically, the treatment time had insignificant effect upon the interfiber bonding. The influence of temperature and alkali charge at a constant cooking time of 1.5 h is presented in Fig. 3. In the region of low temperature (160 °C), the increase in alkali charge from 20% to 30% had no significant effect. However, at 180 °C the tensile index is significantly improved by the increase in alkali charge. It should also be noted that at low (20%) alkali charge, the tensile index is not significantly affected by the increase in temperature from 160 to 180 °C. This implies that the maximum tensile index occurred when the temperature and alkali charge were at high levels, corresponding to the lowest point of screened yield (tensile-yield relationship is shown in Fig. 8).
Fig. 1. Three-dimensional graph showing the response of screened yield at 1.5 h.
Fig. 3. Three-dimensional graph showing the response of tensile index at 1.5 h.
3.5. Tensile index
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3.6. Burst index It is obvious from Eq. (7) and Table 2 that temperature was the most significant followed by alkali charge while the treatment time was the least. The cooking temperature is the main driving force for the alkali reaction that improves the burst index of paper made from fibers. In the low temperature region of 160 °C, the increase in alkali charge from 20% to 30% had no significant effect on burst index. In the high temperature region of 180 °C the burst index was marginally improved by the increase in alkali charge. The interaction of alkali and temperature is shown in Fig. 4. 3.7. Tear index In terms of the main effects on tear index, it is surprising that treatment time has the greatest, followed by temperature and alkali charge to a lesser extent (Table 2 and Eq. (8)). It has however been established that tear strength is a function of both fiber strength and fiber bonding (Page and MacLeod, 1992; Seth and Page, 1988). The dependency on time is most probably related to these parameters. At short cooking times, the degree of delignification is relatively small; hence a considerable amount of lignin is still left in the pulp, resulting in lower bonding and consequently reduced tear strength. At the other end of longer cooking times, the degree of delignification is much higher, and some degree of fiber damage is to be expected, leading to a reduction in tear strength. The interaction effects (at 1.5 h) in form of a response surface graph is shown in Fig. 5.
Fig. 5. Three-dimensional graph showing the response of tear index at 1.5 h.
alkali charge was the most influential factor in relation to the brightness of frond pulp, followed by the temperature, in order of importance. The effect of cooking time was comparatively small. Statistical analyses of the interaction effects of the pulping variables show that the cooking time had no significant effect on pulp brightness at all levels of temperature and caustic usage. Conversely, the increase in caustic charge significantly augmented the brightness at both levels of temperature. However, at a low alkali charge (20%), temperature had no significant influence when the cooking time was 1.5 h or lower. A response surface graph showing the interaction effects on brightness (at 1.5 h) is presented in Fig. 6.
3.8. Brightness 3.9. Discussion The main effects of temperature, alkali charge and treatment time on brightness (measured as ISO) are shown in Table 2 and Eq. (9). It is apparent that the
The study on the responses of pulp properties to the process variables provides a useful means for optimizing
Fig. 4. Three-dimensional graph showing the response of burst index at 1.5 h.
Fig. 6. Three-dimensional graph showing the response of brightness at 1.5 h.
W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240
seen that over the broad range of pulp yield from about 32% to 44%, the variation in tear index (9–10 mN m2 /g) was rather small when compared with those of tensile and burst indices. As shown in Fig. 11, burst index is strongly correlated with tensile index (R2 ¼ 0:7593) while the tear index shows a much smaller significant relationship with the tensile index (R2 ¼ 0:3422).
ISO Brightness
40 30 20
2
R = 0.7567
10 0 0
20
40
60
80
100
Kappa Number
Tensile Index, Nm/g
Fig. 7. Brightness versus Kappa number.
60 50 40 30 20 30
32.5
35
37.5
40
42.5
45
Screened Yield, %
Burst Index, kPa m2/g
Fig. 8. Tensile index as function of screened yield.
5 4 3 2 1 30
32.5
35
37.5 40 Screened Yield, %
42.5
45
Fig. 9. Burst index as a function of screened yield.
12
Tear Index, Nm2/g
the pulping conditions. It gives, however, little insight into the chemical and physical changes that the raw material has undergone during the process. In this investigation, the chemical agent (NaOH) used is the only variable that has direct impact on the physical and chemical nature of the resulting pulp. The treatment temperature may be considered as a catalyzer that accelerates the alkali reaction in dissolving the lignin and carbohydrates from the raw material; it exerts no direct influence on the nature of the pulp produced. The latter is in fact affected by the alkali action that causes delignificaton, hydrolysis of carbohydrates and swelling of the fiber matrix. Even at low temperature sodium hydroxide could significantly modify the nature of the material. Similarly, the treatment time maintains the chemical reaction and has no direct influence in determining the characteristics of the resulting pulp. As noted earlier, the cooking time has practically no significant effect upon almost all properties discussed, within the scope of the study. Besides, the development of each pulp property in chemical pulping has its own limitation, which is dictated by both the chemical and morphological characteristics of the constituent elements of the raw material, that is the individual fibers. For example, the range of strength properties such as tensile, burst and tear indices is finite for each particular type of fiber. The increase in one property is not necessarily always in parallel with the changes in other properties of the same pulp. For instance, the tensile strength is principally associated with the effective number of bonding sites (hydrogen bonds) available on the fiber surface while the tear index depends mainly on fiber length. The average length of fibers of a particular raw material would remain unchanged during the course of chemical pulping while the degree of hydrogen bonding, which is finite in nature, may depend, to a certain extent, on the severity of chemical treatment or the extent of dissolution of fiber constituents. These relationships may also be complicated by the degree of depolymerization of the cellulosic material or the inherent mechanical strength of fibers. It is of interest to notice that the increase in alkali charge improved the brightness, which is associated with the amount of chromophoric groups remaining in the pulped frond fiber. Fig. 7 clearly reveals the close relationship of brightness and Kappa number (R2 ¼ 0:7567). Pulp yield is one of the key factors determining the physical characteristics of pulp fibers. The inter-relationships of tensile, burst and tear indices with screened yield are shown in Figs. 8–10, respectively. As seen in Figs. 8 and 9, the fiber-bonding dependent properties such as tensile and burst indices tend to increase with decreasing screened yield while the fiber-length dependent tear index seems to have a maximum value in the neighbourhood 37–38% yield (Fig. 10). It could also be
239
11 10 9 8 7 30
32.5
35
37.5 40 Screened Yield, %
42.5
Fig. 10. Tear index as a function of screened yield.
45
240
W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240
12 10
2
Acknowledgements
2
Financial support from Universiti Sains Malaysia in the form of IRPA short-term grant 304/PTEKIND/ 633074 and IRPA EA grant 305/PTEKIND/612602 is gratefully acknowledged.
R = 0.3422
Tear Index, Nm2/g
8
R = 0.7593
6
Burst Index, kPa m2/g
4 2 0 30
35
40
45
50
55
60
Tensile Index, Nm/g Fig. 11. Tear and burst indices versus tensile index.
Evidently, it is the desired properties of the final product that dictate the optimum pulping conditions for a particular raw material. It is noteworthy that the pulp characteristics presented in the study were obtained using unbeaten pulps, that is they had not been mechanically treated or refined. The freeness was high (670 ± 25 ml CSF). A mechanical treatment would certainly improve the tensile and burst indices and it might change the tear index either positively or negatively due to the expected fiber fibrillation and shortening effect caused by beating or refining. For this reason, the effects of the pulping variables as well as the relationships between the paper properties discussed earlier might differ somewhat depending on how the pulps would respond to the mechanical treatment.
4. Conclusion Caustic pulping of oil-palm frond fiber requires a relatively short reaction time (about 60 min) within the limits of treatment temperature (160–180 °C) and of alkali charge (20–30% NaOH) used. The delignification of frond fiber can be achieved with ease using sodium hydroxide as the sole cooking agent. The caustic reaction is greatly enhanced by the increases in temperature. Each property studied varies somewhat differently with the pulp yield. As such, it would be the desired properties of the final product that will dictate the optimized pulping conditions.
References Anon., 1991. Annual Report, Pulp and Paper International 33 (7), 26– 27. Anon., 1997. Industrial News––Malaysia studies making paper from palm waste. Appita 50 (2), 88. Anon., 2001. Annual Report, Pulp and Paper International 43 (7), 8–9. Chan, K.W., 1999. Biomass production in the oil palm industry. In: Singh, G. et al. (Eds.), Oil Palm and the Environment: A Malaysian Perspective. Malaysian Oil Palm Growers’ Council, Kuala Lumpur, pp. 41–53. Fuad, M.A., Rohana, A.R., Chua, B.G., 1999. Socio-economic considerations in the development of jungle to oil palm. In: Singh, G. et al. (Eds.), Oil Palm and the Environment: A Malaysian Perspective. Malaysian Oil Palm Growers’ Council, Kuala Lumpur, pp. 1–7. Husin, M., Hassan, A.M., Tarmizi, A.M., 1986. Availability and potential utilisation of oil palm trunks and fronds up to year 2000. Palm Oil Research Institute Malaysia Occasional Paper No. 20, pp. 1–17. Law, K.N., Wan Rosli, W.D., 2001. Nonwood materials (with special reference to oil palm fibers) as papermaking materials: potentials and challenges in the new millennium. In: Proceedings of USMJIRCAS Joint International Symposium on Lignocellulosic Materials, Penang, Malaysia, pp. 1–13. Lim, K.O., 1998. Oil palm plantations––a plausible renewable source of energy. RERIC Int. Energy J. 20 (2), 107–116. Lubis, A.U., Guritno, P., Darnoko, A., 1994. Prospects of oil palm solid wastes based industries in Indonesia. In: Proceedings of the 3rd National Seminar on Utilisation of Oil Palm Tree and other Palms, Kuala Lumpur, Malaysia, FRIM, pp. 62–69. Mohd Yusoff, M.N., 1997. High yield pulping of oil palm frond fibers in Malaysia. In: Proceedings of the Nanjing International Symposium on High Yield Pulping, Nanjing, China, Chinese Academy of Forestry, pp. 201–210. Ott, L., 1988. An Introduction to Statistical Methods and Data Analysis, third ed. PWS, Kent, Boston. Page, D.H., MacLeod, J.M., 1992. Fiber strength and its impact on tear strength. Tappi 75 (1), 172–174. Seth, R.S., Page, D.H., 1988. Fiber properties and tearing resistance. Tappi 71 (2), 103–107. Wise, L.E., Murphy, M., D’Addieco, A.A., 1946. Chlorite holocellulose––its fractionation and bearing on summative wood analysis and on studies on the hemicelluloses. Paper Trade J. 122 (2), 35–43.