Bioresource Technology 93 (2004) 233–240

Effect of pulping variables on the characteristicsof oil-palm frond-fiber

W.D. Wan Rosli a,*, K.N. Law b, Z. Zainuddin a, R. Asro a

a Universiti Sains Malaysia, 11800 Penang, Malaysiab Pulp and Paper Research Center, University of Quebec in Trois-Rivi�eres, Box 500, Trois-Rivi�eres, 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-EXPERT�). 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.

� 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 oflife 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 conser-

vationists and environmental groups. To maintain the

paper industry growth, governments as well as industry

executives have to establish and implement policies andplans to ensure a sustainable fiber supply, including

reforestation program, plantation management, recyc-

ling, and development of nonwood fibers.

The ever-increasing manufacturing costs and uncer-

tainty 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: wanrosli@usm.my (W.D. Wan Rosli).

0960-8524/$ - see front matter � 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 fi-

bers, 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, Indonesiaand 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 prob-

lems in replanting operations, and tremendous envi-

ronmental 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 bio-

mass 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 hectar-

age of oil palm in Malaysia could reach 3.151 million hain 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

234 W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240

2000, produced an estimated 56.9 million tonnes of oil-

palm biomass (Chan, 1999). Taking into account the

proportion of useful fibrous elements that can be ex-

tracted 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 pul-

ping characteristics of oil-palm fibers have been recentlyreviewed 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 an-

nual pruning of 11 t/ha (Husin et al., 1986), the avail-ability 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 oil-palm 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 compositionof 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 a-cellulose 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 theTappi methods as T 222 om-98 and T 204 cm-97.

2.2. Experimental design

Response surface methodology was utilized to opti-

mize the soda pulping process and a CCD was adopted.

It involves outlining the composition of the experimen-tal process conditions subsequently used to develop the

regression models. The basic CCD for k variables con-sists of a 2k factorial design with each factor at two levels

ð�1;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 af-

fect 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 thecoded 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 ð1Þtcode ¼ ðt � 1 hÞ=0:5 h ð2ÞAcode ¼ ðAC� 25%Þ=5% ð3ÞThe 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, DESIGN-

EXPERT� 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 tem-

perature were maintained at a constant of 6:1 and 90min 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 wasmeasured following the method T 227 om-94. Hand-

sheets 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 and50% RH for at least 24 h before testing.

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

Table 1

A three-variables CCD as composed by DESIGN EXPERT� and the corresponding response for soda pulping of EFB

No. Pulping variables Response

Coded Values Reject (%) Screened

yield (%)

Kappa

no.

Burst index

(kPam2/g)

Tear index

(mNm2/g)

Tensile index

(Nm/g)

ISO bright-

ness (%)T AC t T (�C) AC (%) t (h)

1 )1 )1 )1 160.0 20.00 1.00 2.8 42.25 63.39 2.9 9.21 46.31 20.93

2 1 )1 )1 180.0 20.00 1.00 0.8 38.19 36.31 3.4 9.84 45.11 21.29

3 )1 1 )1 160.0 30.00 1.00 0.9 39.61 40.46 2.75 9.33 42.38 22.61

4 1 1 )1 180.0 30.00 1.00 0 35.57 12.11 3.64 9.86 48.88 29.79

5 )1 )1 1 160.0 20.00 2.00 1.6 43.93 63.24 3.54 9.11 46.17 20.93

6 1 )1 1 180.0 20.00 2.00 0.6 39.79 37.76 3.67 8.99 49.4 15.82

7 )1 1 1 160.0 30.00 2.00 0.3 39.09 26 3.31 9.15 45.95 25.68

8 1 1 1 180.0 30.00 2.00 0 32.31 9.64 3.46 8.85 50.84 31.08

9 )1.68 0 0 153.2 25.00 1.50 2.3 40.81 50.58 2.13 8.71 36.37 21.11

10 1.68 0 0 186.8 25.00 1.50 0.38 34.59 17.1 4.04 9.25 58.38 28.86

11 0 )1.68 0 170.0 16.59 1.50 8.4 39.67 87.5 1.92 9.11 29.9 12.58

12 0 1.68 0 170.0 33.41 1.50 0.1 33.76 21.19 3.51 9.87 47.5 30.48

13 0 0 )1.68 170.0 25.00 0.66 0.5 41.26 30.06 4.72 11.09 58.78 25.26

14 0 0 1.68 170.0 25.00 2.34 0.2 39.31 22.49 4.14 9.96 53.37 26.86

15 0 0 0 170.0 25.00 1.50 0.4 39.68 21.53 4.15 10.02 50.96 26.28

16 0 0 0 170.0 25.00 1.50 0.4 38.82 24.49 4 10.1 51.09 25.71

17 0 0 0 170.0 25.00 1.50 0.3 36.81 23.5 4.06 10.06 54.56 26.19

Note: T––cooking temperature (�C); t––time-at-temperature (h); AC––NaOH level (w/w based on oven dried fiber).

W.D

.W

an

Rosli

etal.

/B

ioreso

urce

Tech

nolo

gy

93

(2004)

233–240

235

Table2

Statisticalanalysisofreducedmodelsandcoefficientofscreenedyield,Kappano.,viscosity,a-celluloseandashcontent

Factor

Screenedyield(%)

Kappano.

Burstindex(kPam2/g)

Tearindex(mNm2/g)

Tensileindex(Nm/g)

BrightnessISO

CE

Prob>

jtjCE

Prob>

jtjCE

Prob>

jtjCE

Prob>

jtjProb>

jtjCE

Prob>

jtjCE

Intercept

37.81

23.93

4.22

10.19

51.79

25.48

T)2.16

<0.0001

)11.25

<0.0001

0.36

0.0113

0.12

0.1668

3.69

0.0172

1.53

0.0066

AC

)2.02

<0.0001

)16.40

<0.0001

0.17

0.1763

0.097

0.2614

2.24

0.1188

4.41

<0.0001

t)0.28

0.3716

)2.08

0.1305

0.0236

0.8485

)0.30

0.0040

0.043

0.9751

0.12

0.8012

T2

2.99

0.0471

)0.39

0.0091

)0.48

0.0001

AC2

10.24

<0.0001

)0.52

0.0014

)0.30

0.0045

)4.72

0.0048

)1.58

0.0062

t20.93

0.0111

TAC

2.17

0.0041

Tt ACt

)0.88

0.0441

1.23

0.0620

Prob>

F<0.0001

<0.0001

0.0039

0.0006

0.0089

<0.0001

RootMSE

1.10

4.70

0.44

0.30

4.94

1.65

R-squared

0.9121

0.9654

0.7569

0.8312

0.6509

0.9329

Note

:(1)Allthecoefficientsareintermsofthecodedfactorssincethesizeofcoefficientsinacodedmodelrelatesdirectlytotheobservedchangeintheresponseandthecoefficientsinactualmodel

cannotbecomparedtooneanotherduetotheirdependenceonunitofmeasure.(2)CEreferstocoefficientestimates.

236 W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240

EXPERT�, a computer-aided response surface analyzer,

the most compatible model among mean, linear, qua-

dratic 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 toreduce the number of terms in the model that could

enable creation of a simple and practical model with aminimum 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:

Screened yield ¼ 37:81� 2:16T � 2:02AC� 0:28t

þ 0:93t2 � 0:88AC � t ð4ÞKappa no: ¼ 23:93� 11:25T � 16:40AC� 2:08t

þ 2:99T 2 þ 10:24AC2 ð5ÞTensile index ¼ 51:79þ 3:69T þ 2:24ACþ 0:043t

� 4:72AC2 ð6ÞBurst index ¼ 4:22þ 0:36T þ 0:17ACþ 0:0236t

� 0:39T 2 � 0:52AC2 ð7ÞTear index ¼ 10:19þ 0:12T þ 0:097AC� 0:30t

� 0:48T 2 � 0:30AC2 ð8Þ

Brightness¼ 25:48þ 1:53T þ 4:41ACþ 0:12t� 1:58AC2

þ 2:17T �ACþ 1:23AC � t ð9Þ

In Table 2 are summarized some of the statistical ana-

lysis 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 of0.001 or less. Also shown are the coefficient estimates for

each term in the selected models for every dependent

variable.

3.2. Rejects

Rejects of pulp may indicate the uniformity of rawmaterial 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 therejected fibers did not constitute part of the pulps eval-

uated, the rejects content will not be subjected to sta-

tistical analyses.

Fig. 2. Three-dimensional graph showing the response of Kappa

number at 1.5 h.

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 ran-

ged 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. Statis-

tical analyses (Table 2) indicated that the treatment timehad 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.

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. Statis-

tically, the treatment time showed no significant influ-

ence, 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.

3.5. Tensile index

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

Fig. 1. Three-dimensional graph showing the response of screened

yield at 1.5 h.

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 inter-

fiber 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), theincrease in alkali charge from 20% to 30% had no sig-nificant 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 themaximum tensile index occurred when the temperature

and alkali charge were at high levels, corresponding to

the lowest point of screened yield (tensile-yield rela-tionship is shown in Fig. 8).

Fig. 3. Three-dimensional graph showing the response of tensile index

at 1.5 h.

Fig. 5. Three-dimensional graph showing the response of tear index at

1.5 h.

238 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 temper-

ature 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, theincrease in alkali charge from 20% to 30% had no sig-

nificant effect on burst index. In the high temperature

region of 180 �C the burst index was marginally im-

proved 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 sur-

prising that treatment time has the greatest, followed by

temperature and alkali charge to a lesser extent (Table 2and 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.

3.8. Brightness

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

Fig. 4. Three-dimensional graph showing the response of burst index

at 1.5 h.

alkali charge was the most influential factor in relation

to the brightness of frond pulp, followed by the tem-

perature, 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. Con-versely, the increase in caustic charge significantly aug-

mented 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 inter-

action effects on brightness (at 1.5 h) is presented in

Fig. 6.

3.9. Discussion

The study on the responses of pulp properties to the

process variables provides a useful means for optimizing

Fig. 6. Three-dimensional graph showing the response of brightness at

1.5 h.

R2

= 0.7567

0

10

20

30

40

0 20 40 60 80 1000Kappa Number

ISO

Bri

ghtn

ess

Fig. 7. Brightness versus Kappa number.

20

30

40

50

60

30 32.5 35 37.5

Screened Yield, %

Ten

sile

Ind

ex, N

m/g

40 42.5 45

Fig. 8. Tensile index as function of screened yield.

1

2

3

4

5

30 32.5 35 37.5 40 42.5 451

2

3

4

5

30 32.5 35 37.5 40 42.5 45

Screened Yield, %

Bur

st I

ndex

, kP

a m

2 /g

Fig. 9. Burst index as a function of screened yield.

7

8

9

10

11

12

30 32.5 35 37.5 40 42.5 45Screened Yield, %

Tea

r In

dex,

Nm

2 /g

Fig. 10. Tear index as a function of screened yield.

W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240 239

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 ligninand 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 deter-mining 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 dic-

tated by both the chemical and morphological charac-

teristics 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 indexdepends mainly on fiber length. The average length of

fibers of a particular raw material would remain un-

changed 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 compli-

cated by the degree of depolymerization of the cellulosicmaterial 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 ¼0:7567).Pulp yield is one of the key factors determining the

physical characteristics of pulp fibers. The inter-rela-

tionships 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 depen-

dent tear index seems to have a maximum value in the

neighbourhood 37–38% yield (Fig. 10). It could also be

seen that over the broad range of pulp yield from about

32% to 44%, the variation in tear index (9–10 mNm2/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 signifi-

cant relationship with the tensile index (R2 ¼ 0:3422).

R2 = 0.3422

R2= 0.7593

0

2

4

6

8

10

12

30 35 40 45 50 55 60

Tear Index, Nm2/g

Burst Index, kPa m2/g

Tensile Index, Nm/g

Fig. 11. Tear and burst indices versus tensile index.

240 W.D. Wan Rosli et al. / Bioresource Technology 93 (2004) 233–240

Evidently, it is the desired properties of the final product

that dictate the optimum pulping conditions for a par-

ticular 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 cer-

tainly improve the tensile and burst indices and it mightchange 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 be-

tween 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 arelatively 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 reac-

tion 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 prop-erties of the final product that will dictate the optimized

pulping conditions.

Acknowledgements

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.

References

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