J. Pac .Sci. Tech.

Vol.18No.6（2009）

一般論文〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜〜

Papermaking Properties of Salix Serissaefolia Pulps
Prepared Under Different Pulping Conditions
※

*

**

Emmanuel ASUNCION , Kyoji SUZUKI , Hiromu WATANABE****
and Yasushi KAMAYA***

The papermaking properties of Salix serissaefolia, a fast growing willow species were evaluatedto determine its potential as a raw material for pulp and paper production. Its chemical composition wasmeasured, and soda-anthraquinone (AQ) and kraft pulping processes under varied conditions were
employed. The material has cellulose and lignin contents comparable to commercially used wood species
suggesting its suitability for pulping. The different cooks provided nearly zero reject yields and an
acceptable range of screened yield which was highest in standard soda-AQ pulping. Kappa numbers ofthe different pulps especially those cooked under higher levels of chemical charges were remarkably low.
Willow pulps cooked with kraft method particularly at a higher chemical charge generally provided betterbrightness and strength properties. However, soda-AQ pulps responded better to the mechanical treatment
providing handsheets with higher strength values. At about the same freeness level, strength properties ofS. serissaefolia pulps cooked under standard conditions and at a higher level of chemical charge arecomparable or even more superior to other fast growing hardwoods.
Keywords：fast growing tree, papermaking, kraft pulping, soda-AQ pulping

1. Introduction
For the past years, the utilization of fast growing trees as raw materials has become popular in thepulp and paper industry. Fast growing tree species can be grown in plantations and thus, a manageable
and steady supply of wood pulp that could meet the increasing global demands can be guaranteed. At
present, only a handful of fast growing tree species are being used for commercial pulp production, one ofwhich is the eucalyptus. In fact, eucalyptus pulps are now increasingly dominating the world hardwood
pulp markets.1)
Willow or Salix constitutes another genus of fast growing hardwoods. Detailed reports about willow
pulping is scarce and in one study, only the trimmings of a plantation-grown North American species※ A part of this paper was presented at the 18th Annual Meeting of the Society of Packaging Science and Technology, Japan* Emmanuel ASUNCION (Student, The United Graduate School of Agricultural Science, Gifu University):
Tel: (81)9042331276 Email: easuncion_02@yahoo.com** Prof. (Dr.) Kyoji SUZUKI: Tel: (81)54-238-4859, Fax: (81)54-237-3031, Email: afksuzu@agr.shizuoka.ac.jp*** Prof. (Dr.) Hiromu WATANABE: Tel: (81)54-238-4589, Fax: (81)54-237-3028, Email: ahwatanabe@agr.shizuoka.ac.jp**** Prof. (Dr.) Yasushi KAMAYA: Tel: (81)54-238-4857, Email: ahykama@agr.shizuoka.ac.jp
All from Shizuoka University Faculty of Agriculture, 422-8529 Shizuoka City, Ohya 863− 389 −

Papermaking Properties of Salix Serissaefolia Pulps Prepared Under Different Pulping Conditions

were used to produce pulp under varied alkali charges and cooking time conditions.2) In central Japan, one
species that is growing abundantly along riverbanks is Salix serissaefolia, which is locally known as
kogomeyanagi (Fig.1). This willow species can grow to a height of 25 meters and a diameter of one
meter at maturity.3) In this research, the papermaking potential and properties of kogomeyanagi under
different pulping conditions were evaluated, and how some of the resulting pulps would respond to a
specific beating period was determined.

Fig. 1 Salix serissaefolia

2. Materials and Methods
2.1 Wood Chips Preparation
Willow chips were prepared manually from a debarked 4-year old tree harvested from the Aberiverbanks in Shizuoka City. For comparison purposes, a mixture of eucalyptus chips with E. grandis as
the main component was obtained from a paper mill. The chips were then air dried for several days before
they were used in the cooking process.

2.2 Measurement of Chemical Composition
A sample of the material was milled and sieved to obtain a 40-mesh pass wood meal fraction which
was then used for the measurement of major wood chemical composition. Amount of alcohol extractives
was determined based on TAPPI T204 in which 95% ethanol was used as a solvent. Lignin, holocellulose,and α–cellulose contents were measured using the Klason technique, Wise method, and sodium hydroxide
extraction, respectively. The chemical composition of the eucalyptus was also analyzed.

− 390 −

J. Pac .Sci. Tech.

Vol.18No.6（2009）

2.3 Pulping and Pulp Properties Evaluation
Willow chips were cooked in a laboratory-type rotary digester at different conditions of sodaanthraquinone (AQ) and kraft pulping processes. High and low levels, specifically: 15% and 18% NaOH
in soda-AQ, and 16% and 20% active alkali in kraft for chemical charge; 170 and 180℃ for cooking
temperature; and, 3.0 and 3.5 hours for cooking time operational variables were employed. The low levels
represent standard cooking conditions. Combinations of these varied conditions applied to a particular
cook are listed in Table 2. For facility, each cook was given a code based on the name of the material (Wfor Willow, E for Eucalyptus), pulping process (S for soda-AQ and K for kraft), and level of conditions(0-7, 0 representing the standard conditions). Cooking was done at 5:1 liquor to material ratio. The time
to attain the maximum cooking temperature was 1.5 hours and this temperature was maintained foranother 1.5 or 2 hours to complete the cooking time as described above. The digester was then opened
after 2 hours of cooling. In the soda-AQ process, 0.1% AQ was added to the cooking liquor. Cooking
under the same pulping conditions was done at least three times. The eucalyptus material was also cooked
under standard conditions of both pulping processes.
Pulps obtained from the different cooks were evaluated in terms of yield, freeness and kappa number.
Freeness and kappa number were measured based on T227 and T236, respectively, of TAPPI standards. In
addition, average fiber length and width distributions were determined using HiRes Fiber Quality
Analyzer (OpTest Equipment Inc.). The effect of beating at varied time lengths for pulps cooked under
the low level conditions was also investigated.

2.4 Preparation and Evaluation of Handsheets
Standard handsheets were prepared from the unbleached, unbeaten and beaten pulps. Theirmechanical and optical properties were then evaluated. Folding endurance, tensile strength, bursting
strength, and tearing resistance were measured in accordance with T511, T494, T404 and T414,
respectively of TAPPI test standards. For the optical properties, ISO brightness and opacity of thehandsheets were measured.

3. Results and Discussion
3.1 Chemical Composition
The percentage composition of the chemical components of S. serissaefolia and Eucalyptus sp. arepresented in Table 1. These values are somewhat comparable to each other and to the typical amounts
exhibited by North American hardwoods.4) The percentage of cellulose and lignin are also comparable tothose of eucalyptus species reported by Khristova.5) 6) In S. serissaefolia, both extractives and ash contents
are low which are respectively within the 1-5% and 0.4-0.8% ranges in North American hardwoods as
described by Biermann4). Extractives consume a certain portion of the pulping chemical during thecooking process, which can result to a lower pulp yield.7) Thus, lower amount of this component in raw− 391 −

Papermaking Properties of Salix Serissaefolia Pulps Prepared Under Different Pulping Conditions

materials is more desired.

Table 1 Chemical composition of willow and eucalyptus.
Willow

Eucalyptus

0.77

0.28

3.5

3.0

Holocellulose

77.7

81.2

**

22.0

20.9

α-Cellulose**

41.2

46.9

Ash

*

Alcohol Extractives**

Lignin**based on OD weight material
based on OD weight of extractive-free material**

Chemical composition can suggest the suitability of a material for pulping and papermaking. It wasreported by Nieschlag et al. that from a chemical composition point of view, plant materials with at least
34% α–cellulose contents are characterized as promising materials for pulp and paper manufacture. 1) 8) 9)
10)This therefore indicates the potential of S. serissaefolia as a good raw material.

3.2 Pulp and Handsheet Properties
The pulping method and conditions can greatly affect the extent of delignification process duringcooking, and the characteristics of the resulting pulp.8) 11)̶14) Wan Rosli15) stated that among the pulping
variables, only the chemical agents have a direct impact on the physical and chemical nature of theresulting pulp. Temperature may be considered as a catalyzer that accelerates the delignification process
while cooking time maintains the chemical reactions. Determining the conditions that can provide better
properties of the product is therefore important in order to maximize the potential of the material. In thisstudy, this was done through the application of different combinations of cooking conditions.
The properties of the different pulp cooks are presented in Table 2. Except for WS0, a nearly zero
percent pulp rejects was obtained in all of the different willow pulps. The slightly lower screened yields inthe kraft process were computed to be significantly different from that of soda-AQ process. WK2 andWK4 cooks gave lower accept yields compared to the rest. This is because the high levels of chemicalcharge and temperature as well as longer cooking time applied caused greater dissolution of the material
components particularly hemicelluloses and some cellulose together with lignin. Based on the result of at-test, under standard pulping conditions, pulp yields of both willow and eucalyptus are statisticallycomparable. These values are also comparable to the yields of other hardwoods studied. 1) 5) 6) 11) 19)− 392 −

J. Pac .Sci. Tech.

Vol.18No.6（2009）

Table 2 Cooking conditions and properties of the different pulp and their respective handsheets.
Chemi- Cooking
Cook cal Charge Time Temp Accept Reject Kappa CSF
Code(%)(Hrs) (℃) Yield Yield No. (ml)

ISO
(%)

Tear TensileOpa- Folding Burst
city (No. of Index
Index Index(%)
times) (kPm2/g) (mNm2/g) (Nm/g)

WS0

15

3

170

51.0

6.4

29

638

24.0

98.7

7

0.60

7.3

44.4

WS1

18

3

170

49.8

0.082

12

608

34.1

96.2

8

0.74

8.0

46.0

WS2

18

3

180

49.6

0.11

11

615

31.7

98.3

5

0.64

7.7

41.2

WS3

18

3.5

170

50.7

0.2

12

630

32.0

99.7

5

0.54

7.9

41.8

WS4

18

3.5

180

48.6

0.24

13

620

28.5

99.1

4

0.54

7.2

39.6

WK0

16

3

170

49.9

0.032

12

619

34.1

98.3

11

0.83

7.9

46.7

WK1

20

3

170

48.4

0.005

12

600

39.2

98.2

11

0.64

7.2

49.9

WK2

20

3

180

44.8

0.011

7

620

32.0

99.2

8

0.98

7.1

49.8

WK3

20

3.5

170

47.7

0.003

7

610

33.9

99.1

9

0.93

7.5

48.6

WK4

20

3.5

180

44.3

0

7

610

31.7

99.3

7

0.75

6.0

49.8

WK5

16

3.5

170

50.6

0.093

9

625

33.2

99.4

8

0.92

7.7

48.3

WK6

16

3

180

47.7

0.077

11

615

30.3

97.7

9

0.93

8.1

49.2

WK7

16

3.5

180

48.2

0.027

11

620

29.6

98.8

10

1.0

6.9

49.5

ES0

15

3

170

51.8

2.0

28

630

24.2

98.5

12

1.0

10.4

55.4

EK0

16

3

170

50.0

0

18

610

27.1

98.4

15

1.8

7.7

65.1

The differences in kappa numbers of the willow pulp cooks can be accounted from the different
chemical charges applied. As expected, the use of higher chemical charges resulted to lower kappa
numbers. Cooking under the combination of higher levels of chemical charge and temperature or timeeffectively lowered the pulp lignin content. Kappa numbers of pulps cooked under these conditions weresignificantly lower compared to pulps cooked under conditions where only one of the three process
variables is at a higher level, or when both higher levels of temperature and cooking time combined
together were applied. Pulps cooked with kraft process have lower kappa numbers in contrast to soda-AQ
cooked pulps that indicate greater delignification. Under standard soda-AQ process, kappa numbers of
willow and eucalyptus pulps were almost similar, but under standard kraft process willow pulp is slightly
lower.
Measurement of the fiber dimensions of willow and eucalyptus pulps cooked with standard soda AQ
and kraft processes revealed WS0 as having the highest values for average weighted fiber length− 393 −

Papermaking Properties of Salix Serissaefolia Pulps Prepared Under Different Pulping Conditions(0.91mm) and width (20.6µm). The other pulps showed measurements comparable with each other at a
range of 0.704 to 0.783mm for fiber length and 15.7 to 16.86µm for fiber width. In Figs. 2 and 3, which
respectively show the % length weighted distribution, and % width distribution of the four pulps (A-C),
WS0 pulp cook has a wider range and higher upper limit of length measurement. In addition, thepercentages of longer and thicker fibers of this pulp are higher compared to the others. The measured
fiber lengths of willow fibers are comparable to some known papermaking raw materials. 7) 16)

Cumulative % Distribution

90%

6%

80%
5%

70%
60%

4%

50%
3%

40%
30%

2%

Distribution, %

20%
1%

10%
0%
1

2

3

4

5

9%

90%

8%

80%

7%

70%

6%

60%

5%

50%
4%

40%

3%

30%
20%

2%

10%

1%

0%

0%
0

100%

0%
0

6

0.5

1

1.5

2

Fiber length, mm

3

3.5

4

Ｄ

C
10%

100%

10%

90%

9%

90%

9%

80%

8%

80%

8%

70%

7%

70%

7%

60%

6%

60%

6%

50%

5%

50%

5%

40%

4%

40%

4%

30%

3%

30%

3%

20%

2%

20%

2%

10%

1%

10%

1%

0%

0%

0%

0

0.5

1

1.5

2

2.5

Cumulative % Distribution

100%

Distribution, %Cumulative % Distribution

2.5

Fiber length, mm

3

0%
0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Fiber length, mm

Fiber length, mm

Fig. 2 Percent length weighted length distribution of willow and eucalyptus standard soda-AQ
and kraft pulps. (A. WS0, B.WK0, C. ES0, D. EK0 pulps)
Opacity of the different handsheets as influenced by different cooking conditions reveals nosignificant differences (Table 2). However, % ISO brightness values agree with the kappa number results
in which higher level of chemical charge resulted to a higher ISO brightness. Although the ISO brightness
values of willow and eucalyptus soda-AQ pulps are almost comparable, brightness of the kraft pulp of theformer is much higher than of the latter.

− 394 −

Distribution, %Cumulative % Distribution

7%

Distribution, %

B

A
100%

J. Pac .Sci. Tech.

Vol.18No.6（2009）

A

B

14%

20%
18%

12%

% D istrib u tio n% D istrib u tio n

16%
10%
8%
6%
4%

14%
12%
10%
8%
6%
4%

2%

2%

Width,µm

.7
5

.7
5

54

51

48

.7
5

.7
5

.7
5

45

42

.7
5

.7
5

.7
5

.7
5

.7
5
54

57

.7
5
51

.7
5

.7
5
48

45

.7
5
42

39

36

.7
5

.7
5

.7
5

30

33

27

.7
5
24

.7
5

.7
5
21

18

.7
5

15

0.
75

.7
5
57

.7
5

.7
5

.7
5
54

51

48

.7
5

.7
5
42

45

.7
5

.7
5
39

36

.7
5

.7
5

30

33

.7
5

.7
5
27

24

21

18

.7
5

0%
.7
5

2%

0%
.7
5

4%

.7
5

6%

2%

15

.7
5

8%

4%

.7
5

33

10%

12

6%

12%

9.
75

8%

14%

6.
75

10%

3.
75

12%

12

36

16%

9.
75

39

18%

14%

% D istrib u tio n

16%

6.
75

.7
5

Ｄ
20%

3.
75

.7
5

C

% D istrib u tio n

27

Width, µm

18%

0.
75

.7
5

Width, µm

30

24

.7
5

.7
5

.7
5

21

18

.7
5

.7
5
12

15

6.
75
9.
75

0.
75
3.
75

.7
5
57

.7
5

.7
5

.7
5

.7
5
54

51

48

.7
5
42

45

.7
5

.7
5
39

36

.7
5

.7
5

30

33

.7
5

.7
5
27

24

.7
5

.7
5
18

21

.7
5

.7
5

15

9.
75

12

6.
75

3.
75

0%

0.
75

0%

Width, µm

Fig. 3 Percent width distribution of willow and eucalyptus standard soda-AQ and kraft pulps.
(A. WS0, B.WK0, C. ES0, D. EK0 pulps)
As expected, the strengths of the different willow pulp handsheets differ from each other as aconsequence of the impact of cooking. Although the final strength of the handsheets are related to themorphological properties of the fibers,5) 17) the processing variables can greatly influence how these fibers
eventually end up in the paper web. A pulp cook that gives greater extent of delignification and lower
degree of lignin condensation, higher amount of conserved hemicelluloses and celluloses will likely give
better strength properties1) 18). In this study, among the different pulp cooks, higher bursting and tensile
indices, and folding counts were observed in kraft pulps compared to soda-AQ pulps at the same level ofparameter conditions. In both pulping processes, tensile index values of handsheets from pulps cookedwith higher chemical charge were higher than those from the standard conditions. Also a high folding
count is evident in handsheets made from pulps cooked at a shorter time and lower temperature, while aslightly lower tear index is exhibited by those derived from longer time and higher temperature-cooked
pulps. WK4 handsheets which are from pulps cooked with the three process variables all in the highlevels gave the lowest strength values particularly for folding and bursting. Among the kraft pulps, alower tear index is observed in handsheets of pulps cooked at higher chemical charge. In soda-AQ pulps
on the other hand, higher bursting and tear indices were observed in handsheets of pulps cooked with− 395 −

Papermaking Properties of Salix Serissaefolia Pulps Prepared Under Different Pulping Conditions

higher level of chemical charge.

Table 3 Strength values of willow in comparison with other studied pulpwood materials.
Pulping Method
Material

Freeness(ml)

Tear Index Tensile Index Burst Index(mNm2/g)(Nm/g)(kPm2/g)

Soda-AQ (WS0) 425 (CSF)*

6.9

80

3.9

Soda-AQ (WS1) 425 (CSF)
425 (CSF)
Kraft (WK0)

6.7

80

3.6

5.7

84

3.4

425 (CSF)

6.6

70

2.4

Soda-AQ (ES0) 425 (CSF)

9.2

92

4.2

Kraft (EK0)
Kraft

425 (CSF)

9.4

87

3.7

432 (CSF)

6.3

90

-

Kraft

450 (CSF)

4.5

73

3.3

Kraft

30oSR

8.1

61.8

4.3

Soda-AQ

o

30 SR

6.4

54.8

3.3

Kraft

o

30 SR

8.4

76.9

4.4

Soda

o

30 SR

6.9

61.7

3.1

Kraft

o

30 SR

10

85

5.5

Soda

o

30 SR

8

68.7

4.3

Eucalyptus
camaldulensis5)

Kraft

30oSR

8.1

74

4.7

Eucalyptus microtheca5)

Kraft

30oSR

8.4

73.1

4.9

Salix
serissaefolia

Kraft (WK1)
Eucalyptus sp.**
Populus sp.

19)

Albizia julibrissin20)
Acacia seyal(var. fistula)6)
Eucalyptus citriodora5)
Eucalyptus
tereticornisss5)*425 ml CSF converts to 30oSR based on the freeness conversion table published by Aikawagroup**This study
Fig. 4 shows the tensile index-tear index plot of the different willow pulp cooks. In general,
handsheets from pulps cooked with kraft process exhibited higher strength as indicated by theirsignificantly higher tensile index at comparable tear index values with their soda-AQ counterparts. WK1and WK2 in which pulps were cooked at a higher level of chemical charge show greater tensile and tearstrength combination in comparison to the others. WK6 is also remarkably strong having the highest tearindex and one of the highest values for tensile index.

− 396 −

J. Pac .Sci. Tech.

Vol.18No.6（2009）

Tear index (mN・m 2 /g)

9
WS0
WS1
WS2
WS3
WS4
WK0
WK1
WK2
WK3
WK4
WK5
WK6
WK7

8

7

6

5
38

40

42

44

46

48

50

Tensile index (N・m/g)
Fig. 4 Tensile index‒tear index plots of the different willow pulp handsheets.

3.3 Effect of Beating
The response of willow and eucalyptus pulps cooked under standard conditions (WS0 and WK0) as
well as WS1 and WK1 pulps which provided handsheets that have the highest tensile and tear strengths
among the willow pulps to beating is given in Fig. 5.A. The narrow differences in CSF levels among
most of the unbeaten pulps were greatly magnified after 60 minutes of mechanical treatment. Among thewillow pulps, WS0 that had the highest initial CSF reading exhibited the biggest drop.
Folding, tensile and burst strengths of the willow pulps greatly improved after 60 minutes of beating(Fig. 5.B-D). Although ES0 pulp gave a higher folding count, that of EK0 pulp is lower than the willow
soda-AQ pulps. The tensile index of the willow pulps after the last beating period increased to almost
100% of the unbeaten values, and which are about 10 points lower than those of eucalyptus pulps. WK1
pulp which initially had the highest tensile index among the willow pulps gave slightly lower value than
the rest of the willow pulps beaten for 60 minutes. The bursting index of willow pulps improved at least 4
times from their unbeaten measurements. Willow soda-AQ pulps attained bursting index values that are
not more than 2 points lower than those of the eucalyptus pulps. Although the tearing strength of both
willow and eucalyptus standard kraft and soda-AQ pulps improved after 15 minutes of beating, the values
declined when the refining action was continued to beyond 30 minutes. A drop of about 2 points from theinitial unbeaten pulp tear index can be observed in the willow pulps after the final beating period. These
are slightly lower than those of the eucalyptus pulps as shown in the Fig.5.E.

− 397 −

Papermaking Properties of Salix Serissaefolia Pulps Prepared Under Different Pulping Conditions

Fig 5. Effect of beating time on the properties of willow and eucalyptus pulps.
(A. CSF, B. folding endurance, C. tensile index, D. bursting index, E. tear index)− 398 −

J. Pac .Sci. Tech.

Vol.18No.6（2009）

The above-mentioned results suggest that the strength properties of S. serissefolia could be improved
with the appropriate degree of mechanical treatment to values that are within acceptable ranges fordifferent paper applications.
Table 3 shows the strength values of willow tree pulp handsheets as compared to different species of
eucalyptus tree and other fast growing trees used in other published studies at about the same freenesslevel. It is evident that depending on the material species and strength property under consideration,
willow tree may have slightly lower strength in some aspects, but it also has comparable or even more
superior strength values. In addition, its tensile and burst strengths still improves at a lower freeness as aneffect of longer beating time.

4. Conclusions
The chemical composition of S. serissaefolia particularly its cellulose and lignin components arecomparable to other hardwoods and fast–growing tree species. This makes this raw material suitable for
pulping. When cooked at different combinations of pulping methods and levels of chemical charge,
cooking temperature, and cooking time, the resulting pulps showed different properties. The use of higher
or lower levels of the operational variables gave better properties to some pulps while it was
disadvantageous in others. Pulp yields of S. serissaefolia in both soda-AQ and kraft process arecomparable to other studied hardwoods. The most desirable strength and optical properties were obtained
at higher level of chemical charge (WK1) or higher levels of both chemical charge and temperature(WK2) cooking combinations. The application of a specific combination of cooking conditions eventuallydepends on the important property of the product suited to its use.
The folding, tensile, and bursting strength properties of S. serissaefolia were further improved withmechanical treatment. Immediate improvement of the folding, bursting and tensile strengths after 30
minutes of beating in soda-AQ pulps eventually resulted to higher values compared to kraft pulps by theend of 60 minutes beating period. The tear strength which initially improved within the first few minutesof beating however, weakened with prolonged beating. This suggests that beating duration of the material
depends on the strength property of interest.
Compared to the eucalyptus, S. serissaefolia standard kraft pulp handsheets have higher ISO
brightness readings. Although its burst and tearing strength values are slightly lower than those obtainedin the eucalyptus used in this study after refining, S. serissaefolia is comparable or even more superior toother eucalyptus species or fast growing trees at about the same freeness level (425 ml CSF).

References
1.

Patt, R., Kordsachia, O. Fehr, J.: Wood Science Technology, 40, 39-48 (2006)

2.

Makkonen H., Granzow, S., Cheshire, 2nd Annual Partnerships for Environmental Improvement− 399 −

Papermaking Properties of Salix Serissaefolia Pulps Prepared Under Different Pulping Conditions

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（原稿受付 2009 年 8 月 25 日）（審査受理 2009 年 10 月 9 日）

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J. Pac .Sci. Tech.

Vol.18No.6（2009）

異なるパルプ化条件におけるコゴメヤナギの製紙特性*
アサンシオンエマヌエル 、静岡大学

**

鈴木恭治

、渡邊

***

拡

****

、釜谷保志

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