Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

Changes in Crystallinity and Re-swelling Capability of Pulp Fibers by Recycling Treatment

Khantayanuwong Somwang, Toshiharu Enomae, Akira Isogai, and Fumihiko Onabe
Paper Science Laboratory, Department of Biomaterial Sciences
Graduate School of Agricultural and Life Sciences, The University of Tokyo, JapanAn integrated technique was purposed for clarifying changes in amounts of amorphous andcrystalline regions of fibers as well as for estimating possibility of their irreversible conversion due torecyc ling treatment. The crystallinity of fibers in handsheets was moderately changed by the recycling
treatment as observed by X-ray diffractometry.

Because most of the fibers consisting of the stable

crystalline region which was hardly affected by the recyc ling treatment, the change in crystallinity was
possibly stemmed from a slight increase in crystallinity of amorphous region of fibers during recycling.
The decrease in the amount of the amorphous region by the recycling treatment, which affected the water
adsorbability of fibers, was indirectly detected by differential scanning calorimetry. Because of the lackof re-opening of recycled fiber lumens in a wet state, the amount of bound water adsorbed to fiber wall
substantially influenced the re-swelling capability of recycled fibers. The loss in re-swelling capability of
wet recycled fibers was consistent with sub-morphological changes of fiber wall possibly due to thedecrease in the amount of the amorphous region. FT-Raman spectroscopy was found not suitable fordetermining the effect of recycling treatment on changes in amounts of amorphous and crystalline regionsof fibers.

Keywords: Amorphous region, Crystallinity, Recycling treatment, Re-swelling capability

1.

Introduction

Microfibrils in bleached chemical pulp fibers consist of two regions of cellulose: crystalline andamorphous.1-3) The crystalline region is normally very stable with highly ordered cellulose molecules
hardly accessed by water molecules. On the other hand, water molecules could access and adsorb to theamorphous region consisting of less-ordered cellulose molecules. Because a trace amount of adsorbed
water on the surface of crystalline region is almost negligible, the amount of adsorbed water in fibers,
which is also called “bound water”, almost totally relies on accessible sorption sites of amorphous region.1)
Therefore, determination of the amount of amorphous region of fibers can be conducted by differential
scanning calorimetry (DSC) that is commonly used for determining the amount of bound water in fibers.1, 4)
For a study focusing on the crystalline region of fibers, one of the methods typically used is X-ray
diffractometry. 3, 5, 6) This method can be used for determining ratios of crystalline region as a crystallinity
index that is basically proportional to the peak intensity ratio of reflected X-ray, which is derived from the
200 plane, for the crystalline region to that for the total regions.
As the advantages of these methods are specifically characterized by measurement of either theamount of amorphous or crystalline region, it seems doubtfully to use them separately for determiningKhantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)changes in amounts of both the regions and discussing their irreversible conversion due to recycling
treatment.

Though some researchers 7) stated the possibility of FT-Raman spectroscopy to detect anddistinguish the proportional changes in amounts of amorphous and crystalline regions in cellulosic
materials conditioned by some chemical and biochemical treatments, it has rarely been applied to study a
stepwise effect of recycling treatment on changes in amounts of both the regions of fibers as in a case of
DSC.
Therefore, it is the purpose of the present paper to provide an integrated technique of DSC,
FT-Raman spectroscopy, and X-Ray diffractometry, which are possibly useful to clarify changes in amountsof amorphous and crystalline regions of fibers including their irreversible conversion due to the recycling
treatment. Furthermore, because the re-swelling capability of dried fibers seems to be caused by two
phenomena, i.e. the displacement of morphological features in fibers and sub-morphological swellingcaused by bound water, 8) the effect of recycling treatment on re-swelling capability of fibers which isprobably related to the amount of bound water in fibers is also demonstrated.

2. Materials and methods

Handsheets R0 were made from a virgin hardwood bleached kraft pulp beaten to a freeness of
480 ml CSF (Canadian Standard Freeness), according to TAPPI test methods.
recycling process,9)

As a model of papersome of them were treated in a well-ventilated electric oven at 105 o C for 24 hours

and then soaked in de-ionized water for 24 hours before disintegration for making handsheets R1 (recycledonce). This procedure is called “recycling treatment” hereafter. The recycling treatment was repeated forone, two and three more cycles to produce handsheets R2, R3 and R4 from some of handsheets R1,
respectively.

Every handsheet was conditioned at 23 o C with 50 % relative humidity for two months,

according to Japanese Industrial Standards (JIS). The amount of bound water and crystallinity were
determined by using a differential scanning calorimeter (Pyris 1, Perkin Elmer Instrument Inc., USA) andan X-ray diffractometer with Cu Kα radiation (RINT 2000, Rigaku, Japan), respectively, with six
replications for sheets chosen randomly from conditioned handsheets R0-R4.

Small pieces of the rest ofhandsheets R0-R4 were soaked in de-ionized water for 24 hours and then disintegrated to fiber slurries fordetermining the aspect ratio of wet single fibers by using a confocal laser-scanning microscope (LSM 510,
Carl Ziess Jena GmbH, Germany).

Seventy single fibers were observed for each fiber slurry.10)

FT-Raman spectroscopy (Magna-IR 860 equipped with Raman accessory, Nicolet Instrument Co., USA)was also attempted for determining changes in amounts of amorphous and crystalline regions of fibers in
the handsheets.

3. Results and discussion

The pattern of X-ray diffraction of a handsheet, as shown in Fig. 1, was used for calculating acrystallinity index following the empirical method of Segal et al. 6)

As can be seen in Fig. 2, thecrytallinity indices of handsheets appear to be moderately changed by the recycling treatment. This result

Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

indicates that the crystalline region of cellulose, which is major part of bleached kraft pulp fibers,1, 11) in thehandsheets was quite stable and hardly affected by the recycling treatment whereby the amount of
lingo-hemicellulose of the fibers is considerably negligible. 12)

The change in crystallinity index of fibers

in the handsheets was possibly reflected by some changes of amorphous region of fibers as the remarkablechange in structure of amorphous region of natural cellulose untreated with any chemicals is probably
influenced easily by the recycling treatment.

As demonstrated in the research of Isogai et al.,3) the

regenerated amorphous cellulose, which is stable under aqueous conditions as the amorphous region incellulosic materials, can be changed in its structure to be higher crystallinity and possessed lower water
accessibility by irreversible hydrogen bonds formation induced through hydrothermal and dry thermal
treatments, respectively.

Matsuda et al. 13) also confirmed that heat treatment promoted hardwood

bleached kraft pulp fibers lower water accessibility with the increased irreversible hydrogen bonds in somepart of amorphous region in the fibers. Therefore, part of amorphous region of fibers in the present study
could possibly be also distorted to lose in their water adsorbability, i.e. due to irreversible hydrogen bonds
formation, by the thermal condition in the recycling treatment. This part of the amorphous region lost inwater adsorbability is named as “distorted amorphous region” hereafter.
Fig. 3 demonstrates the noticeable changes in broad endothermic peak areas of handsheets, whichwere measured by using DSC, due to the recycling treatment. The endothermic peak area attributed to theheat of dehydration of bound water (△H) of handsheets was calculated based on dried weight of samples
following the procedure suggested by Bertran and Dale. 1) According to our previous research,9) the same
recycling treatment performed in this study gave handsheets with constant and fairly small amounts of fines
content. The negligible loss in carbohydrates and lignin of kraft pulp fibers during recycling is also
credible. 14) Therefore, the change in △H values considerably relied on the change in the amount ofbound water adsorbed to fibers in the handsheets. Fig. 4 shows the decrease in △H values of fibers in
the handsheets was affected by the recycling treatment. As can be seen, even though the △H value ofR0-fibers was not statistically different from that of recycled fibers, the △H value of the recycled fibers
was significantly decreased when they were recycled for three times. This result possibly demonstrates
that the inferior adsorbability of water of recycled fibers was influenced by irreversible hydrogen bonds of
distorted amorphous region in the fibers which were increasingly formed remarkably through the heatingstage of the recycling treatment.3, 13)
Even though the decrease in △H values represented mostly the increase in the amount ofdistorted amorphous region of fibers that was induced by the heating stage of the recycling treatment, thegood relationship between the crystallinity index and the △ H value was still in an agreement asdemonstrated in Fig. 5.

As can be seen, the fibers with high values of crystallinity index have low valuesof △H, i.e. they have low water adsorbability possibly by increasing in crystallinity of the amorphous
region. The increase in crystallinity of amorphous region in the fibers was possible during recycling
because the hydrothermal condition was possibly induced, during the initial stage of heating in therecycling treatment, with the moisture content of fibers mostly consisted of bound water ads orbed to theamorphous region.3) However, this phenomenon was likely to cause the crystallinity index of fibers in thehandsheets to change very slightly by the recycling treatment, which was hardly determined byKhantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

conventional X-ray diffractrometry, as shown in Figs. 1 and 2.
Figs. 6, 7 and 8 represent the measurement method, the mean values, and the frequency
distribution of the aspect ratio of wet single fibers, respectively. Because fully swollen wet fibers withalmost completely round cross-sections gave the values of aspect ratio close to 1.00, most of the wet
R0-fibers were more swollen than those of the wet recycled ones. Moreover, most of the wet recycled
fibers were also irreversibly collapsed after the first recycling time. This phenomenon was similar to theresult in our previous research9) in which the same kind of chemical pulp fibers and recycling treatment
were conducted. Therefore, the re-swelling capability of wet recycled fibers considerably depended on
their cell wall swelling because of the lack of re-opening ability of their lumens.
Fig. 9 demonstrates the relationship between the △H value and the value of the aspect ratio.
As can be seen, at low △H values, i.e. small amounts of bound water was adsorbed to fibers, the fibers
had a less swelling capability. Because wet fibers could be swelling when the internal strain relaxation ofcellulose microfibrils in fiber wall is caused by introducing water molecules to the amorphous region, 10)
this result confirms that the re-swelling capability of recycled fibers collapsed even in the wet state reliedstrongly on the amount of bound water adsorbed to their cell wall. In other words, the loss in re-swellingcapability of recycled fibers was consistent with the loss in the amount of bound water adsorbed to theircell wall, which was possibly caused by the increase in crystallinity and distorted part of amorphous region,
as is known as sub-morphological changes of fiber wall. 8) As a result, both the △H value and the valueof aspect ratio could reflect highly sensitively the changes in physical features of fibers affected by therecycling treatment. This finding is proved by the fact that there were certain differences demonstrated
significantly among the recycled fibers with both the parameters as shown in Figs. 4 and 7. Especially for
the DSC, it could probably show that the recycling treatment gave the fibers more uniformity as statisticalconfidence levels of the △H values were gradually narrowed with recycling times, as also demonstrated inFig. 4.

The evaluation method of X-ray diffractometry seems to be lacking in sensitivity of thisphenomenon as previously mentioned above and shown in Figs. 1 and 2.
Fig. 10 shows the intensity and pattern of FT-Raman spectrum of R0-fibers were similar to thoseof FT-Raman spectrum of R4-fibers. Because changes in intensity of FT-Raman spectrum at 900 and
1098 cm-1 represent to changes in amounts of amorphous and crystalline regions, respectively, 7) therefore,
the FT-Raman spectroscopy was found not suitable for determining the change in the ratio of amorphousand crystalline regions in the fibers affected by the recycling treatment. This is possibly caused by thefact that the ratio was not statistically different between R0-and R4-fibers, as shown in Figs. 2 and 4, andnot caused by changes in chemical aspects of fibers due to the recycling treatment. Moreover, a possible
cause for the similarity of the two FT-Raman spectra is that the sample preparation and treatments in thepresent study were different from those in others’ research.

4.

Conclusion

The crystallinity index of fibers in the handsheets was moderately changed by the recycling
treatment. This phenomenon is suggestively caused by some part of amorphous region of fibers in theKhantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

handsheets was slightly changed to be higher crystallinity during recycling. Because of the lack of
re-opening of recycled fiber lumens in the wet state, the amount of bound water adsorbed to fiber wall
substantially influenced the re-swelling capability of recycled fibers. The loss in re-swelling capability ofrecycled fibers was consistent with the loss in the amount of bound water adsorbed to their cell wall, which
was possibly caused by the loss in amorphous region, as is known as sub-morphological changes of fiber
wall.

Only the DSC and the measurement of the aspect ratio of wet single fibers could sensitively

determine the changes in physical features of fibers affected by the recycling treatment. The FT-Raman
spectroscopy was found not suitable for determining the effect of recycling treatment on the changes inamounts of amorphous and crystalline regions of fibers.

Acknowledgements

The authors are indebted to Professor Shigenori Kuga and Mr Yasutomo Noishiki, Department of
Biomaterial Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, fortheir useful advices on the DSC operation.

References

1) Bertran M. S. and Dale B. E.: J. Appl. Polym. Sci. 32 4241-4253 (1986)
2) Young R. A.: Cellulose-Structure, modification and hydrolysis, eds. by Young R. A. and Rowell R. M.,
John Wiley and Sons, New York, 1986, Chapter 63) Isogai A., Akishima Y., Onabe F. and Usuda M.: Sen-i Gakkaishi 47 (11) 573-579 (1991)
4) Nakamura K., Hatakeyama T. and Hatakeyama H.: Text. Res. J. 51 (9) 607-613 (1981)
5) Isogai A. and Usuda M.: Sen-i Gakkaishi 46 (8) 62-67 (1990)
6)

Segal L., Creely J. J., Martin Jr. A. E. and Conrad C. M.: Text. Res. J. 29 (10) 786-794 (1959)

7) Stewart D., Wilson H. M., Hendra P. J. and Morrison I. M.: J. Agric. Food Chem. 43 2219-2225 (1995)
8) Weise U. and Paulapuro H.: J. Pulp Pap. Sci. 25 (5) 163-166 (1999)
9) Somwang K., Enomae T. and Onabe F.: Japan Tappi J. (in press)
10) Nakamura K., Hatakeyama T. and Hatakeyama H.: Text. Res. J. 53 (11) 682-688 (1983)
11) Kolseth P. and Ruvo A. D.: Paper structure and properties, eds. by Bristow J. A. and Kolseth P.,
Marcel Dekker, Inc., New York, 1986, Chapter 112) Scallan A. M. and Tigerstrom A. C.: J. Pulp Pap. Sci. 18 (5) J188-J192 (1992)13) Matsuda Y., Isogai A. and Onabe F.: J. Pulp Pap. Sci. 20 (11) J323-J327 (1994)
14) Ackermann C., Gottsching L. and Pakarinen H.: Papermaking science and technology: Recycled fiberand deinking, eds. by Gottsching L. and Pakarinen H., Fapet Oy, Helsinki, 2000, Chapter 10

0.70

60

0.65

50

0.60

40

0.55

30

0.50

20

0.45

10

0.40

Tensile index(Nm/g)

3

Apparent density (g/cm )Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

0
R0

R1

R2

R3

R4

Number of handsheets recycling

Fig. 1. Decrease in apparent density and tensile index of HBKP handsheets due to the recycling treatment.
A pair of bars denotes a range of 95% confidence level.

1Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

20μm

Fig. 2.

CLSM micrograph of typical fines in post-R0 slurry.

2Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

X
Z

20μm
Y
X

Fig. 3.

CLSM XZ-sectioned micrograph (top) along the dotted white line in XY-micrograph (bottom)
shows a thin layer of fines (arrowed) covering a fiber surface of post-R0 slurry surface in the dry
state at the potentially interfiber crossing as a kind of strengthening material.

3

Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

15

0.86

0.82
10

0.80
0.78

Mean fiber length(length weighted, mm)

Fines content (%)

0.84

0.76
5

0.74
R0

R1

R2

R3

R4

Number of handsheets recycling

Fig. 4.

Fines content and mean fiber length of post-R0 to R4 slurries. A pair of bars denotes a range of
95% confidence level.

4Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

Post-R0

Post-R1

Post-R2

Post-R3

Post-R420μm

Fig. 5.

CLSM micrographs of HBKP fiber (wet) cross-sections show the stepwise effect of recycling
treatment on the re-swelling ability.

5Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

Post-R0

Post-R1

Post-R2

Post-R3

Post-R420μm

Fig. 6.

CLSM micrographs of HBKP fiber (dry) cross-sections at the same location as in Fig. 5.

6

Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

Wet post-R0 fibers

Dry post-R0 fibers

20μm

Wet post-R4 fibers

Dry post-R4 fibers

20μm

Fig. 7.

CLSM micrographs of HBKP fiber cross-sections at the interfiber crossings show theconformability of wet-swollen fibers of post-R0 slurry is superior, for promoting the goodinterfiber contact in the dry state, to that of wet-collapsed fibers of post-R4 slurry.

7

Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

X
Z

20μm
Y
X

Fig. 8.

CLSM XZ-sectioned micrograph (top) along the dotted white line in XY-micrograph (bottom)
shows an un-bonded area at the interfiber crossing of dried fiber of post-R4 slurry.

8Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

42

2

Light scattering coefficient/ k g(m
)

44

40
38
36
34
32
30
R0

R1

R2

R3

R4

Number of handsheets recycling

Fig. 9.

The increase in light scattering coefficient of recycled HBKP handsheets due to the recycling
treatment. A pair of bars denotes a range of 95% confidence level.

9Khantayanuwong, S., Enomae, T. and Onabe F., "Changes in crystallinity and re-swelling capability of pulp fibers by recycling treatment", Japan Tappi J., 56 (6): 103-106(2002)

50

Tensile index (Nm/g)

45
40
35
30
25
20
15
y = -3.9257x + 177.71
2
R = 0.9551

10
5
0
30

32

34

36

38

40

42

44

2

Light scattering coefficient (m /kg)

Fig. 10. Relationship between light scattering coefficient and tensile index of HBKP handsheets.

10