WAYS TO MEASURE THE BONDING ABILITY DISTRIBUTION OF FIBERS IN
MECHANICAL PULPS
Sofia Reyier(1,2), Olof Ferritsius(3), Oleg Shagaev(4)
(1)
Mid Sweden University, FSCN, SE-85170 Sundsvall, Sweden
(2)
Stora Enso Kvarnsveden, SE-781 91 Borlänge, Sweden
(3)
Stora Enso Falun Research Center, S Mariegatan 18, SE-791 80 Falun, Sweden
(4)
Noss AB, Box 20, SE-60102, Norrköping, Sweden
ABSTRACT
In this paper, experiences are reported from our work of developing a method for characterizing fibers with respect
to their distribution in fiber bonding ability. As a first step to develop a method, fibers from two commercial TMPs
have been fractionated in a four stage hydrocyclone system. The feed pulp was separated into five streams. The fiber
bonding ability of R16, P16/R30 and P30/R50 Bauer McNett fractions collected from each stream were analyzed.
Five different ways of evaluating fiber bonding ability showed that the fibers were separated in the hydrocyclones
according to bonding ability.
It was found that both fibrillation and collapse resistance index (CRI) of the fibers are required in order to well
predict tensile strength of handsheets made from fiber fractions. CRI was calculated from optical measurements of
cell wall thickness and fiber width. We also propose how to describe the distribution in fiber bonding ability for
mechanical pulps. A method to calculate fracture toughness of handsheets based on acoustic emission is also
illustrated. A more rapid method for characterizing fibers in mechanical pulps with respect to their bonding ability
distribution needs to be developed in the future.
1. BACKGROUND
Optical methods existing today allow characterizing fibers and shives with respect to their size distributions, e.g.
length and for shives also width. Meanwhile, mechanical pulp strength, drainability and bonding ability of fibers is
usually reported as an average value. The share of mechanical pulps with higher amount of long fibers for printing
grades has increased over the past. Due to increasing quality demands of paper and board products, it is important to
consider the distribution of bonding ability of different fibers.
2. INTRODUCTION
Almost 40 years ago Forgacs [1] presented a classic paper where he showed that at least two quality variables are
needed in order to characterize the physical properties of mechanical pulps. These quality variables could be defined
by two measurements or factors: the shape-factor (S), i.e. the specific surface of the P48-R100 Bauer McNett fiber
fraction, and the length-factor (L), the fraction by weight retained on a 48-mesh screen.
In the eighties Strand [2] introduced a somewhat different approach by using factor analysis, which is a type of
multivariate data analysis. The principle is that the variations in all measured pulp and handsheet properties can, to a
great extent, be explained by only two independent common factors, which describe fundamental fiber properties.
Factor 1 is referred to as ”fiber bonding” and Factor 2 as ”fiber length”. These factors correlate well with Forgacs’
S- and L-factors.
Twenty years ago Stora Enso started to apply factor analysis to quality related pulp data from on-line and lab
measurements in some mills [3]. The F1 factor is related to fiber bonding and F2 factor to long fiber influence.
However, the variations in shives content don’t seem to be included in neither of these factors [4]. This implies that
at least three fundamental parameters are required in order to characterize physical properties of mechanical pulp;
fiber bonding, long fiber influence and shives. Recently developed methods allow characterizing shives in a more
relevant way compared to laboratory screening or devices based on optical devices [5].
The importance of the bonding ability of the long fibers was reported almost 30 years ago [6]. However, since wood
contains a wide distribution of thin walled and thick walled fibers, it is important to evaluate mechanical pulp fibers
with respect to distribution in their bonding ability.
Among other researchers, this study was inspired by the work of A. Karnis and co-workers who used multi-stage
hydrocyclone fractionation to evaluate the specific surface distribution of different mechanical pulps [7]. The use of
hydrocyclones for fractionating fibers with different morphology was shown at the last IMPC in 2005 [8]. Also, with
respect to independent common factors F1 and F2, it has been shown that screens and hydrocyclones separate fibers
based on different mechanisms [3]. Screens separate fibers mainly by length (F2), while hydrocyclones separate
fibers by specific surface (F1) [4].
During recent years many papers have focused on the importance of fiber properties by using cross-sectional SEM
images of fibers and papers [9-13]. The rapid development of optical analyzers allows obtaining more detailed
characterization of fibers, such as fibrillation, fiber diameter, as well as fiber wall thickness [14] and collapse
resistance index [15]. A rather new method, acoustic emission (AE), is used for evaluation of paper fracture
properties [16,17].
The main objective of this study was to develop a method to characterize fibers with respect to their distribution in
bonding ability. Fibers from two commercial TMPs were fractionated into five streams in a four stage hydrocyclone
system. Fibers from different fiber length classes from all five streams were analyzed with respect to their bonding
ability. Since there is no common definition of the “bonding ability”, the fractionated fiber streams of each pulp
were analyzed in five different ways:
1.
2.
3.
4.
5.
the split of fibers by weight in each stream,
tensile index, fracture toughness and apparentdensity of handsheets produced from long fiber fractions,
optical measurement of fiber width, cell wall thickness and external fibrillation of long fiber fractions,
cross-sectional SEM images of long fibers,
acoustic emission (AE) of orientated handsheets made out of long fiber fractions.
3. EXPERIMENTAL
3.1 Trial setup and split of fibers by weight
Two commercial Norway spruce newsprint grade termomechanical pulps were used in this study, pulp-A and pulpB. Pulps were fractionated in an arrangement of hydrocyclones at Noss AB pilot plant in Norrköping, Sweden. Five
streams were obtained where the fiber bonding ability was predicted to be the highest in stream 1 and the lowest in
steam 5, with consecutively reduced bonding in between.
Pulp-A was fractionated first with about 20 % of R100 Bauer McNett fiber fraction in each stream. Process
condition settings from this trial were used as a reference to fractionate pulp-B, using the same settings as from
previous fractionation trial. The amount of fibers by weight in each stream was calculated based on flow and
consistency. All settings are based upon R100 fibers (fibers not passing through a 100 mesh screen).
Feed =
stream 0
R16 P16/R30 P30/R50
Stream 1
R16
P16/R30
P30/R50
Stream 2
R16
P16/R30
P30/R50
Stream 3
R16
P16/R30
P30/R50
Stream 4
R16
P16/R30
P30/R50
Stream 5
P16
P16/R30
P30/R50
Figure 1. Fractionation trial setup.
3.2 Handsheet physical properties
In order to evaluate the efficiency of hydrocyclones to fractionate fibers according to their bonding ability, extended
laboratory work has been carried out. Pulps collected in each hydrocyclone stream were fractionated further in
Bauer McNett classifier using 16, 30, 50 and 100 mesh screens. Since this method is intended to evaluate fibers, the
physical properties of handsheets (e.g. tensile index and apparent density) produced from R16, P16/R30 and
P30/R50 Bauer McNett fiber fractions were studied.
Sheets were also produced in a Dynamic sheetformer from P16/R30 Bauer McNett fraction from each pulp stream
and analyzed for fracture toughness. These orientated Formette sheets are more similar to commercially produced
printing paper than normal lab sheets. The fracture toughness results were later compared to fracture toughness
calculated from acoustic emission test results.
3.3 Optical measurements of fiber properties
The external fibrillation (fibrillation index), cell wall thickness and fiber width of the P16/R30 and P30/R50 Bauer
McNett fractions were analyzed using FiberLabTM [14]. Fibrillation index is measured by comparing area of fiber
“body” with area of fiber “body” plus area of fibrils. Between 5 000 and 20 000 fibers were measured in each run.
The number of fibers measured depended on Bauer McNett fraction and triplicate runs for each sample have been
performed.
Dickson [12] described in 2005 how it is possible to calculate collapse resistance index based on fibre dimensions.
The vast extent of data obtained from FiberLabTM was used to calculate the collapse resistance index of fibers
measured optically [15].
The collapse resistance index (CRI) is based on the assumption that fibers are circular and that fiber walls have the
same E-modulus throughout whole fiber length. Since the FiberLabTM cell wall thickness measurement was not
calibrated to a reference standard, we assume the calculated CRI values to be proportional to a “true” value.
Collapse resistance is calculated as CRI =
t = fiber wall thickness
w = fiber width
2t 2
where
w−t
3.4 Image analysis
The fibers from the P16/R30 Bauer McNett fraction were aligned, frozen and cut across. Obtained cross-sectional
images taken have been used for evaluation by image analysis program as well as manually.The fiber wall thickness
distribution was one of the parameters obtained from these measurements. The image analysis of fiber cross-section
micrographs was performed at Stora Enso Research Center Falun, and inspired by the work at PFI and Mid Sweden
University [9-13]
3.5 Acoustic Emission
Initially, acoustic emission (AE), a way of recording the number of breaks by microphone during tensile testing is a
method developed for analyzing papers described in [16,17]. In this work, AE was introduced as a method for
measuring physical properties of papers. The acoustic emission measurements have been made with oriented lab
sheets produced in Formette Dynamique from the P16/R30 Bauer McNett fraction. AE was performed as vertical
tensile testing with a microphone attached to the test strip by a magnet. Each test was performed with ten strips per
sample. While stretching the test strip, the microphone records the acoustic waves of the energy released when fiber
bonds are breaking. Graphs are obtained with cumulative number of hits and load versus time. Physical parameters,
such as fracture toughness, characterizing the toughness of the fibers, can be calculated from the graphs, further
described in the paper to be published by Reyier et al. In order to evaluate this method, the orientated sheets were
also analyzed for fracture toughness defined as J-integral.
4. RESULTS AND DISCUSSION
4.1 Split of fibers by weight
The basic idea with this method of measuring “bonding ability” was to run the hydrocyclones at fixed process
conditions, and let the properties of the fibers decide in which stream they end up. Figure 2 shows the amount of
R100 fibers in each hydrocyclone stream. The pulp-A R100 were divided into five streams with about 20 % of the
R100 fibers per stream. At the same fractionation process conditions, fractionation of pulp-B resulted in higher
amount of fibers in stream 1 and 2, suggesting that pulp-B contains a larger amount of fibers with high bonding
ability.
Amount of total P16/R30 fibers [%]
Amount of total R100 fibers [%]
PulpA
30
PulpA
30
PulpB
PulpB
20
20
10
10
0
0
1
2
3
4
5
Stream #
Figure 2. Percent of total amount of R100 fibers per
stream.
1
2
3
4
5
Stream #
Figure 3. Percent of total amount of P16/R30 fibers
per stream.
Since in this study we are focusing on the bonding ability of the long fiber fractions, it was of great importance to
find the distribution of certain Bauer McNett fractions in each stream. From Figure 3 it is obvious that the P16/R30
fiber fraction is split in a similar way as the R100 fraction fibers.
The higher amount of P16/R30 fibers in stream 1 and stream 2 for pulp-B compared to pulp-A suggests pulp-B had
higher proportion of fibers with high bonding ability in this particular fraction. Correspondingly, the amount of
fibers in stream 3 and 4 was lower for pulp B. In order to understand better these differences in proportion of the
fibers going to the stream 1 and 2, the properties of the fibers in each stream were measured. The results are
discussed below.
4.2 Physical properties of lab sheets
To evaluate the bonding ability of the fiber fractions independently from the fiber length, the evaluation was focused
on the P16/R30 and P30/R50 fiber fractions mainly. The R16 fraction is assumed to have a larger variation with
respect to fiber length. Fibers with the highest bonding ability, as measured by the tensile index of the handsheets
produced from the P16/R30 and P30/R50 fractions respectively, are concentrated in stream 1, Figure 4 and 5. Fibers
with the lowest bonding ability were found in the last reject stream, stream 5. This is valid for both pulp-A and -B.
Tensile index P16/R30 fraction
Tensile index P30/R50 fraction
25
Pulp-B
20
Pulp-A
40
Pulp-B
Pulp-A
30
15
20
10
10
5
0
0
0
Feed
1
2
3
4
Stream #
Figure 4. Tensile index per stream, P16/R30
fraction.
5
0
Feed
1
2
3
4
5
Stream #
Figure 5. Tensile index per stream, P30/R50
fraction.
The tensile index is the highest in stream 1 and lowest in stream 5 for both P16/R30 and P30/R50 fractions, with
consecutively reduced bonding values in between. The tensile index for pulp-B is higher than that of pulp-A
throughout the streams. This suggests that the pulp-B fibers have higher bonding ability than pulp-A fibers, which is
also supported by the “Split of fibers by weight” evaluation. It is also obvious that the feed pulp-B had an average
higher bonding ability compared to pulp-A.
The handsheet density reflects the degree of fiber collapse in the sheet. Figure 6 and 7 below show that the trend of
higher density in stream 1 and lower density in stream 5 is similar to that of the tensile index trend , with the
exception of stream 2 for pulp-A.
Apparent density
P16/R30 fraction [kg/m3]
Apparent density
P30/R50 fraction [kg/m3]
300
400
Pulp-B
Pulp-B
350
Pulp-A
Pulp-A
250
300
250
200
200
0
1
Feed
2
3
4
5
0
1
Feed
Stream #
Figure 6. Handsheet density, P16/R30 fraction.
2
3
4
5
Stream #
Figure 7. Handsheet density, P30/R50 fraction.
Both the tensile strength and apparent density measurements of the handsheets suggest that hydrocyclone separated
fibers according to their bonding ability. The tensile index of all three long fiber fractions R16, P16/R30 and
P30/R50 within each pulp is presented in Figure 8 and 9.
Tensile index Pulp-A [Nm/g]
Tensile index pulp-B [Nm/g]
40
P30/R50
40
P16/R30
P30/R50
30
P16/R30
R16
R16
30
20
20
10
10
0
0
0
Feed
1
2
3
Stream #
4
5
Figure 8. Tensile index of pulp-A fiber fractions.
0
1
Feed
2
3
4
5
Stream #
Figure 9. Tensile index of pulp-B fiber fractions.
Remarkably, for both pulp-A and -B the fibers with lowest bonding show a tendency of converging towards similar
tensile index value in stream 5 regardless of the length of the fibers. This indicates that fiber bonding and fiber
length are independent of each other and that the hydrocyclone fractionation was performed with respect to fiber
bonding and not by fiber length.
To get another indication of how the fibers were separated with respect to quality, fracture toughness defined as Jintegral was measured on orientated sheets produced from the P16/R30 fraction. For both pulps, the fracture
toughness is the highest for stream 1 and the lowest for stream 5 with consecutively reduced fracture toughness
values in between (Figure 10). It can also be seen that overall the pulp-B fibers had higher fracture toughness than
the pulp-A fibers.
P16/R30 fraction
Fracture toughness J-integral [N/m]
0,3
Pulp-B
Pulp-A
0,2
0,1
0
0
1
2
Feed
3
4
5
Stream #
Figure 10. Fracture toughness for orientated long fiber lab sheets of the P16/R30 fraction.
4.3 Optical measurements of fiber properties
Since “bonding ability” is not so clearly defined, a study was performed of how the long fibers have been
fractionated in hydrocyclones with respect to more fundamental fiber properties as compared to testing of strength
properties of handsheets. All streams were therefore analyzed with respect to cell wall thickness, fiber width as well
as degree of fibrillation of individual fibers in a FiberLabTM device. It is seen that hydrocyclone separated fibers in
both P16/R30 and P30/R50 fractions according to the degree of fibrillation (Figure 11 and 12).
Fibrillation index
P16/R30 fraction [%]
Fibrillation index
P30/R50 fraction [%]
9
PulpB
14
PulpB
PulpA
PulpA
12
8
10
7
8
6
6
0
Feed
1
2
3
4
5
Stream #
Figure 11. Fibrillation index of the P16/R30 fraction.
0
Feed
1
2
3
4
5
Stream #
Figure 12. Fibrillation index of the P30/R50fraction.
It can also be observed that fibers in the P30/R50 fraction of pulp-A in stream 4 and 5 are actually less fibrillated as
compared to that of pulp-B long fibers in P16/R30 fraction of stream 1,2 and 3, although they are shorter. The
difference in fibrillation index of fraction P16/R30 fibers, stream 1 and stream 5, is numerically rather small but it
should be stressed that the standard deviation is very small for each stream. It seems that external fibrillation is one
of several parameters affecting the fiber bonding ability. The hydrocyclones have fractionated the fibers not only by
the degree of fibrillation but also with respect to other parameters which influence fiber bonding, e.g. cell wall
thickness and fiber width (Figure 13 and 14).
Fibre width [μm]
Cell wall thickness index [μm]
12
35
10
8
PulpA 16-30
30
PulpB 16-30
PulpA 16-30
PulpA 30-50
PulpB 30-50
PulpB 16-30
6
PulpA 30-50
PulpB 30-50
25
4
0
1
Feed
2
3
4
0
5
1
Feed
Stream #
Figure 13. Cell wall thickness index per stream,
pulp-A and pulp-B, P16/R30 and P30/R50 fractions.
2
3
4
5
Stream #
Figure 14. Fiber width per stream, pulp-A and pulpB, P16/R30 and P30/R50 fractions.
The cell wall thickness index is higher for pulp-A fibers than for pulp-B fibers. Considering also lower external
fibrillation of pulp-A, it appears that the pulp-B fiber walls have been more peeled and fibrillated than the pulp-A
fiber walls, which resulted in overall thinner fiber walls for the pulp-B fibers.
Collapse resistance index, CRI, has been calculated using fiber width and fiber thickness, as described in
“experimental”, section 3.3. The collapse resistance index is the lowest for stream 1 fibers and the highest for the
stream 5 fibers of the P16/R30 fraction (Figure 15). The fibers which are more likely to collapse (have the lowest
CRI) are the fibers that exhibit the highest bonding ability, measured as tensile index of the handsheets (Figure 16).
Collapse resistance index
P16/R30 fraction
Tensile index
[Nm/g]
11
25
10
20
9
15
8
10
P16/R30 fraction
PulpB
PulpA
PulpA
7
5
PulpB
0
6
0
Feed
1
2
3
4
5
Stream #
Figure 15. Collapse resistance index, CRI, for the
P16/R30 fraction.
6
7
8
9
10
11
Collapse resistance index
Figure 16. Correlation of collapse resistance index
and tensile index for the P16/R30 fraction.
From Figure 15 it can also be seen that pulp-A contains fibers with higher CRI than pulp-B, making the fibers less
likely to collapse. Compared at a given CRI, the fibers in pulp-B exhibit a slightly higher tensile index of the
handsheets (Figure 16). This suggests that the bonding strength between the fibers in pulp-B is somewhat higher.
One indication that supports this is that the pulp-B fibers are more fibrillated at a given tensile index. This is shown
for both P16/R30 and P30/R50 fractions (Figures 17 and 18).
Tensile index
[Nm/g]
Tensile index
[Nm/g]
P16/R30 fraction
25
40
20
30
P30/R50 fraction
15
20
10
Pulp-B
5
Pulp-A
Pulp-B
10
0
Pulp-A
0
6
7
8
6
9
8
10
12
14
Fibrillation index [%]
Fibrillation index [%]
Figure 17. Correlation between fibrillation index and
tensile index for the P16/R30 fraction.
Figure 18. Correlation between fibrillation index and
tensile index for the P30/R50 fraction.
For each pulp type A and B there appears to be a specific correlation between tensile index and degree of
fibrillation, as well as CRI of the fibers. Correspondingly, the fibrillation or CRI measurements of the fibers alone
are not enough to predict tensile index. However, with the use of factor analysis it appears possible to combine the
CRI and fibrillation as input data to be able to predict the tensile index of pulp-A and -B and get a unique correlation
(Figure 19).
Predicted
Tensile index [Nm/g]
long fiber fractions
40
30
20
Pulp-B 30-50
Pulp-A 30-50
Pulp-B 16-30
Pulp-A 16-30
10
0
0
10
20
30
40
Measured
Figure 19. It is possible to predict tensile index from CRI and fibrillation for the long fiber fractions P16/R30 and
P30/R50.
A third pulp was been also studied where this correlation was confirmed. It further supports that bonding ability,
measured as tensile strength, depends on both how likely the fibers are to collapse and get into contact with each
other (bonding area), as well as to what extent the fibers are fibrillated and bond to each other (bond strength).
4.4 Image analysis
In order to get a deeper understanding of how the fibers are separated in the hydrocyclones, the fibers cross-sectional
images of the P16/R30 fraction were taken by SEM. Examples are shown from the highest and lowest bonding
fibers in pulp-A (Figures 20 and 21). Stream 1 to the left contains fibers with thinner fiber walls than stream 5 to the
right.
Figure 20. Cross-sectional images of long fibers
(P16/R30 fraction, Stream 1, Pulp-A).
Figure 21. Cross-sectional images of long fibres
(P16/R30 fraction, Stream 5, Pulp-A).
The distribution of fiber wall thickness was calculated using image analysis of the cross-sectional micrographs.
Although there is a wide fiber wall thickness distribution for fibers in all streams, it is clear that fibers with highest
bonding in stream 1are more thin-walled (Figure 22).
Frequency [%]
Pulp-A, P16/R30 fraction
Stream 1
20
Feed
15
10
Stream 5
5
0
0
1
2
3
4
5
6
Cell wall thickness [μm]
Figure 22. Distributions of fiber wall thickness, pulp-A, P16/R30 fraction.
7
The average cell wall thickness was 2,4μm for the fibers in stream 1, while it was 2,8μm for the fibers in stream 5.
As seen in Figure 22, the high amount of the thick-walled latewood fibers are found in stream 5, with a wall
thickness value of about 4μm.
4.5 Acoustic Emission
To get a different view, as compared to conventional handsheet testing, of how the fibers in the fractionated streams
are bonding with each other, the orientated handsheets were analyzed for acoustic emission during tensile testing. To
simplify, only graphs for the feed, the highest bonding fibers (stream 1) and lowest bonding fibers (stream 5) for
pulp-A and -B are shown (Figure 23 and 24).
Number of Hits
Load [N]
40
Pulp-A
Pulp-B
800
Stream 1
600 30
20
0
0
Number of Hits
Stream 1
30
10
Load [N]
800 40
Feed
Stream 5
20
40
Time [s]
600
400 20
200 10
0
60
Figure 23. Acoustic Emission curve, pulp-A fraction
P16/R30. Load and number of hits as a function of
time.
0
0
Feed
Stream 5
20
40
Time [s]
400
200
0
60
Figure 24. Acoustic Emission curve, pulp-B fraction
P16/R30. Load and number of hits as a function of
time.
For both pulps, stream 1 exhibits the highest strength and stream 5 the lowest, as expected. The feed stream is in
between stream 1 and stream 5. The acoustic emission measurement provides the number of hits, i.e. the number of
fiber bonds broken during tensile testing. This could be associated with the measurement of fiber flexibility since
more flexible fibers will have more opportunities of establishing contact with other fibers. The fibers with highest
bonding have a slower increase in the number of breaks per time which represents a sheet with a higher toughness.
The graphs obtained from the AE measurements can be used to calculate the fracture toughness of a paper or a
handsheet. This will be further described in future publications by Reyier et al. The bonding ability, as expressed in
AE fracture toughness, has been evaluated and show similar trend as fracture toughness measured as J-integral. The
correlation between fracture toughness measured as J-integral (Figure 10) and predicted fracture toughness based on
acoustic emission measurements is shown in Figure 25.
Measured
Fracture toughness
P16/R30 fraction
0,3
0,2
Pulp-A
0,1
Pulp-B
0
0
100
200
300
400
500
Predicted (Acoustic Emission)
Figure 25. Correlation between toughness measured traditionally, and fracture toughness predicted through
Acoustic Emission. Tested on orientated handsheets produced from P16/R30 fraction.
As can be seen in Figure 25, the pulp-B fibers are stronger than the pulp-A fibers, sustaining load a longer time
before rupture. Figures 23 and 24 show that the load at break is quite similar between pulp-A and pulp-B fibers but
the difference in number of breaks between pulp-A and pulp-B is significant: the pulp-B stream 1 fibers have only a
third of the fiber bond breaks of the pulp-A stream 1 fibers. This suggests that the pulp-B fibers have very strong
specific bonds. In order to get the relative measurement of how strong the bonds are, we have calculated the ratio of
the load after 20 seconds of elongation and the number of breaks detected during 20 seconds (Figure 26).
Specific load at 20s [N]
2,5
2,0
Pulp-A
1,5
Pulp-B
1,0
0,5
0,0
0
Feed
1
2
3
4
5
Stream #
Figure 26. Specific load of each detected break between fibers.
It is evident that fibers, which have shown to have high bonding ability measured by other methods, exhibit stronger
fiber bonds also.
4.6 Final discussion
Previously, in this paper, it was shown that hydrocyclones separate fibers according to their bonding ability and
different methods of measuring fiber bonding were applied to prove that. All methods correlate quite well with each
other. The results of the hydrocyclone fractionations provide valuable knowledge of which parameters contribute to
fiber bonding ability. Also, it was possible to illustrate the distribution of fiber bonding ability for the fibers in pulpA and -B. However, this laboratory method is quite time consuming. The objective now is to develop a rapid method
for characterizing fibers in mechanical pulps with respect to bonding ability distribution.
It is therefore very promising that it appears possible to calculate the bonding ability (as measured by tensile index)
for each hydrocyclone stream and/or specific fiber fraction (e.g. P16/R30 and P30/R50) using fiber properties
measured by FiberLabTM (i.e. optical measurement of fiber width, cell wall thickness and external fiber fibrillation
of long fiber fractions). Knowing the split of the fibers by weight in each stream and the calculated value of tensile
index of each stream it is possible to plot the bonding distribution similar to that used for illustrating fiber length
distribution (Figures 27 and 28).
Frequency, %
40
Frequency, %
30
30
20
20
10
10
0
0
0
5
10
15
20
25
Tensile index P16/R30 predicted, [Nm/g]
Pulp-A
Pulp-B
Figure 27. Bonding ability distribution of P16/R30
fraction. Arrow indicating value of feed.
0
10
20
30
40
Tensile index P30/R50 predicted, [Nm/g]
Pulp-A
Pulp-B
Figure 28. Bonding ability distribution of P30/R50
fraction. Arrow indicating value of feed.
The pulps exhibit different distributions with respect to bonding ability for both P16/R30 and P30/R50 fractions.
Pulp-B has a higher proportion of fibers with higher bonding ability, as well as a higher level of bonding strength of
these fibers.
5. CONCLUSIONS
In our work of developing a method for characterizing fibers with respect to their distribution in fiber bonding
ability it was found that:
the hydrocyclones we have used separate fibers with respect to bonding ability
both fibrillation and collapse resistance index (CRI) of the fibers are required in order to well predict tensile
strength of handsheets made from fiber fractions. CRI was calculated from optical measurements of cell wall
thickness and fiber width
it is possible to describe the distribution in fiber bonding ability for mechanical pulps. However, a more rapid
method will be developed
it is possible to calculate fracture toughness of handsheets based on acoustic emission
it is time to move away from characterizing pulps only from average values based on pulp suspensions and
conventional handsheet properties
6. ACKNOWLEDGEMENTS
The authors wish to thank
Professor Hans Höglund and professor Per Gradin, Mid Sweden University, Sundsvall, Sweden for academic
support with enthusiasm and minds open for new ideas
Rita Ferritsius, Anders Hansson, Mikael Rautio, Anders Wigsten, Örjan Sävborg, Olle Henningson and all
laboratory personnel, Stora Enso Research Center, Falun, Sweden for careful work in the lab, with microscope
images, with data analysis, great thinking minds and inspiring discussions
Elisabeth Kurula, Martin Gustavsson, Annika Bjärestrand, Bernt Bergström, Noss AB, Norrköping, Sweden for idea
input in the hydrocyclone fractionation planning and well performed pilot runs
Hans Ersson, development manager and Fredrik Lundström, development engineer at Stora Enso Publication Paper
Divison, Kvarnsveden Mill, Sweden, and all development department for encouraging discussions
Olle Hallgren, production manager at Stora Enso Board Divison, Fors Mill, Sweden, for his open mind to implement
fiber fundamentals into production
Last but not least; Thanks to all operators in our mills and their supporting staff. A special thank you to Luigi
Alfonsetti, Pulp Department at Stora Enso Publication Paper Divison, Corbehem Mill, France, who challenged us by
asking the question “How many of our fibres have too low bonding?”
7. REFERENCES
1
Forgacs, O.L., “The characterization of Mechanical Pulps”, Pulp and paper Magazine of Canada, 64: T89T116 (1963)
2
Strand, B., "Factor Analysis as Applied to the Characterization of High Yield Pulps", TAPPI Pulping
Conference, 61-66 (1987)
3
Ferritsius, O. and Ferritsius,R., "Experiences from Stora Enso mills of Using Factor Analysis for Control of
Pulp and Paper Quality.", International Mechanical Pulping Conference, Oslo, 495-504 (2001)
4
Ferritsius, O. and Ferritsius, R., "Improved Quality Control and Process Design in Production of Mechanical
Pulp by the Use of Factor Analysis", International Mechanical Pulping Conference, Oslo, 111-126 (1997)
5
Ferritsius, R., Rautio, M. “Differences on fibre level between GW and TMP for magazine grades”, Int.
Mechanical Pulping Conference, Minneapolis, (2007)
6
Mohlin, U-B “Fiber Bonding Ability – a Key Pulp Quality Parameter for Mechanical Pulps to Be Used in
Printing Papers.” Int. Mechanical Pulping Conf. Preprints, Helsinki, June 6-8, Finland, p.49-57 (1989)
7
Karnis, A., "Refining of Mechanical Pulp Rejects", International Mechanical Pulping Conference, Oslo,
(1981)
8
Shagaev, O., and Bergström, B. ”Advanced Process for Production of High Quality Mechanical Pulps for
Value-Added Paper Grades.” Proceedings, 24th Int. Mechanical Pulping Conf., Oslo, Norway, June 7-9, pp.
169-179 (2005)
9
Reme, P A, Some effects of wood characteristics and the pulping process on mechanical pulp fibres, Doktor
ingenioravhandling 2000: 21, Trondheim, Norway: Norwegian University of Science and Technology,
172pp, (2000)
10
Kure, K-A, “The Alteration of the Wood Fibres in Refining”, Int. Mechanical Pulping Conference, Oslo, pp.
137-150 (1997)
11
Norman, F., and Höglund H. “Moisture-induced Surface Roughness in TMP-based Paper – The Influence of
Fiber Cross-section Dimensions.” Proceedings, 23rd Int. Mechanical Pulping Conf., Quebec, Que., Canada,
pp. 409-414 (2003)
12
Dickson, A.R., Corson, S.R., Dooley, N.J. “Fibre collapse and de-collapse determined by cross-sectional
geometry”, Proceedings, 24th Int. Mechanical Pulping Conf., Oslo, Norway, June 7-9, (2005)
13
Mörseburg, K “Development and characterization of Norway spruce pressure groundwood pulp fibres”,
Academic dissertation, Turku, Finland: Abo Akademi University, (2000)
14
Kauppinen, M. “Prediction and Control of Paper Properties by Fiber Width and Cell Wall Thickness
Measurement with Fast Image Analysis”, PTS Symposium: Image analysis for Quality and Enhanced
productivity” (1998)
15
Vesterlind, E-L, Höglund, H., “Chemithermomechanical Pulp Made From Birch at High Temperature”,
Proceedings SPCI International Conference, Stockholm, Sweden, June 14 - 16 (2005)
16
Gradin, P.A et al., ”Acoustic Emission Monitoring of Light-Weight Coated Paper”. Journal of Pulp & Paper
Science 23(3), IPPS, p J113-J118 (1997).
17
Isaksson, P., Gradin, P.A. and Kulachenko, A., ”The onset and progression of damage in isotropic paper
sheets”, International Journal of Solids and Structures 43, p 713-726 (2006)