Suitable pulp grades for preparing nanofibrillated...
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Suitable pulp grades for preparing nanofibrillated
cellulose
Tiemo Arndt, Papiertechnische Stiftung
Valerie Meyer, Centre Technique du Papier
Ulf Germgård, Karlstad University
SUNPAP Workshop 5.10.2011
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2
Outline
• Introduction and objectives
• Material and methods
• Results
• Conclusions
• Acknowledgment
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Introduction and objective
• The technical challenges of preparing NFC using industrial scale
techniques and the currently high costs of producing NFC limit the
acceptance of NFC on the market.
• One important factor in this sense is that the fibre structure itself
and consequently the pulping and bleaching conditions used have
a major impact on the ability to produce NFC with a minimum
amount of energy.
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Introduction and objective
• Many studies are known which deal with the pulp pre-treatment
and its influence on the energy composition
• It is obviuosly that depending on the decomposition in the pre-
treatment stage the energy consumption in final homogenization
stage can be reduced to a great extend by using for example a
chemical pretreatment (e.g. TEMPO-oxidation) or an enzyme
pretreatment.
• In most cases today is NFC produced from dissolving spruce pulp
and the price of dissolving pulp is now about 2.5 times the
corresponding price for conventional kraft pulp.
• Why is one pulp suitable for preparing NFC while another is not?
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Material and methods
General approach
Market pulps of different
chemical compostion
Laboratory pulps cooked
to defined composition
Mechanical-enzymatical pre-treatment
Homogenization to MFC by a Microfluidizer M-110EH
with a 200 µm chamber
Analysis of chemical
composition
Morphological fibre
properties, refining energy
SEM and light microscopic
images
Preparation of MFC in according to Pääkko et al. Biomacromolecules, 8 (6), 1934-1941.
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Materials and methods
• Chemical composition were analyzed by following methods
• Intrinsic viscosity and LODP
• Carbohydrate composition were determined using anion
exchange chromatography /1/
• WRV
• Fibre morphology were analyzed by using
• MorFi analyzer (refined pulps)
• Light microscopic images (MFC)
• Scanning electron microscopy (MFC)
/1/ Hausalo, T. 8th International Symposium on Wood and Pulping Chemistry, Helsinki, Finland, 6-9 June, 1995, Vol. III, p 131-136 .
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Materials and methods
• Market pulps
Pulp
Reference
Pulping Wood
source
ISO
brightness
[%]
Limited
viscosity
number [ml/g]
A Dissolving pulp Pine / spruce > 91 550
B Paper pulp Spruce / pine > 89 820
C Paper pulp Birch > 89 760
D Dissolving pulp Eucalyptus > 91 435
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Materials and methods
• Laboratory cooked and bleached pulps based on mill spruce chips
Pulp
Reference
Prehydrolysis Cooking ISO
brightness
[%]
Limited
viscosity
number [ml/g]
Kappa
number target
E Yes Kraft 87 909 30
F Yes Soda + AQ 84 782 30
G No Kraft 85 964 30
H Yes Kraft 87 863 20
• 320 g chips/ 2,5 l autoclave. Pre-hydrolysis were done in water at 1 h 160°C after ramping from 90°C
with 1°C/min . The autoclaves were then cooled, opened and new cooking liquor was added. Finally,
new ramping to 160°C using time as control variable.
• Bleaching was done as chlorite delignification in according to “Chlorite delignification of cellulosic
materials” Useful method G..10 U. Reissued in May 2005 by PacTac, Canada”
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Materials and methods
Market pulps
• Mechanical enzymatical pre-treatment
• Pre-refining with a 12“ pilot-disc refiner to SR 26-29
• Enzymatical pre-treatment (Cellulase Novo 476)
• Refining was continued until the highest drainage index was
reached for each pulp without pulp darkening
• Homogenization to MFC by a Microfluidizer M-110EH with a
200 µm chamber (5 passes)
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Materials and methods
Laboratory cooked pulps
• Mechanical enzymatical pre-treatment
• Refining was done in a Voith-Sulzer refiner to a target SR 18-23. (3.5% consistency, SEL 1.8 Ws/m, 140 kWh/t)
• After the enzymatic stage (endoglucanase) the pulps were refined to a target SR-level of 80 (consistency 3.0%, SEL 0.9 Ws/m, SRE up to 620 kWh/t).
• An additional laboratory refining was also performed with a Valley beater for 30 min, because the fibres were up to 2 mm long
• Homogenization to MFC by a Microfluidizer M-110EH with a 200 µm chamber (5 passes)
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Chemical composition of the market pulps
Property Pulp A -
Diss. SW
Pulp B - Kraft
SW
Pulp C - Kraft
Birch
Pulp D - Diss.
EUC
Viscosity (cm³/g) 550 820 760 435
LODP (cm³/g) 123 123 171 120
WRV (%) 104 129 163 96
Galactose (rel %) < 0,05 0.2 < 0,05 <0.05
Glucose (rel %) 96.5 85.5 74.9 96.9
Mannose (rel %) 2 5.7 0.6 0.8
Arabinose (rel %) < 0,05 0.7 < 0,05 <0.05
Xylose (rel %) 1.5 8.5 24.4 2.2
L(w)c - Morfi (mm) 1.553 2.224 0.929 0.637
Fines(l)c - Morfi (%) 7.1 3.54 2.11 14.01
Unrefined
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Refining response of the market pulps
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600 700 800
SEC (kWh/t)
SR
400
600
800
1000
1200
1400
1600
1800
2000
2200
0 100 200 300 400 500 600 700 800
SEC (kWh/t)
Pulp C, EGL
Pulp C, Control
Pulp B, EGL
Pulp B, Control
Pulp A, EGL
Pulp A, Control
Avera
ge length
weig
hte
d in a
rea (
µm
)
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Refining response of the market pulps
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350 400 450 500
SEC (kWh/t)
Pulp D, _Cellulase Z
Pulp D, Control
Pulp A, _Cellulase Z
Pulp A, Control
SR
300
400
500
600
700
800
900
1000
1100
1200
1300
0 50 100 150 200 250 300 350 400 450 500 SEC (kWh/t)
Pulp D, EGL
Pulp D, Control
Pulp A, EGL
Pulp A, Control
Avera
ge length
weig
hte
d in a
rea (
µm
)
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Pulp A Diss. - no enzymatic pre-treatment
Pulp A Diss. – EGL pre-treatment
Light microscopic images of MFC
- market pulps -
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Pulp D Euca - EGL pre-treatment
Light microscopic images of MFC
- market pulps - Pulp B SW Kraft– EGL pre-treatment
Pulp C Birch Kraft– EGL pre-treatment
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Conclusions for the market pulps
• The two dissolving pulps showed significantly lower energy
consumption to reduce the fibre length to a minimum level before
final homogenization compared to spruce/pine and birch Kraft
pulps.
• The refining resistance were much slower of the dissolving grades
as compared to the Kraft pulps.
• Based on these results in the laboratory different pulps with
dissolving-like properties were cooked.
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Chemical composition of the laboratory cooked pulps
Pulp A -
diss. SW
Pulp D - diss.
EUC
Pulp E Pulp F Pulp G Pulp H
Market Market Pre-H. /
Kraft / κ 30
Pre-H. / Soda
AQ / κ 30
Kraft /
κ 30
Pre-H.
Kraft / κ 20
Viscosity (cm³/g) 550 435 909 782 964 863
LODP (cm³/g) 123 120 128 133 182 121
Galactose (rel %) < 0.05 <0.05 0.1 0.1 0.3 0.1
Glucose (rel %) 96.5 96.9 94.2 93.6 84.7 94.3
Mannose (rel %) 2 0.8 2.4 2.7 7 2.4
Arabinose (rel %) < 0.05 <0.05 <0.05 <0.05 0.6 <0.05
Xylose (rel %) 1.5 2.2 3.3 3.7 7.5 3.3
L(w)c - Morfi (mm) 1.6 0.637 2.71 2.68 2.71 2.71
Fines(l)c - Morfi (%) 6.76 14.01 1.08 0.95 1.04 1.14
Unrefined
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Refining response of the laboratory cooked pulps
1700
1900
2100
2300
2500
2700
2900
0 100 200 300 400 500 600 700
Pulp E
Pulp F
Pulp G
Pulp H
Mean area-weighted length (µm)
Specific energy consumption, kWk/t
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700
Pulp E
Pulp F
Pulp G
Pulp H
SR
Specific energy consumption, kWk/t
• The shown data are after refining with a conical refiner.
• In order to avoid clogging of the microfluidizer the pulps were again
refined with a Valley Beater for 30 min to a fibre length 0.47 – 0.66 mm
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Pulp F - pre-hydrolysis - soda AQ cooking Pulp G - conventional kraft Pulp H - pre-hydrolysis kraft cooking (kappa 20)
Pulp D – Diss. Euca Pulp E – pre-hydrolysis - kraft cooking (kappa 30) Pulp A – dissolving spruce
200 µm chamber
Light microscopic images of MFC
- laboratory cooked pulps -
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200 µm chamber
SEM images of MFC
- laboratory cooked pulps & market pulps -
Pulp B SW Kraft– EGL pre-treatment
Pulp D Euca - EGL pre-treatment
Pulp G - conventional kraft
Pulp H - pre-hydrolysis kraft cooking (kappa 20)
Diameter and thickness
of the fibrils of the
laboratory cooked pulps
are higher
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Conclusions laboratory cooked pulps
• The reduction in fibre length during refining of the laboratory
cooked pulps were much more difficult as expected, even if the
pulps had properties like dissolving pulp grades.
• Even if the chemical composition of the laboratory cooked pulps E,
F, and H were close to dissolving market pulp properties, the
morphology of the MFC particles looked completely different than
the MFC suspensions prepared from the market dissolving pulps. It
can be seen that the suspensions contained many more coarse
particles and non-disintegrated intact fibre structures.
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Why is one pulp suitable for preparing NFC while another
is not?
Some speculations:
• From the literature it is known that the pulp pre-treatment had to the greatest extend influence on the energy consumption during NFC preparation, but also on the chemical structure of the NFC.
• Pulp cooking in the laboratory is gentler with respect to mechanical forces than mill cooking.
• It can only be speculated that the introduction of mechanical fibre wall damage during mill pulping was responsible for the lower energy requirements during post-refining and the more homogeneous structure of the MFC.
• If this assumption can be confirmed, future pulping strategies for preparing pulps suitable for MFC production can be easily introduced into existing Kraft pulping lines.
• In addition, this might also help to reduce the pulp raw material costs of MFC production since conventional Kraft pulps are always cheaper than dissolving pulps.
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Acknowledgment
• The research leading to these results received funding from the
European Community’s Seventh Framework Programme under
Grant Agreement No 228802.