CHEMICAL
CROSSLINKING OF SOFTWOOD KRAFT FIBRE NETWORKS TOWARDS
AN ABSORPTION PRODUCT
Hanna de la Motte, Kristoffer Lund, Harald Brelid, Gunnar Westman
Chalmers University of Technology
Organic Chemistry, Forest Products and Chemical Engineering
Karlstad 091118
Hanna de la Motte
WooDi
The aim of the research is to invent a more
sustainable
absorption structure by
improving the properties
of the wood-based materials and concurrently
reduce the dependency
on non-renewable additives
Hanna de la Motte
Introduction
Porous network from pulp fibres
Super absorbent polymers (SAP)
Decrease the use of non-
renewable materials
Better understanding of network
Hanna de la Motte
Introduction
Wet stiffness of the fibre network has to be increased
Intra-fibre crosslinking in the fibre walls
Hanna de la Motte
Experimental
Never-dried bleached Scandinavian softwood kraft pulp supplied by Södra Cell Väro
Fractionation
Crosslinking
Preparation of porous test pads
WRV (Water Retention Value)
Compression test
Hanna de la Motte
Crosslinkers
The reactions were performed in acetone, isopropanol or water at for 10-60 min using
different crosslinker concentrations.
Hanna de la Motte
ResultsWRV
•Sodium hydroxide activates the hydroxy groups, while uncatalysed reaction occurs
at carboxylate groups belonging to hemicelluloses.
• The crosslinked fibres have a substantially lower WRV than the reference fibres.
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
Reference (with
activation)
Reference (no
activation)
(S) with activation
(S) no activation
(L) with activation
(L) no activation
WR
V (
g/g
)
Hanna de la Motte
ResultsWRV
• The cationic crosslinker showed a higher WRV compared to the non-cationic
crosslinkers.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Cationic (L) Neutral
WR
V (
g/g
)
Hanna de la Motte
ResultsWet bulk, 15 kPa
y = -6,6211x + 10,729R² = 0,8717
5.00
5.50
6.00
6.50
7.00
7.50
8.00
0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9
We
t b
ulk
(cm
³/g
)
WRV (g/g)
Crosslinker (L)
• Only minor differences between the pads in the dry bulk test, strong hydrogen bonds.
• The wet bulk follows the trend of the WRV, a high wet bulk gives a low WRV.
• Crosslinking increases the stiffness of the network.
Hanna de la Motte
ResultsStructure recovery
•Crosslinked pads regain most of their initial structure.
• Indicates that an increase in crosslinking in the fibre wall give more stable fibrils.
• The data correlates well with the WRV and wet bulk.
0
2
4
6
8
10
12
14
16
18
Reference (with
activation)
Reference (no
activation)
(S) with activation
(S) no activation
(L) with activation
(L) no activation
Str
uctu
re r
ec
ove
ry (
cm
³/g
)
Hanna de la Motte
ResultsMultivarate analysis
• Longer reaction times are favourable as well as acetone as solvent.
• A longer reaction time does not require the highest temperature for an improved
structure recovery.
Wet bulk Structure recovery
Tim
e (
min
)
Temperature Temperature
Tim
e (
min
)
Hanna de la Motte
Conclusion
The new crosslinking method increases the wet bulk
and the structure recovery
An evident correlation between the wet bulk and the
water retention value (WRV) can be seen
Longer reaction times are favourable to improve the
structure recovery of the fibre network
Hanna de la Motte
Future work
The results presented are the outcome of initial efforts
in a larger research project
The future requires more fundamental knowledge
about the influence of chemical modifications towards
specific fibre network properties
Improvement of analytical methods on a molecular
scale
