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High reactivity cellulose
– challenges
Lennart Salmén
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Pulp which easily may be
– converted to cellulose II
– enzymatically hydrolysed
– derivatized
– disintegrated into CNF
What do we mean with high-
reactivity cellulose?
CNF
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Specific surface area
Purity
Porosity
Cellulose molecular weight
What are the requirements/challenges?
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concentric
lamellas
S2 fibril
angle
cellulose aggregate
size distribution
undulating cellulose
aggregate structure
cellulose aggregate
glucomannan
condensed lignin
xylan
non-condensed lignin
The wood cell wall –
a highly intermixed
composite
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Ultra-structure across cell wall
lumen side middle lamella side
500nm
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Aggregate size distribution
Cellulose fibril aggregate size (nm)
0 5 10 15 20 25 30
Fre
qu
en
cy
0
2
4
6
8
10
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S 2 wall
ML side interior lumen side
Ce
llu
los
e a
gg
reg
ate
siz
e,
nm
10
12
14
16
18
dried wood
never dried wood
10
11
12
13
S 2 wall
ML side interior lumen side
Matrix size/aggregate size
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Three-dimensional
lenticular structure of cell wall
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ap
pare
nt
po
re v
olu
me (
ml/g
)
0.0
0.1
0.2
0.3
0.4
0.5
pore size (Å)
8 22 33 48 70 105 147 217
Pores created during delignification
wood
kraft
bleached kraft
sorbed
moisture moisture in pores
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Cellulose fibril aggregation during cooking
180
140
100
60
Tem
pera
ture
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Cellulose aggregate
structure
Cooking leads to increased association
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Cooking leads to increased association
temperature
matrix softening
cellulose relaxation
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Cooking leads to increased association
temperature
matrix softening
cellulose relaxation
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Cooking – aggregate size distribution
Cellulose fibril aggregate size, nm
0 5 10 15 20 25 30 35 40
Fre
qu
en
cy
0
2
4
6
8
10
12
Native wood
After cooking
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Cellulose aggregate size
10
15
20
25
Wood
Pulp fibers
Near middle lamella
Interior of fiber wall
Near lumen
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Cellulose aggregate size – hemicellulose content
Hemicellulose in pulp (% of carbohydrate content) Fib
ril ag
g. w
idth
aft
er
hyd
roly
sis
(n
m)
14.0
15.0
16.0
17.0
18.0
19.0
20.0
21.0
15.0 20.0 25.0
Tommy Iversen
Thomas Larsson
NMR
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Spacers – key role
Without spacers Cooking or drying Irreversible
aggregation
With spacers Cooking or drying Reversible
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Aggregation – pure cellulose
removal of matrix
polymers
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Hornification due to drying a
pp
are
nt
po
re v
olu
me
(m
l/g
)
-0,1
0,0
0,1
0,2
0,3
pore-size interval (Å)
8 22 33 48 70 105 147 217
Bleached kraft pulp
virgin
effect of
drying
wet < 100m2/g
dry 1m2/g
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Hemicellulose content, weight %
12 14 16 18 20 22 24 26 28
Ag
gre
gate
siz
e,
nm
15
16
17
18
19
wood
kraft pulps
sulphite
pulps
Cellulose aggregate size – cooking processes
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Aggregation - wood polymers
Relative hemicellulose content, %
0 10 20 30 40
14
16
18
20
22
h olo
cellulose
wood
Ce
llu
los
e a
gg
reg
ate
siz
e,
nm
Removal of
lignin under mild
conditions –
no aggregation
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Aggregation - wood polymers
Relative hemicellulose content, %
0 10 20 30 40
14
16
18
20
22
h olo
cellulose
extraction of
xylan
wood
Ce
llu
los
e a
gg
reg
ate
siz
e,
nm
Xylan extraction –
no aggregation
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Aggregation - wood polymers
Relative hemicellulose content, %
0 10 20 30 40
14
16
18
20
22
h olo
cellulose
extraction of
xylan
extraction of
glucomannan
wood
Ce
llu
los
e a
gg
reg
ate
siz
e,
nm
Glucomannan
extraction –
aggregation
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Aggregation - wood polymers
glucomannan cooperate
highly with cellulose -
obstructs aggregation
Relative hemicellulose content, %
0 10 20 30 40
14
16
18
20
22
h olo
cellulose
extraction of
xylan
extraction of
glucomannan
wood
Ce
llu
los
e a
gg
reg
ate
siz
e,
nm
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Cellulose ultra-structure
Solid state NMR –
determine accessible
surface area
d (ppm)
76 78 80 82 84 86 88 90 92 94
C = crystalline cellulose
AS = accessible surfaces
PC = paracrystalline
cellulose
IAS = i naccessible
surfaces
AS AS IAS
PC
C
C
C
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C
AS
PC IAS
Fibrill and aggregate size
n is the number of polymers along a side, polymer ‘width’: 0.57 nm
NMR – atom counter
2
44
n
nq
Ratio surface molecules
all molecules
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ASaggregate
Tot
Iq
I
Fibrill and aggregate size
C
AS
PC IAS
NMR – atom counter
IIIq
Tot
IASAS
fibril
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Specific surface area
4A
M a
Surface area per unit mass:
Fibrils
<a> = 4 nm and = 1500 kg/m3
sat = 667 m2/g
Fibril aggregates
<a> = 20 nm and = 1500 kg/m3
sat = 133 m2/g
a
a
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Pore volume – Fibre Saturation Point
pore water
inaccessible
water
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Average pore size
Pore size = volume of inaccessible water
specific surface area
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Pore size > 20 nm
Specific surface area > 100 m2/g
Aggregate size < 20 nm
Targets
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Pre-hydrolysis –
key to regulate aggregate size?
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Preferential dissolution of
hemicelluloses
Lignin as spacer elements
Pre-hydrolysis –
key to regulate aggregate size?
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Partial aggregation
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Increased reactivity - Enzymatic hydrolysis
Enzyme sizes are around 10 nm
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120 140
Co
nve
rsio
n t
o g
luco
se (
%)
Time (min)
softwood pulp, wet
modified pulping
eucalyptus pulp,
(best commercial)
wet
dry
Avicell cellulose
Tomas Larsson, 2013
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High reactivity cellulose
– control of aggregation process
purity
molecular weight
Summary
