Methods to analyse cellulose pulps
for the viscose production
Roland Agnemo
Domsjö Fabriker AB
1
2
Standard analysis of the cellulose pulps
in the pulping industry





Brightness
Viscosity
R18
Extractives
Cleanliness
3
These analysis are often sufficient in order to produce
the right cellulose quality for a fixed customer.
But they are not sufficient if you are trying to elucidate
problems in the viscose mill originate from the used
cellulose pulps.
Also if you wish to optimize your cellulose pulps for the
viscose producer in the respect of yield, production rate
and product qualities.
4
Viscosity measurements versus weight
average molecular weight distributions
The viscosity number is an average of the molecular weight
distribution of the cellulose, it doesn't inform how wide or
narrow the distribution is. Uneven cellulose molecular weight
distribution, especially on the high molecular weight side can
cause gel formation on the mercerized cellulose after the
xanthogenation. The cellulose gel can clog the viscose filter or
the nozzles in the spin bath. This results in reduced production
capacity and broken filaments and other deteriorating qualities
of the produced fibres.
5
Sample from clogged
nozzles
(transparent material)
A
Mercerized
cellulose
(cellulose II or βcellulose)
4
0
0
0
,
0
3
0
0
0
2
0
0
0
c
1
m
5
-
0
0
1
0
0
0
54
00
00
,
0
1
0
5
0
8
2
9 9
.
s
p
-
2
0
0
5
-
0
6
-
0 8
-
K A 2
0
2
0
1
1
8 5
.
s
p
-
2
0
0
2
-
0
2
-
0 1
-
M
e
6
7
The molecular weight obtained by measuring the viscosity,
is a different from either number average or the weight
average molecular weight. But it is closer to the weight
average than the number average.
Mn=ΣMiNi/ΣNi Mw=ΣMi2Ni/ΣMiNi Mz=ΣMi3Ni/ΣMi2Ni
Mv=(ΣMi1+αNi/ΣMiNi)1/α α ≈ 1
If so, that means Mv=Mw.
Is it true?
8
Mark-Houwink equation
( ) = KMva
For cellulose solved in Cuen(copper ethylenediamine)
solution, K=9.8*10-3, a=0.9
Mw
500000
Viscosity, ml/g
545
463
413
380
Mv
187836
156715
138021
125823
Mw
499804
431967
385099
284706
Mn
49710
47910
45731
41389
450000
400000
350000
300000
250000
120000
140000
160000
180000
200000
Mv
9
The effect of too high molecular weight of the used cellulose
can cause formation of gel particles in the viscose solution.
Measuring the cellulose viscosity is not enough.
Sample
1
2
3
4
5
6
7
Mw
347000
367000
373000
376000
452000
371000
361000
Mn
47800
48100
47200
50900
48400
52700
50300
Mz
879000
962000
965000
945000
1278000
907000
889000
Mz+1 Polydispersivity Viscosity, cm³/g
1471000
7.3
511
1687000
7.6
515
1628000
7.9
541
1605000
7.4
544
2201000
9.3
535
1477000
7.1
548
1448000
7.2
559
10
The influence of MnSO4 on the viscosity and molecular weight
distributions after the preripening stage
Viscosity initial
cm³/g
556
556
556
556
556
556
Temp.
°C
43
43
43
43
43
43
Time
min
60
60
60
60
60
60
NaOH
g/l
220
220
220
220
220
220
MnSO4
%
0
0
0,0014
0,0027
0,0069
0,0138
Temp
°C
53
45
45
45
45
45
Time
h
1,3,6
1,3,6
1,3,6
1,3,6
1,3,6
1,3,6
Viscosity after shredding
cm³/g
451
465
452
451
442
421
Viscosity after 1 h
cm³/g
291
358
337
331
328
299
Viscosity after 3 h
cm³/g
197
367
251
242
236
214
Viscosity after 6 h
cm³/g
145
206
196
190
185
166
Mw after 6 h
88976
139731
134181
119122
114662
103688
Mn after 6 h
33044
43892
44080
41151
39447
39399
Polydispersivity
2,69
3,18
3,04
2,89
2,91
2,63
Mercerisation
Preripening
Analyses
11
Alkali solubility of cellulose pulp
Normally the solubility of cellulose materials is tested in 18%
NaOH solution. Retention time 1 hour, 20° C. The method is
named R18 or S18. The numbers from R18 measurements
mean the amount of the cellulose material, which is not solved
in the NaOH solution.
S18 is 100-R18. If for example R18= 95%, 5 % is solved
material, which is often regarded as the amount of residual
hemicelluloses content in the pulp. But this number is also used
to calculate the alkali cellulose yield, which is important for the
viscose producer. But how accurate is this estimation, if the
viscose mill runs the mercerization stage at a lower or higher
temperature(20°), time(1hour) and NaOH-concentration(18%)?
12
R24 to R16 at different temperatures, 1 hour
CellulosePulp
Temperature, ° C
R24, %
R22, %
R20, %
R19, %
R18, %
R17, %
R16, %
Cellulose pulp 1
20
96,8
95,4
95
94,9
94,8
94,6
94,2
Cellulose pulp 1
30
95,8
95,3
95
95,3
95,3
94,6
95,2
Cellulose pulp 1
40
95,3
95,2
95,2
94,4
95,1
94,1
94,6
Cellulose pulp 1
50
94,9
94,3
94,5
95
94,9
94,6
94,8
Cellulose pulp 1
60
94,6
94,2
94
94,7
93,9
94,4
94
Cellulose pulp 2
20
96,9
96,3
96,6
96
95,6
95,6
95,1
Cellulose pulp 2
30
97,7
96,6
96,2
96
95,9
95,7
95,3
Cellulose pulp 2
40
96,3
96,1
96
95,6
95,8
95,2
95,5
Cellulose pulp 2
50
95,5
95,1
95,8
96
95,9
95,8
95,5
Cellulose pulp 2
60
95,7
95,2
95,1
95,2
94,8
94,8
95,3
Cellulose pulp 3
20
97,9
97,9
97,6
97,6
97,6
97,3
97,2
Cellulose pulp 3
30
98,2
97,9
97,5
97,6
97,8
97,4
96,8
Cellulose pulp 3
40
97,5
97,3
97
96,9
96,8
97
96,7
Cellulose pulp 3
50
96,2
97
96,2
97,3
96,8
97,3
97,3
Cellulose pulp 3
60
96,2
96,7
96,4
98
96,2
97,2
96,5
13
How well correlates the R18 values with the residual content
of the hemicelluloses?
Analysis
Cellulose 1 Cellulose 1 Cellulose 2 Cellulose 3 Cellulose 4 Cellulose 5
R18%
94.5
94.6
95.4
97.3
95.2
95
Hemicellulose, %
5.5
5.4
4.6
2.7
4.8
5
from R18 value
Hemicellulose, %
4.4
2.3
3.3
3.0
4.6
3.0
Hexoses, %
2.5
1.1
1.6
0
1.8
0.4
Pentoses,%
1.9
1.2
1.7
3
2.8
2.6
from carbohydrate
analysis
Viscosity, ml/g
583
431
555
431
596
528
14
Comparison of the cellulose reactivity of
dissolving pulps according to Fock´s method
Small amounts of cellulose pulps are xantogenated
in an excess of carbon sulphide and sodium hydroxide.
The reactivity numbers are the yield of dissolved cellulose
under fixed conditions.
The reproducibility and repeatability of the Fock´s method
are good.
The method is a comparing method.
15
The cellulose reactivity for mixed pulps
Market pulp
Cellulose yield,%
A
91,5±0.5
B
86,8±0,4
C
92,4±0,2
50% A+50% B
87,1±0,4
50% A+50% C
91,2±0,7
16
The influence of the cellulose viscosity on the reactivity
Viscosity
ml/g
545
463
413
380
Fock 9% NaOH
Yield, %
76
84
94
92
Fock 8% NaOH Fock 7% NaOH
Yield, %
Yield, %
45
16
55
22
78
21
72
19
17
The cellulose yield of spruce sulphite and
prehydrolysed eucalyptus fibres
9 0
L
8 0
L
7 0
L
6 0
5 0
4 0
Celuosicyd,%
3 0
2 0
1 0
0
0
0
0
0
0
1
1
,
,
,
,
0
,
2
,
4
,
6
8
0
2
e r
18
Conclusions
If the viscose producer would like to know more about the used
cellulose pulps, normal analysis methods as brightness, viscosity,
and R18 can be improved by using more specific methods.
Molecular weight distribution, carbohydrate and Fock´s reactivity
analysis are shown to be some of many useful analysis
techniques to do that.
Unreacted fibres in the viscose
19