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Methods to analyse cellulose pulps
for the viscose production
Roland Agnemo
Domsjö Fabriker AB
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Standard analysis of the cellulose pulps
in the pulping industry
Brightness
Viscosity
R18
Extractives
Cleanliness
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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.
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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.
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0 5 0 8 2 9 9 . s p - 2 0 0 5 - 0 6 - 0 8 - K A 2 0 0 5 0 8 2 9 / D ü s e n lä p p c h e n E N K A / T r a n s p a r e n t m t r l/ M ic / T r a n s m .
0 2 0 1 1 8 5 . s p - 2 0 0 2 - 0 2 - 0 1 - M e r c e r iz e d c e llu lo s e f r o m D o m s jö F a b r ik e r A B ( c e llu lo s e I I ) / K B r
4 0 0 0 , 0 3 0 0 0 2 0 0 0 1 5 0 0 1 0 0 0 5 0 04 0 0 , 0
c m - 1
A
Sample from clogged
nozzles
(transparent material)
Mercerized
cellulose
(cellulose II or β-
cellulose)
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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=ΣMi
3Ni/ΣMi2Ni
Mv=(ΣMi1+αNi/ΣMiNi)
1/α α ≈ 1
If so, that means Mv=Mw.
Is it true?
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Mark-Houwink equation
( ) = KMva
For cellulose solved in Cuen(copper ethylenediamine)
solution, K=9.8*10-3, a=0.9
Viscosity, ml/g Mv Mw Mn
545 187836 499804 49710
463 156715 431967 47910
413 138021 385099 45731
380 125823 284706 41389
250000
300000
350000
400000
450000
500000
120000 140000 160000 180000 200000
Mw
Mv
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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 Mw Mn Mz Mz+1 Polydispersivity Viscosity, cm³/g
1 347000 47800 879000 1471000 7.3 511
2 367000 48100 962000 1687000 7.6 515
3 373000 47200 965000 1628000 7.9 541
4 376000 50900 945000 1605000 7.4 544
5 452000 48400 1278000 2201000 9.3 535
6 371000 52700 907000 1477000 7.1 548
7 361000 50300 889000 1448000 7.2 559
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Viscosity initial cm³/g 556 556 556 556 556 556
Mercerisation
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
Preripening
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
Analyses
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
The influence of MnSO4 on the viscosity and molecular weight
distributions after the preripening stage
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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%)?
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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
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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
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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.
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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
The cellulose reactivity for mixed pulps
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Viscosity Fock 9% NaOH Fock 8% NaOH Fock 7% NaOH
ml/g Yield, % Yield, % Yield, %
545 76 45 16
463 84 55 22
413 94 78 21
380 92 72 19
The influence of the cellulose viscosity on the reactivity
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0,00,20,40,60,81,01,2
0
10
20
30
40
50
60
70
80
90
Ratio sulphite long fiber pulp/eucalyptus pulp
Cellulosic yield, % LS/Euc, 7% NaOH
LS/Euc, 8% NaOH
LS/Euc, 9% NaOH
The cellulose yield of spruce sulphite and
prehydrolysed eucalyptus fibres
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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