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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

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30

40

50

60

70

80

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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