Methods to analyse cellulose pulps for the viscose production. Roland Agnemo Domsjö Fabriker AB

Transcription

1 Methods to analyse cellulose pulps for the viscose production Roland Agnemo Domsjö Fabriker AB 1

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3 Standard analysis of the cellulose pulps in the pulping industry Brightness Viscosity R18 Extractives Cleanliness 3

4 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

5 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

6 Sample from clogged nozzles (transparent material) A Mercerized cellulose (cellulose II or β- cellulose) , , 0 c m s p K A s p M e 6

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8 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. M n =ΣM i N i /ΣN i M w =ΣM i2 N i /ΣM i N i M z =ΣM i3 N i /ΣM i2 N i M v =(ΣM i 1+α N i /ΣM i N i ) 1/α α 1 If so, that means Mv=Mw. Is it true? 8

9 Mark-Houwink equation ( ) = KM a v For cellulose solved in Cuen(copper ethylenediamine) solution, K=9.8*10-3, a=0.9 Mw Viscosity, ml/g Mv Mw Mn Mv 9

10 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

11 The influence of MnSO4 on the viscosity and molecular weight distributions after the preripening stage Viscosity initial cm³/g Mercerisation Temp. C Time min NaOH g/l MnSO 4 % 0 0 0,0014 0,0027 0,0069 0,0138 Preripening Temp C 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 Viscosity after 1 h cm³/g Viscosity after 3 h cm³/g Viscosity after 6 h cm³/g Mw after 6 h Mn after 6 h Polydispersivity 2,69 3,18 3,04 2,89 2,91 2,63 11

12 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

13 R24 to R16 at different temperatures, 1 hour CellulosePulp Temperature, C R24, % R22, % R20, % R19, % R18, % R17, % R16, % Cellulose pulp ,8 95, ,9 94,8 94,6 94,2 Cellulose pulp ,8 95, ,3 95,3 94,6 95,2 Cellulose pulp ,3 95,2 95,2 94,4 95,1 94,1 94,6 Cellulose pulp ,9 94,3 94, ,9 94,6 94,8 Cellulose pulp ,6 94, ,7 93,9 94,4 94 Cellulose pulp ,9 96,3 96, ,6 95,6 95,1 Cellulose pulp ,7 96,6 96, ,9 95,7 95,3 Cellulose pulp ,3 96, ,6 95,8 95,2 95,5 Cellulose pulp ,5 95,1 95, ,9 95,8 95,5 Cellulose pulp ,7 95,2 95,1 95,2 94,8 94,8 95,3 Cellulose pulp ,9 97,9 97,6 97,6 97,6 97,3 97,2 Cellulose pulp ,2 97,9 97,5 97,6 97,8 97,4 96,8 Cellulose pulp ,5 97, ,9 96, ,7 Cellulose pulp , ,2 97,3 96,8 97,3 97,3 Cellulose pulp ,2 96,7 96, ,2 97,2 96,5 13

14 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% Hemicellulose, % from R18 value Hemicellulose, % Hexoses, % Pentoses,% from carbohydrate analysis Viscosity, ml/g

15 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

16 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

17 The influence of the cellulose viscosity on the reactivity Viscosity Fock 9% NaOH Fock 8% NaOH Fock 7% NaOH ml/g Yield, % Yield, % Yield, %

18 The cellulose yield of spruce sulphite and prehydrolysed eucalyptus fibres Celulosicyield,% L 1 0, er L L 18

19 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