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Yield and bleachability of hardwood and softwood kraft/polysulphide pulps

Increasing PS concentration leads to slightly increased pulp yields

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By: J.L. Colodette, J.L. Gomide, K. Gleysys, J. Kogan, A.-S. Jaaskel
2001-09-02
It has been shown that polysulphides (PS) have a beneficial effect on pulp yield. Also, PS make it possible to operate pulping at lower kappa numbers than usual without penalizing yield. The mechanism of PS action during kraft pulping has been traced to the oxidation of carbohydrate reducing end groups to gluconic acid, thus stabilizing the polysaccharides against peeling reactions (Equation 1). Even better yield results are obtained when PS are combined with anthraquinone (AQ), with the latter promoting additional carbohydrate stabilization besides improving lignin degradation reactions [1-8].

RCHO + SnS2- + HO- Æ RCOO- + HS- + OH- (1)

It has been reported [8] that PSs are unstable at temperatures above 120-130°C, and when digester temperature reaches this level a "disproportionation" reaction occurs generating Na2S and Na2S2O3 (Equation 2).

SnS2- + HO- Æ S2O3- + HS- + OH- (2)

Although the yield benefits derived from PS use in kraft pulping are well known, only few mills worldwide (nine mills in 1998) have adopted this technology. This is attributable to uncertainties with regard to pulp strength, recovery-cycle drawbacks, corrosion problems, unproven technology, capital costs, etc. [1, 7]. Some studies have shown tear strength reduction when PS is used in kraft pulping [7, 9-11]. However, other studies have shown that PS by itself or in combination with AQ have no detrimental effect on pulp strength [2, 4, 5, 8, 12-14].

A combination of PS/AQ cooking and oxygen delignification has been suggested as a fibreline configuration for improved yield [3, 6]. Moreover, the use of PS and AQ in modern modified pulping processes has been shown to improve pulp yield and quality even further [9, 12-16].

PS can be generated by adding elemental sulphur to white liquor or by the use of partially oxidized causticized white liquor [17-19]. These methods produce PS of relatively low concentration in the white liquor, which limits the process. However, newly developed methods such as electrolysis of white liquor [20] and black liquor gasification [21] allow for the generation and use of highly concentrated PS (> 10 g/L).

Although the impact of PS on pulping chemistry, pulp yield, pulp properties, alkali requirements, etc. has already been thoroughly investigated [1], only limited information exists on bleachability of PS pulps [8, 14, 16], and even less on the effect of PS concentration on bleachability. Therefore, this study was conducted in order to investigate yield and bleachability of kraft-PS pulps obtained at low, medium or high concentrations of PS in the white liquor.

EXPERIMENTAL

Eucalyptus mill chips and laboratory made pine chips were used. PS were generated "in situ" by adding elemental sulphur to white liquor and heating the mixture to 90°C with agitation. Using this technique, more sulphur is charged in polysulphide cooks than in corresponding kraft cooks, which gives the polysulphide cooks a higher HS- concentration during the cook. Three different dosages of elemental sulphur were used to obtain low (2.0 g/L), medium (5.5 g/L) and high (9.2 g/L) PS concentrations. Consumption of NaOH and Na2S in the white liquor during PS generation was compensated by addition of these chemicals to the orange liquor. Therefore, for a given wood species, all cooks were conducted at approximately the same alkali charge, Table I. Correction for sulphidity was also quite successful, which Table I shows.

A 7-litre capacity M/K digester was used for cooking approximately 1000 grams of chips. Warm cooking liquor (80°C) was added to the chips in the digester. For PS cooks, the temperature was raised to 85°C in 30 minutes and maintained for an additional 30 minutes to allow sufficient time for the PS to react. Each cook was carried out with three repetitions.

The general bleaching conditions are shown in Table II. Pressurized bleaching stages were carried out with 280-g oven-dry (od) samples in a Quantum Mark V mixer/reactor; the medium consistency ozone stage was carried out using the Ozone Cart system made by Quantum Technologies. Conventional bleaching stages were carried out with 150-g od samples contained in polyethylene bags. Pulp washing between stages was performed with excess distilled water. Pulp analyses, including physical strength tests, were performed according to TAPPI standard procedures. Heat reversion was measured on hand sheets heated for one hour at 105±3°C and 0% RH. Pulp beating was carried out on never-dried samples in a PFI mill.

Isolation of residual lignin for 31P NMR analyses was carried out by a slight modification of the acidolysis procedure described elsewhere [22]. Quantitative 31P NMR analyses were carried out on a Varian XL-500-MHz spectrometer using published procedures [23]. Carbohydrate composition analysis was carried out by high-performance liquid chromatography with UV detection after pulp acid hydrolysis using the klason method. The same procedure was used for determination of HexAs (2-furoic acid was used as the reference standard). Alkali-leachable lignin was measured indirectly through evaluation of the kappa number before and after pulp alkali soaking at pH 12.5 (initial), 100°C, for 60 min at 10% consistency.

RESULTS, DISCUSSION

Pulping: Kraft and K-PS pulps of kappa number 16-17 and 26-27 were prepared from eucalyptus and pine, respectively. The pulping results obtained when three different concentrations of PS were used (2.0, 5.5 and 9.2 g/L) are shown in Table I. Those cooks were labelled as K-PS2, K-PS5 and K-PS9, respectively. For comparison purposes conventional kraft cooks were also included.

It can be seen that PS improved pulp yield significantly and the beneficial effects were directly related to their concentration in the cooking liquor. A high concentration of PS (9.2 g/L) caused a screened yield increase of 2.1% for eucalyptus and 4.2% for pine (Table I). These yield benefits due to PS use are attributable to protection of cellulose chains, but especially to the retention of more hemicelluloses in the pulp. Half of the yield gain in the eucalyptus case was caused by retention of about 1% more xylans in the pulp, whereas 73% of the yield gain in the pine case was caused by retention of 3.1% more mannans (Table I). The more pronounced effect of PS in the pine wood is attributable to their effective protection of mannans against the strong alkali charge, which was required for this wood. An intriguing fact observed in the case of the eucalyptus wood is that the content of HexAs in the PS pulp was lower than that of the kraft pulp in spite of its higher content of xylans. Since the alkalinity and temperature of both kraft and kraft-PS cooks were similar it is difficult to rationalize the more extensive alkali-induced hydrolysis of the HexAs in the kraft-PS cook.

The higher viscosity of the K-PS pulps in relation to the reference shows the protective action of PS against alkali promoted depolimerization of carbohydrates as has been shown earlier [24]. For pinewood, the viscosity improvements were directly proportional to PS concentration. For eucalyptus the highest increase in viscosity was 31% (K-PS2) and for pine, it was even more pronounced reaching 61% (K-PS9). PS showed a small detrimental effect on pulp brightness and this effect was more significant for eucalyptus.

Residual lignin: The contents of aliphatic-OH, total phenolic-OH and condensed phenolic-OH in the residual lignin isolated from the kraft and K-PS9 pulps were quite similar. Their contents in the various pulps were remarkably constant at an approximate value of 1.8-1.9 and 2.1-2.2 mmoles/g for eucalyptus and pine, respectively (Table I). It should be noted that the phenolic hydroxyl moieties present within residual kraft lignin are considered to be among the most reactive lignin sites during pulp bleaching. The contents of acid-COOH groups of the eucalyptus kraft and K-PS9 pulps were similar, whereas the K-PS9 pulp made from pine presented 2.5 times more acid groups than reference (Table I).

Oxygen delignification: For the eucalyptus pulps, neither the kappa drop nor the brightness gain across the double O-stage were affected by the use of PS in the pulping process, Table III. Previous work carried out with a different eucalyptus wood showed a slight positive effect of PS cooking on oxygen delignification performance [25]. On the other hand, for the pine pulp samples both the kappa drop and brightness gain across the O-stage decreased with increasing PS concentration in the pulping liquor. The kappa reduction for the pulp cooked with 9.2 g/L of PS was about 5.7% lower than that of the conventional kraft pulp. The slight negative impact of PS pulping on oxygen delignification performance for the pine pulps may be traced to their lower content of alkali-leachable lignin (Table III). Pulps containing low content of these low molecular weight and free phenolic-rich-type of lignin tend to respond poorer to oxygen delignification. It is worth noting that no HexAs were removed across the oxygen delignification, in agreement with results of other workers [26]. The contents of HexAs in the eucalyptus pulps were 2-2.5 times higher than those in the pine ones.

ECF bleaching of the pine pulps -- Pulp bleachability: The results in Table IV indicate that the bleachability of pine pulps with the sequences DEopDD and Z/DEopDD, measured by the amount of ClO2 consumed per kappa unit, is improved with increasing concentration of PS in the white liquor. However, these differences had no impact on total chemical costs since the K-PS pulps had higher initial kappa number, which derived from their lower performance in the O-stage. The lowest bleaching costs were achieved with the sequence DEop(ZE)D by virtue of the very high ClO2/O3 replacement ratio. Over-all the relative chemical cost of this sequence was around 15-20% lower than that of the sequences DEopDD and Z/DEopDD. A value of 100 was used to designate the lowest bleaching cost and served as reference to calculate the other values.

For the sequence DEop(ZE)D no significant differences in bleachability were observed among the K-PS and kraft pulps. This was probably due to the very low ClO2 requirement of this sequence in relation to the others, which was caused by the high ozone stage efficiency. Each kilogram of ozone applied replaced, in certain cases, up to 3.5 kg of ClO2. The same ozone efficiency was not observed when it was applied to the sequence Z/DEopDD.

The differences in bleachability among the kraft and K-PS pulps are difficult to rationalize. Previous work carried out with eucalyptus wood has also indicated better bleachability of K-PS cooked pulps in relation to conventional ones [25]. K-PS cooking has been reported to leave less HexAs in the pulp than conventional kraft, which may improve bleachability [26]. However, the impact of HexAs on pulp bleachability has not yet been totally clarified. In any case, the contents of HexAs in the pine samples studied were very low and did not vary significantly amongst the various pulps. On the other hand, differences in the residual lignin alone cannot explain the bleachability differences since the nature of the residual lignin extracted from the K-PS and kraft pulps were quite similar, except for the content of acid-COOH groups which were higher in the K-PS pulps (Table I).

ECF bleaching of the pine pulps -- Pulp quality: The final viscosities of the K-PS pulps were over-all higher than that of the reference, with the highest values being achieved for the pulps cooked with a high PS concentration. The improved final viscosities are attributable to the higher initial viscosities of the K-PS pulps, which derived from the more selective pulping. Despite the fact that the K-PS cooked pulps had higher viscosities, this did not translate into better pulp strength. The values of tear and MOE for the various K-PS pulps at a tensile index of 70 N.m/g were quite similar, regardless of PS concentration and bleaching sequence (Table IV). It is worth noting, however, that K-PS pulps presented better refinability than kraft, as shown by their lower number of PFI revolutions to reach a similar tensile index. The better refinability is attributable to the higher retention of hemicelluloses in the K-PS pulps than in the kraft. It should be also noted that the ECF pulps bleached with sequences containing ozone presented better refinability than that of the pulp bleached with chorine dioxide only. Pulp brightness reversion was not significantly affected by the PS concentration during cooking or by the bleaching process.

CONCLUSIONS

1. Increasing PS concentration resulted in increased pulp yield and viscosity for both softwood and hardwood pulps.

2. Yield enhancements of 2.2 and 4.2% were obtained for eucalyptus and pine, respectively, when 9.2g/L of PS were added to the pulping liquor.

3. The yield benefits were 50% due to xylan retention in the eucalyptus case and about 73% due to mannan retention in the pine case.

4. Polysulphide pulping resulted in viscosity gains of up to 31 and 61% for eucalyptus and pine, respectively.

5. Pine K-PS pulps show better bleachability than conventional ones when treated with ECF sequences.

6. The lower amounts of alkali-leachable lignin in the kraft-PS pulps negatively affected O-stage performance.

7. Residual lignins isolated from K-PS pulps show similar amounts of aliphatic and phenolic-OH groups.

8. Pine K-PS pulps show higher final bleached viscosity than kraft pulp, but the benefits do not result in improved strength properties.

9. Among the sequences evaluated, DEop(ZE)D resulted in the lowest relative chemical cost.

LITERATURE

1. KLEEPE, P.J and MINJA, R.J.A. The possibility to apply polysulfide-AQ pulping in kraft mills. Proc., TAPPI Breaking the Pulp Yield Barrier Symposium, Atlanta, GA. 113-122 (1998).

2. THOMPSON, B., STURGEOFF, L., GOYAL, G. and HANNA, R. Boosting pulp yield of western softwood with anthraquinone/polysulfide kraft pulping. Proc., TAPPI Breaking the Pulp Yield Barrier Symposium, Atlanta, GA. 133-143 (1998).

3. MINJA, R.J.A., MOE, S.T., and KLEPPE, P.J. Improving the pulp yield by using PS/AQ and/or two stage oxygen delignification. Proc., TAPPI Breaking the Pulp Yield Barrier Symposium, Atlanta, GA. 213-217 (1998).

4. ROBLES, Y.A.M., GOMIDE, J.L., OLIVEIRA, R.C. and COLODETTE, J.L. Utilização de antraquinona e polissulfetos como aditivos do processo kraft para produção de celulose de Eucalyptus. Proc., ABTCP Pulp and Paper Annual Meeting, Brazilian Technical Association of the Pulp and Paper Industry, Sao Paulo, Brazil, 267-282 (1996).

5. KYIOHARA, R.S., GOMIDE, J.L., COLODETTE, J.L. and OLIVEIRA, R.C. Deslignificação kraft intensiva de madeira de Eucalyptus pelo uso de antraquinona e polissulfeto. Proc., ABTCP Pulp and Paper Annual Meeting, Brazilian Technical Association of the Pulp and Paper Industry, Sao Paulo, Brazil, 63-76 (1994).

6. COLODETTE, J.L., GOMIDE, J.L., ROBLES, Y.A.M., ALMEIDA, J.M., BRITO, A.C.H., MEHLMAN, S.K. and ARGYROPOULOS, D.S. Effect of the pulping process on pulp bleachability with ECF, Z-ECF and TCF bleaching sequences. Proc., International Pulp Bleaching Conference, IPBC, Helsinki, 61-70 (1998).

7. DEAL, H. Anthraquinone and polysulfide -- Applicability for use in pulp mill operations. Proc., TAPPI Pulping Conference, Nashville, TN. 73-80 (1996).

8. PARTHASARATHY, V.R., SMITH, G.C., RUDIE, G.F., DETTY, A.E. and STEFFY, J.J. Application of anthraquinone in extending the delignification of kraft and polysulfide pulps. Tappi J. 78(2):113-125 (1995).

9. HAKANEN, A. and TEDER, A. Modified kraft cooking with polysulfide: yield, viscosity, and physical properties. Tappi J. 80(7):189-196 (1997).

10. MINJA, R.J.A., KLEPPE, P.J. and KARLSEN, T. Modified polysulfide (AQ)-pulping of hardwood. Proc., TAPPI Pulping Conference, San Francisco, CA. 721-727 (1997).

11. PRASAD, D.Y., JAMEEL, H., GRATZL, J. and TU, X. Use of AQ/PS pulping additives for the production of linerboard pulp. Proc., TAPPI Pulping Conference, Nashville, TN. 59-72 (1996).

12. JIANG, J.E. Extended delignification of southern pine with anthraquinone and polysulfide. Tappi J. 78(2):126-132 (1995).

13. JIANG, J.E. Extended modified cooking of southern pine with polysulfide -- effects on pulp yield and physical properties. Tappi J. 77(2):120-123 (1994).

14. JIANG, J.E. Extended modified cooking of southern pine with polysulfide -- effect on elemental-chlorine-free bleaching. JPPS 21(3):J76-J80 (1995).

15. CHIVUKULA, S., CHANG, H-M., JAMEEL, H. and WIZANI, W. Effect of pretreatment with green liquor, AQ and polysulfide on the performance of an extended batch system. Proc., Tappi Pulping Conference, Montreal, QC. 419-425 (1998).

16. KLEPPE, P.J. Experience on high kappa pulping and oxygen delignification to improve productivity and achieving environmental goals. Proc., Tappi Pulping Conference, San Francisco, CA. 835 (1997).

17. HOMER, G., JOHNSON, S. and EPINEY, M. State of the art ECF -- Pulping and bleaching with oxygen, ozone, and chlorine dioxide. Part 2. Proc., Tappi Pulping Conference, Nashville, TN. 81-91 (1996).

18. HU, T.O., CHOW, W., HEEK, R.V., ULOTH, V. and WEARING, J.T. Polysulfide pulping of softwood using oxidized mill white liquor generated from Paprican's PS process. Proc., Tappi Pulping Conference, Montreal, QC. 561-569 (1998).

19. TENCH, L., ULOTH, V., DORRIS, G., HORNSEY, D. and MUNRO, F. Mill scale implementation of Paprican's process for polysulfide liquor production in kraft mill causticizers. Part 1: Batch trials and process optimization. Proc., Tappi Pulping Conference, Montreal, QC. 571-592 (1998).

20. WATANABE, K., SHIMIZU, M. and NANRY, Y. New process for producing highly concentrated polysulfide liquor by electrolysis of white liquor. Proc. Tappi Pulping Conference. Orlando, 397-406, Oct. 31-Nov. 4 (1999).

21. SADOWSKI, R.S., PARTHASARATHY, P., HENDERSON, S. and Kinstrey, B. Black liquor gasification: A combination Approach. Tappi J. 82(11):5959-62 (1999).

22. GRANATA, A. and ARGYROPOULOS, D.S. 2-Chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane, a Reagent for the Accurate Determination of the Uncondensed and Condensed Phenolic Moieties in Lignins. J. Agr. And Food Chem. 43(6):1538 (1995).

23. SUN, Y. and ARGYROPOULOS, D.S. Fundamentals of high-pressure oxygen and low-pressure oxygen-peroxide (Eop)delignification of softwood and hardwood kraft pulps: a comparison. JPPS. 21(6):J185 (1995).

24. LINDSTRON, M. and TEDER, A. The effect of polysulfide pretreatment when kraft pulping to very low kappa numbers. Nordic Pulp and Paper Research J. (10):8-10 (1995).

25. COLODETTE, J.L., GOMIDE, J.L., ARGYROPOULOS, D.S., ROBLES, Y.A.M., ALMEIDA, J.M., BRITO, A.C.H. and MEHLMAN, S.K. Effect of pulping processes on bleachability with ECF, Z-ECF and TCF bleaching. Appita J. 52(5):368 (1999).

26. JIANG, Z-H., VAN LIEROP, B., NOLIN, A. and BERRY, R. A new insight into the bleachability of kraft pulps. International Pulp Bleaching Conference. Halifax, Oral sessions, 163-168, June 27-30 (2000).

Abstract: Eucalyptus and pine pulps of kappa 16-17 and 26-27, respectively, were produced by the kraft and kraft-polysulphide (K-PS) processes and ECF bleached. K-PS pulps were manufactured with variable PS concentrations. Polysulphides (PS) improved yield (up to 4% for pine) due to higher mannans and xylans retention. Yield increased with increasing PS concentration. PS improved pulp viscosity and refinability but had no effect on strength properties. PS also improved pulp bleachability with ECF sequences.

Reference: COLODETTE, J.L. GOMIDE, J.L., GLEYSYS, K., KOGAN, J., JAASKELAINEN, A.-S., ARGYROPOULOS, D.S. Yield and bleachability of hardwood and softwood kraft/polysulphide pulps. Pulp Paper Can. 102(9): T269-272 (September 2001). Paper presented at the 86th Annual Meeting of the Pulp and Paper Technical Association of Canada in Montreal, QC, on January 31 to February 4, 2000. Not to be reproduced without permission of PAPTAC. Manuscript received November 16, 1999. Revised manuscript approved for publication by the Review Panel April 12, 2001.

Keywords: KRAFT PULPS, POLYSULPHIDE PULPS, EUCALYPTUS, PINUS, CHLORINE FREE BLEACHING, BLEACHED PULPS, YIELD, POLYSULPHIDES, CONCENTRATION, PULP PROPERTIES.

Résumé: Des pâtes à base d'eucalyptus et de pin à indice Kappa de 16 et 17 et de 26 et 27 respectivement ont été fabriquées selon des procédés kraft et kraft-polysulfures (K-PS), puis blanchies sans chlore élémentaire. Les pâtes K-PS ont été fabriquées à des concentrations variables de PS. Les polysulfures (PS) ont amélioré le rendement (jusqu'à 4 % dans le cas du pin) en raison de la rétention accrue des mannanes et des xylanes. Le rendement a augmenté proportionnellement à l'accroissement de la concentration en PS. Les PS ont amélioré la viscosité de la pâte et son aptitude au raffinage, sans toutefois augmenter sa résistance. Ils ont aussi accru l'aptitude au blanchiment de la pâte grâce à des séquences de blanchiment réalisées sans chlore élémentaire.

Table I. Pulping conditions and results for different concentrations of polysulphide.

EucalyptusPine
Cooking conditions
and pulping resultsKraftK-PS2K-PS5K-PS9KraftK-PS2K-PS5K-PS9
Active alkali, %20.419.521.922.127.526.624.225.2
Sulfidity, %24.624.725.025.125.025.025.025.0
Max. temperature, °C168168168168170170170170
Time to 85°C--303030--303030
Time at 85°C--303030--303030
Time to max. temp., min9060606090606060
Time at max. temp., min6060606060606060
H factor8908908908901042104210421042
Kappa number16.817.117.017.126.626.127.327.1
Screened yield, %52.052.753.054.144.145.047.048.3
Total yield, %52.353.253.454.544.545.347.448.7
Viscosity, mPa.s43.857.650.249.922.126.631.435.6
Brightness, % ISO36.133.633.632.628.928.426.826.7
Lignin aliphatic-OH, mmol/g2.82----2.832.55----2.50
Lignin phenolic-OH, mmol/g1.87----1.822.07----2.25
Lignin condensed phenolic-OH, mmol/g--------0.99----1.06
Lignin Acid-COOH, mmol/g0.28----0.290.11----0.29
Pulp hexenuronic acids, mmol/kg41.337.236.736.416.015.815.715.8
Pulp glucans, %80.3----79.980.6----77.5
Pulp xylans, %11.5----12.55.5----5.9
Pulp manans, %0.6----0.55.9--

Table II. General bleaching conditions.

StageBleaching conditions
Time,Temperature,Cst.,Pressure,Final
min°C%kPapH
D0 456510--3.0
Eop 60901020011.5
D11807010--3.5
D21807010--4.5
Z1-23010--2.5
E 306010--9.0

Table III. Double-stage O2 delignification results for eucalyptus and pine pulps1.

Pulp sample
ResultsKraftK-PS2K-PS5K-PS9
Eucalyptus pulp:
Kappa In16.116.815.916.8
Kappa Out9.19.58.99.4
HexA's Out, mmol/kg41.537.136.436.1
Kappa Drop, %43.543.543.844.0
Visc. Drop, %16.424.117.317.3
Bright. Gain, % ISO19.219.220.019.6
Leachable lignin, kappa units1.51.61.51.5
Pine pulp:
Kappa In24.824.425.926.2
Kappa Out10.811.012.212.9
HexA's Out, mmol/kg16.916.216.116.7
Kappa Drop, %56.554.952.950.8
Visc. Drop, %7.59.410.912.9
Bright. Gain, % ISO8.48.38.06.9
Leachable lignin, kappa units2.31.81.51.1

1O/O-stage: 10% consistency, 30/60 min, 95/105°C, 600 kPa, 18-20 kg/t NaOH, 20 kg/t O2, 4 kg/t MgSO4.7 H2O.

Table IV. Bleaching results to 90% ISO with ECF sequences: O2-delignified pine pulps.

Bleaching resultsKraftK-PS2K-PS5K-PS9
DEopDD:
Total ClO2, kg/t16.116.316.216.8
kg ClO2/k unit1.491.481.331.30
Relative chemical cost116117116119
Viscosity, mPa.s10.912.215.017.0
Bright. Reversion, % ISO3.53.32.92.9
Tear (at 70 N.m/g), mN.m2/g15.916.215.416.1
MOE* (at 70 N.m/g), MNm/kg6.66.56.66.5
CSF (at 70 N.m/g), mL471500503530
PFI Revolutions (at 70 N.m/g)3421312528322446
Z/DEopDD:
Total ClO2, kg/t12.112.213.313.7
kg ClO2/k unit1.121.101.091.06
kg ClO2/kg O31.331.370.971.03
Relative chemical cost119120125127
Viscosity, mPa.s10.211.613.515.4
Bright. Reversion, % ISO3.63.73.43.3
Tear (at 70 N.m/g), mN.m2/g15.916.016.615.6
MOE* (at 70 N.m/g), MNm/kg6.46.66.46.5
CSF (at 70 N.m/g), mL463427500487
PFI Revolutions (at 70 N.m/g)3047335924352428
DEop(ZE)D:
Total ClO2, kg/t5.65.76.56.8
kg ClO2/k unit0.520.520.530.53
kg ClO2/kg O33.503.532.272.30
Relative chemical cost100101104106
Viscosity, mPa.s9.711.613.615.5
Bright. Reversion, % ISO3.03.23.23.1
Tear (at 70 N.m/g), mN.m2/g14.915.414.914.

Photos

J.L. COLODETT, White Martins Gases Ind, RJ, Brazil
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J.L. GOMIDE, Federal U. of Viçosa, Viçosa, Brazil
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