BLEACHING GROUNIDWOCI) PULPSWITH IHYPOCIILOPITES

February 1949

INFORMATION REVIEWED

AND REAFFIRMED

March 1956

No. 81736

UNITED STATES DEPARTMENT OF AGRICULTUREFOREST SERVICE

FOREST PRODUCTS LABORATORYMadison 5, Wisconsin

In Cooperation with the University of Wisconsin

BLEACHING GROUNDWOOD PULPS WITH HYPOCHLORITES-l'a

BY

RALPH M. KINGSBURY, ChemistFORREST A. SIMMONDS, Chemist

andEARLE S. LEWIS, Physical Science Aid

Forest Products Laboratory,2 Forest ServiceU. S. Department of Agriculture

am, .,n• .10

Summary

Bleaching experiments were made at the Forest Products Laboratory ongroundwood pulps from 13 hardwoods, 6 softwoods, and also a mixture of 6hardwoods alone and in a mixture with Eastern white pine, as occurnaturally on Northeast farm wood lots. The results show that calciumhypochlorite is a satisfactory bleaching agent for the hardwood pulps, butprobably is not satisfactory for the softwood pulp. In general, the bright-ness of the hardwood pulps, individually and in mixtures, was increased tothe range of 70 to 79 percent with 10 percent available chlorine. Uponexposure to carbon arc light, the recession in brightness ranged from 4 to11 points, Bleached pulp yields were 98 to 100 percent of the unbleachedpulp. The only consistent effect of the bleaching on drainage and strengthproperties was an increase in tensile strength.

In order to get a good bleaching effect with hypochlorite, its tendency toreact very rapidly with groundwood pulp must be retarded considerably,especially at the start of the reaction. This was done by use of low den-sity, low temperature, and a high alkalinity, with the latter being themost critical of the three. The lime requirement for control of alkalinityranged from 3 to 6 percent, including the free lime in the bleaching liquor.Substitution of sodium silicate for a part of the lime in the bleaching of

-Presented at TAPPI Mechanical Pulping Conference, Poland Spring House,Poland Spring, Maine, Sept. 27-29, 1948.

?The results included in this report are taken in part from an investigationundertaken with funds furnished under the Research & Marketing Act,

-Maintained at Madison 5, Wis., in cooperation with the University ofWisconsin.

Report No, R1736

some pulps further improved brightness up to 5 points. Final addition ofsulfurous acid, or equivalent, to the stock had a similar effect. Althoughthe hue of hypochlorite-bleached pulps was in the yellow range, in the caseof hardwood pulps, it is believed to be light enough to be generallysatisfactory.

Experimental results indicated that pulps from mixtures of hardwoods can bebleached satisfactorily with hypochlorite and that the brightness of themixtures will be proportional to that obtainable on pulps from the individualwoods. Although the Eastern white pine pulp did not respond satisfactorilyto hypochlorite, a 50-50 mixture of it and the mixed hardwood pulp wasbleached to about 70 brightness with 10 percent available chlorine.Essentially the same result was obtained, however, by blending bleachedmixed hardwood pulp with unbleached pine pulp. This procedure would bethe more economical of the two.

Introduction

The use of local supplies of pulpwood is advantageous not only to the pulpmanufacturer but also to any farmers of those regions owning stands oftimber. However, supplies of wood available on farm wood lots within easyreach of the mills, are, in many instances, of poor quality or not thekinds ordinarily used. If it can be shown how to produce satisfactory pulpfrom these species and from mixtures of them as they occur, the marketabilityof farm-lot wood will be increased. For example, these woods can be used toa greater extent for the production of groundwood pulps when practical waysof bleaching the pulps become available. The purpose of this work was todevelop bleaching procedures suitable for groundwood pulps made from avariety of individual woods and from mixed species. The mixed species usedwas representative of certain stands on farm woodlots in the Northeast,

The requirements for a process for bleaching groundwood pulps are that itschemical cost will be low, that it will effect an appreciable increase inbrightness that will not recede too rapidly, that it will not develop astrong yellow hue, and, finally, that it will cause only a small loss inweight of pulp by chemical action. It appears that no one bleaching processmeets these requirements for all goundwood pulps. The most promising agentsfor the commercial bleaching of groundwood pulps are hydrosulfites, peroxides,and hYpochlorites (1, 4, 6, 7).

Important Factors in the Use of Hypochloritez

The rate of reaction between calcium or sodium hypochlorite and groundwoodwith 10 percent available chlorine is normally extremely rapid, Forsatisfactory result in any instance, the density, temperature, and alkalinitymust be adjusted so that the rate of reaction will be definitely retarded atthe start. It appears, however, that the alkalinity is the most critical ofthe three variables. In general, density should not exceed 6 percent, and

Report No. 81736

no apparent .benefit was observed for lower values. Temperature does notneed to exceed 30° C., and alkalinity should be equivalent initially to thePH range of 11 to 12 and : at the end of the reaction, to not less than pH 8.Examples of the influence of alkalinity and of the use of sodium silicate inthe buffer system are given in a previous publication (4). Depending on thepulp, the use of sodium silicate as a part of the buffer system will give asomewhat better brightness than otherwise. It further appears that the reac-tion should be stopped a little short of complete chlorine consumption inorder to realize the maximum brightness. The addition of sulfur dioxide atthe end of the reaction is usually beneficial to brightness, but it does notimprove its stability.

Effects of Bleaching

Brightness

The brightness of the hardwood pulps reported . on here was increased from 8 to23 points with calcium hypochlorite at the level of 10 percent availablechlorine. It is shown in table.1 that those increases resulted in brightnessvalues of 70 to 79 percent for the bleached pulps. In some instances, with,for example, the sugar maple and sweetgum pulps, sodium hypochlorite gave from4 to 8 points higher brightness values than calcium hypochlorite. In general,however, calcium hypochlorite gave higher brightness values for the hardwoodground pulps than did sodium perioxide under the conditions used.

Pulps made from two different lots each of quaking aspen, paper birch,yellow-poplar, and sugar maple woods were studied to note possible variationswithin species. Although little difference was observed between the lots ofaspen and paper birch, the results obtained for the yellow-poplar and sugarmaple pulps indicate that variation within some species is to be expected.The experience with the two lots of yellow-poplar was especially interesting.The fresh pulp from lot II in its natural condition did not respond to hypo-chlorite nor to sodium peroxide. When the pulp was extracted with alcohol,however, either before or after treatment with 10 percent chlorine ascalcium hypochlorite, a brightness increase of 7 points resulted. Thealcohol removed a yellow-colored material. After a portion of the unex-tracted pulp at about 25 percent density had been in storage about 50 daysat 5° C., it did not respond to hypochlorite, but another portion at thesame density after storage at room temperature during the same period didrespond to the extent of 11 points in brightness.

No difficulty was experienced in bleaching a pulp from a mixture of hardwoodscomprising 29 percent each of red maple and paper birch, 16 percent eachsugar maple and yellow birch, and 5 percent each of white ash and Americanbeech by weight. On a volume basis, the percentage values were essentiallythe same as on the weight basis because of the similarity of the specificgravities. The optimum conditions for calcium hypochlorite bleaching werethe same as for the other hardwood pulps. Uhen a brightness value wascalculated for the mixture on the basis of direct proportionality from theexperimental brightness values for the bleached pulps from the individual

Report Not 4.736

woods, the calculated value agreed with the value determined experimentally.Although pulps from two of the component woods, white ash and American beech,contained numerous shives that were not bleached satisfactorily, there was noevidence of unbleached shives in the bleached pulp from the mixture.

The brightness values obtained for the softwood mechanical pulps indicatethat, as a class, they do not respond well to hypochlorites. Of five soft-wood pulps, only a white spruce pul p reached a brightness value possibly ofpractical significance when treated with 10 percent available chlorine ascalcium hypochlorite. With sodium hy pochlorite equivalent to 10 percentchlorine, a southern yellow pine pulp reached only 63 brightness, with theincrease being 8.5 points. The Eastern white pine pulp required 15 percentchlorine as calcium hypochlorite for a brightness approaching 70, and eventhen the bleached pulp was quite yellow in hue.

The use of silicate in conjunction with lime as the buffer system with calciumhypochlorite gave no improvement in the brightness of the Eastern white pinepulp. The use of sodium hypochlorite or extractions with hot water, sodiumhydroxide, or hydrochloric acid had little effect. Extraction with alcohol,however, removed a yellow material; and when the extracted pulp was treatedwith 10 percent chlorine as calcium hypochlorite and this was followed with afinal treatment with sulfurous acid, a brightness increase of 4.2 points re-sulted. At the present time, hypochlorites show little promise as practicableagents for bleaching softwood mechanical pulps.

stability of Brightness

Relative stability of the brightness of the mechanical pulps after bleachingwith hypochlorites is compared to that of those bleached with sodium peroxideby the recession values given in table 2. The values were obtained byexposure of test sheets to single-arc carbon arc light. Because of differ-ences in exposure time, all pairs of pulps are not directly comparable, butit appears that the greater proportion of recession effected by carbon arclight occurs at the end of 1 hour (5). The data show that the brightnessof pulps after bleaching with hypochlorite was less stable than afterbleaching with sodium peroxide, The hardwood Pulps bleached with hypo-chlorite, including the mixed hardwood pulp, retained, however, 50 to 80percent of the original brightness increase. Owing to a generally higherinitial brightness than that of the peroxide-bleached pulps, they were atleast as bright as the latter after both had been subjected to exposure.

IHue

Because of the hue of mechanical pulps, either bleached or unbleached, thebrightness value alone is inadequate to characterize appearance. Conse-quently, the appearance of the pulps dealt with in this report is given interms of brightness, dominant wave length, and purity (2), as shown in table1. It was previously suggested (4) that a yellowness value (3) might be asufficient supplementary value for a numerical comparison of the appearanceof bleached groundwood pulps. Further experience, however, indicates that

Report No. 81736 -4-

the usefulness of the yellowness value is limited, apparently becausebleached groundwood pulps are too far removed from the degree of whitenessfor which the yellowness value was originally intended to be used, Theamber, green, and blue filters used in the tristimulus measurements had maxi-mum transmission values of approximately 590, 555, and 156 millimicrons.

The range of dominant wave length for all pulps, both bleached and unbleached,was from 562 millimicrons for the hypochlorite-bleached white spruce pulp toabout 582 millimicrons for the unbleached yellow birch and sugar maple pulps.The range for green is considered to be 500 to 570 millimicrons, and that foryellow, 570 to 590 millimicrons (2). On that basis, the experimental pulpswere all essentially yellow in hue. If 580 millimicrons are taken arbitrar-ily as yellow, the indication is that bleaching with hypochlorites consist-ently gives hues slightly toward the green, or lower, wave length. Withsodium peroxide the trend toward the green is, in general, the same, butthe effect is slightly less, In general, the purity of hue resulting fromhypochlorite bleaching appeared to be about the same as that resulting frombleaching with sodium peroxide, The high purity values of the bleachedyellow-poplar II (table 1), Western hemlock, and the Eastern white pinepulps after bleaching with 10 percent available chlorine accords well withtheir strong yellow appearance.

Yield

The yield values given in table 1, determined without loss of fiber, showthat losses in weight due to the chemical action of calcium hypochloriteaveraged 0.9 percent, with a maximum of 2.7 percent. Those results appearvery favorable in comparison to those obtained with sodium peroxide.

Freeness and Strength

All of the experimental pulp were not made under grinding conditions foroptimum freeness and strength. Consequently, the effect of bleaching onthose properties is expressed as a percentage change in table 3.

A decrease in freeness was obtained more frequently than an increase, withthe changes ranging from a negligible to an appreciable amount. Althoughthe percentage values for changes in bursting strength were large becausethe bases for calculation were all small, they represent only small actualchanges in points. The same was true of the changes in tearing strength.Since there was no definite trend toward higher or lower values, it isapparent that there was no significant effect of bleaching on bursting andtearing strengths.

There was a definite trend toward relatively large increases in tensilestrength as a result of hypochlorite bleaching, although the tensilestrength of the southern yellow pine and American beech pulps was decreasedabout 80 pounds per square inch, With those two pulps excluded, the averageincrease in tensile strength was 365 pounds per square inch, the maximumbeing 972 pounds per square inch, As previously reported (4), a somewhat

Report No, 81736 -.5-

smaller increase in tensile strength can be expected when bleaching withsodium peroxide.

Hardwood and Softwood Mixtures

The possibilities of processing mixtures of hardwoods and softwoods are ofinterest to manufacturers lof groundwood papers. Results are given in table4 of hypochlorite-bleaching experiments on stocks composed of mixtures of anEastern white pine groundwood with one made from a mixture of hardwoods.

The failure of the Eastern white pine pulp to respond to a treatment of 10percent available chlorine as hypochlorite, except for improvement intensile strength, was discussed above. When mixtures of the pine and mixedhardwood pulps were treated with 10 percent available chlorine as calciumhypochlorite, the brightness was increased in proportion to .the amount of'iardwood pulp in the mixture. This is shorn by the fact that the experi-mental values can be calculated almost exactly on a direct proportionalitybasis from the brightness values of the unbleached pine pulp and of thebleached mixed hardwood pulp. The indication is that when the mixture ofthe unbleached pine and mixed hardwood pulp was treated with hypochlorite,the effective rates at which chlorine was consumed by the two pulps wereequal despite the large difference in the reaction times when the pulpswere bleached separately.

In the preparation of a mixed pulp in the brightness range of 65 to 73 fromEastern white pine and mixed hardwoods of the composition dealt with here,less chlorine would be required by mixing unbleached pine pulp with hypo-chlorite-bleached hardwood pulp than by bleaching the mixture with hypo-chlorite.

Report No, 81736 -6-

Literature Cited

(1) Andrews, I. H. Zinc Hydrosulfite Treatment of Groundwood. Pulp &Paper Magazine of Canada 46(9)679-81,, Aug. 1945. Pulp cc PaperIndustry 19(8)58, 60, Aug. 1945.

(2) Hardy, Arthur C. and staff. Handbook of Colorimetry. The TechnologyPress, Cambridge, Mass. 1936.

(3) Hunter, Richard S. Photoelectric Tristimulus Colorimetry with ThreeFilters. Natl.Bureau of Standards Circ. C429, July 30, 1942.

(4) Kingsbury, R. M. Simonds, F. A., and Lewis, E. S. Observations onBleaching Groundwood Pulps, Paper Trade Jour. 126(24)49-59,June 10, 1948. Pulp & Paper Magazine of Canada, Oct. 1948.

(5) Lewis, Harry F., Reineck,, Edward A., and Fronmuller„ Douglas. TheFading of Groundwood by Light. Paper Trade Jour. 120(8)44-48,Aug. 23, 1945.

(6) McEwen, Robert L. High Density of Mechanical Pulp with HydrogenPeroxide. Paper Trade Jour. 122(17), Apr. 25, 1946.

(7) Reichert, J. S. Sodium Peroxide Bleaching of Mechanical Pulps.Paper Trade Jour. 118(11)45-52, Mar. 16, 1944.

Report No. 81736 -7-

Table 1.--Influence et hvpochlorites and sodium peroxide on appearance and yield of mechanical pulp.

_ Specie, :Bleaching agent1-: Stock :Temper-: Alkalinity :Duration : brightness-2:Dominant wave length: purity :Yield of

:density: ature : : or • .1 : :bleat.hqd: Lind :Amount : :Initial: Final:treatment:Unbleathed:Bleached:Unbleached:Bleached :Unbleached:Bleaohed: pulp4I t i •

. : pulp : null, : pulp : pulp : pulp : pulp • : • : : : : : : : : :

:Peroent:Percent: .0: : pa : 2ff :Hr. :Min.: Percent : Percent: Mmu. : Mau. : Percent : pervlal:fIrclulk

Hardwood.

Sweetgum :os(o0112: 10 : 6 : 35 : 10.7 : 8.6 : 1 1 : 53,5 : 74.1 98.8

Black tupelo :101.:02

11,2;12 1

1040 10.4: 9.0 r 2 2

. , 10.6 : 36 : 10.9 : 10.0 : : 4 :

53.5 98.8

Water tupelo TaLF:5 21}212 10.3: 9.2 , 2 3 : 61.3 657

10 2 41 : : . : . '

7 2.6 *

6 : 35 : 11.3 : 8.2 1 , : 66.0 : 73.9

100.0

97.599.3

2 66.0 : 76.6 • 100.0

Yellow-poplar I lia3F2.g 11, 21 1012 ' '40 ' 10.5 : 9.2 : 2 2 1 :6 : 37 : 11.1 : 8.9 1 1 : : 61.0 72.0 : 98.8

2 12 : 41 : 10.3 : 8.5 1 4 1 • 61.0 • 70.3 • 99.0Yellow-poplar .//tc:011, 2 10 6 : 37 - : 11.7 : 8.3 : 1 ; : k : li

Eastern ;;_11:FO 112:2

10 12 I 40 : 10.3 : 9.2 2 1

46 : '34 : ,11.4 : 10.0 : : •

:

,1.3 --3.0 : 578.2 : 576.5 :-. 10.5 : 16.1 61.3 : ‘60.5 578.2 577.5 : 10.5 : 13.

96

52.z : 271.2 : 580.4 : 576.5 : 13.5 : 9. :

qur,Itznaloped. I ;g:f0S1)2 2f 2

12 1 42 : 10.7 : 9.7 : 1 : : 52.2 : 66.7 : 580.4 : 577.2 : 13.5 1 10.2 2 19947.311.2 : 8.5 : I : 63.4 : 75.7 •10 : . . 99.2

6 : a.

: 10.5 97.9

: 8.7 : 2 1 63.4 : 77.0 ' 97Quaking aspen IIIICI:fgal)2;'

2 1 10 6 : 27 . 1 11.0 : 8.4 : 2 : 3 : 63.5 : 76.0 : 576

.5, .5 : -573.5 : 9.9 : 7.9 : ..

TX61)2; 2-12 1 40 : 10.3 : 8.5 : 2 : 4 : 63.5 2: _76.9: 576.5 : 577.0 : 9.9 : 6.0 '

6 : 36 --Paper birth I 10 : 10 .5 : 8 .9 : 2 4 : 59.0 275.0 • 11.3 '

Paper birch II ; g:FgL) 2 : 212 41 :

101

6 : 3010.2 : 8.5 2 2 : 59.0 : 75.612.018.8:2:51.560279.0:5743.84.3

: 8.3: .3 ... :28 2 42 10.3 : 8.8 : : 3 1 56.3

Yellow birth 10

; 241?g61) 2 ; 228 : Z?

11.9 : 8.4 1 2 : 4 :10.3 2 9.0 2 : 2 I 53.8

: 575.0 : 12.0 : 8.7 : 99.753.8 i liv. 11 gm t 5.79.5 : 14.3 : 88:77 •

98.

Sugar maple I 10

; 1=61) 2 : 2 6 : 36 3.1.0 : 10.1 : I 2 z

: 113..8

._6.9 : 581.2 : 580.0 : 12.0 : 10.5 : 98.6266.0 : 581.3 : 570.0 : 15.7 : 6.0

Ma0C1, : 10 6 : 35 1 11.4 1 9.2 : 1 4 :

:Na0C12 I 10 6 11.2: 9.0 : 1 : :71.3 1 581.3 2 575.3 : 15.7 : 6,4

49.5 : 74.2 : 581.3 4 576.7 I 15.7. : 9.111e,,0,• : 2 12 ; ?i54 '; 10.5 : 7.3 : 1 : 2 49:5 12 55.0 1 581.3 1 580.0 1 15.7 : 12.4 : 96.2

Sugar maple' II 180081)2 1 10 6 : 577.1 1 12.0 : 7.6 : 97,31842021 2 12 ; 41

, 1 12.3 ! 8.6 : 2 : 57.9 178.6 : 581.2I 10.3 : 9.1 : 1 : 1 57.9 : 71.4: 581.2 : 577.5 : 12.0 : 6.0 : 99.8sil. 11202 : 2 28 1 42 I 10,4 : 9.3 : I 4 : 57.9 : ,73.9 : 581.2 : 574.4 : 12.0 : 7.6 : 98.9

Red maple 10.(001)21 10 6 1 30 : 12.0 : 8.3 2 1 : 4 : 57.6 1 278.9 1 580.0 : 575.0 : 10.5 . 99.32 .3, 4:99.

Ash, white :104:Fggli2 1028 1 39 : 10.6 9.2 : : 4 t 57.6 72.6: 580.0 : 577.8 1 10.5 16 : 31 : 11.7 : 8.0 : 1 : 1 : 57 274.8 : 577.3 : 571.4 : 11.3 : 10.0 2 99.8.2 ;

teag1)2: 228 43 : 10.2 : 9.3 2 57.2 ‘70.6 : 577.3 : 572.4 1 1/.3 : 9.0 99.1

American beech 10 6 : 30 : 11.5 : 8.0 : 1 : 4 : 49:1 : a72.0 : 580.4 : 576.0 : 13.5 : 11.3 : 101.0

2 28 : 40 : 10.3 : 9.8 : : 30 : 49.1 : ,62.0 580.4 578.2 : 13.5 : 12.1 : 99.4

Mixed hardwooder081) 2; 10 3 : 30 1 11.6 : 8.3 : 2 I 15 : 54.5 : 277.2: 580.9 : 576.0 1 12.0 I 9.1 : 99.0

'84202 • 2 28 1 42 : 10.4 : 10.1 : : 25 , 54.5 • 70.9 : 580.9 • 576.5 • 12.0 : 9.9 : 99.2

Softwoods

Eastern white zCs.COC1)2: 10Pine ,c.(0C1121 15

iMe.202 2 2Southern - yellow :Ca(0C1) 2 : 15

pine 01.001 : 10:11.,02 2Tack pine t0e2COC1/2: 15

White .prateIN,21

2!2

1002(2000 10

:0222.(0C1 2 1 15! 2

Western bowie,* a(001) 2 . 10zNa0C1 : 101. 842°2 ! 2

6 : 31 : 11.2: 9.9 1 : 33 63.5 • i23.4 : 578.5 : 577.8 : 12.0 : 14.3 6 : 30 : 11.4 : 10.1 : 1 : 37 : 63.5 : 9.6 : 578.5 : 576.5 : 12.0 : 11.4 : 99.428 1 41 : 10.7 : 10.2 : : 15 :10 : 36 : 11.3 : 10.9 : 1 : 55 :

g2,..3 ; 2:g ! 578.5 : 576.0 : 12.0 : 9.9 : 99.599.o

10 : 36 : 11.4 , : 9.1 : 1 : 50 • 54.5 : 63.o • 97.612 : 42 : 10.3 1 9.1 : 3 : 0 1 54.5 : 65.5 97.510 : 36 : 11.3 1 10.2 : : 20 : 57.1 : 60.6 99.312 : 45 : 10.3: 9.1 : 4 , 0 : 57.161.7 • 96.76 : 25 1 11.1: 9.6 : : 40 : 61.4 : 467.9 100.66 : 25 : 11.2 : 7.9 : 2 : 0 : 61.4 : 274.0 577.0 • 11.7 : 100.012 : 40 : 10.4 : 9.6 : 1 : 30 i 61.4 : 70.9 1 11.1 : 100.06 : 37 : 10.3 : 9.6 : 2 10 : 48.9 : ,45.0 : 580.0 : 40 : 15.4 : 20.4 : 98.84 : 27 : 12.8 : 12.6 : : 30 : 48.9 : 254.7 : 580.0 15.4 98".812 : 40 : 10.2: 9.9 : 1 1 0 1 48.9 : 52.2 : 580.0 I 580.0 : 15.4 ! 15.8 ! 98.2

1 [

1Percentage values refer to weight of available chlorine, sodium peroxide, or other chemicals and are based on unbleached pulp. The calciumhypoohlorite solution contained 0.3 to 0.7 percent free alkali as hydroxide and required 1 to 6 percent additional lime for adjustinginitial pH. The sodium hypoohlorite contained 3.6 percent free alkali as hydroxide and required up to 2 percent additional caustic foradjusting initial pH. The peroxide bleaching solution contained 2 percent sodium peroxide, 5 percent sodium silicate, 0.05 percentmagnesium sulfate, and up to 1.5 percent sulfuric &old to adjust initial pH.

2Measured on air-dry teat sheets. Except as noted, test sheets of the hypochlorite-bleached pulps were formed at pH 7.5 from pulp washedwith tap water of pH 7.5. In the case of peroxide-bleached pulps a final adjustment of pH to 5 was made with eulfurous acid and thetest sheets were formed at pH 5 from unwashed pulp.

IBased on unbleached pulp.

-This sample of pulp was freshly made. When bleached after 53 days . storage at room temperature the brightness obtained was 71.5 percent.IA final adjustment of pH to 5 was made with sulfurous acid and test sheets were formed at pH 5.0 from unwashed pulp.

Two percent sodium meta silicate was added to the bleach mixture.

2Twenty-nine percent each of red maple and paper birch, 16 percent each of sugar maple and yellow birch, and 5 percent each of Americanbeech and white ash on • weight basis and essentially the same by volume.

K 79943 P

Table 2.--Recession of brightness of bleached groundwood .ulps upon exposureto carbon arc light

Pulp :•

:

Bleaching

agent': Brightness : Duration : Recession: increase when : of 2: bleached : exposure- ::

Points : Hours : Points:

Paper birch I : Ca(0C1)2 : 16.0 : 2 : 7.9: Na202 16.6 : 2 : 8.6

Paper birch II ! Ca(0C1) 1 22.6 : 1 : 9.9

Yellow birch

Na202

Ca(0C1)2 :

19.8

19.7

: 1

1

:

:

7.74.2

Sugar maple I

2

:

Na202

-Na0Cl :

13.1

24.7::

1

2

:

:

3.38.7

: : 5.5 : 2 : 4.5Sugar maple II : Ca(0C1) 2 : 20.7 : 1 : 10.6

: Na_ 2 _0 2 16.0 : 1 : 5.3Red maple • Ca(0C1) ' 21.3 1 9.1

Na2 0215.0 1 5.8

White ash : ca(oc1)2Na202

, 22.413.4

::

11

::

6.85:5

.American beech • Ca(0C1) 2

Na2 02! 22,9

12.9 :1 : 6.4

4.3

Mixed hardwood ••. Ca(0C1)2

:: 22.7 •. 1 : 7.6

Ns 0_. _.2 _2 : 16.4 : 1 : 5.2

Eastern cottonwood : Ca(0C1)2 : 21.0 2 : 8,7: Na202 14.5 2 : 4.7

Eastern white pine 2 --Ca(OC1) 2 1 6.1 1 : 12.1Na2 o2 4.5 1 : 2.4

:White spruce 'Ca(0C1)2 : 6.5 2 : 13.1

•:

5-Ca(0C1)2 : 12.6 2 : 18.3

• Na2°2 9.5 2 : 11.5

-The amount of hypochlorite was 10 percent expressed as available chlorine,except in the two instances footnoted, and the amount of sodium peroxidewas 2 percent.

?Single-arc, carbon arc light.

-Two percent of sodium metasilicate was added to the bleach mixture.4-Twenty-nine percent each of red maple and paper birch, 16 percent each of

sugar maple and yellow birch, and 5 percent each of white ash and Americanbeech on the weight basis.

-Fifteen percent available chlorine.

Report No. 81736

Table 3.--Change in freeness and strength resulting from bleaching ground-

wood pulps with hypochlorites.

Pulp : Bleaching : Freeness :Bursting:Tearing :Tensile: agent : :strength:strength:strength: :Canadian:Shopper-: : :: :standard: Riegler: : :

••nn• -----r-:

:Percent :Percent :Percent :Percent : Percent-------

Sweetgum : Ca(0C1) 2 : -1: Na0C1 :

1Black tupelo I : Ca(0C1) 2 :: Na0C1 : -11

Black tupelo II : Ca(0C1) 2 : -23: Na0C1 : -16

Water tupelo : Ca(0C1)2 : -19

Yellow,Toplar I : Ca(OC1) 2 : 27Quaking aspen I : Ca(0C1) 2 -35Quaking aspen II : Ca(0C1) 2 : -20

Sugar maple I : ?Na0C1 -3Red maple : Ca(0C1) 2 / 6White ash : Ca(0C1) 2 : 4.12

American beech : ,Ca(0C1) 2 ; 14

Mixed hardwood : Ca(0C1) 2 : -1: 3 :

Eastern white pine : -Ca(0C1) 2 : 5

Southern pine t Ca(0C1) 2 : -24: 4a(oc1) 2 ; -3

4 :

-The amount of hypochlorite, except as noted, was 10 percent expressed asavailable chlorine.

?Two percent sodium metasilicate was added to the bleach mixture.

-Fifteen percent available chlorine.

: -10 : 57 : -8 : 80

: -13..6:

:8527

::

-1420

::

9535

: -11 : 36 : 22 : 55: -4 : -24 : 75 : 294: -4 : -34 : 42 : 260: -6 : 20 : 67 : 1i2

3 ' 33 ' 0 : 52: -19 ; 110 : 33 : 132

: -17 1 45 25 : 94

3 22 5 35; -4 ; 19 : -17 : 38

: 6 : 0 : 0 : 11

: -12 ! -25 : 11 -15

: 25 : 70 : 107 : 198:

2

6

;

•

22

-83

,

'

-2

-8:::

42

-12: -3 : 0 -8 11

Report No. 81736

cd 11) •0 Cr\

11)

4-2 3 a)4-3

cr14-2

04) 004 .0

440

n0 0

H CD 0..,0

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