US2353823A - Bleaching cellulosic materials - Google Patents

Description

Patented July 18, 1944 BLEACHING CELLULOSIC MATERIALS Clifford A. Hampel, Niagara Falls, N. Y., assignor to The Mathieson Alkali Works, Inc., New York, N. Y., a corporation of Virginia No Drawing.

Application September 26, 1941,

Serial No. 412,438

produced by the kraft process, the sulfite process Claims.

It has hitherto been proposed to bleach cellulosic materials with aqueous solutions of chlorites. Such bleaching processes have the general advantage that, properly applied, the degradation of the.

cellulosic material normally incident to the use of conventional bleaching agents, such as chlorine, hypochlorites and permanganates, particularly when a high degree of bleaching is required, is avoided. My invention relates to improvements in the bleaching of cellulosic materials with chlorites and in completing the bleaching of materialspartially bleached with such conventional bleaching agents.

I have discovered that cellulosic materials can be bleached to an exceptionally high degree, as reflected by whiteness for example, without substantial degradation, as reflected by loss of strength for example, by subjecting the cellulosic.

material to the joint action of chlorites and persulfates in aqueous solution at a pH of about3-11. The useful chlorites comprise the chlorites of the alkali metals and the alkaline earth metals, such as sodium chlorite, NaClOz, and calcium chlorite, (Ca(Cl O2) 2. The useful persulfates comprise the persulfates of the alkali metals, such as sodium persulfate, Naisnoa, and potassium persulfate, K2S20a, and the persulfates of the alkaline earth metals. Temperatures and concentrations are widely variable. Increased temperature increases the rate of bleaching. The ratio of chloriteto persuliate may vary widely, although a molar ratio of 2:1 is generally useful. The consistency of the bleaching solution, the ratio of the weight of the cellulosic material to the weight of the- 'solution, may also vary over a wide range. For

example, the bleaching of pulp can be carried out at pulp consistencies of about 5%, as in conventional practice, or at much higher consistencies such as l5% and 25%. At higher consistencies, higher concentrations of chlorite and persulfate can also be used to accelerate the bleaching rate.

The bleaching is with'advantage carried out at lulose fibers derived from wood or woody material by any of the generally practiced fiber liberation processes and to the bleaching of cellulose fibers commonly used in textile manufactures. My invention is applicable to the bleaching of wood pulp chlorite.

and the soda process, to the bleaching of cotton linters, of hemp, of derivatives of cellulose such as rayon and of woven fabrics produced from cellu- The bleaching of my invention is useful, with particular advantage, in a combined operation in which the cellulosic material is partially bleached with one or more conventional bleaching agents and in which the bleaching is completed with a chlorite and a persulfate in accordance with my invention. The partial or preliminary bleaching canbe carried to a degree short of that at which substantial degradation of the cellulosic materials begins and the bleaching then carried to a high degree to produce a product of the combined steps of exceptional whiteness, for example, and of unusually high strength. For example, kraft pulp can usually be bleached to a degree characterized by a whiteness in the range of 70-78 (G. E. reflectometer) without substantial degradation by conventional practices-with chlorine or a hypo- By applying my invention, such partially bleached pulp can be brought to a whiteness of 85 or better, for example, without loss of strength or'other degradation.

My invention will be further illustrated by the following examples;

Example I r 125 grams ofa kraft pulp were added to 2500 cc.

of an aqueous solution containing 0.96 grams of sodium chlorite and 1.25 grams of sodium persulwashed. The following physical tests were conducted at F. and 50% relative humidity:

Original Bleached p p p p Total available chlorine applied. Q erccnt Total available chlorine consumednfndouu H 1:96 Bursting strength (Mullen) l. 51. 0 50. 7 Tearing strength (Elmendori) 48 50 Tensile strength (Schopper) 207 191 Brightness (percent reflectance wi l filter m G. E. reflectometer) 78 87. 16

Example II gram or sodium chlorite and 1.25 grams of sodium persulfzitc. This suspension was brought to and maintained at a pH of 7.5 with half normalsodium hydroxide, the pH being checked at regular intervals. The suspension wasmaintained ata temperature of 7080 C. for two hours and the pulpwas then separatedand washed; The fol: lowing. physical tests Were relative humidity:

Original Bleached p p p p 'luial available chlorine applied... percent; .J. 1.0 'lotul available chlorine consumed do f 0.31 Bursting strength (Mulleni. 51.0 50.0 'lcuring strength (Elmendorf)..- 48 l 47 'Iensile strength (SChOpfiil) 207 200v liriuhtness (percent re eetance v with No. l filter in G. E. rcflectomete 78 I 87. 67

.. Example III 125" grams of the same kraft. pulp were added to 2500 cc. of an aqueous solution containing096.

gram of sodium chlorite and"1.25-grams oi sodium persulfate. The suspension was bufiered" at a-pI-I of 8.5 with half normal sodium hydrox ide, the pH being" checked at"regular intervals.

Thissuspension' was maintained at aftempera,

ture of 75 80 C. for two hours and the pulp was then separated and washed. The following physical tests were conducted at 70; F. and0%' relativehumidity:

made at 70fF. and 50% or trisodium phosphate'and 1.0 gram of sodium Original Bleahhed P. D D D' h p Total available chlorine applied... percent.. ..i.0 V Total available chlorine consumed do i'. 0; i0 Bursting strength (Mullen)'.. .f 4 5 'learing strength (Elmendori 7 J5 Tensile strength (Sehopper) 207 Brightness (percent reflectanc 1 40 filter in G. E. reflectometer) I 47. 42

.. h ExampleIV- 125 grams of 2500 cc. of an aqueous solution.- containing"4.8v grams of sodium chlorite and6.25 grams of so; dium persulfate. This suspension was buiTered at a pH 01"9 with half normal sodium hydroxide, the'pI-I being checked at regular intervals.

The suspension-wasmaintained at a tempera.- 1

ture 0L2? C. for two hours and the pulp was then separated and washed. The following phys ical tests were conducted at 70 F. and-% relative humidity;

Original Bleached pu p p' Total available chlorine applied..- peroent. 5.0 Bursting strength (Mullen). 51.0 51.1 'lenring strength (Elmendori). 1 48 47 Tensile strength (Schopper)..-. 207 191- Brightness (percent reflectance h N l :filter in G. E. reflecto neter) V 78 83. 91

)7 Example V vkraft 'p ulp w ere suspended in Original Bleached pulp pulpv Total available ehlorineapplied. percent" l. 5 Bursting strength-(.\lullen). 51.0 49.8 Tearing strength (Elmendorf) 48 46 Tensile strength (Schopper) 207 217 Brightness (percent reflectance with No. 1

filter in G. E. reilectometer) -L 78 83. 42

Example Vi 12-5 grains ofanother kraft pulp were added to 2500-"ce'. of an aqueous solution containing -:-0.96 gram of sodium .chlorite and 1.25'grams of sodium persulfate.

The suspension was. buffered at a pH of 9.1 with"half 'norma1 sodium hydroxide, the pH being checked, at regular intervals. This suspensionwasmaintained at :60? C. for. two hours'andrthe pulpv was'then separated and washed. ,The followingphysieal tests were made at F. andz50% relative'humidityz Original "Bleached p p: :p p.

Total available chlorine applied .percent. v 1. 0: Bursting strength (Mullen) 51.0 49. 6 'learing strength (Elniendori).... 48 45 -'lensile strength (Sehoppvr) 207 v I 200 Brightness (percent'reilectance with No. 1

filter in G. E. reileetometer) 84. 5

Ercdrnple VII pieceof 'uritreate d greig e cotton muslin, x 80 threads per inch, weighing 36 grams and measuring 12inches by 38 inches; was placed in 500 ccfof water containing 1.5 grams of sodium chlorite, 2.0 grains ofsodium persulfate. .LOQgram ethane 1-palmitate 2 -su1fonate. This solution, with the cloth init, was maintained at a temcloth was then washed, soured, in aqueous sulfuriea'cid containing 1% jIC lfiSOQ rewashed'and ironed dry. The brightness was increased from 5638 to 82.5,"the absorbency was good,j,the starch removal was 'quite'complete, all motes had been removed and thejclotl had notheentendered.

" Example VIII 36 gramsof the same muslin in 500 oc.of,wa, a .ter containing 1.0 gram of sodiurn chlorite, 2

grams of sodium persulfate, 1.0 gram of .trisodiurn phosphateandJLO gram of sodium ethane 1- palmitate 2-s'ulfonate vweren' aintainedat a. tem

perature bf C.1for thirty minutes. I The cloth was then washed, soured with aqueous1%"I-IaSO rewashed and ironed dry. :The brightness was 1 increased from 56.8 to "83.5, the'absorbency was good, starch removal was quite complete, the- 4 motes had been removed and thecloth had not 1 been tendered.

'125 grams of anotherkraft were Inbred. 1

with-840 cc. of an aqueous solution containing 1.44 grams of sodium-chlorite and 1.5 grams 01 sodium persulfate, bufiered at a'pH of 8.5 with half normal sodium hydroxide, the pH being checked at regular intervals. This suspension had a consistency of'15%. .The suspension was maintained at a temperature of 35-43 C. for

two hours and the pulp was then separatedand "Exa ple I f 1 36 grams of the same. muslin. in=500 cc. of water containing 0.5 gram of sodium 'chlorite, 1.0 gram of sodium persulfate,.1.01 gram of trisodium phosphate and 1.0 gramof'sodium ethane 1-palmitate -2-suifonate were maintained at "a temperature of.

95C. for one hour, Theeloth wasthen washed, soured with; aqueous 1% Hzso urewa'shed and ironed dry. The brightness was increased from 56.8 to 8 2.3, the-absorbency was good. the starch and mote-removal was quite complete and the "cloth had not been tendered.

washed. The following physical tests'were cond l duced at 70 F. and 50% relative humidity:

l which steam was passed for ten minutes. cloth was then washed and soaked in an aqueous Example X 18 grams of the same muslin were soaked in an aqueous solution containing grams per liter of sodium chlorite, grams per liter of sodium persulfate and 50 drops per liter of sodium diamyl sulfosuccinate as a wetting agent, buffered at a pH of 8;8. The cloth was then drained until it held about its own weight of solution and then hung in a vessel through which steam was passed for ten minutes. The cloth was then washed. soured, rewashed and ironed dry. The brightness was increased from 56.8 to 78.

Example XI 18 grams of the same muslin were soaked in an aqueous solution containing 20 grams per liter of sodium hydroxide, 2 grams per liter of sodium chlorite and 50 drops per liter of sodium diamyl sulfo'succinate as a wetting agent. The cloth was then drained until it contained about its own weight of solution and hung in a vessel through The solution containing 10 grams per liter of sodium 1 chlorite and 20 grams per liter of sodium persulfate, drained until it contained about its own ironed dry. The brightness was increased from 56.8 to 83, thestarch and mote removal was quite complete, the absorbency was good and the cloth had not been tendered.

Example XI! 125 grams of a Swedish kraft pulp were added to 2500 cc. of an aqueous solution containing 0.19 grain of sodium chlorite and 0.37 gram of sodium 1 persulfate. This suspension was buffered at a pH of 8 with half normal sodium hydroxide, the pH being checked at regular intervals. The suspension was maintained at a temperature of 60 C. fortwo hours, and the pulp was then separated and washed. The following physical tests were In one aspect my invention affords important economies. Many complicated processes involving critical controls of time, temperature and concentrations have been devised to effect high degrees of bleaching with minimum degradation but none of them has been entirely satisfactory when applied to produce high degrees of bl aching, and all of them have been expensive to apply. As compared to a number of such processes, the bleaching process of my invention will produc comparable degrees of whiteness with substantial cost savings and without substantial degradation of the cellulosic material. Also, the bleaching process of my invention will produce exceptionally high degrees of whiteness with relatively short bleaching times as compared to a number of such processes.

I claim:

1. In the bleaching of cellulosic material, the improvement which comprises subjecting the material to be bleached to the action of an aqueous solution containing a compound selected from the group consisting of chlorites of the alkali metals and alkaline earth metals and a compound selected from the group consisting of persuliates of alkali metals and alkaline earth metals at a pH of about 3-11.

2. In the bleaching of cellulosic material, the improvement which comprises completing the bleaching by subjecting partially bleached material to the action of an aqueous solution contain ing a compound selected from the group consisting of chlorites of alkali metals and alkaline earth metals and a compound selected from the group consisting of persulfates of alkali metals and alkaline earth metals at a pH of about 3-11.

3. In the bleaching of cellulosic material, the improvement which comprises subjecting the material to be bleached to the action of an aqueous solution containing a compound selected from the group consisting of chlorites of alkali metals and alkaline earth metals and a compound selected from the group consisting of persull'ates of alkali metals and alkaline earth metals at a pH of about 3-11 and at a temperature of about -80 C.

4. In the bleaching of cellulosic material, the improvement which comprises subjecting the material to be bleached to the action of an aqueous solution containing a compound selected from the group consisting of alkali metal chlorites and alkaline earth metal chlorites and also containing a. compound selected from the group consisting of alkali metal persulfates and alkaline earth metal persulfates at a pH of about about 7-11 and at a temperature of about 60-80 C.

5. In the bleaching of cellulosic material, the improvement which comprises subjecting the material to be bleached to the action of an aqueous solution containing a compound selected from the group consisting of alkali metal chlorites and alkaline earth metal chlorites and also containing a compound selected from the group consisting of alkali metal persulfates and alkaline earth metal persulfates at a pH of about 7-11.

CLIFFORD A. HAMPEL.