US2367771A - Bleaching cellulosic materials - Google Patents

Description

concentrations are widely variable.

Patented Jan. 23, 1945 BLEACHING CELLULOSIC MATERIALS Clifford Allen Hampel, Niagara Falls, N. Y., as-

signor to The Mathieson Alkali Works, Inc. New York, N. Y., a corporation of Virginia No Drawing. Application October 8, 1941, Serial No. 414,139

4 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 reslates to improvements in the bleaching of cellulosic materials with chlorites and in completing the bleaching of materials partially bleached with such conventional bleaching agents.

2 I have discovered that cellulosic materials can bebleached to an exceptionally high degree, as reflected by whiteness, for example, without substantial degradation, as reflected by loss of comprise, for example, formaldehyde, acetaldehyde, paraformaldehyde, furfural, b'enzaldehyde,

the 5- and fi-carbon atom aldose sugars and inverted sucrose; All of these compounds are char acterized by'the CHO group. Temperatures and Increased temperature increases the rate of bleaching. The ratio of chlorite to aldehyde may vary widely, although a molar ratio of 1:1 is generally useful.

An excess of the aldehyde does no'damage tothebleached product.

metals, are'pres'ent.

For example, the eflcct' appears whenphosphates'; such as monosodium phosphate and'disodium phosphate, are used to control the pH of the bleaching solution. In the presence of such phosphates, comparable whiteness with a consumption of chlorite less than half that otherwise required can frequently beyobtained- The improvements of my invention are applicable to cellulosic materials generally. My invention isiparticularly applicable; to the bleaching .of cellulose fibers derived from wood'or woody material by any of the generally practiced fiber For example,

liberation processes and for bleaching cellulose fibers commonly used in textile manufactures. My invention is applicable to the bleaching of wood pulp produced by the kraft process, the sulfite' process 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 cellulose fibers.

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 an aldehyde in accordance with my invention. The partial or preliminary bleaching can be carried to adegree 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 awhiteness of the range of 70-78 (G. E. reflectometer) without substantial degradation by conventional practices with chlorine or a hypochlorite. By applying my invention, such partially. bleached pulp can be brought to a whiteness of 85 or better, for ex- ,ample, without loss of strength or other degradation.

[ fMy invention will be further illustrated by the following examples:

Example I perature of 60 C. for two hours 'and the pulp was then separated and washed. The following physical tests were conducted at 70 F. and relative humidity: j

. Original Bleached P p P l Total available chlorine applied percent.-

0. Total formaldehyde applied .do l. Bursting strength (Mullen)- 67. 0 06. Tearing strength (Elmendorl). 57 6 Tensile strength (Schopper) 244 24 Brightness. (percent reflectance filter in G. E. rcflcctometer) 32. 7 67.1

Example I:

This suspension. of 5% consistency, was buffered at a pH of 7.1 by the addition of sodium bicarbonate and monosodium phosphate, the pH being checked at regular intervals. The suspension was maintained at about 25, C. for three hours and the pulp was then separated and washed. The following physical tests were conducted at 70 F and 50% relative humidity:

Original Bleached pulp pulp 'lotal available chlorine applied. .percenL. 0. 23 Total formaldehyde applied .do 2.0 Bursting strength (Mullen).... 51.0 51.4 Fearing strength (E1mcndori). 48 4l Tensile strength (Schopper) 207 207 Brightness (percent reflectance with #1 78 8 1 filter in G. E. reflectometer) Example III 50% relative humidity:

Original Bleached p p p l Total available chlorine applied percent 0.23 Total formaldehyde applied do. 2. Bursting strength (Mullen) 51. 0 48. 5 Tearing strength (Elrnendorl) 207 214 Brightness (percent reflectance with #l filter in G. E. refiectometer) 78 85. 0

Example IV 125 grams of a kraft pulp were added to 2500 cc. of an aqueous solutioncontaining 0.0625 gram of formaldehyde. The suspension was buffered at a pH of 7.1 with a phosphate buffer. The suspension was maintained at a temperature of 50 C. for one hour and the pulp was then separated and washed. This pulp was then added to 2500 cc. of an aqueous solution containing 0.20 gram of sodium chlorite and 0.0625 gram of formaldehyde. This suspension was buffered at a pH of '7.4 with a phosphate buffer. The suspension was maintained at a temperature of 50 C. for one hour and the pulp was then separated and washed. The following physical tests were conducted at 70 F. and 50% relative humidity:

Original Bleached p p P p Total available chlorine applied .percent 0. 25 Total formaldehyde ap lied d 0.10 Bursting strength (Mu len) 41.5 42. 0 Tearing strength (Elmendori) 41 41 Tensile strength (Schopper) 176 104 hiightness (percent reflectance with #1 filter in G. E. reflectometer) 74. 3 83. 1

Example V 100 grams of a kraft pulp were added to 2000 cc. of an aqueous solution containing 0.18 gram of sodium chlorite and 0.85 gram of acetaldehyde. The suspension was buifered at a pH of 7.1 with a phosphate buffer. The suspension was maintained at a temperature of 50 C. for one hour and the pulp was then separated and washed. 76

Example. VI

23 grams of a cotton muslin cloth, previously kier boiled, was soaked in an aqueous solution containing 2.3 grams per liter of sodium chlorite and 0.72 gram per liter of formaldehyde. The cloth was drained until it contained only about its own weight of solution and was then placed in a closed vessel in which it was maintained at a temperature of C. for one hour. It was then washed and ironed dry. The brightness had increased from '74 to 84.2, while the tensile strength. was not affected.

Example VII 23 grams of the same cloth was soaked in the same solution (see Example VI) and was then drained until it contained about its own weight of solution (50% consistency). The cloth was then placed in a closed vessel and maintained at a temperature of about 25 C. for two hours. It was then washed and ironed dry. The brightness had increased from '74 to 84.2, while the tensile strength was not affected.

Example VIII 23 grams of the same cloth (see Example VI) was soaked in an aqueous solution containing 2.3 grams per liter of sodium chlorite and 0.72 gram per liter of formaldehyde, buflered at a pH of 7.0 with a phosphate buffer. The cloth was drained until it contained about its own weight of solution and placed in a closed vessel in which it was maintained at a temperature of 25 C. for one hour. It was then washed and ironed dry. The brightness had increased from '74 to 85.4, while the tensile strength was unaffected.

Example IX 45 grams of damp kraft pulp, containing 10 grams of dry pulp, were added to 165 cc. of water, buffered at a pH of 7.1 with a phosphate buffer. 1.4 cc. of an aqueous solution of sodium chlorite containing 0.0169 gram. of available chlorine per cubic centimeter and 0.5 cc. of benzaldehyde (technical) were added to this suspension. The suspension was then maintained at a temperature of 50 C. for one hour and the pulp was then separated and washed. The brightness had increased from '78 to 81.0, while the strength of the pulp was not affected.

Example X 1.4 cc. of an aqueous solution of sodium chlorite containing 0.0169 gram of available chlorine per cubic centimeter and 0.1 cc. of furfural (technical) were added to 165 cc. of water, butfered at a pH of 7.1 with a phosphate buffer to which 10 grams of dry kraft pulp (similar to that used in Example IX) had been added. This suspension was maintained at a temperature of 50 C. for one hour and the pulp was then separated and washed. The brightness had increased from 78 to 81.1, while the strength of the pulp was not affected.

Example XI grams of a kraft pulp were added to 2500 cc. of an aqueous solution containing 5 grams of NaH2PO4 and 30 grams of NazHPOalZHz-O, 6.25 cc. of an aqueous solution containing 50 grams per liter of available chlorine as sodium chlorite and 7.5 cc. of an aqueous solution containing 9.16 grams per liter of formaldehyde. This suspension was maintained at a temperature or 56-58 C. for one hour, during which period the pH remained between 6.95 and-7.0. The pulp was then separated and washed. The following physical tests were conducted at 70 F. and 50% relative humidity:

Example XII 125 grams of the same kraft pulp used in Example XI were added to 2500 cc. of an aqueous solution containing 37.4 cc. of an aqueous solution containing 33.4 grams per liter of available chlorine as sodium chlorite and 30 'cc. of an aqueous solution containing 9.16 grams per liter oi! formaldehyde. sistency, was bufiered at a pH of '7 by the addition of half normal sulfuric acid, the pH being checked at regular intervals by the use of a Beckman meter. The suspension was maintained at a temperature of 50 C. for two hours and the pulp was then separated and washed. The following physical tests were conducted at 70 F. and 50% relative humidity:

Original Bleached P p P p Total available chlorine applied percent. 1.0 Total available chlorine consumed do 0. 246 Total formaldehyde ap lieddo.. 0.22 Bursting strength (M len) 51.0 49. 9 Tearing strength (Elmendorf) 48 42 Tensile strength (Schopper) 1'07 189 Brightness (percent reflectance with #1 filter in G. E. reflectometer) 78 86 In one aspect my invention affords important This suspension, of 5% coneconomies. Many complicated processes, involving critical controls oi. time, temperature and concentrations, have been devised to effect high degrees of bleaching with minimum degradation. None of them has been entirely satisfactory, when applied to produce high degrees of bleaching, but all of them have been expensive to apply. As compared to a number of such processes, the bleaching process of my invention will produce comparable degrees of whiteness, for example, with cost savings of as much as and more and withoutsubstantial degradation of the cellulosic material.

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 having a pH of about 3-9 andcontaining an aldehyde and a compound selected from the group consisting of alkali metal chlorites and alkaline earth metal chlorites.

2. In the bleaching of cellulosic material, the improvement which comprises introducing the material to be bleached into an aqueous solution having a pH of about 3-9 and containing an aldehyde and a compound selected from the group consisting of alkali metal chlorites and alkaline earth metal chlorites.

3. In the bleaching of cellulosic material, the improvement which comprises subjecting the material to be bleached to the action of an aqueous solution having a pH of about 3-9 and containing an aldehyde, an alkali metal phosphate and a compound selected from the group consisting of alkali metal chlorites and alkaline earth metal chlorites.

4. 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 having a pH of about 3-9 and containing an aide- 'hyde and a compound selected from the group consisting of alkali metal chlorites and alkaline earth metal chlorites.

CLIFFORD ALLEN HAMPEI...