DE1546261C3 - Process for bleaching cellulose for the manufacture of rayon - Google Patents

Description

The invention relates to a method for bleaching soluble cellulose pulps that are used in manufacture of textiles or rayon for tires. Due to the improved bleaching process should properties such as B. the rayon strength and rayon fatigue can be improved. In which improved bleaching processes lack the common chlorination step. Cellulose pulps with high brightness and high viscosity are instead achieved through the combined use of hypochlorite and chlorine dioxide and an alkali extraction.

In the past, chlorination, ie the treatment of cellulose pulp with elemental chlorine gas, was necessary as a pre-bleaching stage in order to produce cellulose pulps with high brightness without degradation. The direct chlorination acts on the lignin in the unbleached cellulose pulp, making it soluble in alkali extractants. The chlorination is therefore generally followed by such an extraction, the chlorinated lignins being dissolved. If the lignin content of unbleached soluble cellulose pulps from softwood, e.g. B. from southern spruce or pine, when using a force digestion process with pre-hydrolysis is about 3 to 4% or when the same type of digestion of hardwood, z. B. Styrax balm and oak, or of grasses, e.g. B. bamboo or bagasse, lignin contents of 1 to 2% before bleaching, then about 80 ¹ Vo of the lignin contained in the unbleached cellulose pulp is removed by a combination of chlorination and caustic extraction. After the chlorination and caustic extraction, further bleaching steps are necessary in order to remove the remaining lignin and colored material in order to produce a very light and pure cellulose pulp.

With the bleaching agents available until 1953 for the final bleaching and cleaning of the cellulose pulp the lignin and colored materials are removed from the cellulose pulp, but will at the same time, the cellulose is also severely attacked or degraded. Generally hypochlorite and chlorine dioxide used in the alkaline range. More recently, however, the application has also been chlorine dioxide in the acidic range is possible and you get very light and clean, bleached Cellulose fibers with little cellulose degradation. The development of more corrosion-resistant Substances and processes for the economical production of chlorine dioxide allow economical use these funds in large quantities.

From US-PS 15 80136 it is known that chlorine dioxide to decolorize organic materials can be used in acidic or neutral solution.

From DT-PS 9 72 448 is a method for treating cellulose with alkali and after removal of the alkali with chlorine dioxide or a chlorite at a pH value of preferably about 4 is known.

However, these known methods do not lead to a cellulose with which a particularly strong and less tiring artificial silk can be produced.

It has now been found that cellulose material,

e.g. cellulose pulps made from hardwood or grass, which have a very low value before the start of the bleaching step Have lignin content, can be bleached in an economical manner, omitting the chlorination step by using a chlorine dioxide treatment or a weak hypochlorite treatment instead is carried out. This process has the bleaching sequence DED (see footnote 1 to table 1), d. That is, there are two bleaching steps with chlorine dioxide and an extraction with alkali in between, whereby the first chlorine dioxide treatment is carried out in an acidic medium. According to one implementation the inventive method can be a bleaching step with sodium hypochlorite before first treatment with chlorine dioxide. This is illustrated in the following Tables explained in more detail. Such an approach is not only practical for economic reasons, but cellulose pulps with improved rayon resistance and rayon fatigue are also produced Cellulose pulps, which are in the normal order, i.e. H. can be bleached with chlorination. This The result has been confirmed in the laboratory and in many tests.

It has also been found that if the chlorination step is omitted, it becomes necessary to Cellulose pulp to remove the minerals in the first stage with an acid, since the Otherwise minerals interfere with the bleaching process and lead to a low brightness of the cellulose pulp. the However, the acidic state present in the normal chlorination step is sufficient to remove the minerals, essentially iron and manganese, and therefore there is no pretreatment in this bleaching process with an acid necessary.

Because Kraft cellulose pulps made from softwood for conversions have about twice the content Have lignin and therefore require about twice the amount of bleaching agent as similar cellulosic pulps from hardwood or grass and because chlorine dioxide is twice as expensive as chlorine, it is created during bleaching of Kraft cellulose brcien from softwood without chlorination considerable additional costs. Against it leads the bleaching of cellulose pulps from softwood by this method compared to the usual methods with chlorination to improve rayon strength, rayon stability and rayon fatigue Values.

Cellulose pulps, also called cellulose reaction pulps, which are specific to conversions, are followed by others Procedure, e.g. B. after the sulfite process, be digested and a relative before bleaching have low lignin content, can also be easily bleached without chlorination, and one obtains compared to similar cellulose pulps bleached with chlorination an improved rayon resistance and rayon fatigue.

For a better understanding of the invention, the following tables 1 to 4 are used, in which all features of the invention are included and in which the new products (N) according to the invention are compared with the comparison products (V) produced using chlorine gas as the bleaching agent. Table 2 shows for example, that suitable for textiles rayon having from without chlorination bleached Bambusbrei in the air-dry state is about the same tensile strength and after oven drying at about 105 ⁰ C for about 16 hours, a substantially better tensile strength compared with rayon of the same type cellulose pulp, the is bleached with chlorination. Tables 3 and 4 show that, within their range, bleaching without chlorination significantly improves the tensile strength in the air-dry state or in the post-dried state and the yarn and cord fatigue of the finished rayon for tire cord.

Table 1 (continued)

Table 1

Bamboo reaction pulp

N V

Raw material
Bleaching process

bamboo
without.
Chlorination

8.4
130

With

Chlorination
8.4
130

Permanganate number

Viscosity (unbleached)

TAPPI T-230,

1 ° / o copper ethylenediamine, cps

Order of bleaching AHDEDH ¹ ) CEHEDH ¹ )

Sample number 224 223

I. Chlorination or
sulfuric acid
(3.0% consistency ² )
60 minutes)

Cl ₂ , »/ 0-2.45

H ₃ SO ₄ , ° / o 0.80 -

Temperature, C 28 27 ⁰

Backlog, avail. - 0.10
Cl ₂ (g / l)

Bamboo reaction pulp N V

If. Alkali extraction or
Sodium hypochlorite
(120 minutes standing time)

NaOH,% 1.39 cps 1.25 NaOCl,% 3.72 avail. chlorine Temperature, ° C 44 71 Consistency ² ), ° / o 12.0 10.0 Final pH 10.3 10.3 Residue, g / l 0.20 - avail. Cl., Residue NaOH, g / l - 0.37 viscosity 28 50 TAPPI T-230, I ¹ Vo copper ethylenediamine,

III. Sodium hypochlorite
or chlorine dioxide

NaOCl,% avail. Chlorine -

NaOH,% -

ClO ₂ ,% 0.62

Temperature, ⁰ C 71

Consistency ² ), ⁰ / «10.0

Standing time, minutes 180

Final pH 4.2

Residue, g / l 0.10 avail. Cl ₂

Viscosity, 27.5 TAPPI T-230
l ° / o copper-ethylenediamine, cps

IV. Alkali Extraction
(10.0% consistency,
120 minutes, 71 ° C)

NaOH, 0/0
Final pH

Residue NaOH, g / l
Viscosity,
TAPPI T-230,
I ¹ Vo copper ethylenediamine, cps

V. chlorine dioxide or
Sodium hypochlorite
(10% consistency)

ClO ₂ ,%
NaCCl,% avail. chlorine

NaOH,%

Temperature, ° C

Standing time, minutes
Final pH

Residue, g / l

avail. Cl ₂

Footnotes at the end of the table

0.50 11.2 0.33 26.5

0.20

71 180 5.1 0.13

1.10 0.43

52

12.0

120

10.2

0.14

27

0.25 11.4 0.21 25.0

0.25

71 180 4.3 0.10

Table 1 (continued)

Table 2 (continued)

Bamboo reaction pulp 5 Filterability by a Bamboo reaction pulp V N V Nylon filter up to ver
plug the filter, N 34 viscosity 26.2 24.8 Vol. Parts 86 TAPPI T-230,
1% copper ethylenediamine, cps IO Sodium hypochlorite ^{: 1} ) (One or more Rayon quality Steps three hours Denier, g long at a consi Tensile, g / denier
Cond. Air dry 174.6 stence of 6.5% and at 173.0 2.41 Temperatures and
former concentrations, 15th Elongation, ¹ Vo cond. 2.41 the one to get the Tensile, g / denier 18.0 desired viscosity Cond. Wet 17.7 1.07 are necessary.) Elongation, ° / u wet 1.09 Final G. E. 91.1 91.0 20th Tensile, g / denier 34.6 Brightness TAPPI Cond. 34.5 0.99 Final viscosity, 16.8 17.8 Strain, % 2.32 TAPPI T-230, Cond. Oven dry 3.2 1 ⁿ / o copper ethylenediamine, cps Tensile, g / denier 16.2 Total proportions (corrected for 35 Cond. Wet, new cond. 0.22 excess chlorine and Elongation,% wet 1.03 Sodium hypochlorite return Heat loss,% 7.5 was standing) Rayon brightness 31.3 69.1 Cl. ,, ° / o 4.05 3.63 3d desulphurized 5.0 69.6 Na'OH, ο / « 7.21 3.40 Rayon staining 71.6 ClO. ,,% 0.82 0.25 desulphurized 43.0 H ₂ SO ₄ , »/ ο 0.80 - 38.2 SO. ,,% 1.89 1.50

') A - sulfuric acid pretreatment, C - chlorination, E - alkali extraction, D - chlorine dioxide, H - sodium hypochlorite.

² ) Share of pulp fibers in the total weight of fibers and liquid.

¹⁾ According to the hypochlorite steps, the pulps are centrifugally cleaned and in each case 30 minutes at consistencies of 5.0 ^o / o, pH values of 2.5 to 3.0 and at temperatures of 51.7 to 54.4 ° C for two Subjected to sulfur dioxide treatments before making viscous, hand-scooped leaves.

Table 2

Bamboo reaction pulp N V

Physically. properties
Basis weight, g / dm ²

Apparent density, g / ml

Brightness,% G.E.

(MgO = - 100%)
Fineness, ^u / o (100 mesh)

Dirt, stains

on 0.465 m ²

6.425 6.425 0.72 0.72 91.1 91.0 21.3 20.3 878 774

Raw material
Bleaching process

No. of the sample
Order in bleaching

Viscous solution, quality
Aging temperature, ° C

Aging time (hours) until
Reaching a viscosity
from 40 cps

Requires. Temperature to
Reaching a viscosity
from 40 cps

Spin viscosity (36 hours)
Filterability ² ) by a
Canton filter,%
Filterability ² ) by a
Nvlon filter, ¹ Vu

Bamboo without with

Chlorine chlorination CO-224 CO-223 AHDED ¹ ) CEHEDO

25.0 25

23.0

35.8 86

25.0 25

23.2

35.7 74

Filter clogged. Chem. Analysis

Paper pulp viscosity 16.8 17.8 TAPPI T-230,
1 o / o copper ethylenediamine, cps

«-Cellulose, o / o 93.3 93.0

^ -Cellulose, »/ ο 5.4 5.7

rCellulose,% 1.3 1.3

Ash,% 0.044 0.038

Hemicelluloses (Pento- 3,7 3,8 sane), ° / o

Resins,%> 0.082 0.106

Fe, p.p.m. 20 22

Si, p.p.m. 46 28

Cu, p.p.m. 7.1 4.4

Mn, p.p.m. 0.4 0.2

7.14 o / o NaOH solubility 10.6 10.4

Copper number 0.60 0.68

') A - sulfuric acid pretreatment, C - chlorination, E - alkali extraction, D - chlorine dioxide, H - sodium hypochlorite.

") The percentage filterability is equal to the volume in ml filtered in twice as much time as 50 ml viscose.

Table 3 15 46 261 8th 7th Harlholz reaction pulp N N Order in bleaching V V Paper pulp variety bleaching A ₁₁ EHDED ¹ ) C ₁₁ EHDED ¹ ) Mixture of styrax Permanganate number Mixture of styrax balm and hardwood viscosity balm and hardwood 4.3 5.6 TAPPI T-230, 4.3 5.6 158 187 1% copper ethylenediamine, cps 158 187 No. of the sample 246 247 248 245

I. Sulfuric acid or chlorination (3.0 ¹ vol consistency, 60 minutes) Cl ₂ , »/» ClO ₂₁ ¹¹ A, H ₂ SO ₄ , ¹ vol pH adjusted to temperature, ⁰ C final pH

Residue, 30 min / 60 min g / l avail. CI ₂

II. Alkali Extraction

(10.0 ¹ Vo consistency, 120 minutes) Temperature, ° C initial pH final pH residue, g / l NaOH viscosity TAPPI T-230 1% copper ethylenediamine, cps

III. Sodium hypochlorite (10.0% consistency, 120 minutes)

NaOCl, «/ ο avail. Cl ₂ NaOH,%

Temperature, ° C final pH residue, g / l avail. Cl ₂ GE brightness (MgO = 100%) heat dry,% viscosity TAPPI T-230 1% copper ethylenediamine, cps

IV. Chlorine dioxide

(10.0% consistency, 180 min, 60 ⁰ C) ClO _2,% NaOH,% final pH residue, g / l availabl. Cl ₂ footnotes at the end of the table

0.75 1.30 - - 0.10 0.10 0.40 0.40 - - 0.79 0.85 - - 2.8 2.8 26.1 26.7 37.8 37.8 2.7 2.7

0.03 / 0.01 0.09 / 0.06 0.02 / 0.05 0.03 / 0.01

0.54

0.32

0.42

54.4 71.1 54.4 71.1 11.2 11.4 11.3 11.4 10.2 9.8 10.4 10.6 0.08 0.17 0.09 0.18 122 141 140 163 - 0.20 - 0.30 - 0.08 - 0.09 - 32.2 - 32.2 - 10.6 - 10.6 - 0.06 - 0.12 - 74 72

134

149

0.40 0.26 0.49 0.42 0.05 - 0.08 - 3.0 3.6 3.0 3.0 0.13 0.16 0.13 0.18

Table 3 (continued)

10

Hardwood reaction pulp V V

bleaching

7.7 8.7 8.0 7.6 0.16 0.09 0.15 0.15 82 84 82 83

126

111

88.4
100

89.4
100

124

112

87.4 102

131

0.18 0.22 0.22 0.20 10.8 10.9 10.9 11.0 0.14 0.16 0.16 0.16 108 120 116 121

0.20 0.20 0.20 0.21 4.3 4.4 4.2 4.3 0.15 0.19 0.16 0.18 0.05 0.06 0.05 0.06 8.2 8.4 8.1 8.0 87 89 88 88

pH after neutralization NaOH for neutralization,%

G. E. Brightness (MgO = 100%) heat dry, ° / o

viscosity

TAPPI T-230

1% copper ethylenediamine, cps

V. Alkali Extraction

(10.0 », Ό consistency, 120 min, 6O ⁰ C) NaOH,%

Final pH

Residue, g / l NaOH

viscosity

TAPPI T-230

1% copper ethylenediamine, cps

VI. Chlorine dioxide

(10.0% consistency, 180 min, 60 ^c C) ClO ₂ ,%

Final pH

Residue, g / l avail. Cl ₂ NaOH for neutralization,% pH after neutralization GE brightness (MgO = 100%) heat dry,%

viscosity

TAPPI T-230

1% copper ethylenediamine, cps

VII. Sodium Hypochlorite

(one or more stages at a consistency of 6.5% over 3 hours at Temperatures and former concentrations that lead to the desired viscosities)

Final GE brightness, TAPPI ² ) Final viscosity

TAPPI T-230,

1% copper ethylenediamine, total cps

(corrected for excess chlorine

and sodium hypochlorite residue) Cl ₂ ,%
NaOH,%
ClO ₂₁ %
H ₂ SO ₄ ,%
SO ₂ ,%

') C ^ chlorination with chlorine dioxide addition, A ^ sulfuric acid with chlorine dioxide addition, H - sodium hypochlorite, D —chlorine dioxide, Ε - alkali extraction.

^s ) The paper pulp is cleaned by centrifugal force and subjected to two sulfur dioxide treatments for 30 minutes each at a consistency of 5.0%, a pH value of 2.0 to 2.5 and temperatures between 51.7 and 54.4 ° C before making viscous, hand-scooped sheets.

116

88.7 101

0.75 1.42 - 0.23 0.84 1.21 0.82 1.22 0.70 0.56 1.09 1.02 - - 0.79 0.85 0.68 0.75 1.00 0.64

Table 4

12th

I hardwood reaction pulp V V

Paper pulp

Number of the sample bleaching in the laboratory Viscous solution, quality aging temperature, ° C Aging time (h) until a viscosity of 40 cps is reached

Required temperature to achieve a viscosity of 40 cps Spinning viscosity (36 h) filterability -) through a Canton filter, ¹ Vo filterability ² ) through a nylon filter,%

Reyon, quality

Hardwood mix

CO-245 C ₁ EHDED ')

26.2 73

25.6

35.3 84

78

100% Sty rax- hardwood- 100 ¹ Vo Sty rax-

balm mixture balm

CO-248 CO-247 CO-246

C ₁₁ EHDED ') A ₁₁ EHDED') A ₁₁ EHDED ')

27
73

86

(Heat gain (+), ° / o draft, loop,
g / denier, air dry draw, knot, g / denier elongation, loop, ° / o elongation, knot, ° / o physical. Properties Basis weight, g / dm Apparent density, g / ml brightness, »/ ο, GE (MgO = 100" / ο) fineness,%, (100 mesh) dirt, stains on 0.465 m ²

Footnotes at the end of the table

2.38 2.49

27.8
73

28.2

43.4
84

2.48

26.2 73

26.0

38.3 90

84

Denier, g 173.6 175.2 174.2 173, Tension, g / denier, cond.
air dry 4.00 4.34 4.32 4.47 Elongation, ° / o cond. 9.2 10.2 10.0 10.7 Tensile, g / denier wet 2.52 2.80 2.77 2.84 Elongation,% wet 16.6 18.0 17.2 18.4 Dynamic compensated
Fatigue, 2.86 g / denier 5.3 7.6 13.1 13.5 Yarn, cord, 12/12 10.6 22.8 29.4 32.1 Tension, g / denier, cond. 3.43 3.90 4.27 4.36 Elongation, ° / o cond.
oven dry 8.4 10.0 10.6 11.2 Tensile, g / denier wet
new cond. 2.29 2.56 2.72 2.82 Elongation,% wet 14.7 16.5 16.8 18.2 Heat loss (-) or -12.3 -9.5 -1.4 1,

2.51

2.07 2.09 2.07 2.08 5.7 6.0 5.8 5.5 4.9 5.1 4.6 4.4 6.84 6.93 6.84 6.84 0.73 0.73 0.73 0.73 89.4 88.4 88.7 87.4 21.1 11.4 21.8 12.0 500 580 526 414

15th 46 261 V N 14th 13th Table 4 (continued) 100 101 Hardwood reaction pulp N V Chem. Analysis 102 viscosity 100 95.4 95.2 TAPPIT-230 0.02 0.03 1% copper ethylenediamine, 3.3 3.5 cps 0.047 0.064 95.3 α-cellulose, ° / o 95.0 0.03 Ash,% 0.03 5.39 5.97 3.2 Hemicelluloses 3.6 0.24 0.18 0.044 (Pentosans), ° / o 0.076 Resins, ° / o 5.09 7.14% NaOH solubility 6.03 0.16 Copper number 0.32

¹ ) C _d -chlorination with addition of chlorine dioxide, Aj-sulfuric acid with addition of chlorine dioxide, H-sodium hypochlorite, D-chlorine dioxide, E-alkali extraction.

² ) The percentage of filterability is equal to that in twice the time as 50 ml of viscose filtered
Volume in ml.

The process according to the invention is particularly suitable for use after firstly from previously herge application to cellulose pulps intended for reactions, cellulose pulp ready for bleaching by means of loose pulps, which have been displaced to water during a process, after they are secondly production, cleaning and preparation for Lead has been used to leach previously produced cellulose sludge (see patent 16 92 857) an after-treatment pulp before it is subjected to. Here, cellulose fiber material is displaced with water for bleaching, rial continuously with an alkaline liquid and after it, thirdly, for displacement and re-digested, the cellulose pulp and generation of previously produced, used up disintegration liquid results, which regenerates final liquid in previously produced Cellulose pulp will. Furthermore, all of the alkaline 35 had been introduced.
Liquid together with the cellulose fiber material

Claims (4)

Patent claims: 1. Process for bleaching cellulose for the production of stronger and less tiring Rayon, where the cellulose pulp has undergone a series of bleaching steps including two chlorine dioxide bleaches and is subjected to at least one alkali extraction, characterized in that that the first chlorine dioxide bleaching of the pulp in the acidic range is carried out with chlorine dioxide, including the pulp before or during the chlorine dioxide treatment is treated with a strong acid, and that between two Chlorine dioxide bleaching steps at least one alkali extraction is carried out, but that last bleaching step no further alkali extraction follows. 2. The method according to claim 1, characterized in that before the first bleaching step with chlorine dioxide the pulp with a water-soluble acid or chlorine dioxide in a water-soluble Acid is treated, whereby the water-soluble acid in water does not contain elemental chlorine forms, and that the treatment medium is kept acidic, so that the mineral content of the cellulose pulp is decreased. 3. The method according to claim 1, characterized in that after the first chlorine dioxide treatment the cellulose pulp is treated at least once with a hypochlorite. 4. The method according to claim 1, characterized in that the first chlorine dioxide treatment preceded by a bleaching step with sodium hypochlorite.