CA2033694A1

CA2033694A1 - Process for extracting impurities from natural cellulose

Info

Publication number: CA2033694A1
Application number: CA002033694A
Authority: CA
Inventors: Berthold Magin
Original assignee: MTM Obermaier GmbH and Co KG
Current assignee: MTM Obermaier GmbH and Co KG
Priority date: 1990-01-08
Filing date: 1991-01-07
Publication date: 1991-07-09
Also published as: JPH04153364A; EP0436849A1; AR244367A1; DE4000347C1; BR9100042A

Abstract

ABSTRACT OF THE DISCLOSURE
Disclosed is a method of extracting impurities from natural cellulose. The method includes placing the material in a kettle and evacuating the material preferably in the dry state. Subsequently, a treatment liquid is introduced into the kettle to impregnate the material. The treatment liquid may be lye or acid and may optionally contain other chemicals.
The amount of the treatment liquid is not more than 3 parts by weight per part of the material. Subsequently, saturated steam of a temperature above 100°C is conducted through the impregnated material until an excess pressure of at most 8 bar is reached in the kettle. The material is kept at this pressure for about 1 to 5 minutes. After releasing the pressure from the kettle, the material is washed in the hot state. If necessary, the treatment steps can be repeated, possibly with the use of different recipes for the treatment liquids. By employing the evacuation step and a small amount of the treatment liquid, the treatment time is substantially reduced.

Description

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BACKGROUND OF THE INVENTION
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1. Field of the Invention ~ ;
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The present invention relates to a method of extracting impurities from natural cellulose in the form of linters, `~
flake, yarn or piece goods. The invention also relates to a ~ -~
;-' method of bleaching natural cellulose and of reducing the .
degree of polymerization of natural cellulose.
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2. DescriPtion o* the Related Art Cellulose used in the textile industry is derived either ~` from the seed hair of cotton or from the bast fibers from the stems of flax, hemp, ramie and jute. Because of their ;`~
natural origin, these cellulose fibers contain substantial -~
amounts of impurities. These impurities are wax, : . :
! hemicellulose, proteins, mineral salts, and residues of the ;- seed and seed capsules and, in the case of bast fibers, `.3 additionally lignins. The average degree of polymerization :,;l (AP-value) of cotton i8 between 2500 and 3000, and that of ;;~

untreated flax and ramie is between 2500 and 3500.

Cellulose used in the paper industry is derived from conifers, hardwoods, straw, esparto, jute, manila, and also from cotton. This cellulose also contains impurities depending on its origin.

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In addition to the fibers from untreated cellulose, there are also fibers from regenerated cellulose, i.e., the viscose fibers. Among these f ibers are staple fiber and ., rayon and, as a specialty, the modal fibers. Compared to `
natural cellulose fibers, these fibers have a low degree of polymerization (AP-value) of between 250 and 300, to a maximum of 800. However, dus to the regenerative, i.e., artificial manufacture, these fibers are practically free from natural impurities.

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Textile material of natural cellulose fibers must be pretreated before it can be finished, i.e., dyed and imprinted. The goods must be free from seed shells. The cellulose should have an AP-value which is as high as possible and should not be damaged oxidatively by the pre~
treatment. The degree o bleaching must be sufficiently high in order not to impair the purity particularly of bright ~` colors. The capacity to take up dyes and the absorbing capacity of the goods must be high and uniform.

~'~ However, if high~grade paper is to be manufactured on , ~ the basis of sellulose, in addition to a good extractive pre~
~` treatment, a controlled decomposition of the cellulose chains must be obtained.

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~, When pretreating desized loom-state woven goods of cotton, it is necessary to remove, for example, ~ to 12% ~;~
natural impurities of the cotton. Thus, for each ton of cotton fabric, it is nece~isary to decompose, dissolve, or disperse and wash out the huge amount of 80 to 120 Kg ~- ~
impurities. Large amounts of treatment liguids and washing ~ ;-j water are reguired ~or this purpose. ~;
: , ~ The pretreatment of cellulose fibers or materials made ¦ of cellulose fibers includes the method steps of singeing, desizing, possibly precleaning with acid, treating with alkali or acids, treating with caustic soda, mercerizing and bleaching. The present invention is directed to the method `
steps of treating with alkali or acid, i.e., boiling off or ~l bucking, and bleaching.

o~ For the pretreatment o~ natural cellulose in the form of linters, flakes, combed sliver, card sliver, lap, hank yarn, knitted goods and fabrics, a plurality of vertically and radially as well as discontinuously or continuously operating, open and closed apparatus are available which can -~
be equipped with the inserts needed in each case.

For the pretreatment of piece goods, continuously operating plants are used predominantly. In these plants, `~ the woven material is guided in rope form or at full width, - while knitted goods are in rope form or in hose form The " , , ~ :~
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guidance at full widths ensures creaseless run of the goods and careful treatment.
.' ~ '~' The alkaline extraction in the form of boiling off or bucking is a very time-consuming process, usually requiring 1 -~
` to 6 hours. Accordingly, it was always a goal to find less time-consuming processe~. However, this was succes~ful only to a limited extent.

When knitted goods and woven goods are pretreated ;
., ~ . .
; practically exclusively in the alkaline pH-range, the acidic extraction is frequently used in the pretreatment of yarns.
~'! The process uses weak acids, for example, acetic acid and '~ also diluted hydrochloric acid. After the acidic extraction, the natural waxes remain on the cellulose fiber which imparts good running properties to the yarn.

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In the continuous treatment of textile material at full ~
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widths, the use of steaming units plays an important role.
;~j Depending on whether the goods are bound, guided, put down or treated in the pack, the reaction temperatures are set .~, ,, ~
between 100 and 135C and the reaction times are set at 30 -~

~` minutes.
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SUMMARY OF THE INVENTION
It is the object of the present invention to provide a method of extracting impurities from natural cellulose and possibly also of bleaching the cellulose, wherein the cellulose , is present in the form of linters, flakes, spooled yarns or `~
piece goods on the beam, and wherein an optimum treatment result is obtained with an extremely concentrated liquor ratio ;
" and with an extremely short treatment time. `
~ In accordance with the present invention, the above-; 10 described method of extracting impurities from natural cellulose, which is present in the form of linters, flakes, ` `
- ~ :
yarns (such as in the form of warp beams or cheeses) or as piece goods on the beam, includes impregnating the material to be treated with a treatment liquid which contains lye or an acid and optionally additional chemicals, such as, dispersing agents, emulsifying agents, wetting agents, sequestering agents ;~
and/or anti-oxidants or oxidants. For the impregnation, the material is placed in a kettle, and then the kettle is , ..... , , ~
evacuated and the treatment liquid is introduced into the kettle. The amount of the treatment liquid relative to the material is less than 3. Then saturated steam of temperatures .:
above 100C is conducted through the material until an excess pressure of at most 8 bar is reached in the closed kettle. The material is maintained for 1 to 5 minutes at the pressure which has been reached before the pressure is released from the ;~
kettle. Subsequently the material is washed out in the hot state.

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As to the amount of the treatment liquid, the expression "liquor ratio" is sometimes employed in this specification. This is understood a weight ratio of the material: the treatment liquid.
By evacuating the goods which have preferably been ;
placed in the kettle in the dry state, the treatment liquid ;;~
penetrates the material to be treated quickly, completely, and most importantly r uniformlyO The kettle itself remains ~ `
practically free of a liquid. As a result, the quantity of 10 the treatment liquid required is minimal, and the ~uantity of ;
chemicals and the required quantity of steam are also m:inimal.
The chemicals themselves are utilized practically completely.
This reduces the burden on sewage treatment plants and the environment.
.: -In spite of the small liquor ratio and the resulting ;~
small quantity of the liquid and in spite of the fact that the material to be treated is present as a compact blockl the ~ ;
., impurities of the natural cellulose can be practically completely removed. When oxygen-free conditions are strictly maintained, which is made particularly possible by the evacuation of the kettle and the use of a closed kettle, the AP-values of the cellulose are practically not lowered.

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on the other hand, when oxygen is used in the treatment liquid, preferably in the form of peroxides, the molecule .: ~
~ chains of the cellulose can be shortened to such values as ~ ~
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they are required for further processing, for example, to high-grade paper.

Experience has shown that the degree of bleaching of the cellulose fibers after acidic extraction, usually also after .: .
l alkaline extraction of the impurities is still not sufficient ~
., for further processing in the textile industry, particularly for the manufacture of textile material which is undyed or dyed with bright colors. In these cases, a bleaching step is added, wherein bleaching with peroxide is used most often.

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Surprisingly, it has also been found that the method steps described above for the extraction of impurities are ` -also suitable for bleaching the textile material. It is only necessary to replace the treatment liquid by a bleaching liquid which preferably contains peroxides, is alkaline and ;~-~
may possible be weakly acidic. After washing out the material to be treated followlng the extraction, the material ~ ~
is kept in the kettle. The materîal is then again ;
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;` evacuated, impregnated with bleaching liquid with a predetermined concentrated liquor ratio, steamed under excess pressure and finally washed out.
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Accordingly, the method of the invention provides an extremely simple and economical control oi` the two pretreatment steps, while the material to be treated is moved ~`
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very little, the requirements of energy and material are ~
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minimal and th~ treatment results are very uniform.
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In accordance with an advantageous feature, the treated material is evacuated to approximately 0.1 bar prior to the . . .
extraction and also prior to the bleaching.
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~ In accordance with a preferred further development of .:, . .
the invention, after the material has been impr~gnated with the treatment liquid or bleaching liquid, a portion of the :
liquid is drawn off, preferably until a liquor ratio of about 1 is reached. The liquid which has been drawn off can be returned to a tank and reused. It has been found that excellent and completely uniform results are obtained with a . :. : .
liquor ratio of 1 : 1 to 1 : 0.5. Such results have been considered impossible in the past.

Saturated steam is used in the conventional manner for . , .
~ heating the impregnated material to be treated and for -5.";' building up the excess pressure and the excess temperature in the kettle, in order to avoid overdrying of the material, on ' the one hand, and dilution of the treatment or bleaching - liquidl on the other hand.

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, -In accordance with an advantageous ~eature, the liquid pressure in the kettle is adjusted to greater than 1 bar and ;~
up to 8 bar, wherein values between 2 and 4 bar are preferred because this range results in the gr~atest acceleration of the process. Basically, higher pressure and temperature values result in shorter reaction times. However, since the ., - .
reaction times are already only between one and five minutes, ; . , reductions of the reaction times do not lead to significant reduction of the total treatment time. The important reduction of the required time is obtained by the evacuation ~ of the goods and by the concentrated liquor ratio.

; In order to even further reduce as much as possible the period of time required for heating the material after the . .
impregnation to reaction pressure and reaction temperature, :
it is recommended to heat the treatment or heating liquid ~-prior to the impregnation to temperatures of up to 90 C.

However, the temperature must also be adjusted to take into ~ ;

` consideration the negative pressure in the kettle.

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The method according to the present invention shall be explained in more dQtail below with the aid of the following `
examples.

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In all of the following examples, kettle and goods are evacuated to about 0.1 bar. Subse~uentlyr the predetermined quantity of treatment or heating liquid is introduced into -the goods. If necessary, a portion of the liquid is drawn .-. . .
off until the stated liquor ratio is reached. Washing out after the extraction is always carried out with hot water; .
after bleaching, washing may be carried out with cold water. ~ :
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Example 1: :;

.~ Precleaning of cotton yarn with acetic acid ~,; ., ~, -3 ml/l 60% acetic acid l g/l wetting agent ("Leophen U"~
1 liquor ratio ~;- 125C treatment temperature 3 minute reaction time :

Example 2:

Alkaline extraction o~ cotton yarns with sodium ~,. hydroxlde , ~, ,:
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0.5 g/l reduction agent ("Rongalit C"}
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0.5 g/l wetting agent ("Leophen U") .. 0.5 g/l combination of washing agent and wetting agent ~ :

(Kieralon B") l 1 : 1 liquor ratio ~
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::. 3.5 bar pressure :
. 5 minutes reaction time ~ ~

After the reaction time has concluded, initially only :;. .
the steam is turned off. As soon as excess pressure is no longar present, Lnitially hot rinsing water is added from the top, subsequently warm rinsing water is added and finally . , -cold rinsing water is added.
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' When methods known from the prior art are carried out, :~ ~.. .
` the use of the above-mentioned recipe requires a treatment time of 4 to 6 hours.

~';.``J, Example 3~
, . 1 Alkaline extraction of cotton flake in a pack apparatus 10 g/l caustic soda ~ :

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3 g/l combination of dispersing agent, emulsifying .
; agent, sequestering agent and reducing agent :
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("Lufibrol KB 74") .:
1 g/l wetting agent ("Leophen U") 1 : 1.5 liquor ratio :
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-~ 130C reaction temperature 3.5 minutes reaction time :~

In carrying out the known methods, the use of the above recipe reguires a treatment time of about 1 hour.

Example 4 Alkaline pretreatment of piece goods of cotton with :-~
polyester in an autoclave with piece beam ~` :

30 g/l caustic soda :~ 9 g/l combination of dispersing agent, emulsifying : agent, sequestering agent and reducing agent ~ . .
("Lufibrol KB 74") ~-2 g/l wetting agent ("Leophen U") 1 : 1 liquor ratio , 130C reaction temperature ~:

4 minutes reaction time :, . , e.' ' Bxample 5~
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: Alkaline pretreatment of cotton faibric in an autoclave . ~ , with piece beam ~; :

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.: 50 g~l caustic soda . 12 g/l combination of dispersing agent, emulsifying ..
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agent, sequestering agent and reducing agent ("Lufibrol KB 74") 0.5 g/l wetting agent ~"Leophen U") 1 : 1 liquor ratio .: 40 C impregnating temperature 132 C reaction temperature : , i 4 minutes reaction time ~:

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~ Washing out must be carried out as hot as possible.
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When using known methods, the use of the above recipe requires a treatment time of about 1 hour and an impregnating ;
temperature of 60 - 95 C.
.l Example 6~
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Peroxide bleaching of cotton or cotton~polyester cheeses .-' 25 ml/l 35% hydrogen peroxide :,: . , ,~.i 5 ml/l water glass ~ :
~i 10 g/l peroxide stabilizer ("Prestogen P") Trade-mark " :
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: , ~ 3 g/l caustic soda * ;~
: 2 g/l wetting agent ("Leophen U"~
20 c impregnation temperature ~-~
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130 C reaction temperature ~ ; ;
3 minutes reaction time ~ ~
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Example 7: ~ .

Weakly acidic peroxide bleaching of cheeses or piece beam ;
:. , :., 5 ml/l 35% hydrogen peroxide ;~
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3 g/l peroxide stabilizer for weakly acidic bleaching *
("Prestogen SP"~
~ 0.5 g/l wetting agent ("Leophen U") .:~
:~; pH-value maximum 7.5 for white goods , ~ .
pH-value maximum 7.0 for dyed goods .~ ;
1 : 1.2 liquor ratio 125C reaction temperature : . ..
~ 4 minutes reaction time ~ ~
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`- When using known methods, the use of the above recipe ::

requires a treatment time of about 1 hour. ~
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Example 8 Alkaline pretreatment of cotton linters ~, 8 g/l caustic soda ;
3 g/l combination of dispersing agent, emulsifying . agent, sequestering agent and reducing agent . ("Lufibrol KE") ~.
l 1 g/l combination of washing.agent and wetting agent :l ("Kieralon CD
0.5 g/l wetting agent ("Leophen M") ~: 1 : 0.8 liquor ratio .
130 C reaction temperature 5 minutes reaction time :
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~ A reduction of the AP-value was observed.

`~l In the case of known methods, the use of the above ~ recipe requires a treatmsnt time of about 2 hours.
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ril Example 9: ~ ~
. . ~, : Peroxide bleaching of cotton linters . 6 ml/l 35% hydrogen peroxide 1 ml/1 water glass 1.5 ml peroxide stabilizer ~"Prestogen PL") .; Trade-mark j7.-~ 1 ~'`"

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1 g/l combination of washing agent and wetting agent (Kieralon*CD") ;~
1.5 g/l caustic soda `~
1 : 2 liquor ratio ;
138 C reaction temperature .
4 minutes reaction time .. ~

While specific embodiments of the invention have been ` :
shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of extracting impurities from a natural cellulose fiber material which is in the form of linters, flakes, yarns or piece goods, the said piece goods being on a beam, which method comprises:
placing the material in a kettle and evacuating the kettle;
introducing a treatment liquid that contains lye or an acid into the kettle, the amount of the treatment liquid being less than 3 parts relative to a part by weight of the material, thereby impregnating the material with the treatment liquid;
introducing saturated steam of a temperature above 100°C through the material in the kettle closed until an excess pressure of at most 8 bar is reached in the kettle;
maintaining the material for 1 to 5 minutes at the said excess pressure in the kettle;
releasing the pressure of the kettle; and washing out the material in the hot state.

2. The method according to claim 1, wherein the treatment liquid also contains a chemical capable of shortening the molecular weight of the natural cellulose fiber.

3. The method according to claim 2, wherein the chemical is a peroxide.

4. The method according to claim 1, which further comprises:
evacuating, the material in the kettle for a second time after washing, introducing a bleaching liquid into the material, the amount of the bleaching liquid being less than 3 parts by weight relative to a part by weight of the material introducing saturated steam through the material until an excess pressure of at most 8 bar is reached in the kettle, maintaining the material at the reached pressure for 1 to 5 minutes, releasing the pressure from the kettle and initiating another washing procedure.

5. The method according to any one of claims 1 to 4, wherein the evacuation is conducted at a pressure of about 0.1 bar.

6. The method according to any one of claims 1 to 4, wherein after impregnating a portion of the liquid is drawn off until a liquor ratio of about 1 : 1 is reached.

7. The method according to claim 6, wherein the liquid which has been drawn off is reused.

8. The method according to any one of claims 1 to 4, wherein the excess presssure in the kettle is between 2 and 4 bar.

9. The method according to claim 8, wherein the pressure is between 2 and 3 bar.

10. The method according to any one of claims 1 to 4, wherein the treatment liquid or the bleaching liquid is used in such an amount that a ratio of the material: the liquid is between 1 : 0.5 and 1 : 3.

11. The method according to claim 10, wherein the ratio is 1: 1.

12. The method according to any one of claims 1 to 4, the liquid is heated to a temperature of up to about 90°C
prior to impregnating.

13. The method according to claim 4, wherein the bleach-ing liquid contains a peroxide.

14. The method according to claim 1 or 4, wherein the material is placed in a dry state in the kettle.

15. The method according to claim 1 or 4, wherein the treatment liquid further contains at least one member selected from the group consisting of dispersing agents, emulsifying agents, sequestering agents, antioxidants and oxidants.

16. The method according to any one of claims 1 to 4, wherein the treatment liquid contains acetic acid.

17. The method according to any one of claims 1 to 4, wherein the treatment liquid contains sodium hydroxide.