WO1998055673A1

WO1998055673A1 - Regenerated cellulosic moulded body

Info

Publication number: WO1998055673A1
Application number: PCT/AT1998/000139
Authority: WO
Inventors: Susanna Schiemer; Jörg Schlangen
Original assignee: Lenzing Aktiengesellschaft
Priority date: 1997-06-05
Filing date: 1998-06-04
Publication date: 1998-12-10
Also published as: ATA96697A; AU7629698A; AT405949B

Abstract

The invention relates to a regenerated cellulosic moulded body obtained using the viscose method, especially viscose fibres with a basic structure consisting of regenerated cellulose. The inventive moulded bodies are characterised in that a polygalactomannan is contained inside the cellulosic basic structure. Said polygalactomannan is preferably guaran. The inventive moulded bodies can be obtained by mixing a viscose with a solution of the galactomannan and demoulding. The inventive moulded bodies are particularly suitable for use in absorbent products.

Description

Regenerated cellulosic molded body

The invention relates to a regenerated cellulosic molding obtained by the viscose process, in particular viscose fibers, according to the preamble of claim 1, a process for their production and the use of the molding according to the invention.

For the purposes of the present invention, the term “regenerated cellulosic moldings” is to be understood to mean all cellulosic moldings which are produced by dissolving the cellulose xanthate in alkali (viscose), shaping and coagulating in a precipitation bath while restoring the pure cellulose (e.g. viscose fibers).

It is known to modify regenerated cellulose fibers in order to achieve improved absorption properties of the fibers.

For this purpose, it has in particular already been proposed to mix absorbent substances, in particular absorbent polymers, into the viscose. When these mixed solutions are spun, fibers are formed that have the absorbent polymers embedded in a cellulosic framework.

In this regard, mixing viscose with polymers of acrylic acid, methacrylic acid (e.g. US-A 4,104,214), polyvinylpyrrolidone (US-A 4,041,121) and polymers of ethylene dicarboxylic acids (US-A 4,165,743) is known.

Furthermore, it has already been proposed to mix absorbent polysaccharides to form viscose. For example, US Pat. No. 4,063,558 describes the addition of a solution of alginate to the viscose. US Pat. No. 4,144,079 describes the mixing of an aqueous starch solution and a viscose. US-A 4J 69,121 describes the production of modified viscose fibers from a viscose which contains 5 to 20% carboxymethyl cellulose. The production of fibers from a mixed solution of viscose and cellulose carbamate is known from WO 97/04148.

In all these cases, viscose fibers result, which have a greatly increased absorption capacity compared to unmodified viscose fibers, which is expressed in most cases in increased swelling values or sometimes also in increased values for the water retention capacity. However, the methods mentioned have not yet become commercially successful. This is due to the fact that either the feed products are too expensive or the modified viscose fibers produced still leave something to be desired in terms of their absorption properties or other fiber properties.

It is therefore an object of the present invention to provide regenerated cellulose moldings which have an increased absorbency and do not have the disadvantages of the prior art.

This object is achieved by regenerated cellulosic molded articles according to the preamble of claim 1, which are characterized in that a polygalactomannan is contained within the cellulosic framework.

It can be seen that cellulose moldings containing polygalactomannans have a very strongly increased absorption capacity with good usage properties, such as e.g. Have strength and elongation values. In comparison to the processes of the prior art, the polygalactomannans are based on an inexpensive raw material and therefore enable the molded articles according to the invention to be produced economically, even on an industrial scale.

In a dissertation by Luo, Mengkui, "Characterization of cellulose and galactomannan blends from the N-methylmoφholine N-oxide / water system", 1994 the production of cellulosic molded articles from solutions of cellulose and galactomannans, in particular guaran, in N-methylmoφholin- N-oxide described.

DE 195 44 097 Cl (published after the priority date of the present application) also describes a process for the production of cellulosic molded articles from solutions of cellulose and a second or third polysaccharide in N-methylmoφholin-N-oxide. Polygalactomannans such as e.g. Guaran mentioned.

Neither publication mentions the production of molded articles which contain a polygalactomannan and cellulose by the viscose process.

Suitable cellulose moldings according to the invention are, in particular, fibers, but also films or, for example, particles obtained by extrusion and fluidization. In the case of the shaped bodies according to the invention, the dimensional stability is obtained through the high crystallinity and strength of the cellulose, which is why the present invention speaks of a cellulosic backbone even at high levels of polygalactomannans.

If the polygalactomannan is contained in a proportion of 1% by weight to 18% by weight, preferably 2% by weight to 10% by weight, based on cellulose, molded bodies according to the invention in fiber form are particularly suitable as components because of their higher strength and dimensional stability of absorbent nonwoven articles or tampons.

Shaped bodies according to the invention with a proportion of polygalactomannan of 30% by weight to 70% by weight, preferably 40% by weight to 50% by weight, based on cellulose, are particularly suitable for use in the area of highly absorbent polymers (super Absorbent Polymers), such as as an absorbent component in diapers.

However, molded articles according to the invention with a polygalactomannan content of 10% by weight to 30% by weight, based on cellulose, are also outstandingly suitable for various fields of application.

It has been found that the polygalactomannan, even if it is not crosslinked, is not or only insignificantly washed out of the molded body in all post-treatment steps and, after drying, can be detected in yields of up to 90% to 100% in the molded body.

However, the polygalactomannan can also be crosslinked with preferably bi- or polyvalent cations or preferably with borate ions. A crosslinked polygalactomannan obviously has the advantage that the polygalactomannan is washed out even less during the aftertreatment of the molded body. An already crosslinked polygalactomannan can be used for the production of the molded body, or the crosslinking takes place in the course of the production of the molded body, e.g. held in the precipitation bath.

The guar gum contained in guar gum has proven to be particularly suitable for use as polygalactomannan. Other suitable polygalactomannans are e.g. the carabin obtained from the locust bean gum.

It has also proven to be advantageous if a further polysaccharide is contained within the cellulosic framework. Suitable polysaccharides are in particular those that also have an increased absorption capacity and show synergistic viscosity effects with the polygalactomannans used. In particular, agar, carraghenan, xanthan or starch have proven to be particularly favorable. With these polysaccharides, the polygalactomannan is embedded in the double helix of the other polysaccharide, whereby gel formation is achieved.

Furthermore, polyvinyl alcohol can advantageously also be contained in the molded body according to the invention within the cellulosic framework.

Polyvinyl alcohol carries - as well as possibly additionally contained polysaccharides or the use of cross-linked! Polygalactomannan - to ensure that the polygalactomannan is practically not washed out in the aftertreatment of the molded body.

A method is used to produce the moldings according to the invention, in which an aqueous solution of the polygalactomannan, in which the polygalactomannan is present in a proportion of up to 10% by weight, typically up to 5% by weight, is prepared, the aqueous solution in the desired mixing ratio a viscose is added, optionally further polysaccharides and / or polyvinyl alcohol are added and the mixed solution is extruded in a manner known per se via a shaping tool into a precipitation bath, insoluble constituents, for example, from the aqueous solution of the polygalactomannan and / or the mixed solution be separated by filtration.

To prepare the solution of the polygalactomannan, the native raw material, e.g. Guar gum dissolved. Solutions of polygalactomannans are compared to solutions of other polysaccharides, e.g. Alginates, highly viscous. Depending on the native raw material, the

Viscosities of 1% aqueous solutions at 2 to 10 Pas. It is quite surprising that these viscous solutions can be mixed excellently with the cellulose solution and that it is possible to produce molded articles which contain the polygalactomannans homogeneously distributed.

The desired mixing ratio of the polygalactomannan solution to the cellulose solution results from the desired content of polygalactomannan in the resulting molded article, since essentially no polygalactomannan is washed out in the aftertreatment of the cellulosic molded article known from the prior art.

Since insoluble constituents remain in the aqueous medium when the native raw materials of the polygalactomannans are dissolved, it is necessary to remove these constituents from the aqueous Separate solution and or the mixed solution before shaping. A filtration step is particularly suitable for this.

The other polysaccharides or polyvinyl alcohol can e.g. can be added to the mixed solution in a dissolved form, but can also be dissolved at the same time with the polygalactomannan.

Viscose is an alkaline solution of cellulose xanthate. It is particularly advantageous if the aqueous solution of the polygalactomannane is alkaline and preferably has an alkali content of up to 15% by weight. The polygalactomannan can e.g. already dissolved in dilute sodium hydroxide solution or the alkali content can only be adjusted after the polygalactomannan has dissolved.

If the polygalactomannan is used in an alkaline aqueous solution, it is oxidatively degraded under the influence of air, the viscosity of the solution decreasing. Surprisingly, molded articles which contain non-degraded polygalactomannan do not differ in their properties from those which contain partially degraded polygalactomannan. This makes it possible to simplify the method according to the invention, since solutions with a lower viscosity can be used.

An advantageous embodiment of the method according to the invention is accordingly characterized in that the aqueous solution before being added to the viscose at least 30 minutes of exposure to an oxidative medium, e.g. Exposed to air. The aqueous solution can preferably be exposed for 1 hour to 24 hours. The solution can optionally be stirred at elevated temperature.

The composition of the viscose in terms of cellulose concentration, alkali and sulfur content can be in the range of the common values known from the prior art.

At higher levels of polygalactomannan, in particular from about 20% by weight based on cellulose, it proves to be advantageous to use in the precipitation bath either as an additional component or as an essential component of organic solvents, e.g. Provide isopropanol or other alcohols.

Bi- or polyvalent cations or borates can also be provided in the precipitation bath in order to crosslink the polygalactomannan contained in the molded body. In contrast to numerous modified regenerated celluloses known from the prior art, the moldings according to the invention are completely biodegradable and toxicologically harmless due to the use of polygalactomannans.

The shaped bodies according to the invention have a greatly increased swelling value in comparison to both unmodified and shaped bodies modified according to the prior art, even with low contents of polygalactomannan. With viscose fibers according to the invention e.g. Depending on the guaran content, the following swelling values were measured:

Guaran content in fiber (% by weight) Swelling value (%)

5 Up to 110-120, typically 105-110

10 Up to 200, typically up to 150

30 Up to 300, typically up to 280

The swelling value, also called water retention capacity (WRV), indicates the amount of moisture that water-soaked fibers can retain if the wet fiber is spun off at high speeds of rotation. The amount of water determined is essentially within the fibers.

To determine the swelling value, about 0.5 g of the fiber was placed in a centrifugal vessel and the vessel was filled with an aqueous solution containing 1.5% by weight of a surfactant (Nekal BX, manufacturer BASF). The filled vessel was left to stand for 2 hours and then centrifuged for 10 minutes at 3500 revolutions per minute. The fibers were then weighed (gives measured value Ml), then dried at 105 ° C. for 16-18 hours and weighed again (gave measured value M2). The source value is according to the formula

calculated.

The molded article according to the invention, in particular fibers, are particularly suitable as a component of absorbent products. The invention accordingly also relates to an absorbent product which contains a molded body according to the invention. Example 1:

10 g / kg of a solution of a commercial guar gum (manufacturer: UWE WEHLEN) were stirred into a 5% NaOH solution while stirring with a paddle stirrer. The solution was stirred for an additional 15 minutes and left in a closed vessel for 24 hours.

3750 grams of this guaran solution were stirred into 11000 g of viscose with the following composition using a paddle stirrer:

8.6% cellulose 5.1% alkali 2.3% sulfur

After stirring, the mixture was stirred for a further 15 minutes and then filtered first through a polypropylene filter fleece with a pore size of 10 μm and then through a polypropylene filter fleece with a pore size of 3 μm.

The filtered mixture was deaerated in vacuo and then spun into a spinning bath with the following composition by means of two nozzles, each with 800 spinning holes with a diameter of 80 μm:

95-100 g / l H ₂ SO ₄ 340-350 g / l Na ₂ SO ₄ 16-18 g / l ZnSO ₄

The spun fibers were passed through a second bath in a known manner and desulfurized, washed and dried in further baths.

The fibers obtained had a guarane content of 2.71% by weight. Assuming a guar gum content of 80% in guar gum, this corresponds to a yield of 89%.

The fibers had a strength of 18 cN / tex and a swelling value of 103% according to the method described above. A viscose fiber spun by the same method, but without the addition of a guaran solution, had a strength of 20 cN / tex and a swelling value of 75%. The fibers according to the invention thus show a significant increase in the swelling value with only a slight decrease in the fiber strength. Example 2:

A guar gum solution was produced as in Example 1, this time using 20 g guar gum / kg NaOH solution. Commercial guar gum from Fim a ALDAG was used in this experiment.

This guar gum solution was added to a spinning viscose as described in Example 1 in an amount such that, assuming a content of 100% guar gum in the guar gum, a theoretical content of 4% guar gum based on cellulose resulted.

The mixed solution obtained was filtered by means of a filter pot, a polypropylene nonwoven having a pore size of 5 μm and a polypropylene nonwoven having a pore size of 10 μm being located on the filter base.

After the filtered mixed solution had been deaerated, it was spun as described in Example 1 and aftertreated.

The fibers obtained again had a swelling value of 103% with only a slight drop in fiber strength.

Example 3:

30 g / kg of a solution of a commercial guar gum (manufacturer: UWE WEHLEN) were stirred into a 5% NaOH solution while stirring with a paddle stirrer. The solution was stirred for an additional 15 minutes and left in a closed vessel for 24 hours.

1270 grams of this guaran solution were stirred into 11000 g of viscose with the following composition using a paddle stirrer:

8.6% cellulose 5.1% alkali 2.3% sulfur

After stirring, the mixture was stirred for a further 15 minutes and then filtered first through a polypropylene filter fleece with a pore size of 10 μm and then through a polypropylene filter fleece with a pore size of 3 μm. The filtered mixture was deaerated in vacuo and then spun into a spinning bath with the following composition by means of two nozzles, each with 800 spinning holes with a diameter of 80 μm:

95-100 g / 1 H ₂ SO ₄ 340-350 g 1 N ^ S, 16-18 g / 1 ZnSO ₄

The fibers obtained had a guar gum content of 3.80% by weight. This corresponds to a yield of 98.8%.

The fibers had a strength of 19 cN / tex, an elongation of 17% and a swelling value according to the method described above of 103%>. A viscose fiber spun by the same method, but without the addition of a guaran solution, had a strength of 21 cN / tex and a swelling value of 75%. The fibers according to the invention thus show a significant increase in the swelling value with only a slight decrease in the fiber strength.

Example 4:

A guar gum solution was produced as in Example 3, this time using 25 g guar gum / kg NaOH solution. Commercial guar gum from ALDAG was used in this experiment. After standing for 24 hours, the solution was stirred in air for 1 hour.

This guar gum solution was added to a spinning viscose as described in Example 3 in an amount that, assuming a guar gum content of 100% guar gum in the viscose, resulted in a theoretical content of 14% guar gum based on cellulose.

After the filtered mixed solution had been deaerated, it was spun as described in Example 1 and aftertreated. The fibers obtained had a swelling value of 139% with only a slight drop in fiber strength to 18 cN / tex.

Claims

Claims:

1) Regenerated cellulosic molded body, obtained by the viscose process, in particular viscose fiber, with a basic structure of regenerated cellulose, characterized in that a polygalactomannan is contained within the cellulosic basic structure.

2) Shaped body according to claim 1, characterized in that the polygalactomannan is contained in a proportion of 1% by weight to 18% by weight, preferably 2% to 10% by weight, based on cellulose.

3) molded article according to claim 1, characterized in that the polygalactomannan is contained in a proportion of 30 wt.%> To 70 wt.%, Preferably 40 wt.% To 50 wt.%, Based on cellulose.

4) molded article according to one of claims 1 to 3, characterized in that the polygalactomannan is guar gum.

5) molded article according to one of the preceding claims, characterized in that a further polysaccharide, in particular, within the cellulosic framework

Agar, carraghenan, xanthan or starch is included.

6) Process for producing a molded article according to one of the preceding claims, wherein an aqueous solution of the polygalactomannan, in which the polygalactomannan is contained in a proportion of up to 10% by weight, is prepared, the aqueous solution is added to a viscose in the desired mixing ratio , if appropriate, further polysaccharides are added and the mixed solution is extruded in a manner known per se into a precipitation bath using a shaping tool, insoluble constituents, for example, from the aqueous solution of the polygalactomannan and / or the mixed solution be separated by filtration.

7) Method according to claim 6, characterized in that the aqueous solution is alkaline and preferably has an alkali content of up to 15% by weight.

8) Method according to claim 6 or 7, characterized in that the aqueous solution is exposed to the action of an oxidative medium, for example air, for at least 30 minutes before being added to the viscose. 9) Use of a molded body according to one of claims 1 to 5 as a component of absorbent products.

10) absorbent product containing a molded body according to any one of claims 1 to 5.