CONTINUOUS FIBRES BASED ON CELLULOSE AND/OR CELLULOSE DERIVATIVES, METHOD FOR THE PRODUCTION THEREOF AND USE THEREOF

Abstract

A description is given of continuous fibers based on cellulose and/or cellulose derivatives, more particularly for producing flame-retardant textiles or carbon fibers. The cellulose and/or the cellulose derivatives are in a dehydrated form in the continuous fibers. The oxygen content is 29 to 39 wt %, the limiting oxygen index LOI is 25 to 40 (according to DIN EN ISO 6941; 2004-05) and the density is 1.3 to 1.45 g/cm.sup.3 (according to DIN 65569-1; 1992-10). The continuous fibers may be produced advantageously by impregnating the starting fibers with a solution, more particularly an aqueous solution, of a specific salt which under thermal conditions releases a dehydrating acid which brings about the dehydration of cellulose and/or of cellulose derivatives in a subsequent thermal stage. The continuous fibers of the invention can be used in particular to produce advantageous carbon fibers.

Claims

1. Continuous fibers based on cellulose and/or cellulose derivatives characterized in that the cellulose and/or the cellulose derivatives are present in dehydrated form, the oxygen content is 29 to 39 wt %, the limiting oxygen index LOI is 25 to 40 according to DIN EN ISO 6941; 2004-05, and the density is 1.3 to 1.45 g/cm.sup.3 according to DIN 65569-1; 1992-10.

2. The continuous fibers as claimed in claim 1, characterized in that the degree of dehydration of the cellulose and/or of the cellulose derivatives is at least 1.0.

3. The continuous fibers as claimed in claim 2, characterized in that the degree of dehydration is at least 2.5.

4. The continuous fibers as claimed in claim 1, characterized in that the oxygen content is 29 to 32 wt %, the limiting oxygen index LOI is to 37 and/or the density is 1.35 to 1.45.

5. The continuous fibers as claimed in claim 1, characterized in that they have a fiber strength of 5 to 30 cN/tex, an elongation at break of 12 to 25% according to DIN EN ISO 5079; 1996-02, and/or a linear density of 0.5 to 18 dtex according to DIN EN ISO 1973; 1995-12.

6. The continuous fibers as claimed in claim 1, characterized in that the continuous fibers comprising dehydrated cellulose originate from regenerated cellulose fibers and the continuous fibers which comprise dehydrated cellulose derivatives originate from continuous fibers of esters or ethers of cellulose.

7. A method for producing continuous fibers based on cellulose and/or cellulose derivatives as claimed in claim 1, characterized in that (1) continuous fibers based on cellulose and/or on cellulose derivatives are contacted with a solution of a salt which under the subsequent thermal conditions releases a dehydrating acid for the dehydration of cellulose and/or cellulose derivatives in the form of the ammonium salt of a sulfonic acid, (2) the continuous fibers thus furnished are heated to a temperature of 180° C. to 300° C. for a period of at least 5 minutes wherein, during the respective heating and between the heating steps, the furnished continuous fibers are placed under a reduced pressure of 5 mbar to 500 mbar, in an inert gas atmosphere, thus leading, as a result of the dehydrating acid formed, to the dehydration of the cellulose and/or of the cellulose derivative.

8. The method for producing continuous fibers based on cellulose and/or cellulose derivatives as claimed in claim 7, characterized in that in stage (2) the continuous fibers furnished in accordance with stage (1) are heated to a first temperature, of between 180° C. to 240° C. for a period of at least 5 minutes, and subsequently the furnished continuous fibers are heated to at least one second temperature, of between 240° C. to 300° C. for a period of at least 5 minutes, wherein the furnished continuous fibers, during the respective heating and between the heating steps, are placed under a reduced pressure of 5 mbar to 500 mbar in an inert gas atmosphere, thus leading, as a result of the dehydrating acid formed, to a dehydration of the cellulose and/or of the cellulose derivative.

9. The method as claimed in claim 7, characterized in that between stages (1) and (2) a drying is provided at a temperature of 60° C. to 140° C., wherein the moisture content of the continuous fibers supplied to stage (2) is adjusted to about 1 to 4 wt %.

10. The method as claimed in claim 7, characterized in that the sulfonic acid salt has the formula (I) ##STR00003## in which R.sup.1 is a hydrocarbon group and K.sup.+ is a cation of the formula (II) ##STR00004## in which R.sup.2 to R.sup.5 independently of one another are an H atom or an organic group having 1 to 20 C atoms and the cation represents a substituted or unsubstituted ammonium ion.

11. The method as claimed in claim 10, characterized in that the furnished continuous fibers contain 0.1 to 5 wt % of sulfur, based on the dry weight of the furnished continuous fibers.

12. The method as claimed in claim 10, characterized in that the sulfonic acid salt of the formula (I) in water has a solubility of at least 10 parts by weight to 100 parts by weight of water.

13. The method as claimed in claim 7, characterized in that the furnished continuous fibers in stage (2) are heated in stages from the first temperature to at least one further temperature and then up to the second temperature, where the temperature difference between the temporally successive heating steps is at least 5° C., and where the furnished continuous fibers are held at the at least one temperature for a period of at least 3 minutes.

14. The method as claimed in claim 7, characterized in that the second temperature in stage (2) is set to be higher by at least 30° C. than the first temperature.

15. The method as claimed in claim 7, characterized in that the furnished continuous fibers in stage (2) are held for at least 10 minutes, at the first temperature, the second temperature, and at least one optional intermediate temperature.

16. The use of the continuous fibers as claimed in claim 1 for producing flame-retardant textiles for use in fire-resistant vocational clothing, fire-resistant leisure clothing, as fire-resistant textile material for technical use, and in filtration or in thermal insulation, and also as fire-resistant textile material in the construction sector.

17. The use of the continuous fibers as claimed in claim 1 for producing carbon fibers by carbonization.

18. Carbon fibers produced from continuous fibers of claim 1, characterized by a density of 1.55 to 1.75 g/cm.sup.3 according to DIN 65569-1; 1992-10, a fiber strength of 2.0 to 5 GPa according to DIN EN ISO 5079; 1996-02, and an elongation at break of 2 to 5% according to DIN EN ISO 5079; 1996-02.

Description

EXAMPLE 1

[0045] The production of a flame-retarded cellulose fiber of the invention is described. For furnishing with the additive, a technical regenerated cellulose fiber yarn which is used as tire cord fiber is presented, having a single-filament density of 2.2 dtex and comprising 1000 filaments.

[0046] The fiber is furnished and dried in a continuous operation on godets. All of the godets have a speed of 10 m/min. The first godet serves as an unwind unit for the fibers. Prior to being furnished, the fibers are washed by washing with water (95° C.) in washing baths and godets sprayed with water. The fiber is subsequently passed through an aqueous ammonium tosylate solution (ammonium tosylate concentration: 0.35 mol/kg). This is followed by drying on a heated godet (80° C.). The dried fiber is wound up using a tension-controlled winder under an initial tension of 0.3 cN/tex (stage 1).

[0047] The regenerated cellulose fiber furnished with the dehydrating additive is subsequently processed further under protective gas (nitrogen) and under reduced pressure (200 mbar). This processing takes place using a low-pressure oven with 24 heating zones. The fibers are unwound over a triple godet and taken into the process tunnel of the oven through three pressure locks. The pressure locks are sealed off from one another by a respective pair of rolls. The pressure in the locks and in the process tunnel is regulated by vacuum pumps and by supply of nitrogen. The furnished cellulose fibers are drawn through the oven at a speed of 0.2 m/min, corresponding to a residence time of 60 min. The temperature is set between 195 and 240° C. The fibers are subsequently removed from the oven again via three pressure locks and are wound up with an initial tension of 4 cN/tex (stage 2).

[0048] The residual mass of fiber is 86 wt %, the density of the fibers is 1.42 g/cm.sup.3, the strength is 16 cN/tex, the elongation at break is 25%, the LOI is 30.5 and the oxygen content is 30 wt %.

EXAMPLE 2

[0049] The fiber is produced as in example 1. The residence time in the low-pressure oven is shortened to 30 min.

[0050] The residual mass of fiber is 86 wt %, the density of the fibers is 1.40 g/cm.sup.3, the strength is 16 cN/tex, the elongation at break is 21%, the LOI is 29, and the oxygen content is 32 wt %.

EXAMPLE 3

[0051] The fiber is produced as in example 1. The residence time in the low-pressure oven is shortened to 15 min.

[0052] The residual mass of fiber is 86 wt %, the density of the fibers is 1.39 g/cm.sup.3, the strength is 13 cN/tex, the elongation at break is 21%, the LOI is 26, and the oxygen content is 38 wt %.

EXAMPLE 4

[0053] The production of carbon fibers from the flame-retarded cellulose fibers of the invention is described. The flame-retarded cellulose fibers are produced, as described in example 1, by means of an additized regenerated cellulose fiber, a so-called tire cord fiber, which is processed using the low-pressure process. The flame-retarded cellulose fibers thus produced are subsequently processed under protective gas in two stages to give carbon fibers. In the first stage the fiber is treated at a maximum temperature of 750 ° C. Thereafter the fibers are treated further in a second stage at 1400 ° C.

[0054] The carbon yield is 72 wt %, the strength of the carbon fibers is 2.5 GPa, the elasticity modulus is 96 GPa, the elongation at break is 2.5%, and the density is 1.42 g/cm.sup.3.

EXAMPLE 5

[0055] The production of carbon fibers from the flame-retarded cellulose fibers of the invention is described. The flame-retarded cellulose fibers are produced, as described in example 2, by means of an additized tire cord fiber, which is processed using the low-pressure process. The flame-retarded fibers are subsequently processed under protective gas in two stages, as described in example 4, to give carbon fibers.

[0056] The carbon yield is 72 wt %, the strength of the carbon fibers is 23.2 GPa, the elasticity modulus is 110 GPa, the elongation at break is 2.8%, and the density is 1.7 g/cm.sup.3.

EXAMPLE 6

[0057] The production of carbon fibers from the flame-retarded cellulose fibers of the invention is described. The flame-retarded cellulose fibers are produced, as described in example 3, by means of an additized tire cord fiber, which is processed using the low-pressure process. The flame-retarded fibers are subsequently processed under protective gas in two stages, as described in example 4, to give carbon fibers.

[0058] The carbon yield is 82 wt %, the strength of the carbon fibers is 2.6 GPa, the elasticity modulus is 82 GPa, the elongation at break is 2.5%, and the density is 1.68 g/cm.sup.3.

EXAMPLE 7

[0059] The production of flame-retarded cellulose fibers of the invention is described. The starting material used is regenerated cellulose fibers from an air gap spinning process, spun directly from ethyl-, methyl-imidazolium octanoate (IL fibers), having a single-filament density of 2.2 dtex and comprising 1000 filaments. The flame-retarded cellulose fibers are produced as in example 1 after furnishing with an additive (ammonium tosylate) by the low-pressure process.

[0060] The residual mass of fiber is 78 wt %, the density of the fibers is 1.38 to 1.42 g/cm.sup.3, the strength is 12 cN/tex, the elongation at break is 13%, and the LOI is 31.

EXAMPLE 8

[0061] The production of carbon fibers from the flame-retarded IL fibers of the invention is described. The flame-retarded cellulose fibers are produced as in example 7. The flame-retarded fibers are subsequently processed under protective gas in two stages, as described in example 4, to give carbon fibers.

[0062] The carbon yield is 80 wt %, the strength of the carbon fibers is 2.5 GPa, the elasticity modulus is 90 GPa, the elongation at break is 2.5%, and the density is 1.69 g/cm.sup.3.