WO2013144261A2

WO2013144261A2 - Cellulose filaments with improved thermostability

Info

Publication number: WO2013144261A2
Application number: PCT/EP2013/056629
Authority: WO
Inventors: Dennis MÖSSINGER; Britta Zimmerer; Kurt Uihlein; Alfred Zengel; Rudolf Einsiedel; Frank Kiesling
Original assignee: Cordenka Gmbh & Co. Kg
Priority date: 2012-03-27
Filing date: 2013-03-27
Publication date: 2013-10-03
Also published as: WO2013144261A3; EP2831334A2; EP2831334B1

Abstract

The invention relates to a cellulose fiber coated with a coating agent which contains a mixture comprising urea, nonionic surfactants, and antioxidants. The coated cellulose fiber is characterized in that the tensile strength of said fiber is up to four times greater than the tensile strength of the corresponding uncoated cellulose fiber after a defined thermal aging process. The average degree of polymerization of the coated cellulose fiber material is up to six times greater than the remaining degree of polymerization of an uncoated cellulose fiber after the same aging procedure. The invention further relates to thermal aging methods for identifying effective stabilizers and for characterizing coated cellulose fibers and filaments with improved thermostability.

Description

Cellulosic filaments with improved thermostability

1. Description of the material:

Cellulose is the most common and important naturally occurring polymer in the world. In addition to cellulosic moldings such as paper, blown film, cellophane and sponge cloths, cellulose fibers are among the important technical products that are used primarily for clothing, as insulating materials and as technical strength carriers.

The present invention relates to cellulosic fibers having improved thermostability for applications of increased continuous use or processing temperature. Cellulosic fibers for industrial applications, also referred to as technical viscose, rayon or lyocell, are known and commonly used as reinforcements for technical products, e.g. for reinforcement of elastomeric components and products such as in the form of tire cords, as a hose reinforcement, or as a reinforcing material in belts and conveyor belts. Recently, cellulosic fibers in the form of fiber short cut but also increasingly find application in the thermoplastic reinforcement, e.g. in PP-rayon composites, in the form of unidirectional and bidirectional fabrics, also for reinforcing thermosets, e.g. Epoxy resins.

Cellulosic fibers, filaments and multifilaments can be obtained in a variety of ways and in various forms, which are also known and familiar to the art. The classification can be made according to the manufacturing process - for example direct dissolving or regenerating - and / or on the nature of the product obtained, either in turn of cellulose with modified crystal structure (so-called Hydratcellulose or cellulose II) exists - for example viscose - or a polymer-analogous derivative of the cellulose represents, as for example cellulose acetates or cellulose triacetates.

As a direct release method u.a. Processes are known in which the extraction of cellulosic fibers from solutions in sodium hydroxide, copper oxide-ammonia (Cuoxam), tertiary amine oxides such as N-methylmorpholine-N-oxide (NMMO), ionic liquids or phosphoric acid and subsequent precipitation in suitable Coagulation media takes place. Such filaments are i.a. known as Cupro, Lyocell and Bocell.

Other common processes for producing cellulosic filaments used for yarn or cord making are regenerative processes in which cellulose is first reacted and dissolved chemically to soluble labile derivatives (e.g., cellulose xanthogenates). The solution is pumped through spinnerets and finally regenerated in the precipitation bath to cellulosic filaments. Nevertheless, it is possible to regenerate cellulose from more stable derivatives such as cellulose carbamates, cellulose acetates and cellulose triacetates in a hydrolytic aftertreatment step ("saponification") .Such fibers are known under the name viscose, rayon, regenerated cellulose, acetate rayon or carbacell, etc. The processes for their preparation are likewise known ,

2. Description of the invention:

During further processing or in continuous use, cellulosic fibers, multifilament yarns and the products containing such fibers or yarns are often exposed to high temperatures. In contrast to thermoplastic fibers, in cellulosic fibers, the registered thermal energy can only to a small extent in the form of latent heat to aggregate state change (increase the chain mobility, in consequence Reorientation, softening and melting). This is due to the comparatively high chain stiffness of cellulose and the large number of functional groups, which result in high intermolecular binding energies. Once the cellulose physisorbed on cellulose is evaporated and mobile molecules segments are excited, the entry of thermal energy leads directly into thermal decomposition processes and accelerates hydrolytic and oxidative degradation reactions. High thermal loads consequently lead to accelerated aging of the fibers, which is associated in particular with a decrease in the yarn strength and the average degree of polymerization of cellulose. Thermal decomposition reveals itself however at the same time by yellowing, with extreme loads also browning and finally charring. For a number of applications, however, a high temperature stability over a long service life is desirable, for example when using cellulosic fibers as Garngestricke in coolant hoses, as Kordgewebe in tire carcasses, especially in run-flat tires, or as continuous or staple fiber in insulation materials.

US Pat. No. 2,278,285 discloses the stabilizing function of urea as an aging stabilizer for rayon yarns. In the cited patent urea is applied in the form of an aqueous solution by dipping and optionally a subsequent annealing above the melting temperature of urea (2-6 hours at> 135 ° C) is applied, which is to serve the homogeneous distribution of the stabilizer in the fiber.

There it is also described that urea-impregnated rayon yarns can subsequently be treated with adhesion promoters such as resorcinol-formaldehyde-latex (RFL). However, it is not mentioned whether the thermostabilizing effect is still detectable on the adhesion-impregnated yarn. Nor are the effects of urea pretreatment on the effectiveness of the liability mediator discussed. It is therefore an object of the present invention to provide a cellulosic fiber having improved thermostability while retaining adhesion to rubber. The solution to this problem is surprisingly achieved by a cellulosic fiber which is coated with a urea-containing stabilizer mixture, wherein the stabilizer mixture may additionally comprise nonionic surfactants and antioxidants. Urea is the main component of the claimed thermal stabilizer in a coating process together with an RFL adhesion promoter system applied, the resulting impregnated fiber also shows improved thermal stability, with consistent or slightly lower adhesion to common rubber types. The heat stabilization succeeds in this case, regardless of whether the stabilizer is added before the post-condensation of the RFL dispersion or only immediately before the dip impregnation. The addition of urea can be carried out both as a solid and in the form of an aqueous solution. The mass fraction of urea in the RFL impregnation solution may be 0.5-25%.

Depending on the additive concentration and aging method (see section Aging Methods and Examples), the thermostable cellulosic fiber disclosed herein exhibits higher tensile strengths (measured as maximum tensile strength), higher degrees of polymerization (viscometric one-point measurement, Cuen), and correspondingly lower thermal discoloration (unquantified) than a corresponding unstabilized thermal stress Cellulosic fiber. Preferably, the remaining tensile strength of the coated cellulosic fiber is at least 10%, more preferably at least 50%, most preferably at least 100% higher than a corresponding uncoated fiber after identical thermal loading. After long-term aging, up to 400% higher residual tensile forces were measured in the cellulosic fibers according to the invention than in an unstabilized comparative sample. The object of the invention is particularly characterized by a significantly increased long-term thermostability, but also shows at the same time favorable behavior during short loads at extremely high temperatures (high temperature processing).

The variant of the stabilizer applied together with an RFL adhesion promoter gives cellulosic fibers whose adhesion values according to ASTM D 4393-00 are practically of the same order of magnitude, at most 25% lower than with an unstabilized, RFL-coated cellulosic fiber or filaments lie

The high stabilizing effect is obtained in particular with those cellulosic fibers in which the nonionic surfactants in the coating agent are linear or branched polyethylene glycol alkyl ethers and / or long-chain, branched alcohols. Furthermore, it is advantageous if the antioxidants are sterically hindered phenols.

The composition, type or presentation of the coated cellulosic fibers is not limited in itself. Optimum results are obtained by using high purity cellulose fibers with high degrees of polymerization. Apart from that, the corresponding coated fiber may be a cellulosic fiber or a corresponding multifilament yarn consisting either predominantly of cellulose or of a polymer-analogous derivative of the cellulose, e.g. Cellulose acetate or cellulose triacetate.

Likewise, the recovery process for the inventively coated cellulosic fiber or filaments is not limited. Thus, the cellulosic fiber or filament used in the coating may be applied by a direct dissolving method, such as a spin coating. from solutions in caustic soda, copper oxide-ammonia, phosphoric anhydrides, tertiary amine oxides such as N-methylmorpholine-N-oxide (NMMO) or ionic liquids, and subsequent precipitation in suitable coagulation media.

Furthermore, it is possible and also preferred if the cellulosic fiber is recycled by a regenerating process in which the cellulose (in the form of chemical pulp) initially chemically soluble derivatives (xanthates or carbamates) is reacted and dissolved. The solution is pumped through spinnerets and the spun fibers are finally coagulated and regenerated in the precipitation bath, washed and sized (functionally coated) in one or more post-treatment steps and finally either wound on endless coils or processed into fiber cut.

High strength coated cellulosic fibers generally have a tenacity of at least 20 cN / tex, more preferably at least 35 cN / tex, most preferably greater than 45 cN / tex, prior to thermal aging or application. In general, the theoretical limit of strength for cellulosic multifilament yarns is about 90 cN / tex. These strength values refer to tensile tests according to BISFA, i. After more than 16 hours of conditioning at 20 ° C and 65% relative humidity.

The functional cellulosic fiber of the present invention may consist of fiber cut of any length or any number of continuous filaments, such as are common in technical and consumer products. In general, the yarn has a total titer in the range of 30 to 20,000 dtex and consists of 10 to 5000 correspondingly coated single filaments. The elongation at break of a yarn according to the invention is 5 to 30%, preferably 10 to 20%.

The invention is further directed to a process for coating cellulosic fiber or filaments in which the cellulosic fibers or filaments are contacted with an aqueous dispersion or solution of a stabilizer mixture containing urea, and the dried cellulosic fibers or filaments are subsequently dried and further processed wherein the dispersion or solution may additionally comprise nonionic surfactants and antioxidants. Appropriately, this is done by means of passage (immersion), wetting with a Preparation roller, or spraying with the aqueous stabilizer dispersion. The cellulosic fibers or continuous yarns treated in this way can then be dried and, if necessary, wound up or processed into fiber short cuts. The coated yarn in the oven-dry state (little physisorbed water content) in the inventive embodiment contains at most 25% by mass of additive components, preferably at most 15% by mass of additive components. The dipping or spraying solution used for the yarn coating preferably contains at least 5% by mass, preferably at least 10% by mass, most preferably at least 15% by mass of the stabilizer mixture.

It has proven to be favorable for the process according to the invention if the pH of the immersion dispersion is in the moderately alkaline range. According to the invention, the target pH value can already be set during the preparation with sodium hydroxide solution or just before use with solid sodium hydroxide.

The anhydrous stabilizer mixture preferably contains 25-60% by mass of urea, preferably 25-60% by weight of polyethylene glycol alkyl ethers and optionally preferably 5-25% by mass of long-chain, preferably branched, monoalcohols and preferably less than 5% by mass of antioxidants , The polyethylene glycol alkyl ethers used (equivalent to polyalkylene glycol ethers, alkyl alcohol ethoxylates, fatty alcohol polyglycol ethers and fatty alcohol ethoxylates) preferably consist of branched C 6 -C ₄ -alkyl radicals and 1 to 60 ethylene oxide (EO) repeat units. The latter are preferably hydroxy (OH) -terminated. The preferably branched, monoalcohols used according to the invention preferably consist of C 12-C ₃₆ -alkyl units.

A particularly preferred dispersion of these components (hereinafter also referred to as stabilizer solution) has the following composition:

80% by mass of water, 5-12% by mass. Urea, 5-12 mass% of polyethylene glycol ethers, eg, dodecaethylene glycol mono (/ so- / n-) tridecyl ether, and 0-6 mass% long chain iso- or n-alcohols, for example dodecanol or hexadecanol and 0-1% antioxidants from the class of sterically hindered phenols, eg 2,6-di-tert-butyl-4-methylphenol (BHT).

Surprisingly good results have been achieved with a solution which finds use as textile auxiliaries for reducing thermal yellowing in polyamide fibers. Conveniently, this very successfully used formulation, which has a solids content of about 41% by mass commercially available, should be diluted with sodium hydroxide to 25 to 75 vol .-% before use, so that solids contents of 10 to 30 mass% can be achieved , The native pH of the additive - if not already done by dilution with sodium hydroxide solution - moderately alkaline by stirring solid sodium hydroxide.

The yarn may be used by itself, or as a fiber short or after processing into a cord or subsequent processing into a woven or knitted fabric as a reinforcing material for synthetic and natural elastomers, or for other synthetic or renewable raw materials based materials, for example thermoplastic and thermosetting plastics , serve. These elastomeric, thermoplastic, and duromeric materials include natural rubber, other poly (isoprene) s, poly (butadiene) s, polyisobutylenes, butyl rubber, poly (butadiene-co-styrene) s, poly (butadiene-co-acrylonitrile) s, poly (ethylene) co-propylene) s, poly (ethylene-co-propylene-co-diene) s, also known as EPDM, poly (isobutylene-co-isoprene) s, poly (chloroprene) s, polyacrylates, polyamide, polyesters, polylactic acid, polycarbonates , Polyglucans, polyurethanes, polysulfides, silicones, polyvinyl chloride, poly (ether-esters), thermoplastic polyesters, crosslinked unsaturated polyesters, epoxy resins, or mixtures thereof.

The invention is likewise directed to adhesion promoters, preferably based on

Resorcinol-formaldehyde latex, isocanate or resorcinol-formaldehyde-silica, for the Bonding of fiber-containing reinforcements to rubber, which is characterized in that the bonding agent additionally contains urea.

The concentration of in aqueous solution within the primer

present urea is preferably between 0.5 and 25%, more preferably between 2.5 and 15%,

Resorcinol-formaldehyde precondensates are known as adhesion promoter component for rubberized fabrics. For the preparation of the dips is doing the

Precondensate processed together with the latex dispersions and other ingredients to form so-called resorcinol-formaldehyde-latex (RFL) dips.

In order to exploit the thermostabilizing effect of the urea, it is added during or shortly after the production of the dipping agent.

The fibrous reinforcements contain fibers or filaments, which consist predominantly of viscose, lyocell or a polymer-analogous derivative of

Cellulose, e.g. Cellulose acetate or cellulose triacetate.

Surprisingly, the liability remains at least at a good level.

3. Explanations of the coating processes:

The production of the yarns according to the invention by wetting with a stabilizer dispersion takes place with the aid of a coating apparatus. Reference samples (without stabilizer) are passed through deionized water on the same coating equipment, dried and conditioned analogously. By comparison of 10 meter long yarn samples with and without coating, the percentage coating amount is determined (mass increase compared to the reference fiber). All coating amounts mentioned in this context are therefore referred to as "mass of the reference fiber + X For fiber coating, several types of apparatus have proved suitable:

Example of fiber coating on a laboratory scale:

A simple fiber coating equipment consists of a braked spool, a passively driven impeller through a flat, unheated, non-circulated immersion tray (5-10 cm immersion distance, approx. 100 mL immersion solution), a simple scraper, a dryer unit from a passively driven heating grid duo ( 100 ° C surface temperature, approx. 3 m heating distance), a drive roller (5 - 10 m / min) and an automatic winding. For a test duration of a few minutes, the concentration of the dipping solution can be considered approximately constant. Following coating trials, about 30-50 m of coated yarn are rewound onto test tubes for textile tests and aging tests.

Example fiber coating pilot scale:

A pilot-scale fiber-coating equipment consists of a braked unwinding system, a jet-jet impregnation unit with metering pump, heated and stirred 5-liter storage vessel, staggered scraper teeth with collecting trough and return, a multi-stage roller dryer with active drive (50-60 m / min) and automatic rewinding , Following coating trials, about 30-50 m of coated yarn are rewound onto test tubes for textile tests and aging tests.

4. Selection of aging scenarios

The selected conditions of the aging tests are based on two basic application scenarios. These are on the one hand increased processing temperatures, on the other hand increased elevated service temperatures: 4.1. Short-term exposure at elevated processing temperatures

For example, the resistance of the cellulosic materials to short term high temperature (> 200 ° C) loads is of great benefit for injection molding of rayon-thermoplastic composites, i. of yarn short cut in a polymer melt. With a view to wider application as reinforcing fibers in polyolefins, polyamides and polyesters, the test temperature approximated the processing temperatures of the higher melting materials (240 ° C). The maximum life in a hot extruder or an injection molding machine was estimated to be 20 minutes.

4.2. Long-term exposure at elevated continuous service temperatures

In addition, with regard to Rayon's established applications in tire carcasses and other engineering rubber products such as hoses or conveyor belts, the aim is to increase the long-term thermal stability (LTTS) of cellulosic fibers. Here, under extreme conditions, temperatures reached in runflat tires and the desired long-term stability of radiator hoses were used as an order of magnitude. In order to limit the duration of the experiments, conditions were chosen in which a slower and steady decrease ("plateau") had set in preliminary experiments after an initially strong decrease in the average degree of polymerization (DP) and the mechanical properties, the first approximation being a Thus, the conditions of the standard long-term aging were set at 7 days (168 hours) at 150 ° C. For promising stabilizer candidates that stood out in the screening, the aging tests additionally became common aging conditions in the automotive supply industry (1000 h at 120-150 ° C) extended. 5. Verification of thermal aging according to the selected scenarios

For the present invention, the thermal stability of the cellulosic materials according to the invention was investigated by means of rayon yarn. In principle, additive-coated yarn samples and untreated reference yarns are aged under identical conditions, ideally in the same experiment and in duplicate.

During the aging test, it must be prevented that adjacent samples in a drying cabinet influence, ie contaminate each other by outgassing of volatile stabilizer components or decomposition products. Since fibers are often used in "hidden", ie encapsulated or vulcanized form as reinforcements, it has proven useful to limit the air supply during the experiment by carrying out all the aging tests on encapsulated yarn samples on which this invention is based Both experiments under air and under N ₂ -enriched atmosphere can be carried out comparatively easily The aging capsules are preferably made of glass and temperature-stable plastics.

The yarn is generally very sensitive to the choice of aging method, which is why strict attention must be paid to reproducible performance. The decisive factor for the level of residual tensile strength and residual polymerization after stress is the exact preparation of the yarn sample. Here on the one hand, the ratio of capsule volume to amount of sample has an influence, but more important is the extent to which the yarn is accessible to oxygen and volatile decomposition products (differences between 2 meter yarn sample on a steel hanger and 250 meter yarn samples on cardboard cores). For the experimental implementation are depending on Aging scenario and sample preparation different aging methods differentiated:

Aging method A:

Pieces of two meters length of the coated yarn and the untreated output yarn are wound on separate steel wire hanger (10 turns of 20 cm) and predried at 105 ° C in a drying oven for 3 hours. Each stirrup is taken out of the oven one at a time and placed in a heated test tube filled with ambient air, which is sealed airtight with a glass stopper and PTFE tape. Another drying oven, which was previously adjusted so that the temperature inside an empty test tube is 240 ° C, is preheated for one hour. The aging samples in test tubes are placed horizontally on a slide in the center of the oven. After 5 minutes, the target temperature of 240 ° C in the test tube is reached, after 20 more minutes, the test tubes are removed and opened. The yarn samples are carefully stripped from the yarn straps and prepared for tensile testing (Eplexor 500 N) and DP determination.

Aging method B:

Pieces of two meters length of the coated yarn and the untreated output yarn are wound on separate steel wire hanger (10 turns of 20 cm) and predried at 105 ° C in a drying oven for 3 hours. Each stirrup is taken out of the oven one at a time and placed in a heated and air-filled test tube which is closed with a thermally stable rubber septum. With the aid of two cannulas, a vigorous stream of nitrogen is passed through the test tube for 20 minutes (> 3 bubbles / s). One another drying oven, which was previously adjusted so that the temperature inside an empty test tube is 240 ° C, is preheated for one hour. The aging samples in test tubes are placed horizontally on a slide-in plate in the middle of the oven where, after 5 minutes, the setpoint temperature of 240 ° C in the test tube is reached. The samples are loaded for a further 20 minutes at 240 ° C and then removed from the oven. After cooling for 5 minutes, the encapsulated test tubes are opened and the aging samples are removed. The yarn samples are carefully stripped from the yarn straps and prepared for tensile testing (Eplexor 500 N) and DP determination.

Aging method C:

Pieces of two meters length of the coated yarn and the untreated output yarn are wound on separate steel wire hanger (10 turns of 20 cm) and predried at 105 ° C in a drying oven for 3 hours. Each stirrup is taken out of the oven one at a time and placed in a heated test tube filled with ambient air, which is sealed airtight with a glass stopper and PTFE tape. Another drying oven, which was previously adjusted so that the temperature inside an empty test tube is 150 ° C, is preheated for one hour. The aging samples in test tubes are placed horizontally on a slide in the center of the oven. After 7 days (168 hours), the test tubes are removed and opened. The yarn samples are carefully stripped from the yarn straps and prepared for tensile testing (Eplexor 500 N) and DP determination.

Aging method D:

250 meters of the coated yarn and the untreated starting yarn are wound on cardboard tubes (diameter 4 cm) and pre-dried at 105 ° C in a drying oven for at least 3 hours. Each yarn package is sold individually taken out of the oven, into a heated and filled with ambient air wide-mouth vessel, which is sealed with a PTFE screw cap with polysulfone seal. Another drying oven, which was previously adjusted so that the temperature inside an empty wide-mouth vessel is 150 ° C, is preheated for one hour. The wide-mouthed containers filled with aging samples are placed upright on a slide-in tray. After 7 days (168 hours), the glass jars are removed and opened. The wound yarn samples are prepared for the tensile test (Statimat 4U) and DP determination.

Aging method E:

250 meters of the coated yarn and the untreated starting yarn are wound on cardboard tubes (diameter 4 cm) and pre-dried at 105 ° C in a drying oven for at least 3 hours. Each bobbin is taken out of the oven one at a time, placed in a heated and filled with ambient air wide-mouth vessel (1, 25 liters), which is sealed with a PTFE screw cap with polysulfone seal. Another drying oven, which was previously adjusted so that the desired aging temperature prevails inside an empty wide-mouth vessel, is preheated for one hour. The wide-mouthed containers filled with aging samples are placed upright on a slide-in tray. After 41 days and 16 hours (1000 hours), the glass jars are removed and opened. The wound yarn samples are prepared for the tensile test (Statimat 4U) and DP determination.

Tab. 1: Overview of the aging methods used. All experiments were stored in closed vessels in convection ovens; RG: test tube 20 mL, WHG:

Wide-necked vessel 1, 25 L.

Aging temperature duration [h] vessel length of atmosphere method [° C] fiber sample [m]

A 240 0.33 RG 2 air B 240 0.33 RG 2 nitrogen

C 150 168 RG 2 air

D 150 168 WHG 250 air

E s. Ex. 1000 WHG 250 air

6. Analytical Methods for Assessing Thermal Stability

6.1. Tensile tests on unloaded and aged fiber samples:

By measuring the residual tensile force ("breaking strength"), combined aging effects on the mechanical structure of the fibers are detected, including the thermal change of the supramolecular structure and fiber morphology as well as the thermohydrolytic degradation of the individual cellulose chains.

Eplexor 500N: Laboratory rapid tests with 50 mm clamping length

After conditioning for more than 16 hours in the measuring room (27 ± 2 ° C, 25 ± 5% RH), the tensile strength of thermally stressed fibers is tested in a rapid test. The measurement is either performed on pre-twisted Z100 samples, or the protective swirl is applied manually immediately prior to measurement. Useful is the use of 10 cm long, kink-free pieces (1/2 turn on the steel bracket). The tensile test is carried out on a GABO Eplexor 500N dynamic testing machine with a clamping length of 50 mm and a breaking rate of 100% (50 mm / min) .Your yarn sample is subjected to 5 individual measurements and the mean value of the remaining maximum tensile force ("breaking strength") is calculated. Statimat 4L): tensile tests in standard climate with a clamping length of 500 mm

After conditioning the bobbins for more than 16 hours in the test laboratory at (20 ± 1) ° C and (65 ± 2)% relative humidity (BISFA conditioning), the tensile strength of the thermally stressed fibers in a standardized tensile test on a "Textechno Statimat 4U The measurement is either performed on pre-twisted Z100 samples, or the protective swirl is applied immediately prior to measurement by the tensile tester, It is convenient to measure directly from the coil after overdrawing mm and tear rate 100% (500 mm / min) an average of the remaining maximum tensile force ("breaking strength") was obtained.

6.2. Degree of polymerisation of cellulose fibers by viscometry:

Values of the degree of polymerization (DP _V ) determined by single-point viscometric measurements are approximately equated in the literature with the mass-average degree of polymerization (DP _W ). This value again corresponds to twice the number-average degree of polymerization (DP _W = 2 DP _n ) assuming randomly distributed polymer samples. As a relative method, the method must be calibrated with polymers of known degree of polymerization or the average molecular weight of the intrinsic viscosity and the Mark-Houwink parameters tabulated for various polymer-solvent systems must be calculated. For the present project, all DP _v values of cellulose solutions in Cuen (1 .0 mol / L Cu (II) (H ₂ NC ₂ H ₄ NH 2) 2 in H ₂ O) were measured by the one-point method. The assignment of "relative viscosity to DP _V " is made with the aid of a calibration table whose values agree very well with the approximate formula of Salomon Situa (calculation of the intrinsic viscosity [η]) and the Mark Houwink parameters K _n = 0.420 mL / g and α _η = 1 .0 (calculation of DP _V ) The relative accuracy of the DPv values obtained in this way is usually ± 10. When analyzing coated yarns, a correction of the Weighing be made. Since single celluose chains are ideally dissolved in a DP _v measurement, only those thermal changes of the supramolecular structure that increase the average chain length, ie, thermally induced cross-linkages, can be detected. The thermal degradation of the individual cellulose chains as a sum of thermolysis, hydrolysis and thermal crosslinking is thus fully recorded.

7. Examples

The invention is explained in more detail below with reference to experimental examples. Analogously to the stabilized fibers, reference fibers mentioned in the examples were dip-treated (distilled water instead of stabilizer dispersion), predried for at least 3 hours at 105 ° C., encapsulated, subjected to the appropriate aging program and tested on the identical tensile tester.

Example 1 :

In a laboratory coating plant Z100-twisted rayon multifilament yarn (f1350) of fineness 2440 dtex is impregnated at room temperature of a stabilizer solution and then dried. Dipping medium is a 20 mass% stabilizer solution in the sense of this invention or a 20 mass% solution of the main components urea and polyethylene glycol alkyl ether. Subsequent aging tests are carried out according to Methods A and B (air and nitrogen) (20 min at 240 ° C). The highest tensile forces and degrees of polymerization measured after thermal stress are shown graphically in FIG. 1. After aging in air, the stabilized fibers show a 25-30%, under nitrogen 17-21% higher relative residual strengths than the unstabilized fiber. The series of degrees of polymerization follow this trend with similar or greater percentage differences. At 240 ° C are mainly the two Main components of the stabilizer, urea and Polyethylenglykolalkylether, responsible for the stabilizing effect of the mixture, as a comparison with a fiber which has been coated only with these components (basic stabilization).

Example 2:

In a laboratory coating plant, Z100-twisted rayon multifilament yarn (f1350) having a fineness of 2440 dtex is impregnated at room temperature with a stabilizer solution and then dried. Dipping medium is a 20 mass% stabilizer solution according to the invention or a 20 mass% solution of the main components urea and polyethylene glycol alkyl ether. Subsequent aging tests are carried out according to method C (air, 7 days at 150 ° C). The maximum tensile forces and degrees of polymerization measured after thermal stress are shown graphically in FIG. 2. While the strength of an untreated fiber breaks down after aging to about 45% of the initial value, with additivated fibers still 64-67% residual strength is measured. This corresponds to 41-47% higher relative residual strengths. The series of degrees of polymerization follow this trend with larger percentage differences. Also at 150 ° C, the two major components of the stabilizer, urea and polyethylene glycol alkyl ethers, are responsible for most of the stabilizer effect, as shown by comparison with a fiber that has only been coated (base stabilization). The optimization of the composition leads to a further increase in the stabilizing effect.

Example 3:

In a laboratory coating plant, Z100-twisted rayon multifilament yarn (f1350) having a fineness of 2440 dtex is impregnated at room temperature with a stabilizer solution according to the invention and then dried. At a stabilizer concentration in the dipping solution of 2% by mass, a stabilizer uptake of about 7% by mass based on the titer of the untreated yarn, at a concentration of 15% by mass. The yarn absorbs about 17% by mass of stabilizer. Subsequent aging tests are carried out according to Methods A and B (20 min at 240 ° C, air or nitrogen). The maximum tensile forces and degrees of polymerization measured after thermal stress are shown graphically in FIG. 3. The residual strengths after thermal stress, starting from the unstabilized fiber (0%), increase linearly with increasing stabilizer content, irrespective of whether it was aged under air or in a nitrogen-enriched atmosphere. The series of degrees of polymerization, however, shows a non-linear course. While the relative residual strength at a stabilizer content of 7% by mass (based on the fiber titer) is only about 5-8% above the level of the unstabilized fiber, with 17% by mass stabilizer 14-22% higher strengths are achieved.

Example 4:

In a laboratory coating plant, Z100-twisted rayon multifilament yarn (f1350) having a fineness of 2440 dtex is impregnated at room temperature with a stabilizer solution according to the invention and then dried. At a stabilizer concentration in the dipping solution of 2% by mass stabilizer uptake of about 7% by mass based on the titer of the untreated yarn is achieved, at a concentration of 20% by mass, the yarn absorbs about 19% by mass of stabilizer , Subsequent aging tests are carried out according to method C (7 days at 150 ° C). The maximum tensile forces and degrees of polymerization measured after thermal stress are shown graphically in FIG. 4. The residual strength and residual polymerization after thermal stress increase disproportionately from the unstabilized fiber (0%) with increasing stabilizer content. The curve of both quantities is described in a good approximation by a quadratic relationship. While the relative residual strength at a stabilizer content of 7 mass% (based on the Fiber titer) is only about 10% above the level of the unstabilized fiber, with 19% by mass of stabilizer is achieved by almost 60% higher strengths.

Example 5:

In a laboratory coating plant, Z100-twisted rayon multifilament yarn (f1350) having a fineness of 2440 dtex is impregnated at room temperature with a stabilizer solution according to the invention and then dried. The aqueous immersion solutions have a constant stabilizer content of 10%, but vary from pH 9 to 12. Subsequent aging tests are carried out according to Methods A and B (20 min at 240 ° C, air or nitrogen). The maximum tensile forces and degrees of polymerization measured after thermal stress are shown graphically in FIG. The residual strength and residual polymerization after thermal stress depend not only on the concentration but also on the pH of the stabilizer dispersion. The best properties after aging show yarns which have been impregnated with dip solutions at pH 1 1. While the strengths after impregnation at pH 12 are still comparable to the values at pH 1 1, the more sensitive degree of polymerization is already off the plateau. The effectiveness of the formulation as a processing stabilizer can thus be further optimized by adjusting the pH.

Example 6:

In a laboratory coating plant, Z100-twisted rayon multifilament yarn (f1350) having a fineness of 2440 dtex is impregnated at room temperature with a stabilizer solution according to the invention and then dried. The aqueous immersion solutions have a constant stabilizer content of 10% but vary from pH 9 to 12. Subsequent aging tests are carried out according to the method C performed (7 days at 150 ° C). The highest tensile forces and degrees of polymerization measured after thermal stress are shown graphically in FIG. The residual strength and residual polymerization after thermal stress depend not only on the concentration but also on the pH of the stabilizer dispersion. While the strengths in the short-term test remain stable up to pH 12 after impregnation, the optimum in the long-term test is between pH 10 and 11. By adjusting the pH, the effectiveness of the stabilizer can therefore also be optimized for applications with elevated continuous service temperatures.

Example 7:

In a pilot coater Z100-twisted 100% fine lyocell multifilament yarn (f900) is impregnated at room temperature with a 20% strength by weight stabilizer solution for the purposes of the invention and then dried. Subsequent aging tests are carried out according to Methods A and C (20 min at 240 ° C and 7 days at 150 ° C). The highest tensile forces and degrees of polymerization measured after thermal stress are shown graphically in FIG. While the strength of an untreated fiber breaks down after long-term aging (A) to about 62% of the initial value, with stabilized fibers still 82% residual strength is measured. After short-term aging (C), the strength of an untreated fiber is still around 58% of the initial value. A stabilized fiber still retains about 70% of the original fiber's strength for the same aging program.

Example 8:

On a pilot plant untwisted rayon multifilament yarn (f1350) of fineness 2440 dtex room temperature is impregnated with a stabilizer solution according to the invention, then dried and rewound about 250 m yarn on cardboard tubes (0 = 40 mm). At a stable isatorkonzentration in the Dipping solution of 14 mass%, a stabilizer uptake of about 13% by mass based on the titer of the untreated yarn is achieved. Subsequent aging tests are carried out according to Method D (7 days at 150 ° C in a wide-mouth bottle). The highest tensile forces and degrees of polymerization measured after thermal stress are shown graphically in FIG. Even under the changed configuration of a pilot plant installation (untwisted fibers, controlled thread tension), the same relative stability trends as in the laboratory experiment can basically be identified after aging. However, the absolute strength level of the samples (normal and stabilized fiber) strongly depends on the aging method even at identical temperatures and loading times (see Example 2). In the present example, an untreated fiber breaks after aging to about 69% of the initial value, a corresponding stabilized fiber shows after aging still 89% residual strength. The range of degrees of polymerization follows this trend.

Example 9:

On a pilot plant untwisted rayon multifilament yarn (f1350) of fineness 2440 dtex room temperature is impregnated with a stabilizer solution according to the invention, then dried and rewound about 250 m yarn on cardboard tubes (0 = 40 mm). At a stabilizer concentration in the dipping solution of 10 or 14 mass%, a stabilizer uptake of about 10 and 15% by mass based on the titer of the untreated yarn is achieved. Subsequent aging tests are carried out according to Method E (1000 hours at 150 ° C in a wide-mouth bottle). The maximum tensile forces and degrees of polymerization measured after thermal stress are shown graphically in FIG. Aging method E is well suited for differentiating stabilizer effects in the extreme long-term test. The strength of the unstabilized fiber is drastically reduced, its average degree of polymerization is below the limit of quantification. A fiber with 10 mass% stabilizer achieves a three times higher residual strength compared to the unstabilized fiber thermal load under air. An increase of the stabilizer content to 15% by mass results in this experiment also a disproportionate increase in the residual strength as well as the degree of polymerization in the long-term aging test.

Example 10:

On a pilot plant untwisted rayon multifilament yarn (f1350) of fineness 2440 dtex room temperature is impregnated with a stabilizer solution according to the invention, then dried and rewound about 250 m yarn on cardboard tubes (0 = 40 mm). At a stabilizer concentration in the dipping solution of 14% by mass, a stabilizer absorption of about 15% by mass based on the titer of the untreated yarn is achieved. Subsequent aging tests are carried out according to method E (1000 hours in a wide-mouth bottle). The highest tensile forces and degrees of polymerization measured after thermal stress are shown graphically in FIG. The initial strength of the stabilized, unaged fiber is slightly lower than that of an unstabilized sample. However, 91-86% of this strength is retained after 1000 hours of aging over a wide temperature range of 120 to 150 ° C. The degrees of polymerization reach a level around 400, almost independent of the temperature. The stabilizer according to the invention therefore has in optimal composition and concentration the potential to equip cellulosic products for applications with increased continuous service temperatures of 150 ° C and more.

Example 11:

For the application of an impregnation solution of RF precondensate, aqueous SBR latex and formaldehyde, a 10% by mass urea solution is added so that the total concentration of urea in the batch is about 7% by weight. The mixture is post-condensed in the presence of urea overnight. The dispersion is then applied to a rayon cord of construction 1840 dtex x1 x2 at room temperature on a pilot plant by means of dipping, dried, crosslinked at 150-200 ° C., then dried and approximately 125 m of the impregnated cord on cardboard cores (0 = 40 mm). rewound. The total amount of adhesion promoter and stabilizer applied is about 6-7% by mass. Subsequent aging tests are carried out according to Method D (168 hours in a wide-mouth bottle at 150 ° C). The adhesion values before thermal stress and the maximum tensile forces before and after thermal stress are shown graphically in FIG. 11. The adhesion value determined in peel tests remains at a high level despite stabilizer addition and is still about 94% of the peel force of the unstabilized adhesion-impregnated sample. The initial strength of the stabilized, unaged fiber is slightly higher than an unstabilized sample. However, 86% of this strength is retained after 168 hours of aging at 150 ° C.

Example 12:

800 g of a standard batch of an impregnation solution of RF precondensate, aqueous SBR latex and formaldehyde is postcondensed over Nach. Subsequently, 90 g of solid urea are stirred into the impregnating solution, so that the total concentration of urea in the batch is about 10 wt .-%. The mixture is post-condensed in the presence of urea overnight. The dispersion is then applied by dip coating to a Rayon cord of construction 1840 dtex x1 x2 at room temperature, dried, crosslinked at 150-200 ° C, then dried and about 125 m of the impregnated cord on cardboard tubes (0 = 40 mm). rewound. The total amount of adhesion promoter and stabilizer applied is about 7-8% by mass. Subsequent aging tests are carried out according to Method D (168 hours in a wide-mouth bottle at 150 ° C). The adhesion values before thermal stress and the maximum tensile forces before and after thermal stress are shown graphically in FIG. 11. The adhesion value determined in peel tests remains at a good level despite stabilizer addition and is still about 85% of the peel force of the unstabilized adhesion-impregnated sample. The initial strength of the stabilized, unaged fiber is slightly lower than that of an unstabilized sample. However, 96% of this strength remains after 168 hours of aging at 150 ° C.

Claims

Cellulosic filaments with improved thermostability Claims:

1 . Cellulosic fiber coated with a urea-containing stabilizer mixture, characterized in that the

Stabilizer mixture additionally comprises nonionic surfactants and antioxidants.

2. The cellulosic fiber according to claim 1, characterized in that the surfactants are linear or branched polyethylene glycol alkyl ethers and / or long-chain, linear or branched monoalcohols.

3. The cellulosic fiber according to one or more of the preceding claims 1-3, characterized in that it is hindered phenols in the antioxidants.

The cellulosic fiber according to one or more of the preceding claims, characterized in that the cellulosic fiber is a fiber or a filament consisting predominantly of viscose, lyocell or a polymer-analogous derivative of cellulose, e.g. Cellulose acetate or cellulose triacetate.

The cellulosic fiber according to one or more of the preceding claims, characterized in that the cellulosic fiber has been obtained via a direct dissolving method, such as from solutions in tertiary amine oxides or ionic liquids or phosphoric anhydride, and subsequent precipitation in suitable coagulation media.

The cellulosic fiber according to one or more of the preceding claims 1 - 4, characterized in that the cellulosic fiber is recycled by a regenerating process in which the initial viscose is first converted by chemical conversion into a soluble modification, e.g. a xanthate or a carbamate, followed by coagulation and regeneration in suitable baths.

The cellulosic fiber according to one or more of the preceding claims, characterized in that the cellulosic fiber is a multifilament yarn having a strength of at least 20 cN / tex.

8. A method for coating cellulosic fiber or filaments, characterized in that the cellulosic fibers or filaments with an aqueous dispersion or solution of a stabilizer mixture containing urea, are brought into contact and then treated cellulosic fibers or filaments are then dried and further processed, characterized characterized in that the dispersion or solution additionally comprises nonionic surfactants and antioxidants.

9. The method according to claim 9, characterized in that the cellulosic fibers or filaments are brought into contact with the mixture by means of passing or spraying or via a preparation roller with the aqueous dispersion or solution.

10. The method according to claim 9 and 10, characterized in that the aqueous dispersion or solution contains a solids content of 10-30% by mass.

1 1. The method according to one or more of the preceding claims, characterized in that the pure, anhydrous stabilizer mixture contains from 25 to 60% by mass of urea.

12. The method according to one or more of the preceding claims, characterized in that the pure, anhydrous Stabilisatormischnug contains 25 to 60 mass% polyethylene glycol (n- or / ^'so-) alkyl ethers.

13. The method according to one or more of the preceding claims, characterized in that pure, anhydrous stabilizer mixing drying additionally ^'contains 5 to 30% by mass of long-chain n- or / so-alcohols.

14. The method according to one or more of the preceding claims, characterized in that the pure, anhydrous stabilizer mixture additionally contains 1 to 5 mass% of antioxidants.

15. The method according to one or more of the preceding claims, characterized in that the pH of the dispersion or solution is in a moderately alkaline range.

16. Adhesive, preferably based on resorcinol-formaldehyde latex, isocanate or resorcinol-formaldehyde silica, for the bonding of fibrous reinforcements to rubber, characterized in that the adhesion promoter additionally contains urea.

17. The adhesion promoter according to claim 16, characterized in that the fiber-containing reinforcing elements contain fibers or filaments which are predominantly of viscose, lyocell or of a polymer-analogous Derivatives of cellulose, such as cellulose acetate or cellulose triacetate exist