WO1997030197A1

WO1997030197A1 - Process for preparing cellulose yarn having a high tenacity

Info

Publication number: WO1997030197A1
Application number: PCT/EP1997/000692
Authority: WO
Inventors: Hendrik Maatman; Hendrik Lammers; Marco Ypma; Bernardus Maria Koenders
Original assignee: Akzo Nobel N.V.
Priority date: 1996-02-14
Filing date: 1997-02-14
Publication date: 1997-08-21

Abstract

The invention pertains to a process for producing cellulose yarn having a tenacity higher than 1000 mN/tex, in which process: cellulose is dissolved in a solvent containing 65-80 wt.% of phosphorus pentoxide; the resulting anisotropic solution, with cellulose with a degree of polymerisation (DP) of more than 700 dissolved in it, is extruded through one or more spinning orifices, with the DP of the cellulose in the solution being determined just prior to the extrusion of the solution; the obtained extrudates are coagulated and washed; and the filaments produced in this manner are dried and wound.

Description

PROCESS FOR PREPARING CELLULOSE YARN HAVING A HIGH TENACITY

The invention pertains to a process for preparing cellulose yarn having a tenacity higher than 1000 mN/tex.

Processes for preparing cellulose yarn with a high tenacity (> 1000 mN/tex) are well-known.

EP 103 398 describes a process for making high-strength cellulose filaments. In this well-known process cellulose triacetate is dissolved in an appropriate solvent (e.g., a mixture of trifiuoroacetic acid and water), yielding an anisotropic cellulose triacetate solution. This solution is spun, after which the resulting cellulose triacetate filaments are saponified/ regenerated. In this way high-strength cellulose filaments can be obtained.

However, this process has the drawback of being fairly labour-intensive. If cellulose is used as the starting material, first of all cellulose triacetate has to be formed, followed by this cellulose derivative being dissolved and the resulting solution being spun. Finally, the resulting filaments have to be regenerated in a separate process step. Moreover, keeping in mind the personal safety of those involved in such a process, the chemicals and solvents used require special attention.

WO 85/05115 also describes a process for obtaining high-tenacity cellulose yarn from an anisotropic solution of a cellulose derivative (cellulose formate). However, this process suffers from the same drawbacks as the process described in EP 103 398.

The invention pertains to a process by means of which an anisotropic cellulose solution can be obtained simply and within a short period of time, which anisotropic cellulose solution can be converted, without any additional sapon if ication/ regeneration step, into cellulose filaments having a high tenacity.

The invention consists in that:

» cellulose is dissolved in a solvent containing 65-80 wt.% of phosphorus pentoxide, β the anisotropic solution thus obtained, with cellulose with a degree of polymerisation (DP) of more than 700 dissolved in it, is extruded through one or more spinning orifices, the DP of the cellulose in the solution being determined just prior to extrusion of the solution, » the resulting extrudates are coagulated and washed, and

• the filaments thus formed are dried and wound.

The term phosphoric acid in this patent application refers to all inorganic acids of phosphorus and their mixtures. Orthophosphoric acid is the acid of pentavalent phosphorus, i.e. H₃P0₄. Its anhydrous equivalent, i.e. the anhydride, is phosphorus pentoxide (P₂0₅). In addition to orthophosphoric acid and phosphorus pentoxide there is, depending on the quantity of water in the system, a series of acids of pentavalent phosphorus with a water-binding capacity in between those of phosphorus pentoxide and orthophosphoric acid, such as polyphosphoric acid (H₆P₄0₁₃, PPA).

In the present patent specification the solvent by definition is made up of the added phosphoric acid and/or its anhydrides and all the free water present in the solution. For that reason this description always includes in the solvent the water originating from the cellulose, which is usually added at a later time, while water from substances which are among the remaining constituents also is part of the solvent. The phosphorus content of the solvent is determined by converting the quantities by weight of phosphoric acid in the solvent into the equivalent quantity by weight of the corresponding anhydride. Converted in this manner, orthophosphoric acid is made up of 72,4 wt.% of phosphorus pentoxide and residual water, and H₆P₄0₁₃ of 84 wt.% of phosphorus pentoxide and residual water.

The weight percentage of phosphorus pentoxide in the solvent is calculated by starting from the overall quantity by weight of phosphoric acid including its anhydrides and the total quantity of water in the solvent, converting the acids into phosphorus pentoxide and water, and calculating the percentage of said overall quantity by weight made up by phosphorus pentoxide.

In this description water derived from cellulose or from substances which are part of the other constituents and water which is added to obtain the solution are not included in the calculation of the concentration of phosphorus pentoxide in the solvent.

The weight percentage of phosphorus pentoxide in the solution is calculated by starting from the overall quantity by weight of phosphoric acid including its anhydrides and the total quantity of water in the solution, converting the acids into phosphorus pentoxide and water, and calculating which percentage of said overall quantity by weight is made up by phosphorus pentoxide. For that reason in this description water derived from cellulose or from substances which are part of the other constituents and water which is added to obtain the solution are included in the calculation of the concentration of phosphorus pentoxide in the solution.

The weight percentage of cellulose in the solution is calculated by starting from the overall quantity by weight of all constituents in the solution. In addition to water, phosphoric acid and/or its anhydrides, and cellulose and/or reaction products of phosphoric acid and cellulose, other substances may be present in the solution. The solution can be prepared by mixing constituents classifiable into four groups: cellulose, water, phosphoric acid including its anhydrides, and other constituents. The "other constituents" may be substances which benefit the processability of the cellulose solution, solvents other than phosphoric acid, or adjuvants (additives), e.g., to counter cellulose degradation as much as possible, or dyes and the like.

In the case of cellulose derivatised with phosphoric acid the percentages by weight of cellulose in the solution listed in this patent specification refer to quantities calculated back on the cellulose. This applies in analogous fashion to the quantities of phosphorus mentioned in this specification.

Preferably, the solution is composed of 94-100 wt.%, more particularly 96-100 wt.%, of the constituents cellulose, phosphoric acid and/or its anhydrides, and water. Preferably, no solvents other than phosphoric acid are employed, and adjuvants or additives are present only in amounts of 0 to 4 wt.%, calculated on the overall quantity by weight of the solution. More favoured still is a solution containing the lowest possible quantity of substances other than the constituents cellulose, phosphoric acid and/or its anhydrides, and water, i.e., with from 0 to 1 wt.% of additives.

Anisotropic cellulose solutions which can be obtained by dissolving cellulose in a solvent containing 65-80 wt.% of phosphorus pentoxide have been described in non-prepublished patent application WO 96/06208 in the name of Applicant. This application discloses a very favourable process for obtaining such an anisotropic solution. In addition, the application discloses a very favourable process for making use of this solution to obtain cellulose yarn.

It was found that the process as described in WO 96/06208 can produce cellulose yam having a high breaking tenacity (i.e. breaking tenacity > 1000 mN/tex) if the DP of the cellulose in the yarn is higher than 700. Given that there is hardly any cellulose degradation during extrusion, coagulation, and washing, this means that the DP of the cellulose in the solution will have to be higher than 700 immediately prior to the solution's extrusion. Preferably, the DP of the cellulose in the solution will be in the range of 1000 to 2000 just prior to the extrusion of the solution. The cellulose DP just prior to extrusion is deemed to be equal to the DP of the yarn. The DP of cellulose yarn can be measured by the procedure mentioned in this patent specification.

During its dissolution there will be some degradation of the cellulose. This means that the DP of the cellulose used as starting material for the solution should also be higher than 700. Preferably, the DP of the cellulose used as starting material is higher than 1000, more particularly higher than 1500.

There was also found to be a decrease of the cellulose DP in the solution. This decrease can be limited by selecting a lower temperature at which to store or process (spin) the solution. However, a lower temperature of the solution will give an increase in its viscosity. It was further found that the content of cellulose-bound phosphorus will increase when the solution is stored or processed at a higher temperature.

For spinning good fibres from the anisotropic solution it is recommended to employ dissolving pulp having a high α-content, e.g., such as is commonly used to make fibres for textile and industrial applications. Examples of suitable types of cellulose include Buckeye V60 and Alphacell C-100.

Cellulose as commercially available generally contains some water (about 5 wt.%) and can be employed as such without any objection. Of course, it is also possible to use dried cellulose, but this is not required.

The anisotropic solution is extruded through a spinneret plate having one or more orifices. The extrusion of spinning solutions having a cellulose concentration between 15 and 20 wt.% preferably is carried out at a temperature in the range of 0 to 65°C, with the briefest possible residence time at the higher temperatures. Preference is given to such solutions being extruded at a temperature in the range of 20 to 70°C, more particularly in the range of 40 to 60°C. For other concentrations it holds that as the concentration gets higher, the spinning temperature preferably will also exceed the ranges indicated here, and vice versa.

The desired number of orifices in the spinneret plate is dependent on the future use of the fibres to be obtained. Thus, a single spinneret plate may be used not only for extruding monofilaments but also for extruding the multifilament yarns much in demand in actual practice which contain from 30 to 10 000, preferably from 100 to 2000, filaments. The manufacture of such multifilament yarns preferably is carried out on a cluster spinning assembly containing a number of spinning orifice clusters, as described in EP 168 876 or on a spinning assembly with one or more spinnerets, which spinnerets are described in WO 95/20969. In view of the high pressures which may occur when spinning viscous, anisotropic cellulose solutions, it is particularly favourable to make use of the spinnerets described in WO 95/20969. Following extrusion, the extrudates are passed through an air gap the length of which is selected depending on the thickness of the extrudates and their desired degree of drawing among others. In general, the air gap will have a length in the range of 4 to 100 mm. Next, the obtained extrudates are passed through a coagulation bath in a manner known in itself. As suitable coagulants may be selected low boiling, a-polar organic liquids which have only a limited swelling effect on cellulose, water, or mixtures thereof, such as alcohols, ketones, esters, water, or mixtures thereof. Examples of such suitable coagulants are propanol, ethanol, and acetone, or mixtures thereof. Preference is given to the use of acetone or ethanol as coagulants, since they display very good coagulating action and in most cases have better properties when it comes to safety and ease of handling than the other means mentioned.

The coagulation bath preferably has a temperature in the range of -40°C (providing the coagulant selected allows this) to 30°C.

After coagulation there may be washing out, in combination or not with a neutralising treatment. The washing out may take the form of placing a spool of coagulated yarn in a vessel containing the washing agent, or else by passing the fibres through a vessel containing the appropriate liquid in a continuous process and then winding them onto a roller. According to a process highly suited for use in actual practice, washing out is performed with so-called jet washers, such as described in British patent specification GB 762,959. The washing agent employed may be the same as the agents mentioned for coagulation. Highly suitable to be used are methanol, ethanol, acetone and/or water or mixtures thereof. Washing out may be performed at any temperature below the boiling temperature of the washing agent, at any rate preferably below 100°C.

Neutralisation may be carried out either immediately following the washing step, or in between the coagulation and washing steps. Alternatively, neutralisation may take place after the washing step and be followed by a next washing step. The neutralising agent used may be a solution in water of NaOH, KOH, LiOH, NaHC0₃, Na₂C0₃ 10H₂O, NH₄OH, sodium ethanolate or sodium methanolate, e.g., using a batchwise process, such as immersion, or a continuous process, such as passing through a bath, spraying, the use of a kiss roll, or a bath equipped with jet washers.

Non-prepublished patent application WO 96/06207 in the name of Applicant describes an aftertreatment in order to obtain cellulose yarn with high heat stability.

The resulting cellulose fibres have very good mechanical properties such as strength, modulus, and favourable elongation. Since there is hardly any reaction between the solvent and the cellulose, the properties obtained from the cellulose structure, such as the chain modulus, are retained, while the anisotropy of the solution makes it possible to attain properties desired in many mechanical applications.

In this way cellulose yarns can be obtained which have a breaking tenacity higher than lOOO mN/tex. The fibres possess good adhesion to rubber after a single impregnation with conventional adhesives, e.g., dipping with a resorcinol- formaldehyde latex (RFL) mixture.

The process according to the present invention is especially favourable because it permits the solution's preparation and spinning to be carried out as a continuous process on a single line. In addition, the solution has the advantage that when products are made therefrom, in particular when no constituents other than phosphoric acid, water, and cellulose are employed, there is hardly any reaction between the cellulose and the phosphoric acid, and hence there is no need for cellulose regeneration.

Especially in industrial applications the solution now found offers particular advantages with regard to ease of handling and safety, there being little if any corrosion of the equipment to be used and comparatively easy recovery of the solvent, especially if the solution is prepared using only cellulose and the solvent. In addition, the now found process is significantly less harmful to the environment than the known processes for preparing high-tenacity cellulose yarn. All of this is reflected in an economically highly advantageous process.

Thus are obtained in a highly advantageous manner cellulose fibres especially suited to be used in rubber articles subjected to mechanical load, such as vehicle tyres, conveyor belts, rubber hose, and the like. The fibres are particularly suited to be used as a reinforcement in vehicle tyres, e.g., car and truck tyres.

Generally speaking, the fibres constitute an advantageous alternative to industrial yarns such as nylon, rayon, polyester, and aramid.

Further, the fibres can be pulped. Such pulp, which may be mixed with other materials, such as carbon pulp, glass pulp, aramid pulp, or not, is highly suited to be used as a reinforcing material, e.g., in asphalt, cement and/or friction materials. Measuring methods

Determination of anisotropy

Visual determination of the isotropy or anisotropy was performed with the aid of a polarisation microscope (Leitz Orthoplan-Pol (100x)). To this end about 100 mg of the solution to be defined were arranged between two slides and placed on a Mettler FP 82 hot-stage plate, after which the heating was switched on and the specimen heated at a rate of about 5°C/min. In the transition from anisotropic to isotropic, i.e., from coloured (birefringent) to black, the temperature is read off at virtual black. The transition temperature is indicated as T_πi.

The visual assessment during the phase transition was compared with an intensity measurement using a photosensitive cell mounted on the microscope. For this intensity measurement a specimen of 10-30 μm was arranged on a slide such that no colours were visible when crossed polarisers were employed. Heating was carried out as described above. The photosensitive cell, connected to a recorder, was used to write the intensity as a function of time. Above a certain temperature (differing for the different solutions) there was a linear decrease of the intensity. Extrapolation of this line to an intensity of 0 gave the Tni. In all cases, the value found proved a good match for the value found by the above-mentioned method.

A solution is deemed to be anisotropic when it displays birefringence at room temperature. This means that T_nι is above 25°C.

Determination of DP The degree of polymerisation (DP) of the cellulose was determined with the aid of an Ubbelohde type 1 (k=0,01). To this end the cellulose specimens to be measured were dried in vacuo for 16 hours at 50°C after neutralisation, or the amount of water in the copper II ethylene diamine/water mixture was corrected to take into account the water in the cellulose. In this way an 0,3 wt.% of cellulose- containing solution was made using a copper II ethylene diamine/water mixture (1/1). On the resulting solution the viscosity ratio (vise. rat. or η_rel) was determined, and from this the limiting viscosity (η) was determined in accordance with the formula:

. [η ,] = vise, rat - 1 x 100 c + (k x c x (vise, rat- 1))

wherein c = cellulose concentration of the solution (g/dl) and k = constant = 0,25 From this formula the degree of polymerisation DP was determined as follows:

DP - - - (for [η]< 450 ml / g), or 0,42 ^v '

DP⁰⁷⁶ (for [η]>450 ml / g)

Determining the DP of the cellulose in the solution proceeded as described above after the following treatment:

20 g of the solution were charged to a Waring Blender (1 litre), 400 ml of water were added, and the whole was then mixed at the highest setting for 10 minutes.

The resulting mixture was transferred to a sieve and washed thoroughly with water. Finally, there was neutralisation with a 2%-NaHC0₃ solution for several minutes and after-washing with water to a pH of about 7. The DP of the resulting product was determined as described above, starting from the preparation of the copper II ethylene diamine/water/cellulose solution.

Mechanical properties The mechanical properties of the filaments and the yarns were determined in accordance with ASTM standard D2256-90, using the following settings. The filament properties were measured on filaments clamped with Arnitel® gripping surfaces of 10 10 mm. The filaments were conditioned for 16 hours at 20°C and 65% relative humidity. The length between grips was 100 mm, the filaments were elongated at a constant elongation of 10 mm/mm. The yarn properties were determined on yarns clamped with Instron 4C clamps. The yarns were conditioned for 16 hours at 20°C and 65% relative humidity The length between grips was 500 mm, the yarns were elongated at a constant elongation of 50 mm/mm. The yarns were twisted, the number of twists per meter being 4000/Vlιnear density [dtex]

The linear density of the filaments, expressed in dtex, was calculated on the basis of the functional resonant frequency (ASTM D 1577-66, Part 25, 1968), the yarn's linear density was determined by weighing

The tenacity, elongation, and initial modulus were derived from the load- elongation curve and the measured filament or yarn linear density The initial modulus (In Mod ) was defined as the maximum modulus at an elongation of less than 2% The final modulus was defined as the maximum modulus at an elongation of more than 2%.

Example

The invention will be illustrated with reference to the example.

Unless otherwise specified, the following starting materials were employed to prepare the solutions in the example.

Material Manufacturer and product code Content P₂Q₅ [%]

P₂O_s J.T. Baker, 0193 98

H₃P0₄ La Fonte Electrique SA, Bex Suisse 71,2 crystallised, >99% (98,3% analysed) H₄P₂0₇ Fluka Chemika, 83210, 97% (98,8% anal.) 78,8 PPA^* Caldic 84j>

*PPA = polyphosphoric acid

Example

An anisotropic cellulose solution containing 18,3 wt.% of cellulose (Buckeye V60, DP=820), obtained by the process described in non-prepublished patent application WO 96/06208 in the name of Applicant, i.e., by mixing cellulose with a solvent containing 73,9 wt.% P₂0₅ at about 20°C, which solvent was obtained by mixing and kneading 65,4 pbw (parts by weight) H₃P0₄ and 16,4 pbw polyphosphoric acid at elevated temperature for some time. Directly after preparation, the cellulose solution was extruded at 61 °C through a spinneret having 375 capillaries each with a diameter of 65 μm. The extruded solution was passed through an air gap of 35 mm, drawn in the air gap 9,1 times, and coagulated in an acetone/polyphosphoric acid mixture. This mixture was obtained by mixing 12 pbw acetone with 1-2 pbw polyphosphoric acid and was kept at a temperature of -2,6°C. The resulting yarn was washed with water, finished with RT32A, neutralised by treatment with an aqueous 2,5 wt.% Na₂CO₃-10H₂O solution, dried at 150°C, and wound onto a bobbin at a speed of 140 m/min.. During coagulation, washing, and drying the tension exerted on the yarn was kept below 50 mN/tex.

The thus obtained yarn has the following properties: Linear density 477 dtex

Breaking tenacity 1030 mN/tex

Elongation at Break 5,2 %

Initial modulus 28,5 N/tex

Final modulus 25,0 N/tex Breaking toughness 25,0 J/g

Claims

1. A process for producing cellulose yarn having a tenacity higher than 1000 mN/tex, which process comprises the following steps: • cellulose is dissolved in a solvent containing 65-80 wt.% of phosphorus pentoxide, the resulting anisotropic solution, with cellulose with a degree of polymerisation (DP) of more than 700 dissolved in it, is extruded through one or more spinning orifices, with the DP of the cellulose in the solution being determined just prior to the extrusion of the solution, the obtained extrudates are coagulated and washed, and the filaments produced in this manner are dried and wound.

2. A process according to claim 1 , characterised in that cellulose having a DP above 1000 is dissolved.

3. A process according to either of the preceding claims, characterised in that the extrudates are coagulated in acetone.

4. A process according to any one of the preceding claims, characterised in that the extrudates are washed with water.