MXPA99001436A - Manufacture of extruded articles - Google Patents

Abstract

Use in the manufacture of extruded lyocell articles of cellulose having a value of Pipe Flow Index (as defined) to Jet Flow Index (as defined) in the range from 0.85 to 6 can offer a number of advantages, particularly in cellulose solution transport and in spinning stability. Pipe Flow Index is designed to assess the flow performance of cellulose solution under low shear conditions typically experienced in transfer pipework. Jet Flow Index is designed to assess the flow performance of cellulose solution under high shear conditions typically experienced during extrusion. The extruded lyocell articles are made by a method which comprises the steps of:(1) dissolving cellulose in an aqueous tertiary amine N-oxide solvent to form a solution;(2) extruding the solution through a die by way of a gaseous gap into a coagulating bath to form an extruded lyocell precursor;(3) washing the extruded lyocell precursor freefrom tertiary amine N-oxide;and (4) drying the washed lyocell precursor, thereby forming the extruded lyocell article.

Description

MANUFACTURE OF EXTRUDED ARTICLES Field of the Invention This invention relates to methods for the manufacture of Lyocell extruded articles such as fibers and films, where a cellulose solution in a tertiary amine N-oxide solvent is extruded through a die inside a coagulation bath. Lyocell is the generic name for cellulose produced by the extrusion of solvent or centrifuged solvent processes of this type. The tertiary amine N-oxides are sometimes referred to below for convenience, as amine oxides. Background of Technology The manufacturer of polymer articles formed through the extrusion of a cellulose solution in an aqueous solvent of tertiary amine N-oxide (which solution can also be referred to as an additive) within a coagulating aqueous bath is described as an example in US-A-4,246,221, the content of which is incorporated herein by reference. Cellulose in the conventional dissolution grade, for example in the form of wood pulp and cotton wool, is used as a raw material in these processes.

EP-AO, 648, 808 states that the extrusion conditions for these solutions must be chosen to provide freedom in the instability of melt flow within the extrusion orifice, which can result in a melted fracture and as a consequence a shutdown in the production (loss of centrifugal stability). Instability in the melt flow can be found without reducing the extrusion productivity by reducing the viscosity of the solution. for example, by reducing the concentration or degree of polymerization (D.P.) of the cellulose in the solution. This reduction also allows for increases in the design ratio which can be applied to extruded fibers and in the speed of removal of these fibers. However, this reduction is observed due to the disadvantages caused in any other part of the process, notably by the reductions in productivity and through increases in the load to the solvent recovery system. EP-A-0,648, 808 discloses an aqueous solution of cellulose in N-methyl-morpholine N-oxide where the cellulose is comprised of a mixture of (1) a first cellulose component with a degree of polymerization (DP) in the range from 500 to 2000, and (2) a second cellulose component with a DP in the range of 350 to 900, with the proviso that the ratio of D.P. from component (2) to D.P. of component (1) is not greater than 0.9: 1, the ratio by weight of component (1) and component (2) is in the range from 95: 5 to 50: 50. It is said that these solutions can be extruded at high speed with a process stability to obtain lyocell fibers with properties similar to those produced by conventional lyocell processes. Disclosure of the invention According to the invention, a method for the manufacture of an extruded article of lyocell has been provided, which comprises the following steps: (1) dissolving the cellulose in an aqueous solvent of Tertiary amine N-oxide to form a solution; (2) extruding the solution through a die by means of a gaseous range into a coagulating bath to form an extruded precursor of lyocell; (3) washing the extruded lyocell precursor to remove the tertiary amine N-oxide; and (4) drying the washed lyocell precursor, thereby forming the extruded lyocell article.

Characterized because the cellulose exhibits a ratio of the Tube Flow Index (as defined in Test Method 2) to the Jet Flow rate (as defined in Test Method 3) in the range from 0.85 to 6.0. The Tube Flow Index (PFI) is designed to evaluate the performance of the flow of the cellulose solution in the low-cut condition of the type typically experienced in the transfer pipe in a manufacturing plant. The Jet Flow Index (JFI) is designed to evaluate the performance of the flow of a cellulose solution under the high cut conditions of the type typically experienced in a centrifugal apparatus or other extrusion die. In both cases, the higher values of the index correspond to an increase in the flow rate at a certain pressure or at a lower pressure required to induce a given flow rate. The tertiary amine N-oxide is preferably an N-methyl-morpholine N-oxide (NMMO). The amount of cellulose in the solution is preferably within the range from 5 to 25, or more preferably from 10 to 20 percent by weight. The amount of water in the solution is often in the range of 7 to 14 percent by weight, although this will be appreciated from the known behavior of the cellulose / NMMO / water compositions in that the acceptable range of concentration of water may vary with the concentration of cellulose. The steps of dissolution, extrusion, washing and drying can be carried out in a conventional manner. The cellulose solution can be conveniently carried out by dispersing the cellulose in a 60/40 mixture of NMMO and water to form a slurry or premix, followed by an evaporation removal of the excess water, for example a thin film evaporator as the Filmtruder (trademark of Buss AG) to achieve the desired solution. The gas in the gaseous range is preferably air, although other inert gases such as nitrogen can also be used. The length of the gaseous interval is commonly found in the range from 10 to 100 mm. The gas can be blown through the gaseous range. The coagulant bath is typically comprised of aqueous NMMO. The washing and drying steps can be performed in any convenient way. The extruded article of lyocell can take the form of fibers, for example in the form of continuous filament spinning, tow or strand fibers, or film in the form of a sheet or tube. In the case of fibers, the extrusion die or centrifugal apparatus is typically comprised of orifices with a diameter in the range of 50 to 200, often 70 to 120, microns. We have found in general that the value of the PFI / JFI ratio increases with increasing polydispersity (broader D.P. distribution) of cellulose. The value of this ratio can therefore be increased by mixing the cellulose of different D.P. or by selecting the cellulose source which has a D.P. distribution. inherently wider. The above to these alternatives is generally preferred in the present, because we have found that commercially available dissolved pulps provide PFI / JFI values within the range of 0.5 to 0.8. It is generally preferred that the D.P. it must be diverted towards the lower end of the range. We have estimated that the PFI / JFI ratio of the cellulose mixtures disclosed in EP-A-0, 648, 808 is within the range of 0.3 to 0.8.

When a mixture of cellulose sources is used, we have found that the value of PFI / JFI varies to some extent with the average of D.P. of the cellulose in the mixture. In general, we have found that the relationship that exhibits a maximum in an average of D.P. falling between the average D.P.s of the individual sources of cellulose that form the mixture and the operation within or near this maximum are preferred. Mixtures that are comprised of a low viscosity cellulose component with an average of D.P. in the range of 200 to 750, preferably from 250 to 500, and the cellulose component with high viscosity with average D.P. in the range of 800 to 1500 may be preferred. The D.P. of the cellulose component with low viscosity is generally found at the lower or lower end of the commercial range for the dissolved pulp. The viscosity of the cellulose raw material can be reduced if desired by the known techniques such as irradiation, steam explosion, chemical treatment (including in particular acid hydrolysis and division of the oxidizing chain) or enzymatic treatment ( example, using a cellulase). Alternatively, the previously processed cellulose material, for example the waste of viscose rayon, can be used as part or all of the low viscosity component. The width of the distribution of D.P. from a single source of cellulose can, if desired, be increased by subjecting a proportion of the cellulose to one or more of the aforementioned techniques to reduce the viscosity of the cellulose. Such a process may be employed in the same cellulose (which may be preferred), or in a cellulose slurry or premixture in NMMO / water. The JFI value is preferably at least 0.1, more preferably at least 0.5, and preferably no more than 10. A low value for JFI corresponds to a high back pressure in the extrusion apparatus. A JFI value within the range from 1.0 to 2.0 may also be preferred. The model experiments indicate that the maximum value of the PFI / JFI ratio for practical purposes is around 6. These experiments also indicate that the JFI may have the tendency toward undesired low values towards this end of the range for this relationship. A value of the PFI / JFI ratio within the range from 0.9 to 4 or from 1.0 to 2.0 may be preferred. When an additive of the type provided by the invention is replaced by a conventional additive in a lyocell manufacturing plant, we have surprisingly found that productivity can be substantially increased. First, we have found that the substitution is generally met by improved centrifugal stability. This can become an advantage by increasing the production rate through the extrusion head. Second, we have generally found that, otherwise under conditions without change, the pressure drop decreases through the large diameter of the tube used in the preparation of the additive and the handling area, while the back pressure in the Centrifugal device remains unchanged or falls slightly. Correspondingly, the cost of pumping the additive through the transport system of the additive can be reduced; or alternatively, the rate of flow through the transport system of the additive can be increased without additional capital expenditure. The improved centrifugal stability allows the use of an additive with a lower viscosity (for example of a reduced concentration1 of cellulose, of a D.P. reduced cellulose or an increase in temperature) without loss of product quality. As a consequence, the pumping costs can also be reduced, or the flow rate through the additive transport system can also be increased. We have found that these benefits can more than overcome both the increased load in the recovery process of the solvent imposed by the reduced concentration of cellulose as well as the need to increase the flow rate of the additive to obtain a determined yield of cellulose. In contrast, by reducing the viscosity of the conventional additive (for example by reducing the concentration of cellulose or D.P. or by increasing the temperature) centrifugation under optimized conditions generally results in reduced centrifugal stability. The PFI and JFI values and their ratios measured in an extruded lyocell article can be correlated with the respective measurements of the cellulose source. In the following Test Methods and Examples, parts and proportions are by weight except where otherwise specified.

Test Method 1: Preparation of Cellulose Solutions for Testing A Z-blade mixer such as the Win worth 8Z (registered trademark) (with a capacity of 4 liters) equipped with "a vacuum connection and an overheated jacket" is used. The jacket temperature is set at 100 ° C. The operating mixer is charged with a mixture containing nominally 60% NMMO and 49% water, a cellulose sample and a small amount of propylene gallate (thermal stabilizer) dissolved in isopropanol The mixer is then operated for 5 minutes or more until a uniform slurry (premix) has been obtained Vacuum is applied (conveniently about 6.5 kPa (50 mm Hg) absolute pressure) to remove excess water This is how the dissolution of cellulose is enabled, mixing and evacuation are continued until a solution (additive) with a refractive index of 1.4895 and free of any excessive amount is obtained. e undissolved fibers. This corresponds to the nominal load weight of 2 kg. and to a solution nominally containing 15% cellulose and 10% water. The cellulose content can be determined gravimetrically. The solution is allowed to cool and solidify, and can be conveniently cut into chips and sifted in preparation for testing. The additive chips should be stored in sealed plastic bags in an airtight container containing a small amount of silica gel as a desiccant to avoid a noticeable change in moisture content. For use in Test Methods 2 and 3, the cellulose concentration of the samples for testing should be 15 ± 0.25%. Test Method 1 is applied to cellulose sources such as dissolved pulp, cotton wool and regenerated or reconstituted cellulose articles such as fiber and films (preferably free of foreign chemicals such as dyes and finishes). Test Method 2: Determination of Tube Flow Rate (PFI) The Tube Flow Index (PFI) is designed to evaluate the flow performance of a cellulose solution under low cut conditions of a type typically experienced in the transfer pipe in a manufacturing plant. A higher value of PFI corresponds to the lower viscosity (and correspondingly an easier to use flow) in these low cut conditions. The additive chips are prepared according to Test Method 1. The PFI is measured using a Bohlin VOR Rheometer (Trade Mark) equipped with a high-torque measuring head (2000 gcm as maximum torque) and using a cone 30mm diameter /5.44° on a geometric plate. A hollow cylindrical gualdera retaining liquid is removably mounted on the perimeter of the plate, extending upwardly beyond the base of the cone. The instrument is heated to 105 ° C, and the measurement interval between the cone and the plate is adjusted to 150 micrometers. The additive chips (approximately 5 g.) Are placed on the plate, and the insulating covers are fitted to the instrument. The interval is then slowly adjusted to 600 micrometers, taking care to keep the reading of the Normal force in the instrument below 20% to avoid damage to the equipment or to the sample under test. The covers are removed, and any excess solution is removed from the outside of the cone and plate assembly. The covers are replaced, the normal range is slowly adjusted to 230 micrometers (keeping the Normal force reading below 15%), and any excess additive is removed as was done previously. The silicone oil (Dow Corning 200 / 10cs (Trade Mark)) is drained over the cone and plate assembly so that the base of the cone is covered (to inhibit the loss of volatile components), and the covers are replaced. The interval is then slowly adjusted to 150 micrometers (keeping the Normal force reading below 10%). After allowing 10 minutes or a similar time to obtain the thermal equilibrium, the measurements of cut in steady state are carried out under the following conditions: cutting range 0.0927 to 9.27 s-1 (11 points), the delay time of 180 s (tightness), integration time of 15 s, automatic zero (10 s delay), continuous cutting on. The experiment is repeated to confirm the results. A fresh sample of the additive chips should be used for each group of measurements. In preliminary experiments, it was determined that a cutoff rate of 1 s "1 yielded reliable results.The tightness of the cut with this cutoff rate was determined by adjusting a curve of the energy law to the two data points immediately above and the two data points immediately below 1 s-1, as follows: Effort is cut = A x (Cutoff Rate) 3 where A and B are derived constants - Following these preliminary experiments, a sample of additive containing 14.71 percent by weight of cellulose in which the values of A and B were 1440 and 0.4195 respectively were selected as arbitrary control for use in the PFI calculation according to the equation: PFI = Cx / Ax.As / Cs. ( (3Bs + l) / Bs) Bs. (Bx / (3B + 1)) Bx .025 (Bs_Bx) where the identification letters syr refer to the control sample and to the sample under the test respectively, C represents the percentage of cellulose in the solution and A and B with the constants of the ey of energy. The values As, Bs and Cs are therefore 1440, 0.4195 and 14.71 respectively. The values of Ax and Bx are calculated by adjusting the curve of the energy law to the two data points immediately above and the two data points immediately below the shear stress 1440 Pa. This equation makes the tolerance of the thinning of the cut. The same wood pulp and the same additive were used to establish the arbitrary norm of Test Method 3.

On the occasion, the specified shear stress (1440 Pa) can not be obtained within the established strain range. For samples with high viscosity, a range of adequate minor tightness should be selected, and measurements should be made with a delay time of 180 s (constant). For samples with low viscosity, an adequate range of tightness should be selected. In the latter case, the erroneous results can be obtained with a superior tension (shown by a break in the line in the curve of the energy law); if so, the PFI can be determined through interpolation or extrapolation of the three data points closest to the specified shear stress. A cutoff rate of 1 s-1 can be considered as representative of the cut experienced by lyocell additives during transportation through the factory pipeline, although higher cutting rates (for example up to 10 or 20 s) 1) can be experienced under some factory circumstances, and lower cutoff rates can be experienced in a design team (for example a pilot silver or a factory producing at low capacity) Test Method 3: Determination of the index Jet Flow (JFI) This test is designed to evaluate the flow performance of a cellulose solution under high cutting conditions of the type typically experienced in centrifugal devices and other extrusion dies. The high values of JFI correspond to a low viscosity (and correspondingly an easy to use flow under a certain pressure or a lower back pressure at a given flow rate) under these high cut conditions. The additive chips are prepared according to Test Method 1. The JFI is measured using a piece of specially designed equipment called Jet Rheometer. This is comprised of a heated barrel equipped with one end with a pressurized nitrogen gas feed and in the other end with a plate containing a single hole for extrusion of the additive 100 micrometers in diameter. The barrel assembly is also equipped with a pressure release device to safeguard against the potential danger of exothermic degradation. The barrel is a stainless steel tube 150 mm long x 20 mm internal diameter. A tubular stainless steel insert at one end of the barrel defines an axial bore of 8.5 mm in diameter and is stepped to provide a bend directed downward from that end of the barrel. A stainless steel mesh filter (nominal pore size of 40 micrometers) is supported by a perforated plate 3 mm thick containing holes with a diameter of 12 x 1.5 mm (a breaker plate) seated in the elbow. The filter and the plate are retained in place at the elbow by an extrusion head seated within the insert. The extrusion head defines an internal passage comprising! a portion of trunk - 20.5 mm long tapered from 8.5 mm to 3.5 mm in diameter and a 2 mm long cylindrical portion of 3.5 mm in diameter, towards the end of which the extrusion plate is secured. The extrusion plate is 1400 micrometers thick. The extrusion hole has the following specification: first the truncated-conical section of 400 micrometers deep, 45 ° conical angle (rear face); the second truncated-conical section of 300 micrometers of I depth, 36 ° of conical angle; the third truncated-conical section of 300 micrometers deep, 36 ° conical angle; the fourth truncated-conical section of 300 micrometers deep, 10 ° conical angle; 100 micrometers of capillarity, 100 micrometers in diameter (face of extrusion). The additive chips (25 g) are charged into the barrel at room temperature. The barrel is placed inside a shirt preheated to 105 ° C, and is kept at this temperature for 30 minutes to allow the chips to melt. After this time, the chips are compacted to remove excess trapped air. The Jet Rheometer is then maintained for an additional 30 minutes at 105 ° C to allow the completion of melting and to obtain thermal equilibrium. The nitrogen is then supplied to the barrel to force the additive into the orifice of the centrifugal apparatus. The additive that emerges from the orifice is collected in a container with pitch, mounted on a top receptacle balance (0.1 mg sensitivity). The container contains a small amount of liquid paraffin to cover the collected additive and in this way minimize the loss of volatile components. The flow of the additive is measured at nitrogen pressures (manometer) in the range from 40 bar (4 x 106 Pa) to 2 bar being completed within 1 hour, and expressed in mg / s. The specified times should not be exceeded in order to minimize the risk of degradation during the course of the experiment. If desired, the experiment can be repeated in order to ensure that the results obtained are not erroneously influenced by a partial blockage of the hole. In preliminary experiments, it was found that an arbitrary standard additive containing 14.7% cellulose (made from the same cellulose that was used to establish the arbitrary norm of Test Method 2) required a nitrogen pressure of 25.3 bar (2.53 x 106 Pa) ( gauge) to provide an additive flow rate of 1 mg / s through the orifice of the centrifugal apparatus. This pressure was adopted correspondingly as an arbitrary norm for the measurement of the JFI. The JFI is calculated from the following equation: I JFI = V.C / 14.71! where V represents the flow rate at the specified pressure in mg / s and C the percentage of the cellulose in the additive. V is determined by the linear interpolation between the recorded data points. The invention is illustrated by the following Example: - Example The Lyocell additive was made and centrifuged in a conventional manner in a pilot silver in a dtex 1.7 fiber. The centrifugation speed was 75 m / min. and the diameter of the centrifugal apparatus is 70 micrometers. The air was blown transversely within an air gap separating the rotating apparatus and the coagulating bath. Various mixtures of two components of wood pulp were used as starting material. The pressure drop between the centrifugal pump I and the final filter (P psig) and the back pressure in the rotary device assembly (J psig) were measured to assess the ease of transport through the plant pipeline and through of the centrifugal device respectively. (It will be appreciated that P and J are arbitrary measures, whose absolute values are only relevant in this particular pilot plant). The range of transverse air velocities in which the centrifuge was stabilized was measured; a minimum speed corresponds to conditions; more stable centrifuges. As a guide, the reduction in the minimum speed from 14 up to 7 units allows the production of centrifugation to be increased by around 20%. Other relevant details appear in Table 1.

TABLE 1? Ef. Source Source DP PFI / JFI CiD% Temp P psig J psig Range Pulp A DP% Pulp B DP% ° C air speed 1 Viscokraft HV 850 33 Viscokraft LV 470 67 600 9.7 15 105 86 720 14-47 2 Estercell 1020 30 Viscokraft ELV 415 70 600 0.86 15 105 88 735 7-35 3 Estercell 1020 30 Viscokraft ELV 415 70 600 0.86 15 105 93 769 7-38 4 Estercell 1040 14 Viscokraft ELV 415 86 500 0.92 15 105 27 595 15-40 Estercell 1020 14 Viscokraft ELV 415 86 500 0.62 15.7 105 57 730 14-47 6 Estercell 1020 30 Viscokraft ELV 415 70 600 0.86 15 113 46 720 15-47 7 Estercell 1020 30 Viscokraft ELV 415 70 600 0.86 13.6 105 45 650 12-47 Viscokraft HV, Viscokraft LV, Viscokraft ELV and Estercell are Trademarks. The different viscosity grades of Estercell were used in runs 2-3 and 5-7 on the one hand and in run 4 on the other. The D.P. of the pulp is quoted by the manufacturer or is derived from the viscosity grade quoted by the manufacturer. The CiD represents the concentration of cellulose in the additive. Run 1 represents a control of the experiment. The tensile properties of all the fiber samples were closely similar. The comparison of replica runs 2 and 3 with run 1 shows improved spin stability and productivity (reducing the minimum air velocity), with similar flow behavior (similar values for P and for J). The comparison of run 4 with Run 1 shows a similar centrifugation stability but the values are markedly reduced for P and J. The average of D.P. it was lower in run 4 than in run 1, but nevertheless, the value of P was significantly low. Run 5 illustrates a way to take advantage of the PFI / JFI ratio of run 4: an increase in cellulose concentration returned to J and for centrifugation stability to values similar to those of run 1, while P was maintained considerably below those of run 1. Run 6 demonstrates an alternative way of taking advantage of the invention: an increase in the temperature of the additive resulted in similar values for J and spin stability for run 1 , but a markedly lower value for P. In contrast, the additive used in Run 1 had poor spin stability at this temperature. Run 7 demonstrates an additional alternative form of -exerving advantage of the invention: a reduced concentration of cellulose resulted in lower values of P and J without loss of centrifugation stability. Greater ease of transportation allows a higher flow rate of the cellulose through the plant, although an increase in the flow rate of the additive is required for a given cellulose flow rate. This should eliminate any disadvantages resulting from the increased load in the solvent recovery system.

Claims (9)

1. CLAIMS 1. A method for manufacturing an extruded lyocell article comprising the following steps: (1) dissolving the cellulose in an aqueous solvent of tertiary amine N-oxide to form a solution; (2) extruding the solution through a die by means of a gaseous range into a coagulating bath to form an extruded precursor of lyocell; (3) washing the extruded lyocell precursor to remove the tertiary amine N-oxide; and (4) drying the washed lyocell precursor, thereby forming the extruded lyocell article characterized in that the cellulose exhibits a ratio of the Tube Flow Index in the range from 0.85 to 6.0.
2. 2. A method according to claim 1, further characterized in that the ratio of the Tube Flow Index to the Jet Flow index is in the range of 0.9 to 4.0.
3. 3. A method according to Claim 2, further characterized in that the ratio of the Tube Flow Index to the Jet Flow Index is in the range of 1.0 to 2.0.
4. 4. A method according to any of the preceding claims, further characterized in that the value of the jet flow rate of the cellulose is in the range of 0.1 to 10.
5. 5. A method according to claim 4, which is also characterized because the value of the Pulp Flow rate of pulp is in the range of 1.0 to 2.0.
6. 6. A method according to any of the preceding Claims, further characterized in that the cellulose is comprised of a cellulose mixture with different D.P.
7. 7. A method according to claim 6, further characterized in that the cellulose is a mixture of (a) a first cellulose of D.P. in the range from 200 to 750 and (b) a second average cellulose of D.P. in the range from 800 to 1500.
8. 8. A method according to Claim 7, further characterized by the D.P. of the first cellulose (a) is in the range of 250 to 500.
9. 9. A method according to any of the preceding Claims, further characterized in that the extruded article of lyocell takes the form of a fiber.