IE911316A1 - A process for preparing a solution of cellulose in¹n-methylmorpholine-n-oxide and water - Google Patents

Abstract

In order to prepare a solution of cellulose in N-methylmorpholine N-oxide and water which, compared with known solutions, has a higher water content at the given cellulose content, a mixture of the three components is subjected to shear rates of 400-3000 s<-1>, preferably 500-800 s<-1>. This process allows solutions to be prepared which satisfy the following conditions (ccell = proportion by weight of cellulose; = proportion by weight of water):

Description

A process for preparing a solution of cellulose in N-methylmorpholine-N-oxide and water.

The present invention relates to a process for preparing a solution of cellulose in N-methylmorpholine-N-oxide and water, in which the three components are mixed together, as well as a solution of cellulose in N-methylmorpholine-N-oxide and water.

A process of this kind is known from us-patent 4 196 282, for example. To determine the maximum cellulose concentration experimentally, the three-component system was prepared in accordance with this US-patent as a heterogeneous mixture of substances, and a homogeneous spinning mass was produced from this by raising the temperature, stirring, and evaporating water. It has in fact been shown that the maximum cellulose concentration falls as the proportion of water rises, i.e. that there is a maximum permissible water concentration for a given cellulose concentration. If the water concentration falls during the evaporation of water, the cellulose will completely dissolve at some stage. From the mass proportions existing at this point in time in the solution, a related maximum cellulose proportion can be determined for a definite water proportion.

By means of extensive series of tests the following relationships, according to the US-patent cited, could be determined between the mass proportion or the concentration of the cellulose (cQe]]) and the mass proportion or the concentration of the water (c^q)· cCell - 0*3469-1.695 c^q (I) te 11 - nzu ί-τη' cCe11“°·3469~1 * 695cH20+0'0081v1’65+0'1<100cH2012 *76 <11) Both of these inequalities are illustrated in Fig. 5 of the us patent, in which curve A corresponds to inequality II and curve B corresponds to inequality I. 0582S IE 911316 - 2 If inequality I is fulfilled ( inequality II is then automatically also fulfilled), the cellulose will dissolve with certainty in N-methylmorpholine-N-oxide ( called NMMO in the following text) and water. Should only inequality II and not inequality I be fulfilled, complete solution of the cellulose occurs only with a certain probability, but not with certainty.

In the US- patent cited, lower limits for the water and cellulose content are also given (curves C and D in Fig. 5). Should the water content in fact sink too low, the solution can crystallise out even at very high temperatures through shear induction. Such a solution cannot be processed further even by raising the temperature higher. In addition, when there is a low water content, a temperature and concentration region is reached which lies close to the decomposition and explosion limit of the NMMO-cellulose system. According to DSC* measurements, decomposition starts just above 170°C. In order to ensure the safety of a process, the distance from the initial temperature of decomposition should be as large as possible.

Water has several functions in the solution of cellulose in NMMO and water. One of the advantages is that more cellulose can be dissolved in a mixture of NMMO and water than in pure NMMO. Thus, extrusion of the solution, for the purpose of spinning threads for instance, is possible. The water content should not, however, be too high, as raising the water content leads to a linear reduction in the maximum possible cellulose concentration ( inequality I).

When the solution is extruded, an aqueous NM40 solution is then employed as precipitating agent. The precipitating bath can be increased in concentration in a chemical cycle, and can be cleaned and then fed back into the production of the solution.

* DSC = Differential Scanning Calorimetry - 3 The entire economic viability and ecological compatibility of the process depends upon the measure of control available over the coupled IWIO-water cycle. If NMMO, an extremely expensive solvent, can be partially substituted by water in the spinning mass, then direct savings can be made in the cost of the process.

If solutions with raised water content are used for extrusion, savings in respect to the precipitating bath can also be made.

For the reasons given, an object of the invention is to provide a process for preparing a solution of cellulose in NMMO and water with a raised water content, in order to achieve a raising of the safety of the process, a raising of the initial temperature of decomposition, and savings in expensive solvent and precipitating agent, which must be regenerated.

This object is attained in accordance with the invention by means of a process of the type initially described, in that the mixture is subjected to shear rates of between 400 - 3000s1, preferably between 500 - 800s1, and in that the mass proportion of cellulose c^-j and the mass proportion of water c^q fulfills the following condition: cCell > θ’3469-1.695 c^q (HI) It was, surprisingly, in fact found that substantially more cellulose dissolves for a given water concentration if the mixture is subjected to high shear rates. It actually does not depend as much upon the stirring energy as upon the shear rates thus attained.

The NMMO employed can be either technically cleaned NMMO or, as previously described, NMMO that has already been conducted through the cycle. - 4 It is advantageous for the temperature to be between 70 120°C, preferably about 100°C, while the mixture is subjected to the shear rates. Cellulose dissolves particularity well at these temperatures and one is still sufficiently far removed from the decomposition temperature of the NMMO. 0-1 % of a known stabiliser such as gallic acid and its esters, particularly gallic acid propyl ester, pyrocatechin, ellagic acid, pyrogallol, oxalic acid, phosphoric acid and sodium hexametaphosphate, is preferably added to one of the components or to the mixture. Stabilisers of this kind prevent or reduce the decomposition of NMMO and the breakdown of cellulose.

The maximum cellulose concentration which can be achieved by means of the process according to the invention can be expressed by the following inequality: cCell ^°·582·23 cH20 A solution of cellulose in N-methylmorpholine-N-oxide and water is also to be protected in so far as the mass proportion of cellulose cCell and the mass proportion of cH20 fulfill the following conditions: cCe]1>0.3469-1,695cH2Q+0.0081Jl,65+0.1(100 cH2Q-12.76)2'(V) cCell ~ 0,582,23 cH20 The inventors found a theoretical explanation for inequality IV, but they do not wish to be bound by this theory. The theory is explained in more detail with reference to the accompanying drawings. Fig. 1 shows the maximum solubility of cellulose, depending upon the water content. Fig. 2 shows a binary diagram for the NMM0/H20 system; and Fig. 3 shows the result of an X-ray structure analysis of cellotetrose and anhydrous NMMO. - 5 It is known that the NMMO/water system does not show one eutectic point only, but two ( see Fig. 2). Until now, it was only possible to make use of the eutectic point which has monohydrate (MH) as its basis for dissolving cellulose. By using higher shear rates it is, surprisingly, also possible to make use of the second eutectic point at 26% water and 74% NMMO. The melting point of this eutectic mixture is 36°C; it corresponds to a molar ratio of 1 mol NMMO to 2.3 mol water (NMM0-2.3-hydrate, DH) The NMM0-2.3-hydrate is therefore advantageous because the water molecules can be substituted by cell-OH molecules when the solution is being formed. Thus an X-ray structure analysis of cellotetrose and anhydrous NMMO (AF) for example shows that only one glucose unit is bound.

(S. Maia, E.R.; Peguy, A.; Perez, S.; Cellulose organic solutions.I. The structure of anhydrous NMMO and NMMO monyhydrate. Acta Crystallogr., Sect.B 1981, B37(10), 1858-62, Jan.l, 1981.) By assuming that NW10-2.3 hydrate also in the liquid phase (L), is also capable of substituting the water molecules by cell-OH as required, solutions with a substantially higher water content than stated in the above-mentioned US- patent 4 196 282 can be obtained.

By taking the above-mentioned assumptions into consideration, i.e. that in a solution the free MYMO is present in the form of NMMO-(2 to 2.3 H-bonding) (corrpare with the eutectic mixture in Fiq. 2) and that every anhydrous glucose unit of the cellulose binds an anhydrous NMMO, the dissolving region can be extended as follows: the maximum possible water concentration in a NMMO-cellulose-water solution is given by the binary diagram (Fig. 2), i.e. the cellulose concentration = 0% here. cH20 = 26% = 0,26 - 6 The maximum cellulose concentration (water-free solution) is given by Fig. 3, according to which every anhydrous glucose unit can bind at most one NMMO; i.e. the molar ratio of NMMO : anhydrous glucose is 1. (cCe 11 “^anhydrous glucose^7 ^cNM107^NMM0^ “ 1 (cCell /162)Z<cNMM0/117) = 1 ^cCell7cNMM0^ = 1627117 = 1,38 cCell = 1-38* CNMMO 10 cCell + CNMMO = 1θθ% = 1 There results from these two equations: CNMMO = 42%; cCell = 58% There thus results for the right hand limit (C) of the solubility region in Fig. 1, by linear interpolation; cCell = 0,58 “ 2,23 * cH20 or transformed : cH20 = 0,26 “θ’448 * cCell There must also apply: CNMMO = 1 “ cH20 cCell “ cstabiliser The two concentration limits, which are specified in the above-mentioned US- patent 4 196 282, namely curves A and B in its Fig. 5, are also shown in Fig. 1 and are similarity denoted by A and B. The region between the curves A and B on the one hand and C on the other hand is exploited by means of the present invention. Furthermore points are illustrated in Fig. 1, which correspond to the examples described below.

In the examples, the determination of the cellulose content was effected gravimetrically, by precipitating the cellulose with water. The concentration of NMMO is potentiometrically determined in the filtrate. The determination of the water concentration is effected after precipitating the cellulose with methanol in the filtrate by means of Karl-Fischer-reagent.

The DP* of the cellulose was determined by calculating the average and by determining the limiting viscosity number in accordance with the Cuen method TAPPI T230. Measurements were made in the oscillation mode (w = angular velocity).

Evaluation of the solution : - optically : under the microscope - in respect of viscosity : by means of a rotational viscometer made by HAAKE, RV20 type, plate-plate system, (PQI, Gap : 1mm, Measuring Temperature : 95°C, Oscillation mode).

Examples 1 to 21 : In a 31 kneader, type Werner & Pfleiderer, LUK S III-l, the components cellulose, NMMO (recrystallised from acetone), water and GPE (gallic acid propyl ester) as stabiliser were kneaded for 15 to 115 minutes at 70°C to 120°C (Table 1), until a transparent solution as seen under the microscope resulted.

The exact parameters of the test and the results are summarized in Table 1.

Examples 1 and 21 lie in the known region and not in the region according to the invention. They were only included to show that using a stabiliser is useful in all cases to reduce the decomposition of the cellulose. The higher the concentration of the stabiliser, the less the decomposition of the cellulose (DP).

Examples 13, 14 and 20 lie outside the predicted dissolving region; the cellulose does not dissolve. Many undissolved fibre fragments were still present in the case of Example 17.

*DP = Degree of polymerization (average) TABLE 1.

Patent Cell. H20 NMMO GPE Temperature Length of Viscosity DP Example (%) (%) (%) (%) (°C) treatment (min)*) at w=0.31 [1/s] in [Pas] 1 9.8 13.4 76.8 0.02 78- 87 20- 95 2,93.102 440 2 14.0 13.3 72.7 0.02 87-103 25- 85 1,11.104 580 3 15.3 12.1 72.6 0.02 98-105 15- 60 6,06.103 470 4 14.9 13.5 71.6 0.02 97-105 15- 60 5,08.103 440 5 13.9 14.3 69.8 0.02 89-104 15- 60 7,10.103 510 6 15.2 15.3 69.5 0.02 100-104 60 1,04.104 550 7 15.0 18.5 66.5 0.08 100-104 55 1,29.104 590 8 18.3 12.1 69.6 0.02 83-107 20- 85 8,10.103 320 9 22.0 14.8 65.2 0.02 99-105 20- 60 9,88.103 340 10 21.2 12.0 66.8 0.02 89-105 20- 60 9,38.103 330 11 20.7 12.6 66.7 0.02 98-105 15- 60 1,40.104 230 12 21.7 11.1 67.2 0.08 110 15- 70 1,02.104 310 13 20.0 17.5 62.5 0.08 107-112 90 3,36.102 330 14 20.0 27.0 53.0 0.08 108-115 115 1,61.103 220 15 22.8 11.0 66.2 0.02 73-115 20- 40 1,37.104 220 16 25.8 9.9 64.3 0.02 110-119 15- 70 2,63.103 200 **) 17 24.4 16.4 59.2 0.02 110-120 15- 70 9,45.103 190 18 26.3 9.7 64.0 0.02 110-120 15- 70 1,50.104 190 19 30.2 8.6 61.2 0.02 115-120 15- 90 not measurable 200 20 35.0 11.5 53.5 0.08 115-120 15- 90 not measurable no solution 21 9.6 12.9 77.5 - 95- 98 30-300 5,85.101 380 *) Start of dissolving - End of dissolving **) Measuring Temperature : 105°C - 9 Examples 22 to 27 : In a 11 stirring container, water is distilled off under vacuum from a suspension consisting of an approximately 60% aqueous NWIO solution, cellulose and 0.01% GPE as stabiliser. (See Table 2). The formation of the solution is followed by means of the increase in viscosity (power consumption of the stirrer) or under the microscope.

The exact parameters of the test and the results are summarized in Table 2.

Explanation : Line 1 : Start of formation of the solution (viscosity increase) Time = 0; by that stage a certain amount of water had already evaporated - see composition Line 2 : Time = XX; End of the dissolving process - ίο TABLE 2.

Example Time Cell H20 employed Amount (g) H20 Composition of the Solution NMMO total distilled Cell% H20% NMM0% off Cellulose: Buckeye V5 22 0 20 30 30 160 143 486 486 676 659 166 183 4.44% 4.55% 23.67% 21.70% 71.89% 73.75% 23 0 42 168 480 690 156 6.09% 24.35% 69.56% 15 30 42 140 480 662 184 6.34% 21.15% 72.51% 24 0 54 162 477 693 296 7.79% 23.38% 68.83% 25 54 125 477 656 333 8.23% 19.05% 72.72% 20 Waste Paper 25 0 30 160 486 676 166 4.44% 23.67% 71.89% 20 30 143 486 659 183 4.55% 21.70% 73.75% 25 26 0 42 168 480 690 156 6.09% 24.35% 69.56% 30 42 140 480 662 184 6.34% 21.15% 72.51% Avicell 27 0 90 115 390 595 149 15.1% 19.3% 65.6% 30 90 92 390 573 172 15.7% 16.1% 68.2% - 11 Example 28 : Spinning Test, 51 Stirring Container In a 51 stirring container, water is distilled off under vacuum from a suspension consisting of an approximately 60% aqueous NMMO solution, cellulose (Buckeye V5 cellulose ) and GPE. After approximately three hours, 3000g of solution of the following composition were obtained : 9.0% cellulose (Buckeye V5) 18.3% water 79.5% NMMO 0.02% GPE Solution temperature : 94 - 96°C Complex viscosity of the spinning mass at 95°C (RV 20, oscillation at an angular velocity of w = 0,31 1/s): 550 Pa.s Shear rate: 500 This solution was forced through a 100 hole/ 130 jjm spinneret at lOg/min, was streched in an air gap and coagulated in a precipitating bath, by means of which fibres were obtained.

Example 29 : Spinning Test, 51 Stirring Container In a 51 stirring container, water is distilled off under vacuum from a suspension consisting of an approximately 60% aqueous NMMO solution and cellulose. After approximately five hours, 3000g of solution of the following composition were obtained. .9% cellulose (Avicell, DP - 170) 14.4% water 69.7% NMMO 0.02% GPE Solution temperature : 94 - 96°C Complex viscosity of the spinning mass at 95°C (RV 20, oscillation at w = 0.31 1/s) : 293 Pa.s Shear rate : 500 s1 This solution was forced through a 100 hole / 130 Jim spinneret at 10 g/min, streched in a 2 cm air gap and coaulated in a - 12 precipitating bath. The fibre thus obtained had the following characteristics : Avicell Titre (dtex) 4.8 Tenacity of fibres (conditioned)(cN/tex) 23 Elongation of fibres (conditioned)(%) 8.2 Example 30 : Spinning Test, 501 Stirring Container 2276g of a beech sulfite cellulose (solid matter content or dry content 94%, DP 750, & = 90%) and 0.02% GPE as stabiliser are suspended in a 26139g of approximately 60% aqueous N-methylmorpholine oxide solution and 9415g of water are distilled off over two hours at 100°C, in a vacuum of 50 to 300 mbar. The solution thus created is judged according to its viscosity and under the microscope.

Shear rate : 370 Vs Dissolving time : the time required in total to distill off the water and for the formation of the solution.

Parameters of the spinning solution : Cellulose % 9.95 Water % 15.4 ΝΜΜ0 % 74.65 Dissolving time (hours, minutes) 5.25 Complex viscosity of the spinning mass at 95°C (RV20, oscillation at w = 0,31 1/s) : 1680 Pa.s Spinning parameters : Spinning temperature (°C) 75 Number of spinneret holes 589 Spinneret hole diameter ( pm) 150 Air gap (mm) 9 Flow rate (g/min) 103 Stretching 8.25 Take up speed (m/min) 68 - 13 Character i st i cs: Titre (d/tex) 3.0 Tenacity (conditioned) (cN/tex) 34.6 Elongation (conditioned) (%) 9.6 Examples 31 to 34 : Tests with a film extruder Solutions were produced on a film extruder made by BUSS in Switzer 2 land (type hs-0050 : 0.5 m area, shear rate approximately 10 3000 1/s, gap : 1.5mm). A slurry consisting of approximately 60% aqueous NMMO solution and cellulose was fed in from above and water was evaporated under vacuum (100 mbar) until the composition detailed below was attained: Rotations of the Rotor: 450 rpm Analysis Data 20 Example Cell % Water % Cellulose Heating Temperature °C Viscosity w=0.31 1/s Pa.s 31 8.39 24.64 Buckeye V5 170 1670 25 32 9.95 15.7 Buckeye V5 185 2360 33 14.6 13.13 Buckeye V5 210 9860 30 34 8 16 Beech- wood cellulose DP=750 220 1970 Vicosity *.. velocity of complex viscosity: measured at an angular 0.31 , measured in the oscillation mode on a HAAKE RV20 at 95°C. =90% - 14 The mean dwell time of the cellulose was approximately four minutes. From a rheological point of view, these are solutions. Many are somewhat thick, i.e. undissolved portions are present.

Examples 35 to 39 In these examples, the decomposition temperature was determined by means of DSC-measurements made on NMMO monohydrate and cellulose solutions. Of these examples, only example 40 lies in the region according to the invention. The results are summarized in Table 3.

In this, the following meanings apply: Start ... of decomposition (initial temperature) Maximum ... temperature at which the exothermal passes its maximum End ... of the exothermal TABLE3 Temperatures °C Example s Cell NMMO Water Start Maximum End % % % 35(NMMO.H20)- 87.7 13.3 197 233 240 25 36 9 77.5 13.5 190 225 236 37 10 78.0 12.0 184 212 230 30 38 23 72.0 5.0 164 205 218 39 23 66.0 11.0 173 217 230 35 Cellulose in the solution reduces the ί initial temperature of decomposition (compare with Example 36). In solutions with higher water concentration, higher initial temperatures are attained for corresponding cellulose concentrations.

Claims (8)

1. Claims 51. A process for preparing a solution of cellulose in N-methylmorpholine-N-oxide and water, in which the three components are mixed together, characterised in that the mixture is subjected to shear rates of between 400 - 3000s 1 , preferably between 500 - 800s 1 , and that the mass proportion 10 of cellulose c Q e -jq and of water c^q fulfills the following conditions : c Cell > 0,3469 1,695 c H20 ίΙΠ)
2. 2. A process according to claim 1, characterised in that while 15 the mixture is being subjected to the shear rates, the temperature is between 70 - 120°C, preferably approximately 100°C.
3. 3. A process according to claim 1 or claim 2, characterised in 20 that 0 - 1% of a known stabiliser such a gallic acid and its esters, particularity gallic acid propyl ester, pyrocatechin, ellagic acid, pyrogallol, oxalic acid, phosphoric acid and sodium hexametaphosphate, is added to one of the components or to the mixture.
4. 4. A process according to one of claims 1 to 3, characterised in that the additional following condition is fulfilled : ^Cell “ 2.23 c^q (IV) 30
5. 5. A solution of cellulose in N-methylmorpholine-N-oxide and water, characterised in that the mass proportion of cellulose c Cell an8 mass proportion of c H2 q fulfill the following conditions : __ ( c Ce 11 >0,3469-1 · 695 ο Η2θ +0.008ψ.65+0.l(100c H20 -12,76) 2 (V) 35 c Cell ~ 0,58 2,23 c H20 (VI) - 16
6. 6. A process according to Claim 1, substantially as described herein by way of Example.
7. 7. A solution according to Claim 5, substantially as described herein by way of Example.
8. 8. A solution of cellulose in N-methylmorpholine-N-oxide and water prepared by the process of any of Claims 1 to 4 or Claim 6.