CELLULOSE ETHERS WITH TEMPORARY CROSS-LINKS, A PROCESS TO MAKE THEM, AND THEIR USE

Abstract

The invention relates to temporary cross-linked cellulose ethers, a process to make them, as well as their use to influence the rheological profile of an aqueous medium in which they are dissolved. The temporary cross-linked cellulose ethers are characterized in that they are cellulose ethers that are Cross-linked with at least one or more compounds of the formula (C.sub.1-4 alkyl)-OC(O)CHOHO(C.sub.1-4 alkyl).

Claims

1. Temporary cross-linked cellulose ether characterized by being a cellulose ether cross-linked with one or more cross-linking agents selected from the group of compounds with formula (C1-4 alkyl)-OC(O)CHOHO(C1-4 alkyl).

2. Temporary cross-linked cellulose ether of claim 1 characterized in that the one or more cross-linking agents are selected from the group of compounds of formulae MeOC(O)CHOHOMe, MeOC(O)CHOHOEt, EtOC(O)CHOHOMe, and EtOC(O)CHOHOEt.

3. Temporary cross-linked cellulose ether of claim 1 comprising 0.01 to 10 parts by weight the cross-linking agent per 100 parts by weight of cellulose ether.

4. Temporary cross-linked cellulose ether of claim 1 which further comprises cross-links of glyoxal.

5. Process to make a temporary cross-linked cellulose ether of claim 1, wherein in a first step the cellulose ether is contacted with one or more cross-linking agents selected from the group of compounds with formula (C1-4 alkyl)-OC(O)CHOHO(C1-4 alkyl) and in a second step said cellulose ether is reacted with said cross-linking agents.

6. Process according to claim 5 wherein the second step is performed at a temperature of 30 C. or more.

7. Process according to claim 5 wherein alcohol or alcohols that are formed during the cross-linking reaction step are being removed from the reaction mixture.

8. Process to make an aqueous solution of a cellulose ether, comprising a first step of preparing a temporary cross-linked material according to claim 1, a step wherein the temporary cross-linked material is added to an aqueous medium, and a later step wherein the temporary cross-linked material is hydrolysed.

9. Process to make a solution of a cellulose ether by first dispersing a temporary cross-linked cellulose ether of claim 1 in an aqueous medium followed by the step of hydrolyzing the temporary cross-linked cellulose ether.

10. Process of claim 9 wherein the pH of the aqueous medium during the hydrolysis step is 7.0 or greater.

11. Process of claim 8 wherein the aqueous medium is an aqueous paint or glue formulation.

12. (canceled)

13. (canceled)

14. A mixture comprising one or more compounds of the formula (C1-4 alkyl)-OC(O)CHOHO(C1-4 alkyl) and glyoxal, suitable for use in the process to make a temporary cross-linked cellulose ether.

15. The process of claim 5 wherein the second step is performed at a temperature of 40 C. or more.

16. The process of claim 5 wherein the second step is performed at a temperature of 50 C. or more.

Description

EXPERIMENTAL

[0031] The cellulose ether (CE) used in these examples is Bermocoll E511X (a non glyoxal treated cellulose ether available from AkzoNobel).

[0032] Glyoxylic acid HC(O)C(O)OH was supplied as a 50% w/w aqueous solution by Alfa Aesar.

[0033] MeOC(O)COHOMe was supplied by TCI Europe N.V.,

[0034] EtOC(O)COEtOEt by Acros

[0035] Glyoxal 40% aqueous solution by Alfa Aesar.

[0036] Other chemicals were sourced from SigmaAldrich.

[0037] The process to evaluate the cross-linking of cellulose ethers to produce tCEs was performed using a Waring blender Model 8010. The cellulose ether was added to the blender. Thru a hole in the lid the cross-linking agent was added during 1 minute whilst mixing the cellulose ether material at room temperature. Thereafter the blender was activated for another minute. Subsequently, without blending, the blender with content was heated to the reaction temperature and kept at that temperature for the time specified, in order to study the crosslinking behavior (method A). Thereafter the product was cooled to room temperature.

[0038] In another test method, 20 g of the cellulose ether was slurried in 60-100 ml acetone at 25 C. after which the cross-linker is added. After evaporation of the acetone, in a fume hood, by a flow of pressurized air, the sample is treated in a OBH Nordica coffee mill 2393 at room temperature for 1 min. After such mixing of cross-linker and CE, the mixture is heated in an oven at different temperatures for various times to study the crosslinking behavior (method B).

[0039] The viscosity of solutions of cellulose ether or hydrolyzed tCE is determined using a 1% w/w solution and a Brookfield viscosimeter. 2.00 g of the (t)CE is added into a 250 ml glass beaker (diameter 6.5 cm). The sample is dispersed in about 50 ml boiling distilled or de-ionized water. The dispersion is swirled until lump-free. Then, 50 ml buffer solution at ambient temperature is added, followed by further addition of distilled or de-ionized water at room temperature until a concentration of 1% w/w is achieved. Dispersion of E511X and similar (M)EHEC products is efficient in hot water due to their inherent cloudpoint. However, this is not general for all cellulose ethers and other means to first disperse the material might be needed for certain other types of cellulose ethers. The beaker is mounted to a magnetic stirrer plate, a PTFE-coated magnetic stirrer bar of 6 mm diameter and 3 cm length is added, and a plastic lid is placed on top to avoid evaporation. The dispersion is then stirred for two hours at 60 rpm and placed in water bath for 1.5 hours at 20 C. before viscosity measurement. The viscosity measurement is performed on Brookfield Viscometer LV at 12 rpm using spindle 3. The value recorded after 2 min is the viscosity.

[0040] The dissolution behavior of a t(CE) is determined by analyzing the course of dissolving a cellulose derivative in a buffer solution by continuous viscometry. The time for reaching 10% of the final viscosity of the solution is called t1, whereas t2 is the time for reaching 95% of the final viscosity. The t1 value correlates to the time delay before dissolution starts and an abrupt viscosity increase is seen due to reversal of crosslinks. Hereto a viscometer of the type Rheomat RM 180, equipped with measuring system cup and anchor stirrer, referred to by the supplier as Special relative System type 72, and of which the output is recorded, is used. The temperature of the measuring cup is controlled at 20 C. using a water bath with thermostat. 0.5 grams of (t)CE is added to the measuring cup of the viscometer, the rheometer is fitted, and the cup is place in the water bath. The stirring of the rheometer is started at 425 rpm. Then 50 ml of a buffer solution with a temperature of 20 C. is added and the recording of the viscosity is started. The process and data collection was controlled using RSI Orchestrator software. The pH of the buffer solution can vary as indicated in the examples. If no details are presented, the measurement took place using a solution buffered at pH 7.0 using Phosphate buffer pH 7 ex Labservice AB. The viscosity is measured until a stable (final) viscosity is achieved. If the product dissolved with lump formation, then the test conditions are changed and the measuring cup of the rheometer is filled with 0.5 g of (t)CE and 5 g of acetone, before the buffer solution is added. The t1 value is the time (in minutes) until the starting viscosity increased with 10% of the total increase to the final viscosity. The t2 value is the time (in minutes) for the viscosity to reach 95% of the final viscosity.

Examples 1-3

[0041] Using method A, examples 1-3 were conducted with MeOC(O)COHOMe (MHMA) as the cross-linker and reaction conditions as indicated in Table 1. The results that were obtained are presented in the table.

TABLE-US-00001 TABLE 1 amount of MHMA reaction reaction (% w/w on temp time t1 t2 Viscosity Example CE) ( C.) (min) (min) (min) (mPa .Math. s) 1 0.6 75 30 9.1 49.9 2 0.6 100 40 19.8 81.9 3 1.0 100 60 29.4 158

[0042] All three products are tCEs according to the invention with varying degrees of crosslinking and an improved dissolution behavior.

[0043] The amount of reacted MeOC(O)COHOMe was found to be more than 30%.

[0044] More specifically, the amount of MeOC(O)COHOMe in the tCE was found to be at least 85% of the methoxy hydroxyl methyl acetate.

Examples 4-17

[0045] Using method B, examples 4-12 were conducted using MHMA as the cross-linker and reacting as indicated in Table 2. The results that were obtained are presented in the table. When the buffering was at pH 8, it was by means of a 0.5 M sodium phosphate buffer ex Alfa Aesar.

TABLE-US-00002 TABLE 2 amount of MHMA reaction reaction (% w/w on temp time t1 t2 Viscosity Example CE) ( C.) (min) (min) (min) (mPa .Math. s) 4 0.1 80 30 11.7 36.1 5 0.1 80 60 14.6 47.9 6 0.2 100 65 15.6 49.2 7 0.25 80 30 14.9 46.2 8 0.25 80 60 18.4 52 9a 0.4 75 40 9.7 29.1 9b 0.4 75 40 8.5 25.2 9c 0.4 75 40 9.6 25.9 10 0.5 100 60 24.7 75.4 11 0.5 80 30 13.5 40.1 12 0.5 80 120 23.2 70.4 7333 13 0.6 100 60 33.2 108.3 14 1.0 25 120 15.8 45.3 15 1.0 100 30 41.6 131.6 7.3 (pH 8.0) 28.5 (pH 8.0) 16 1.0 100 60 8.5 (pH 8.0) 33.3 (pH 8.0) 7300 17 1.0 100 120 9.2 (pH 8.0) 37.7 (pH 8.0)

[0046] All products are tCEs according to the invention with varying degrees of crosslinking and good dissolution behavior. From the viscosity data it follows that the products are not degrading during the cross-linking step. The example wherein the reaction temperature was 25 C. showed cross-linking but the reaction was probably not complete.

Examples 18-21

[0047] Using method B, examples 18-12 were conducted using the MHMA cross-linked Bermocoll E511X of Example 8. The tCE was intimately mixed with salts to analyze the influence of the salts on the dissolution behavior. Dry mixing for 2 hours in a Turbulamixer using a plastic vessel and four porcelain marbles was found to be sufficient. In the test with mono sodium citrate, 8% by weight of the citrate was used, and for the mono sodium phosphate and citric acid, 1% by weight was used, all based on the amount of tCE. The buffer solutions at pH 7 and pH 8 were as mentioned above. The pH 8 weak buffer was a borax/HCl buffer ex Labservices. The results that were obtained are presented in table 3.

TABLE-US-00003 TABLE 3 pH 8 with weak pH 8 buffer pH 7 Ex Additive t1 t2 t1 t2 t1 t2 18 None 4.1 14 2.2 8.2 14 42 19 Mono 4.5 17 52 150 14.5 50 sodium citrate 20 Mono 4.1 14.5 3.1 9.7 13 42 sodium phosphate 21 Citric acid 3.4 13.5 4.4 15.1 12.5 45

[0048] These results show that, particularly in weakly buffered aqueous systems, acidic salts and weak acids can be used to retard the dissolution rate.

Comparative Examples A-B

[0049] In these examples the Bermocoll E511X was not cross-linked but used as is and evaluated in accordance with method A. The reaction conditions and results are presented in Table 4.

TABLE-US-00004 TABLE 4 amount of MHMA reaction reaction (% w/w on temp time t1 t2 Viscosity Example CE) ( C.) (min) (min) (min) (mPa .Math. s) A 0 0 0 0.3 6.0 6200 B 0 100 120 6350

[0050] These results show that the cellulose ether itself is stable, also when heated, but the dissolution time is too short, resulting in an undesired dissolution behavior (gel formation was observed).

Comparative Examples C-F

[0051] In these examples the Bermocoll E511X was cross-linked using glyoxylic acid (GA) using method A. The reaction conditions and results are presented in Table 5.

TABLE-US-00005 TABLE 5 amount of reaction reaction GA (% w/w temp time t1 t2 Viscosity Example on CE) ( C.) (min) (min) (min) (mPa .Math. s) C 1.0 100 30 1.7 20.2 4850 D 1.0 100 60 4.3 22.3 E 1.0 100 120 6.4 83.2 2420 F 1.0 100 180 8.2 117.5 650

[0052] These results show that reaction of CE with glyoxylic acid leads to cross-linking, which is seen by the longer t1 and t2 times. However, after reversing the cross-links, the cellulose ether showed a too low viscosity due to undesired degradation and also some insolubles were noted. In comparison with MHMA higher amounts of glyoxylic acid and more extensive heating is needed to reach the desired t1.

Comparative Examples G-K

[0053] In these the performance of glyoxylic acid (GA) in method B was evaluated. The reaction conditions and results are presented in Table 6.

TABLE-US-00006 TABLE 6 amount of reaction reaction GA (% w/w temp time t1 t2 Viscosity Example on CE) ( C.) (min) (min) (min) (mPa .Math. s) G 0.5 100 120 7.2 50.3 6530 H 0.5 100 210 12.0 111.0 4350 I 1.0 100 120 10.2 85.4 450 J 1.0 100 40 8.2 26.9 6850 K 0.5 100 60 4.2 15.8 6550

[0054] These results show that the reaction with glyoxylic acid is difficult to control. An efficient use of the glyoxylic acid, requiring the longer reaction time, results in degradation of the cellulose ether.

Comparative Examples L-N

[0055] In these examples the Bermocoll E511X was cross-linked using glyoxal (GL) using method A. The reaction conditions and results are presented in Table 7.

TABLE-US-00007 TABLE 7 Yield amount of reaction reaction glyoxal GL (% w/w temp time t1 t2 reaction Example on CE) ( C.) (min) (min) (min) (%) L 0.5 80 10 24.4 87.8 45 M1 0.3 60 10 17.3 71.7 52 M2 0.3 60 10 20.3 71.8 62 N 0.1 80 10 12.2 45.8 50

[0056] These results show that reaction of CE with glyoxal leads to products with a desired dissolution behavior. However, the amount of glyoxal that was bound to the tCE was found to be undesired low, resulting in contamination of end product, high amounts of volatiles in the process, and an inefficient process with associated costs. The reaction yield glyoxal reaction is expressed as the percentage of glyoxal used and calculated as % w/w bound glyoxal/% w/w total added amount of glyoxal*100%. The amount of bound glyoxal was determined as described in the Cefic brochure of September 2002 marked depot legale D/3158/2002/9.

Comparative Examples O-Y

[0057] In these the performance of glyoxal (GL) in method B was evaluated. The reaction conditions and results are presented in Table 8.

TABLE-US-00008 TABLE 8 Yield amount of reaction reaction glyoxal GL (% w/w temp time t1 t2 reaction Example on CE) ( C.) (min) (min) (min) (%) O 0.05 40 10 8.3 35.0 57 P 0.05 100 10 9.8 36.6 50 Q 0.05 40 120 9.5 34.4 63 R 0.05 100 120 8.1 35.3 45 S 0.275 70 65 20.6 59.4 45 T 0.275 70 65 20.9 57.5 38 U 0.275 70 65 21.8 58.8 35 V 0.5 40 10 27.2 71.1 32 W 0.5 100 10 27.8 72.1 45 X 0.5 40 120 27.4 69.5 34 Y 0.5 100 120 29.2 100.3 39

[0058] These results again show that the amount of glyoxal that was bound to the tCE was found to be undesired low, resulting in contamination of end product, high amounts of volatiles in the process, and an inefficient process with associated costs.

Comparative Example Z

[0059] In this example the performance of ethyldiethoxyacetate EtOC(O)COEtOEt was evaluated using method A. Reaction took place at 80 C. for 2 hours. The resulting tCE showed undesired dissolution behavior and gel formation did not allow the determination of t1 and t2. Also when additionally 1% w/w of acetic acid was present during the cross-linking (comparative example Z2), the product gelled in the test.

Comparative Example AA-AB

[0060] Examples 18 and 19 were repeated using a commercial glyoxal-cross-linked tCE ex Ashland, i.e. Natrosol 250 HBR. The result is presented below.

TABLE-US-00009 pH 8 with weak pH 8 buffer pH 7 Ex Additive t1 t2 t1 t2 t1 t2 AA None 4.6 28 9.1 44 28 61 AB Mono 5.2 35 Dnd* Dnd* 38 88 sodium citrate *= Dnd means that the sample did not dissolve fast enough

[0061] These examples show that the influence of salts is comparable. However, after dissolution the solutions of these comparative examples will contain glyoxal-derived hydrolysis products in the aqueous phase. Furthermore, in comparison with examples 18-19 it is shown that complete dissolution times are longer for the conventional product of comparative examples AA-AB.