ETHYLCELLULOSE DISPERSION AND POWDER

Abstract

Provided is an aqueous composition having pH of 8 or higher and comprising (i) a solid phase comprising dispersed particles that comprise ethylcellulose polymer, (ii) fatty acid, wherein 25 mole % to 100 mole % of said fatty acid is in ionic form, (iii) 0% to 0.1% colloid stabilizer, by weight based on the dry weight of said ethylcellulose polymer, (iv) 0% to 7% plasticizer, by weight based on the dry weight of said ethylcellulose polymer, and (v) one or more cations of an alkali metal or an alkaline earth, wherein the equivalent ratio of said cations to said fatty acid is 0.1:1 to 2:1. Also provided are a method of spray drying an aqueous composition and a powder composition.

Claims

1. An aqueous composition having pH of 8 or higher and comprising (i) a solid phase comprising dispersed particles that comprise an amount of ethylcellulose polymer, (ii) 0.5% to 7% fatty acid, by weight based on the total dry weight of the solid phase, wherein 25 mole % to 100 mole % of said fatty acid is in ionic form, (iii) 0% to 0.1% colloid stabilizer, by weight based on the dry weight of said ethylcellulose polymer, (iv) 0% to 7% plasticizer, by weight based on the dry weight of said ethylcellulose polymer, and (v) one or more cations of an alkali metal or of an alkaline earth, wherein the equivalent ratio of said cations to said fatty acid is 0.1:1 to 2:1.

2. The aqueous composition of claim 1, wherein the amount of said ethylcellulose polymer is 45% to 90% by weight based on the dry weight of said solid phase.

3. The aqueous composition of claim 1, wherein said ethylcellulose powder has viscosity of 16-30 mPa-s, wherein the viscosity of said ethylcellulose powder is defined as the viscosity of a 5 weight percent solution of said ethylcellulose polymer in a solvent, based on the weight of the solution, wherein the solvent is a mixture of 80% toluene and 20% ethanol by weight based on the weight of the solvent.

4. The aqueous composition of claim 1, wherein the equivalent ratio of said cations to said fatty acid is 0.5:1 to 2:1.

5. The aqueous composition of claim 1, wherein the equivalent ratio of said cations to said fatty acid is 0.2:1 to 1:1 wherein said aqueous composition additionally comprises one or more fugitive bases, and wherein the equivalent ratio of cations of said fugitive base to said fatty acid is 0.2:1 to 1:1.

6. A method of making a powder comprising spray drying the aqueous composition of claim 1.

7. A powder composition comprising (a) 0% to 2% water by weight based on the weight of said powder composition, (b) particles that comprise (I) an amount of ethylcellulose polymer, (II) 0.5% to 7% fatty acid, by weight based on the weight of said powder composition, wherein 25 mole % to 100 mole % of said fatty acid is in the form of an alkali metal or alkaline earth salt, (III) 0% to 0.1% colloid stabilizer, by weight based on the dry weight of said ethylcellulose polymer, (IV) 0% to 7% plasticizer, by weight based on the dry weight of said ethylcellulose polymer.

8. The powder of claim 7, wherein the amount of said ethylcellulose polymer is 45% to 90% by weight based on the dry weight of said powder.

9. The powder composition of claim 7, wherein said ethylcellulose powder has viscosity of 16-30 mPa-s, wherein the viscosity of said ethylcellulose powder is defined as the viscosity of a 5 weight percent solution of said ethylcellulose polymer in a solvent, based on the weight of the solution, wherein the solvent is a mixture of 80% toluene and 20% ethanol by weight based on the weight of the solvent.

Description

Example 1

Preparation of Aqueous Dispersion

[0073] A dispersion was prepared using a Berstorff™ ZE25 twin screw extruder rotating at 450 rpm, with 25 mm screw diameter and length to diameter ratio of 36. Materials were as follows: [0074] Ethocel™ STD20 ethylcellulose (Dow Chemical Company) [0075] Oleic Acid [0076] Potassium Hydroxide (KOH), 30% solution by weight in water

[0077] The ethylcellulose was delivered using a volumetric feeder equipped with a large tube and large open helix. The polymer phase was then melted and conveyed down the extruder barrel to an emulsification zone where it is combined with an initial amount of water and a base to create a high internal phase emulsion. The emulsion was then conveyed down the extruder barrel to the diluting and cooling zone. The initial water, base, and dilution water are each supplied separately to the extruder with Isco™ syringe pumps. The oleic acid was delivered using an Isco™ syringe pump, plumbed into the melt zone. The barrels were initially set to 145° C. The front end heaters on the exit piping and back pressure regulator remained on during the run and set to 180° C. The initial water heater was turned on to deliver at approximately 140° C. The dilution water heater was set to 120° C. The relative feed rates of oleic acid and KOH were adjusted to provide an equivalent ratio of 1:1. The extruder exit temperature was 140° C.

[0078] The extruder was run with feed rates adjusted to give a mass ratio of ethylcellulose to oleic acid of 95:5, to produce Example 1-1. The feed rates were then adjusted to give a mass ratio of ethylcellulose to oleic acid of 97:3, to produce Example 1-2.

[0079] The results were as follows:

TABLE-US-00001 Property Example 1-1 Example 1-2 Weight ratio of 95:5 97:3 ethylcellulose:oleic acid pH 9.59 9.68 % Solids.sup.(1) 28.77% 29.47% Viscosity.sup.(2) 20 mPa-s 18 mPa-s Vmean.sup.(3) 0.129 μm 0.584 μm

[0080] (1) amount of solid material in the dispersion, by weight based on the total weight of the dispersion, determined using a microwave solids analyzer or an infrared solids analyzer. One analyzer used was the OHAUS™ MB45 infrared moisture analyzer (available from Ohaus Corporation).

[0081] (2) Brookfield RV viscometer, spindle #3, 50 rpm, 25° C.

[0082] (3) volume-average particle diameter, determined by using a COULTER™ LS-230 or COULTER™ LS-13-320 particle size analyzer (Beckman Coulter Corporation).

Comparative Example C2

Preparation of Aqueous Dispersion Neutralized with Ammonia

[0083] An aqueous dispersion of ethylcellulose was prepared as in Example 1, with the following differences: [0084] Neutralizing base: aqueous solution of 28% wt ammonia (as NH.sub.3) [0085] Weight ratio of ethylcellulose to oleic acid: 89.1:10.9 [0086] Equivalent ratio of ammonia to oleic acid: 1.4:1

[0087] The results were as follows:

TABLE-US-00002 Property Comp. Ex. C2 Weight ratio of 89.1:10.9 ethylcellulose:oleic acid pH  9.11 % Solids.sup.(1) 26.64 Viscosity.sup.(2) 22 mPa-s Vmean.sup.(3) 0.211 μm .sup.(1)as in Example 1 .sup.(2)Brookfield RV, number 2 spindle, 50 rpm .sup.(3)as in Example 1

Comparative Example C3

Preparation of Aqueous Dispersions with Colloid Stabilizer

[0088] The aqueous dispersion of Comparative Example C3 was modified by the addition of colloid stabilizer, either polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP). Colloid stabilizer in 10 wt % aqueous solution was added into the ethylcellulose dispersion under agitation. The PVA used was MOWIOL™ 488 PVA from Kuraray Co, having average molecular weight of 31 kg/mol. The PVP used was purchased from Sigma Aldrich, the average molecular weight was 10 kg/mol. The amounts used were as follows, by weight based on the sum of the dry weights of ethylcellulose polymer and oleic acid:

TABLE-US-00003 Comparative Colloid Amount of Example Stabilizer colloid stabilizer C3-1 PVA 8% by weight C3-2 PVP 8% by weight

Example 4

Spray Drying and Re-Dispersing of Aqueous Dispersions

[0089] Aqueous dispersions were spray dried to produce dry powder. Spray drying was conducted on a Mobile Minor™ Spray Dryer under nitrogen with a two-fluid nozzle atomizer. The dry powder was then tested for re-dispersibility as follows: The redispersibility of the spray-dried powders was evaluated based on the comparison of the particle size of the spray-dried powder dispersed in water and the original particle size of the starting dispersion. The spray-dried powder was dispersed into deionized water at 1% solids and vortexed for 30 seconds twice. The particle size of the redispersion was then measured by a Coulter LS 13 320 Laser Light Diffraction Particle Size analyzer. The desired particle size of ethylcellulose polymer dispersion is below 1 μm. The redispersibility “yield” is defined as the volume percentage of particles below 1 μm in the redispersion. For instance, if the redispersion shows 20% of particles below 1 μm by volume, the redispersibility yield of this powder is 20%.

[0090] Moisture in the dry powder is the amount of water by weight based on the weight of the powder. “na” means not analyzed. For Example 1, the Vmean was measured (by the methods described above) of the dispersion produced by re-dispersing the dry powder in deionized water. The results were as follows. The notation “<20%” means “less than 20%.”

TABLE-US-00004 Comp. Ex. Comp. Ex. Comp. Ex Ex. 1 C3-1 C3-2 C3-3 weight ratio of 95:5 89.1:10.9 89.1:10.9 89.1:10.9 ethylcellulose:oleic acid Colloid Stabilizer none PVA PVP none Base KOH ammonia ammonia ammonia Spray Drier inlet 135° C. 140° C. 120° C. 135° C. Spray Drier outlet  50° C.  39° C.  47° C.  42° C. Moisture in powder 1.75%  1.60%  1.14%  1.24% redispersibility yield  100%  <20%  <20%  <20% Vmean of redispersed 129 nm 10.2 μm 6.8 μm 8.2 μm powder

[0091] Comparative Examples C3-1, C3-2, and C3-3 used ammonia as the base and showed poor redispersibility in deionized water. All three showed very low redispersibility yield, and all three showed redispersed Vmean over 50 times the Vmean of Example 1.

Comparative Example C5

Varied Amounts of Oleic Acid When Ammonia is Used

[0092] Comparative Example C5-1 was a repetition of Comparative Example C2. As in Comparative Example C2, ammonia was used as the base. After collecting sample dispersion under the conditions of Comparative Example C2 (to produce Comparative Example C5-1), the extrusion was continued with a ratio of ethylcellulose to oleic acid changing in steps to reduce the relative amount of oleic acid. Vmean was measured as above. The results were as follows:

TABLE-US-00005 Weight Ratio of Example ethylcellulose:oleic acid Vmean Observation C5-1 89.1:10.9 0.6 μm C5-2 90.2:9.8 approximately 1.1 μm C5-3 91.4:8.6 approximately 10 μm C5-4 92.5:7.5  50 μm gritty

[0093] Comparative Example C5 demonstrates that, when ammonia is used as the base, more than 7.5% oleic acid is required to produce a useful dispersion. In order to be useful, dispersion particle size should be significantly less than 1 μm.

Example 6

Film Properties

[0094] To each aqueous dispersion, triethyl citrate, a plasticizer, was added to give 27% by weight plasticizer based on the total solids weight of the aqueous dispersion. Then, films were cast from aqueous dispersions as follows: Films were cast at thickness of 0.5 mm (20 mil) wet onto a precleaned glass plate using a BYK four sided draw down bar. Films were covered and transferred to an oven set to 60° C. to cure for 2 hr. Films were then taken to a controlled humidity room (55% relative humidity, 22° C.) for at least 12 hrs for the moisture content of the films to equilibrate.

[0095] Aqueous dispersions were either “original” or “re-disp”, defined as follows: [0096] original: aqueous dispersion produced by the extruder, then mixed with plasticizer, then cast as a film. [0097] re-disp: aqueous dispersion produced by the extruder, then spray dried, then redispersed in water to give 27% solids content, then mixed with plasticizer, then cast as a film.

[0098] Examples C6-1 and C6-2 are Comparative Examples. Aqueous dispersions were as follows:

TABLE-US-00006 Example Dispersion EC:OA.sup.(4) base Type Vmean.sup.(5) C6-1 C6-1a.sup.(6) 89.1:10.9 ammonia original 0.208 μm C6-2 C6-1a.sup.(6) 89.1:10.9 ammonia re-disp 10.2 μm.sup.(7) 6-3 Ex. 1   95:5 KOH original 0.136 μm 6-4 Ex. 1   95:5 KOH re-disp 0.138 μm .sup.(4)weight ratio of ethylcellulose to oleic acid .sup.(5)measured after addition of plasticizer .sup.(6)repetition of Comparative Example C2 .sup.(7)redispersibility yield = <20%

[0099] Films were removed from the substrate prior to tensile measurements. Tensile measurements were taken on 10 or more sample strips cut from at least three different films. The thickness of each sample strip was determined by measuring along three points using a Mitutoya Digimatic Indicator and averaging. The Young's modulus was measured by fitting the points in the linear area of the stress/strain curve. The maximum stress (reported as Tensile Strength) and strain at break (reported as % Elongation) were manually determined by placing the cursor over the curve and reading the value. Results were as follows:

TABLE-US-00007 Example Young's Modulus Maximum Elongation Tensile Strength C6-1 23 MPa  39% 1.3 MPa C6-2 39 MPa  18% 1.4 MPa 6-3 78 MPa 7.3% 3.0 MPa 6-4 60 MPa 9.6% 2.9 MPa

[0100] Comparative Example C6-2 showed maximum elongation less than half of the maximum elongation of Comparative Example C6-1. This result shows that, when a dispersion was made with ammonia, spray dried, and then redispersed, the resulting dispersion cannot make as good a film as a film made from a dispersion that had not been spray dried and re-dispersed. In contrast, Examples 6-3 and 6-4 had similar properties to each other, and that result shows that the process of spray drying and redispersing did not degrade the ability of the inventive dispersion to form a good film.