Method for manufacture of films containing insoluble solids embedded in cellulose-based films
View Patent ↗A film which slowly releases solids is prepared by dissolving cellulose in a solvent such as an alkali metal salt, for example L 1 Cl in a polar solvent such as DMAC, dispersing the solid in the solution and gelling the solution with water to form a film.
1. A method for the manufacture of a cellulose film containing a dispersion of insoluble solids embedded in said film for use in the controlled release of said solids from said film comprising the steps of:
dissolving cellulose in a solvent comprising an alkali metal salt and an organic polar solvent to form a cellulose solution;
adding to the solution solids insoluble in the cellulose solution with mixing to form a uniform dispersion of the said solids in the cellulose solution;
casting the dispersion to form a gel matrix containing a dispersion of said solids;
rinsing the gel matrix to remove the alkali metal salt and the organic polar solvent from the gel matrix containing said dispersion of solids; and
drying the rinsed gel matrix to form a cellulose film containing a dispersion of said solids.
2. A method according to claim 1 wherein the cellulose selected from the group consisting of microcrystalline cellulose, cotton fiber paper and microgranular cellulose.
3. A method according to claim 2 wherein the degree of polymerization of the cellulose is in the range of 200–1200.
4. A method according to claim 1 wherein the salt is lithium chloride, the solvent is dimethylacetamide and the concentration range of lithium chloride to dimethylacetamide is 3–8% by weight.
5. A method according to claim 4 wherein the concentration range of the cellulose to solvent is 1–11% by weight.
6. A method according to claim 1 where in the dispersed solids are released from the gel matrix at a rate of 1 ppm/hour to 40 ppm/hour when the film is in contact with a liquid environment.
7. A method according to claim 1 wherein the solids added to the cellulose solution is selected from a water insoluble element, a dye and a slowly dissolving salt having a solubility in water less than 1 mg/L.
8. A method according to claim 7 wherein the slowly dissolving salt is selected from the group consisting of a phosphate salt, a metaphosphate salt, a sulfide, a chromate, a halide, a cyanide, an iodate, a carbonyl, an oxide, a boride, a molybdate, a carbonate and a niobate.
9. A method according to claim 8 in which the salt is AlPO 4 .
10. A method according to claim 8 in which the metaphosphate is Al(PO 3 ) 3 .
11. A method according to claim 8 wherein the sulfide is selected from the group consisting of NaS, KS, ZnS and Bi 2 S 3 .
12. A method according to claim 8 wherein the niobate is selected from the group consisting of Ba(NbO 3 ) 2 and Cd(NbO 3 ) 2 .
13. A method according to claim 8 wherein the slowly dissolving salt added to the solution is a silver salt.
14. A method according to claim 13 wherein the silver salt is a silver halide.
15. A method according to claim 13 wherein the silver salt is AgCN.
16. A method according to claim 13 wherein the silver salt is AgIO 3 .
17. A method according to claim 8 wherein the slowly dissolving salt added to the solution is Mn 2 (CO) 10 .
18. A method according to claim 8 wherein the oxide is a heavy metal oxide.
19. A method according to claim 18 wherein the heavy metal oxide selected from the group consisting of is ZrO 2 and TiO 2 .
20. A method according to claim 8 wherein the dye is selected from the group consisting of copper pthallocyanine and zinc pthallocyanine.
21. A method according to claim 1 wherein the concentration of the solids in said film does not exceed 50% by weight of cellulose.
22. A method according to claim 1 wherein a softener is added to the solution.
23. A method according to claim 21 wherein the softener is glycerol.
24. A method according to claim 22 wherein the softener is decane.
25. A method according to claim 1 wherein the casting step is conducted at ambient temperature.
26. A method according to claim 1 wherein casting of the film is effected by direct application of a water stream to the solution.
27. A method according to claim 25 wherein the casting step is performed at a relative humidity of 35–80% and a temperature range of 15–30 degrees Celsius.
28. A method according to claim 1 wherein the rinsing step involves the application of water to the film.
29. A method according to claim 28 wherein the rinsing step involves the use of a water/alcohol mixture in which the alcohol does not exceed a 50% by volume ratio.
30. A method according to claim 1 wherein the drying step involves air drying.
31. A method according to claim 1 wherein the drying step involves vacuum drying.
32. A method according to claim 1 wherein the drying step involves press-drying.