Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
1999-08-12
2003-12-30
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S124000
Reexamination Certificate
active
06670469
ABSTRACT:
The invention is concerned with a process for producing regular porous pearl celluloses having a particle size in the range from 2 to 1,000 &mgr;m. Furthermore, the invention is concerned with a pearl cellulose with specific properties as well as the use of the pearl cellulose with specific properties as well as the use of the pearl celluloses produced according to the process of the invention.
Regular porous pearly celluloses are a relatively inexpensive, stable material with variably adjustable chemical properties compared with other separator and carier materials. To an increasing extent cellulosic molded articles are gaining significence as chromatographic material, carriers for enzymes, cells and other ligands, e.g. after activation and coupling of proteins.
The known processes for producing such molded cellulose articles differ substantially from each other by the type of the cellulose material used, the solvent used, the manner of coagulation or regeneration, as well as the technology of division.
Thus, the patent rights JP 48-2173, JP 48-60753, JP 62-191033, Cs 172 640, U.S. Pat. No. 2,543,928, DE 2 005 408, etc., specify the use of alkaline solutions of cellulose xanthate (viscose) which are either sprayed into an acid precipitating bath or regenerated by an acid or thermal decomposition after having been dispersed in a solvent immiscible with water. A disadvantage of the procedure is that a considerable danger potential for the environment is associated with the sulfur compounds released with the regeneration, the resulting dilute acids and salt solutions and by the used organic solvents, respectively.
Other processes, e.g. according to DD 259 533, propose the use of solutions of cellulose carbamate. A specific disadvantage of this process is the necessity of an expensive after-treatment in which urea must be removed with hot water and residual carbamate groups must be decomposed with soda lye.
According to a further group of protective rights one of them from highly substituted organo-soluble cellulose esters among which cellulose acetate with an average substitution degree (DS) between 2 and 3 is preferably used. The principle of these processes passing via pearls of cellulose acetate as an intermediate results in that cellulose acetate is preferably dissolved in a halogenated hydrocarbon, the polymer solution is dispersed and solidified by vaporisation of the solvent. After separating the cellulose acetate particles the acetate groups are usually split off by a treatment with sodium hydroxide solution, e.g. JP 53-7759. As with this procedure only particles with a low porosity are obtained, many processes have been proposed which aim at a higher porosity of the resulting molded cellulose bodies. The chosen method is the addition of various pore forming agents to the cellulose acetate solution. The patents JP 56-24429, JP 24430, JP 62-267339, JP 63-68645 and U.S. Pat. No. 4,312,980 propose the use of linear alcohols. Motozato et al, J. Chromatogr. 298 (3), (1984) 499-507 prefer for this purpose hydrocarbons, such as hexane, cyclohexane, petroleum ether, toluene and similar compounds. Furthermore the patent JP 63-68645 proposes the use of long-chain carboxylic acids or esters of carboxylic acids for this aim. With all of these modifications the disadvantage is the necessity to use toxic halogenated hydrocarbons as the solvent.
The process of the patents SU 931 727 and SU 1 031 966 the subject of which is the production of cellulose pearls from cellulose acetate with a DS of 2 from a mixture of ethylacetate and n-butanol allows no adjustment of porosities of <75%. The proposed use of oleic acid requires additional washing processes with use of volatile organic solvents.
A procedure for producing pearly cellulose particles with use of cellulose silylethers as specified in the patent DD 295 861 also uses volatile hydrocarbons or toxic halogen hydrocarbons as the solvent. With the acid or alkaline regeneration substantial amounts of silyl side groups remain behind on the cellulose which groups substantially restrict the use for chromatographic and medical purposes.
Up to now for the direct cellulose dissolution solvents have been proposed which are difficult to handle. Thus, the patents DE 1 792 230, FR 1 575 419, U.S. Pat. No. 3,597,350 specify the use of cuoxam and similar compounds.
The protective right JP 80-44312 and Kuga, J. Chromatogr. 195, (1980), 221-230 propose working in melts of CaSCN.
Furthermore, in JP 82-159802 mixtures of dimethylsulfoxide and paraformaldehyde are specified as solvents. Especially the multi-component solvents cause substantial problems when introducing celluloses of higher molecular weight in amounts above 5%. In addition these solvent mixtures can be recycled only to a very restricted extent.
With regard to dispersing the polymer solution after having left the nozzle in principle three technologies have been specified. The patents U.S. Pat. No. 5,047,180 and U.S. Pat. No. 5,328,603 teach the production of spherical molded pieces by spraying (atomizing) a polymer solution. In the last of said patents the multicomponent solvent dimethylacetamide/LiCl is used as a solvent for cellulose. Such a system requires salt additions of more than 10% for the manufacture of regular particles. The EP 0 268 866 realizes the division into polymer droplets by superposition of the longitudinal motion of the polymer solution exiting from the nozzle by a rotating vibration motion. Finally in DE 44 24 998 spherical particles are produced by dividing a polymer solution exiting from the nozzle by means of extremely thin rotating cutters. All the process variants are identical in that an irreversible coagulation step follows directly after dividing the polymer solution. With this it is necessary that the polymer particles adopt the regular shape when passing a more or less short distance of falling. This results in problems with forming an ideal spherical shape by premature hardening, deformations as a result of the impact on the surrounding collecting cylinder and possibly gluey coatings on the cutters so that more or less distinct variations of the shape must be accepted.
It is an object of the invention to provide a process for producing regular porous cellulose pearls which is technically simple and economical and allows the production of pearl bodies having a defined particle diameter with a narrow particle size distribution in the overall range from 2 to 1,000 &mgr;m and with a broad range of variation of the adjustable porosities. Especially the process should allow to produce cellulose pearls with particle sizes in the partial range from 2 to 50 &mgr;m or in the partial range from 40 to 1,000 &mgr;m. With this process salt-free solvents, particularly one-component solvents are to be used which are little toxic or non-toxic. A further object is to provide a process in which the indicated drawbacks of the known processes are avoided. Finally it is the object of the invention to provide a new pearly cellulose with new applications. Further advantages can be gathered from the following specification.
With the process mentioned at the beginning these objects are achieved according to the invention in that
a) a cellulose having a degree of polymerisation in the range from 150 to 2,000 is dissolved in a solvent to form a solution of 0.5 to 25% by mass cellulose,
b) the cellulose solution is finely divided and dispersed in a dispersant which is not miscible with said solution and has a viscosity in the range from 10 to 80,000 mpa·s,
c) the dispersed solution particles are solidified to regular pearl particles by precipitating with a liquid precipitating agent miscible with the solvent
1) after cooling the dispersion to below the melting temperature of the cellulose solution and separating the frozen particles of the cellulose solution from the dispersant or
2) directly in the dispersion, and
d) the pearl particles are separated from the liquid mixture of solvent, precipitating agent and possibly dispersant.
step a) may include other than cellulose particles
Beyer Christine
Meister Frank
Michels Christoph
Riedel Bernd
Taeger Eberhard
Ellis Howard M.
Thuringisches Institut fur Textil-und Kunststoff-Forschung E.V.
White Everett
Wilson James O.
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