WO1993018853A1 - Procede de coacervation - Google Patents

Procede de coacervation Download PDF

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Publication number
WO1993018853A1
WO1993018853A1 PCT/GB1993/000533 GB9300533W WO9318853A1 WO 1993018853 A1 WO1993018853 A1 WO 1993018853A1 GB 9300533 W GB9300533 W GB 9300533W WO 9318853 A1 WO9318853 A1 WO 9318853A1
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WO
WIPO (PCT)
Prior art keywords
polymeric material
process according
solution
core
polymer
Prior art date
Application number
PCT/GB1993/000533
Other languages
English (en)
Inventor
Kishor Kumar Mistry
John Graham Langley
Kenneth Charles Symes
Jeremy William Peatfield
Original Assignee
Allied Colloids Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Allied Colloids Limited filed Critical Allied Colloids Limited
Priority to EP93906672A priority Critical patent/EP0631523A1/fr
Publication of WO1993018853A1 publication Critical patent/WO1993018853A1/fr
Priority to FI944237A priority patent/FI944237A/fi
Priority to NO943440A priority patent/NO943440D0/no

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/02—Making microcapsules or microballoons
    • B01J13/06—Making microcapsules or microballoons by phase separation
    • B01J13/08—Simple coacervation, i.e. addition of highly hydrophilic material

Definitions

  • This invention relates to processes for forming particles which have a core of core material within a shell of polymeric material that has been deposited by coacervation.
  • Coacervation processes are well known as a class and involve providing a dispersion of particles (liquid or solid) of core material in an aqueous medium containing coacervating polymer and causing the polymer to phase- separate and deposit around the particles. It is common to promote coacervation by adjusting the conditions in the aqueous medium so as to cause the polymer to deposit. For instance the concentration of a non-solvent may be increased to bring about deposition or two polymers in the medium may be caused to interact to form a polymeric complex as a coacervate.
  • Some polymeric materials are pH-sensitive, i.e., they are soluble'at one pH and insoluble at another pH. It is known to use pH-sensitive polymeric material as a coating or matrix around a pharmaceutically active ingredient to protect that active ingredient from ambient conditions at which the polymeric material is insoluble, and then to release the active ingredient by exposing the polymeric material to pH conditions at which it is soluble.
  • pH-sensitive polymeric material As a coating or matrix around a pharmaceutically active ingredient to protect that active ingredient from ambient conditions at which the polymeric material is insoluble, and then to release the active ingredient by exposing the polymeric material to pH conditions at which it is soluble.
  • Various techniques are known for depositing the pH-sensitive polymeric material around the active ingredient. Most of them involve forming relatively large particles but coacervation can be used to form small particles if the active ingredient can be supplied initially as a dispersion of small particles.
  • Coacervation processes of this general type suffer from a number of disadvantages.
  • the use of organic solvents in large quantities is undesirable because it necessitates the provision of suitable solvent handling apparatus and because the solvents themselves can exhibit some phytotoxicity.
  • the changes in concentration or other conditions necessary to cause coacervation are liable to occur rather suddenly (for example at the point of addition of a non-solvent) and it is difficult to obtain uniform coacervation under these conditions.
  • a coacervation process for forming particles having core of core material within a shell of pH-sensitiv polymeric material comprises providing a dispersion of particles of core materia in an aqueous solution of the polymeric material at a pH a which the polymeric material is soluble, and depositing th polymeric material as a shell around the core material, characterised in that the polymeric material i deposited as a shell and is insolubilised by adjusting th pH of the solution to a pH at which the polymeric materia is insoluble, wherein the adjustment of the pH is conducted at rate that is sufficiently slow and homogeneous throughou the solution that the polymeric material deposit substantially only as a substantially uniform coacervat around individual particles.
  • the encapsulating polymer can change from a totall water soluble state to a totally water insoluble state ove a relatively small pH range.
  • the polymer is usually one that has a very shar change from insolubility to solubility, for instance goin from a wholly soluble form to an insoluble form over a p change of less than 1 pH unit, often less than 0.5 pH unit and frequently is in the range 0.05 to 0.2 or 0.3 pH units For instance if the viscosity of the composition i measured, it may be found that this is at a substantiall constant high value down to a pH of, for instance, 6.8 an that it then drops very fast to a value at around 6.3 an that it then remains substantially constant with furthe decreases in pH.
  • turbidity can be measure in which event it may be low at pH values down to about 6. (indicating full solution) and may then increase rapidly t a substantially constant high value at pH values below 6. (indicating an emulsion) .
  • the precise pH band over whic this rapid change in solubility occurs will vary accordin to the particular composition of the polymer but is usuall located within the range 5.5-8.5, most usually 6 to 7.5.
  • the rate of change of pH must be controlled i accordance with the invention so as to be slow an homogeneous as it passes through this critical range. Th rate of change approaching this range, and passing beyon it, is less important.
  • the pH change should not only be slow bu that it should be homogeneous in the sense that it is slo in all parts of the solution, and not just in some parts o the solution.
  • conventional pH adjustment by, fo example, addition of acid or alkali would change the p slowly in the bulk of the solution but would creat localised rapid pH changes, causing uncontrollabl precipitation of the polymer with little or n encapsulation of the core material, at the point o addition of the acid or alkali. If the pH adjustment is sufficiently slow and homogeneous throughout the solution, the encapsulating polymer will deposit predominantly around the individual particles of core material, resulting in efficient encapsulation.
  • One way of determining whether the process has been conducted satisfactorily is to subject the end product to centrifugation since this can be used to determine whether the great majority of particles are of the desired similar particle size and shape or whether the particles vary considerably in size, for instance between random agglomerates of polymer and small particles of core material.
  • Another good indication of the product can be obtained by scanning electron microscopy. By this technique it is easily possibly to differentiate between coated materials of approximately uniform size and random agglomerates and other particulate materials.
  • the majority of the polymeric material for instance at least 75%, preferably at least 90% and most preferably at least 95% by weight is present as particles of substantially uniform size and that enclose core material, and the majority of core particles, generally at least 75%, preferably at least 90% and most preferably at least 95% by weight, are enclosed within a shell of polymeric material.
  • the process can be conducted in such a manner that coacervation occurs first and the coacervated particles may then aggregate to some extent and this can be satisfactory since the polymer is deposited as a substantially uniform coacervate around individual particles.
  • This type of product is in contrast with a product in which the polymer deposits too fast and in an irregular manner leaving significant numbers of particles uncoated.
  • the preferred products of the invention have at least 90% by weight of the core material microencapsulated within the polymeric material and at least 90% by weight of the polymeric material present as coacervate coating around the core material.
  • the pH change is homogeneous, and the desired slow rate can be achieved merely by controlling the rate of reaction, for instance by adjusting the temperature or the dilution of the solution.
  • the pH-adjusting material should be one that will liberate alkali.
  • the polymeric material is a material that is soluble in alkali and insoluble in acid in which event the latent pH-adjusting material should be one that will react in the solution to liberate acid in the solution.
  • the polymer itself may serve as the latent pH- adjusting material if it is included initially as a salt with ammonia or a volatile amine, since heating of the solution will drive off the ammonia and convert the polymer from its soluble, salt, form to an insoluble, acidic, form.
  • the solution may include an added heat decomposable salt of a volatile base (ammonia or a volatile amine) with an acid, so that when the solution is heated the salt decomposes, the base volatilises and the acid that is formed reduces the pH. It is necessary to ensure that the salt does not cause a significant change of pH before heat decomposition occurs, for instance as a result o being sufficiently acidic before decomposition.
  • a volatile base ammonia or a volatile amine
  • salts with a weak acid with a volatile bas for instance a salt of acetic acid or other organic wea acid with ammonia or a volatile amine
  • salts with stronger acids can b used, especially if the reaction temperature i sufficiently low that they decompose slowly.
  • the need to heat the solution to decompose the sal can be undesirable, especially when the core materia comprises Bt toxin or other heat-sensitive material and s preferably the latent pH-adjusting material is one tha undergoes hydrolysis in the aqueous polymer solution t cause the desired liberation of acid (or alkali) .
  • Th preferred materials are lactones that hydrolyse in th polymer solution to form a carboxylic acid.
  • the preferre lactone is gluconolactone. Again, it can be useful t incorporate a buffer.
  • a dispersion of pH-adjusting material may b distributed through the solution.
  • the bead may be of ion exchange material (generally a weak base o weak acid ion exchange material) or they may be bead comprising a polymeric matrix enclosing acid or alkali tha can permeate slowly through the matrix.
  • bead of polyacrylic acid scale inhibitor or the other weak aci in a polymeric matrix can be used to liberate acid. It i essential to apply vigorous stirring so as to prevent th concentration of acid or alkali at the surface of the bead increasing sufficiently to cause local precipitation.
  • dialysis could be used to generate hydrogen o hydroxyl ions within the solution on a molecular scale, fo instance using one or more dialysis sheets, tubes or particles with acid or base on one side of the membrane and the polymer solution on the other. Again, however, very vigorous agitation will be needed to prevent the pH changing too fast locally, thus leading to unwanted polymer deposition.
  • the pH-sensitive polymeric material is normally a copolymer of a blend of ionic and non-ionic ethylenically unsaturated monomers where both the blend and the polymer are insoluble at one pH and soluble at a different pH.
  • the ionic monomer is an amino or amido monomer, for instance a dialkylaminoalkyl (meth) -acrylate or acrylamide as acid addition or quaternary ammonium salt
  • the polymer can be insolublised by raising the pH.
  • the enteric polymer is an anionic polymer, generally a copolymer of ethylenically unsaturated carboxylic acid monomer with water insoluble ethylenically unsaturated non-ionic monomer.
  • Suitable carboxylic monomers include acrylic acid, ethacrylic acid, maleic acid or anhydride, crotonic acid and itaconic acid.
  • Suitable non-ionic monomer include aromatic ethylenically unsaturated monomers such as styrenes, vinyl halides, acrylonitrile, and alkyl esters of carboxylic monomers, for instance alkyl (meth) acrylates.
  • Preferred copolymers are formed from (meth) acrylic acid with styrene and/or alkyl (meth) acrylate.
  • the amount of ionic monomer is generally in the range 5 to 40%, usually 15 to 30%, by weight, with the balance being insoluble non-ionic monomer.
  • Copolymers of acrylic acid or other water soluble ionic monomer with a hydrocarbo monomer such as styrene are preferred.
  • the polymer can be formed by polymerisation at a pH a which it is soluble or by polymerisation in an organi solvent or in an aqueous organic solvent mixture, fo instance at a pH at which it would be insoluble in th absence of the organic solvent.
  • i is formed by oil-in-water emulsion polymerisation at a p at which it is insoluble.
  • the polymer solution is usually free o organic solvent, in some instances it may include solven (for instance from the initial polymerisation) or solven may be included in a small amount (generally less than 50 and usually less than 10% by weight of the solution) i order to modify the polymerisation or coacervation process.
  • solven for instance from the initial polymerisation
  • solven may be included in a small amount (generally less than 50 and usually less than 10% by weight of the solution) i order to modify the polymerisation or coacervation process.
  • the molecular weight of the polymer must not be to low since otherwise it may fail to coacervate out o solution adquately and/or any coating that is formed ma have inadequate properties. Generally therefore th molecular weight is at least 50,000, preferably at leas 100,000 and usually at least 200,000. If the molecula weight is too high it may be difficult to cause the polyme to come out of solution sufficiently slowly and s generally the molecular weight is below 5 million, an preferably below 2 million and most preferably below million.
  • the core material can be a variety of water insolubl liquid or solid materials.
  • the material shoul be broken down into a dispersion of droplets of th appropriate size by conventional mechanical homogenisation and/or the use of appropriate oil-in-water emulsifying agent.
  • the core material (irrespective of whether it is liquid or solid) has a size of below 30 ⁇ m and most preferably below lO ⁇ m and best results are achieved when the size is below 5 ⁇ m, for instance 0.1 to 3 ⁇ m.
  • the particle size it can be desirable for the particle size to be much larger, e.g., 30 or 50 to lOO ⁇ m or up to 300 ⁇ m or larger.
  • a particular advantage of the invention is that it is possible to control the coacervation so accurately that, even when the particle size is very small, substantially every particle in the final particulate composition is a monoparticle of the core material with a substantially complete coating of the pH-sensitive polymer.
  • conventional.coacervation techniques tend to be unsuitable or difficult to operate if the particle size is to be, for instance, less than lO ⁇ m
  • in the invention it is easily possible to make coated monoparticles having a size of 0.1 to 3 ⁇ m, typically up to around 1 or 2 ⁇ m.
  • Another advantage of the invention is that this very accurate control of coacervation can be achieved without the need to include large amounts of organic solvents.
  • a further advantage of the invention is that it is possible to synthesise the polymer from a monomer blend that is selected according to the physical properties that are required of the final polymer coating, provided always sufficient pH-sensitive monomer is included to render the polymer pH sensitive. Thus it is possible to optimise the polymer for its ultimate performance qualities. - This is in contrast to conventional coacervation techniques where the polymer normally had to be selected primarily from the point of view of its ability to form a coacervate when, for instance, the solvent concentration or temperature changed. The resultant polymers often gave rather poor wall properties, and so were often further reacted in an attemp at improving wall strength and other wall properties.
  • the core material may be a material that relies upo the pH-sensitive nature of the polymer coating to protec the material during storage or use, or it may be a materia where the pH-sensitive nature of the polymer is merel required for the formation of the coating.
  • the cor material can be, for instance, an ink, a fragrance, sythetic pesticide or a biologically produced material suc as enzyme (for instance a protease, especially of the typ used as a detergent enzyme) , a mycelium or insecticida toxin such as insecticidal virus, bacteria or fungi, suc as are described in U.S. 4,948,586.
  • the invention is of particular value for th encapsulation of crystals of the toxin of Bt, Bacillu thuringiensis.
  • This material is preferably present in th form of crystals and/or spores and conveniently i introduced into the aqueous solution of polymer merely b combining a fermentation broth of the Bt toxin or othe microbiological product with the polymer solution.
  • the broth may be combined with an emulsion o the polymer and the pH then adjusted to put the polyme into solution.
  • a nove product which is a composition of a coating polymer and particulate biologically produced material wherein at leas 50% (of the weight of coating polymer and biologicall produced material) is present in the form of particle which have a size below 5 ⁇ m (preferably below 3 ⁇ m) an which have a core of the biologically produced material an a substantially continuous coacervate shell of the polymer, wherein the polymer is a pH-sensitive polymer.
  • an biologically produced material is present in the form o particles having a size of below 3 ⁇ m. Most preferably th particles have a size of below 2 ⁇ m, often around l ⁇ . Th particle size is generally above O.l ⁇ m, frequently above 0.5 ⁇ m.
  • the particulate core material is preferably solid, e.g., Bt toxin crystals and/or spores. Preferably there is generally only one solid particle in each core. Thus by the invention it is possible to formulate Bt crystals into a form that is particularly suitable for efficient application and use.
  • coated particles of the invention may be collected and dried as a powder, but usually they are produced and maintained as a suspension in the aqueous medium in which they are formed.
  • polymer A is a polymer prepared by oil-in-water emulsion polymerisation of 30% by weight acrylic acid with 70% by weight styrene
  • polymer B is prepared in the same way from 15 weight percent methacrylic acid, 30 weight percent ethyl acrylate and 55 weight percent methyl methacrylate.
  • EXAMPLE 1 Microencapsulation of Bt Bioinsecticide with Polymer A A fresh sample of Bacillus thuringiensis fermentation broth (100 parts) containing approximately equal amounts of Bt crystals and spores at pH 7 was vigorously stirred whilst a solution (25%) of polymer A in water at pH 8.8 was added.
  • the starting broth On examination by scanning electron microscopy (SEM) the starting broth was seen to contain roughly equal numbers of diamond shaped Bt crystals and rounded spores in the 1-2 micron size range.
  • the reaction product by contrast contained very few diamond shapes and almost all particles had a rounded shape but still in the 1-2 micron region.
  • the alkali-soluble polymer A had been deposited as a film around the crystals when it was phase separated under acid conditions.
  • Trifluralin Microcaosules An oil phase was prepared consisting of the insecticide Trifluralin 70 parts) , a solvent (Shellsol A; 25 parts) and an 0/W e ulsifier (Tensiofix B7416; 5 parts) .
  • This oil phase (50 parts) was mixed vigorously with water (50 parts) to give a smooth orange O/W emulsion.
  • This emulsion was next added to a clear solution of polymer A in water (6%) at pH 9. Glacial acetic acid was added dropwise to reduce the pH to 7. It was noted that during this stage local precipitation of Polymer A occurred and prolonged stirring at pH 7 was necessary to re-dissolve these polymer clumps.
  • the final product consisted of finely dispersed yellowish orange particles in water. On standing for several days these particles tended to aggregate at the top of the solution with about 25% of the volume consisting of a clear colourless lower aqueous phase. With slight agitation the aggregates easily redispersed.
  • An aqueous phase (100 parts) at pH 7.5 containing 10% w/w Polymer B was prepared.
  • a solution (2% w/w) of crystal violet lactone in a hydrocarbon solvent (15 parts) was added to the aqueous solution of polymer B to form an O/W emulsion.
  • a slurry of ammonium acetate (5 parts) in water (10 parts) was next added.
  • the pH of this mixture at 20°C was 7.3. On warming and stirring the pH dropped steadily to pH 7 (50°C) and pH 6.2 (70°C) .

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Dispersion Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Manufacturing Of Micro-Capsules (AREA)
  • Immobilizing And Processing Of Enzymes And Microorganisms (AREA)
  • Processes Of Treating Macromolecular Substances (AREA)

Abstract

L'invention concerne des procédés qui permettent de former des particules renfermant un noyau d'un matériau donné dans une enveloppe polymère déposée par coacervation. L'invention porte sur une dispersion des particules du matériau devant former les noyaux dans une solution aqueuse d'un matériau polymère sensible au pH, à un pH où le polymère est soluble. Ce dernier se dépose sous la forme d'enveloppe autour du matériau des noyaux par une insolubilisation due à une modification du pH de la solution. Cette modification survient à un rythme suffisamment lent et de manière assez homogène dans la solution pour que le polymère ne se dépose en pratique que sous forme d'un coacervat pratiquement uniforme autour des particules constituant les noyaux.
PCT/GB1993/000533 1992-03-16 1993-03-15 Procede de coacervation WO1993018853A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP93906672A EP0631523A1 (fr) 1992-03-16 1993-03-15 Procede de coacervation
FI944237A FI944237A (fi) 1992-03-16 1994-09-13 Koaservaatioprosessit
NO943440A NO943440D0 (no) 1992-03-16 1994-09-15 Koaservasjonsprosesser

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9205712.4 1992-03-16
GB929205712A GB9205712D0 (en) 1992-03-16 1992-03-16 Coacervation processes

Publications (1)

Publication Number Publication Date
WO1993018853A1 true WO1993018853A1 (fr) 1993-09-30

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ID=10712235

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1993/000533 WO1993018853A1 (fr) 1992-03-16 1993-03-15 Procede de coacervation

Country Status (6)

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EP (1) EP0631523A1 (fr)
CA (1) CA2131548A1 (fr)
FI (1) FI944237A (fr)
GB (1) GB9205712D0 (fr)
NO (1) NO943440D0 (fr)
WO (1) WO1993018853A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0823993A2 (fr) * 1996-08-15 1998-02-18 American Cyanamid Company Microcapsules sensibles au PH.

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE60100150T2 (de) 2000-01-13 2004-02-19 Kureha Kagaku Kogyo K.K. Mikrokapsel und sein Herstellungsverfahren

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1470724A (fr) * 1965-03-05 1967-02-24 Keuffel & Esser Co Procédé de préparation de capsules garnies de substances liquides ou solides
DE2027819A1 (de) * 1969-06-05 1970-12-17 Fuji Photo Film Co. Ltd., Kanagawa (Japan) Verfahren zur Herstellung ölhaltiger Mikrokapseln
EP0229565A1 (fr) * 1985-12-17 1987-07-22 Roquette FrÀ¨res Procédé de fabrication de fromages à pâte pressée cuite
EP0261686A1 (fr) * 1986-09-25 1988-03-30 Canon Kabushiki Kaisha Procédé pour la production de toner capsulé

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1470724A (fr) * 1965-03-05 1967-02-24 Keuffel & Esser Co Procédé de préparation de capsules garnies de substances liquides ou solides
DE2027819A1 (de) * 1969-06-05 1970-12-17 Fuji Photo Film Co. Ltd., Kanagawa (Japan) Verfahren zur Herstellung ölhaltiger Mikrokapseln
EP0229565A1 (fr) * 1985-12-17 1987-07-22 Roquette FrÀ¨res Procédé de fabrication de fromages à pâte pressée cuite
EP0261686A1 (fr) * 1986-09-25 1988-03-30 Canon Kabushiki Kaisha Procédé pour la production de toner capsulé

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0823993A2 (fr) * 1996-08-15 1998-02-18 American Cyanamid Company Microcapsules sensibles au PH.
EP0823993A3 (fr) * 1996-08-15 1998-04-15 American Cyanamid Company Microcapsules sensibles au PH.
US6022501A (en) * 1996-08-15 2000-02-08 American Cyanamid Company pH-sensitive microcapsules
US6500447B1 (en) 1996-08-15 2002-12-31 Basf Aktiengesellschaft pH-sensitive microcapsules

Also Published As

Publication number Publication date
CA2131548A1 (fr) 1993-09-30
NO943440L (no) 1994-09-15
FI944237A0 (fi) 1994-09-13
EP0631523A1 (fr) 1995-01-04
NO943440D0 (no) 1994-09-15
GB9205712D0 (en) 1992-04-29
FI944237A (fi) 1994-09-13

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