Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2002-10-23
2004-05-25
Barts, Samuel (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S001110, C536S020000, C536S055200, C536S055300, C536S123100, C210S702000
Reexamination Certificate
active
06740752
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for preparing particles of chitosan. Chitosan particles in this form which are prepared according to the process herein are “activated” in the sense that they are especially useful for providing plant care benefits.
BACKGROUND OF THE INVENTION
Chitosan is a modified carbohydrate polymer derived from the chitin component of the shells of crustaceans such as crabs, shrimp and cuttlefish. Chitosan is used for a wide variety of purposes including plant care, cosmetics additives, food and nutrition supplements and medical care uses.
Both Polish Patent No. 125,995 and the periodical “Journal of Applied Polymer Science” Vol. 33 p. 177, 1987 disclose a method for producing a form of chitosan with a developed internal surface. This is done via a batch process in which the chitosan is periodically precipitated from its solutions in aqueous organic or inorganic acids or their salts by means of neutralization with hydroxides of alkali metals. The precipitation mixture is vigorously stirred. The precipitated chitosan in gel or suspension form is washed several times with water. This known method permits production of chitosan having a developed internal surface with a yield of 70-90% of theoretical. However, the procedure is a batch process which requires at least 12-24 hours for a production cycle. The single batches of the product are lacking homogeneity. The product has a distinct tendency toward degradation and its sorption capacity is rather poor resulting from the relatively low degree of development of the inner surface of the chitosan particles.
Polish Patent No. 164,247 and Finnish Patent No. 83,426 both disclose a continuous method for producing microcrystalline chitosan. In this method a solution of chitosan in aqueous acids and/or their salts is introduced to a reactor along with an aqueous solution of alkali metal hydroxides or salts. This results in formation of suspension of microcrystalline chitosan particles with a suspension pH>7. Simultaneously, this alkaline suspension of the formed microcrystalline chitosan particles is continuously removed from the reactor. The alkaline solution may also be introduced directly to a recirculation system. This method has several drawbacks including a yield below 90%, and realization of chitosan agglomerates with an average particle size above 1 &mgr;m and water retention value below 5000%. The water retention value is an indication of the development of the inner surface. Moreover, it is not possible to control the molecular, supermolecular and morphological structure of the chitosan particles produced. This continuous process also causes a substantial decrease of the average molecular weight of the generated microcrystalline chitosan as result of intensive degradation effects.
SUMMARY OF THE INVENTION
The present invention provides a process for preparing particles of “microcrystalline” chitosan in the form of an aqueous suspension of such particles. As a consequence of the specific steps used to carry out the process, the chitosan particles in the suspension are “activated” in the sense that the chitosan material in this form is especially useful for a number of purposes including in particular the provision of a variety of plant care benefits.
In the first step of the process herein, an aqueous solution is formed, generally containing at least 0.001% and preferably from 0.01% to 10.0% by weight of chitosan which can be provided by any conventional chitosan source. This solution contains organic or inorganic acids and/or salts of such acids in an amount sufficient to maintain the solution at a pH which is low enough to completely solubilize the chitosan.
In the next step of the process, the aqueous solution of the first step is partially neutralized by adding a neutralizing agent while subjecting the solution to shear agitation. The neutralizing agent addition and the agitation are sufficient to convert the solution into a continuous gel phase having a pH of from 5.0 to 6.9
In the next process step, the partially neutralized gel formed in the previous step is maintained under shear agitation for at least 10 seconds after the gel phase has been formed in order to homogenize the gel phase. This agitated homogenized gel is then further neutralized under continuing agitation by addition of more neutralizing agent sufficient to raise the pH within the homogenized gel phase to above 6.9, preferably above 7.3. Agitation is preferably continued for at least another 10 seconds after this elevated pH is reached. This then forms a gel-like suspension of discrete particles of activated microcrystalline chitosan having desirable properties.
In preferred embodiments of the present process, the aqueous solution formed in the initial step can be filtered prior to neutralization to remove insoluble matter such as may have been introduced with the chitosan source. Also preferably the chitosan particles of the eventually formed gel-like suspension may be washed, e.g., with water, to remove such materials such water soluble salts.
Preferably the chitosan particles produced by the process of this invention are characterized by having an average particle size of from 2 to 20 &mgr;m. Preferably also such particles further have a water solubility of at least 90% at pH 6 after 24 hours.
DETAILED DESCRIPTION OF THE INVENTION
In the first step of the process described above, an aqueous solution of chitosan is formed. This can be accomplished by combining chitosan with an aqueous solution containing organic or inorganic acids or their salts. Such acids can include, for example, acetic acid, lactic acid, salicylic acid, hydrochloric acid, and the like. Sufficient acid or salt thereof must be utilized to maintain this solution at a pH wherein the chitosan is essentially completely dissolved, i.e., solubilized. Agitation sufficient to facilitate chitosan dissolution may be utilized.
Any conventional source of chitosan may be utilized to form the chitosan solution. Such chitosan sources may be those derived from shellfish or may be fungally derived. Commercially available chitosan sources are marketed, for example, under the tradenames “Chitosan” by Vanson, Inc. of Redmond, Wash., USA and “Chitoclear” by Primex Ingredients SA of Avaldsnes, Norway.
The chitosan is utilized to an extent which is sufficient to form a concentration of chitosan in the aqueous solution of at least 0.001% by weight. More preferably, the solution will contain from 0.01% to 10.0% by weight, most preferably from 0.01% to 1.5% by weight.
After the aqueous chitosan solution has been formed in the first essential step of the process herein, such a solution may optionally be filtered before further processing in order to remove therefrom any insoluble material which might remain therein. Such insoluble material, for example, may have been introduced into the solution from the chitosan source.
In a second essential step of the process herein, the chitosan solution formed in the first essential process step is partially neutralized. This is accomplished by adding a neutralizing agent to the solution while maintaining the solution under shear agitation. Neutralization agents which can be used in this step include hydroxides such as sodium, potassium and ammonium hydroxides and their salts. Preferably these neutralization agents are combined with the first step chitosan solution in the form of aqueous solutions having a neutralizing agent concentration of from 0.01% to 20% by weight.
Partial neutralization in this second essential process step is effected while the combined chitosan
eutralizing agent solution is maintained under shear agitation. Both the addition of the neutralizing agent and the shear agitation should be sufficiently carried out in order to convert the solution into a continuous gel phase having a pH within the range of from 5.0 to 6.9. Typically shear agitation to the extent of from 10 to 1000 sec
−1
(rpm) can be used.
After this continuous gel phase has been formed, the gel phase is next subjected to continued
Kucharska Magdalena
Niekraszewicz Antoni
Struszcyk Henryk
Urbanowski Alojzy
Wisniewska-Wrona Maria
Barts Samuel
Krishnan Ganapathy
Meyer Peter D.
The Procter & Gamble & Company
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