Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2001-08-03
2003-09-30
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S056000, C536S124000, C428S364000
Reexamination Certificate
active
06627750
ABSTRACT:
The present invention relates to highly carboxylated cellulose fibers and a process for making such fibers. The highly carboxylated cellulose fibers of the inventions are water-insoluble and have enhanced absorbency toward water and body fluids, making them desirable for use in personal hygiene articles, high strength paper making, cellulose ester coatings with low volatile organic components (VOC), as well as in many other applications. The process of the invention is based on the reaction of organic dicarboxylic acid anhydrides, such as phthalic anhydride, maleic anhydride, succinic anhydride, glutaric anhydride, trimellitic anhydride, 1,2-cyclohexanedicarboxylic anhydride, and oxalyl chloride and cellulosic fibers.
BACKGROUND OF THE INVENTION
Carboxylated cellulose fibers have been used and proposed for use in a number of applications where the presence of carboxyl groups on the fibers is believed to enhance some properties of the cellulose fibers. However, the limited extent to which cellulose fibers could heretofore be carboxylated in a cost-effective and environmentally benign fashion has limited the use of such fibers.
Polymer composites or blends employing cellulose exhibit limited compatibility with certain polymeric materials, including nylon-6 and polypropylene. This incompatibility diminishes the mechanical properties of the polymer composite or blend products. The compatibility of cellulose to such polymeric materials is improved by adding carboxylic acid groups to the cellulose, where it is believed that the carboxyl groups enhance the compatibility between polymers and cellulose.
A need also exists for water-insoluble fibers having improved absorbency towards water or body fluids such as urine, blood, mucus, menses, lymph and other body exudates. Fibers having improved absorbency would find ready application in areas such as personal hygiene, medicine, house keeping, clothing and electronics, as well as in other products. One of the most important applications of water-insoluble fibers having improved absorbency is in disposable absorbent articles, such as diapers or incontinence pads. It would be particularly desirable if articles incorporating such fibers could be processed using conventional commercial equipment. To enable such processing, improved absorbency fibers must meet certain minimal values with regard to fiber strength and fiber length.
In the art of papermaking, there are materials which are used to improve the wet strength of paper. These materials are known in the art as “wet strength agents.” Cationic wet strength agents are perhaps the most widely used variety. The effectiveness of cationic wet strength agents is often limited by the low retention of the wet strength agent on conventional cellulose fibers. This low retention is frequently due to the cationic agents not finding suitable anionic sites for attachment to the fiber, which causes them to remain in solution or to be washed off the fiber after application. Although cationic promoters can be used to increase wetting agent retention, they do not increase the number of anionic sites on a fiber surface, and in some cases may actually decrease the number of such sites, thus inhibiting the wet strength agent from performing its function. It is desirable to increase the number of anionic sites on a fiber to improve the efficiency of wet strength agents. The anionic sites on conventional cellulose pulps can be measured in terms of the carboxyl group content of cellulose, which is typically in the range of about 20 to about 120 milliequivalents per kilogram (meq/kg) of cellulose. U.S. Pat. No. 5,935,383 discloses a method for improving the efficiency of aqueous cationic wet strength additives by pretreating cellulose surfaces with reactive anionic compounds, thus providing the cellulose surface with additional anionic sites suitable for retaining cationic wet strength additives on the cellulose.
Cellulose esters are often used in pharmaceuticals and industrial coatings. However, they frequently exhibit relatively low solid contents in suitable solvents, necessitating use of large amounts of solvent. The use of high solvent levels is undesirable since it is associated with prolonged drying times and atmospheric contamination through solvent evaporation. Although solvent borne cellulose esters provide desirable coatings properties, the current trend is to formulations which require reduced amounts of the volatile organic components (VOC), or which employ water soluble coating formulations, thereby entirely eliminating VOC. This trend has limited the use of solvent borne cellulose esters in coatings applications. WO99/40120 describes an attempt to make carboxylated cellulose esters having improved solvent solubility to enable high solids coating compositions. The method described in WO 99/40120 utilizes oxidized cellulose which is activated with water. The water in the activated cellulose is then displaced with acetic acid and the product esterified and then hydrolyzed. Cellulose esters using carboxylated cellulose fibers as starting material prepared according to the present invention overcome the poor solubility of conventional cellulose esters in aqueous media and thus reduce the need to use VOC in the production of coatings, for example, cellulose esters.
Cellulose fibers having high carboxyl content would be useful in all of the above applications. Carboxylated cellulose can be made through: (a) oxidation of cellulose, (b) etherification of cellulose with monochloroacetic acid, (c) esterification of cellulose with some dicarboxylic acid anhydrides or chlorides, such as phthalic anhydride, maleic anhydride, succinic anhydride and oxalyl chloride.
Some oxidants such as hypohalite, chlorine dioxide, nitrogen dioxide (dinitrogen tetraoxide), permanganate, dichromate-sulfuric acid and hypochlorous acid can be used to make carboxylated cellulose fiber; however, the obtained oxidized celluloses (or oxycelluloses) either have low carboxyl content (lower than 250 meq/kg) or very low intrinsic viscosity as measured in cupriethylenediamine (Cuene I.V.) In addition, some oxidized celluloses may contain aldehyde and/or ketone functionalities besides carboxyl group depending on the nature of the oxidant and the reaction conditions used in their preparation. This can impair their performance as coatings. Sodium (or potassium) periodate is a very effective oxidant, however, it cannot be used cost effectively because there is no viable method to recover periodate. Furthermore, carboxylated cellulose fibers made by the periodate method with carboxyl contents higher than 1000 meq/kg, have Cuene I.V. less than 2 dL/g, which limits their applications.
Etherification of cellulose by monochloroacetic acid yields carboxylated cellulose (carboxymethyl cellulose) with relatively high carboxyl content and high I.V.; however, the carboxylated cellulose products produced in this fashion are usually particles, instead of fibers, if the degree of substitution (DS) of carboxyl group is higher than 0.3. Particles are susceptible to water absorption except when present in the acid form and/or crosslinked. U.S. Pat. No. 4,410,694 discloses a method for preparing carboxylated fibers in water using monochloroacetic acid; however, the degree of substitution (DS) of the carboxylated fibers is very low.
U.S. Pat. No. 4,734,239 describes the production of water-insoluble fibers of cellulose monoesters of maleic acid, succinic acid and phthalic acid, having an high absorbability for water and physiological liquids. The carboxylated cellulose was prepared via esterification of cellulose by dicarboxylic acid in the presence of dimethylacetamide/lithium chloride (DMAc/LiCL) as solvent and potassium acetate as catalyst. The solvent medium, DMAc/LiCL is costly to use and DMAc is toxic. Further, the carboxylated cellulose produced according to the patent is substantially dissolved and must be spun to produce a fiber.
Accordingly, there exists a need for an economical and environmentally benign method of making highly carboxylated fibers fr
Henry Michael C.
Kramer Levin Naftalis & Frankel LLP
Rayonier Inc.
Wilson James O.
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