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Patent US6919447 - Hypochlorite free method for preparation of stable carboxylated carbohydrate ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA method of making a carboxylated carbohydrate is disclosed, cellulose being a preferred carbohydrate material. Carboxylated cellulose fibers can be produced whose fiber strength and degree of polymerization is not significantly sacrificed. The method involves the use of a catalytic amount of a hindered...http://www.google.com/patents/US6919447?utm_source=gb-gplus-sharePatent US6919447 - Hypochlorite free method for preparation of stable carboxylated carbohydrate productsAdvanced Patent SearchPublication numberUS6919447 B2Publication typeGrantApplication numberUS 09/875,177Publication dateJul 19, 2005Filing dateJun 6, 2001Priority dateJun 6, 2001Fee statusPaidAlso published asCA2383464A1, CA2383464C, EP1264845A2, EP1264845A3, US7109325, US7135557, US20030083491, US20040266728, US20050014669Publication number09875177, 875177, US 6919447 B2, US 6919447B2, US-B2-6919447, US6919447 B2, US6919447B2InventorsJoseph Lincoln Komen, S. Ananda Weerawarna, Richard A. JewellOriginal AssigneeWeyerhaeuser CompanyExport CitationBiBTeX, EndNote, RefManPatent Citations (40), Non-Patent Citations (28), Referenced by (2), Classifications (21), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetHypochlorite free method for preparation of stable carboxylated carbohydrate productsUS 6919447 B2Abstract A method of making a carboxylated carbohydrate is disclosed, cellulose being a preferred carbohydrate material. Carboxylated cellulose fibers can be produced whose fiber strength and degree of polymerization is not significantly sacrificed. The method involves the use of a catalytic amount of a hindered cyclic oxammonium compounds as a primary oxidant and chlorine dioxide as a secondary oxidant in an aqueous environment. The oxammonium compounds may be formed in situ from their corresponding amine, hydroxylamine, or nitroxyl compounds. The oxidized cellulose may be stabilized against D.P. loss and color reversion by further treatment with an oxidant such as sodium chlorite or a chlorine dioxide/hydrogen peroxide mixture. Alternatively it may be treated with a reducing agent such as sodium borohydride. In the case of cellulose the method results in a high percentage of carboxyl groups located at the fiber surface. The product is especially useful as a papermaking fiber where it contributes strength and has a higher attraction for cationic additives. The product is also useful as an additive to recycled fiber to increase strength. The method can be used to improve properties of either virgin or recycled fiber. It does not require high α-cellulose fiber but is suitable for regular market pulps.
5. A method of making a carboxylated carbohydrate product which comprises: oxidizing a carbohydrate compound by reacting the carbohydrate in an aqueous system with a sufficient amount of a primary oxidant selected from the group consisting of hindered heterocyclic oxammonium salts in which the carbon atoms adjacent the oxammonium nitrogen lack .alpha.-hydrogen substitution, the corresponding amines, hydroxylamines, and nitroxides of these oxammonium salts, and mixtures thereof, in which the nitroxides are compositions having the structure in which R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R1 may together be included in a five or six carbon alicyclic ring structure, and R6 is hydrogen or C1-C5 alkyl, and R7 is hydrogen, C1-C5 alkyl, phenyl, carbamoyl, alkyl carbamoyl, phenyl carbamoyl, or C1-C8 acyl, and a secondary oxidant selected from chlorine dioxide and latent sources of chlorine dioxide in a sufficient amount to induce an increase in carboxyl substitution in the carbohydrate of at least 2 meq/100 g.
8. A method of making a carboxylated carbohydrate product which comprises: oxidizing a carbohydrate compound by reacting the carbohydrate in an aqueous system with a sufficient amount of a primary oxidant selected from the group consisting of hindered heterocyclic oxammonium salts in which the carbon atoms adjacent the oxammonium nitrogen lack .alpha.-hydrogen substitution, the corresponding amines, hydroxylamines, and nitroxides of these oxammonium salts, and mixtures thereof, in which the nitroxides are compositions having the structure in which R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may together be included in a five or six carbon alicyclic ring structure, and X is oxygen, sulfur, NH, N-alkyl, NOH, or NOR8 where R8 is lower alkyl, and a secondary oxidant selected from chlorine dioxide and latent sources of chlorine dioxide in a sufficient amount to induce an increase in carboxyl substitution in the carbohydrate of at least 2 meq/100 g.
10. A method of making a carboxylated carbohydrate product which comprises: oxidizing a carbohydrate compound by reacting the carbohydrate in an aqueous system with a sufficient amount of a primary oxidant selected from the group consisting of hindered heterocyclic oxammonium salts in which the carbon atoms adjacent the oxammonium nitrogen lack .alpha.-hydrogen substitution, the corresponding amines, hydroxylamines, and nitroxides of these oxammonium salts, and mixtures thereof, in which the nitroxides are compositions having the structure wherein R1-R1 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may be linked into a five or six carbon alicyclic ring structure, X is oxygen, sulfur, -alkyl amino, or acyl amino, and a secondary oxidant selected from chlorine dioxide and latent sources of chlorine dioxide in a sufficient amount to induce an increase in carboxyl substitution in the carbohydrate of at least 2 meq/100 g.
12. A method of making a carboxylated carbohydrate product which comprises: oxidizing a carbohydrate compound by reacting the carbohydrate in an aqueous system with a sufficient amount of a primary oxidant selected from the group consisting of hindered heterocyclic oxammonium salts in which the carbon atoms adjacent the oxammonium nitrogen lack .alpha.-hydrogen substitution, the corresponding amines, hydroxylamines, and nitroxides of these oxammonium salts, and mixtures thereof, in which the nitroxides are compositions having the structure wherein R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may be linked into a five or six carbon alicyclic ring structure, and a secondary oxidant selected from chlorine dioxide and latent sources of chlorine dioxide in a sufficient amount to induce an increase in carboxyl substitution in the carbohydrate of at least 2 meq/100 g.
14. A method of making a carboxylated carbohydrate product which comprises: oxidizing a carbohydrate compound by reacting the carbohydrate in an aqueous system with a sufficient amount of a primary oxidant selected from the group consisting of hindered heterocyclic oxammonium salts in which the carbon atoms adjacent the oxammonium nitrogen lack .alpha.-hydrogen substitution, the corresponding amines, hydroxylamines, and nitroxides of these oxammonium salts, and mixtures thereof, in which the nitroxides are compositions having the structure wherein R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may together be included in a five or six carbon alicyclic ring structure, X is methylene, oxygen, sulfur, or alkylamino, and R9 and R10 are one to five carbon alkyl groups and may together be included in a five or six member ring structure which, in turn, may have one to four lower alkyl or hydroxy alkyl substituents, and a secondary oxidant selected from chlorine dioxide and latent sources of chlorine dioxide in a sufficient amount to induce an increase in carboxyl substitution in the carbohydrate of at least 2 meq/100 g.
21. The method of claim 20 in which the nitroxides are compositions having the structure in which R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may together be included in a five or six carbon alicyclic ring structure, and X may be methylene, sulfur, oxygen, �NH, or NR11, in which R11 is a lower alkyl.
23. A method of making a carboxylated carbohydrate product which comprises: oxidizing a carbohydrate compound by reacting the carbohydrate in an aqueous system with a sufficient amount of a primary oxidant selected from the group consisting of hindered cyclic nitroxides having the composition wherein R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may together be included in a five or six carbon alicyclic ring structure, X is methylene, oxygen, sulfur, or alkylamino, and R9 and R10 are one to five carbon alkyl groups and may together be included in a five or six member ring structure which, in turn, may have one to four lower alkyl or hydroxy alkyl substituents; and a secondary oxidant selected from chlorine dioxide and latent sources of chlorine dioxide in a sufficient amount to induce an increase in carboxyl substitution in the carbohydrate of at least 2 meq/100 g.
BACKGROUND OF THE INVENTION Carbohydrates are polyhydroxy aldehyde or ketone compounds or substances that yield these compounds on hydrolysis. They frequently occur in nature as long chain polymers of simple sugars. As the term is used in the present invention it is intended to be inclusive of any monomeric, oligomeric, and polymeric carbohydrate compound which has a primary hydroxyl group available for reaction.
Cellulose is a carbohydrate consisting of a long chain of glucose units, all β-linked through the 1′-4 positions. Native plant cellulose molecules may have upwards of 2200 anhydroglucose units. The number of units is normally referred to as degree of polymerization or simply D.P. Some loss of D.P. inevitably occurs during purification. A D.P. approaching 2000 is usually found only in purified cotton linters. Wood derived celluloses rarely exceed a D.P. of about 1700. The structure of cellulose can be represented as follows: Chemical derivatives of cellulose have been commercially important for almost a century and a half. Nitrocellulose plasticized with camphor was the first synthetic plastic and has been in use since 1868. A number of cellulose ether and ester derivatives are presently commercially available and find wide use in many fields of commerce. Virtually all cellulose derivatives take advantage of the reactivity of the three available hydroxyl groups. Substitution at these groups can vary from very low; e.g. about 0.01 to a maximum 3.0. Among important cellulose derivatives are cellulose acetate, used in fibers and transparent films; nitrocellulose, widely used in lacquers and gun powder; ethyl cellulose, widely used in impact resistant tool handles; methyl cellulose, hydroxyethyl, hydroxypropyl, and sodium carboxymethyl cellulose, water soluble ethers widely used in detergents, as thickeners in foodstuffs, and in papermaking.
Brasey et al, in U.S. Pat. No. 4,100,341, describe oxidation of cellulose with nitric acid. They note that the reaction was specific at the C6 position and that secondary oxidation at the C2 and C3 positions was not detected. They further note that the product was � . . . stable without the need for subsequent reduction steps or the introduction of further reactants [e.g., aldehyde groups] from which the oxidized cellulose has to be purged�.
A year following the above noted Besemer PCT publication, the same authors, in Cellulose Derivatives, T. J. Heinze and W. G. Glasser, eds., Ch. 5, pp 73-82 (1996), describe methods for selective oxidation of cellulose to 2,3-dicarboxy cellulose and 6-carboxy cellulose using various oxidants. Among the oxidants used were a periodate/chlorite/hydrogen peroxide system, oxidation in phosphoric acid with sodium nitrate/nitrite, and with TEMPO and a hypochlorite/bromide primary oxidant. Results with the TEMPO system were poorly reproduced and equivocal. The statement that � . . . some of the material remains undissolved� was puzzling. In the case of TEMPO oxidation of cellulose, little or none would have been expected to go into water solution unless the cellulose was either badly degraded and/or the carboxyl substitution was very high. The homogeneous solution of cellulose in phosphoric acid used for the sodium nitrate/sodium nitrite oxidation was later treated with sodium borohydride to remove any carbonyl function present.
P.-S. Chang and J. F. Robyt, Journal of Carbohydrate Chemistry 15(7): 819-830 (1996), describe oxidation of ten polysaccharides including α-cellulose at 0� C. and 25� C. using TEMPO with sodium hypochlorite and sodium bromide. Ethanol addition was used to quench the oxidation reaction. The resulting oxidized α-cellulose had a water solubility of 9.4%. The authors did not further describe the nature of the α-cellulose. It is presumed to have been a so-called dissolving pulp or cotton linter cellulose.
SUMMARY OF THE INVENTION The present invention is directed to a method for preparation of a carboxylated carbohydrate product using a catalytic amount of a hindered cyclic oxammonium salt as the effective primary oxidant. This may be generated in situ by the use of a corresponding amine, hydroxylamine, or nitroxide. The catalyst is not consumed and may be recycled for reuse. The method does not require an alkali metal or alkaline earth hypohalite compound as a secondary oxidant to regenerate the oxammonium salt. Instead, chlorine dioxide has proved to be very satisfactory for this function. If maximum stability of the product is desired, the initially oxidized product may be treated, preferably with a tertiary oxidant or, alternatively, a reducing agent, to convert any unstable substituent groups into carboxyl or hydroxyl groups.
In the discussion and claims that follow, the terms nitroxide, oxammonium salt, amine, or hydroxylamine of a corresponding hindered heterocyclic amine compound should be considered as full equivalents. The oxammonium salt is the catalytically active form but this is an intermediate compound that is formed from a nitroxide, continuously used to become a hydroxylamine, and then regenerated, presumably back to the nitroxide. The secondary oxidant will convert the amine form to the free radical nitroxide compound. Unless otherwise specified, the term �nitroxide� will normally be used hereafter in accordance with the most common usage in the related literature.
The method is broadly applicable to many carbohydrate compounds having available primary hydroxyl groups, of which only one is cellulose. The terms �cellulose� and �carbohydrate� should thus be considered equivalents when used hereafter.
The �cellulose� used with the present invention is preferably a wood based cellulose market pulp below 90% α-cellulose, generally having about 86-88% α-cellulose and a hemicellulose content of about 12%.
When cellulose is the carbohydrate being treated, the usual procedure is to slurry the cellulose fiber in water with a small amount of sodium bicarbonate or another buffering material for pH control. The pH of the present process is not highly critical and may be within the range of about 4-12, preferably about 6-8. The nitroxide may be added in aqueous solution and chlorine dioxide added separately or premixed with the nitroxide. If the corresponding amine is used, they are preferably first reacted in aqueous solution with chlorine dioxide at somewhat elevated temperature. Additional chlorine dioxide is added to the cellulose slurry and the catalytic solution is then added and allowed to react, preferably at elevated temperature for about 30 seconds to 10 hours at temperatures from about 5�-110� C., preferably about 20�-95� C.
Alkali metal chlorites are one class of oxidizing agents used as stabilizers, sodium chlorite being preferred because of the cost factor. Other compounds that may serve equally well as oxidizers are permanganates, chromic acid, bromine, silver oxide, and peracids. A combination of chlorine dioxide and hydrogen peroxide is also a suitable oxidizer when used at the pH range designated for sodium chlorite. Oxidation using sodium chlorite may be carried out at a pH in the range of about 0-5, preferably 2-4, at temperatures between about 10�-110� C., preferably about 20�-95� C., for times from about 0.5 minutes to 50 hours, preferably about 10 minutes to 2 hours. One factor that favors oxidants as opposed to reducing agents is that aldehyde groups on the oxidized carbohydrate are converted to additional carboxyl groups, thus resulting in a more highly carboxylated product. These stabilizing oxidizers are referred to as �tertiary oxidizers� to distinguish them from the nitroxide/chlorine dioxide primary/secondary oxidizers. The tertiary oxidizer is used in a molar ratio of about 1.0-15 times the presumed aldehyde content of the oxidized carbohydrate, preferably about 5-10 times. In a more convenient way of measuring the needed tertiary oxidizer, the preferred sodium chlorite usage should fall within about 0.01-20% based on carbohydrate, preferably about 1-9% by weight based on carbohydrate, the chlorite being calculated on a 100% active material basis.
When stabilizing with a ClO2 and H2O2 mixture, the concentration of ClO2 present should be in a range of about 0.01-20% by weight of carbohydrate, preferably about 0.3-1.0%, and concentration of H2O2 should fall within the range of about 0.01-10% by weight of carbohydrate, preferably 0.05-1.0%. Time will generally fall within the range of 0.5 minutes to 50 hours, preferably about 10 minutes to 2 hours and temperature within the range of about 10�-110� C., preferably about 30�-95� C. The pH of the system is preferably about 3 but may be in the range of 0-5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Abundant laboratory data indicates that a nitroxide catalyzed cellulose oxidation predominantly occurs at the primary hydroxyl group on C-6 of the anhydroglucose moeity. In contrast to some of the other routes to oxidized cellulose, only very minor reaction has been observed to occur at the secondary hydroxyl groups at the C-2 and C-3 locations. Using TEMPO as an example, the mechanism to formation of a carboxyl group at the C-6 location proceeds through an intermediate aldehyde stage. The TEMPO is not irreversibly consumed in the reaction but is continuously regenerated. It is converted by the secondary oxidant into the oxammonium (or nitrosonium) ion which is the actual oxidant. During oxidation the oxammonium ion is reduced to the hydroxylamine from which TEMPO is again formed. Thus, it is the secondary oxidant which is actually consumed. TEMPO may be reclaimed or recycled from the aqueous system. The reaction is postulated to be as follows: As was noted earlier, formation of the oxammonium salt in situ by oxidation of the hydroxylamine or the amine is considered to be within the scope of the invention.
The following groups of nitroxyl compounds and their corresponding amines or hydroxylamines are known to be effective primary oxidants: in which R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may together be included in a five or six carbon alicyclic ring structure; X is sulfur or oxygen; and R5 is hydrogen, C1-C12 alkyl, benzyl, 2-dioxanyl, a dialkyl ether, an alkyl polyether, or a hydroxyalkyl, and X with R5 being absent may be hydrogen or a mirror image moiety to form a bipiperidinyl nitroxide. Specific compounds in this group known to be very effective are 2,2,6,6-tetramethylpiperidinyl-1-oxy free radical (TEMPO); 2,2,2′,2′,6,6,6′,6′-octamethyl-4,4′-bipiperidinyl-1,1′-dioxy di-free radical (BI-TEMPO); 2,2,6,6-tetramethyl-4-hydroxypiperidinyl-1-oxy free radical (4-hydroxy-TEMPO); 2,2,6,6-tetramethyl-4-methoxypiperidinyl-1-oxy free radical (4-methoxy-TEMPO); and 2,2,6,6-tetramethyl-4-benzyloxypiperidinyl-1-oxy free radical (4-benzyloxy-TEMPO). in which R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may together be included in a five or six carbon alicyclic ring structure; R6 is hydrogen or C1-C5 alkyl; R7 is hydrogen, C1-C8 alkyl, phenyl, carbamoyl, alkyl carbamoyl, phenyl carbamoyl, or C1-C8 acyl. Exemplary of this group is 2,2,6,6-tetramethyl-4-aminopiperidinyl-1-oxy free radical (4-aminoTEMPO); and 2,2,6,6-tetramethyl-4-acetylaminopiperidinyl-1-oxy free radical (4-acetylamino-TEMPO). in which R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may together be included in a five or six carbon alicyclic ring structure; and X is oxygen, sulfur, NH, N-alkyl, NOH, or NOR8 where R8 is lower alkyl. An example might be 2,2,6,6-tetramethyl-4-oxopiperidinyl-1-oxy free radical (2,2,6,6-tetramethyl-4-piperidone-1-oxy free radical). wherein R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may be linked into a five or six carbon alicyclic ring structure; X is oxygen, sulfur, -alkyl amino, or acyl amino. An example is 3,3,5,5-tetramethylmorpholine-4-oxy free radical. In this case the oxygen atom takes precedence for numbering but the dimethyl substituted carbons remain adjacent the nitroxide moiety. wherein R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may be linked into a five or six carbon alicyclic ring structure. An example of a suitable compound is 3,4-dehydro-2,2,6,6,-tetramethylpiperidinyl-1-oxy free radical. wherein R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may together be included in a five or six carbon alicyclic ring structure; X is methylene, oxygen, sulfur, or alkylamino; and R9 and R10 are one to five carbon alkyl groups and may together be included in a five or six member ring structure, which, in turn may have one to four lower alkyl or hydroxy alkyl substitutients. Examples include the 1,2-ethanediol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol, and glyceryl cyclic ketals of 2,2,6,6-tetramethyl-4-piperidone-1-oxy free radical. These compounds are especially preferred primary oxidants because of their effectiveness, lower cost, ease of synthesis, and suitable water solubility. in which R1-R4 are one to four carbon alkyl groups but R1 with R2 and R3 with R4 may together be included in a five or six carbon alicyclic ring structure; and X may be methylene, sulfur, oxygen, �NH, or NR11, in which R11 is a lower alkyl. An example of these five member ring compounds is 2,2,5,5-tetramethylpyrrolidinyl-1-oxy free radical.
EXAMPLE 1 Use of the Glyceryl Ketal of Triacetone Amine to Form the Primary Oxidizing Agent The glyceryl ketal of triacetone amine (gk-TAA) is 7,7,9,9-tetramethyl-1,4-dioxa-8-azaspiro[4.5]decane-2-methanol. This is a commercially available chemical. However, it may be synthesized by reaction of 2,2,6,6-tetramethyl-4-piperidone with glycerine under strongly acidic conditions.
Part 1: 10.3 mg of gk-TAA was reacted with 2 g of a 6.7 g/L solution of ClO2 at 60� for about 2 minutes. To this was then added an additional 2 g of the ClO2 solution and the reaction continued for an additional 2 minutes at 60� C. The reaction mixture was added to 30 mL of the ClO2 solution and 60 mL water. This solution was placed in a sealable polyethylene bag and to it was then added a 45 g wet sample (10 g O.D. basis) of cellulose combined with 1 g NaHCO3. The pH at this time was 7.3. The bag with its contents was placed in a 60-70� C. water bath for 31 minutes. The oxidized pulp was drained leaving a wet mass of 34 g. The 98 g of liquor recovered was retained in order to recycle the catalyst. A small portion of the oxidized pulp was retained for analysis. The remainder was stabilized by adjusting the pH to about 3 with 1 M H2SO4 solution and adding 30 mL of the 6.7 g/l ClO2 solution, 3 mL of 3% H2O2, and 40 mL water. The stabilization reaction was continued for about 1 hour at 60�-70� C. The pulp was washed and converted to the sodium form by treating it in a solution of Na2CO3 at about pH 8-9.
Part 2: The recovered liquor from the oxidation step above was combined with 41 g (10 g O.D.) of the never dried cellulose pulp, 30 mL of the 6.7 g/L ClO2 solution and 1 g NaHCO3. These were placed in a sealed polyethylene bag as before and reacted in a 60-70� C. water bath for 40 minutes. The oxidized pulp was drained and stabilized as above.
Part 1, unstabilized
Part 1, stabilized
Part 2, Unstabilized
Part 2, Stabilized
EXAMPLE 2 Investigation of Effect of Primary Catalyst Loading A catalyst solution was made by adding 20.0 mg gk-TAA to �2.0 g of a solution of 6.7 g/L ClO2 at 70� C. for 1-2 minutes. The gk-TAA appeared to be totally dissolved. Cellulose was oxidized as above using 41 g (10 g O.D.) of the never dried pulp, 0.5 g NaHCO3, 75 mL water, and 14 mL of the 6.7 g/L ClO2 solution. To this was added either 0.11 g, 0.26 g, 0.50 g, or 0.75 g of the catalyst solution. These catalyst additions correspond to 0.011%, 0.026%, 0.050%, and 0.075% by weight based on dry cellulose. After 30 minutes reaction time at 70� C. the samples with the two highest catalyst usages were white in appearance, the next lower usage sample had a faint off-white color and the lowest catalyst usage sample was a light yellow. After 2 hours the samples were removed from the water bath and drained. The unwashed oxidized material was stabilized by treatment with 30 mL of the 6.7 g/l ClO2 solution and 3 g 3% H2O2. The pH was adjusted to �1 by 1 M H2SO4. Treatment was continued for about 30 minutes at 60� C. The samples were then filtered off and washed with deionized water. Carboxyl analyses indicated the following levels of substitution:
EXAMPLE 3 Use of 1,3-Propanediol Ketal of Triacetone Amine to Form the Primary Oxidizing Agent A catalyst solution was formed by reacting 10.5 mg of the 1,3-propane-diol acetal of triacetone amine and 1.5 mL of a 5.7 g/L solution of ClO2 in a sealed tube for about 1 minute. The resulting dark material readily dissolved in the liquid. Water (75 mL), 0.5 g NaHCO3, 15 mL of the 5.7 g/L ClO2 solution, and the activated catalyst solution, along with a few mL of rinse water were combined in that order. This was combined with 41 g of the wet (10 g O.D.) cellulose and mixed in a sealed polyethylene bag. The mixture was placed in a 70� C. water bath and allowed to react for 33 minutes. The slurry was acidified with 1 M H2SO4 to �pH 3. Then 5.0 mL of the 5.7 g/L ClO2 solution and 1.5 mL of 3% H2O2 were mixed in. The sealed bag was again placed in the 70� C. hot water bath for about 1 hour. The resulting stabilized carboxylated cellulose was washed and dried as before. Carboxyl content was measured as 8.3 meq/100 g.
EXAMPLE 4 Use of TEMPO as a Primary Oxidizing Agent with a ClO2 Secondary Oxidant A 10.6 g dried sample (10.0 g O.D.) of the northern softwood pulp was slurried in 200 g water with 3 g NaHCO3. Then 0.1 g TEMPO and �2 mL of a 6 g/L ClO2 solution were combined and gently heated to form an oxidation catalyst. An additional 68 mL of the 6 g/L ClO2 solution was stirred into the pulp slurry, then the catalyst mixture. The slurry was contained in a sealed polyethylene bag and immersed in a 70� C. water bath for 30 minutes. The reacted cellulose was then washed and stabilized by combining 0.7 g 30% H2O2, 0.7 g NaClO2, wet pulp, and water to make 100 g total. The pH was reduced to below 3 by adding about 1.5 g of 1 M H2SO4 and the mixture was heated and allowed to react for about 1 hour at 70� C. Analyses showed that the unstabilized material had a carboxyl content of 8.7 meq/100 g while the stabilized sample had 17 meq/100 g carboxyl.
EXAMPLE 5 Use of 2,2,6,6-tetramethylpiperidine to Form Primary Oxidation Catalyst Rather than use the nitroxide form of TEMPO as a starting catalyst material, the corresponding amine was employed to generate a catalyst. A water solution containing 7.1 g/L ClO2 was prepared. About 5 mL of this was reacted with about 80 mg 2,2,6,6-tetramethylpiperidine to form the oxammonium salt. Then 85-90 mL of the ClO2 solution was combined with 41 g (10.0 g O.D.) of the never dried pulp, 3 g of NaHCO3, and 0.08 g of 3.3% H2O2. The catalyst solution was added and the whole, contained in a sealed polyethylene bag, was immersed in a 70� C. water bath for 40 minutes. The pH was then adjusted below 3 with 1 M H2SO4. Then 3 g of 3.3% H2O2 and 30 mL of the ClO2 solution were mixed in and again placed in the 70� C. water bath for 1 hour for stabilization. The stabilized carboxylated cellulose was washed and dried as before. Carboxyl content was 22 meq/100 g.
EXAMPLE 6 Use of 4-oxo-TEMPO-1,3-propanediol Ketal to Form the Primary Oxidizing Agent A catalyst mixture was formed by mixing 0.10 g of 2,2,6,6-tetramethyl-4-piperidone-3-propanediol ketal was reacted with about 3 g/L of a 6.8 g/L ClO2 solution to form the corresponding catalytic oxammonium compound. Then 41 g (10 g O.D.) of never dried bleached northern softwood kraft pulp was added to 87 mL of the ClO2 solution along with 3 g NaHCO3 followed by the rapid addition of the catalyst solution. The mixture at pH 7.5 was placed in a sealed polyethylene bag and submerged in a 70� C. hot water bath for about 30 minutes. The pH of the reaction mixture was reduced below 3 with 1 M H2SO4. At this time about 6 g of 3.2% H2O2 and 30 mL of the 6.8 g/L ClO2 solution were added. The polyethylene bag was again sealed and placed in the 70� C. water bath for 1 hour. The stabilized pulp was then washed and dried as before. Upon analysis the carboxyl content was 23 meq/100 g.
EXAMPLE 7 Effect of Oxidation pH on Carboxyl Content The catalyst mixture of Example 6 was again made up, this time using a fresh 7.1 g/L solution of ClO2. Instead of the NaHCO3 buffer used earlier, which gave a pH of about 7.5, the buffering system used was a mixture of Na2HPO4 and citric acid as shown in the table that follows. With the exception of the buffers, the procedure used was generally similar to that of Example 6 with the following exceptions. Only 30 mL of the 7.1 g/L ClO2 solution was used and the initial reaction time was extended to 2� hours. Stabilization was under similar conditions except that only 25 mL of the ClO2 solution was used, the temperature was 60� C., and the bags with the samples were removed from the water bath after 1 hour but allowed to remain at room temperature over the weekend. Reaction conditions and carboxyl content were as follows.
0.2 M Na2HPO4,
0.1 M citric acid,
EXAMPLE 8 Effect of Stabilization on Brightness Reversion of Oxidized Pulps A catalyst mixture was made by reacting 0.11 g of 2,2,6,6-tetramethylpiperidine with about 25 mL of 6.9 g/L ClO2 solution at 70� C. for a few minutes. Then the activated catalyst, 10 g NaHCO3, 410 g (100 g O.D.) of never dried northern bleached kraft softwood pulp, and 575 mL of the 6.9 g/L % ClO2 solution were intimately mixed. The pH of the mixture was in the 8.0-8.5 range. The sealed container was placed in a 70� C. hot water bath. Gases given off during the reaction were vented as necessary. After 38 minutes the product was divided into two portions. A first portion was washed and treated with a solution of about 2 g/L Na2CO3 for about 5 minutes at a pH between 9-10. The unstabilized product was then washed with deionized water but left undried. The second portion was stabilized by removing about 200 mL of the remaining reaction liquor which was replaced by an equal amount of a solution of 5.0 g 80% NaClO2, 5.0 g of 3% H2O2, and 12.8 g of 1M H2SO4. This was again reacted for 45 minutes at 70� C. The product was drained and washed, treated with basic water at pH �10, and again washed.
1650 � 100
13.7 � 0.5 Stabilized
1390 � 60 21.6 � 0.1 *D.P. results of unstabilized materials are unreliable due to degradation in the alkaline cuene solvent. Handsheets were then made of the above three samples for study of color reversion after accelerated aging. These were dried overnight at room temperature and 50% R.H. Brightness was measured before and after samples were heated in an oven at 105� C. for 1 hour. Heated samples were reconditioned for at least 30 minutes at 50% R.H. Results are as follows:
Initial ISO
Oven-aged ISO
sion, %
89.84 � 0.13
88.37 � 0.12
90.13 � 0.07
88.61 � 0.13
91.43 � 0.16
78.85 � 0.28
12.59 Unstabilized
91.93 � 0.08
87.38 � 4.55
92.68 � 0.09
90.74 � 0.12
92.89 � 0.14
91.31 � 0.12
*Base washed before testing The superior brightness retention of the stabilized samples is immediately evident from the above test results.
EXAMPLE 9 Stabilization Retaining Primary Oxidation Liquor A catalytic composition was formed by reacting 12 mg of TEMPO and about 2 mL of 7 g/L ClO2 solution at 70� C. for about 1 minute. The activated catalyst was added to a slurry of 41 g (10 g O.D.) of northern mixed conifer bleached kraft pulp and 2 g Na2CO3 in about 88 mL of the 7 g/L ClO2 solution. The mixture was contained in a sealed polyethylene bag and placed in a 70� C. water bath for 30 minutes. The mixture was occasionally mixed and vented as needed. After the initial oxidation the sample was divided into two equal portions of about 66 g each.
One portion was stabilized by acidification to a pH below 3 with 1 M H2SO4 and again placed in the hot water bath at 70� C. for 1 hour. No ClO2 or H2O2 was added. The fiber was then recovered, thoroughly washed, treated with a Na2CO3 solution at a pH �10, and again washed and dried.
The second portion was stabilized by treatment with 2.3 g of 3% H2O2 and then with 1 M H2SO4 to adjust pH below 3. This too was retained in the hot water bath at 70� C. for 1 hour. The stabilized cellulose was then treated as above. Carboxyl content was measured for both samples.
Neither H2O2 or ClO2 1050
H2O2 but no ClO2 1100
EXAMPLE 10 Oxidation of Starch using ClO2 and the Glyceryl Ketal of Triacetoneamine A 10.7 mg portion of the glyceryl ketal of triacetoneamine was reacted with about 2 mL of 5.2 g/L ClO2 at 70� C. Then a solution of 61 g of 16.4% (10.0 g O.D.) FilmFlex� 50 starch, which had been solubilized by heating the starch in water, 3 g of NaHCO3, and about 98 mL of the 5.2 g/L ClO2 was prepared. FilmFlex is a registered trademark of Cargill Corp. for a hydroxyethyl corn starch product. The activated catalyst was added. System pH was about 7.5. After about 5 minutes a first small (about 10 g) portion was removed (Sample A). The remainder was placed in a sealed polyethylene bag and then in a 70� C. water bath for 23 minutes. A second portion of about 71 g was then removed from the bag (Sample B). Then 30 mL of the ClO2 solution and 9 mL of 3% H2O2 was added to the remainder of the material in the bag after the pH had been reduced to about 3 with 1M H2SO4. The bag was again placed in the 70� C. water bath for 40 minutes (Sample C). The starch remained in solution for all treatments.
An 18 g control sample of the 16.4% FilmFlex� 50 starch was diluted to 50 mL with deionized water. The pH was then adjusted to about 2 with 1 M H2SO4 (Sample D).
Samples A (about 0.4 g) and B (about 3 g) which had been dried at 105� C. for about 1 hour were dissolved separately in about 10 mL water. The pH was reduced to about 1 with 1 M H2SO4. Then 25 mL acetone was stirred into each of the samples and later decanted off. Following this 125 mL absolute ethanol divided into four separate aliquots was used to treat the samples so that the product was no longer gummy and was loose and granular in appearance. After each ethanol wash the supernatant liquid was decanted off The slightly yellow granular washed products were dried at 105� C. for about 1 hour and sent for analysis.
To isolate the treated Sample C starch, 150 mL of acetone was stirred slowly into the solution. After the resulting precipitate had settled, the supernatant liquid was decanted off Then 150 mL ethanol in four separate portions was added to the gummy precipitate to extract remaining water and chemicals and each time the supernatant was decanted off. The white granular product was oven dried at about 105� C. for 1 hour and a sample submitted for carboxyl analysis.
Sample D was treated in a similar manner except the initial treatment was with 100 mL ethanol rather than acetone. Again the washed material was oven dried at 105� C. for about 1 hr.
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Journal of Organic Chemistry 64: 2564-2566 (1999).* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS7109325 *Aug 30, 2004Sep 19, 2006Weyerhaeuser CompanyHypochlorite free method for preparation of stable carboxylated carbohydrate productsUS8641863Sep 5, 2012Feb 4, 2014Weyerhaeuser Nr CompanyCatalytic carboxylation of cellulose fibers in a continuous process with multiple additions of catalyst, secondary oxidant and base to a moving slurry of cellulose fibers* Cited by examinerClassifications U.S. Classification536/124, 536/1.11, 536/63, 536/56, 536/105, 536/110, 536/102International ClassificationD21C9/00, C08B15/04, D21H11/20, C08B31/18, D21H11/14, C07B61/00Cooperative ClassificationD21H11/20, D21C9/005, C08B31/18, D21H11/14, C08B15/04European ClassificationC08B15/04, C08B31/18, D21C9/00B2DLegal EventsDateCodeEventDescriptionJan 2, 2013FPAYFee paymentYear of fee payment: 8Apr 21, 2009ASAssignmentOwner name: WEYERHAEUSER NR COMPANY, WASHINGTONFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WEYERHAEUSER COMPANY;REEL/FRAME:022835/0233Effective date: 20090421Owner name: WEYERHAEUSER NR COMPANY,WASHINGTONFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WEYERHAEUSER COMPANY;US-ASSIGNMENT DATABASE UPDATED:20100203;REEL/FRAME:22835/233Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WEYERHAEUSER COMPANY;US-ASSIGNMENT DATABASE UPDATED:20100225;REEL/FRAME:22835/233Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WEYERHAEUSER COMPANY;US-ASSIGNMENT DATABASE UPDATED:20100316;REEL/FRAME:22835/233Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WEYERHAEUSER COMPANY;US-ASSIGNMENT DATABASE UPDATED:20100329;REEL/FRAME:22835/233Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WEYERHAEUSER COMPANY;US-ASSIGNMENT DATABASE UPDATED:20100330;REEL/FRAME:22835/233Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WEYERHAEUSER COMPANY;US-ASSIGNMENT DATABASE UPDATED:20100511;REEL/FRAME:22835/233Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WEYERHAEUSER COMPANY;US-ASSIGNMENT DATABASE UPDATED:20100518;REEL/FRAME:22835/233Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WEYERHAEUSER COMPANY;REEL/FRAME:22835/233Dec 19, 2008FPAYFee paymentYear of fee payment: 4Jun 6, 2001ASAssignmentOwner name: WEYERHAEUSER COMPANY, WASHINGTONFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:KOMEN, JOSEPH LINCOLN;WEERAWARNA, S. 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