Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
  • C08B15/02—Oxycellulose; Hydrocellulose; Cellulosehydrate, e.g. microcrystalline cellulose

Definitions

• Microcrystalline cellulose a processed cellulose, has been utilized extensively in the pharmaceutical, food and paper industries.
• microcrystalline cellulose can be used as a direct compression vehicle for solid dosage forms and is commercially available under the trade name EMCOCEL® from Penwest Pharmaceuticals Co. Compared to other directly compressible excipients, microcrystalline cellulose is generally considered to exhibit superior compressibility and disintegration properties.
• microcrystalline cellulose can be used as a stabilizer, texturizing agent, and fat replacer. It is used in many products such as reduced-fat salad dressings, dairy products including cheese, frozen desserts and whipped toppings, and bakery products.
• microcrystalline cellulose is manufactured by hydrolyzing dissolving grade woodpulp with mineral acids. For example, woodpulps in the range of 92% - 98% alpha cellulose content with a brightness level of 92 - 95 (iso) are typically used as starting material. In a typical reaction, the woodpulp is subjected to an acid solution under heat and pressure. The cellulose polymers in the pulp are reduced to small chain polymers or microcrystals. The resulting microcrystalline cellulose is at least 98% alpha cellulose and has the same brightness level as the starting raw material. The microcrystalline cellulose is then washed and dried prior to packaging.
• U.S. Patent No. 5,769,934 describes a method for producing microcrystalline cellulose by subjecting a cellulose source material to steam explosion treatment, extracting the steam treated cellulosic material to remove hemicellulose and lignin, and recovering microcrystalline cellulose that is described as substantially colloidal in particle size and essentially free of fibrous cellulose.
• U.S. Patent No. 4,745,058 describes a method for producing microcrystalline cellulose comprising the steps of generating cellulose fibers by placing a cellulose fiber producing bacteria of the genus Acetobacter in a growing medium. The cellulose fibrils produced by the bacteria are then removed from the medium and excess medium is removed from the fibrils. The fibrils are then immersed in an aqueous solution of a base for a predetermined period of time after which the fibrils are neutralized by immersing the fibrils in an acidic solution. The fibrils are thereafter subjected to a treatment with a hot strong acid and are disintegrated to produce microcrystalline cellulose.
• the cellulose starting material e.g. wood pulp,
• the cellulose starting material can be bleached and whitened by treatment with peroxy acids at a high pH.
• This preliminary bleaching step of the pulp prior to hydrolysis provides a final microcrystalline cellulose product which has increased brightness.
• the final microcrystalline cellulose product can be bleached and cleaned after the hydrolysis step.
• U.S. Patent No. 3,954,727 describes a method of producing microcrystalline cellulose by acid hydrolyzing a cellulose containing material and de-aggregating the resulting crystalline mass, the acid hydrolysis being performed at the same time as the chemical de-aggregating of the material. The de-aggregated material is then bleached and cleaned, preferably by a peroxy acid in a separate step.
• L* color lightness
• the term "pulp" refers to any fibrous cellulosic material formed from wood or any other plant material.
• the material can be formed by any procedure known in the art such as chemical digestion processes (e.g. sulfite, soda or organosolv processes), thermo-mechanical processes (e.g. steam explosion) and mechanical processes (e.g. grinding).
• the pulp starting material can be any grade and can have an initial color lightness (L*) value of less than 70, less than 80, less than 90 and less than about 93.
• L* initial color lightness
• suitable starting materials unbleached kraft pulp (utilized in the production of cardboard), fluff pulp or Northern Bleached Softwood Kraft.
• a "one-step process” is meant to be inclusive of hydrolysis and bleaching, and is not meant to include any related preliminary or subsequent steps.
• color lightness (L*) refers to the color lightness dimension of the brightness measurement as quantified by a colorimeter, e.g., a Minolta® Chroma Meter®.
• the specified value is from 0 -100, the lighter the color, the larger the L* value.
• green to red color value (a) refers to the green to red dimension of the brightness measurement as quantified by a colorimeter such as a Minolta Chroma Meter.
• the green color has a negative value (0 to - 60), and the red color has a positive value (0 to 60).
• blue to yellow color value (a) refers to the blue to yellow dimension of the brightness measurement as quantified by colorimeter.
• the blue color has a negative value (0 to -60), and the yellow color has a positive value (0 to 60).
• absolute white color should have an L*ab value as 100-0-0.
• a process for the production of microcrystalline cellulose comprising hydrolyzing pulp with a sufficient amount of active oxygen in an acidic environment in a one step process and recovering the microcrystalline cellulose, wherein the microcrystalline cellulose has a color lightness (L*) greater than the color lightness (L*) of the pulp starting material.
• This process is reacted in a sufficient amount of a suitable reagent medium, preferably an aqueous medium, e.g., H 2 O.
• the active oxygen can also be derived from other sources known to those skilled in the art such as oxygen, ozone, organic peroxides, hydroperoxides, peroxyacids, peroxyesters and mixtures thereof. This list is not meant to be exclusive. Specific agents which are suitable for providing active oxygen in the present invention include benzoyl peroxide, oxaloyl peroxide, lauroyl peroxide, acetyl peroxide, t-butyl peroxide, t-butyl peracetate, t- butyl peroxy pivalate, cumene hydroperoxide, dicumyl peroxide, 2-methyl pentanoyl peroxide, hydrogen peroxide and mixtures thereof.
• the active oxygen and the acid environment are both provided by a suitable active oxygen compound e.g. a peroxy acid.
• a further acid can be introduced into the medium such as a mineral acid, an organic acid or a combination thereof e.g., hydrochloric acid or acetic acid.
• the acidic conditions are preferably less than a pH of about 5.
• Peroxy acids which can be used in the present invention also include peroxy acid salts such as the alkali metal salts of peroxymonosulfuric acid, which acid is commonly known as caro's acid.
• OXONE® is a commercially available product that is derived from KOH neutralization of a caro's acid mixture. OXONE® contains approximately 49% potassium peroxymonosulfate per unit of charge.
• Other useful salts include ammonium peroxydisulfate, potassium peroxydisulfate, sodium peroxymonocarbonate, potassium peroxydiphosphate, potassium peroxydicarbonate, salts of peroxymonophosphoric acid, potassium peroxydiphosphoric acid, peroxyoxalic acid, peroxytitanic acid, peroxydistannic acid, peroxydigermanic acid, peroxychromic acid, peroxy formic acid, peroxy benzoic acid and peroxy acetic acid.
• the peroxy acid can be produced in the reaction medium by reacting a sufficient amount of an acid with a sufficient amount of a peroxide and adding this reactant to a sufficient amount of a reaction solvent, e.g. an aqueous solvent such as H 2 O.
• the acid can be selected from the group consisting of a mineral acid , an organic acid and combinations thereof.
• the mineral acid can include hydrochloric acid, sulfuric acid, phosphoric acid, boric acid, nitric acid and mixtures thereof.
• the organic acid can be a carboxylic acid e.g., acetic acid, formic acid, oxalic acid and combinations thereof.
• the peroxide can be e.g. hydrogen peroxide. In this embodiment, it is preferable to drip the acid into the peroxide.
• the peroxide can be pure or can be a diluted solution.
• a diluted solution of peroxide is used, it is preferably at least 50% peroxide as the production of the peroxy acid is negatively affected by increasing the dilution of the peroxide. This is evident by example 9, wherein sulfuric acid and hydrogen peroxide were added to the H 2 O without performing the drip procedure discussed above. This method had decreased production of peroxy acid and resulted in a decrease in the brightness of the final product.
• the final reaction medium will contain an effective amount of active oxygen and an effective amount of acid to bleach/hydro lyze the pulp to produce microcrystalline cellulose in accordance with the invention. Further optimization of the ratio of active oxygen and acid to solid material can be readily ascertained by one skilled in the art in view of the appended examples.
• the hydrolysis and bleaching of the pulp with peroxy acids under an acidic pH can be optimized by performing the reaction under heated temperatures, for example, but not limited to, boiling temperatures.
• the reaction can also optionally be performed under increased pressure.
• the optimum heated and pressurized conditions can be ascertained by one skilled in the art.
• L*ab values can have variance based on control factors, e.g. whether the microcrystalline cellulose is compressed into a tablet, the hardness of the tablet and whether the reading is taken from the sheet form of the pulp or the dried cake form of the microcrystalline cellulose.
• the first experiment for persufluric acid bleaching and hydrolysis was carried out on fluff pulp, the conditions were: 40 g pulp, + 3 L 2N H 2 SO 4 , + 10 g Oxzone, boiling for 90 minutes. Meanwhile, fluff pulp was also hydrolysed with 2 N HC1 at the same conditions. After hydrolysis, cellulose was filtered out, washed with hot water, then it was freeze-dried.
• the hydrolyzed cellulose was pressed into a tablet, and the brightness measurement was carried out with a Chroma Meter.
• the L*ab value for peroxysulfuric acid hydrolyzed fluff pulp and HC1 hydrolysed fluff pulp is shown in the following table. Apparently, peroxysulfuric acid hydrolysis increased the brightness of the cellulose.
• DCM extractive The hydrolyzed fluff pulp was extracted with dichloromethane, the amount of extractive was determined gravometrically, and the data are shown in the following table.
• Unbleached Kraft pulp of southern pine was hydrolyzed respectively with 2 N HC1 and
• Bleached kraft pulp with a starting degree of polymerization of 1407 was hydrolyzed with hydrochloric acid and peroxymonosulfuric acid in separate experiments and the results were compared.
• the resulting degree of polymerization for the microcrystalline cellulose hydrolyzed by hydrochloric acid was 224 and the degree of polymerization for the microcrystalline cellulose hydrolyzed by the peroxy acid was 218.
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• the cellulose exhibited the following characteristics: Degree of Polymerization: 245
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• the cellulose exhibited the following characteristics: Degree of Polymerization: 248 L*ab(measured with a Minolta CR-321 chroma meter) 91-.53-6.1.
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• the cellulose exhibited the following characteristics: Degree of Polymerization: 257
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• H 2 0 was admixed with 72 ml of sulfuric acid quantum sufficum to 1 liter. The pulp was introduced followed by a reaction time of 2 hours at ambient pressure at 100° C. The resultant microcrystalline cellulose was then filtered and washed with deionized water. The resultant cellulose cake was then added to a 1% sodium hydroxide solution at about 100° C. The cellulose was again filtered and washed with deionized water and dried at ambient temperatures.
• the cellulose exhibited the following characteristics: Degree of Polymerization: 291
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• the cellulose exhibited the following characteristics: Degree of Polymerization: 222
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• the cellulose exhibited the following characteristics: Degree of Polymerization: 240
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• H 2 0 was admixed with 170 ml hydrochloric acid quantum sufficum to 1 liter.
• the pulp was introduced followed by a reaction time of 3 hours at ambient pressure at 100° C.
• the resultant microcrystalline cellulose was then filtered and washed with deionized water.
• the resultant cellulose cake was then added to a 1% sodium hydroxide solution at about 100° C.
• the cellulose was again filtered and washed with deionized water and dried at ambient temperatures.
• the cellulose exhibited the following characteristics: Degree of Polymerization: 223
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• H 2 O 2 was added to 170 ml hydrochloric acid.
• H 2 0 was then admixed with this mixture quantum sufficum to 1 liter.
• the pulp was introduced followed by a reaction time of 2 hours at ambient pressure at 100° C.
• the resultant microcrystalline cellulose was then filtered and washed with deionized water.
• the resultant cellulose cake was then added to a 1% sodium hydroxide solution at about 100° C.
• the cellulose was again filtered and washed with deionized water and dried at ambient temperatures.
• the cellulose exhibited the following characteristics: Degree of Polymerization: 243
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• the cellulose exhibited the following characteristics: Degree of Polymerization: 248
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• a one step hydrolysis and bleaching of wood pulp was performed on raw unbleached wood pulp having a L*ab value of 67.2-5.7-19.5.
• the cellulose exhibited the following characteristics: Degree of Polymerization: 254
• H 2 0 was admixed with 170 ml hydrochloric acid quantum sufficum to 1 liter.
• the pulp was introduced followed by a reaction time of 2 hours at ambient pressure at 100° C wherein the temperature dropped below 100° C for 1 hour.
• the resultant microcrystalline cellulose was then filtered and washed with deionized water.
• the resultant cellulose cake was then added to a 1% sodium hydroxide solution at about 100° C.
• the cellulose was again filtered and washed with deionized water and dried at ambient temperatures.
• the cellulose exhibited the following characteristics: Degree of Polymerization: 227
• the cellulose exhibited the following characteristics: Degree of Polymerization: 208
• Example 16 was performed without peroxy acid and Example 17 was performed with peroxy acid.
• Example 17 had a brighter final product as compared to the final product of Example 16. This demonstrates that there was bleaching with peroxy acid, even with a pulp starting material with a high L* value (95.5).
• the fact that the final product actually had a slightly lower L* value than the starting material may be due to variances in colorimeter readings with respect to various physical forms of the cellulose and their corresponding surface characteristics.
• the starting material was in sheet form and the final product was in dried cake form.

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• 2000
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