ENHANCED GEL STRENGTH METHYLCELLULOSE

Abstract: In a first embodiment, the present invention is a process for producing methylcelluloses having greater gel strength than methylcelluloses of the prior art. According to the process of the present invention, methylcellulose is produced by methylating cellulose pulp in two separate stages. In a second embodiment, the present invention is a methylcellulose having a methoxyl substitution of about 29 to about 32 weight percent based upon the weight of the methylcellulose and a gel strength greater than about 223 x (v<0.273>), wherein v represents the viscosity of the methylcellulose.

Description: ENHANCED GEL STRENGTH METHYLCELLULOSE The present invention relates to methylcelluloses having enhanced gel strength, processes for making such methylcelluloses, and compositions containing such methylcelluloses. Cellulose ethers have been employed as additives to food compositions and processes to provide physical properties such as thickening, freeze/thaw stability, lubricity, moisture retention and release, film formation, texture, consistency, shape retention, emulsification, binding, suspension, and gelation. For example, methylcellulose has been utilized in food applications ever since it was discovered that the thermal gel property of certain methylcelluloses is similar to that of egg white. That is, solutions of methylcellulose undergo a heat-catalyzed gelation much like fresh raw egg white. In fact, there has been a long felt need in the food industry for replacing egg whites in foods. This long felt need has been motivated by various reasons including health and religious reasons. An important characteristic of both egg whites and methylcellulose is their ability to bind food ingredients together. It has been noted that the gel strength of these two food hydrocolloids is responsible for this binding force in foods. Methylcellulose has partially met the industry's long felt need by replacing egg whites in certain food applications. However, the gel strength of methylcellulose has been insufficient to replace egg whites in other food applications. Accordingly, there has continued to be a long felt industry need to replace egg whites in certain food applications, which have heretofore not been replaceable by conventional (that is, known in the art) methylcelluloses. It is generally known in the art that methylcelluloses having higher viscosity also have higher gel strength. The present invention is directed to methylcelluloses that exhibit significantly greater gel strength at a given viscosity than any methylcellulose of the prior art. Methylcelluloses of the present invention enable the development of food compositions with superior binding, consistency, and shape retention. The present invention allows one of ordinary skill in the art to use a methylcellulose with greater gel strength at a given viscosity. The present invention also allows one of ordinary skill in the art to use a methylcellulose with a lower viscosity at a given gel strength. Methylcelluloses having higher molecular weight (that is, viscosity) tend to bind moisture too tightly, which can give rise to a final formed food product having a dry feel to the mouth. The present invention allows one of ordinary skill in the art to improve moisture release and overall texture of a formed food product by using a methylcellulose with lower viscosity while maintaining the required gel strength. In a first embodiment, the present invention is directed to a methylcellulose having a gel strength ("G"') greater than 223 x (v 0273 ), where V represents the viscosity of the methylcellulose for a 2 percent aqueous solution at 20°C. This relationship of gel strength to viscosity can be represented by the equation G' > 223 x (v 0273 ), where " > " means "greater than or equal to. Methylcelluloses of the present invention also have a methoxyl substitution of 21 percent to 42 percent based upon the weight of the methylcellulose. Gel strengths can be measured by dynamic rheometry. The elastic modulus component of the complex viscosity is quantified in measuring gel strength. This dynamic elastic modulus represents the force component known generally as gel strength (G'). Techniques for measuring elastic modulus (storage modulus) are described in Kinetics of Thermal Gelation of Methylcellulose and Hydroxypropylmethylcellulose in Aqueous Solutions, Carbohydrate Polymers, volume 26, no. 3, pp. 195-203, which is incorporated herein by reference. Unless stated otherwise, all gel strengths in the present specification were determined by measuring the elastic modulus of a 1.5 weight percent aqueous solution of the methylcellulose in a dynamic rheometer. In a second embodiment, the present invention is directed to a process for making methylcelluloses having a desired level of methoxyl substitution. The process comprises the steps of: a) reacting a cellulose pulp with a first amount of aqueous alkali and a first amount of a methylating agent at reaction conditions sufficient to methylate the cellulose pulp to a first level of methoxyl substitution which is about 20 percent or more of the desired level of methoxyl substitution; and b) reacting the methylcellulose of first level of methoxyl substitution with a second amount of aqueous alkali and a second amount of a methylating agent at reaction conditions sufficient to methylate it to a second level of methoxyl substitution which is about 40 percent or more of the desired level of methoxyl substitution. A third embodiment of the present invention is directed to food compositions comprising a methylcellulose of the present invention. A fourth embodiment of the present invention is directed to a pharmaceutical capsule comprising a methylcellulose of the present invention. The Figure is a graphical representation depicting the elastic modulus of methylcelluloses of the present invention and those of the prior art. The present invention provides novel methylcelluloses having elevated gel strength for a given viscosity grade and percent methoxyl substitution compared to that of conventional methylcelluloses. Preferred methylcelluloses of the present invention may also exhibit lower gelation temperatures than conventional methylcelluloses of equivalent viscosity and percent methoxyl substitution. Preferred methylcelluloses of the present invention may also exhibit longer meltback times than conventional methylcelluloses of equivalent viscosity and substitution. Lower gelation temperature may be desired or preferred in some applications, but are a non-essential property of the present invention. Reduced gelation temperature is useful in food manufacturing and processing. Food compositions can be gelled at lower temperatures saving energy and processing time during heating/cooling cycles. Further, food compositions can retain form at broader temperature ranges during processing. Gelation temperature is determined by heating a 1.5 percent by weight percent aqueous solution of the methylcellulose and observing the narrow temperature range at which gelation takes place. Meltback time generally refers to the length of time required for a thermally formed gel of a methylcellulose to melt while cooling to an ambient temperature. Longer meltback time may be desired or preferred for some applications, but are a non-essential property of the present invention. Longer meltback time at ambient temperature is useful in food processing and manufacturing. Gelation can be maintained over a wider temperature range and longer and better retention of texture during food processing and consumption are possible. Meltback time is determined according to the following: provide 15 grams of a 1.5 weight percent of an aqueous solution of the methylcellulose in a 20 milliliter beaker; heat the solution for 8 minutes in boiling water - the solution will gel in the beaker; invert the beaker onto a flat surface in an ambient temperature environment; allow the gel to cool and subsequently melt to form a puddle on the surface. Meltback time is measured from the time cooling begins (removal from the boiling water) to when a clear puddle forms. The methylcelluloses of the present invention are useful in the same applications wherein conventional methylcelluloses are currently utilized, as well as additional applications where conventional methylcelluloses are not currently effective. Methylcelluloses of the present invention are particularly useful in food compositions and pharmaceutical capsules. Methylcelluloses having viscosities of up to about 1 ,000,000 centipoise (cP) in a two percent aqueous solution at 20°C can be prepared according to the present invention. Preferred methylcelluloses may have viscosities of about 1 to about 600,000 cP (two percent solution 20°C). More preferred methylcelluloses may have viscosities of about 1 to about 100,000 cP (two percent solution at 20°C). For purposes of the present specification, all viscosities of aqueous solutions are determined by Ubbelohde tube according to ASTM D1347-72 and D2363-79 (unless stated otherwise). Methylcelluloses that can be produced according to the present invention include, but are not limited to, hydroxyethylmethylcellulose ("HEMC"), hydroxypropylmethylcellulose ("HPMC"), hydroxybutylmethylcellulose ("HBMC"), methylethylcellulose ("MEC"), and carboxymethylmethylcellulose ("CMMC"). Preferred HPMCs of the present invention will have a hydroxypropyl substitution of from about 1 to about 32 percent, more preferably from about 1 to about 14 percent, and most preferably from about 3 to about 12 percent. Methylcelluloses preferred for use in food compositions will have a non-methoxyl substitution content or level of about 5 percent or less, more preferably about 1 percent or less, and even more preferably about 0.2 percent or less. Methylcelluloses most preferred for use in food compositions will be substantially free of non-methoxyl substitution content. For purposes of the present specification, all non-methoxyl substitutions are expressed in weight percent based upon the weight of the methylcellulose (unless stated otherwise). Methylcelluloses of the present invention that are useful in food compositions generally have a methoxyl substitution of about 21 to about 42 weight percent based upon the weight of the methylcellulose. For purposes of the present specification, all methoxyl substitutions are expressed in weight percent based upon the weight of the methylcellulose (unless stated otherwise). For purposes of the present specification, all methoxyl substitution is determined according to ASTM D2363-72 (unless stated otherwise). Preferred (for purposes of use in food compositions) methylcelluloses have a methoxyl substitution of at least about 25 percent. More preferred methylcelluloses have a methoxyl substitution of at least about 29 percent. Preferred (for purposes of use in food compositions) methylcelluloses of the present invention have a methoxyl substitution of less than about 35 percent. More preferred methylcelluloses have a methoxyl substitution of less than about 32 percent. Methylcelluloses of the present invention are produced by a novel process. It is well known in the art to alkylate cellulose to produce ethers (such as methylcellulose). In conventional processes, cellulose pulp is completely alkalized with sodium, hydroxide and etherified (that is, methylated) with a methylating agent (usually methyl chloride) in a single stage. The degree to which the cellulose is methylated is referred to as the percent methoxyl substitution. This process and the underlying chemistry has been well known in the art for a long time. Contrary to conventional processes for producing methylcellulose, the methylcelluloses of the present invention are produced via a novel process that methylates cellulose pulp in two or more separate stages. According to the present invention, cellulose pulp is partially alkalized with alkaline hydroxide and partially methylated with a methylating agent (preferably methyl chloride) in a first stage. While the present invention should not be limited by any particular theory, it is believed that the methylated sites on the cellulose after the first stage are more selective for methylating in subsequent stages. That is, methylation in subsequent stages is more likely to occur near the sites that were methylated in the first stage, causing a less uniform distribution of methylated sites on the cellulose than occurs in conventional methylcelluloses. This less uniform distribution can be referred to as "blocky" substitution. The partially methylated cellulose produced in the first stage is further alkalized and further etherified with additional alkaline hydroxide and methyl chloride to the desired level of completion in a later stage or stages. Preferably, the methylating agent utilized in subsequent stages is introduce via continuous addition or incremental addition at reaction conditions sufficient to produce the desired level of methoxyl substitution. The cellulose utilized in producing methylcelluloses of the present invention is typically cellulose pulp obtained from wood or cotton. The pulp is preferably provided in a powder or chip form. Wood pulp is preferred. The alkylating of the cellulose pulp is carried out in a stepwise manner in stages. A "stage" refers to a reaction sequence in which an alkalization reaction and a methylation reaction (or substitution) takes place. A stage effectively increases the level of methoxyl substitution of the cellulose pulp or partially methylated cellulose. Optionally, other types of etherification such as hydroxypropyl substitution can be effected along with or in addition to methoxyl substitution. According to the present invention, cellulose pulp is alkalized in two or more stages in one or more reactors with an aqueous alkali, preferably aqueous sodium hydroxide. The pulp may be alkalized with alkaline hydroxide by any means known in the art such as steeping in a bath or stirred tank containing aqueous alkali or spraying aqueous alkali directly on dry pulp. Reaction time varies according to hydroxide concentration, temperature, and retention time. The aqueous alkali is preferably used at an alkaline hydroxide content of about 30 to about 70 percent by weight based upon the weight of the water. The temperature of alkalization preferably ranges from about 30°C to about 110°C and most preferably about 30°C to about 90°C. Uniform swelling and alkali distribution in the pulp may be controlled by mixing and agitation. The rate of addition of aqueous alkali may be governed by the ability to cool the reactor during the exothermic alkalization reaction. The rate of addition of aqueous alkali is not critical to the present invention. If desired, an organic solvent such as dimethyl ether may be added to the reactor as a diluent and a coolant. If desired, the headspace of the reactor or reactors may be evacuated or purged with an inert gas such as nitrogen to control oxygen-catalyzed depolymerization of the alkali cellulose. According to the present invention, alkalized cellulose pulp is etherified (that is, methylated) in two or more stages in one or more reactors to form methylcellulose. Reaction time for etherification will depend on concentration, pressure, temperature, retention time, and the ability to control the exothermic reaction. The preferred etherifying agent is a methylating agent such as methyl chloride or dimethyl sulfate. Methyl chloride is preferred. The methylating agent may be added via batch load addition, continuous addition, or incremental addition in one or more of the stages. Preferably, the methylating agent is added via continuous addition or incremental addition in at least one stage after the first stage, preferably in the second stage. "Batch load addition" means addition substantially without pause over a relatively short period of time. "Continuous addition" means addition substantially without pause over a longer period of time. "Incremental addition" means periodic addition of smaller, discrete amounts over a longer period of time. The alkaline hydroxide and the methylating agent may be added to the reactor at the same time but are preferably added sequentially with the alkaline hydroxide being added first and the methylating agent second. A two-stage process is preferred for making methylcelluloses of the present invention. In stage one, the aqueous alkaline hydroxide and the methylating agent are reacted with cellulose pulp to form a methylcellulose of a first level of methoxyl substitution. Each of the alkaline hydroxide and the methylating agent may be added in stage one via a batch load addition, continuous addition, or incremental addition. The rate of addition is not critical. The reaction temperature in the first stage is preferably controlled so that generally uniform contact and reaction can occur between the alkaline hydroxide, the methylating agent, and the cellulose pulp. In the second stage, additional amounts of the aqueous alkaline hydroxide and the methylating agent are reacted with the partially methylated cellulose to form a methylcellulose with a second level (that is, desired level) of methoxyl substitution. The alkaline hydroxide and the methylating agent may be added in the second stage via a batch load addition, continuous addition, or incremental addition. The rate of addition of hydroxide in the second stage is not critical. The methylating agent is added in the second stage at a reaction mass temperature of about 65°C to about 120°C over an elapsed addition of time of 15 minutes or more; preferably at about 75°C to about 100°C at 20 minutes or more; and most preferably at about 80°C to about 90°C at 25 minutes or more. Although the methylating agent can be added continuously or incrementally over any extended period of time in the second stage, it is preferred for reasons of time economy to carry out the addition in about 120 minutes or less, more preferably in about 60 minutes or less, and most preferably in about 25 to about 45 minutes. After addition of the methylating agent in the second stage, etherification can be carried out at any temperature at which the reaction can proceed, but it is preferred for reason of time economy to carry it out at about 65°C to about 120°C and more preferably from about 80°C to about 90°C. Temperature within the reactor can be determined by any means known in the art. Temperature determination means include using vapor temperature control and using a thermocouple which protrudes into the contents (cellulose pulp/methylcellulose mass) of the reactor. In a preferred two-stage process, both stages are carried out in the same reactor. Preferably, about 20 to about 80 percent of the total methoxyl substitution is carried out in the first stage and about 80 to about 20 percent in the second stage. More preferably, about 30 to about 70 percent of the total methoxyl substitution is carried out in the first stage and about 70 to about 30 percent in the second stage. Most preferably, about 40 to about 60 percent of the total methoxyl substitution is carried out in the first stage and about 60 to about 40 percent in the second stage. Some embodiments of two-stage processes are described in Table 1. A three-stage process is also useful for making the present methylcellulose. The first stage is carried out in a manner similar to that of the first stage of the two-stage process described above. Either or both of the second and third stages are carried out in the same manner as the second stage in the two-stage process described above (the methylating agent is preferably added continuously or incrementally over a period of time). In a preferred three-stage process, about 20 to about 60 percent of the total methoxyl substitution is carried out in each of the first and second stages and about 5 to about 30 percent in the third stage. Some embodiments of three-stage processes are described in Table 1. It is also possible to have processes with four or more stages. The first stage of such a process would be carried out in the same manner as the first stage in the two- stage process described above. One or more of the subsequent stages would be carried out in the same manner as the second stage in the two-stage process described above (the methylating agent is preferably added continuously or incrementally over a period of time). 44554 Table 1 Some Useful Embodiments of the Process of the Present Invention I I Methylcelluloses such as HEMC, HPMC, HBMC, MEC, and CMMC can be prepared by reacting the cellulose pulp or a methylcellulose with another etherifying agent in addition to the methylating agent (also an etherifying agent). Useful etherifying agents include ethyl chloride, ethylene oxide, propylene oxide, and butylene oxide. The other etherifying agent can be reacted in any stage before, during, or after reaction by the methylating agent at process conditions sufficient to effect the desired reaction. The other etherifying agent may be added to the reactor via a batch load addition, continuous addition, or incremental addition. Preferably, the other etherifying agent is reacted in the first stage. Preferably, the other etherifying agent is reacted before or along with the methylating agent. The methylating agent and any other etherifying agent may be added to a reactor in a liquid or vapor form. Liquid form is highly preferred. The reactor is preferably maintained at pressures such that the agents remain predominantly in liquid phase. After etherification, the methylcellulose is washed to remove salt and other reaction by-products. Any solvent in which salt is soluble may be employed, but water is preferred. The methylcellulose may be washed in the reactor, but is preferably washed in a separate washer located downstream of the reactor. Before or after washing, the methylcellulose may be stripped by exposure to steam to reduce residual organic content. The methylcellulose is dried to a reduced moisture and volatile content of preferably about 0.5 to about 10.0 weight percent water and more preferably about 0.8 to about 5.0 weight percent water and volatiles based upon the weight of methylcellulose. The reduced moisture and volatiles content enables the methylcellulose to be milled into particuiate form. The methylcellulose is preferably dried at a temperature of from about 40°C to about 130°C. Useful dryers include tray dryers, fluid bed dryers, flash dryers, agitation dryers, and tube dryers. The methylcellulose is milled to particulates of desired size. If desired, drying and milling may be carried out simultaneously. Milling may be accomplished by any means known in the art such as a ball mill, an impact pulverizer, knife grinder, and air- swept impact mill. The present methylcellulose is useful in a variety of food compositions. Examples of food compositions include vegetable, meat, and soy patties; reformed seafood; reformed cheese sticks; cream soups; gravies and sauces; salad dressing; mayonnaise; onion rings; jams, jellies, and syrups; pie filling; potato products such as french fries and extruded fries; batters for fried foods, pancakes/waffles, and cakes; pet JO- foods; beverages; frozen desserts; cultured dairy products such as ice cream, cottage cheese, yogurt, cheeses, and sour creams; cake icing and glazes; whipped topping; leavened and unleavened baked goods; and the like. In forming food compositions, the methylcellulose is typically admixed with foodstuffs during the process and formation of the compositions. The foodstuffs may be in any known form such as particle form or unitary form. Excellent teachings to the preparation of food compositions with methylcellulose are found in the following: METHOCEL® (trademark of The Dow Chemical Company) product publications: METHOCEL Premium Food Gums. Form Nos. 192-1037-87, 192-1047-87, 192-1046-87, 192-1051 -87, 192-1050-87, 192-1049-87, 192-1053-87, 192-982-87, 192-979-87, 192-985-87, 192-1054-87, 192-1048-87, 192- 987-87, 192-986-87, 192-989-87, 192-988-87, 192-984-87, 192-983-87, 192-981 -87, 192-991 -87, 192-980-87, 192-990-87, and 192-1052-87 (all published in 1987); Selecting METHOCEL Food Gums. Form NoJ 92-855-1281 R (published in 1981); METHOCEL Food Gums In Non-Dairy Whipped Topping. Form No. 192-877-482 (published in 1982); METHOCEL Food Gums In Fried Foods. Form Nos. 192-875-482 and 192-881 -482 (all published in 1982); METHOCEL Food Gums In Salad Dressings and Sauces. Form Nos. 192-876-482, 192-880-482, and 192-905-1282 (all published in 1982); and METHOCEL Food Gums In Bakerv Products. Form Nos. 192-874-482 and 192-878-482 (all published in 1982). The teachings of all the above publications are incorporated herein by reference. Methylcelluloses particularly useful in food compositions are methylcelluloses having little or no non-methoxyl substitution and hydroxypropylmethylcellulose. Methylcelluloses are typically used in food compositions at levels of about 0.01 to about 5 percent based upon the total weight of the food composition. Methylcelluloses are useful in other applications such as building products, industrial products, agricultural products, personal care products, household products, and pharmaceutical products. Useful pharmaceutical applications include as capsules, encapsulants, tablet coatings, and as an excipient for medicaments and drugs. Useful excipient functions include as sustained-release and timed-release tablets. Useful building applications include drywall tape-joint compounds, mortars, grouts, cement plasters, spray plasters, cement stucco, adhesives, pastes, and wall/ceiling texturizers. Useful industrial applications include binders and processing aids for tape casting, extrusion forming, and injection molding and ceramics. Useful agricultural applications include spray adherents and suspending/dispersing aids for pesticide, herbicide, and fertilizer powders. Useful personal care and household products include shampoos, lotions, creams, and cleaning products. The present methylcelluloses are particularly useful in compositions for pharmaceutical capsules. Capsules formed from the present methylcelluloses may exhibit substantially less distortion after drying than capsules formed from conventional methylcelluloses. Particularly useful methylcelluloses are methylcellulose having little or no non-methoxyl substitution and hydroxypropylmethylcellulose of low molecular weight, i.e. about 3 to about 100 cP and preferably about 3 to about 15 cP in a two percent aqueous solution. Low molecular weight methylcelluloses can be prepared directly from the processes described above or can be prepared from high molecular weight methylcelluloses via acid-catalyzed depolymerization. Useful acids include anhydrous hydrogen chloride and hydrochloric acid. Following depolymerization to the desired degree, the acid is neutralized and the depolymerization stopped by contact with a base such as sodium bicarbonate. Useful teachings relating to making low molecular weight methylcelluloses are seen in U.S. Serial No. 09/203,324, filed December 1 , 1998, which is incorporated herein by reference. Methylcellulose capsules are typically manufactured by dipping hot pins in a cold, aqueous methylcellulose coating solution or by dipping cold pins in a hot, aqueous methylcellulose coating solution. The solutions gel on the pins and water evaporates during a drying step to form thin film layers of dried methylcellulose around the pins. The thin films take the form of caps and bodies, which are removed from the pins and mated to form capsules. Processes for making capsules are seen in U.S. Patent Nos. 3,617,588; 4,001 ,211 ; 4,917,885; and 5,756,036, which are incorporated herein by reference. When drying takes place non-uniformly during the manufacture of pharmaceutical capsules with conventional methylcelluloses, caps and bodies can sometimes become distorted and difficult to mate or assemble into capsules. Caps and bodies formed from the present methylcelluloses may better resist such distortion because of their enhanced gel strength. The following are examples of the present invention. Unless otherwise indicated, all percentages, parts, and proportions are by weight. EXAMPLES Example 1 A methylcellulose of the present invention was made in accordance with a process of the present invention. Finely ground cellulose wood pulp was loaded into a jacketed, agitated reactor. The reactor was evacuated and purged with nitrogen to remove oxygen and then evacuated again. The reactor was used in two stages. In the first stage, 50 percent sodium hydroxide in water by weight was sprayed onto the cellulose at a weight ratio of 0.45/1.0 NaOH/cellulose and the temperature adjusted to 40°C (starting temperature). After stirring the NaOH/cellulose for about 10-20 minutes, a mixture of dimethyl ether and methyl chloride was added to the reactor with additional methyl chloride so that the weight ratio of methyl chloride/cellulose was about 0.64/1.0. The contents of the reactor were then heated from 40°C to 80°C over the next 40 minutes. After reaching 80°C (cook temperature), the first stage reaction was allowed to proceed for another 30 minutes (cook time). The second stage was effected by adding the remainder of the sodium hydroxide and methyl chloride and allowing for additional reaction. A second quantity of 50 percent NaOH in water by weight was added over 10 minutes at a weight ratio of 0.65/1.0 NaOH/cellulose (the cellulose is actually partially etherified at this point in time). A second quantity of methyl chloride was added over about 35 minutes to a level of 0.90/1.0 weight ratio of methyl chloride/cellulose. The reaction was continued at 80°C for an additional 30 minutes (cook time) to complete the etherification. Table 2 depicts process information and data pertaining to alkalization and etherification. After the reaction, the reactor was vented and cooled to 50°C. The contents of the reactor were removed and transferred to a tank containing hot water to form a slurry, which was subsequently agitated for 15 minutes. This slurry was pumped from the hot tank to a filter where it was de-watered and washed with hot water to remove the salt and organic by-products. The wet methylcellulose was then transferred to a dryer where moisture and volatiles content was reduced to 1 to 4 weight percent based upon the weight of the methylcellulose. The methylcellulose was then ground to a particle size of about 40 mesh (420 micrometers). The methylcellulose product was analyzed and found to contain 31.8 percent methoxyl substitution (a methoxyl degree of substitution of 1.96). It exhibited a viscosity of 17,000 centipoise (cP) in a 2 percent by weight aqueous solution by weight, a gelation temperature (T_ of 105°F - 108°F (40.6°C - 42.2°C), and a elastic modulus (G') of 5445 Pascals for a 1.5 percent by weight aqueous solution, and a meltback time of 35 minutes. Product properties are set forth in Table 3. These physical properties are more desirable than those of conventional methylcelluloses of similar substitution and viscosity level. Such conventional methylcelluloses typically exhibit a T gel of about 52° - 59°C for a 1.5 percent aqueous solution and a G' of 800-2000 Pascals for a 1.5 percent aqueous solution. Thus, the methylcellulose of the present invention has the advantages of both a significantly higher G' and a significantly lower gelation temperature compared to a conventional methylcellulose of similar substitution and viscosity grade. In the various examples disclosed herein, G' was measured for a 1.5 percent by weight aqueous solution in a Bohlin VOR Rheometer (Bohlin Corp.) with C25 serrated bob and cup system. Examples 1 A-1 D Samples of the methylcellulose product of Example 1 were depolymerized by reaction with anhydrous hydrogen chloride for varying lengths of time followed by neutralization with sodium bicarbonate. After depolymerization, a sample exhibited a viscosity of 614 cP (two percent solution), a G' of 2250 Pascals and a meltback time of 20 minutes. After another depolymerization, a sample exhibited a viscosity of 219 cP, a G' of 1400, a T gβl of 108°F (42°C), and a meltback time of 40 minutes. After another depolymerization, a sample exhibited a viscosity of 81 cP, a G' of 1390 Pascals, a T gel of 103°F (39°C) and a meltback time of 19 minutes. After another depolymerization, a sample exhibited a viscosity of 66 cP, a G' of 1680 Pascals, and a meltback time of 25 minutes. Product properties are set forth in Table 4. Example 2 Another methylcellulose of the present invention was made in accordance with a process of the present invention. The process is as in Example 1 except where indicated otherwise in Table 2. The methylcellulose product had a methoxyl substitution of 31.3 percent and exhibited a viscosity of 26,000 cP in a 2 percent aqueous solution by weight, a T gβl of 34.4°C, a G' of 3740 Pascals, and a meltback time of greater than 50. These physical properties compare very favorably with those of a conventional methylcellulose of similar substitution and viscosity level. Product properties are set forth in Table 3. Examples 2A-2B Samples of the methylcellulose end product of Example 2 were depolymerized by reaction with anhydrous hydrogen chloride for varying lengths of time followed by neutralization with sodium bicarbonate. After depolymerization, a sample exhibited a viscosity of 357 cP (2 percent solution), a G' of 1080 Pascals, and a meltback time greater than 50 minutes. After another depolymerization, a sample exhibited a viscosity of 29 cP, a G' of 569 Pascals, a T gβl of 87°F (31 °C), and a meltback time of 30 minutes. Product properties are set forth in Table 4. Example 3 Another methylcellulose of the present invention was made with the process of the present invention. The process is as in Example 1 except where indicated otherwise in Table 2. The methylcellulose product had a 29.9 percent methoxyl substitution and exhibited a viscosity of 30,000 cP (2 percent solution), a T gβl of 89°F (31.7°C), and a G' of 3200 Pascals, and a meltback time greater than 50 minutes. Product properties are set forth in Table 3. Example 4 Another methylcellulose of the present invention was made with the process of the present invention. The process is as in Example 1 except where indicated otherwise in Table 2. The methylcellulose product had a 32.9 percent methoxyl substitution and exhibited a viscosity of 1 1 ,000 cP (2 percent solution), a T gβl of 122°F (50°C), a G' of 3180 Pascals, and a meltback time of 17 minutes. Product properties are set forth in Table 3. Example 5 Another methylcellulose of the present invention was made with the process of the present invention. The process is as in Example 1 except where indicated otherwise in Table 2. The methylcellulose product had a 32.7 percent methoxyl substitution and exhibited a viscosity of 2600 cP (2 percent solution), a T gβl of 118°F (48°C), a G' of 1460 Pascals and a meltback time of 20 minutes. Product properties are set forth in Table 3. Example 6 Another methylcellulose of the present invention was made with the process of the present invention. The process is as in Example 1 except where indicated otherwise in Table 2. The methylcellulose product had a 26.9 percent methoxyl substitution and exhibited a viscosity of 330 cP in a 2 percent aqueous solution by weight, a T gβl of 128°F (54°C), a G' of 1470 Pascals and a meltback time of 8 minutes. Product properties are set forth in Table 3. Example 7 Another methylcellulose of the present invention was made with the process of the present invention. The process is as in Example 1 except it has an additional (third) stage. Process information is set forth in Table 5. The methylcellulose product had a 35.4 percent methoxyl substitution and exhibited a viscosity of 461 ,000 cP (2 percent solution), a T gβl of 45°C, and a G' of 6900 Pascals and was stable to meltback at ambient temperature. This methylcellulose product has the advantages of a significantly higher G' and a significantly lower T gβl compared to conventional methylcelluloses of similar methoxyl substitution and viscosity level. Product properties and composition are set forth in Table 6. Example 8 Another methylcellulose of the present invention was made with the process of the present invention. The process is as in Example 1 except it has an additional (third) stage. Process information is set forth in Table 5. The methylcellulose product had a 36J percent methoxyl substitution and exhibited a viscosity of 26,000 cP (2 percent solution), a T gβl of 1 13°F (45°C), a G' of 7990 Pascals, and was stable to meltback at ambient temperature. This methylcellulose product has the advantages of a significantly higher G' and a significantly lower gelation temperature compared to conventional methylcelluloses of similar methoxyl substitution and viscosity level. Product properties and composition are set forth in Table 6. Example 9 Another methylcellulose of the present invention was made with the process of the present invention. The process is as in Example 1 except it has an additional (third) stage. Process information is set forth in Table 5. The methylcellulose product had a 34.9 percent methoxyl substitution and exhibited a viscosity of 25,000 cP (2 percent solution), a T gβl of 95°F(35°C), and a G' of 7565 Pascals and was stable to meltback at ambient temperature. This methylcellulose product has the advantages of a significantly higher G' and a significantly lower T gel compared to conventional methylcelluloses of similar methoxyl substitution and viscosity level. Product properties and composition are set forth in Table 6. A number of methylcellulose samples were generated using a conventional process known in the art. The product properties of these samples are set forth in Table 7. The gel strength and viscosity properties of the prior art samples set forth in Table 7 were graphed along with the gel strength and viscosity properties of examples 1 , 1 A, 1 B, 1 C, 1 D, and examples 2, 2A, and 2B as set forth in Tables 3 and 4. The corresponding graph is shown in Figure 1. The relationship between gel strength (expressed on logarithmic scale) and viscosity (logarithmic scale) is approximately linear. Lines were drawn for each set of data using a best fit algorithm. The equations approximating each line are indicated on the graph. The graph in Figure 1 demonstrates that the gel strength of methylcelluloses of the present invention having methoxyl substitution of between about 29 percent and 32 percent is greater than approximately 223 x v 0273 . It should be understood that this gel strength to viscosity relationship is an approximation and methylcelluloses of the present invention may fall slightly below this approximation. For example, the data from Table 3 indicates that Example 3 falls slightly below the line representing Examples 2, 2A, and 2B, but is well above the line representing the prior art. While embodiments of the process and compositions of the present invention have been shown with regard to specific details, it will be appreciated that the present invention may be modified while still being fairly within the scope of the novel teachings and principles set forth herein. Table 2 Process Information for Examples 1- Table 3 Product Properties and Composition of Examples 1-6 G' - elast c modulus n Pascals n a 1.5 percent aqueous solut on; corresponds to gel strength. Viscosity - viscosity in 2 percent aqueous solution in centipoise (cP) . MeO % - percent methoxyl substitution based upon weight of methylcellulose. MeO DΞ - methoxyl degree of substitution. Tgei - gelation temperature Table 4 Product Properties of Examples 1A-1D and Examples 2A-2B Table 5 Process Information for Examples 7-9 Table 6 Product Properties and Compositions for Examples 7-9 G' - elastic modulus in Pascals in a 1.5 percent aqueous solution. Viscosity - viscosity in 2 percent aqueous solution in centipoise (cP) . MeO % - percent methoxyl substitution based upon weight of methylcellulose. MeO DS - methoxyl degree of substitution. Table 7 PROPERTIES OF CONVENTIONAL PRIOR ART METHYLCELLULOSES Percent methoxyl substitution G' = dynamic elastic modulus on Bohlin Rheometer at 1.5% aq. Meltback time (minutes) of gel from 1.5% solution Thermal gelation temperature of 1.5% solution

Claims: CLAIMS 1. A process for making methylcelluloses having a desired level of methoxyl substitution, comprising the steps of: a) reacting a cellulose pulp with a first amount of aqueous alkali and a first amount of a methylating agent at reaction conditions sufficient to methylate the cellulose pulp to a first level of methoxyl substitution which is about 20 percent or more of the desired level of methoxyl substitution; and b) reacting the methylcellulose of first level of methoxyl substitution with a second amount of aqueous alkali and a second amount of a methylating agent at reaction conditions sufficient to methylate it to a second level of methoxyl substitution which is about 40 percent or more of the desired level of methoxyl substitution. 2. The process of Claim 1 , wherein the second level of methoxyl substitution is essentially 100 percent of the desired level of methoxyl substitution. 3. The process of Claim 1 , wherein the first level of methoxyl substitution is about 30 percent or more of the desired level of methoxyl substitution. 4. The process of Claim 1 , wherein the first level of methoxyl substitution is about 40 percent or more of the desired level of methoxyl substitution. 5. The process of Claim 1 , wherein the second amount of methylating agent is added at about 65°C to about 120°C for 15 minutes or more. 0 6. The process of Claim 1 , wherein the second amount of methylating agent is added at about 75°C to about 100°C for 20 minutes or more. 7. The process of Claim 2, wherein the second amount of methylating agent is added at about 80°C to about 90°C for 25 minutes or more. 8. The process of Claim 3, wherein the methylation reaction is carried out 5 at a temperature of about 65°C to about 110°C. 9. The process of Claim 1 , wherein the methylation reaction is carried out at a temperature of about 80°C to about 90°C. 10. The process of Claim 1 , wherein contact with the cellulose pulp or the methylcellulose is effected in the first or the second stage with an amount of o propylene oxide at reaction conditions sufficient to form a methylcellulose with hydroxypropyl substitution. 11. The process of Claim 1 , wherein contact with the cellulose pulp or the methylcellulose is effected in the first or the second stage with an amount of butylene oxide at reaction conditions sufficient to form a methylcellulose with hydroxybutyl substitution. 12. The process of Claim 1 , wherein contact with the cellulose pulp or the methylcellulose is effected in the first or the second stage with an amount of ethylene oxide at reaction conditions sufficient to form a methylcellulose with hydroxyethyl substitution. 13. The process of Claim 1 , wherein contact with the cellulose pulp or the methylcellulose is effected in the first or the second stage with an amount of ethyl chloride at reaction conditions sufficient to form a methylcellulose with ethoxyl substitution. 14. The process of Claim 1 , wherein the desired level of methoxyl substitution is from about 21 to about 42 weight percent. 15. The process of Claim 1 , wherein the desired level of methoxyl substitution is from about 25 to about 35 weight percent. 16. The process of Claim 1 , wherein the desired level of methoxyl substitution is from about 29 to about 32 weight percent. 17. The process of Claim 1 , wherein the process further comprises c) dipping a pin into a solution of the methylcellulose of the total level of methoxyl substitution; d) allowing the solution to gel on the pins; e) drying the solution to form thin, dried layers of methylcellulose in the form of caps and bodies which are capable of being mated to form pharmaceutical capsules; f) removing the caps and the bodies from the pins. 5 18. The process ether of Claim 1 , wherein the process further comprises c) dipping a pin into a solution of the methylcellulose of the total level of methoxyl substitution; d) allowing the solution to gel on the pins; e) drying the solution to form thin, dried layers of methylcellulose in the form of caps and bodies which are capable of being mated to form pharmaceutical capsules; f) removing the caps and the bodies o from the pins. 19. A methylcellulose made according to the process of Claim 1. 20. A methylcellulose having a methoxyl substitution of about 29 to about 32 weight percent based upon the weight of the methylcellulose and a gel strength greater than about 223 x (v 0273 ), wherein v represents the viscosity of the methylcellulose. 21. The methylcellulose of Claim 20, wherein the gel strength is greater than about 490 x (v 0241 ). 22. The methylcellulose of Claim 20, wherein the methylcellulose has a viscosity of about 1 to about 600,000 centipoise in a two percent aqueous solution. 23. The methylcellulose of Claim 20, wherein the methylcellulose has a viscosity of about 1 to about 100,000 centipoise in a two percent aqueous solution. 24. The methylcellulose of Claim 20, wherein the methylcellulose has a viscosity of about 3 to about 15 centipoise in a two percent aqueous solution at 20°C. 25. The methylcellulose of Claim 20, wherein the methylcellulose has a non-methoxyl substitution of about 1 weight percent or less based upon the weight of the methylcellulose. 26. The methylcellulose of Claim 20, wherein the methylcellulose has a non-methoxyl substitution of about 0.2 weight percent or less based upon the weight of the methylcellulose. 27. The methylcellulose of Claim 20, wherein the methylcellulose is substantially free of non-methoxyl substitution. 28. The methylcellulose of Claim 20, wherein the methylcellulose is in the form of a pharmaceutical capsule. 29. The methylcellulose of Claim 20, wherein the methylcellulose is in the form of an excipient for a pharmaceutical tablet. 30. The methylcellulose of Claim 20, wherein the methylcellulose is in the form of a ceramic. 31. The methylcellulose of Claim 20, wherein the methylcellulose is in the form of any selected from the group consisting of any of the following: a pharmaceutical encapsulant, capsule, tablet coating, and excipient; a drywall tape- joint compound; a mortar; a grout; a cement plaster; a spray plaster; a cement stucco; an adhesive; a paste; a wall/ceiling texturizers; a binder or processing aid for tape casting, extrusion forming, and injection molding; an agricultural spray adherent; a suspending/dispersing aid for pesticide, herbicide, and fertilizer powders; a shampoo; a lotion; a cleaner; and a ceramic. 32. A food composition, wherein the food composition comprises a methylcellulose according to Claim 20. 33. The food composition according to Claim 32, wherein the food composition is selected from the group consisting of vegetable, meat, and soy patties; reformed seafood; reformed cheese sticks; cream soups; gravies and sauces; salad dressing; mayonnaise; onion rings; jams, jellies, and syrups; pie filling; formed potato products such as trench fries and extruded fries; batters for fried foods, pancakes/waffles, and cakes; pet foods; beverages; frozen desserts; cultured dairy products such as ice cream, cottage cheese, yogurt, cheeses, and sour creams; cake icing and glazes; leavened and unleavened baked goods; and whipped topping. 34. The food composition of Claim 32, wherein the food composition comprises from about 0.01 to about 5 weight percent methylcellulose based upon the total weight of the composition. 35. The food composition of Claim 32, wherein the methylcellulose has a viscosity of about 1 to about 600,000 centipoise in a two percent aqueous solution at 20°C. 36. The food composition of Claim 32, wherein the methylcellulose has a gel strength greater than about 490 x (v 0241 ) and viscosity of about 1 to about 100,000 centipoise in a two percent aqueous solution at 20°C. 37. The food composition of Claim 32, wherein the non-methoxyl substitution is about 0.2 weight percent or less based upon the weight of the methylcellulose.

Inventors: CONKLIN JERRY R, REIBERT KENNETH C, CONKLIN, JERRY, R., REIBERT, KENNETH, C.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 2000
Main classification: C08B11
IPC codes: A23L1, A61K9, A61K47, C04B35, C08B11