Patent Application
20180327326
Porous ceramic articles are useful to facilitate filtering of gases and fluids to remove undesirable components. For example, porous ceramic honeycomb articles are known to filter exhaust gases from an engine before releasing the filtered exhaust gas to the atmosphere. Additionally, ceramic articles can be used as substrates and support catalysts.
In the formation of ceramic articles, e.g., silicon carbide, cordierite, mullite, alumina, or aluminum titanate articles, ceramic batch compositions are prepared by mixing various inorganic and organic components. In order to form the ceramic articles, the ceramic batch composition may be fed through an extrusion die after the ceramic batch components are mixed.
In one aspect, a ceramic-forming mixture (or “ceramic batch composition”, both of which terms are used herein to denote a mixture of components that can comprise ceramic and/or ceramic-forming components, which can be formed into green ware and sintered or reactively sintered upon firing to result in a ceramic ware or product) comprises one or more starches having an aggregate average amylose content of 35% or higher by total weight of the starch(es), as well as methods of manufacturing green ware, and porous ceramic bodies. In another aspect, methods for making ceramic articles are disclosed herein, comprising mixing a ceramic batch composition, said ceramic batch composition comprising amylose and amylopectin, wherein said ceramic batch has an amylose:amylopectin ratio ranging from about 5:95 to about 95:5, extruding the ceramic batch composition through an extrusion die to form an extruded green ceramic article, and drying the extruded green ceramic article. In various embodiments, the amylose:amylopectin ratio ranging from about 20:80 to about 80:20. In further embodiments, the ceramic batch composition comprises at least one starch comprising amylose and amylopectin at a ratio ranging from about 5:95 to about 95:5, such as about 20:80 to about 80:20. In further embodiments, the at least one starch is chosen from native starches, cross-linked starches, and lightly cross-linked starches, for example corn, rice, or potato starches. The at least one starch may be present in an amount up to about 20% by weight, relative to the total weight of the ceramic batch, as a super addition. In further embodiments, the methods further comprise measuring the amount of pressure required to extrude the ceramic batch through the extrusion die. In yet further embodiments, the methods further comprise adjusting the amylose:amylopectin ratio in the ceramic batch after measuring the pressure.
The disclosure further relates, in various embodiments, to methods for reducing extrusion pressure during a process of making a ceramic article, comprising mixing a ceramic batch composition, said ceramic batch composition comprising amylose and amylopectin, wherein said ceramic batch has an amylose:amylopectin ratio ranging from about 35:65 to about 95:5, extruding the ceramic batch composition through an extrusion die to form an extruded green ceramic article, measuring the extrusion pressure of the extruding step, and adjusting the amylose:amylopectin ratio in the ceramic batch composition. The at least one starch may be present in an amount up to about 20% by weight, relative to the total weight of the ceramic batch, as a super addition. In further embodiments, the methods comprise measuring the amount of pressure with a pressure transducer. In yet further embodiments, the methods further comprise adjusting the amylose:amylopectin ratio in a ceramic batch after measuring the pressure, by using at least one starch having a different amylose:amylopectin ratio.
Additional features and advantages of the invention as claimed will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as claimed herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description present various embodiments of the disclosure, and are intended to provide an overview or framework for understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the disclosure and together with the description serve to explain the principles and operations of the disclosure.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, together with the description serve to explain the principles of the invention.
Ceramic-forming mixtures (or “ceramic batch compositions”, both of which terms are used herein to denote a mixture of components that can comprise ceramic and/or ceramic-forming components, which can be formed into green ware and sintered or reactively sintered upon firing to result in a ceramic ware or product) are disclosed herein which comprise one or more starches having an aggregate average amylose content of 35% or higher by total weight of the starch(es), as well as methods of manufacturing green ware, and porous ceramic bodies, from such ceramic-forming mixture. Such ceramic-forming mixture can be implemented in methods for reducing the amount of pressure required to extrude a ceramic batch composition, as well as methods of making porous ceramic articles. The ceramic batch composition useful in exemplary methods according to the disclosure comprises one or more starches have an aggregate average amylose content of 35% or greater by weight of total amount of starch. Thus, the ceramic-forming mixtures can in some embodiments contain a single starch (or starch type), or a combination of two or more starches, which give an overall amylose content of the starches (aggregate average) which is greater than or equal to 35% by weight, in some embodiments greater than or equal to 50% by weight, in some embodiments greater than or equal to 70% by weight, and in some embodiments greater than or equal to 80% by weight of the total starch content. In some embodiments, the median particle size of at least one of the starches (or of the starch if only one starch) is less than 15.0 micrometers, and in some embodiments, less than 10.0 micrometers, and in some embodiments between 5.0 and 15.0 micrometers, and in some embodiments between 5.0 and 10.0 micrometers. In some embodiments, the one or more starches is selected from the group consisting of corn starch, rice starch, potato starch, and combinations thereof. Thus, in some embodiments, the ceramic-forming mixture can comprise a single starch, such as a corn starch, or a plurality of starches, such as a plurality of corn starches, or a corn starch and a rice starch, for example. In some embodiments, a high overall amylose content of the starches can be achieved with one or more high amylose content starches, or with a combination of one or more high amylose content starches with one or more low amylose content starches. As used herein, a high amylose content starch is one which has 35% or greater amylose content for that particular starch (the remainder being predominantly if not exclusively amylopectin), and a low amylose content starch is one which has less than 35% amylose content for that particular starch. Accordingly, the aggregate average amylose content of the ceramic-forming mixture can be adjusted by selecting a greater or lesser quantity of one or more starches each having a certain individual amylose content, in order to increase or decrease the overall amylose content of the batch. In some exemplary embodiments, one or more the starches in the ceramic-forming mixture, such as one or more high amylose starches, can be crosslinked, hydrophobically treated, or both, as well as non-crosslinked, which may be hydrophobically treated or not.
The amount of pressure needed to feed the ceramic batch composition through the extruder, as well as the rate at which the composition can be pushed through the die (“feed rate”), is limited by a variety of parameters, for example viscosity of the composition and “wall drag” encountered while the composition travels through the extrusion die.
Pore formers can be chosen from a variety of components that form pores in the ceramic article when they are burned out on firing leaving voids or “pores,” thus providing a ceramic article having high porosity. Starches are used because they are cost effective and allow for tailoring the substrate/filter design to meet various requirements. Starches having a particular ratio of amylose to amylopectin can provide a ceramic batch composition having a rheology that allows for a reduced amount of pressure needed to extrude a ceramic batch composition, and a reduced wall drag of the ceramic batch composition through the extrusion die, and thus can increase the feed rate at which the ceramic batch composition can be extruded.
According to various embodiments, starches with a higher amylose content may provide a decrease in wall drag of the ceramic batch composition during extrusion. As used herein, the terms “higher amylose content,” “higher amylose starches,” and the like, are intended to signify a relative increase in the amylose content, relative to the amylopectin content. For example, this may mean that the starch has an amylose:amylopectin ratio of greater than 30:70, such as, for example, greater than about 35:65, greater than about 40:60, greater than about 50:50, greater than about 60:40, greater than about 70:30, greater than about 80:20, or greater than about 90:10.
Additionally, the hydrophobicity of higher amylose starches reduces water demand of the ceramic batch, which reduces binder competition for water and increases binder gelation temperature. Higher amylose content in the starch may also provide higher pasting temperatures, which maintains granule structure of the native material and reduces requirements on crosslinking/hydrophobic treatments that may result in unwanted contaminants.
According to various embodiments of the disclosure, at least one starch may be included in the ceramic batch compositions as a source of the amylose and amylopectin. The starch may be chosen as the pore forming component. Exemplary starches that may be chosen from native starch or cross-linked starch having a ratio of amylose to amylopectin ranging from about 30:70 to about 95:5.
In some embodiments, the amylose:amylopectin ratio may range from about 35:65 to about 80:20. In some embodiments, amylose and amylopectin may be present in an amylose:amylopectin ratio of about 35:65, about 40:60, about 45:55, about 50:50, about 55:45, about 60:40, about 65:35, about 70:30, about 75:25, about 80:20, about 85:15, about 90:10, or about 95:5.
As used herein, the terms “amylose:amylopectin ratio,” “ratio of amylose to amylopectin,” and the like, are intended to include only the amounts of amylose and amylopectin, relative to each other. Any other components of the ceramic batch composition or pore former are considered separately from this ratio. Thus, the reference to a “pore former chosen from starches having an amylose to amylopectin ratio of 80:20,” means that the pore former comprises at least one starch comprising amylose and amylopectin in an amount of 80% amylose and 20% amylopectin, relative to each other only, but may comprise other components.
A native or cross-linked starch may be used in accordance with the embodiments disclosed herein. As used herein, a native starch is a starch that has been extracted from a plant, without further modification. in some embodiments, the starch is chosen from lightly cross-linked starches, moderately cross-linked starches, highly cross-linked starches, or completely cross-linked starches. As used herein, a lightly cross-linked starch may be cross-linked with about 1, such as about 2 or about 3 equivalents of cross-linking agent; a moderately cross-linked starch may be cross-linked with greater than about 3, such as about 4 or about 5 equivalents of cross-linking agent; a highly cross-linked starch may be cross-linked with greater than about 5, such as about 6, about 7, about 8, or about 9 equivalents of cross-linking agent; and a completely cross-linked starch may be cross-linked with about 10 or more equivalents of cross-linking agent.
Non-limiting examples of starches that may be used in accordance with various embodiments include rice starches, potato starches, pea starches, corn starches, sago starches, and mixtures thereof, in native or cross-linked form. By way of example, Hylon® VII and/or Hylon® V, sold by Ingredion, may be selected. In other embodiments, Dura-Bond® from Henkel Corp. or Amioca® from Inter-National Starch, Inc., may be selected.
In certain embodiments, the at least one starch may be present in the ceramic batch composition in an amount up to about 30% by weight, such as up to about 25%, up to about 20%, up to about 15%, up to about 10%, up to about 8%, up to about 5%, or up to about 3%, relative to the total weight of the ceramic batch, as a super addition. As used herein, the term “super addition” refers to adding additional ingredients or materials to a ceramic batch composition or formulation in excess of, or in addition to, a 100 wt % base ceramic formulation where the base ceramic formulation comprises only the ceramic-forming inorganic components.
As used herein, the term “ceramic-forming powder” is intended to denote only the inorganic components that are included in the ceramic batch composition to form the base ceramic formulation, including by way of example cordierite-forming powders, mullite-forming powders, and aluminum titanate-forming powders. The terms “ceramic batch,” “ceramic batch composition,” “ceramic-forming mixture” and the like, are used herein to denote a substantially homogenous mixture comprising at least one ceramic or ceramic-forming powder and the at least one starch, as well as any other inorganic or organic component used in preparing batch compositions for making ceramic articles.
For example, the ceramic batch composition may further comprise at least one binder. By way of example only, the at least one binder may be chosen from organic binders, such as cellulose-containing components, for example, methylcellulose, hydroxypropyl methylcellulose, methylcellulose derivatives, and combinations thereof. In certain non-limiting embodiments, the binder may be present in the ceramic batch composition in an amount ranging from about 1% to about 10% by weight, for example, from about 2% to about 6%, or about 3% to about 5%, relative to the total weight of the ceramic batch composition.
By way of further example, ceramic batch compositions may optionally comprise one or more additional pore forming components in addition to the at least one starch component described above. Such additional pore formers may be chosen from, for example, carbon (e.g., graphite (natural or synthetic), activated carbon, petroleum coke, and carbon black), starches other than those comprising the specified ratio of amylose to amylopectin (e.g., corn, barley, bean, potato, rice, tapioca, pea, sago palm, wheat, canna, and walnut shell flour), and polymers (e.g., polybutylene, polymethylpentene, polyethylene (preferably beads), polypropylene (preferably beads), polystyrene, polyamides (nylons), epoxies, ABS, Acrylics, and polyesters (PET)). In various embodiments, the optional additional pore forming component may be present in the ceramic batch composition in an amount up to about 30% by weight, such as up to about 25%, up to about 20%, up to about 15%, up to about 10%, up to about 8%, up to about 5%, or up to about 3%, relative to the total weight of the ceramic batch, as a super addition.
In further embodiments, the total pore forming component, including the at least one starch component described above and the optional additional pore forming component, when present, may be present in the ceramic batch composition in an amount up to about 30% by weight, such as up to about 25%, up to about 20%, up to about 15%, up to about 10%, up to about 8%, up to about 5%, or up to about 3%, relative to the total weight of the ceramic batch, as a super addition.
Solvents may also be included in the ceramic batch composition. It is within the ability of a skilled artisan to select an appropriate solvent, if desired, for the ceramic batch. The solvent may, for example, be used to wet the ceramic-forming powders and/or to provide a medium for the binder to dissolve, thus providing plasticity to the ceramic batch. In various exemplary embodiments, the at least one solvent may be aqueous, for example water and water-miscible solvents, or organic, or some combination thereof. In at least one exemplary embodiment, the solvent comprises water, for example, deionized water. According to various embodiments, the solvent may be present in the batch composition in an amount ranging from about 20% to about 50% by weight, such as about 25% to about 40%, or about 30% to about 35%, relative to the total weight of the ceramic batch.
Additional ceramic batch components may include, by way of non-limiting example, various organic additives used to modify the rheology of the batch such as lubricants, dispersants, surfactants, and plasticizers. Such optional components may be added as a superaddition of about 2% to about 20%, such as about 6% to about 15%, or about 8% to about 12%, by weight relative to the weight of the ceramic batch composition.
The batch materials may be mixed to obtain a substantially homogeneous batch composition using any method known in the art. For example, the at least one ceramic-forming powder may be wetted with at least one component chosen from solvents, binders, and combinations thereof. The solvent and/or binder may be added in an amount that is suitable to wet and/or plasticize the batch. The mixing and/or plasticization of the batch may take place in a suitable mixer in which the batch will be plasticized. For example, a ribbon mixer, twin-screw extruded/mixer, auger mixer, muller mixer or double arm mixer may be used to mix the ceramic batch composition.
In various embodiments, the disclosure relates to methods of making ceramic articles. Methods of making ceramic articles comprise mixing the components to form a ceramic batch composition and extruding the mixed batch composition. Further, methods according to various embodiments may include measuring the pressure during extrusion, and/or adjusting the ratio of amylose to amylopectin.
In yet further embodiments, the disclosure relates to methods for reducing extrusion pressure of the ceramic batch during a process for making a ceramic article, comprising mixing the components to form a ceramic batch composition, extruding the mixed batch composition, measuring the pressure during extrusion, and adjusting the ratio of amylose to amylopectin. Various ceramic batch compositions according to the disclosure demonstrate decreased wall drag at a given stiffness, resulting in higher feed-rate capabilities and thus require less pressure for the extrusion step.
The ceramic-forming powders, at least one starch, binder component, solvent, and any additional optional components may be mixed by any known method, such as, for example, in a muller or Littleford mixer. By way of non-limiting example, the solvent may be added to the ceramic-forming powders, at least one starch, and binder component, in an amount that is less than is needed to plasticize the batch. For example, with water as the solvent, the water hydrates the binder and the powder particles. A surfactant and/or lubricant, if desired, may then be added to the mix to wet out the binder and powder particles.
The batch may then be plasticized by shearing the wet mix in any suitable mixer in which the batch will be plasticized, such as, but not limited to, a twin-screw extruder/mixer, auger mixer, muller mixer, or double arm, etc. The extent of plasticization is dependent on the concentration of the components (binder, solvent, starch, surfactant, lubricant, and ceramic-forming powders), temperature of the components, the amount of work put in to the batch, the shear rate, and extrusion velocity.
The mixed and plasticized ceramic batch composition may then be extruded, for example through an extrusion or forming die, to form a green ceramic article having any desired shape and/or size. It may be desirable in various embodiments to measure the pressure during the process of extruding the ceramic batch composition, for example with a pressure transducer.
In certain exemplary and non-limiting embodiments, methods according to the disclosure may comprise adjusting the ratio of amylose to amylopectin in the ceramic batch composition. A process of adjusting the ratio of amylose to amylopectin may, in certain embodiments, comprise keeping all or substantially all the components of the ceramic batch composition substantially the same, but adding at least one starch having a different amylose:amylopectin ratio, for example a higher amylose:amylopectin ratio. For example, after a ceramic batch composition is prepared by mixing and plasticizing the components, and extruding the mixture through a die, if it is desired to reduce the amount of pressure needed for the extrusion step, and/or to increase the feed rate through the die, a subsequent ceramic batch composition may be prepared with at least one starch having a different ratio of amylose to amylopectin. The steps of measuring the extrusion pressure during the extruding step and adjusting the amylose:amylopectin ratio in the ceramic batch can be repeated until a desired extrusion pressure and/or feed rate is obtained.
By way of example, if a first ceramic batch composition is prepared with ceramic-forming powder, Hylon® V corn starch, which has a 50:50 ratio of amylose:amylopectin, at least one binder, and at least one solvent, and it is desired to reduce the amount of pressure needed to extrude the batch, and/or increase the feed rate, to form the green ceramic article, a second ceramic batch composition can be prepared substantially identically to the first ceramic batch composition (i.e. using substantially the same types and amounts of ceramic-forming powder, at least one binder, and at least one solvent), but comprising Hylon® VII corn starch, which has a 70:30 ratio of amylose:amylopectin, in place of the Hylon® V corn starch. In such an exemplary embodiment, according to at least certain aspects of the disclosure, the second ceramic batch composition may need less pressure and/or may have a greater feed rate for extrusion than the first ceramic batch composition.
After mixing, plasticizing, and extruding the ceramic batch composition to form a green ceramic article, the extrudate may be dried and fired. The firing conditions of temperature and time may depend on the composition and size and geometry of the body, and are within the ability of those of skill in the art to determine.
As set forth herein, various aspects of the disclosure are described with reference to the exemplary embodiments and/or the accompanying drawings in which exemplary embodiments of the invention are illustrated. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments shown in the drawings or described herein. It will be appreciated that the various disclosed embodiments may involve particular features, elements or steps that are described in connection with that particular embodiment. It will also be appreciated that a particular feature, element or step, although described in relation to one particular embodiment, may be interchanged or combined with alternate embodiments in various non-illustrated combinations or permutations.
It will also be understood that, as used herein the terms “the,” “a,” or “an,” mean “at least one,” and should not be limited to “only one” unless explicitly indicated to the contrary. Thus, for example, reference to “a pore former” includes examples having two or more pore formers unless the context clearly indicates otherwise.
Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not expressly recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred.
While various features, elements or steps of particular embodiments may be disclosed using the transitional phrase “comprising,” it is to be understood that alternative embodiments, including those that may be described using the transitional phrases “consisting” or “consisting essentially of,” are implied.
This application claims the benefit of priority of U.S. Provisional Application Ser. No. 62/261,119 filed on Nov. 30, 2015 the content of which is relied upon and incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US16/64205 | 11/30/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62261119 | Nov 2015 | US |
