Patent Application
20120006499
This application relates generally to hydrophilic debonders for defiberizing pulp boards.
Fast wicking of liquids is desirable in many commercial products such as diapers, personal hygiene, sanitary products, etc. Usually this is achieved by converting paperboard products into defiberized fluff pulp that has a high surface area to enable fast wicking. Such fluff pulp is utilized in a variety of different designs to enable wicking of bodily fluids from the point of insult.
Fluff pulp is formed from paperboards made by conventional papermaking technologies. The absorbent core for hygienic products is typically manufactured on a continuous production line in which wood fluff pulp is provided as a sheet (manufactured, for example, by a wet-laid process) and is defiberized mechanically using means such as a hammermill. The defiberized fluff pulp is then air-laid with particles of superabsorbent polymers or other super-absorbent materials capable of absorbing up to one hundred times their weight in water, thereby forming the absorbent core for the product.
Formation of fluff pulp from paperboard depends on mechanical mechanisms to break the strong intermolecular hydrogen bonds that form between neighboring cellulose fibers during the papermaking process. A significant amount of energy is required to overcome the strength of the intermolecular bonds and break a paperboard into individual fibers.
Because the energy required for mechanical breakdown methods is expensive, alternate technologies have been employed to reduce the formation of hydrogen bonds during papermaking. As an example, debonder compounds are used for this purpose. Debonders bind to the fiber surface, preventing the formation of hydrogen bonds by acting as a spacer between neighboring cellulose molecules and fibers.
Many approaches in the art use quaternary ammonium salts as debonders. Such debonders contain a cationic group that attaches the molecule to the anionic fiber surface, and a hydrophobic chain that acts like a spacer between cellulose fibers/molecules. With fewer bonds between fibers, less energy is required to break the fibers apart. Although these debonders can reduce the energy required to produce fluff pulp, the hydrophobic moiety decreases the wicking property of the resulting fluff pulp. Hence there is a need for an approach that reduces the hydrogen bonding while unaffecting the hydrophilicity of the fluffed pulp. Desirably, an appropriate debonder would both decrease the energy of defiberization and maintain comparable or improved wicking speeds.
In some aspects of the invention, fiber-containing compositions are disclosed that are suitable for use in improving fluid distribution in materials such as paper-based materials and/or at least a portion of an absorbent fiber-based article. The fiber-containing compositions can include a fibrous material comprising fibers. A debonding agent can impart the fiber-containing composition with a transition temperature such that the debonding agent has a higher affinity for the fibers when the temperature is above a transition temperature relative to when the temperature is below the transition temperature, and/or the debonding agent enhances fluid distribution in the fiber-containing composition when the temperature of the debonding agent is below the transition temperature relative to when the temperature is above the transition temperature. Such fiber-containing compositions can include, or be substantially free of, a conventional debonding agent such as a salt (e.g., ammonium salt) or other charged specie; for example, free of the salt and/or charged specie such that the presence of any such specie does not affect the wicking of the fiber-containing composition and/or the LCST behavior of a polymer composition in the debonding agent.
In some embodiments of the invention, the debonding agent comprises a polymer composition exhibiting a lower critical solution temperature (LCST). The polymer composition can include a copolymer and/or a blend of different polymer molecules. In particular embodiments, the debonding agent can comprise a plurality of alkylene oxide units. In some embodiments, the debonding agent can comprise at least one of polyethylene oxide units and polypropylene oxide units. The debonding agent can comprise a polymer with two distinct alkylene-oxide units, each alkylene-oxide unit can exhibit a different LCST at a given concentration and molecular weight distribution. In some embodiments herein, a debonding agent can be substantially free of a charged specie (e.g., an ammonium salt, a polyelectrolyte, or other specie carrying an ionic charge).
In some embodiments, the fiber-containing composition exhibits a transition temperature in a range between about 5° C. and about 95° C. In some embodiments, the fiber-containing compositions disclosed herein can comprise a transition temperature-modifier capable of changing the LCST of the debonder agent in the fiber-containing composition. Such a LCST modifier can comprise at least one of a chaotropic salt and a surfactant.
Other aspects of the invention are directed to methods of improving wicking of a fiber-based material as disclosed herein (e.g., an absorbent fiber-based article). Such methods can include the steps of providing a fiber-containing composition comprising a polymeric debonding agent disposed with a plurality of fibers; and subjecting the fiber-containing composition to a temperature below a transition temperature such that the fiber-containing composition exhibits enhanced wicking relative to a fiber-composition without the debonding agent.
The polymeric debonding agent can be consistent with any of the debonding agents including a polymer composition as disclosed herein (e.g., a copolymer or a blend of different polymer molecules). For instance, the polymer composition can exhibit LCST behavior. In embodiments, the fiber-containing composition optionally includes an ammonium salt. In another embodiment, the fiber-containing composition can be free of ammonium salt, or substantially free of ammonium salt (e.g., in an amount capable of substantially affecting wicking of the fiber-containing composition). In embodiments, the debonding agent can comprise a plurality of alkylene oxide units. In embodiments, the fiber-containing composition can comprise a transition temperature modifier capable of changing the LCST of the debonding agent in the fiber-containing composition, the transition temperature modifier comprising at least one of a chaotropic salt and a surfactant.
In some embodiments, the step of providing the fiber-containing composition comprises forming a mixture comprising at least a portion of the fiber-containing composition; and drying the mixture to provide the fiber-containing composition. The step of forming the mixture, which is optionally performed at a temperature below the transition temperature, can comprise forming the mixture with the debonding agent. In embodiments, the debonding agent can be applied while the mixture is being dried. The step of drying the mixture can comprise subjecting the mixture to a temperature above the transition temperature. The step of drying can comprise using the debonding agent to inhibit hydrogen bonding between at least some fibers during the step of drying.
In other aspects of the invention, methods of utilizing a debonder in a paper-based composition are disclosed. The method can comprise inserting a debonder composition in a paper-based mixture including fibers. The debonder composition can include at least one polymeric component exhibiting a LCST) and at least one modifying component. The modifying component can be selected to alter the LCST of the at least one polymeric component so that the altered LCST falls within a temperature range between about 5° C. and about 95° C.
In some embodiments, the at least one polymeric component comprises a first block of a copolymer. In some embodiments, the at least one modifying component comprises a second block of the copolymer. The copolymer can optionally comprise a plurality of alkylene-oxide unit types. The plurality of alkylene-oxide unit types can comprise at least one of an ethylene-oxide and a propylene oxide. The at least one polymeric component can comprise a first polymer comprising a repeat unit type, and the at least one modifying component can comprise a second polymer comprising a different repeat unit type. For instance, the repeat unit type comprises an alkylene-oxide unit type, and the different repeat unit type comprises a different alkylene-oxide unit type. In some embodiments, the at least one polymeric component comprises a first polymer characterized by a first repeat unit or a selected polymer type and the at least one modifying comprises a second polymer characterized by the first repeat unit or the selected polymer type, the first polymer and the second polymer differing in at least one of molecular weight, branching, and the first polymer having a second repeat unit not present in the second polymer. In some embodiments, the at least one modifying component can comprise a chaotropic salt and/or a surfactant.
The methods disclosed herein can further comprise the step of maintaining the paper-based mixture at a temperature above a transition temperature to inhibit adhesion between at least a plurality of fibers of the paper-based mixture. The methods disclosed herein can further comprise the step of maintaining the paper-based mixture at a temperature below the transition temperature such that the at least one polymeric component exhibits hydrophilic behavior.
Aspects of the present invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings (not necessarily drawn to scale), in which:
Disclosed herein are systems, compositions, and methods for making and using debonders to reduce bonding between fibers while preserving or enhancing wicking properties in a material made using the fibers (e.g., a fluff pulp). In some embodiments, debonding agents can be combined with fibers (e.g., cellulose-based fibers) to produce a material having substantial wicking properties while decreasing fiber-fiber interactions that can require substantial energy to overcome in materials processing. The debonding agent can act to create a paper-based product exhibiting a transition temperature in which the agent has a higher affinity for the fibers at temperatures above the transition temperature, and a product exhibiting enhanced wicking properties at temperatures below the transition temperature. The disclosed debonding agents can provide benefits over existing debonding agent formulations, such as ammonium salts, by exhibiting improved wicking performance while still decreasing fiber-fiber interactions. Accordingly, in some embodiments, a debonder agent can be substantially free of salt and/or charged species. In some instances, the presence of a charged specie can hinder performance of debonders such as are disclosed herein (e.g., by decreasing wicking and/or affecting debonder interactions with the fibers).
In some embodiments, a debonding agent can include a polymer (either a portion of or the entirety of the molecule) or other material exhibiting a lower critical solution temperature (e.g., a copolymer containing ethylene oxide and propylene oxide units) that can be useful for enhancing wicking properties of fiber-containing compositions while hindering fiber-fiber attractions. It is understood that many agents (e.g., polymers) exhibit a temperature-dependent solubility phenomenon called Lower Critical Solution Temperature (LCST). Such agents, including certain polymers such as those containing ethylene oxide and propylene oxide monomers, are soluble in water or aqueous solutions at temperatures below the LCST, while heating the solutions leads to polymer precipitation from the solution above the LCST.
In embodiments, the LCST property of certain polymers can be used to support a class of debonder agents especially suitable for use in manufacturing liquid wicking materials such as fluff pulp because the papermaking exposes the pulp and additives to different temperatures during the manufacturing process. In some embodiments, the LCST of the debonder agent component acts to provide a transition temperature in the fiber-containing material utilizing the debonder agent. While this transition temperature is often close, if not the same, as the LCST, the presence of the other components of the material, or other environmental factors or components, can act to offset the transition temperature from the LCST. In some embodiments, a debonder can impart a sufficiently low transition temperature, thereby effectively reducing the solubility of the debonder at temperatures above the transition temperature. While not necessarily being limited to any particular theory, it is believed that the reduction in solubility tends to deposit the debonder on fiber surfaces, which can help inhibit fiber-fiber attractions due to hydrogen bonding. At temperatures below the transition temperature, which may include ambient use temperatures of a wicking material, it is believed that the debonder can become soluble, thereby enhancing fluid distribution through the fiber network, e.g., relative to the use of conventional ammonium salt debonders which are hydrophobic and hinder wicking between the fibers.
It is understood that while many fiber-containing compositions described herein utilize the described debonders in the context of making water-based wicking materials, these concepts can readily be applied to organic-based wicking materials or non-aqueous based wicking materials. For instance, fibrous materials could utilize synthetic fibers that are organophilic. Accordingly, appropriate debonder agents imparting a transition temperature (e.g., an organophilic polymer composition having a LCST) such that the agent tends to deposit on the synthetic fiber above the transition temperature and become soluble below the transition temperature can also be utilized.
Embodiments of debonders can be designed to enable addition at different points along the paper making line. In embodiments, the debonder molecule can be added at the wet end or after the slurry has been deposited onto the moving wire, e.g., at a temperature below the transition temperature such that the debonder component is water soluble when added to the slurry. In the drying process of papermaking, the temperature will be elevated above the transition temperature, causing the debonder component to precipitate out of solution onto the fiber surface. This precipitation may help in the drying process by inhibiting the hydrogen bonding between neighboring fibers. After the sheet is dried, the temperature of the paper falls below the transition temperature, so that the molecule reverts back to a hydrophilic state. This enhances the wicking properties of the dried paper sheet, because the now-hydrophilic debonder does not prevent flow of water through the fibrous web, as do many debonders in current use.
A variety of debonding agents can be utilized with embodiments of the present invention. In many instances, various types of polymer compositions that exhibit LCST behavior can be utilized. As utilized within the present application, the term “polymer” refers to a molecule comprising repeat units, wherein the number of repeat units in the molecule is greater than about 10 or about 20. Repeat units can be adjacently connected, as in a homopolymer. The units, however, can be assembled in other manners as well. For example, a plurality of different repeat units can be assembled as a copolymer. If A represents one repeat unit and B represents another repeat unit, copolymers can be represented as blocks of joined units (e.g., A-A-A-A-A-A . . . B-B-B-B-B-B . . . ) or interstitially spaced units (e.g., A-B-A-B-A-B . . . or A-A-B-A-A-B-A-A-B . . . ), or randomly arranged units. In general, polymers include homopolymers, copolymers (e.g., block, inter-repeating, or random), cross-linked polymers, linear, branched, and/or gel networks, as well as polymer solutions and melts. Polymers can also be characterized as having a range of molecular weights from monodisperse to highly polydisperse. A “type of polymer” refers to a polymer formed from a particular set of repeat units, e.g., A units and B units. A designated polymer type can or cannot have all the polymer molecules be of the same molecular weight and/or have the repeat units oriented identically.
Polymer compositions used in debonder agents can be utilized in a number of different dispositions, e.g., having a polymer where at least one section of the polymer exhibits LCST behavior. These include polymers where the segments are known to exhibit LCST behavior to those skilled in the art. As examples, suitable debonders can include polymers having segments such as polyalkylene oxides (e.g., polyethylene oxide (PEO) or polypropylene oxide (PPO) or a mix of such oxides), ethyl(hydroxyethyl)cellulose, poly(N-vinylcaprolactam), poly(methylvinyl ether), poly(N-isopropylacrylamide), and derivatives of such including those understood by ones skilled in the art. In some embodiments, the polymer composition can comprise only uncharged species. In embodiments, for example, the polymer composition can be at least substantially free of polyelectrolytes (e.g., being substantially or totally free of charges associated with the polymer structure). Thus, in some embodiments utilizing uncharged polymers, the transition temperature of a fiber-containing composition and/or the behavior of a debonder agent, can be substantially dictated by the LSCT of the polymer as opposed to the charges of a specie interacting with fibers.
Polymer composition can include a homopolymer, a copolymer, or a blend of polymers. A blend of polymers can include polymers of different types, e.g., a blend of at least one homopolymer and one copolymer, a blend of copolymers, a blend of a type of polymer where the molecules differ in molecular weight and/or branching. In some embodiments, a blend of polymers of a debonder agent can be disposed as an emulsion (e.g., a blend of a polymer rich in polypropylene oxide segments and a polymer rich in polyethylene oxide segments). The emulsion can allow polymers having different solubilities to be blended to form an appropriate debonding agent.
In some cases, the polymers can have a character that is different from that of conventional ammonium salts used as debonders (e.g., being anionic or neutral in nature). Alternatively, or in addition, the presence of an anchoring group (such as a cationic group or a chemical group such as epoxy or anhydride) in a component of a debonding agent can enhance the stability of the attachment of the debonder to a cellulose fiber.
In some embodiments, the polymer composition can be formulated to impart a selected transition temperature range for the fiber-containing composition utilizing the debonder agent. For instance, it can be advantageous to select the polymer composition such that the transition temperature is in the range of temperatures relevant to a papermaking process, e.g., selecting the polymer composition such that wet end processing of paper typically takes place at temperatures below the transition temperature and drying takes place at temperatures above the transition temperature. Accordingly, in some embodiments the components of the polymer composition (e.g., the polymers of a blend or the blocks of a copolymer) of a debonder agent are selected such as to impart a transition temperature for the fiber-containing composition in a range from about 5° C. to about 95° C. For example, a polymer composition can be designed to achieve a certain LCST, and thus impart a corresponding transition temperature when the composition acts as a portion of a debonder agent in a fiber-containing composition, by utilizing a first component having a designated LCST and another component to modify the first LCST.
In some particular embodiments, polymer having different alkylene oxide segment types can be utilized to tailor a transition temperature in a range from about 5° C. to about 95° C. For instance, polymers made of propylene oxide monomers exhibit a LCST of around 5-10° C. while those made with ethylene oxide exhibit a LCST of ˜90° C. These transition temperatures are concentration and molecular weight dependent, and can also be affected by the presence of other components in a fiber-containing composition. In particular, the ratio of EO and PO blocks in the molecule can determine the LCST of the resulting copolymer. A copolymer formed using these components can have an LCST that falls between these two temperatures, depending on the relative content of EO and PO blocks in the polymer. Likewise, a blend of polypropylene oxide polymers and polyethylene oxide polymers can also be used with the transition temperature dictated at least in part by the sizes of the individual polymers and their relative amounts.
Herein, features of a polymer composition utilizing PPO segments and PEO segments are disclosed. It is understood, however, that such features can also be imparted generally to other polymer composition consistent with other embodiments of the present invention. Accordingly, such features are not confined to PEO/PPO segment compositions, and can be extended generally to other polymer compositions that can physically achieve such features, consistent with embodiments of the present invention.
Not to be bound by any particular theory, it is believed that the debonder molecule binds to the pulp because the temperature of the aqueous environment reduces the solubility of either or both the EO or the PO units. In case of block copolymers that contain EO and PO blocks, increasing the temperature of the polymer solution in presence of the pulp can lead to selective precipitation of either the EO or the PO block onto the pulp fibers. The debonder molecule can be chosen such that the transition temperature of the composition would be in the range of temperatures seen on a papermaking line. For example, a composition with a transition temperature of 35° C. can be deposited into the wet slurry in the headbox where it would precipitate onto the fibers due to the fact that the temperature in the headbox is higher (˜45° C.) than the transition temperature of the debonder.
It will be appreciated by those of ordinary skill in the art that the behavior of the subject polymers as disclosed herein contrasts with that of other debonders that are hydrophobic at ambient temperatures. A hydrophobic debonder will impede flow of water through the fibrous web of the paper product. By contrast, the hydrophilic character of debonders as disclosed herein can facilitate water transport through the fibrous web of the paper product, a desirable behavior in a fluff pulp material.
In some embodiments, commercially available polymers can display certain advantageous properties of a hydrophilic debonder imparting a transition temperature that allows its precipitation during the drying phase of papermaking, as described above, along with its reversion to a hydrophilic state at room temperature. For example, the PLURONIC® line of polyethylene oxide (PEO)-polypropylene oxide (PPO) block copolymers (BASF) display these properties when used according to the systems and methods disclosed herein, as described in Examples below.
In other embodiments, a debonder molecule can be prepared that self-assembles around cellulose fibers, thereby preventing hydrogen bonding between neighboring fibers. In embodiments, the debonder molecule can be a polymer.
As examples, debonder molecules according to these systems and methods can include oligomeric or polymeric segments including ethyleneoxide (EO) or propyleneoxide (PO) segments or a combination of the two with the segments varying in sizes from n=2-10000. In embodiments, the temperature-sensitive solubility behavior of the PPO and PEO blocks in the polymer backbone can produce an affinity towards the cellulose fibers when the temperature of the solution is above the transition temperature of either of the EO or PO based blocks, so that the polymer attaches itself to the cellulose fiber.
In other embodiments, the LCST of a polymer composition, and thus the transition temperature, can be changed by the use of chaotropic salts such as those based on potassium, sodium, and calcium. In some embodiments, for example, potassium salts function well as chaotropic agents for EO based polymers, with the EO blocks self-assembling around potassium ions forming a crown ether like structure. The presence of chaotropic salts can alter the solution behavior of the debonders by precipitating them out of solution at temperatures lower than the actual LCST. Without being bound by theory, it is understood that adding salt to the polymer can change the structure of water around the molecules, leading to an association of the polymer with the salt and subsequent precipitation, effectively lowering the LCST of the polymer. For example, if a PEO-containing polymer has an LCST of 90° C., the presence of a chaotropic salt in the solution (preferably sodium based) can lower the LCST. Other polymer/salt systems can exhibit similar behaviors, for example, systems using NaCl and the like, whereby a polymer/salt arrangement can self-assemble around the cellulosic fibers. The LCST of the polymer in solution can also be changed by adding suitable surfactants, for example sodium dodecylsulfate or sodium laureth sulfate. For example, addition of sodium dodecylsulfate to a solution of Pluronic L31 [PEO-PPO-PEO] increased the LCST by about 5° C.
The following examples are provided to illustrate some aspects of the present application. The examples, however, are not meant to limit the practice of any embodiment of the invention.
In the examples below, the following materials were used (unless otherwise indicated, percentages are weight percentages):
Softwood pulp
Processed pulp sheets
A 0.6% slurry was prepared by mixing 84.45 g refurnished softwood pulp (22.5% solids) in 3 L of water for 6-10 minutes.
Handsheets were prepared using a Mark V Dynamic Paper Chemistry Jar and Hand-Sheet Mold from Paper Chemistry Laboratory, Inc. (Larchmont, N.Y.). The appropriate volume of 0.6% pulp slurry was functionalized with the appropriate polymer(s) (based on dry weight), as listed above. Polymer additions were done at 10 minute intervals. This combined slurry was added to the handsheet maker. The slurry was mixed at a rate of 1100 RPM for 5 seconds, 700 RPM for 5 seconds, and 400 RPM for 5 seconds. The water was then drained off. The subsequent sheet was then transferred off of the wire, pressed and dried.
Tensile tests were conducted on samples using an Instron Model 3343. Samples were cut into 1 in wide strips with a paper cutter. The gauge length region was set at 4 in and the crosshead speed was 1 in/minute. Thickness was measured to provide stress data as was the weight to be able to normalize the data by weight of samples. The samples were tested to failure with an appropriate load cell. At least three strips from each sample were tested and the values were averaged together.
To determine the wicking speed for a sample, a 1″ wide strip of the paper was prepared. The strip was clamped onto a fixture such that it hung vertically. A 500 mL beaker was filled with 100 mL of water and placed below the paper strip on a stage that could be raised and lowered. The stage was raised such that 5 mm of the bottom of the paper strip was submerged in the water. The strip was marked with pencil lines above the water level at 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, and 6 cm. Wicking speed was determined by the time taken by the water level to reach the different heights.
Handsheets were produced with the method in Example 2 using of the solution prepared in Example 1. The final paper weight was approximately 19 g for the control sheets. The final basis weight was about 670 gms.
Handsheets were produced with the method in Example 2 using of the solution prepared in Example 1. A debonder selected from the list in Table A and/or Table B was added at a concentration of up to 10% of the final paper weight and mixed for 10 minutes into the solution prepared in Example 1.
By changing the concentration of salt in the solution, the temperature at which cloudiness was observed in the polymer solution could be lowered or increased (cloudiness indicating polymer precipitation). Different concentration solutions of hydrophilic debonders selected from the list in Table A and/or Table B were made in water. To these solutions, salt solutions were added to make 0.1M, 0.2M and 0.3M final salt concentration. The salts were at least one of sodium chloride, potassium chloride, and potassium sulfate. The polymer-salt solutions were heated to different temperatures to observe the onset of precipitation of the polymer by monitoring cloudy streaks of polymer precipitation from solutions.
Tensile load at failure was measured for paper strips treated with hydrophilic debonders and conventional debonders (post-headbox treatment) by dipping 1″ by 6″ strips of 670 GSM basis weight paper strips in 50 mL centrifuge tubes containing solutions containing BASF Pluronic polymers in deionized water at concentration of 1%/wt, until the strips were saturated for approximately 2 minutes. The samples were then pressed and dried at 110° C. for 45 minutes. The protocol of Example 3 was used to determine the Energy and Max Load values. Corresponding wicking speeds were measured using the protocol described in Example 4; the wicking time corresponded with the time required for the water level to reach 6 cm. For this experiment, samples were prepared using polymers listed in Table 1 below, with an untreated sample as the control. Table 1 and
Samples were prepared by dipping 1″ by 6″ strips of 670 GSM basis weight paper strips in 50 mL centrifuge tubes containing solutions containing BASF Pluronic polymer L31 in deionized water at concentrations ranging from 0 to 10%/wt, until the strips were saturated for approximately 2 minutes. The samples were then pressed and dried at 110° C. for 45 minutes. The tensile load at failure was then measured using the apparatus described in Example 3, and the wicking time was measured using the protocol of Example 4; the wicking time corresponded with the time required for the water level to reach 6 cm. Table 2,
Samples were made by dipping untreated and conventional-debonder-treated 1″ by 6″ strips of 670 GSM basis weight paper in 50 mL centrifuge tubes containing solutions containing a hydrophilic debonder. For the hydrophilic debonder, the BASF Pluronic polymer L35 in deionized water was used at concentration of 1%/wt. Sample strips remained in contact with this solution for approximately 2 minutes, until the strips were saturated. The samples were then pressed and dried at 110° C. for 45 minutes. For each strip, the tensile load at failure was then measured, using the apparatus described in Example 3 and the wicking time was measured using the protocol of Example 4; the wicking time corresponded with the time required for the water level to reach 6 cm. The results of these tests are shown in
While specific embodiments of the subject invention have been discussed, the above specification is illustrative and not restrictive. Many variations of the invention will become apparent to those skilled in the art upon review of this specification. The features illustrated or described in connection with one embodiment may be combined with features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention. Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. The words “a” and “an” are equivalent to the phrase “one or more.”
This application is a continuation of International Application No. PCT/US2010/020440, which designated the United States and was filed on Jan. 8, 2010, published in English, which claims the benefit of U.S. Provisional Application No. 61/143,252, filed on Jan. 8, 2009. The entire teachings of the above applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61143252 | Jan 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US10/20440 | Jan 2010 | US |
| Child | 13178053 | US |
