Patent Application
20250215643
The disclosure relates to composite fibers and method for making composite fibers and more particularly to mineralized nanocellulose with calcium carbonate and methods of precipitating calcium carbonate for attachment onto nanocellulose.
Various techniques are known in the art for precipitation of calcium carbonate. Precipitated calcium carbonate (PCC) is used in various papermaking manufactures of fine papers like copy paper, mechanical grade papers like SC, container, and carton board. Various forms of precipitated calcium carbonate and cellulose-calcium composite materials have been used in the paper industry as filler material. Conventional cellulose-calcium carbonate materials incorporate the calcium carbonate such that the essential fibrous nature of the cellulose component is maintained. It was generally recognized in the art that the fibrous nature of the composite materials was needed to better incorporate the composite materials in the fiber matrix of paper.
U.S. Pat. No. 9,150,738 teaches an inverse carbonation process for forming various crystal forms of precipitated calcium carbonate. The inverse carbonate process has been found to be beneficial for particularly targeting scalenohedral morphology. The '738 patent teaches a key feature is initial addition of carbon dioxide into a reaction vessel until a controlled pH of 5-7 is obtained. After such pH control, the calcium hydroxide slurry is added at a rate such that a target conductivity is achieved to thereby precipitate the calcium carbonate.
WO 97/01670 teaches porous aggregates of calcium carbonate particles precipitated on the surface of cellulose fibers. EP 0 930 345 and EP 0 935 020 teach similar fillers, but without precipitation of the calcium carbonate on the surface of the fibers, but rather mixed with them. U.S. Pat. No. 10,683,616 teaches a method of producing a composite that introduces microfibrillated cellulose during the calcium carbonate precipitation process after a portion of the calcium hydroxide has been reacted with the carbon dioxide.
Surface mineralized fibers are also known, such as disclosed in WO2021/252572. Such fibers are generally produced using sodium carbonate for carbonation and have low fiber attachment amounts.
A need remains in the art for improved filler materials. Fibers produced in accordance with methods of the disclosure have significant improvements in mineral attachment. For various applications, the mineral can beneficially be provided as long chains of scalenohedral PCC attached to the nanocellulose fiber for improved properties.
A filler in accordance with the disclosure can include composite fibers, each composite fiber comprising mineral attached to a fiber, wherein the mineral is at least about 90 wt % based on the total weight of the composite fiber, the uncoated fiber has an average length of less than 300 μm, and the composite fiber has a Horiba d90 of at least 10 μm. For example, the fiber can be nanocellulose and the mineral can be calcium carbonate.
A method of making composite fibers in accordance with the disclosure can include preparing a calcium hydroxide slake by diluting lime in water; admixing an aqueous fiber slurry with dilution water in a reactor; adding the calcium hydroxide slake and a CO2 containing gas into the reactor containing the aqueous fiber slurry admixed with the dilution water to precipitate calcium carbonate onto the fiber; and continuing a flow of the CO2 containing gas into the admixture after the addition of the calcium hydroxide slake has started until a pH of 7.0 is reached. The calcium hydroxide slake is added at a rate to maintain a target conductivity that is 50% to 80% of saturation and the target conductivity is maintained until the addition of the calcium hydroxide slake is complete, the fiber slurry comprises fibers having a length of 300 μm or less, and the fiber slurry comprises an amount of fiber such that fiber content in the composite fibers is 10 wt % or less based on the total weight of the composite fibers. The calcium hydroxide slake can be added concurrently, before, or after the start of CO2 addition.
Composite fibers and methods of the disclosure unexpectedly and beneficially provide improved bulking and strength properties when used as fillers in making paper products. Typically, it was expected that high strength fillers densify the paper sheet, disadvantageously affecting the stiffness of the sheets. It was surprisingly found that the composite fibers of the disclosure can improve both bulk and strength resulting in improved stiffness. Additionally, methods of the disclosure can beneficially result in significant improvements in the percent of attached mineral. Still further, methods of the disclosure can allow for control over the mineral morphology and can beneficially provide composite fibers where all or substantially all of the mineral is present in a desired morphology, such as a scalenohedral morphology.
For example, the composite fibers of the disclosure can have long chains of scalenohedral mineral, for example, scalenohedral calcium carbonate, attached to the fiber template, which can advantageously result in the composite fibers maintaining fiber like qualities when used as fillers in papermaking.
Composite fibers of the disclosure when used as fillers in papermaking can provide high bulk and stiffness, as well as good natural retention and drainage while imparting increased physical strength. The process of the disclosure results in significantly more surface coverage of the fiber with all or substantially all of the precipitated mineral being attached to the fiber.
Composite fibers in accordance with the disclosure include a fiber and the mineral attached thereto. For example, the mineral can be in the form of long chains that attach to and surround the fiber, thereby coating the fiber, such as shown in
Composite fibers in accordance with the disclosure advantageously exhibit fibrous-like properties when included as a filler. Composite fibers in accordance with the disclosure have a Horiba doo of at least about 10 μm, at least about 20 μm at least about 25 μm, at least about 30 μm, at least about 40 μm, or at least about 50 μm.
The fiber can be nanocellulose. The nanocellulose is a cellulosic material having at least one dimension such as fibril particle diameters or width on the order of nanometers, for example, 100 nm or less. The fibers have a length of 300 μm or less. For example, the fibers before coating with the mineral can have a length of about 100 μm to about 300 μm. For example, the fibers can have a length of about 200 μm. Any nano-structured cellulose can be used as the fiber.
A method of forming a composite fiber in accordance with the disclosure includes forming an aqueous slurry containing the fiber. The amount of fiber in the aqueous slurry is selected such that the fiber is present in the composite fiber in an amount of about 0.1 wt % to about 10 wt %, about 0.25 wt to about 5 wt %, about 0.5 wt % to about 8 wt %, about 0.25 wt % to about 1 wt % based on the total weight of the composite fiber. For example, the fiber can be present in an amount, based on the total weight of the composite fiber, of about 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 wt %, or any ranges defined by such values. The slurry can have a solids content of about 0.1% to about 3%, about 0.1% to about 1%, about 0.5% to about 1.5%, about 0.1% to about 6%. Other suitable solids contents include 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, or any ranges defined by such values. The aqueous fiber slurry is added to the reactor as the heel.
A mineral slake can be prepared by mixing a suitable mineral containing material with water. For example, the mineral slake can be a calcium hydroxide slake. The calcium hydroxide slake is prepared by mixing lime and water. The water to lime ratio can be about 4:1 to about 15:1, about 5:1 to about 10:1, or about 5:1 to about 7:1. For example, the water to lime ratio can be 7:1. The lime and water can be mixed to form the slake. In various embodiments control of the initial temperature of the water is not necessary and can be dependent on process water in the plant. For example, the initial water temperature can be 32° C. Once mixed, the slake can optionally be screened to remove larger grit particles. For example, the slake can be screened through a 30 mesh screen, a 60 mesh screen or a 200 mesh screen.
The heel can be mixed in reactor and then the slake and a gas containing CO2 can be added to precipitate the mineral onto the fiber present in the heel. The initial reactor temperature can be, about 1° C. to about 50° C., about 11° C. to about 45° C., or about 35° C. to about 50° C., but need not be controlled during the process.
For example, the slake can be added and then CO2 containing gas can be flowed. Alternatively, the CO2 containing gas can be flowed and then slake can be added shortly thereafter. For example, the two components can be added in either order within seconds of one another, for example within 10 seconds.
Methods of the disclosure utilize reverse addition where the calcium hydroxide slake is metered into the aqueous fiber containing heel with control over the addition rate to limit the conductivity to be about 50% to 80% of saturation. The calcium hydroxide slake addition rate is controlled throughout the precipitation process to maintain the target conductivity. As used herein, “saturation” refers the conductivity of the starting calcium hydroxide slurry of fully saturated form. A conductivity of about 70% of saturation refers to a conductivity that is less than 70% of the conductivity of the starting calcium hydroxide slurry. Control over the conductivity can be achieved within about 1% of the reaction being complete. The target conductivity can be for example 50% of saturation, 60% of saturation, 70% of saturation, or 80% of saturation. For example, target conductivity can be 50% of saturation. Actual conductivity values can vary depending on the conductivity of the starting slake and the reactor. However, the actual conductivity values for controlling the reaction to be 70% of saturation can readily be determined by measuring the conductivity of the slake prior to addition and setting the conductivity to less than 70% of the measured value. For example, 50% of saturation can be maintained at conductivity values of about 3000 μs/cm to 5500 μs/cm depending on the starting conductivity of the slake as illustrated in the various examples.
It has been found that the pH need not be strictly controlled during the precipitation process. Once all slake has been added, the flow of the CO2 containing gas can be continued until the pH reaches 7.0.
The CO2 containing gas can be, for example, a blend of CO2 and air. For example, the gas or blended gas can include about 5% CO2 to about 100% CO2.
The process of the disclosure results in composite fibers in a slurry. The slurry cannot be screened due to the fibrous nature of the resulting composite fibers. The slurry can be used as is, for example, as a filler in papermaking. Alternatively, the composite fiber slurry can be dried to provide a dried product, which can be used for other applications.
A mineralized nanocellulose fiber was prepared in accordance with the method of the disclosure. A calcium hydroxide slake was prepared by mixing water and lime at a mass ratio of 7:1. In particular, 357 g lime were mixed with 2500 ml water. The water had a starting temperature of 32° C. The lime was added to the water while mixing at 750 rpm and mixing was continued for 15 min. The resulting slurry was screened through a No. 200 mesh screen to remove +200 mesh grit.
147.48 g of nanocellulose having a solids content of 0.5% was diluted in 800 ml water to form a slurry having a solids content of 0.5% 8% solids. The target PCC % in the PCC/fiber composition was 99. Nanocellulose template addition was calculated to be 1 wt % of the final product weight. The nanocellulose was added to the reactor first as the carbonator heel and mixed at 1250 rpm. The initial temperature was 40.8° C. CO2 gas was flowed into the reactor with a flow set-points of 0.76 sim CO2 and 3.1 slm air. Within 10 seconds, the calcium hydroxide slake was then added to the carbonator heel pumping at a rate of 14 ml/min over 120 min. The slake addition rate was adjusted to maintain conductivity of 4.5-5.0 ms/cm, which was 50% of the conductivity of the starting slake. Once all of the slake was added, CO2 addition was continued to an endpoint reaction to pH 7.0. The resulting product could not be screened 325 mesh due to the fibrous nature.
The resulting product was characterized for Horiba Particle Size and BET surface area. The characterization is shown in Table 1:
A composite fiber was produced in accordance with the method described in Example 1, except the CO2 addition was started after starting the addition of the calcium hydroxide slake. It was found that the order of addition of the CO2 addition and slake did not impact the composite fiber features and significantly, control over pH prior to calcium hydroxide slake was not needed to obtain good fiber properties. The table below provides a comparison of fiber properties made in accordance with Example 1 (CO2 addition before slake) and the present Example 2 (CO2 addition after slake addition). Both examples were produced maintain 50% saturation in the heel within 1% of the total reaction time.
Composite fibers produced in accordance with Example 1 was tested in the production of a copy paper hand-sheet. The composite fiber of the disclosure was compared to standard precipitated calcium carbonate, and a method in which nanocellulose was added to furnish.
The conventional nanocellulose containing precipitated calcium carbonate was formed by adding nanocellulose as a precursor additive to the calcium hydroxide slurry prior to passing CO2 gas through it to precipitate calcium carbonate at 100% saturation. Referring to
The copy paper handsheets were prepared with eucalyptus pulp refined to 400 Canadian Standard Freeness. The handsheets were produced at a target basis weight of 80 gsm. Filler amounts were adjusted to achieve a target level of 15, 25, 35, or 50%. The additives were added, as follows: cationic starch (Stalok 310) at 3 kg/tonne of paper, filler at target level, retention aid (Percol 175) at 0.01 kg/tonne of papers. All chemicals were added on a dry-on-dry basis. The handsheets were formed on a Formax (Nobel and Wood) sheet former. They were pressed at 4 psi while the sheet was still on the forming wire sandwiched between pieces of paper machine felt material. The handsheets were then removed from the forming wire and sandwiched between two pieces of unsized blotting paper and pressed at 25 psi. The handsheets were then dried for 1 min at 125° C. on a drum dryer. Finally, the handsheets were conditioned at 23° C. and 50% relative humidity.
The composite fiber of the disclosure demonstrated an unexpected improvement in both bulking properties and strength. Referring to
To analyze the performance benefit imparted by the presence of the fiber, composite fibers were made in accordance with the method described in Example 1 (maintaining 50% saturation) and compared to precipitated calcium carbonate generated using the same method except no fiber was present in the heel. The properties of the resulting calcium carbonate produced with and without fiber are shown in the table below:
It was found that without the nanocellulose present, the precipitated calcium carbonate was in the form of non-fibrous large calcium carbonate structures, such as shown in
Large scale production of composites in accordance with the disclosure was produced using nanocellulose produced at the University of Maine. The nanocellulose had an average fiber length of 224 μm, a fiber width of 21.9 μm. The product had 74.7% fines, a Kink Index of 1.2, a Kink angle of 13.96, and a mean curl of 0.114.
The slake was prepared by diluting lime to a target slake solids of 15-17% and prepared by screening through a 60 mesh screen, and then drained to 470 gallons. The slake was held at about 50-55° C. using heating coils in a slake holding tank.
Water was added to the reactor and heated to the target starting temperature if needed. The starting temperature was 11° C., 25° C. or 40° C. Once the target starting temperature was reached, the water was drained to 202 gallons as the target starting volume. The water was agitated at half speed and Aqua nanocellulose was added at an addition amount of 0.5 wt % dry nanocellulose on a dry total final product weight based on the slake volume and slake concentration (MO). The agitation was then turned up to full speed and the aqueous fiber containing heel was mixed for 5 minutes.
CO2 containing gas was flowed into the reactor as a blend of CO2 and air at target flow rates specified in the table below. Once the gases reach their full flow rates, the slake addition was pumped into the reactor from the slake holding tank using a Moyno pump. The slake was added at a rate to maintain about 50% saturation, which was a conductivity value of 3.0-3.5 ms/cm, or about 70% saturation, which was conductivity value of 4.0-4.5 ms/cm. Once all of the slake was added, the reaction mixture was gassed until reaching pH 7.0. 1-liter and 5 gallon samples were collected for characterization.
A comparative sample in which no fiber was added was also produced using the same procedure except no fiber was added to the aqueous heel. The conditions tested and resulting calcium carbonate properties are shown in the table below.
Modifications and other embodiments disclosed herein will come to mind to one skilled in the art to which the disclosed compositions and methods pertain having the benefit of the teachings presented in the foregoing descriptions. Therefore, it is to be understood that the disclosures are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. As used in the specification and in the claims, the term “comprising” can include the aspect of “consisting of.” Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed compositions and methods belong. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined herein.
As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.
The use of the terms “a,” “an,” “the,” and similar referents in the context of the disclosure herein (especially in the context of the claims) are to be construed to cover both the singular and the plural, unless otherwise indicated. Recitation of ranges of values herein merely are intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended to better illustrate the disclosure herein and is not a limitation on the scope of the disclosure herein unless otherwise indicated. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the disclosure herein.
The benefit of priority to U.S. Provisional Patent Application No. 63/326,240 filed Mar. 31, 2022, is hereby claimed and the disclosure is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2023/016399 | 3/27/2023 | WO |
