阅读说明：本技术 处理微纤化纤维素的方法 (Method for treating microfibrillated cellulose ) 是由 K·李 G·泰利耶 F·J·G·贝肯 戴维·罗伯特·斯丘斯 于 2014-03-14 设计创作，主要内容包括：本发明涉及一种改善微纤化纤维素的纸耐破强度增强属性的方法,和包含如此获得的微纤化纤维素的水性悬浮液。(The present invention relates to a method for improving the paper burst strength enhancing properties of microfibrillated cellulose, and to an aqueous suspension comprising microfibrillated cellulose thus obtained.)

1. A method of improving the paper burst strength enhancing properties of microfibrillated cellulose, the method comprising: subjecting an aqueous suspension comprising microfibrillated cellulose to high shear, wherein the high shear is at least partially generated by a moving shearing element, thereby improving the paper burst strength enhancing properties of the microfibrillated cellulose,

wherein, prior to high shear, the microfibrillated cellulose fibers d of the aqueous suspension comprising microfibrillated cellulose₅₀At least 50 μm and a fiber steepness of 20 to 50;

wherein, the high shear means that the shear rate is 10,000s^-1～120,000s^-1；

Wherein the paper burst strength enhancing properties of the microfibrillated cellulose after the high shear are increased by at least 1% for a paper product made from a papermaking composition comprising the microfibrillated cellulose made after the high shear compared to a comparative paper product comprising an equivalent amount of microfibrillated cellulose before the high shear.

2. The method of claim 1, wherein the aqueous suspension further comprises an inorganic particulate material.

3. The method of claim 1, wherein the moving shearing element is housed in a high shear rotor/stator mixing device, and the method comprises subjecting the aqueous suspension comprising microfibrillated cellulose to high shear in the rotor/stator mixing device to improve the paper burst strength enhancing properties of the microfibrillated cellulose.

4. The method of claim 2, wherein the moving shearing element is housed in a high shear rotor/stator mixing device, and the method comprises subjecting the aqueous suspension comprising microfibrillated cellulose and inorganic particulate material to high shear in the rotor/stator mixing device to improve the paper burst strength enhancing properties of the microfibrillated cellulose.

5. The method of claim 1, wherein the aqueous suspension comprising microfibrillated cellulose is obtained by a process comprising the steps of: microfibrillating a fibrous substrate comprising cellulose in an aqueous environment in the presence of a grinding medium.

6. The method according to claim 2, wherein the aqueous suspension comprising microfibrillated cellulose is obtained by a process comprising the steps of: microfibrillating a fibrous substrate comprising cellulose in an aqueous environment in the presence of an inorganic particulate material.

7. The method of claim 2, wherein the inorganic particulate material is selected from the group consisting of: an alkaline earth metal carbonate or sulfate; hydrated kaolinite group clays; anhydrous kaolinite group clays, talc, mica, perlite, diatomaceous earth; magnesium hydroxide; aluminum trihydrate; or a combination thereof.

8. The process of claim 7, wherein the alkaline earth carbonate or sulfate is selected from calcium carbonate, magnesium carbonate, dolomite or gypsum; the hydrous kaolinite group clay is selected from kaolinite, halloysite or ball clay; the anhydrous kaolinite group clay is selected from metakaolin or fully calcined kaolin.

9. The method of claim 8, wherein the calcium carbonate is selected from natural calcium carbonate or precipitated calcium carbonate.

10. The method of claim 7, wherein (i) the inorganic particles are calcium carbonate; or (ii) the inorganic particulate material is kaolin.

11. The process of claim 10 wherein (i) the inorganic particles are calcium carbonate and at least 50% by weight of the calcium carbonate has an equivalent spherical diameter of less than 2 μ ι η; or (ii) the inorganic particulate material is kaolin, and at least 50% by weight of the kaolin has an equivalent spherical diameter of less than 2 μm.

12. A process according to claim 1 or 2, wherein the microfibrillated cellulose fibres d are, after high shear₅₀The reduction is at least 5%.

13. A process according to claim 1 or 2, wherein the microfibrillated cellulose fibres d are, after high shear₅₀The reduction is at least 10%.

14. A process according to claim 1 or 2, wherein the microfibrillated cellulose fibres d are, after high shear₅₀The reduction is at least 50%.

15. The method of claim 1 or 2, wherein the microfibrillated cellulose has an increase in paper burst strength enhancing properties of at least 5% after high shear.

16. The method of claim 1 or 2, wherein the microfibrillated cellulose has an increase in paper burst strength enhancing properties of at least 10% after high shear.

17. The method of claim 1, wherein the aqueous suspension comprising microfibrillated cellulose is stirred in a mixing tank before and/or during the method.

18. An aqueous suspension comprising microfibrillated cellulose obtainable by the process of any one of claims 1 to 17.

19. The aqueous suspension of claim 18, further comprising an inorganic particulate material.

Technical Field

The present invention relates to a method for modifying the paper burst strength enhancing properties of microfibrillated cellulose, an aqueous suspension comprising said microfibrillated cellulose, and a papermaking composition and a paper product comprising said microfibrillated cellulose.

Background

Mineral fillers are often added in the manufacture of paper. While this may in some cases reduce the mechanical strength of the paper (i.e., relative to paper made from pure fiber pulp), it is tolerable because the mechanical strength (although reduced) is still acceptable and has cost, quality, and environmental benefits as the amount of fiber in the paper can be reduced. A common property used to evaluate the mechanical strength of paper is paper burst strength. Generally, paper made from pure fiber pulp will have higher paper burst strength than comparative paper in which a portion of the fiber pulp is replaced with mineral filler. The paper burst strength of filled paper can be expressed as a percentage of the paper burst strength of unfilled paper.

WO-A-2010/131016 discloses A process for preparing microfibrillated cellulose which comprises microfibrillating A fibrous material comprising cellulose (e.g. by grinding), optionally in the presence of A grinding medium and an inorganic particulate material. When used as a filler in paper, for example, as an alternative or partial alternative to conventional mineral fillers, it has been unexpectedly found that microfibrillated cellulose obtained by the above process (optionally together with inorganic particulate material) can improve the burst strength properties of the paper. In other words, the paper filled with microfibrillated cellulose was found to have improved burst strength compared to paper filled with mineral filler only. In other words, it was found that the microfibrillated cellulose filler has paper burst strength enhancing properties. In a particularly advantageous embodiment of the invention, the fibrous material comprising cellulose is milled in the presence of milling media, optionally together with inorganic particulate material, to obtain microfibrillated cellulose having a fibre steepness of 20 to about 50.

Although the microfibrillated cellulose obtainable by the process described in WO-A-2010/131016 has shown advantageous paper burst strength enhancing properties, it would be desirable to be able to modify (e.g. further improve) one or more of the paper property enhancing properties of the microfibrillated cellulose, e.g. the paper burst strength enhancing properties of the microfibrillated cellulose.

Disclosure of Invention

According to a first aspect, there is provided a method of treating microfibrillated cellulose, the method comprising subjecting an aqueous suspension comprising microfibrillated cellulose and optionally inorganic particulate material to high shear, wherein the high shear is at least partially caused by a moving shearing element. The treatment advantageously alters (e.g., improves) the paper property enhancing properties of the microfibrillated cellulose, e.g., the paper burst strength enhancing properties of the microfibrillated cellulose.

According to a second aspect, the method of the first aspect further comprises preparing a papermaking composition comprising microfibrillated cellulose and optionally inorganic particulate material, obtainable by the method of the first aspect.

According to a third aspect, the method of the second aspect further comprises preparing a paper product from the above-described papermaking composition.

According to a fourth aspect, there is provided an aqueous suspension comprising microfibrillated cellulose and optionally inorganic particulate material, obtainable by the process of the first aspect of the present invention.

According to a fifth aspect, there is provided a papermaking composition obtainable by the process of the second aspect of the present invention.

According to a sixth aspect, there is provided a paper product obtainable by the process of the third aspect of the invention, wherein the first paper property (e.g. burst strength) of the paper product is greater than the second paper property (e.g. burst strength) of a comparative paper product comprising an equivalent amount of microfibrillated cellulose prior to high shear.

Drawings

Fig. 1 is a schematic plan view of a rotor/stator configuration suitable for use in the present invention.

Fig. 2 is a schematic plan view of another rotor/stator configuration suitable for use with the present invention.

Fig. 3 is a schematic illustration of an integrated process for making microfibrillated cellulose with altered (e.g., improved) paper burst strength enhancing properties.

Detailed Description

A method of treating microfibrillated cellulose comprises subjecting an aqueous suspension comprising microfibrillated cellulose and optionally inorganic particulate material to high shear, wherein the high shear is at least partially generated by a moving shearing element. This treatment may advantageously alter (e.g., improve) the paper property enhancing properties of the microfibrillated cellulose. The paper properties may be mechanical and/or optical properties. In some embodiments, the paper property is a mechanical property.

In some embodiments, the method is for modifying (e.g., improving) the paper burst strength enhancing properties of microfibrillated cellulose and comprises subjecting an aqueous suspension comprising microfibrillated cellulose and optionally inorganic particulate material to high shear, wherein the high shear is at least partially created by moving shear elements to modify the paper burst strength enhancing properties of the microfibrillated cellulose.

As used herein, the term "high shear" refers to subjecting an aqueous suspension comprising microfibrillated cellulose to shear sufficient to treat the microfibrillated cellulose to alter (e.g., improve) the paper property-enhancing properties of the microfibrillated cellulose. In some embodiments, the microfibrillated cellulose is subjected to high shear sufficient to alter (e.g., improve) the paper burst strength enhancing properties of the microfibrillated cellulose. Advantageously, the aqueous suspension comprising microfibrillated cellulose is subjected to shear sufficient to improve the paper property enhancing properties of the microfibrillated cellulose (e.g. the paper burst strength enhancing properties of the microfibrillated cellulose). One skilled in the art will be able to determine by conventional means a shear sufficient to improve the paper property enhancing properties of the microfibrillated cellulose (e.g. the paper burst strength enhancing properties of the microfibrillated cellulose), for example by comparing the paper property enhancing properties of the microfibrillated cellulose before the shear treatment (e.g. the paper burst strength enhancing properties of the microfibrillated cellulose) and the paper property enhancing properties of the microfibrillated cellulose after the shear treatment (e.g. the paper burst strength enhancing properties of the microfibrillated cellulose) in a suitably controlled manner. Further details of such analysis are provided in the examples below.

In some embodiments, the paper property is selected from one or more of the following properties: burst strength, burst index, tensile strength, z-direction (internal (Scott) bond) strength, tear strength, porosity, smoothness, and opacity.

A moving shearing element is a component or assembly that at least partially produces mechanical shear. As used herein, "mechanical shear" refers to shear produced by the action of moving mechanical parts or components on a material to be subjected to shear, and further refers to shear produced in the substantial absence of a pressure drop. An example of a device that relies on shear generated by pressure drop is a homogenizer. Typically, in such devices, the feed travels from a high pressure zone to a low pressure zone through a valve (sometimes referred to as a homogenizing valve) having an adjustable but fixed gap. Thus, there are no moving shearing elements in the homogenizer that apply shear directly to the material.

In some embodiments, shear is generated by the action of a moving mechanical part or component and a complementary stationary (i.e., stationary) part or component, wherein the moving mechanical part or component and/or the complementary stationary part or component has more than one aperture, such as more than 100 apertures, or more than 1000 apertures. In some embodiments, at least complementary fixation components or assemblies have more than one aperture, such as more than 100 apertures, or more than 1000 apertures.

In some embodiments, the term "high shear" refers to a shear rate of at least about 10,000s^-1For example, the rate is about 10,000s^-1About 120,000s^-1Or 20,000s^-1About 120,000s^-1Or 40,000s^-1About 110,000s^-1Or 60,000s^-1About 100,000s^-1Or 70,000s^-1About 90,000s^-1Or 75,000s^-1About 85,000s^-1。

In some embodiments, the mobile shearing element is a component or assembly of a high shear mixing device. The moving shear element is housed in a high shear mixing device and applies shear directly to the microfibrillated cellulose. In some embodiments, the moving shear element is a rotor having a mixing unit at one end, the mixing unit is housed within or positioned adjacent to a stationary non-moving part or compartment (e.g., a stator), and the mixing unit rotates about a central axis within the stationary part or compartment and applies shear directly to the microfibrillated cellulose. The rotational speed of the rotor and hence of the mixing unit is sufficient to generate high shear. The mixing unit may have any suitable form including, for example, a plurality of teeth arranged about the central axis of the rotor, or an impeller or paddle, etc.

In some embodiments, the stationary part or compartment is a cylindrical stator with a diameter larger than the radial length of the mixing unit, such that there is a gap, sometimes referred to as a close clearance, between the tip of the mixing unit and the inner surface of the stator when the mixing unit rotates around the central axis of the rotor. Referring to fig. 1, fig. 1 is a schematic view (plan view) of an exemplary rotor/stator configuration, the radius R of the stator (1)₁Is greater than the radial length of the rotor blades (3) placed around the central axis (5) of rotation of the rotor (7), thereby creating a gap (9). The gap is small enough so that a high shear zone is formed in which the microfibrillated cellulose is subjected to further shear, which is high enough to alter (e.g. improve) the paper burst strength enhancing properties of the microfibrillated cellulose. In some embodiments, the gap is less than about 1mm, for example, less than about 0.9mm, or less than about 0.8mm, or less than about 0.7mm, or less than about 0.6mm, or less than about 0.5 mm. The gap may be greater than about 0.1 mm. Shear is the speed difference between the stator and rotor divided by the gap size between the stator and rotor.

Thus, in some embodiments, a method of modifying (e.g., improving) the paper burst strength enhancing properties of microfibrillated cellulose comprises subjecting the aqueous suspension comprising microfibrillated cellulose and optionally inorganic particulate material to high (mechanical) shear in a high shear mixing device, wherein the shear is generated at least in part by the moving shearing element to modify the paper burst strength enhancing properties of microfibrillated cellulose. In some embodiments, the high shear mixing device is a high shear stator/rotor mixing device.

In some embodiments, further shear events are generated by using the following stators: the stator has a series of perforations (e.g., machined holes, slots, or cuts) around its cylindrical boundary through which the aqueous suspension containing microfibrillated cellulose is forced by the action of the stator and mixing unit. Another rotor/stator configuration is depicted in fig. 2 (plan view). In this construction, the rotor (17) has a peripheral surface surrounding the rotorThe plurality of teeth (13) aligned on the central axis (15) serve as a mixing unit. The stator (11) has a series of cut-outs (21) around its cylindrical boundary. Likewise, the radial length R of the stator (11)₁Is greater than the radial length of the plurality of teeth (13), thereby creating a gap (19).

Suitable high shear mixing devices are various and include, but are not limited to: batch high shear mixers, tandem high shear mixers, and ultra high shear tandem mixers. An exemplary high shear mixing device is a silverson (rtm) high shear in-line mixer manufactured by silverson (rtm). Other exemplary rotor/stator configurations include those manufactured by kinematica (rtm) AG, such as those sold under the trademark megatron (rtm), and the Kady mill manufactured by Kady International. Another exemplary high shear mixing device is a super fine particle mill (supermasscolloid) having moving mechanical parts and complementary stationary parts for generating shear, wherein either the moving mechanical parts or the complementary stationary parts have only one opening.

In some embodiments, the high speed rotation of the rotor generates a strong suction force that draws the aqueous suspension feed containing microfibrillated cellulose into a stationary compartment, such as a stator. As the sheared material is withdrawn from the stator, for example by extrusion through holes, slots or slits around the cylindrical periphery of the stator, fresh feed is drawn (optionally continuously) into the stator, maintaining a mixing cycle.

The aqueous suspension comprising microfibrillated cellulose may be subjected to high shear for a period of time and/or total energy input sufficient to alter (e.g., improve) the paper burst strength enhancing properties of the microfibrillated cellulose, or any other paper property enhancing properties described herein. In some embodiments, the period of time is from about 30 seconds to about 10, for example, from about 30 seconds to about 8 hours, or from about 30 seconds to about 5 hours, or from about 30 seconds to about 4 hours, or from about 30 seconds to about 3 hours, or from about 30 seconds to about 2 hours, or from about 1 minute to about 2 hours, or from about 5 minutes to about 2 hours, or from about 10 minutes to about 2 hours, or from about 15 minutes to about 2 hours, or from about 20 minutes to about 100 minutes, or from about 25 minutes to about 90 minutes, or from about 30 minutes to about 90 minutes, or from about 35 minutes to about 90 minutes, or from about 40 minutes to about 90 minutes, or from about 45 minutes to about 90 minutes.

In some embodiments, the total energy input is from about 1 kWh/ton (kWh/t) to about 10,000kWh/t, e.g., from about 50kWh/t to about 9,000kWh/t, or from about 100kWh/t to about 8,000kWh/t, or from about 100kWh/t to about 7,000kWh/t, or from about 100kWh/t to about 6,000kWh/t, or from about 500kWh/t to about 5,000kWh/t, or from about 1000kWh/t to about 5,000kWh/t, or from about 1500kWh/t to about 5,000kWh/t, or from about 2000kWh/t to about 5,000kWh/t, based on the total dry weight of cellulosic material in the aqueous suspension comprising the fibrillated cellulose and, optionally, inorganic particulate material.

In some embodiments, the total energy input is from about 100kWh/t to about 5,000 kWh/t.

The total energy input E during high shear can be calculated from the following equation:

E＝P/W (1)

wherein E is the total energy input (kWh/t) per ton of cellulosic material in the aqueous suspension comprising microfibrillated cellulose, P is the total energy input (kWh), and W is the total dry weight (ton) of cellulosic material.

In some embodiments, the microfibrillated cellulose is subjected to more than one stage of high shear, e.g., multiple (more than two) passes through the high shear mixing device. For example, the aqueous suspension may be subjected to high shear for a first period of time according to the process described above, sent to an intermediate zone (e.g., a mixing tank) that operates without shearing the microfibrillated cellulose, and then subjected to high shear for a second period of time, and so on. In some embodiments, the above process is a continuous process in which a feed of the aqueous suspension comprising microfibrillated cellulose is continuously fed (e.g., from a mixing tank) to a high shear mixing device, subjected to high shear, withdrawn from the high shear mixing device and recycled back into the mixing tank, then recycled back into the high shear mixing device, and so on. The microfibrillated cellulose-containing product, which has altered (e.g., improved) paper burst strength enhancing properties, may be withdrawn from any stage of the process, for example, via a product withdrawal point (e.g., a discharge valve located between the mixing tank and the high shear mixing device). Typically, the aqueous suspension comprising microfibrillated cellulose is circulated at a constant flow rate and the product is periodically withdrawn, for example at intervals of 5 minutes, and/or 10 minutes, and/or 15 minutes, and/or 20 minutes, and/or 25 minutes, and/or 30 minutes, and/or 35 minutes, and/or 40 minutes, and/or 45 minutes, and/or 50 minutes, and/or 55 minutes, and/or 60 minutes, and/or 65 minutes, and/or 70 minutes, and/or 75 minutes, and/or 80 minutes, and/or 90 minutes, and/or 100 minutes, and/or 110 minutes, and/or 120 minutes.

In some embodiments, the high shear treatment may be performed in a high shear device cascade, such as a high shear rotor/stator mixing device cascade (e.g., two or three or four or five or six or seven or eight or nine or ten high shear rotor/stator mixing devices operatively connected in series, parallel, or a combination of series and parallel). The output and/or input of one or more high shear vessels in the cascade may be subjected to one or more screening steps and/or one or more fractionation steps.

In some embodiments, the high shear treatment may be carried out in a single high shear device, for example, in a single high shear rotor/stator mixing apparatus having a plurality (i.e., at least two) high shear zones that are operationally distinct. For example, a suitable high shear rotor/stator mixing device may have multiple high shear zones, each with its own rotor/stator.

In some embodiments, the aqueous suspension comprising microfibrillated cellulose and optional inorganic particulate material has a solids content of no greater than about 25 wt%, for example, a solids content of about 0.1 wt% to about 20 wt%, or about 0.1 wt% to about 18 wt%, or about 2 wt% to about 16 wt%, or about 2 wt% to about 14 wt%, or about 4 wt% to about 12 wt%, or about 4 wt% to about 10 wt%, or about 5 wt% to about 9 wt%, or about 5 wt% to about 8.5 wt%, based on the total weight of the aqueous suspension. At any stage of the process, additional water may be added to vary the solids content of the aqueous suspension comprising microfibrillated cellulose and optionally inorganic particulate material.

In some embodiments, the aqueous suspension comprising microfibrillated cellulose has a fiber solids content of no greater than about 8% by weight.

The microfibrillated cellulose may be derived from any suitable source. In some embodiments, the composition comprising microfibrillated cellulose can be obtained by a process comprising microfibrillating a fibrous substrate comprising cellulose in the presence of a grinding medium. Advantageously, the process is carried out in an aqueous environment.

In some embodiments, the composition comprising microfibrillated cellulose and optionally inorganic particulate material can be obtained by a process comprising grinding a fibrous substrate comprising cellulose in the presence of grinding media and optionally said inorganic particulate material. In some embodiments, the aqueous suspension comprises microfibrillated cellulose and inorganic particulate material, and the aqueous suspension can be obtained by a method comprising grinding a fibrous substrate comprising cellulose in the presence of a grinding medium and inorganic particulate material. Suitable methods are described in WO-A-2010/131016, the entire contents of which are hereby incorporated by reference.

"microfibrillation" refers to a process in which microfibrils of cellulose are released or partially released, either as individual species or as aggregates smaller than the fibers of the slurry before microfibrillation. Common cellulosic fibers suitable for use in papermaking (i.e., pre-microfibrillated pulp) include large aggregates of hundreds or thousands of individual cellulosic fibers. By microfibrillating cellulose, particular characteristics and properties, including those described herein, can be imparted to microfibrillated cellulose and compositions comprising the microfibrillated cellulose.

In some embodiments, microfibrillation is carried out in the presence of grinding media used to promote microfibrillation of the cellulose prior to microfibrillation. Additionally, when present, the inorganic particulate material may act as a microfibrillating agent, i.e., when the cellulosic starting material undergoes co-processing (e.g., co-milling) in the presence of the inorganic particulate material, it can be microfibrillated with relatively low energy input. In some embodiments, microfibrillation is performed by other procedures known in the art, including procedures that are not performed in the presence of grinding media.

The fibrous substrate comprising cellulose may be from any suitable source, such as wood, grass (e.g. sugar cane, bamboo) or worn cloth (e.g. textile waste, cotton, hemp or flax). The cellulosic containing fibrous substrate may be in the form of a slurry (e.g., a suspension of cellulosic fibers in water) that may be prepared by any suitable chemical or mechanical treatment, or combination thereof. For example, the pulp may be a chemical pulp, or a chemical thermomechanical pulp, or a mechanical pulp, or a recycled pulp, or paper mill broke, or a paper mill waste stream, or a paper mill waste, or a combination thereof. The cellulose pulp may be beaten (e.g., in a wary pulper) and/or otherwise refined (e.g., processed in a cone or disc refiner) to any predetermined freeness, which may be in the art using Canadian Standard Freeness (CSF) (in cm)³In units) to report. CSF refers to the value of freeness or drainage rate measured using the rate at which a slurry suspension can be drained. For example, the cellulose pulp may have about 10cm before being microfibrillated³The above canadian standard freeness. The cellulose pulp may have about 700cm³CSF, e.g., equal to or less than about 650cm³Or equal to or less than about 600cm³Or equal to or less than about 550cm³Or equal to or less than about 500cm³Or equal to or less than about 450cm³Or equal to or less than about 400cm³Or equal to or less than about 350cm³Or equal to or less than about 300cm³Or equal to or less than about 250cm³Or equal to or less than about 200cm³Or equal to or less than about 150cm³Or equal to or less than about 100cm³Or equal to or less than about 50cm³. The cellulose pulp may then be dewatered by methods well known in the art, e.g., the pulp may be filtered through a screen to obtain a wet sheet comprising at least about 10% solids, e.g., at least about 15% solids, or at least about 20% solids, or at least about 30% solids% solids, or at least about 40% solids. The slurry may be used in an unrefined state (in other words, not beaten or dewatered or otherwise refined).

The fibrous substrate comprising cellulose may be added to the grinding vessel in a dry state. For example, dried waste paper may be added directly to the grinding vessel. The aqueous environment in the grinding vessel will then facilitate the formation of the slurry.

The microfibrillating step may be carried out in any suitable apparatus, including but not limited to a refiner. In one embodiment, the microfibrillating step is carried out in a grinding vessel under wet grinding conditions. In another embodiment, the microfibrillating step is carried out in a homogenizer.

● Wet grinding

The milling is a friction milling process in the presence of particulate milling media. Grinding media refers to media other than inorganic particulate materials that are optionally co-ground with a fibrous substrate comprising cellulose. It is understood that the grinding media are removed after grinding is complete.

In certain embodiments, the microfibrillation process (e.g., milling) is carried out in the absence of a millable inorganic particulate material.

The particulate grinding media may be natural or synthetic materials. The grinding media may comprise, for example, balls, beads or pellets of any hard mineral, ceramic or metallic material. The material may include, for example, alumina, zirconia, zirconium silicate, aluminum silicate, mullite, or a mullite-rich material produced by calcining kaolinite clay at a temperature of about 1300 ℃ to about 1800 ℃.

In certain embodiments, the particulate grinding media comprises particles having an average diameter of from about 0.1mm to about 6.0mm, more preferably from about 0.2mm to about 4.0 mm. The grinding media(s) may be present in an amount up to about 70% by volume of the charge. The grinding media may be present in an amount of at least about 10% by volume of the charge, for example at least about 20% by volume of the charge, or at least about 30% by volume of the charge, or at least about 40% by volume of the charge, or at least about 50% by volume of the charge, or at least about 60% by volume of the charge. In certain embodiments, the grinding media is present in an amount from about 30% to about 70% by volume of the charge, such as from about 40% to about 60% by volume of the charge, such as from about 45% to about 55% by volume of the charge.

"charge" refers to the composition as a feed to the polishing vessel. The charge comprises water, grinding media, a fibrous substrate comprising cellulose, and inorganic particulate material, and any other optional additives as described herein.

In certain embodiments, the grinding media is media comprising particles having an average diameter of about 0.5mm to about 12mm, for example, about 1mm to about 9mm, or about 1mm to about 6mm, or about 1mm, or about 2mm, or about 3mm, or about 4mm, or about 5 mm.

The specific gravity of the grinding media can be at least about 2.5, for example, at least about 3, or at least about 3.5, or at least about 4.0, or at least about 4.5, or at least about 5.0, or at least about 5.5, or at least about 6.0.

In certain embodiments, the grinding media comprises particles having an average diameter of about 1mm to about 6mm and a specific gravity of at least about 2.5.

In certain embodiments, the grinding media comprises particles having an average diameter of about 3 mm.

In one embodiment, the average particle size (d) of the inorganic particulate material₅₀) Reduced during the co-grinding process. E.g. of inorganic particulate material₅₀Can be reduced by at least about 10% (as measured by conventional methods well known and used in the laser light scattering arts using a Malvern Mastersizer S machine), e.g., the d of the inorganic particulate material₅₀May be reduced by at least about 20%, or by at least about 30%, or by at least about 40%, or by at least about 50%, or by at least about 60%, or by at least about 70%, or by at least about 80%, or by at least about 90%. E.g. before co-grinding d₅₀Co-ground to 2.5 μm₅₀Is 1.5 μm, and the particle diameter thereof undergoes a 40% reduction. In certain embodiments, the average particle size of the inorganic particulate material is not significantly reduced during the co-milling process. By "not significantly reduced" is meant co-investigationD of inorganic particulate material during grinding₅₀Reduced by less than about 10%, e.g. d of inorganic particulate material₅₀Less than about 5%.

The fibrous substrate comprising cellulose may be microfibrillated to obtain d as measured by laser light scattering₅₀Microfibrillated cellulose of about 5 μm to about 500 μm. The fibrous substrate comprising cellulose may be microfibrillated to obtain d₅₀Microfibrillated cellulose of equal to or less than about 400 μm, e.g. d₅₀Equal to or less than about 300 μm, or equal to or less than about 200 μm, or equal to or less than about 150 μm, or equal to or less than about 125 μm, or equal to or less than about 100 μm, or equal to or less than about 90 μm, or equal to or less than about 80 μm, or equal to or less than about 70 μm, or equal to or less than about 60 μm, or equal to or less than about 50 μm, or equal to or less than about 40 μm, or equal to or less than about 30 μm, or equal to or less than about 20 μm, or equal to or less than about 10 μm.

In some embodiments, the microfibrillated cellulose of the aqueous suspension before being subjected to high shear has a fiber d₅₀Is at least about 50 μm, for example, at least about 75 μm, or at least about 100 μm, or at least about 110 μm, or at least about 120 μm, or at least about 130 μm, or at least about 140 μm, or at least about 150 μm. In some embodiments, the microfibrillated cellulose of the aqueous suspension before being subjected to high shear has a fiber d₅₀From about 100 μm to about 160 μm, for example, from about 120 μm to about 160 μm. In general, the fibers d of the cellulose are microfibrillated in a high shear process₅₀The reduction will be, for example, at least about 1%, or at least about 5%, or at least about 10%, or at least about 20%, or at least about 30%, or at least about 40%, or at least about 50%. For example, pre-high shear fiber d₅₀120 μm and post-high shear fiber d₅₀Microfibrillated cellulose at 108 μm will be referred to as fiber d having undergone 10%₅₀And decreases.

The fibrous substrate comprising cellulose may be microfibrillated in the presence of inorganic particulate material to obtain microfibrillated cellulose having a fibre steepness equal to or greater than about 10 as measured by Malvern. The fiber steepness (i.e., the steepness of the particle size distribution of the fibers) is determined by the following formula: steepness 100 in yield(d₃₀/d₇₀)。

The microfibrillated cellulose may have a fiber steepness equal to or less than about 100. The microfibrillated cellulose may have a fiber steepness of equal to or less than about 75, or equal to or less than about 50, or equal to or less than about 40, or equal to or less than about 30. The microfibrillated cellulose may have a fiber steepness of about 20 to about 50, or about 25 to about 40, or about 25 to about 35, or about 30 to about 40.

In some embodiments, the microfibrillated cellulose of the aqueous suspension has a fiber steepness of about 25 to about 50.

The procedure for determining the particle size distribution of minerals and microfibrillated cellulose is described in WO-A-2010/131016. In particular, suitable procedures are described in WO-A-2010/131016, page 40, line 32 to page 41, line 34.

The grinding can be carried out in a vertical mill or a horizontal mill.

In some embodiments, milling is carried out in a milling vessel, such as a roller mill (e.g., rod, ball, and autogenous), a stirred mill (e.g., SAM or IsaMill), a tower mill, a stirred media crusher (SMD), or a milling vessel comprising rotating parallel milling plates between which the feed material to be milled is fed.

In one embodiment, the grinding vessel is a vertical mill, such as an agitated mill, or an agitated media breaker, or a tower mill.

The vertical mill may comprise a screen positioned above one or more grinding zones. In one embodiment, the screen is positioned adjacent to the quiescent zone and/or the classifier. The screen is sized to separate the aqueous product suspension containing microfibrillated cellulose and inorganic particulate material from the grinding media and to promote the settling of the grinding media.

In another embodiment, the milling is carried out in a screen mill (e.g., a stirred media mill). The screen mill may comprise one or more screens sized to separate the grinding media from the product, i.e., the aqueous suspension comprising microfibrillated cellulose and inorganic particulate material.

In certain embodiments, the fibrous substrate comprising cellulose and the inorganic particulate material are present in the aqueous environment at an initial solids content of at least about 4% by weight, of which at least about 2% by weight is the fibrous substrate comprising cellulose. The initial solids content may be at least about 10 wt.%, or at least about 20 wt.%, or at least about 30 wt.%, or at least about at least 40 wt.%. At least about 5% by weight of the initial solids content can be a fibrous substrate comprising cellulose, for example, at least about 10% by weight, or at least about 15% by weight, or at least about 20% by weight of the initial solids content can be a fibrous substrate comprising cellulose. Generally, the relative amounts of the fibrous substrate comprising cellulose and the inorganic particulate material are selected to obtain a composition comprising microfibrillated cellulose and inorganic particles according to the first aspect of the present invention.

The milling process may include a pre-milling step in which the coarse inorganic particles are milled in a milling vessel to a predetermined particle size distribution, after which the fibrous substrate comprising cellulose is combined with the pre-milled inorganic particulate material and milling is continued in the same or another milling vessel until the desired level of microfibrillation is obtained.

Since suspensions of the material being ground may have a relatively high viscosity, suitable dispersing agents may be added to the suspension before or during grinding. The dispersant may be, for example, a water-soluble condensed phosphate ester, polysilicic acid or salt thereof, or a polyelectrolyte, such as a water-soluble salt of poly (acrylic acid) or poly (methacrylic acid) having a number average molecular weight of no more than 80,000. The amount of dispersant used is typically from 0.1 to 2.0% by weight based on the weight of dry inorganic particulate solid material. The suspension may be suitably milled at a temperature of from 4 ℃ to 100 ℃.

Other additives that may be included in the microfibrillating step include: hydroxymethyl cellulose, amphoteric hydroxymethyl cellulose, an oxidizing agent, 2,6, 6-tetramethylpiperidine-1-oxyl (TEMPO), TEMPO derivatives and wood degrading enzymes.

When present, the amount of inorganic particulate material and cellulosic pulp in the mixture to be co-mulled may vary from about 99.5:0.5 to about 0.5:99.5 based on the dry weight of the inorganic particulate material and the amount of dry fibers in the pulp, for example, from about 99.5:0.5 to about 50:50 based on the dry weight of the inorganic particulate material and the amount of dry fibers in the pulp. For example, the ratio of the amount of inorganic particulate material and dry fiber may be from about 99.5:0.5 to about 70: 30. In some embodiments, the weight ratio of inorganic particulate material to dry fibers is about 95: 5. In another embodiment, the weight ratio of inorganic particulate material to dry fiber is about 90: 10. In another embodiment, the weight ratio of inorganic particulate material to dry fiber is about 85: 15. In another embodiment, the weight ratio of inorganic particulate material to dry fiber is about 80: 20.

In an exemplary microfibrillation process, the total energy input per ton of dry fiber in a fibrous substrate comprising cellulose will be less than about 10,000kWh t^-1E.g. less than about 9000kWht^-1Or less than about 8000kWht^-1Or less than about 7000kWh t^-1Or less than about 6000kWh^-1Or less than about 5000kWht^-1E.g. less than about 4000kWht^-1Less than about 3000kWht^-1Less than about 2000kWht^-1Less than about 1500kWh^-1Less than about 1200kWht^-1Less than about 1000kWht^-1Or less than about 800kWht^-1. The total energy input varies depending on the amount of dry fibers in the fibrous substrate being microfibrillated and optionally the grinding speed and grinding time.

In some embodiments, the milling is performed in a cascade of milling vessels, one or more of which may comprise one or more milling zones. For example, a fibrous substrate comprising cellulose may be ground in a cascade of more than two grinding vessels, such as a cascade of more than three grinding vessels in series, or a cascade of more than four grinding vessels, or a cascade of more than five grinding vessels, or a cascade of more than six grinding vessels, or a cascade of more than seven grinding vessels, or a cascade of more than eight grinding vessels, or a cascade of more than nine grinding vessels, or a cascade comprising at most ten grinding vessels. The cascade of grinding vessels may be operatively connected in series, in parallel, or a combination of series and parallel. The output and/or input of one or more milling vessels in the cascade may be subjected to one or more screening steps and/or one or more classification steps.

In some embodiments, for example, in embodiments where the microfibrillated cellulose produced by microfibrillating (optionally in the presence of an inorganic particulate material) a fibrous substrate comprising cellulose in a batch process has a steep particle size distribution, the resulting (optionally co-processed) microfibrillated cellulose (and optionally inorganic particulate material) composition (i.e. microfibrillated cellulose-comprising product) having the desired microfibrillated cellulose steepness may be washed out of the microfibrillating apparatus (e.g. milling vessel) with water or any other suitable liquid.

The inorganic particulate material may be, for example, an alkaline earth metal carbonate or sulphate, such as calcium carbonate (e.g. natural calcium carbonate and/or precipitated calcium carbonate), magnesium carbonate, dolomite, gypsum; hydrated kaolinite group clays, such as kaolin, halloysite, or ball clays; anhydrous (calcined) kaolinitic clays, such as metakaolin or fully calcined kaolin, talc, mica, perlite or diatomaceous earth; or magnesium hydroxide; or aluminum trihydrate; or a combination thereof.

In certain embodiments, the inorganic particulate material comprises or is calcium carbonate. Hereinafter, the present invention will be discussed in terms of using calcium carbonate and in relation to processing and/or treating calcium carbonate. The present invention should not be construed as being limited to the embodiments.

The particulate calcium carbonate used in the present invention may be obtained from natural sources by grinding. Ground Calcium Carbonate (GCC) is generally obtained by: the mineral source, such as chalk, marble or limestone, is crushed and then ground, and may then be subjected to a size classification step to obtain a product with the desired fineness. Other techniques such as bleaching, flotation and magnetic separation can also be used to obtain a product having the desired fineness and/or color. The particulate solid material may be autogenously ground, i.e. ground by friction between the particles of the solid material itself, or alternatively, may be ground in the presence of a particulate grinding medium comprising particles of a material other than the calcium carbonate being ground. These processes may be performed in the presence or absence of dispersants and biocides, which may be added at any stage of the process.

Precipitated Calcium Carbonate (PCC) may be used as a source of particulate calcium carbonate in the present invention and may be produced by any known method known in the art. The 30 th topic "Paper Coating Pigments" of TAPPI, pages 34-35, describes three major commercial processes for the preparation of precipitated calcium carbonate (which is suitable for the preparation of products used in the Paper industry), which can also be used in the practice of the present invention. In all three processes, a calcium carbonate feed, such as limestone, is first calcined to produce quicklime, which is then slaked in water to produce calcium hydroxide or milk of lime. In the first process, milk of lime is carbonated directly using carbon dioxide gas. The process has the following advantages: no by-products are formed and the nature and purity of the calcium carbonate product is easier to control. In the second process, milk of lime is contacted with soda ash to produce a calcium carbonate precipitate and a sodium hydroxide solution by metathesis. If the process is to be used commercially, the sodium hydroxide can be substantially completely separated from the calcium carbonate. In the third major commercial process, milk of lime is first contacted with ammonium chloride to obtain a calcium chloride solution and ammonia gas. The calcium chloride solution is then contacted with soda ash to produce precipitated calcium carbonate and a sodium chloride solution by metathesis. The crystals can be produced in a variety of different shapes and sizes depending on the particular reaction process employed. The three main forms of PCC crystals are aragonite, rhombohedral and scalenohedral, all of which are suitable for use in the present invention, and mixtures thereof.

Wet grinding of calcium carbonate involves the formation of an aqueous suspension of calcium carbonate, which may then be ground, optionally in the presence of a suitable dispersant. Reference may be made, for example, to EP- ｃA-614948 (incorporated by reference in its entirety) for more information on the wet grinding of calcium carbonate.

In some cases, minor additions of other minerals may be included, for example one or more of kaolin, calcined kaolin, wollastonite, alumina, talc or mica may also be present.

When the inorganic particulate material is obtained from naturally occurring sources, there may be instances where some mineral impurities contaminate the milled material. For example, naturally occurring calcium carbonate may be present in combination with other minerals. Thus, in some embodiments, the inorganic particulate material comprises a certain amount of impurities. Typically, however, the inorganic particulate material used in the present invention contains less than about 5 wt%, preferably less than about 1 wt%, of other mineral impurities.

The particle size distribution of the inorganic particulate material may be such that at least about 10 wt%, such as at least about 20 wt%, for example at least about 30 wt%, such as at least about 40 wt%, for example at least about 50 wt%, for example at least about 60 wt%, for example at least about 70 wt%, for example at least about 80 wt%, for example at least about 90 wt%, for example at least about 95 wt%, or for example about 100% of the particles have an e.s.d of less than 2 μm.

In certain embodiments, at least about 50% by weight of the particles have an e.s.d of less than 2 μm, for example, at least about 55% by weight of the particles have an e.s.d of less than 2 μm, or at least about 60% by weight of the particles have an e.s.d of less than 2 μm.

Unless otherwise indicated, the particle size properties of the inorganic particulate materials referred to herein are measured in a well-known manner by settling the particulate material in an aqueous medium under conditions of complete dispersion using a Sedigraph 5100 machine, referred to herein as a "Micromeritics Sedigraph 5100 unit," provided by Micromeritics Instruments Corporation (Norcross, georgia, usa) (website: www.micromeritics.com). The machine provides a measurement and mapping of the cumulative weight percent of particles having a particle size (referred to in the art as the "equivalent spherical diameter" (e.s.d)) that is less than a given e.s.d value. Average particle diameter d₅₀Is the value of the e.s.d of the particles determined in this way, the equivalent spherical diameter being smaller than d₅₀The particles of value account for 50% by weight.

Alternatively, where mentioned, the particle size properties described herein for the inorganic particulate material are using Malvern supplied by Malvern Instruments LtdMastersizer S machine, by conventional methods well known in the art of laser light scattering (or by other methods that can provide substantially the same results). In laser scattering techniques, the size of particles in powders, suspensions and emulsions can be measured using laser beam diffraction based on the application of mie theory. The machine provides a measurement and mapping of the cumulative volume percentage of particles having a particle size (referred to in the art as the "equivalent spherical diameter" (e.s.d)) that is less than a given e.s.d value. Average particle diameter d₅₀Is the value of the e.s.d of the particles determined in this way, the equivalent spherical diameter being smaller than d₅₀The particles of value account for 50% by volume.

Thus, in another embodiment, the particle size distribution of the inorganic particulate material, as measured by well-known conventional methods employed in the art of laser light scattering, may be such that at least about 10 volume percent, such as at least about 20 volume percent, such as at least about 30 volume percent, such as at least about 40 volume percent, such as at least about 50 volume percent, such as at least about 60 volume percent, such as at least about 70 volume percent, such as at least about 80 volume percent, such as at least about 90 volume percent, such as at least about 95 volume percent, or such as about 100 volume percent of the particles have an e.s.d of less than 2 μm.

In certain embodiments, at least about 50% by volume of the particles have an e.s.d of less than 2 μm, for example, at least about 55% by volume of the particles have an e.s.d of less than 2 μm, or at least about 60% by volume of the particles have an e.s.d of less than 2 μm.

Details of procedures that can be used to characterize the particle size distribution of a mixture of inorganic particulate material and microfibrillated cellulose by using well known conventional methods employed in the art of laser scattering are discussed above.

In some embodiments, the inorganic particulate material is kaolin clay. This part of the specification will be discussed below in terms of kaolin and aspects relating to processing and/or treating kaolin. The present invention should not be construed as being limited to the embodiments. Thus, in some embodiments, the kaolin may be used in a raw form.

The kaolin clay used in the present invention can be a processed material derived from natural sources (i.e., the native natural kaolin clay minerals). The processed kaolin clay can typically contain at least about 50% by weight of kaolinite. For example, most commercially processed kaolin clays contain greater than about 75% by weight kaolinite, and can contain greater than about 90% by weight (sometimes greater than about 95% by weight) kaolinite.

The kaolin clay used in the present invention can be prepared from the raw natural kaolin clay minerals by one or more other processes known to those skilled in the art, such as by known refining or beneficiation steps.

For example, clay minerals can be bleached using a reductive bleaching agent such as sodium bisulfite. If sodium bisulfite is used, the bleached clay mineral may optionally be dewatered, and optionally washed, and optionally dewatered again after the sodium bisulfite bleaching step.

The clay minerals may be treated to remove impurities by, for example, flocculation, flotation or magnetic separation techniques well known in the art. Alternatively, the clay mineral used in the first aspect of the present invention may also be in a solid form or as an aqueous suspension without treatment.

The process for preparing the particulate kaolin clay used in the present invention may also include one or more comminution steps, such as grinding or milling. Light dilution (light dilution) of the crude kaolin was used to provide its proper delamination. The comminution may be by the use of beads or granules of plastics (e.g. nylon), sand or ceramic grinding or milling aids. The crude kaolin may be refined using well-known procedures to remove impurities and improve physical properties. The kaolin clay can be treated to obtain a kaolin having the desired d by known particle size classification procedures, such as sieving and centrifugation (or both)₅₀Particles of a value or particle size distribution.

In some embodiments, the product removed from the high shear process is treated to remove at least some or substantially all of the water to form a partially dried or substantially completely dried product. For example, at least about 10 vol% of the water, such as at least about 20 vol%, or at least about 30 vol%, or at least about 40 vol%, or at least about 50 vol%, or at least about 60 vol%, or at least about 70 vol%, or at least about 80 vol%, or at least about 90 vol%, or at least about 100 vol% of the water, may be removed from the product of the co-milling process. Any suitable technique may be used to remove the water from the product, including, for example, by gravity or vacuum assisted drainage (with or without pressurization), or by evaporation, or by filtration, or by a combination of these techniques. The partially dried or substantially completely dried product will comprise microfibrillated cellulose and inorganic particulate material (when present) and any other optional additives that may have been added prior to drying. The partially dried or substantially completely dried product may optionally be rehydrated and incorporated into papermaking compositions and paper products described herein.

As mentioned above, it has been found that microfibrillated cellulose obtained by the process described in WO-A-2010/131016 has advantageous paper burst strength enhancing properties. However, the present inventors have found that the paper burst strength enhancing properties of microfibrillated cellulose cannot be further improved by only further grinding. In this regard, and without wishing to be bound by theory, it appears that an equilibrium point is reached during grinding beyond which the paper burst strength enhancing properties of microfibrillated cellulose cannot be further improved, regardless of the additional energy applied by grinding. However, the present inventors have surprisingly found that one or more paper property enhancing properties of microfibrillated cellulose (e.g. paper burst strength enhancing properties of microfibrillated cellulose) may be improved by subjecting microfibrillated cellulose (e.g. microfibrillated cellulose obtained by the grinding process described in WO-A-2010/131016) to high shear treatment according to the above-described first aspect. In other words, it has been found that paper comprising microfibrillated cellulose obtainable by the high shear process described herein has one or more paper properties (e.g. burst strength) improved relative to paper comprising an equivalent amount of microfibrillated cellulose not subjected to the high shear process described herein (e.g. microfibrillated cellulose obtained with the grinding process described in WO-A-2010/131016).

The paper burst strength can be determined using a Messemer Buchnel burst tester according to SCAN P24. Further details are provided in the examples below.

As mentioned above, paper made from pure fiber pulp will have higher paper burst strength than comparative paper in which a portion of the fiber pulp is replaced by filler (e.g., mineral filler). Thus, the paper burst strength of filled paper is typically expressed as a percentage of the paper burst strength of unfilled paper. When used as A filler in paper, for example as an alternative or partial replacement for conventional mineral fillers, it has surprisingly been found that microfibrillated cellulose obtained by the process described in WO-A-2010/131016 (optionally together with inorganic particulate material) can improve the burst strength properties of the paper. That is, papers filled with microfibrillated cellulose were found to have improved burst strength compared to papers filled with mineral filler only. In other words, it was found that the microfibrillated cellulose filler has paper burst strength enhancing properties.

In some embodiments, the paper burst strength enhancing properties of the microfibrillated cellulose obtained by the high shear process described herein are increased by at least about 1%, for example, at least about 5% or at least about 10%, compared to the paper burst strength enhancing properties of the microfibrillated cellulose before the high shear treatment. In other words, in some embodiments, the paper burst strength of A paper comprising microfibrillated cellulose obtainable by the high shear process described herein is greater than the paper burst strength of A comparative paper comprising an equivalent amount of microfibrillated cellulose that has not been subjected to the high shear process described herein (e.g., microfibrillated cellulose obtained by the grinding process described in WO-A-2010/131016), e.g., at least about 1% greater, or at least about 5% greater, or at least about 10% greater.

In some embodiments, additionally or alternatively, paper products comprising microfibrillated cellulose obtained by the high shear process described herein exhibit one or more advantageous properties in addition to improved paper burst strength. For example, paper comprising microfibrillated cellulose obtained by the high shear process described herein may exhibit an improved burst index, or an improved tensile strength (e.g., machine direction tensile index), or an improved tear strength (e.g., cross direction tear index), or an improved z-direction (internal bond) strength (also referred to as Scott bond strength), or an improved (reduced) porosity (e.g., Bendsten porosity), or an improved smoothness (e.g., Bendsten smoothness), or an improved opacity, or any combination thereof.

In one embodiment, L is used based on TAPPI method T403 om-91&And (4) measuring the burst index by using a W burst strength tester. In some embodiments, the paper product comprising microfibrillated cellulose obtained by the high shear process described herein has A burst index greater than, e.g., at least about 1% greater, or at least about 5% greater, or at least about 10% greater, than A comparative paper comprising an equivalent amount of microfibrillated cellulose that has not been subjected to the high shear process described herein (e.g., microfibrillated cellulose obtained by the grinding process described in WO-A-2010/131016). In some embodiments, the paper product comprising microfibrillated cellulose obtainable by the high shear process described herein has a burst index of at least about 1.25kPa m²g^-1For example, at least about 1.30kPa m²g^-1Or at least about 1.32kPa m²g^-1Or at least about 1.34kPa m²g^-1Or at least about 1.36kPa m²g^-1For example, about 1.25kPa m²g^-1About 1.50kPa m²g^-1Or about 1.25kPa m²g^-1About 1.45kPa m²g^-1Or about 1.25kPa m²g^-1About 1.40kPa m²g^-1Or about 1.30kPa m²g^-1About 1.40kPam²g^-1Or about 1.32kPa m²g^-1About 1.40kPa m²g^-1Or about 1.34kPa m²g^-1About 1.38kPa m²g^-1。

In one embodiment, tensile strength (e.g., machine direction tensile index) is determined using a Testometrics tensile tester according to SCAN P16. In some embodiments, the tensile strength, e.g., tensile strength, of A paper product comprising microfibrillated cellulose obtainable by the high shear process described herein is greater than the tensile strength, e.g., tensile strength, of A comparative paper comprising an equivalent amount of microfibrillated cellulose that has not been subjected to the high shear process described herein (e.g., microfibrillated cellulose obtained by the grinding process described in WO-A-2010/131016)At least about 1% greater, or at least about 5% greater, or at least about 10% greater. In some embodiments, the paper product comprising microfibrillated cellulose obtainable by the high shear process described herein has a machine direction tensile index of at least about 31.5Nm g^-1E.g., at least about 32.0Nm g^-1Or at least about 32.5Nm g^-1Or at least about 33.0Nm g^-1Or about 32.0Nm g^-1About 50.0Nm g^-1Or about 32.0Nm g^-1About 45Nm g^-1Or about 32.0Nm g^-1About 45Nm g^-1Or about 32.0Nm g^-1About 40Nm g^-1Or about 32.0Nm g^-1About 35Nm g^-1Or about 33.0Nm g^-1About 35Nm g^-1。

In one embodiment, the transverse tear strength index (paper internal tear strength (Elmendorf type method)) is determined according to TAPPI method T414 om-04. In some embodiments, the paper product comprising microfibrillated cellulose obtainable by the high shear process described herein has A tear strength index that is greater than the tear strength index of A comparative paper comprising an equivalent amount of microfibrillated cellulose that has not been subjected to the high shear process described herein (e.g., microfibrillated cellulose obtained by the grinding process described in WO-A-2010/131016), e.g., the tear strength index is at least about 1% greater, or at least about 5% greater, or at least about 10% greater. In some embodiments, the paper product comprising microfibrillated cellulose obtainable by the high shear process described herein has a tear index of at least about 5.45mN m²g^-1E.g. at least about 5.50mN m²g^-1Or at least about 5.60mN m²g^-1Or at least about 5.70mN m²g^-1Or at least about 5.80mN m²g^-1E.g. about 5.45mN m²g^-1About 6.50mN m²g^-1Or about 5.45mN m²g^-1About 6.25mN m²g^-1Or about 5.45mN m²g^-1About 6.00mN m²g^-1Or about 5.55mNm²g^-1About 6.00mN m²g^-1Or about 5.65mN m²g^-1About 6.00mN m²g^-1Or about 5.75mN m²g^-1About 6.50mN m²g^-1Or about 5.80mN m²g^-1About 6.00mN m²g^-1。

In one embodiment, the z-direction (internal binding) strength is determined using a Scott binding tester according to TAPPI T569. In some embodiments, the z-direction (internal (Scott) bond) strength of A paper product comprising microfibrillated cellulose obtainable by the high shear process described herein is greater than the z-direction (internal (Scott) bond) strength of A comparative paper comprising an equivalent amount of microfibrillated cellulose not subjected to the high shear process described herein (e.g., microfibrillated cellulose obtained by the grinding process described in WO-A-2010/131016), e.g., the z-direction (internal (Scott) bond) strength is at least about 1% greater, or at least about 5% greater, or at least about 10% greater, or at least about 20% greater, or at least about 30% greater, or at least about 40% greater, or at least about 50% greater. In some embodiments, the paper product comprising microfibrillated cellulose obtainable by the high shear process described herein has a z-direction (internal (Scott) bond) strength of at least about 130.0J m^-2E.g., at least about 150.0J m^-2Or at least about 170.0J m^-2Or at least about 180.0J m^-2Or at least about 190.0J m^-2E.g., about 130.0J m^-2About 250.0Jm^-2Or about 130.0J m^-2About 230.0J m^-2Or about 150.0J m^-2About 210.0J m^-2Or about 170.0J m^-2About 210.0J m^-2Or about 180.0J m^-2About 210.0J m^-2Or about 190.0J m^-2About 200.0J m^-2。

In one embodiment, porosity is determined using a Bendsten Model 5 porosity tester, in accordance with SCAN P21, SCAN P60, BS 4420, and TAPPI UM 535. In some embodiments, the porosity of A paper product comprising microfibrillated cellulose obtainable by the high shear process described herein is lower than the porosity of A comparative paper comprising an equivalent amount of microfibrillated cellulose not subjected to the high shear process described herein (e.g., microfibrillated cellulose obtained by the grinding process described in WO-A-2010/131016), e.g., the porosity of A comparative paperThe porosity is at least about 1% lower, or at least about 5% lower, or at least about 10% lower, or at least about 20% lower, or at least about 30% lower, or at least about 40% lower, or at least about 60% lower, or at least about 70% lower, or at least about 80% lower. In some embodiments, the paper product comprising microfibrillated cellulose obtainable by the high shear process described herein has a Bendsten porosity of less than about 1000cm³min^-1E.g. less than about 950cm³min^-1Or less than about 900cm³min^-1Or less than about 875cm³min^-1Or less than about 850cm³min^-1Or less than about 825cm³min^-1Or less than about 815cm³min^-1Or less than about 805cm³min^-1E.g. about 700cm³min^-1About 1000cm³min^-1Or about 750cm³min^-1About 950cm³min^-1Or about 750cm³min^-1About 900cm³min^-1Or about 750cm³min^-1About 850cm³min^-1。

In one embodiment, Bendsten smoothness is determined according to SCAN P21: 67. In some embodiments, the smoothness of A paper product comprising microfibrillated cellulose obtainable by the high shear process described herein is greater than the smoothness of A comparative paper comprising an equivalent amount of microfibrillated cellulose that has not been subjected to the high shear process described herein (e.g., microfibrillated cellulose obtained by the grinding process described in WO-A-2010/131016), e.g., the smoothness is at least about 1% greater, or at least about 5% greater, or at least about 10% greater, or at least about 20% greater, or at least about 30% greater. In some embodiments, the paper product comprising microfibrillated cellulose obtainable by the high shear process described herein has a Bendsten smoothness of at least about 560cm³min^-1E.g., at least about 580cm³min^-1Or at least about 600cm³min^-1Or at least about 620cm³min^-1Or at least about 640cm³min^-1Or at least about 660cm³min^-1Or at least about 680cm³min^-1E.g. about 560cm³min^-1About 800cm³min^-1Or about 600cm³min^-1About 750cm³min^-1Or about 640cm³min^-1About 725cm³min^-1Or about 660cm³min^-1About 705cm³min^-1。

In one embodiment, paper samples (80 gm) are measured with an Elrepho Datacolor3300 spectrophotometer using wavelengths suitable for opacity measurement^-2) Opacity of (c). The standard test method is ISO 2471. First, the measurement of the percent reflection of incident light was performed using a stack of at least 10 sheets of paper on a black cavity (R infinity). The stacked sheets were then replaced with single sheets and the percent reflectance (R) of the single sheets on the black cover sheet was again measured. The percent opacity is then calculated from the formula: percent opacity is 100 × R/R infinity. In some embodiments, the opacity of A paper product comprising microfibrillated cellulose obtainable by the high shear process described herein is greater than the opacity of A comparative paper comprising an equivalent amount of microfibrillated cellulose that has not been subjected to the high shear process described herein (e.g., microfibrillated cellulose obtained by the grinding process described in WO-A-2010/131016), e.g., the opacity is at least about 0.10% greater, or at least about 0.15% greater, or at least about 0.20% greater, or at least about 0.25% greater, or at least about 0.30% greater.

The viscosity of the post-high shear product comprising microfibrillated cellulose is generally greater than the viscosity of the microfibrillated cellulose before the high shear treatment. In some embodiments, the post high shear product comprising microfibrillated cellulose and optionally inorganic particulate material has a Brookfield viscosity (spindle 4, 10rpm, fiber content 1.5 wt%) of at least about 2,000mpa.s, for example, from about 2,500mpa.s to about 13,000mpa.s, or from about 2,500mpa.s to about 11,000mpa.s, or from about 3,000mpa.s to about 9,000mpa.s, or from about 3,000mpa.s to about 7,000mpa.s, or from about 3,500mpa.s to about 6,000mpa.s, or from about 4,000mpa.s to about 6,000 mpa.s. Brookfield viscosity was determined according to the following procedure. A sample of the composition (e.g., the product after high shear) was diluted with sufficient water to give a fiber content of 1.5 wt%. The diluted sample was then mixed well and its viscosity was measured using a Brookfield r.v. viscometer (spindle No. 4) at 10 rpm. The reading was taken after 15 seconds to allow the sample to stabilize.

The integrated production of microfibrillated cellulose is summarized in figure 3. Water (2), fiber slurry (4) and optional inorganic particles (6) are fed into a grinding vessel (8) containing a suitable grinding medium (not shown), such as a tower mill or stirred media mill. The fibre slurry is milled in the presence of milling mediA and optionally inorganic particulate material according to the following process and/or according to the preparation process of microfibrillated cellulose as disclosed in WO-A-2010/131016. The resulting aqueous suspension comprising microfibrillated cellulose (10) and optionally inorganic particulate material is then fed to an in-line high shear mixer (12). The mill is equipped with one or more screens (not shown) of suitable size to separate the grinding media from the aqueous suspension containing microfibrillated cellulose and optional inorganic particulate material. Optionally, the aqueous suspension or a portion thereof may be fed to a mixing tank (14) and combined with additional water (16) to reduce its solids content, resulting in a lower solids aqueous suspension (18), and then fed to an in-line high shear mixer (12). For example, if the solids content of the aqueous suspension withdrawn from the mill is greater than about 10%, it may be directed to a mixing tank to reduce the solids content to less than 10%. The aqueous suspension comprising microfibrillated cellulose and optionally inorganic particulate material is subjected to high shear in an in-line high shear mixer. Periodically, the post-high shear product (20) may be recycled to the mixing tank (14) for further mixing and optionally further dilution. The final high shear product (22) is removed from the in-line high shear mixer (12) and sent to other processing areas (24). The other processing zone (24) may comprise a unit (not shown) for incorporating the high shear product into a papermaking composition, and a unit (not shown) for making a paper product from the papermaking composition. The other processing area (24) may also contain units (not shown) for coating paper products.

In some embodiments, the microfibrillated cellulose is prepared at a first location and subjected to high shear at a second location separate (e.g., remote) from the first location, prior to the high shear treatment. The microfibrillated cellulose produced at the first location may be transported to the second location by road, rail, ship or air, or pipeline, or any combination thereof. In some embodiments, the microfibrillated cellulose produced at a first location is treated to reduce its water content, and optionally combined with other additives (e.g., flocculants, preservatives and/or biocides), and then transported to a second location where it can be made to a suitable solids content and subjected to a high shear treatment. Other additives include, for example, one or more high molecular weight cationic modified polyacrylamide flocculants, and/or one or more of BIT (2-benzisothiazolin-3-one), CMIT (5-chloro-2-methyl-4-isothiazolin-3-one), and MIT (methylisothiazolinone) biocides (available from the Dow Chemical Company), DBNPA biocides (available from the Dow Chemical Company), hydrogen peroxide, glutaraldehyde, and/or THPS (tetrakis (hydroxymethyl) phosphonium sulfate). A blend of BIT, MIT and CMIT may be added, such as a blend of BIT and MIT or a blend of CMIT and MIT. For shipping, the microfibrillated cellulose may be in the form of a partially dried or substantially dried product, as described herein. Any suitable technique may be used to remove water from the microfibrillated cellulose product, for example, by gravity or vacuum assisted drainage (with or without pressurization), or by pressurization, or by evaporation, or by filtration, or by a combination of these techniques. For example, prior to delivery to the second location, at the first location, the water content of the microfibrillated cellulose may be reduced to less than about 80 vol.%, or less than about 70 vol.%, or less than about 60 vol.%, or less than about 50 vol.%, or less than about 40 vol.%, or less than about 30 vol.%, or less than about 20 vol.%, or less than about 15 vol.%, or less than about 10 vol.%, or less than about 5 vol.%, or less than about 2 vol.%, or less than about 1 vol.%, based on the total volume of water in the microfibrillated cellulose product prior to the removal of water. The distance between the first location and the second location may be from about 100m to about 10,000km, for example, from about 1km to about 7,500km, or from about 1km to about 5,000km, or at least about 10km, or at least about 50km, or at least about 100km, or at least about 250km, or at least about 500km, or at least about 750km, or at least about 1,000km, depending on the mode of transport and route.

Paper products and papermaking compositions

The term "paper product" as used in connection with the present invention is to be understood as referring to all forms of paper including board such as white board liner and hanging board, cardboard, paperboard, coated board and the like. There are many types of coated or uncoated paper that can be made according to the present invention, including paper suitable for books, magazines, newspapers, and the like, as well as office paper. The paper may be calendered or super-calendered as desired; super-calendered magazine papers for rotogravure and offset printing, for example, can be produced according to the method of the invention. Paper suitable for Light Weight Coating (LWC), Medium Weight Coating (MWC) or machine-to-machine coloration (MFP) can also be manufactured according to the present method. Coated paper and board having barrier properties suitable for food packaging and the like can also be manufactured according to existing methods.

In some embodiments, the paper product comprises from about 0.1 wt% to about 10 wt% of microfibrillated cellulose that has been subjected to high shear according to the methods described herein, for example, from about 0.1 wt% to about 8.0 wt% microfibrillated cellulose, or from about 0.1 wt% to about 7.0 wt% microfibrillated cellulose, or from about 0.1 wt% to about 6.0 wt% microfibrillated cellulose, or from about 0.25 wt% to about 6.0 wt% microfibrillated cellulose, or from about 0.5 wt% to about 6.0 wt% microfibrillated cellulose, or from about 1.0 wt% to about 6.0 wt% microfibrillated cellulose, or from about 1.5 wt% to about 6.0 wt% microfibrillated cellulose, or from about 2.0 wt% to about 6.0 wt% microfibrillated cellulose, or from about 2.5 wt% to about 5.5 wt% microfibrillated cellulose, or from about 2.5 wt% to about 5.0 wt% microfibrillated cellulose.

In some embodiments, the paper product comprises from about 1 wt% to about 50 wt% inorganic particulate material, for example, from about 5 wt% to about 45 wt% inorganic particulate material, or from about 10 wt% to about 45 wt% inorganic particulate material, or from about 15 wt% to about 45 wt% inorganic particulate material, or from about 20 wt% to about 45 wt% inorganic particulate material, or from about 25 wt% to about 45 wt% inorganic particulate material, or from about 30 wt% to about 45 wt% inorganic particulate material, or from about 35 wt% to about 45 wt% inorganic particulate material, or from about 20 wt% to about 40 wt% inorganic particulate material, or from about 30 wt% to about 50 wt% inorganic particulate material, or from about 30 wt% to about 40 wt% inorganic particulate material, or from about 40 wt% to about 50 wt% inorganic particulate material.

The paper product may contain other optional additives including, but not limited to, dispersants that can facilitate the interaction of the mineral particles and fibers, biocides, suspension aids, salt(s), and other additives, such as starch or carboxymethyl cellulose or polymers.

In some embodiments, the paper product has improved paper burst strength compared to A comparative paper product comprising an equivalent amount of microfibrillated cellulose that has not been subjected to the high shear process described herein (e.g., microfibrillated cellulose obtained by the grinding process described in WO-A-2010/131016).

In some embodiments, the paper product has a paper burst strength of at least about 85, e.g., at least about 86, or at least about 87, or at least about 88, or at least about 89, or at least about 90, or at least about 91, or at least about 92, or at least about 93, or at least about 94, or at least about 95, as determined using the Messemer Buchnel burst tester according to SCAN P24.

The present invention also provides a papermaking composition that can be used to prepare the paper product of the present invention.

In a typical papermaking process, a cellulose-containing slurry is prepared by any suitable chemical or mechanical treatment or combination thereof known in the art. The pulp may be from any suitable source, such as wood, grass (e.g. sugar cane, bamboo) or rags (e.g. textile waste, cotton, hemp or flax). Pulp may be bleached according to processes well known to those skilled in the art, and those suitable for use in the present invention will be apparent. The bleached cellulose pulp may be pulped and/or refined to achieve a predetermined freeness (in the art as Canadian Standard Freeness (CSF) in cm³Reported in units). Then bleaching and pulpingThe slurry of (a) makes a suitable paper stock.

The papermaking composition of the present invention comprises a suitable amount of a slurry, optionally an inorganic particulate material, and optionally other conventional additives known in the art, to obtain the paper product of the present invention therefrom.

The papermaking composition may further comprise a nonionic, cationic or anionic retention aid or a particulate retention system in an amount of from about 0.01 wt.% to about 2 wt.%, based on the weight of the paper product. Generally, the greater the amount of inorganic particulate material, the greater the amount of retention aid. It may further comprise a sizing agent, which may be, for example, a long chain alkyl ketene dimer, a wax emulsion, or a succinic acid derivative. The papermaking composition may further comprise a dye and/or an optional optical brightener. The papermaking composition may further comprise dry and wet strengthening aids, for example, starch or epichlorohydrin copolymers.

In some embodiments, the paper product may be coated with a coating composition.

The coating composition may be a composition that imparts a particular quality to the paper, including weight, surface gloss, smoothness, or reduced ink absorbency. For example, paper products may be coated with a composition comprising kaolin or calcium carbonate. The coating composition may include a binder such as styrene-butadiene latex and natural organic binders such as starch. The coating formulation may also contain other known additives for coating compositions. Exemplary additives are described on page 21, line 15 to page 24, line 2 of WO-A-2010/131016.

In some embodiments, the coating composition may comprise microfibrillated cellulose obtained by the process described herein, for example microfibrillated cellulose obtainable by the process described in the first aspect of the present invention and/or microfibrillated cellulose obtainable by the process described in WO-A-2010/131016.

Methods of coating paper and other sheets and apparatus for carrying out these methods are widely published and well known. These known methods and devices can be conveniently used to prepare coated paper. For example, an overview of these methods is published in Pulp and Paper International (5.1994, page 18, and below). The sheet may be coated on the sheet former, i.e., "on-machine coating" or "off-machine coating" on a coater or coater. The use of a high solids composition in the coating process is desirable because it leaves less moisture to be subsequently evaporated. However, as is well known in the art, the solids content should not be so high as to cause problems of high viscosity and leveling. The coating process may be carried out using an apparatus comprising (i) an application device for applying the coating composition to the material being coated and (ii) a metering device for ensuring that the correct level of coating composition is applied. When an excess of coating composition is applied to the applicator, a metering device is located downstream thereof. Alternatively, the correct amount of coating composition may be applied to the applicator using a metering device (e.g., as a film press). The paper web support may range from a backing roll (e.g., via one or two applicators) to intangible (i.e., tension only) at the point of coating application and metering. The time that the coating is in contact with the paper before the final removal of excess coating is the dwell time-this time can be shorter, longer or variable.

The coating is typically added through a coating head located at the coating station. Paper grades are divided into uncoated, primary coated, secondary coated and even tertiary coated depending on the desired quality. When more than one coating is provided, the initial coating (pre-coating) can have a less expensive formulation and optionally a coarser pigment in the coating composition. Coaters that apply coating to each side of the paper have two or four coating heads, depending on the number of coatings applied on each side. Most coating heads can only coat one side at a time, but some roll coaters (e.g., film presses, gate rolls, and size presses) can coat both sides in a single pass.

Examples of known coaters that can be used include, but are not limited to, air knife coaters, blade coaters, rod coaters, bar coaters, multi-head coaters, roll or blade coaters, die coaters, lab coaters, gravure coaters, kiss coaters, liquid application systems, reverse roll coaters, curtain coaters, spray coaters, and extrusion coaters.

Water may be added to the solids comprising the coating composition to provide a solids concentration that is preferably such that when the composition is coated on a sheet to achieve a desired target coating weight, the composition has a rheology suitable to enable the composition to be coated at a pressure of 1 bar to 1.5 bar (i.e., blade pressure).

Calendering is a well-known process in which the smoothness and gloss of the paper are improved and the bulk reduced by passing the coated paper more than once between the calender nips or rolls. Typically, an elastomer coated roller is used to provide pressure to the high solids content composition. Elevated temperatures may be employed. One or more passes through the nip may be used (e.g., up to about 12 passes, or sometimes more).

Supercalendering is a paper finishing operation consisting of an additional degree of calendering. Supercalenders, like calendering, are a well known process. Supercalendering imparts a high gloss finish to the paper product, and the degree of supercalendering determines the degree of gloss. A typical supercalender comprises vertically alternating stacks of hard polished steel and soft cotton (or other elastomeric) rolls, for example, elastomer coated rolls. The hard roll is pressed against the soft roll to compress the material. As the web passes through the nip, the force generated by the soft roll trying to return to its original size "soft polishes" the paper, thereby creating an additional bright and supercalendered paper-like finish common to paper.

The steps of forming the final paper product from the papermaking composition are conventional and well known in the art, and generally include forming a sheet of paper having a target basis weight depending on the type of paper being made.

For the avoidance of doubt, the present invention relates to the subject matter described in the following numbered paragraphs:

1. a method of modifying the paper burst strength enhancing properties of microfibrillated cellulose, the method comprising subjecting an aqueous suspension comprising microfibrillated cellulose and optionally inorganic particulate material to high shear, wherein the high shear is generated at least in part by a moving shearing element, thereby modifying the paper burst strength enhancing properties of the microfibrillated cellulose.

2. The method of paragraph 1, for improving the paper burst strength enhancing properties of microfibrillated cellulose, comprising subjecting an aqueous suspension comprising microfibrillated cellulose and optionally an inorganic particulate material to high shear, thereby improving the paper burst strength enhancing properties of the microfibrillated cellulose.

3. The method of any preceding numbered paragraph, wherein the moving shearing element is housed in a high shear rotor/stator mixing device, and the method comprises subjecting an aqueous suspension comprising microfibrillated cellulose to high shear in the rotor/stator mixing device to alter (e.g., improve) the paper burst strength enhancing properties of the microfibrillated cellulose.

4. The method of any of the preceding numbered paragraphs, wherein the microfibrillated cellulose of the aqueous suspension comprising microfibrillated cellulose has a fiber steepness of about 20 to about 50 prior to high shear.

5. The method of any of the preceding numbered paragraphs, wherein the microfibrillated cellulose fibers d of the aqueous suspension comprising microfibrillated cellulose are, prior to high shear₅₀Is at least about 50 μm.

6. The method of any preceding numbered paragraph, further comprising obtaining the aqueous suspension comprising microfibrillated cellulose, optionally wherein the aqueous suspension comprising microfibrillated cellulose is obtained by a process comprising: microfibrillating a fibrous substrate comprising cellulose in an aqueous environment in the presence of a grinding medium and optionally in the presence of a suspension of said inorganic particulate material comprising fibrous material and optionally inorganic material.

7. The method of numbered paragraph 6, wherein the microfibrillating process comprises: the fibrous substrate comprising cellulose is ground in the presence of grinding media and optionally inorganic particulate material.

8. The method of any preceding numbered paragraph, wherein, when the inorganic particulate material is present, the inorganic particulate material is: alkaline earth metal carbonates or sulfates, for example calcium carbonate, such as natural calcium carbonate and/or precipitated calcium carbonate, magnesium carbonate, dolomite, gypsum; hydrated kaolinite group clays, such as kaolin, halloysite, or ball clays; anhydrous (calcined) kaolinitic clays, such as metakaolin or fully calcined kaolin, talc, mica, perlite or diatomaceous earth; or magnesium hydroxide; or aluminum trihydrate; or a combination thereof.

9. The method of numbered paragraph 8, wherein the inorganic particles are calcium carbonate, optionally wherein at least about 50% by weight of the calcium carbonate has an equivalent spherical diameter of less than about 2 μm.

10. The method of numbered paragraph 8, wherein the inorganic particulate material is kaolin, optionally wherein at least about 50% by weight of the kaolin has an equivalent spherical diameter of less than about 2 μm.

11. The method of any of the preceding numbered paragraphs, wherein the microfibrillated cellulose fiber d after high shear₅₀The reduction is, for example, at least about 1%, or at least about 5%, or at least about 10%, or at least about 50%.

12. The method of any preceding numbered paragraph, wherein the microfibrillated cellulose has an increase in paper burst strength enhancing properties of at least about 1%, e.g., at least about 5%, or at least about 10%, after high shear.

13. The process of any of the preceding numbered paragraphs, wherein the microfibrillated cellulose has a Brookfield viscosity (spindle 4, 10rpm, fiber content 1.5 wt%) of at least about 2,000MPa.s after high shear.

14. The method of any of the preceding numbered paragraphs, wherein the method is a batch process or a continuous process.

15. The method of any preceding numbered paragraph, wherein the aqueous suspension comprising microfibrillated cellulose is stirred in a mixing tank before and/or during the method.

16. The method of any preceding numbered paragraph, wherein the total energy input, E, during the high shear is calculated as E ═ P/W, where E is the total energy input (kWh/t) per ton of cellulosic material in the aqueous suspension comprising microfibrillated cellulose, P is the total energy input (kWh), and W is the total weight of cellulosic material (ton).

17. The method of any preceding numbered paragraph, further comprising: preparing a papermaking composition comprising microfibrillated cellulose and optionally inorganic particulate material, obtainable by the method of any one of the preceding numbered paragraphs.

18. The method of numbered paragraph 17, further comprising preparing a paper product from the papermaking composition.

19. An aqueous suspension comprising microfibrillated cellulose and optionally an inorganic particulate material obtainable by the method of any one of numbered paragraphs 1 to 16.

20. A papermaking composition obtainable by the method of numbered paragraph 17.

21. A paper product obtainable by the method of numbered paragraph 18, wherein the paper product has a first burst strength that is greater than a second burst strength of a comparative paper product comprising an equivalent amount of microfibrillated cellulose (prior to high shear) as defined in any of numbered paragraphs 1, 4 and 5.

22. The paper product of numbered paragraph 21, wherein the paper product comprises from about 0.1 wt.% to about 5 wt.% microfibrillated cellulose and optionally up to about 50 wt.% inorganic particulate material.

For the avoidance of doubt, the present application relates to the subject matter described in the following numbered paragraphs:

a method of treating microfibrillated cellulose, the method comprising subjecting an aqueous suspension comprising microfibrillated cellulose and optionally inorganic particulate material to high shear, wherein the high shear is at least partially generated by a moving shearing element.

A method as described in numbered paragraph 1a for modifying (e.g. improving) one or more paper property enhancing properties of microfibrillated cellulose, the method comprising subjecting an aqueous suspension comprising microfibrillated cellulose and optionally inorganic particulate material to high shear, thereby modifying (e.g. improving) the paper property enhancing properties of the microfibrillated cellulose.

The method of numbered paragraph 1a or 2a, wherein the moving shearing element is housed in a high shear rotor/stator mixing device and the method comprises subjecting an aqueous suspension comprising microfibrillated cellulose to high shear in the rotor/stator mixing device to alter (e.g., improve) one or more paper property enhancing properties of the microfibrillated cellulose.

The method of any of paragraphs 1 a-3 a, wherein (i) the fiber steepness of the microfibrillated cellulose of the aqueous suspension comprising microfibrillated cellulose is about 20 to about 50 before high shear, and/or (ii) the fiber d of the microfibrillated cellulose of the aqueous suspension comprising microfibrillated cellulose is before high shear₅₀Is at least about 50 μm.

The method of any of paragraphs 1 a-4 a, further comprising obtaining the aqueous suspension comprising microfibrillated cellulose, optionally wherein the aqueous suspension comprising microfibrillated cellulose is obtained by a process comprising: microfibrillating a fibrous substrate comprising cellulose in an aqueous environment in the presence of a grinding medium and optionally in the presence of a suspension of said inorganic particulate material comprising fibrous material and optionally inorganic material.

The method of paragraph 5a, wherein the microfibrillating process comprises: the fibrous substrate comprising microfibers is milled in the presence of milling media and optionally inorganic particulate material.

The method of any of paragraphs 1 a-6 a, wherein, when the inorganic particulate material is present, the inorganic particulate material is: alkaline earth metal carbonates or sulfates, for example calcium carbonate, such as natural calcium carbonate and/or precipitated calcium carbonate, magnesium carbonate, dolomite, gypsum; hydrated kaolinite group clays, such as kaolin, halloysite, or ball clays; anhydrous (calcined) kaolinitic clays, such as metakaolin or fully calcined kaolin, talc, mica, perlite or diatomaceous earth; or magnesium hydroxide; or aluminum trihydrate; or a combination thereof.

The method of numbered paragraph 7a, wherein (i) the inorganic particles are calcium carbonate, optionally wherein at least about 50% by weight of the calcium carbonate has an equivalent spherical diameter of less than about 2 μ ι η; or (ii) the inorganic particulate material is kaolin, optionally wherein at least about 50% by weight of the kaolin has an equivalent spherical diameter of less than about 2 μm.

The method of any of paragraphs 1 a-7 a, wherein after high shear, the microfibrillated cellulose fiber d₅₀The reduction is, for example, at least about 1%, or at least about 5%, or at least about 10%, or at least about 50%.

The method as in any of paragraphs 1 a-9 a, wherein, after high shear:

(i) the microfibrillated cellulose has an increase in paper burst strength enhancing properties of at least about 1%, such as at least about 5%, or at least about 10%; and/or

(ii) An increase in the paper burst index enhancing properties of the microfibrillated cellulose of at least about 1%, or at least about 5%, or at least about 10%; and/or

(iii) An increase in the tensile strength enhancing properties of the microfibrillated cellulose of at least about 1%, or at least about 5%, or at least about 10%; and/or

(iv) An increase in z-direction (internal (Scott) bond) strength enhancing properties of the microfibrillated cellulose of at least about 1%, or at least about 5%, or at least about 10%, or at least about 20%, or at least about 30%, or at least about 40%, or at least about 50%; and/or

(v) An increase in tear strength enhancing properties of the microfibrillated cellulose of at least about 1%, or at least about 5%, or at least about 10%; and/or

(vi) The microfibrillated cellulose has an increase in porosity enhancing (i.e., porosity reducing) property of at least about 1%, or at least about 5%, or at least about 10%, or at least about 20%, or at least about 30%, or at least about 40%, or at least about 50%, or at least about 60%, or at least about 70%, or at least about 80%; and/or

(vii) An increase in smoothness enhancing properties of the microfibrillated cellulose of at least about 1%, or at least about 5%, or at least about 10%, or at least about 20%, or at least about 30%; and/or

(viii) The microfibrillated cellulose has an increased opacity enhancing property of at least about 0.10%, or at least about 0.15%, or at least about 0.20%, or at least about 0.25%, or at least about 0.30%.

The method of numbered paragraph 5a or 6a, wherein after milling is complete and prior to the high shear treatment, the product comprising microfibrillated cellulose is washed out of the microfibrillating apparatus with water or any other suitable liquid.

The method of any of paragraphs 1 a-11 a, wherein the aqueous suspension comprising microfibrillated cellulose is stirred in a mixing tank before and/or during high shear.

The method of any of paragraphs 1 a-12 a, wherein the aqueous suspension comprising microfibrillated cellulose and optional inorganic particulate material after being subjected to high shear has a solids content of no greater than about 25 wt% and/or a fiber solids content of no greater than about 8 wt%.

The method of any of paragraphs 1 a-13 a, wherein the one or more paper properties are selected from the group consisting of: (i) paper burst strength; (ii) a burst index; (iii) tensile strength; (iv) z-direction (internal (Scott) bonding) strength; (v) tear strength; (vi) porosity; (vii) smoothness; and (viii) opacity.

A method as described in any of numbered paragraphs 1 a-14 a, further comprising: preparing a papermaking composition comprising microfibrillated cellulose and optionally inorganic particulate material, obtainable by the method of any one of the preceding numbered paragraphs, optionally further comprising preparing a paper product from the papermaking composition.

An aqueous suspension obtainable by the method of any of the numbered paragraphs 1a to 14a, comprising microfibrillated cellulose and optionally an inorganic particulate material.

A papermaking composition obtainable by the process of numbered paragraph 15a.

A paper product obtainable by the method of numbered paragraph 15a, wherein the paper product has the following properties:

(i) a first burst strength greater than a second burst strength of a comparative paper product comprising an equivalent amount of microfibrillated cellulose (prior to high shear) as defined in any one of numbered paragraphs 1 and 4; and/or

(ii) A first burst index greater than a second burst index of a comparative paper product comprising an equivalent amount of microfibrillated cellulose (prior to high shear) as defined in any one of numbered paragraphs 1 and 4; and/or

(iii) A first tensile strength greater than a second tensile strength of a comparative paper product comprising an equivalent amount of microfibrillated cellulose (prior to high shear) as defined in any one of numbered paragraphs 1 and 4; and/or

(iv) (ii) has a first z-direction (internal (Scott) bond) strength greater than a second z-direction (internal (Scott) bond) strength of a comparative paper product comprising an equivalent amount of microfibrillated cellulose (prior to high shear) as defined in any one of numbered paragraphs 1 and 4; and/or

(v) A first tear strength greater than a second tear strength of a comparative paper product comprising an equivalent amount of microfibrillated cellulose (prior to high shear) as defined in any one of numbered paragraphs 1 and 4; and/or

(vi) A first porosity lower than a second porosity of a comparative paper product comprising an equivalent amount of microfibrillated cellulose (prior to high shear) as defined in any one of numbered paragraphs 1 and 4; and/or

(vii) (ii) has a first smoothness greater than a second smoothness of a comparative paper product comprising an equivalent amount of microfibrillated cellulose (prior to high shear) as defined in any one of numbered paragraphs 1 and 4; and/or

(viii) Having a first opacity greater than a second opacity of a comparative paper product comprising an equivalent amount of microfibrillated cellulose (prior to high shear) as defined in any one of numbered paragraphs 1 and 4,

optionally, wherein the paper product comprises from about 0.1 wt% to about 5 wt% microfibrillated cellulose and optionally up to about 50 wt% inorganic particulate material.