Process for the production of nano-fibrillar cellulose suspensions

[0001] The present invention relates to a method for producing a suspension of nanofibrillary cellulose and nanofibrillary cellulose obtained by this method.

[0002] Cellulose is a structural element of the basic cell wall of green plants and is the most common organic compound on Earth. Is an object of interest in many applications and industries.

[0003] Cellulose is the main component of paper and cardboard as well as textile materials made of cotton, linen and other plant fibers. Cellulose can be processed into cellophane, a thin transparent film and in artificial silk, an important fiber that has been used in textiles since the early 20th century. Both cellophane and rayon are known as "regenerated cellulose fibers".

[0004] Cellulose fibers are also used in liquid filtration to form a filter bed from inert material. Cellulose is also used to make hydrophilic and very absorbent sponges.

[0005] For use in industry, cellulose is mainly obtained from wood pulp and cotton. It is mainly used for the production of cardboard and paper, and to a lesser extent it is transformed into a wide range of derivative products.

[0006] Cellulose pulp as a raw material is processed from wood or plant stems such as hemp, flax and manila. Pulp fibers are mainly made of cellulose and other organic components (hemicellulose and lignin). Cellulose macromolecules (composed of β-D-glucose molecules linked by a 1-4 glycosidic bond) are bonded together by hydrogen bonds to form the so-called primary fibril (micelles) that has crystalline and amorphous domains. Several primary filaments (about 55) form a so-called microfiber. About 250 of these microfibers form a filament.

[0007] Fibrils are arranged in different layers (which may contain lignin and / or hemicellulose) to form a fiber. The individual fibers are also bonded together with lignin.

[0008] Pulps used in the manufacture of paper are often obtained by grinding wood and optionally processing using heat and chemical compounds to remove unwanted compounds from cellulose fibers [0009] The fibers have been ground and cut to a certain degree of fragmentation (depending on the properties desired) . Fiber milling is achieved using a breaking mill (such as conical rotor-stator mills or double disc mills). The breaking mill is also used to fibrillate fibers on the surface, which means that some fibrils are partially pulled from the surface of the fibers. This leads to better retention and often better adhesion to pigments that can be added in the papermaking process, as well as to increased hydrogen bonding potential between the paper fibers. This results in improved mechanical properties. A side effect is also that the paper becomes denser and more transparent due to the loss of light scattering, because the size of the scattering centers moves away from the acceptable optimum of half the wavelength of light (satin and fat-resistant parchment papers).

[0010] After the fibers are broken with the use of applied energy, they become subjected to fibrillation because the cell walls disintegrate and tear into joined strips, i.e. into fibrils. If this cracking continues to separate the fibrils from the fiber body, it releases the fibrils. Fiber breakage into microfibers is referred to as "microfibrillation." This process can be continued until no fibers remain, and only nano-sized (thickness) fibers.

[0011] If the process continues and the fibers are broken up into smaller and smaller fibers, they eventually become cellulose fragments. Grinding to virgin fibers can be referred to as "nano-fibrillation", which can be a smooth transition between two states.

[0012] The achievable fragmentation of conventional breaking mills is however limited. In addition, many other apparatus for grinding particles is not able to crush cellulose fibers for nano-fibers, such as the loosening devices mentioned in US 2001/0045264, which are only able to separate fractions of a given fiber size from each other.

[0013] Similarly, WO 02/090651 describes a method for recycling waste pulp generated during the production of paper, cardboard or cardboard, where cleaner waste containing fibers, pigments and / or fibers, among others, was fined to grains of a certain size using ball mills. However, there is no mention of fibrillation of the current fibers, let alone fibrillation into nano-fibrils.

[0014] If further refining of the fibers into nano-fibers is desired, other methods are necessary.

[0015] For example, US 4,374,702 describes a method of making microfibrillated cellulose comprising passing a liquid cellulose fibrous suspension through a high pressure homogenizer having a small hole diameter in which the suspension is subjected to a pressure drop of at least 3,000 psi, and a shear action of high speed, then hitting the solid surface at high speed, repeating the passage of this suspension through the opening until this cellulose suspension becomes a substantially stable suspension, thereby converting this cellulose into microfibrillated cellulose without a substantial chemical change in the starting cellulosic material.

[0016] US 6,183,596 B1 discloses a method of producing super-microfibrillated cellulose by passing a slurry of previously grated pulp through a grinding apparatus having two or more grinding mills that are positioned so that they can co-grind for microfibrillation of the pulp to obtain microfibrillated cellulose and then for further super-microfibrillation of the obtained microfibrillated cellulose using a high pressure homogenizer, to obtain super-microfibrillated cellulose.

[0017] In addition, highly comminuting grinding mill can be used, where the grinding mill reduces the fibers to fine particles due to mechanical shear (see e.g. US 6,214,163 B1).

[0018] There are a number of problems regarding cellulose fiber fibrillation that need to be overcome.

[0019] For example, the mechanical production of nanofibrillary cellulose often has the problem of increasing viscosity during the fibrillation process. This can stop the process completely or increase the demand for specific energy.

[0020] The efficiency of comminution processes is often quite low and the amount of fibers only cut but not fibrillated is significant.

[0021] Thus, there is a continuing need to provide more efficient methods for producing nanofibrillary cellulose suspensions, and one object of the present invention is to provide a new and effective method for producing cellulose nanofibrillary suspensions.

[0022] The addition and co-processing of pulp containing certain fillers and / or pigments with cellulose fibers has been found to have a positive effect on the fibrillation process in many references as described in more detail below.

[0023] Thus, the method of the present invention is characterized by the following steps:

(a) providing cellulose fibers in the form of a suspension;

(b) providing at least one filler and / or pigment;

(c) combining cellulose fibers and at least one filler and / or pigment;

(d) fibrillating cellulose fibers in the presence of at least one filler and / or pigment until no fibers remain and only primary cellulose fibrils are obtained.

[0024] Nanofibrillary cellulose in the context of the present invention means fibers that break down into primary fibers.

[0025] In this regard, fibrillation in the context of the present invention means any process that mainly breaks down the fibers and filaments along their long axis resulting in a reduction in the diameter of the fibers and filaments, respectively.

[0026] The cellulose fibers that can be used in the method of the present invention may be those contained in pulp selected from the group consisting of eucalyptus pulp, spruce pulp, pine pulp, beech pulp, hemp pulp, cotton pulp and mixtures thereof. In this regard, the use of sulfate pulp, especially bleached long fiber sulfate pulp may be particularly advantageous.

[0027] Cellulose fibers are provided in the form of a suspension, especially an aqueous suspension. Preferably, such suspensions have a solids content of 0.2 to 35% by weight, more preferably 0.25 to 10% by weight, especially 1 to 5% by weight, and most preferably 2 to 4.5% by weight, e.g. 3 wt. or 3.5 wt.

[0028] At least one filler and / or pigment is selected from the group consisting of precipitated calcium carbonate; natural ground calcium carbonate; dolomite; talc; bentonite; clay; magnesite; satin white; sepiolite, huntite, diatomite; silicates; and mixtures thereof. Precipitated calcium carbonate, which may have a wateritic, calcitic or aragonitic crystal structure, and / or natural ground calcium carbonate, which may be selected from marble, limestone and / or chalk, are particularly preferred.

[0029] In a particular embodiment, it may be advantageous to use ultra-fine, separate prismatic, scalenohedral or rhombohedral precipitated calcium carbonate. [0030] Fillers and / or pigments may be provided in the form of a powder, although they are preferably added in the form of a suspension, such as an aqueous suspension. In this case, the solids content of the suspension is not critical as long as it is a pumpable liquid.

[0031] In a preferred embodiment, the filler and / or pigment particles have an average particle size determined by sedimentation from 0.5 to 15 pm, preferably 0.7 to 10 pm, more preferably 1 to 5 pm, and most preferably 1.1 to 2 pm e.g. 1.5 pm or 3.2 pm

[0032] To determine the average particle size, a Sedigraph 5100 device from Micromeritics, USA was used. The measurement was carried out in an aqueous solution of 0.1 wt. Na4P2O7. Samples were dispersed using a high speed stirrer and ultrasound. [0033] Fillers and / or pigments may be associated with dispersing agents, such as those selected from the group consisting of homopolymers or copolymers of polycarboxylic acid salts based on, e.g., acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acrylamide and mixtures thereof; alkali metal polyphosphates, phosphonic, citric and tartaric acid and their soluble salts; or a mixture thereof.

[0034] The combination of fibers and at least one filler and / or pigment can be carried out by adding the filler and / or pigment to the fibers in one or more stages. The filler and / or pigment may be added in whole or in part before, during the fibrillation step. However, pre-fibrillation is preferred.

In one embodiment, the pH of the combination of cellulose fibers and at least one filler and / or pigment is adjusted to a pH of 10 to 12, e.g. 11, before fibrillation.

[0036] This adjustment to an alkaline pH can be carried out by adding preferably milk (Ca (OH) 2) or any other base. After co-processing, the pH in the suspension may then be adjusted again to about 7.5 to 9.5, e.g. 8.5.

[0037] Generally, the pH of the suspension containing the combination of fibers and pigment and / or filler should not be less than 6.

[0038] It may also be necessary to stabilize the pH, e.g. after adding PCC to the fiber suspension, which may lead to an increase in pH and a decrease in ° SR. In this case, the pH can be re-adjusted by using commonly used acids or buffers to avoid a decrease in the Schopper Riegler degree due to the effect of pH increase. In addition, in one embodiment, the combination is stored for 2 to 12 hours, preferably 3 to 10 hours, more preferably 4 to 8 hours, e.g. 6 hours before its fibrillation, because in the ideal case it results in swelling of the fibers, facilitating the fibrillation, which leads to an increase in the grinding degree (° SR) and a lower specific energy consumption of breaking particles for the same degree of grinding ° SR.

[0039] Fiber swelling can be facilitated by storage at elevated pH, as well as by the addition of cellulose solvents e.g. ethylenediamine copper (II), ferric sodium tartrate or lithium / dimethylacetamine chloride, or by another method known in the art.

[0040] Preferably, the weight ratio of fibers to fillers and / or pigments based on dry weight is from 1:10 to 10: 1, more preferably 1: 6 to 6: 1, even more preferably 1: 4 to 4: 1, especially 1 : 3 to 3: 1, most preferably 1: 2 to 2: 1, e.g. 1: 1.

[0041] For example, in one particularly preferred embodiment, 70 wt. bleached long fiber sulphate pulp is fibrillated in the presence of 30 wt. ultra-fine separate prismatic (or rhombohedral) PCC, relative to pulp and PCC dry matter, respectively.

[0042] One sign of cellulose fibrillation according to the present invention is an increase in the degree of Schopper Riegler (° C).

[0043] The Schopper-Riegler degree (° SR) is a measure of the rate at which the diluted pulp suspension can be dewatered and is determined according to Zellcheming Merkblatt V / 7/61 and normalized with ISO 5267/1.

[0044] The value is determined by gently dispersing the pulp in water and introducing it into the drainage chamber, where the sealing cone is closed. The sealing cone lifts pneumatically from the drain chamber, and depending on the state of the fiber suspension, water flows out faster or slower from the drain chamber through a side outlet to the measuring cylinder. Water is measured in the cylinder, with 10 ml of water corresponding to 1 ° SR, and the higher the Schopper-Riegler value, the finer the grinding.

[0045] For measuring the Schopper Riegler degree, any suitable device can be used, such as the "Automatic Freeness Tester" provided by Rycobel, Belgium. [0046] Preferably, the combination is fibrillated until the Schopper Riegler degree increases by> 4 ° SR, in particular> 6 ° SR, more preferably> 8 ° SR, most preferably> 10 ° SR, especially> 15 ° SR.

In a preferred embodiment, the combination of fibers and filler and / or pigment is fibrillated until a final Schopper Riegler degree of suspension obtained> 30, preferably> 45 ° SR, more preferably> 50 ° SR, in particular> 60 ° SR, e.g. > 70 ° SR, especially> 80 ° SR.

[0048] In a particular embodiment, it is however preferred that the final Schopper Riegler degree is <95 ° SR.

[0049] The initial Schopper-Riegler degree may be from about 5 to about 90 ° SR, preferably <10 ° SR, preferably <25 ° SR, more preferably <40 ° SR, e.g. <60 or <75 ° SR. It can also be greater than 80 ° SR if the Δ ° SR obtained as a result of the fibrillation step is> 4 ° SR.

[0050] Looking at the Schopper Riegler degree, it has also been found that the method of the present invention is much more efficient than subjecting fibrillation to fiber suspensions without pigments and / or fillers.

[0051] This can be seen by the increased ° SR per transition. To optimize fibrillation, the fiber suspension is usually processed by subjecting it to several passages through a fibrillation device.

[0052] In this regard, it can be seen that, according to the method of the present invention, the SR per transition is much larger than just for fiber suspensions. [0053] This effect can be observed immediately and occurs up to a certain number of passes until a further increase in ° SR is already achieved.

[0054] Thus, in a particular embodiment, the Schopper Riegler grade per transition is higher for the method of the present invention relative to the fibrillated fiber suspension in the absence of pigment and / or filler until a significant increase can be observed in both cases.

[0055] Furthermore, due to the method of the present invention, it is possible to obtain nanofibrillary cellulose suspensions whose Brookfield viscosity is lower than the Brookfield viscosity of the corresponding nanofibrillary cellulose suspension to be fibrillated in the absence of fillers and / or pigments.

[0056] Brookfield viscosity can generally be measured by any Brookfield viscometer using routine operations known to a person skilled in the art.

[0057] Fibrillation is carried out by any device useful for this, as mentioned above. Preferably the device is selected from the group consisting of highly comminuting grinding mills such as Super Mass Colloider, breaking mills and homogenizers.

[0058] In this connection, it can be seen that the pulp combined with pigments and / or fillers for the method of the present invention has better working properties, so that pulp which usually does not pass through the breaking mill can be used if it is processed according to of the present invention.

[0059] Another aspect of the present invention is a suspension of nanofibrillary cellulose obtained by the methods of the invention.

[0060] Furthermore, an aspect of the present invention is the preferred use of a suspension of nanofibrillary cellulose obtained by the methods of the invention in the production of paper and / or finishing of paper.

[0061] The nanofibrillary cellulose suspensions of the present invention may improve the strength of the paper and may allow an increase in filler load in uncoated papers with a low wood pulp content.

[0062] Due to their mechanical strength properties, nanofibrillary cellulose is, however, also preferably used in applications such as material composites, plastics, paints, rubber, concrete, ceramics, adhesives, food or wound healing applications.

[0063] The figures described below and the examples and experiments serve to illustrate the present invention and should not limit it in any way.

Description of figures:

[0064] Figure 1 shows ° SR / transition for fibrillated pulp suspensions with or without various natural ground calcium carbonates.

Examples

1. Growth ° SR / transition using GCC [0065] For the development study ° SR / transition, eucalyptus pulp with ° SR 25 was first treated in a highly grinding abrasive mill at 4 wt. solids content and without adding GCC. A similar experiment was carried out in a homogenizer with eucalyptus pulp at 1.5% by weight solids content, with or without GCC.

Material [0066]

GCC:

Omyacarb 1-AV (solids content 100% by weight based on the weight of the fibers present) available from Omya AG. The weight median particle size d50 = 1.7 pm when measuring Sedigraph 5100.

Omyacarb 10-AV (solids content 100% by weight based on the weight of the fibers present) available from Omya AG. The weight median particle size d50 is 10.0 pm when measured with the Sedigraph 5100.

Pulp:

25 ° SR eucalyptus pulp.

Example 1 - Highly grinding grinding mill [0067] For the comparative example, eucalyptus pulp was used in the form of 500 g dry mats per mat (700 x 1000 x 1.5 mm). 170 g of pulp is ripped into 40 x 40 mm pieces. 3 830 g of tap water were added. The suspension was stirred in a 10 dm bucket³ at 2000 rpm with a 70 mm diameter dissolution facilitating disc. The suspension was stirred for at least 15 minutes at 2000 rpm.

[0068] The suspension was then filtered using a highly comminuting grinding mill (Supermasscolloider from Masuko Sangyo Co. Ltd, Japan (Model MKCA 6-2). The grinding stones were made of silicon carbide with a grain size of 46 (grain size 297 420 pm). between the grinding stones was chosen so that point 0 was dynamic, as described in the instructions provided by the supplier. The speed of the rotating grinding mill was set at 1200 rpm. The suspension was recirculated several times and samples were taken. The Schopper-Riegler degree (° SR) was measured according to Zellcheming Merkblatt V / 7/61 and normalized to ISO 5267/1.

[0069] In the example of the invention, eucalyptus pulp was used in the form of 500 g dry mats per mat (700 x 1000 x 1.5 mm). 170 g of pulp is ripped into 40 x 40 mm pieces. 160 g Omyacarb 1-AV was added. 3 830 g of tap water were added. The suspension was stirred in a 10 dm bucket³ at 2000 rpm with a 70 mm diameter dissolution facilitating disc. The suspension was stirred for at least 15 minutes at 2000 rpm.

[0070] The suspension was then filtered using a highly comminuting grinding mill (Supermasscolloider from Masuko Sangyo Co. Ltd, Japan (Model MKCA 6-2). The grinding stones were made of silicon carbide with a grain size of 46 (grain size 297 420 pm). between the grinding stones was chosen so that point 0 was dynamic, as described in the instructions provided by the supplier. The speed of the rotating grinding mill was set at 1200 rpm. The suspension was recirculated several times and samples were taken. The Schopper-Riegler degree (° SR) was measured according to Zellcheming Merkblatt V / 7/61 and normalized to ISO 5267/1.

[0071] In the example of the invention, eucalyptus pulp was used in the form of 500 g dry mats per mat (700 x 1000 x 1.5 mm). 170 g of pulp is ripped into 40 x 40 mm pieces. 160 g Omyacarb 10-AV was added. 3 830 g of tap water were added. The suspension was stirred in a 10 dm bucket³ at 2000 rpm with a 70 mm diameter dissolution facilitating disc. The suspension was stirred for at least 15 minutes at 2000 rpm. The suspension was then filtered using a fine fraction mill (Supermasscolloider from Masuko Sangyo Co. Ltd, Japan (Model MKCA 6-2). The grinding stones were made of silicon carbide with a grain size of 46 (grain size 297-420)). The gap between the grinding stones is chosen so that point 0 is dynamic, as described in the instructions provided by the supplier. The speed of the rotating grinding mill was set at 1200 rpm. The suspension was recirculated several times and samples were taken. The Schopper-Riegler degree (° SR) was measured according to Zellcheming Merkblatt V / 7/61 and normalized to ISO 5267/1.

Results [0072] Figure 1 shows the ° SR changes as a function of passing through the Supermasscolloider. It will be obvious that adding GCC increases the device's performance per transition.

Example 2 - Homogenizer [0073] For the comparative example, eucalyptus pulp was used in the form of 500 g dry mats per mat (700 x 1000 x 1.5 mm). 47 g of pulp is ripped into 40 x 40 mm pieces. 2,953 g of tap water was added. The suspension was stirred in a 5 dm bucket³ at 2000 rpm with a 70 mm diameter dissolution facilitating disc. The suspension was stirred for at least 15 minutes at 2000 rpm.

[0074] This suspension was introduced into a homogenizer (GEA Niro Soavi NS2006L) but not passed through the machine.

[0075] In the example of the invention, eucalyptus pulp was used in the form of 500 g dry mats per mat (700 x 1000 x 1.5 mm). 47 g of pulp is ripped into 40 x 40 mm pieces. Omyacarb 1-AV 45 g was added. 2,953 g of tap water was added. The suspension was stirred in a 5 dm bucket³ at 2000 rpm with a 70 mm diameter dissolution facilitating disc. The suspension was stirred for at least 15 minutes at 2000 rpm.

[0076] This suspension was introduced into a homogenizer (GEA Niro Soavi NS2006L). The flow through the homogenizer was between 100 and 200 g min^-1and the pressure was set between 200 and 400 bar. The suspension was recirculated several times and samples were taken. The Schopper-Riegler degree (° SR) was measured according to Zellcheming Merkblatt V / 7/61 and normalized to ISO 5267/1.

Results [0077] A reference sample that did not contain GCC could not be introduced through the homogenizer. Only the sample containing GCC showed good performance. The Schopper-Riegler values ​​are given in Table 1, after 5 and 10 passes through a homogenizer.

Table 1:

<td>transitions</td><td>° SR</td>

<td> 0</td><td> 25</td>

<td> 5</td><td> 74</td>

<td> 10</td><td> 91</td>

2. Increase in ° SR using PCC in a breaking mill

Example 3 - Ultra PCC

Material [0078]

PCC:

Ultra-fine prismatic PCC. The weight median particle size d50 = 1.14 pm when measuring Sedigraph 5100 (100% by weight of the particles have a diameter &lt;2 pm; 27% by weight of the particles have a diameter of &lt;1 [mu] m).

This PCC was provided as an aqueous suspension having a solids content of 7.9% by weight.

Pulp:

Bleached sulphate pulp with a long fiber of 16 ° SR.

[0079] The aqueous suspension was formed from the above carbonate and pulp, so that this suspension had a solids content of about 4 wt. and the carbonate: pulp weight ratio was 29: 71.

[0080] About 12.5 dm³ this suspension was recirculated during a 9 minute period by Escher Wyss R 1 L Labor-Refiner at 5.4 kW.

[0081] The Schopper-Riegler degree (° SR) of the resulting suspension of 92 ° SR was measured according to Zellcheming Merkblatt V / 7/61 and normalized to ISO 5267/1.

Example 4 - coarse-grained PCC

a) Suspension according to the invention

Material [0082]

PCC:

Scalenohedral PCC. The weight median particle size d50 = 3.27 pm when measuring Sedigraph 5100 (11 wt% of the particles have a diameter &lt;2 pm; 4 wt% of the particles have a diameter of &lt;1 [mu] m). This PCC was provided as an aqueous suspension having a solids content of 15.8%.

Pulp:

Eucalyptus at 38 ° SR.

[0083] The aqueous slurry was formed from the above carbonate and pulp, so that this slurry had a solids content of about 9.8 wt% and a carbonate: pulp weight ratio is 75: 25. This slurry showed 18 ° SR.

[0084] About 38 m³ this suspension was recirculated during a 17.5 hour period through Metso Refiner RF-0 at 92 kW with a flow rate of 63 m³/hour.

[0085] The Schopper-Riegler degree (° SR) of the resulting suspension of 73 ° SR was measured according to Zellcheming Merkblatt V / 7/61 and normalized to ISO 5267/1.

b) Comparative suspension

Material [0086]

PCC:

Scalenohedral PCC. The weight median particle size d50 = 3.27 pm when measuring Sedigraph 5100 (11 wt% of the particles have a diameter &lt;2 pm; 4 wt% of the particles have a diameter of &lt;1 [mu] m). This PCC was provided as an aqueous suspension having a solids content of 15.8%.

Pulp:

Eucalyptus at 38 ° SR.

[0087] The aqueous suspension was formed from the above pulp, such that this suspension had a solids content of about 4.5 wt.

[0088] About 20 m³ this suspension was recycled during a 17.5 hour period by Metso Refiner RF-0 at 92 kW with a flow rate of 63 m³/hour.

[0089] The Schopper-Riegler degree (° SR) of the resulting suspension of 65 ° SR was measured according to Zellcheming Merkblatt V / 7/61 and normalized to ISO 5267/1.

[0090] To this suspension, the above scalenohedral PCC was added in an amount to obtain a weight ratio of carbonate: pulp of 75: 25. The Schopper-Riegler degree (° SR) of the obtained 25 ° SR suspension was measured according to Zellcheming Merkblatt V / 7/61 and normalized from ISO 5267/1.

[0091] This clearly shows that the presence of calcium carbonate during the fibrillation step is significant for obtaining a high degree of Schopper Riegler, i.e. an effective fibrillation of cellulose fiber.