Process for the production of nano-fibrillar cellulose suspensions

PROCESS FOR PRODUCTION OF NANOFIBRILLARY CELLULOSE SUSPENSIONS

The present invention relates to a process for producing nanofibrillary cellulose suspensions and the nanofibrillary cellulose obtained by this process.

Cellulose is the structural component of the primary cell wall of green plants and is the most common organic compound on earth. It is of great interest in many applications and industries.

Cellulose is the main constituent of paper and board and textiles made of cotton, linen and other vegetable fibers. Cellulose can be converted into cellophane, a thin transparent film, and rayon, an important fiber that has been used for textiles since the early 20th century. Both cellophane and rayon are known as regenerated cellulose fibers.

Cellulose fibers are also used in liquid filtration to create a filter bed of inert material. Cellulose is additionally used to make hydrophilic and highly absorbent sponges.

For industrial use, 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 converted into a wide variety of derived products.

Cellulose pulp as raw material is processed from wood or stems from plants such as hemp, flax and abaca. Pulp fibers consist mainly of cellulose and other organic components (hemicellulose and lignin). Cellulose macromolecules (composed of β-D-glucose molecules with 1-4 glycosidic bonds) are linked together by hydrogen bonds to form the so-called primary fibril (micelles) which has crystalline and amorphous domains. Several primary fibrils (about 55) form what is called microfibrils. About 250 of these microfibrils form a fibril.

The fibrils are arranged in different layers (which may contain lignin and / or hemicellulose) to form a fiber. Individual fibers are also linked together by lignin.

Pulps used in papermaking are often obtained by milling the wood and optional heat and chemical processing to remove unwanted compounds from the cellulosic fibers.

The fibers are ground and cut to a certain fineness (depending on the desired properties). Fiber milling is achieved with a refiner (such as a rotor-stator or conical grinder or disc or double disc refiners). The refiner also fibrils the fibers on the surface, which means that some fibrils are partially pulled off the fiber surface. This leads to better retention, and often better adhesion to pigments that can be added in papermaking, and also to an improved potential for hydrogen bonding between paper fibers. This results in improved mechanical properties. A side effect is also that the paper becomes denser and more transparent because of a loss of light scattering as the size of the scattering centers moves away from the optimal acceptability of half the wavelength of light ( crystal paper and greaseproof paper).

When fibers become refined under applied energy, they become fibrillated once the cell walls are broken and torn into attached strips, i.e. fibrils. If this rupture is continued to separate the body's fibrils from the fiber, it releases the fibrils. Microfibril fiber breakage is referred to as microfibrillation. This process can be continued until there are no more fibers and only nano size (thickness) fibrils remain.

If the process goes further and breaks these fibrils into smaller and smaller fibrils, they eventually become cellulose fragments. The rupture in primary fibrils may be referred to as nano-fibrillation, where there may be a smooth transition between the two regimens.

mixer fibers

The fineness achievable with conventional refiners, however, is limited. In addition, various other particle breakers are not capable of breaking the cellulose into nano-fibrils (fluffers) mentioned in

2001/0045264, which are only capable of separating fractions of a certain fiber size from each other.

such as US document

Similarly, WO 02/090651 describes a method for recycling pulp waste generated during the manufacture of paper, cardboard or paperboard, in which the cleanest scrap containing, inter alia, fibers, pigments and / or fibers are milled to a certain grain size by ball mills. However, no mention is made of fibrillation of the fibers present, let alone nano-fiber fibrillation.

If additional nanofiber fiber decomposition is desired, other methods are required.

For example, US 4,374,702 discloses a process for the preparation of microfibrillated cellulose which comprises passing a light suspension of fibrous cellulose through a high pressure homogenizer which has a small diameter hole in which the suspension is subjected to a suspension. at least 206.84 bar (3000 psi) and a high-speed shear action followed by a high-speed deceleration impact against a solid surface, repeating the passage of said suspension through the orifice until said cellulose suspension becomes a substantially stable suspension, said process converting said cellulose to microfibrillated cellulose without substantial chemical alteration of the cellulose starting material.

US 6,183,596 Bl discloses a process for producing super microfibrated cellulose by passing a slurry from a previously beaten pulp through a friction apparatus, which has two or more crushers, which are arranged so that they can be scrubbed at one end. another to microfibrillate the pulp to obtain microfibrillated cellulose and still super microfibrillate the microfibrillate obtained with a pressure homogenizer to obtain the super microfibrillate cellulose high

In addition, they can ultrafine, where mechanical shear being used mill reduces (eg cf.

fine fiber friction mills by US 6,214,163 Bl).

There are numerous problems related to cellulose fibers that have to be overcome.

fibrillation of

For example, mechanical production often has the problem of one during the process of completely or increasing fibrillation process required.

nanofibrillary cellulose, increased viscosity This can stop the specific energy

The efficiency of the rupture processes is often quite low, and there is a considerable amount of fibers just cut but not fibrillated into fibrils.

Accordingly, there is a continuing need to provide more efficient processes for producing nanofibrillary cellulose suspensions, and it is an object of the present invention to provide a new and efficient process for producing nanofibrillary cellulose suspensions.

It has been found that the addition and co-processing of certain pulp-containing cellulose fiber fillers and / or pigments can have a positive influence on the shredding process in many ways as described in more detail below.

Thus, the process of the present invention is characterized by the following steps:

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

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

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

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

Nanofibrillary cellulose in the context of the present invention means fibers which are decomposed into primary fibrils.

In this regard, fibrillation in the context of the present invention means any process which predominantly decomposes the fibers and fibrils along their longitudinal axis, resulting in a decrease in fiber and fibril diameter, respectively.

<td>Cellulose fibers,</td><td>gue</td><td>may</td><td>to be</td><td>used</td><td>at the</td>

<td colspan="2">process of the present invention,</td><td>may</td><td>to be</td><td>the contained</td><td>in</td>

<td>selected folders from</td><td>group</td><td>gue</td><td colspan="2">understands folder</td><td>in</td>

Eucalyptus, spruce paste, pine paste, beech paste, hemp paste, cotton paste, and mixtures thereof. In this regard, the use of kraft pulp, especially bleached long fiber kraft pulp may be especially preferred.

Cellulose fibers are provided in the form of a suspension, in particular an aqueous suspension. Preferably, these suspensions have a solids content of 0.2 to 35 wt%, more preferably 0.25 to 10 wt%, especially 1 to 5 wt%, and more preferably 2 to 4.5 wt%. weight, for example 1.3 wt% or 3.5 wt%.

The at least one filler and / or pigment is selected from the group comprising precipitated calcium carbonate; natural ground calcium carbonate; dolomite; baby powder; bentonite; clay; magnesite; white satin; sepiolite, huntitis, diatomitis; silicates; and their mixtures. Precipitated calcium carbonate, may have vateritic, calcitic or aragonitic crystal structure, and / or ground natural calcium carbonate, may be selected from marble, limestone and / or chalk, are especially preferred.

In a special embodiment, the use of discrete, scalenohedral or rhombohedral prismatic ultrafine precipitated calcium carbonate may be advantageous.

Fillers and / or pigments may be provided as a powder, although preferably they are added as 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.

In a preferred embodiment, the filler and / or pigment particles have an average particle size determined by the settling method from 0.5 to 15 pm, preferably 0.7 to 10 pm, more preferably from 1 to 5. pm and more preferably 1.1 to 2 pm, for example 1.5 pm or 3.2 pm.

To determine the average particle size, a Sedigraph 5100 device from Micromeritics, USA was used. Measurement was performed in a 0.1 wt% aqueous solution of Na4P2Cg. Samples were dispersed using a high speed stirrer and ultrasound.

Fillers and / or pigments may be associated with dispersing agents, such as those selected from the group comprising polycarboxylic acid salt homopolymers or copolymers based on, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acrylamide or mixtures thereof; alkaline polyphosphates, phosphonic acids, citric and tartaric acids and their soluble salts; or a mixture thereof.

The combination of fibers and at least one filler and / or pigment may be accomplished by adding the filler and / or pigment to the fibers in one or several steps. The filler and / or pigment may be added completely or in portions prior to or during the fibrillation step. However, addition is preferred prior to fibrillation.

In one embodiment, prior to fibrillation, the pH of the cellulose fiber blend and at least one filler and / or pigment is adjusted to a pH of 10 to 12, for example 11.

This adjustment to alkaline pH can be made by the addition of preferably lime 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.

Generally, the pH of the suspension comprising the combination of fiber and pigment and / or filler should not be less than 6.

It may also be necessary to stabilize the pH, for example by the addition of PCC to a fiber suspension, which may lead to an increase in pH, and a drop of ° SR. In this case the pH may be readjusted by commonly used acids or buffers in order to prevent the Schopper Riegler grade from dropping due to the influence of an increase in pH.

Furthermore, in one embodiment, the combination is stored for 2 to 12 hours, preferably 3 to 10 hours, more preferably 4 to 8 hours, for example 6 hours, before fibrillation, as this ideally results in fiber dilation. which facilitates fibrillation and thereby leads to a faster increase in freeness (° SR) and lower specific refining energy consumption for the same freeness ° SR.

Fiber swelling may be facilitated by storage at increased pH, as well as by the addition of solvents such as sodium and cellulose, such as lithium tartrate / dimethylacetamine, or as known in the art.

copper (II) ethylendiamine, iron, or chloro any other method

Preferably, the weight ratio of fibers to filler and / or pigments on a dry weight basis is 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, and more preferably 1: 2 to 2: 1, for example, 1: 1.

For example, in an especially preferred embodiment, 70% by weight of long fiber bleached kraft pulp is fibrillated in the presence of 30% by weight of discrete (or rhombohedral) prismatic ultrafine PCC relative to the total dry weight of pulp and PCC, respectively.

An indication of cellulose fibrillation according to the present invention is the increase in Schopper Riegler grade (° C).

Schopper-Riegler grade (° SR) is a measure of the speed at which a dilute slurry suspension can be dehydrated and is specified according to Zellcheming Merkblatt V / 7/61 and standardized to ISO 5267/1.

The value is determined by gently dispersing the paste in water and placing it within a drainage chamber where a sealing cone is closed. The sealing cone is pneumatically lifted from the drainage chamber, and, depending on the condition of the fiber suspension, water flows more or less rapidly from the drainage chamber through a side outlet to a graduated cylinder. Water is measured in the cylinder, where 10 mL of water corresponds to 1 ° SR, and the higher the Schopper-Riegler value, the finer the freeness.

To measure suitable, Automatic Belgium.

the Schopper Riegler grade any devices can therefore be used as the

Freeness Tester provided by Rycobel,

Preferably, the combination is fibrillated until the Schopper Riegler grade is increased by&gt; 4 ° SR, particularly&gt; 6 ° SR, more preferably&gt; 8 ° SR, more preferably&gt; 10 ° SR, especially&gt; 15 ° SR.

In a preferred embodiment, the combination of fibers and filler and / or pigment is fibrillated until a final Schopper-Riegler grade of the resulting suspension of&gt; 30, preferably&gt; 45 ° SR, more preferably&gt; 50 ° SR, is reached, particularly&gt; 60 ° SR, for example&gt; 70 ° SR, especially&gt; 80 ° SR.

In a special embodiment, however, it is preferred that the final Schopper Riegler grade is d 95 ° SR.

Schopper-Riegler grade at about 90 ° SR, preferably ° SR, for example &lt;60 or

<td>greater than 80 fibrillation for</td><td>° SR, if the &gt; 4th SR.</td><td>Δ</td>

<td>By observing the</td><td colspan="2">Schopper grade</td>

<td>that the process</td><td>according</td><td>with</td>

<td colspan="2">more efficient than</td><td>at</td>

<td>fibrillation</td><td>absence</td><td>in</td>

filling.

The starting point may preferably be d 10 &lt;25 ° SR, more preferably &lt;75 ° SR. The resulting SR of 5 ° SR, &lt;40 may also be from the

Riegler, it has also been found the present invention is very pigment fiber suspensions and / or

This can be observed by an increased ° SR per pass. In order to optimize fibrillation, the fiber suspension is usually processed by subjecting it to several passes through the fibrillation device.

In this regard it can be seen that according to the process of the present invention the SR ° per pass is markedly higher than with fiber suspensions only.

This effect can be observed immediately and occurs up to a number of passages when no further increase in ° SR can be achieved.

Thus, in a special embodiment, the Schopper Riegler grade per pass is higher for the process of the present invention than for fibrillated fiber suspensions in the absence of pigment and / or filler until an additional essential increase is already achieved. cannot be observed in both cases.

Further, by the process of the present invention, nanofibrillary cellulose suspensions can be obtained, the Brookfield viscosity of which is lower than the Brookfield viscosity of a corresponding nanofibrillary cellulose suspension, which has been fibrillated in the absence of fillers and / or pigments.

Brookfield viscosity can generally be measured with any conventional Brookfield viscosimeter using routine operations known to those skilled in the art.

Fibrillation is therefore performed by any useful device as mentioned above. Preferably, the device is selected from the group comprising ultrathin friction mills such as a Super Mass Colloider, refiners, and homogenizers.

In this regard, it can be seen that the pulp combined with pigments and / or fillers for the process according to the present invention has a better operability, such that the pulp, which normally cannot be passed through a refiner, may be used if processed in accordance with the present invention.

Another aspect of the present invention is the nanofibrillary cellulose suspension obtained by the processes according to the invention.

Furthermore, an aspect of the invention is the advantageous use of the nanofibrillary cellulose suspension obtained by the processes according to the invention in the manufacture and / or finishing of paper.

Nanofibrillary cellulose suspensions according to the present invention may improve paper strength and may allow an increase in filler load on uncoated chemical pulp papers.

Due to its mechanical resistance properties to nanofibrillary cellulose, however, it is also advantageously used in applications such as composite materials, plastics, paints, rubber, concrete, ceramics, adhesives, food products, or wound healing applications.

The following figures and examples and experiments serve to illustrate the present invention and should not limit it in any way.

Description of the figures:

Figure 1 shows the ° SR / passage for fibrillated pulp suspensions with and without different natural ground calcium carbonates.

Examples

1. SR ° increase / pass using GCC

To examine the development of ° SR / passage, eucalyptus pulp with an ° SR of 25 was first treated in a 4 wt% ultrafine solids friction mill with and without the addition of GCC. A similar experiment was performed on a 1.5 wt% eucalyptus paste homogenizer with and without GCC.

Material

CCG: Omyacarb 1-AV (100 wt.% Solids content based on fiber weight present) available from Omya AG. The average particle size weight dso = 1.7 pm measured by Sedigraph 5100.

Omyacarb 10-AV (100% by weight solids content based on fiber weight present) available from Omya AG. The average particle size weight of this is 10.0 µm measured by Sedigraph 5100.

Paste: 25 ° SR eucalyptus paste.

Example 1 - Ultrathin Friction Mill

For the comparative example, eucalyptus pulp was used in the form of dry mats of 500 g per mat (700 x 1,000 x 1,5 mm). 170 g of pulp thereof was torn into 40 x 40 mm pieces. 3,830 g of tap water were added. The suspension was stirred in a 10 dm bucket.³ at 2,000 rpm using a 70 mm diameter dissolving disc. The suspension was stirred for at least 15 minutes at 2,000 rpm.

The suspension was then fibrillated with an ultrafine friction mill (Supermasscolloider from Masuko Sangyo Co. Ltd, Japan (Model MKCA 6-2) .The grinding stones were silicon carbide with a grain class of 46 (grain size 297- 420 pm) .The gap between the grinding stones was chosen to be the dynamic 0 point as described in the supplier supplied manual.The mill rotational speed was set to be 1,200 rpm. The suspension was recirculated several times and samples were taken. Schopper-Riegler grade (° SR) was measured according to Zellcheming Merkblatt V / 7/61 and standardized to ISO 5267/1.

For the example of the invention eucalyptus pulp was used in the form of 500 g dry mat per mat (700 x 1,000 x 1,5 mm). 170 g of pulp thereof was torn into 40 x 40 mm pieces. 160 g of Omyacarb 1-AV were added. 3,830 g of tap water were added. The suspension was stirred in a 10 dm bucket.³ at 2,000 rpm using a 70 mm diameter dissolving disc. The suspension was stirred for at least 15 minutes at 2,000 rpm.

The suspension was then fibrillated with an ultrafine friction mill (Supermasscolloider from Masuko Sangyo Co. Ltd, Japan (Model MKCA 6-2) .The grinding stones were silicon carbide with a grain grade 46 (grain size 297-420 The gap between the grinding stones was chosen to be the dynamic 0 point, as described in the manual provided by the supplier The mill rotational speed was set to be 1,200 rpm. The suspension was recirculated several times and samples were taken. Schopper-Riegler grade (° SR) was measured according to Zellcheming Merkblatt V / 7/61 and standardized to ISO 5267/1.

For the example of the invention eucalyptus pulp was used in the form of 500 g dry mat per mat (700 x 1,000 x 1,5 mm). 170 g of pulp thereof was torn into 40 x 40 mm pieces. 160 g of Omyacarb 10-AV was added. 3,830 g of tap water were added. The suspension was stirred in a 10 dm bucket.³ at 2,000 rpm using a 70 mm diameter dissolving disc. The suspension was stirred for at least 15 minutes at 2,000 rpm.

The suspension was then fibrillated with an ultrafine friction mill (Supermasscolloider from Masuko Sangyo Co. Ltd, Japan (Model MKCA 6-2) .The grinding stones were silicon carbide with a grain grade 46 (grain size 297-420 The gap between the grinding stones was chosen to be the dynamic 0 point, as described in the manual provided by the supplier The mill rotational speed was set to be 1,200 rpm. The suspension was recirculated several times and samples were taken. Schopper-Riegler grade (° SR) was measured according to Zellcheming Merkblatt V / 7/61 and standardized to ISO 5267/1.

Results

Figure 1 shows the development of ° SR as a function of passages through the Supermasscolloider. It is evident that the addition of GCC increases the efficiency of the device per pass.

Example 2 - Homogenizer

For the comparative example, eucalyptus pulp was used in the form of dry mats of 500 g per mat (700 x 1,000 x 1,5 mm). 47 g of pulp was torn into 40 x 40 mm pieces. 2,953 g of tap water were added. The suspension was stirred in a 5 dm bucket.³ at 2,000 rpm using a 70 mm diameter dissolving disc. The suspension was stirred for at least 15 minutes at 2,000 rpm.

This suspension was fed into the Homogenizer (GEA Niro Soavi NS2006L), but was not passed through the machine.

For the pulp of the example of the invention eucalyptus pulp was used as dry mats of 500 g per mat (700 x 1,000 x 1,5 mm). 47 g of pulp thereof was torn into 40 x 40 mm pieces. 45 g of Omyacarb 1-AV were added. 2,953 g of tap water were added. The suspension was stirred in a 5 dm bucket.³ The

2,000 rpm using a 70 mm diameter dissolving disc. The suspension was stirred for at least 15 minutes at 2,000 rpm.

This suspension was fed into the Homogenizer (GEA Niro Soavi NS2006L). The flow through the homogenizer was between 100 and 200 g min.^-1 and the pressure was adjusted to be between 200 and 400 bar. The suspension was recirculated several times and samples were taken. SchopperRiegler grade (° SR) was measured according to Zellcheming Merkblatt V / 7/61 and standardized to ISO 5267/1.

Results

The comparative sample that did not contain GCC could not be fed through the homogenizer. Only the sample containing GCC showed good operability. Schopper-Riegler values ​​are reported in Table 1 after 5 and 10 passes through the homogenizer.

Table 1:

<td>Tickets</td><td>° SR</td>

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

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

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

2. Increase SR ° using PCC in a refiner

Example 3 - Ultrathin PCC

Material

PCC: Ultrathin Prismatic PCC. The average particle size weight dso = 1.14 pm measured by Sedigraph 5100 (100 wt% of particles have a diameter &lt;2 pm; 27 wt% of particles have a diameter &lt;1 pm).

This PCC was supplied as an aqueous suspension with a solids content of 7.9 wt%.

Pulp: 16 ° SR long fiber bleached kraft pulp.

An aqueous suspension was formed from the above carbonate and paste such that this suspension had a solids content of approximately 4 wt% and a carbonate: paste weight ratio of 29: 71.

About 12.5 dm³ of this suspension were circulated for a period of 9 minutes through an Escher Wyss R 1 L Labor-Refiner under 5.4 kW.

The Schopper-Riegler grade (° SR) of the suspension obtained at 92 ° SR was measured according to Zellcheming Merkblatt V / 7/61 and standardized to ISO 5267/1.

Example 4 - Wholesale CCP

a) Suspension according to the invention

Material

CCP: Scalenohedral CCP. The average particle size weight dso = 3.27 pm measured by Sedigraph 5100 (11 wt% of particles have a diameter of &lt;2 pm, 4 wt% of particles have a diameter of &lt;1 pm). This PCC was supplied as an aqueous suspension with a solids content of 15.8%.

Paste: Eucalyptus with 38 ° SR.

An aqueous suspension was formed from the above carbonate and slurry such that this suspension had a solids content of about 9.8 wt% and a carbonate: slurry weight ratio of 75: 25.

About 38 m³ of this suspension were circulated for a period of 17.5 hours through a Metso Refiner RF-0 under 92 kW at a flow rate of 63 m³/hour.

The Schopper-Riegler grade (° SR) of the suspension obtained at 73 ° SR was measured according to Zellcheming Merkblatt V / 7/61 and standardized to ISO 5267/1.

b) Comparative Suspension

Material

CCP: Scalenohedral CCP. The average particle size weight dso = 3.27 pm measured by Sedigraph 5100 (11 wt% of particles have a diameter of &lt;2 pm, 4 wt% of particles have a diameter of &lt;1 pm). This PCC was supplied as an aqueous suspension with a solids content of 15.8%.

Paste: Eucalyptus with 38 ° SR.

An aqueous suspension was formed from the above slurry so that this suspension had a solids content of approximately 4.5% by weight.

About 20 m³ of this suspension were circulated for a period of 17.5 hours through a Metso Refiner RF-0 under 92 kW at a flow rate of 63 m³/hour.

The Schopper-Riegler grade (° SR) of the suspension obtained at 65 ° SR was measured according to Zellcheming Merkblatt V / 7/61 and standardized to ISO 5267/1.

To this suspension, the above scalenohedral PCC was added in an amount to obtain a 75: 25 weight ratio of carbonate: paste. The SchopperRiegler grade (° SR) of the suspension obtained at 25 ° SR was measured according to Zellcheming Merkblatt. V / 7/61 and standardized on ISO 5267/1.

This clearly demonstrates that the presence of calcium carbonate during the fibrillation step is essential for achieving a high Schopper Riegler grade, ie efficient fibrillation of the cellulose fibers.