PROCESS FOR THE PRODUCTION OF NANO-FIBRILLAR CELLULOSE GELS

Abstract

The present invention relates to a process for the production of naso-fibrillar cellulose gels by providing cellulose fibres and at least one filler and/or pigment; combining the cellulose fibres and the at least one filler and/or pigment; and fibrillating the cellulose fibres in the presence of the at least one filler and/or pigment until a gel is formed, as well as the nano-fibrillar cellulose gel obtained by this process and uses thereof.

Claims

1-17. (canceled)

18. A process for the production of a nano-fibrillar cellulose gel, characterized by the steps of: (a) providing cellulose fibres, wherein all or part of the cellulose fibres may be obtained from a recycled pulp; (b) providing at least one filler and/or pigment; (c) combining the cellulose fibres and the at least one filler and/or pigment of step (b); and (d) fibrillating the cellulose fibres in an aqueous environment in the presence of the at least one filler and/or pigment in a homogenizer or an ultra-fine friction grinder until a nano-fibrillar cellulose gel is formed, wherein the formation of the gel is verified by monitoring the viscosity of the cellulose fibres in the aqueous environment in the presence of the at least one filler and/or pigment in step (d) in dependence of the shearing rate, wherein the viscosity decrease upon step-wise increase of the shearing rate is stronger than the corresponding viscosity increase upon subsequent step-wise reduction of the shearing rate over at least part of the shear rate range as shearing approaches zero; and wherein in step (d) the weight ratio of fibres to filler on a dry weight basis is from 1:33 to 10:1.

19. The process according to claim 18, wherein the cellulose fibres in step (a) are provided in the form of a suspension.

20. The process according to claim 19, wherein the cellulose fibres in step (a) are provided in the form of a suspension at a solids content of from 0.2 to 35 wt-%.

21. The process according to claim 19, wherein the cellulose fibres in step (a) are provided in the form of a suspension at a solids content of from 0.25 to 10 wt-%.

22. The process according to claim 19, wherein the cellulose fibres in step (a) are provided in the form of a suspension at a solids content of from 0.5 to 5 wt-%.

23. The process according to claim 19, wherein the cellulose fibres in step (a) are provided in the form of a suspension at a solids content of from 1 to 4 wt-%.

24. The process according to claim 19, wherein the cellulose fibres in step (a) are provided in the form of a suspension at a solids content of from 1.3 to 3 wt-%.

25. The process according to claim 18, wherein the filler in step (b) is in the form of particles having a medium particle size of from 0.01 to 15 μm.

26. The process according to claim 18, wherein the filler in step (b) is in the form of particles having a medium particle size of from 0.1 to 10 μm.

27. The process according to claim 18, wherein the filler in step (b) is in the form of particles having a medium particle size of from 0.3 to 5 μm.

28. The process according to claim 18, wherein the filler in step (b) is in the form of particles having a medium particle size of from 0.5 to 4 μm.

29. The process according to claim 18, wherein the filler in step (b) comprises a dispersing agent.

30. The process according to claim 29, wherein the dispersing agent is selected from homopolymers or copolymers of polycarboxylic acids and/or their salts or esters, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acryl amide or acrylic esters, or mixtures thereof alkali polyphosphates, phosphonic-, citric- and tartaric acids, salts or esters thereof or mixtures thereof.

31. The process according to claim 18, wherein in step (d) the weight ratio of fibres to filler on a dry weight basis is from 1:10 to 7:1.

32. The process according to claim 18, wherein in step (d) the weight ratio of fibres to filler on a dry weight basis is from 1:5 to 5:1.

33. The process according to claim 18, wherein in step (d) the weight ratio of fibres to filler on a dry weight basis is from 1:3 to 3:1.

34. The process according to claim 18, wherein in step (d) the weight ratio of fibres to filler on a dry weight basis is from 1:2 to 2:1.

35. The process according to claim 18, wherein in step (d) the weight ratio of fibres to filler on a dry weight basis is from 1:1.5 to 1.5:1.

36. A material composite, plastic, paint, rubber, concrete, ceramic, adhesive, food or wound-healing composite comprising the nano-fibrillar cellulose gel according to claim 18.

Description

DESCRIPTION OF THE FIGURES

[0061] FIG. 1 shows the Brookfield viscosity progression during homogenizing of pulp mixtures with and without calcium carbonate.

[0062] FIG. 2 shows the Brookfield viscosity of pulp mixtures with and without calcium carbonate, added before or after homogenization.

[0063] FIG. 3 shows the dependence of the viscosity of pulp mixtures with and without calcium carbonate added before or after homogenization on the shearing rate.

[0064] FIGS. 4a and b show SEM images of only fibres (FIG. 4a), fibres and 100 wt.-% calcium carbonate based on weight of fibres present before homogenization (FIG. 4b).

[0065] FIGS. 5a and b show SEM images of only fibres (FIG. 5a), fibres and 100 wt.-% calcium carbonate based on weight of fibres present after 2 hours of homogenization (FIG. 5b).

[0066] FIGS. 6a to b show SEM images of only fibres (FIG. 6a), fibres and 100 wt.-% calcium carbonate based on weight of fibres present after 10 hours of homogenization (FIG. 6b).

[0067] FIG. 7 shows the efficiency of gel formation of mixtures with and without calcium carbonate fillers.

[0068] FIG. 8 shows the efficiency of gel formation of mixtures containing nanometer-sized calcium carbonate and talc as fillers.

EXAMPLES

A) Rheological Characterization

[0069] For exemplifying the present invention, highly refined pulp (standard eucalyptus pulp with 20° SR refined to 80-83° SR using a pulp refiner used in paper plants) and a mixture of this pulp with a defined amount of carbonate (100 wt-% based on the dry weight fibres present, dry on dry (d/d), was fibrillated using a homogenizer. The pulp (reference) and the mixture were homogenized for 10 hours at around 1 000 bar pressure and viscosity measurements and SEM pictures were taken at defined time intervals.

[0070] The viscosity (at 50° C.) of the reference of 560 mPa.Math.s after 10 hours homogenizing could be decreased to 435 mPa.Math.s by co-homogenizing with 100 wt-% calcium carbonate (Omyacarb 1 AV) based on the dry weight fibres present.

[0071] In order to chock whether the addition of calcium carbonate alone leads to a decrease of the viscosity of the homogenized pulp or the co-homogenizing is necessary, a sample of already homogenized pulp was mixed with calcium carbonate (100 wt-% calcium carbonate based on the dry weight fibres present, d/d), which is referred to as blend.

[0072] The viscosity of the “blend” (865 mPa.Math.s) was higher than the viscosity of the co-homogenized mixture (435 mPa.Math.s) and even higher than the viscosity of the homogenized reference (560 mPa.Math.s) without calcium carbonate present.

[0073] Carbonate slurries with the same solids content but without homogenized pulp, on the other hand, do not show a significantly higher viscosity than the fibre-containing samples.

2. Material

[0074] Carbonate: Ornyacarb 1 AV (GCC, solids content 100 wt % based on weight of fibres present, weight median particle size d.sub.50=1.7 μm measured by Sedigraph 5100) available from Omya AG [0075] Pulp: Standard eucalyptus pulp (20° SR) fibrillated to 80-83° SR using a refiner used in paper plants. The Schopper-Riegler degree (′SR) was measured according to the Zellcheming Merkblatt V/7/61 and standardized in ISO 5267/1.

3. Experimental Setup

3.1 Sample Preparation

[0076] For one homogenizer long term trial 1 000 g (solids content of about 3 wt-%) of the pulp as received was mixed with 1 250 g tap water using a stirrer (dissolver disc operating a rotation speed of 4 000 rpm) resulting in a solids content of about 1.3 wt-%. If necessary, the corresponding amount of calcium carbonate (Omyacarb 1 AV) was added while stirring further (cf. table 1). According amounts of this slurry were taken to perform viscosity experiments and SEM micrographs as described below. The rest of the slurry was transferred in the reservoir of the homogenizer. The samples which were used for the viscosity measurements were recycled in the process after performing the measurements.

TABLE-US-00001 TABLE 1 Starting Final Amount solids solids Total time in Sample. Calcium [wt-%, content content homogenizer No. Carbonate d/d] [wt-%] [wt-%] [h] 1 Omyacarb 0 1.3 1.7 10 1 AV 2 Omyacarb 100 2.6 2.4 10 1 AV

3.2 Homogenizer

[0077] A homogenizer (GEA Niro Soavi; type NS 2006 L) was used for the fibrillation experiments. The reservoir was stirred with an external double propeller stirrer to prevent sedimentation of the slurry and to maintain a good conversion.

[0078] The machine was started with no pressure applied (the pistons on both homogenizing stages were completely pulled back) and the lowest pumping velocity. For adjusting the pressure of about 1 000 bar only the piston of the first stage was pushed in. The reaction time started when a pressure of 1 000 bar was achieved, wherein fluctuations of the pressure by ±200 bar were observed. Consistent under- or overpressure was compensated for by changing the position of the piston.

[0079] The slurry was held in circulation. Samples were taken out after the homogenizing chamber (before entering the reservoir again) to ensure at least one passage of the fibres through the homogenizing chamber.

4. Methods

4.1 Viscosity Measurements

4.1.1 Brookfield Viscosity

[0080] The viscosity measurements were performed on a Brookfield DV-II+viscometer. The motor speed was set to 100 rpm and the viscosity was read out after 10, 60 and 600 seconds. The samples were measured either at room temperature or at 50° C. The samples were heated in a thermally controlled ultrasonic bath.

4.1.2 Rheology Measurements

[0081] Rheological measurements were performed using a Paar-Physika MCR 300 with the CC28.7 measuring system. The samples were measured at 20° C.

4.2 SEM

[0082] The scanning electron micrographs (SEM) were obtained by adding 0.5 g samples to 200 cm.sup.3 distilled water which then was filtered through a 0.8 μm pore nitrocellulose filter. The filter with overlying sample was dried in a vacuum drier. Preparations obtained on the membrane filter in this way were sputtered with 50 nm gold and evaluated in the SEM at various magnifications.

5. Results

5.1 Viscosity Measurements

[0083] From FIG. 1 the evolution of the viscosity (Brookfield) during homogenizing can be taken. The viscosity was read out after 600 seconds. The samples were. measured at about 35° C. (which was the temperature of the samples taken directly after the homogenization chamber). Sample 1 is only pulp and therefore used as reference material for the calcium carbonate containing sample 2. As already mentioned, the viscosity increases during fibrillation. As can be seen, sample 2 containing 100 wt-% calcium carbonate (based on the dry weight fibres present; d/d) always had a lower viscosity than the reference, but also increases with increasing homogenization time.

[0084] For verifying whether the presence of calcium carbonate is necessary during the homogenizing for lowering the viscosity, also a blend of homogenized (10 h) sample 1 and 100 wt-% calcium carbonate (based on the dry weight fibres present; d/d) added after homogenization was produced and investigated. The viscosity was read out after 10, 60 and 600 seconds. The samples were heated in a thermally controlled ultrasonic bath and measured at 50° C.

[0085] FIG. 2 shows the viscosities of pure homogenized pulp (sample 1), and pulp co-homogenized with 100 wt-% calcium carbonate (based on the dry weight fibres present; d/d) (sample 2), and mixtures of homogenized pulp and 100 wt-% calcium carbonate (based on the dry weight fibres present; d/d) added after homogenization (blend). In this respect, “10s”, “60s” and “600s” refer to the values of the Brookfield viscosity taken after 10, 60 and 600 seconds after the “power on” of the motor.

[0086] As can be seen, the co-homogenized mixture has a lower viscosity than the reference, whereas the blend has a higher viscosity than the corresponding co-homogenized mixture (sample 2) and the reference (sample 1).

[0087] Comparing the final viscosities (at 10 h homogenizing time) in FIG. 1 and in FIG. 2, slightly different values can be seen. This difference is accredited to the temperature dependence of the viscosity of the pulp mixtures.

5.2 Rheology Measurements

[0088] As one can see in FIG. 3, all the samples show a shear thinning behaviour. Table 2 shows the viscosities of the reference and the 100 wt-% calcium carbonate co-homogenized mixture and a 100 wt-% blend at 18 000 s.sup.−1. Similar to the data of the Brookfield measurements (FIG. 2), the 100 wt-% carbonate co-homogenized has the lowest viscosity (8 mPa.Math.s) and the 100 wt-% carbonate blend the highest viscosity (17 mPa.Math.s).

TABLE-US-00002 TABLE 2 Viscosity [mPa .Math. s] Sample at 18 000 s.sup.−1 Sample 1 (ref) 14 Sample 2 (co-homogenized 8 with 100 wt.-% carbonate) Sample 3 (blend with 100 17 wt.-% carbonate)

[0089] Furthermore, it can clearly be taken from FIG. 3 that there is a hysteresis in the case of sample 2, representing the case of fibres co-homogenized with 100 wt.-% calcium carbonate.

[0090] At low shearing rates, the viscosity decreases progressively as shear is increased until a shearing rate of about 18 000 s.sup.−1. Upon subsequently slowly decreasing the shearing rates, lower viscosities can be observed than at the corresponding shearing rates in the previous increasing step, wherein the viscosity now always remains lower than the viscosities in the previous step, and lower than the viscosity of the blend and the pulp only sample 1 under similar shear conditions.

[0091] This behaviour not only shows the low viscosities, which can be achieved according to the invention, but also is a clear indication of the formation of a gel.

5.3 SEM

[0092] Comparing FIG. 4a (referring to sample 1) and FIG. 4h (referring to sample 2) before homogenization, respectively, with FIGS. 5a and 5b after 2 hours homogenizing, respectively, and FIGS. 6a and 6b after 10 hours homogenizing, respectively, it can be seen that the pulp fibres become finer with increasing homogenizing time, and, without wishing to be bound to this theory, it appears that after a certain fineness of the fibrils is achieved they wrap around the carbonate particles and form a kind of layer on top of the carbonate particles.

B) Efficiency of Gel Formation

[0093] “Efficiency” in the context of the present invention is defined as the Brookfield viscosity (higher Brookfield viscosity means a more stable gel that means higher degree of fibrillation) achieved per specific energy consumption:

1. Processing

[0094] All Examples (samples 4-9) were processed with an ultra-fine friction grinder (Supermasscolloider from Masuko Sangyo Co. Ltd, Japan (Model MKCA 6-2) with mounted silicon carbide stones having a grit class of 46 (grit size 297-420 μm). The gap between the stones was adjusted to “−50” μm (dynamic 0-point, as described in the manual delivered by the supplier). The speed of the rotating grinder was set to 2500 rpm for passes 1-5, to 2000 rpm for passes 6 and 7, to 1500 rpm for passes 8 and 9, to 1000 rpm for passes 10 and 11, to 750 rpm for passes 12 and 13 and to 500 rpm for passes 14 and 15.

2. Energy Measurement

[0095] The Energy measurement was performed by installing an electric meter (ELKO Syteme AG, DIZ D665Di) between the main power supply and the transformer to measure the energy take up of the whole Supermasscolloider system (as delivered from the supplier). The electric meter sends one signal per Wh to a digital counter (IIengstler, tiro 731) to be able to read out the energy consumption per pass at the end of a pass with an accuracy of one Wh.

3. Weight Measurements

[0096] The solids content was measured using a Mettler Toledo HB 43-S Halogen solids balance. The end total mass was measured using a Mettler PK 36 Delta Range balance. The initial dry mass is the sum of all dry weight-ins at the beginning of an experiment (detailed compositions can be found in the formulations of the single experiments)

4. Brookfield Viscosity Determination

[0097] Brookfield viscosity was measured with Brookfield Model DV-II-f Viscometer.

[0098] To have a better comparability of the Brookfield measurement data, the Brookfield viscosity was measured in a dilution row to calculate the Brookfield viscosity at a fixed solids content. Additionally it was defined that only the ratio of dry cellulosic content (originating from dry pulp) to water is taken as reference parameter for Brookfield viscosity. The following formula was used to calculate the cellulosic solids content (s.c..sub.c):

[00001]$s.c{.}_c=\frac{\frac{sc}{p_c+p_f}}{100-\left(p_f.Math.\frac{s.c.}{p_c+p_f}\right)}$

s.c..sub.c: cellulosic solids content
s.c.: measured solids content of a sample
p.sub.c: part cellulosic content, per definition=1
P.sub.f: parts filler. weight ratio to part cellulosic content

[0099] The standardized Brookfield viscosity BV.sub.2% was determined by the following method: [0100] 1. The solids content and the Brookfield viscosity (100 rpm, measuring after 30 s) of the original product are measured. [0101] 2. Three dilutions of the original products are produced by adding according amounts of tap water of which the solids contents (weight in at least 10 g) and the Brookfield viscosities (100 rpm, measuring after 30 s) are measured. [0102] 3. An xy-scaller diagram (x: solids content, y: Brookfield viscosity) is made and the points are fitted with a power law curve (y=ax.sup.b). [0103] 4. Use the parameters a and b to calculate the Brookfield viscosity at the standardized cellulosic solids content x.sub.s of 2 wt %

[0104] To correct the intrinsic influence of Omyacarb 1 AV (samples 5-7) on the Brookfield viscosity of gels, a comparative gel containing no filler (sample 4) was mixed with according amounts of Omyacarb 1 AV (to have similar ratios as in samples 5-7). The BV.sub.2% of these mixtures was determined according to the above mentioned procedure and percentage corrections with reference to the gel containing no filler were calculated. The percentage corrections are: for 0.1 p (part by weight; d/d; cf. sample 5) filler: <0.1% (neglected), 3p (parts by weight; d/d; cf. sample 6) filler: −14.5%, 10p (part by weight; d/d; cf. sample 7) filler: −37.5%.

[0105] According corrections for samples 8 and 9 were not performed, such that the presented “efficiency” values described below will be overestimated in a range of about 15 to 20%)

5. Calculation of Specific Energy Consumption

[0106] The specific energy consumption per pass E.sub.T, is calculated as follows:

[00002]$E_n=\frac{E_n}{m_n}$$m_n=m_1-\frac{n}{14}\left(m_1-m_{15}\right)$$m_{15}=\sigma .Math.M$

E.sub.n: specific energy of pass n [Mwh/dmt]
E.sub.n: measured energy of pass n [Wh]
m.sub.n: dry mass of pass n [g]
m.sub.1: initial dry mass [g]
m.sub.15: end thy mass [g]
n: pass number
σ: solids content of final mass [wt %]
M: final total mass [g]

6. Calculation of “Efficiency”

[0107] “Efficiency” (□) in the context of the present invention is defined as the Brookfield viscosity (higher Brookfield viscosity means a more stable gel that means higher degree of fibrillation) achieved per specific energy consumption:

[00003]$\mathrm{.Math.}=\frac{{\mathrm{BV}}_{2\%}}{E_{1-15}}$$\mathrm{.Math.}\text{:}“\mathrm{Efficiency}”\left[\frac{\mathrm{mPas}}{\mathrm{MWh}/\mathrm{dmt}}\right]$${\mathrm{BV}}_{2\%}\text{:}\mathrm{Brookfield}\mathrm{viscosity}\mathrm{at}2\mathrm{wt}\%\mathrm{solids}\left[\mathrm{mPas}\right]$$E_{1-15}\text{:}\mathrm{Total}\mathrm{specific}\mathrm{energy}\mathrm{of}\mathrm{one}\mathrm{example}\left[\mathrm{MWh}/\mathrm{dmt}\right]$

7. Material

[0108] Omyacarb 1 AV: available from Omya AG; Fine calcium carbonate powder, manufactured from a high purity white marble; The weight median particle size d.sub.50 is 1.7 μm measured by Sedigraph 5100. [0109] Nano GCC: Natural ground calcium carbonate (marble from Vermont); Dispersed slurry (solids content 50 wt %); The volume median particle size d.sub.50 is 246 nm measured by Malvern Zetasizer Nano ZS. [0110] Finntalc F40: Finntalc P40 available from Mondo Minerals; Talc filler for paper and board. [0111] Eucalyptus pulp: Dry mat, brightness: 88.77%, 17° SR [0112] Pine pulp: Dry mat, brightness: 88.19%, 20° SR

8. Sample Preparation

Sample 4 (Comparative):

[0113] 180 g dry Eucalyptus pulp and 5820 g tap water were mixed using a Pendraulik stirrer at 2000 rpm with a mounted dissolver disk (d=70 mm) for at least 10 minutes. This mixture was processed with the Supermasscolloider as described above in the according paragraph. This example was performed three times to show its reproducibility.

Sample 5:

[0114] 180 g dry Eucalyptus pulp, 5820 g tap water and 18 g Omyacarb 1 AV (10:1 pulp to filler, dry/dry) were mixed using a Pendraulik stirrer at 2000 rpm with a mounted dissolver disk (d=70 mm) for at least 10 minutes. This mixture was processed with the Supermasscolloider as described above in the according paragraph. This example was performed three times to show its reproducibility.

Sample 6:

[0115] 180 g dry Eucalyptus pulp, 5820 g tap water and 540 g Omyacarb 1 AV (1:3 pulp to filler, dry/dry) were mixed using a Pendraulik stirrer at 2000 rpm with a mounted dissolver disk (d=70 mm) for at least 10 minutes. This mixture was processed with the Supermasscolloider as described above in the according paragraph. This experiment was performed two times to show its reproducibility.

Sample 7:

[0116] 180 g dry Eucalyptus pulp, 5820 g tap water and 1800 g Omyacarb 1 AV (1:10 pulp to filler, dry/dry) were mixed using a Pendraulik stirrer at 2000 rpm with a mounted dissolver disk (d=70 ram) for at least 10 minutes. This mixture was processed with the Supermasscolloider as described above in the according paragraph.

Sample 8:

[0117] 180 g dry Pine pulp, 5820 g tap water and 180 g Finntalc F40 (1:1 pulp to filler, dry/dry) were mixed using a Pendraulik stirrer at 2000 rpm with a mounted dissolver disk (d=70 mm) for at least 10 minutes. This mixture was processed with the Supermasscolloider as described above in the according paragraph.

Sample 9:

[0118] 180 g dry Eucalyptus pulp, 5820 g tap water and 360 g Nano GCC (1:1 pulp to filler, dry/dry) were mixed using a Pendraulik stirrer at 2000 rpm with a mounted dissolver disk (d=70 mm) for at least 10 minutes. This mixture was processed with the Supermasseolloider as described above in the according paragraph.

9. Results

Samples 4-7:

[0119] When comparing samples 4-7 it is obvious that the efficiency increases for gels that were produced in the presence of more filler, namely by up to 250%. The efficiency gain has to be more than 15% compared to a gel that was formed in the absence of filler.

Samples 8 and 9:

[0120] Samples 8 and 9 did not undergo the Brookfield viscosity-correction due to the intrinsic Brookfield viscosity increase of filler addition (see section “Brookfield viscosity determination”).

[0121] However, as can be taken from FIG. 8, the efficiency is about 75% higher than the one of comparative sample 4, and still 40% higher if a correction of minus 20% of the measured efficiency value is assumed.