Method for producing microfibrillated cellulose and microfibrillated cellulose

Abstract

The invention relates to a method for producing microfibrillated cellulose, where a suspension comprising cellulose derivative in a liquid phase which comprises an organic solvent is provided. The suspension of cellulose derivative is mechanically treated and microfibrillated cellulose is obtained. At least a part of the liquid phase from the microfibrillated cellulose is separated and microfibrillated cellulose with a dry solids content of >30 weight-% is obtained.

Claims

1. Method for producing microfibrillated cellulose, comprising steps (a) providing a suspension comprising cellulose derivative in a liquid phase which comprises an organic solvent, (b) mechanically treating the suspension of cellulose derivative and obtaining microfibrillated cellulose, and (c) separating at least a part of the liquid phase from the microfibrillated cellulose and obtaining microfibrillated cellulose with a dry solids content of >30 weight-%.

2. Method according to claim 1, wherein the cellulose derivative is anionic cellulose derivative, such as carboxymethyl cellulose, which has degree of substitution DS<0.6, preferably <0.4, more preferably <0.2.

3. Method according to claim 1, wherein the cellulose derivative is microcrystalline cellulose, which has been produced through acid hydrolysis from cellulose material.

4. Method according to claim 1, wherein the liquid phase comprises 50-100 weight-%, preferably 40-99 weight-%, more preferably 70-95 weight-%, of organic solvent and 0-50 weight-%, preferably 1-60 weight-%, preferably 5-30 weight-%, of water.

5. Method according to claim 1, wherein the organic solvent is alcohol, such as ethanol, methanol, tent-butanol; acetone; or any mixture thereof.

6. Method according to claim 1, wherein in step (b) the suspension comprising cellulose derivative is mechanically treated by homogenization or fluidization.

7. Method according to claim 1, wherein in step (c) is obtained microfibrillated cellulose with a dry solids content of >40 weight-%, preferably >60 weight-%, more preferably >80 weight-%.

8. Method according to claim 1, wherein in step (a) the suspension comprising cellulose derivative is obtained by replacing and/or displacing water in an aqueous suspension comprising cellulose derivative by the organic solvent.

9. Method according to claim 1, wherein the dry solids content of the suspension comprising cellulose derivative during the mechanical treatment, e.g. homogenization, is <15 weight-%, preferably <10 weight-%, more preferably <5 weight-%.

10. Method according to claim 1, wherein rccirculating the separated liquid phase comprising organic solvent is recirculated from step (c) back to step (a).

11. Microfibrillated cellulose produced by a method according to claim 1 and having dry solids content >30 weight-%.

Description

EXPERIMENTAL

[0031] Some embodiments of the invention are described more closely in the following non-limiting examples.

EXAMPLE 1

Homogenisation of CMC to Produce MFC

[0032] Carboxymethyl cellulose, CMC, was made in laboratory according to Wagberg et al., Langmuir 2008, 24, 784-795. The degree of substitution of the produced CMC was determined to be 0.05 by a conductometric titration. After carboxymethylation, the obtained samples comprising cellulose derivative, i.e. CMC, were washed with water and diluted in a selected liquid phase, which was either pure water or a mixture of water and ethanol. These sample suspensions of cellulose derivative were mechanically treated by fluidizing in a Microfluidics fluidizer at pressures of 1500 bar. Experimental details are given in Table 1.

[0033] The fibrillation of the sample suspensions was characterised by light transmittance, which is known to correlate with the changes in degree of fibrillation as described for example in Kangas H., Lahtinen P., Sneck A., Saariaho A-M., Laitinen O., Hellen E.: Characterization of fibrillated celluloses. A short review and evaluation of characteristics with a combination of methods. Nordic Pulp and Paper Research Journal 29, p. 129-143, 2014. The light transmittance was measured with a Perkin Elmer Lambda 900 UV/VIS/NIR spectrophotometer from a homogenised sample diluted to 0.1 weight-%. The results are shown in Table 1. The transmittance wavelengths 400 nm, 600 nm, 800 nm and 1000 nm were compared. Higher transmittance is considered as a clear sign of fibrillation.

[0034] It is seen from the Results in Table 1 that microfibrillated cellulose, MFC, can be produced from carboxymethylated cellulose, i.e. a cellulose derivative, with chemically induced charges, when a mixture of ethanol and water is used as the solvent.

TABLE-US-00001 TABLE 1 Light transmittance data for CMC suspension samples, indicating the degree of fibrillation in the sample. Number of Transmittance, % fluidizing wavelength, nm Sample Solvent in fluidizing passes 600 800 1000 No 1 water 1 46.2 48.3 50.1 (reference) No 2 water 2 57.5 61.5 64.4 (reference) No 3 water 3 64.4 70.1 74.0 (reference) No 4 Water:ethanol; 50:50 1 43.4 47.8 51.6 No 5 Water:ethanol; 50:50 2 44.2 50.6 55.7 No 6 Water:ethanol; 50:50 3 45.3 52.9 59.2

EXAMPLE 2

Homogenisation of MCC in Ethanol

[0035] Microcrystalline cellulose, MCC, which was made through acid hydrolysis as described in WO2011/154601 from kraft softwood pulp to achieve a degree of polymerization of 450, was used in Example 2.

[0036] 50 g of MCC at a dry solids 40 weight-% was washed with 3000 g of ethanol and thereafter diluted with ethanol to consistency of 1.5%. This material was run through a Microfluidics fluidizer at pressure of 2000 bar. The fibrillation was determined by using light transmittance of the obtained microfibrillated cellulose, MFC, as described in Example 1.

[0037] The light transmittance results are given in Table 2.

[0038] The Example 2 shows that MFC can be produced from MCC, i.e. a cellulose derivative without chemically induced charges, when ethanol is used as the solvent.

TABLE-US-00002 TABLE 2 Light transmittance data for MCC/ethanol suspension samples, indicating the degree of fibrillation in the sample. Transmittance, % Number of wavelength, nm Sample fluidizing passes 400 600 800 1000 No 1 1 8.98 13.2 17.0 20.6 No 2 2 8.91 15.0 20.7 26.3 No 3 3 10.4 18.6 26.0 32.1

REFERENCE EXAMPLE 3

Homogenisation of MCC in Water

[0039] Microcrystalline cellulose, MCC, was produced as described in Example 2. MCC was diluted with water to consistency of 1.5%, after which the MCC was homogenized in a GEA Niro Soavi NS3006H homogenizer to produce microfibrillated cellulose. The pressure in homogenisation was 1500 bar. The light transmittance was measured as described in Example 1 in order to measure for the degree of fibrillation. The results are given in Table 3.

[0040] The Example 3 shows that MFC can be produced from MCC when water is used as the solvent. When compared to the results obtained in Example 2, it is seen that the fibrillation results in pure water are inferior to those obtained in Example 2, where the suspension comprised ethanol.

TABLE-US-00003 TABLE 3 Light transmittance data for MCC/water suspension samples, indicating the degree of fibrillation in the sample. Transmittance, % Number of wavelength, nm Sample homogenizing passes 400 600 800 1000 No 1 1 2.91 5.25 7.99 11.3 No 2 2 3.52 6.98 10.9 15.1 No 3 3 4.47 9.22 14.5 20.0

EXAMPLE 4

Dewatering of MFC

[0041] Microcrystalline cellulose, MCC, which was prepared as described in Example 2, was used in tests.

[0042] In samples where water was used as solvent, MCC was diluted to consistency of 1.5%.

[0043] In samples where ethanol was used as solvent, 50 g of MCC at a dry solids 40 was washed with 3000 g of ethanol and thereafter diluted with ethanol to consistency of 1.5%. All the samples were prepared by running three times through a Microfluidics fluidizer at pressure of 1500 bar.

[0044] After fibrillation the MFC samples were dewatered in a pressure filter with 2.5 bar applied pressure. The sample size was 200 g of 1.5% suspension. The filter area was 115 cm.sup.2.

[0045] The results are shown in FIG. 1. It is seen that the MFC sample comprising ethanol was much easier to dewater, i.e. a higher solids content was achieved much faster than then when the liquid phase of the suspension comprised pure water.

[0046] Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.