Process for the production of a microfibrillated cellulose composition

Abstract

The present invention relates to a process for the production of microfibrillated cellulose composition, wherein the microfibrillated cellulose has an average fiber length in the range from 500 to 1300 m and a percentage of fiber length in the category 200 m of at least 15%, obtained by subjecting an aqueous mixture comprising 30 to 70% by weight of cellulose containing fibers to mechanical shearing at a temperature in the range of from 40 C. to 120 C. in the presence of at least one thermostable biocide, to the microfibrillated cellulose composition obtained in this process and their use in a process for production of paper, card and board comprising draining a paper stock comprising the microfibrillated cellulose composition with sheet formation in the wire.

Claims

1. A process for the production of a microfibrillated cellulose composition, the process comprising: subjecting an aqueous mixture comprising 30 to 70% by weight of cellulose containing fibers to mechanical shearing at a temperature of from 40 C. to 120 C. in the presence of at least one thermostable biocide thereby forming the microfibrillated cellulose, wherein the microfibrillated cellulose in the composition has an average fiber length of from 500 to 1300 m and a percentage of a fiber in the composition having a length of 200 m or less is at least 15%, and wherein the thermostable biocide is a combination of octylisothiazolinone, glutaraldehyde, and sodium pyrithione.

2. The process according to claim 1, wherein the cellulose containing fibers are bleached chemical pulp and/or wastepaper.

3. The process according to claims 1, wherein the cellulose containing fibers are mechanically sheared in a single screw, twin screw or conical extruder or with a refiner.

4. The process according to claim 1, wherein the microfibrillated cellulose has a freeness of at least 60 SR.

5. The process according to claim 1, wherein the microfibrillated cellulose has a BET surface area of from 20 to 100 m.sup.2/g.

6. The process according to claim 1, wherein the mechanical shearing is performed with an energy input of from 0.3 to 10 MWh/t of dry fiber.

7. The process according to claim 1, wherein the cellulose containing fibers, which are virgin fibers, are a starting material for the microfibrillated cellulose.

8. The process according to claim 1 wherein the octylisothiazolinone is utilized in an amount of 185 parts per million on a weight by weight basis, the glutaraldehyde is utilized in an amount of 460 parts per million on a weight by weight basis, and the sodium pyrithione is utilized in an amount of 200 parts per million on a weight by weight basis.

9. The process according to claim 8, wherein the cellulose containing fibers are derived from linerboard from recycled paper and/or old corrugated carton.

10. The process according to claim 1, wherein the cellulose containing fibers are derived from linerboard from recycled paper and/or old corrugated carton.

11. A process for the production of a microfibrillated cellulose composition, the process comprising: subjecting an aqueous mixture comprising 30 to 70% by weight of cellulose containing fibers to mechanical shearing at a temperature of from 40 C. to 120 C. in the presence of at least one thermostable biocide thereby forming the microfibrillated cellulose, wherein the microfibrillated cellulose in the composition has a weight-weight averaged fiber length of 800 m determined according to Tappi standard T 271 and a percentage of a fiber in the composition having a length of 200 m or less is about 19%, and wherein the thermostable biocide is a combination of octylisothiazolinone, glutaraldehyde, and sodium pyrithione, wherein the octylisothiazolinone is utilized in an amount of 185 parts per million on a weight by weight basis, the glutaraldehyde is utilized in an amount of 460 parts per million on a weight by weight basis, and the sodium pyrithione is utilized in an amount of 200 parts per million on a weight by weight basis, wherein the thermostable biocide is added during the step of mechanical shearing, and wherein the cellulose containing fibers are derived from linerboard from recycled paper and/or old corrugated carton.

12. The process according to claim 11 wherein the thermostable biocide is added only during the step of mechanical shearing.

Description

(1) The examples which follow illustrate the invention. Percentages reported in the examples are by weight, unless stated otherwise.

(2) MFC is made according to the process and equipment described in W02010/149711, example 3 but with the addition of the biocid.

(3) Twin Screw Configuration

(4) The method according to the invention has been performed with a co-rotating intermeshing twin screw as the twin screw refining system. In this example, the barrel internal diameter was 24mm, the screw outer diameter (OD) was 23.6 mm, the screw internal diameter (ID) was 13.3 mm, the distance between the centre lines of the screws was 18.75 mm, the pitch is positive with respect to rotation-although negative elements can be used-and the screw design was of a bi-lobal type. The configuration of this twin screw is given in Table 1 in WO 2010/149711. The Table 1 gives the number and type of screw elements of each screw in successive order from the inlet side-upper side of the tableto the outlet side-lower side of table-of the screw. From this table it follows that the total L/D ratio of the screw is 40: 1 and that the diameter of each screw element is 23.6 mm and the diameter of the barrel is 24 mm. Table 1: Configuration of twin screw refining system

(5) The following MFC types were prepared:

(6) TABLE-US-00001 TABLE 1 MFC types used: Fiber source Moisture BET Sample (starting content SR- value L.sub.w P.sub.l, 200 m Name material) [%] value [m.sup.2/g] [m] [%] MFA-A Bleached 49.5 85 65 770 16.3 eucalyptus pulp MFC-B Liner board 48.3 90 59 800 18.8 from recycled paper and old corrugated carton MFC-C Oat husks 49.7 15 72 650 22.1 MFC-D Hemp fibers 50.0 87 55 930 19.6 MFC-E Wheat straw 51.2 25 62 670 21.4 L.sub.w: weight-weighted average fiber length determined according to Tappi standard T 271 P.sub.l, <200 m: percentage of length in the category 200 m

(7) Determination of the moisture content: The resulting MFC was dried in an oven at 120 C. until constant weight.

(8) Determination of the SR-Value followed the procedure given in ISO 5267-1 using a Schopper-Riegler measurement device (Frank PTI).

(9) Determination of specific surface area (BET value):

(10) The specific surface area of the microfibrillated cellulose (BET value) is obtained by the following procedure: An aqueous microfibrillated cellulose formulation (suspension, gel) is placed on a frit and washed with tert-butanol. The resulting tert-butanol suspension of microfibrillated cellulose is then transferred from a frit to a pre-cooled metal plate (ca. 0 C.) having a glass cover (lyophilisator). The sample is dried under vacuum while cooling overnight. Tert-butanol sublimes slowly, leaving the microfibrillated cellulose structure lyophilized. The resulting sponge-like solid microfibrillated cellulose is analyzed by physisorption of nitrogen (measurement in a surface area BET analyzer (Micromeritics ASAP 2420); the N.sub.2 load on the surface is plotted vs. the N.sub.2 partial pressure and assessed by BET theory), leading to the surface area of the sample.

(11) Description of the test method for bio contamination:

(12) Samples of the MFC prepared according to table 1 were stored at room temperature in plastic bags. The samples were analyzed for their bio contamination according to the following procedure after one, two, four and eight weeks.

(13) The MFC sample was dispersed in DI water to give a 4 wt % fiber dispersion using a high shear disperger (Ultraturrax RW28 with R1302 dissolver stirrer, Fa. IKA, 6000 rpm, 5 min, room temperature). 7.8 ml of the fiber suspension were evenly distributed on a round petri disc (100 mm diameter), filled 5 mm high with agar based culture medium. By the use of different media, aerobic bacteria, anaerobic and sulfate reducing bacteria, mould and yeast can be detected separately.

(14) The spiked agars are stored in an incubator for a certain time. Then the number of colonies on the culture medium is evaluated visually with the help of a scale.

(15) Bacteria growth rate

(16) 0=no growth

(17) 1=minimal growth; 1 to 10 colonies in entire culture

(18) 2=light growth; max. 100 colonies

(19) 3=medium growth; max. 300-400 colonies

(20) 4=even growth; individual colonies still visible, >400 colonies

(21) 5=strong growth; to many colonies to count, but still uncovered areas visible

(22) 6=entire surface covered

(23) Fungi growth rate:

(24) 0=no visible growth

(25) X=minimal growth

(26) XX=light growth

(27) XXX=medium growth

(28) XXXX=strong growth

(29) Results are given in table 2

(30) TABLE-US-00002 TABLE 2 Microbiological testing of unstabilized MFC duration Sample MFC-A MFC-B MFC-C MFC-D MFC-E 1 week bacteria 3 4 3 3 3 2 weeks bacteria 5 6 5 5 5 4 weeks bacteria 6 6 6 6 6 8 weeks bacteria 6 6 6 6 6 1 week fungi 0 0 0 X 0 2 weeks fungi X XX XX XX XX 4 weeks fungi XXXX XXXX XXXX XXXX XXXX 8 weeks fungi XXXX XXXX XXXX XXXX XXXX

(31) In the next step, the same MFC types were prepared, but a biocide was added before, during, or after the extrusion step. When the biocide was added before the extrusion step, it was added to the water which was used to moisturize the base material for the MFC. When the biocide was added during the extrusion step, it was dosed via a displacement pump to an inlet in the first mixing zone of the screw extruder. When the biocide was added after the extrusion step (these examples are for comparison), a sample of the MFC which was obtained after the extrusion step was placed in a lab blender and the biocide was added to the MFC material, followed by mechanical mixing of the materials for 5 min.

(32) The material containing the biocide was then stored at room temperature in a plastic bag and analyzed for antimicrobial growth according to the procedure described above after 1, 4 and 8 weeks.

(33) The following biocides were used: All components were aqueous based formulations:

(34) Octylisothiazolinone (OIT)

(35) Glutaraldehyde (GA)

(36) Sodium pyrithione (NaP)

(37) Benzalkonium chloride (BAC)

(38) The following preparations were made. Amounts of antimicrobial components are given as parts per million on a weight by weight basis. The dosing position shows if the dosing of the biocide addition was before or during the shearing step e) (both according the invention) or after the shearing step (not according the invention)

(39) TABLE-US-00003 TABLE 3 Preparations of stabilized MFC formulations Sample ID MFC type Biocide addition ppm Dosing position MFC-B-TB1 MFC-B 62 OIT + 1150 GA Before MFC-B-TB2 MFC-B 225 OIT + 460 GA Before MFC-B-TB3 MFC-B 185 OIT + 460 GA + Before 200 NaP MFC-B-TB4 MFC-B 160 OIT + 200 NaP + Before 2000 BAC MFC-A-TB1 MFC-A 62 OIT + 1150 GA Before MFC-C-TB1 MFC-C 62 OIT + 1150 GA Before MFC-D-TB1 MFC-D 62 OIT + 1150 GA Before MFC-E-TB1 MFC-E 62 OIT + 1150 GA Before MFC-B-TD1 MFC-B 62 OIT + 1150 GA During MFC-B-TD2 MFC-B 185 OIT + 460 GA + During 200 NaP MFC-B-TA1 MFC-B 62 OIT + 1150 GA After MFC-B-TA2 MFC-B 225 OIT + 460 GA After MFC-B-TA3 MFC-B 185 OIT + 460 GA + After 200 NaP MFC-B-TA4 MFC-B 160 OIT + 200 NaP + After 2000 BAC

(40) The following results were obtained after the analysis for microbial activity

(41) TABLE-US-00004 TABLE 4 Results of microbiological testing of stabilized MFC 1 1 4 4 8 8 week - week - week - week - week - week - Sample ID bacteria fungi bacteria fungi bacteria fungi MFC-B- 0 0 0 0 3 X TB1 MFC-B- 0 0 1 X 3 XX TB2 MFC-B- 0 0 2 X 4 XX TB3 MFC-B- 0 0 1 0 3 X TB4 MFC-A- 0 0 1 0 3 X TB1 MFC-C- 0 0 1 0 3 X TB1 MFC-D- 0 0 2 X 4 XX TB1 MFC-E- 0 0 1 0 3 X TB1 MFC-B- 0 0 1 0 3 X TD1 MFC-B- 0 0 1 0 3 X TD2 MFC-B- 0 0 2 X 4 XX TA1 MFC-B- 0 0 3 XX 6 XXX TA2 MFC-B- 0 0 2 XX 5 XXX TA3 MFC-B- 0 0 2 X 4 XX TA4

(42) As can be seen from Table 4, the addition of the biocide formulations before and during the extrusion step leads to better results than addition afterwards.

(43) The results show that MFC can be effectively stabilized against biological degradation with the proposed formulations. Combination products (bactericide+fungicide) are more suitable than one component systems.

(44) To see the effect in the paper making process, a dispersing and filtration test was used. The MFC material was stored for a defined time at room temperature. Then water was added to the MFC material to give a dry fiber concentration of 1% (e.g. 20 g MFC with 50% moisture content +980 g of water). This mixture was stirred for 5 min using a standard dispersing lab stirrer. Then the resulting MFC suspension was poured through a weighed sieve with a mesh size of 1 mm. 1.0 liter of MFC suspension was poured through the sieve. Then the sieve was dried at 120 C. for 30 min and the remaining MFC material on the sieve was measured by weighing the sieve after drying and determining the MFC deposited on the sieve. The result of the sieve test is then expressed as percentage of the remaining MFC on the sieve in respect to the original fiber material present in the sample (=sieve residue [%])

(45) TABLE-US-00005 TABLE 5 Results of the filtration test Sample Storage time Sieve residue [%] MFC-B 1 day <0.1 MFC-B 1 week 0.2 MFC-B 4 weeks 2.7 MFC-B 8 weeks 12.3 MFC-B-TB1 1 day <0.1 MFC-B-TB1 1 week <0.1 MFC-B-TB1 4 weeks 0.1 MFC-B-TB1 8 weeks 1.3

(46) Table 5 shows, that the microbiological stabilization is indeed affecting the filtration results and thereby has an influence on the runnability in a paper machine.

(47) Production of Paper

(48) The microfibrillated cellulose composition (stabilized) was used in paper making (hand sheet).

(49) Hand sheets containing MFC were made from recycled paper by the following procedure.

(50) A mixture of 95% by weight of recycled linerboard and 5% MFC made from the same linerboard was suspended in water at a solids content of 4% and pulped in a laboratory pulper for 20 minutes, after which the suspension was diluted to 0.3% solids. Polyvinyl formamide with a degree of hydrolysis of 20% was added to the suspension. The metered amount for the polyvinyl formamide addition was 0.2%, based on the solids content of the paper stock suspension. Then, 1% of bentonite, based on the solids content of the paper stock suspension was added.

(51) Sheets were formed according to the Rapid-Kothen method (ISO 5269-2) with a sheet weight of 100 g/m.sup.2. The dry tensile strength (as breaking length, Tappi method T 494 (ISO 1924-2) and burst index (burst strength according to ISO 2758 divided by the grammage) were measured.

(52) TABLE-US-00006 TABLE 6 Testing of the paper sheets Paper Base MFC MFC Tensile Burst sample material sample storage time [m] [kPam.sup.2/g] P1 Liner board MFC-B 1 week 4590 3.31 P2 Liner board MFC-B 8 weeks 3881 2.67 P3 Liner board MFC-B-TB1 1 week 4578 3.32 P4 Liner board MFC-B-TB1 8 weeks 4467 3.15

(53) Table 6 shows that the microbiological stabilization affects also the paper strength properties of paper made with stabilized MFC. Stabilized MFC results in paper with higher paper strength.

(54) Samples of MFC-B were prepared in the twin-screw extruder using different biocides added before the extrusion step. Octylisothizolinone and glutaraldehyde were added in combination during the same run. The temperature of the water-cooled extruder barrel was monitored in ten zones during the extrusion process using thermoelements embedded in the metal barrel blocks. The material was passed through the extruder two times with an energy uptake of 1.1 MWh/t per pass. Samples were taken before the extruder and after each pass. The amount of remaining active biocide was measured in each sample. Table 7 shows the temperatures measured in the barrel blocks during extrusion and the amount of biocide found in the material.

(55) TABLE-US-00007 TABLE 7 Thermostability of biocides Biocide BAC OIT GA NaP Biocide before 970 60 790 43 extruder [ppm] Pass 1 2 1 2 1 2 1 2 T2 [ C.] 36 41 36 42 36 42 35 41 T3 [ C.] 37 41 36 42 36 42 32 41 T4 [ C.] 66 70 65 69 65 69 60 69 T5 [ C.] 60 63 60 63 60 63 56 63 T6 [ C.] 48 52 46 55 46 55 42 53 T7 [ C.] 48 52 48 54 48 54 43 68 T8 [ C.] 63 68 64 68 64 68 56 68 T9 [ C.] 37 42 38 42 38 42 27 42 T10 [ C.] 31 34 35 33 35 33 23 34 T11 [ C.] 26 30 27 30 27 30 21 31 Biocide after 870 850 60 50 720 650 31 23 extrusion [ppm] % undegraded 90% 88% 100% 83% 91% 82% 72% 53% biocide

(56) It can be seen that all biocides maintain more than 50% activity after two passes. The temperature in the cooled barrel blocks reaches up to 70 C., but it may be assumed that the extruded material itself has an even higher temperature, as there is no direct contact to the thermoelements.