Adsorbent and packaging material

Abstract

The present invention relates to an adsorbent suitable for the adsorption of MOAH and/or MOSH compounds, the use of the adsorbent for the production of a packaging material or a container comprising the adsorbent, the process of production of the packaging material or container as well as the respective packaging material and container.

Claims

1. Adsorbent suitable for adsorption of mineral oil aromatic hydrocarbon (MOAH) and/or mineral oil saturated hydrocarbon (MOSH) compounds, the adsorbent characterized by (i) a specific surface area of from 140 to 700 m.sup.2/g; and (ii) a pore volume of pores from 20 to 500 Å of from 0.1 to 1.2 ml/g; and (iii) a total pore volume of from 0.25 to 1.2 ml/g.

2. Adsorbent according to claim 1, further characterized by a wet sieve residue of from 90 to 100% less than 53 μm.

3. Adsorbent according to claim 1, characterized by a water content of from 5 to 30 wt %.

4. Adsorbent according to claim 1, characterized by a swelling capacity of less than 15 ml/2 g.

5. Adsorbent according to claim 1, which is selected from the group consisting of bentonites, attapulgites, saponites, sepiolites, mixed layer saponites/kerolites, natural and synthetic aluminum silicates and mixtures thereof.

6. Adsorbent according to claim 1, wherein the adsorbent is an acid-activated adsorbent.

7. Packaging material comprising at least one adsorbent according to claim 1.

8. Packaging material according to claim 7 comprising at least one component selected from paper and cardboard material.

9. Packaging material according to claim 7, comprising at least two layers of cardboard material and/or paper.

10. Packaging material according to claim 9, wherein at least one of the layers comprises at least one adsorbent as defined in claim 1 and at least one layer comprising recycled paper or cardboard material.

11. Container comprising the packaging material according to claim 7.

12. Container according to claim 11, wherein the at least one layer of the packaging material comprising the at least one adsorbent is positioned between the inside of the container and the at least one layer comprising the recycled paper and/or cardboard material.

13. Process for the production of a packaging material comprising the steps (a) providing a slurry of fibrous material and water; (b) adding to the slurry from 1 to 25 wt % of at least one adsorbent according to claim 1; (c) draining the slurry; and (d) drying the drained slurry.

14. Process according to claim 13, wherein the at least one adsorbent is added in form of a slurry with a solid content of from 15 to 35 wt % at a Brookfield-viscosity at 100 rpm of 1000 mPas.

Description

LIST OF FIGURES

(1) FIG. 1 shows a corrugated cardboard comprising 5 layers ((1), (2), (3), (4), (5)) of cardboard material and one layer (5) with an additional content of inventive adsorbent.

(2) FIG. 2 shows a corrugated cardboard comprising 3 layers ((6), (7), (8)) of cardboard material and one layer (8) with an additional content of inventive adsorbent.

(3) FIG. 3 shows a flat cardboard comprising 4 layers ((9), (10), (11), (12)) of cardboard material and one layer (11) with an additional content of inventive adsorbent.

Example 1: Characterization of Adsorbents and Determination of MOSH and MOAH Adsorbent Capacity

(4) Test for the determination of MOSH and MOAH adsorbent capacity was performed as follows:

(5) A migration cell was used consisting of a glass storage vessel for the hydrocarbons which was equipped on top with a fine metal fabric. An additional glass cap allowed a hermetic closure of the migration cell.

(6) The storage vessel served as a reservoir for the synthetic MOSH/MOAH mixture, which consists of a mixture of mineral oils of the companies Gravex, Total and Edwards containing a MOSH/MOAH ratio of 80/20. For the experiments 2.00+/−0.01 g of the hydrocarbon mixture was weighed into the reservoir. The metal fabric was placed on the reservoir and 1.00+/−0.01 g of the adsorbent was distributed evenly on the fabric. The cell was closed with the glass cap and stored under 60° C./atmospheric pressure for 16 hours. Under these conditions the hydrocarbons slowly move in gas form through the fabric and onto the adsorbent.

(7) After the storage time the adsorbent was quantitatively transferred into a glass beaker, 100 ml of n-hexane (n-hexane anhydrous, Sigma-Aldrich) was added and the hydrocarbons were extracted from the adsorbents by shaking the beaker for 2 hours at room temperature. The n-hexane solution was separated from the adsorbent by filtration and the extracts were analyzed according to the method described and published by the German Bundesinstitut für Risikobewertung (BfR) under the title “Bestimmung von Kohlenwasserstoffen aus Mineralöl (MOSH und MOAH) oder Kunststoffen (POSH, PAO) in Verpackungsmaterialien und trockenen Lebensmitteln mittels Festphasenextraktion und GC-FID” on 04.05.2012. The principle of this method is the separation of the extracts over a with silver-nitrate doped silica-gel column into MOSH and MOAH fractions and their quantitative determination with the aid of a gas chromatography/flame ionization detector (GC-FID). The results of the double determinations were recorded in mg MOSH/MOAH per kg adsorbent.

(8) Wet sieve residue at 53 μm was determined as follows:

(9) 100 g of oven dry pigment was added under stirring at 930 rpm (Pendraulik LD 50 stirrer) to 1500 g of tap water within 2 minutes. Stirring was continued for 18 minutes at 1865 rpm. The suspension was afterwards transferred on a 53 μm sieve (diameter 200 mm) and washed under gentle knocking by means of flowing tap water until the wash water was clear. Afterwards the sieve was placed in a supersonic bath for 5 minutes in order to destroy pigment agglomerates and washed again with tap water until the wash water was completely clear. The sieve with the residue was dried in a drying cabinet until weight constancy. The residue was transferred by means of a brush on a tray and weighed on an analytical balance. The weight of the residue in grams corresponded to its percentage.

(10) Water content was determined as follows:

(11) 10 g of the adsorbent was weighed onto an aluminum tray and dried for 90 minutes at 130° C. in a drying cabinet to constant weight. The sample was cooled in a desiccator to room temperature and the weight was measured on an analytical balance.

(12) Water content in %=weight before drying—weight after drying×10

(13) Specific surface area was determined as follows:

(14) Specific surface was measured by the BET-method (single-point method using nitrogen, according to DIN 66131) with an automatic nitrogenporosimeter of Micrometrics, type ASAP 2020.

(15) Pore volume was determined as follows:

(16) The pore volume was determined in an ASAP 2020 (Accelerated Surface Area and Porosimetry System) of Micromeritics according to the BJH-method (E. P. Barett, L. G. Joyner, P. P. Hienda, J. Am. Chem. Soc. 73 (1951) 373), which uses nitrogen gas at the temperature of liquid nitrogen (−196° C.) and increasing partial nitrogen pressure to cover the surface and to fill the pores of the pigment/adsorbent. Before measurement, the sample (0.5 to 1.0 g) was completely degased by heating it in a sample tube to 250° C. under vacuum for 20 hours. After cooling down to room temperature, the tube including the sample was weighed (for the exact determination of the sample weight) and inserted in the analyzer. After cooling with liquid nitrogen to −196° C. the flushing with nitrogen gas was started whereas the partial pressure P/Po was increased in steps until close to 1 to guarantee that all pores were filled with nitrogen. The software of the system recorded over decreasing pore diameter ranges (2500 to about 10 Angstroem Å) the corresponding incremental pore volumes in cm.sup.3/g. These incremental values were added up to the total pore volume of the sample. The pore volume of the mesopores were calculated by adding up the incremental pore volumes between the pore diameters of 500 and 20 Å. An average pore diameter in Angstroem was calculated according to BJH.

(17) Swelling capacity was determined as follows:

(18) A graduated 100 ml measuring cylinder was filled with 100 ml distilled water. 2.0 g of the pigment were added slowly in small portions of 0.1 to 0.2 g by means of a spatula. After each addition it was waited until the pigment sank to the bottom of the cylinder, than the procedure was continued. After termination of the addition, the pigment was allowed to swell for 1 hour—then the volume of the swollen pigment in ml was recorded. The swelling volume (1 h) was documented in ml/2 g.

(19) For testing purposes, all adsorbents were adjusted to wet sieve residues of below 2% at 53 μm and to water contents of 8 to 12%. Adsorbents according to the invention (No. 4 to 9) provide higher specific surface area and total pore volume than the comparative examples 1 to 3.

(20) Table 1 shows a comparison of adsorbents according to the present invention (No 4 to 9) and adsorbents of the state of the art (No 1 to 3) in view of the measured parameters (see above).

(21) TABLE-US-00001 TABLE 1 Characterization of Adsorbent Average Spec. Pore volume ml/g pore surface % diameter No. Adsorbent area m.sup.2/g total micro meso macro meso Å 1 Ca-bentonite 73 0.094 0.011 0.055 0.028 59 50 (Montmorillonite) 2 Saponite 138 0.179 0.024 0.122 0.033 68 51 3 Attapulgite 102 0.248 0.007 0.185 0.056 75 94 4 Bentonite, acid 236 0.342 0.016 0.288 0.038 84 60 act. 5 nat. silica 244 0.643 0.015 0.512 0.116 80 100 6 Sepiolite 190 0.410 0.020 0.248 0.142 60 80 7 Sepiolite, acid 218 0.270 0.024 0.220 0.025 81 50 act. 8 Saponite/Kerolite 231 0.252 0.015 0.182 0.055 72 47 mixed layer 9 Al-silicate 506 0.985 0 0.856 0.129 87 73 synthetic  6a nat. silica 199.5 32.0 7.0  6b nat. silica 201.0 39.0 14.0 7 Sepiolite 201.6 38.5 13.5 8 Sep. acid act. 198.8 39.0 14.0  9a Saponite/Kerolite 201.2 32.5 7.5 mixed layer  9b Saponite/Kerolite 202.3 39.5 14.5 mixed layer 10  Al-silicate synth. 200.8 39.0 14.0

(22) The results of table 2 show that a high mesopore (20 to 500 Å) and total pore volume as well as a high specific surface area are mandatory for the performance of the adsorbent.

(23) TABLE-US-00002 TABLE 2 Adsorption of MOSH/MOAH Trial MOSH μg/g MOAH μg/g no. Adsorbent ≤C 25 ≤C 25 Total 1 Ca-bentonite 380 35 415 (Montmorillonite) 2 Saponite 487 34 521 3 Attapulgite 465 32 497 4 Bentonite, acid act. 694 54 748 5 nat. silica 725 50 775 6 Sepiolite 740 35 775 7 Sepiolite, acid act. 804 61 865 8 Saponite/Kerolite 629 35 672 mixed layer 9 Al-silicate synthetic 820 58 878

(24) Adsorbents according to the present invention show high adsorption of the MOSH/MOAH-fraction<C 25. Given the applied test method predominantly the more volatile hydrocarbons below C 25 are mobilized and thus adsorbed. Consequently, fractions between C 25 and C 35 have not been determined within example 1. However, given the problem to be solved by the invention, only the fraction below C25 is primarily relevant for practical applications as they are prone to migrate from the packaging material into the product.

(25) The adsorbents according to the invention (4 to 9) adsorbed between 629 and 878 mg MOSH<C 25 per kg of adsorbent, whereas the comparative examples (1 to 3) were able to adsorb 360 to 487 mg MOSH<C 25 per kg. The picture is similar for MOAH<C 25 where the adsorbents according to the invention (4 to 9) were able to bind 35 to 61 mg/kg and the comparative examples (1 to 3) 32 to 35 mg/kg.

Example 2: Performance of the Adsorbents in Paper

(26) Preparation of Paper Sheets

(27) Within example 2 it was shown that the good adsorption rates of the adsorbents on MOSH/MOAH shown in example 1 were maintained after incorporation of the adsorbents into the paper mass. A problem well known within the art is the fact that a component mandatory for paper production (paper fillers with a high specific surface area) often have a high demand for retention aids and thus specific surface and pore volume of the adsorbents may be reduced as pores become clogged by these chemicals. The adsorbents of the invention did not show this problem.

(28) Paper sheets were prepared in a Rapid-Köthen sheet-former applying the following conditions: Pulp: mixed recycled fibers from a German cardboard mill Density: diluted with mill white water to 1% solid content Flocculation agent: Gilufloc 40H (polyaluminiumchloride, BK Giulini, 40% solids)dosage 5 kg telquel/mton pulp Retention aid: Polymin SK (high molecular poly-ethylenimin, BASF, solids 25%) dosage 2 kg dry/mton pulp Adsorbents: dispersed in water at 30% solids; remark: with bentonite only 15% solids could be reached due to high pigment viscosity dosage 10 and 20% on pulp

(29) Procedure: For each trial the pulp was freshly prepared with mill white water to a solid content of 1%. Under stirring at 400 rpm the dosage sequence of the chemicals was PAC/adsorbent/retention aid, followed by a stirring time of 1 min after each dosage. Thereafter round sheets of 20 cm diameter were formed on a Rapid-Köthen sheet-former at grammages of 200 g/m2 (between 198 and 202.5 g/m2). The paper sheets were characterized and used for the determination of the MOSH/MOAH adsorption/retention potential. Benchmark sheets were prepared following the same procedure, but without the addition of adsorbents.

(30) Determination of the Paper Weight

(31) The round sheets with 20 cm diameter were dried in a drying cabinet at 110° C. for 2 to 3 minutes and afterwards weighed on an analytical balance.

(32) The paper weight in g/m.sup.2 was calculated according to:

(33) Weight of sheet in g/0,1.sup.2×πm.sup.2

(34) Ash Content

(35) Ash content was measured in an incineration tube of Greiner and Gassner GmbH at temperatures up to 1100° C. in pure oxygen atmosphere (incineration time 5 minutes) and was reported in % of the paper mass. The difference in ash content between the paper sheets in which adsorbents are incorporated and the benchmark without adsorbents gives directly the amount of adsorbent retained in the sheets.

(36) Determination of MOSH/MOAH migration

(37) A simple migration cell was used consisting of a stainless steel bottom plate on which a stainless steel ring with an inner diameter of 10 cm, height 1 cm is placed. The cell was covered with another stainless steel plate of the same size as the bottom plate. The paper sheet to be measured (circular with a diameter of 10 cm) was placed on the bottom plate and covered with semolina flour, which was used to mimic the food in contact with the paper. After closure of the cell with the top plate, the cell was covered with the top plate and stored for 5 days at 60° C.

(38) Paper/semolina flour ratio used:

(39) measuring area: π×radius.sup.2=3.14×0.5 dm.sup.2=0.785 dm.sup.2

(40) paper: 200 g/m.sup.2=200 g/100 dm.sup.2=2 g/dm.sup.2

(41) Semolina flour: 8.6 g on 0.785 dm.sup.2 corr. to 11 g/dm.sup.2

(42) After the storage time the semolina flour was completely transferred into a glass beaker, 250 ml of n-hexane (anhydrous, Sigma-Aldrich) were added and MOSH/MOAH was extracted by shaking the beaker for 2 hours at room temperature. After separation from the semolina flour by filtration, MOSH and MOAH were analyzed following the method of BfR-institute described above. The MOSH/MOAH values were recorded in μg/kg.

(43) Table 3 shows test sheets with a grammage of 200+/−2.5 g/m.sup.2. The ash content of the benchmark without addition of an adsorbent was recorded to 25.0%. The dosages of the adsorbents were calculated for incorporation levels of 10 and 20%. As can be taken from table 3 incorporation levels of 7.0 to 7.5% (“dosage 10%”) and 13.5 to 14.5% (“dosage 20%”) were achieved, which corresponds to good filler retentions around 70%.

(44) TABLE-US-00003 TABLE 3 Characterization of the Test Sheet Paper Ash Adsorbent Trial weight content incorp. no. Adsorbent g/m.sup.2 % % Remarks 1 none 198.3 25.0 — benchmark  2a Ca-bentonite 200.5 32.0 7.0 comparison  2b Ca-bentonite 201.4 38.5 13.5 comparison 3 Saponite 202.5 39.5 14.5 comparison 4 Attapulgite 200.3 38.5 13.5 comparison 5 bentonite acid act. 202.3 39.0 14.0  6a nat. silica 199.5 32.0 7.0  6b nat. silica 201.0 39.0 14.0 7 Sepiolite 201.6 38.5 13.5 8 Sep. acid act. 198.8 39.0 14.0  9a Saponite/Kerolite 201.2 32.5 7.5 mixed layer  9b Saponite/Kerolite 202.3 39.5 14.5 mixed layer 10  Al-silicate synth. 200.8 39.0 14.0

(45) Table 4 gives a summary of the effect of the adsorbents on the migration of MOSH and MOAH from the recycled paper into the semolina flour. In the benchmark trial (no. 1) 80 μg/g of MOSH and 27 μg/g of MOAH, together 107 μg/g were detected after the storage time. Incorporation of adsorbents reduces the migration of MOSH and MOAH by adsorption and fixation.

(46) TABLE-US-00004 TABLE 4 Migration of MOSH/MOAH Adsorbent Trial incorp. MOSH μg/g MOAH μg/g Total Reduction no. Adsorbent % <C25 C 25-C35 <C25 C 25-C35 μg/g % 1 none — 57 23 19 8 107 0  2a Ca-bentonite 7.0 34 14 18 8 74 31  2b Ca-bentonite 13.5 25 12 11 4 52 51 3 Saponite 14.5 25 8 4 5 42 61 4 Attapulgite 13.5 24 10 5 5 44 59 5 Bentonite, acid 14.0 4 3 1 4 12 89 act.  6a nat. silica 7.0 36 7 18 6 67 37  6b nat. silica 14.0 11 3 1 4 19 82 7 Sepiolite 13.5 8 2 1 3 14 87 8 sep. acid act. 14.0 3 2 1 2 8 93  9a Saponite/Kerolite 7.5 16 4 3 2 25 77 mixed layer  9b Saponite/Kerolite 14.5 0.5 3 0.5 4 8 93 mixed layer 10  Al-silicate 14.0 7 3 3 2 15 86 synth.

(47) As a high incorporation rate (more than 20%) of adsorbents with a high specific surface area would damage the paper strength and/or will demand very high use of chemicals (retention aids, sizing agents), it is a particular advantage of the adsorbents of the present invention that a significant reduction (MOSH & MOAH migration, all fractions) of up to 93% could be achieved at an incorporation rate of 14.5%, 77% at 7.5% respectively.