A METHOD FOR CONTROLLING THE DEPOSITION OF STICKIES IN PULPING AND PAPERMAKING PROCESSES

Abstract

A method for controlling the deposition of stickies in pulping and papermaking processes comprises adding to fibre pulp or stock an additive comprising an organo-modified siloxane comprising units of the formula: [R.sup.1.sub.aZ.sub.bSiO.sub.(4-a-b)/2].sub.n in which each R.sup.1 is independently selected from a hydrogen atom, an alkyl, aryl, alkenyl, aralkyl, alkaryl, alkoxy, alkanoyloxy, hydroxyl, ester or ether group, and each Z is independently selected from an alkyl group substituted with an amine, amide, carboxyl, ester, or epoxy group, or preferably at least one or more groups —R.sup.2—(OC.sub.pH.sub.2p).sub.q(OC.sub.rH.sub.2r).sub.S—R.sup.3; wherein n is an integer greater than 1; a and b are independently 0, 1, 2 or 3; R.sup.2 is an alkylene group or a direct bond; R.sup.3 is a group as defined for R.sup.1 or Z above; p and r are independently an integer from 1 to 6; q and s are independently 0 or an integer such that 1≦q+s≦400; and wherein each molecule of the organo-modified siloxane contains at least one group Z. The organo-modified siloxane is preferably a hydroxyl- or alkyl-endcapped linear polydimethylsiloxane, in which 5 to 18 mole percent of silicon atoms are substituted by Z groups of the formula —R.sup.2—(OC.sub.pH.sub.2p).sub.q(OC.sub.rH.sub.2r).sub.s—R.sup.3, in which p is 2, r is 3 and q and s are independently 10 to 20, R.sup.2 is an alkylene group having from 1 to 6 carbon atoms or a direct bond, and R.sup.3 is a hydrogen atom or a hydroxyl, alkoxy, ester or ether group.

Claims

1. A method for controlling the deposition of stickies in pulping and papermaking processes which comprises adding to fibre pulp or stock an additive comprising an organo-modified siloxane comprising units of the formula:
[R.sup.1.sub.aZ.sub.bSiO.sub.(4-a-b)/2].sub.n in which each R.sup.1 is independently selected from a hydrogen atom, an alkyl, aryl, alkenyl, aralkyl, alkaryl, alkoxy, alkanoyloxy, hydroxyl, ester or ether group; each Z is independently selected from an alkyl group substituted with an amine, amide, carboxyl, ester, or epoxy group, or a group —R.sup.2—(OC.sub.pH.sub.p).sub.q(OC.sub.rH.sub.2r).sub.s—R.sup.3; n is an integer greater than 1; a and b are independently 0, 1, 2 or 3; R.sup.2 is an alkylene group or a direct bond; R.sup.3 is a group as defined for R.sup.1 or Z above; p and r are independently an integer from 1 to 6; q and s are independently 0 or an integer such that 1≦q+s≦400; and wherein each molecule of the organo-modified siloxane contains at least one group Z.

2. A method according to claim 1 wherein the additive is added in the stock preparation unit, the pulper outlet, or in paper recycling systems at the pre-flotation inlet.

3. A method according to claim 1 or 2 wherein the additive is added to the pulp or stock either before, during or after fibre disintegration of either virgin or recycled cellulosic material.

4. A method according to any one of claims 1 to 3 wherein the additive is added to the fibre pulp or stock neat or diluted.

5. A method according to any preceding claim wherein in the organo-modified siloxane at least one or more Z groups are —R.sup.2—(OC.sub.pH.sub.2p).sub.q(OC.sub.rH.sub.2r).sub.s—R.sup.3.

6. A method according to claim 5 wherein p and/or r are independently 2, 3 or 4.

7. A method according to claim 5 or 6 wherein q and s are each independently from 5 to 30.

8. A method according to claim 7 wherein q and s are each independently from 10 to 25.

9. A method according to any one of claims 5 to 8, wherein p is 2, r is 3, and q and s are each independently 15 to 20.

10. A method according to any one of claims 5 to 9 wherein R.sup.2 is a direct bond, methylene, ethylene, propylene, butylene, pentylene or hexylene group.

11. A method according to any one of claims 5 to 10 wherein R.sup.3 is a hydrogen atom, or a hydroxyl, alkoxy, ester or ether group.

12. A method according to any preceding claim wherein at least one or more Z groups are an alkyl group substituted with an amine, amide, carboxyl, ester, or epoxy group.

13. A method according to claim 12 wherein at least one or more Z groups are an alkyl group having from 1 to 6 carbon atoms.

14. A method according to claim 13 wherein at least one or more Z groups are a substituted methyl, ethyl, propyl, butyl, pentyl or hexyl group.

15. A method according to any preceding claim wherein the organo-modified siloxane is linear or contains branching.

16. A method according to any preceding claim wherein at least one or more Z groups are —R.sup.2—(OCF.sub.pH.sub.2p).sub.q(OC.sub.rH.sub.2r).sub.s—R.sup.3 and R.sup.3 is a hydroxyl, alkoxy or alkanoyloxy group.

17. A method according to any preceding claim wherein 2 to 20 mole percent of silicon atoms in the siloxane molecule are substituted by a group Z.

18. A method according to claim 17 wherein 5 to 18 mole percent of silicon atoms in the siloxane molecule are substituted by a group Z.

19. A method according to any preceding claim wherein the molecular weight of the siloxane is 1,000-500,000.

20. A method according to claim 19 wherein the molecular weight of the siloxane is 8,000-100,000.

21. A method according to any preceding claim wherein the organo-modified siloxane is a hydroxyl- or alkyl-endcapped linear polydimethylsiloxane, in which 5 to 18 mole percent of silicon atoms are substituted by Z groups of the formula —R.sup.2—(OC.sub.pH.sub.2p).sub.q (OC.sub.rH.sub.2r).sub.3—R.sup.3, in which p is 2, r is 3 and q and s are independently 10 to 20, R.sup.2 is an alkylene group having from 1 to 6 carbon atoms or a direct bond, and R.sup.3 is a hydrogen atom or a hydroxyl, alkoxy, ester or ether group.

22. A method according to claim 21 wherein 11 mole percent of silicon atoms are substituted with said Z groups, q and s are both 18, and the organo-modified siloxane has a molecular weight of approximately 60,000.

23. A method according to any preceding claim wherein the additive consists of organo-modified siloxane alone.

24. A method according to any one of claims 1 to 22 wherein the additive comprises the organo-modified siloxane together with one or more components selected from a polydimethylsiloxane, an organic polyether or a fatty acid ester thereof, a fatty acid ester with C.sub.1-4 mono or polyvalent alcohol or an unsaturated or saturated fatty acid of natural origin or a soap thereof.

25. A method according to claim 24 wherein the fatty acids are selected from saturated and unsaturated monobasic aliphatic carboxylic acids.

26. A method according to claim 25 wherein the fatty acids have from 8 to 22 carbon atoms.

27. A method according to claim 26 wherein the fatty acids are selected from lauric, myristic, palmitic, stearic, arachidic, behenic, lignoceric, palmitolic, oleic, linoleic, linolenic, and arachidonic acids.

28. A method according to any preceding claim wherein the additive comprises an organic polyether having the formula R.sup.4—(OC.sub.pH.sub.2p).sub.q(OC.sub.rH.sub.2r).sub.s—R.sup.5 in which R.sup.4 and R.sup.5 are independently selected from a hydrogen atom, hydroxyl, alkyl, alkoxy or ester groups, p and r are independently an integer from 1 to 6, and q and s are independently 0 or an integer such that 1≦q+s≦400.

29. A method according to any preceding claim wherein the additive is in the form of a solution, micro-emulsion, emulsion, dispersion or any combination thereof.

30. A method according to any preceding claim wherein the additive comprises a water soluble and/or emulsifying siloxane.

31. A method according to any preceding claim wherein the additive is added in an amount of less than 0.01 weight % of fibre in the pulp as dry material.

32. A method according to claim 31 wherein the additive is added in an amount of less than 0.005 weight % of fibre in the pulp as dry material.

33. A method according to claim 32 wherein the additive is added in an amount of 0.003-0.004 weight % or less of fibre in the pulp as dry material.

34. A method according to any preceding claim wherein the additive is used in addition to deinking chemicals.

35. A method according to claim 34 wherein the deinking chemicals include one or more of an alkali, waterglass, and peroxide.

36. A method according to claim 34 or 35 wherein a fatty acid, or an alkali or alkaline earth metal soap of a fatty acid is used in a pre- and/or post-flotation stage.

37. A method according to any preceding claim wherein the detection and measurement of stickies is performed through flow cytometry.

38. A method according to the present invention substantially as hereinbefore described.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0025] The presently disclosed and/or claimed inventive concept(s) will now be described in detail by way of example, with reference to the accompanying drawings, in which:

[0026] FIG. 1 shows the measured levels of hydrophobic micro-stickies in samples taken from the deinked pulp (DIP) plant of an integrated paper mill, “Mill A”;

[0027] FIG. 2 shows a graph of the cumulative build-up per month of hydrophobic micro-stickies on the doctor blade on drying cylinder number 3 of the paper machine Mill A over a period of months, both before and after the addition of an organo-modified siloxane;

[0028] FIG. 3 shows the measured levels of hydrophobic micro-stickies in samples taken from the DIP plant of an integrated paper mill “Mill B”; and

[0029] FIG. 4 shows the average change in the level of hydrophobic micro-stickies at different positions relative to the level at pre-flotation inlet of the DIP plant in Mill B.

DETAILED DESCRIPTION

[0030] According to the presently disclosed and/or claimed inventive concept(s) there is thus provided a method for controlling the deposition of stickies in pulping and papermaking processes which comprises adding to fibre pulp or stock an additive comprising an organo-modified siloxane comprising units of the formula:

[R.sup.1.sub.aZ.sub.bSiO.sub.(4-a-b)/2].sub.n [0031] a) in which each R.sup.1 is independently selected from a hydrogen atom, an alkyl, aryl, alkenyl, aralkyl, alkaryl, alkoxy, alkanoyloxy, hydroxyl, ester or ether group; [0032] b) each Z is independently selected from an alkyl group substituted with an amine, amide, carboxyl, ester, or epoxy group, or a group —R2-(OCpH2p)q(OCrH2r)s-R3; [0033] c) n is an integer greater than 1; [0034] d) a and b are independently 0, 1, 2 or 3; [0035] e) R.sup.2 is an alkylene group or a direct bond; [0036] f) R.sup.3 is a group as defined for R.sup.1 or Z above; [0037] g) p and r are independently an integer from 1 to 6; [0038] h) q and s are independently 0 or an integer such that 1≦q+s≧400; [0039] i) and wherein each molecule of the organo-modified siloxane contains at least one group Z.

[0040] The addition of an additive comprising an organo-modified siloxane to fibre pulp or stock, and in certain non-limiting embodiments, occurs early in the process chain, for example in the stock preparation unit, the pulper outlet, or in paper recycling systems at the pre-flotation inlet. The additive may be added to the pulp or stock either before, during or after fibre disintegration of either virgin or recycled cellulosic material. It has been surprisingly found to effectively control deposits of stickies in a papermaking system, for example on wires, felts, rolls, blades and calenders. It is believed that this is achieved by an increased separation of sticky materials from the fibre pulp or stock, and/or a pacifying effect on sticky materials still present in the fibre current entering the papermaking system.

[0041] The additive comprising the organo-modified siloxane may be added to the fibre pulp or stock neat or diluted. It can be easily stored and handled, and has not been found to disturb the charge balance of the wet end of the paper machine. Also, it does not create extra sludge or dusting.

[0042] Whilst not wishing to be bound by theory, the effect of the organo-modified siloxane in controlling stickies might be explained through a selective interaction with the hydrophobic stickies, whereby an increased separation may be achieved from the fibre pulp or stock, for example in the flotation unit of a paper recycling plant.

[0043] In addition, the organo-modified siloxane might also have a pacifying effect on stickies, whereby the tackiness of the stickies is reduced, so stickies which are not removed from the fibre stream, for example in a flotation unit, have a reduced tendency to adhere to surfaces. Some non-harmful colloidal adhesion to the fibres may also occur, such that the stickies following the flow of fibres to the paper machine become stabilised in a finely dispersed manner.

[0044] In certain non-limiting embodiments, the organo-modified siloxane used in the presently disclosed and/or claimed inventive concept(s), Z is a group —R.sup.2—(OC.sub.pH.sub.2p).sub.q(OC.sub.rH.sub.2r).sub.s—R.sup.3, such as (but not limited to) wherein p and/or r are independently 2, 3 or 4. In certain non-limiting embodiments, q and s are each independently from 5 to 30, such as (but not limited to) from 10 to 25. In a particular (but non-limiting) embodiment of group Z, p is 2, r is 3, and q and s are each independently 15 to 20. In certain non-limiting embodiments, R.sup.2 is a direct bond, methylene, ethylene, propylene, butylene, pentylene or hexylene group. In certain non-limiting embodiments, R.sup.3 is a hydrogen atom, or a hydroxyl, alkoxy, ester or ether group.

[0045] Additionally or alternatively, Z may be an alkyl group substituted with an amine, amide, carboxyl, ester, or epoxy group, for example an alkyl group having from 1 to 6 carbon atoms, i.e. a substituted methyl, ethyl, propyl, butyl, pentyl or hexyl group.

[0046] The organo-modified siloxane may be linear or may comprise units in which a+b=0 or 1, i.e. the siloxane may contain branching. In certain non-limiting embodiments, when Z is a group —R.sup.2—(OC.sub.pH.sub.2p).sub.q(OC.sub.rH.sub.2r).sub.s—R.sup.3, R.sup.3 is a hydroxyl, alkoxy or alkanoyloxy group.

[0047] In certain non-limiting embodiments, 2 to 20 mole percent of silicon atoms in the siloxane molecule are substituted by a group Z, such as (but not-limited to) 5 to 18 mole percent.

[0048] In certain non-limiting embodiments, the molecular weight of the siloxane is 1,000-500,000, such as (but not limited to) 8,000-100,000.

[0049] In particular (but non-limiting) embodiments, the organo-modified siloxanes for use in the method of the presently disclosed and/or claimed inventive concept(s) are hydroxyl- or alkyl-endcapped linear polydimethylsiloxanes, in which 5 to 18 mole percent of silicon atoms are substituted by Z groups of the formula —R.sup.2—(OC.sub.pH.sub.2p).sub.q(OC.sub.rH.sub.2r).sub.s—R.sup.3, in which p is 2, r is 3 and q and s are independently 15 to 20, R.sup.2 is an alkylene group having from 1 to 6 carbon atoms or a direct bond, and R.sup.3 is a hydrogen atom or a hydroxyl, alkoxy, ester or ether group. In particular (but non-limiting) embodiments, 11 mole percent of silicon atoms are substituted with said Z groups, q and s are both 18, and the organo-modified siloxane has a molecular weight of approximately 60,000.

[0050] The additive for use in the method of the presently disclosed and/or claimed inventive concept(s) may consist of organo-modified siloxane alone to control the deposition of stickies, or may comprise the organo-modified siloxane together with one or more components selected from a polydimethylsiloxane, an organic polyether or a fatty acid ester thereof, a fatty acid ester with C.sub.1-4 mono or polyvalent alcohol or an unsaturated or saturated fatty acid of natural origin or a soap thereof. For example, suitable fatty acids include saturated and unsaturated monobasic aliphatic carboxylic acids, for example having from 8 to 22 carbon atoms, such as lauric, myristic, palmitic, stearic, arachidic, behenic, lignoceric, palmitolic, oleic, linoleic, linolenic, and arachidonic acids.

[0051] Suitable organic polyethers for use with the organo-modified siloxane in the method of the presently disclosed and/or claimed inventive concept(s) include those of the formula R.sup.4—(OC.sub.pH.sub.2p).sub.q(OC.sub.rH.sub.2r).sub.s—R.sup.5 in which R.sup.4 and R.sup.5 are independently selected from a hydrogen atom, hydroxyl, alkyl, alkoxy or ester groups, p and r are independently an integer from 1 to 6, and q and s are independently 0 or an integer such that 1≦q+s≧400.

[0052] The additive may be in the form of a solution, micro-emulsion, emulsion, dispersion or any combination thereof. The additive may comprise a water soluble and/or emulsifying siloxane.

[0053] The amount of additive to be used can be very low, and hence can be very economical, whereby the cost of the additive is outweighed by the benefits achieved. Thus, in certain non-limiting embodiments, the additive is added in an amount of less than 0.01 weight % of fibre in the pulp as dry material, such as (but not limited to) in an amount of less than 0.005 weight %, for example 0.003-0.004 weight %. For example, a particular (but non-limiting) example of an amount of organo-modified siloxane to be added is 30-40 g/tonne of paper.

[0054] In paper recycling processes, the additive used in the presently disclosed and/or claimed inventive concept(s) may be used in addition to standard deinking chemicals, for example for use in flotation deinking processes. Such standard deinking chemicals may include, for example, alkalis (such as alkali metal hydroxides, e.g. sodium hydroxide), waterglass (e.g. sodium silicate), and H.sub.2O.sub.2 (peroxide). A fatty acid, or an alkali or alkaline earth metal soap of a fatty acids (suitable fatty acids include those referred to hereinabove) may be used in pre- and post-flotation stages, for example sodium soap of fatty acids (which can convert to calcium soap in hard water).

[0055] The detection and measurement of stickies particles in a pulping or papermaking system may be performed through flow cytometry, or another optical method, and sticky deposits may be controlled by visual inspections and/or gravimetric measurements.

Example 1—“Mill A”

[0056] Mill A is an integrated paper mill using recycled paper grades as furnish for producing printing grades of paper.

[0057] An ordinary two loop RCF (recycled fibres) unit is used to produce deinked pulp (DIP) for newsprint.

[0058] The raw material contained standard household quality ONP and OMG (old news print and magazine grades respectively). The process temperature was between 40 and 50° C., water hardness between 10 and 30° dH and pH between 7 and 9.

[0059] A standard chemical mix containing NaOH (caustic soda), waterglass (silicate) and H.sub.2O.sub.2 (peroxide) was used in the DIP plant for ink detachment, and prevention of ink redepositioning and yellowing. In addition, a sodium soap was added for ink removal in the pre- and post-flotation loop. The soap was at least partly converted into calcium soap due to the water hardness. The soap was dosed in an amount of 2-3 kg/tonne (calculated as fatty acid per tonne of dry outlet from the pulper/drum).

[0060] The amount of hydrophobic “micro-stickies” (<50 μm) was measured in the RCF plant by flow cytometry. The flow cytometry equipment counts the number of hydrophobic “micro-stickies”, i.e. particles having the potential to aggregate into larger stickies thus building up tacky deposits on surfaces in the process system. In flow cytometry the degree of deflection of laser beams combined with dyes having an affinity to the particles of concern are used for the detection of particles, with computer processing of the signals. The sample volume for measurements was 0.2 ml.

[0061] The degree of build-up of deposits of stickies was also observed from the doctor blade of the drying cylinder number 3 of the paper machine.

[0062] An organo-modified siloxane was added to the outlet of the pulper in an amount of 40 g/tonne of incoming paper (0.004 wt %). In particular (but non-limiting) embodiments, the organo-modified siloxane was a polydimethylsiloxane in which 11 mole percent of silicon atoms are substituted by Z groups of the formula —R.sup.2—(OC.sub.pH.sub.2p).sub.q(OC.sub.rH.sub.2r).sub.s—R.sup.3, in which p is 2, r is 3 and q and s are each 18, R.sup.2 is a direct bond, and R.sup.3 is a hydroxyl group, or another end-capping group, having a molecular weight of approximately 60,000.

[0063] During the dosage period of the organo-modified siloxane, depositions of stickies in the paper machine system were significantly reduced. When the organo-modified siloxane stopped being added to the pulper outlet the deposits of stickies in system once again increased. When the organo-modified siloxane was once again added to the pulper outlet, the level of deposits of stickies in the system once again reduced.

[0064] FIG. 1 shows the measured levels of hydrophobic micro-stickies through the DIP plant. The level of micro-stickies at the inlet to pre-flotation is defined as 100%, and the levels in the other positions are calculated relative to this level.

[0065] FIG. 1 shows that without the addition of the organo-modified siloxane, (i.e. just the standard deinking chemicals and sodium soap) no reduction in micro-stickies was seen between the pre-flotation inlet and the outlet of the DIP storage tower. However, when the organo-modified siloxane was added in an amount of 40 g/tonne of incoming paper accept (0.004 wt %), a significant reduction in the level of micro-stickies was found in samples taken from the same positions. Thus, the measured level of micro-stickies reduced from 100% at the pre-flotation inlet to 68% in the DIP storage tower outlet.

[0066] FIG. 2 shows a graph of the cumulative average build-up (g/h) per month of hydrophobic micro-stickies on the doctor blade on drying cylinder number 3 of the paper machine Mill A over a period of months, both before and after the addition of an organo-modified siloxane (March through December). Thus, the average build-up of micro-stickies (g/h) was measured each day, from which a cumulative average amount for each month was calculated.

[0067] The graph shows that the stickies deposits peaked in July (approximately 16500 g/h per month cumulative) prior to introduction of the organo-modified siloxane additive in the second half of this month. After this, the build-up of stickies lowered significantly, to approximately 3000 g/h in August, 1500 g/h in September, 425 g/h in October, and negligible amounts in November and December.

Example 2—“Mill B”

[0068] Mill B is a two loop RCF unit used to produce DIP for newsprint production. The raw material compositions comprise standard household quality ONP and OMG.

[0069] The same chemical mix containing caustic, silicate and peroxide was again used for ink detachment, and prevention of ink redepositioning and yellowing.

[0070] Again, in addition to this chemical mix, sodium soap, transformed into calcium soap due to the water hardness, was added for ink removal in the pre- and post-flotation loops.

[0071] The process temperature was between 45 and 50° C., the water hardness level between 10 and 30°dH and the pH between 7 and 9.

[0072] The potential for the formation of deposits of stickies on surfaces in the process system was assessed by investigating the amount of hydrophobic micro-stickies present in the RCF plant, and in positions in the wet end of the paper machine, performed by flow cytometry.

[0073] In a reference period, 1.5 kg of sodium soap/tonne (as fatty acids) was dosed to the RCF plant, in addition to the other chemicals used for the DIP manufacturing.

[0074] In a test period a combined dosage of 1 kg of sodium soap/tonne and 36 g organo-modified siloxane/tonne of incoming dry accept were dosed (0.0036 wt %), in addition to the standard deinking chemicals.

[0075] FIG. 3 shows the levels of hydrophobic micro-stickies in samples taken from the DIP plant in Mill B relative to the level at the pre-flotation inlet, as measured by flow cytometry. Again, the level of hydrophobic micro-stickies at the pre-flotation inlet is defined as 100%.

[0076] When dosing with standard chemicals only, including 1.5 kg sodium soap/tonne, there is no significant reduction of the levels of hydrophobic micro-stickies observed through the deinking system.

[0077] When dosing the organo-modified siloxane to the accept after the drum pulper in an amount of 36 g/tonne (0.0036 wt %), in combination with a reduced amount of sodium-soap (I kg/tonne), a significant reduction in the level of hydrophobic micro-stickies was measured.

[0078] FIG. 4 shows the average change in level of hydrophobic micro-stickies at different positions relative to the level at pre-flotation inlet of the DIP plant in Mill B, during the reference period (4 runs over 3 months) and during the test period with a dosage of organo-modified siloxane to the RCF plant (8 runs over 11 months), measured by flow cytometry.

[0079] FIG. 4 shows that the amount of hydrophobic micro-stickies is in most positions reduced during the test period using the organo-modified siloxane compared to the reference period.