CA2135694A1 - Water soluble graft copolymers for laser print deinking loop and recycled fiber water clarification - Google Patents

Abstract

A method for clarifying the laser print deinking loop water and the recycled process water containing recycled fiber in a papermaking proc-ess by using a water soluble graft copolymer having the structure:

wherein E is the repeat unit obtained after polymerization of an .alpha., .beta.ethylenically unsaturated compound, the molar percentage of a:b is from about 95:5 to 5:95, with the proviso that the sum of a and b equals 100%;
G comprises the structure:

Description

213~694 WATER SOLUBLE GRAFT COPOLYMERS FOR
LASER PRINT DEINKING LOOP AND
RECYCLED FIBER WATER CLARIFICATION

FIELD OF THE INVENTION

The present invention pertains to novel water soluble graft copoly-mers which are useful for water treatment, such as sludge dewatering and water clarification. More particularly, it relates to the use of a novel graft copolymer for the clarification of water in the deinking loop of a 5 papermaking process using recycled laser print paper and for the clarifi-cation of process water of a papermaking process using recycled fiber process water.

BACKGROUND OF THE INVENTION
There is an increasing usage of water soluble polymers and co-polymers in wastewater treatment industries. These compounds have shown desirable utility for the purpose of dewatering sludge and clarifying contaminated water.

.213569q The efficacies of the poiymers or copolymers used will vary de-pending upon the type of monomers chosen to form the polymer or co-polymer, the molecular weight of the synthesized molecule and, in the case of a copolymer, the placement of the selected monomers on the 5 backbone of the copolymer. It is the latter characteristic that is the focus of the present invention.

Polymers with long sequences of two monomers can be catego-rized as block copolymers or graft copolymers. In graft copolymer 10 sequences of one monomer are "grafted" onto a "backbone" of the second monomer type, ~, etc.
B B B
B B B

Graft copolymers have unique and highly desirable properties as 20 compared to random copolymers or the blend of two homopolymers.
Therefore, there is a great interest in preparing them. Few techniques described in the literature satisfy the need.

Furthermore, with ever increasing usages of water soluble poly-25 mers and copolymers in industries such as wastewater treatment, cool-ing, boiler and deposit control, coating, textile, mining, detergency, cos-metics, and papermaking, etc., there is an urgent need to synthesize novel water soluble graft copolymers for this broad range of applications.

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More specifically, the use of recycled fibers is becoming an impor-tant aspect of papermaking and environmental considerations. The pre-liminary manufacturing steps in the use of recycled fibers for papermak-ing consists of repulping the paper sources, then removing the printing S inks from the fibers. A typical deinking process utilizes a combination of chemical and mechanical techniques in several stages. Large amounts of water are used in the washing or flotation stages, wherein chemically treated ink particles and other conta"linants are physically removed from the fibrous slurry. As the recycled effluent contains dispersed inks, fiber 10 fines and inorganic fillers, these conla",inants must be removed to pro-vide a clean water source for the deinking process and to prevent the dispersed inks from being reintroduced into the fibers.

Recycled fiber generally is derived from waste paper and paper 15 products such as old corrugated containers (OCC), old newsprint (ONP) and office waste paper. The preliminary manufacturing step in the use of recycled fiber for papermaking consists of repulping the secondary fiber source. The repulping of the fiber, in combination with the typical paper-making process, utilized copious amounts of water. The process water 20 from the recycled and papermaking process is typically recycled back into the paper mill for reuse in many process steps. The fiber, fiber fines and other potential CGi ,taminants in the process water must be removed for reuse in the papermaking pr~ass to improve the overall system efficacy.
These solid materials must also be removed from the process water to 25 provide a clean water source for usa~e in other process steps. The efflu-ent may also be discharged from the mill; thus, suspended solids must be removed from the wastewater to m~t environmental regulations.

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Process water from recycled fiber contains high levels of fiber fines and other constituents compared to applications without recycled fiber.
The high fines and other constituents will impact polymer performance.
Fiber fines possess higher surface area than long fiber; furnishes that contain higher percen~ages of fines can consume more polymer ionic charges. Contaminants in these systems may include coatings, waxes, and adhesives that originate with the secondary fiber and are liberated from the fibers during the pulping process. While nonionic and hydro-phobic in nature, they may i"te, rere with polymer interactions. Addition-ally, the process water may contain high levels of soluble organics (total.
organic compounds - TOC) and inorganic salts; the salts would provide high alkalinity and conductivity properties. The soluble organics would originate from the secondary fiber; the salts would result from processing additives required with secondary fiber. It is well established in the litera-ture that salts and soluble organics of specific types and concenlralions will impact polyelectrolyte properties and performance. Therefore, the high fines and various water conta",inants and constituents will impact ionic polymer pe, ror"~ance, and dictate the use of specific products for effective clarification.
Clarification chemicals are typically utilized in conjunction with mechanical clarifiers for the removal of solids from the effluent. Clarifica-tion generally refers to the removal of material by coagulation, and/or floccul^tion, then sedimentation or flotation. See the Betz Handbook of Industrial Water Conditioning, 9th Edition, 1991, Betz Laboratories, Inc., Trevose, PA, pages 23 through 30.

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Conventional polyacrylamide copolymers have been used in this application. However, there still exists a need to provide a novel polymer in a more effective and economic treatment process. This objective is achieved by the present invention. The novel graft copolymers exhibit 5 the desired efficacy for laser deink clarification processes and for recy-cled fiber water clarification applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a graph demonstrating water clarification (supernatant NTU) of OCC furnish versus polymer dosage for the inventive graft co-polymers and comparali~e linear polymers.

Figure 2 is a graph demonslraling water clarification (supernatant 15 NTU) of deinking process water versus polymer dosage for the inventive graft copolymers and comparative linear polymers.

Figure 3 is a graph demonstrating water clarification (supernatant NTU) of deinking process water versus polymer dosage for the inventive 20 graft copolymers and comparative linear polymers.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the use of novel water soluble 25 graft copolymers as laser print deinking loop clarifiers and clarifiers for recycled fiber process water.

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Specifically, the graft polymers in the invention contain polymeric segments obtained from the polymerization of acrylamide and cationic monomers which are attached or "grafted" to another polymer chain which is comprised of the repeating units of one or more monomers.
5 The resulting graft copolymers are soluble in an aqueous medium.

The graft copolymer of the invention has the general structure:

Formula I

_ [ E ]a [fH - Ic]b _ G C=0 wherein E in the above formula (Formula 1) is the repeat unit obtained 20 after polymerization of an a, ,B ethylenically unsaturated compound, pref-erably carboxylic acid, amide form thereof, alkyl (C1-C8) ester or hy-droxylated alkyl (C1-C8) ester of such carboxylic acid. Compounds en-compassed by E include the repeat unit obtained after polymerization of acrylamide, methacrylamide, acrylic acid, methacrylic acid, maleic acid or 25 anhydride, styrene sulfonic acid, 2-acrylamido-2-methylpropyl sulfonic acid, itaconic acid, and the like. Ester derivatives of the above mentioned acids such as 2-hydroxypropyl acrylate, methyl methacrylate, and 2-ethyl-hexyl acrylate, are also within the purview of the invention.

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The molar percentage of a:b is from about 95:5 to 5:95, with the proviso that the sum of a and b equals 100%.

G in the above formula (Formula 1) is a polymeric segment com-5 prising repeat units having the structure:

Formula ll _ [ (CH2-- IC)c (CH2 -- lC)d ]--C=O C=O

wherein R1, R2 and R3 in Formulae I and ll are the same or different and are hydrogen or a lower alkyl group having C1 to C3. F in the above formula is a salt of an ammGnium cation, such as NHR3N+R(4 5 6)M- or 20 OR3N~R(4 5 6)M-, wherein R3 is a C1 to C4 linear or branched alkylene group, and R4, R5 and R6 can be selected from the group consisting of hydrogen, C1 to C4 linear or branched alkyl, Cs to C8 cycloalkyl, aromatic or alkylaromatic group; and M is an anion, such as chloride, bromide, or methyl or hydrogen sulfate. Typical cationic monomers are 2-acryloyl-25 oxyethyltrimethylammonium chloride (AETAC), 3-(meth)acrylamidopropyl-lri,.,ell,ylammonium chloride (MAPTAC or APTAC), 2-methacryloyloxy-ethyltrimethylammonium chloride (METAC) and diallyldimethyla,r""onium chloride (DADMAC), etc.

., It is understood that more than one kind of cationic monomer may be present in Formula ll.

The molar percentage c:d in Formula ll may vary from 95:5 to 5 5:95, with the proviso, however, the sum of c and d equals 100%.

There is no limit to the kind and mole percent of the monomers chosen so long as the total adds up to 100 mole % and the resulting copolymers are water soluble.
At present, the prefer, ed water soluble graft copolymer for use as a recycled fiber process water clarifier is:

Formula lll [cH2-lcH]a ~fH-fH]b f=o G f=o The molar percentage of a:b is from about 95:5 to 5:95, with the proviso that the sum of a and b equals 100%. G in Formula lll is:

~1~5694 Formula IV

[ (CH2-- IC)c [ (CH2--CH)d ]
C=0 C=0 NH2 ' H3C--N+--CH3 Cl-The cationic monomer is 2-acryloyloxyethyltrimethylammonium chloride (AETAC). The molar percentage c:d in the polymer segment G
(Formula IV) is the ratio of acrylamide:AETAC. It may fall within the 20 range between 95:5 and 5:95. The sum of c and d must add up to 100%.

The number average molecular weight (Mn) of the polymeric seg-ment G is not critical and may fall within the range of 1,000 to 1,000,000.
Preferably, the number average molecular weight will be within the range 25 of 5,000 to 500,000, with the range of about 10,000 to about 200,000 being even more desirable. The key criterion is that the resulting graft copolymer be water soluble.

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The graft copolymer is prepared via a two-step polymerization process. First, a macror"onomer comprised of acrylamide and AETAC is prepared by a water-in-oil inverse emulsion polymerization method using peroxide as an initiator. Such processes have been disclosed in U.S.
Patents 3,284,393, Reissue 28,474 and Reissue 28,576, herein incorpo-rated by reference. The initiator may be selected from peroxides, persul-fates, bromates, and azo-type initiators such as 2,2'-azobis-(2-amidino-propane) dihydrochloride, 2,2'-azobis-(2,4-dimethylvaleronitrile). Copper (Il) sulfate is added in the process as an oxidative chain transfer agent to generate a terminal unsaturated double bond in the polymer chain. It is conceivable that transition metal ions other than copper, such as iron, cobalt, and nickel etc., may be used in the invention.

Ethylenediaminetetraacetic acid or diethylenetriamine pentaacetic acid and their salts or their amino analogue are used as chelating agents to chelate or to form complexes with copper prior to the second polymeri-zation step.

The resulting macromonomer is then copolymerized with acryla-mide or other monomers to form graft copolymers by a similar water-in-oil inverse emulsion technique.

Branching agents such as polyethyleneglycol di(meth)acrylate, N,N'-methylenebis(meth)acrylamide, N-vinyl acrylamide, allyl glycidyl ether, glycidyl acrylate and the like may also be added, providing the resulting graft copolymer is water soluble. Any of the well known chain transfer agents familiar to those who are skilled in the art may be used to control the molecular weight. Those include, but are not limited to, lower alkyl alcohols such as isopropanol, amines, mercaptans, phosphites, thioacids, formate, allyl alcohol and the like.

213~694 Conventional initiators such as peroxide, persulfate, along with sulfite/bisulfite and azo compounds may be used depend on the system chosen.

High HLB inverting surfactants such as those described in U.S.
Patent Re. 28,474 are then added to the emulsion to convert the resulting emulsion to a "self-inverting" emulsion. Using the procedure described herein, a unique graft copolymer in emulsion form is obtained.

The resulting copolymer may also be further isolated by precipitat-ing it in an organic solvent such as acetone and dried to a powder form.
The powder can be easily dissolved in an aqueous medium for use in the desired applications.

It is to be understood that the aforementioned polymerization methods do not in any way limit the synthesis of copolymers according to this invention.

The resulting emulsion disperses and dissolves rapidly into an aqueous solution upon addition to water under moderate shear condi-tions. Within minutes, a maximum solution viscosity is obtained. The emulsion dissolves well even in water containing a high level of hardness and it also retains most of its solution viscosity in brine water.

The structure of the graft copolymer is substantiated by a conven-tional solution viscosity study and C13 NMR spectroscopy. The molecu-lar weight of the resulting graft copolymer is not critical, as long as the polymer is soluble in water. The molecular weight may vary over a wide range, e.g., 10,000 - 30,000,000 and may be selected depending upon the desired application.

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The graft copolymer is added to the clarifier influent water flow. It is added in an amount of from about 0.5 to 100 ppm of active polymer per total influent volume. Preferably 2 to 25 ppm of polymer per total influent volume is employed for laser print deinking loop clarification. Preferably 5 0.5 to 50 ppm of active polymer per total influent volume is employed for recycled fiber process water.

ExPerimental Properties of a water soluble graft copolymer prepared according to the procedure described above are shown in Table 1. The copolymer contains an overall amount of 5 mole % AETAC and 95 mole % acryla-mide.

TABLE I
Physical Properties of the Graft Copolymers Polymer Solids (%) UL~ ViscositY (cPs) ~UL viscosity: 0.3% solids of polymer dissolved in 4% NaCI solution, as measured with a UL adapter in a Brookfield viscometer.

25 Performa"cc Test Example 1 In the following test, the performance of the water soluble graft co-polymers described in this invention is demonstrated in laboratory tests.
30 OCC plant clarifier influent process water from a Southern linear board ~35694 .

mill was obtained for the test sub~l~ale. The subslrate had the following properties: pH, 4.0, suspended solids, 0.089% and a total turbidity of 790 NTU.

Test Pl~ce~ure 1. 250 milliliters (ml) of stock at 25C is measured in a gradu-ated cylinder and poured into a 400 ml glass beaker. The beaker con-tains a Teflon coated magnetic stirring bar, and is centered on a mag-10 netic stirring plate. The stir plates have been previously calibrated toprovide approximately equivalent shear mixing speeds at "high" and "low"
speeds.

2. The beakers are turned on to high speed; once the samples 15 have equilibrated, the test level of coagulant is introduced into the center of the vortex with a previously filled syringe. The polymer is allowed to mix for a predetermined time consistent with the individual mill's clarifier design, typically 10 to 60 seconds.

3. After the polymer mix time, the speed of the mixer is re-duced to "low" speed for a time period consistent with the actual clarifier, typically 30 to 60 seconds. Afler the low speed mixing time is completed, the mixers are turned off, and the floo~'^ted particles are allowed to settle. The settling volumes and times are recorded.

4. Supernatant is then removed from the beaker, and the turbidity is recorded on a turbidi"~eter for each polymer and polymer dosage level.

The results are shown in Table ll and Figure 1. Comparative polymers 1 and 2 are conventional linear polymers with a 90: 10 molar ratio of acrylamide:AETAC. All polymers tested are cationic water-in-oil emulsion polymers with an active polymer content of approximately 33%.

TABLE ll OCC Fumish - DAF Clarifier Influent Dosage Polvmer (PPm asProduct) NTU
Blank ---- 665 The data presenled in Table ll and graphically represented in Fig-ure 1 demonslrale the improved clarification efficacy of recycled process 25 waters of the water soluble graft copolymers over the linear, non-grafted water soluble polymers.

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Properties of five water soluble graft copolymers prepared accord-ing to the procedure described above are shown in Table lll. The copoly-mers contain an overall amount of 20 mole % AETAC and 80 mole %
acrylamide.

TABLE lll Physical P~ o"e. lies of the Graft Copolymers PolYmer Solids (%) UL* Viscosity (cPs) B 39.6 9.0 C 35.8 11.4 D 38.5 12.2 E 41.4 18.1 F 33.2 25.1 15 *UL viscosity: 0.3% solids of polymer dissolved in 4% NaCI solution, as measured with an UL adapter in a Brookfield Viscometer.
Perfonnance Test Example 2 In the following test, the performance of the water soluble graft copolymers described in this invention is demonstrated. The test sub-strate is a deinking process water containing 100% recycled laser print fiber from a Midwest paper mill. The substrate had the following proper-25 ties: pH, 7.0-7.5, solids, 0.126% and a total turbidity of 1300-1400 NTU.

The results are shown in Table IV and Figure 2. Comparative polymers A and B are commercially available linear copolymers containing 20 mole % and 40 mole % of AETAC, respectively (the 30 remainder, acrylamide). The above data demonsl, ate that the graft copolymers in this ; 2I35694 invention are more effective in water clarification than the comparative linear polymers.
TABLE IV
Clalrification Test Polymer Dosaqe (ppm) SuPernatant (NTU) TABLE IV (cont'd) Clarification Test Polymer Dosa~e (PPm) SuPernatant (NTU) Cor"paralive Polymer A 5 860 Comparative PolymerB 5 684 Example 3 Where the previous example tested deinking process water that contained 100% recycled laser print, many paper mills will only utilize a portion of laser print in the total fiber composition. In the following exam-ple, process water from a Northwest paper mill was tested. It contained approximately 20% to 40% recycled laser print fiber with the remainder 20 being made up of nonimpact print fiber. The subsl, ale exhibited a pH of 6.6 and had a solids content of 0.052%. The same test protocol as in Example 2 was followed and the polymers used are as defined previous-ly. Results are shown in Table V and Figure 3.

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TABLE V
Clarification Test Polymer Dosa~e (ppm) suPernatant (NTU) Blank 0 835 Comparative ExampleA 5 362 The foregoing tests demonstrate that the graft configuration of the subject polymer is more efficient at clarifying process water containing laser print fiber than is the linear configuration of the same molecule.
While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modi-fications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to 20 cover all such obvious forms and ,-odif;cations which are within the true spirit and scope of the present inv~l~lion.

Claims (31)

1. A method for clarifying recycled process water containing recycled fiber in a papermaking process comprising adding to said proc-ess water a sufficient amount for the purpose of a water soluble graft copolymer having the structure:

wherein E is the repeat unit obtained after polymerization of an .alpha., .beta.ethylenically unsaturated compound, the molar percentage of a:b is from about 95:5 to 5:95, with the proviso that the sum of a and b equals 100%;
G comprises the structure:

wherein d is a cationic monomer, R1, R2 and R3 are the same or different and are hydrogen or a lower alkyl group having C1 to C3. F is a salt of an ammonium cation and the molar percentage of c:d is from 95:5 to 5:95 with the proviso that the sum of c and d equals 100%.

2. The method of claim 1 wherein the .alpha., .beta. ethylenically un-saturated compound is selected from the group consisting of a carboxylic acid, the amide form thereof, the alkyl (C1-C8) ester thereof and the hy-droxylated alkyl (C1-C8) thereof.

3. The method of claim 2 wherein the .alpha., .beta. ethylenically un-saturated compound is selected from the group consisting of acrylamide, methacrylamide, acrylic acid, methacrylic acid, maleic acid, maleic anhy-dride, styrene sulfonic acid, 2-acrylamido-2-methyl propyl sulfonic acid, itaconic acid, 2-hydroxylpropyl acrylate, methyl methacrylate and 2-ethyl-hexyl acrylate.

4. The method of claim 1 wherein F is selected from the group consisting of NHR3N+R(4,5,6)M- or OR3N'R(4,5,6)M-, wherein R3 is a C1 to C4 linear or branched alkylene group, and R4, R5 and R6 are selected from the group consisting of hydrogen, C1 to C4 linear or branched alkyl, C5 to C8 cycloalkyl, aromatic or alkylaromatic group; and M- is an anion selected from the group consisting of chloride, bromide, methyl sulfate and hydrogen sulfate.

5. The method of claim 4 wherein the cationic monomer is selected from the group consisting of 2-acryloyloxyethyltrimethylammo-nium chloride, 3-(meth)acrylamidopropyltrimethylammonium chloride, 2-methacryloyloxyethyltrimethylammonium chloride and diallyldimethyl-ammonium chloride.

6. The method of claim 1 wherein said copolymer has the structure:

wherein the molar percentage of a:b is from about 95:5 to 5:95, with the proviso that the sum of a and b equals 100%, and G has the structure:

7. The method of claim 1 wherein the number average molecu-lar weight of G is from about 1,000 to about 1,000,000.

8. The method of claim 7 wherein the number average molecu-lar weight of G is from about 5,000 to about 500,000.

9. The method of claim 8 wherein the number average molecu-lar weight of G is from about 10,000 to about 200,000.

10. The method of claim 1 wherein the graft copolymer has a number average molecular weight of from about 10,000 to 30,000,000.

11. The method of claim 10 wherein the graft copolymer has a number average molecular weight of from about 1,000,000 to 30,000,000.

12. The method of claim 1 wherein the graft copolymer is added to the clarifier influent in an amount of from about 0.5 to 100 ppm active polymer per total influent volume.

13. The method of claim 1 wherein the amount is from about 0.5 to 50 ppm active polymer per total influent volume.

14. The method of claim 1 wherein the graft copolymer is added to the influent flow prior to the clarifier.

15. The method of claim 1 wherein said process water contains old corrugated containers.

16. The method of claim 1 wherein said process water contains old news print.

17. The method of claim 1 wherein said process water contains office waste paper.

18. A method of clarifying laser print deinking loop water of a papermaking process comprising adding to the clarifier influent an amount sufficient for the purpose of a water soluble graft copolymer having the structure:

wherein E is the repeat unit obtained after polymerization of an .alpha., .beta.ethylenically unsaturated compound, the molar percentage of a:b is from about 95:5 to 5:95, with the proviso that the sum of a and b equals 100%;
G comprises the structure:

wherein d is a cationic monomer, R1, R2 and R3 are the same or different and are hydrogen or a lower alkyl group having C1 to C3, F is the salt of an ammonium cation and the molar percentage of c:d is from 95:5 to 5:95 with the proviso that the sum of c and d equals 100%.

19. The method of claim 18 wherein the .alpha., .beta. ethylenically un-saturated compound is selected from the group consisting of a carboxylic acid, the amide form thereof, the alkyl (C1-C8) ester thereof and the hy-droxylated alkyl (C1-C8) thereof.

20. The method of claim 19 wherein the .alpha., .beta. ethylenically un-saturated compound is selected from the group consisting of acrylamide, methacrylamide, acrylic acid, methacrylic acid, maleic acid, maleic anhy-dride, styrene sulfonic acid, 2-acrylamido-2-methyl propyl sulfonic acid, itaconic acid, 2-hydroxypropyl acrylate, methyl methacrylate and 2-ethyl-hexyl acrylate.

21. The method of claim 18 wherein F is selected from the group consisting of NHR3N+R(4,5,6)M- or OR3N+R(4,5,6)M-, wherein R3 is a C1 to C4 linear or branched alkylene group, and R4, R5 and R6 are selected from the group consisting of hydrogen, C1 to C4 linear or branched alkyl, C5 to C8 cycloalkyl, aromatic or alkylaromatic group; and M- is an anion selected from the group consisting of chloride, bromide, methyl sulfate and hydrogen sulfate.

22. The method of claim 21 wherein the cationic monomer is selected from the group consisting of 2-acryloyloxyethyltrimethylammo-nium chloride, 3-methacrylamidopropyltrimethylammonium chloride, 2-methacryloyloxyethyltrimethylammonium chloride and diallyldimethyl-ammonium chloride.

23. The method of claim 18 wherein said copolymer has the structure:

wherein the molar percentage of a:b is from about 95:5 to 5:95, with the proviso that the sum of a and b equals 100%, and G has the structure:

24. The method of claim 18 wherein the number average molecular weight of G is from about 1,000 to about 1,000,000.

25. The method of claim 24 wherein the number average molecular weight of G is from about 5,000 to about 500,000.

26. The method of claim 25 wherein the number average molecular weight of G is from about 10,000 to about 200,000.

27. The method of claim 28 wherein the graft copolymer has a number average molecular weight of from about 10,000 to 30,000,000.

28. The method of claim 27 wherein the graft copolymer has a number average molecular weight of from about 1,000,000 to 30,000,000.

29. The method of claim 18 wherein the graft copolymer is added to the clarifier influent in an amount of from about 0.5 to 100 ppm polymer per total influent volume.

30. The method of claim 29 wherein the amount is from about 2 to 25 ppm per total influent volume.

31 The method of claim 18 wherein the graft copolymer is added to the influent flow prior to the clarifier.