CA2127011C - Water soluble graft copolymers and methods of use thereof - Google Patents

Abstract

A water soluble graft copolymer useful as retention and drainage aids in papermaking processes having the structure:
wherein E is the repeat unit obtained after polymerization of and, .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

L-692~/A-2 WATER SOLUBLE GRAFT COPOLYMERS AND
METHODS OF tJSE THEREOF
FIELD OF THE INlfENTION
The present invention pertains to novel water soluble graft copoly-mers which are useful for water treatment, such as sludge dewatering and water clarification. In addition they are also effective as retention 1 ~ and drainage aids in the papermaking process.
BACKGROUND OF ThIE fN~JENTION
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.

The effiicacies of the polymers 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 backbone of the copolymer. It is the Batter 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 copolymers sequences of one monomer are °'grafted" onto a "backbone" of the second monomer type, __ ~ __p,~__,q~p,__, etc.
B B
t i B B B
Graft copolymers have unique and highly desirable properties as 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-mers and copolymers i.n 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.

This invention prepares distinctive water soluble graft copolymers for water treatment applications and specifically for papermaking processes.
5 U.S. Patent 3,869,418 describes a graft copolymer comprising a polymeric N-vinyl lactam such as N-vinyl pyrrolidone with unsaturated carboxylic acids, like acrylic acid and methacrylic acid in an emulsion process. The resulting copolymer is not water soluble and is used for adhesive and coating applications.

U.S. Patent 4,271,053 discloses a quaternary ammonium graft copolymers prepared by grafting quaternary ammonium ionene-type poly-meric side chains onto a polymer backbone formed by the reaction of a difunctional amine and an epihalohydrin or diperoxide. The polymers are 15 different than the present invention.
U.S. Patent 4,400,496 and European Patent Application 0 356 241 teach grafting acrylamide or acrylic acid with starch in the presence of ceric ions. The product has to be precipitated and separated in acetone 20 prior to use.
Smirnova et al., Journal of Polymer Science, Vol. 29, pp. 139-145 describe a graft copolymerization of methacrylic acid with polycapro-amide by the persulfate/sulfite redox system in the presence of copper 25 ions. It is a different reaction mechanism and results in a different co-polymer than the present invention.
U.S. Patent 4,916,191 discloses a gra~'t copolymer prepared from a macromonomer with hydrophilic and fluorinated monomers for dispersion 30 stabilizer in an emulsion polymerization process.

Compared to the related art disclosed above, there exists a need to prepare water soluble graft copolymers in a convenient and economic process. This is achieved by the present invention. The resulting copolymers exhibit desired efficacy as paper retention and drainage aids.
DETAILED DESCRIPTION OF THE INVENTION
The present invention pertains to novel water soluble graft co-polymers which are useful as retention and drainage aids in paperlpulp making processes.
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.
The resulting graft copolymers are soluble in an aqueous medium.
These graft copolymers may be utilized along with bentonite clay to form an effective retention and drainage aid. When these two com-pounds are combined, the most desirable weight ratio of copolymer to bentonite is between about 2 to 1 and 1 to 20.
..........w_.~-,-~... rv...~ _:. . .. ,~,.._..F~,w.~"~-~...~._~.e_....-. ~.. .
._.__~~~..._.-~.. ... _ The graft copolymer of the invention has the general structure:
Formula I

--t ~ l~- fC~l- i lb G- C=0 wherein E in the above formula (Formula !) is the repeat unit ob-tained after polymerization of an a, (i ethylenically unsaturated com-pound, preferably carboxylic acid, amide form thereof, alkyl (C1-C8) ester or hydroxylated alkyl (C1-C8) ester of such carboxylic acid. Compounds encompassed by E include the repeat unit abtained after polymerization of acrylamide, methacrylamide, acrylic acid, methacrylic acid, malefic acid or 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 acryiate, are also within the purview of the invention.
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°fo.

2.~~'~~~:~.

~G in the above formula (Formula I) is a polyrneric segment com-prising repeat units having the structure:
Formula 11 I~ 13 -I (CR2- i )c (CHZ_.r i )d ~--C=0 C=0 ~lElz F
wherein R~, R2 and Ra in Formulae I and II are the same or different and are hydrogen or a lower alkyl group having C~ to C3. F in the above formula is a salt of an ammonium cation, such as NHR3N~'R(4,5,~) M- or OR3N+R(a,s,g) M-, wherein R3 is a C~ to C~ linear or branched alkylene group, and R4, R5 and R6 can be selected from the group consisting of hydrogen, C~ to C~ linear or branched alkyl, C~ to Cs 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-oxyethyltrimethylammonium chloride (AETAC), 3-(meth)acrylamido-propyltrimethylammonium chloride (MAPTAC or APTAC), 2-methacryloyl-oxyethyltrimethylammonium chloride (METAL) and diallyldimethyl-ammonium chloride (t7A~MAC), etc.
It is understood that more than ane kind of cationic monomer may be present in Formula II.

The molar percentage c:d in Formula II may vary from 95:5 to 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 preferred water soluble graft copolymer for use as retention and drainage aids is:
Formula III
-~-CH-CHI iCM-CH~--2 ~ a ~ ~ b C=0 G C=0 N~i ~IH

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 III is:

Formula IV
w'E (CH2- i ~--°~°E (CH2"'° i )d W-' C=0 C=0 NHS O

H3C N+ CH3 C1-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 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 b~ within the range 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.

The bentonite can be any of the materials commercially referred to as bentonites or bentonite-type clays, i.e., anionic swelling clays such as sepialite, attapulgite or, preferably, montmorillinite. The montmorillinites are preferred. Bentonites broadly as described in U.S. Patent No.
5 4,305,781 are suitable. Suitable montmorillinite clays include Wyoming bentonite or Fullers Earth. The clays may or may not be chemically modified, e.g., by alkali treatment to convert calcium bentonite to alkali metal bentonite. The swelling clays are usually metal silicates wherein the metal comprises a metal selected from aluminum and magnesium, 10 and optionally other metals, and the ratio silicon atoms: metal atoms in the surface of the clay particles, and generally throughout their structure, is from about 5:1 to 1:1.
The graft copolymer is prepared via a two-step polymerization 15 process. First, a macromonomer 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. The initiator may be selected from peroxides, persulfates, bromates, and azo-type initiators 20 such as 2,2'-azobis-(2-amidinopropane) dihydrochloride, 2,2'-azobis-(2,4-dimethylvaleronitrile). Copper (II) 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 25 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 acryl-amide or other monamers to form grafit copolymers by a similar water-in-oil inverse emulsion technique.
Branching agents such as polyethyleneglycol di(meth)-acrylate, N,N'-methylenebis(meth)acrylamide, PJ-vinyl acrylamide, allyl glycidyl ether, giycidyl acrylate and the like may also be added, providing the resulting graft copolymer is water soluble. Any of tho 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, formats, allyl alcohol and the like.
Conventional initiators such as peroxide, persulfate, along vvith sulfite/bisultite and azo compounds may be used depending 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. Within minutes, a maximum solution viscosity is obtained. The emulsion dissolves well even in water containing a high level of hardness and it also rotains most of its solution viscosity in brine water.
The structure of the graft copolymer is substantiated by a conven-tional solution viscosity study and C~3 lVMR spectroscopy. The molecu-lar weight of the resulting graft copolymer is not critical, as song 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.
The graft copolymer is added to the pulp furnish prior to the paper forming stages. It is added in an amount of from about 0.5 to 25 pounds per ton of furnish. Preferably about 1.0 to 10 pounds of copolymer per ton of furnish is used.

~:~~'1~:~ _~

When used in conjunction with bentonite, dosage levels for the graft copolymer range from 0.05 to 10 pounds per ton, and preferably 0.10 to 5 pounds per ton, active polymer to active furnish solids. The copolymer is best applied to the furnish as a dilute aqueous solution.
Dosage levels for the bentonite clay are in the range of about 0.25 to 25 pounds per ton of active clay to active furnish solids. The preferred range is about 0.5 to 10 pounds per ton.
Examples Utilizing the procedure described above, numerous water soluble graft copolymers were prepared. Table I hereinbelow summarizes the physical properties of the resulting acrylamide>AETAC graft copolymers.

Physical erties of f9~e olvrtaers Prop Craft Cop AETAC Content UL Viscosity Solids Example mole % % f cps) J-2 5 34.4 11.6 J-10 5 34.9 21.0 J-14 5 35.1 12.6 J-19 5 31.3 13.0 J-21 5 31.9 14.1 J-28 5 32.0 11.0 J-30 10 33.2 12.7 J-31 10 35.0 11.6 J-23 10 34.7 4.5 J-25 10 34.5 19.3 J-07 10 37. 9 16.1 J-20 10 34.3 12.6 Performance Evaluation Papermaking retention aids are used to increase the retention of fiber and filler fine furnish solids in the web during the turbulent process of draining and forming the paper web. The eaten;>ive use of retention aids is well documented in the paper industry. For example, see "Retention Chemistry", Chapter 17, Pulp and Paper, James P. Casey, Volume 3, 3rd edition, pages 1593 to 1607. Without adequate retention of the fine solids, they are either lost to the process effluent, which is a cost consideration for expensive fillers, or accumulate to excessively high concentrations in the recirculating white water loop and cause production difficulties including deposit buildup and impaired paper machine drain-age.
Additionally, insufficient retention of the fine solids and the dispro-portionate quantity of chemical additives which are adsorbed on the surface reduces the paper-maker's ability to achieve necessary paper quality specifications such as opacity, strength, sizing, basis weight, and formation (sheet uniformity}, In the following tests, the performance of the resulting water sol-uble graft copolymers as retention and drainage aids in the papermaking process is demonstrated. The standard ~ritt jar test as well as tests using a pulp drainage testing device were used for evaluation.

.

Laboratory prepared acid and alkaline furnishes were used as the substrates. Hardwood and softwood market pulp were refined separately to respective 300 and 500 Canadian Standard Freeness, and mixed at a 50/50 ratio. Alkaline furnish was prepared with the addition of precipi-tated calcium carbonate at a level of 20% of the total furnish solids. The resulting pH was 8.5. Acid furnish was prepared with the addition of rosin size at 10 Ibs/ton and alum at 15 Ibs/ton based upon fiber solids. 20%
clay and 5% Ti02 based upon fiber solids was then added, and the pH
was adjusted to 4.5.
Fines retention tests were conducted on the Britt jar with thin stock at 0.5% consistency. Polymers at the specified dosage were added to stock in the 8ritt jar at 1400 rpm shear speed and allowed to mix for 15 seconds. 100 mls of filtrate was collected and filtered to determine the fines content per standard procedure. Polymers were tested at 1.5, 2.25, 3.0 and 3.75 Ibs/ton based upon furnish solids, and compared to blank samples. Drainage tests were conducted with the CSF tester. Thin stock was prepared at 0.30% consistency. Polymers were added to the stock at 1400 rpm and mixed for 15 seconds before testing on the CSF. Poly-mers were tested at 1.5, 2.25, and 3.0 Ibs/ton, and compared to blank tests.
The results are shown in Tables II and lll.

TABLE
II

Polymer Pounds Dosage (Ibs) in Polymer per ton (T) of Furnish Example 1.51bs/T2.251bs/'f3.OIbs/T3.751bsIT

J-2 55.2 60.0 65.0 66.2 J-10 61.6 71.1 76.5 80.6 J-30 54.5 66.1 70.6 74.0 J-31 55.3 56.5 63.6 68.7 J-23 40.4 46.4 50.0 46.0 J-25 50.7 59.8 62.0 65.3 10J-O7 40.1 46.7 56.0 59.5 J-20 52.3 61.3 66.4 70.0 Blank 16.3%

TABLE
III

15Polymer Pounds Dosage (Ibs) in Polymer per ton (T) of Furnish Example 1.51bsrf2.251bs~1'3.OIbsl1'3.751bsf'f J-2 36.9 44.3 58.9 72.4 J-10 40.4 51.8 61.8 74.6 J-30 38.6 47.7 61.1 68.2 20J-31 41.3 52.9 62.8 74.3 J-23 39.6 42.1 50.6 50.9 J-25 39.1 45.3 59.3 65.9 J-07 36.6 42.1 46.6 56.1 J-20 39.8 51.8 60.0 67.5 25 Blank 18.5%

A drainage testing device equipped with a rotating hydrofoil (300 rpm), and vacuum capability underneath the wire screen (100 mesh) was also used to evaluate the graft copolymers of the invention. The device can be operated for multi-pass of substrate and reach an equilibrium stage. It is a closer simulation of the actual paperrnaking process than the conventional Britt jar and CSF tests. Both the retention and drainage behavior of the tested paper pulp and treatment can be easily character-ized. The testing conditions are:
A) Foil = 300 rpm (equivalent to a 1500 ft/min machine);
Mixer = 1400 rpm; Wire screen = 100 mush. Vacuum dewatering starts when the white water drainage (by gravitylpulsation forces) reaches 80% of the initial furnish volume.
Couch vacuum = 14 inch-Ng.
B) Furnish: Headbox stock from Hawesville:
Fiber fines = 40.69, CSF = 350.
C) Multi-pass test and white water recirculation: For the first-pass, the stock (178ccm %con = 0.56) was diluted with process water to 1000cc before test. For the subsequent passes, the stock was diluted with the white water generat-ed from the previous pass (only about 82% of the white water can be recovered in this process). A total of six passes were conducted for each tested system. The results are shown in Table IV.

'f~A~f_E I!!
1 st Pass 6th ~E uilibrium Pass Treatment %FR p~4DF2vDR RES
%~'R
pg~R
vDR
RES

J-14 49.5 15.8 1.09 0.1249.7 34.4 2.57 0.27 J-19 60.9 16.4 -___ ____51.3 30.2 ____ ____ J-21 56.8 15.8 ---- ----52.4 28.5 ____ ..___ J-28 51.4 14.6 0.94 0.1143.7 28.9 2.13 0.23 J-10 51.5 14.0 0.88 0.1154.1 34.1 2.65 0.,27 J-2 53.5 15.5 0.99 0.1146.6 29.7 2.09 0.24 J-07 42.1 12.7 0.93 0.1038.0 25.9 2.05 0.23 J-20 52.3 14.9 0.77 0.1046.7 24.8 1.97 0.23 J-23 49.2 14.0 0.82 0.1140.1 28.9 2.10 0.24 J-25 48.8 14. 5 0.93 46.2 34.1 2.51 0.27 0.1 't J-30 42.7 12.0 0.99 0.1150.7 25.7 2.56 0.28 J-31 48,2 13.3 0.88 0.1148.3 26.0 2.07 0.23 A 57.7 14.8 ---- ----51.4 30.1 ---- ----blank 49.5 16.5 0.99 0.1344.0 32.2 2.61 0.30 ,'ol=Rthe percentage of = fines retained in the sheet.

pgDR pulsation/gravity (sec). r the R
= drainage time The pgD is, smalle the better; a 5% gnificant.
difference is si vDR vacuum drainage the etter.
= time (sec). The vDR
smaller is, the b RES air flaw resistance ure The = of the wet pad, of a meas formation.

greater the RES
is, the better.

A = a commercial acrylamidelAETAD
copolymer with a linear configuration.

2~~ ~~.~~>~

Examples: Graft Copolymer plus bentoraite Canadian Standard Freeness procedures were followed for drain age results. Dosages of the respective polymers wand bentonite clay are as shown in Table V.
Test samples consisted of 1000 ml of a synthetic alkaline furnish, having a consistency of .286%. The samples with polymer were sub-jected to shearing at 1400 for 15 seconds, and far those samples con-taining the bentonite clay, followed by shearing at 1400 rpm for 60 seconds which was reduced to 1000 rpm for 15 more seconds.
To demonstrate retention properties, Standard Britt Jar Retention testing was performed utilizing the same dosages as for drainage testing.
The test samples were 500 m! of synthetic alkaline furnish at .467%
consistency. Shear speed and contact times were as described above.
For calculating retention, 100 ml of effluent was drained, filtered, dried and weighed.
TAi3l_E V
Dosage CSF % Fines Treatment Ibs/ton Drainage Retention Blank ---- 456 11.5 Example 1 1.5 508 65.0 2.25 526 74.7 3.0 528 75.2 'TALE ~/ (corat'~~
Dosage CSF % Fines Treatment Ibs/ton Drainage Ft~tention Example 11 1.5/4 587 74.5 Bentonite 2.5/4 639 88.2 Clay 3.0/4 666 92.3 Example 2 1.5 510 67.7 2.25 527 74.0 3.0 542 77.2 Example 2/ 1.5/4 562 74.3 Bentonite 2.2514 611 88.3 Clay 3.0/4 644 88.6 Comparative 1.5 492 63.3 Example 1 2.25 500 68.5 3.0 507 7'I .6 Comparative 1.5/4 588 78.5 Example 1/ 2.25/4 634 90.3 Bentonite 3.014 666 93.4 Glay T~~L~E ~ (cont'd) Dosage C,SF % Fines Treatment Ibs/ton Drainage Retention Comparative .5 524 80.6 Example 2* .75 542 77.0 1.0 552 78.6 Comparative .5/4 587 75.0 Example 2*/ .75/4 649 90.8 Bentonite Glay 1.0/4 671 91.5 *powder form: dosage different, so that results are based on an equal actives basis.
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 cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.

Claims (12)

1. A process for the production of paper from pulp furnish having improved retention and drainage properties, comprising:
adding to the furnish 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 R,, RZ and R3 are the same or different and are hydrogen or a C, to C3 alkyl group, F is the salt of an ammonium ration 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%; and bentonite clay, wherein the weight ratio of said graft copolymer to said bentonite clay ranges from about 2:1 to 1:20.

2. The process of claim 1, wherein the water soluble graft copolymer is added to the furnish before at least one shear stage.

3. The process of claim 2, wherein the bentonite clay is added to the furnish containing the water soluble graft copolymer after at least one shear stage.

4. The process of claim 1, 2 or 3, wherein from about 0.05 to 10 pounds of active graft copolymer is added per ton of furnish.

5. The process of any one of claims 1 to 4, wherein from about 0.25 to 25 pounds active clay is added per ton of furnish.

6. The process of any one of claims 1 to 5, wherein the ethylenically unsaturated compound is (a) an ethylenically unsaturated carboxylic acid, the amide form thereof, the alkyl (C1 -C8) ester thereof or the hydroxylated alkyl (C1 -C8) ester thereof, or (b) an ethylenically unsaturated sulfonic acid.

7. The process of claim 6, wherein (a) is acrylamide, methacrylamide, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, 2-hydroxypropyl acrylate, methyl methacrylate or 2-ethylhexyl acrylate.

8. The process of claim 6, wherein the ethylenically unsaturated sulfonic acid is styrene sulfonic acid or 2-acrylamido-2-methylpropyl sulfonic acid.

9. The process of any one of claims 1 to 8, wherein F is the group NHR3 N+R(4,5,6) M-, wherein R3 is a C1 to C4 linear or branched alkylene group, R4, R5 and R6 are hydrogen, C1 to C4 linear or branched alkyl, or a C5 to C8 cycloalkyl, aromatic or alkylaromatic group; and M- is chloride, bromide, methyl sulfate or hydrogen sulfate.

10. The process of claim 9, wherein the is 2-acryloyloxyethyltrimethyl ammonium chloride, 3-methacrylamidopropyltrimethyl ammonium chloride, 2-methacryloyloxyethyltrimethylammonium chloride or diallyl dimethylammonium chloride.

11. The process of any one of claims 1 to 5, wherein the 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:
wherein 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%.

12. The process of any one of claims 1 to 11, wherein the water soluble graft copolymer has a number average molecular weight of from about 10,000 to 30,000,000.