Note: Descriptions are shown in the official language in which they were submitted.
213~694
L- 692C/ 1
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
R1
_ [ E ]a [fH - Ic]b _
G C=0
NH2
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
R2 R3
1 1
_ [ (CH2-- IC)c (CH2 -- lC)d ]--
C=O C=O
NH2 F
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.
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.,
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
NH2 NH2
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 '
CH2
ICH2
H3C--N+--CH3 Cl-
CH3
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)
A 33 15
33 30
2 40 10
~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.
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14
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
625
610
1 15 595
2 5 590
2 10 576
2 15 531
A 5 509
A 10 466
A 15 413
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.
21356.9~
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
16
invention are more effective in water clarification than the comparative
linear polymers.
TABLE IV
Clalrification Test
Polymer Dosaqe (ppm) SuPernatant (NTU)
B 5 550
356
273
250
C 5 520
347
240
178
D 5 456
291
212
158
E 5 512
325
175
150
F 5 538
340
234
185
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TABLE IV (cont'd)
Clarification Test
Polymer Dosa~e (PPm) SuPernatant (NTU)
Cor"paralive Polymer A 5 860
702
542
500
Comparative PolymerB 5 684
411
284
200
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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18
TABLE V
Clarification Test
Polymer Dosa~e (ppm) suPernatant (NTU)
Blank 0 835
F 5 270
1 0 220
195
Comparative ExampleA 5 362
1 0 290
242
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.
