CA1101158A - Strengthening agents - Google Patents

Abstract

TITLE OF THE INVENTION

QUATERNIZED DIALKYLAMINOMETHYLATED ACRYLAMIDE
POLYMERS AS STRENGTHENING AGENTS AND
DRAINAGE AIDS IN THE MANUFACTURE
OF CORRUGATING MEDIUM

ABSTRACT OF THE DISCLOSURE

A process for improving the dry strength and drain-age of corrugating medium with a polymer containing quater-nized dialkylaminomethylated acrylamide linkages which com-prises adding said polymer to a fibrous suspension contain-ing said corrugating medium at an alkaline pH, and corrugat-ing medium made therefrom.

Description

1101158 `--26,016 BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to quaternized dlalkyl aminomethylated acrylamide polymers as strengthening agents and drainage aids in the manufacture of corrugating medium.
More specifically, the present invention relates to quater-nized dimethylaminomethylated acrylamide polymers as strength-ening agents and drainage aids in paper manu~acture of cor-rugating medium in highly anionic furnishes, and in furnishes containing high quantities of spent pulping liquor.
The production of corrugating medium of imp~oved dry strength from pulps composed of unbleached fibers, especi-ally when the pulp contains highly anionic furnishes or high ; quantities of pulping liquor, has presented a special prob-lem to the paper manufacturing art. Most dry strength poly-mexs (both anionic and cationic), of ordinary excellent dry strengthening capabilities, and drainage aids provide a commercially inadequate amount of dry strength and drainage -improvement when used with such pulps.
Because most natura~ly occurring cellulose fibers are normally anionic, the presence of cationic linkages in the polymers will improve the substantivity of the polymers for the cellulose. Also, the incorporation of a hydrophobic comonomer, for example, styrene, in some applications wiIl make the polymer more substantive a~ it will tend to precipi-tate onto the cellulose fibers.
~uaternary cationic polymers have been used as dry strength agents. Generally, however, dry strength agents have not been used with corrugating medium.
In the art, cationic polymer have been used as drainage aids in corrugating medium. But the amounts re-quired are so large as to uneconomical. See, e.g., Water--Soluble Polymers, N. Bikales, Ed., Plenum Pre~s, N.Y., 1973, p. 16.

`\ ` ~ ~ -

2~ ~16 LlS8 The utility of quaternized polymers is generally lndependent of pH. Thus, the quaternized polymer can impart dry strength and be used as a drainage aid for corrugating medium which is normally proces~ed at an alkaline pH.
Wet strength resins are hard to repulp. The prac-tice in the trade is to repulp corrugating medium. There-fore, pulp and paper mill~ usually do not want corrugating medium with wet strength properties. The quaternary polymers of the present invention do not produce wet strength.
Corrugating medium is generally processed by neutral sulfite semi-chemical or green liquor pulping processes.
The discovery has now been made that a quaternized polymer will improve the dry strength of corrugating medium.
I have also discovered that I can improve the dry strength of corrugating medium without substantially decreasing the drainage. In fact, addition of a certain proportion of the quaternary polymer improves the drainage of the corrugating medium. B~cause it is quaternized, the polymer can retain more of its cationic charge at a higher pH than nonquater-nized cationic polymers. Therefore, it should be more econo-mical to use than nonquaternized cationic polymers at the higher pH found in corrugating medium pulp~.
More specifically, the discovery has now been made that certain dialkylaminomethylated acrylamide polymerq quaterni7ed with a dialkyl sulfate, for example, dimethyl ~ulfate, or with an alkyl chloride, for example, methyl chloride, po~se~c the function of being valuable dry streng-thening agents which will not substantially decrease the drainage and which, therefore, render~ them ueeful as gen-eral purpose strengthening agent~ in the manufacture of corrugating medium from pulps containing high quantities of spent pulping liquor, and fxom highly anionic furnishes.

11(~1158 Accordingly, the invention provides a process for improving the dry strength of corrugating medium with a polymer containing at least about 10% by weight acrylamide linkages, and between aDout 5 and 60 mole percent of quaternized dialkyl-aminometnylated acrylamide linkages, which comprises adding to a fibrous suspension of said corrugating medium between about 0.10 and 3 weight percent of said polymer based on the dry weight of the fiber at a pH of about 6 to 10; forming a web of said corrugating medium, and drying said web.

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, . . . . . . .
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~6,016 1~ 58 Excellent results have been obtained with dimethyl-aminomethylated acrylamide polymers quaternized with a di-alkyl sulfate. Therefore, a quaternized dimethylamino-methylated acrylamide polymer is preferred Because of these excellent results, similar polymers~ e,g., a diethylamino-methylated acxylamide or dipropylaminomethylated acrylamide polymer quaternized with dialkyl sulfate m~y show similar result~, For this reason, the~e polymers are al~o preferred.
The quaternized polymer contains between about 5 and 60 mol percent of quaternized dialkylaminomethylated acrylamide linkage~, and at lea~t about 10% by weight acrylamide linkage~. In another preferred embodiment, the quaternized polymer can contain between about 0% and 30%
by weight styrene linkages. In yet another preferred embodiment, the quaternized polymer can contain between about o% and 20% by weight acrylonitrile linkages.
- When the quaternized polymers de cribed above are added to a fibrou~ suspension of corrugating medium in an amount between about 0.10 and 3 weight percent based on the 2a dry weight of the fiber in the fibrous quspension, the dry strength of the corrugating medium ;i8 improved. For mo~t application~, the dry strength of corrugating medium i~ improved when the quaternized polymers described above are added to a fibrous ~uspension of coxrugating medium in an amount ~etween about 0.15 and one weight percent based on the dry weight of the fiber.
In certain instances, the quaternized polymer3 de~cribed above can improve the dry ~trength and drainage o~ the corrugating medium. Compound~ which have been e~fective in - 30 quaterni~ing the polymer~ of dim~hylaminomethylatea --acrylamide, diethylaminomethylated acrylamide~ and dipropylam~nomethylated acrylamide are from the gxoup:
dialkyl ~ulfate and alkyl chloride. These compounds are, 26,016 11~1158 therefore, preferred. In the dialkyl sulfate class of compounds, dimethyl sulfate is mo~t preferred~ in the alkyl chloride class of compounds, methyl chloride i~ most preferred.
The special superiority of the quaternized polymers as dry strengthening agent~ in the manufacture of corrugating medium from pulps of unbleached fi~er~ is a consequence of their ability to be substantive to celluloRic ~ibers at a pH above about 6. It is to ~e understood, however, that the drainage of the corrugating medium can also be improved by the~e polymers. Therefore, the quaternized polymers are also effective in improving the dry strength and dralnage of corrugating medium.
DESCRIP~ION OF THE P~EFERRED EMBODIMENT

The quaternized polymers of the present invention ca~ be prepared by mixing formaldehyde and a di(Cl-3 alkyl)-amine and a polymer containing acrylamide linkages in an aqueou~ medium a~d allowing the mixture to ~tand at an alkaline pH (for example, pH iO-12) and at about 10C.-40C. until the polymer ha~ become sufficiently cationic to be adsorbed by cellulose fiber~ in aqueou~ ~uspen~ion.
Thi~ polymer is then treated at about 25C.
with a quantity of dimethyl ~ulfate equimolar to the dimethylamine originally in the Mannich réaction.
Conditions ~uitable for the per~ormance o~ the ~annich reaction are di~clo3ed in U,S f Patent 3,323~979.
The quaternizatlon i9 allowed to proceed ox several hour~, The chemlc~l equation for the re~ction i~

.. . . . . . ..

26, 016 ~ 158 a~ follows:
-CH -CH- + (CH 0 ) SO ~D -Cl~ -CH-2 1 3 ~ ;' 2 1 C=O ~=0 NH ~H

(CH 3 ) 2 ~h(CH 3 ) ~ -CH 3S04 In addition to quaternizing the polymeric amine, the dimethyl ~ulfate could react with any free dlmethylamine pre~ent in the polymer.
lb $he molecular weight we have found effective, and which is, therefore, preferred, is between about 200,000 and 15,000,000.
In the quaternized pol~mer of the present invention, - the un~ub~tituted amide linkages provide dry ~trength once the polymers have been deposited on the fibers. These link-ages are, therefore, generally pre~ent in as high a proportion as possible. The hydrophobic vinyl linkages, when present, and the quaternized dialkylaminomethyl acrylamlde linkages cooperate in depo~iting the polymer on the fibers at a pH above about 6 and in a highly anionic fiber composition range. A pH
above about 6 and a highly anionic fiber composition are cus-tomarily found in pulps used fox making corrugating medium.
; Hydrophi~ic anionic linkage~ may be pre~ent as a re3ult of hydrolysis of the amide linkages, It i~ to be understood, however, that hydrophilic anionic linkage~ may but do not have to be pre~ent to practic~ the invention.
Corrugating medium o~ impro~ed ~trength and drainage can be manu~actured according ~o the pr~sent invention by fonm-inq an aqueous ~u~pension of cellulose coxrugat~ng medium fiber in a normal p~ r~nge o~ about 7 to 9~ adding the~eto a ~u~icient amount of a quaternized polym~r to pro~de the de-~ired strengt~ening ~nd drainage e~ectr and t~en form~n~ the ~i~er~ into A W~ an~ drying the we~. Tt i8 to be understood, howeve~ that the invention can be practiced at ~ny pH
_ 5 _ 26,016 ~ S ~

range used to make corrugating medium. This pH r~nge should generally be from about pH 6 to 10, The fibers may be any of the fibers commonly used for the manu~cture of corrugating medium. Howe~er, it i5 preferred to use neutral sulfite semichemical pulps or green liquor pulps.
As a general statement, the quaternized polymer of the present invention can be added at ~ny point after the refiners. For example, the polymer can be added at the regulatcr ~ox or at the fan pump. Corrugating medium can be made on a multi-cylinder machine or a Fourdrinier maehine.
A preferred location, thereforel for adding the quaternized polymer would be any location after refining which is a ~ufficient di~tance upstream from the head~ox to provide good mixing.
Generally, the papermaker will try different polnts to determine which works best. ~ecau~e they supply ea~y ac-ces ibility and inherent mixing, the following points could be u~ed: the outlet side of the centrifugal ~creens, and the inlet ~ide of the fan pump.
The amount o~ quaternized polymer which is added to the corrugatin~ medium pulp is that which i~ ~ufficient to impart the desired strength improvement to the paper. In general, a sufficient amount i5 that which supplies an ef-fective amount for the purpo~e, ganerally, in the range of about O . 01 to 3 percent based on the dry weight of the fibers.
The polymer~ of the pre~ent invention produce their ~trengthening ef~ect when the paper is air dried, but ~hi~
~trengthening effect is not si~ni~ic~ntly harmed when the ~ paper ls dried at elev~ted tempe~ture~, Accordin~ly, the p~per m~y be dried on steam-heated drying rolls ha~ing sur-` ~

26,016 1 ~ 1 1 5 8 ~ace temperature~ in the range o 190F,.~250F, a is customary.
The invention is more p~xticularly de~cribed by the Examples which follow. These examples axe pxe~exxed embodiments o~ the in~ention and are not to be con~trued as a limitation to the express, implied or app~rent scope of the cl~ims.

The following illustrate~ the pxeparation of corrugating medium according to the present i~ention. The Noble-Wood laboratory hand~.heet machine waB utilized to simulate white water conditions found in paper mills producing corrugating medium. An initial white water i8 prepared by adding 150 ml. of brown liquor containing 3.6 g.
of brown liquor solid~, and 3.6 g. of sodium ~ul~ate to 12 . liters of deionized water, followed b~ adju~tment to . pH 7.3 with sul~uric acid. This ~olution contains 0.08%
brown liquor ~olids and 200 ppm of ~ulfate ion. ~he ~olution i8 placed in the ~ump of the hand heet machine ~or ~0 use in sub~equent dilutions of concentrated fiber ~ pen~ions.
A concentrated fiber ~u~pen3ion i~ prepared at 2.5%
consi~tency from neutral ~ulfite semichemlcal pulp beaten to a Canadian Standard Freene~s of 401 ml. and to this i~ added .
2.8 percent brown liquor solid~ ~ba~ed on the dry weight of .25 the fibers). The pH of the su~pension i9 ~d~u~ted to 7.3 with .-sul~ur~ acld and then 200 ppm o~ sul~ate ion $8 added ~ba~ed on total ~u~pension, added as ~odium sul~ate~. Slx 880 g.
aliquot~ of the 2,5% fiber ~u3pen~0n at pH 7.3 Are taken to ~orm ~ix setfi o~ hand3heet~ ~t 100 lb, basis w~i~ht ~25 in-che~ x 40. inches~5UQ ream~. All white water ~5 retained in the hand~.eet m~cn~ne BUmp and all d~lut~on~ to sheet-making .

2 ll~llSI~
6~ol6 consistency (approximately 0.06%) are performed with this white water. Only the last three sheet sets (three sheets each) are used for testing because the first three sets are unrepresentative of equilibrium white water conditions. For each handsheet set, a 1000 ml. aliquot at 0.5% consistency is used for measurement of freeness using the Canadian Stan~
dard Freeness tester.
The polymer is prepared by dimethyl sulfate quater-nization of 85 weight percent acrylamide - 15 weight percent styrene copolymer containing 5 mole percent Mannich subs~itu-tion on acrylamide. Viscosity of the acrylamide - styrene copolymer at 10% solids is 67,000 cps at 27C. measured with a Brookfield viscosimeter.
Polymer treated sheets are made by the same procedure as control sheets except that the polymer disper~ion i8 added to the 2.5% fiber cuspension.
The test sheets are conditioned by ~torage for 24 hours at 73F. and 50% relative humidity and their Concora crush strengths are determined. Results are as follows:

Run Polymer Concora No. Added3 Freenessl Crush2 Control 0 493 32.2 1 0.2 535 36.3 Measured at 0.5% consistency with the Canadian Standard Freeness Tester.
~TAPPI Sta~dard kesting prooedure T 809 os-71;
lb., average of three qheet ~ets.

3~a~ed on dry weight of fiber EX~PLE 2 The following illustrates the proce~s of utilizing the quaternized polymer in a concentrated fibrou suspension.
A resln was prepared by dimethyl sulfate quaterniza-tion of 85 wt. ~ acrylamide - 15 wt. ~ styrene copolymer con-26,~ o ~ 5 ~

taining 5 mole % Mannich substitution on acrylamide. Vis-cosity of the product at 5% polymer solids solution was ap-proximately 800 centipoise at 25C., measured with a Brook-field viscometer.
The resin was tested on corrugating medium produced on a small scale Fourdrinier paper machine at Herty Founda-tion, Savannah, Georgia. The machine produced a 36 in. wide sheet at 83 feet/min. with 95-100 lb. basi weight (25 inches x 40 inches/500 ream).
The furnish was green liquor pulp containing 8~
total bxown liquor solids on fiber. A quaterni~ed polymer latex of Example 1 was fed to the 3~ thick stock stream at ~ -th~ Jordan refiner outlet. Tray water pH wa~ controlled at 7.3. Results were as follows:
% Average Average Run Polyme~ Drainage Conco~a No. Added ml./sec.l Crush Control 0 165 55.6 1 0.15 162 60.4 2 0 30 176 65.~ -.
easured by collecting the drainage water under the seventh table roll in a 5" x 12" tray.
2Based on dry weight of fiber.
3'1'APPI Stanaard testing procedure T 809 o~-71; Lb.
Examples 3-6 illustrate preferred embodiments for the preparation of water soluble quaternized dimethylaminomethy-lated acrylamide polymers (Polymer No. 1-~ in Example 5 and Polymer No. 4 in Example 6 are water~dispersible~ and the pro-cess of utilizing them in corrugating medium fibrous suspen-sions.

~A) Preparation of Polymers For each polymer preparation, the starting material is an aqUeOUB solution of polyacrylamide. A Mannich re-_g_ , 26 l6 1~ 5~

action to yield dimethylaminomethyl substituents is per-formed ~y adding formaldehyde solution and dimethylamine solution to the polymer solution; the molar ratio of di-methylamine to formaldehyde is 2 to 1. After ~tanding for 18 hours at room temperature, dimethyl sulfate in quantity equimolar to the dimethylamine is added and the mixture is allowed to stand for 18 hours at room temperature.
The results are as follows:

Molecular wt.
Polymer of starting Moles CH2O
No. Polyacrylamide M~e 1 12-14 MMl) 15

4 2 MM 15 6 2 r~M 60 7 250 M2) 15 g 250 M 60 . = 103 2) M = 10 (B) Preparation of Corrugating Medium A fiber suspension is prepared at 0.65% consistency from neutral sulfite semichemical pulp beaten to a Canadian Standard freeness of 377 ml. The pH of the ~u3pension is adjusted to pH 9.0 with sulfuric acid and then 1000 ppm of y sulfate i~n is added (based on total suspension, added as sodium sulfate). Four 850 ml. aliquots are taken and one handsheet at lO0 lb. basis weight (25 inches x 40 inches/500 ream) is formed from each aliquot by standard laboratory procedures using the Noble-Wood hand~heet machine; dilutions in the 3heet mold to sheet-making con3istency (approximately 0.06~) are made with deionized water. The wet webs are dried for 1 l/2 minutes in a laboratory drum dryer having a drum temperature of 240F. The sheets are conditioned 26,~16 ~ S ~

by storage for 24 hours at 73F. and 50% relative humidity and their Concora crush strengths and internal bonds are determined. For each handsheet set, a 770 ml. aliquot is taken and diluted with deionized water to 1000 mlO at 0.5%
consistency and the freenes~ is measured using the Canadian Standard freeness tester.
Polymer-treated sheets are made by the 6ame pro-cedure as control sheets except that polymer solution is added to the 0.65% fiber suspension. For freeness measure-ments, the polymer solution is added to 1000 ml. of pulp diluted to 0.5~ consistency wi~h delonlzed water.

The results are as follows:
%
: . RunPolymer Polymer Concora Internal No. No. Added' Freeness2 Crush3 Bond4 : . Control - 0 350 56.0 0.115 1 1 0.25 610 63.0 0.205 : 2 2 0.25 555 68.5 0.203 : . 3 3 0.25 520 58.0 0.174 4 4 0.25 400 70.5 0.216 -. 5 5 0.25 425 71.6 0.228 6 6 0.25 410 67.7 0.196 7 7 0.25 370 65.4 0.162 8 8 0.25 .405 67.0 0.157 9 9 0.25 380 68.4 0.170 : ~5 . 1) Ba~ed on dry welght of flber .
: %) Ml., measured at 0.5Z consistency wlth the Canadlan Srandar~ ene~ t.es~er 3) l'APPI stand~d testing procedure T 8Q9 oa~71; Lbl, average of four sheets 4) Ft.-lb./in.2, average of four ~heets ..

.

-~,016 11~115~

(A) Preparation of Polymers Polymers 1, 4 and 7 described in Example 3 are used.
(B) Preparation of Corrugating Medium A concentrated fiber suspension is prepared at 2.6~
consistency from neutral sulfite semichemical pulp beaten to a Canadian Standard reenes6 of 420 ml. One thousand ppm.
of sulfate ion is added (based on total suspension, added as sodium sulfate) and the suspension is divided into five parts. One part is left untrea~ed and four parts are treated with sufficient brown liquor to provide respectively, 1.0%, 3.0~, 5.0~, and 10.0% brown liquor solids based on the dry weight of the fiber. The pH of the five fiber suspensions is ; adjusted to 9Ø
A 925 g. portion of each 2.6% fiber suspension is taken and diluted to 0.5~ fiber consistency with 3875 ml.
.
of water containing brown liquor solids- and 1000 ppm. of sulfate ion. The brown liquor content of the dilution water ; is adjusted to produce total added brown liquor solids of 0%, 6~, 17~, 28~, and 55% (based on dry weight of the fiber), ~:
~ respectively, in the suspensions initially containing 1%, .
3%, 5%, and 10~ brown liquor solids.
Three 1100 ml. aliquots of each 0.5% fiber suspension are taken and one handsheet at 100 lb. basis weight (25 inches x 40 inches, 500 ream) is formed by standard labo-ratory procedures using the Noble-Wood handsheet machine.
Dilutions in ~the sheet mold to sheet-making consi~tency (ap~ ;
proximately~0.06~) are made with water at pH 9.0 containing 1000 ppm. sulfate ion and brown liquor solids at approxi-~ 30 ~ mately the same concentration as the 1100 ml. ali~uot. The ; sheets are drum-dried and conditioned by storage for 24 hours .

: ~ at 73F. and 50~ relative humidity and their Concora crush .

,.

26,C

~10115~

str~ngths and internal bonds are determined. For each hand-sheet set, a 1000 ml. aliquot of 0.5% f1ber suspension is taken and the freeness is measured using the Canadian Standard freeness tester.
Polymer-treated sheets are made by the same procedure as control sheets except that polymer is added to the 2.6%
fiber suspension.
The results are as follows:
. .
%
Added %
Run Brown Polymer Polymer Concora Internal No. Liquorl No. Added2 Freenes~3 Crush4 Bond' Control 0 - 0 425 46.8 0.110 1 0 10.25 670 61.6 0.203 2 0 40.25 48G 64.8 0.228 3 0 70.25 455 62.6 0.203 Control 1 - 0 425 46.2 0.131 4 1 10.2S 620 61.2 0.218 1 40.25 455 . 70.5 0.234 6 1 70.25 405 59.0 0.162 Control 3 - 0 405 47.2 0.136 7 3 10.25 580 64.0 0.20?
8 3 40.25 420 71.1 0.227 9 3 70.25 395 56.1 0.133 Con~rol 5 - 0 430 45.4 0.121 10.25 565 60.0 0.213 11 5 -40.25 405 .68.0 0.206 12 5 70.25 390 57.2 0.148 Control 10 - 0 420 45.2 0.113 13 10 10.~5 530 66.6 O.lg9 14 10 40.25 385 62.3 0.148 70.25 395 52.9 . 0.143 - 1) Brown liquor ~olids added in 2.6% fiber suspens~on, ba~ed on dry welght of fiber 2) Based on dry weight of fiber 3) Ml., measured at 0.5% consistency with the Canadian Standart freene~s tes~e~
4) TAPPI Standard testing procedure T 809 os-71;
Lb., average of four shee~s

5) Ft~-lb./ln.~, a~erage of ~our sheet~ :
~ ~:

26,~ , `
lS8 (A) Preparation of Polymers ~ he polymers are made as des~ribed in Example 3, with the exceptions described in the table below:
Starting ~oles CH~0 Polymer Polymer l~lole~crylaml~e No. Starting Polymer Viscosity,cp 1 85 Acrylamide/15 Styrene ) 300 ) 5 2 85 Acrylamide/15 Styrene3) 67000 5 3 85 Acrylamide/15 Styrene3) 13001) 5 4 Polyacrylamide, Molec. Wt.2MM4) - 5 Polyacrylamide, Molel~. Wt.~MM - lO

6 Polyacrylamide, Molec. W~.2MM - 20

7 Polyacrylamide, Molec. Wt.2MM - 40 1) Mea~ured at 5.3% solid6, 25C., with Brookfield Vi~cometer 2) Measured at 10% ~ol~ds, 27C., wlth Brookfield - Vi cometer 3) Weight percent 4) MM = 106 , ~ . .
~ (B) Preparation of Corrugating Medium ~ ~ .
A concentrated fiber suspension is prepared at 2.5% consistency from corrugating medium pulp ~75% green liquor pulp and 25% unbleached Kraft) beaten to a Canadian ~ .
Standard freeness of 194 ml. The suspension COntaLnS suffi-cient added spent green liquor to provide 12% added green liquor solids based on the dry weight of the fiber. The pH of the suspension is adjusted to ~.5.
An 880 g. portion of the 2.5% fiber suspension is taken and diluted to 0.5~ fiber consistency with water at . ~ . .
pH 8 . 5 containing 200 ppm of sulfate ion (based on total - ~ 30 suspension, added as sodium sulfate). Three 1100 ml. aliquots -~
are taken and one handsheet at 100 lb. basls weight (25 inches - -` x 40 inches, 500 ream) is formed from aach aliquot by 1~115~

26,016 standard laboratory procedures using the Noble-Wood handsheet machine. Dilutions to sheet-making consistency (approximately 0,06%) are made with water at pH 805 con-taining 200 ppm of sulfate ion. The sheets are drum-dried and conditioned by storage for 24 hours at 73F. and 50%
relative humidity and their Concora crush strengths are determined. For each handsheet set, one 1000 ml. aliquot of 0.5% fiber suspension is taken and ~he freene~s i8 measured using the Canadian Standard freene~s te~ter.
Polymer-treated sheets are made by t~e 3ame procedure as control sheets except tha~ polymer ~olution is added to the 2.6% fiber suspension.
The results are as follow3:

Run Polymer Polymer Concora 15 No. No.Addedl Freenes~2 Cru~h3 Control - 0 238 53.3 0.3 255 65.2 2 2 0.3 2~5 63.8 3 3 0.3 2-~0 63.2 . 4 4 0~3 235 57.2 - 5 5 0.3 300 62.0 6 6 0.3 290 62.6 7 7 0.3 250 55.7 1) Ba3ed on dry welght of fiber 2) M1., measured at 0.5% con~istency wlth the Canadlan Standard freenes~ tester 3) T~PPI ~tandard testing proced~lre T 809 os-71;
Lb., average of three sheets , 26,0`

(A) Preparation of Polymers The polymers are made as described in Example 3, except that equimolar quantities of formaldehyde and di-methylamine are used to prepare Polymers 1, 2 and 3.
- The results are as follows:

Starting Polymer. Moles CH20 Polymer Viscosity Mole~ Acryl-No Starting PolYmer cp. amide 1 80 Acrylamide/20 Acrylonitrile - 5 2 80 Acrylamide/20 Acrylonitrile2 - 10 3 80 Acrylamlde/20 Acrylonitrile2 - 20 4 85 Acrylamide/15 StyreneZ500 10 1) Measured at 5.2~ solids, 25C., with Brookfield Viscometer 2) Weight ~
B) Preparation of Corrugating Mbdium A concentrated fiber suspension is prepared at 2.6 consistency from corrugating medium pulp (75% green liquor pulp and 25% unbleached kraft) beaten to a Canadian Standard freeness of 163 ml. The fiber suspension i~ divided into several 840 g. portions and spent g~een liquor i8 added to provide portio~s with liquor solids content of 3 g./l., 4 g./l., 5 g./l., 6 g./l., i g./l.l and 8 g./l., which amount to, re-spectively, 12%, 15%, l9~, 23%, 27~ and 31~ green liquor solids based on the dry weight of the fiber. The pH of the fiber suspensions is adjusted to 8.5.
An 840 g. portion of 2.6% fiber suspension is diluted to 0.5~ with water at pH 8.5 containing 200 ppm of sulfate ion (based on total, added as sodium sulfate). Three aliquots of the 0.5~. fiber suspension are taken and one handsheet at 100 lb~. basis weight (25 inches x 40 inches/500 ream) is formed from each aliquot by standard laboratory procedurea using the 26, 15~

Noble-Wood handsheet machine. Dilutions in the sheet mold to sheet~making consistencies (approximately 0.06%) are made with water at pH 8.5 containing 200 ppm of sulfate ion. The sheets are drum-drled and conditioned by storage for 24 hours at 73F. and 50~ relative humidity and their Concora crush strengths are determined. For each handsheet set, a lO00 ml.
aliquot of 0.5% fiber suspension is used to measure the free-ness using the Canadian Standard freeness tester.
Polymer-treated sheets are made by the same procedure as control sheets except that polymer solution i~ added to the 2.6~ fiber suspension.
The results are as follows:

%
Added %
Run Green Polymer Polymer Concora 15No. Liquorl ~o.Added2 Freeness9 Cru~h4 Control 12 - 0 230 53.4 1 12 10.3 300 66.1 2 12 20.3 290 63.5 : : 3 12 30.3 265 64.9 - 4 15 20.3 380 60.5 19 20.3 370 62.2 6 23 20.3 360 64.4 7 27 20.3 335 56.3

8 31 20.3 335 60.5

9 12 40.3 280 64.7 .40.3 285 63.6 11 19 40.3 285 59.0 12 23 40.3 270 58.3 13 27 4~.3 295 58.7 14 31 40.3 270 53.7 1) Green liquor solids added in 2.6% flber susp2n~10n, ba~ed on dry weight of fiber 2) Based on dry welght of fiber 3j Ml., measured at 0.5% consistency wlth the Canadian Standard freçness te~ter 4) TA1?PI atandar~ tes~$ng procedur~ T 809 o~71 Lb,, averige o~ three ~heets

Claims (9)

26,016 I CLAIM:

1. A process for improving the dry strength of corrugating medium with a polymer containing at least about 10% by weight acrylamide linkages, and between about 5 and 60 mole percent of quaternized dialkylaminomethylated acrylamide linkages, which comprises adding to a fibrous suspension of said corrugating medium between about 0.10 and 3 weight percent of said polymer based on the dry weight of the fiber at a pH of about 6 to 10; forming a web of said corrugating medium; and drying said web.

2. A process of Claim 1 wherein said polymer contains between about 0% and 30% by weight styrene linkages.

3. A process of Claim 1 wherein said polymer contains between about 0% and 20% by weight acrylonitrile linkages.

4. A process of Claim 1 wherein said fibrous suspension is a neutral sulfite semichemical pulp.

5. A process of Claim 1 wherein the pH of said fibrous suspension is about 7-9.

6. A process of Claim 1 wherein said polymer is quaternized with a dialkyl sulfate.

7. A process of Claim 6 wherein said dialkyl sulfate is dimethyl sulfate.

8. A process of Claim 1 wherein said polymer is quaternized with an alkyl chloride.

9. A process of Claim 8 wherein said alkyl chloride is methyl chloride.