CA1136032A

CA1136032A - Method for determining the effectiveness of water- soluble polymers for controlling pitch deposits in paper mill systems

Info

Publication number: CA1136032A
Application number: CA000365313A
Authority: CA
Inventors: Margaret J. Molnar
Original assignee: Alchem Ltd
Current assignee: Alchem Ltd
Priority date: 1980-11-24
Filing date: 1980-11-24
Publication date: 1982-11-23

Abstract

ABSTRACT OF THE DISCLOSURE
A method for determining the efficacy of water-soluble polymers for reducing the concentration of colloidal pitch particles in aqueous pulps which comprises the steps of:
(a) filtering a portion of a pulp sample to remove the fibers therefrom under conditions of agitation which corresponds to the approximate degree of agitation of the pulp in the papermaking system and collecting the filtrate;
(b) counting the colloidal pitch particles in the filtrate in a hemacytometer, thereby establishing a blank count value for the untreated pulp, (c) treating another portion of the same pulp sample with a water-soluble cationic polymer and repeating steps (a) and (b), and then (d) comparing the colloidal pitch count of the treated sample against the blank to determine the degree of colloidal pitch particle reduction.

Description

113~03Z

The problem of pitch control in papermaking has previously been recognized. The pitch in the fibers of wood pulps is associated with natural-ly occurring lignin dispersing agents. Cooking and mechanical agitation which occur during the pulping by the sulfite process liberates pitch and natural dispersing agents. But, the natural dispersing agents liberated along with the pitch are inadequate to keep the pitch from depositing, as a result of the mechanical work on the fibers, on the equipment employed in beating, hydrating, refining, bleaching, and even on the wire used for forming the sheet.
Because of the tendency of the pitch to agglomerate within the pulp suspension or deposit on the surfaces of the wire or other equipment and then to break free in the form of particles of considerable size, the pitch fre-quently causes the formation of spots or holes in the sheet formed or may adhere to the wire or press rolls or drier rolls and cause tearing of the sheet.
This results in occasional tearing of the sheet during formation or in the pro-duction of sheets with numerous imperfections. Among other consequences in-volved are the expense of cleaning the machinery frequently either with sol-vents or steam, and the loss of production during cleaning and during relacing operations caused by breakdown of the sheet.
In the article entitled, "Pitch Particle Concentration: an Important Parameter in Pitch Problems," by L. H. Allen, which appears in the Transactions of the Technical Section of the Canadian Pulp and Paper Association for June, 1977, it is demonstrated that those wood pulps which cause pitch problems con-tain a high concentration of suspended colloidal pitch particles. The pitch deposit potential of a pulp is shown to be proportional to the concentration of colloidal pitch particles suspended in the pulp.
This article also shows that it is possible to measure by microscopic observation the concentration of colloidally suspended pitch droplets in pulps ~3~.~3Z

by using a blood counting chamber known as a hemacytometer.
It is known that certain water-soluble polymers are capable of act-ing as pitch dispersants whereby the pitch can be maintained in a colloidal state of subdivision without agglomeration of the particles occurring. It is further known that certain polymers and, in particular, low molecular weight water-soluble cationic polymers, will cause the pitch particles to become at-tached to the fibers in the pulp. This removes the colloidal pitch particles from the whitewater and tends to prevent deposit formation from occurring.
If it were possible to provide a method for quickly determining the efficacy of water-soluble polymers for reducing the concentration of colloidal pitch particles in aqueous pulps, an advance would be afforded to the art.
This invention thus seeks to provide a method for determining the efficacy of water-soluble polymers for reducing the concentration of colloidal pitch particles in aqueous pulps which comprises the steps of:
(a) filtering a portion of a pulp sample to remove the fibers there-from under conditions of agitation which corresponds to the approximate degree of agitation of the pulp in the papermaking system and collecting the filtrate;
(b) counting the colloidal pitch particles in the filtrate in a hemacytometer, thereby establishing a blank count value for the untreated pulp, (c) treating another portion of the same pulp sample with a water-soluble cationic polymer and repeating steps (a) and (b)J and then (d) comparing the colloidal pitch count of the treated sample against the blank to determine the degree of colloidal pitch particle reduction.
The first step of the process requires that the pulp be filtered to separate the larger particles and the fibers. While any suitable filter may be used, e.g., see the Allen article, it is preferred in the practice of this in-~3~)32 vention to use a Britt jar to conduct the filtration.
The Britt jar is nothing more than a jar having a r~movable bottom.
The bottom is adapted to receive a screen, the screen size of which may bc varied depending upon the filtering operation to which the jar is to be put.
After the material passes through the filter screen, it may be collected in a suitable container. This collection is accomplished by a swing-out base at the bottom of the Britt jar which, in effect, is a stopper for the filtrate which passes through the screen. The Britt jar is conveniently mounted on a labora-tory ring stand which contains a motor-driven propeller mixer used to stir the contents of the Britt jar.
The speed of pulp flowing towards the papermaking machine wire or feed will vary depending upon the nature of the pulp, the papermaking equipment process requirements, and the like. The flow rate may be arbitrarily estimated as to whether it is slow or fast. This estimation of slow or fast can be readily done by those familiar with papermaking operations.
In practicing the invention, the speed of the stirrer used in agitat-ing the pulp samples in the Britt jar should be adjusted so that the pulp sample contained in the Britt jar approximates the flow rate of the pulp stream from which the sample was taken. A typical range of speeds for the stirrer is between 500 - 1000 rpm.
As indicated above, the Britt jar may be fitted with a variety of filter screens. For the present invention, it is recommended that the screen size used in the Britt jar have openings within the range of 100 - 200 microns.
This allows the fiber to be retained on the screen along with other large di-mensioned particles contained within the pulp yet allowing passage of the col-loidal pitch particles.
In the practice of the invention, a sample of pulp is taken and divid-1~3Çi~32 ed into 2 or more portions. One portion is filtered through the Britt jar and then subjected to pitch particle counting in the hemacytometer as described in the Allen paper. It is possible by running a series of such tests under a variety of mill conditions to build up a correlative picture of colloidal pitch particle concentration versus the deposit characteristics of the pulp. Thus, it is a rather simple matter to determine what may be called the critical colloidal pitch concentration. Above this critical colloidal pitch concentration, pitch deposits will begin to appear on the mill equipment. Below this critical con-contration, pitch deposit formation will not occur.
It is known that anionic water-soluble polymers are capable of main-taining pitch in a colloidally suspended state to prevent deposit formation.
They do not, however, seem to attach the particles to the fiber. These anionic polymers apparently work by a different mechanism than do the cationic polymers.
Certain cationic polymers are used to treat aqueous pulp systems to better suspend the colloidal particles of pitch. Also, they are capable in certain instances of combining with the colloidal pitch particles and anchoring them to the fibers. This incorporates these colloidal particles into the finished sheet or paper product. In so acting, these polymers tend to reduce the amount of suspended colloidal pitch particles, thereby reducing pitch deposits while, at the same time, increasing the tonage yield of the paper product.
It is further known that not all cationic polymers are effective in stabilizing or reducing colloidal pitch particles in any particular pulp. Until the present invention, it has been necessary to run actual mill evaluations with water-soluble cationic polymers to determine whether or not they would be effective in reducing the pitch deposition properties of a pulp.
The present invention overcomes this obstacle by determining the con-centration of the colloidal pitch particles in the pulp by means of the Britt jar and hemacytometer as described above. Other samples of the same pulp are treated with the polymers to be evaluated and subjected to the identical Britt jar hemacytometer steps previously described. The counts of the treated vs.
the untreated colloidal pitch particles are compared to the blank and optionally against the critical concentration of the pitch particles in the pulp to deter-mine the efficacy of the polymer in reducing the number of pitch particles. This technique can allow a rapid screening of a number of polymers as well as allow-ing for a rapid method for determining the optimum dosage concentration of any particular polymers.
Typical of cationic polymers that may be used in the practice of the invention are the following:
One class of materials is a polymeric polyamine substance. Generally these polymers have molecular weights in excess of 1,000 and, more preferably, in excess of 2,000. The most preferred polymers of this type have molecular weight ranges of 2,000 - 50,000. Such above polymeric polyamines may be formed by a wide variety of reactions such as by the reaction of alkylene polyamines and difunctional alkyl materials.
One class of polyamine polymers are condensation polymers of alkylene polyamines and halohydrins. Exemplary polymers of this type are those disclosed in Green United States Patent 2,969,302,.
Yet another species of polyamines falling within the above class is formed by reaction of an alkylene dihalide and an amine. Preferred amine reac-tants include ammonia, ethylene diamine, diethylene triamine, tetraethylene pentamine and triethylene pentamine. Of these, the most preferable due to ex-cellent reactivity, low cost and availability is ammonia. The alkylene dihalide reactant may be chosen from a wide variety of difunctional organics including ethylene dichloride and 1,2-propylene dichloride. Of these, the most preferred 113f~(~3~

is ethylene dichloride. One excellent cationic polymer for use in the in-stant invention is formed by reaction of ammonia and ethylene dichloride under super-atmospheric pressures and with heating.
In addition to the above preferred condensation type polymers, many other condensation polymeric cationics are also admirably suited for use in the invention. Effective water-soluble cationic polymers or resins are to be found among the class consisting of amine-aldehyde resins and amide-aldehyde resins, preferably hydrophilic melamine-formaldehyde resins. Such colloidal cationic resin solutions may be prepared by dissolving ordinary melamine-aldehyde condensation products~ such as methylol melamines, in acids such as hydrochloric acid, to form acidified or acid-type resin solutions having a glass electrode pH value within the range of about 0.5 to about 3.5 when measured at 15% solids, or pH values up to 4.5 when measured in more dilute solutions, followed by aging to the colloidal condition, as described in United States Patent 2,345,543.
Another class of cationic melamine-aldehyde resins that may be used in practicing the present invention are the resinous polymers of melamine, urea and aldehydes such as formaldehyde containing at least 0.7 mole of melamine for each 4 molesof urea and about 1 to 4 moles of combined formaldehyde for each mole of melamine plus urea. Such resins are described in United States Patent

2,485,079. These cationic melamine resin copolymers are obtained by first pre-paring an acidified aqueous solution of an aldehyde condensation product of melamine and urea containing 1 to 70 mole percent of urea and 30 to 99% of melamine and about 0.2 to 1.5 moles of acid per mole of melamine, depending on the strength of the acid, and aging the solution until the colloidal cationic condition is reached.
Another suitable class of cationic coagulants are those of the polyimine ~13~ 3~J

type. The polyimincs are derived, for example, by the homopolymerization of monomers containing the imino radical, -N-H
and have a molecular weight of at least 1000.
Ethyleneimine, as well as many of its derivatives, may be prepared by any of several well-known methods such as are described in the "Journal of ~nerican Chemical Society," Vol. 57, p. 2328, ~1935), and Ber., Vol. 21, p. 1094 (1888).
The polymeri~ation of ethyleneimine and its derivatives is usually conducted at reduced temperatures using acid catalysts such as HCl and the like.
The polymerization of the various monomers listed above is described in detail in the "Journal of Organic Chemistry," Vol. 9, p. 500 ~1944).
The molecular weight of the useful imine polymers should be at least l,OOO and is preferably from 5,000 to 50,000. If the condensation reactions from which these polymers are derived are allowed to continue for too long a period of time or the conditions are not suitable, infusible, water-insoluble resins may result. In the case of 2,2 dimethylethyleneimine, care must be used to control the reaction so that the materials produced are sufficiently water-soluble so that they can be employed at effective concentrations. Simi-larly, long chain water-soluble cationic polymers may be prepared by condensing formaldehyde with a polyalkylene polyamine such as tetraethylenepentamine to link the polyamines with a plurality of methylene bridges.
Still other suitable cationics include cationic starch which is generally formed by reaction of starch with a suitable amine-containing material whereby an amino alkoxy group is produced.
Yet another class of cationic coagulants include addition-type polymers which in aqueous medium will form organic cations having a substantial number ~3$~3Z

of positive charge distributed at a plurality of positions on the polymer.
Generally~ these materials have a molecular weight in excess of 100,000 and con-tain in a side chain a hydrophilic group possessing the ability to form the above described positive charge. Typical members of this group are polyvinyl pyridine or other similar monomers having nitrogen-containing nuclei. Another specific material of this type is polyvinyl pyrrolidone. Salts of the above may also be employed.
Still other suitable cationics include the well-known vinyl benzyl quaternary ammonium compounds such as the homopolymers of vinyl benzyl quaternary ammonium salts or copolymers thereof formed by a copolymerization reaction with acrylamide, methacrylamide, etc. The vinyl benzyl quaternary materials are generally formed by chloromethylating polystyrene and subsequently substituting the chloro group with a tertiary amine to produce the corresponding nitrogen quaternary.
Other examples of cationic polymers suitable as a treating agent in the invention includes homopolymers and water-soluble copolymers of aminoethyl acrylate hydrochloride, aminoethyl methacrylate hydrochloride, or substituted ammonium alkyl acrylates or methacrylates such as N-methyl or N-N-dimethyl-aminoalkyl acrylate or methacrylate wherein the alkyl groups contain 2 - 3 car-bons or suitable materials. Other cationic polymers may be formed when the cationic monomer of the type just described is copolymerized with any one or more mono-ethylenically unsaturated monomers capable of vinyl polymerization such that the resulting copolymer is water-soluble or water dispersible. Suit-able monomers of this type which may be copolymerized with the cationic monomers include acrylamide, methacrylamide, acrylonitrile, the lower alkyl esters of acrylic and methacrylic acids, vinyl methyl ether, etc.
The above list of materials are just a few of the available cationic 113~3'~

coagulants which may be suitably employed in the practice of the instant in-vention. It is understood, of course, that other cationic substances may be used other than those listed above without departing from the scope of the in-vention.
Polymers falling within the anionic class are those consisting of substances which in an aqueous medium will form organic anions having a mea-surable negative electric charge. Greatly preferred anionic materials are those substances polymeric in nature having a substantial number of negative electrical charges distributed at a plurality of positions on the polymer. These polymeric anionic substances preferably should have a molecular weight of bet-ween 1,000 - 100,000 when formed as addition-type polymers or copolymers are derived by polymerization of at least one mono-olefinic compound through an aliphatic unsaturated group. These polymers should be water dispersible and have a structure substantially free of cross linkage and are therefore available for solubilization. Preferred anionic substances found to be especially effec-tive for the purpose of the invention are water dispersible synthetic polymers having a linear hydrocarbon structure and containing in a side chain a hydro-philic group selected from the class consisting of carboxylic acid, carboxvlic acid anhydride, carboxylic acid salt groups, and copolymers of any of the fore-going.
A suitable anionic copolymer may be derived from a polycarboxylic acid monomer and at least one other monomer copolymerizable therewith. The polycarboxylic acid may be maleic anhydride, acrylic acid, maleic acid, fumaric acid, itaconic acid, aconitic acid, citraconic acid, etc., which may be copoly-merized with the amides of these acids, the alkali metal derivatives (e.g., sodium, potassium and lithium), the alkaline earth metal derivatives (e.g., magnesium, calcium, barium and strontium), and ammonium salts of these acids, the ~13~S)3~:

partial alkyl esters (e.g., methyl, ethyl, propyl, butyl, mono esters), the salts of said partial alkyl esters, and the substituted amides of these poly-carboxylic acids or a variety of other different monomers. Where a hydrophi-lic polycarboxylic acid such as maleic acid is used as one of the starting com-ponents to form the copolymer, a hydrophobic comonomer may be used, as for example, styrene, alpha-methylstyrene, vinyl toluene, chlorostyrene, vinyl acetate, vinyl chloride, vinyl formatej vinyl alkyl ethers, alkyl acrylates, alkyl methacrylates, ethylene, propylene, and/or isobutylene. The foregoing synthetic copolymers are preferably obtained by reacting equimolar proportions of a polycarboxylic acid and at least one other monomer. However, certain of the unsaturated polycarboxylic acids can be polymerized in less than equimolar proportions with some of the less hydrophobic comonomers.
A variety of other anionic polymeric substances may be employed such as hydrolyzed polyacrylonitrile-sodium salt thereof, sodium carboxymethyl cellu-lose, the sodium salt of an acid-ester of starch, the sodium salt of a sulfo-nated polystyrene, phosphorylated starches, such as those obtained by treating corn starch with phosphorus oxychloride in pyridine, anionic polysaccharides, and combinations of any of the above or other anionic coagulant materials.
Another class of anionic materials particularly suitable in the practice of the invention are copolymers of sodium acrylate and acrylamide.
The most preferred copolymers of this type comprise 5 - 95 % by weight of sodium polyacrylate and 5 - 95 % by weight of polyacrylamide. Other polymers or copolymers of acrylic acid types are particularly preferred and are typified by those obtained by vinyl polymerization of acrylic acid, methacrylic acid, sulfoethyl acrylate, carboxyethyl acrylate or salts thereof or copolymers thereof of the acids or salts obtained by suitable copolymerization with monomers such as acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, lower 1~3603Z

alkyl esters, alkyl esters of the acrylic acids, vinyl alkyl ethers, and the like.
Another greatly preferred class of anionic polymers is a linear high molecular weight polymer or copolymer of a vinyl aryl hydrocarbon, such as styrene, vinyl toluene, alpha-methylstyrene, vinyl xylene or the like, which are polymerized and then sulfonated under controlled conditions to produce a water-soluble substantially linear polymer sulfonate.
In most cases the preferred polymeric materials are of relatively low molecular weight, e.g. 10 - 50,000 being a preferred molecular weight range, although molecular weights as low as 1000 up to slightly less than 1,000,000 may be used to good advantage.
The invention has applicability for testing polymers on all types of pulps and also is capable of giving good results over a wide range of pulp pH's. The invention is also capable of showing that certain polymers increase the concentration of colloidal pitch particles.
Typical dosages based on active polymers can range between 0.1 - 1 killogram per ton of the pulp based on dry fiber weight.
Examples Using the test methods of the invention, a large number of polymers were screened on a variety of pulps. The results are reported in terms of pitch particles per milliliter. In other cases it is reported in percent of pitch particles fixed onto fibers by the polymers. This result is determined by the following equation:
Number of pitch Number of pitch particules/mL - _ particules/mL - % pitch particulec untreated sampl treated sample X 100= fixed onto fibers [umber of pitch particules~ lbY polymer L - untreated sample ~3~i~3~2 The results of these tests are sct forth in Tables I - VII. In the Tables, the polymers designated by the number 1 - 10 have the following des-cription:
Polymer 1: Low molecular weight aqueous solution polymer of dimethyl-amine and epichlorohydrin.
Polymer 2: Low molecular weight aqueous solution polymer of dial-lyldimethylammonium chloride.
Polymer 3: Low molecular weight aqueous solution polymer of diallyl-trimethyl ammonium chloride (20% by weight) (methyl chloride quat.) Polymer 4: Polyacrylamide having a molecular weight in excess of 1, 000, 000.
Polymer 5: Sodium polyacrylate--molecular weight greater than 1, 000, 000.
Polymer 6: Aqueous solution of polyacrylamido methyltrimethyl ammonium chloride.
Polymer 7: Copolymer of acrylamide-acrylic acid having a molecular weight greater than 1,000,000.
Polymer 8: Copolymer of acrylic acid-acrylamide (7:93 by wt.) having a molecular weight greater than 1,000,000.
Polymer 9: High molecular weight copolymer of acrylamide and dimethyl-aminoethyl methacrylate, methyl sulfate quaternary.
Polymer 10: High molecular weight water-soluble polyacrylamido methyl dimethyl ammonium chloride.
The following procedures leading to the predictability of percent ef-ficiency for the various polymers tested in regards to pitch control were used to generate all of the results in the following tables:
1. ~ake representative white water samples throughout the system as far l~3~n3~

back as the grinder showers in the gro~mdwood mill but at a point in the system prior to pitch deposits appearing and presenting a problem.
2. Place a known aliquot of these white water samples in the Britt Dynamic Jar or BDJ. Set the speed variable of the stirrer for the Britt Jar in a range of 500-1000 rpm for 2 minutes and draw off a small quantity of the white water prior to the polymer addition. This would be considered a blank or a control count absent treatment chemica:Ls.

3. Add a known dosage of polymer to the aliquo1 of white water still con-tained in the BDJ, set the speed variable of the stirrer at the same speed used for the control with no treatment, and agitate it for 5 minutes at this speed.

4. The filtrate should immediately be withdrawn. If the pitch particle concentration count is extremely high, a dilution factor can be introduced. If this dilution step is not necessary, then a known aliquot of this filtrate is placed on the hemacytometer. The hemacytometer is placed under the microscope and colloidal pitch particles are counted. Thus, a count can be completed in a known volume of liquid over a small square in the American optical hemacyto-meter. The measurement of this volume in the hemacytometer is 2-5.10 7cm3 and the particle concentration would be expressed as the number times 106cm3.
TABLE I - GROUNDWOOD

Polymers Pitch particules - - /mL

Control 107,500 Polymer 1 4S,750 Control 60,000 Polymer 2 37,500 ~3~;5~3~

TABLF, II - GROUNDWOOD
Polymers Pitch particules /mL
Control 58,750 Polymer 2 65,000 Polymer 1 36,250 TABLE III - GROUNDWOOD
Polymer Pitch particules /mL
Control 106,250 Polymer 1 52,500 Polymer 2 95,000 Control 73,750 Polymer 3 53,750 Polymer 4 63,750 Polymer 9 131,750 Polymer 10 83,750 Polymer 7 g, Polymer 8 73,750 Polymer 6 133,750 Control 67,500 Polymer 5 140,000 Polymer 4 130,000 Note: Following the addition of polymer, each sample was agitated for 5 minutes at 500 RPM prior to filtering.

~L~L3G.i1)32 TABLE IV - SULP~-IITE PULP
Polymer Pitch particules I mL
Control 63,750 Polymer 1 30,000 Polymer 2 62,500 TABLE V - SULPHITE PULP
Polymer Pitch particules /mL
Control 88,750 Polymer 4 51,250 Polymer 4 25,000 Polymer 9 38,750 Polymer 10 38,750 Polymer 8 65,000 Control 52,500 Control 231,875 Polymer 1 100,000 Polymer 2 152,500 Polymer 3 91,250 Control 186,250 Polymer 4 73,750 Control 120,000 Polymer 4 175,000 Polymer 9 107,500 Polymer 10 101,500 Control 196,250 3~

TABLE V - SULPHITE PULP ~continued) -Polymer Pitch particules /mL
Polymer 8 110,000 Polymer 7 242,500 Control 132,500 Polymer 6 158,750 Polymer 5 115,000 Polymers 1 ~ 4 127,500 Polymers 1 ~ 4 108,750 Polymer 1 ~ competitive product 201,250 Control 107,500 Note: Following the addition of polymer, above samples were agitated for 5 minutes at 800 RPM prior to filtering.

TABLE VI - GROUNDWOOD PULP
Polymer % of pitch particules fixed onto fibres by polymer.
Polymer 1 45%
Polymer 3 40%
Polymer 4 30%
Polymer 7 18%
Polymer 8 11%
Polymer 2 7%
Polymer 10 7%

-1~3~SQ32 TABLE V[I - SULPHITE PULP
~ymer % of pitch particules fixed onto fibres by polymer Polymer 1 55%
Polymer 3 51%
Polymer 4 48%
Polymer lO 32%
Polymer 9 29%
Polymer 4 23%
Polymer 2 18%
Polymer 5 4%

-From the above, it is obvious that an advance in the paper treating art has been achieved.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for determining the efficacy of water-soluble polymers for reducing the concentration of colloidal pitch particles in aqueous pulps which comprises the steps of:
(a) filtering a portion of a pulp sample to remove the fibers therefrom under conditions of agitation which corresponds to the approximate degree of agitation of the pulp in the papermaking system and collecting the filtrate;
(b) counting the colloidal pitch particles in the filtrate in a hemacytometer, thereby establishing a blank count value for the untreated pulp, (c) treating another portion of the same pulp sample with a water-soluble cationic polymer and repeating steps (a) and (b), and then (d) comparing the colloidal pitch count of the treated sample against the blank to determine the degree of colloidal pitch particle reduction.

2. The method of Claim 1 where the filtering is done with a Britt jar having a screen size range between 100 - 200 microns.