Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/06—Paper forming aids
  • D21H21/10—Retention agents or drainage improvers
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/33—Synthetic macromolecular compounds
  • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H17/37—Polymers of unsaturated acids or derivatives thereof, e.g. polyacrylates
  • D21H17/375—Poly(meth)acrylamide
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/33—Synthetic macromolecular compounds
  • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H17/41—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups
  • D21H17/42—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups anionic

Definitions

• hydrophobic polymers or copolymers provide unanticipated retention and drainage activity and can function as contaminant control aids in applications including papermaking applications
• synthesis methods employed are generally known to those skilled in the art, there is no prior art suggesting that the unique physical characteristics would result in the unanticipated activity observed.
• the present invention is directed to water compatible hydrophobic polymers and copolymers and cellulosic fiber compositions containing the hydrophobic polymers and copolymers, particularly a cellulosic sheet such as paper or paperboard.
• the invention is also directed to a method for making the hydrophobic polymers and copolymers and the cellulosic fiber compositions.
• the present invention provides a method of making a cellulosic fiber composition comprising adding, to a cellulosic pulp slurry, a water compatible polymer or copolymer that contains a hydrophobic group.
• the invention further relates to cellulosic fiber compositions, including an aqueous slurry of cellulosic pulp, containing such water compatible polymers and copolymers.
• copolymer is understood to be polymer compositions consisting of two or more different monomeric units.
• composition comprising water compatible hydrophobic polymers and copolymers and cellulose fibers and optionally, a siliceous material is disclosed.
• the present invention provides for enhanced retention and/or drainage in a papermaking process by addition of a water compatible hydrophobic polymer or copolymer to a papermaking slurry.
• the present invention also provides for a composition
• a composition comprising a water compatible hydrophobic polymer or copolymer and cellulose fiber.
• the present invention also provides for the use of water compatible polymer(s) and copolymer(s) that interact or associate, via non covalent bonding to form an aggregation of two or more polymer chains.
• the driving force for the molecular association can be electrostatic or hydrophobic in nature. Preferred are molecular associations driven by hydrophobic forces.
• the polymer is described to be water compatible.
• water compatible means that the polymer can be water soluble or water swellable or water dispersible.
• Water swellable polymers are those that can imbibe the aqueous solvent and swell to a limited extent. Water swellability can be influenced by a number of factors including, but not limited to, crosslinking and electrostatic interactions. Thus, the interactions between polymer and solvent are limited. Although a visible homogeneous solution may be obtained, it is not a uniform molecular dispersion.
• a water swellable polymer is a crosslinked polymer. Cross linked polymers can be water compatible and water dispersible. In contrast, a branched polymer can be soluble.
• the hydrophobic polymers of the present invention are amphiphilic in nature in that they have regions that are more hydrophobic in nature and regions that are more hydrophilic in nature.
• the relative extent of hydrophobicity and hydrophilicity will determine the solubility of the material. In practice, the materials that are, overall, more hydrophobic will be relatively more water insoluble and oil soluble. Conversely, the more hydrophilic materials will be relatively more water soluble and oil insoluble.
• Hydrophobic polymers are water compatible polymers onto which hydrophobic groups are chemically attached, either at the ends of the chain (telechelic or end-capped) or randomly along the polymer chain (comb-like or pendant).
• a polymer with hydrophobic group can undergo intermolecular association with another chain, forming a network mediated by self-association of the hydrophobes. That this association occurs without the formation of covalent bonds is an important facet of the invention.
• This network formation results in, amongst other unique properties, a strong viscosifying or thickening effect.
• a molecule with at least two hydrophobes on a single chain can also undergo intra-molecular association, altering the structure of the molecule in solution and hence, its viscosity.
• hydrophobic substances are materials that are soluble in many nonpolar solvents, but can be sparingly soluble in water. There is an attraction between hydrophobic materials (i.e., oil) and water; this is, however, not nearly as strong as the attraction that water has for itself. Hydrogen bonding between water molecules induces segregation of hydrophobic materials, effectively resulting in hydrophobe-hydrophobe association. This water-induced attraction is termed a hydrophobic interaction. Thus, the hydrophobic effect occurs only in an aqueous environment.
• hydrophobic molecules require the removal of water from the regions between them.
• association of polymer bound hydrophobes results in a region not solvated by water molecules.
• these aggregates are not free draining and can act as small water insoluble (particulate) regions. Without being bound by theory, it is believed that this is the mechanism by which the polymers of the present invention provide their performance properties.
• One approach to producing a hydrophobic polymer is by direct polymerization of monomers, which includes a least one hydrophobic monomer, to form a copolymer.
• Polymerization may be done by any method known in the art, including solution, dispersion and inverse emulsion polymerization.
• nonionic monomers include, but are not limited to, acrylamide; methacrylamide; N-alkylacrylamides, such as N-methylacrylamide; N,N-dialkylacrylamides, such as N,N-dimethylacrylamide; methyl acrylate; methyl methacrylate; acrylonitrile; N-vinyl methylacetamide; N-vinyl formamide; N-vinyl methyl formamide; vinyl acetate; N-vinyl pyrrolidone; alkyl acrylates; alkyl methacrylates; alkyl acryamides; alkyl methacrylamides; and alkyloxylated acrylates and methacrylates such as alkyl polyethyleneglycol acrylates, alkyl polyethyleneglycol methacrylates; mixtures of any of the foregoing and the like.
• N-alkylacrylamides such as N-methylacrylamide
• N,N-dialkylacrylamides such as N,N-dimethyl
• Exemplary anionic monomers include, but are not limited to, the free acids and salts of acrylic acid; methacrylic acid; maleic acid; itaconic acid; acrylamidoglycolic acid; 2-acrylamido-2-methyl-1-propanesulfonic acid; 3-allyloxy-2-hydroxy-1-propanesulfonic acid; styrenesulfonic acid; vinylsulfonic acid; vinylphosphonic acid; 2-acrylamido-2-methylpropane phosphonic acid; mixtures of any of the foregoing and the like.
• the hydrophobic monomer can be any monomer that has a hydrophobic moiety as an integral part of its structure.
• the hydrophobic moiety may be linear or cyclic, aliphatic or aromatic.
• Preferred hydrophobic moieties are typically alkyl groups such as, but not limited to, propyl, butyl, hexyl, octyl, decyl, dodecyl (lauryl), cetyl, stearyl and behenyl groups.
• hydrophobic monomers include, but are not limited to, ethylenically unsaturated monomers having hydrophobic moieties.
• the hydrophobic groups include hydrophobic organic groups, such as those having hydrophobicity comparable to one of the following: aliphatic hydrocarbon groups having at least six carbons (preferably from C 8 to C 22 alkyls and preferably from C 6 to C 22 cycloalkyls); poly-nuclear aromatic hydrocarbon groups such as benzyls, substituted benzyls and naphthyls; alkaryls wherein alkyl has one or more carbons; haloalkyls of four or more carbons, preferably perfluoroalkyls; polyalkyleneoxy groups wherein the alkylene is propylene or higher alkylene and there is at least one alkyleneoxy unit per hydrophobic moiety.
• Suitable hydrocarbon groups containing ethylenically unsaturated monomers include the esters of amides of the C 6 and larger alkyl groups.
• Particularly suitable esters include, but are not limited to, dodecyl acrylate, dodecyl methacrylate, tridecyl acrylate, tridecyl methacrylate, tetradecyl acrylate, tetradecyl methacrylate, octadecyl acrylate, octadecyl methacrylate, nonyl-alpha-phenyl acrylate, nonyl-alpha-phenyl methacrylate, dodecyl-alpha-phenyl acrylate, and dodecyl-alpha-phenyl methacrylate.
• the C 10 -C 20 alkyl esters of acrylic and methacrylic acid are preferred. Of these, dodecyl acrylate and methacrylate are particularly preferred.
• hydrocarbon group-containing ethylenically unsaturated monomers may be used: N-alkyl ethylenically unsaturated amides, such as N-octadecyl acrylamide, N-octadecyl methacrylamide, N-octyl acrylamide, N,N-dioctyl acrylamide and similar derivatives thereof; alpha-olefins, such as 1-octene, 1-decene, 1-dodecene, and 1-hexadecene; vinyl alkylates wherein the alkyl has at least eight carbons, such as vinyl laurate and vinyl stearate; vinyl alkyl ethers, such as dodecyl vinyl ether and hexa-vinyl alkyl ethers, such as dodecyl vinyl ether and hexa-decyl vinyl ether; N-vinyl amides, such as N-vinyl lauramide and
• the hydrophobic monomer is present in the hydrophobic copolymer in an amount up to about 10 mole percent, preferably up to 5 mole percent and even more preferably up to 2 mole percent. It is preferred that the hydrophobic monomer be present in an amount from at least about 0.01, preferably at least 0.1 mole percent. It is preferred that the hydrophobic monomer be present in an amount from about 0.01 to about 2 mole percent and most preferred that the hydrophobic monomer be present in an amount from about 0.1 to about 1 mole percent.
• Preferred hydrophobic monomers are octylacrylamide and lauryl acrylate.
• the molar ratio of the hydrophobic, anionic, cationic and nonionic monomer can be varied to contain any relative amount of the monomers necessary to achieve the desired solubility.
• Polymerization of the emulsion may be carried out in any manner known to those skilled in the art. Initiation may be effected with a variety of thermal and redox free-radical initiators including, but not limited to, azo compounds such as azobisisobutyronitrile and the like. Polymerization may also be effected by photochemical irradiation processes, irradiation or by ionizing radiation with a 60 Co source.
• Preferred initiators are oil soluble thermal initiators.
• Typical examples include, but are not limited to, 2,2′-azobis-(2,4-dimethylpentanonitrile); 2,2′-azobisisobutyronitrile (AIBN); 2,2′-azobis-(2,-methylbutanonitrile); 1,1′-azobis-(cyclohexanecarbonitrile); benzoyl peroxide and lauroyl peroxide.
• the aqueous solution typically comprises an aqueous mixture of monomers.
• the aqueous phase may also comprise such conventional additives as are desired.
• the mixture may contain chelating agents, pH adjusters, initiators, chain transfer agents as described above, and other conventional additives.
• the pH of the aqueous solution is below 12 and is preferably equal to or greater than 2, more preferably the pH is about 4 to about 6.
• surfactants include sorbitan monooleate, sorbitan sesquioleate, sorbitan trioleate, polyoxyethylene sorbitan monooleate, and surfactants sold by BASF under the Pluronic® trade name and surfactants by Uniqema under the Atlas® and Arlacel® trade names.
• Yet another method for preparation of hydrophobic water compatible polymer is by derivatizing an existing synthetic polymer. This can be achieved by a number of technical approaches, which include but are not limited to, the grafting of a hydrophobic amine via the Mannich reaction.
• Yet another method for preparation is the use of a water dispersible macromer, sometimes referred to as polymerizable surfactant, such as nonylphenoxy poly(ethylene oxide) acrylate that can be copolymerized with an ethylenically unsaturated monomer to a self-assembling hydrophobically modified polymer.
• a water dispersible macromer sometimes referred to as polymerizable surfactant, such as nonylphenoxy poly(ethylene oxide) acrylate that can be copolymerized with an ethylenically unsaturated monomer to a self-assembling hydrophobically modified polymer.
• Yet another method for preparation is to modify an already prepared polymeric backbone. This method implies either utilization of an aprotic solvent common for the polymer and a hydrophobic entity to be grafted upon the polymer, or selective hydrophilization of a hydrophobic water insoluble block copolymer.
• Hydrophobically modified alkali-swellable emulsion, or HASE are also useful in the present invention. These materials are hydrophobically modified acrylate copolymers.
• An example would be a copolymer of methacrylic acid, ethylacrylate and a third monomer termed an associative macromonomer.
• An example of associative macromonomer is an ethylenically unsaturated monomer with a pendant hydrocarbon of more than 6 carbons linked to the monomer by an ethylene oxide chain. Key variables are the chemistry of the hydrocarbon and the length of these ethylene oxide chains.
• Additional polymers useful in the present invention are hydrophobically modified polymers based on natural occurring polymers such as proteins and polysaccharides. Derivatized natural materials, including starch and cellulose derivatives can also be used. Exemplary based polymers include, but are not limited to, hydroxyethyl cellulose and cationic starch. Preferred are nonionic water soluble cellulose ether can be used as the cellulose ether substrate used to form the products of this invention. Thus, e.g., hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, ethyl hydroxyethyl cellulose, and methyl hydroxyethyl celluose can all be modified. The amount of nonionic substituent such as methyl, hydroxyethyl or hydroxypropy; does not appear to be critical so long as there is sufficient to assure that the ether is water soluble.
• the preferred cellulose ether substrate is hydroxyethyl cellulose (HEC). Accordingly, control of the modification process and control of the properties of the modified product can be more precise with this substrate. Hydrophilicity of the most commonly used nonionic cellulose ethers varies in the general direction: hydroxyethyl>hydroxypropyl>hydroxypropyl>methyl.
• Long chain alkyl modifier can be attached to the cellulose ether substrate via an ether, ester or urethane linkage.
• ether linkage as the reagents most commonly used to effect etherification are readily obtained, the reaction is similar to that commonly used for the initial etherification, and the reagents are usually more easily handled than the reagents employed for modification via the other linkages. The resulting linkage is also usually more resistant to further reactions.
• the preferred procedure for preparing the mixed ethers of this invention comprises slurrying the nonionic cellulose ether in an inert organic diluent such as a lower aliphatic alcohol, ketone, or hydrocarbon and adding a solution of alkali metal hydroxide to the resultant slurry at a low temperature.
• an inert organic diluent such as a lower aliphatic alcohol, ketone, or hydrocarbon
• Residual alkali is then neutralized and the product is recovered, washed with inert diluents, and dried.
• the etherification can also be effected with a C 10 to C 24 halide or halohydride but these are sometimes less reactive, less efficient and more corrosive so it is preferred to use epoxide.
• siliceous materials can be used as an additional component of a retention and drainage aid used in making paper and paperboard.
• the siliceous material may be any of the materials selected from the group consisting of silica based particles, silica microgels, amorphous silica, colloidal silica, anionic colloidal silica, silica sols, silica gels, polysilicates, polysilicic acid, and the like. These materials are characterized by the high surface area, high charge density and submicron particle size.
• silica sols This group includes stable colloidal dispersion of spherical amorphous silica particles, referred to in the art as silica sols.
• the terms sol refers to a stable colloidal dispersion of spherical amorphous particles.
• Silica gels are three dimensional silica aggregate chains, each comprising several amorphous silica sol particles, that can also be used in retention and drainage aid systems; the chains may be linear or branched.
• Silica sols and gels are prepared by polymerizing monomeric silicic acid into a cyclic structure that result in discrete amorphous silica sols of polysililcic acid. These silica sols can be reacted further to produce a three-dimensional get network.
• the various silica particles (sols, gels, etc.) can have an overall size of 5-50 nm. Anionic colloidal silica can also be used.
• the siliceous material can be added to the cellulosic suspension in an amount of at least 0.05 Kg per metric ton based on dry weight of the cellulosic suspension.
• the amount of siliceous material may be as high as 5 Kg per metric ton.
• the amount of siliceous material is from about 0.05 to about 25 Kg per metric ton. Even more preferably the amount of siliceous material is from about 0.25 to about 5 Kg per metric ton based on the dry weight of the cellulosic suspension.
• the components of a retention and drainage system may be added substantially to the cellulosic suspension.
• the term retention and drainage system is used here to encompass two or more distinct materials added to the papermaking slurry to provide improved retention and drainage.
• the components may be added to the cellulosic suspension separately either at the same stage or dosing point or at different stages or dosing points.
• any two or more of the materials may be added as a blend.
• the mixture may be formed in situ by combining any two or more of the materials at the dosing point or in the feed line to the dosing point.
• the inventive system comprises a preformed blend of the any two or more of the materials.
• the components of the inventive system are added sequentially. A shear point may or may not be present between the addition points of the components.
• the components can be added in any order.
• the inventive system is typically added to the paper process to affect retention and drainage.
• the inventive system may be added to the thick stock or thin stock, preferably the thin stock.
• the system may be added at one feed point, or may be split fed such that the inventive system is fed simultaneously to two or more separate feed points.
• Typical stock addition points include feed points(s) before the fan pump, after the fan pump and before the pressure screen, or after the pressure screen.
• the amount of siliceous material in relationship to the amount of associative polymer copolymer used in the present invention can be about 100:1 to about 1:100 by weight, or from about 50:1 to 1:50 or about 10:1 to 1:10.
• aluminum sources such as alum (aluminum sulfate), polyaluminum sulfate, polyaluminum chloride and aluminum chlorohydrate.
• the copolymers useful in the invention can be used in papermaking systems and processes.
• the copolymers are useful as drainage and retention aids as well as contaminant control aids.
• a slurry of cellulosic fibers or pulp is deposited on a moving papermaking wire or fabric.
• the slurry may contain other chemicals, such as sizing agents, starches, deposit control agents, mineral extenders, pigments, fillers, organic or inorganic coagulants, conventional flocculants, or other common additives to paper pulp.
• a sheet forms. Ordinarily the sheets are then pressed and dried to form paper or paper board.
• the copolymers of the invention are added to the slurry before it reaches the wire to improve the drainage or dewatering and the retention of the fiber fines and fillers in the slurry.
• the polymers of the present invention inhibit the deposition of pitch and stickies from the virgin or recycled pulp stock on the papermaking equipment.
• the aid is added to the pulp slurry where it interferes with the agglomeration of the pitch and stickies that would otherwise detrimentally affect the paper, paper making equipment or paper making processes.
• a method of inhibiting deposition of pitch and stickies comprises adding a hydrophobic polymer to a cellulosic pulp slurry.
• Suitable cellulosic fiber pulps for the method of the invention include conventional papermaking stock such as traditional chemical pulp. For instance, bleached and unbleached sulfate pulp and sulfite pulp, mechanical pulp such as groundwood, thermomechanical pulp, chemi-thermomechanical pulp, recycled pulp such as old corrugated containers, newsprint, office waste, magazine paper and other non-deinked waste, deinked waste, and mixtures thereof, may be used.
• copolymers useful in the invention may be provided to the end use application in a number of physical forms.
• inventive copolymer may also be provided as an aqueous solution, dry solid powder, or dispersion form.
• the present invention provides for a method of improving retention and or drainage of a cellulosic pulp slurry wherein the method comprises adding hydrophobic polymer to a cellulosic pulp slurry to improve drainage.
• This dilute solution of the copolymers used in the invention is added to the paper process to affect retention and drainage.
• the inventive copolymer may be added to the thick stock or thin stock, preferably the thin stock.
• the copolymer may be added at one feed point, or may be split fed such that the copolymer is fed simultaneously to two or more separate feed points.
• Typical stock addition points include feed point(s) before the fan pump, after the fan pump and before the pressure screen, or after the pressure screen.
• Atlas® G-946 is sorbitan monoleate marketed by Uniqema, New Castle, Del.
• Hypermer® B246SF is triblock polymeric surfactant marketed by Uniqema, New Castle, Del.
• OA is t-octylacrylamide obtained from Monomer-Polymer & Dajac Labs, Inc., Feasterville, Pa.
• COPS1 is Sipomer® COPS1, a sodium alkylhydroxypropyl sulfonate monomer marketed by Rhodia, Inc., Cranbury, N.J.
• BEM-25 is Sipomer® BEM-25, a behenyl polyethoxymethacrylate monomer marketed by Rhodia, Inc., Cranbury, N.J.
• SEM-25 is Sipomer® SEM-25, a tristyriphenol polyethoxymethacrylate monomer marketed by Rhodia, Inc., Cranbury, N.J.
• Maxemul® 5010 an alkenyl functional non-ionic surfactant marketed by Uniqema, New Castle, Del.
• Acrylic acid was obtained from Rohm and Haas, Philadelphia, Pa.
• An aqueous phase is prepared separately which comprises 53-wt. % acrylamide solution in water (126.5 g), acrylic acid (68.7 g), deionized water (62.12 g), and Versenex® 80 (Dow Chemical) chelant solution (0.7 g).
• the aqueous phase is then adjusted to pH 5.4 with the addition of ammonium hydroxide solution in water (33.1 g, 29.4-wt. % as NH 3 ).
• the temperature of the aqueous phase after neutralization is 39° C.
• the molar ratio of acrylic acid to acrylamide to OA is 50:49.25:0.75.
• Examples 2-5 were prepared as described in example 1 except that the molar composition of monomer was as shown in Table 1.
• Table 1 Exam- Monomer 1 Monomer 2 Monomer 3 ple Monomer (a) % (b) Monomer (a) % (b) Monomer (a) % (b) 2 Acrylic Acid 50.00 Acrylamide 49.75 COPS1 0.25 3 Acrylic Acid 50.00 Acrylamide 49.60 BEM-25 0.40 4 Acrylic Acid 50.00 Acrylamide 49.90 SEM-25 0.10 5 Acrylic Acid 50.00 Acrylamide 49.70 5010 0.30
• Example 6 is PerForm® 9232 Retention and Drainage Aid (Hercules Incorporated, Wilmington, Del.)
• Example 9 is poly(N-isopropylacrylamide) obtained from Scientific Polymer Products, Inc., Ontario, N.Y.
• Example 10 is poly(N,N-dimethylacrylamide) obtained from Scientific Polymer Products, Inc., Ontario, N.Y.
• the furnish employed in this series of tests is a synthetic alkaline furnish. This furnish is prepared from about 70% by wt of hardwood and 30% by wt of softwood dried market lap pulps, and from water and further materials. First the hardwood and softwood dried market lap pulp are separately refined in a laboratory Valley Beater (Voith, Appleton, Wis.). These pulps are then added to an aqueous medium.
• the aqueous medium utilized in preparing the furnish comprises a mixture of local hard water and deionized water to a representative hardness.
• Inorganic salts are added in amounts so as to provide this medium with a total alkalinity of 75 ppm as CaCO 3 and hardness of 100 ppm as CaCO 3 .
• the hardwood and softwood are dispersed into the aqueous medium at typical weight ratios of hardwood and softwood (typically about 70:30).
• Precipitated calcium carbonate (PCC) is introduced into the furnish at 25 weight percent, based on the combined dry weight of the pulps, so as to provide a final furnish comprising 80% fiber and 20% PCC filler.
• a cationic potato starch Stalok® 400 (A. E. Staley, Decatur, Ill.), is added at a level of 5 kg per metric ton, based on dry pulp, and then alum, (aluminum sulfate octadecahydrate available as a 50% solution from Delta Chemical Corporation, Baltimore, Md.), is added at a level of 2.5 kg per metric ton.
• a cationic flocculent (Perform® PC 8138, Hercules Incorporated) is added at a level of 0.25 kg/metric ton, based on dry pulp.
• the device setup is similar to the Buchner funnel test as described in various filtration reference books, for example see Perry's Chemical Engineers' Handbook, 7 th edition, (McGraw-Hill, New York, 1999) pp. 18-78.
• the VDT consists of a 300-ml magnetic Gelman filter funnel, a 250-ml graduated cylinder, a quick disconnect, a water trap, and a vacuum pump with a vacuum gauge and regulator.
• the VDT test is conducted by first setting the vacuum to the desired level, typically 10 inches Hg, and placing the funnel properly on the cylinder. Next, 250 g of 0.5 wt.
• % paper stock is charged into a beaker and then the required additives according to treatment program (e.g., starch, alum, and testing flocculants) are added to the stock under the agitation provided by an overhead mixer. The stock is then poured into the filter funnel and the vacuum pump is turned on while simultaneously starting a stopwatch. The drainage efficacy is reported as the time required to obtain 230 ml of filtrate.
• treatment program e.g., starch, alum, and testing flocculants
• the principle of the VDT is based on the cake filtration theory, for reference see L. Svarovsky, editor, Solid - Liquid Separation, 3 rd edition (London, Butterworths, 1990), Chapter 9.
• the solids in the slurry are deposited on a relative thin filter medium that serves to support the filter cake.
• the rate of filtrate passing through the filter cake (or mat) is dependent on floc density, floc size distribution in the mat, and levels of residual polymeric materials in the aqueous phase.
• a flocculant that forms dense and uniform-sized flocs and has low residual level in water (i.e., good formation characteristics) will demonstrate good drainage in the VDT test, and vice versa.

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