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
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B16/00—Regeneration of cellulose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B9/00—Cellulose xanthate; Viscose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
  • C08L1/02—Cellulose; Modified cellulose
• • 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
  • D21H17/21—Macromolecular organic compounds of natural origin; Derivatives thereof
  • D21H17/24—Polysaccharides
  • D21H17/25—Cellulose
• • 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
  • D21H17/44—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups cationic
  • D21H17/45—Nitrogen-containing groups
  • D21H17/455—Nitrogen-containing groups comprising tertiary amine or being at least partially quaternised

Definitions

• the present invention relates to improvements of dewatering and retention in the production of paper and board.
• the invention is directed to cellulose particles modified by cationic polyelectrolytes useful for this purpose, said particles con- sisting of regenerated cellulose and comprising cationic polyelectrolytes having low and high molecular weights on the outer surface thereof.
• the invention is further directed to a process for the preparation of cellulose particles modified by polyelectrolytes, use thereof in the manufacture of paper and board, and to a process for manufacturing paper or board.
• Pulps for the production of paper and board mainly consist of cellulose fibres, fines, and fillers.
• Charged polymers having high molecular weights are generally added to said pulp as dewatering and retention aids for the adsorption of fines and fillers on the fibres, thus preventing them from being washed off from the web with the water removed.
• Pulps further comprise variable amounts of so-called interfering substances, this term generally referring to dissolved or colloidal anionic oligomers or polymers, and non-ionic hydrocolloids. Said substances in- crease cationic demand of the pulps and lower the efficiency of retention aids and agents improving paper strength. This results e.g.
• interfering agents are present in pulps containing recycled fibre, and in mechanical pulps. Influence of anionic interfer-ing substances may be neutralized by the addition of cationic polymers having low molecular weights prior to other aids, thus particularly improving the performance of dewatering and retention aids to be added later.
• Patent EP 0 752 496 Bl discloses a process for producing paper with improved dewatering and retention wherein low molecular weight (LMW) cationic polymer, high molecular weight (HMW) cationic or amphoteric polymer, and anionic inorganic particles are added to pulps for paper production.
• LMW low molecular weight
• HMW high molecular weight
• Molecular weights of said HMW and LMW polymers are over 1 000 000 and less than 700 000, respectively.
• Said HMW polymer may be for instance cationic starch, cationic guar gum, or cationic polymer based on acrylamide.
• Said cationic LMW polymer may for instance be modified starch, polyamine, polyethylene imine, or a homo or copolymer based on diallyl dimethyl ammonium chloride, vinyl amine, (meth)acrylamide, or (meth)acrylate monomers, or mixtures thereof.
• Particles based on silica, clays of the smectite type, and titanyl sulfate sols are mentioned as anionic inorganic particles.
• the polymers are added to the pulp substantially at the same time and at the same stage, such as in the form of a mixture, preferably prior to the addition of the inorganic particles.
• Patent US 6,184,302 Bl discloses solid particles substantially insoluble in water, the surface of said particles being cationized for the most part by a cationic polymer or copolymer comprising alkyl and/or vinyl double bonds and nitrogen, proc- ess for the preparation thereof and the use thereof in paper manufacturing process.
• Said cationized solid particles are prepared by cross-linking an aqueous solution of the cationic polymer or copolymer in the presence of the solid particles with itself and/or with solid particles using a free radical initiator, reaction times vary- ing between 1 and 12 hours. The reaction is for instance performed by spraying an aqueous solution of the polymer and initiator on the solid particles while vigorously mixing and heating.
• Solid substances to be cationized are e.g. cellulose or mineral particles of different shapes, or even fibres, films or textiles having at least 80 percent insolubility in water.
• Linear polyethylene imines, polyallyl amines, polydiallyl amines, hydrolyzed poly-N-vinyl pyrrolidones, hydro lyzed polyvinyl caprolactames, peptides with an amino group, and chitosan are mentioned as polymers and copolymers to be cationized.
• Said cationized solid particles may be used as retention aid and fixing agent in the production of paper.
• Published patent application EP 0 845 495 A2 discloses cellulose particles substantially insoluble in water, having cationic groups on the surface thereof, a process for the preparation of such cellulose particles, and the use thereof for the manufacture of paper and board as fixing agent for interfering substances, and as flocculation agent in waste water treatment.
• Said particles may be prepared for instance by binding a polymer having cationic groups or groups to be cationized later on the surface of cellulose using a catalyst or an initiator under nearly dry conditions and at elevated temperatures.
• reagents of at least one type that may be copolymerized or cross-linked, of which at least one comprises cationic groups or groups to be cationized later are impregnated on the surface of cellulose particles serving as carriers and polymerized under suitable conditions in the presence of the cellulose, polymerization and cross-linking resulting in the formation of mechanical bonds with the surface of cellulose.
• the material to be cationized may be bleached unsubstituted chemical pulp, or a cellulose derivative such as ether or ester, chitin and derivatives thereof.
• Low molecular weight poly- DADMAC as concentrated aqueous solutions or other polymers soluble in water, comprising cationic or cationizable groups, may be used as cationizing agent, said polymers being able to further react when free radical initiators serving as the catalysts are used.
• the cationized cellulose particles may be produced by spraying an aqueous solution of the free radical initiator serving as the catalyst on a substantially dry finely divided cellulose powder in the mixer. A solution of the cationizing polymer such as polyD ADMAC to be reacted is slowly added to the moist powder thus obtained.
• the catalyst and the cationic polymer may also be mixed in advance, and added together. Water content of the powder is kept low.
• reaction vessel air is replaced by nitrogen, and the temperature is elevated to at least 65 °C while mixing, the reaction time being several hours.
• the cation- ized cellulose particles thus obtained are added to the pulp for the production of paper and board prior to retention aids, said particles thus fixing interfering anionic substances to the paper, and further improving the performance of the retention aids such as polyacrylamide, and the retention of fillers.
• Said cationized cellulose particles may also be mixed with an aqueous solution of the polymer solu- ble in water such as polyethylene imine or polyacrylamide prior to use.
• WO 96/26220 discloses cationized cellulose particles, in which preferably at least 50 % of the cationic groups are located within the particles, cationic groups being thus bound across the total cross section of the particle.
• the cellulose may be unsubstituted chemical pulp, substituted cellulose such as cellulose ester or ether, or an alkaline cellulose.
• Cationization reaction may be performed between dry substances by trituration or by dissolving cellulose to form a solution, followed by the addition of the cationizing agents and precipitation of the thus cationized cellulose to give particles.
• Dissolved cellulose having a high degree of substitution such as carboxymethyl cellulose may be precipitated to give particles also in aqueous solutions of cationic polyelectrolytes, thus yielding cationized cellulose particles.
• An aluminium salt, cationic polyelectrolyte, and a reactive monomer may serve as the cationizing agent.
• Said cationized cellulose particles may be spherical or fibrous.
• the cationized cellulose particles may be used in the production of paper, in which case a fibrous structure is preferable, or as flocculation agent in the treatment of waste water. In paper production, the par- tides are said to improve the strength of paper and retention of fines to the web.
• the particles may be used as a solid substance or as a suspension alone or in combination with polymers soluble in water such as cationic polyacrylamide, polyethylene imine and cellulose derivatives soluble in water, in paper production, the particles being preferably added to the pulp at an early stage, and the polymer immediately prior to web formation, while in water treatment, the particles and the polymer are preferably added as a mixture.
• polymers soluble in water such as cationic polyacrylamide, polyethylene imine and cellulose derivatives soluble in water
• Patent EP 1 047813 Bl presents cationic cellulose fibrides comprising more than 10 % to 50 % of polymeric amine by weight of the polymer, said polymeric amine having a weight average molecular weight of between 100 000 and 1 000 000 and comprising monomeric units represented by the formula
• X is selected from the group consisting of chemical bond, O, and NR ;
• R 1 and R 2 are identical or different and selected from the group consisting of H, Ci -C 4 alkyl, phenyl, or a phenyl mono-, di- or trisubstituted with substituent(s) selected from the group consisting of CpC 4 alkyl, Ci-C 4 alkoxy, F, Cl, and Br;
• R 3 and R 4 independently represent H, methyl, and ethyl;
• m is a variable ranging between 1 and 4; and
• n is a variable ranging between 0 and 4.
• a process for the production of cationic cellulose fibrides wherein an aqueous solution of said polymeric amine is added to a viscose solution, the solution thus obtained is mixed with a coagulating and regenerating solution in turbulent flow, followed by recovering the cationic cellulose fibrides formed from the slurry.
• the particles are washed with water, dissolution of the cationizing polymer into regenerating agent and cleavage of the polymer from the cellulose surface is avoided by using specific polymeric amines for cationization.
• the cationic cellulose fibrides may be used as additives in the production of paper and board, particularly for the improvement of web formation and dewatering.
• Particles composed of unmodified regenerated cellulose are in many ways similar to fines present in chemical pulp, formed during chemical and mechanical treatment. In comparison to cellulose, they both have small particle sizes, and thus large hydrodynamic surface areas. Moreover, they absorb more water than fibres, and are slightly anionic. Both particles of regenerated cellulose and fines increase the strength and density of paper and lower the scattering of light by reducing the number of optical boundaries between solid matter and air. Particles of regenerated cellulose differ from fines of chemical pulp in that the shape thereof is clearly spherical, and the surface thereof is somewhat colloidal, while fines of chemical pulp are filamentous. Another significant difference is found in particle size distribution particularly playing a role in light scattering behaviour.
• All particles passing a sieve of 200 mesh are defined as fine matter, and accordingly, this fine matter is composed of very heterogeneous group of particles with wide ranges of particle sizes from some nanometers to 76 ⁇ m.
• Mean size of the particles of regenerated cellulose in typically about a few micrometers, the particle size distribution being rather narrow. Thus the structure of regenerated cellulose particles is more preferable with respect to light scattering.
• Modification with cationic polyelectrolytes considerably improves the retention of cellulose particles in the web, and thus in case regenerated cellulose particles are to be used as fillers in paper or board, they may be partly or totally replaced by modified cellulose particles of the invention. Also the retention of other components used in the production of paper and board is improved by the addition of cellulose particles of the invention to the pulp. Use of the modified cellulose particles of the invention also results in improved dewater- ing compared to using corresponding unmodified particles or particles modified by a single cationic polymer.
• modified cellulose particles of the present invention the cationic groups are found on the outer surface of the particles, being thus better able to bind interfering substances in comparison to the solution where the cationizating agent is added to the cellulose solution.
• the cationic groups are enclosed within the particles during regeneration of the cellulose solution.
• considerable amounts of the cationizating solution may remain in the regenerating solution.
• the particles acting as carriers of the cationic groups are organic.
• an additional benefit achieved with the modified cellulose particles of the invention is the fact that they are lightweight and non-abrasive, and accordingly, grammage of paper and board and wear of the equipment is reduced by the use of modified • cellulose particles of the invention.
• An object of the invention is to provide cellulose particles modified with cationic polyelectrolytes.
• Another object of the invention is also to provide a process for preparing cellulose particles modified with cationic polyelectrolytes. Still another object of the invention is the use of modified cellulose particles in the production of paper and board.
• an object of the invention is to provide a process for the production of paper and board.
• Cellulose particles modified with cationic polyelectrolytes, process for the preparation thereof, use in the production of paper and board, and the process for the production of paper and board according to the invention are characterized as dis- closed in the claims.
• the invention is directed to cellulose particles modified by cationic polyelectro- lytes, said cellulose particles being composed of regenerated cellulose, and comprising on the outer surface thereof molecules of a first cationic polyelectrolyte having a molecular weight of 20 000 to 500 000 g/mol, and charge density of more than 3 meq/g, and molecules of a second cationic polyelectrolyte having a molecular weight of 2 to 10 million g/mol, and charge density of between 0.5 and 3 meq/g.
• the invention is also directed to a process for producing cellulose particles modified by cationic polyelectrolytes.
• a solution of cellulose is passed to a regenerating solution to precipitate cellulose particles;
• the cellulose particles formed are washed with water to a substantially constant pH value, followed by washing with a basic solution to a basic pH value;
• the outer surface of the cellulose particles is modified in an aqueous solution comprising a first cationic polyelectrolyte having a molecular weight of 20 000 to 500 000 g/mol, and charge density of more than 3 meq/g; and then (d) the outer surface of the cellulose particles is modified in an aqueous solution comprising a second cationic polyelectrolyte having a molecular weight of 2 to 10 million g/mol, and charge density of between 0.5 and 3 meq/g; the steps (c) and (d) being successively carried out in the same aqueous solution.
• Cellulose particles modified by cationic polyelectrolytes of the invention may be added to the pulp for the production of paper or board, thus improving both retention and dewatering in comparison to the case where corresponding cellulose particles that are unmodified or modified by a single cationic polyelectrolyte are added to the pulp.
• Figure l is a graph showing the dewatering time in seconds for pulps containing 6 % and 14 % by weight of cellulose particles of the invention produced according to example 1, comprising cationic polyD ADMAC and polyacrylamide molecules (C-PAM), particles added to one of the pulps moreover comprising sodium dode- cyl sulfate (SDS).
• Pulps containing 6 % and 14 % by weight of cellulose particles that were either unmodified or modified to zeta potentials of -10 mV and +20 mV with polyDADMAC alone were used as controls.
• Cellulose particles used in this comparative study were prepared as described in example 1. Part of the particles was washed and modified at a concentration of 1.0 g/1 in polyDADMAC solutions having concentrations of 0.6 mg/1 (zeta potential of -10 mV) and 1.8 mg/1 (zeta potential of +20 mV).
• Figure 2 is a graphical presentation of the retentions of cellulose particles that are either unmodified or modified with a single cationic polyelectrolyte in the formed sheets for the desired particle contents of 6 %, and 14 % by weight, and further, the retentions of cellulose particles modified with two cationic polymer in the formed sheets for the desired particle contents of 6 %, 14 %, and 22 % by weight.
• the invention is based on the finding that both retention and dewatering may be clearly improved by modifying regenerated cellulose particles by low and high molecular weight cationic polyelectrolytes and by adding the modified cellulose particles thus obtained to pulp for paper and board production, in comparison to cases where cellulose particles that are either unmodified or modified with a single cationic polymer are added to the pulp.
• the invention relates to cellulose particles modified by cationic polyelectrolytes, said cellulose particles being composed of regenerated cellulose particles, the outer surface thereof comprising molecules of a first cationic polyelectrolyte having a low molecular weight and molecules of a second cationic polyelectrolyte having a high molecular weight.
• Regenerated cellulose particles refer to particles regenerated from dissolved cellulose in a known mamier, the starting material being then for instance cellulose xanthate, i.e. viscose, or alkaline cellulose, pre- cipitation being for instance carried out by spraying the cellulose solution to an acid solution.
• the particles may be spherical, needle-like, fibrous, granular or the like, and they may have some porosity.
• Outer surface of the cellulose particles refers here to the surface area accessible to the molecules of the cationic polyelectrolyte for contact in case the cellulose particles are cationized in an aqueous polyelectrolyte solution.
• low molecular weight refers to mean molecular weight ranging from 20 000 to 500 000 g/mol, preferably from 100 000 to 500 000 g/mol. It is required that the charge density of the cationic polyelectrolyte having a low molecular weight is over 3 meq/g, preferably from 5 to 8 meq/g.
• high molecular weight refers to mean molecular weight ranging from 2 to 10 million g/mol, preferably from 5 to 10 million g/mol. It is required that the charge density of the cationic polyelectrolyte having a high molecular weight is between 0.5 and 3 meq/g, preferably between 0.5 and 1.5 meq/g. All cationic polyelectrolytes soluble in water, complying with the above requirements, may be used as polyelectrolytes. Useful polyelectrolytes may either be linear or branched. Accordingly, for example starch may be used.
• Zeta potential, reflecting the mobility of charged particles in an electrical field, of the cellulose particles modified with the first and second cationic polyelectrolytes is preferably at least +5 mV, as measured at a pH of 8.
• the first cationic polyelec- trolyte is preferably polydiallyl dimethyl ammonium chloride (polyDADMAC), while the second cationic polyelectrolyte is preferably cationic polyacrylamide.
• the molecular weight thereof is preferably from 100 000 to 500 000 g/mol
• the molecular weight thereof is preferably from 5 to 10 million g/mol.
• the modified cellulose particles of the present invention may have any shapes and sizes. According to the application, the particles may for instance be spheres, fibres, granules or the like. In the production of paper and board, the modified cellulose particles of the invention are e.g. spherical, having a mean par- tide size ranging from 0.05 to 10 ⁇ m.
• outer surfaces of the cellulose particles may be modified with anionic surfactants for the provision of hydrophobicity to said cellulose particles.
• outer surfaces of the cellulose particles comprise any anionic surfactant such as an oleate, stearate, or SDS. SDS is a preferable anionic surfactant.
• the invention is also directed to a process for producing cellulose particles modified by cationic polyelectrolytes.
• (a) solution of cellulose is passed to a regenerating solution to precipitate cellulose particles;
• (b) the cellulose particles formed are washed with water to a substantially constant pH value, followed by washing with a basic solution to a basic pH value;
• (c) the outer surface of the cellulose particles is modified in an aqueous solution comprising a first cationic polyelectrolyte having a molecular weight of 20 000 to 500 000 g/mol, and charge density of more than 3 meq/g; and then (d) the outer surface of the cellulose parti- cles is modified in an aqueous solution comprising a second cationic polyelectrolyte having a molecular weight of 2 to 10 million g/mol, and charge density of between 0.5 and 3 meq/g; the steps (c) and (d) being successively carried out in the same aqueous solution.
• Cellulose solution used in step (a) of the process of the invention may be a solution of any dissolved regenerable cellulose, for instance a viscose solution or alkali cellulose solution. Suitable concentration range for the cellulose solution is between 0.5 and 7 %.
• the regeneration of the dissolved cellulose to give cellulose particles is performed for instance by spraying or mixing the cellulose solution to a regenerating solution. In case regeneration is carried out by mixing, for instance by the gradual addition of the cellulose solution by means of a burette, vigorous agitation of the regenerating solution is necessary, e.g. using a magnetic stirrer at a rate of 600 to 1000 rpm. In case regeneration is carried out by spraying, e.g.
• Spray angle of the nozzle may for instance be selected between 10° and 150°. Among other things, suitable spray angle depends on the distance between the nozzle and the regenerating solution. The greater the dis- tance, the narrower spray angle may be used. When spraying to the regenerating solution is performed at a distance of 20 to 30 cm, a suitable spray angle is between 20° and 60°.
• Regenerating solution is preferably acid, more preferably a dilute e.g. IM sulfuric acid solution.
• Alternatives include other strong acids like HCl, and HClO 4 , HI, HBr and HNO 3 may also be useful.
• the mean particle size of said cellulose particles is preferably between 0.05 and 10 ⁇ m.
• Particle sizes of the cellulose particles to be precipitated may be adjusted to the desired range by suitably selecting the parameters for the production process, including concentration of cellulose in the solution and droplet size, or agitation speed in case the cellulose solution is sprayed into, or mixed with the regenerating solution, respectively.
• step (b) of the process according to the invention the cellulose particles formed are first washed with water to obtain a substantially constant pH value, followed by washing with a basic solution to a basic pH value. Suitable basic solutions in- elude aqueous solutions of alkali metal hydroxides, and hydrogen carbonates, or mixtures thereof. Washing with water is for instance carried out on a filter, thus allowing for the monitoring of the pH change from the filtrate.
• Regenerated cellulose particles are preferably washed with water to a pH of the filtrate of at least 4.
• cellulose particles are preferably washed with NaOH/NaHCO 3 solu- tion with concentrations of both NaOH and NaHCO 3 being e.g. about 1 mmol/1. Washing with the basic solution is continued to a pH value of the filtrate of > 7, preferably to a pH of about 8. After said washing operations, wet cellulose particles are directly passed to the modification step.
• step (c) of the process according to the invention the outer surfaces of the cellulose particles are modified in an aqueous solution comprising a first cationic polyelectrolyte having a molecular weight of 20 000 to 500 000 g/mol, and charge density of more than 3 meq/g; and thereafter (d) the outer surfaces of the cellulose particles are modified in an aqueous solution comprising a second cationic polye- lectrolyte having a molecular weight of 2 to 10 million g/mol, and charge density of between 0.5 and 3 meq/g; the steps (c) and (d) being successively carried out in the same aqueous solution.
• Outer surfaces of the cellulose particles refer here to that surface area of the cellulose particles suspended in the aqueous solution of the cationic polyelectrolyte, which is accessible to the cationic polyelectrolyte mole- cules for contact. Outer surfaces of the cellulose particles are preferably modified in an aqueous solution of the first cationic polyelectrolyte, followed by the addition of the second cationic polyelectrolyte to said aqueous solution.
• the concentrations of the first and the second polyelectrolyte it is preferable to select the concentrations of the first and the second polyelectrolyte to obtain after the first modification step, and after the second modification step a zeta potential of the modified cellulose particles between -10 and —5 mV, and at least +5 mV, respectively, as measured at a pH of 8.
• Concentration of the cationic polyelectrolyte necessary to provide a certain zeta potential change of the cellulose particles is found out for instance as follows. Serial dilutions of the cationic polyelectrolyte at a suitable concentration range are made, small amounts of regenerated cellulose particles washed as described above are modified by each dilution, followed by measuring the zeta potential of the modified cellulose particles using a Coulter Delsa 440 instrument. Zeta potential being influenced by pH, the measurements are carried out at the same pH obtained by washing the cellulose particles to be modified, e.g. at pH value of 8.
• a zeta potential curve of the cellulose particles as a function of the concentration of the cationic polyelectrolyte is obtained. Concentration of the polyelectrolyte necessary for the desired zeta potential value is read from the curve.
• Molecular weights of the first and the second cationic polyelectrolyte are preferably between 100 000 and 500 000 g/mol, and between 5 and 10 million g/mol, respectively.
• Charge densities of the first and the second cationic polyelectrolyte are preferably between 5 and 8 meq/g, and between 0.5 and 1.5 meq/g, respec- tively.
• said first cationic polyelectrolyte is preferably a polyDADMAC, while the second cationic polyelectrolyte is a cationic poly- acrylamide.
• the molecular weights thereof are preferably between 100 000 and 500 000 g/mol, and between 5 and 10 million g/mol, respectively.
• the process of the invention may further comprise a step where the outer surface of cellulose particles are modified with an anionic surfactant, preferably with SDS.
• Modification with said anionic surfactant is preferably carried out by mixing the surfactant together with the first or the second cationic polyelectrolyte used for the second modification, and accordingly, modification by the surfactant is performed at the same time with the second modification where either the first or the second cationic polyelectrolyte is used.
• modification with said anionic surfactant may be earned out in a separate step after modifications by the first and the second cationic polyelectrolytes, by adding said surfactant at a suitable concentration to a solution where the second modification with the cationic polyelectrolyte was performed, or by collecting the cellulose particles modified by cationic polyelectrolytes for instance by filtration, followed by suspending to an aqueous solution of the anionic surfactant.
• the suspension composed of the aqueous solution of the cationic polyelectrolyte and the cellulose particles may be agitated or shaken during the modification operation. Modification may be carried out at a temperature ranging from 5 to 95 0 C, preferably from 20 to 50 °C. It is moreover preferable to carry out the modification at an ionic strength of less than 0.1 M.
• the cellulose particles are recovered for instance by f ⁇ ltra- tion, and added to a pulp for the production of paper and board.
• the modified cellulose particles may be stored at low temperatures, for instance at +5 0 C, prior to use.
• the particles are added during the production to the pulp at a suitable point of the system, prior to the press, preferably to the short circulation, and particularly preferably near the head box, such as to the suction side of the mixing pump or near the feeding pump of the head box to obtain an amount of the modified cellulose particles in the paper or board of between 0.01 and 50 % by weight.
• Particle sizes of the modified cellulose particles according to the invention used for the production of paper and board preferably ranges between 0.05 and 10 ⁇ m.
• Said modified cellulose particles according to the invention are suitable for both fine papers, and papers comprising mechanical pulp, including LWC, ULWC, MWC, and SC.
• the isoelectric point of the cellulose particles and zeta potential curve as the function of the concentration of the cationic polyelectrolyte used for modification were then determined.
• Serial dilutions were made from the cationic polyacryla- mide (Fennopol K3400R, MW between 6 and 7x10 6 g/mol, charge 1.1 meq/g), and from polyD ADMAC (Salcare SC30, MW > 300 000 g/mol), followed by modifying low amounts of cellulose particles using these dilutions, and determining the zeta potentials of the thus modified cellulose particles.
• the zeta potential of the washed cellulose particles was —19.2 mV. From the curve, suitable concentrations of the cationic polyelectrolytes were selected to obtain the desired zeta potential of +5 mV.
• cellulose particles modified by cationic polyelectrolytes 5.08 g (dry weight) of the cellulose particles prepared and washed as described above were suspended to give a concentration of 1.0 g/1 in a polyD ADMAC solution having a concentration of 0.9 mg/1, while agitating. By this treatment lasting no longer than 30 min, the cellulose particles reached 70 % of the value of the isoelectric point. Then cationic plyacrylamide was added to the polyD ADMAC solution containing the cellulose particles to give a concentration of 1.6 mg/1, and the treatment was continued again while agitating until the zeta potential of the cellulose particles reached the desired value of +5 mV. The treatment time was no more than 30 min.
• a batch of the same size of cellulose particles modified by cationic polyelectrolytes and SDS was prepared. 5.08 g (dry weight) of the cellulose particles prepared and washed as described above were suspended to give a concentration of 1.0 g/1 in a polyD ADMAC solution having a concentration of 0.9 mg/1, while agitating. As above, by this treatment the cellulose particles reached 70 % of the value of the isoelectric point. Then cationic polyacrylamide and SDS were mixed, followed by the addition of this mixture to the polyD ADMAC solution containing the cellulose particles to give the same concentration of the cationic polyacrylamide as above, that is 1.6 mg/1, whereas the amount of SDS was 0.1 % based on the dry weight of the cellulose particles. The treatment of the cellulose particles modified by the first cationic polyelectrolyte was continued in this solution for no longer than 30 minutes, while agitating. The zeta potential of the finished modified cellulose particles was measured to be -15 mV.
• Example 2 Use of cellulose particles modified by cationic polyelectrolytes for the production of paper
• Dewatering times for pulps were determined by the Dynamic Drainage Analyzer instrument, using the following parameters: Wire M 0.15 mesh, duration of pre- treatment 30 s, agitation speed 500 rpm, pressure 0.25 kPa, sample density 1 g/1, sample volume 600 ml. Retentions were calculated on the basis of the data from sheet formation.
• Figure 1 is a graph showing the dewatering time in seconds for pulps containing respectively 6 % and 14 % by weight of cellulose particles of the invention produced according to example 1, comprising cationic po IyD ADMAC, and C-PAM molecules, particles added to one of the pulps moreover comprising sodium dode- cyl sulfate (SDS), whereas controls contain cellulose particles that were either unmodified or modified to zeta potentials of -10 mV and +20 mV with poly- DADMAC alone.
• Figure 1 shows that dewatering of pulps containing modified cellulose particles of the invention may be carried out in a clearly shorter time than that of pulps containing unmodified cellulose particles.
• dewatering is hardly accelerated by the modification of cellulose particles with only a cationic polyelectrolyte having a low molecular weight, but dewatering is only accelerated by cellulose particles comprising both cationic polyelectrolytes with a low molecular weight and those with high molecular weight on the outer surface thereof.
• Figure 2 is a graphical presentation of the retentions of cellulose particles that are either unmodified or modified with a single cationic polyelectrolyte in the formed sheets, for the desired particle contents of 6 % and 14 % by weight, and further, the retentions of cellulose particles modified with two cationic polymer in the formed sheets, for the desired particle contents of 6 %, 14 %, and 22 % by weight.
• the retention of .cellulose particles is hardly improved by modification thereof by polyD ADMAC alone to obtain a zeta potential value of +20 mV, and in fact the retention of unmodified cellulose particles is 10 % better for a filler content of 14 % by weight.
• cellulose particles are however clearly improved by weaker cationization with polyD ADMAC alone to a zeta potential value of - 10 mV.
• Best retentions are however obtained by incorporating cellulose particles modified by both cationic polyelectrolytes with a low molecular weight and those with a high molecular weight according to the present invention to the sheets.
• the best retention of nearly 100 % is attained by using the modified cellulose particles of the invention for a filler content of 14 % by weight, the outer surface of said particles comprising SDS in addition to both cationic polyelectrolytes with a low molecular weight and those with a high molecular weight.

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  • 2006-09-05 FI FI20065550A patent/FI119481B/fi active IP Right Grant
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