WO2007131874A1

WO2007131874A1 - Process for making paper and paperboard

Info

Publication number: WO2007131874A1
Application number: PCT/EP2007/054229
Authority: WO
Inventors: Christina Northfleet; Michael Singh; Kenneth Charles Symes; Robert Cockcroft; Valerie Reynolds; Andrew Mccann; Gary Peter Richardson; Simon Donnelly; Fritz Herren
Original assignee: Ciba Holding Inc
Priority date: 2006-05-12
Filing date: 2007-05-01
Publication date: 2007-11-22
Also published as: GB0609477D0

Abstract

A process of making paper or paper board which comprises providing a cellulosic suspension comprising cellulosic fibres and optionally fillers, including a strength additive, and then dewatering the cellulosic suspension on a wire or mesh to form a sheet and drying the sheet, in which the strength additive is a polymer comprising i) a synthetic polymeric component; and ii) a protein component comprising a polysaccharide binding domain protein, preferably a cellulose binding domain protein, wherein the cellulosic suspension a) further comprises recycled cellulosic material and/or b) has a conductivity of at least 1500 μS (micro Siemens). Significant improvements in strength have been achieved by this process.

Description

Process for Making Paper and Paperboard

The present invention relates to a process for making paper and paperboard with improved dry strength. In particular the process overcomes the deleterious effects of cellulosic suspensions with high conductivity and/or containing recycled cellulosic material.

It is known that the paper strength characteristics tend to depend on the strength of individual cellulosic fibres and the ability to form strong bonds between cellulosic fibres and also the network of cellulosic fibres forming the cellulosic sheet. Poor quality cellulosic fibres can result in diminished strength characteristics. Furthermore, a non uniform distribution of cellulosic fibres that results in poor formation will also compromise strength of the cellulosic sheet that is formed.

It is known to add polymeric additives to improve both the wet strength characteristics during papermaking and the dry strength characteristics of the paper thus formed. Typically, such polymeric additives, described herein as resins that are commercially available include natural, partially modified natural, or synthetic water-soluble polymers, such as cationic starches, anionic starches, sodium carboxymethyl cellulose, polyacrylamides, anionic polyacrylamides and low molecular weight cationic polymers such as PoIyDADMAC (diallyl dimethyl ammonium chloride), polyamide amine epichlorohydrin, polyamine epichlorohydrin, polydicyandiamide.

US-A-3, 311 ,594, discloses the preparation of aminopolyamide-epichlorohydrin APAE wet strength resins. The resins are prepared by reacting epichlorohydrin with aminopolyamides, and the APAE resins can exhibit storage problems in concentrated form and gel during storage, although generally to a lesser extent than the GPA resins. For this reason it has been common practice to dilute the APAE resins to low solids levels to minimize gelation. The APAE resins impart dry and wet strength to paper.

Glyoxylated polyacrylamide-diallyldimethyl ammonium chloride copolymer resins are known for use as dry strength and temporary wet strength resins for paper. US-A-4,605,702 teaches the preparation of a wet strength additive by glyoxalating an acrylamide copolymer having a molecular weight of about 500 to 6000. The resulting resins have limited stability in aqueous solution and gel after short storage periods even at non-elevated temperatures. Accordingly, the resins are typically supplied in the form of relatively dilute aqueous solutions containing only about 5-10 wt % resin.

US-A-5783041 describes a method for improving the dry strength characteristics of paper by adding to a pulp slurry during a paper-making process a mixed resin solution containing an aminopolyamide-epichlorohydrin resin, a glyoxylated acrylamide-diallyldimethyl ammonium chloride resin, and a high charge density cationic resin.

US-A-3,556,932 descibes water-soluble, glyoxalated, acrylamide polymer wet strength agents. These wet-strength agents are made from polymers with molecular weights ranging from less than about 1 ,000,000, although preference is given to polymers with molecular weights less than about 25,000. The polymers are reacted with glyoxal in a dilute, aqueous solution to impart - CONHCHOHCHO functionalities onto the polymer and to increase the molecular weight of the polymer through glyoxal cross-links. Low molecular weight polymers and dilute solutions are required to impart at least a 6% - CONHCHOHCHO functionality to the polymers without infinitely cross-linking, or gelling, in which condition the polymers are useless for wet-strength applications. Even at these low solids concentrations (dilute conditions), cross- linking continues and limits the shelf life of the product. For example, commercial products, supplied as 10% solid solutions, gel within about 8 days at room temperature.

US-A-5041503 attempts to overcome the disadvantages of glyoxylated polyacrylamides by producing them as microemulsions. The polymer molecules are said to be kept separate in the microemulsions thereby preventing cross- linking and thus enabling higher molecular weight polymers to be used. The polymers are said to be capable of providing improved or wet and dry strength in papermaking even when the polymers are cross-linked.

WO-A-01 /34091 describes the cross-linking of polysaccharides using a polysaccharide binding domain fusion protein. The cellulose binding domain fusion proteins are specifically described. Cellulose containing materials such as paper and textiles exhibiting increased wet strengths and/or elasticity are described.

An article by Takuya Kitaoka et al, entitled "Novel paper strength additives containing cellulose binding domain of cellulase", J Wood Sci (2001 ) 47: 322- 324 describes covalently bonding cellulose binding domain proteins to anionic polyelectrolytes which are modified so that they are reactive towards the protein. The anionic polyelectrolytes contain carboxylic groups which are not directly reactive with the protein and which are first reacted with a carbodiimide hydrochloride compound. The post treated reaction product was then combined with the cellulose binding domain protein to produce a synthetic polymer covalently bonded to the protein. The reaction product was found to be less effective as a dry or wet strength additive than conventional dry and wet strength additives.

Chemical Abstracts reference (accession number 2004: 222096) describes a similar disclosure to the Journal of Wood Science (2001 ) 47: 322-324. GB 1471226 provides a process for the preparation of fine paper using an aqueous dispersion of modified cellulosic fibres, formed by treating cellulosic fibres with a cross-linking agent, forming at least a partly cross-linked cellulose mixture and then treating it with a polymer containing hydroxyl and/or amino groups.

EP-A-1054103 describes a paper coating composition that has particular realisable properties and containing an intercalated vegetable protein and an acrylate polymer as adhesive binder.

WO-A-01 /38637 refers to the use of CBD polysaccharide adducts in papermaking and is not concerned with compounds containing CBD and covalently bonded to acrylate polymers.

GB-A-2376017 refers to the synthesis and use of a CBD-polysaccharide adduct in papermaking.

In recent years there has been a trend towards recycling the process water used in papermaking processes, such that a high proportion of the white water is returned into the process to minimise the environmental impact in polluting watercourses and also the demand on fresh mains water introduced into the papermaking process is reduced. Recycling of process water tends to result in a build-up of ionic substances, such as so called anionic trash including lignosulphonat.es. Consequently the level of ionic substances contained in the process water tends to be much higher in closed systems. Conventional ionic dry and wet strength resins employing electrostatic attraction as a means to bind to cellulose have been found to be less effective in closed loop systems.

International application number PCT/EP 2005/011833 (attorney docket number 22369) (unpublished at the priority date of the present application), published as WO 2006 050865, discloses a polymer comprising i) a synthetic polymeric component that has been formed from an ethylenically unsaturated water-soluble or potentially water-soluble monomer and an ethylenically unsaturated monomer carrying a reactive group wherein the reactive group is directly reactive with a cellulose binding domain protein; and ii) a protein component comprising a cellulose binding domain protein (CBD). This reference describes using such polymers as dry or wet strength resins in the papermaking process. However, this reference does not describe improving strength in processes employing furnishes of very high conductivity, i.e. at least 1500μS (micro Siemens), often at least 2500μS or 3500μS or more.

In the interests of conserving natural sources of cellulosic material, another important trend in recent years has been to incorporate recycled (i.e. waste) cellulosic material into the paper or board furnish. In papermaking, employment of such recycled material into the stock can bring about significant disadvantages in regard to the strength of paper that is formed. Conventional strength aids have been used in order to counter these problems. However, it is normally quite difficult to consistently achieve paper or board having acceptable dry strength. Typically waste furnishes are harder to increase in strength due to the shorter fibres, that can be formed as a result of mechanical attrition or chemical breakdown of the waste paper in the recycling process, build up of electrolytes which can occur in recycled waste paper, and because of the higher quantities of fines which have a high surface area and which are detrimental to strength.

It would therefore be desirable to provide a means of obtaining paper or paperboard with improved dry strength from a furnish that has very high conductivity i.e. at least 1500μS or a furnish that contains recycled cellulosic material, especially significant levels of recycled or waste paper or other cellulosic products. In many cases the furnish that contains recycled cellulosic material will also exhibit very high conductivity due to the high electrolyte resulting from the recycling of waste paper. The present invention provides a process of making paper or paper board which comprises providing a cellulosic suspension comprising cellulosic fibres and optionally fillers, and then dewatering the cellulosic suspension on a wire or mesh to form a sheet and drying the sheet, in which a strength additive is included in the cellulosic suspension or is applied to the formed sheet and in which the strength additive is a polymer comprising i) a synthetic polymeric component; and ii) a protein component comprising a polysaccharide binding domain protein, preferably cellulose binding domain protein (CBD), wherein the cellulosic suspension a) further comprises recycled cellulosic material and/or b) has a conductivity of at least 1500 μS (micro Siemens).

Paper or board having significantly improved dry strength can be obtained using these difficult furnishes when employing this strength additive comprising polymeric component and polysaccharide binding domain protein, especially the cellulose binding domain protein, by comparison to conventional dry strength additives. In addition paper or board having equivalent dry strength to conventional strength additives can be achieved using a significantly lower dose. The process enables paper and board to be prepared from high conductivity furnishes or stocks containing recycled cellulosic material in which the paper or board exhibit improved mechanical properties such as tensile index values.

In addition we also find improvements in wet web strength during the papermaking process by using i) a synthetic polymeric component; and ii) a protein component polysaccharide binding domain protein, preferably cellulose binding domain protein (CBD) wherein the cellulosic suspension a) further comprises recycled cellulosic material and/or b) has a conductivity of at least 1500 μS (micro Siemens).

The ability of the wet web of paper to resist breakage can be critical to the efficiency of the papermaking process. It is frequently considered necessary to increase the proportion of long fibres such as softwood kraft or CTMP fibres. However, this at a disadvantage that this would tend to make the paper more floccy and nonuniform which can also impair strength. Low or variable wet web strength is sometimes due to the effects of surfactants in the furnish. Low initial wet strength and low wet web strength can often be found when the papermaking furnish is a high conductivity and /or especially when the furnish comprises recycled waste paper. The process of the present invention employing the polymer comprising synthetic polymeric component and protein component brings about improvements in the wet web strength.

We have also found that the process of the present invention provides paper with improved initial wet strength. Initial wet strength is often regarded as increased strength of treated paper, apparent initially after complete wetting and which diminishes within a few minutes of hours.

The invention also concerns the use of a polymer for improving strength, preferably dry strength or initial wet strength, of paper or paperboard which is manufactured in a process from a cellulosic suspension, in which the polymer comprises i) a synthetic polymeric component; and ii) a protein component comprising a polysaccharide domain protein, preferably a cellulose binding domain protein, wherein the cellulosic suspension a) further comprises recycled cellulosic material and/or b) has a conductivity of at least 1500 μS (micro Siemens).. In a further aspect invention concerns the use of a polymer for improving wet web strength during a papermaking process in which paper or paperboard is manufactured in a process from a cellulosic suspension, in which the polymer comprises, i) a synthetic polymeric component; and ii) a protein component comprising a polysaccharide domain protein, preferably a cellulose binding domain protein, wherein the cellulosic suspension a) further comprises recycled cellulosic material and/or b) has a conductivity of at least 1500 μS (micro Siemens).

The polymeric strength additive may be a mixture of the synthetic polymeric component and protein component but preferably the two components are in close association. Preferably the synthetic polymeric component has been formed from an ethylenically unsaturated water-soluble or potentially water- soluble monomer and an ethylenically unsaturated monomer carrying a reactive group, in which the reactive group is directly reactive with the polysaccharide binding domain protein e.g. cellulose binding domain protein. More preferably the synthetic polymeric component has been chemically bonded to the protein component. This bonding may be ionic but it is especially preferred that the two components are covalently bonded together. It is particularly preferred that the cellulose binding domain protein is covalently bonded to the synthetic polymer component through one or more of the reactive groups.

The strength additive polymer may comprise a protein component which is covalently bonded to one or more synthetic polymeric components. It may be desirable that a single protein moiety is bonded to two or more synthetic polymer molecules. In some instances a protein molecule may be bonded to several synthetic polymer chains, for instance five or six or even up to ten or more polymer chains. Alternatively the synthetic polymer component could be bonded covalently to at least two protein components. In this form a single polymer chain may be bonded to a multiplicity of protein components, for instance five or six and may be up to ten or more.

In a further form at least two synthetic polymer components may be covalently bonded to at least two protein components. It may be desirable for several synthetic polymeric chains to be bonded to several protein moieties. Therefore the polymer may exist as a branched on network structure.

The mole reaction ratio of the reactive groups in the synthetic polymeric component to the polysaccharide binding domain protein, such as cellulose binding domain protein, will generally be in the range of 1 :10 to 10:1 on a molar basis, preferably 4:1.

The ethylenically unsaturated monomer containing the reactive group may be any suitable monomer that will copolymerise with the water-soluble or potentially water-soluble monomer. The reactive group may be any suitable reactive group provided that it is directly reactive with a polysaccharide binding domain protein, preferably cellulose binding domain protein. By directly reactive we mean that under suitable reaction conditions the reactive group will be reactive directly with at least one group on the polysaccharide binding domain protein, preferably cellulose binding domain protein and that it is unnecessary to chemically modify the group in order to render it reactive towards the polysaccharide binding domain protein, such as cellulose binding domain protein. Particularly suitable reactive groups include epoxides, isocyanates, amido methylol groups. Particularly suitable monomers which carry the reactive group include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, N- methyolacrylamide and 3-isopropenyl dimethyl benzyl isocyanate. Especially preferred amongst these are glycidyl acrylate, glycidyl methacrylate and 3- isopropenyl dimethyl benzyl isocyanate. The ethylenically unsaturated monomer can be prepared synthetically from a suitable starting material and using synthetic catalysts or alternatively by biocatalytically converting a suitable substrate that is capable of being converted into the ethylenically unsaturated monomer. Typically the substrate is brought into contact with a biocatalyst and thereby converting the substrate into the ethylenically unsaturated monomer containing the cellular material and optionally components of a fermentation. Alternatively the ethylenically unsaturated monomer can be produced as a product of the fermentation process.

The polysaccharide binding domain proteins may be any suitable binding domain depending upon polysaccharide contained within the cellulosic suspension. Typically the polysaccharide binding domain protein can be any of cellulose binding domain proteins (CBD), starch binding domain proteins, maltodextrin binding domain proteins, dextran binding domain proteins, β-glucan binding domain proteins or chitin binding domain proteins.

The polysaccharide binding domain protein is preferably a cellulose binding domain protein which maybe be derived from a microbial source and furthermore it may, for instance, be any of the CBD's described in WO-A- 01/34019. The polysaccharide binding domain protein can be a native protein, a genetically modified protein and/or a recombinant protein. Suitably cellulosic binding domain protein may be obtainable from a microorganism, which may include microorganisms from genera such as Cellulomonas, Trichoderma, Clostridium, Microbispora, Neurospora, Penicillium, Pseudomonas, Phanerochaete, and any of the numerous other (40 or so) species which contain these binding domain proteins. Preferably the cellulose binding domain proteins may be selected from the group consisting of Clostridium cellulovorans. Cellulomonas fimi. Trichoderma reesei and Microbispora. Bispora. Particularly preferred are cellulosic binding domain proteins obtained from Clostridium cellulovorans species. The cellulosic binding domain protein may be in the form of aggregates that are formed by intermolecular hydrophobic interactions of exposed hydrophobic patches of the cellulose binding domain protein or alternatively it may be in nonaggregated forms.

The water-soluble ethylenically unsaturated monomer desirably has a solubility in water of at least 5g monomer per 100 mis of water at 25°C. When the monomer is potentially water-soluble it can be modified, for instance after polymerisation, to provide a monomer unit that would have been soluble in water, for instance having the above defined solubility.

Suitable water-soluble or potentially water-soluble monomers are selected from the group consisting of acrylamide, methacrylamide, N-alkylacrylamides, hydroxy alkyl (meth) acrylates (e.g. hydroxyethyl acrylate), N-vinylpyrrolidone, vinyl acetate, vinyl acetamide, acrylic acid (or salts thereof), methacrylic acid (or salts thereof), itaconic acid (or salts thereof), crotonic acid (or salts), 2- acrylamido-2 -methyl propane sulfonic acid (or salts thereof), (meth) allyl sulfonic acid (or salts thereof), vinyl sulfonic acid (or salts thereof), dialkyl amino alkyl (meth) acrylates or quaternary ammonium or acid addition salts thereof, dialkyl amino alkyl (meth) acrylamides or quaternary ammonium and acid addition salts thereof and diallyl dialkyl ammonium halide (e.g. diallyl dimethyl ammonium chloride). Preferred cationic monomers include the methyl chloride quaternary ammonium salts of dimethylamino ethyl acrylate and dimethyl aminoethyl methacrylate.

Desirably the synthetic polymeric component is formed from a monomer blend comprising water-soluble or potentially water-soluble ethylenically unsaturated monomer and up to 20 mole% of an ethylenically unsaturated monomer carrying a reactive group (as defined previously). The preferred amount of monomer containing the reactive group is generally up to 10 mole%, more preferably up to 5 mole%. Usually the reactive group containing monomer will be present in an amount of at least 0.0001 mole%, preferably at least 0.001 mole% and more preferably at least 0.01 mole%. The synthetic polymeric component may be formed entirely of the monomer containing the reactive group and the water-soluble or potentially water-soluble monomer. Typically the water-soluble or potentially water-soluble monomer may be present in amount of up to 99.9999 mole%, preferably up to 99.999 mole% and more preferably up to 99.99 mole%.

It may be desirable to include other ethylenically unsaturated monomers, for instance acrylic esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, iso butyl acrylate, iso butyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, stearyl acrylate and stearyl methacrylate; styrene; halogenated monomers such as vinyl chloride and vinylidene chloride. The amount of other monomer will typically be up to 50 mole% although usually will be up to 20 mole%, and more desirably will be less than 10 mole%.

More preferably the synthetic polymeric component is formed from a monomer blend comprising 50 to 99.995 mole% water-soluble or potentially water-soluble ethylenically unsaturated monomer; 0.005 to 2 mole% ethylenically unsaturated monomer carrying a reactive group; and 0 to 50 mole% other ethylenically unsaturated monomer. More preferably still the amount of water-soluble or potentially water-soluble monomer will be between 80 (especially above 90) and 99.995 mole% and the amount of other ethylenically unsaturated monomer (if included) will be up to 20 mole% (especially below 10 mole%).

A particularly preferred synthetic polymeric component is formed from a monomer blend comprising acrylamide and a reactive monomer selected from glycidyl methacrylate and 3-lsopropenyl-α,α-dimethylbenzylisocyanate. Especially preferred is the polymer in which the amount of glycidyl methacrylate or 3-lsopropenyl-α,α-dimethylbenzylisocyanate is as defined previously for the reactive group containing monomer. A particularly preferred polymer will contain between 0.005 and 5 mole% glycidyl methacrylate or 3-lsopropenyl-α,α- dimethylbenzylisocyanate the remainder being acrylamide.

The synthetic polymeric component used in the invention may have a weight average molecular weight as low as a few thousand, for instance 6000 or 7000 or may be very high, for instance several tens of millions. However, we have found that the polymer functions particularly well as a dry strength additive in the paper making process of the invention if the synthetic polymeric component has a weight average molecular weight of below one million. More preferably the weight average molecular weight will be below 500,000, especially within the range 50,000 to 200,000, in particular between 100,000 and 150,000.

The strength additive may be prepared in accordance with the description given in international application number PCT/EP 2005/011833. A typical preparation is given in the Examples.

The synthetic polymeric component may be formed by combining the aforementioned monomers to provide a monomer blend and then subjecting this monomer blend to polymerisation conditions. Typically this may include introducing polymerisation initiators and/or subjecting the monomer blend to actinic radiation, such as ultraviolet light and/or heating the monomer blend. Preferably the monomer blend is dissolved or dispersed in an aqueous medium and water-soluble initiators are introduced into the aqueous medium in order to effect polymerization. It would be possible to effect polymerization using a variety of conventional initiator systems. For instance it is common practice to polymerise water soluble monomers using redox initiator couples, in which radicals are generated by admixing with the monomer a redox couple which is a reducing agent and an oxidising agent. It is also conventional practice to use either alone or in combination with other initiator systems a thermal initiator, which would include any suitable initiator compound that releases radicals at an elevated temperature. Other initiator systems include photo and radiation induced initiator systems, which require exposure to radiation to release radicals thereby effecting polymerisation. Other initiator systems are well known and well documented in the literature.

Typically redox initiators include a reducing agent such as sodium sulphite, sulphur dioxide and an oxidising compound such as ammonium persulphate or a suitable peroxy compound, such as tertiary butyl hydroperoxide etc. Redox initiation may employ up to 10,000 ppm (based on weight of monomer) of each component of the redox couple. Preferably though each component of the redox couple is often less than 1000 ppm, typically in the range 1 to 100 ppm, normally in the range 4 to 50 ppm. The ratio of reducing agent to oxidizing agent may be from 10:1 to 1 :10, preferably in the range 5:1 to 1 :5, more preferably 2:1 to 1 :2, for instance around 1 :1.

Polymerisation may also be effected by employing a thermal initiatior alone or in combination with other initiator systems, for instance redox initiators. Thermal initiators would include any suitable initiator compound that releases radicals at an elevated temperature, for instance azo compounds, such as azobisisobutyronitrile (AZDN), 4,4'-azobis-(4-cyanovalereic acid) (ACVA). Typically thermal initiators are used in an amount of up 10,000 ppm, based on weight of monomer. In most cases, however, thermal initiators are used in the range 100 to 5,000 ppm preferably 200 to 2,000 ppm, usually around 1 ,000 ppm.

The reaction of the polysaccharide binding domain protein, preferably cellulose binding domain protein, with the synthetic polymeric component is desirably achieved by raising the temperature of the mixture for a suitable period of time. Suitably, the reaction mixture is subjected to a temperature of between 20 and 70°C for a period of at least 20 minutes. The reaction may proceed over a number of hours, for instance up to three hours but it will not usually exceed two hours. Preferably the reaction temperature should be held at between 50 and 70°C, particularly around 60°C, for at least 30 minutes and usually up to 90 minutes.

The reaction product of the polysaccharide binding domain protein, which is preferably a cellulose binding domain protein, and the synthetic polymeric component may be provided and used as an aqueous liquid containing the reaction product dissolved therein. Alternatively, it may be desirable to provide the reaction product as a particulate dry product. This may be achieved by, for instance forming a thin film and allowing the water to evaporate, followed by pulverizing or comminuting the thin film to form a powdered product. It may be desirable to elevate the temperature in order to assist the evaporation of the water.

In one preferred form, the reaction product of the polysaccharide binding domain protein, preferably a cellulose binding domain protein, and the synthetic polymeric component is prepared in bead form. This can be achieved by suspending an aqueous solution of the reaction product in a water immiscible liquid, such that the aqueous reaction product exists as droplets dispersed in the water immiscible liquid, and then dehydrating the aqueous reaction product droplets to form substantially dry beads of the reaction product. Alternatively, the reaction mixture containing the unreacted polysaccharide binding domain protein, such as cellulose binding domain protein, and synthetic polymeric component may be dispersed directly into a water immiscible liquid and subjected to reaction conditions followed by dehydration as above. Dehydration may be assisted by using an elevated temperature, for instance between 20 or 30 and 70 or 80 °C. It may also be desirable to dehydrate the dispersed reaction product by subjecting the dispersion to reduced pressure or vacuum. This is frequently referred to as azeotropic dehydration. Desirably one or more surfactants and/or dispersion stabilisers may be introduced into the water immiscible liquid.

The size of the substantially dry particles is dictated by the size of the dispersed aqueous phase particles in the immiscible liquid. It is often desired that the dry particles are beads that have a size of at least 30 microns, often at least 100 microns, for instance up to 500 microns or up to 1 mm or even 2mm or larger. With particles of this size, the substantially dry particles will be separated from the water immiscible liquid by filtration, centrifugation or other conventional separation methods and may be subjected to further drying after the separation. This further drying may be by solvent exchange but is preferably by warm air, for instance in a fluidised bed.

The beads should be dried sufficiently that they are non-sticky and are generally dried to a moisture content that is in equilibrium with the environment or is drier than this.

The polymeric stabiliser is generally an amphipathic stabiliser, for instance, formed from hydrophilic and hydrophobic acrylic monomers. Suitable surfactants, non-aqueous liquids and polymeric stabilisers, and suitable azeotroping conditions, are described in, for instance, EP-A-128661 and EP-A- 126528. The stabilisers described in GB-A-2,002,400 or, preferably, GB-A- 2,001 ,083 or GB-A-1 ,482,515 are particularly preferred.

The immiscible liquid is non-aqueous and desirably includes liquid that can form an azeotrope with water. Often the water immiscible liquid is a blend of a relatively high boiling liquid that remains in the dispersion and a low boiling liquid that is azeotroped from the dispersion. The temperature at which azeotroping occurs is generally below 100⁰C and is controlled by the choice of liquid and, especially, the pressure at which the distillation is conducted. Generally the distillation is conducted under reduced pressure and in some cases, in order to avoid possible damage to the protein component, it is preferably that the azeotroping (dehydration under reduced pressure) occurs at a maximum temperature of not more than 80⁰C, often below 70 ⁰C and most preferably below 50 °C. For instance by applying a relatively high vacuum it is possible to azeotropic at very low temperatures, for instance as low as 20 or 30 ⁰C. Sodium sulphate or other salt may be added to allow the azeotroping temperature to refer the reduced.

In the process of the present invention the furnish (cellulosic suspension) will either have very high conductivity of at least 1500μS or it will contain recycled cellulosic material or both. When the suspension has a very high conductivity this can be and usually is as a result of relatively high levels of electrolyte in the cellulosic suspension. The electrolyte in the suspension can be of organic origin and so can be anionic trash from the original cellulosic pulp or recycled cellulosic suspension. Alternatively or additionally it can be of in organic origin and so it can be due to partial association of the alkaline filler such as calcium sulphate or carbonate, or the hardness of the water. Electrolyte can be added deliberately.

By referring to a cellulosic suspension having high conductivity and usually high electrolyte content we mean that the white water that drains from the suspension has high conductivity. Thus as stated previously the conductivity of a white water would be above 1500μS, and often much higher. Preferably the cellulosic suspension (and therefore white water drained therefrom) has a conductivity often at least 2000μS and more preferably at least 2500μS or more. In some cases the conductivity of the cellulosic suspension is at least 3000μS and more preferably at least 3500μS or higher. The conductivity may be as high as 10,000μS but is usually up to 5000μS. The conductivity can be measured by conventional techniques. A TetraCon 325 standard conductivity cell connected to a Cond 34Oi conductivity pocket meter both produced and supplied by WTW (Wissenschaftlich-Technische Werkstatten GmbH). The cellulosic suspension of the present invention often also contains high levels of anionic trash. Typically the cellulosic suspension may be formed from crude pulp. The cellulosic component may contain a significant amount of a mechanical pulp (such as the ground wood) and/or a thermo- mechanical pulp and/or deinked waste is at least 10% and usually at least 50% and is some cases at least 80% and is some preferred instances would be the entire amount of the cellulosic material in the suspension.

Where the conductivity is due to electrolyte content the amount of electrolyte can, alternatively or additionally, arise from alkaline filler, especially calcium sulphate, that dissolves slightly into the suspension. Accordingly other suspensions to which the invention is usually applied are suspensions that contain at least 5%, and generally 10 to 50% (based on the dry solids content of the suspension) calcium sulphate or other very slightly soluble alkaline filler.

The invention is of particular value when using such cellulosic material and/or filler in a closed mill in which the white water from the drainage stage is repeatedly recycled for diluting the thick stock to make the thick stock suspension that is often treated with retention aid and subsequently drained, to form paper or board. Prolonged recycling of white water, as a result of the mill being substantially entirely closed in extreme cases can cause accumulation of electrolyte and as a result high conductivity.

When there is low conductivity (i.e. below 1500μS) a mill will often achieve adequate dry strength with conventional polymeric strength aids. However, this is not so when the conductivity is at least 1500μS. Therefore, it is unexpected that the present invention provides a process where high dry strength is achieved at high conductivity to the same degree as low conductivity suspensions. The invention is also of value when electrolyte is deliberately added to the suspension, which subsequently may be subjected to prolonged recycling. For instance NaCI or other monovalent metal salt (or other water soluble electrolyte) can be added to a suspension or thick stock to provide a conductivity value such that the strength additive of the process is suitable by comparison to conventional strength aids. For instance NaCI may be added when the pulp is a dirty pulp having high cationic demand, thereby suppressing the cationic demand (as measured by titration against a cationic polymer) and making it suitable for use in the invention.

Another instance when the invention is of particular value is in the production of liner board from a suspension that has been treated with a large amount of alum.

The invention is also of value in processes where relatively low molecular weight cationic high charge density polymeric coagulants or alternatively inorganic coagulants such as alum are added to thick stock or the thin stock.

The process of the present invention provides exceptional dry strength characteristics also when the furnish (cellulosic suspension) contains at least some recycled (for instance waste) cellulosic material irrespective of the conductivity. Typically it is normally not possible with such furnishes to obtain high dry strength using conventional strength additives. Typically the recycled or waste cellulosic material can be derived from usual sources. Typically this can be post consumer waste which can include old newspapers, old corrugated cardboard, mixed office waste, catalogues, magazines, waste folding boxboard etc. Pre consumer waste usually comes from the paper manufacturing and converting industries and also encompasses the aforesaid materials. The pre- consumer waste is usually higher quality than the post consumer waste. The amount of recycled cellulosic material in the cellulosic suspension can be for instance manufactured paper that can contain up to 100% of recycled materials depending on the paper grade produced. Grades demanding higher strength properties typically use a quantity of virgin hardwood or softwood fibres to increase strength in cases up to 50% or even higher.

Preferably, when the furnish contains high levels of recycled cellulosic material it will also have a high conductivity, usually as a result of high levels of electrolyte present in the recycled cellulosic component. Typically the furnish would have a conductivity of at least 1500μS or higher for instance as described previously in regard to furnishes of high conductivity.

According to the process the strength additive may typically be included in the wet end of the paper or paperboard making process. One possibility is to include the strength additive with any other stock components, for instance cellulosic feedstock. It may be included in the mixing chest all the blend chest of the paper or board making process or into the thick stock prior to dilution. Alternatively this dry strength additive is added into the thin stock. This may be immediately after dilution of the thick stock or possibly after one of the fan pumps. The additive may be included after the centri screen but before draining but in general it will be added before the centri screen. Usually the strength additive would be added to the cellulosic suspension in an effective amount up to 20 kg per tonne based on the dry weight of the cellulosic suspension. Typically the additive would be included in an amount between 500 grams per tonne and 20 kg per tonne, preferably between 1 and 5 kg per tonne.

The polymeric strength additive may be supplied as and used as an aqueous solution. In one form the polymer may be provided as a relatively concentrated aqueous solution, for instance having a concentration of above 2% by weight, for instance at least 5 or 10% by weight. The aqueous polymer solution may be used directly or instead it may be diluted to a relatively dilute concentration before use, for instance up 1 % by weight or less, for instance between 0.05 and 0.5 %, such as 0.1 % by weight. The polymer product can be in particulate form, for instance as a powder but preferably as a bead. The particulate polymer may be dissolved into water to form an aqueous solution having a concentration for instance as described above. In one further form, it may be desirable to use the particulate polymer directly in the process. Preferably the particulate polymer would be in the form of beads which are introduced into the process directly.

In addition to introducing the strength additive into the wet end alternatively it may be applied to the surface of the formed sheet. The polymeric strength additive may be applied at the size press, for instance either as a solution as supplied our diluted with water using a degraded starch to delude the polymer further. In some cases it may be preferred to use the more dilute solution since this may have a tendency to penetrate the paper and to act on the paper as a whole and not just the surface. The amount of additive may be for instance up to 10 g/m² starch and addition levels of polymer comprising protein and synthetic polymer e.g. CBD polymeric adduct being for instance up to 10%.

However as little as 1 g/m² starch may be applied e.g. to a linerboard (10 kg per tonne for a 100 g/m² linerboard).

Other methods of applying the composition of polysaccharide binding domain protein, preferably CBD, and synthetic polymer either as a strength aid include the use of a spray boom. When the protein such as CBD and polymer composition is a strength aid as stated previously it is preferable that it is in a dilute solution for some applications in order to a permit better penetration. In other circumstances it may be desirable to apply the protein e.g. CBD and composition neat or in conjunction with a starch. The protein, for instance CBD, polymeric composition may in some cases be more effective when it is sprayed on the wet sheet for instance after the wet line on the wire. Alternatively it could be sprayed before the press section although care must be taken in order to prevent removal by passing it through the press. A further possibility is to apply the protein, such as CBD, composition after the press section back-end be taken to avoid rehydration of the sheet which would reduce the effectiveness of the presses. A still further alternative can be to apply the protein e.g. CBD, composition at the calendar stack.

If a multi-ply board is being produced, a preferred place to apply the polysaccharide binding domain protein composition, e.g. CBD composition, can be just before the two (or more) sheets are joined together. These sheets are still wet webs and are typically joined prior to the press section on a paper machine. This is usually achieved by applying a glue (starch) to the ply joint and the protein composition, e.g. CBD composition, could desirably be added to the starch solution.

The strength additive may also be used to improve the re wet strength of a sheet of paper.

The strength additive used in the process of the invention may be prepared by reacting the protein component comprising the polysaccharide binding domain protein, preferably cellulose binding domain protein, with the synthetic polymeric component. Paper having particularly good dry strength properties can be produced by the process when the strength additive has been obtained by reacting polysaccharide binding domain protein, preferably cellulose binding domain protein, in an aggregated form, for instance as the dimer. Usually at least one synthetic polymer chain will become bonded to each protein component, such as cellulose binding domain component, of the aggregated protein. The aggregated polysaccharide binding domain protein component, preferably cellulose binding domain protein component, of the reaction product can then be converted into the non-aggregated form whilst covalently bonded to the synthetic polymeric component. This can provide the advantage that the synthetic polymer becomes bonded to the protein remotely from the cellulose binding site. This may create a product which has improved binding capacity to cellulosic fibres. Alternatively, it may be desirable to employ a strength additive that has been prepared by reacting the polysaccharide binding domain protein, preferably a cellulose binding domain protein, whilst in a non-aggregated form with the synthetic polymeric component followed by converting the protein component e.g. cellulose binding domain protein component into the aggregated form. Such aggregation of the reaction product may be advantageous because it could bring about structuring of the polymer, which for certain applications may be desirable.

The paper or board making process using the additive may also use further additives that are conventionally used, such as fixatives. In the process it will often also be desirable to include other additives in order to achieve effective drainage, retention and formation. Typically one or more polymeric retention aids and other drainage/retention additives such as siliceous microparticulate material can be used for this purpose. The additives such as cationic polymers and bentonite may be added in accordance with the description of EP-A- 235893, commercialised as Hydrocol® by Ciba Specialty Chemicals. The process of the present invention may be used with any conventional retention/drainage aids and process parameters known in the art.

The following examples illustrate the invention.

Examples

Example 1. Polymer Synthesis Information

General Method

1. Into a suitable reaction vessel place water, and diethylenetriaminepentaacetic acid, penta sodium salt (DETAPA)

2. Raise the temperature of the contents and maintain at 80 ⁰C. 3. Add initiator (1 ) to reaction vessel

4. Introduce a solution of the monomer and also a solution of initiator(2) into the reaction vessel immediately after the introduction of initiator [1].

5. After all that monomer and initiator have been introduced continued stir the contents of the reaction vessel for a further 30 minutes maintaining a temperature of 8O⁰C.

Synthesis of an Acrylamide:Glycidyl Methacrylate Polymer (99.99:0.01 mole ratio) (T841 )

Vessel : Water 350.Og

(DETAPA) @6% 0.5mls

(acetic acid to ~pH5)

Initiator (1 ) Ammonium persulphate 0.431 g in 10 mis water

Monomer: Acrylamide @50% 396.Og

Glycidyl methacrylate @97% 0.0396g

Water 192.46g

Initiator (2)

(2.25 hour feed): Ammonium persulphate 0.569g in 50 mis of water Synthesis of an Acrylamide: 3-lsopropenvl-α,α-dimethvlbenzylisocvanate Polymer (99:1 mole ratio) (T841 )

Vessel : Water 350.Og

(DETAPA) @6% 0.5mls (acetic acid to ~pH5)

Initiator (1 ) Ammonium persulphate 1g in 10 mis water

Monomer: Acrylamide @50% 396.Og

3-lsopropenyl-α,α-dimethylbenzylisocyanate @97% 5.97g Water 185.53g

Initiator (2)

(2.25 hour feed): Ammonium persulphate 1 in 50 mis of water

Example 2. Reaction of the Polymer with CBD

Reaction of a Polyacrylamide-Glvcidylmethacrylate (99.99:0.01 mol ratio) Copolymer with CBD (N 10 Sample)

Cellulose binding domain (obtained from Clostridium cellulovorans) (0.0241 parts) is dissolved in 8M urea solution (34.1 parts) and added to 18.31 parts of an aqueous copolymer solution of polyacrylamide-glycidylmethacrylate (99.99:0.01 mol ratio, Molecular weight average (Mw) of 217,000), which contained 3.18 parts polymer. The mixture is heated to 6O⁰C for 1 hour.

Reaction of a Polyacrylamide- 3-lsopropenyl-α,α-dimethylbenzylisocvanate (99:1 mol ratio) Copolymer with CBD (Sample 7)

Cellulose binding domain (obtained from Clostridium cellulovorans) (0.0995 parts) is dissolved in 8M urea solution (2.25 parts) and added to 0.21 parts of an aqueous copolymer solution of polyacrylamide-3-lsopropenyl-α,α- dimethylbenzylisocyanate (99:1 mol ratio, Molecular weight average (Mw) of 147,000), which contained 0.04 parts polymer. The mixture is heated to 6O⁰C for 1 hour.

Example 3. Analytical Method

The polymers are analysed by size exclusion chromatography (SEC) using TSK PWXL columns (G6000 + G3000 + guard) or equivalents. The mobile phase is 0.2 molar sodium chloride (NaCI) with 0.05 molar dipotassium hydrogen phosphate (K₂HPO₄) in purified water that is pumped through the system at a nominal flow rate of 0.5 ml/min.

The polymers have little UV activity at 280nm but absorb strongly at 210nm due to the carbonyl chromophore. Molecular weight values and molecular weight distributions of the polymers are determined by detection at 210 nm by calibration of the columns with a set of sodium polyacrylate standards with known molecular weight characteristics. The retention time of each standard in the SEC system is measured and a plot is made of the logarithm of the peak molecular weight versus the retention time.

Example 4. Handsheet Preparation and Evaluation

A 0.5 % standard waste furnish is prepared. For IOLtrs of stock A measuring jug containing 25g old newsprint, 25g old corrugated cardboard and 10g Manilla (old Envelopes) is placed in a laboratory disintegrator along with 2 litres of water. This slurry is disintegrated for 2000 counts and then the sample diluted to 0.5% by the addition of a further 8 Ltrs of water.

500 mis of a 10% CaCI₂ solution is added to 60 ltrs of the stock to achieve a 3650 μScrrf¹ conductivity.

The following polymer samples are prepared

1.0% cationic Polyacrylamide (CPAM) is a copolymer of acrylamide with methyl chloride quaternised dimethyl amino ethyl acrylate (80%/20% by weight) prepared as a bead and having an intrinsic viscosity of 9 dl/g.

0.5% Raisamyl® 50021 (a cationic potato starch available from Ciba Specialty Chemicals)

5.0% Water-swellable montmorrilonite clay (WSMC) is an ion-exchanged 3- layer water swellable smectite clay mineral (montmorillonite) . The raw material is ion-exchanged with sodium carbonate. The separated platelets have the general formula (AI_{3 2}MgOs)(Si₈)O₂O(OH)₄X₀ S It has Anionic density ~ 0.6 Millieq/g, is Amphoteric with a surface area (swollen) of about 800m²/g

The CBD containing materials are not diluted prior to use. WSMC, and CPAM were diluted to 0.1 % active before use.

Order of Additions

ΘO mins 30 s 30s 15s

CBD

→ (Starch) → CPAM → WSMC →

Polymer

500 1500 500

Adduct

500 rpm rpm 500gt rpm 2kgt rpm

After the 60 minutes of CBD reaction 5 x 471 mis aliquots are taken and treated with the relevant retention and drainage aid system. The samples are formed into sheets using a semi automatic sheet maker, pressed and dried.

The paper sheet samples are then conditioned for at least 24 hour at 50% relative humidity and 23°C according to the Tappi test method T402. 2 x 15 mm strips are taken from each handsheet and are tested for tensile strength according to Tappi T494 using an EJA Single column tensile tester.

Polymers Evalauted

From these results it can be seen that Sample N10 gives equivalent performance to the cationic wet end starch at a fifth of the addition level.

Claims

1. A process of making paper or paper board which comprises providing a cellulosic suspension comprising cellulosic fibres and optionally fillers, and then dewatering the cellulosic suspension on a wire or mesh to form a sheet and drying the sheet, in which a strength additive is included in the cellulosic suspension or is applied to the formed sheet and in which the strength additive is a polymer comprising i) a synthetic polymeric component; and ii) a protein component comprising a polysaccharide binding domain protein, wherein the cellulosic suspension a) further comprises recycled cellulosic material and/or b) has a conductivity of at least 1500 μS (micro Siemens).

2. A process according to claim 1 in which the polysaccharide binding domain protein is a cellulosic binding domain protein (CBD).

3. A process according to claim 1 or claim 2 in which the synthetic polymeric component has been formed from an ethylenically unsaturated water-soluble or potentially water-soluble monomer and an ethylenically unsaturated monomer carrying a reactive group, in which the reactive group is directly reactive with a polysaccharide binding domain protein.

4. A process according to any preceding claim in which the polysaccharide binding domain protein is covalently bonded to the synthetic polymer component through one or more of the reactive groups.

5. A process according to any preceding claim in which the reactive group is selected from the group consisting of epoxides, isocyanates, amido methylol groups.

6. A process according to any preceding claim in which the polysaccharide binding domain protein is obtainable from a microorganism.

7. A process according to any preceding claim in which the polysaccharide binding domain protein is a native protein, a genetically modified protein and/or a recombinant protein.

8. A process according to any preceding claim in which the polysaccharide binding domain protein is a cellulose binding domain protein which is obtainable from the group consisting of Clostridium cellulovorans, Cellulomonas fimi. Trichoderma reesei and Microbispora. Bispora

9. A process according to any preceding claim in which the synthetic polymeric component is formed from a monomer blend comprising at least one water- soluble or potentially water-soluble ethylenically unsaturated monomer and up to 20 mole % ethylenically unsaturated monomer carrying a reactive group.

10. A process according to any preceding claim in which the synthetic polymeric component is formed from a monomer blend comprising acrylamide and a reactive monomer selected from glycidyl methacrylate and 3-lsopropenyl- α,α-dimethylbenzylisocyanate.

11. A process according to any preceding claim in which the synthetic polymeric component has a weight average molecular weight of below one million.

12. A process according to any preceding claim in which the strength additive is obtainable by reacting a dimeric form of cellulose binding domain protein with the synthetic polymeric component to form a product containing the cellulose binding domain protein dimer followed by converting the dimer into a monomeric form.

13. A process according to any preceding claim in which the cellulosic suspension has a conductivity of at least 2500μS, preferably at least 3500μS.

14. A process according to any preceding claim in which the strength additive is added to the cellulosic suspension in an amount between 500 grams per tonne and 20 kg per tonne based on dry weight of cellulosic suspension, preferably between 1 and 5 kg per tonne.

15. Use of a polymer for improving dry strength or initial wet strength of paper or paperboard which is manufactured in a process from a cellulosic suspension, in which the polymer comprises i) a synthetic polymeric component; and ii) a protein component comprising a polysaccharide binding domain protein, preferably a cellulose binding domain protein, wherein the cellulosic suspension a) further comprises recycled cellulosic material and/or b) has a conductivity of at least 1500 μS (micro Siemens).

16. Use of a polymer for improving wet web strength during a papermaking process in which paper or paperboard is manufactured in a process from a cellulosic suspension, in which the polymer comprises, i) a synthetic polymeric component; and ii) a protein component comprising a polysaccharide any domain protein, preferably a cellulose binding domain protein, wherein the cellulosic suspension a) further comprises recycled cellulosic material and/or b) has a conductivity of at least 1500 μS (micro Siemens).