GB2093491A - Method of Improving Wet Tensile Strength of Paper - Google Patents

Abstract

The wet tensile strength of paper is improved by treating paper pulp with pH-adjusted polyurethane prepolymer amine salt and then producing paper from the treated pulp. The polyurethane prepolymer amine salt has an unadjusted pH of about 3.5-5.5. After adjustment, the pH of the amine salt can range from 6.0 to 9.0.

Description

SPECIFICATION Method of Improving Wet Tensile Strength of Paper This invention relates to improving the wet tensile strength of paper.

In this specification the term "paper" is used to refer to products obtained from aqueous suspensions of cellulose fibers, wood pulp, or synthetic fibers and mixtures thereof. The fibrous structure of paper limits its resistance to the action of water and other liquids, thus rendering it unsuitable for many applications. Water loosens the bonds existing between the paper-forming fibers with the result that the mechanical strength of paper, when wet, is reduced considerably.

It is common knowledge that the physical properties of an ordinary sheet of paper are drastically impaired when the sheet is wet. Numerous additives have been employed to improve physical properties of paper sheet when the sheet is wet.

In our Application No. 8102604 filed January 28th 1981 (Serial No. 2068034) based on Isguret at, U.S. Application Serial No. 11 6,287 filed January 28th, 1980, entitled "Polyurethane Polymer Amine Salt As A Paper Additive", we have disclosed an additive which helps to improve certain physical properties of paper. Among these properties are wet tensile strength, dry tensile strength, dry burst strength, crush resistance, tear factor, fold endurance, and pick resistance. We have now discovered a method of further improving the wet-tensile strength of paper by using the polyurethane polymer amine salt of the aforementioned application after the pH of this salt has been adjusted by the addition of a base thereto.

The present invention provides a method of improving wet-tensile strength of paper by treating the pulp with a curable waterborne polyurethane polymer amine salt that has had its pH level raised to a level whereby neither premature gelation nor water separation of the polyurethane polymer amine salt will occur. The pH of the waterborne polyurethane polymer amine salt is adjusted by adding a basic solution thereto so as to raise the pH to between about 6.0 and about 9.0.

According to the present invention therefore, a method of tnaking paper of improved wet tensile strength comprises forming paper from a paper pulp treated with a polyurethane prepolymer amine salt having pH between about 6.0 and about 9.0.

The waterborne polyurethane polymer amine salt used in the present invention is the subject of our Application No. 8014327 filed April 30than 980 (Serial No.2048289) based on U.S. Application Serial No. 34,375 filed on April 30, 1979. To the extent not provided for in this specification, the disclosure of that specification is incorporated by reference herein.

The polyurethane polymer amine salt is made in four basic steps. First, a polyol is reacted with a polyisocyanate to prepare an NCO-terminated prepolymer. The prepolymer is blocked with an oxime in the second step. Third, the oxime blocked NCO-terminated prepolymer is reacted with one or more selected polyfunctional amines as will hereinafter be described. The amine reaction product is then reacted with an acid. in order to obtain a product with suitable properties, a reactant having functionality greater than 2 should be used in the first and/or third steps. Thus, the functionality of the NCO-terminated prepolymer plus the functionality of the polyfunctional amine will be greater than four.

The reaction product of the polyfunctional amines with the oxime blocked NCO-terminated prepolymer tends to increase in viscosity with time until a complete gelation/setting up of the product occurs. The gelation time and viscosity of the waterborne polyurethane polymer dispersion can be controlled and/or adjusted by the addition of a secondary amine to the reaction product.

The NCO-terminated prepolymer is prepared by reacting polyoxyalkylene polyol with an excess of polyisocyanate. A suitable polyisocyanate is toluene diisocyanate. The polyol should have a molecular weight of from about 200 to about 20,000, and preferably from about 600 to 6,000. The hydroxyl functionality of the polyol and the corresponding isocyanate functionality following the reaction is from 2 to about 8. When the isocyanate functionality of the prepolymer is two the functionality of the amine reactant in step 3 must be greater than two. When the isocyanate functionality of the prepolymer is greater than two the functionality of the amine reactant in step 3 may be as little as two.

The preferred NCO-terminated prepolymer consists of a mixture of (1) an isocyanate capped hydrophilic polyoxyethylene diol, having an ethylene oxide content of at least 40 mole percent; and (2) an isocyanate capped polyol having a hydroxy functionality in the range 3 to 8 prior to capping; the isocyanate capped polyol should be present in an amount in the range 2.9 to 50% by weight of (1) and (2).

The polyoxyethylene diol is the reaction product of alkylene oxides, of which at least 40 mole percent is ethylene oxide, with an initiator such as ethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol or mixtures thereof. The molecular weight of the diol is preferably between 400 to about 6,000.

Examples of suitable polyols (to be capped with polyisocyanates) include: (A) essentially linear polyols formed, for example, by reaction of ethylene oxide with ethylene glycol as an initiator. Mixtures of ethylene oxide with other alkylene oxides can be employed so long as the mole percent of ethylene oxide is at least 40 percent. Where the linear polyethers are mixtures of ethylene oxide with other alkylene oxides, e.g., propylene oxide, the polymer can be either a random or a block copolymer. A second class of polyol (B) includes those having a hydroxy functionality of 3 or more. Such polyols are commonly formed by reacting alkylene oxides with a polyfunctional initiator such as trimethylolpropane, pentaerythritol, etc. In forming the polyol B, the alkylene oxide used can be ethylene oxide or mixtures of ethylene oxide with other alkylene oxides as described above.Useful polyols are further exemplified by (C) linear branched polyfunctional polyols as in A and B above together with an initiator or crosslinker. A specific example of C is a mixture of polyethylene glycol (molecular weight about 1,000) with trimethylolpropane, trimethylolethane or glycerine. This mixture can be subsequently reacted with excess polyisocyanate to provide a prepolymer useful in the invention. Alternatively, the linear or branched polyols, (e.g., polyethylene glycol) can be reacted separately with excess polyisocyanate. The initiator, e.g., trimethylolpropane, can also be separately reacted with polyisocyanate. Subsequently the two capped materials can be combined to form the prepolymen Polyoxyalkylene polyol is terminated or capped by reaction with a polyisocyanate.The reaction may be carried out in an inert moisture-free atmosphere, such as under a nitrogen blanket, at atmospheric pressure with a temperature in the range of from about OOC to about 1 200C for about 20 hours. The precise time depends upon the temperature and degree of agitation. This reaction may be effected also under atmospheric conditions provided the product is not exposed to excess moisture.

Capping of the polyoxyalkylene polyol may be effected by using stoichiometric amounts of reactants. It is preferred that an excess of isocyanate be used to insure complete capping of the polyol.

Thus, the ratio of isocyanate groups to the hydroxyl groups used is between about 2 to about 4 isocyanate groups per hydroxyl group, and preferably about 2 to about 2.5 isocyanate groups per hydroxyl group.

To obtain the maximum strength, solvent resistance, heat resistance and the like, the isocyanate capped polyoxyalkyiene polyol reaction products are formulated in such a manner as to give crosslinked polymer network.

For the second step, any ketoxime is effective. Among the suitable ketoximes are acetone oxime, butanone oxime, cyclohexanone oxime and the like. An oxime based on a relatively volatile ketone is preferred. The most preferred oxime is butanone oxime, also commonly known as methyl ethyl ketoxime. Mixtures of oximes may also be used. The proportions of oxime utilized may range from about 0.7 to about 1.2 equivalents of the isocyanate groups present. A more preferred range is 1.05 to 1.15 equivalents.

To prepare the blocked prepolymer, the ketoxime and prepolymer are simply admixed at temperatures of from 50 to 700C for from about 1/2 to 1-1/2 hours. A solvent is not generally, necessary although solvents such as butyl cellosolve acetate can be employed. Other appropriate solvents include materials which are not reactive with either the oxime or urethane groups. Based on the moles of reactive oxime and NCO groups involved, the NOH/NCO molar ratio should be from about 0.7 to about 1.2 and preferably from about 1.05 to about 1.1 5. Generally it is most effective to use sufficient oxime to completely react with the NCO groups.

In preparing the blocked prepolymer, the ketoxime is selected to provide a product that will undergo curing reactions in a reasonable time at a reasonable temperature. Numerous ketoximes and catalysts which can be employed are described in: Petersen, Liebigs Ann. Chem., 562 (1949), p.215; Wicks, Progress In Organic Coatings, 3 (1975), pp. 73-99; and Hill et al, Journal Of Paint Tech., 43 (1971) p. 55. Oximes having the above unblocking temperatures are liquid materials at temperatures of about 800 C, and the condensation products with urethane prepolymers are either miscible with water or can be dispersed in water with the aid of surfactants. Generally the oximes are aliphatic, cyclic, straight-chain or branched materials containing 2-8 (preferably 3-6) carbon atoms.

The oxime block, NCO-terminated prepolymer is reacted with an amine that is capable of causing the polymer to cure at a low temperature. Many of the amines suitable for this step are well known in the art and are referred to as polyfunctional amines. Specific examples of amines include, but are not limited to, ethylenediamine, 1, 3 propanediamine, diethylenetriamine, triethylenetetramine, iminobispropylamine, tetraethylenepentamine, methyliminobispropylamine, 2 (2-aminoethylamine)ethanol, and the polyoxypropyleneamines manufactured by Jefferson Chemical Company, Inc. and sold under the tradenames JEFFAMINE D-400, D-2000 and T---403. These polyoxpropyleneamines are aliphatic polyether primary di- and tri-functional amines derived from propylene oxide adducts of diols and triols.

As can be observed from the amines listed, some of the amines can be represented by the general formulae, NH2-R' and HO-R' -NH2, where R' is a C2 to C6 group.

Polyfunctional amines with a functionality of at least 2 primary amine end groups are the preferred amines for insuring adequate curing of the polymer subsequently produced.

Some of the polyfunctional amines may be presented by the formula

where z is an integer from 1 to 4; n is an integer larger than 1; and R is hydrogen, an alkyl group of 1 to 4 carbons atoms, or a hydroxyalkyl group of 1 to 4 carbon atoms.

The polyoxypropyleneamines may be represented by the formula NH2CH(CH3)CH240CH2CH(CH3)+NH2 where x is greater than 2, and by the formula

where X+Y+Z is about 5.3. The molecular weights of these polyoxypropylene amines range from about 200 to 2000 or larger with the preferred polyoxypropyleneamines having molecular weights of about 400 and 2000.

The amount of polyfunctional amine added to the oxime blocked NCO-terminated prepolymer should be in the range of 0.6 to 1.5 equivalents, with the preferable range being between 0.9 to 1.1 equivalents, based on the total equivalents of all the isocyanate groups present in the NCO-terminated prepolymer.

Where the isocyanate functionality of the NCO-terminated prepolymer is two, a polyfunctional amine having a functionality of greater than two is required in order to provide satisfactory crosslinked products. When the isocyanate functionality of the NCO-terminated prepolymer is greater than two, the functionality of the polyfunctional amine may be as iittle as two. It is to be understood that in the same reactive system the total functionality of the NCO-terminated prepolymer and the amine or polyoxypropyleneamines will be greater than four.

The reaction between the oxime blocked prepolymer and the polyfunctional amine is controlled by adding an acid or a mixture of acid and water prior to the completion of the reaction. Failure to control the amine-oxime blocked prepolymer reaction at the proper time may result in an amine reaction product that is too viscous. The proper portions of the blocked prepolymer and polyfunctional amine are placed in a reaction vessel and reacted under controlled conditions of heating and stirring.

The state of the reaction is determined by observing the increase in viscosity. The reaction can be carried out more rapidly at elevated temperatures. Reaction times can be as short as about 3 minutes at about 950C, 4 minutes at about 800 C, etc. Preferred reaction times are from about one-half hour to about one hour with temperatures between about 400C and 600 C. Sufficient acid or water-acid mixture is stirred into the amine reaction product to lower the pH value to about 5 or lower.

The cationicaliy stabilized waterborne polyurethane polymers are prepared by dispersing the amine reaction product in water in the presence of sufficient acid to provide a pH of from about 5 or less. In the preferred method of preparing the waterborne polymers, a concentrated acid solution is added directly to the amine reaction product, admixed therewith and followed by dilution with water.

However, it is also possible to first add the acid to the water and then disperse the amine reaction product in the water. Other additives such as surfactants, ultraviolet absorbers, stabilizers, pigments, etc., may be formulated into the waterborne polyurethane polymers as required.

It has been found that if the pH is not controlled within the broad range set forth above, settling problems are encountered and/or portions of the amine reaction product react with the water to form a crust. The pH range is obtained by monitoring the amine reaction product with a pH meter (Beckman, Model 96) equipped with a standard combination electrode (Fisher Scientific, 1363990) while adding the acid. The acid addition is stopped once the desired pH level is attained. These waterborne polymers have been found to be stable for periods of several months at ambient temperature, e.g., 200C. They also exhibit excellent resistance to freeze/thaw cycles.

While any organic or inorganic acid will form the amine salt and perform the function of controlling the pH value, the acids which are actually used include glacial acetic acid, acrylic acid, citric acid, ethylene-diaminetetracetic (EDTA) acid, formic acid, glycine (aminoacetic acid), hydrochloric acid, lactic acid (alpha-hydroxypropinic acid), orthophosphoric acid (H3PO4), phosphorous acid (H3PO3), sulfamic acid, sulfuric acid, tartaric acid (dihydroxysuccinic acid), paratoluenesulfonic acid and mixtures thereof.

Some of these acids, for example sulfuric, hydrochloric and acetic acids tend to discolor the final product. However, additives such as pigments and ultraviolet absorbers can be added to the waterborne polyurethane, to reduce the tendency for discoloration by the acids. A blend of acetic and phosphoric acids seems to discolor less than other acids or combination of acids. Phosphoric acid alone provides good color stability.

The paper pulp to be treated by this method is dispersed in water to a consistency so that a web can be formed on a wire mesh screen. Suitable paper pulps include bleached and unbleached Kraft paper pulp, bleached and unbleached High Alpha Southern Sulfite, Hardwood Kraft, and used newspaper stock.

To the waterborne polyurethane prepolymer amine salt is added a sufficient amount of basic solution to raise the pH to a range of 6.0 to 9.0. The preferred range is 7.0 to 8.3. However, if the pH is raised above about 1 0.0, the waterborne polyurethane will not improve wet tensile strength of the paper product to be produced; it will in fact impair wet tensile strength of the paper. Suitable basic solutions include a 10 percent to 30 percent aqueous solution of ammonium hydroxide and a 10 percent to 50 percent aqueous solution of sodium hydroxide. Other basic solutions which are also suitable include potassium hydroxide, calcium hydroxide, tetramethyl ammonium hydroxide, diethanolamine, diethylamine, dibutylamine, and diethylenetriamine.

The selected paper pulp is mixed with water to form a slurry. The concentration of pulp in the slurry can range from 0.1% to 5% based on the weight of the slurry.

The pH-adjusted polyurethane prepolymer amine salt is added to the slurry and mixed thoroughly.

The concentration of pH-adjusted polyurethane prepolymer amine salt to paper pulp can range from 0.02 to 30 parts per hundred by weight. The preferred concentration is 1 part by weight of amine salt per 100 parts by weight of paper pulp. The pH of the slurry should be between 4.5 and 8.0.

Hand sheets for testing purposes are then prepared from the treated paper pulp in a conventional manner. A Wiliiams Standard Sheets Moulder can be used for preparing hand sheets.

For the purpose of demonstrating the efficacy of the novel process, a typical polyurethane prepolymer amine salt is first prepared.

The following method is used to prepare HYPOL(R) WB4000, a waterborne polyurethane prepolymer amine salt manufactured by W. R. Grace a Co., Cambridge, Massachusetts.

A preferred isocyanate terminated polyol prepolymer is prepared by mixing a hydrophilic polyoxyethylene diol having an ethylene oxide content of at least 40 mole percent with a polyol having a hydroxyl functionality in the range of 3 to 8. The concentration of polyol in the mixture should range from one percent to 20 percent by weight. An amount of diisocyanate equal te 1.8 to 1.9 equivalents of NCO/equivalent of OH is reacted with the mixture at a temperature from 0 to 1 200C for a period of time sufficient to cap substantially all the hydroxyl groups of the admixture.Additional diisocyanate is added to provide 0.1-0.3 equivalents of NCO per initial equivalent of OH in excess of the theoretical amount necessary to react with the hydroxyl groups To 300 parts of the NCO-terminated polyol prepolymer at 240C in a stainless steel vessel is added 54.6 parts of butanone oxime with stirring. The reaction of the oxime with the isocyanate is exothermic and the temperature rises to 600C. A hot water bath is used to control the temperature to 800C-900C for about 20 minutes.

After about 20 minutes, 29.4 parts of diethylenetriamine is added with stirring. The reaction with the amine is exothermic, thus accelerating chain extension.

The viscosity continues to increase. Once the viscosity reaches 10,000 to 12,000 cps a solution of 50 parts of glacial acetic acid and 50 parts of o-phosphorjc acid dissolved in 1 50 parts of deionized water is slowly added to control the viscosity. After the acid solution is added, the product is cooled.

Typical physical properties of the polyurethane prepolymer amine salt are listed in the following Table: Table A Percent nonvolatiles 53.8 pH 4.3 Viscosity (Brookfield LVF-;ÇE2 spindle at 30 rpm at 260 C) 1980 cps Appearance Amber liquid The following examples illustrate the invention. All such variations which do not depart from the basic concept of the invention disclosed above are intended to come within the scope of the appended claims.

Example I HYPOLR) WB4000, which is manufactured by W. R. Grace s Co., Cambridge, Massachusetts, is the waterborne polyurethane prepolymer amine salt to be used in the preparation of the improved paper. HYPOLR) WB4000 contains 53.8 percent nonvolatiles. Water is added to the WB4000 salt to reduce the nonvolatile content to about 35 percent. A sufficient amount of concentrated ammonium hydroxide is added to the Waterborne polyurethane prepolymer amine salt (35% nonvolatiles) until the pH of the salt reaches 6.1. The pH-adjusted salt is diluted with water to a level of 1 0 percent nonvolatiles.

50 gm of unbleached Kraft paper pulp is added to 4000 gm of water to form a slurry. 5 cc of the pH adjusted polyurethane prepolymer amine salt solution (10% nonvolatiles) is added to the paper pulp slurry, and the resulting solution is mixed for about 5 minutes. Hand sheets are prepared from the treated paper pulp with a Williams Standard Sheets Moulder. The sheets are then subjected to 1 500 psi (105 kg/cm2) for about one minute with a Williams 2-post hand operated hydraulic press, 12 inches by 12 inches (30cmx30cm). The sheets are then dried for 10 minutes on each side with a Williams Standard Sheet Drier. The sheets are finally cured for one hour at 2200F (1 040C) in a forced air oven.

Eight samples are cut from each sheet, four from each direction. The samples are 1 in.x4.5 in.

(2.5x 11.4 cm). The cut samples are soaked for 1824 hours in a 10% solution of AEROSOL OT (sodium dioctyl sulfosuccinate from American Cyanamid Co.). The wet tensile strengths are run on an Instron Testing Machine and are an average of 8 samples. The process is repeated with the following modifications: (1) the pH of the polyurethane prepolymer amine salt is raised to 7.4 with concentrated NH40H; (2) the pH of the polyurethane polymer amine salt is raised to 7.5 with NaOH; (3) the pH of the polyurethane prepolymer amine salt is raised to 8.3 with concentrated NH40H; (4) the pH of the polyurethane prepolymer amine salt is raised to 10.0 with concentrated NH4OH.

Table I sets forth the results obtained when the pH of the polyurethane prepolymer amine salt is varied.

Table I pH of Polyurethane Wet Tensile Strength Base PrepolymerAmine Salt (Ibs/in) None 5.3 (unadjusted; base not added) 1 2.5(2.2kg/cm) Conc.NH40H 6.1 14.5 (2.6kg/cm) Conc. NH4OH 7.4 1 6.3 (2.9kg/cm) NaOH 7.5 16.2 (2.9kg/cm) Conc. NH40H 8.3 19.4(3.5kg./cm) Conc. NH40H 10.0 8.4(1 .5kg/cm) Example II The procedure in Example I was repeated with the following exception: The polyurethane prepolymer amine salt was allowed to stand for three weeks prior to having the pH adjusted.

Table II sets forth the results obtained when the aging period of the polyurethane prepolymer amine salt is varied before pH adjustment.

Table II Age ofPoly pH ofPoly- urethane Prepoly- Wet Tensile urethane Prepoly- merAmine Salt Strength Base merAmine Salt Before pHAdjustment (Ibs/in) None 5.3 3 Weeks 16.2(2.9kg/cm) NH40H 6.1 3 Weeks 22.2(4.0kg/cm) None 5.3 1 Day 12.5(2.2kg/cm) NH40H 6.2 1 Day 15.2(2.7kg/cm) Example Ill The procedure in Example I was repeated with the following exception: The pH-adjusted polyurethane prepolymer amine salt stood at room temperature for 1 5 days before the paper sheets were prepared. The waterborne salt contained 10 percent nonvolatiles.

Table III sets forth the results obtained when the pH-adjusted polyurethane prepolymer amine salt (10% nonvolatiles) is allowed to age.

Table Ill Age of pH Adjusted Poly urethane Prepoly merAmine Salt Wet pH OfPoly- 110% nonvolatives) Tensile urethane Poly- Prior to Sheet Strength Base merAmine Salt Formation (Ibs/in) None 5.3 1 5 days 18.4(3.3kg/cm) NH4OH 6.1 15 days 20.5(3.7kg/cm) NH40H 7.4 1 5 days 22.0(3.9kg/cm) Example IV The procedure of Example I was repeated with the following exception: The pH of the polyurethane prepolymer amine salt was adjusted to 8.3 and 10.0 Table IV sets forth the results obtained when the pH of the polyurethane additive is raised to an extremely high level.

Table IV pH OfPolyurethane Wet Tensile Strength Base PrepolymerAmine Salt ((b s/in) None 5.3 21 .81(3.9kg./cm) NH40H 8.3 19.42(3.7kg./cm) NH4OH 10.0 8.42(1.5kg./cm) From the foregoing Tables, it can be seen that the process described improves the wet tensile strength of paper.

Table I shows that merely raising the pH of the polyurethane prepolymer amine salt additive improves the wet tensile strength of the paper formed from pulp that has been treated with the additive.

Table II shows that even if the polyurethane prepolymer amine salt is allowed to age before its pH is adjusted, an improvement in wet tensile strength of the paper formed from pulp treated with the additive is brought about.

1 The sample containing 10% nonvolatiles was allowed to stand at'220C for 18 days before the sheets were made.

2 The samples were held at 40C before the pH was raised.

Table Ill shows that even if the pH-adjusted polyurethane prepolymer amine salt is allowed to age, an improvement in wet tensile strength of the paper formed from pulp treated with the additive is brought about.

Table IV shows that raising the pH of the polyurethane prepolymer amine salt additive to too high a value decreases the wet tensile strength of the paper formed from pulp that has been treated with the additive.

Claims (9)

Claims

1. Method of making paper of improved wet tensile strength which comprises forming paper from a paper pulp treated with a polyurethane prepolymer amine salt having pH between about 6.0 and about 9.0.

2. Method for making paper of improved wet tensile strength which comprises: (1) preparing a slurry of paper pulp, (2) treating the paper pulp with a polyurethane prepolymer amine salt having pH between about 6.0 and about 9.0, and (3) forming paper from the treated paper pulp.

3. The method of claim 1 or 2 wherein the polyurethane prepolymer amine salt is a curable waterborne polyurethane prepolymer amine salt.

4. The method of any of claims 1 to 3 wherein the polyurethane prepolymer amine salt has been pretreated with a base to raise its pH to about 6.0 to about 9.0.

5. The method of claim 3 wherein the curable waterborne polyurethane has been prepared by; (a) reacting an isocyanate capped prepolymer consisting of a mixture of (1) from about 2.9 to about 50% by weight of isocyanate capped polyol having a hydroxyl functionality in the range of 3 to 8 prior to capping, and (2) from about 97.1 to about 50% by weight of an isocyanate capped hydrophilic polyoxyethylene diol, said diol having an ethylene oxide content of at least 40 mole percent, with (b) from about 0.8 to 1.2 equivalent of a ketoxime to form an oxime blocked prepolymer, (c) reacting said oxime blocked prepolymer with a poiyfunctional amine containing at least two functional groups and capable of causing polyurethane polymers to cure at low temperatures to form an amine reaction product, (d) reacting said amine product with an acid to form an infinitely water dilutable, low temperature curable polyurethane polymer amine salt, and (e) adjusting the pH of said polyurethane prepolymer amine salt to about 6.0 to about 9.0 with a base.

6. The method of claim 4 or 5 wherein the base is NH40H.

7. The method of Claim 4 or.5 wherein the base is selected from sodium hydroxide, calcium hydroxide, tetramethyl ammonium hydroxide, diethanolamine, diethylamine, dibutylamine and diethylenetriamine.

8. Method of making paper as claimed in claim 1 substantially as described in any one of the foregoing Examples.

9. Paper when made by the process of any of the preceding claims.