Paper prepared from aldehyde modified cellulose pulp and the method of making the pulp

Paper comprising aldehyde modified cellulose pulp having selected aldehyde content. Another embodiment involves a method of preparing celullose aldehydes using selective oxidation with a limited amount of oxidant and a nitroxyl radical mediator and defined reaction conditions to provide oxidized cellulose material with effective aldehyde content making it particularly suitable for use in making paper with desirable wet strength, temporary wet strength and dry strength properties.

BACKGROUND OF THE INVENTION
 This invention relates to paper comprising aldehyde modified cellulose pulp
 or fiber and further to the method of preparing aldehyde modified
 cellulose and cellulose pulp or fiber using selected oxidation conditions
 to generate aldehyde functionality. More particularly, this invention
 involves paper made from cellulose pulp having a defined amount of
 aldehyde content. A method for preparing the selected aldehyde modified
 cellulose and cellulose pulp involves using a nitroxyl radical mediated
 oxidation with a limited amount of oxidant and defined reaction
 conditions. This aldehyde modified pulp is used in the production of
 tissue/towel and other paper products which exhibit unexpected high wet
 strength, temporary wet strength and dry strength properties and high wet
 strength/dry strength ratios without the use of other additives.
 The term "paper" as used herein, includes sheet-like masses and molded
 products made from pulp or fibrous cellulosic material which may be
 derived from natural sources. Paper may also be made from synthetic
 cellulosic fibers and regenerated cellulose as well as recycled waste
 paper. In addition, paper made from combinations of cellulosic and
 synthetic materials are applicable herein. Paperboard is included within
 the broad term "paper".
 Papermaking, as it is conventionally known, is a process of introducing an
 aqueous slurry of pulp or wood cellulosic fibers (which have been beaten
 or refined to achieve a level of fiber hydration and to which a variety of
 functional additives can be added) onto a screen or similar device in such
 a manner that water is removed, thereby forming a sheet of the
 consolidated fibers, which upon pressing and drying can be processed into
 dry roll or sheet form. Typically in papermaking, the feed or inlet to a
 papermaking machine is an aqueous slurry or water suspension of pulp
 fibers which is provided from what is called the "wet end" system. In the
 wet end, the pulp along with other additives are mixed in an aqueous
 slurry and subject to mechanical and other operations such as beating and
 refining. Various additives are commonly added to help provide different
 properties in the paper product.
 The preparation of aldehyde containing starches and the use of such
 aldehyde derivatives in the paper industry as wet and dry strength
 additives is well known. Both oxidative and non-oxidative methods are
 known for introducing aldehyde groups into starch. Use of these products
 in papermaking to provide wet and dry strength properties involves the
 addition of this separate starch additive component.
 The use of nitroxyl radicals and nitrosonium salts in organic chemistry as
 an oxidative route to produce aldehydes and carboxylic acids from primary
 and secondary alcohols is disclosed in an article entitled "Organic
 Nitrosonium Salts As Oxidants in Organic Chemistry" by J. M. Bobbitt and
 C. L. Flores, in Heterocycles, Vol. 27, No. 2, 1988, pp. 509-533.
 Recently, application of this chemistry was extended to the selective
 oxidation of primary alcohols in various carbohydrates to carboxylic acids
 in an article entitled "Selective Oxidation of Primary Alcohols Mediated
 by Nitroxyl Radical in Aqueous Solution. Kinetics and Mechanism" by A. E.
 J. de Nooy and A. C. Bessemer, in Tetrahedron, Vol. 51, No. 29, 1995, pp.
 8023-8032. Patent publication WO 95/07303 dated Mar. 16, 1995 further
 discloses the use of this technology where carbohydrates having a primary
 hydroxyl group are oxidized under aqueous conditions to form products
 having a high content of greater than 90% carboxyl groups. This art
 involving the oxidation of primary alcohols generally describes the
 preparation of polyglucuronic acids with high carboxylic acid content.
 Similarly, the process of oxidation has been used to prepare various
 polysaccharides with high carboxyl content as described in "Oxidation of
 Primary Alcohol Groups of Naturally Occurring Polysaccharides with
 2,2,6,6-Tetramethyl-1-piperidine Oxoammonium Ion" by P. S. Chang and J. F.
 Robyt in J. Carbohydrate Chemistry, 15(7), 1996, pp. 819-830. It should be
 noted that in some applications high carboxylic acid content is
 undesirable.
 Recent patent publications WO 99/23240 and 99/23117, both dated May 14,
 1999, respectively disclose methods of oxidizing starch and cellulose
 using an oxoammonium ion producing reagent in the presence of an enzyme
 oxidizing agent.
 Despite the various methods described above, there still is the need for
 cellulose pulp which is suitable for use in paper applications to provide
 the desired high degree of wet strength, temporary wet strength and dry
 strength properties and does not involve the use of separate additive
 components.
 SUMMARY OF THE INVENTION
 This invention is directed to paper having wet strength, temporary wet
 strength and dry strength properties and comprising aldehyde modified
 cellulose pulp wherein the pulp has from 1 to 20 mmoles of aldehyde per
 100 g of cellulose.
 Another embodiment of this invention involves the selective preparation of
 cellulose aldehyde and cellulose pulp aldehyde under defined oxidation
 conditions using a nitroxyl radical mediated aqueous oxidation procedure
 to provide derivatives with effective aldehyde content particularly useful
 in papermaking. More particularly, this invention involves the oxidation
 of cellulose or cellulose pulp in an aqueous solution with an oxidant
 having an equivalent oxidizing power of up to 5.0 g of active chlorine per
 100 g of cellulose and an effective mediating amount of nitroxyl radical,
 the reaction being carried out at a pH of about 8.0 to 10.5, and a
 temperature of from about 5 to 50.degree. C., the resulting product having
 an aldehyde content of about 1 to 20 mmole/100 g of pulp.
 This invention further involves aldehyde modified cellulose or cellulose
 pulp having defined aldehyde content.
 Still another embodiment involves the method of preparing paper having wet
 strength, temporary wet strength and dry strength properties comprising
 using the cellulose aldehyde pulp prepared by the selective oxidation
 procedure as described above, as the paper or pulp stock or a component
 thereof.
 DETAILED DESCRIPTION OF THE INVENTION
 The cellulose or cellulose pulp aldehyde derivatives of this invention have
 effective aldehyde functionality or content of from about 1 to 20 and
 preferably from about 5 to 20 mmoles/100 g of cellulose material, i.e.,
 cellulose or cellulose pulp.
 The cellulose aldehyde derivatives of this invention can be prepared by a
 method which involves the selective oxidation of cellulose and cellulose
 pulp or fiber using a limited amount of oxidant mediated with a nitroxyl
 radical under defined conditions to provide derivatives with effective
 aldehyde content making them particularly suitable for use in providing
 paper with desired wet strength, temporary wet strength and dry strength
 properties.
 The nitroxyl radical mediator used herein is a di-tertiary alkyl nitroxyl
 radical having one of the following formulas:
 ##STR1##
 where A represents a chain of preferably two or three atoms, in particular
 carbon atoms or a combination of one or two carbon atoms with an oxygen or
 nitrogen atom, and the R groups represent the same or different alkyl
 groups. Chain A may be substituted by one or more groups such as alkyl,
 alkoxy, aryl, aryloxy, amino, amido or oxo groups, or by a divalent group
 or multivalent group which is bound to one or more other groups having
 formula I. Particularly useful nitroxyl radicals are di-tertiary alkyl
 nitroxyl radicals having the formula:
 ##STR2##
 where Y is either H, OH or
 ##STR3##
 and each of the R groups represent the same or different alkyl groups of 1
 to 18 carbon atom and more particularly methyl groups. Nitroxyl radicals
 of this type include those where a) the R groups are all methyl (or alkyl
 of 1 carbon atom) and Y is H, i.e., 2,2,6,6-tetramethyl-1-piperdinyloxy
 (TEMPO); b) R groups are methyl and X is OH and identified as 4-hydroxy
 TEMPO; and c) R groups are methyl and X is
 ##STR4##
 and identified as 4-acetamido-TEMPO. The preferred nitroxyl radical is
 TEMPO or 4-acetamido-TEMPO. The nitroxyl radical is used in an effective
 amount to mediate the oxidation and more particularly from about 0.001 to
 20% by weight, preferably from about 0.01 to 0.1% by weight, based on the
 weight of cellulose, cellulose pulp or fiber. The nitroxyl radical can be
 added to the reaction mixture or generated in situ from the corresponding
 hydroxylamine or oxoammonium ion.
 The oxidant used in this invention can be any material capable of
 converting nitroxyl radicals to their corresponding oxoammonium salt.
 Particularly useful oxidants are the alkali or alkaline-earth metal
 hypohalite salts such as sodium hypochlorite, lithium hypochlorite,
 potassium hypochlorite or calcium hypochlorite. An alkali or alkaline
 earth-metal hypobromite salt may also be used and it may be added in the
 form of the hypobromite salt itself, such as sodium hypobromite, or it may
 be formed in situ from the addition of a suitable oxidant such as sodium
 hypochlorite and an alkali or alkaline-earth metal bromide salt such as
 sodium bromide. The bromide ion is generally in the form of sodium
 bromide. Additional oxidants that can be used in this method include
 hydrogen peroxide in combination with a transition metal catalyst such as
 methyltrioxorhenium (VII); hydrogen peroxide in combination with an
 enzyme; oxygen in combination with a transition metal catalyst; oxygen in
 combination with an enzyme; peroxyacids such as peracetic acid and
 3-chloroperoxybenzoic acid; alkali or alkaline-earth metal salts of
 persulfates such as potassium persulfate and sodium persulfate; alkali or
 alkaline-earth metal salts of peroxymonosulfates such as potassium
 peroxymonosulfate; chloramines such as
 1,3,5-trichloro-1,3,5-triazine-2,4,6(1H,3H,5H)trione,
 1,3-dichloro-1,3,5-triazine-2,4,6(1H,3H,5H)triione sodium salt,
 1,3-dichloro-5,5-dimethylhydrantoin,
 1-bromo-3-chloro-5,5-dimethylhydrantoin, and
 1-chloro-2,5-pyrrolidinedione; and alkali or alkaline-earth metal salts of
 ferricyanide. This list of oxidants is only illustrative and is not
 intended to be exhaustive. The oxidants can be used alone or in
 combination with an alkali or alkaline-earth metal bromide salt. The
 preferred oxidant is sodium hypochlorite or sodium hypobromite formed from
 the addition of sodium hypochlorite and sodium bromide.
 The important factor in the use of the oxidant is that it must be used in a
 limited amount that has the equivalent oxidizing power of up to 5.0 g of
 active chlorine per 100 g of cellulose or cellulose pulp. More
 particularly, the amount of oxidant used will have an equivalent oxidizing
 power of from about 0.05 to 5.0 g of active chlorine and preferably from
 about 0.5 to 2.5 g of active chlorine per 100 g of cellulose or cellulose
 pulp. When sodium hypochlorite is used, it is used in a limited amount of
 up to about 10 percent by weight based on the weight of cellulose or
 cellulose pulp, more particularly from about 0.1 to 10% and preferably
 from about 1 to 5% by weight based on the weight of cellulose or cellulose
 pulp. Bromide in the form of sodium bromide will generally be used in an
 amount of from about 0.1 to 5% by weight and preferably from about 0.25 to
 2% by weight based on the weight of cellulose or cellulose pulp. By
 limiting the amount of oxidant under defined aqueous conditions, the
 cellulose aldehyde derivatives are selectively prepared at effective high
 aldehyde levels. Such high aldehyde cellulose products are particularly
 useful in preparing paper with wet strength, temporary wet strength and
 dry strength properties.
 The cellulose material used as the starting material may be any cellulose,
 cellulosic fiber or pulp material. This includes hardwood or softwood
 cellulosic fibers such as bleached and unbleached sulfate (Kraft),
 bleached and unbleached sulfite, bleached and unbleached soda, neutral
 sulfite, semi-chemical, groundwood, chemi-groundwood, and any combination
 of these fibers. In addition, synthetic cellulosic fibers of the viscose
 rayon or regenerated cellulose type can also be used, as well as recycled
 waste papers from various sources. The consistency in water of the
 cellulose or pulp that is used will be from about 0.1 to 15% by weight
 solids in water and preferably from about 1 to 5% by weight. When used in
 papermaking other additives such as desired inert fillers or retention
 aids may be added to the cellulose pulp. Such materials include clay,
 titanium dioxide, talc, calcium carbonate, calcium sulfate and
 diatomaceous earth. Rosin or synthetic internal size may also be present,
 if desired. Other additives commonly used in paper may also be used in
 combination with the oxidized pulp of this invention.
 The oxidation reaction of the cellulosic material is carried out in an
 aqueous solution. The pH of the reaction is maintained at about 8.0 to
 10.5, preferably about 9 to 10, the temperature is maintained at from
 about 5 to 50.degree. C., preferably from about 20 to 30.degree. C. The
 extent of the reaction is controlled by the amount of oxidant used or the
 reaction time. Generally the reaction time will be from about 5 to 60
 minutes, and more particularly from about 20 to 30 minutes.
 By using the reagent and component amounts as defined previously and the
 noted reaction conditions, controlled amounts of aldehyde functionality,
 particularly C-6 aldehyde, can be obtained that are suitable and effective
 in providing desired wet strength, temporary wet strength, and dry
 strength properties and wet strength/dry strength ratios desired in the
 final prepared paper product. The cellulose aldehyde derivatives prepared
 in accordance with this invention will have effective aldehyde
 functionality of from about 1 to 20 and preferably from about 5 to 20
 mmole/100 g of cellulosic material i.e., cellulose or cellulose pulp.
 Carboxylic acid functionality will also be generated or formed during the
 oxidation process. Amounts of carboxyl content generated will generally be
 from about 1 to 40 mmole/100 g of cellulose or cellulose pulp,
 particularly from about 1 to 20 and more particularly from about 1 to 10
 mmole/100 g cellulose or cellulose pulp. It should be noted that this
 amount of carboxylic acid functionality is in addition to what may already
 be present in the cellulose or cellulose pulp naturally or by virtue of
 the type of processed pulp used, such as bleached sulfate, bleached
 sulfite, etc. The effective level of aldehyde is an important aspect of
 this invention and one way this can be defined is by the ratio of aldehyde
 to generated carboxylic acid functionalities. Such levels can be defined
 by aldehyde to generated carboxylic acid ratios of greater than or equal
 to 0.5 (based on mmole/100 g of cellulose or cellulose pulp of each
 functionality) and preferably greater than or equal to 1.0. While
 recognizing that the amount of additional carboxylic functionality (i.e.,
 other than generated) will vary and may be fairly low, there nevertheless
 will be some present and this will affect the level of total carboxylic
 acid functionality. Considering this and based on total carboxylic acid,
 the ratio of aldehyde to carboxylic acid functionality will be from about
 0.2 or more. The significance of this aldehyde content is particularly
 manifested in the resulting properties found in paper prepared from the
 oxidized cellulose material. High wet strength, temporary wet strength and
 dry strength properties are found. Products having high wet strength/dry
 strength ratios of greater than 20% have been obtained in paper using
 these selectively modified cellulose aldehyde derivatives indicating
 improved properties such as softness.
 It is noted that use of the modified aldehyde cellulose derivatives of this
 invention in papermaking may involve the use of such derivatives as the
 whole or entire pulp or paper stock or it may be used as a component of
 the paper stock (i.e., in amounts of 20, 40, 60% by weight etc.).

The following examples will more fully illustrate the embodiments of this
 invention. In the examples, all parts and percentages are by weight and
 all temperatures in degrees Celsius unless otherwise noted. Also, when
 referring to the pulp by weight, it is the weight of the pulp per se,
 i.e., it includes equilibrium moisture content.
 EXAMPLE 1
 Modification of Northern Softwood Kraft (NSK) Pulp:
 To a 1600 g stirred suspension of NSK pulp at 3% consistency (48 g pulp)
 was added 4.8 mg 4-acetamido-TEMPO and 0.24 g sodium bromide [0.01% and
 0.5% on weight of pulp (owp) respectively]. The pH of the mixture was
 adjusted to 9.5 with 0.49 N sodium hydroxide. Sodium hypochlorite (10.11
 g; 9.5% solution; 2% owp), whose pH was also adjusted to 9.5 using
 concentrated HCl, was then added all at once and the mixture was stirred
 at 25.degree. C. for 30 minutes. The pH of the suspension was maintained
 throughout using a Brinkmann pH STAT 718 Titrino at 9.5 with 0.49 N NaOH
 (7.9 mL). At the end of the treatment period, the reaction was terminated
 by adding ascorbic acid to the mixture until its pH was lowered to 4.0 to
 4.5 range (ca. 1 g).
 The pulp was filtered and washed extensively with water whose pH was
 adjusted to 4.5 to 5.5. It was then either re-slurried in water for
 subsequent use in handsheet making or dried in air at room temperature for
 future use.
 EXAMPLE 2
 The procedure described in Example 1 was repeated with the exception that
 it was carried out based on 248 g pulp and the 4-acetamido-TEMPO was
 omitted from the treatment. This control treatment consumed 1.22 mL of
 0.98 N NaOH during maintenance of pH of the mixture at 9.5 during the 30
 minute treatment.
 EXAMPLE 3
 Modification of Hardwood Pulp:
 To a 1600 g stirred suspension of hardwood pulp at 3% consistency (48 g
 pulp) was added 4.8 mg 4-acetamido-TEMPO and 0.24 g sodium bromide. The pH
 of the mixture was adjusted to 9.5 with 0.49 N sodium hydroxide. Sodium
 hypochlorite (10.11 g; 9.5% solution; 2% owp), whose pH was also adjusted
 to 9.5 using concentrated HCl, was then added all at once and the mixture
 was stirred at 25.degree. C. for 30 minutes. The pH of the suspension was
 maintained throughout using a Brinkmann pH STAT 718 Titrino at 9.5 with
 0.49 NaOH, consuming 4.8 mL. At the end of the treatment period, the
 reaction was terminated by adding ascorbic acid to the mixture until its
 pH was lowered to 4.0 to 4.5 range (ca. 1 g). The pulp was filtered and
 washed extensively with water whose pH was adjusted to 4.5 to 5.5. It was
 then either re-slurried in water for subsequent use in handsheet-making or
 air-dried at room temperature for future use.
 EXAMPLE 4
 The procedure described in Example 3 was repeated with the exception that
 it was carried out based on 248 g pulp and the 4-acetamido-TEMPO was
 omitted from the treatment. This control treatment consumed 1.96 mL of
 0.98 N NaOH during maintenance of pH of the mixture at 9.5 during the 30
 minute treatment time.
 EXAMPLE 5
 Determination of Aldehyde Content on Modified Pulps:
 Aldehyde content of modified pulps were determined using hydroxylamine
 hydrochloride titration via oxime derivatization to the following reaction
 and the procedure.
EQU RCHO+NH.sub.2 OH.HCl.fwdarw.RCHNOH+HCl
 An oxidized pulp suspension in water 1200 g at 3% consistency was pH
 adjusted to 4 with aqueous HCl. To this mixture was added dropwise a large
 excess of an aqueous solution of 2 M hydroxylamine hydrochloride solution
 (ca. 15 mL), whose pH was also adjusted to 4 with HCl. During the
 reaction, the pH of the mixture was maintained at 4 via titration with a
 0.49 N NaOH solution using a Brinkmann pH STAT 718 Titrino. The titration
 was continued until no further reduction in pH of the mixture could be
 detected (ca. 1 h). Aldehyde levels are then calculated based on the total
 consumption of NaOH using the following equation:
 ##EQU1##
 Table 1 lists the --CHO content of pulp samples prepared in Examples 1 to
 4.
 Carboxylic Acid Content of Modified Pulps:
 The level of carboxylic acid formed during these treatments was calculated
 from the amount of NaOH titrant consumed to maintain the pH of the
 reactions. This provides a direct measure of the additional carboxylic
 acid generated on the pulp and was calculated using the following
 equation:
 ##EQU2##
 Table 1 lists the --COOH content of modified pulp samples prepared in
 Examples 1 to 4.
 TABLE 1
 Aldehyde and carboxylic acid moieties generated in pulp treatments
 described in Examples 1 to 4.
 Pulp Prepared in Aldehyde Content Carboxylic Acid Generated
 EXAMPLE # (mmole/100 g) (mmole/100 g)
 1 8.7 8.1
 2 &lt;0.5 0.5
 3 10.1 4.9
 4 &lt;0.5 0.8
 EXAMPLE 6
 Following their modification by the oxidative process described in the
 prior examples, modified pulp samples (600 to 650 CSF) were formed into 18
 Ib/3300 sq.ft handsheets from 0.3% consistency and at pH 5 to 6 on an M/K
 Sheet Former. Test strips (1" wide) were cut from handsheets and tested
 for initial wet strength and dry tensile strength at the breaking point
 according to the TAPPI Standard Test Method T 456. Table 2 lists the
 tensile strength performance data from handsheets of surface modified pulp
 samples prepared in Examples 1 to 4.
 TABLE 2
 Wet and dry tensile strength performance of handsheets prepared from
 pulps modified as described in Examples 1 to 4.
 Wet Dry
 Tensile Tensile Wet/Dry Ratio
 Strength Strength (Wet st./Dry st.
 Pulp Used (g/in) (g/in) .times. 100)
 Untreated NSK 19 2028 1
 Example 1 614 2504 25
 Example 2 38 2018 2
 Untreated Hardwood 19 1243 2
 Example 3 278 1399 20
 Example 4 16 949 2
 EXAMPLE 7
 Modification of 70/30 Blend of Softwood/Hardwood Pulps:
 To an 800 g stirred pulp suspension of 1.3% consistency in water comprising
 of a 70/30 (w/w) mixture of softwood/hardwood (10.4 g total pulp) was
 added 10.4 mg 4-acetamido-TEMPO and 1.24 g sodium bromide (0.1% and 3% on
 weight of pulp respectively). The pH of the mixture was adjusted to 9.5
 with 0.98 N sodium hydroxide. Sodium hypochlorite (9.81 9 of 10.6%
 solution; 10% owp as hypochlorite), whose pH was also adjusted to 9.5
 using concentrated HCl, was then added all at once and the mixture was
 stirred at 25.degree. C. for 10 minutes. The pH of the suspension was
 maintained throughout using a Brinkmann pH STAT 718 Titrino at 9.5 with
 0.98 N NaOH (0.57 mL). At the end of the treatment period, the reaction
 was terminated by by adding ascorbic acid to the mixture until its pH was
 lowered to 4.0 to 4.5 range (ca. 2 g).
 The pulp was recovered as described in Example 1. Handsheets made from this
 pulp exhibited 301 g/in and 1355 g/in wet and dry tensile strengths
 respectively.
 EXAMPLE 8
 Softwood pulp was modified under the conditions described in Example 7. The
 pulp was filtered-off and washed extensively with water whose pH was
 adjusted to 4.5 to 5.5. It was then re-slurried in water at neutral pH.
 Portions of this pulp suspension were then mixed with unoxidized hardwood
 pulp suspensions in order to determine the effect of increasing modified
 softwood fraction in untreated hardwood. Handsheets were made from these
 pulp mixtures and tested as described in Example 6. Table 3 lists the
 tensile strength results of handsheets made from these pulp compositions.
 TABLE 3
 The effect of blending oxidized softwood pulp with an unmodified
 hardwood pulp on the wet and dry tensile strength of handsheets prepared
 from such pulp compositions.
 Pulp Composition
 Modified Softwood/ Wet Tensile Dry Tensile Wet/Dry
 Unmodified Hardwood Strength Strength Ratio
 (w/w) (g/in) (g/in) (%)
 0/100 20 1012 2
 10/90 39 1231 3
 20/80 75 1291 6
 30/70 125 1490 8
 40/60 183 1722 11
 50/50 232 1714 14
 100/0 557 2243 25
 EXAMPLE 9
 The process described in Example 1 was repeated under similar conditions on
 NSK pulp in order to determine the effect of process variables on aldehyde
 generation and paper strength properties. Therefore, 4.8 mg
 4-acetamido-TEMPO and 0.24 g sodium bromide were added to stirred pulp
 suspensions in water of 1600 g slurry at 3% consistency (48 g pulp). pH of
 the mixtures were adjusted to required level with 0.49 N NaOH. Sodium
 hypochlorite (7.68 g as 12.5% solution at desired pH) was then added all
 at once and the mixtures were stirred for a prescribed period at a given
 temperature. The pH of the mixtures were maintained throughout using a
 Brinkmann STAT 718 Titrino with 0.49 N NaOH. At the end of the treatment
 period, the reactions were terminated by adding ascorbic acid to the
 mixture until its pH was lowered to 4.0 to 4.5 range (ca. 1 g).
 The pulps were filtered and washed extensively with pH adjusted water (4.5
 to 5.5). They were then re-slurried in water and tested for aldehyde
 content and handsheet wet tensile strength and dry strength performance as
 described in Examples 5 and 6 respectively. Table 4 lists the testing
 results.
 TABLE 4
 The effect of process variables during NSK treatment on the properties of
 the
 modified pulp and handsheets.
 Oxidation
 Conditions Pulp Properties Paper Properties
 --COOH
 --CHO Gener- Wet Dry
 Content ated --CHO/ Tensile Tensile Wet/Dry
 T Time (mmole/ (mmole/ --COOH Strength Strength Ratio
 pH (.degree. C.) (min.) 100 g) 100 g) Ratio (g/in) (g/in)
 (%)
 Untreated NSK pulp 18 2142 1
 9.5 25 30 8.7 8.1 1.1 614 2504 25
 11.0 25 30 1.5 4.0 0.4 240 2237 11
 8.0 25 30 5.9 4.2 1.4 479 2258 21
 9.5 50 30 4.3 11.5 0.4 246 2230 11
 9.5 25 60 7.3 9.8 0.8 578 2430 24
 EXAMPLE 10
 The process described in Example 1 was repeated under similar conditions on
 NSK pulp in order to determine the effect of process variables of pulp
 consistency, 4-acetamido-TEMPO, sodium bromide and sodium hypochlorite
 concentrations on the wet and dry strength and wet/dry ratio of the
 handsheets prepared from modified pulps. Therefore, appropriate quantities
 of 4-acetamido-TEMPO and sodium bromide were added to stirred pulp
 suspensions in water of either 800 g at 1.3% consistency or 1600 g slurry
 at 3% consistency (10.4 9 or 48 g pulp respectively). pH of the mixtures
 were adjusted to 9.5 with 0.49 N sodium hydroxide. Required amounts of
 sodium hypochlorite (as 10 to 13% solutions at pH 9.5) were then added all
 at once and the mixtures were stirred at 25.degree. C. for 30 minutes. The
 pH of the mixtures were maintained throughout using a Brinkmann pH STAT
 718 Titino at 9.5 with 0.49 N NaOH. At the end of the treatment period,
 the reactions were terminated by adding ascorbic acid to the mixture until
 its pH was lowered to 4.0 to 4.5 range (ca. 1 g).
 The pulps were filtered and washed extensively with pH adjusted water (4.5
 to 5.5). They were then re-slurried in water and formed into handsheets
 and tested as described in Example 6.
 Table 5 lists the handsheet testing results obtained from NKS pulp treated
 with different reagent concentrations
 TABLE 5
 The effect of reagent concentrations during NSK oxidation on strength
 properties of handsheets made from resulting pulp
 Oxidation Conditions Paper properties
 NSK 4- Sodium Wet Dry
 Consis- acetamido- Sodium Hypo- Tensile Tensile Wet/Dry
 tency TEMPO bromide chlorite Strength Strength Ratio
 (%) (wt %)* (wt %)* (wt %)* (g/in) (g/in) (%)
 Untreated NSK Pulp 18 2142 1
 1.3 0.1 3.0 10.0 552 2282 24
 1.3 0.02 2.0 2.5 550 2253 24
 1.3 0.02 1.0 2.5 395 2230 18
 1.3 0.02 0 2.5 197 2108 9
 3.0 0.02 2.0 2.5 743 2518 30
 3.0 0.01 0.5 2.0 625 2456 25
 3.0 0.005 0.5 1.5 528 2383 22
 *All reagent quantities given are based on weight of pulp.
 EXAMPLE 11
 Three sets of handsheets prepared in Example 10 were also tested for their
 temporary wet strength characteristics in the following manner. Following
 the testing of the initial wet strengths, involving a soaking time of
 approximately 5 seconds in neutral pH water, strips from the corresponding
 handsheets were tested for their residual wet tensile strength after a
 soaking time of 30 minutes under similar conditions. This allows the
 determination percent of "decay" in wet strength, expressed as the percent
 loss of the average initial wet strength. Results from these samples are
 given in Table 6.
 TABLE 6
 The wet tensile strength of handsheets made from oxidized NSK
 pulps after prolonged soaking (initial wet strengths are from Example 10
 and Table 5).
 Wet Tensile
 Initial Wet Tensile Strength After Wet Strength
 Strength 30 min. Soaking Time Decay
 (g/in) (g/in) (%)
 743 111 85
 625 81 87
 550 63 89
 EXAMPLE 12
 The process de scribed in Example 1 was repeated under similar conditions
 on NSK pulp in order to determine the effect of oxidation pH on the wet
 and dry strength and wet/dry ratio of the handsheets. Therefore, 1600 g
 stirred mixtures of 3% consistency NSK pulp in water (48 g pulp)
 containing 4.8 mg 4-acetamido-TEMPO and 0.24 g sodium bromide were treated
 with 7.56 g sodium hypochlorite (as 12.7% solution). Mixtures were then
 stirred at 25.degree. C. for 30 minutes at different pH's which was
 maintained throughout using a Brinkmann pH STAT 718 Titrino at using 0.49
 N NaOH. At the end of the treatment period, the reactions were terminated
 by adding ascorbic acid to the mixture until its pH was lowered to 4.0 to
 4.5 range (ca. 1 g).
 The pulps were filtered and washed extensively with pH adjusted water (4.5
 to 5.5). They were then re-slurried in water and made into handsheets and
 tested as described in Example 6. The wet and dry tensile strength of the
 handsheets made from NSK pulps modified at different pH's are given in
 Table 7.
 TABLE 7
 The effect of pH during treatment of NSK pulp on the strength
 properties of handsheets made from resultant pulps
 Paper Properties
 Wet Tensile Dry Tensile Wet/Dry
 Oxidation Strength Strength Ratio
 pH (g/in) (g/in) (%)
 7.5 363 2101 17
 8.0 401 1955 21
 8.5 541 2223 24
 9.0 607 2277 27
 9.5 595 2376 25
 10.0 565 2429 23
 10.5 470 2460 19
 11.0 258 2161 12
 EXAMPLE 13
 The process described in Example 11 was repeated under similar conditions
 on NSK pulp in order to determine the effect of oxidation time and
 temperature on the wet and dry strength and wet/dry ratio of the
 handsheets. Therefore, 1600 g stirred mixtures of 3% consistency NSK pulp
 in water (48 g pulp) containing 4.8 mg 4-acetamido-TEMPO and 0.24 g sodium
 bromide were treated with 7.56 g sodium hypochlorite (as 12.7% solution).
 Mixtures were then stirred at 25.degree. C. for 30 minutes at different
 4.8 mg 4-acetamido-TEMPO and 0.24 g sodium bromide were treated with 7.56
 g sodium hypochlorite (as 12.7% at pH 9.5) for different periods of time
 at different temperatures. The pH was maintained at 9.5 throughout using a
 Brinkmann pH STAT 718 Titrino at using 0.49 N NaOH. At the end of the
 treatment period, the reactions were terminated by adding ascorbic acid to
 the mixture until its pH was lowered to 4.0 to 4.5 range (ca. 1 9). The
 pulps were filtered and washed extensively with pH adjusted water (4.5 to
 5.5). They were then re-slurried in water and made into handsheets and
 tested as described in 6.
 The effect on wet and dry tensile strength of handsheets made from NSK
 pulps modified at different treatment time and temperatures are listed in
 Table 8.
 TABLE 8
 The effect on the strength properties of handsheets made from NSK
 pulps modified at different treatment time and temperatures
 Paper Properties
 Oxidation Conditions Wet Tensile Dry Tensile Wet/Dry
 Temperature Time Strength Strength Ratio
 (.degree. C.) (min) (g/in) (g/in) (%)
 Untreated NSK Pulp 31 2170 1
 25 10 562 2461 23
 25 40 609 2288 27
 35 10 506 2166 23
 35 40 469 2029 23