WO1997038158A1

WO1997038158A1 - Persulfate-based system for repulping high kappa wet strength broke

Info

Publication number: WO1997038158A1
Application number: PCT/US1997/005676
Authority: WO
Inventors: Robert H. Tieckelmann; Dean S. Thorp
Original assignee: Fmc Corporation
Priority date: 1996-04-08
Filing date: 1997-04-04
Publication date: 1997-10-16
Also published as: AU2442797A

Abstract

A method for repulping high kappa wet strength broke using persulfate, pH adjuster, metal catalyst, and an effective surfactant. A formulation containing persulfate, pH adjuster, metal catalyst and a nonionic or anionic surfactant.

Description

Persulfate-Based System for Repulping High Kappa Wet Strength Broke

Field of the Invention

This invention relates to the repulping of wet strength broke. More particularly the invention relates to compositions and methods used for repulping high kappa wet strength broke.

Background

A wet paper, typically, retains only 2-7% of its dry strength. The addition of a wet strength resin, such as a polyamide-epichlorhydrin resin, during the production of the paper, provides a wet strength paper that can retain 15% or more of its dry strength when wet. This very benefit, however, makes it more difficult to recycle such paper, because in recycling, the paper to be recycled must first be pulled apart in an aqueous environment before it can be reworked to produce recycled paper.

The paper that is introduced to the recycling process for reworking is called broke. Since wet strength broke is more resistant to being pulled apart in water than other broke, repulping wet strength broke requires the use of special techniques and procedures.

Broke often contains unbleached fibers with a high lignin content. A high lignin (high kappa) content broke, having unbleached fibers, can also present a recycling problem, since that broke needs to be repulped without bleaching the lignin. Several techniques are used in the paper making industry for addressing the problem of recycling papers that have either a high kappa content or a wet strength resin. One of these is to use hypochlorite; the other is to use a persulfate.

SUBSTTTUTE SHEET (RULE 26) Hypochlorite (hypo) is used by many paper mills to repulp bleached wet strength broke, since it reacts with, and degrades, the wet strength resin. Hypo is also used to bleach pulp that contains lignin, since it reacts with lignin to form soluble chlorinated molecules. Thus, lignin, which is responsible for the brown color found in a high kappa pulp such as unbleached kraft (also known as

"UBK"), can be removed from the pulp. However, paper products prepared from UBK pulp, such as linerboard, paper bags, cardboard, and toweling, often contain both high lignin levels and a wet strength resin. Hypo does not effectively repulp such high lignin wet strength broke products because the reactions between the hypo and the lignin occur faster than do the reactions between the hypo and the wet strength resin.

Peroxydisulfate is, also, used by paper mills to repulp wet strength broke. For this purpose, formulations containing peroxydisulfate, an alkali source, and a metal catalyst have been effective. However, like hypo, peroxydisulfate repulping efficacy of wet strength broke is lower in the presence of lignin. Although peroxydisulfate is generally effective for oxidizing wet strength resins, it is relatively inactive in the presence of lignin.

The need to provide a viable means for repulping such materials is acute, since currently, large quantities of wet strength resins, including an estimated 25% of the poly amide-poly amine epichlorhydrin wet strength resins sold, are used to produce UBK papers. Because there is no viable repulping aid, much of the UBK wet strength broke is landfilled or burned. It would be beneficial to the environment, and economically beneficial , if a repulping aid could be developed that would permit the repulping of wet strength broke having high lignin levels. Summary of the Invention

In accordance with the present invention, it has been discovered that wet strength broke having high lignin levels can be repulped using from 51-94 weight percent of a persulfate; 4-43 weight percent of a pH adjuster; from 0.05-2 weight percent of an effective surfactant, and from 0.05 - 0.2 weight percent of a metal catalyst selected from the group consisting of copper, iron, silver, and nickel. These may be applied separately or as a formulated product.

Description of the Preferred Embodiments

High lignin broke (also known as high kappa broke) is generally any broke that contains more than 7 weight percent lignin; while UBK broke is a high lignin broke that generally contains more than 15 weight percent lignin and that may contain more than 24 weight percent lignin.

Lignin is a macromolecule of very high molecular weight. Although the structure of lignin is complex, there are two different kinds of inter-unit bonds: ether bonds (-C-O-C-) and carbon-carbon bonds (-C-C-). These inter-unit groups link lignin to lignin, lignin to wet strength resin, lignin to cellulose, and wet strength resin to wet strength resin. High lignin levels impair repulping with a formulated persulfate. This impairment probably occurs because lignin provides a great number of bonding sites for the wet strength resin and because lignin, being essentially hydrophobic, hinders the approach of the persulfate anion radicals to the surface of the paper. Also, some of the persulfate may react with the lignin, instead of the wet strength resin. The surfactant of this invention, permits the persulfate to react more efficiently with the wet strength resin, in any broke that contains lignin. The term "surfactant" denotes a chemical compound with a calculable HLB (hydrophilic/lipophilic balance) within the range of from 1 to about 40. A surfactant has at least two types of moieties, a hydrophilic moiety and a hydrophobic moiety. Although HLB was developed as a means for categorizing emulsifiers according to their tendency to form emulsions containing oil and water, the HLB system has been and here is applied to surfactants. Generally, the lower the HLB the greater the tendency is for the surfactant to dissolve in oil, and the higher the HLB the greater the tendency is for the surfactant to dissolve in water. A low HLB surfactant has an HLB of about 2 to 8 and is usually oil soluble or at least oil dispersible. A high HLB surfactant has an HLB of about 13 or greater and is usually water soluble or at least water dispersible. Intermediate HLB surfactants have intermediate tendencies. This system, which was developed by Griffin at ICI America, is now a widely accepted empirically derived standard that is used to help select alternative surfactants based on the HLB of the surfactant being used. It is also used to select groups of surfactants which individually may not have the desired HLB, but collectively have a net HLB within the needed range.

The term "persulfate" includes peroxymonosulfate as well as peroxydipersulfate, which is also known as dipersulfate. The actual experiments reported herein use peroxydisulfate, unless otherwise indicated.

A persulfate-based system for repulping high kappa wet strength broke can include a formulation that contains persulfate and surfactant, or alternatively, the persulfate and surfactant can be separately added to the broke to be, or being, treated. The surfactant can be liquid or solid. If the surfactant is a solid, it may be heated to form a liquid. The surfactant, whether a liquid or a solid, may be blended with the other ingredients and a solid formulation will be formed. Those surfactants which are incompatible with the other ingredients, may be encapsulated, prior to formulation, according to encapsulation procedures generally known in the industry.

The following table (Table 1) gives preferred, more preferred and most preferred formulations, which can be used for repulping high kappa wet strength broke.

Table 1

Formulation - Ranges (% of mixture)

Range Persulfate pH Adjuster¹ Metal Catalyst² Surfactant³

Preferred 51-94 4-43 0.05-6 0.05-2

More Preferred 61-85 14-39 0.1-3 0.1-1

Most Preferred 70-80 20-29 0.1-2 0.2-0.5

1. pH adjuster can be any salt of carbonate, bicarbonate, or sesquicarbonate, preferably an alkali metal salt. Sodium sesquicarbonate is preferred.

2. The metal catalyst must be a soluble salt of copper, iron, silver, or nickel. Copper is preferred. 3. Surfactants must be non-ionic or anionic. Non- ionic is preferred.

Effective surfactant chemistry includes, but is not limited to, tristyrylphenols and ethoxylated alcohols. The hydrophilic-lipophilic balance (HLB) was found to be the main factor that determines surfactant efficacy in this application. Although any surfactant can be effectively employed, Table 2 provides preferred, more preferred and most preferred HLB ranges and surfactant types that can be used in the practice of this invention.

Table 2

Effective Surfactant HLB - Ranges

Range Surfactant Chemistry HLB %wt/wt of Formulation

Preferred Non- ionic, Anionic 2-13 0.05-2 More Preferred Non-ionic 2-11 0.1-1 Most Preferred Non-ionic 2-7 0.2-0.5

Table 3 provides the dosage ranges at which the formulation of this invention may be applied.

Table 3

Dosage Ranges (on the weight of dry fiber)

Range Formulation % Preferred 0.5-15

More Preferred 1.0-10

Most Preferred 2.5-7.5

Even where the ingredients of the formulated dosage form are not added as a formulated dosage form, the dosage of those ingredients can be determined from the above information. Generally, the dosage can be expressed as a weight ratio of persulfate to pH adjuster to surfactant to metal ion with the total percent based on the weight of dry fiber (owf) corresponding to the dosage for the formulated product, as expressed above. For example, in a preferred dosage of 0.1- 15 % owf, the ratio is 51-94 to 4-43 to 0.05-6 to 0.05-2, in a more preferred dosage of 1-10% owf, and the rato is 61-85 to 14-39 to 0.1-3 to 0.1-1 ; and in a most preferred dosage of 2.5-7.5 % owf, the ratio is 70-80 to 20-29 to 0.1-2 to 0.2- 0.05.

In addition to the concentration of the surfactant, its hydrophilic- lipophilic balance (HLB) is also a critical parameter for effective repulping of high kappa wet strength broke. Nonionic surfactants with low HLB are most effective. Surfactants with lower HLB are more lipophilic and have greater affinity to the organic lignin structure. With a low HLB surfactant present, the activated oxidant (sulfate anion free radical) is better able to access the wet strength resin. Bonds between the wet strength resin and lignin are then more effectively destroyed.

In practice, high lignin wet strength broke is repulped at a faster rate when low HLB surfactants are present than when sodium persulfate formulations are used without surfactants. A sodium persulfate formulation that contains such surfactants allows for effective repulping of UBK wet strength broke. Surprisingly, this repulping formulation can defiber UBK/ wet strength broke without bleaching the lignin. Moreover, the surfactant/ persulfate, as formulated or used, according to this invention, also improves the defibering of bleached wet strength broke, generally.

For repulping, an aqueous slurry of broke and either ingredients of the formulated product, or the formulated product itself, is prepared and agitated. The repulping aid, whether the formulated product or as the separately added ingredients of the formulated product, is generally dosed based on the weight of the fiber, also referred to as "owf". The agitation is for sufficient time and a sufficient temperature to produce the desired pulp.

Generally the slurry is maintained within a pH range of from 2-11; however, a pH of from 7 to 10 is preferred. Any pH adjuster can be used. However, alkali metal sesquicarbonate carbonate, or bicarbonate are preferred.

The embodiments of this invention work best if the temperature of the system is greater than 50" C. A temperature within the range of 40^* C to 75 ° C is generally sufficient to activate the persulfate and/or metal ion to support the oxidation of the wet strength resin during repulping. Conservatively, a temperature of 60 'C may be employed.

Laboratory studies have demonstrated that tristyrylphenol, and ethoxylated alcohol surfactants are effective. Nonionic surfactants are most effective. Cationic surfactants are generally not effective; since they react with the activated oxidant.

The following examples are intended as a further illustration of the invention, but not as a limitation on the scope of the invention. All parts and percentages in the examples, and throughout this specification and claims, are by weight, and all temperatures are in degrees centigrade, unless otherwise indicated.

SUBSTΓTUTE SHEET (RULE 26) Repulping High Kappa Wet Strength Paper with Activated Peroxydisulfate

Repulping

In the Examples, the degree to which a sample has been repulped is characterized by which of the six repulping stages it has been repulped to. A stage 6 pulp is characterized as a broke that has been repulped to finely separated fibers, while a stage 5 pulp is characterized as a broke that consists of primarily finely separated fibers and a few bonded fibers; while a stage 4 pulp is characterized as a broke that consists of primarily a few small flakes and numerous bonded flakes.

Generally, the more complete the degree of fiber separation in a pulp is , the higher the repulping stage number will be, and the finer the paper produced from the repulped broke can be. Similarly, the finished paper good will tend to have a greater degree of dumpiness and surface irregularity, the less complete the degree of fiber separation is.

Properties of the paper: In the experiments exemplified herein, the paper used came from

American Tissue Mills of Massachusetts, Inc. The paper had a Kappa content of about 20 and a wet strength resin content of from 5 to 10 lbs of Kymene^®wet strength resin per dry ton. The surfactants employed in the examples are characterized as follows:

Brand name Source Type HLB

Soprophor S/25 Rhone-Poulenc nonionic 14.5

Soprophor BSU π 12.5

Soprophor 796-P 13.5

Soprophor CY/8 13.5

Trycol 574-U Henkel nonionic 15.1

Trycol 5940 11.4

Trycol 5993A 7.9

Atlox 4913 ICI nonionic 11-12

Atlox 4914 5-7

Soprophor 3D33 " anionic

Span 85 ICI nonionic 1.8 Geropon WT-27 Rhone-Poulenc anionic NA

These brand names can be further categorized as follows :

Soprophor S/25 ethoxylated phenol; more particularly a tristyryl phenol; Soprophor BSU ethoxylated alkyl phenol; more particularly a tristyryl phenol; Soprophor 796/P propoxy lated & ethoxylated fatty acids, alcohols or alkyl phenols; more particularly a tristyryl phenol; Trycol 574-U ethoxylated alcohol; Trycol 5940 ethoxylated alcohol; more particularly a polyoxyethylene (6) tridecyl alcohol; Trycol 5993A ethoxylated alcohol; more particularly a polyoxyethylene (3) tridecyl alcohol; Atlox 4913 methyl methacrylate graft copolymer; Atlox 4914 alkyd-polyethylene glycol resin; Span 85 sorbitan trioleate; Geropon WT-27 sulfosuccinates and derivatives; more particularly a sulfonated aliphatic ester. The following lists include the equipment and the experimental procedure used herein.

Equipment:

1) A stainless steel disintegrator, having stainless steel pipe, baffles, and conforming to TAPPI method T-205-os71 was employed. Also used were the following components: a. Talboy Model 401 high speed mixer mounted to the base. b. Propeller per TAPPI method T-205-os71 mounted to stainless steel shaft. c. Cole-Parmer heating mat with Variac voltage output regulator.

2) Assorted beakers/ 200-2000 mL, 1000 mL graduated cylinder.

3) Paper cutter, timer, pH meter, metal thermometer, gloves, safety glasses, lab coat, and a 10 mL sampling device.

4) Microwave oven.

5) Standard pulp samples: stages 1-6.

Procedure:

1) Each sample weighed 20 grams and consisted of broke that had been cut into 1 inch squares.

2) A 2 L pyrex beaker, preheated in a microwave oven, was filled with

1600 mL water and heated to 70'C.

SUBSTΓTUTE SHEET (RULE 26) 3) After preheating the water, 1500 mL was poured into a second 2 L pyrex beaker.

4) That water was poured into preheated disintegrator vessel and the temperature was adjusted to provide a maintenance temperature of

65'C.

5) Immediately following step 4, the broke sample and chemical treatment(s) were added to the disintegrator vessel, and the pH was adjusted, if required. The disintegrator was started with a propeller speed preset at 2800 rpm. As a chemical treatment, 1.2 g of Kybreak 300 repulping aid was employed to yield 600 ppm Na₂S₂0_g and one ppm copper ion in the disintegrator solution; and surfactant was employed as described in Experiments 1-16 below.

6) At five minute intervals: the temperature of the pulp was taken and recorded, and a 10 mL sample was taken.

7) The 10 mL sample was diluted to 200 mL with tap water, and compared with premade standard stages 1-6 and a record was made of the comparison that most closely described sample.

8) Sampling was repeated until 60 minutes had passed or a stage 6 was obtained; and then the final pH, temperature, and residual oxidizer measurements were recorded.

9) The sample was retained for preparation of handsheets, if required. Experiments 1-16:

The following describes the experiments performed using the just described procedure and equipment.

Experiment 1 is a control that provides a baseline time of about 60 minutes for repulping an American Tissue Mills (ATM) paper, while Experiments 2 through 5 and 9 demonstrate that a high HLB surfactant is no more effective than the control. Experiments 6-14 demonstrate that an intermediate or a low HLB surfactant can affect repulping. Experiment 6 through 8, demonstrate that increasing the dosage level of an intermediate HLB surfactant, such as Trycol 5940, which has an HLB of 11.4, decreased the time needed to achieve stage 6; that is, repulping occurred more quickly as the dosage level increased. Experiments 11 through 13 demonstrate that for a low HLB surfactant a lower dosage may suffice. Thus, surfactants having an HLB of less than 13 benefit the repulping of high kappa wet strength papers. Example 15 demonstrates that an anionic surfactant also has efficacy in repulping high kappa wet strength papers.

SUBSTTΓUTE SHEET (RULE 26)

Claims

We Claim:

1). A formulation for repulping a high kappa wet strength broke, comprising from 51-94 weight percent of a persulfate; 4-43 weight percent of a pH adjuster; from 0.05-2 weight percent of an effective surfactant, and from 0.05 - 0.2 weight percent of a metal catalyst selected from the group consisting of copper, iron, silver, and nickel.

2). The formulation of claim 1, wherein the surfactant is a nonionic or an anionic surfactant having an HLB within the range of from 2-13, and from 0.05- 0.2 weight percent of a metal catalyst selected from the group consisting of copper and nickel.

3). The formulation of claim 2, wherein there is 61-85 weight percent persulfate; from 14-39 weight percent pH adjuster; from 0.1-1 weight percent surfactant, which has an HLB within the range of from 2-11; and from 0.1-3 weight percent metal catalyst.

4). The formulation of claim 2, wherein there is 70-80 weight percent persulfate; from 20-29 weight percent pH adjuster; from 0.2-0.5 weight percent surfactant, which has an HLB within the range of from 2-7; and from 0.1-2 weight percent metal catalyst.

5). The formulation of claim 2, wherein the persulfate is a dipersulfate and the metal catalyst is copper.

6). The formulation of claim 3, wherein the persulfate is a dipersulfate and the metal catalyst is copper. 7). The formulation of claim 4, wherein the persulfate is a dipersulfate and the metal catalyst is copper.

8). A method for repulping, comprising dosing an aqueous slurry of high kappa wet strength broke with from 0.5-15 % owf of the formulation of claim 1 ; heating the aqueous slurry to a temperature sufficient to initiate repulping; and maintaining that temperature or above until at least a stage 5 pulp is obtained.

9). The method of claim 8, wherein the formulation is dosed at 0.1-10% owf; heating the slurry to a temperature sufficient to initiate repulping; and maintaining that temperature or above until at least a stage 5 pulp is obtained.

10). The method of claim 9, wherein the formulation is dosed at 2.5-7.5 % owf.

11). A method for repulping, comprising dosing an aqueous slurry of a high kappa wet strength broke with a dipersulfate; a metal ion selected from the group consisting of copper, iron, silver, and nickel; a nonionic or anionic surfactant, which has an HLB within the range of from 2-13; and a pH adjuster are added at a total dosage of 0.5-15% owf, and the ratio of dipersulfate to pH adjuster to surfactant to metal ion is 51-94 to 4-43 to 0.05-2 to 0.05-2; heating the slurry to a temperature sufficient to initiate repulping; and maintaining that temperature or above until at least a stage 5 pulp is obtained.

12). The method of claim 11, wherein the total dosage is 1-10% owf; the surfactant has an HLB within the range of from 2-11; the rato is 61-85 to 14-39 to 0.1-3 to 0.1-1; and the aqueous slurry is heated to a temperature of at least 60 ^*C and maintained at that temperature until at least a stage 5 pulp is obtained. 13). The method of claim 12, wherein the total dosage is 2.5-7.5 % owf and the ratio is 70-80 to 20-29 to 0.1-2 to 0.2-0.05.