NZ211119A

NZ211119A - Cationic cellulose product and preparation

Info

Publication number: NZ211119A
Application number: NZ21111985A
Authority: NZ
Inventors: J M Gess; M J Harding; R C Gaines
Original assignee: Weyerhaeuser Co
Priority date: 1985-02-14
Filing date: 1985-02-14
Publication date: 1987-07-31

Description

<div class="application article clearfix" id="description"> I o PATENTS FORM NO. 5 2 ! t 1 1 9 ferity Date(s): Complete Specification Filsd: Class: . 'on t>'p: „— 3. J. JUL J93Z-,.... -.•••• aq6 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "CATIONIC CELLULOSE PRODUCT AND METHOD FOR ITS PREPARATION" WE WEYERHAEUSER COMPANY, a corporation organized under the laws of the State of Washington, of Tacoma, Washington, 98477, U.S.A. hereby declare the invention, for which -f/we pray that a patent may be granted to-ste/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- -1- (fc!lov/»r< by p-.rt | A.) P 41 11,657F 1<V CATIONIC CELLULOSE PRODUCT AND METHOD FOR ITS PREPARATION BACKGROUND OF THE INVENTION The present invention is a fibrous, cationic cellulose pulp product and the method for preparing it. The product is especially advantageous in papermaking for its improved retention of certain dyestuffs and filler materials. 5 The surface of cellulose fibers is normally slightly anionic in nature due to the presence of carboxyl and carbonyl groups introduced during the pulping and bleaching process. This negative charge is responsible for a number of undesirable effects in papermaking. Principal among these is the tendency of the longer fibers to repel fine cellulose particles 10 which result from refining and the similar tendency to repel many additives such as fillers, pigments, dyes, and sizes, many of which also bear negative charges. As a result, these fine particles tend to go into the white water during sheeting where they represent an economic loss and a pollution problem. In response to this problem, alum has traditionally been added to 15 adjust the electrical charge of surfaces to which it is adsorbed. However, alum is not very efficient; therefore, relatively large amounts are required. This produces an undesirable, relatively highly acidic environment both in the sheeting process and in the final paper product. In the papermaking process, this acidity tends to corrode equipment. In paper it results in 20 relatively rapid loss of physical properties such as tear strength and fold resistance. A number of routes have been explored using materials besides alum to overcome the anionic nature of cellulose fibers. One such route, which has seen commercial use for approximately 30 years, has been the use 25 of additives which are cationic in nature; e.g., cationic starch. These additives are attracted to the anionic cellulose and serve to modify or neutralize the electrical charge so that the fibers have less tendency to repel anionic additives. Today a relatively wide variety of cationic papermaking additives are available. These include materials for improving 30 drainage rate, reducing fines and pigment loss, and increasing wet strength. Cationic additives also make the use of less acidic sizing agents possible. p«i 7 1 M 11,657F 2 v J Alkyl ketene dimers are such a sizing agent applied in the pH range of 6-8. Articles to McKenzie, Appita 21 (4): 104-116 (1968) and to Moore, Tappi 58:99-101 (1975) are informative of the state of the art. Another route to overcoming the anionic nature of cellulose 5 fibers has received considerable research although no products have yet evolved which have been of commercial importance. This approach has been to make the fibers themselves cationic in nature, usually by reaction with a material that introduces positively charged nitrogen atoms into a substituent side chain. Uwatoko, Kagaku Kogyo (Japan) 25 (3):360-362 10 (1974) briefly summarizes the state of the art in regard to cationic fibers. Uwatoko lists six major approaches that have been taken. Without putting them in any chronological order, these are as follows: the first method introduces side chains containing a tertiary nitrogen atom. These side chains are attached to the cellulose molecule at the hydroxyl groups as 15 ethers. One product of this type which has received considerable study is the quaternized diethylaminoethyl derivative of cellulose. A second route to the preparation of cationic cellulose is the reaction of cellulose in the presence of sodium hydroxide with ethanolamine, aqueous ammonia or melamine. A third process is the reaction between cellulose and a material 20 such as 2-aminoethyl sulfuric acid in the presence of sodium hydroxide. Another product has been formed by iminating an aminated cellulose by reaction between the aminated cellulose and ethylene imine. An approach which has received considerable study is the reaction of various trimethyl ammonium salts. Of particular importance has been glycidyl trimethyl 25 ammonium chloride reacted with cellulose in the presence of a catalytic amount of sodium hydroxide. A related approach has been the reaction of — 2-chloroethyldiethyl amine with alkali cellulose. This product is then —/ quaternized with methyl iodide in anhydrous alcohol. Finally, Uwatoko describes a modified cellulose described in more detail in J. Soc. Fiber Sci. 30 Technol. (Japan) 30 (5/6):T313-3l4 (1974). In this process cellulose is reacted with a solution of sodium acid cyanamid at a concentration of 50-200 g/L at a pH in the range of 10-13 and temperature of 10-40°C for 4-24 hours. One approach not specifically discussed by Uwatoko is the 35 reaction of cellulose with a mixture of epichlorohydrin and a tertiary amine with cellulose in the presence of aqueous sodium hydroxide. This process is 1i M P 3 EN discussed by McKelvey and Benerito in J. Appl. Polymer Sci. 11:1693-1701 (1967). Paschall, in U.S. Patent 2,876,217 describes the use of this process to make a granular cationic starch useful as a papermaking additive. Benerito et al., Anal. Chem. 37:1693-1699 (1965) describe in detail the 5 production of quaternary ammonium ethers of cellulose by the reaction of diethylaminoethyl cellulose with either methyl iodide or ethyl bromide under completely anhydrous conditions. Kaufer et al., Papier (Darmstadt) 34(12):575-579 (1980) describes several applications of cellulose made cationic by the reaction of glycidyl 10 trimethyl ammonium salts. These authors also teach the usefulness of {3-methacryloxyethyltrimethyl ammonium chloride as a cationizing agent. Krause et al., Papier (Darmstadt) 35(IOA):33-38 (1981) building on the work of Kaufer and his coworkers, show the superiority of cationic pulps in retaining alkyl ketene dimer sizing materials as opposed to the 15 conventional use of cationic starches as retention aids. It is known in the art that only part of the fiber in a papermaking stock needs to be cationized in order to achieve significant benefit. The preparation of 20 a wide variety of quaternary nitrogen-containing cellulose ethers which function as cationic materials are also known in the art. Lewis et al., in U.S. Patent 3,694,393 show the treatment of cellulose with the reaction product of epichlorohydrin and dimethylamino-ethyl methacrylate. 25 There appear to be a number of reasons why a cellulose pulp having cationic substituents has never appeared commercially in the marketplace as a papermaking fiber. One of the principal reasons is the expense. In many cases the raw materials themselves are very expensive. Along with this is the problem that the reaction conditions of the cellulose 30 with the sub6tituent materials are such as to cause the cost of the product to be greatly elevated. Many of the cationic cellulose materials produced by straightforward chemical reaction are not of fibrous nature. This is a problem with relegates them to the nature of an additive in papermaking as opposed to use as a primary fiber. A number of the products which are 35 fibrous must be produced by grafting reactions. Here free radical sites are induced in the cellulose chains by means such as eerie ion activation or high t9JUNV>873 V. I P 41 11,657F 1 energy irradiation. An appropriate polymerizable monomer having vinyl unsaturation is then coupled to the cellulose and polymerized in the presence of a free radical initiator. The overall result has been a group of products which are either technically unsuitable or far too expensive for 5 general use. Cationic starches, which have been available commercially for over 30 years, do have some relationship to the cationic celluloses just described. One who sits on the edge of this particular scientific art might question why the processes used for the preparation of cationic starches 10 have not successfully been applied to cellulose fibers. There is a ready answer. In the first place, most of the cationic starches are modified in physical nature by cooking or partially cooking during the chemical reaction which introduces cationic sites. There is not any need for these products to retain their original physical form. A second reason is that cationic 15 starches are used in relatively small percentages in papermaking. Therefore, they form only a small portion of the ultimate product. This fact makes their relatively high costs more tolerable to the papermaker. While there is no need to review all of the extensive technical literature relating to cationic starches, a few recent patents bear some relationship to the 20 present invention. Aitken, U.S. 3,674,725 describes a product in which a polyepichlorohydrin is modified with an amine, preferably trimethylamine. This product can then be reacted with a starch under strongly alkaline conditions. The same inventor, in U.S. Patents 3,854,970 and 3,930,877 teaches an approximately equal molar composition of epichlorohydrin and 25 dimethylamine reacted under alkaline conditions and then acidified to produce a quaternary ammonium salt. The preferred compositions have 10-20% ammonia substituted for an equivalent of the dimethylamine. These polymers can be used to prepare liquid cationic starches by reaction under rather strongly alkaline conditions with partially hydrolyzed starches. 30 Buikema, U.S. 4,029,885, shows the use of those starches for sizing paper. Buikema et al., U.S. 4,146,515 treat a lightly oxidized starch with an epichlorohydrin-dimethylamine polymer at about 60-80C for one hour- This product is subsequently acidified to make an amine salt. Cosper et al., U.S. 4,268,532, use a dimethylamine-35 epichlorohydrin polymer with a second polymer (which may or may not be anionic) for retaining starch in repulped broke. In a series of control :Un 19 samples using the Epi-DMA polymer by itself the starch retention efficiency in the simulated paper mill broke was markedly better in an acidic environment. A system of this type would be essentially ionic in nature. Because of the enormous surface area of the swollen starch grains, 5 compared with the cellulose, the polymer will preferentially combine with the starch at a rate from two to three orders of magnitude greater than with the cellulose. In the Cosper system using 5% oxidized starch, studies have shown that a maximum of about 7-996 of the polymer charged to the system will associate with the cellulose at pH 9. 10 The use of an Epi-DMA polymer with cellulose in an acidic (ionic) environment to enhance dye retention is known. It is interesting that none of these inventors appear to have considered the possibility of reacting their epichlorohydrin-dimethylamine IS polymer directly with cellulose under conditions which would produce a product which could be both fibrous and permanently cationic in nature. : The present invention describes a cationic cellulose made by reaction, under mildly alkaline aqueous conditions, of cellulose fibers with any of a group of polymers based on the reaction product of epichlorohydrin 20 and dimethylamine. The reaction conditions and nature of the materials involved is such that a fibrous product results which is little more expensive to manufacture than the cellulose itself. SUMMARY OF THE INVENTION The present invention is a fibrous cationic cellulose product and 25 a process for making it which comprises an additive of cellulose with a material which is either a polymer of epichlorohydrin and dimethylamine or a polymer of this type which has been further modified by replacing a portion of the dimethylamine with a cross-linking or branching agent which may be ammonia or a primary aliphatic diamine of the type H^N-R-NHg, 30 where R is an alkylene radical having from two to eight carbon atoms. The proportions of epichlorohydrin and dimethylamine may vary within the range of about 0.8 to 3 moles of epichlorohydrin for each mole of dimethylamine. The preferred polymers will be approximately equal molar in proportion. Ammonia and the primary aliphatic diamines serve to act as cross-linking or branching agents for the polymers. Further, their use increases the number of tertiary nitrogen atoms which may be quaternized = 19 jUNt987n| IP 1 ^ P 41 11,657F to provide sites for positive charges. Up to 30 molar percent of the dimethylamine may be replaced by ammonia or the aliphatic diamine in the reaction process. Irt general, it is preferred that the molar percentage of ammonia or aliphatic diamine be in the range of 10-20%. Preparation of polymers suitable for use in the present invention is described in U.S. Patent 3,930,877 to Aitken. It should be considered within the scope of the invention to use mixtures of any of the above polymers. While the cationic cellulose product of the present invention is described as an "additive" of cellulose with the epichlorohydrin-dimethylamine polymer, it will be understood by those skilled in the art that the polymer is probably covalently bonded to the cellulose, when used under alkaline reaction conditions, by virtue of pendant epoxy moieties which react by etherification with the hydroxyl groups on the cellulose molecules. Alternatively, the polymers may in part be hydrogen bonded or otherwise attached to the cellulose. When acidic conditions are used, the polymer tends to bond ionically. It can then be easily removed by washing or by exposure to other ionic species in an aqueous environment. Among the modifying agents which serves as potential cross linkers for the polymer, ethylene diamine and hexamethylene diamine are preferred materials. The polymer may be used effectively over a relatively wide range. Typically usage will be in the range of 0.5-20 kg/t. The preferred range of usage is about 2-10 kg/t. These usages are somewhat nominal and are based on manufacturer specified solids percentages in the aqueous solutions of polymers sold commercially. Solids percentages are only approximate for active epichlorohydrin-dimethylamine polymer since they are based on raw materials charged to the synthesis reactor. This approximation procedure is necessary because of the great difficulties in analyzing the polymer solutions without inducing decomposition of the product. In subsequent examples, calculations will assume that the percent solids as specified by the polymer manufacturer are equivalent to percent active epichlorohydrin-dimethylamine polymer. The cationic cellulose product should preferably contain at least 0.02% combined nitrogen as measured by the Kjeldahl method. Combined nitrogen is considered to be that remaining after repeated water washing of the product. P 41 11,657F 7 4$ rf*Ss. One of the unique aspects of the present invention is the method of making the cationic cellulose product. It has been discovered against all expectations that it is only necessary to add an aqueous solution of the polymer to a suspension of cellulose in water which has had the pH raised 5 into the alkaline range, preferably to the range of approximately 10.0-10.5 where reaction efficiency is higher, and to agitate this mixture for 30 minutes or less at room or elevated temperature. Most surprisingly, the process may be carried out at an alkaline stage in the bleaching process, preferably after any hypochlorite treatments, whereupon the resulting 10 additive appears resistant to further bleaching operations. In the usual bleaching schedule for a kraft pulp, the polymer is conveniently added during an alkaline extraction stage or hydrogen peroxide stage during the latter part of the bleaching sequence. In this way, no changes in the bleaching sequence are necessary nor are any additional steps required to 15 produce the cationic additive. This discovery flies in the face of expectations that the oxidizing environment in bleaching stages during or following the addition of the polymer would either remove it or destroy its effectiveness. It is thus an object of the present invention to provide a fibrous 20 cellulosic product which is cationic in nature. It is another object of the invention to provide a cationic cellulose product with improved effectiveness in retaining anionic paper-making polymers. It is a further object to provide a cationic cellulose which has 25 extremely high retentivity of acid dyes. It is another object of the invention to provide a simple and inexpensive process for the preparation of a fibrous cationic cellulose product. It is still another object to provide a process for the manufacture 30 of a cationic cellulose product which can be carried out during an alkaline bleaching stage and which does not require a separate process step. These and many other objects will become readily apparent to one skilled in the art upon reading the following detailed description of the invention taken in conjunction with the figures. I P 41 11,657F 8 4! 111 BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph showing the relationship between the point in the bleach sequence at which the polymer was combined with the cellulose and the color intensity of the dyed product. 5 Figures 2 and 3 are graphs showing the color intensity versus the amount of dye used for a family of cationic cellulose products having different amounts of polymer. Figure 4 is a graph showing the amount of titanium dioxide retained versus that added for a family of cationic cellulose products 10 treated with different amounts of polymer. Figure 5 shows opacity of the ultimate paper products plotted against the amount of titanium dioxide added to a family of cationic cellulose products having different amounts of polymer. Figures 6 and 7 are graphs similar to figures 4 and 5 but in which 15 a different polymer was used. Figures 8 and 9 are graphs showing the effectiveness of cellulose fibers treated with various amounts of cationic polymer in adsorbing an acid dye from an aqueous solution. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 20 The cationic cellulose product of the present invention is readily prepared by adjusting the pH of a water slurry of cellulose to a pH which is preferably about 10.5 and then adding an amount of an aqueous solution of the epichlorohydrin-dimethylamine (Epi-DMA) polymer product sufficient to give at least 0.02% combined nitrogen in the product. Temperature is not 25 critical. The system works equally well at room or elevated temperatures. The slurry is agitated for about 10-30 minutes whereupon the resulting treated pulp is drained and washed. From this point it may either be sheeted or sent in the wet state for further processing. It is surprising and totally unexpected that a cationic cellulose product could be made under the 30 mild conditions outlined above. This is especially so in view of the harsh (5% alkali and near boiling temperatures) outlined in U.S. Patent 3,854,970 for preparation of cationic starches from Epi-DMA polymer products similar to those used in the present invention. What is also surprising and unexpected about the process alter-35 natives for making the cationic cellulose product is that the Epi-DMA polymer product can be added at any later alkaline stage of a pulp bleaching J P 41 " •' ^ 11,657F 9 sequence where the pH is preferably about 10 or higher. The stage at which the polymer is added should preferably be later in the bleach sequence than any hypochlorite stage. The presence of highly oxidizing conditions in the stage at which the polymer product is added, or in subsequent bleaching 5 stages, appears to make little or no difference. It also makes no difference whether the bleaching stage is one carried out at ambient or elevated temperatures. The discovery that the Epi-DMA polymer product may be added during an alkaline bleaching step is of great importance to the process 10 economics. For the first time it enables a cationic cellulose product to be made without any additional process steps over those normally required for making a bleached fiber. The only process expense is the cost of the polymer product. In the present case these products are articles of commerce made from readily available and relatively inexpensive com-15 modity chemicals. They are used only in modest amounts in the range of 0.5-20 kg/t. Process efficiency, in terms of polymer product which actually bonds to the cellulose, ranges from essentially 10096 at the low end of usage to over 60% at high end. The following examples give detailed instructions on the best 20 mode known to the inventors of making and using the products of the invention. Example 1 Bleached, spruce kraft pulp (Sample 1) was obtained from a pulp mill. Samples having 15.5 g of dry fiber were slurried in water at 2% 25 consistency (759.5 g total water). The pH was adjusted to 10.5 with NaOH and 0.31 g of a 50% solution (10 kg/t on an active material basis) of an unmodified Epi-DMA polymer (Nalco N-7655 Nalco Chemical Co., Oak Brook, Illinois) was added to the slurry. Temperature of the slurry was 20-23°C. After agitation for about 30 minutes, the slurry was diluted to 30 about 0.5% consistency and a handsheet was made. The sample was not washed other than by dilution during sheeting. Kjeldahl nitrogen content of the treated pulp (Sample 2) was 0.046% indicating an add-on of 8.7 kg/t and a retention efficiency of about 87%. Nitrogen content of the polymer solution was measured as 5.3% on an as received (50%) basis. The untreated 35 pulp control had a nitrogen content of less than 0.001%. 211119 Example 2 A sample of partially bleached Douglas-fir kraft pulp was taken from the bleach plaht of a pulp mill after the third of a five or six-step bleach sequence. The normal mill bleach sequence consists of a first stage chlorination using 75 kg/t Clg for about 30 minutes at a temperature of about 32°C. At the end of the bleach stage the pH is approximately 1.8. After washing following the chlorination, the pulp was given a treatment using about 37.5 kg/t NaOH and about 15 kg/t sodium hypochlorite at a pH in the range of 10-11 and temperature in the 60-71°C range for about one hour. While this is usually referred to as a "neutral hypochlorite" stage, it is essentially an alkaline extraction step with hypochlorite being present. Following washing after the alkaline hypochlorite treatment, the pulp was given a hypochlorite bleach using 15 kg/t sodium hypochlorite at about 40°C for approximately one hour. The pH toward the end of the step was maintained at a level slightly above 9 by the addition of caustic as necessary. While the pulp samples for laboratory treatment were taken on the washers following the hypochlorite step, the rest of the steps in a normal mill sequence will be described here. Alkaline extraction follows next, using about 10 kg/t NaOH at 60-71°C for about 30-60 minutes. The pH in this treatment is about 10.5 making it an ideal point in a plant bleach sequence for the addition of the Epi-DMA polymer product to the pulp. After washing following extraction, the pulp is given a chlorine dioxide treatment using about 7.5 kg/t ClOg with about 2 kg/t NaOH added later in the step for pH control. The pH at the end of the treatment will be about 3.5. This is a hot treatment with temperatures usually in the 65-82°C range, typically about 70°C. The time will vary between 30 minutes and 3-1/2 hours although 1/2 to 1 hour is most common. For many pulp products the chlorine dioxide stage is the final bleach treatment. If a customer wishes a whiter product, from 2-4 points additional brightness can be gained by using a peroxide treatment following the chlorine dioxide stage. This was about 1.5 kg/t of hydrogen peroxide at about 71°C with the pH raised by NaOH to about 10.5. Again, time is variable ranging from 30 minutes to 6 hours, more typically about 1 hour. P 41 11.657F 5 10 15 20 25 30 35 40 45 P 41 11.657F 11 While a detailed description of various pulp bleaching sequences is not of importance to the present invention, the reader wishing more detail can refer to any of several standard pulping texts and to U.S. patents 4,303,470 (Meredith, et al.) and 4,298,426 (Torregrossa, et al.). Using the pulp samples taken in the pulp mill after the hypochlorite stage, a series of samples was made in which two additional bleaching stages were completed in the laboratory. Epi-DMA polymer (Nalco 7655) was added at the alkaline extraction step. In each bleach trial 30 g of O.D. pulp was used. The following table shows the conditions and results of the trials. Table I Laboratory Final Stage Bleaching Sample No. 3 4 Extraction Stage nvNaOH, % 0.9 0.9 Epi-DMA, % - 1.0 Time, min. 45 45 Temp. °C. 70 70 Initial pH 12.4 12.45 Final pH 11.9 11.75 Chlorine Dioxide Stage C109, % 0.85 0.85 NaOH, % 0.34 0.34 Time, min. 180 180 Temp, °C 70 70 Final pH 3.3 3.1 Properties , .KjeldahlN, % < 0.001 0.041 ^Epi-DMA Retention, % - 78 Dye Intensity, L Value 91.4 69.5 (1) Nalco 7655. Calculated on active material basis. All percentages are based on pulp. (2) Retention as % of material charged. (3) Based on treatment in aqueous slurry with 1% Amafast Turquoise 8GPB dye. (Ciba-Geigy, Greensboro, North Carolina). Color intensity expressed as "L Value" on Hunter Colorimeter. Lower values indicate more intense color. P 41 11.657F 12 Example 3 Another bleached pulp sample was taken from the pulp mill bleach plant following the chlorine dioxide stage but prior to a hydrogen peroxide treatment. The peroxide stage was completed in the laboratory in 5 similar fashion to the bleaching done in Example 2. The following table shows conditions and results. Table II 30 10 Sample No. 5 6 Extraction Stage % 0.12 0.12 N&OH, % 0.10 0.10 15 n^Na Silicate, % 0.6 0.6 Epi-DMA, % - 1.0 Time, min. 150 150 Temp. °C. 65 65 Initial pH 10.5 10.3 20 Final pH 10.3 10.0 Properties 0.044 25 KjeldahlN, % <0.001 0 /«<Epi-DMA Retention, % 83 Dye Intensity, % dye 91.9 70.2 Please refer to Table I for footnotes. Example 4 Dyeing tests were made on the product of Sample Nos. 1, 2, 4 and 6 of Examples 1-3. Sample 1 is an untreated fully bleached kraft pulp. Sample 2 is a fully bleached pulp treated with 10 kg/t of Epi-DMA polymer. 35 Sample 4 had 10 kg/t of Epi-DMA added at the caustic extraction stage prior to the chlorine dioxide stage. Sample 6 had 10 kg/t of Epi-DMA added at the final peroxide bleach stage. In order to study dye retentivity of the cationic cellulose product, 5g dry weight of pulp was slurried at 1% consistency in room 40 temperature tap water and run for two minutes in a high shear blender. The dye was added and mixing was continued as necessary to disperse the dye in order to simulate light refining. Handsheets were made of the dyed fiber and color intensity was then measured on a Hunter Colorimeter, Type D-25A (Hunter Laboratories, Research Triangle Park, North Carolina). P 41 11,657F >9 .4 13 o, Tests were made using 0.5, 1.0, 1.5 and 2.0%, based on dry pulp weight, of Amafast Turquoise 8GBP, a sulfonated pigment made by Ciba-Geigy Corp., Greensboro, North Carolina. Results of the tests are shown graphically in Figure 1. The untreated fiber showed essentially no gain in 5 color intensity with increase in dye concentration. The three treated samples showed a relatively linear increase in intensity with increasing dye usage. Differences between the three samples treated with the Epi-DMA polymer are probably not statistically significant. This confirms the surprising and unexpected results of earlier tests indicating that the 10 bleaching treatments given to the treated pulp were not deleterious. Example 5 In order to determine the effect of the amount of Epi-DMA polymer used, a bleached kraft market pulp, the mill sheeted product of Example 1, was obtained and reslurried in water at 2% consistency. Sodium 15 hydroxide was added to adjust pH to about 10.5. Samples were then made using 1, 2, 5 and 10 kg/t Epi-DMA polymer (Nalco 7655), calculated on an active material basis. The resulting products were dyed, using the procedure of Example 4, with 0.5, 1.0, 1.5 and 2.0%, based on dry pulp, of Pergacid Blue Black B and Pergacid Orange 5R, acid dyes also available 20 from Ciba-Geigy. Additional sets of dyed samples were made with untreated pulp using 10 kg/t of alum as a dye fixative. Results with the blue dye are shown graphically in Figure 2 and with the orange dye in Figure 3. Results confirmed the general trend established in the previous example, although using the present dyes all of the samples treated with the 25 Epi-DMA polymer showed higher color intensities than those in the previous series. The best results using alum with 2.0% dye were about equal to the color intensities of fiber treated with only 2 kg/t polymer and only 0.5% dye. There does not appear to be any advantage of the highest polymer usage over the results achieved at 10 kg/t. 30 Example 6 Bleached kraft pulps having 1, 2 and 5 kg/t of Epi-DMA polymer, calculated on an active material basis, were used in an experiment to determine whether the increased cationicity improved pigment retention. To this end a sodium tetrapyrophosphate dispersed rutile-type titanium 35 dioxide was added to a slurry of the fiber in amounts of 5, 10, 15 and 20% based on the weight of dry fiber present. A slurry of 10 g dry weight fiber p 41 r; 11.657F 14 , f,: in 750 mL of water was refined in a high shear blender for three minutes. Then 2 g of titanium dioxide was added and refining was continued for an additional minute. The slurry was further diluted with water and handsheets were made. 5 An untreated control series was run as were series using 10 kg/t alum and 10 kg/t alum with 0.2 kg/t Reten 210 retention aid, a trademarked, low cationic charge density polyacrylamide product made by Hercules, Inc., Wilmington, Delaware. Titanium dioxide retention of the polymer treated samples, as 10 measured by ash content, was significantly improved over untreated pulp but was inferior, especially at higher pigment usages, to the simple use of alum. Untreated fiber with both alum and retention aid was markedly superior to any of the other treatments (Figure 4). Quite surprisingly, the Epi-DMA treated series fared much 15 better when sheet opacity was compared with the amount of pigment used (Figure 5). Opacity, as opposed to retention, is actually a much better measure of pigment efficiency. Differences between the Epi-DMA treated fiber and the alum or alum plus retention aid samples were relatively minor. When fiber treated with 4 kg/t of additive was used with a small amount of 20 alum (2.5 kg/t) opacity values were equal to the best obtained by any means for the one level of titanium dioxide tested. Example 7 Another series of samples was run using a crosslinked cationic polymer in which a portion of the dimethylamine was replaced by hexa-25 methylene diamine (HMDA) in the epichlorohydrin-dimethylamine polymer product. This product is available as Nalco N-7135 from Nalco Chemical Co. Bleached kraft fiber was treated with 1.25, 2.5, 5 and 10 kg/t, active material basis of the polymer in the manner taught in Example 1. This fiber was compared with samples of fiber treated with 1, 2 and 5 kg/t of the 30 unmodified Epi-DMA polymer. Additionally, samples of untreated pulp were used with 10 kg/t alum and 10 kg/t alum with 0.2 kg/t Reten 210 retention aid. The fiber samples were treated as described in Example 6 using 20% sodium tetrapyrophosphate dispersed titanium dioxide based on dry 35 fiber. Retention results are shown graphically on Figure 6 and opacity values on Figure 7. I • P41 *"$<•<«■/! 11,657F 15 i.' The HMDA modified Epi-DMA is superior to the unmodified Epi-DMA polymer in pigment retention (Figure 6). It is also superior to the use of alum by itself.' Only the combination of alum and the cationic polyacrylamide retention aid exceeded the treated modified polymer in 5 titanium dioxide retention efficiency. There was little advantage seen in using more than 10 kg/t of the HMDA modified polymer. As noted in the previous example, opacity is actually a better measure of pigment efficiency than is pigment retention. By this measure, as is seen in Figure 7, even very low usages of the HMDA modified Epi-DMA 10 polymer perform in superior fashion to any of the other treatments. Again, most of the benefit appears to be gained below 10 kg/t addition rate of the polym er. Example 8 An additional series of samples was made in which the fiber was 15 treated with 1.2, 2.5, 5 and 10 kg/t of an ethylene diamine (EDA) modified Epi-DMA polymer (Nalco N-8100). Titanium dioxide retention tests were made as described in Examples 6 and 7, again using 20% TiO^ based on fiber weight. Pigment retention and opacity results are seen on Figures 6 and 20 7 respectively. The EDA modified polymer is marginally poorer than the hexamethylene diamine (HMDA) modifed polymer although it results in opacities better than those obtained with alum and a retention aid. Example 9 Samples were made in similar fashion to the cationic pulps 25 described in Example 1 except that an ammonia crosslinked Epi-DMA polymer (Nalco 7607) was used. Two 20 g dry weight samples of spruce kraft pulp were added to about 750 mL of water and run for 5 minutes in a high shear blender to simulate refining. The pH was adjusted to 10.5 with NaOH. To one sample 30 was added 0.1 g of the 35% active material polymer solution to achieve an equivalent usage of 1.75 kg/t. Twice this amount was added to the other sample for a 3.5 kg/t equivalent usage. The treated fiber was allowed to stand for 30 minutes at room temperature, drained and washed to pH 7, and made into handsheets. 35 The handsheets were sampled and 3 g dry basis of the cationic pulp was slurried in 400 mL of water and run for 2 minutes in the high shear / P 41 11,657F 16 / 4* 1 blender. Amafast Bond Blue dye was added equivalent to 40 kg/t of pulp. The samples were diluted to 900 mL and small handsheets made. While colorimetric readings were not made, the dyed samples were compared visually with a dyed untreated control sample. The higher 5 color intensity of the cationic fiber was immediately apparent. This was reflected in the much lower color level of the white water of the two treated samples as compared with the white water from the untreated pulp. Nitrogen contents of the samples treated with 1.75 and 3.5 kg/t °f NHj modified Epi-DMA were 0.021% and 0.025% respectively, indicating 10 about 91% and 54% retention of the polymer. Example 10 Trials were made to see if the cationic cellulose products of the invention were effective in retaining anionic latices. One product was made as in Example 1 using 10 kg/t of Epi-DMA polymer. A second product was 15 made using 5 kg/t of the hexamethylene diamine (HMDA) modified polymer as taught in Example 7. Both usages were calculated on an active material basis. The treated samples were slurried in water and varying amounts of self-crosslinking acrylic emulsion latex (UCAR 872, Union Carbide Corp., New York, New York) were added. Handsheets were then made from the 20 fiber latex mixtures. In addition to the two treated materials, trials were run on untreated pulp and untreated pulp with alum in ranges from 2.5 to 12.5 kg/t alum. Untreated fiber, untreated fiber with alum and the fiber treated with 10 kg/t Epi-DMA were ineffective at retaining latex which was 25 essentially all lost with the white water. Fiber treated with HMDA modified polymer showed excellent latex retention, as measured by increase in sheet weight. When small amounts of alum were added to the mixture of Epi-DMA treated fiber and latex, the latex was effectively retained at alum 30 usages of 5 kg/t and greater. Alum at usages of about 2.5 kg/t also improved latex retention of fiber treated with HMDA modified polymer although not to the same extent as with the Epi-DMA treated fiber. With the HMDA modified sample, there did not appear to be significant advantage in using alum in amounts greater than 2.5 kg/t. 35 It is apparent and not unexpected that the particular additive used will have some effect on the final properties of the fiber. An optimum I m P 41 11,657F 17 i 1 additive for dye retention might not be optimum for pigment retention. However, in combinations with small quantities of a supplementary cationic additive, such as altfm, a synergistic effect is noted and an improved result is achieved that is not possible with either the treated fiber or the cationic 5 additive standing by themselves. Example 11 produced by treating a cellulosic fiber with a polymer of epichlorohydrin and dimethylamine has been demonstrated as shown in Figures 1-3. Similar 10 improvements are noted using Epi-DMA polymers modified with ammonia, ethylene diamine (EDA), and hexamethylene diamine (HMDA). These cationic fibers enable the production of papers dyed with acid dyes that have intensities not generally achieved before the discoveries of the present invention. However, there is an ancillary but extremely important aspect of 15 the invention which results from the greater efficiency of dye utilization. That is the greatly reduced amount of dye in the white water resulting from papermaking. The high color intensity of this water has represented an extremely serious waste cleanup problem in the past. 20 cationic fiber at reducing dye in effluent. Bleached kraft fiber was treated as in Example 7 with hexamethylene diamine (HMDA) modified epichlorohydrin-dimethylamine polymer using 5, 10, 15, 20, 25 and 30 kg/t, active material basis, of the polymer based on dry pulp. A sample of 5 g of the treated fiber was beaten in a high shear blender in 1000 mL of water for 2 25 minutes. Amafast Bond Blue 10GLP dye was then added. After the dye was dispersed, a 200 mL sample of the pulp slurry was taken and filtered on a cellulose filter paper on a Buchner funnel. The effluent was analyzed colorimetrically using a set of known standards to determine dye content. Results showing the amount of dye in the effluent white water are shown in 30 Figure 8. Results of a similar test series using ethylene diamine modifed Epi-DMA polymer as the additive are given in Figure 9. adsorbed by the cationic cellulose product. This compares with untreated cellulose fiber run as a control in which only about 76-84% of the dye was 35 adsorbed. These results are remarkable since many of the dye concentrations used with treated fiber in this test are far greater than would ever be The dye retention efficiency of the cationic cellulose product The following examples show the effectiveness of the present In all cases in this example in excess of 92% of the dye was I P 41 11,657F 21 18 10 15 20 considered practical for commercial use. Typical dye usage in a paper mill to produce a deep dyed product is about 5-10 kg/t. Since there was some adsorption of dye by the filter paper used to retain the dyed fiber, a series of tests was made using dye alone. With dye concentrations equivalent to 5, 10 and 20 kg/t, from 91-93% of the original dye was recovered in the effluent. This shows that adsorption by the filter paper was of minor significance. Example 12 The following example shows the effect of pH on pickup efficiency of the Epi-DMA polymer. A series of samples was made in which bleached spruce kraft pulp was treated with 5 kg/t, active material basis, of a hexamethylene diamine modified Epi-DMA polymer (Nalco 7135) at various pH levels between 7 and 10.5, according to the procedure of Example 1. The treated fiber was drained and washed and then reslurried in water. Pergacid Blue Black B dye (Ciba-Geigy) was added to each fiber sample at a rate of 40 k^t and handsheets were made. A second series of samples was made in which a bleached Douglas-fir sawdust kraft pulp was treated with 10 kg/ton of the Nalco 7135 polymer at pH values between 6 and 10.5. The following results were obtained. Table III 25 30 35 40 45 Fiber Treatment PH 7 8 9 10 10.5 6 7 8 9 10 10.5 Color Intensity, L Value Kjeldahl N, % Spruce Pulp, 5 kg/t Usage 44.5 41.5 42.0 38.0 33.8 0.018 + 0.006 0.058 + 0.001 Douglas-fir Pulp, 10 kg/t Usage 0.029 0.031 0.031 0.034 0.044 0.068 Cationic Additive Retention, % 35 112 25.3 27.0 27.0 29.6 38.3 59.2 Nitrogen content of the as received (50% solids) N-7135 polymer used for the spruce series was 5.4% and for the Douglas-fir series 5.74 + 0.04%. P 41 _ 11.657F 19 J' I f 1 f f\; There appears to be an approximately linear relationship between eolor intensity and treatment pH over the range studied. Because of the high level of polymer reacted at pH 10.5, as seen by nitrogen determination, there is little advantage seen in using a higher treatment pH 5 at the 5 kg/t level of usage. There is a sharp break in polymer efficiency between pH 9 and pH 10.5 at the 10 kg/t usage. As noted earlier, overall efficiency is greater at lower levels of polymer usage. This is confirmed by the present data. In addition to the dyes, latices, and pigments described in the 10 previous examples, the cationic fibers of the present invention would be expected to be advantageous for retention of many other papermaking additives. Included among these might be sizes, fillers, and wet strength additives. It will be understood by those skilled in that art that consideration must be given to the overall chemistry of the system and that the 15 cationic fibers will not necessarily perform in a superior manner with all possible additives. It has already been seen that there are differences in performance between the various species of Epi-DMA polymers. While theoretical predictions can be made, much of papermaking remains a poorly understood art and expectations are not always borne out by results. An 20 example of this is the surprising synergism seen in latex retention when small quantities of alum are used with the cationic cellulose product. Example 13 The following example shows the performance of bleached kraft fiber treated with two types of Epi-DMA polymer and with two types of wet 25 strength additive. The treated products were dyed and qualitative observations made on color intensity. The cationic cellulose product was made by dispersing 100 g, oven-dry basis, of a sheeted bleached kraft spruce pulp in water at 1.5% consistency using a propellor-type mixer and British disintegrator. To 30 successive 100 g pulp batches, 0.38, 1.00 and 2.00 g of as is hexamethylene diamine modified Epi-DMA polymer (Nalco 7135, 50% solids) was added. This corresponds to as is usages of 3.8, 10 and 20 kg/t. A similar sample was made using 115 g oven-dry equivalent of kraft fiber to which was added 1.15 g of uncrosslinked Epi-DMA polymer (Nalco 7655, 50% solids material), 35 corresponding to 10 kg/t as is usage. The treated fiber slurries were allowed to stand 30 minutes without agitation. Then the fiber was washed to a pH of approximate 7, sheeted and dried. P 41 11,657F 20 2 1111 The above handsheets were divided into 10 g, oven-dry basis portions, reslurried in about 750 mL of water and agitated for 2 minutes in a high shear blender to simulate beating. The wet strength agent was then added and stirred by hand for 1 minute. Finally, a solution of Amafast Bond 5 Blue 10 GLP dye was added at a 20 kg/t usage equivalent. The slurry was again stirred by hand for 1 minute after which handsheets were made. Two different wet strength agents were used. The first was a highly cationic polyamine-epichlorohydrin polymer (SR-31, Monsanto Company, St. Louis, Missouri). The other was an experimental weakly 10 cationic resin (CX-252 Nalco Chemical Co., Oak Brook, Illinois). SR-31 is. sold as a liquid at 35% solids content and CX-252 as a 6% solids liquid. The SR-31 wet strength agent was added to attain equivalent usages of 2.5, 5 and 10 kg/t while the CX-252 material was added at 2.5 and 5 kg/t, when used with the HMDA crosslinked Epi-DMA treated fiber. Each wet strength 15 agent was used at only 10 kg/t when used with the unmodified Epi-DMA treated fiber. Handsheets were tested for wet and dry tensile strengths and the ratio of the two values calculated. Higher ratios indicate better wet strengths. Results are shown in the following tables. 20 Table IV Ratio of Wet to Dry Tensile Strengths x 100 SR-31 Wet Strength Agent 25 Cationic Material Cationic Material Usage, kg/t Wet Strength Agent, kg/t 2.5 5 10 HMDA Modified Epi-DMA 5 10.49 11.86 16.52 HMDA Modified Epi-DMA 10 8.94 12.76 11.88 HMDA Modified Epi-DMA 20 10.91 12.23 - Unmodified Epi-DMA 10 9.45 14.26 15.97 None 0 6.46 7.52 12.79 35 11 4 I c, P 41 11,657F 21 Table V Ratio of Wet to Dry Tensile Strengths x 100 CX-252 Wet Strength Agent Cationic Material Wet Strength Agent, kg/t Cationic Material Usage, kg/t 2.5 10 HMDA Modified Epi-DMA 5 9.45 10.33 HMDA Modified Epi-DMA 10 8.76 10.60 Unmodified Epi-DMA 10 9.01 10.86 None 0 11.74 13.58 15 These results show that under the conditions of these trials, the polyamine-epichlorohydrin wet strength agent, in combination with the cationic cellulose product, gives superior performance as compared with unmodified cellulose fiber. On the other hand, the mildly cationic wet strength agent performed better with unmodified fiber. As a qualitative 20 observation, the color intensity of the dyed sheets was inversely related to the amount of wet strength agent used. Example 14 A sample of chlorinated Douglas-fir pulp was obtained from a pulp mill bleach plant. Chlorination is the first of a five-stage bleach 25 sequence as outlined in Example 2. The final four stages of the sequence were completed in the laboratory. In this example, hexamethylene diamine modifed Epi-DMA (Nalco 7135) was added at the neutral hypochlorite stage to see if it would remain on the pulp through the balance of the bleaching process. The chlorinated pulp was slurried in water and the equivalent of 30 2.5 kg/t NaOH added. The pH increased to 11.9. Sodium hypochlorite solution equivalent to 15 kg/t was added. The pH of the mixture dropped to 10.3. At this point, the HMDA modified Epi-DMA polymer was added at an equivalent usage of 10 kg/t active material. The bleach was continued for 60 minutes at a temperature about 37°C. Following washing, hypochlorite, 35 alkaline extraction and chlorine dioxide treatments were given as described previously. Nitrogen analysis of the fully bleached pulp showed a N content of 0.008%, equivalent to about 15% retention of the added polymer. It is apparent that while some of the polymer is retained by the cellulose much is 40 lost in either or both of the hypochlorite stages. It is thus preferred to add the Epi-DMA polymer after any hypochlorite treatments and at a later P 41 11,657F 22 1 1 alkaline stage in the bleaching sequence. This would normally be the caustic extraction step in a five-stage sequence or the hydrogen peroxide step if one is used. The cationic nature of the product of the invention appears to be 5 permanent; i.e., essentially unaffected by any of the normal papermaking processes, many of which tend to remove the usual cationic "additives" used in papermaking. It will be readily apparent to those skilled in the art that many product variations can be made that will be considered to be within the 10 scope of the invention. One of the principal advantages of the present invention is that the degree of cationicity in the product can be readily varied. This is accomplished very simply by adjusting the amount of polymer added to the fiber. As shown in the examples, the final properties of the pulp will be somewhat dependent upon the particular modification of 15 the epichlorohydrin-dimethylamine polymer used to modify the cellulose. It will also be evident that because of its extreme simplicity, many process variations can be made without departing from the scope of the invention. While it is preferred that the polymer be added during a relatively highly alkaline stage near the end of the bleach sequence, this is not absolutely 20 essential and many variations are possible. It is further preferred that the polymer be added later than any bleaching stage in which chlorine or sodium hypochlorite is present. One of the major advantages of the present invention is that acid dyes such as the tartrazine types can now be used for producing dyed papers 25 without any need for retention aids. The acid dyes as a class are desirable because their high tinctorial values would otherwise enable less dye to be used to attain a given color level. The need for alum and the acidic conditions which it promotes is no longer necessary when making a dyed product using the cationic material of the present invention. 30 Another significant advantage of the present invention is the improved pigment retention characteristics which dictate that either no alum or much less alum or other retention aid is necessary for a given level of paper opacity. In part, this is due to the fact that the cationic cellulose of the present invention can apparently attain higher levels of cationicity 35 that is possible with the use of external retention aids. P 41 11,657F 23 2 1111 Since many other features of the invention other than those disclosed above will be apparent to those skilled in the art, the invention is to be considered limited only as it is defined by the following claims. </div>

Claims

<div class="application article clearfix printTableText" id="claims"> P 41 11,657F 24 111 9 CirAfMS WHATVtfWE CLAIM IS:-What is claimed is.

1. A cationic cellulose product comprising an additive of 5 cellulose made under alkaline conditions with a cationizing agent selected from the group consisting of crosslinked and uncrosslinked polymers of epichlorohydrin and dimethylamine, and mixtures thereof wherein the ~ crosslinking agent, if present, is selected from the group consisting of ammonia and a primary aliphatic diamine of the type H2n-R-NH2 where R 10 is an alkylene radical of from 2 to 8 carbon atoms, said cationic product having a nitrogen content of at least 0.02%.

2. The cellulose product of claim 1 which is the additive under alkaline conditions of cellulose with a polymer of essentially i equimolar portions of epichlorohydrin and dimethylamine. 15

3. The cellulose product of claim 2 in which up to 30 molar percent of the dimethylamine is replaced by hexamethylene diamine.

4. The cellulose product of claim 2 in which up to 30 molar percent of the dimethylamine is replaced by ammonia.

5. The cellulose product of claim 2 in which up to 30 molar 20 percent of the dimethylamine is replaced by ethylene diamine.

6. The cellulose product of claim 1 made at a pH of at least 9.5.

7. A method for making a cationic cellulose product which comprises treating an aqueous suspension of cellulose under alkaline condi- 25 tions with a cationizing agent selected from the group consisting of crosslinked and uncrosslinked polymers of epichlorohydrin and dimethylamine, and mixtures thereof wherein the crosslinking agent, if present, is selected from the group consisting of ammonia and a primary aliphatic diamine of the type HgN-R-NI^ where R is an alkylene radical of 30 from 2 to 8 carbon atoms, said cationizing agent being used in a sufficient amount to introduce at least 0.02% nitrogen into the cationic product.

8. The method of claim 7 in which the cellulose is treated with a polymer having essentially equimolar portions of epichlorohydrin and dimethylamine. 35

9. The method of claim 8 in which up to 30 molar percent of the dimethylamine is replaced by ammonia. f m 1 a m' 25

10. The method of claim 8 in which up to 30 molar percent of the dimethylamine is replaced by ethylene diamine.

11. The method of claim 8 in which up to 30 molar percent of the dimethylamine is replaced by hexamethylene (famine. 5

12. The method of claim 7 further comprising treating the aqueous suspension of cellulose at a pH of at least 9.5 or higher.

13. A method of making a cationic bleached cellulose product which comprises adding to an alkaline stage of a fiber hleaching sequence at least 0.5 kg/t based on the dry weight of the cellulose present of a 10 cationizing agent selected from the group consisting of crosslinked and uncrosslinked polymers of epichlorohydrin and dimethylamine, and mixtures thereof wherein the crosslinking agent, if present, is selected from the group consisting of ammonia and a primary aliphatic diamine of the type HjN-R-NI^ where R is an alkylene radical of from 2 to 8 carbon atoms. 15

14. The method of daim 13 wherein said bleaching sequence includes at least one hypochlorite stage and the polymer treatment is later than the last hypochlorite stage.

15. The method of claim 14 In which the bleaching sequence includes an alkaline extraction treatment following the last hypochlorite 20 stage and the polymer treatment is made diring the alkaline extraction stage.

16. The method of claim 15 in which the alkaline extraction stage is followed by a chlorine dioxide stage.

17. The method of claim 14 in which the bleaching sequence 25 includes an alkaline peroxide bleaching stage following the last hypochlorite stage and the polymer treatment is made during the alkaline peroxide bleaching stage.

18. The method of claim 13 in which the treatment is made with a polymer having essentially equimolar portions of epichlorohydrin and 30 dimeth^amine.

19. The method of claim 18 in which up to 30 mciar percent of the dimethylamine is replaced by ammonia.

20. The method of claim 18 in which up to 30 molar percent of the dimethylamine is replaced by ethylene diamine. 35

21. The method of claim 18 in which up to 30 molar percent of the dimethylamine is replaced by hexamethylene diamine. 19 JUN1987 m| // I t 1 .,L I i 1 p 26

22. The method of claim 13 which further comprises using the polymer in an amount 0.5-20 kg/t based on the dry weight of cellulose present.

23. The method of claim 22 which further comprises using the polymer in an anounc 2-10kg/t based on the dry weight of the cellulose present.

24. The method of claim 13 in which the pH of the bleaching stage at which the polymer is added is at least 9.5 or higher.

25. A cationic cellulose product as claimed in any one of claims 1 to 6 substantially as herein described with reference to any one of the Examples.

26. A method of making a cationic cellulose product as claimed in any one of claims 7 to 24 substantially as herein described with reference to any one of the Examples. 6 f/V 19JUNI987 n rn! </div>